NATCO
Elect lectro rost sta atic ti c Te Techno ch nolo logy gy Dehydr hy dra ation ti on and De Desalting salti ng
Table of Contents Introduction......................................................................................................................................1 Description of Processes..................................................................................................................1 Mechanical Forces for Coalescence and Sedimentation......................................................1 Electrostatic Forces..............................................................................................................2 AC Field Devices.................................................................................................................3 Plate AC Field Devices........................................................................................................5 DC Field Devices.................................................................................................................8 Dual Polarity® Devices........................................................................................................6 Pulsed and Modulated Dual Polarity® Devices...................................................................8 TM Dual Frequency Devices................................................................................................13 Conductivity in Dehydrator and Desalter Design..............................................................13 Composite Electrodes ............................................ ................................................... .........14 ElectroDynamic® Desalters ................................................... ............................................16 Electromax® Dehydrators..................................................................................................20 Summary of Processes ...................................................... ........................................................................................................... .............................................................20 ........20 AC Configurations.............................................................................................................20 Dual Polarity® (AC/DC) Configurations...........................................................................21 TM Dual Frequency Configurations.....................................................................................22 ElectroDynamic® Desalter.................................................................................................22 Electromax® Dehydrators..................................................................................................23 Performance Case Studies: Actual Installations Installations .............................................. ..............................24 Operational Parameters..................................................................................................................28 Chemical Treatment...........................................................................................................28 Operating Temperature ............................................ ................................................... .......29 Process Flux.......................................................................................................................30 Dilution Water ............................................ ................................................... ....................30 Water Recycle....................................................................................................................31 Effluent Water Treatment ............................................ ................................................... ...31 Water Solubility in Crude Oil............................................................................................32 Incompatibilities of Fluids ............................................... ................................................ ..32 Analytical Methods............................................................................................................32 Power Consumption...........................................................................................................34 Sub-System Specifications ............................................... ................................................... ..........34 Power Supplies ..................................................... ............................................................................................................. .............................................................34 .....34 Transformers................................................. Transformers ................................................. ................................................... ......34 Controllers ............................................... ................................................... ...........34 Insulators............................................................................................................................35 Entrance Bushings ................................................... ..............................................35
Table of Contents Introduction......................................................................................................................................1 Description of Processes..................................................................................................................1 Mechanical Forces for Coalescence and Sedimentation......................................................1 Electrostatic Forces..............................................................................................................2 AC Field Devices.................................................................................................................3 Plate AC Field Devices........................................................................................................5 DC Field Devices.................................................................................................................8 Dual Polarity® Devices........................................................................................................6 Pulsed and Modulated Dual Polarity® Devices...................................................................8 TM Dual Frequency Devices................................................................................................13 Conductivity in Dehydrator and Desalter Design..............................................................13 Composite Electrodes ............................................ ................................................... .........14 ElectroDynamic® Desalters ................................................... ............................................16 Electromax® Dehydrators..................................................................................................20 Summary of Processes ...................................................... ........................................................................................................... .............................................................20 ........20 AC Configurations.............................................................................................................20 Dual Polarity® (AC/DC) Configurations...........................................................................21 TM Dual Frequency Configurations.....................................................................................22 ElectroDynamic® Desalter.................................................................................................22 Electromax® Dehydrators..................................................................................................23 Performance Case Studies: Actual Installations Installations .............................................. ..............................24 Operational Parameters..................................................................................................................28 Chemical Treatment...........................................................................................................28 Operating Temperature ............................................ ................................................... .......29 Process Flux.......................................................................................................................30 Dilution Water ............................................ ................................................... ....................30 Water Recycle....................................................................................................................31 Effluent Water Treatment ............................................ ................................................... ...31 Water Solubility in Crude Oil............................................................................................32 Incompatibilities of Fluids ............................................... ................................................ ..32 Analytical Methods............................................................................................................32 Power Consumption...........................................................................................................34 Sub-System Specifications ............................................... ................................................... ..........34 Power Supplies ..................................................... ............................................................................................................. .............................................................34 .....34 Transformers................................................. Transformers ................................................. ................................................... ......34 Controllers ............................................... ................................................... ...........34 Insulators............................................................................................................................35 Entrance Bushings ................................................... ..............................................35
Electrode Hangers..................................................................................................36 Electrodes...........................................................................................................................36 Bar Grating or "Grids" .................................................. .........................................36 Steel Plates.............................................................................................................37 Composite Plates....................................................................................................37 Liquid Distribution Systems .......................................... ................................................ ....37 Inlet Spreaders ............................................ ................................................... ........37 Outlet Collectors .................................................. ..................................................3 9 Dilution Water Distributors ............................................ .......................................40 Instrumentation and Safety Systems..................................................................................40 Safety Grounding Floats .................................................. ......................................40 Low Level Shutdowns ...................................................... ...........................................................................................40 .....................................40 Interface Controls .............................................. ................................................... .40 Solids Removal Systems....................................................................................................40 Mud Wash or Sand Jet Systems.............................................................................41 Interface Sludge Drains ............................................... ..........................................41 Mixing Devices..................................................................................................................42 Mixing Valves........................................................................................................42 Static Mixers ............................................... ................................................... ........43 Electrostatic Mixing...............................................................................................43 Design Aids....................................................................................................................................43
Appendix I: Publications “How to Design an Efficient Crude Desalting System” “Dual Polarity Oil Dehydration” “Field Desalting: A Growing Producer Problem Worldwide” “Field Desalting of Wet Crude in Kuwait” “Crude Oil Desalting by Counter-flow Electrostatic Mixing” “Desalting Heavy Crude Oil by Counter-flow Electrostatic Mixing” “Reduction of Corrosion through Improvements in Desalting” “Tandem Mechanisms Facilitate Dehydration of Crude” “Dual Polarity Desalter Testing” “Electrostatic Fields: Essential Tools for Desalting” “Desalting Heavy Crude Oils: The Venezuelan Experience” “New Tools for Heavy Oil Dehydration” “Field Trials Scheduled for New Compact Dehydration Technology”
Appendix II: Users II: Users Lists Refinery Desalting Desalting Systems Systems Composite Electrode Systems Dual Polarity® Polarity® Retrofit Projects Projects Electro-Dynamic® Electro-Dynamic® Desalting Desalting Systems Systems NATCO Electrostatic Electrostatic Crude Oil Dehydrato Dehydrators rs NATCO Field Field Desalting Desalting NATCO Canada Canada Electrostatic Electrostatic Dehydrator Dehydratorss NATCO HOWMAR HOWMAR TriVolt® TriVolt® Dehydrators Dehydrators and and Desalters Desalters NATCO HOWMAR HOWMAR Dehydrators Dehydrators and and Desalters Desalters NATCO Electrostatic Electrostatic Dehydrators Dehydrators – Very Heavy Heavy Oils
Appendix III: Components Composite Electrodes Electrostatic Electrostatic Transformers Transformers Installation Installation Procedure Procedure for New or Replacement Replacement Entrance Entrance Bushings and Bushing Bushing Housings Housings Transformer Oil Specifications Transformer Oil Filtration Procedure for Operating Units Electrostatic Electrostatic Dehydrator/Desalte Dehydrator/Desalterr Inspection Inspection Punch-List Punch-List Products Made for NATCO by ELECTROTECH (Hangers, Entrance Bushings, Tester)
Appendix IV: Sample Dual Polarity® Users Manual Appendix V: Sample Electro-Dynamic® Desalter Users Manual Appendix VI: Brochures
Crude Oil Dehydration and Desalting Solutions Desalting: Field or Refinery Electro-Dynamic® Desalters: Field or Refinery Dual Polarity® Electrostatic Treater TriVolt and TriVoltmax Electrostatic Dehydrators and Desalters TriGrid and TriGridmax Electrostatic Dehydrators and Desalters Electromax® Treater Horizontal Performax® Treater Horizontal Vertical-Flow Treater Vertical Emulsion Treater Direct Current Electrostatic Treaters Laboratory Services: Dehydration and Desalting Computational Fluid Dynamics Dual Polarity® Performance Enhancers Electro-Dynamic® Desalters Research and Development
Date of Publication: August 18, 2003
by Kenneth Warren PhD
©
NATCO, Houston, Texas 1997, revised March 2000, August 2003
Acknowledgements Technical progress is made through building upon previous contributions of many others. Therefore, it becomes almost impossible to truly acknowledge all contributors; however, there are people whose contribution has been significant and personal that must be mentioned. Of special note is the man who initially taught me the craft of oil dehydration and desalting, Mr. Floyd Prestridge. Also in this category, I must acknowledge the counsel of Mr. Don Burris and Mr. Harry Wallace. Through the years, others have joined in the efforts to advance electrostatic technology and have made many valuable contributions. These individuals include Mr. Gary Sams, Mr. Carroll Edwards, and Mr. John Armstrong of our company, and Dr. Philip Bailes and Professor Manabu Yamaguchi who participated as academic partners. To all of these gentlemen, I offer my thanks.
NATCO Electrostatics Dehydr ation and Desalting Introduction Since it’s founding as an oilfield storage tank producer in 1926, NATCO has become a leading producer of oil processing equipment worldwide with an impressive series of innovations in the separation and purification of crude oils. Most of its early processes involved the use of heat, chemicals, mechanical devices, and retention time to achieve separation of oil and water. These separation devices all depend upon gravity separation of the dispersed phase through Stokes’ Law sedimentation, and improvement of processing rates depends upon maximizing growth of the dispersed phase drops. Electrostatic fields were first applied to drop growth in liquids processing in the early 1900s as an outgrowth of electrostatic precipitator development. The early applications of electrostatic technology to crude oils were largely limited to the “clean” feedstocks of refineries which had already been processed to some degree in the oilfields. In the early 1960s this technology began its transition to oilfield production operations. NATCO electrostatic processes for dehydration and desalting have been in use since 1961 and cover a wide range of process variations suitable for dehydration, production desalting, and refinery desalting. These processes are the result of a long and on-going research and development effort involving not only NATCO research and engineering teams, but also research institutions and universities around the world.
Description of Processes Separation of two-phase liquid mixtures typically depends upon (1) destabilizing the dispersion (coagulation) and (2) gathering the destabilized drops of the dispersed phase together (flocculation) and causing them to coalesce into larger drops which then separate from the continuous-phase liquid by gravity sedimentation. Mechanical Forces for Coalescence and Sedimentation In a mechanical dehydrator, coalescence occurs via collisions resulting from Brownian motion of the drops, and separation occurs via Stokes’ La w sedimentation. Coalescence is enhanced by increased temperature, chemical treatment, and provision of impingement surfaces in the flow path. Chemical treatment often serves both to destabilize (coagulate) the drops and to assist in bringing them together (flocculation). The drop size “cut point” is determined by the balance between viscous drag and weight.
-1-
f = 6 π µ r v Viscous Drag Stokes’ Law Sedimentation Rate
vs =
w= Where:
4 3
πr
3
g(ρ2 − ρ 1)
0.22 gr 2 ( ρ 2 − ρ 1 ) µ
Weight
f = viscous drag force µ = viscosity r = drop radius v = velocity w = weight g = gravitational constant ρ2 = density of dispersed phase ρ1 = density of continuous phase vs = Stokes’ Law sedimentation rate
Electrostatic Forces If the dispersed liquid is polar or polarizable, electrostatic fields can be used to assist in the flocculation process (electroflocculation). In the specific case of water or aqueous solutions dispersed in crude oils, the asymmetric arrangement of charges within the water molecules causes them to align with the electrostatic field creating dipolar drops. The polarization of the water drops results in a stretching deformation producing ellipsoidal shapes. Since adjacent ends of two water drops would be oppositely polarized, an attractive force exists which can result in coalescence if the drops are very close together. The coalescence process in the presence of electrostatic fields is then divided with chemicals supplying coagulation and the electrostatic field supplying flocculation. There are three major electrostatic forces available: • Dipolar Attraction • Electrophoresis • Dielectrophoresis These forces assume different degrees of importance depending upon the electrostatic field configuration. -2-
Definitions of Electrostatic Forces •
•
•
Dipolar Attraction: Electrical force produced by positive and negative centers on induced dipoles of water drops. Electrophoresis: Electrically induced movement of polar bodies in a uniform field toward closest electrode. Dielectrophoresis: Movement of polar bodies induced by a divergent electric field toward increasing gradient.
+
-
+ +
-
+
-
-
+
+
+
-
A drop in an AC electrostatic field primarily experiences dipolar attraction. Electrophoretic movement is mostly cancelled by the rapid field reversal. Some dielectrophoretic movement is possible due to the field asymmetry associated with the electrode geometry. Other coalescing mechanisms include impingement due to differential velocity an d collision with a water film on an electrode. Although each of these mechanisms may be active to some degree, induced dipolar attraction remains the “workhorse” of electrostatic dehydration in the AC field. The illustration below shows induced dipolar attraction. On the left are photomicrographs of water drops in an electrostatic field and a schematic representation of the charge distribution within the drops is shown on the right. The attractive forces between the induced dipoles of water drops are short range in effect and coalescence depends upon other forces to bring the polarized drops sufficiently close together for dipolar attraction to be effective.
-3-
No Field Applied Random Charge Distribution
Water Dipoles Align with Field
Adjacent Drops Attracted The dipolar attractive force between drops of equal size can be expressed as follows:
F =
6K E 2 r 6 d
4
Inter-drop Attractive Force in an Electrostatic Field Where: F = Force of attraction K = Dielectric constant E = Electric field gradient r = Drop radius d = Inter-drop distance Inspection of this equation illuminates both the a dvantages and weaknesses of an electrostatic field in flocculation. Note that the dipolar attractive force is highly dependent on drop size (as the sixth power exponent testifies), with limited benefit in the coalescence of small drops. Also note the rapid decline in dipolar force with distance.
-4-
Electrophoresis: Small Drop Reverses Direction Dielectrophoresis: Large Drop Reverses Polarization
+
-
+ +
+
--
+
+
-
-- ++
AC Field Devices The first applications of electrically induced flocculation utilized alternating current (AC) fields in the range of 16 to 23 kilovolts (KV). The rapid reversal of polarity in an AC system (every 8.3 milliseconds with 60 hertz power) causes most electrically induced chemical reactions to remain reversible since the reaction products do not have time to diffuse away from the reaction site. This eliminates most electrically induced corrosion. However, this rapid reversal of the electrical field also precludes the production of any significant electrically-induced drop travel. The flocculating effect of an AC field is primarily dependent upon the mechanism of induced dipolar attraction. In an AC field, the efficacy of electroflocculation is dependent upon diffusion and fluid flow to bring dispersed water drops into close proximity. The AC field is most effective in removing large drops that are close together. Very small drops are not significantly affected by the field. Therefore, the AC field is most effective on the high water conten t emulsion at the inlet of a separation vessel and on the large drops that accumulate at the oil/water interface. An additional benefit of the oscillating elongation of the drops produced by the AC field is the rupture of any stabilizing films that might have formed. This effect is of particular advantage in resolving slowly condensing dispersions in the zone of hindered settling at the oil/water interface. The rod electrodes used in AC dehydrators and desalters produce an asymmetric field in the zone close to the electrodes and therefore cause some dielectrophoretic movement of the polarized drops -5-
although induced dipolar attraction remains the primary means of coalescence. Electrostatic fields are used primarily as a coalescing mechanism to produce growth of the dispersed water drops and thereby enhance the rate of separation. It should be noted that they work on dispersions that are not chemically stabilized, but are not effective on true emulsions. These require the use of chemicals to counteract the stabilizing forces of the emulsifiers. Electrostatic fields may be used in both dehydration processes in which the goal is the production of “dry” oil and in desalting process in which the goal is both to produce “dry” oil and a lso to lower the salinity of the oil. Desalters consist of a mixing device (mixing valve, static mixer, etc.) in which fresh water is used to wash the crude oil and a separation vessel in which an electrostatic field is used to separate the oil and water. AC dehydrators and desalters most commonly use an arrangement of charged horizontal bar gratings or grids for establishing the electric field within the vessel. A two-grid system, known as “single-hot” AC, uses a lower charged grid and an upper electrically grounded grid with a separation of six to eight inches (sometimes adjustable) between them. The incoming oil is introduced near the oil/water interface and flows upward through the grids to an outlet collector. The water layer is also grounded through the shell of the vessel. AC fields are then established between the water and the charged grid and between the charged grid and the grounded grid. Oil flows across both of these fields as it transits the vessel. Newer designs, “double-hot” and “triplehot” AC systems, use a multiplicity of charged grids to improve efficiency and throughput. Also employed is a technique known as “high velocity” AC for spreading the incoming emulsion between the energized electrodes. All of these variations are aimed at increasing the retention time of the dispersion within the most intense zone of the electric field and depend upon diffusion and/or flow patterns to carry polarized drops within the range of dipolar attractive forces. Transformers for AC dehydration and desalting are usually built with at least 16KV and 23KV secondary taps. Single-phase transformers are most commonly used with multiple transformers wired for load balancing on large installations. In some cases, three phase transformers are employed with multiple grids wired to accept different phases. In order to protect the transformers during process upsets, an internal reactor equal to 100% of the transformer reactance is placed in series with the primary winding. As the load on the transformer increases, the voltage drop across the reactor (inductor or core air gap design) increases thereby limiting the current to the transformer. A transformer with 100% reactance can tolerate a short circuit on its secondary output for a -6-
reasonable period without overheating. An unfortunate side effect of this protection scheme is that when the process is most in need of power (during process upsets), the reactor prevents the transformer from delivering it. The diagram below illustrates a modern three-electrode AC dehydrator/desalter (TriVolt AC Electrostatic Coalescer).
Power Unit 1
Power Unit 2
Earth Phase A Phase B
Earth
Phase B Phase C Grid 1
Power Unit 3
Earth
Phase C Phase A Grid 2
Grid 3
Earth
Power Unit Primary Connections
Grid Connections
Power Unit Secondary Connections Grid 1 Power Unit 1
DELTA
Phase A Power Unit 1
Power Unit 1
Power Unit 2
Grid 1
Power Unit 3
Grid 2 Grid 3
STAR
Power Unit 3
Power Unit 2
Phase B Grid 3
Phase C
Power Unit 2
Grid 2 Earth
TriVolt AC Electrostatic Coalescer Plate AC Field Devices Another technique developed by NATCO for achieving extended retention time in the highintensity field involves the use of an electrode array consisting of vertically hung parallel plates with alternate plates charged and grounded. This geometry provides additional benefits in having the electrostatic field perpendicular to the fluid flow to reduce electrical retardation of the settling water drops. This technique has proved to be useful as the first stage of multistage systems in which the feed-stream contains high -7-
levels of dispersed water. DC Field Devices It has long been recognized that direct current (DC) fields present some advantages in promoting coalescence. In a DC field the electrical forces are sustained and unidirectional. Therefore, polarized drops are able to move along the lines of force of the field, thereby increasing the probability of encounters with other drops. Electrophoretic movement becomes the major contributor to coalescence in a DC field. However, if a sustained DC current is produced, electrolytic corrosion will result. For many years this limited the application of DC fields to coalescers used in processes treating non-conductive refined oils such as in the Merox Process. Dual Polarity® Devices A system was perfected by NATCO in the early 1970s for combining the freedom from galvanic corrosion of the AC coalescer with the advantages of drop transport of the DC system. The electrodes in this combination AC/DC system consist of parallel plates connected to oppositely oriented diodes in such a manner that alternate plates are oppositely charged. Both diodes are connected to the same end of the transformer secondary winding; therefore, the plates are charged on alternate half cycles of the AC power supply.
Dual Polarity® Electrostatic Fields
} -8-
Bulk Water Removal
Since positive and negative plates are not charged by the power supply at the same time, the potential for sustained DC current is greatly reduced. The other end of the secondary winding is connected to ground, so that the electric field projected from the electrode array to the vessel is still AC. Also, the AC field is still available at the oil/water interface to assist in condensation of the settling dispersion as well as to provide coalescence and settling of the loosely dispersed water fraction of the incoming crude oil. Because the plates can only charge on alternate half cycles, the current between them is limited to discharge of capacitively stored energy and is unable to produce significant electrolysis. These plates are also operating in relatively dry, non-conductive oil since the bulk dehydration has been accomplished in the AC field below the electrodes. This further limits DC current dissipation. This system, known as Dual Polarity®, has been widely used for both dehydration and desalting. To understand the relative contributions of the various electrical forces, it is helpful to consider an example: Process Conditions: • 750 micron “cut point” drop • 32 kV applied peak voltage • 6” electrode spacing • 0.5% BS&W • Low oil conductivity
Magnitude of Forces: • Electrophoretic force = 53 dynes • Drag = Weight = 0.01 dynes • Dipolar attractive force = 0.004 dynes • Dielectrophoretic force = 0.002 dynes
The example above shows the importance of utilizing electrophoresis in promoting coalescence. The diagram below illustrates the Dual Polarity® process. The wet oil dispersion is introduced just above the oil/water interface. The AC field between the electrodes and water layer performs the bulk dehydration of the oil. The oil carrying the residual water from this process then enters the electrode zone where it is exposed to the DC field. The DC field supplies translational energy to the very small residual drops (electrophoresis). These drops approach the nearest plate, become charged, and are either coalesced with the film on the plate or repelled toward the opposite plate on a collision course with oppositely charged drops from that plate. Rapid coalescence ensues. This electrophoretic movement is the major contributor to coalescence in a DC field.
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Dual Polarity Process
Dual Polarity® desalters use mechanical mixing devices for phase dispersion and co ntact as do AC desalters. However, the electric field is established with a horizontal array of vertically hung parallel plates as described above. This electrical arrangement gives a DC plate-to-plate field and an AC plate-to-ground field. In this way, the advantages of drop movement and drop charge in a DC field are combined with the film rupturing capability and corrosion resistance of an AC field. Transformers for Dual Polarity® dehydrators and desalters are similar to those used for AC desalters with the addition of an oil-filled secondary junction box which houses the diode packs. Pulsed and Modulated Dual Polarity® Devices Since an electrostatic coalescer works by introducing electrical power into a potentially cond uctive medium, some means of protecting the power supply is necessary. This is accomplished in conventional systems by incorporating a reactance in series with the primary winding of the transformer. As the load increases, the voltage drop across the reactor increases, thus limiting the output voltage of the transformer. A 100% reactance transformer is therefore capable of sustaining a full short circuit in its output for a reasonable period of time without damage to itself. While this arrangement is very effective in protecting the power supply, it has the unfortunate consequences of being unable to supply power to the process during times of process upset and in reducing the - 10 -
efficiency of the power supply. The diagram below illustrates both the reactor circuit and its effect on output voltage.
Conventional Transformer Protection Reactor in Primary Circuit
Primary
Secondary
Provides Protection Only! Dual Polarity® dehydrators and desalters may be fitted with a power supply known as a Load Responsive Controller ® (LRC). The LRC® consists of a 35% reactance transformer in combination with an electronic device that senses the load being drawn and adjusts the power to the transformer accordingly. The power adjustment is accomplished by silicon controlled rectifiers (SCRs) which switch the power on and off rapidly so that very short bursts of high power are interspersed with “off” periods. Therefore, the transformer is maintained within its average heat dissipation and power output ratings. This allows power to be delivered to the process under upset conditions without compromising the integrity of the power supply. This controller differs in action from a 100% reactor in that power is reduced on the basis of time rather than by reduction of maximum voltage. Therefore, pulses of high intensity energy are applied to the wet oil with duration of the pulses limited by the power output rating of the transformer. Research has shown that much of the coalescing action of an electric field occurs during the rapid change of voltage with time (high dV/dt) during an electrical pulse. Therefore, much of the coalescing ability of the electric field is preserved during this pulsing action. This is shown below.
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Time-based Power Cycle Another way to control power … g a t l o V
Crude Oil Conductivity The LRC® may also be programmed to modulate power to the process. A water-in-oil dispersion in an electrostatic field will exhibit a mean drop size that is inversely related to the intensity of the field with higher field gradients producing smaller mean drop sizes. Thus it would seem that use of lower gradients would be desirable to produce larger, more rapidly settling drops; unfortunately, the lower gradients are limited in their ability to energize very small drops sufficiently to produce coalescence. This has always necessitated a compromise in operating voltage between coa lescing efficiency and maximum mean drop size. Modulation of the field can help to eliminate this compromise.
Slow Modulation Voltage Cycle
e g a t l o V
Time
Field Control by Load Responsive Controller (LRC®) There are three important variables to consider in modulation of the electrostatic field: - 12 -
• •
•
Threshold Voltage Gradient: This is the minimum gradient at which the field induces coalescence. Critical Voltage Gradient: This gradient, defined in terms of interfacial tension, drop diameter, and dielectric constant, is the maximum field sustainable by a given drop size. Above this value, the energy imparted to the drop causes it to shatter. Modulation Frequency: The frequency of the modulation affects drop transport, drop relaxation, and drop surface energy. Low frequency modulation can be used to control mean drop size, while higher frequencies can be used to vary drop surface energy.
Low frequency modulation, <1 Hz, is used to enhance drop growth and increase the tolerance for conductivity. The critical voltage gradient and threshold voltage gradient define the upper and lower limits, respectively, of the modulation cycle. High frequency modulation, in the kilohertz range, has been shown to energize drops at or near their resonant frequency resulting in drop deformation. Other research has confirmed that the high surface energy of these deformed drops significantly enhances the coalescence rate. TM
Dual Frequency
Devices
NATCO has developed a power supply capable of delivering both high and low frequencies simultaneously to the dehydrator or desalter. This power supply uses a three-phase power connection and a low reactance transformer producing a balanced load and efficient power utilization. It allows selection of waveform, base frequency, and pulse frequency for optimization of electrical parameters to the crude oil being processed. The device has shown significant improvements in performance and capacity in pilot tests of a wide variety of oils and is now moving to the field test stage. It is expected to be an easy retrofit to existing Dual Polarity® or ElectroDynamic® installations since only a change of power supply is required. Conductivity in Dehydrator and Desalter Design Electrostatic coalescence is primarily derived from the effects of the electrostatic field (voltage gradient) rather than the effects of electrical current. Useful effects are therefore mostly due to the reactive (capacitive and inductive) components of conductivity rather than the resistive component. Conductivity due to low resistance results in excessive electrical current with the production of heat instead of coalescence. Resistive conductivity problems in crude oil dehydration can result from carriage of excess water into the electrode zone, excess polar components in the oil, or solidsstabilized emulsions that respond poorly to conventional demulsifiers. High conductivity is conventionally handled by increasing chemical dosage, variation of the operating temperature, lowering the applied voltage, or providing additional upstream facilities for water and solids removal. These approaches are limited by the general ineffectiveness of chemicals on polar components of the oil, excessive viscosity at lower temperatures, and poor coalescence of small drops at lower applied voltage. The establishment of the electrostatic field may result in current across reactive components - 13 -
(capacitance and inductance), resistive heating of high conductivity materials such as rich emulsion layers, and arcing. The first of these is desirable while the second is not. Arcing falls in between. It is helpful to subjectively divide arcing into “hard” (high energy) arcs and “soft” (low energy) arcs. “Hard” arcs occur when the arc extends from an electrode to ground or between differently charged electrodes. In either case the “hard” arc is detrimental to the process and consumes energy while producing minimal benefits. “Soft” arcs occur between electrodes and water drops or from drop to drop and can aid the coalescence process by disrupting the stabilizing films around the drops. Arcing is a natural part of the electrostatic coalescing process, but it must be controlled to prevent field loss and hardware damage. High conductivity must be dealt with both operationally and in the design phase of the dehydrator or desalter. Operational issues include selection of demulsifier type and dosage, possible use of wetting agents to assist in transferring the solids to the water phase, temperature, interface control, and removal of accumulated solids via mud wash (sand jets) and interface sludge drains. Oil conductivity increases with temperature, often necessitating a compromise between reduction of viscosity and limitation of oil conductivity. Design options in addition to provision of solids removal mechanisms include the use of current-limiting composite electrodes and modifications to the electrostatic field. Composite Electrodes Composite electrodes are fiber-epoxy plates with an embedded longitudinal strip of conductive material. The conductive material distributes the electrical charge along the length of the plate. The remainder of the plate surface contains a hydrophilic filler material, which results in the adsorption of a thin layer of water, which then becomes a highly resistive electrode. Electrical current passing from the electrode plate into the process then must pass through the resistive surface water layer, which results in a rapid drop in voltage at the point of departure. If the departure point is an arc, the falling voltage at the root of the arc quenches the arc while only discharging the electrode area in the vicinity of the arc root. By contrast, an arc in a steel electrode array momentarily discharges the entire array, and if there are a significant number of arcs, the time of discharge can produce diminished performance of the coalescer. A conceptual illustration of composite electrodes is shown below.
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Composite Electrodes
+
Conductive Strip
-
+
-
Epoxy Plate
If electrical current passes from the composite electrode into a c onductive fluid, e.g. a zone of high water content, the voltage of the plate in the vicinity of the conductive fluid will be diminished. The reduced voltage will cause a similar reduction in current with the result that the electrode be comes self-regulating. This variation in field strength with conductivity can cause the lower portion of the plate, which is closest to the water-rich portion of the dehydrator, to be at a lower voltage than the upper portion, which is in contact with drier oil. A settling water drop will therefore encounter a declining voltage gradient as it moves downward. Since lower gradients are associated with larger mean drop sizes, drop growth is enhanced. Devices that modify the electrostatic field, such as the Load Responsive Controller ® previously discussed, can achieve a similar reduction of arcing. Since arcs are more difficult to initiate than to sustain, they tend to persist until something reduces the voltage feeding them or interrupts the conductive structure (such as a chain of drops) upon which they depend. In a modulated field, the low voltage portion of the cycle can produce quenching of any arcs present while allowing the larger drops to fall from the field thereby destroying any “daisy chain” arc paths that might have formed. A photograph of a composite electrode array is shown below. The darkened zones along the plates are the conductive areas. Electrical contact is made via the support rails through the support straps to the conductive material. The insulating hangers which normally support the array may be seen - 15 -
protruding up from the rails, although support in the display assembly is through the steel frame. Note the fiber epoxy channels at the ends of the plates which are used for maintaining plate spacing.
Composite Electrodes
Electro-Dynamic® Desalters Conventional desalters use mechanical mixing devices such as mixing valves and static mixers to shear the dilution (wash) water into the crude oil stream. The mixed stream is then dehy drated in a high efficiency electrostatic dehydrator. Mixing intensity must be carefully balanced against the ability of the dehydrator to resolve the resulting dispersion. The physical arrangement closely approximates a typical mixer/settler system and suffers from the same limitation of maximum possible contact efficiency of one theoretical stage per physical stage. Therefore if process requirements call for more efficient contact, it is ne cessary to provide multiple stages in series. By manipulating the relation of drop size to field strength, the electric field can be used to both mix and separate. Drops of dilution water subjected to high field strength can be sheared to uniform sizes by the combination of translational shear and shattering due to charge density instability, and then as the field strength is lowered, they coalesce with the entrained brine and settle out. It is worth noting that most of the contact between the brine and the dilution water occurs as the two are coalesced together, not in the mixing device which shears them. Therefore, multiple coalescence - 16 -
events contribute much more to contact efficiency than increasing shear in a mechanical device. By cycling the field strength, the process can be repeated many times during the retention time of the drops within the electric field. As a result, the contact efficiency of a multi-stage mixer-settler can be realized in a single vessel. Since the electrical force is concentrated on the dispersed phase, loss of energy due to shear of the continuous phase is reduced. Turndown and low dilution water flow rates are readily accommodated. Introducing dilution water above the electrodes so that it falls by gravity into the electrostatic field field leads to an electrostatic mixing systems that operates with countercurrent contact as opposed to conventional systems which are limited to concurrent con tact by the nature of the mixing device. Countercurrent flow optimizes dilution water use by ensuring contact between the freshest water the cleanest oil. This ensures maximum effectiveness of the dilution water and results in minimum dilution water requirements. This flow pattern also has the effect of placing fresh water near the outlet so that any residual water carry-over will be free of salt. The Electro-Dynamic® Desalter incorporates the principles of field strength control, electrostatic mixing, and countercurrent flow. Field strength control can be accomplished in several ways. One approach is the use of composite electrodes of varying conductivity. High field strength exists across zones of high electrode conductivity, and reduced field strength is found in the regions of lower electrode conductivity. Such electrode plates have the advantage of maintaining graduated field strength under a range of operating conditions. They are also "self limiting" under arcing conditions. These characteristics are necessary for operation with the high water content in the electrode zone produced by countercurrent dilution water addition. Another method of controlling field strength is variation of the transformer output voltage to create time-based field decay rather than a spatial variation in strength. Since this method is based on time, it can easily be tailored to the kinetic needs of the process. It also can be used to eliminate excessive "hold-up" of small drops in the zones of high field intensity, which could lead to excessive arcing if unchecked. The electrostatic mixing process requires both the composite plate technology and the modulating controller. Four distinct stages have been identified in the mixing and coalescing process with unique field strength requirements for optimum performance of each stage. These are as follows:
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Dispersal: A fast ramp-up of voltage to the mixing voltage provides rapid reduction of the large drop population and coalescence of small drops. Mixing: Sustained high intensity field for maximum drop subdivision and dispersal. Coalescing: Voltage ramp-down permits optimum drop growth. It is in this stage that most of the contact between the dilution water and the entrained brine occurs. Settling: Sustained low intensity field for drop growth and sedimentation and to control aqueous phase hold-up between the electrodes. During this interval, the large drops move downward, resulting in a step-wise sedimentation over several cycles of modulation. Each of these stages can be adjusted for optimum intensity and duration using the Load Responsive Controller ® (LRC). Often it will be found necessary to institute a small compromise between dehydration (coalescing and settling) and contact efficiency (dispersal and mixing). The compromise is small because, in the presence of countercurrent flow, the water carry-over produced by intense mixing is mostly fresh water; therefore, desalting efficiency is not diminished. Countercurrent flow is essential for realization of the full potential to be gained by multiple stages of mixing and coalescence. To achieve this benefit it is necessary to introduce dilution water above the electrodes in the zone of dry oil. The water must remain as coarse drops in this area to prevent carry-over. Uniform distribution is desired, although the electric field produces some amount of distribution and will overcome mild maldistribution. The simplest way of spreading the dilution water above the electrodes is through a system of laterals with orifices sized to produce a small pressure drop at design flow rates. Because of increased contact efficiency, less dilution water is usually required in this system. Sometimes other benefits may accrue in injecting any excess water into the feed stream,e.g., reduced upstream heat exchanger - 18 -
fouling, satisfaction of solubility requirements of water in oil as the temperature increases, or crystalline salt removal. This water can be either additional dilution water or recycled desalter effluent water. Use of recycled water in this manner can reduce dilution water requirements and minimize waste water production. A mixing device (valve and/or static mixer) is used upstream of the EDD desalter for mixing either the additional dilution water or recycled water. The Electro-Dynamic Desalter ® is a system consisting of electrostatic mixing, the Load Responsive Controller ®, composite electrodes, and countercurrent flow of the dilution water. Both the composite electrodes and the LRC® have been applied in oilfield dehydration systems for many years and have proven to be reliable and effective. Current implementations of EDD systems use the modulated Dual Polarity® field; however, it is anticipated that future versions may utilize the Dual TM Frequency field. Use of the Electro-Dynamic® Desalter should be considered in any of the following circumstances: 1. Space is limited and more than one stage of desalting is required. 2. Outlet salt specifications are very low (less than one pound per thousand barrels of oil, PTB). 3. Dilution water quantity or quality is limited. 4. Minimization of wastewater is required.
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Electromax® Dehydrators The Electromax® Dehydrator utilizes a combination of electrostatic and mechanical coalescing mechanisms. The electrostatic section is constructed as a Dual Polarity® coalescer with two major differences: the flow through the electrodes is in a downward direction producing a downward acceleration on the settling water drops, and the flux is much higher than that obtained using normal sizing criteria. The liquids then flow horizontally through a Performax® matrix plate coalescing section that produces rapid coalescence. These dehydrators have found wide application in Canadian medium heavy oils.
Electromax® Treater
Summary of Processes AC Configurations Application: Field and refinery desalting systems, particularly where inlet water concentration is high and outlet salt requirements are moderate.
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Strengths: • • • • •
Provides dipolar attraction for coalescence Electrode asymmetry produces dielectrophoretic transport Disrupts stabilizing films by stretching action Tolerates relatively large water concentrations Assists in condensation of interface band dispersions
Weaknesses : • Very limited drop movement • Short-range attractive forces • Low charge density on drops results in small attractive forces • Little influence on small drops • Electrostatic instability limits use of high strength fields • Depends upon diffusional movement for coalescence of residual water Experience: Hundreds of units deployed in oilfield and refinery dehydration/desalting worldwide. Improvements: Any of the configurations that result in increased retention in the high intensity zone of the electrostatic field will result in improved performance. These include both multiple electrode and plate electrode designs.
Dual Polarity® (AC/DC) Configurations Application: Refinery and oilfield dehydration/desalting systems requiring dehydration to low levels. Strengths: • • • • • • • •
Dipolar attractive forces High charge density due to charge transfer to drops Electrostatic attraction beyond dipolar forces Electrophoretic drop transport reduces reliance on diffusional movement Remains effective in coalescence of residual water Sustains higher flux due to increased coalescence Disrupts stabilizing films Reverts to AC mode during severe process upsets
Weaknesses : • Maximum field strength dictated by electrostatic instability limit • Loses DC component during severe process upsets • Excessive conductivity (such as high interface or large emulsion band) may - 21 -
result in DC current flow to the interface. Experience: Over 2000 in use in refineries and oilfields worldwide in both dehydration and desalting applications. Improvements: Can be fitted with composite electrodes for high water tolerance and the Load Responsive Controller ® for difficult or conductive oils. May be operated in Pulsed Dual Polarity® mode to obtain maximum coalescence with difficult feed-streams and to preserve effectiveness during process upsets. TM
Dual Frequency
Configurations
Application: Refinery or oilfield dehydration and desalting systems requiring maximum throughput and maximum dehydration performance.
Strengths: • • • • • •
Superior coalescence Higher throughput Better power utilization Balanced electrical load Three-phase power feed Tolerates conductive oils
Weaknesses: • More expensive controller • Limited field experience Experience: The system has successfully completed pilot testing on a variety of oils. Preparations for field testing of a full-scale dehydrator are on-going.
Electro-Dynamic® Desalter Application: Refinery or oilfield desalting systems requiring maximum desalting performance, operations with low quantity or poor quality of dilution water, or offshore applications with space limitations. Strengths: • • • • •
Dual Polarity® field for superior coalescence Composite Electrodes for maximum water tolerance Load Responsive Controller® to minimize process upsets Electrostatic mixing for multiple contacts Multistage contact through countercurrent flow - 22 -
• • • •
Minimum dilution water usage High strength electrode array Maximum washing of suspended solids by countercurrent dilution water Minimum outlet salt
Weaknesses : • Larger transformer used to supply mixing energy in addition to coalescence • Transformer input limited to 520 VAC due to limitations of SCRs • Excessive conductivity can result of loss of mixing intensity Experience: Approximately thirty of these systems have been sold to date in applications ranging from refinery desalting to turbine fuel treatment to floating production oil processing. Improvements: Entrance bushings for very high voltage, composite material electrode plates for high temperature applications, and controllers employing the latest in microprocessor technology have become standard features.
Electromax® Dehydrators Application: Oilfield crude oil dehydration systems treating heavy or difficult emulsions, particularly where heat is limited or chemical usage is high. Strengths: • Combines the coalescing force of both electrostatic and mechanical processes • Optional LRC® provides most efficient use of electrostatic field with minimum upsets • Dual Polarity® field provides superior coalescence • Composite Electrodes provide high degree of water tolerance • Sedimentation in co-current flow minimizes adverse viscosity effects Weaknesses : • Insoluble hydrocarbons (waxes, asphaltenes) can necessitate periodic cleaning of coalescer matrix-plate section Experience: Over fifty units are now in service in Canada, Ecuador, and Russia on oils o ranging from 12º to 39 API. Time-in-service ranges back to 1984.
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Performance Case Studies: Actual Installations Client: Refinery, New Mexico, USA Desalter Type: Electro-Dynamic®, Single Stage, 8' x 19' Year Installed: 1991 Throughput: 16,000 to 19,000 BPD Crude Oil Properties: o Gravity: 43 API Inlet BS&W: 0.32% Inlet Salt: 17 PTB o o Viscosity: 76 cp @ 110 F; 14 cp @ 180 F o Operating Temperature: 220 F Operating Pressure: 200 psig Outlet Conditions: Salt: 0.53 PTB (year-long average; 48% of readings are 0.3 or less) BS&W: 0.18% Performance: Averaged data taken for the period of one year after retrofit indicated crude oil rate of 16,000 BOPD, inlet salt of 16.8 PTB, inlet BS&W of 0.32%, outlet salt of 0.53 PTB (48% of the data points are 0.3 PTB or less), and outlet BS&W of 0.18%. Dilution water is added both in the counter-flow mode (2%) and upstream of the mixing valve operating at 12 psid. Notes: This is a retrofit of an AC unit which had averaged 1.40 PTB at an average crude oil rate of o 14,161 BPD and treating temperature of 219 F for the year prior to retrofit.
Client: Refinery, The Netherlands Desalter Type: Dual Polarity®; two trains of two stages each Year Installed: 1984-1986 Throughput: 540,000 BPD total Crude Oil Properties: o Gravity: 32 - 43 API Inlet BS&W: 0.2 - 0.3% Inlet Salt: 10 - 50 PTB Viscosity: NA o Operating Temperature: 240 - 280 F Operating Pressure: NA psig Outlet Conditions: Salt: 1 PTB BS&W: <0.1% Performance: Salt is reported as usually down to 1 PTB as measured by atomic absorption in the atmospheric residual. Outlet salt tends to peak d uring feedstock changes to 3 PTB and then declines - 24 -
to 0.5 PTB over the course of the run. Notes: Solids removal >70% reported for Middle East crude oil. Various crude oil blends including Maya and Arabian Heavy crude oil are processed. This installation uses static mixers downstream of the mixing valves. Two of the vessels are retrofits and two were new construction. The original installation of AC desalters produced an output of 3 - 10 PTB prior to conversion to Dual Polarity®.
Client: Refinery, Japan Desalter Type: Electro-Dynamic®; three vessels Year Installed: 1993 - 1995 Throughput: 190,000 BPD total Crude Oil Properties: Chinese Arabian Heavy Gravity: 25 27 Inlet BS&W: 0.6 0.3 Inlet Salt: 3 5 Viscosity: 55 12 Operating Temperature: 275 262 Operating Pressure: Outlet Conditions: Salt: 0.9 0.5 BS&W 0.3 0.2
Arabian 31 0.05 1.8 8 266
o
0.7 0.2
PTB %
API % PTB o cSt @ 50 C o F psig
Notes: These vessels are operated as second stage desalters following conventional AC units. The previous AC units were unable to process the Chinese Shouri crude oil satisfactorily due to its high conductivity and high solids content. Chlorides in the crude tower overhead s were reduced from 16 ppm with the two-stage AC system to 5 ppm after retrofit of the second stage to EDD. Two of the vessels are retrofits and one is new.
Client: Petrochemical Plant, Thailand Desalter Type: Electro-Dynamic® Year Installed: 1995 Throughput: 27,000 BPD** Crude Oil Properties: o Gravity: 37 API Inlet BS&W: 0.01 -0.04% Inlet Salt: 2.9 PTB Viscosity: 0.46 cp @ Operating Temperature o Operating Temperature: 265 F Operating Pressure: 150 psig Outlet Conditions: Salt: 0.22 PTB BS&W: 0.16% - 25 -
Notes: Performance data were taken during performance test. Dilution water: 1.6%water injected ahead of pre-heat train, 2.9% counter-flow, and 0.5% recycle to the mixing valve. Mixing valve differential pressure = 14 psid. **Vessel designed for expansion to 52,000 BPD.
Client: Field Desalters, Egypt Desalter Type: Dual Polarity®: two stage with recycle; seven trains Year Installed: 1976 through 1989 Throughput: > 500,000 BPD total Crude Oil Properties: o Gravity: 31 API Inlet BS&W: 10% Inlet Salt: 5,000 PTB Viscosity: NA o Operating Temperature: 165 F Operating Pressure: 100 psig Outlet Conditions: Salt: 10 PTB (typical Middle Eastern shipping specification) BS&W: <0.2% Notes: These are oilfield desalters. The early trains were installed in the 1960's as double-hot AC units. The AC trains have all been retrofitted to Dual Polarity® resulting in an 82% increase in capacity. Some of the first-stage units are configured as NATCO Plate AC.
Client: Field Desalters, Kuwait Desalter Type: Dual Polarity® (first stage) and Electro-Dynamic® (second stage); six trains Year Installed: 1992 Throughput: 30,000 BPD per train Crude Oil Properties: o Gravity: 32 API Inlet BS&W: 3-6% Inlet Salt: 300-900 PTB Viscosity: 6 cp at operating temperature o Operating Temperature: 148 F Operating Pressure: 80 psig Outlet Conditions: First Stage Second Stage Salt: 60 PTB 1 PTB BS&W: 0.1% 0.1% Notes: These are oilfield desalters. Dilution Water: 1.5% ahead of second stage mixing valve, 1.8% second stage counter-flow, 3% inter-stage recycle. Mixing valve differential pressure = 10 - 11 psid. Second stage Electro-Dynamic® units were specified based on poor quality of available dilution - 26 -
water.
Client: Field Desalters, Saudi Arabia Desalter Type: Double-Hot AC and Dual Polarity®; 31 trains Year Installed: 1979-1993 Throughput: >8,000,000 BPD total Crude Oil Properties: o Gravity: 27-40 API Inlet BS&W: 5-30% Inlet Salt: 5,000 to 30,000 PTB Viscosity: NA o Operating Temperature: 90-200 F Operating Pressure: 150 psig Outlet Conditions: Salt: <10 PTB BS&W: <0.2% Notes: These oilfield desalters are configured in two- and three-stage trains with recycle water.
Client: Refinery, Ecuador Desalter Type: Dual Polarity® Year Installed: 1988 Throughput: 10,000 BPD Crude Oil Properties: o Gravity: 31 API Inlet BS&W: 0.5% Inlet Salt: 60 PTB o Viscosity: 3.2 cSt @ 115 C o Operating Temperature: 248 - 300 F Operating Pressure: NA psig Outlet Conditions: Salt: 3 PTB BS&W: 0.2%
Client: Power Company, Korea Desalter Type: Electro-Dynamic®, two vessels Year Installed: 1992 Throughput: 42,000 BPD total Crude Oil Properties: - 27 -
Gravity: Inlet BS&W: Inlet Salt: Viscosity: Operating Temperature: Operating Pressure:
o
34 - 38 API Varies (BS&W derived from salt water contamination during transit) + + 2.3 ppm Na + K NA o 100 F NA psig
Performance: The units were tested and accepted by the client. Specific performance data are not available. Notes: These desalters are used to reduce sodium and potassium salts to 0.5 ppm in turbine fuel at power generation facilities.
Operational Parameters Chemical Treatment Resolution of water-in-oil emulsions requires both chemical and physical interven tion and may be considered as a three-step process. 1. Coagulation: The chemical destabilization of the system. Before dispersions can be coalesced by electrostatic fields, it is necessary to destabilize any true emulsion present. True emulsions can be defined as drops that would remain suspended indefinitely due to the effects of chemical surfactants, films of precipitated matter, or collections of suspended solids at the interfacial surface. Electrostatic forces alone cannot overcome these stabilizing agents. Chemical treatment with demulsifiers is used to counteract the natural surfactants present, and wetting agents or other chemicals are sometimes used to carry the suspended solids into the water layer. The presence of a band of emulsion in centrifuged samples indicates that further chemical treatment may be needed. 2. Flocculation: The gathering of the destabilized particles into larger units. Although chemicals can be used to flocculate a system, this is undesirable where recovery o f clean oil is the goal, since chemically flocculated oils tend to be sludges. Electrostatic processes are usually the method of choice for rapid agglomeration of water drops in oil. 3. Sedimentation: Settling of the flocculated particles resulting in phase separation. Sedimentation efficiency is controlled by physical design of the dehydrator or desalter vessel and operating conditions such as control of viscosity with temperature. Design of the fluid distribution systems and elimination of excessive interface accumulations are critical to realizing optimum sedimentation rates. Types of Chemicals: Although demulsifiers are the primary chemicals used in dehydrators and desalters, wetting agents to aid in separation of solids from the oil, “reverse” emulsion breakers for separation of oil drops from the water phase, and specialty chemicals such as paraffin inhibitors, asphaltene solvents, etc. may also be employed. - 28 -
Selection of Chemicals: It is common practice to screen a variety of demulsifiers for a given application. The “bottle test”, in which the oil is shaken with a chemical sample and the volumes of the separated phases are measured, is the most common screening technique. The dehydrated oil quality is estimated visually by “brightness”. However, since bottle testing relies on the chemical for both coagulation and flocculation, it is often not representative of performance with an electrostatic field in which the field is the flocculating agent. An electrostatic test apparatus produces much more reliable results for chemicals to be used with electrostatic dehydrators. The following table illustrates the differences obtained with bottle testing and electrostatic testing.
Comparative Results: 19.5ºAPI Brazilian Crude Oil Chemical Bottle Test Electrostatic Bench Test Water in Oil BS&W % by Difference Measured % A 2.2 2.12 B 4.6 2.01 C 5.3 4.62 D 5.7 1.20 E 6.0 2.35 Best Performance It should always be remembered that the chemicals and electrostatic fields play mutually supportive roles. Operating Temperature Operating temperature is used as the primary control of viscosity in an oil dehydrator or desalter. The lower the viscosity, the better the performance as drag on the settling drops is reduced. As a rule of thumb, the maximum viscosity for effective dehydration is usually assumed to be approximately 20 centistokes while the maximum viscosity for effective desalting is about 7 centistokes. The temperatures at which these viscosities are obtained are therefore the minimum operating temperatures for these operations. Lower viscosities are desirable, but care should be taken that differential density between the phases, which is also a function of temperature, is not adversely affected. For conductive oils, the increase in conductivity with temperature must also be considered. Likewise, the increased solubility of water in oil at elevated temperatures must be factored into performance when absolute dehydration is a factor.
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Process Flux The process flux is the volume of oil per unit of time that passes through a unit area as measured at the horizontal longitudinal plane through the vessel centerline. Since the settling water drops must fall through the rising flow of oil, the minimum drop size capable of achieving a net downward velocity increases as process flux increases. Therefore, to achieve high process flux (minimum vessel size) it is necessary to coalesce the drops to larger sizes, to reduce the viscosity, and to maximize differential density in order to produce high sedimentation rates. Mechanical dehydrators, those that depend upon retention time alone for sedimentation, are often configured for horizontal flow of the oil, so that the settling water drops do not have to counter the upward velocity of the oil. This configuration does not work well for electrostatic dehydrators because the requ ired electrical clearance between the electrodes and the oil/water interface allows bypassing of poo rly treated oil. Flow distribution within the dehydrator vessel has been found to be the flux limiting factor in many cases. Recent advances in achieving more uniform flow distribution have significantly increased the available process flux. Dilution Water Dilution water of sufficient quantity to satisfy mass balance requirements for diluting the dispersed brine down to a level such that the salt specification can be met at the residual BS&W of the outlet oil must be available. The effectiveness of this dilution reaction will be diminished by a factor known as “mixing efficiency” which incorporates a variety of influences such as mixing intensity and duration, diffusional transport, inter-drop collision frequency, etc. Dilution water quality must also be considered and can be a problem due to high pH, the presence of surfactants, or other conditions that can lead to increased emulsion stability. It is obvious that in order to remove salt, the dilution water must be sufficiently low in salt content to achieve the required equilibrium concentration in the residual entrained water. However, not as obvious is the need for dilution water quality sufficient to avoid contributing to an emulsification process. Streams containing considerable amounts of coke particles, suspended solids, iron sulfide, or emulsified oil should not be used. Neither should streams containing traces of surfactant chemicals or excess caustic soda. Ammonia should be limited to less than 200 ppm to avoid fouling and corrosion in the crude distillation unit overhead as well as to limit pH excursions. The pH of the water should be below 9.0 and provision for acid injection for pH control should be made if higher values are expected. Neutral pH values (pH 7 – 8) are preferred. High pH may enhance the formation of stable emulsions while pH values under 6.5 may raise corrosion concerns within the desalter vessel, although low pH is not usually detrimental to the dehydration process. The water should contain less than 0.02 ppm oxygen, less than 1 ppm fluoride, and should be low in sodium salts, suspended solids, and hardness. In refineries, the most common source of dilution water is the sour water stripper. The desalter then serves to remove phenols from the stripped sour water, and for that reason, it is often desirable to use the entire stripped sour water stream as dilution water. Dilution water is usually injected into the oil - 30 -
stream just before the mixing device (mixing valve, static mixer, etc.) but may also be injected before the pre-heat train or heater, or, in the case of the Electro-Dynamic® Desalter, into the overhead water distributor. Frequently, a combination of these injection points is used. Oilfield dilution water is often limited in quantity and quality. It may be taken from a fresh water source (aquifer, surface water, reverse osmosis system, or municipal supply), a low concentration brine aquifer, or even seawater in some offshore applications. Of course, use of brine or seawater will limit the ultimate salt removal obtainable. Water Recycle Contact efficiency or collision frequency between drops of dispersed brine and dilution water is dependent upon the drop populations. Increasing the number of dilution water drops results in more efficient contact. Since quantities of dilution water available are usually limited, the recycle of effluent water is often used as a means of increasing drop population. Effluent water from the desalter is much less saline that the dispersed brine, so it can be used to achieve further dilution. Recycle may take one of two forms: inter-stage and intra-stage. Inter-stage recycle is commonly practiced where more than one stage of desalting is required. Fresh dilution water is injected into the mixing zone of the final stage desalter and effluent water from this stage is used as dilution water in the first (or prior) stage desalter. Intra-stage recycle is of limited practicality because it requires mixing of the recycle water and fresh water, thereby lessening the effectiveness of the fresh water. However, with the Electro-Dynamic® desalter, it is feasible to inject recycle water ahead of the mixing valve while injecting fresh water into the counter-flow distributors achieving increased drop population without raising the salinity of the fresh dilution water. A point of caution with all recycle streams involves the quality of the effluent water. If interface sludge or mud wash solids are allowed to recycle, they may produce stable emulsions and cause rapid build-up of the interface sludge layer. If this problem appears likely to occur, the recycle should be taken after an effluent water-cleaning device, or recycle should be discontinued during mud wash. Effluent Water Treatment The effluent water from a properly operating desalter, exclusive of mud wash cycles, is frequently less than 250 ppm oil in water. Field dehydrators may carry more oil in their effluent water depending upon the conditions of the crude oil being treated. Further clarification of the water calls for additional retention time, customized chemical treatment and/or specialized equipment that are more economically provided downstream of the desalter vessel. Clarification devices include skimmers equipped with matrix coalescer plates, granular media coalescers, hydrocyclones, flotation cells, and solvent extraction techniques.
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Water Solubility in Crude Oil Water exhibits an appreciable solubility in crude oil at elevated temperatures. As a rule of thumb, approximately 0.4% water may be o dissolved at temperatures around 300 F. A desalter or dehydrator can separate only dispersed water and has no effect on water that is soluble at operating conditions. However, when the output is sampled through a sample cooler and the sample is further cooled awaiting analysis, a significant quantity of soluble water may be precipitated. This precipitated water may be erroneously assumed to be dispersed water in the effluent oil. A more insidious aspect of water solubility occurs in the preheat train ahead of a desalter. As the oil is heated to operating temperature, water from the dispersed brine is dissolved into the oil phase while leaving behind precipitated salts. This can result in the fouling of the heat exchangers and formation of crystalline salt that is very difficult to remove from the oil. Injection of fresh water or dilution water ahead of the preheat train can help offset these problems. Incompatibilities of Fluids Crude oils may contain quantities of semi-soluble organic materials, such as wax es or asphaltenes that can be precipitated during processing resulting in the production of troublesome sludges or stabilization of emulsions. Although wax precipitation may be controlled through temperature and chemicals, asphaltenes are more troublesome. By definition, asphaltenes precipitate in hydrocarbons of the molecular weight of pentane. Therefore, if light hydrocarbons are blended with asphaltic crudes or recycled as slop oil into a vessel processing asphaltic crude oil, serious sludge precipitation may result. Such sludges can result in short-circuiting of the electrodes and severe deterioration of dehydrator/desalter performance. Dilution water can also be a source of incompatibility. Of particular concern is the precipitation o f alkaline earth sulfates (calcium, barium, or strontium sulfates) when sulfuric acid is used to a djust pH of entrained brines rich in these ions, or when high sulfate dilution water (such as seawater) is used with such brines. Analytical Methods Analysis of bulk sediment and water (BS&W) in oil is commonly done by centrifugal techniques described in ASTM D-96 (field use) or ASTM D-4007 (laboratory use). Alternately, distillation techniques may be employed as described in ASTM D-95 or ASTM D-4006, but these are more - 32 -
cumbersome, and will reflect both insoluble and soluble water. For very low levels of water, particularly soluble water, the Karl Fischer Titration method may be employed. Several analytical procedures for salt in oil are currently in use depending upo n the salt levels to be measured, the accuracy required, and the equipment available. Laboratory results are usually obtained by analysis of total chloride ion followed by conversion to equivalent sodium chloride and reported as pounds of salt per thousand barrels of oil (PTB) or parts per million (ppm). At salt levels of 2 PTB and below, great care is required in order to achieve meaningful and reproducible results. Although several analytical schemes are available for salt analysis, extraction and analysis of soluble salts has proven to be the most reliable method with the least interference from other constituents. The procedure involves diluting an oil sample with xylene and extracting the mixture with boiling deionized water. The extraction funnels are then placed in a water bath at 140º to 160ºF for phase separation to occur. If necessary, acidification, electrostatic cells, or chloride-free emulsion breaker may be used to enhance separation. The aqueous layer is removed and filtered if it is still cloudy or if entrained oil is present. It is then titrated with dilute silver nitrate (0.01N) using chromate indicator under incandescent lighting. The titration procedure is known as the Mohr Method and is more fully described in American Petroleum Institute Recommended Practice RP 45. Endpoint recognition requires a practiced eye when using dilute titrant. Alternately, ion chromatography may be used for chloride determination if available. This technique is extremely accurate for determination of small quantities of chloride, but the equipment is more expensive. Care must be taken to avoid contamination of the sample during handling due to the widespread occurrence of chloride in nature and the very small quantity being measured. Another method in common use is the spectrophotometric determination of the metals – sodium, calcium, and magnesium. These techniques, using atomic absorption or inductively coupled plasma, are accurate and highly automated. However, they do not distinguish between water-soluble salts and those that exist primarily in the oil phase such as metal-organic compounds or mineral precipitates. Therefore, the results obtained with these methods may be poorly related to desalter performance. Analysis by conductivity, as described in ASTM D-3230, is a widely used technique for process monitoring and quality control. It is reliable for salt concentrations above five pounds salt per thousand barrels of oil (PTB); between two and five PTB, it is suitable if careful calibration is done. Below 2.0 PTB, other methods should be utilized. At low salt levels, oil conductivity becomes a function of water content and pH as well as salt content. Since the ions responsible for pH changes are from 2.6 to 4.6 times as conductive as chloride, minor pH changes far outweigh the effects of changes in chloride concentration. Other problems such as variation in the composition of the salt mix in oils also help to preclude the use of this method as a reliable indicator of absolute desalter performance at low effluent salt contents unless exacting calibration procedures are followed.
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Power Consumption The power expended in electrostatic coalescence may be largely consumed by current flow through the conductive liquids. This power is mostly converted to resistive heating with little of it actually used in the coalescence reaction. Transformers are sized according to power flux criteria with adjustments being made for known characteristics of the oil to be treated and the operating temperature. However, it should be remembered that dehydrator and desalter transformers are sized conservatively in order to allow them to operate in the lower 30% of their capacity due to reactive losses associated with the transformer protection scheme. Therefore, the operating load is roughly 30% of the connected load.
Sub-System Specifications Power Supplies Transformers :
Transformers used in dehydrator and desalter power supplies must be capable of sustaining a short-circuited output for a reasonable period of time without damage or overheating. This protection is normally derived by including a reactor of a size equal to the reactance of the transformer winding in series with the primary winding of the transformer. The reactance may be either a separate inductor coil or may be incorporated into the design of the transformer core. As the primary current increases, the voltage drop across the reactor increases, thereby limiting the voltage to the primary winding of the transformer. Therefore, failures in the vessel electrical components or proce ss upsets causing high conductivity will not result in damage to the transformer when sustained for a reasonable period of time. Transformers in this service also experience high mechanical stresses due to rapidly fluctuating loads and must be constructed with cores and windings that are mechanically solid and highly resistant to vibration. See Appendix III for additional details. Controllers :
A weakness of electrostatic coalescers has been the means of protecting the electrical system in the event of excessive power requirements during short term upsets. Unfortunately, the reactor-based protection scheme described above has the effect of reducing power input to the vessel at precisely the time it is most needed – during process upsets. To counteract this situation, an electronic controller capable of sensing the load demand and modifying the power input to the transformer was developed. This Load Responsive Controller ® differs in action from the reactor in that power is reduced on the basis of time rather than by uniformly diminished output. Short bursts of high intensity energy are applied to the process with duration of the pulses limited to maintain an average power output within the rating of the transformer. This action continues to provide coalescing energy even during times of process upset. - 34 -
The Load Responsive Controller ® also assists in the compromise that must be drawn between field strength required for adequate translation of small drops and field strength sufficient to produce subdivision of large drops. As drop size increases and the surface-to bulk ratio decreases, surface tension is no long er able to maintain rigidity of the drop, and viscous drag on the moving drop causes deformation. As velocity or drop size increases, this deformation, in concert with electrically induce d perturbations, becomes sufficient to cause the drop to shatter. At any given field strength there is a range of stable drop sizes limited at the lower end by the ability of the field to transport the drop and at the upper end by drop size that can be transported without shattering. An ideal arrangement would be a field with a high intensity zone for coalescence of very small drops followed by gradually decreasing field strength for shifting the equilibrium drop size range to large values. In order to accomplish this, the LRC® may be programmed to vary the transformer output voltage to create time-based field decay. In addition to providing optimum field strength for coalescence of a wide range of drop sizes, the LRC® can also be used to provide high intensity fields suitable for both mixing (in the case of Electro-Dynamic® desalters) and dehydration. The Load Responsive Controller® has evolved from its original monolithic configuration to a distributed form with the electronic switching mechanism, SCR firing circuit, and interface circuit contained within the transformer housing. The interface provides the signals to the firing circuit and handles lost communication events. It communicates with a controller via a 4-20 ma signal circuit. The controller can be located in a control room, motor control center, or locally. It supplies the set points and waveform information to the interface and also monitors operation. The controller is able to communicate with a computer via an RS 232 interface that enables the operator to change set points and waveforms and to monitor operation. The LRC® software installed on the computer maintains a database of authorized operators, set points for various feed-stocks, and an inventory of power supplies to which it is connected. TM
The Dual Frequency LRC is an advanced power supply combining voltage, waveform, and frequency controls with a specially designed transformer. This power supply is capable of allowing selection of waveform, maximum and minimum voltages, and two frequencies simultaneously for the dehydrator or desalter. It uses a three-phase input and a low reactance transformer for load balance and efficient power utilization.
Insulators Entrance Bushings:
Entrance bushings are the insulated pressure sealing devices used to conduct high voltage into the dehydrator/desalter vessel. NATCO currently offers two styles of entrance bushings: the EBD-1500 (or its variant, the EBD-1500S) and the SBA-2500. The EBD-1500 is a 1.5 inch diameter bushing used in electrostatic dehydrators and desalters operating at up - 35 -
to 23 KV secondary voltages. It is constructed of a polyimide core for strength and temperature resistance and covered by a sleeve of Teflon®. The sleeve is used because of Teflon®’s superior resistance to fouling by foreign substances such as suspended solids or precipitated organic materials. If such materials collect on the surface of the insulator, a resistive electrical path will be formed that will conduct a small current and produce localized heating. This heating can result in the formation of a carbonized track along the insulator surface that will ultimately lead to failure of the insulator. The SBA-2500 is a two-inch diameter entrance bushing used with pulsed transformers and those operating at secondary voltages in excess of 23 KV. It is of all fluorocarbon construction. Details of construction and installation of entrance bushings are given in Appendix III. Electrode Hangers:
Electrode hangers are insulating devices that mechanically support the electrostatically charged elements inside the desalter vessel. NATCO has three types of insulating hangers in general use. These are described as follows: (A) Standard Hanger: This design uses a one-inch diameter Teflon® rod with threaded endcaps attached to swivels and J-hooks or threaded studs. It is widely used in oilfield o dehydrators and desalters operating at temperatures less than 250 F. Allowable loading is adjusted based on temperature. Cast virgin Teflon® is strongly recommended for this service. If extruded rod is used, great care must be taken to insure that “poker chip” discontinuities in density do not occur in the rod. o (B) High Temperature Hanger: For applications up to 300 F, a hanger made of two inch diameter cast virgin Teflon® rod is used. The end-caps for these hangers are pinned sleeves. (C) High Strength Hanger: A high strength hanger consisting of a fiberglass core with a Teflon® insulating sleeve is used for high mechanical stress applications such as are encountered in floating production systems or systems which require the use of a minimum number of hangers. These hangers are also tolerant of high temperatures. Details are shown in Appendix III. Electrodes The electrodes are the devices that provide direct contact between the electrical system and the process fluids. Often these are referred to as grids due to the nature of the electrodes originally used in AC dehydrators and desalters. Several types of electrodes are now in general use. Bar Grating or AC Grids
Electrodes made of rectangular arrays of perpendicular steel rods or small diameter pipes were the original AC grids of electrostatic dehydrators and are still in widespread use in AC field devices. Generally, several of these are hung in vertically separated horizontal planes above the longitudinal centerline of the vessel in order to provide increased liquid retention time in the most intense electrostatic field. The spacing between electrodes may be adjustable. These electrodes have the advantage of being inexpensive to construct and easy - 36 -
to carry into the vessel through a manway. A disadvantage lies in the necessity of providing openings of sufficient electrical clearance through each grid for the supports for the underlying grids. These openings can result in a portion of the process flow bypassing the intense area of the electrostatic field. Steel Plates
Arrays of vertically hung, parallel plates with a plate-to-plate spacing of a pproximately six inches and a plate height of six to ten inches may be used in a Plate AC type electrostatic vessel to achieve high retention time in the intense zone of the electrostatic field. Similar plates are also used to provide the combination AC/DC field of the Dual Polarity® process. Composite Plates
Electrostatic coalescence generally proceeds through a mechanism of drop polarization, alignment of the polarized drops, and “chaining” of these drops along the lines of force of the electrostatic field. These conductive chains lead to frequent electrical discharges or arcing between the electrodes. The arcs are a normal part of the process, and because they are submerged in oil, they do not produce any damage. However, an arc momentarily discharges a steel electrode array, and if the arcs occur with sufficient frequency (as in a wet emulsion), the electrodes may be discharged for a sufficient duration for slippage of process fluids without adequate exposure to the field. Composite plate electrodes may be used to increase the water tolerance of the system under such conditions. These electrodes consist of plates of composite (fiber reinforced epoxy) construction with carbon embedded in the central portion of the plate to impart conductivity along the length of the plate. The remainder of the plate contains filler materials that lead to the adsorption of a lay er of water on the plate surface. This adsorbed water layer then becomes the conductive medium along the height of the plate. Since such an adsorbed layer is quite resistive, any arcing that occurs is quickly quenched due to the voltage drop at the arc root. As a result, only the area in the immediate vicinity of the arc is discharged and slippage is eliminated. Composite plates are normally spaced on 5 to 6 inch centers and are approximately 16 inches high. They are optionally used on Dual Polarity® processes for increased water tolerance and in all ElectroDynamic® Desalters. Liquid Distribution Systems Inlet Spreaders:
NATCO has used an inverted trough or open-bottom box spreader with distributor holes in the upper part of the trough for many years. Flow into the trough depresses the oil/water interface inside the trough to provide a static head for creating uniform flow distribution. Changes in flow are reflected in changes in static head allowing for uniform distribution over a wide range of flow rates. This spreader is designed for equal flow out of the orifices as follows: - 37 -
Q = AC 2gh( D1 - D 2 ) Where: 2 A = Area of diffuser holes in ft 3 Q = Flow in ft /sec C = Orifice factor (0.6 - 0.7) 2 g = 32.2 ft/sec
h = Head in ft D1 = Density of water D2 = Density of oil
The box-type spreader has the advantage of being self-regulating to flow changes and in allowing rapid separation of free water and solids before the fluids pass through the orifices. In some instances, e.g. floating production systems, a header-lateral arrangement with perforated pipe laterals is used for the inlet distributor. Similar orifice calculations are used to assure distribution of flow. In both the pipe and o pen-bottom box spreaders, calculations are done to assure uniform flow from the orifices taking into account velocity head within the distributor.
Box-Type Spreader with Open Bottom
∆h { Oil Water
∆h controls
distribution.
Recently, computerized fluid dynamics (CFD) studies have been undertaken on the - 38 -
hydraulics within dehydrator vessels. Previous assumptions were that uniform flow from the distribution orifices would produce uniform bulk distribution within the vessel. However, the CFD studies proved this to be inaccurate and showed large recirculation zones with both TM pipe and open-bottom box distributors. As a result of these studies, a new spreader, HiFlo , has been designed. It consists of a perforated pipe with a partial annular deflector. TM
HiFlo Spreader
In both the computer models and dye-tracer studies, this spreader has been shown to have superior distribution characteristics with fewer recirculation zones. Also, any recirculation zones that exist are confined to the wall area where the downward motion is next to the vessel shell. This helps to minimize any bypassing the might occur between the electrodes and the vessel shell. This distributor is particularly advantage ous in installations involving high process flux or light oils. Outlet Collectors :
A treated oil collector in the upper part of the vessel is also necessary. This collector is either a perforated pipe or a channel with perforations. The NATCO collector is designed as follows:
- 39 -
Q = 19.65Cn d 2 h where d = hole diameter in inches, n = number of holes, and other variables are as above. CFD studies on collectors have found them to be far less sensitive to design than the inlet distributors, but have proved full length collectors to be necessary.
Dilution Water Distributors
Electro-Dynamic® Desalters incorporate a header/lateral spreader system for injecting dilution water above the electrodes. These distributor pipes are drilled with orifices sized to provide a 2 psi differential pressure across the orifices at a dilution water flow equal to 3% of the oil flow. The electrostatic field provides some distribution of the counter-flowing dilution water and the spacing of the orifices is adjusted to assure uniform distribution. Instrumentation and Safety Systems Safety Grounding Floats :
The Safety Grounding Floats are floats mechanically linked to grounding switches located inside the electrostatic treating vessel. These devices ground the electrical systems inside the vessel upon loss of liquid level. They insure that no electrically energized components are exposed to the gas phase and that the electrodes are not energized accidentally during personnel entry into the vessel. (See Appendix III) Low Level Shutdowns :
Shutdown switches may be provided to shut off transformer power in the event of liquid level loss or to shut down the process in the event of high or low interface level. These may be either located in external cages or inserted into the vessel. Interface Controls:
Several types of interface controls are available including weighted floats, capacitance probes, conductivity probes, and radio frequency or “rf ” probes. Selection of the proper control for an application depends upon crude oil characteristics, compatibility with central control systems, and operator preference. Many installations now use the “rf ” probes. These can be used for interface control, high- and low-level interface alarms, bottom sediment detection, and upstream anticipation of feed-stream changes. Solids Removal Systems Since dehydrator and desalter vessels are designed to promote sedimentation, any suspended solids in the feed-stream will also tend to settle out of the liquid stream. If the solids are - 40 -
water-wetted and heavy they will tend to settle through the interface and collect on the bottom of the vessel. In an oilfield situation, these solids often consist primarily of fine sand while in a refinery the solids are usually fine silts. Corrosion products, bacterial debris, or scale minerals may be present in both. If the solids are oil-wetted or intermediate density between the oil and water they tend to collect in a layer at the oil/water interface as a sludge layer, usually accompanied by poorly resolved emulsions and possibly by precipitated hydrocarbons such as asphaltenes. In either case, it will eventually be necessary to remove the solids from the vessel to prevent process upsets. Mud Wash or Sand Jet Systems:
Mud wash or sand jet systems are used to remove sediments from the bottom of the vessel. They consist of a means of fluidizing the sediments by high velocity jets of water and a means of removing the fluidized material from the vessel through collectors that are connected to discharge valves. Satisfactory performance of mud wash systems dictates that they must be operated before the sediment layer “bridges over” the collector openings. For that reason, it is strongly recommended that mud wash systems be operated either manually on a regular, preset schedule or automatically under timer control.
Mud Wash (Sand Jet) System
Interface Sludge Drains :
Interface sludge drains consist of collectors situated at the oil/water interface connected to discharge valves. Interface sludge tends to collect irregularly and many times reaches an equilibrium depth that does not seriously impair operation. Therefore, the requirement for draining interface sludge is best determined from a regular monitoring of the interface depth and condition by means of samples taken from the trycocks. A continuously increasing interface layer or a layer containing a high concentration of suspended solids is indication for - 41 -
draining. Draining must be done very slowly under careful monitoring to avoid drawing excess oil or water into the collectors. For this reason, it is best done manually. Properly used, interface sludge drains can result in reduction of the load on the downstream water treatment facilities by redirecting the high oil- and solid-content material into a slop oil system where it can be batch treated with heat and chemicals more effectively.
Interface Sludge Drain
Mixing Devices An important facet of desalting is achieving contact between the entrained water in the crude oil and the dilution water used to wash the oil. Mixing Valves
Typically, the dilution water is added to the oil upstream of a valve. The water is injected into the oil flow line through a distributor. The differential pressure across the valve is then used to shear the water drops and mix the two phases. Typical differential pressures are usually in the 5 to 15 psid range. Although mixing valves are generally satisfactory, they do have some disadvantages. Mixing efficiency is generally low at extremes of phase ratio, so the use of small quantities of dilution water (less than 2%) may not be feasible; likewise, turndown in flow rate will require adjustment of the valve to maintain contact efficiency. More serious disadvantages include the requisite compromise between mixing efficiency and excessive emulsification and the waste of energy expended on shear of the continuous phase. Because very small drops act as rigid spheres following flow streamlines, it is unlikely that they will ever achieve sufficient energy to participate in mechanically induced collisions; therefore, their contribution to the salt content of a crude oil represents a fraction unreachable by means of mixing valves. - 42 -
Static Mixers
Mixing efficiency can be improved by adding static mixer elements downstream of the mixing valve to achieve a more homogeneous blend of brine drops and dilution water drops. Static mixers consist of a series of short helical baffles mounted in a pipe with adjacent baffles having reverse twists. These devices continually blend the stream at relatively low shear. Since increasing mixing efficiency by increasing shear rate can result in emulsification problems, the use of low shear devices for blending the stream can be an asset, particularly with difficult crude oils. At best, a mixing valve/desalter combination can function as a single stage mixer-settler. Electrostatic Mixing
As has been previously discussed, the electrostatic field can also used as a mixing device if it is programmed to exceed the critical voltage gradient during a portion of the treating cycle. It is this technique which is used to achieve mixing under counter-flow conditions in the Electro-Dynamic® Desalter.
Design Aids NATCO uses several methods for arriving at the design of dehydrators and desalters. Several key factors required for design are the viscosity of the crude oil and its variation with temperature; the density of the oil; the water and suspended solids content; salinity of the water and the stability of its dispersion; the potential for precipitation of waxes, asphaltenes, or other solids; and available operating parameters such as temperature, pressure, etc. Some of these are usually available from field or laboratory work on the crude oil during reservoir evalua tion or parallel development in the field. Other parameters can be estimated, if necessary, from property correlations. Much better information can be developed through laboratory electrostatic treating tests. NATCO offers both static and dynamic electrostatic tests that can be used to determine electrostatic treatability, optimum treating temperature, maximum process flux, dilution water requirements, and screening of candidate treating chemicals. This testing service is described more fully in the Research & Development brochure in Appendix VI. Design sizing is done using proprietary computer programs developed by NATCO. NATCO also maintains a database of crude oils that have been tested in the laboratory, in field tests, and actual installations. This database covers oils from around the world and provides a means of estimating unknown properties in many cases. Once the design data are determined, several proprietary computer programs are used for determining dilution water needs and injection points, oil properties at operating conditions, and sedimentation rates for the coalesced water. These data are then combined to achieve overall process and equipment design. An Adobe Acrobat form that can be filled out with the necessary process information for - 43 -
developing a dehydrator/desalter inquiry is included with this CD ROM. (Click ROM. (Click here.)
- 44 -
Appendix I Publications “How to Design an Efficient Crude Desalting System” “Dual Polarity Oil Dehydration” “Field Desalting: A Growing Producer Problem Worldwide” “Field Desalting of Wet Crude in Kuwait” “Crude Oil Desalting by Counter-flow Electrostatic Mixing” “Desalting Heavy Crude Oil by Counter-flow Electrostatic Mixing” “Reduction of Corrosion through Improvements in Desalting” “Tandem Mechanisms Facilitate Dehydration of Crude” “Dual Polarity Desalter Testing” “Electrostatic Fields: Essential Tools for Desalting” “Desalting Heavy Crude Oils: The Venezuelan Experience” “New Tools for Heavy Oil Dehydration” “Field Trials Scheduled for New Compact Dehydration Technology”
- 45 -
Desalting Heavy Crude Oils – The Venezuelan Experience Kenneth W. Warren and John Armstrong NATCO Group, Inc. 2950 N. Loop West #700 Houston, TX 77092 © NATCO Group December 2001 Presented at Spring 2002 Annual Meeting, AIChE, Desalting Symposium New Orleans, LA
Abst Ab st ract: rac t: Dehydration of heavy crude oils presents unique challenges due to high viscosity, the presence of suspended solids and semi-soluble components, and the limited differential density for driving the sedimentation-based separation. Desalting these oils adds the complexities of mixing requirements that can produce stable dispersions and the use of fresh wash water that greatly reduces the available differential density. Venezuelan producers have recently begun exploitation of the very heavy crude oils of the Orinoco Tar Belt. This paper examines experiences in dehydration and desalting of these oils at four different sites incorporating sixteen units. Lessons learned regarding overall process requirements, suitable controls, desalter/dehydrator configurations, and operating conditions are discussed.
Introduction: Although Although exploitation exploitation of heavy heavy oil deposits has been carried out out for many years, the methods of production and processing of these crude oils generally limited their commercial development to shallow deposits in areas geologically favorable to thermally enhanced production methods. One of the largest deposits of heavy oil in the world lies in a belt north of the Orinoco River in Venezuela. (Figure 1) Estimates of original oil-inplace are in the range of 1.2 trillion barrels; however, only in recent years have methods been developed to render production of these deposits practical. The oil of the Orinoco Belt is extremely heavy with API gravities ranging from 4 to 9ºAPI, with a range of 7 to 9ºAPI in the zones presently being commercialized. Viscosities of the dead oil range from 20,000 to 100,000 cSt at ambient conditions. It is interesting to note that 10,000 cSt was once proposed as the dividing line between heavy oil and tar. Four projects are in various stages of development at present with others in conceptual development. All of them involve production and dilution of the heavy oil to a blend of approximately 17ºAPI with some treatment (dehydration/desalting) at the field level followed by pipeline transportation to the Jose Petrochemical Complex. Each project - 46 -
entails individual up-grading facilities at the Jose Complex, where the blends are desalted and further dehydrated prior to the up-grading process. Present Present Produc Produc tion: A variety of processing processing schemes schemes have have been chosen chosen for the current current projects. projects. Field facilities and the up-graders were handled as separate projects, often with different consultants, resulting in the selection of differing processing schemes in the upstream and downstream sides of the same project. Company “A” chose to use two trains of two-stage desalting at the field facility with further desalting at the up-grader. The dehydrator/desalters are Dual Polarity combination AC/DC electrostatic units. The desalters operate at 250 to 290ºF with heating by shell-and-tube heat exchangers upstream and firetubes in the desalters. Degassing is accomplished in a three-phase separator operating at 90ºF and 2 psi. Design capacity is 158,000 BOPD. The up-grader associated with this project is not yet in operation. Company “B” chose to use four parallel single-stage dehydrators at the field facility with desalting in four parallel single-stage desalters at the up-grader. All of the dehydrators and desalters are Dual Polarity combination AC/DC electrostatic units operating at 290ºF. Heating is by plate-and-frame heat exchangers. De-gassing is accomplished in the field installation through a two-phase separator operating at 140ºF and 150 psi. Design capacity is 170,000 BOPD. Both facilities are currently operating. Company “C” chose to use four parallel single-stage dehydrators at the field facility with desalting at the up-grader. The dehydrators are of Trivolt deep-field AC design operating at 284ºF. Heating is by a direct-fired heater. De-gassing is accomplished by a two-phase separator operating at 284ºF and 61 psi. Although not intended for desalting, there is provision for water injection prior to the dehydrators. Design capacity is 286,000 BOPD. The up-grader associated with this project is not yet in operation. Challenges Challenges Asso ciated with Desalting Desalting Heavy Heavy Oils: Viscosity – Viscosity – In order to achieve achieve practical practical sedimentation sedimentation rates, rates, it is necessary necessary to reduce the crude oil viscosity by operating at an elevated temperature. This in turn results in several adverse factors. Solubility of Water in the Crude Oil – Water exhibits solubility in crude oil that increases with temperature. (Figure 2) As a rule-of-thumb, this solubility approaches 0.4% by volume at 150ºC. In a desalting process, the water that dissolves in the oil carries no salt with it; however, the loss of water from highly saline drops may result in the precipitation of crystalline salt. The surface of the salt crystals acts as any other interface and tends to collect insoluble or semi-soluble contaminants, which in turn make the crystal difficult to contact with the wash water. Injection of a portion of the - 47 -
wash water prior to heating can help alleviate this problem. A more difficult issue involves attainment of water-in-oil specifications. Process samples are collected through coolers that lower the temperature to prevent loss of volatile liquids. The cooling precipitates some of the soluble water, thereby increasing the reported water content of the oil. Since the desalter can only separate water that exists as a separate phase, this precipitated water represents an untreatable component under conditions existing within the process vessel. The interpretation of true separate phase water content under process conditions is further complicated by incomplete equilibrium in both the dissolution process and the precipitation reaction. Stress on the Electrical Insulators – Desalters utilize insulators for support and electrical isolation of the electrodes and as glands for conducting the electrical power into the vessels. Fluorocarbons such as Teflon® are the materials of choice for these insulators since they possess desirable mechanical and electrical properties and are resistant to fouling. However, fluorocarbons loose mechanical strength at elevated temperatures and tend to distort resulting in compromise of the sealing surfaces. The thermomechanical limitations of the insulators become the limiting conditions for operating temperature in a desalter. (Figure 3) Oil Conductivity – Crude oil becomes more conductive with increased temperature. This conductivity increases the electrical power requirements necessitating larger power supplies and also limits the sustainable magnitude of the electrostatic field. (Figure 4) Limited Differential Density – Separation within the desalter vessel is a Stokes’ Law based gravity separation of phases. As can be seen from inspection of Stokes’ equation, the rate of separation is dependent upon the drop size of the dispersed phase, the differential density of the phases, and the viscosity of the continuous phase. v=
1.78 x10−6 (∆ρ ow )d 2 µ o
where v = Downward velocity of the water droplet relative to the oil, ft/sec, d = Diameter of the water droplet, µm, ∆ ρ ow = Differential density between the oil and water, and o
= Dynamic viscosity of the oil, cp.
In field dehydration operations, the saline produced water is more readily settled than the fresh water encountered in desalting. Since heavy oils are close to the density of water, the driving force for separation is small. At elevated temperatures, this differential becomes even smaller. (Figure 5) Slow Disengagement of Associated Gas – The movement of gas bubbles through these - 48 -
oils is impeded by the inherently high liquid viscosity and by the film strength at the gasliquid interface. The presence of gas within the electrostatic coalescing zone retards the sedimentation process and seriously degrades performance. Conventional degassing techniques relying upon retention time are inadequate for assuring gas-free oil within the coalescer for these heavy crude oils. Effects of Solid Contaminants – In addition to formation solids (sand and silt) and corrosion products, heavy oils often contain substantial quantities of semi-solid petroleum fractions that accumulate in desalter vessels. These solids-based sediments are found both in the bottom of vessels and in the water/oil interface zone where they contribute to stabilized or slowly resolving emulsion layers. Such layers constitute a “hindered settling region” in which sedimentation of water drops is adversely affected by the presence of other suspended phase materials. This interface sludge layer may exist in a steady-state equilibrium, in which case it may be considered part of normal operation. However, if it continues to increase in depth, steps must be taken to either resolve it or remove it from the desalter vessel. Removal is accomplished by interface sludge drains or by agitating the water layer sufficiently to mix the interface sludge into the water layer and remove it during mud washing. Sediments in the bottom of the vessel can become so deep that they interfere with flow distribution within the vessel. These sediments can be removed through a mud-wash or sand-jetting system. Chemical Treatment – Chemical treatment of heavy oil systems usually requires a demulsifier to destabilize the incoming emulsion. Because natural emulsifiers are often present in large quantities, the dosage of chemical required for these systems may be much larger than needed for lighter crude oils. Suspended solids and semi-soluble hydrocarbon fractions are less amenable to chemical treatment and may render the chemical program marginally effective. Often, wetting agents prove useful for separating the suspended solids from the oil and forcing them into the water layer. Process Control – Although there are many aspects to desalter process control – mixing efficiency, separation efficiency, etc. – one of the more difficult items to control in heavy oil installations is interface level control. The combination of small differences in density between the water and oil and the presence of interface sludge renders most displacement-type controls unsuitable. Successful interface control under these circumstances depends upon the ability of the level probe to sense water content of a diffuse interface layer.
Operating Results : The table below summarizes operating results from the previously mentioned companies as of this writing. Since these, like most heavy oil operations, experience variations in performance due to feedstock variations, position in maintenance cycles, - 49 -
and other influences, these results may or may not be indicative of long-term averages, but are offered as a performance “snapshot” valid at the time the data were taken.
Company Diluted Bitumen Design Flow BPD
“A” 158,000
“B” 170,000
“C” 286,000
Upstream Operations Inlet BS&W % Outlet BS&W % Inlet Salt PTB Outlet Salt PTB Operating Temperature ºF Actual Flux BPD/ft 2
2.5 0.5 194 6–8 250/270
1.2 0.5 - 0.7 Not Measured Not Measured 290
2.8 0.6 Not Measured Not Measured 248
103
94
60
Downstream Operations Inlet BS&W % Outlet BS&W % Inlet Salt PTB Outlet Salt PTB Operating Temperature ºF Flux BPD/ft 2
Not Operational Not Operational Not Operational Not Operational Not Operational
0.8 + 8.0 0.7 25 2 290
Not Operational Not Operational Not Operational Not Operational Not Operational
Not Operational
64
Not Operational
Conclusion s – Application of Experience: The experience gained from these units in the dehydration and desalting of diluted bitumen yields several guidelines for similar applications. •
•
•
Viscosity is critical. The limiting sedimentation rate, and thus the size of the desalter vessel, is dependent upon viscosity. Temperature is the primary control for viscosity, and for heavy oils high temperatures, usually limited by the temperature tolerance of the insulators, are necessary. For diluted bitumen, diluent type and quantity also affect viscosity, but these factors are not primarily selected by viscosity concerns. Differential density is minimal. This is another factor in sedimentation rate and is controlled by type and quantity of diluent. Here a compromise between desalter size and diluent recycle cost must be reached. Temperature also has an effect on differential density, but this is secondary to its contribution to viscosity control. Water solubility is substantial. The solubilization of water does not affect desalting performance unless it results in the formation of insoluble salts, but its precipitation upon cooling may affect the apparent dehydration efficiency of the - 50 -
system. True dehydration performance can only be evaluated by measuring total water content and subtracting the soluble component at operating conditions. However, because of incomplete approach to equilibrium, the exact quantity of soluble water is difficult to predict. • Methods of performance measurement must be considered. Specifications for desalting systems normally state the allowable quantities of salt and water (or BS&W) in the treated oil. Occasionally, percentage removal is specified; however, it is much easier to achieve 99% salt removal when the inlet contains 500 PTB (pounds of salt per thousand barrels of oil) than when it contains 10 PTB. It is preferable to specify the allowable quantity of contaminants in the treated oil. Water content may be determined by ASTM D-95 (distillation), ASTM D-96 (field centrifugation), or ASTM D-4007 (laboratory centrifugation) depending upon the facilities available. The results of any of these tests should be interpreted in light of the potential contribution for untreatable soluble water. Salt may be determined by several methods also. For the salt quantities normally targeted for heavy oils, the conductivity method, ASTM D-3230, is satisfactory. For lower salt concentrations (1PTB or less), it is necessary to utilize a method using hot water extraction followed by salt determination of the extract, by titration or other methods. • Solids must be controlled. Control involves both separation of the solids from the oil and prevention of their accumulation in the desalter vessel. Separation from the oil is accomplished by the use of chemical agents to render the solids hydrophilic and thus allow the wash water to carry them into the water layer. Alternatively, organic solids may be dispersed into the oil by chemical treatment. Solids that separate from the oil may end up on the bottom of the vessel or in the interface layer. Removal of bottom sediments requires the use of a mudwash system consisting of water jets and drains. Interface sludge may be removed by sludge drains placed in the interface zone or by vigorous mud washing which stirs the interface sludge into the water layer. Sludge drains have the advantage of producing an lower volume of effluent which may then be treated by batch methods instead of contaminating the entire effluent water stream with refractory sludge. Operation of the mud-wash system should be done on a regularly scheduled basis as opposed to the interface sludge drains that are operated on an as-required basis. • Interface control is difficult. By definition, heavy oils have small density differentials with water, and by nature, they tend to produce diffuse interface layers with very gradual density gradients. These factors render conventional interface controls – displacers, weighted floats, etc. – unsuitable. Various conductance probes and capacitance probes have been utilized in these heavy oils, but it appears that the greatest degree of success has been with radiofrequency capacitance probes. Although these are considerably more expensive than conventional controls, their greater reliability makes them cost-effective in this service.
- 51 -
•
•
Chemical treatment is necessary, but may be marginal. An ideal chemical treatment would produce a quickly separating dispersion with little or no interface layer. In heavy oils, this ideal is far from reality. An operator hopes to achieve a steady-state interface layer that can be maintained over an extended period of operation without excessive compromise of the electrostatic field. Perhaps it is fair to say that “adequate” chemical performance is the somewhat elusive goal. It is important that the chemical be well mixed with the oil and given adequate retention time in the oil before entering the desalter. Remember that the chemical, normally oil-soluble, must be given the time to diffuse through the oil to the drop surfaces and react with the natural emulsifiers there. The thick interface films present in heavy oils can make this a slow reaction. Mixing efficiency vs. dehydration requires a compromise. While this compromise is always present in desalting systems, nowhere is it more critical than in heavy oils. Increasing mixing valve differential pressure can quickly render the water-in-oil dispersion so fine that resolution within the desalter vessel is impossible. The large quantities of natural emulsifiers and suspended solids normally present in heavy oils greatly exacerbate this tendency toward stabilized dispersions.
Desalting of heavy oils is always a challenging operation. The difficulties presented require detailed consideration on the part of desalter designers and constant attention from plant operators. Heavy oil desalting processes are never “set it and forget it” operations. However, when approached with an understanding of the problems involved and vigilance toward operations, it has been demonstrated that these oils can be successfully treated.
- 52 -
Figure 1: Orinoco Belt Developments Me sa 30 B le nd
Nap ht ha B le nd
0.35 0.30 % l o 0.25 v y 0.20 t i l i 0.15 b u 0.10 l o S 0.05 0.00 50
100
150
200
250
Temperature ºF
Figure 2: Solubility of Water in 17ºAPI Blended Bitumen
- 53 -
300
550 ) 500 s b l ( 450 d a o 400 L d e 350 t a R 300
250 150
200
250
300
350
400
Temperature (ºF)
Figure 3: Design Load Curve for 2” Teflon Hangers
14000 m / S 12000 p y 10000 t i v i t 8000 c u d 6000 n o C 4000 2000 50
70
90
110
Temperature ºF Figure 4: Conductivity of Diluted Bitumen
- 54 -
130
17ºAPI Oil
Water
15ºAPI Oil
1.0 y t i s 0.9 n e D
0.8 0
100
200
300
400
Temperatu re ºF Figure 5: Density Variation with Temperature
- 55 -
SPE/Petroleum Society of CIM/CHOA 78944 New Tools for Heavy Oil Dehydr ation Kenneth W. Warren, SPE/NATCO Group
Copyright 2002, SPE ITOHOS/ICHWT conference. This paper was prepared and Heavy Oil Symposium in Calgary, Alberta, Canada, 4–7 November 2002.
for and
presentation International
at
the Horizontal
SPE Well
International Technology
Thermal Conference
Operations held
This paper was selected for presentation by an SPE ITOHOS/ICHWT Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers, the Petroleum Society of CIM/CHOA and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, the Petroleum Society of CIM/CHOA, its officers, or members. Papers presented at SPE ITOHOS/ICHWT meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of t his paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.
Abst ract Heavy oils are becoming increasingly attractive from the standpoint of availability of reserves and economic status as “opportunity” feedstocks. However, they also bring some complex dehydration problems including high levels of suspended solids, conductive organic species, and varying amounts of semi-soluble and precipitated organic materials. Meeting these challenges requires new techniques in both the areas of chemical treatment and dehydrator design. This paper focuses upon improvements in hardware design. Introduction Dehydration of crude oils has historically depended upon the use of heat to control viscosity, chemicals to destabilize natural emulsifying agents, and retention time under quiescent flow conditions to allow gravity sedimentation to occur. In many cases, electrostatic fields have been employed to provide the extra coalescing force needed to grow the water drops to a size large enough to allow sedimentation in economically sized vessels. Sedimentation rate is predicted from Stokes’ Law (Eqn 1): v=
1.78 x10−6 (∆ρ ow )d 2
………………... (Eqn. 1)
µ o
where v = downward velocity of the water droplet relative to the oil, ft/sec, d = diameter of the water droplet, µm, 3 ∆ ρ ow = differential density between the oil and water, g/cm , and o
= dynamic viscosity of the oil, cp.
- 56 -
Heavy crude oils place severe strains upon conventional dehydration practices. Although crude oils occur in a continuum of densities, for practical purposes oils below 20ºAPI may be considered as heavy oils. (1) The native viscosities of these oils are high, and very high operating temperatures are required to reach a suitable viscosity range for rapid sedimentation of the water drops. In some cases, desireable operating temperatures are at the upper extreme of the useful range for the fluorocarbon insulators commonly employed in these devices. High operating temperatures may also severely reduce the differential density between the oil and water that is necessary as a driving force for sedimentation. Chemical treatment of these oils is also problematical. Emulsion stabilizing a gents such as salts of organic acids and semi-soluble organic materials such as asphaltenes are often present in large concentrations. In addition, the high density and viscosity of these oils tend to increase the entrainment of suspended solids. These solids may consist of formation fines, corrosion products, precipitated scale minerals, precipitated organic components, and/or bacterial debris. All of these materials tend to accumulate at the drop surfaces stabilizing the water dispersions. They also accumulate at the phase boundary between the oil and water layers where they retard the sedimentation of water drops and produce a characteristic interface “rag” layer. Chemical treatment must therefore not only destabilize the naturally occurring emulsifiers, but also aid in separation of the solids and condensation of the “rag” layer. New developments in dehydrator design with application to heavy oil dehydration include electrostatic field control techniques and special electrode systems. These minimize the negative impact of the increased conductivity and arcing tendencies of heavy oils.
Electros tatic Fields in Oil Dehydration Electrostatic fields used in dehydration may be unfavorably impacted by the p roperties of heavy oils. The same materials that cause problems in chemically treating these oils contribute to electrical conductivity. As oil conductivity tends to increase with temperature, the requirement for high operating temperature to control viscosity further exacerbates the situation. (Fig. 1) 100 90 m / S n y t i v i t c u d n o C
80
Diluted Bitumen 17ºAPI
70 60
Bohai Bay 17.8ºAPI
50 40
Brazilian 14ºAPI with 12% Diluent
30 20 10 0 0
50
100
150
200
Temperature ºF
Figure 1: Oil Conductivi ty vs. Temperature Electrostatic Field Control. Conventional power supplies for electrostatic crude oil treating incorporate reactance, either in the form of a discrete reactor coil or as reactance built into the transformer core, as a means of protecting the system from electrical overloads. (Fig. 2) As a protection mechanism this system works well; however, from a process standpoint, it renders the power supply ineffective during times of process upset or during periods of high conductivity. - 57 -
Figure 2: Convention al Power Supply Protection Electronic controllers can assume some of the essential protection functions while ex tending the capability of the power supply under severe process conditions. By rapidly switching the primary power, the controller introduces de-energized or “off” periods in the power to the transformer. The controller senses the power drawn by the system and adjusts the length of the “off” periods to maintain the transformer within its heat dissipation rating. (Fig. 3 )
e a t l o V Time Crude Oil Conductivit
Figure 3: Time Based Power Supply Protection Since the power supply continues to provide pulses of high voltage to the process vessel, coalescing ability is largely preserved during process upsets. (2) The controllers are microprocessor based and therefore also provide the means to program modulation of the electrostatic field. It can be shown that modulated fields can significantly improve dehydration over that available with conventional fields. Historically, the selection of the optimum - 58 -
operating voltage for an electrostatic dehydrator necessitated a compromise between flux (the rate at which oil passes through the electrodes) and the extent of dehydration. The necessity for voltage compromise can be avoided by u sing a modulated power supply. The modulated signal can be described in terms of three parameters: Threshold Voltage Gradient: The minimum field gradient at which coalescence occurs. Critical Voltage Gradient: The field gradient at which shattering of the minimum or Stokes’ drop begins. Frequency: The modulation frequency is the repetition rate of the waveform. This affects drop transport, drop growth, and drop oscillation. The amplitude of the modulation must be confined between the minimum set by the threshold voltage gadient and the maximum set by the critical voltage gradient. (Eqn. 2) (3) These are the extremes of modulation and may not represent the optimum operating settings. 1
Ec ≤ ε (σ / d ) 2 …………………………. (Eqn. 2)
where Ec = critical voltage gradient, V/m, 2 2 ε = dielectric constant, C /Nm , σ = interfacial tension, kg/s, and d = Stokes’ droplet diameter, µm. A correlation exists between the mean drop size of a dispersion of water drops in an electrostatic field and the electrostatic field gradient. Higher field gradients are associated with smaller mean drop sizes. This would seem to recommend the use of lower field gradients to maximize drop growth and maximize flux; however, the lower field gradients have insufficient energy to coalesce the smaller drops due to their large drag-to-bulk ratio and more rigid shape. (Fig. 4)
Figure 4: Conceptual Drop Size Variation with Voltage
- 59 -
A relatively slow (less than one hertz) voltage modulation of the proper waveform allows the mean drop size of the dispersion to be shifted in the direction of larger drops, which then settle out of the field faster. (Fig. 5)
Figure 5: Slow Voltage Modulation Waveform Voltage modulation of an intermediate frequency (less than fifty hertz) produces additional benefits to the coalescence process in terms of induced drop oscillation. It has been shown that drops subjected to a modulation frequency close to the resonant frequency of the drop exhibit a range of surface distortions. (4) At higher frequencies (above 500 hertz) these distortions result in an energized drop/continuous-phase interface that disrupts stabilizing films and increases the surface free energy of the drops. High surface free energy results in increased drop-to-drop interaction, which enhances the rate of coalescence. (5)(Fig. 6) Arc Suppression. A side effect of electrostatic coalescing processes is “daisy chain” arcing that proceeds along chains of water droplets between electrodes or between electrodes and ground. A limited amount of this arcing, along partial chains, is normal and possibly beneficial, but when it becomes excessive, as in the case of conductive heavy oils, it can compromise the electrostatic field and impair coalescence. 100 80
) % ( e 60 c n e c s e 40 l a o C
1000 Volts
20
3000 Volts
0 0
500
1000
1500
2000
Frequency (Hertz)
Figure 6: Effect of Frequency on Coalescence (from Ref. 5) - 60 -
Arcing in a metallic electrode array momentarily discharges the array, and excessive arcing results in electrode discharges for significant portions of the operating time. During such periods of discharge, oil may pass through the electrodes without being adequately dehydrated. Specially designed composite plate electrodes may be used to alleviate this problem. Composite electrodes are constructed of a fiberglass material with a conductive strip embedded. (Fig. 7) The high voltage electrical connection is made to the conductive material, which distributes the charge longitudinally along the electrode. A very thin layer of water is adsorbed on the plate due to polar materials in the resin. This water layer then becomes the electrode, albeit a very resistive one.
+
Conductive Strip
-
+
-
Epoxy
Figure 7: Construct ion of Composite Electrod es Arcing will still occur with composite electrodes, but now the current must pass through the resistive water layer to the root of the arc, along the arc path, and through the water layer on the opposite electrode. This high resistance results in a rapid voltage drop at the arc root, which in turn quenches the arc. Only the electrode areas in the immediate vicinity of the roots of the arc are discharged, thereby eliminating the bypassing seen with metal electrodes. The voltage at any point on a composite electrode (and therefore the field gradient between adjacent electrodes) is determined by the electrical current passing through that point. As the rising oil stream with its entrained residual water enters the electrode zone, the electrodes in the entry zone draw more current and their voltage decreases. As dehydration progresses, the conductivity of the oil decreases and the voltage of the electrodes increases. This produces a variable field gradient that “self-adjusts” to the oil conductivity. A water drop settling downward in the electrode zone will thus see a decreasing field gradient, which results in a shift toward a larger equilibrium drop size, thereby complementing the effect of modulated voltage.
Test Circumstances Evaluations involved tests performed on field installations and in a laboratory pilot unit. The electrostatic dehydrator in the pilot unit is a vertical column with one set of electrodes, which can be changed to various electrode types. (Fig. 8) The electrode spacing, electrode size, and electrode-to- 61 -
interface distance are the same as would be found in an eight-foot diameter horizontal dehyd rator. Therefore, all critical dimensions are full-scale. The power supply is capable of supplying AC, AC/DC, various modes of modulation, and voltages up to fifty kilovolts.
Figure 8: The Hydrocarbon Test Unit The feed train consists of a pressurized tank that is stirred and heated, a preheat train, chemical injectors, and a gas equilibration vessel. (Fig. 9) Cumulative sedimentation vs. time determinations are used to determine the amount of agitation required for reconstituting the dispersion to field conditions.
Figure 9: Hydrocarbon Test Unit Simplifi ed Flow Diagram Over 400 pilot studies have been performed using this system including some of the initial studies on dehydration and desalting of diluted Orinoco bitumen. Correlation of flux, optimum temperature, optimum voltage, and chemical performance betwee n this unit and field installations has been very good. Only chemical dosage fails to correlate well due to the short retention time in the feed train and the vagaries of treating aged samples. Comparative field data are of necessity more limited since it is not feasible to vary operating conditions widely in a production environment. For this reason and to better establish trends, data ranges have been extended to include both heavy and near-heavy crude oils. - 62 -
Hardware The performance enhancing devices discussed herein include the electronic voltage controller and the composite electrode array. Both of these have evolved from laboratory prototypes through several commercial models to arrive at their present forms. The voltage controller provides the protection required for operating in a conductive process environment, the flexibility needed for varying feedstocks, and the reliability demanded by production operations. Its basic functions are the sensing of process load, switching the primary power, and management of protection of the power supply while avoiding reactance losses. It also manages arc suppression, lost communication protection, and databases of users, feedstocks, and dehydrator vessels. In modulating service, it controls waveform shape, amplitude, and frequency. The controller has evolved from an original monolithic design to its present modular form (Fig. 10) with modules being distributed between the local power supply a nd a remote environment such as a control room or motor control center. The local modules include the power switching circuit (silicon controlled rectifiers), the firing circuit for the SCRs, and an interface board which modulates a single power supply, handles arc quenching, and assumes the power supply protection function in the event of lost communication. The remote module may be connected to a computer for programming or monitoring purposes. It communicates with the interface boards and the computer, generates the desired waveforms, and stores the set-points for up to three power supplies. Software installed on the computer provides monitoring functions for voltage, current, and arcs, generates the set-point data, recommends optimum operating voltages, stores the databases, and captures any fault messages.
Figure 10: Modul ar Voltage Controller The composite electrode array consists of vertically hung, parallel plates extending across the transverse axis of the dehydrator. (Fig. 11) The plates are sixteen inches in height, and their width is determined by the vessel diameter and the required electrical clearance. The electrode array has - 63 -
evolved through various shapes and materials of construction as greater chemical and temperature resistance were combined with greater mechanical rigidity and ease of installation.
Figure 11: Example Composit e Electrode Arr ay in Lab Data and Results Data have been obtained from various combinations of electrostatic field control and composite electrode installations both in laboratory and field situations. In some cases, data from lighter oils have been included to better establish trends. Results of Electrostatic Field Control. Although the electrostatic voltage controller was originally developed as a power supply protection device for avoiding reactance losses, its utility as a voltage modulator was quickly realized. Most commercial installations have been in counter-flow desalters, but it has also proven valuable as an aid in coalescing difficult oils. Comparative results between using an AC/DC fixed field and a modulated AC/DC field are shown in Table 1.
Crude, Source Brail, Brazil Maureen, North Sea Bozhong, China Milne Point, Alaska
%BS&W, %BS&W, ºAPI Modulated AC/DC AC/DC 14.3 1.50 0.85 16.4 0.63 0.48 17.8 0.55 0.45 19.4 0.42 0.35
Table 1: Effect of Field Modulation From the above data, it can be seen that adding modulated electrostatic fields in the treatment of these heavy oils resulted in an average improvement in dehydration performance of 26%. While the magnitude of improvement may vary with oil characteristics, it is apparen t that positive results may be expected. It was pointed out earlier that a combination of modulation frequencies might provide additional enhancement of the coalescing power of the electrostatic field. Multiple modes of modulation can produce not only the mean drop size shift seen in the previous data, but also an increase in the surface free energy of the drops which can in turn make drops in close proximity more easily coalesced. The data presented in Table 2 illustrates the effect of bimodal modulation of the field. - 64 -
Crude, Source
ºAPI
0.90
%BS&W, Bimodal AC/DC 0.55
0.45
0.42
0.70 1.20 0.10
0.22 0.80 Trace
%BS&W, AC/DC
Captain, North Sea 20.8 Pauls Valley, 23 Oklahoma Oklahoma 30 Oklahoma 34 Oklahoma 40
Table 2: Effect of Bimodal Field Modulation The data above demonstrate an average improvement in dehydration of 49%. While the chemical treatment and operating conditions may not have been optimized, they are identical between pairs of readings. Further studies are planned to extend the data range to heavier crude oils. Conductivity Tolerant Designs. The design of electrostatic dehydrators to accommodate oils of high conductivity involves both adjustment of the electrostatic field as described above and the suppression of excessive arcing. Electrodes fabricated of fiber-epoxy material with the inclusion of conductive materials have demonstrated great effectiveness at arc suppression and enhancement of coalescence. Comparative dehydration results using steel and composite electrodes are shown in Table 3. The average improvement in dehydration as the result of changing the elec trode type was 56%. Improvement expressed as increased capacity can best be demonstrated from a Venezuelan installation where five identical dehydrators are installed in parallel and operating under the same conditions.
Crude
ºAPI
%BS&W In
%BS&W %BS&W Out: Out: Steel Composite
Orinoco Diluted 17 5 0.65 0.43 Bitumen Captain 20 15 1.20 0.60 Maya 23 15 1.2 –1.5 0.72- 0.92 Arabian 27 31 NA* 0.29 Heavy * Unable to process due to current limit of power supply. Table 3: Steel vs. Composite Electrodes
- 65 -
Three of the dehydrators are equipped with steel electrodes and two with composite electrodes. The feedstream is a 27ºAPI oil and all are producing <1% BS&W out. The three dehydrators with the steel electrodes are processing 43,000 barrels per day each while the two with composite electrodes are processing 60,000 barrels per day each.
Conclusions Heavy oils present the process engineer with the dual challenges of high native conductivity combined with high viscosities that contribute to poorly resolving dispersions. Successful dehydration of these oils dictates that all possible coalescence mech anisms, including electrostatic coalescence where practical, should be applied. The use of arc-limiting composite electrodes combined with tailoring of the electrostatic field for the oil to be processed provides important new tools for extending the applicability of the electrostatic process and enabling more efficient dehydration of heavy oils. Nomenclature BS&W: Basic Sediment and Water – A common measure of dehydration efficiency. Usually obtained via ASTM D-96 or D-97 tests. ºAPI: A measure of oil specific gravity defined by the American Petroleum Institute. ºAPI = (141.5/γ) − 131.5 γ = specific gravity of oil v = settling velocity of the water droplet relative to the oil, ft/sec d = diameter of the water droplet, µm 3 ∆ ρ ow = differential density between the oil and water, g/cm o
= dynamic viscosity of the oil, cp
Ec = critical voltage gradient, V/m 2 2 ε = dielectric constant, C /Nm σ = interfacial tension, kg/s nS/m = nanoSiemens/meter
References 1.
2. 3. 4.
Khayan, M.: “Classification and Definitions of Heavy Crude Oils and Tar Oil,” paper presented at Second International Conference on Heavy Crude and Tar Sands, Caracas, Feb. 7 – 17, 1982. Bailes, P. J. and Larkai, S. K. L.: “An Experimental Investigation into the Use of High Voltage D.C. Fields for Liquid Phase Separation,” Trans IchemE, Vol. 59, (1981) 229. Chawla, M. L.,: “Field Desalting of Wet Crude in Kuwait,” paper SPE 15711 presented at the Fifth SPE Middle East Oil Show, Manama, Bahrain, March 7 – 10, 1987. Scott, T. C.; Basaran, O. A.; Byers, C. H.: “Characteristics of Electric-Field-Induced Oscillations of Translating Liquid Droplets,” I&EC Res. 29, 901-9 (1990). - 66 -
5.
Draxler, J. and Marr, R.: “Design Criteria for Electrostatic Demulsifiers,” Intl Chem Eng, 33, No. 1, January 1993.
- 67 -
OTC 15353 Field Trials Scheduled for New Compact Dehydration Technology Gary W. Sams and Harry G. Wallace, NATCO Group Inc.
Copyright 2003, Offshore Technology Conference This paper was prepared for presentation at the 2003 Offshore Technology Conference held in Houston, Texas, U.S.A., 5–8 May 2003. This paper was selected for presentation by an OTC Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Offshore Technology Conference or its officers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of t he Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented.
Abst ract Significant improvements in the capacity and performance of existing oil dehydrators and desalters are expected from an improved, patent pending, transformer and controller system. This electrostatic system is now ready for a field trial in South America. Production at the selected facility is currently at 45,000 bopd per unit on a medium gravity crude oil. This oil is currently being processed by five 10-ft. diameter x 45 ft. long electrostatic dehydrators using combined AC/DC electrostatic technology. Pilot studies utilizing the improved transformer / controller have demonstrated capacity improvements exceeding 30% above existing technology or outlet BS&W reductions between 10 to 30%. To confirm these results and define the limits of this new technology, a series of schedu led field trials has been planned. In addition, several other vessel modifications will include upgrading the inlet spreader design, and installing new high voltage electrodes. Once these improvements are made and the new compact electrostatic technology is implemented, it is estimated the vessel capacity will increase significantly, while maintaining the required oil specification. If successful, this electrostatic transformer and controller may provide producers and refiners with a new technology to process highly conductive, viscous oils. Testin g Objective Utilizing a South American oil facility, a new electrostatic dehydration technology is scheduled to be field tested. The objective of these tests is to quantify improvements to the oil dehydration process, demonstrate the robustness of the equipment and establish confirmation of the laboratory test results. Facility The production facility shown in Figure 1 has five oil dehydration vessels operating in parallel. Each ® horizontal dehydrator is 10 ft OD x 45 feet long x 125 psig with Dual Polarity electrostatic technology, open bottom spreaders, either steel or composite high voltage electrodes and pipe collectors. The Dual Polarity transformers are 480 volt, single phase rated for 150 kVA. Following an upgrade of three vessels to improve performance, a fourth vessel is scheduled to be retrofitted - 68 -
with a new electrostatic transformer including step/start switchgear and PC-based process controller. The facility has the capability to increase the oil flow to the test vessel so the limits of the technology can be investigated.
Figure 1 – Field Site
Appl icati on The facility is currently processing a 27.1 API oil at flow rates varying between 45,000 bopd to 60,000 bopd per vessel. The operating temperature is maintained at 140 F and the operating pressure is 80 psig. At operating temperature the dry oil viscosity is 8.9 cp. The inlet water cut typically ranges between 20 to 30%. The outlet specification is less than 1% BS&W and is routinely met by the dehydration process. These vessels use Dual Polarity electrostatic technology, as shown in Figure 2, to treat the 1 inlet oil/water mixture. Design features Dual Polarity Transformer include inlet spreaders to distribute the Oil Outlet Flow incoming fluid evenly along the length and across the width of the vessel. The spreaders Collector Electrodes are open-bottom box-type, which permits bulk separation of free water and solids. Spreader Interface Level Oil/water interface is established just below Water the spreader holes so the inlet fluids are distributed into the oil phase. Approximately Inlet Flow Water Outlet Flow 24 inches above the interface is an array of Figure 2 – Dual Polarity Vessel Configuration electrodes. These steel electrodes are arranged in parallel at a spacing of 6 inches. The steel electrodes are 6 inches high and at their ends approach within 6 inches of the vessel wall. Alternating electrodes are energized with a positive voltage and adjacent electrodes are energized with a negative voltage. The positive and negative voltages are supplied from a 100% reactance, 23 kV (rms) transformer. A single collector is located at the top of the vessel containing a series of holes located on opposite sides. The collector is optimized to ensure uniform collection along the length of the vessel. - 69 -
A single outlet nozzle is located near the center of the vessel. Following installation of the new electrostatic transformer, it is expected the oil flow can be significantly increased by as much as 30% without an increase in the effluent BS&W levels. Alternatively, the new technology is expected to lower the effluent BS&W 10 to 30%.
Technology The electrostatic technology to be applied utilizes a proprietary process controller and transformer package to produce an electrostatic field that can easily be optimized for any crude oil. This technology has been in development for over 4 years and has demonstrated remarkable performance improvements in pilot facilities. The transformer consists of three primary components that are packaged in a single oil-filled enclosure. Designed to operate on three phase, 480 volts (50 / 60 Hz) the technology overcomes the load balance problem normally encountered with single phase electrostatic processes. First, the 480 volts is conditioned using IGBT technology (isolated ga te bipolar transistors) to produce a variable amplitude and variable frequency voltage supply for the primary of the transformer. Second, the medium frequency transformer steps up the input voltage to a secondary voltage level necessary to promote effective coalescence. Third, the secondary voltage is rectified into positive and negative half-wave outputs. These polarized, half-wave voltages are then applied to the electrodes in a Dual Polarity dehydrator. A PC-based process controller defines the voltage control environment to match the specific needs of the production. For example, where highly conductive crude oils are processed (> 80 nS/m), the frequency can be increased to maximize the energy delivered to the oil dehydration process. Utilizing a medium frequency transformer overcomes the voltage decay a ssociated with conventional 50/60 Hz transformers. In wet crude oils the effective impedance may be very low, resulting in a rapid, voltage decay from the process electrodes. This decay reduces the effectiveness of the dehydration process by pulling the voltage below the threshold level required for effective dehydration. Operating with an increased frequency reduces this voltage decay and effectively sustains the applied voltage above the required threshold. Also, where the interfacial tension between the oil and water is low (< 10 dynes/cm) the waveform can be reduced to minimize destruction of the water droplets normally caused by the application of 50/60 Hz power. Chemicals, temperature, salts and applied voltages combine to reduce the interfacial tension between the dispersed water droplets and the crude oil. This low interfacial tension reduces the natural frequency of the entrained water droplets. Reducing the frequency of the waveform can prevent the destruction of the large water droplet required for effective dehydration. Furthermore, the shape of the voltage waveform can be selected to achieve the best 30000 dehydration results. Finally, the minimum s t 25000 l o and maximum voltage levels can be set to V , e 20000 g increase the percentage of the entrained water a t l o 15000 V that is swept by the electrostatic voltage. y r a d 10000 Maximum voltages reach the smallest water n o c e 5000 droplets with sufficient energy to develop a S 2 surface charge and promote coalescence. 0 0
5
10
15
20
25
30
Elapsed Time, ms
Figure 3 – Typical Exponential Voltage Waveform
35
40
- 70 -
Reducing the voltage to a minimum level will maximize the droplet growth to promote a rapid sedimentation rate. The PC-based controller developed to control the output of the variable voltage / frequency transformer is capable of producing a nearly infinite variety of waveform configurations. Selectable variables include the frequency of the voltage, the maximum and minimum voltages applied to the transformer and the cyclic pattern and rate used to drive the transformer. Figure 3 depicts a typical envelope of the primary voltage using an exponential waveform. The waveform is skewed slightly to ramp up to the maximum voltage slightly faster than it ramps down to the minimum voltage. Sweeping the applied voltage across the threshold voltage optimizes the coalescence and separation of water from the incoming oil/water mixture. Figure 4 schematically shows the component arrangement for the PC-based controller, the power electronics, the medium frequency transformer, the rectifiers (diodes) and the process vessel. The power electronics, transformer and rectifiers have been packaged in an oil-filled container to overcome distance problems between the electronics and the transformer, to provide cooling by the recirculation of dielectric oil and to make the retrofitting of existing AC/DC transformers more convenient.
, l y e t s o l a v p h 0 p P 8 u 3 4 S
High Voltage Power Transformer Electronics
Secondary Voltage (-)
e d o i D
Secondary Voltage (+)
Display
Controller
Figure 4 – Electrostatic Transformer / Controller Schematic
Unlike conventional 100% reactance electrostatic transformer designs that develop a significant drop in output voltage as the load increases, this new transformer is capable of maintaining maximum output voltage, even at the maximum rated current. To provide sufficient voltage to sustain the dehydration process under a wide range of process conditions, conventional transformers cannot be operated beyond 40% of their rated current.
Prelimi nary Results Extensive lab tests have provided ample evidence the variable voltage / frequency technology can be optimized to permit excellent oil dehydration at significantly higher oil flow rates in a given vessel size. To date pilot tests using this technolog y have achieved results similar to those shown in Figure 5 on a 24.85 API crude oil. 1.5
These tests have demonstrated the strong dependence that voltage, frequency, and waveform have on efficient oil dehydration. Additionally, the development program has produced a voltage controller capable of producing a nearly infinite number of waveform
1.4 Conventional Technology
1.3
l o V 1.2 % , 1.1 W & S 1 B l a 0.9 u d i s 0.8 e R
Variable Voltage / Frequency
Water Cut - 10 - 12.8% Process Temperature - 130 - 140 F Demulsifier - 100 ppm
0.7
- 71 -
0.6 0.5 40
50
60
70
80
Oil Flux, BOPD/SF
Figure 5 – Preliminary Pilot Results
90
100
110
configurations.
Test Program The testing will involve documentation of the current operating conditions, voltage configuration, chemical utilization and effluent BS&W. Data will be gathered periodically over a 21-28 day period to establish a strong baseline. While the variable voltage / frequency technology is capable of producing dry oil with low BS&W levels, the testing program will attempt to establish the most aggressive flow rate that achieve a 1% BS&W specification. After the baseline data has been collected, the new variable voltage / freque ncy transformer will be retrofitted to the process vessel. After installation the power supply parameters will be optimized using the effluent BS&W as the dependent variable. Once optimized, a second series of testing will be conducted to document the effluent BS&W at the same maximum process flow rate. If the outlet BS&W declines, then the production rate through the vessel will be increased again to determine the most aggressive flow rate that will achieve 1% BS&W. If possible, additional tests may be conducted to determine the minimum chemical dosage. Expectations Installation of the variable voltage / frequency power supply will achieve the following results immediately: Balanced electric al load – The new electrostatic power supply is designed to o perate on a 480 volt three phase circuit. It immediately converts this AC voltage to a 750 volt DC bus. Therefore, regardless of the energy required by the dehydration or desalting process the load on each branch of the input power will remain balanced at all operating conditions. Increased power available during p rocess up sets – Conventional transformers are designed with 100% reactance. When process upsets occur that require more energy, these transformers can fail to maintain sufficient voltage to sustain coalescence. The variable voltage / frequency power supply is designed with a low reactance permitting the maximum available current to be delivered to the process without a reduction in secondary voltage. Abil it y to select waveform for opti mu m perform ance – Operating the IGBT modulator at a high switching frequency permits the modulation waveform to be easily customized. Matching the waveform to the electrostatic needs of the process it is possible to promote maximum droplet 3 coalescence. Four variables can be used to define the shape of the waveform. Minimum Voltage – used to maximize the water droplet diameter. Maximum Voltage – used to energize the smallest water droplets. Frequency – prevents the voltage applied to the positive and negative electrodes from decaying, thus maximizing the electrostatic energy applied to the dispersed water and controls the droplet growth and maximizes the water droplet population. Waveform – may be any conceivable cyclic wave that can be represented mathematically. The - 72 -
controller has been configured with the following waveforms: logarithmic, exponential, sinusoidal, square, sawtooth, trapezoidal, circular and inverse circular. The exponential waveform is represented in Figure 2. Additionally, the controller permits these waveforms to be skewed to alter the ratio for ramp up and ramp down times. Results have been obtained in laboratory tests using a range of crude oils. In some cases, the actual results were significantly better than those expected in the field trials. Based on laboratory data, the process performance after installation of the variable voltage / frequency power supply is expected to achieve the following results:
Process up to 30% more oil – Once the waveform has been optimized the performance of the process is expected to improve by at least 30% in oil capacity processed through the vessel. In many lab tests, the results have been superior to 30%. In the field vessels that maximum oil flow may be limited by the outlet nozzle diameter and not the electrostatic capacity of the vessel. Achi eve up to 30% red ucti on in the efflu ent BS&W – Alternatively, if the oil flow is held constant, the outlet BS&W is expected decrease by as much as 30%. In some pilot tests the effluent BS&W has been successfully reduced to trace levels. Improve effectiveness of demulsif ying chemic al – Electrostatic processes function on the water droplet surface the same as the demulsifying chemicals. While actual chemical reductions may not be realized, it is likely the effectiveness of the demulsifying chemicals will be improved. Maintain performance at a reduced t emperature – The variable voltage / frequency power supply produces a significant increase in the water droplet diameter, these enlarged droplets will settle rapidly at the operating temperature. With these enlarged droplet diameters the oil viscosity may be permitted to increase by reducing the oil temperature. Conclusions This patent pending, variable voltage / frequency power supply has been developed during the past 4 years by NATCO. With the ability to fashion a waveform that is optimized for any crude oil, this technology will expand the utility of electrostatic dehydration into opportunity crudes including SAGD production in Canada, diluted bitumen in South America, as well as high TAN crudes. The functionality of the transformer permits an electrostatic field to be optimized for oil viscosity, flowrate, oil conductivity, interfacial tension, water droplet population and distribution. This technology will permit a significant reduction in size from conventional electrostatic vessels. It can also be easily retrofitted for debottlenecking existing Dual Polarity treaters without TM vessel entry. This patent pending technology, trademarked as Dual Frequency , will extend the application of electrostatic dehydration to more difficult oils. References 1. Burris, D.: “ Dual Polarity Oil Dehydration,” Petroleum Engineer , Critical Mass Systems, Grapevine, Texas, August 1977. - 73 -
2. Aske, N., Kallevik, H. and Sjoblom, J.: “Water-in-crude oil emulsion stability studied by Critical Electric Field Measurements. Correlation to Physico-Chemical Parameters and Near-Infrared Spectroscopy,” Journal of Petroleum Science and Engineering , Trondheim, Norway, April 2002. 3. Draxler, J. and Marr, R.: “Design Criteria for Electrostatic Deemulsifiers,” Chemie-IngenieurTechnik , Germany, 1990, Vol. 62, No. 7, Page 525.
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Appendix II
Users Lists Refinery Desalting Systems Composite Electrode Systems Dual Polarity® Retrofit Projects Electro-Dynamic® Desalting Systems NATCO Electrostatic Crude Oil Dehydrators NATCO Field Desalting NATCO Canada Electrostatic Dehydrators NATCO HOWMAR TriVolt® Dehydrators and Desalters NATCO HOWMAR Dehydrators and Desalters NATCO Electrostatic Dehydrators – Very Heavy Oils
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Partial User List
REFINERY DESALTING SYSTEM Crude oil entering the refinery contains various contaminants. An effective desalting system removes the majority of these contaminants, principally water, water soluble salts and a large percentage of the suspended mineral matter contained in the feedstock prior to distillation and further processing. The desalter is designed to remove contaminants through stages of fresh water injection, mixing and dehydration. NATCO combines its more than half of a century of crude oil dehydration . . . and over 30 years of field and refinery desalting experience to supply the industry with the most energy and chemically efficient desalting processes available today.
CUSTOMER
LOCATION
MARATHON OIL1 PHILLIPS PETROLEUM3 VAL VERDE1 YPF3 IPAC3 TIPPERARY REFINERY1 CALCASIEU REFINERY1 CONOCO3 VAL VERDE1 DAPSA1 KELLOGG/ADNOC1 BP1 SHELL1 (2 TRAINS) PHILLIPS PETROLEUM1 CAIRO OIL1 PETRO PERU1 UNION OIL1 VAL VERDE1 TPI2 TOHOKU REFINERY2 JAPAN ENERGY2 (3 TRAINS) PETROECUADOR 1 AMAZONAS REFINERY (2 TRAINS) NIPPON OIL1 KYGNUS REFINERY2 ANCAP LA REJA REFINERY1 CORPOVEN SAN ROQUE REFINERY1 CALTEX JET MEROX PLANT1 KASHIMA REFINERY2 NANSEI REFINERY2
ILLINOIS ALABAMA NIGERIA ARGENTINA KHARG ISLAND TEXAS LOUISIANA MONTANA TEXAS ARGENTINA ABU DHABI UK (WALES) NETHERLANDS ALABAMA EGYPT PERU NETHERLANDS RUSSIA THAILAND JAPAN JAPAN ECUADOR JAPAN JAPAN URUGUAY VENEZUELA SOUTH AFRICA JAPAN JAPAN
1
DUAL POLARITY UNITS ELECTRO-DYNAMIC ® UNITS 3 AC UNITS 2
Note: Does not include NATCO Howmar installations. See separate list for these.
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Composite Electrode System Users List Conventional steel electrodes used in electrostati c dehydration and desalting systems suffer performance degradation when used in conductive environments due to excessive discharge of the electrode array. The non-metallic, composite electrode array overcomes many of the limitati ons of steel electrodes by providing intr insic arc-quenching capabilities along with self-adjusting field strength gradation. Composite electrodes permit the processing of oils of high water content and conductivity t hat were unable to be reli ably processed using conventional technology. NATCO combines its more than half of a century of crude oil dehydration . . . and over 40 years of electrostati c experience to supply the industry wit h the most energy and chemically efficient dehydration and desalting processes available today.
CUSTOMER
LOCATION
TPI TOHOKU JAPAN ENERGY (3 TRAINS) KYGNUS KASHIMA NANSEI AMOCO LIUHUA (2 TRAINS) FPSO KOC (8 TRAINS) KEPCO (2 TRAINS) NODCO TEMA BLOOMFIELD EXXONMOBIL KIZOMBA “A” (2 TRAINS) FPSO CHEVRON ALBA BP HARDING TEXACO CAPTAIN FPSO BP CLAIR OCN (4 VESSELS) PDVSA JUSEPIN (2 VESSELS) BP HOLSTEIN BP MAD DOG (2 VESSELS) BP THUNDER HORSE BP ATLANTIS DOMINION DEVILS TOWER BP NORTHSTAR LA TEJA REFINERY CONOCO ENCANA/CITY INVESTING/BDR (2 VESSELS) REPSOL-YPF (BLOCK 16) SCEPTRE RESOURCES (4 VESSELS) UNION PACIFIC RESOURCES (5 VESSELS) RENAISSANCE ENGERGY (15 VESSELS) DOME AMOCO CANADA PETROLEUM (3 VESSELS) CHAUVCO MORGAN (4 VESSELS) SUGAR CREEK FOSSIL OIL INVERNESS RANCHMAN’S PINNACLE (3 VESSELS) RENAISSANCE ALLIANCE (5 VESSELS) NORCEN ALLIANCE (3 VESSELS) PINNACLE RESOURCES/BDR (2 VESSELS) RENAISSANCE/BDR
- 77 -
THAILAND JAPAN JAPAN JAPAN JAPAN JAPAN CHINA KUWAIT KOREA QATAR GHANA NEW MEXICO ANGOLA UK NORTH SEA UK NORTH SEA UK NORTH SEA UK NORTH SEA VENEZUELA VENEZUELA US GULF OF MEXICO US GULF OF MEXICO US GULF OF MEXICO US GULF OF MEXICO US GULF OF MEXICO NORTH SLOPE URUGUAY CANADA ECUADOR ECUADOR CANADA CANADA CANADA CANADA CANADA CANADA CANADA CANADA CANADA CANADA CANADA CANADA CANADA CANADA CANADA CANADA
Dual Polarity Liquid Dehydration Retrofit Project Partial User List Enhance the performance of your liquid dehydration equipment with a NATCO Dual Polarity (AC/DC) Retrofit Package. NATCO’s Dual Polarity Electrostatic liquid dehydration process is the single most effective method of crude oil dehydration and/or desalting available on the market today. Since its introduction in t he early 1970’s, NATCO’s Dual Polarity dehydration system has out performed mechanical and conventional AC electrostatic dehydration and/or desalting processes in hundreds of applications. This patented process provides major benefits to its users, through lower operating temperatures, higher throughput rates, cleaner produced water, greater dehydration capability and lower chemical requirements. Principle of Operation: The Dual Polarity process utilizes both AC and DC electric components to provide maximum dehydration performance. Upon entering the electrostatic coalescing section, the emulsion is first exposed to a low gradient AC field which coalesces the bulk of the larger water droplets. Emulsion bearing smaller water droplets continues upward into a high gradient DC field. The DC field acts as a polishing section to coalesce and separate even the smallest water droplets. As the individual drops approach the electrode plates, they accept the charge of the nearest plate. The droplets are repelled and move toward the other plate. The droplets move back and forth until oppositely charged droplets collide and coalesce and settle. The electrostatic field has a potential of several thousand volts. The transformer that supplies the power is designed to protect itself as well as other components of the system. The DC field is self-regulating and supplies the maximum voltage for optimum resolution of the emulsion. This self-regulated system provides increased operational flexibility and ec onomy.
Vessel Manufactu rer 2 Trains – Petro Double Hot A.D. Desalter 1 Train – Howe Baker A.C. Design 1 NATCO Dual Polarity Coalescer
Size (4) 12’ OD x 65’ x 137 Psig (2) 10’ OD X 36’ x 180 Psig 10’ OD x 25 x 275
Customer Location GUPCO/Amoco Egypt GUPCO/Amoco Egypt CNG Gulf of Mexico
1 NATCO Heater Treater C-E to CWW
10’ OD x 25 x 50
Marathon – Cody, Wyoming
1 – EGI 8’ x 20’ Sauder to D. P. 1 – Petreco Single Hot Chemelectric
8 x 20 x 40
1 NATCO/Petreco A/C Treaters 2 – 10 x 30 Texas Tanque/Sauder
1 – 6 x 15 x 50
15 - NATCO A/C Electrostatics
2 - 20 x 25 4 – 10 x 30 4 – 10 x 35 3 – 10 x 40 2 – 10 x 45 2 – 10 x 30
Mobil Sundown, Texas Mobil Denver City, Texas J. L. Cox Midland, Texas Shell Denver City, Texas Shell Denver City, Texas
2 – Texas Tanque/Sauder
6 x 15 x 50
2 – 10’ x 30’
Shell North Hobbs Unit
- 78 -
Original Design Rate 55,000 bopd each train 30,000 bopd
After Retrofit 100,000 bopd 55,000 bopd
Pending ???
Pending ???
3,000 bopd
4,250 bopd
4,000 bopd
6,500 bopd
1,500 bopd
2,500 bopd
Dual Polarity Dual Polarity
1,200 bopd
2,500 bopd
4,500 bopd
12,000 bopd
Dual Polarity
2,400 to 5,000 bopd each
2 x Original
Dual Polarity
5,000 bopd
8,000 bopd
Retrofit To Dual Polarity Dual Polarity Dual Polarity Electrodynamic Dual Polarity Composite Grids Dual Polarity Dual Polarity
Electro-Dynamic® Desalting System Partial User Lis t
Crude oil contains various contaminants. An effective desalting system removes the majority of these contaminants, principally water, water soluble salts and a large percentage of the suspended mineral matter contained in the feedstock prior to further processing. The desalter is designed to r emove contaminants through stages of fresh water injection, mixing and dehydration. NATCO combines its more than half of a century of crude oil dehydration . . . and over 40 years of desalting experience to supply the industry wit h the most energy and chemically efficient desalting processes available today.
CUSTOMER
LOCATION
TPI TOHOKU JAPAN ENERGY (3 TRAINS) KYGNUS KASHIMA NANSEI AMOCO LIUHUA (2 TRAINS) (FPSO) KOC (8 TRAINS) KEPCO (2 TRAINS) NODCO TEMA BLOOMFIELD EXXONMOBIL KIZOMBA “A” (2 TRAINS) (FPSO) DOMINION (SPAR)
THAILAND JAPAN JAPAN JAPAN JAPAN JAPAN CHINA KUWAIT KOREA QATAR GHANA NEW MEXICO ANGOLA GULF OF MEXICO
- 79 -
NATCO Electrostatic Crude Oil Dehydrators Partial Users List Crude oil dehydration using a high-voltage electrical fi eld for final coalescing is an extremely efficient process. The principles used in the design of electrical dehydrator/coalescers are proven technology and have been used commercially for decades. NATCO’s patented Dual Polarity (AC/DC) Electrostatic dehydrator is the single most effective method of crude oil dehydration. Introduced in 1970, it has out performed mechanical as well as conventional electrostatic dehydrators in hundreds of applications. NATCO’s Dual Polarity Electrostatic Dehydrator consists of a pressure vessel with an optional heating/ degassing section with metered orifice distributors. Using the same, dependable AC power supply as a conventional electrostatic dehydrator, the Dual Polarity Dehydrator supplies a rectified DC signal to pairs of electrode plates charging them in opposition. Water droplets entering the field are elongated and attracted to one or the other plates, providing the droplets with directional coalescent energy. (Combined listing of Conventional AC and Dual Polarity Equipment). Tesoro Texaco
CALIFORNIA - 10° - 26° API Crudes *Exxon Wilmington Shell Mt. Poso Mobil Belridge *Texaco San Ardo *Superior Torrance Conoco Santa Maria-Ventura McCulloch Fellows *Sun Hillhouse Mobil San Ardo *ARCO Ellwood-Santa Barbara Mobil Ventura *Texaco Signal Hill Belridge Belridge
-
Cutbank Roundup
NORTH DAKOTA - 28° - 35° A PI Amerada Tioga Shell Williston KANSAS - 25° - 35° API Exxon Liberal Amoco Great Bend Gulf Great Bend Lewis Eng. Great Bend Champlain Great Bend Sun Great Bend Mobil Liberal Anadarko Liberal Cities Service Liberal Ladd Petro. Liberal
ALASK A - 22° - 35° API Marathon Trading Bay Amoco West Forlands Union Trading Bay Texaco East Forlands Mobil East Forlands Shell West Forlands
OKLAHOMA - 18° - 38° API Exxon Oklahoma City Exxon Enid Gulf Oklahoma City Conoco Oklahoma City Cameron Oklahoma City *Amoco Oklahoma City Gulf Seminole Union Texas Oklahoma City Samedan Ardmore Lonestar Oklahoma City Mobil Oklahoma City Phillips Ardmore ARCO Ardmore ARCO Oklahoma City Tenneco Pawhuska Sun Seminole Sohio Oklahoma City Anson Oklahoma City Sun Oklahoma City ARCO Pawhuska Skelly Ardmore
WYOMING - 13° - 28° API Marathon Byron *NCRA Gillette Tenneco Gillette Mobil Gillette *Ashland Hamilton Dome Shell Pheasant Inexco Gillette Continental Gebo Union Texas Gillette Pasco Sinclair *Marathon Garland Union Oil Casper MONTANA - 18° - 25° API Phillips Cutbank Shell Glendive
- 80 -
Apco Getty Coastal States Union of Calif. Skelly *Sun -
Oklahoma City Oklahoma City Oklahoma City Enid Oklahoma City Davis
Gen. Crude Chevron Phillips Lewis Oper. Dunnigan Crown Central Coastal States *Union of TX -
Snyder Snyder Odessa Snyder Abilene Snyder Hobbs Hobbs
EAST TEXAS - 18° - 40° API Exxon Longview Exxon Houston Exxon (PL) Houston Exxon Shreveport, LA Exxon Corpus Std. Of Texas Houston Amoco Longview Conoco Weber Falls Tenneco Corpus Gulf Shreveport, LA Shell Houston Placid Shreveport, LA Tenneco Longview Mobil Weber Falls Skelly Longview H&J Orig. Corpus Std of TX Weber Falls Shell Weber Falls *Amoco Houston Robbins Petro. Longview South. Miner. Corpus ARCO Houston Quintana Corpus Champlain Houston Texaco Weber Falls Amerada Longview Gulf Houston Greenwich Oil Longview Cities Service Houston Marathon Houston
MICHIGAN, ILLINOIS, INDIANA, OHIO, KENTUCKY- 18° - 40° API Exxon Kentucky Gulf Illinois Gulf Indiana Gulf Ohio Ashland Ohio Sun Illinois Kingwood Kentucky Union of Calif. Illinois Duncan Kentucky Superior Michigan Sinclair Illinois Getty Kentucky *Marathon Illinois Exxon Illinois NEW MEXICO WEST TEXAS 20° - 40° API Exxon Odessa Texaco Hobbs Conoco Odessa Sinclair Odesa Sinclair Snyder Conoco Hobbs Tenneco Farmington Mobil Snyder Shell Hobbs ARCO Odessa Cities Service Hobbs Shell Odessa Ambassador Hobbs Mobil Odessa ARCO Hobbs D. Faskin Hobbs Mobil Hobbs Amoco Farmington Texas Pacific Hobbs Vaughn Petro. Snyder Skelly Farmington Getty Odessa Jack Hammon Odessa Sun Snyder ARCO Hobbs Gulf Odessa *Amerada Hobbs D. Faskin Odessa Union of Calif. Hobbs Kerr-McGee Farmington Amoco Pampa Marathon Iraan Texas Pacific Hobbs Std. Of Texas Snyder Am. Petrofina Snyder Reserve O&G Hobbs Oil Dev. Of TX Hobbs Union of CA Pampa Anadarko Abilene
LOUISIANA - 20° - 40° SPI Exxon Pelican Island Exxon New Iberia Exxon Brookhaven, MS Exxon Pipeln Harvey Exxon Farriday Gulf Harvey Shell Harvey Amoco Lake Charles Shell New Iberia Conoco Harvey Chevron New Iberia Citronell Brookhaven, MS Hunt Harvey ARCO New Iberia Amoco Ferriday Lyons Petro. New Iberia Cameron Ferriday Mobil New Iberia Union of Calif. Harvey Quintana New Iberia Getty Harvey Signal Harvey Placid Harvey Tenneco Harvey Forrest New Iberia
- 81 -
Cage So. Nat. Gas Texaco Phillips Sun
-
New Iberia Harvey New Iberia Brookhaven, MS Harvey
VENEZUELA - 16° - API 1996 (4) Petrozuata San Diego – 120 KBPD 1997 (4) Operadora Cerro Negro (Exxon-Mobil-PDVSA – 150 KBPD° 45 KBPD, delivery March 1996 VENEZUELA -16° - API 1999 (4) SINCOR Project (PDVSA, TOTAL, STATOIL) – 150 KBPD BRAZIL 19-21° - API 1980 (2) Petrobras – Garoupa Platform –16,000 m3/day each ECUADOR – 14.5° API 1995 (2) Repsol-YPF – Block 16 25 KBPD each.
VENEZUELA - 27° - API 1994 (3) Lagoven Jusepin – 45KBPD 1996 (5) Corpoven Musipan and Muri - 45 KBPD, delivery March 1996 1998 (2) PDVSA Jusepin – 67 KBPD with Composite Electrodes VENEZUELA - 22° - API 1996 (1) Perez Compac La Leona –20KBPD
- 82 -
NATCO Field Desalti ng Partial Users List NATCO’s Field Desalter is designed to efficiently remove crude oil impurities, principally water, soluble salts suspended solids which may or may not be associated with the produced water. During field processing, salt levels must be reduced to meet pipeline, sea transport or refinery feedstock standards, typically 5 to 20 pounds of salt per thousand barrels (ptb) of crude oil. The conventional field desalting process consists of required stages of dilution water injection, mixing and dehydration to meet these process specifications. NATCO’s Desalting technologies utilize a proper balance between dilution water, mixing energy (pressure drop), mechanical coalescence and separation time. Enhanced by the application of heat, chemicals and electrostatic treatment, the system provides maximum performance and process efficiencies. The Electro-Dynamic™ Desalter ("EDD") NATCO's premier desalting system, combining Dual Polarity (both AC and DC fields) with two other important NATCO innovations, electrostatic mixing and countercurrent flow. These unique features then make it possible to carry out Multi-Stage desalting within a single unit for unsurpassed desalting efficiency. One of our dehydration and desalting systems, the Electro Dynamic™ Desalter, can be used in oil refineries, where stringent desalting requirements have grown increasingly important. These requirements have increased as crude quality has declined and catalysts have become more sensitive and sophisticated, requiring lower levels of contaminants. The reduced number of vessels employed by our system is particularly important in ref inery applications where space is at a premium. NATCO’s Dual Polarity Electrostatic Desalters
(Over 400 Units in Operations Worldwi de) Cust omer LAPCO IPAC GUPCO Oasis IAPCO Gulf (Chevron) Gulf (Chevron) Amoco SNPA Huffington IOL Amoco Mobil Occidental KOC (phase2) KOC (phase 3) ARAMCO ADMA OSCO KALA GULFAKS (BP) SUCO AGIP/Petrobel SUCO ONGC
NORMAL FLOW (BOPD) 250,000 190,000 625,000 120,000 150,000 650,000* 250,000* 35,000 75,000 50,000 150,000* 15,000 12,000 10,000 350,000* 250,000* 6,600,000* 675,000* 990,000* 100,000* 180,000* 100,000* 180,000* 100,000* 150,000*
- 83 -
LOCATION Iran Iran Egypt Libya Indonesia Nigeria Cabinda Trinidad Tunisia Southeast Asia Canada Venezuela Venezuela Peru Kuwait (D.P) Kuwait (D.P. and E.D.D.) Saudi Arabia Abu Dhabi (Das Island) (D.P.) Iran Iran Norway NS Zeit Bay, Egypt Abu Rudeis Ras Budran Upan, India
Cust omer ARAMCO Amoco Khalda Petro Pecten Cameroon Amoco Lihua Aramco KOC Saudi Arabian Texaco Qarum Petroleum Mobil Cerro Negro Phillips Mahogany
NORMAL FLOW (BOPD) 2,800,000* 55,000 40,000 12,000 70,000 1,300,000 160,000 60,000 42,000 (2 trains) 91,000
- 84 -
LOCATION Safania Gabon Egypt Cameroon S. China Sea (E.D.D.) Zuluf Onshore (D.P.) GC-25 Kuwait (D.P. & E.D.D.) Kuwait N. Zone (D.P.) Egypt Venezuela GOM
NATCO Canada Electrostatic Dehydrators Partial Users List Customer
Oil Flow M3/day
Water
API
Vessel Size
BS&W Out %
Location
Crestar Energy
400
70
13.5
8x35
0.3
Jenner P Pool
Crestar Energy
400
70
13.5
8x35
0.3
Jenner P Pool - Second Unit
Renaissance Energy
970
70
12
12x80
0.3
Jenner (11-21-20-8 W4M)
Crestar Energy
500
50
15
10x35
0.3
Jenner O Pool
Norcen Energy
300
60
17
8x35
0.5
Ret Low
Gulf Canada Resources
350
300
14
10x40
0.3
Surmont
Black Rock Resources
350
300
14
10x40
0.3
Cold Lake
Contour Energy
300
100
15
8x30
0.3
Jenner
Wascana Energy
700
400
14
10x70
0.3
West Buffle Coulee
Canadian Natural Resources
508
600
11
10x70
0.3
Primrose
Wascana Energy
1600
499
16
12x80
0.3
M antorio
Sceptre Resources
600
800
17
8x25
0.5
Battrum
Sceptre Resources
1572
314
17
8x25
0.5
Battrum
Renaissance Energy
2830
2830
17
10x40
0.5
Amisk
Amoco Canada
2516
1570
17
10x40
0.5
Jenner
Amoco Canada
2516
1570
17
10x40
0.5
Jenner
BP Exploration
9981
3535
16
10x60
0.5
Wolf Lake
Chauvco
2075
2075
15
8x40
0.5
Marsden-West (Sask)
25
25
15
8x25
0 .5
Sibbald North Battery
2200
800
14
10x40
0.5
Hayter South
4200
390
12
12x50
0.5
Lindbergh
Morgan Hydrocarbons
3768
1132
12
10x50
0.5
Senlac
Morgan Hydrocarbons
3768
1132
12
10x50
0.5
Senlac
Petro-Canada
1226
1200
12
10x50
0.5
Salt Lake
Renaissance Energy
2500
500
13
10x40
0.5
Jenner
11
10x70
0.5
Lindbergh
BP Exploration Renaissance Energy Amoco Canada
Amoco Canada
3354
Amoco Canada (Dome)
3200
600
11
10x70
0.5
Primrose
Amoco Canada
4560
456
11
12x80
0.5
Lindbergh
Amoco Canada (Dome)
3354
11
10x70
0.5
Lindbergh
Amoco Canada (Dome)
3354
11
10x70
0.5
Lindbergh
10
8x30
0.5
Wolf Lake Jenner
BP Exploration Renaissance Energy
260
6
16
8x30
0.1
Renaissance Energy
190
81
16
8x35
0.45
Renaissance Energy
140
210
14
8x30
0.3
Etzikum
Renaissance Energy
293
97
18
10x50
0.02
Warner
Renaissance Energy
190
257
13.6
12x85
0.2-0.4
Jenner
Renaissance Energy
400
80
17
10x40
0.3
Amisk
Renaissance Energy
574
6
14
12x80
0.4
Jenner
Renaissance Energy
630
10x60
0.3
Webb
Renaissance Energy
625
10x40
0.2
Green Glades
10.9 16-18 47
15
- 85 -
East Cantuar
Renaissance Energy
640
160
16-18
10x60
0.7
Crowsnest
Renaissance Energy
600
400
17
10x40
0.3
Shorncliffe
Crestar Energy
500
50
16
10x50
0.3
Czar
Renaissance Energy
140
19
14
8x30
0.3
Border
Renaissance Energy
216
14
15
10x40
0.1
Hayter South
Renaissance Energy
250
3.8
15.4
8x35
0.4
Red Deer River
- 86 -
NATCO Howmar TriVolt Dehydrator and Desalter Users Li st
COUNTRY
LOCATION
Al Khafji Joint Operations Al Khafji Joint Operations API ARCO BP BP BPCL BRC Ceska Rafinerska Chevron ESSAR Oil Co. Esso Esso Hellenic Aspropyrgos IBP IOCL Kala Naft Karachaganak Petroleum Operating Co. Kuwait Oil Co.Phase IV Madras Refinery Ltd. Mediterranea MRPL NATREF Neste Oy NRL ONGC Pertamina Raffineria Di Roma Saudi Arabian Oil Company Saudi Arabian Oil Company
Hout Khafji Falconara Refinery, Italy Cherry Point, Washington Kinneil, Scotland Grangemouth, Scotland Bombay, India Antwerp, Belgium Kralupy, Czech Republic ascagoula, Mississippi Gujarat, India Fawley Refinery, England Fawley Refinery, England Athens, Greece Numaligarh, India Gujarat, India. (UA-1) Tabriz, Iran Karachaganak, Kazakhstan G.C’s 1, 3, 6, 8 & 12 Kuwait Madras, India Milazzo Refinery, Sicily Madras, India South Africa Porvoo, Finland Karachi, Pakistan Uran, India Indonesia Rome, Italy Haradah GOSP-1 Haradah GOSP-2
Saudi Arabian Oil Company Saudi Arabian Texaco Co. Shell Shell Sincor Singapore Refining Company Sinopec Sohio State Company for Oil Projects State Oil Marketing Organisation for South Oil Company
Uthmaniyah GOSP-13 Wafra, Kuwait Malaysia Malaysia Venezuela Singapore China North Slope, Alaska West Qurna, Iraq South Rumaila “D” & “E” Janubia “C”, Iraq Qurainat “B” Shamiya “B”, Iraq West Qurna DG-8, Iraq
State Oil Marketing Organisation for South Oil Company State Oil Marketing Organisation for South Oil Company State Oil Marketing Organisation for South Oil Company
Zubair Mishrif Hammar Mishrif, Iraq
- 87 -
NO.
CAPACITY (BPD)
2 stage 4 trains, 2 stage 1 1 4 2 1 1 1 2 stage 2 stage 3 1 1 1 2 stage 2 3 trains, 2 stage 10 trains,2 stage 1 2 2 stage 2 stage 2 stage 1 3 2 stage 1 2 stage 2 stage
60,000 440,000 60,000 140,000 528,000 120,000 165,500 90,600 70,000 155,000 229,000 185,000 60,000 85,000 70,000 70,000 64,500 each 250,000 104,000 75,000 110,000 86,000 71,000 50,000 105,000 125,000 92,000 330,000 330,000
2 stage 2 stage 1 1 4 1 1 1 6 5 x 2 stage
330,000 80,000 127,000 45,400 77,665 90,000 74,400 100,700 200,000 140,000 each
3 x 2 stage
80,000 each
2x2 stage 4 x 2 stage
50,000 each 40,000 each
LOCATION
COUNTRY Sunkyong/TOR TRCN/Rayong
Ghana Thailand
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NO.
CAPACITY (BPD)
1 1
45,000 148,000
NATCO Howmar Dehydrator and Desalter Users L ist
COUNTRY Australia Australia CIS Egypt Egypt Egypt England Finland Germany Greece India India Iran Iraq Iraq Iraq Kuwait Kuwait North Sea, Holland North Sea, Norway North Sea, UK North Sea, UK North Sea, UK North Sea, UK North Sea, UK Philippines Russia Russia Russia Russia Russia Russia Russia Saudi Arabia Singapore Sweden Sweden Vietnam
COMPANY, LOCATION
CAPACITY (BPD)
Mobil, Adelaide SIPM/SRAP Ludan, Astrakan Alexander Refining Co. Alexander Refining Co. ZAFCO BNOC, Nigg Bay Neste Oy Shell, Hamburg NAPC, Prinos Refinery, Athens HPCL Refinery, Bombay Madras Refineries Ltd. Kala Naft INOC, Basrah SCOP, Sfaya Field SCOP, West Qurna Field KOC, GC’s 2, 4, 5 KOC, GC 23 AMOCO, P-15 Platform Statoil/Aker/RJSL Veslefrikk Field Amerada Hess Ivanhoe / Rob Roy Fields Bluewater / Talisman Energy Ross Field Phillips, Maureen Shell, Curlew Shell, Fulmar Shell Machinoimport MAG/Salawat IV Tenguiz Field (Trains 1, 2 & 3) Western Siberia Oilfields Western Siberia Oilfields Western Siberia Oilfields Western Siberia Oilfields Aramco, Well Heads Singapore Petroleum Co. Nynas Petroleum Co., Nynashamn Shell, Koppartrans White Tiger Oilfield
24,600 120,000 70,250 40,000 43,300 25,000 100,000 4,100 45,000 27,000 60,000 66,000 60,000 2 units - 80,000 each 25,000 6 units - 52,000 each 12 units - 25,000 each 4 units - 30,000 each 25,000 75,000
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63,400 40,000 80,000 45,000 37,500 12 units - 60,000 each 98,300 12 units - 58,000 each 12 units - 90,000 each 5 units - 60,000 each 20 units - 60,000 each 22 units - 60,000 each 20,000 70,000 25,000 28,600 2 units - 30,000 each
NATCO Electrostatic Dehydrators – Very Heavy Oils Partial Users List Customer Crestar Energy Crestar Energy Renaissance Energy Crestar Energy Norcen Energy Gulf Canada Resources Black Rock Resources Contour Energy Wascana Energy Canadian Natural Resources Wascana Energy Sceptre Resources Sceptre Resources Renaissance Energy Amoco Canada Amoco Canada BP Exploration Chauvco BP Exploration Renaissance Energy Amoco Canada Morgan Hydrocarbons Morgan Hydrocarbons Petro-Canada Renaissance Energy Canada Amoco Canada Amoco Canada (Dome) Amoco Canada Amoco Canada (Dome) Amoco Canada (Dome) BP Exploration Renaissance Energy Renaissance Energy Renaissance Energy Renaissance Energy Renaissance Energy Renaissance Energy Renaissance Energy Renaissance Energy Renaissance Energy Renaissance Energy Renaissance Energy Crestar Energy Renaissance Energy
Oil Fow BPD 2520 2520 6111 3150 1890 2205 2205 1890 4410 3200 10080 3780 9904 17829 15851 15851 62880 13073
13860 26460 23738 23738 7724 15750 21130 20160 28728 21130 21130 1638 1197 882 1846 1197 2520 3616 3969 3938 4032 3780 3150 882
ºAPI
13.5 13.5 12 15 17 14 14 15 14 11 16 17 17 17 17 17 16 15 15 14 12 12 12 12 13 11 11 11 11 11 10 16 16 14 18 13.6 17 14 16-18 15 16-18 17 16 14
Vessel Size 8’ x 35’ 8’ x 35’ 12’ x 80’ 10’ x 35’ 8’ x 35’ 10’ x 40’ 10’ x 40’ 8’ x 30’ 10’ x 70’ 10’ x 70’ 12’ x 80’ 8’ x 25’ 8’ x 25’ 10’ x 40’ 10’ x 40’ 10’ x 40’ 10’ x 60’ 8’ x 40’ 8’ x 25’ 10’ x 40’ 12’ x 50’ 10’ x 50’ 10’ x 50’ 10’ x 50’ 10’ x 40’ 10’ x 70’ 10’ x 70’ 12’ x 80’ 10’ x 70’ 10’ x 70’ 8’ x 30’ 8’ x 30’ 8’ x 35’ 8’ x 30’ 10’ x 50’ 12’ x 85’ 10’ x 40’ 12’ x 80’ 10’ x 60’ 10’ x 40’ 10’ x 60’ 10’ x 40’ 10’ x 50’ 8’ x 30’
- 90 -
%BS&W Out 0.3 0.3 0.3 0.3 0.5 0.3 0.3 0.3 0.3 0.3 0.3 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.1 0.45 0.3 0.2 0.2-0.4 0.3 0.4 0.3 0.2 0.7 0.3 0.3 0.3
Country
Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada Canada
Renaissance Energy Renaissance Energy Petrozuata (Upstream) Petrozuata Jose Operadora Cerro Negro Sincor (Upstream) Perez Companc
1361 1575 160000 160000 150000 175000 10000
15 15.4 17 17 15.2 17 19
10’ x 40’ 8’ x 35’ 10’ x 60’ 12’ x 60’ 14’ x 100’ 12’ x 90’ 10’ x 45’
0.1 0.4 0.7 0.7 0.5-0.6 0.5 0.5
Canada Canada Venezuela Venezuela Venezuela Venezuela Venezuela
NOTE: Please note that many of these applications are at low flux to obtain the very low BS&Ws required f or heavy oil in cold climates.
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Appendix III
Components Composite Electrodes Electrostatic Transformers Installation Procedure for New or Replacement Entrance Bushings and Bushing Housings Transformer Oil Specifications & Material Safety Data Sheet Transformer Oil Filtration Procedure for Operating Units Electrostatic Dehydrator/Desalter Inspection Punch-List Products Made for NATCO by ELECTROTECH (Hangers, Entrance Bushings, Tester)
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Composite Electrodes Electrostatic coalescence generally proceeds through a mechanism of drop polarization, alignment of the polarized drops, and “chaining” of these drops along the lines of force of the electrostatic field. These conductive chains lead to frequent electrical discharges or arcing between the electrodes. The arcs are a normal part of the process, and because they are submerged in oil, they do not produce any damage. However, a steel electrode array is momentarily discharged by an arc, and if the arcs occur with sufficient frequency (as in a wet emulsion), the electrodes may be discharged for a sufficient duration for slippage of process fluids without adequate exposure to the field. Composite plate electrodes may be used to increase the water tolerance of the system under such conditions. These electrodes consist of plates of composite (fiber reinforced plastic) constru ction with graphite or carbon embedded in the central portion of the plate to impart conductivity along the length of the plate. The remainder of the plate contains filler materials that lead to the adsorption of a layer of water on the plate surface. This adsorbed water layer then becomes the conductive medium along the height of the plate. Since such an adsorbed layer is quite resistive, any arcing that occurs is quickly quenched. As a result, only the area in the immediate vicinity of the arc is discharged and slippage is almost eliminated. Composite plates are normally spaced on 5 to 6 inch centers and are approximately 15 inches high. They are used on Dual Polarity ® processes for increased water tolerance and in all ElectroDynamic ® Desalters.
Advantages of Composite Plates • • • • • •
Tolerant of high water content dispersions More effective treatment of conductive liquids Produce a graduated field for better drop growth Less slippage or by-passing of untreated process liquids due to arcs Provide greater retention time in the electrode zone Resistant to vessel motion due to mechanically stable array
Installations Please see the users list. The earliest of these dates back to 1978.
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COMPOSITE ELECTRODES INNOVATIVE IMPROVEMENT IN ELECTROSTATIC DEHYDRATION TECHNOLOGY
For 35 years NATCO has supplied electrostatic dehydration technology and equipment to the oil producing and refining industries. NATCO's commitment to aggressive research has steered the industry's processing expectations, with breakthroughs such as the Dual Polarity and the Electro-Dynamic processes. Electrostatic dehydration is accomplished in pressurized vessels into which an electrode system has been suspended from insulators. The produced crude oil, containing water and mineral contaminants, is treated by passing it through the charged electrodes at low velocity. The high voltage field induces coalescence of tiny dispersed water droplets. Droplet growth forces sedimentation to the underlying oil/water interface, and the accumulated water is discharged as a separate phase. In conventional systems the electrodes are a series of lightweight rods or plates designed to distribute the voltage field across the vessel, yet leave the space unobstructed to the throughflow of oil. They have traditionally been fabricated from carbon steel or stainless steel. Such highly conductive materials easily distribute the electrical charge, but suffer from a potentially crippling limitation. If for any reason a short circuit is developed between the electrodes and the water interface an electrical discharge will instantly bleed all electrical charge from the entire electrode. If the short-circuit persists, the electrodes will remain de-energized and the dehydration process will not be performed. Such short circuits are not uncommon, and may be temporary or longer lasting. To help overcome this problem NATCO has developed the industry's first non-metallic electrode system. The "composite electrode" utilizes a series of plates charged with a Dual Polarity field configuration. The plates are made of a non-conductive high temperature plastic. Special surface properties allow a surface charge to be distributed from a central conductive strip. The strip is located on only one side of each plate as shown in Figure 1. This limits the ability of an electrical arc to form between electrodes. If a short circuit develops from one of the plates to the water surface, the local surface charge will be quickly dissipated. However since the conductivity of the plates is very low, no arc will be sustained since energy cannot feed the discharged area fast enough. During the localized short circuit the electrode remains fully charged except for that small area being discharged. Another benefit of the composite electrode is the reduction of the voltage field toward extreme edges of the plates. The electrical flux is highest near the vertical center of the plates at the conductive portion. Moving away from the conductive strip the field flux degrades as shown in Figure 2. This "softens" the electrical stress at the top and bottom edges which is usually high when metallic electrodes are used. This high stress can result in re-entrainment of separated - 94 -
water. The result is better dehydration performance with composite electrodes. Extremely conductive crude oils can cause corrosion to metal electrodes. Composite electrodes are resistant to such corrosion, and are well suited for severe environments. They have been tested in the laboratory to 400 °F, and have operated in refinery service at 300 °F. These electrodes have been in production service since about 1983. They are now an integral part of NATCO's proprietary Electrodynamic Desalter, an innovative electrostatic counterflow process which is redefining performance limits for refinery and field desalters. IMPROVEMENT IN ELECTROSTATIC CRUDE OIL TREATMENT USING COMPOSITE ELECTRODES The use of a high voltage electrostatic field in crude oil treatment is standard practice in refineries and in many field dehydration facilities. One such apparatus, Natco’s Dual Polarity ®, uses a matrix of parallel steel plates, one charged positive, the next negative, and so on. The entire matrix is submerged in the crude oil phase such that the crude flows between the charged plates. There the electrostatic field causes extensive coalescence of the dispersed contaminants, which are then able to precipitate out of the oil. There are often limitations due to conductivity of the crude oil. Some of the contaminants such as water, mineral salts and undissolved solids increase its conductivity. It may not readily support the high voltage electric field. With steel, the traditional material of construction for such electrodes, anytime there occurs an arc from the electrode, through the oil, to the vessel shell or the oil/water interface the electrode voltage quickly discharges to zero. Such arcing is frequent in some oils, and the electrostatic voltage field is momentarily lost for the entire electrode because of this minute current leakage. To accommodate highly conductive process conditions, Natco has developed the Composite Plate Electrode. It uses electrode plates constructed of a composite of several materials engineered to have specific electrical properties very different from steel. The plates themselves are relatively non-conductive, but have surface properties that promote the migration of a surface charge. They have a charged conductive strip imbedded under one face. The high voltage charge spreads over the whole surface of a plate from the conductive strip, but slowly because of the low conductivity. With Composite Electrodes, when an arc occurs it causes voltage discharge only in the immediate locality of the arc. The electrode, being itself a poor conductor, cannot feed the arc enough current to sustai n it, and it is quenched. The remainder of the electrode is unaffected by this local perturbation. Furthermore, in conductive oils, the more remote edges of the electrode will exhibit a lower voltage than those portions adjacent the conductive strip due to bleed-off of charge from the electrode surface. This produces a “tapered” electrical charge with lower voltages at its edges where electrical stress is concentrated, and arcing is typically most prevalent. There are several benefits to using the Composite Electrode system. Because of its resistance to arcing, it allows a dehydrator or desalter to function in oils that are much more - 95 -
conductive than a steel electrode would allow. This includes higher water-cut feedstocks. It is more tolerant of interface rag build-up, that is the accumulation of stable and highly conductive emulsions on the interface that can build upward into the electrostatic field. Finally Composite Electrodes produce a more constant, sustained electric field, less disturbed by localized voltage discharges. As a result of these qualities a more efficient coalescence occurs. This allows the dehydrator or desalter to achieve lower BS&W in the discharged oil, and higher throughput capacity. These benefits are observed in easy-totreat oils as well as in highly conductive oils. To demonstrate the performance improvement Composite Electrodes will produce, we offer several cases based on laboratory testing. Testing was conducted in Natco’s Research and Development Laboratory in Tulsa, Oklahoma, using imported crude oils from around the world. Case 1 – North Sea FPSO Dehydrator for Heavy Crud e The following tests were run to simulate an existing dehydrator with steel electrodes, to determine the feasibility of converting to Composite Electrodes. These tests were all conducted on 20 API crude samples with 15% water cut, at 200F using the same demulsifier chemical and dosage, with a 23 kv electric field. Grid Load (bpd/sq.ft.)
Outlet BS&W (%) Using Steel Electrodes
Outlet BS&W (%) Using Composite Electrodes
33 53 76 107
1.2 1.3 1.2 1.2
0.4 0.75 0.6 0.6
The performance was quite insensitive to grid load in the range tested. As a result of these tests, the dehydrator was modified to use Composite Electrodes. Field results were similar to test results except that actual BS&W values (for both steel electrodes and Composite Electrodes) were a little lower than those achieved in the laboratory on aged crude samples.
Case 2 –Dehyd ration o f Mayan Crude, Mexico These tests were conducted to determine the best treatment method and other design parameters for a prospective new dehydrator. A large number of tests were performed on this 20 API crude oil sample, not shown here. Near the end of testing, conditions were initiated that created a severe interface rag build-up. The following tests were selected to show the relative response of Composite Electrodes to the rag. The two tests shown were conducted with 15% water cut at 220F and at a grid load of 60 bpd/sq.ft. using an identi cal type and dosage of demulsifier.
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Grid Load (bpd/sq.ft.)
Outlet BS&W (%) Using Steel Electrodes
Outlet BS&W (%) Using Composite Electrodes
60
1.2 - 1.5
0.72 - 0.92
Case 3 – Arabian Heavy Crude Field Desalters Extensive testing was conducted to help determine feasibility of upgrading existing desalters. The test oil was a series of 28 API single-well samples, not representative of the actual desalter feed, but much more stable due to surfactant contamination. The tests shown are for an AC process using both steel electrodes and Composite Electrodes. Operating temperature was 150F. Water Wash Water Content of Addition (% of Feed Stream Crude Flow) (%)
Mix Valve Pressure Drop (psi)
Grid Load (bpd/sq.ft.)
Electrode Type
Steel
3
3
6
64
31
none
0
60
Outlet BS&W (%)
Could not establish voltage due to high current - Process Failure! Composite 0.29
The feed conditions are not identical, but the differences would not have caused process failure in the low BS&W stream. The Composite Electrodes were able to establish a voltage field even in the higher water cut feed, while the steel electrodes were incapacitated by high current and the corresponding loss of voltage. A major university conducted independent tests on Composite Electrodes. Because the tests were underwritten by an oil-producing company, the results were not made available to Natco. However, we were told ‘off-the-record’ that Composite Electrodes showed a distinct advantage over metallic electrodes.
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Electrotech, Inc. SAPULPA, OK
Electrotech, Inc. th
11549 S. 49 W. Ave. Sapulpa, Oklahoma 74066 (918) 224-5869
CATALOG OF PRODUCTS PROVIDED FOR NATCO GROUP
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E lectr otech, I nc. ENTRANCE BUSHINGS
4.2"
7.25"
10.5"
11.7"
15.25"
EBD-1500 (NATCO part no. 48126009) The EBD-1500 Entrance bushing is a 1½” NPT bushing designed to deliver up to 23,000 volts into crude oil electrostatic dehydrator and desalter process vessels. This bushing has undergone continuous improvements in design and materials to optimize its electrical and mechanical performance. When installing an entrance bushing, a specified length of high voltage cable and Teflon tubing will be required. Therefore, when ordering an entrance bushing, the length of high voltage cable and Teflon tubing must be specified. These items will be listed separately and priced by the foot x the length. The High Voltage Cable is a special corona resistant Teflon insulated conductor specifically manufactured for NATCO (NATCO part no. 48126050). The tubing is ¾”od x ½”id PTFE Teflon available in lengths to 6 f eet (NATCO part no. 11650075). The tubing is needed to center the high voltage cable in the conduit. Centering is important to reduce electrical stress on the high voltage cable. - 99 -
EBD-1500S (NATCO part no. 48126008) The EBD-1500S Entrance Bushing includes a 1” NPT x 1½” NPT x 10½” long swage. The “S” version of the EBD-1500 is primarily employed to allow the use of new style bushings with older style process vessels having 1” NPT entrance bushing connections. The swage is used to extend the entrance bushing into the liquid phase of the process. Corona present in the gas phase of electrostatic coalescers will attack Teflon and other materials used in the construction of entrance bushings.
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E lectr otech, I nc. SBA-2500 ENTRANCE BUSHING
The SBA-2500 is a 2” NPT entrance bushing designed for 60 kV to be used on NATCO Electrodynamic Desalters. The Electrodynamic Desalter utilizes electrostatic mixing of the dilution water which requires high voltage modulation on the electrodes. This high voltage modulation generates extra electrical stress on the entrance bushing. The SBA-2500 was tested at the University of Tulsa high voltage lab to 200 kV without failure. The electrical conduit between the SBA-2500 and the transformer is usually a 6” boot filled with transformer oil. A typical installation is shown below.
4.75"
Reli ef valves Boot r eli ef valve TI- 60FT Isolation Bushing TI- 60 Isolat ion Bushing
Sight Oil level
glass
To high voltage winding
High volt age cable DC
3.875"
Oil level 22.18"
Diode pack
AC
Diode compartment
Tefl on centeri ng r ings
Transformer/ reactor tank
1.25"OD x 1"ID Tefl on t ubing
6"schedul e 40 boot
6 in. vessel connect ion
Tefl on centeri ng ri ng
Bleed ri ng
Gr ound wir e
Bleed valve 13.555"
Cr ude oil level
SBA- 2500 entr ance bushing
4"boot extension
Gr ounding fl oat
Contact
Pr ocess vessel shell
r od St ainl ess st eel cable
1.250"
TYPICAL SBA- 2500 INSTALLATION SBA-2500 (NATCO part no. 48126026) - 100 -
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TRANSFORMER ISOLATION BUSHINGS These bushings are installed in the wall of the diode compartment of NWL transformers. They are suitable for submergence in transformer oil to temperatures of 160 F. TI-23 (NATCO part no. 48126035) (NWL part no. H15022) The TI-23 high voltage bushing (photo 1on the right) isolates the diode compartment from the transformer compartment on NWL 23kV transformers. The TI-23 bushing as pictured contains a 3/8”24 threaded connection on the left side of the bushing and a 5/ 16”18 stud on the right side of the bushing. The TI-23 is easily installed through a 1.625” hole. TI-23FT (NATCO part no. 48126036) (NWL part no. H15036) The TI-23FT high voltage feed through bushing (photo 2 on the right) isolates the diode compartment of NWL 23kV transformers from the entrance bushing boot on NATCO electrostatic coalescers. The compression fitting as pictured on the right side of the feedthrough permits the high voltage cable or conductor rod assembly to pass through the bushing into the diode compartment. The TI23FT is also installed through a 1.625” hole.
TI-60 (NATCO part no. 48126040) (NWL part no. H15009) The TI-60 high voltage bushing (photo 1 on the ri ght) isolates the diode compartment from the high voltage transformer compartment on NWL 60 kV transformers. The stainless steel fitting as pictured on the right of the TI-60 bushing has an internal 5/16”-24 connection that will accept a banana plug. A ¼” diameter hole in the stainless steel fitting permits the high voltage wiring to be secured with the ¼”-20 bolt. The TI-60 bushing is installed through a 2.125” hole. TI-60FT (NATCO part no. 48126041) (NWL part no. H15010) The TI-60FT high voltage feed through bushing (photo 2 on the right) isolates the diode compartment of NWL 60kV transformers from the entrance bushing boot on NATCO Electrodynamic Desalters. The compression fitting as pictured on the right side of the feed-through permits a high voltage cable or conductor rod assembly to pass through the bushing into the diode compartment. The TI-60FT is also installed through a 2.125” hole. - 101 -
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E lectr otech, I nc. Relief valve
3" flange Oil level Teflon centering ring
TI-23FT feed through bushing
Oil level Nylon compression fitting
TI-23 bushings
AC connections
5/16"-18 NC threads
Diode pack
3/8"-24 bolt To transformer high voltage winding
Two #324 conductive o-rings DC connection
Diode compartment
THE HIGH VOLTAGE CABLE TO THE ENTRANCE BUSHING CAN BE PASSED DIRECTLY THROUGH THE TI-23FT AS SHOWN HERE OR A CONDUCTOR ROD ASSEMBLY SIMILAR TO THAT USED WITH TI-60FT BUSHINGS BELOW CAN BE USED.
THIS NUT IS PRE TORQUED BY THE MANUFACTURER TO PROVIDE THE PROPER COMPRESSION ON THE SMALL O-RING AT THE OPPOSITE END OF THE CONDUCTOR AND IS LOCKED IN PLACE WITH LOCTITE . DO NOT TORQUE ACROSS THE CONDUCTOR FROM END TO END.
Transformer / reactor tank
TYPICAL TI-23 INSTALLATION
Relief valves
Boot relief valve
TI-60FT feed through Bushing Conductor rod assembly
TI-60 Isolation Bushing
Sight glass Oil level Oil level
To high voltage winding
High voltage cable 1/4"-20 bolt Diode pack
DC
1.25"OD x 1"ID Teflon tubing
AC
6"schedule 40 boot
Teflon centering rings
Diode compartment
TYPICAL TI-60 INSTALLATION - 102 -
internal thread 5/16"-24 will accept a 1/4" banana plug or a conductor rod
Transformer / reactor tank
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E lectr otech, I nc. ELECTRODE HANGERS
The electrode hangers are used to provide electrical insulation between the high voltage electrodes and the vessel shell. They must also provide mechanical support for the weight of the electrodes and any additional fluid forces that might be present.
HSA-15 HIGH STRENGTH ELECTRODE HANGER The HSA-15 is a high strength electrode hanger typically used on Floating Production Storage Off-Loading (FPSO) facilities. This hanger has been designed to handle the fluid forces produced in electrostatic coalescers designed for FPSO applications. Typically, the HSA-15 uses universal joints to connect the hanger directly between the electrode support rails and the vessel support brackets. The HSA-15 hanger wi ll support heavy loads and has been tested to 20,000 lbs. without failur e. In FPSO service, it is rated for 1,000 lbs of continuous load to temperatures of 300 deg. F. The HSA-15U (photo 3 at the right) has universal joints dir ectly connected to both ends of the hanger (NATCO part no. 48012235). The universal joints are tapped to accept ½”-13 NC bolts. Photo 2 shows the same unit with an extension of 1” NPT pipe and a ½”-13 NC stud to provide some length adjustment. The pipe and ½” stud length must be specified separately when ordering. Photo 1 shows the HSA-15S with swivels and ½”-13 x 6” studs on both ends (NATCO part no. 48012234). The HSA-15S is designed for applications other than FPSO facilities.
HTA-2000 HIGH TEMPERATURE ELECTRODE HANGER The HTA-2000 electrode hanger is a 2” solid Teflon hanger. It has been mechanically tested at the NATCO R&D lab and is rated for 350lbs continuous load at temperatures up to 250 deg. F. It is available in two configurations, the HTA-2000S (photo 1 on the right) with swivel connections (NATCO part no. 48012230) and the HTA-2000T (photo 2 at the right) with rigid connections (NATCO part no. 48012232). The HTA-2000S is used on process applications other than FPSO facilities when the process temperature exceeds 200 deg. F.
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E lectr otech, I nc. HSA-15 High Strength Hanger The HSA-15 Electrode Hanger is a 1-1/2 in. High Strength Hanger. It has been pull-tested to 20,000 lbs. without failure. and is rated for 1000 lbs. continuous use @ 300 deg. F.
O C T A N y b d e i f i c e p s e b o t h t g n e L
HSA-15U with universal joints and rigid pipe extensions
HSA-15U with universal joints both ends
HSA-15 Hanger is standard with 1/2"-13 high strength steel studs " 5 7 . 3
" 0 0 . 5 1
" 5 7 . 3
" 0 5 . 2 2
" 0 0 . 5 1
" 5 7 . 3
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" 0 5 . 6 1
" 0 0 . 5 1
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E lectr otech, I nc.
The drawing on the right gives the dimensions of the standard HTA-2000S hanger. The swivels, unless otherwise specified, are fitted with ½”-13 NC B-7 steel studs six inches long. If different material or stud lengths are required it must be specified when ordering. 6"x 1/2"-13 NC
The drawing below gives the dimensions for the HTA-2000T with a ¾”-10 NC steel studs. It is available with other lengths of ½”-13 NC or ¾”-10 steel studs. When ordering HTA-2000T the size and length must be specified.
STEEL STUD
SPHERICAL WASHER 1/2"-13 NC STEEL NUT
0.500 STEEL PIN 3"x 3/4"-10 NC STEEL STUD
3/4"-10 NC STEEL LOCK NUT
14.00"
16.25" 2" SOLID BILLET
0.500" STEEL PIN
16.25"
SOLID BILLET
0.500 STEEL PIN
1/2"-13 NC STEEL NUT
HTA-2000T (NATCO part no. 48012232)
SPHERICAL WASHER
6"x 1/2"-13 NC STEEL STUD
HTA-2000S (NATCO part no. 48012230)
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E lectr otech, I nc. EST-100 EMULSION STABILITY TESTER ELECTROSTATIC FIELD # 1 TEMPERATURE CONTROL HEATERS
HIGH-VOLTAGE TEFLON SHIELD
ELECTROSTATIC FIELD # 2 BACK LIGHTS FOR ELECTROSTATIC FIELD #1 BOTH ELECTROSTATIC FIELDS SIMULTANEOUSLY BACK LIGHTS FOR ELECTROSTATIC FIELD #2
HEATER BLOCK
RECORDER CONNECTIONS
10 0 %
7 5 %
10 0 % 5 0 %
2 5 %
7 5%
5 0 %
POWER INPUT CONNECTION
2 5%
VARIABLE TRANSFORMER INPUT CONNECTION
The Emulsion Stability Tester (EST-100) is a portable device designed to determine and compare the treatability of oil field emulsions. It is extremely useful for comparing and evaluating the effectiveness of various demulsifier chemicals. Equipped with a plotter, it provides a graphic representation of electrostatic dehydration. In the EST-100, a sample of emulsion is exposed to an electrostatic field and the energy and time required to coalesce and separate its components are measured and displayed graphically. The EST-100 has two completely isolated test cells permitting two samples to be evaluated at the same time. Both the voltage and current of each electrostatic test cell are available for plotting. - 106 -
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E lectr otech, I nc.
By using a two-channel recorder, a single graph can display both of these parameters for one test cell, or the currents passing through two separate samples may be plotted for a sample-to-sample comparison. A similar sample-to-sample comparison between two separate samples may be plotted for voltage. The current plots best represents the energy consumed by the coalescing process.
TWO PIN RECORDER The plots below compare the currents for two identical emulsions under similar conditions except one sample contains a demulsifying chemical and the other does not.
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E lectr otech, I nc. 0 0 1
0 0 1
0 0 1
0 9
0 9
0 8
0 8
0 8
0 7
0 7
0 7
0 6
0 6
0 6
0 5
0 5
0 5
0 4
0 4
0 4
0 3
0 3
0 3
0 2
0 2
0 2
0 1
0 1
0 1
0
0
0
Wi t hout Chemi cal 0 9
Wi t h Chemi cal
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Appendix IV Sample Dual Polarity® Dehydrator Operating Manual
- 109 -
INSTRUCTION MANUAL FOR INSTALL ATION, START-UP, AND OPERATION OF CRUDE OIL Dehyd rato r
* * *
“ CLIENT” “ CLIENT” Floating Product ion Facilit y
* * *
The following is an example of a manual for Dual Polarity Dehydrators. This manual was prepared for an installation on a SPAR. Only those details identifying the client have been changed. NOTE: Values specific to the original job are shown in brackets []. These should be replaced with current values when this manual is used as a pattern.
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I.
INTRODUCTION / SCOPE OF SUPPLY It is imperative that this manual be read comp letely prior to startup and that a copy be located at the operating unit at all times.
This order is comprised of one (1) NATCO Crude Oil Degasser / Electrostatic Coalescer package to be installed on Client’s Floating Production Facility. The package is designed for the following parameters: Total Fluid Rate Oil Rate Oil Gravity Dry Oil Viscosity
Water Rate Water Sp. Gr. Gas Rate Inlet Temperature Outlet BS&W Oil in Water Motion Conditions (Operating) [Only for floating applications]
[105,000] bpd (maximum) [94,500] bpd (maximum) [32°] API [10] cp @ [120° F] [5] cp @ [160° F] [3] cp @ [200° F] [10,500] bpd (maximum) [1.025 @ 60° F] [14] mmscfd [160° F] minimum for [32°] API [<0.5%] [1000] ppm (estimated) Maximum Values Pitch and Roll ± [10] degrees with [60 to 70] second period Lateral Acceleration – [0.35] g Vertical Acceleration – [0.35] g Wind Velocity – [158] mph
And consisting of: One (1) NATCO [144” ID x 40’ S/S x 165] psig/FV design pressure, ASME code constructed and stamped, electrostatic coalescer with [120” ID x 30’ S/S x 165] psig/FV top mounted ASME Code constructed and stamped, horizontal two-phase degassing vessel. Internals for both vessels to include the following: 1.
Degasser internals (all shipped installed) a. b. c. d.
2.
Provisions for centrifugal inlet device Wave baffles at the liquid / gas interface Vortex breaker on liquid outlet Vane type (316 SS) structured packing (mist eliminator)
Electrostatic coalescer internals (all shipped installed except where noted) a. b. c. d. e.
Inlet downcomer (interconnecting pipe, shipped loose) Wave baffles at the oil and water interface High voltage electrode section with [composite] electrodes Oil collector pipe Vortex breaker on water outlet
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f.
3.
Vessel Externals a. b. c. d. e.
4.
Shrouded pipe emulsion distributors full length of vessel shell
Saddle supports Lifting lugs Insulation rings Nameplate Ground lugs
Vessel Connections: In accordance with P&ID (section [3.4] of manual) or vessel data sheet
5.
Electrical Accessories: a.
b. c.
d. e. f. g.
Dual Polarity (AC-DC) electrode set to run full length of the vessel, shipped installed. Electrode plates will be constructed of a fiberglass / graphite composite material. One set of insulator hangers [Three (3) 50] KVA, single phase, [480V, 60] HZ primary, 100% reactance transformer with multiple secondary taps up to 23 KV. Transformer is certified for a Class 1, Group D, Div. 2 hazardous area [and constructed of 316 SS]. Two NATCO high voltage entrance bushings with fittings. [Three (3)] Voltmeter, ammeter, and local start/stop station to be mounted on a rack on the side of the vessel. Customer is to provide circuit protection. Two internal low level float switches. The transformers are 100% reactance type which means that they are self protected against any damage in case of a short on the high voltage side. The transformers can operate continuously with the secondary shorted.
The Customer must provide the power supply to the transformer from the motor control center and furnish the circuit protection at the MCC.
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6.
Coating • Internal • Primer – [Interline 955 12.0-14.0 mils DFT White] • Intermediate Coat – [Interline 955 Stripe Welds Buff] • Final Coat – [Interline 955 12.0-14.0 mils DFT Buff] • Bottom Half of Oil Treater only • External • Insulated areas • Primer – [Intertherm 228 4.0-6.0 mils DFT White] • Final Coat – [Intertherm 228 4.0-6.0 mils DFT Gray] •
7.
Non-Insulated areas • Primer – [Interzinc 52 2.5-3.5 mils DFT Manufacturer Standard] • Intermediate Coat – [Intergard 475HS 6.0-8.0 mils DFT Buff] • Final Coat – [Interline 629HS 2.0-3.0 mils DFT Pearl Gray]
Instrument and Electrical Power supply and circuit protection are to be provided by end-user. End-user to supply power cables from the MCC direct to the transformer primary junction box.
8.
Utility Consumption:
Electrical a.
For transformer [480V, 60] Hz, single phase power supply Total [150] KVA [75] KW [30] KW
Connected load Maximum load in shorted condition Normal load
Per Transformer [50] KVA Connected load [25] KW Maximum load in shorted condition [10] KW Normal load
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b.
Chemicals By others but should include the following: Demulsifier Scale Inhibitor Water Treatment Corrosion
9. Insulation By others NATCO’s Scope of Supply comprises only a part of a complete system. The Customer must confirm that all components of the system are compatible. NOTE:
It must be noted by the reader that no manual or set of instructions can foresee all possible situations due to the myriad of combinations of pressure, temperature, and operating conditions possible in operations. The reader is therefore, advised that the services of a competent on-site technical consultant during start-up and operating of this equipment is essential to prudent and safe operation. This manual is furnished for information purposes only. NATCO shall not be liable for the use of this manual or any of the information contained in whole or in part, as that use relates to plant operating efficiently, plant malfunctions, plant operator interpretation, and particularly accidents or unsafe conditions which could arise in any operating facility. The safe operation of any facility remains the responsibility of the Owner or Lessee of the equipment and those directly involved in the operation of such facilities.
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II.
SAFETY IMPORTANT: Read and understand the entire operating and maintenance manual before starting to work. Observe and comply with all cautions and warnings given here, in other sections of the manual, and in vendor literature. A.
Special Special Notes Notes 1.
Make certain that all skids, vessels, and electrical equipment are properly grounded.
2.
Do not enter any vessel until it is vented and checked for dangerous or explosive gas.
3.
Do not work on vessels or equipment while in operation or while under pressure.
4.
Vent all process and instrument gas pressures before working on equipment.
5.
Check for explosive gases in the area before performing any work.
6.
Do not work on this equipment if any other work in the area could result in release of explosive vapor.
7.
WARNING After After equipmen equipmentt has been in service service,, do not cut or weld weld on any process process lines lines or vessels for any reason. Accumulations of hydrocarbons can result result in explosive conditions. Any work work on the vessels vessels or piping piping requires requires special special precauti precautions ons that are are not covered in this manual.
8.
WARNING Keep hands away from mechanical linkages while equipment is in operation. Operation is automatic and may occur without notice.
9.
WARNING The control panel and control circuits operate on 120 VAC and 24 VDC electrical power. Use extreme care when servicing. Lethal electrical shock is possible. Only qualified personnel must service this equipment.
10.
WARNING The high voltage transformer operates on 480 VAC electrical power. Lock power "off" before servicing. Use extreme care care when servicing. servicing. Lethal electric
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shock is possible. Only qualified personnel must service this equipment. 11.
WARNING Power must be turned off prior to operating the manual “OFFLINE “OFFLINE”” Tap switch located on the high voltage transformers. The Electrostatic Treater high voltage electrodes and electrical system components operate on 23,000 VAC electrical power. Lock power "off" before servicing. Lethal electric shock is possible. Only qualified personnel must service this equipment. Make certain power is locked "off" before entering the vessel.
12.
WARNING Before initial testing of transformer and electrical system, the vessel must be vented and carefully checked for any combustible vapor. After the initial startup, the power must never be applied to the transformer unless the vessel is filled with liquid. Any spark generated in the presence of combustible vapors may create a lethal explosion. Only qualified personnel must service this equipment. Operate the equipment within the specified design conditions.
13.
WARNING “ CONFINED CONFINED SPACE ENTRY PROCEDURES” PROCEDURES” must must be followed for any entry into the vessel. Death from asphyxiation is possible. a. b. c. d.
All process and utility connections must be blinded. The vessel must be certified gas free. Personnel must have “ CONFINED CONFINED SPACE ENTRY TRAINING” TRAINING” by an approved authority. A “hole watch” must be provided.
This is not a complete list of safety precautions. Refer to Vessel Entry on pages 9 & 10. NATCO can provide “Confined Space Entry Training”. If there are any questions or concerns about safety issues, please contact NATCO HSE department at 713.683.9292. 14.
CAUTION Only fill or drain the vessel under calm conditions to avoid damage to the vessel internals.
B.
General Safety 1.
Definite safety procedures should be prepared for the employees. Plant
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supervision should make certain that employees understand their duties and responsibilities. Employees should understand that it is their personal responsibility to report to their immediate supervisor any abnormal circumstances, such as: a. b. c. d. e. f.
Leaks Accumulation of gas or vapor. Defective or damaged equipment. Abnormal conditions such as excessively high or low temperature or pressure. Infractions of safety regulations. Unauthorized vehicles or personnel in the area.
Operating personnel should be familiar with location of fire protection and first aid equipment in the area and trained in the use of such equipment. Employees should know how to report repo rt a fire or an emergency and have a clear understanding of their duties during such emergencies. 2.
3.
Normal Operation a.
Procedures for the loading of product should be prepared and should be followed.
b.
Transportation Transportatio n vehicles should not be permitted to operate within plant area or loading area while wh ile area is contaminated with flammable vapors or while loading of product.
c.
Regular inspections of the loading area should be made of items, such as, grounding of electrical equipment, housekeeping, lines, valves or cocks for leaks, proper drainage or venting from loading area, and elimination of nearby open flames during loading operations.
d.
Procedures covering the starting up and shutting down of processing equipment and units should be reviewed and rehearsed thoroughly by those responsible for operation of the equipment.
Emergency Operations a.
General When flammable liqu liquids ids or vapors escape from tanks, vessels, or lines, available means should be used for limiting their spread and preventing their ignition. The extent of the contaminated area should first be defined and the area ar ea identified by suitable warning signs, and patrolled. Spills should be cleaned up as soon as possible.
b.
Liquid Leaks If a break or serious leak occurs in a liquid line, the pumps should be
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shutdown and any block valves closed. If the leak involves a tank or any a ny relatively large vessel, portable pumps may be required to recover the liquid. Trenches, dikes, or diversion walls should be used either to confine the liquid or divert the flow. Foam may be applied to cover the spills spil ls in order to exclude air, but this is not normally necessary. Water spray applied at the point of emission of a leak may aid in the dispersal of vapors and prevent ignition. In the case of very light leaks which give off quantities of vapor, the procedures listed for gas leaks should also be followed. c.
Gas Leaks In the event of a break to a gas or liquefied lique fied petroleum gas (LPG) line li ne or vessel, all fires downwind of the break should be extinguished. Before operations are resumed, tests should be made at pits, trenches, or dikes where gas might accumulate. Portable gas indicators for making such tests will indicate if a flammable gas or vapor is present. If a break occurs in area where adjoining properly is owned by outside interests, prompt measures should be taken to notify those concerned of the potential hazard that exists and to eliminate any sources of ignition. The vapors from large LPG leaks may roll along the ground and blanket large areas under certain weather conditions. conditions. It may be possible at times to disperse flammable mixtures by means of forced ventilation or large quantities of steam or water fog.
4.
Maintenance Procedures a.
General Fire prevention in connection with maintenance work depends primarily upon careful planning and removal of flammable liquids, vapors, and other flammable materials before work starts. In certain instances, it is not possible to remove all flammable materials; and at such times, precautions must be taken to prevent ignition sources from contacting flammable mixtures or to exclude oxygen. A procedure should be set up for warning personnel and stopping maintenance work in the event of a release of flammable vapors or liquids in the area where the work is being done.
b.
Work Permit System A written written work permit permit system system should should be used whenever whenever any maintenance or inspection work is contemplated which requires the use
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of spark or flame-producing equipment. The permit should be issued only after tests have indicated that no flammable vapors are present. It should also be ascertained that no work is being done or contemplated which might create a hazard during the course of the job. The authorized persons should sign the permit, indicating that the equipment to be worked on has been properly prepared for hot work. Any precautionary requirements or procedures to be observed during the work should also be outlined on the permit. c.
Inspection Process units and related equipment should have periodic complete inspections. The length of time between inspections and the type of inspections conducted should be based upon the type of equipment and its condition as determined by previous inspection.
5.
Repairs a.
When any equipment is to be repaired, it should be isolated from other equipment that contains flammables. Connecting piping should be disconnected or blanked, or both, in accordance with a definite procedure. Valves should not be relied on for blanking purposes, blanks of suitable thickness should either be blind flanges or full-face steel plates inserted between gaskets against line flanges. Definite responsibility for their installation and removal should be assigned. When hot work is to be done on equipment that has been gas-freed, connections to the equipment should be removed.
b.
Care should be taken if sludge and scale remain in tanks, vessels, and piping after flushing and washing operations. Such materials often contain flammables and may give off vapors that can be ignited during repairs. Continued ventilation may be necessary.
c.
Hot-tapping devices are available for making repairs or additions to equipment that is either in service or has not been completely cleaned of flammable. Use of such devices can be very effective, and may at times be a safer method of doing a job than would gas-freeing. Each individual instance should be carefully planned to ensure that the proper device is used and that necessary safe practices are followed.
d.
Before hot repair work is started on equipment that has contained or does still contain flammable liquids or gases, careful plans should be made as to the manner in which the work will be done. In most cases, it is desirable to open and completely gas-free equipment before repairs are made; but there are instances when repairs may proceed after some inert material such as flue gas or water has displaced the flammable material.
e.
Fire fighting facilities should be readily available when repairs are being
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made. Minor fires may be quickly extinguished when facilities are readily accessible and employees are trained in their quick and effective use. 6.
Good Housekeeping Good housekeeping is an essential part of maintenance. Containers for scrap material and refuse should be provided at convenient locations. Scheduled emptying of such containers should be strictly adhered to. Oil and grease soaked rags should be placed only in separate metal containers provided for them.
7.
Entries a.
Vessel Entry Vessel entry refers to any tank, vessel, equipment or other enclosed place where there is a hazard of: 1) a toxic, corrosive or flammable substance; 2) insufficient oxygen; 3) severe restrictions that would hinder escape or rescue. Vessel entry normally requires specific approval by plant supervision. Vessel entry should include tank, gauging, sampling and blow down. All vessels should be assumed unsafe for normal entry until the following entry procedures have been followed: 1)
Disconnect and blank off all lines to the vessel
2)
Remove all sources of ignition before removing manway covers
3)
Check all liquid traps and internal lines to assure they are free of hazardous liquid.
4)
Clean the vessel as thoroughly as possible by draining, washing with water, steaming, ventilating or other suitable means. If steam is used, guard against static electricity by grounding the steam nozzle. After steaming, allow the vessel to cool slowly. Sudden cooling with water spray may cause a static electrical charge.
5)
Test the atmosphere for: (a)
Oxygen: Air must contain 20%-21% oxygen and the vessel should have adequate ventilation, either forced or natural.
(b)
Explosive Mixture: A vessel may not be entered if the testing instrument indicated an air-vapor mixture that
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exceeds 50% of the lower explosive limit. (c)
b.
Toxic Fumes: The presence of any toxic fumes requires the use of respiratory protective equipment, normally an air supplied mask with hand blower, or a self-contained breathing unit; otherwise, additional cleaning or purging of the vessel is indicated.
6)
Safety Harness or Belts - The person using respiratory equipment when entering the vessel should wear either a safety harness or belt.
7)
Clothing - Personal protective clothing suitable for the job inside the vessel should be worn.
8)
Observer - An observer should be stationed outside the vessel. His only duty should be watch the person inside the vessel. When respiratory equipment is required for the person entering the vessel, the observer should also have suitable respiratory equipment available.
9)
Emergency Equipment - Fire extinguisher and other emergency equipment should be available as required.
Line Entry 1)
General Line entry should include any work required on any line or valve which contains flammable liquids or vapors, or contents of which are corrosive, toxic, and/or under pressure. The following items should be considered in all work involving line entries: (a) Know the contents of each line being worked upon. (b) Know the pressure ratings of the pipes and fittings. Never install low-pressure connections on high-pressure line. (c) Never hammer on high pressure lines (d) Use extreme caution when thawing frozen lines (e) Never use fire to locate leaks of flammable materials (f) Be very cautious when attempting to tighten pipe fittings while pressure is on a line
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(g) When opening valves, do so slowly to allow pressure to equalize before opening the valve fully. (h) When removing blinds, loosen bolts and allow pressure to bleed down. Gas sometimes leaks into the space between the blind and the valve
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2.
3)
8.
Before breaking lines (a)
Drain the contents into a tank or to the lowest point
(b)
Depressure line to a safe designated area
(c)
Lock out the pump. All gauges and sight glasses should be checked for zero readings.
(d)
Close and tag the nearest upstream and downstream valves.
When breaking lines (a)
Wear suitable personal protective equipment: full clothing and sometimes rubber suits should be worn to guard against chemical splash. Goggles should be worn to protect the eyes against chemical splash and flying particles.
(b)
The placement of a deflector over the flange joint is usually desirable for the initial cracking of corrosive or toxic material lines.
(c)
The worker should slowly open the bolts on the far side so that if there is a spray it will be away from him.
(d)
Sections that have been removed should be handled carefully until they are inspected for trapped material or residues and flushed if required.
Electrical Equipment Probably everyone recognizes that high voltages can be very dangerous but some people fail to realize that so-called "low voltage" can be very hazardous and under certain conditions can produce fatal injuries. Deaths have been recorded due to contact with circuits of less than 50 volts. Actually, it is not voltage but amperage that kills. Under certain conditions, as little as 1/10 ampere is sufficient to cause death. The following may be used as a guide when working with electrical equipment:
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a.
Electrical Equipment Repairs When electrical equipment is to be repaired, switches must be opened and tagged. "Hot circuit” work normally requires the permission of plant supervision. Refer to detailed plant tag-out procedures before proceeding.
b.
c.
d.
Grounding 1)
All electrical equipment is to be grounded
2)
If it is ever necessary to move any equipment, the ground should be replaced before the equipment is used.
Conduits, Cables and Wires 1)
Electrical conduits should not be used to support other equipment
2)
Electrical cables and conduits should be not buried underground except in accordance with engineering standards.
3)
Exposed ends of electric wires must be taped.
4)
Unused and abandoned electric wires must be removed or disconnected at each end.
Fuses 1)
Only authorized personnel should replace fuses.
2)
Fuse tongs and/or rubber electrical gloves should be used and disconnect should be opened. Rubber gloves must always be used for voltages in excess of 150 volts.
3)
Never use pennies or tinfoil in lieu of fuses.
4)
Never use fuses of greater capacity than are specified by the equipment manufacturer.
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e.
f.
g.
Switching 1)
When starting electric motors, handle all switches according to instructions. Make contact so as to prevent arcs. Stand in a safe position.
2)
Never pull a disconnect switch under load except in an emergency.
3)
Always be certain that hands and feet are dry and when operating switches or plugging in electrical appliances.
4)
Keep rubber mats in front of switchboards where possible.
5)
Switch panel fronts should be kept closed.
Hand Tools and Portable Equipment 1)
Extension lights without bulb protectors must not be used. Use only low voltage lights with isolating transformers in tanks and similar places.
2)
All extension cords should be the grounded type. Before each period of use, examine extension cords carefully for any failure of the outer insulation, particularly at terminal points where the cord enters a plug or a fixture.
3)
Lights and tools should not be disconnected from an extension cord while the other end of the cords is in a socket or receptacle.
4)
The ground cable with which each tool is equipped should be secured to a suitable ground before the tool is plugged in to a source of electricity.
Miscellaneous 1)
Contact with electrical conductors should be avoided whether they are energized or not.
2)
Only authorized personnel should enter fenced substation areas.
3)
Faulty electrical equipment must not be used. immediately.
4)
Before changing broken light bulbs, be certain the current is turned off.
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Report it
5)
9.
No employee may work within 15'-0" of a high voltage power line except by special authorization of plant supervision.
Fire Control of Liquefied Petroleum Gas Many fire control demonstrations have been made with LP gas fires under various conditions. Stressing the point that is continually brought out by fire controls experts, it is pointed out that LP gas fires should not in the majority of cases be extinguished, but the fire should be controlled until the gas or liquid can be shut off at its source. This is extremely important for if a flame is put out and the LP gas is allowed to escape into the atmosphere, it might again ignite bringing greater damage in that area than was originally threatened. If the gas cannot be shut off at the source, it is frequently better to let the fire burn, under control, until the liquid is gone from the tank or vessel. Such demonstrations have also shown that LP gas fires can be completely extinguished by straight steam and water spray if chemical extinguishers are not available. Where ignition has occurred, structures or vessels exposed to the flame or close to it should be protected with water streams using spray if available. It has been found possible to prevent ignition of combustible vessels and structures that were actually enveloped by flame by spraying thoroughly and continuously with water. An LP gas fire will usually be less widespread than one involving a comparable stream of gasoline because the LP gas will vaporize and burn all in one place, while the gasoline stream may flow and spread the fire over a greater area. Water applied to a gasoline fire may spread it, but an LP gas fire "stays put" and is not increased in intensity when a water stream is sprayed on it.
10.
Fire Control of Natural Gasoline Fires Foam is an effective extinguishing agent used in flammable liquid protection on many types of hydrocarbon fires and is a preferred fire fighting method of gasoline fires. Foam's extinguishing success comes from its buoyancy and capacity to separate the flammable liquid's surface from the flame-inducing air. Foam consists of air filled bubbles, interconnected to form an airtight surface. It is cohesive enough to keep vapors from permeating its blanket -- yet prevent radiant heat from flames that may be nearby from heating liquid covered by foam. Water is used on gasoline fires to keep nearby vessels and equipment cool but is of very little value in fighting the primary fire at hand. Some combustibles can be extinguished by cooling for instance, in the case of diesel, if it can be cooled below 150°F, it can be extinguished with water. In the case of gasoline, which in open-air produces vapor within the burning
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range of minus 45°F, extinguishment is very difficult; in fact, this cooling cannot be done by water alone in the field. Fire fighters will also have little or no success trying to extinguish a gasoline fire with water fog. Water fog can be made to extinguish a gasoline fire only if the fog is so concentrated as to expel the air to below 94% of the vapor-air mixture. 11.
Fire Protection Equipment a.
General The responsibility of keeping the fire fighting equipment in first class condition should be definitely established. Equipment should be tested periodically in accordance with standard procedures and as dictated by experience. It is imperative that all fire protection equipment be stored, inspected periodically, and maintained for immediate emergency use. Proper records should be kept for such work. Often it is desirable to number the equipment serially to assure complete checking on schedule. Whenever an extinguisher is used, it should be set aside for inspection and recharging. Some operators seal an extinguisher or cabinet so that it may be checked more readily. Others will place the equipment in an expendable plastic bag that serves the same purpose and also keeps the extinguisher clean and free from exposure to corrosive atmosphere. Mobile fire fighting equipment such as portable foam equipment, etc., is now widely used. A periodic study should be made of this equipment to determine that it is adequate and advantageously located for use throughout the plant and at adjoining operations.
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b.
Extinguishing Equipment 1)
Carbon Dioxide Systems An inert gas, such as carbon dioxide, discharged into a closed room or into enclosed spaces, may be an effective extinguishing agent. For example, a carbon dioxide system is one method of extinguishing fires associated with equipment such as petroleum pump rooms, electrical installation, and special machinery or apparatus such as used in laboratories. Care should be taken when extinguishing fire by carbon dioxide due to the fact that carbon dioxide will not support life.
2)
Dry Chemical System The application of dry chemicals is effective for the control and extinguishment of fires that may occur during the processing and handling of flammable liquids, solids and gases. This extinguishing agent is composed of specially treated sodium bicarbonate in dry powder form with components for producing free flow and water repellency. Being nonconductive, it is suitable for fires that involve energized electrical equipment. The dry chemical may be used simultaneously with water fog without practical damage to the powder. The water will not only quench embers and cool hot surfaces but will also reduce flame size and thereby make the fire easier to extinguish with the dry chemical. Portable extinguishers of the hand-operated type which contain 30 lbs of dry chemical or less are recommend for use as first aid equipment for small fires. Several hand-operated extinguishers may be used simultaneously for the extinguishment of larger fires; and reserve, or secondary protection, may be provided by wheeled of stationary extinguishers with capacity ranges up to 350 lbs. of dry chemical discharge.
12.
Fire Alarm and Integrated Activities There are certain functional responsibilities that should be clearly understood by all parties concerned to be sure that the various phases of the fire fighting organization would be effective when required. If and when a general fire alarm is sounded, definite integrated activities should be initiated, such as: a.
An alarm system with annunciation in key location, such as main office, plant area, and control room, should be installed.
b.
An emergency call-out list for key supervisors, local municipal fire department, ambulance service, doctor, etc. In some instances, an independent agency is used for handling this emergency call-out.
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III.
PROCESS DESCRIPTION The equipment includes a Dual Polarity (AC-DC) type electrostatic treater preceded by a separate degassing vessel. The degassing vessel is mounted above the treater and feeds the treater by gravity. Attached is a typical layout of a degassing separator mounted on top of treater. The treater is operated liquid packed with the operating pressure above the liquid bubble point. The purpose of the electrostatic treater is to provide efficient separation of entrained water from the crude oil thereby reducing the water content of the outlet oil to an acceptable level (0.5%). The separation process is possible due to the density difference between the oil and water. Since the water is heavier than oil, with sufficient retention time, the water will settle to the bottom of the treater. The oil/water emulsion enters the treater from the top mounted degasser through a section of interconnecting pipe. The fluid is then conducted into a distributor located above the bottom of the vessel. The distributor will be a perforated pipe type designed to give good distribution for the full cross-sectional area of the vessel. Based on CFD studies, NATCO has designed special deflectors and diffusers that work in conjunction with the perforated pipes to improve the distribution by as much as 100%. After leaving the distributor, the emulsion flows upward through an electric field generated by a high voltage electrode located just above the vessel centerline. The electric field is to increase the rate of coalescence for small water droplets found in the oil. As the size of the droplets increases, the settling rate for the droplets greatly increases. We want to have the highest possible settling rate for the water droplets because the vessel size, weight and cost will be much reduced. For offshore applications, TLP or FPSO applications in particular, vessel size and weight are major considerations since they also impact the support structure size and cost. As the emulsion passes through the electrostatic field, most of the water settles out to the bottom of the vessel and is removed via a level control and dump valve. The dehydrated oil exits from the top of the vessel through a collector pipe. The exiting oil flow is modulated by a pump system designed to control fluid level in the degasser and other upstream equipment. NOTE: The Treater Sizing description included in Section A following was required for the original job. It is suggested that this section NOT be included unless client questions/specifications require some of this information. It is included here for reference only. A.
Treater Sizing Sizing a treater for a specific application requires some basic information or assumptions: 1.
Maximum Design Flowrate This value should be the maximum flow rate anticipated during any time span that is 30% of the vessel retention time. If the vessel retention time is one hour, the design rate should be based on the maximum rate that would be anticipated within any 20-minute period of time. Slugging flows may mean that
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the vessel would need to be sized larger than for a vessel with a consistent flow. 2.
Oil Density or API Gravity The rate of separation is directly proportional to the density difference between the oil and the water. If the oil gravity is not certain when the vessel sizing is determined, then an educated and usually a conservative guess must be made. A heavier oil results in a smaller density difference between the oil and water therefore the separation rate will be slower. Below is a table showing how the differences in specific gravity change with respect to oil API gravity assuming a water specific gravity of 1.0:
Oil API Gravity 24 28 32
3.
Oil Specific Gravity @ 160°F 0.874 0.851 0.823
Specific Gravity Difference 0.126 0.149 0.177
Vessel Sizing Increase to 32 API 40% 19% NA
Water Density Since the rate of separation is directly proportional to the density or specific gravity difference between the oil and water, it is very important to know some information about the expected produced water salinity and specific gravity. Below is a table showing how the differences in specific gravity change with respect to oil API gravity assuming a water specific gravity of 1.04:
Oil API Gravity 24 28 32
Oil Specific Gravity @ 160°F 0.874 0.851 0.823
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Specific Gravity Difference 0.166 0.189 0.217
Vessel Sizing Increase to 32 API 30% 15% NA
4.
Oil Viscosity The vessel sizing is directly proportional to the oil viscosity. If the oil viscosity is doubled, the vessel size will be doubled. Since information on the oil viscosity is not always available when the vessel sizing is done, NATCO had standard tables for viscosity of typical crude oils based on our experience. We can use this typical data for sizing, but there can be very significant variation in oil viscosities even when the API gravity is the same. Oil viscosities can vary 50 to 100% from our tables. NATCO based viscosity values on information supplied by client as follows for 32º API crude: Temperature o ( F) 100 110 120 140 160 180 200
Viscosity (cP) 15 12 10 7 5 3.8 3
Since settling rate is directly proportional to viscosity, the settling rate for the 32º API oil is 6.8 times faster than the 22º API oil and the vessel for the 22º API oil would be 6.8 times larger. 5.
Operating Temperature A higher operating temperature will reduce the oil viscosity and result in an increase in the oil / water separation rate. Sometimes when the fluid is produced at a sufficiently high temperature no additional heat is needed, but often the inlet temperature to the process is too low for efficient separation to occur. Addition of heat to the process is always expensive because of the additional equipment required and the expense of the fuel that is required. Also there are always increased safety concerns when fired heaters are used to provide the extra BTU’s. Below is a table displaying the typical operating range for different oil API gravities:
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Oil API Gravity 22 28 32
Typical Operating Temperature Range 140 – 160° F 110 – 130° F 100 – 120 °F
Viscosity of Oil 16.4 cP @ 160 °F 9.0 cP @ 130° F 5.8 cP @ 120° F
Note that the viscosity of the 22º API oil is 16 cP at 160° F compared to 32 cP at 130° F, at 160° F, the separation rate would be doubled and the vessel size could be cut in half.
Each application must be carefully evaluated to determine the optimum operating temperature based on the overall economics of the facility. For example, if heat is provided from waste heat recovery and would otherwise be lost, the economics would justify using the heat to increase the equipment operating temperatures thus reducing the equipment sizes and weights. In other applications, adding a fired heating section to a vessel to increase the settling rate will result in a smaller coalescing section; however, the addition of the heating unit may result in an overall larger vessel and increase operating expense.
Another item to consider is that a higher operating temperature, demulsifier chemical costs are generally lower and there may be a reduced tendency to collect sludge at the vessel interfaces.
6.
Electrostatic Coalescing System
The efficiency of coalescing very small water drops into larger drops has the greatest impact on separation rates. The water-settling rate is proportional to the square of the drop radius. If the radius of the drop is increased from 5 microns to 50 microns then the settling rate will be increased by 100 times.
The ability to cause the water droplets to coalesce is the reason electrostatic fields are so effective in the crude oil dehydration process. Use of a high voltage electrostatic field can result in much smaller vessels as compared to vessels employing retention time only to accomplish the separation.
Refer to the attached literature for more information about NATCO’s Dual Polarity Electrostatic System.
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7.
Outlet BS&W Requirement:
The required outlet BS&W can have a significant impact on the vessel size. To reach a lower outlet water content we have to be able to separate smaller water drops. In order to separate the smaller drops, drops, the upward oil velocity velocity is decreased which results in a larger vessel.
Achieving a 0.25% BS&W outlet will require a vessel that is twice as large as a vessel designed for 0.5% BS&W outlet.
8.
Other Factors and Unknowns:
Treater sizing is not an exact exact science. There are many factors that can affect the emulsion stability stability and vessel size or performance. Some of the complications complications can include:
• • • • • • • • • • • • • •
Very high pressure drops across chokes that can form incredibly tight emulsions Very long flow lines (pumping oil for 30 miles can cause very stable emulsions) Down hole pumps with large number of stages Power oil systems Fireflood production Chemically stabilized tertiary production Operating temperature below the paraffin cloud point Precipitation of asphaltenes Oil wet solids, iron sulphide in particular Unusual oil chemistry resulting in ineffective demulsifier chemicals Very high GOR with high pressure drops Very low water content can make coalescence more difficult due to low population of water drops Selected vessel diameter (vessels less than 12’ O.D. have a de-rated treating rate. A 8’ x 12.5’ vessel has less retention time than a 10’ x 10’ vessel) Chemical injection point(s)
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See PID 1420-20-PI-DG-4412 for correct level control philosophy
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B.
Operating Variables and Performance Curves 1.
2.
3.
Crude Oil Flow Rate: a.
The flow rate may be varied from 20 to 100% of design
b.
Performance may deteriorate deteriorat e at oil rates in excess of design.
Crude Oil Inlet Temperature a.
Design operating temperatures are specified in the process data sheets.
b.
Normally, operating temperature should be maintained as low as possible while maintaining stable operation and meeting required product quality. Lower operating temperature will reduce fuel consumption.
c.
In general, increasing operating temperature will improve process performance and reduce chemical consumption. consumption. Temperature may be increased periodically as necessary to help eliminate interface sludge accumulation.
Operating Pressure Operating pressure should always be above the crude oil vapor pressure (bubble point) throughout the coalescing system. If the operating pressure of the treater drops below the “Bubble Point”, gas bubbles can be crude oil formed. Formation of gas inside the treater or carryover of gas from the degasser vessel can disrupt the oil/water separation process and result in high outlet BS&W. Quick opening of any of the control valves can cause the operating pressure to drop too low.
4.
Oil/Water Interface Level a.
The exact interface level setting is determined by adjustment in the field to obtain optimum performance.
b.
Increasing the water level will reduce oil retention time, increase water retention time, and increase the AC electrostatic field between the electrodes and oil/water interface.
c.
In offshore applications, the interface level should be carried 6” – 12” below the top of the wave w ave baffles in order to avoid formation of interface waves that could disrupt the process or damage the vessel internals. Refer to information on “Initial Set Points.”
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5.
Chemical Injection Rate/Type (Chemical selection is not included in NATCO scope).
6.
a.
Demulsifier chemical injection rate or type may be varied to suit process conditions. Higher chemical rates (when needed) may help eliminate any interface sludge accumulation.
b.
Demulsifier type and dosage must be determined by field-testing to obtain optimum performance of the system.
Chemical Injection Points a.
The chemical injection point(s) that are selected may affect process performance.
b.
Typical demulsifier injection point(s) may be one or more of the following typical locations:
7.
Down hole in the well At the wellhead either before or after the choke At the manifold(s) On the inlet or outlet of the separator On the inlet or outlet of the crude oil charge pump On the inlet or outlet of the heater
c.
More difficult emulsions may require chemical injection points to be moved upstream to give more mixing or reaction time. Extremely difficult emulsions may require down hole injection to help prevent the difficult emulsion from forming,
d.
Moving the injection point further upstream may also help reduce total chemical consumption
Wave Motion The Electrostatic Treater has been designed for installation on a SPAR, which is subject to the effects of wave wave motion. Movement of the SPAR will result result in forces transmitted to the process equipment that can result in significant movement of the fluids inside the process vessels, which can have a detrimental effect on process performance and process control. control.
The effect on process and control depends on the amount of SPAR movement, movement, location of the equipment on the SPAR , vessel size, and other considerations. The Electrostatic Treater includes interface wave baffles to minimize the effects of wave motion. In order to function properly, the oil/water interface must be carried out at least 7” below the top of the wave baffles. If the water level gets too high, the wave baffles will not work, and water can be carried into the
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electrodes or could impact the electrodes resulting in damage to the equipment. CAUTION FILLING OR DRAINING THE VESSEL: The vessel should only be filled or drained only under CALM WEATHER conditions. On occurrence of a low oil level condition in the vessel, waves at the oil/gas interface can be severe enough to damage the electrodes. Vessel movement and wave motion can affect the operation of level controls resulting in excessive cycling of the valves, and reduced process performance. Process vessels such as Electrostatic Treaters and Separators should be located as near the SPAR center of gravity as possible to minimize the effects of wave motion transferred to the process. Level instruments should be located as near as practical to the center of the process vessel. Vessel roll and pitch will have a greater effect on controls located at the side or ends of a vessel. Instrumentation can also be adjusted to “deaden” the effects, average the readings, or incorporated with time delays to account for wave motion in the vessel.
C.
Initial Set Points All instrumentation is provided and installed by others, end-user to confirm set points. a. Level Settings (inches above bottom of vessels) a.
Degasser Liquid Level (inches above BOV) Inches Above BOV 83” 74” 33” 15” 16”
Item LAHH LAH Control Pt. LAL LALL
b.
Device Number LXT-11602 LT-11601 LT-11601 LT-11601 LXT-11602
Electrostatic Coalescer Oil/Water in Interface Level Inches Above BOV 42” 36” 31” 27”
Item LAHH LAH Control Pt. LAL
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Device Number LSH-11703 LT-11701 LT-11701 LT-11701
LALL
2.
LSL-11704
Setting (Psig) 5 150 7
Device Number PCV-11601 LT-11701 PT-11601
11
PT-11601
2
PXT-11603
5
PXT-11603
12
PXT-11603
16
PXT-11603
Pressure
Item Blanket Gas Relief Valve Control Pt. @ 160F Control Pt. @ 180F PALL @ 160F PALL @ 180F PAHH @ 160F PAHH @ 180F
D.
21”
Other Control Features 1.
Transformer The transformer is a 100% reactance type which means that it is self protected against damage in case of a short on the high voltage side. However, the transformer should not operate continuously with the secondary shorted. The Customer must provide the power supply to the transformer from the motor control center and furnish the circuit protection at the MCC. Power to the transformer must be shut off on: a.
Low Liquid Level in the Vessel An external low-level switch must be wired to a holding coil on the contactor in the MCC so that power is automatically shut off on low level.
b.
Short in the Transformer Primary Winding If a short occurs in the primary winding, the coils will be overheated. A thermal switch is provided in the transformer and must be wired to the
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holding coil on the contactor in the MCC so that power will automatically shut off if the transformer overheats. NATCO has included a local start/stop switch for manually starting or stopping the transformer. This switch should be connected to the holding coil on the contactor in the MCC. A voltmeter and ammeter provide local indication of the status of the transformer. A visual indication is provided by a light wired to the transformer tertiary winding, the light will brighten or dim depending on the performance of the system. Under normal operating conditions the voltage will be high and the amperage will be low. The voltmeter will read 70% of full scale or above. A 50 KVA transformer with 480V primary is rated for up to 104 amps. Under normal conditions the amp-meter will read below 30 amps. The readings on the meters vary depending on the stability of the incoming oil/water emulsion and how much water is carried into the H. V. electrode area. The more “wet” the fluid, the more amps will be drawn and the voltage on the electrodes will be lower. If the ammeter is reading 30 amps or higher, turn off the power, and try a lower tap setting on the transformer. If the amp reading is 20 amps or lower, turn off the power, and try a higher tap setting on the transformer. Chemical type, amount, and injection point can affect the performance and power usage. For a 50 KVA 100% Reactance transformer: Connected Load Maximum Power Normal Power 2.
50 KVA 25 KW 10 KW
Internal Low Level Float Switches Two (2) internal mechanical float devices are installed at the top of the vessel above the electrodes. There is no external connection. The floats are designed to ground and remove voltage from the electrodes on the occurrence of a low level in the vessel. WARNING: You must shut o ff pow er and isolate the transformer externally pri or to vessel entry o r performin g any maintenance on the unit. Death by lethal electrical shock o r explosion is po ssible. The internal mechanical floats do not shut off the power to the electrodes.
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IV.
PRECOMMISSIONING A.
Receipt and Installation of Equipment 1.
The package is shipped with as much of the unit assembled as possible.
2.
Check the equipment on receipt at site: NOTE – NATCO recommends that a NATCO service technician be present to assist with the inspection and precommissioning
3.
Confirm that all materials received are in agreement with the packing list and are in good condition.
4.
Check for any shipping damage. Immediately document any damage with a formal report and photographs. Claims for damages should be sent to the freight company.
5.
The equipment should be set as level as possible on the prepared foundation.
6.
Open all manways and inspect vessel interior for damage or loose parts. Note any damage and make a formal report complete with photographs.
7.
Remove the shipping supports completely from the vessel. Do not leave any debris inside the processing unit.
8.
Check the low level grounding floats to make sure they travel freely and that the cross bar on the float arms contact the vertical high voltage contact rods when the floats are in the down or low fluid level position.
9.
Install transformer, panel and other parts in accordance with the NATCO drawings. Steel mounting lugs are attached to the top of the vessel for attachment of the transformer.
10.
In preparation for entrance bushing installation, drain the insulating oil from the transformer diode box into a CLEAN, DRY container. The insulating oil should be drained only to a level where the connection from the transformer diodes to the high voltage wire can be easily made. The transformer oil should then be covered or placed in a location away from the working area, as it is imperative the insulating oil is not exposed to moisture or contamination.
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11.
Install the high voltage insulated bushings through the 6” 150# RF connections provided near the transformer. The high voltage entrance bushings should be prepared and installed as detailed below. Refer to the appropriate drawing for illustration of assembly and correct installation of the high voltage lead wires (Figure 4). a.
Remove entrance bushings from shipping crate, being careful not to damage the surfaces.
b.
Before installing the entrance bushing into the mounting flange, inspect the threads on both the flange extension and the entrance bushing, making sure they are clean and NOT DAMAGED. Before installing the entrance bushings, apply either a non-conductive thread sealer or Teflon tape.
c.
Tighten all threaded connections so they do not leak . Any leak would contaminate the transformer insulating oil and result in a premature failure of the entrance bushing or transformer components.
d.
Pass the 1/8” stainless steel cable through the entrance-bushing nozzle. The lower end of the cable should be connected to the contact rod on top of the high voltage electrodes. Push the other end of the cable through the hole located in the end of the entrance bushing and tighten the bolt until firm. Be sure that excess wire does not remain free to shift during operation and short out the transformer, however allow sufficient cable for removal of bushing from outside of vessel.
e.
Mount the flange with the entrance bushing into the vessel. At this point, install either the flex conduit or entrance bushing housing (boot) as shown on the transformer hook-up drawing. Insert the 3/4” OD x 1/2” ID Teflon tubing into the entrance bushing, allowing it to extend up and out of the entrance-bushing flange. Be sure that it is seated in the recess in the top of the entrance bushing.
f.
The Teflon tubing must pass completely through the conduit to the diode box.
g.
While holding vertically, insert the high voltage cable through the Teflon tubing. Make sure the banana plug seats firmly into the entrance-bushing receptacle.
h.
Connect the conduit or housing to the diode box on the transformer, being careful not to damage the Teflon tubing or wire. Trim the Teflon tubing so it extends inside the diode housing at least 2 inches.
i.
Attach the high voltage cable to the appropriate polarity of the diode pack.
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j.
Refill the diode box chamber and the entrance-bushing conduit with the clean transformer oil to the mark shown on the inside of the diode housing. Replace the cover on the diode box.
12.
Connect all field piping for process and utilities. Install temporary strainers where necessary. Do not apply power to the electrode system until the unit is ready for commissioning and process fluid is flowing through the vessel.
13.
Installation of Entrance Bushing – Internal Considerations (see Fig, 4) (To ensure that it is oil covered during operation) When installing an Entrance Bushing it is important to locate it such that the Teflon component will be completely “oil covered” at operational levels and anytime before the internal grounding float contacts the contact rod. To accomplish this, the Teflon must be lower than the centerline of the grounding float ball (in the DOWN position) and the holes along the top of the collector pipe (not the weep holes in the outlet pipe near the inside vessel wall). The entrance bushing must be lowered to insure complete submergence of the Teflon (lower than the centerline of the grounding float ball in the DOWN position). Option #1 - Standard Flex Hose Connection Install a 1” NPT pipe nipple at determined length between the 1” collar and the mounting flange as in Option #1, Figure #4, in conjunction with the swage connection fitting that is part of the entrance bushing kit. * NOTE: De-burr and smooth 1” pipe nipple I.D. on both ends, to protect from tearing the high voltage cable insulation. Option #2 - Pipe Boot Connection Pipe boot required and small diameter vessels use a pipe adapter welded to the mounting flange as shown in Option # 2, Figure #4. The opposite end has a threaded half collar welded in place to directly mount the entrance bushing. All piping components used in the installation of Entrance Bushings and which will be used to contain insulating oil, must be completely free of dirt, rust, grease and moisture. This includes nipples, couplings, special swage.
It is imperative to use Teflon tape to dress threads dur ing installation. NOTE: No pipe dope should be used. Under no circumstances should pipe dope which contains conductive materials be used! This could short the high voltage entrance bushing lead to ground prematurely.
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5”
** NOTE: Keep grounding float assembly and ground wire a minimum of away from the contact rod and aircraft cable, with the float in the UP position. *** NOTE: Make aircraft cable long enough to pull entrance bushing out from top of vessel, without vessel entry.
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Option #2
Entrance Bushing & Grounding Float Setup
Option #1
Vessel Ceiling
Ground Wire
1” Collar
**
Grounding Float in DOWN position
1” Pipe Nipple *
1” x 1 1/2” Swage
Hose Clamp
Pipe Adapter
Teflon Cross Bar Float position during liquid loss or maintenance
Aircraft Cable ***
Contact Rod
Slip-on Weight U-Bolts
Entrance Bushing
Bee-Line Channel
* Note: Deburr and smooth 1” pipe I.D. on both ends. ** Note: Keep grounding float assembly assembly and ground wire a minimum minimum clearance of 5” away from the contact rod and aircraft cable, with the float in the UP position. *** Note: Make aircraft cable long enough to pull entrance entrance bushing out from top of vessel, without vessel entry.
Figure 4
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B.
C.
D.
Pneumatic Checkout Procedure 1.
Turn on instrument air supply to treater and degasser instrumentation.
2.
Blow down instrument air header and piping to remove any dirt and scale.
3.
Refer to the instrument instruction manuals and follow the detail instructions instructions for each pneumatic instrument and/or control valve.
4.
Adjust the instrument air regulators to set the supply pressure for each instrument.
5.
Check all connections and fittings for leaks by soap bubble test.
6.
Stroke the control valves from full open to full close several times to confirm functional operation. Operate from the PLC or DCS if applicable to verify valve stroke and related indicators.
Electrical Instrumentation Instrumentatio n Check out Procedure 1.
Hook up field wiring to junction boxes.
2.
Make continuity checks on all field wiring.
3.
Turn on instrument power supply to Electrostatic Treater and Degasser vessels and functionally check each instrument for correct operation.
Testing of insulating (transformer) (transformer ) oil in bushing housings and transformer Refer to Appendix "A" for the dielectric strength testing procedure. The dielectric strength of the transformer oil in the main transformer can, H.V. junction box and bushing housing should not drop below 35 kv.
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E.
Chemical Testing and Selection Chemical testing, selection, or supply is beyond NATCO’s scope of supply. This section is included only for Customer information. Preliminary selection of demulsifier chemical is a necessary part of the precommissioning process. Selection of the proper demulsifier is much different than selection or specification of other commodities that may be used in the operation or maintenance of equipment. The selection/specification of a demulsifier is complicated because the chemical is a blend of two, three, or more base compounds out of a possible selection from hundreds of compounds. comp ounds. The oil/water solubility of each base compound may may be quite different and two or more solvents may be required in the formulation in order to maintain a stable solution. A chemist must consider many factors in preparing a formulation including solubilties, pour points, and volatility. The selection process begins b egins by requesting several (at least three) reputable chemical suppliers to send a representative to visit the plant site to become familiar with the process and equipment and to run preliminary "bottle tests”. Bottle testing on a fresh representative sample of the production to be treated is a fairly reliable method for chemical suppliers to screen possible po ssible formulations. Bottle tests on aged age d samples may be very unreliable unreliab le and give incorrect incorr ect results. If the chemical supplier has experience in the same field and formation with similar production equipment and methods, the bottle testing may not be required. Each supplier should be able to propose pro pose one or two demulsifier formulations based on his preliminary work. The chemist will select the base compounds and make a formulation to fit a specific application. Each oil field, each formation in the field, each location, and sometimes each well, will produce an emulsion with characteristics that are different from any others. The variations in the emulsions are due to the chemical and physical characteristics of the crude oil and aqueous phase including: 1.
Chemical composition (The amount of paraffin, asphaltenes, and natural surfactants have a great affect on the emulsion.)
2.
Amount and type of solids produced.
3.
Oil gravity.
4.
Water gravity (salt content and composition)
5.
Amount of gas.
6.
Production temperature/pressure. temperature/ pressure.
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Other factors affecting the emulsion and chemical selection include: 7.
Method of production (flowing wells, surface pump, down hole pump, water flood, chemical flood, steam flood, fire flood, etc.
8.
Pressure drops.
9.
Length of flow lines.
10.
Retention time in vessels or tanks (age of emulsion).
11.
Other chemicals (water and corrosion).
12.
Type of pumps.
Final demulsifier selection must be based on competitive full-scale plant tests. The “optimum" demulsifier should allow the process to meet the required product specifications at the lowest total operating costs. Total operating costs include chemical, fuel, maintenance maintenan ce and plant upsets. The cheapest chemical may not always always be "optimum" when all factors are considered. Other considerations include condition of oil and aqueous interfaces, buildup of interface sludge, and availability of qualified service personnel
F.
Electrical System Checkout Procedure The following procedure is intended to test the electrical installation of all internal components of an electrostatic electrostatic treater. To avoid electric electric shock shock and possible possible injury, injury, the equipment installer should become familiar with this procedure before performing these electrical checks. 1.
Before connecting line power, be sure all cables and wiring are installed and connected. The power supply should be locked out and tagged out in the off position.
2.
Make sure transformer transformer and vessel are grounded.
3.
Enter the dehydrator vessel using approved safety procedures.
4.
Make sure electrodes are free hanging, with no loose materials to ground them to the vessel interior or to each other.
TEST #1 5.
With a dry, Teflon tube or wooden block support, lift and block all float switches so they cannot come in contact with the vertical high voltage contact rods.
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6.
Thoroughly examine the internals of the treating vessel. All electrical components must be at least 6” from any grounded vessel component.
7.
Check the alignment of the electrodes. Electrode plates should be on a uniform spacing. It should be possible to maintain a tolerance of ±0.5” between electrodes.
8.
Check the position of the cables and weights from the bottom of the entrance bushings to the tie rods on the electrode supports. The cables carry the high voltage from the entrance bushings to the electrodes. The cable and weight must be at least 6” from all grounded vessel surfaces and at least 10” from the other electrode set.
9.
Make sure all Teflon electrode hangers uniformly support the weight of the electrode plates. Angled hangers (used with floating production systems to restrain electrode movement) must be in tension.
10.
Leaving the float switches blocked up, exit the vessel.
11.
Open the diode compartment of the high voltage transformer.
12.
Disconnect the positive and negative cable leads from the diode pack.
TEST #2 13.
Referring to Figure 2, use a 1000 volt or higher megger, connect one lead of the megger to the high voltage cable lead and connect the other lead to the transformer ground connection. (NOTE: Do not make this connection to the diode pack but only to the high voltage cables going into the vessel.)
14.
Follow the procedures for operation of the megger to check the resistance of the electrode system. The resistance should be near infinity. If the resistance is low, see Item 16.
TEST #3 15.
Switch the megger cable to the other high voltage cable lead and repeat the megger check. Again, the megger resistance reading should be near infinity. If the resistance is low, see item 16.
16.
A low megger reading during test #1 or test #2 indicates one or more of the following problems: a.
The high voltage electrodes, cables, weights, or hangers are in contact with the vessel at some point
b.
The shorting float is not properly supported on the Teflon tube or wooden block
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c.
The entrance bushings are internally shorted to the vessel
d.
The electrode hangers are shorted (tracked) from the lower high voltage end to the upper-grounded end
If one of the above problems is evident, the problem should be corrected and the installation re-checked by repeating the megger readings of test #2 and test #3. Units installed with composite electrodes should be checked for continuity as shown in Figure 2. The reading should show low resistance proving continuity through the mounting hardware of the composite plate. TEST #4 17.
Connect the megger between the two high voltage leads and check the resistance. The resistance reading should be near infinity.
18.
A low megger reading during test #4 indicates a short between the electrode plates. In a new installation, a short can be created by improperly installing the electrodes (adjacent electrodes are not connected to alternate support rails) or the 3/16” aircraft cable has been connected to the same electrode set (A or B). Re-enter the vessel and check for locations where adjacent electrodes might be touching each other. Also check to be sure the cables form the lower end of the high voltage entrance bushings are connected to alternate electrode groups. Once the problem is corrected, re-check the installation by repeating the megger readings of test #4.
19.
Once tests 2, 3, and 4 have been successfully completed, re-enter the vessel and release one float switch so that it contacts the vertical high voltage contact rod by removing the support previously used to block the float in the up position from the vessel interior. Make sure the float switch is resting fully on the contact rod and is free to swing upward with fluid rise.
20.
Exit the vessel and make certain no one is in or on the unit.
21.
Recheck the entrance bushing with the megger to verify the electrical ground.
22.
Refer to Item #19 and remove the block from the other grounding float and test as in Item #21
23.
Close and bolt the vessel access manways.
24.
Reconnect the positive and negative cable leads to the diode pack and close the diode compartment of the high voltage transformer.
25.
The unit is now electrically prepared for start-up.
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G.
Leak Test Once all interconnecting piping has been installed, we recommend the unit be hydrotested to ensure all connections are leak proof. Test water should be clean, potable, deoxygenated, with a corrosion inhibitor.
H.
1.
The customer must determine the extent of vessels and piping that will be tested together. All of the components must be rated for the test pressure.
2.
Isolate any component that may be damaged by exposure to water or the designated test pressure. Do not test demulsifier chemical lines with water.
3.
Isolate the vessels and piping to be tested by closing appropriate block valves or by using blinds.
4.
Close all vent, drain, purge and sample valves on the piping, vessels, and instruments.
5.
Make sure that all block valves, control valves, and bypass valves in the piping to be tested are open.
6.
Open isolation valves on relief valves, level switches, level transmitter, and level gauge. Close isolation valves on pressure gauges. Be sure isolation valves around safety relief valves are locked open.
7.
Open high point vent valve(s) as necessary and begin to slowly fill the system with water.
8.
Slowly fill the system until water begins to overflow the vents. Close the vent valves as each section or vessel is filled.
9.
When the system is full and before starting to increase the pressure, check the system to be sure that pockets of air have been eliminated. Open vent valves on level switches, level transmitters, and level gauges to vent trapped air. Open the drain valves under the safety relief valves. Open sample valves on vessels and piping.
10.
The system can now be slowly pressured up to the test pressure. Since the vessel and piping were hydro-tested for Code compliance at the manufacturing facility, we recommend that the field test pressure be limited to 10% above the operating pressure of the vessel. The pressure test should be maintained for several hours while the system is checked for leaks.
Precommissioning Checklist 1.
Commissioning team and operators have read and are thoroughly familiar with the instruction manual and vendor catalog.
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2.
Equipment was inspected on receipt and checked against packing lists and all damage was documented and reported.
3.
Equipment is set level.
4.
Foundation bolts installed.
5.
Internal bolts are tight
6.
Shipping supports/packing removed.
7.
All pipe spools and accessories are installed in accordance with the P&I and assembly drawings.
8.
The pneumatic hook-up has been checked.
9.
Electrical wiring has been checked.
10.
Vessels, skid, and instrumentation are properly grounded.
11.
All piping and accessories have been checked for tightness.
12.
Customer field piping has been connected.
13.
Temporary strainers have been installed
14.
Control panel operation verified.
15.
Transformer and grid system checkout completed.
16.
Vendor literature has been reviewed and all instructions for pre-commissioning, calibration, and adjustment of valves and accessories have been followed.
17.
Leak test completed.
18.
Transformer oil testing completed.
19.
Chemical injection system ready with first fill of chemicals.
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V.
START-UP/COMMISSIONING PROCEDURE
This procedure is furnished as a general guideline and is not intended to replace the services of an experienced start-up Engineer. A.
All support systems should be tested and commissioned before start-up of the electrostatic treater. Refer to other suppliers' instructions for each system. 1. 2. 3. 4. 5. 6.
Instrument Air System and Pneumatic Instruments Main Control Panel and Instrumentation Power supply to the transformer must remain "off" until the Electrostatic Treater is full of oil. Chemical tanks and chemical injection lines are full. Heaters are operational. Pre-Commissioning procedures completed
B.
The Electrostatic Treater vessel should be partially filled with water, up to the interface level.
C.
Open block valves on the oil inlet, oil outlet, safety relief line, and gas outlet. Open isolation valves on instruments, close all vent and drain valves.
D.
The Electrostatic Treater vessel is now ready for the oil production to be started through the system. Open the inlet oil valve a very small amount to fill treater vessel and piping. NOTE: Start up oil rate should be at the minimum.
E.
Start partial oil flow through the system and set the system backpressure control valve to maintain the desired system pressure.
F.
Start demulsifier chemical injection.
G.
Open the valves on effluent water line from the Oil Treater. See PID 1420-20-PI-DG4412/4415 (section 3.4 of manual) for operation of the interface level in the Oil Treater.
H.
Open the valves on oil outlet line from the Oil Treater. See PID [1420-20-PI-DG4412/4415/4417] and Cause and Effect Diagram (section 3.4 and 3.5 of manual) for operation of the level in the Oil Treater Degasser.
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I.
When oil flow is established from the oil discharge line, the transformer circuit breaker may be turned on. The light located on the transformer will indicate when the voltage is on under normal treating conditions. Several hours may be required before outlet specification BS&W is reached.
J.
After the plant is commissioned at the reduced rate, it should be carefully monitored for at least eight hours to ascertain that all systems are functioning correctly.
K.
With all aspects of the process working properly, the throughput rate may be increased to the full production rate. Chemical injection rates must be adjusted proportionally to the production rate.
L.
Adjustments in operating variables can be made to obtain the best performance. Refer to Test Run Procedure in this manual.
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VI.
TEST RUN PROCEDURE A.
After the mechanical operation has been checked, adjustments may be made in operating variables to obtain the optimum performance.
B.
It is extremely important to maintain a consistent normal feed condition for any period of time during optimization and testing of the plant. The flow rate and composition of the feed must be constant. Wells should not be switched on and off during any testing since emulsion characteristics and composition may vary. Variations in feed conditions may invalidate conclusions drawn from test data. Abnormal conditions such as production of well completion or work-over fluids must be avoided.
C.
Provisions must be made for running BS&W tests. These facilities may be portable or temporary, but they must be available during system testing.
D.
Sending samples to a remote laboratory will delay reporting of results and increase the length of time needed to optimize the operation.
E.
Confirm that levels, temperatures, pressures, rates and other operating variables are at the recommended initial set points, and record all of the following information: 1.
BS&W (check each sample with and without knockout drops). a. b. c.
2.
Temperature a. b.
3.
Inlet Outlet Electrostatic Treater interface samples
Inlet Outlet
Pressure Operating pressure
4.
Flow rate a. b. c.
Oil Gas Water
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5.
Levels a. b.
6.
Treater interface Degasser Liquid Level
Transformer Primary current and voltage
7.
Other Data Required: a. b. c. d. e. f. g. h.
Wells that are in production along with rate, BS&W API gravity of dry crude pH of produced water Oil viscosity - dry (at 3 temperatures) Produced water analysis (each well if significant variations exist) Ambient temperature Date and time of samples Data from other sample points as necessary
F.
Maintain stable operating conditions for a minimum of four hours and record all of the data points.
G.
Check all of the data for credibility. For example: The BS&W out of a unit should not be more than the inlet
H.
If the data is consistent for two consecutive sets of samples and the data is credible, proceed with the plant optimization.
I.
Plant Optimization Only one variable should be changed during a test period. There should be a minimum of four (4) hours between changes. The selection of a starting point for the testing will depend on the results of the initial samples and data. 1.
2.
Operating Temperature a.
Reduce the operating temperature until the lower limit is determined.
b.
Increase the operating temperature if necessary to improve performance.
Oil/Water Interface Raise and lower the oil/water interface to determine the maximum and minimum operating points. Water level should never go above the wave
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baffles. J.
It is important to understand that any change in the inlet production or operating variables will result in some variation of equipment performance. The magnitude of variations in performance will depend on the magnitude or importance of any change in inlet fluid or operating variable.
K.
After operating variables are optimized for a specific inlet production, then various wells may be switched on and off to determine if production from specific wells could have any significant effect on plant operation.
L.
Sampling and Analysis Procedure: The method of collecting and handling the samples is extremely important if accurate and repeatable results are expected. •
Sample lines should be a short and as small a diameter as practical.
•
The sample system should be arranged to eliminate as far as possible any trap or pocket where phase separation may occur.
•
Samples should be taken from the center of flowing lines through a stinger.
•
Sample lines should be flushed sufficiently to remove any dead fluid or old material in the lines.
•
Open the sample valve and flush the sample line- then reduce the flow rate and catch the sample while the line is flowing.
•
The most repeatable results may be obtained by catching the sample directly into the clean centrifuge tube, beaker, or flask in which the test is to be run. If this is not possible, then the samples should be caught in a clean container and transported immediately. At the lab, the sample container must be shaken vigorously and samples poured up and tested immediately.
•
Be certain to completely flush the sample lines before taking the next sample.
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VII.
NORMAL OPERATION A.
Routine Work 1.
The operation is automatic and the normal routine only involves checking and recording the following items on a regular (once-per-shift) basis: a) b) c) d) e)
2.
Interface level Operating temperature/pressure Oil flow rate Primary amps on transformer BS&W
The Electrostatic Coalescer is equipped with a “sand jet” and drain system. This system is used to fluidize and remove solids from the bottom of the vessel. To be effective, the system must be used on a regular basis. The required operating frequency depends on the amounts of solids in the inlet production and is determined by operator experience. If the solids build up too deep and plug the openings in the “sand” troughs, the system will not work. Two sand jet systems are installed in the vessel. Each system covers half the length of the vessel. Jet and drain only one side of the vessel at one time. Jetting water should be furnished at a minimum of 50 psig above the vessel operating pressure. Step 1:
Open the isolation valve for the sand jet water and jet one side for 30 seconds.
Step 2:
After 30 seconds and with the jets still running, open the sand drain valves for 30 seconds. Observe the oil/water interface level. If it begins to drop excessively, close the drain valves and cycle them in short cycles.
Step 3:
Close the drain valves.
Step 4:
If necessary, continue running the jetting water to re-establish the proper oil/water interface level.
Step 5:
Shut off the jet water valve.
Repeat the procedure for the other side of the vessel.
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B.
Maintenance NOTE:
Read and follow all safety instructions before working on or entering this equipment.
WARNING: This equipment uses high voltage electricity. Only qualified personnel must perform maintenance. Failure to follow instructions can result in serious injury or death. Turn off and lock off electrical power, isolate, and degas the equipment before performing maintenance. 1.
Refer to Vendor’s published catalog information for instructions on valves, controls and other accessories.
2.
The Electrostatic Treater should be shut down and cleaned at the end of the first six months of operation. Any accumulation of sludge should be removed from vessel internals.
3.
Clean the surface of Teflon hangers and entrance bushings using a cloth and solvent.
4.
Inspect bushings, hangers, and other internals for any damage.
5.
Check di-electric strength of transformer oil in bushing housings.
6.
After the first cleaning and inspection, a more suitable schedule may be determined.
7.
If any work is performed inside the vessel, bottom drain connections must be covered to prevent nuts, bolts, or trash from entering and plugging the drains or fouling the valves.
For more detailed information and expert field service, please contact the nearest NATCO representativ e.
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VIII.
TROUBLESHOOTING The Dual Polarity Electrostatic Oil Processing Unit employs much the same principles as the more conventional oil processing systems. If differs primarily in that it utilizes the powerful coalescing effect of the dual polarity electrostatic field, as well as the conventional coalescing aids. As with any good system where time, and electricity are used in combination to provide treatment, these components are in balance with each other. Therefore, if one component of the system is changed, or lost, another must also be changed to regain this balance this is necessary to compensate for the increased viscosity resulting from a lower operating temperature. Also, it should be kept in mind that this balanced treating program is itself balanced against the emulsion that is being processed. If all components of the program are maintained and the treatment slips, it can be assumed that the emulsion has somehow changed. Changes in emulsion characteristics are most likely to occur following the introduction of new wells, well workovers, etc. Such changes may be temporary or permanent - whatever the cause, a change in the treating program is necessary. If the oil is not treating to specifications, the following troubleshooting checklist should aid in identifying and correcting most of the problems that may occur. A.
Check the system for the following irregularities 1.
Low operation temperature a.
b.
2.
1)
A normal condition that will correct itself with additional production.
2)
A faulty drain or water valve
Failure of heating system (by others)
Excessive sludge build-up on the vessel interface a. b. c.
3.
Low level shutdown
Inadequate heat May require a change or additional type of chemical It may be necessary to remove sludge from the system
High interface level a. b. c.
Interface control malfunction Defective water dump valve Water valve plugged
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4.
Increased flow rate through the system a. b. c.
B.
Field surging Flow control set too high Uneven flow splitting between trains
Electrical Malfunctions 1.
No voltage and no current, treating efficiency decreased:
Loss of electrical power to the transformer 1) Circuit breaker open 2) Master fuse open 3) Master switch open
2.
Low or no voltage and high primary current •
3.
Any of the problems listed in "A" of this checklist can give these indications. If there is even a small secondary voltage or the primary current shows some variation from time to time, the problem is more than likely one or more of those listed under "A" of this checklist and not an electrical problem.
Near zero voltage and current holding steady near maximum. NOTE: The maximum current for your transformer may be determined by dividing the KVA rating by the applied voltage. For example, a 50 KVA transformer operating at 480 volts would draw approximately 104 amps (50,000/480 = 104). A 100% reactance transformer should never pull more than this value of current. a.
A low level in the treater will allow the low level safety float to ground out the high voltage grid, resulting in the above symptom. 1)
This could be the result of excessive water removal from the coalescing section and will likely correct itself when the level is restored to normal production.
2)
Another likely cause is a faulty drain or water control valve.
b.
Any one or more of the irregularities listed under "A" of this checklist, in extreme, could give these symptoms and should be checked out before proceeding.
c.
An electrical short within the high voltage circuitry of the system is the most likely malfunction that will give these symptoms.
Note:
The reactor does not protect the low-voltage side of a 100%
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reactance transformer; thus a problem in the low-voltage side would not give these symptoms. To isolate a short in the high voltage circuitry, take the following steps:
d)
1)
Disconnect and lock the transformer power supply in the "OFF" or "OPEN" position. Be certain that power is not reaching the transformer.
2)
Remove the lid from high-voltage junction box on the transformer and make a visual inspection. Look for burned wiring and/or discolored insulating oil.
3)
If all appears normal, isolate the transformer from the vessel by unplugging transformer secondary wire from top of diode pack. Be sure the plugs and lead are well away form the high-voltage connection.
4)
Temporarily secure the lid on the high-voltage junction box and restore power to the transformer and observe the symptoms.
5)
If the same symptoms are observed, low voltage and high current, the transformer secondary winding or high voltage feed-throughs are faulty.
6)
If power readings return to normal, high volts and low amperage, turn off power to the transformer and lock out the power supply in the "off" position.
7)
Reconnect the diode pack to the secondary, and disconnect the two entrance bushing leads from the diode pack. Make sure leads are away from the diode pack and other high voltage wiring.
8)
Temporarily secure the lid on the high voltage junction box and restore power to the transformer and observe the symptoms.
9)
If the symptoms now return to low voltage and high current, the diode pack or associated wiring is shorted to ground and must be replaced or repaired.
10)
If the readings return to normal and no discoloration of the oil is observed around the entrance bushing conduit openings, the problem is inside the vessel.
If it is determined that the short is inside the unit by Step c. above, the following procedure should be observed:
1)
Reaffirm that the symptoms are not the result of irregularities
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covered in "A" of this checklist. They would appear as an electrical short inside the unit.
4.
2)
Turn off all electrical power to unit.
3)
Remove the production from the system and depressurize the unit.
4)
Disconnect and remove the entrance bushings and visually check for burned appearance. (tracking). Be sure the bushings are clean. Sulfides or B.S. build-up over the length of the bushing can cause shorting. If there are no visible signs of damage, a more complete determination can be made with a "megger" to determine if there are any conductivity between the entrance bushing contact rod and the adaptor flange. Conductivity here indicates a bad bushing.
5)
If the bushings are good, drain the vessel and remove manway cover.
6)
Before entering the vessel, once again be sure the power is off and the power supply switch is locked in the "off" position. Also, be sure the vessel has proper ventilation.
7)
Visually inspect the insulating hangers that support the electrode assembly. Burned or otherwise damaged insulators should be replaced.
8)
Check the electrodes for any foreign material that may be touching either electrode and/or ground. Also, check for proper spacing (at least 6") between the vessel wall and the electrodes and between electrodes themselves.
9)
Inspect the low-level safety switch on the top of the vessel. Be sure the float assembly moves freely with out binding. Also be sure that the float has not leaked and filled with liquid preventing it from floating up when the vessel is filled with liquid.
10)
If a visual inspection has not revealed the problem, a more complete check will be necessary. A 'megger' may be used to check conductivity between each grid and ground, and each other. Any conductivity will indicate that one or more of the insulating hangers are bad. To determine which insulators are causing the problem it may be necessary to remove the insulators one a time and check individually. Any conductivity across an insulator indicates a bad insulator.
Voltage normal, current very low, with treating efficiency decreased
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This is an unlikely symptom but could be caused by an open within the highvoltage circuitry of the unit; A simple check for this problem may be accomplished by raising the interface level in the coalescing section. As the interface approaches the grid section, current should increase drastically if the high voltage circuitry is good. If it does not, an open does exist in the high-voltage circuitry. Note: The high voltage diode pack should be checked out in accordance with Method "A". 5.
Normal voltage, normal current, treating efficiency decreased a)
The high voltage diode pack in this unit is conservatively sized. However, a voltage transient resulting from power interruptions or lightning could result in a shorted diode pack, giving the above symptoms. An open diode package should be checked in accordance with Method "A" attached to this checklist. NOTE: The diode package should be checked in accordance with Method “A” attached to this checklist.
b)
6.
Another possible problem that would display these symptoms is the production of a stable low water cut (2-3%) emulsion so finely dispersed that it is concealed from the electric field. This type of emulsion is likely to be chemically stabilized, and usually the result of well rework or stimulation.
No voltage, normal current, treating efficiency normal •
Fuse blown in 100 V tertiary winding of transformer •
7.
Breaker/contactor kicks off immediately on energizing •
8.
Located in low voltage junction box
Short in primary (low voltage) side of transformer or associated circuitry
Breaker/Contactor kicks off intermittently or on hot days
a) Faulty circuit breaker b) Breaker sized too small
C.
CHECKING OUT HIGH-VOLTAGE CIRCUITS Circuits that are designed to operate on high voltage will sometimes develop problems
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that cannot be detected with normal low voltage test equipment. Although an ohmmeter is a useful tool, it can deceive you. A conductor that is shorted with high voltage applied may appear normal with low voltage. Thus an ohmmeter would not detect this type of high voltage short circuits. An insulation tester, "megger" is a better testing device for troubleshooting high-voltage circuits. Listed below is the recommended method for checking out the high-voltage diode packs on the Dual Polarity unit. 1.
Use of Insulation Tester "Megger" a) Disconnect and padlock transformer power Supply in the "Open" or "Off" position b) Be certain that power is NOT reaching the transformer c) Remove the lid on the high-voltage junction box and isolate the diode pack by disconnecting the high-voltage entrance bushing leads and the transformer secondary lead d) Connect the "Line" lead from the megger to the diode pack input terminal and connect the "Ground" lead to the positive terminal on the diode pack. Activate the megger. It should read high as shown on Reading#1 on the attached sketch. Move the "Ground" lead from the positive terminal to the negative terminal on the diode pack. Again, activate the megger and note the reading. It should read low as in Reading #2 of Figure 3. e) Disconnect "Line" lead of the megger from the input terminal of the diode pack and connect the "Ground" lead to the diode input terminal. Connect the "Line" lead to the positive terminal on the diode pack. Activate the megger. The reading should be low as in Reading #3 of Figure 3. Move the "Line" lead from the positive terminal to the negative terminal on the diode pack. Again, activate the megger. The reading should be high as in Reading #4 of Figure 3.
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Test#4
Test#2
Test#3
Test#1
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Figure 3
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APPENDIX A TEST FOR DIELECTRIC STRENGTH Testing for Dielectric Strength: For testing the dielectric strength of oil, the technique as specified by the American Society for Testing Materials in the test method entitled, “Test for Dielectric Strength of Insulating Oil”, Method D-877, should be followed. A 35 kV, 2 kVa test set is available and may be purchased from the General Electric Company or Westinghouse Electric Company. The following precautions and modifications must be observed:
Set the spacing of the two 1-inch diameter, flat disk electrodes at 0.100 inch. Wipe the test cup and electrodes clean with dry, calendered tissues or clean, dry chamois; and thoroughly rinse with clean, non-leaded gasoline, Standard solvent or water-white kerosene. Fill the cup with a sample of the cleaning fluid and apply the voltage at the rate of 3 kv per second until breakdown occurs. If the breakdown voltage is less than 26 kV, clean the cup again with cleaning fluid and retest. After a satisfactory result, empty the cup immediately and rinse the test unit at once. The temperature of the oil, when tested, should be the same as that of the room which should be between 20°C and 30°C (68°F and 86°F). Testing at oil temperatures appreciably lower than room temperature is likely to give variable results and may be misleading. In order that representative test specimens may be obtained, the oil sample container should be gently inverted and the oil swirled several times before each filling of the test cup. The purpose is to thoroughly mix any impurities present with the oil. Too rapid agitation is undesirable, as it introduces an excessive amount of air into the mixture. Immediately after mixing, pour the oil slowly from the container so that no air bubbles will form. Fill the cup to overflowing. Gently rock the test cup a few times and allow three minutes for entrapped air to escape from the oil before applying voltage. When making the test, apply the voltage at the rate of 3 kV per second. Make only one test per cup filling and fill the cup at least five times. Average the results to get the breakdown voltage for the sample. Since the oil is the major insulation of the apparatus in which it is used, its dielectric strength must be kept up to definite standards as specified previously. If the oil fails to withstand the minimum breakdown kV specified, it is a sign that impurities, particularly moisture, have entered it. In this event the oil is no longer safe for use as an insulating medium and must be filtered to remove the impurities and bring it back to its original conditions. Acidity (Neutralization): The acidity test is one of the most satisfactory indicators of oxidation in the oil. This is true because some of the oxidation products are of an acid nature and thus may be detected by measuring the acidity of the oil. The main hazard of oxidation is the deposition of sludge. Sludge occurs after the oxidation products held in solution finally saturate of the oil and any additional products formed settle out in solid form. The acidity test indicates fairly accurately how far oxidation has progressed.
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Appendix V Sample EDD® Users Manual
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INSTRUCTION MANUAL FOR INSTALL ATION, START-UP, AND OPERATION OF CRUDE OIL DESALTERS
* * *
“ CLIENT” “ CLIENT” REFINERY
* * *
The following is an example of a manual for EDD ® Desalters. This manual was prepared for a retrofit of two second stage desalters from AC to EDD® configuration. Only those details identifying the client have been changed. NOTE: This manual was originally prepared for the "tie rod" style composite electrodes and the original LRC. Modifications will be required for current composite plate mounting and current LRC configuration.
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START-UP AND OPERATION MANUAL TABLE OF CONTENTS INTRODUCTION SAFETY
SPECIAL NOTES GENERAL SAFETY INSTALLATION AND ASSEMBLY
RECEIPT OF EQUIPMENT INSTALLATION PROCEDURE FOR VESSEL MODIFICATION PRECOMMISSIONING
PRECOMMISSIONING CHECKLIST INSPECTION PROCEDURE FOR INTERNAL ASSEMBLY PNEUMATIC CHECK-OUT PROCEDURE ELECTRICAL INSTRUMENTATION CHECK-OUT PROCEDURE HIGH VOLTAGE EL ECTRICAL SYSTEM CHECK-OUT PROCEDURE FLUSHING OF INTERNAL DILUTION WATER HEADERS FOR EDD UNITS HYDROTEST AND LEAK TEST PROCESS DESCRIPTION
DESIGN CONDITIONS GENERAL DESCRIPTION CHEMICAL TESTING AND SELECTION START-UP PROCEDURES
FILL ESTABLISH CRUDE OIL FLOW ESTABLISH PRESSURE CONTROL ESTABLISH TEMPERATURE CONTROL START ELECTROSTATIC SYSTEM OPERATION ESTABLISH OIL/WATER INTERFACE START THE DILUTION A ND RECYCLE PROCESS OPTIMIZE PROCESS NORMAL OPERATION
MONITORING PROCESS PERFORMANCE SWITCHING FEEDSTOCKS PROCESS PERFORMANCE TESTING AND GUARANTEE
ANALYSIS PROCEDURE PERFORMANCE TEST PROCEDURE PROCESS PERFORMANCE GUARANTEE MAINTENANCE OF EQUIPMENT
MAINTENANCE OF THE DESAL TING SYSTEM POWER SUPPLY INSPECTION AND MAINTENANCE OF VESSEL INTERNALS TROUBLESHOOTING
GENERAL GUIDELINES DESALTING PROCESS MAL FUNCTIONS
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ELECTRICAL SYSTEM MALFUNCTIONS WATER QUALITY PROBLEMS
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SECTION I INTRODUCTION It is imperative that this manual be read completely prior to start-up and that a copy be located at the plant site at all times. The system covered by this manual is comprised of two (2) parallel second stage crude oil desalters retrofitted with NATCO's Electro-Dynamic Desalting (EDD) components. These components include three transformers and three Load Responsive Controllers (LRC) for each desalter vessel, programmed for multiple crude oil types.
Tag No.
Oil Rate
Operating Temperature
Desalter Vessel Size
VE-1A
50,000
145 C
12' x 32'-3"
VE-1B
50,000
145 C
12' x 32'
Upstream of these two second stage desalters is a single, larger first stage. The two process stages are intended to work as an integral system to reduce both water and mineral contamination in the crude oil. A more detailed description of the process can be found in Section V of this manual. This manual is intended to provide information necessary for all activities relating to the second stage desalters. Although the existing first stage is not being modified at this time and is not included in the scope of this manual, it nevertheless must work in conjunction with the newly modified second stage vessels. Some of the information contained herein may be applicable in a general way to the first stage desalter. However, the function of the stages is quite different. The first stage in its unmodified condition is a pure AC desalter. The two second stage vessels are NATCO's EDD (AC/DC) process. The first stage desalter should be operated using procedures recommended by its supplier, and time tested by it s operators. No manual or set of instr uctions can foresee all possible situations due to the myriad combinations of pressure, temperature, and operating conditions possible in operations. The reader is, therefore, advised that the services of a competent on-site technical consultant during start-up and operation of this equipment is essential to prudent and safe operation. This manual is furnished for information purposes only. NATCO shall not be liable for the use of this manual or any of the information contained in whole or in part, as that use relates to plant operating efficiency, plant malfunctions, plant operator interpretation, and particularly accidents or unsafe conditions which could arise in any operating f acility. The safe operation of any facility remains the responsibility of the owner or lessee of the equipment and those directly involved in the operation of such f acilities.
NATCO's scope of supply was limited to the retrofit desalter packages. The Customer must confirm that all components of the system are compatible.
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NATCO“ CLIENT”
SECTION II SAFETY
IMPORTANT: Read and understand the entire operating and maintenance manual before starting to work. Observe and comply with all cautions and warnings given here, in other sections of the manual, and in vendor literature contained in the "Mechanical Catalog" or "Vendor Equipment Booklets". SPECIAL NOTES 1.
Make certain that all structures, vessels, and electrical equipment are properly grounded.
2.
Do not enter any vessel until it is vented and checked for dangerous or explosive gas.
3.
Do not work on vessels or equipment in operation or while under pressure.
4.
Vent all process and instrument gas pressures before working on equipment.
5.
Check for explosive gases in the area before performing any work.
6.
Do not work on this equipment if any other work in the area could result in release of explosive vapor.
7.
WARNING: After equipment has been in service, do not cut or weld on any process lines or vessels for any reason. Accumulations of hydrocarbons can result in explosive conditions. Any rework of vessels or piping requires special precautions that are not covered in this manual.
8.
WARNING: Safety relief valves are designed for thermal/fire relief. The Client must confirm that the vessel design pressure is higher than the shut-in pressure produced by feed or water injection pumps (by others).
9.
WARNING: Keep hands away from mechanical linkages while equipment is in operation. Operation is automatic and may occur without notice.
10.
WARNING: The control panel and control circuits operate on 110 VAC and 24 VDC electrical power. Use extreme care when servicing. Lethal electrical shock is possible. This equipment must be serviced only by qualified personnel.
11.
WARNING: The Load Responsive Controllers (LRC) and high voltage transformers operate on 440 VAC electrical power. Lock power "off" before servicing. Use extreme care when servicing. Lethal electric shock is possible. This equipment must be serviced only by qualified personnel.
12.
WARNING: The desalter high voltage electrodes and electrical system components operate on 23,000 to 40,000 VAC electrical power. Lock power "off" before servicing. Lethal electric shock is possible. This equipment must be serviced only by qualified personnel. Make certain power is locked "off" before entering the vessel.
13.
WARNING: Before initial testing of transformer and electrical system, the vessel must be vented and carefully checked for any combustible vapor. After the initial start-up, the
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NATCO“ CLIENT”
power must never be applied to the transformer unless the vessel is filled with liquid. Any spark generated in the presence of combustible vapors may create a lethal explosion. This equipment must be serviced only by qualified personnel. 14.
Operate the equipment within the specified design conditions.
GENERAL SAFETY 1.
Definite safety procedures should be prepared for the employees. Plant supervision should make certain that employees understand their duties and r esponsibilities. Employees should understand that it is their personal responsibility to report to their immediate supervisor any abnormal circumstances, such as: a. b. c. d. e. f. g.
Leaks Accumulation of gas or vapor Defective or damaged equipment Abnormal conditions such as excessively high or low temperature or pressure Infractions of safety regulations Unauthorized hot work Unauthorized vehicles or personnel in the area
Operating personnel should be familiar with the location of fire protection and first aid equipment in the area, and trained in the use of such equipment. Employees should know how to report a fire or an emergency and have a clear understanding of their duties during such emergencies. 2.
3.
Normal Operation a.
Specific operating procedures for the lighting of gas burners should be readily available at each unit where such equipment is located. Furnaces are equipped with pilot lights and with equipment designed to shut off the fuel supply when a malfunction occurs. Manual resetting of shutoff equipment is necessary prior to placing furnace in operation.
b.
Transportation vehicles should not be permitted to operate within plant area or loading area while area is contaminated with flammable vapors or while loading of product.
c.
Procedures for the loading of product should be prepared and should be followed.
d.
Regular inspections of the loading area should be made of items such as grounding of electrical equipment, housekeeping, lines, valves or cocks for leaks, proper drainage or venting from loading area, and elimination of nearby open flames during loading operations.
e.
Procedures covering the starting up and shutting down of processing equipment and units should be reviewed and rehearsed thoroughly by those responsible for operation of the equipment.
Emergency Operations a.
General When flammable liquids or vapors escape from tanks, vessels, or lines, available means should be used for limiting their spread and preventing their ignition. The
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NATCO“ CLIENT”
extent of the contaminated area should first be defined and the area identified by suitable warning signs as well as patrolled. Spills should be cleaned up as soon as possible. b.
Liquid Leaks If a break or serious l eak occurs in a liquid line, the pumps should be shut down and any block valves closed. If the leak involves a tank or any relatively large vessel, portable pumps may be required to recover the liquid. Trenches, dikes, or diversion walls should be used either to confine the liquid or divert the flow. Foam may be applied to cover the spills in order to exclude air, but this is not normally necessary. Water spray applied at the point of emission of a leak may aid in the dispersal of vapors and prevent ignition.
c.
In the case of leaks of very light products, which give off quantities of vapor, the procedures listed for gas leaks should also be followed. Gas Leaks In the event of a break to a gas containing line or vessel, all fires in the vicinity of the break should be extinguished. Before operations are resumed, tests should be made at pits, trenches, or dikes where gas might accumulate. Portable gas indicators for making such tests will indicate if a flammable gas or vapor is present. If a break occurs in area where adjoining property is owned by outside interests, prompt measures should be taken to notify those concerned of the potential hazard that exists and to eliminate any sources of ignition. It may be possible at times to disperse flammable mixtures by means of f orced ventilation or large quantities of steam or water fog.
4.
Maintenance Procedures a.
General Fire prevention in connection with maintenance work depends primarily upon careful planning and removal of flammable liquids, vapors, and other flammable materials before work starts. In certain instances, it is not possible to completely remove all flammable material; and, at such times, precautions must be taken to prevent ignition sources from contacting flammable mixtures or to exclude oxygen. A procedure should be set up for warning personnel and stopping maintenance work in the event of a release of flammable vapors or liquids in the area where the work is being done.
b.
Work Permit System A written work permit system should be used whenever any maintenance or inspection work is contemplated which requires the use of spark or flame producing equipment. The permit should be issued only after tests have indicated that no flammable vapors are present. It should also be ascertained that no other work is being done or contemplated which might create a hazard during the course of the job. The authorized persons should sign the permit, indicating that the equipment to be worked on has been properly prepared for hot work. Any precautionary requirements or procedures to be observed during the work should also be outlined on the permit.
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NATCO“ CLIENT”
c.
Inspection Process units and related equipment should have periodic complete inspections. The length of time between inspections and the type of inspection conducted should be based upon the type of equipment and its condition as determined by previous inspections.
5.
6.
Repairs a.
When any equipment is to be repaired, it should be isolated from other equipment which contains flammables. Connecting piping should be disconnected or blanked, or both, in accordance with a definite procedure. Valves should not be relied on for blanking purposes. Blanks of suitable thickness should either be blind flanges or full-face steel plates inserted between gaskets against line flanges. Definite responsibility for their installation and removal should be assigned. When hot work is to be done on equipment which has been purged of gas, connections to the equipment should be removed.
b.
Care should be taken if sludge and scale remain in tanks, vessels, and piping after flushing and washing operations. Such materials often contain flammables and may give off vapors that can be ignited during repairs. Continued ventilation may be necessary.
c.
Before hot repair work is started on equipment which has contained or does still contain flammable liquids or gases, careful plans should be made as to the manner in which the work will be done. In most cases, it is desirable to open and completely gas-free equipment before repairs are made; but there are instances when repairs may proceed after the flammable materi al has been displaced by some inert material such as flue gas or water.
d.
Firefighting facilities should be readily available when repairs are being made. Minor fires may be quickly extinguished when facilities are readily accessible and employees are trained in their quick and effective use.
Good Housekeeping Good housekeeping is an essential part of maintenance. Containers for scrap material and refuse should be provided at convenient locations. Strict adherence should be observed to scheduled emptying of such containers. Oil and grease-soaked rags should be placed only in separate metal containers provided for them.
7.
Vessel Entry a.
Vessel entry refers to entry of any tank, vessel, equipment or other enclosed place where there is a hazard of: (1) a toxic, corrosive, or flammable substances; (2) insufficient oxygen; (3) severe restrictions that would hinder escape or rescue. Vessel entry normally requires specific approval by plant supervision.
b. c.
Vessel entry should include tank gauging, sampling and blowdowns. All vessels should be assumed unsafe for normal entry until the following entry procedures have been followed: 1)
Disconnect and blank off all lines to the vessel.
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d.
8.
2)
Remove all sources of ignition before removing manway covers.
3)
Check all liquid traps and internal lines to assure they are free of hazardous liquid.
4)
Clean the vessel as thoroughly as possible by draining, washing with water, steaming, ventilating or other suitable means. If steam is used, guard against static electricity by grounding the steam nozzle. After steaming, allow the vessel to cool slowly. Sudden cooling with water spray may cause a static electrical charge.
Test the atmosphere for: 1)
Oxygen: Air must contain 20-21% oxygen and the vessel should have adequate ventilation, either forced or natural.
2)
Explosive Mixture: A vessel may not be entered if the testing instrument indicated an air-vapor mixture that exceeds 50% of the lower explosive limit.
3)
Toxic Fumes: The presence of any toxic fumes requires the use of respiratory protective equipment, normally an air supplied mask with hand blower, or a self-contained breathing unit; otherwise, additional cleaning or purging of the vessel is indicated.
e.
Safety Harness or Belts - Either a safety harness or belt should be worn by the person using respiratory equipment when entering the vessel.
f.
Clothing - Personal protective clothing suitable for the job inside the vessel should be worn.
g.
Observer - An observer should be stationed outside the vessel. His only duty should be to watch the person inside the vessel. When respiratory equipment is required for the person entering the vessel, t he observer should also have suitable respiratory equipment available.
h.
Emergency Equipment - Fire extinguishers and other emergency equipment should be available as required.
Electrical Equipment Probably everyone recognizes that high voltages can be very dangerous, but some people fail to realize that so-called "low voltage" can also be very hazardous and under certain conditions can produce fatal injuries. Deaths have been recorded due to contact with circuits of less than 50 volts. Actually, it is not voltage but amperage that kills. Under certain conditions, as little as 1/10 ampere is sufficient to cause death. The following may be used as a guide when working with electrical equipment. a.
Electrical Equipment Repairs When electrical equipment is to be repaired, switches must be opened and tagged. Working on "hot circuits" normally r equires the permission of plant supervision. Refer to detailed plant tag-out pr ocedures before proceeding.
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b.
c.
d.
Grounding 1)
All electrical equipment is to be grounded.
2)
If it is every necessary to move any equipment, the ground should be replaced before the equipment is used.
Conduits, Cables and Wires 1)
Electrical conduits should not be used to support other equipment.
2)
Electrical cables and conduits should not be buried underground except in accordance with engineering standards.
3)
Exposed ends of electric wires must be taped.
4)
Unused and abandoned electric wires must be removed or disconnected at each end.
Fuses 1)
Fuses should be removed and replaced only by authorized personnel.
2)
Fuse tongs and/or rubber electrical gloves should be used and the disconnect should be opened. Note: Rubber glo ves must always be used for vol tages in excess of 150 volts.
3)
Never use coins, metal foil, or other contrivances in lieu of fuses.
4)
e.
f.
Never use fuses of greater capacity than that specified by the equipment manufacturer. Switching 1)
When starting electric motors, handle all switches according to instructions. Make contact so as to prevent arcs. Stand in a safe position.
2)
Never pull a disconnect switch under load except in an emergency.
3)
Always be certain that hands and feet are dry when operating switches or plugging in electrical appliances.
4)
Keep rubber mats in front of switchboards where possible.
5)
Switch panel fronts should be kept closed.
Hand Tools and Portable Equipment 1)
Extension lights without bulb protectors must not be used. Use only low voltage lights with isolating transformers in tanks and similar places.
2)
All extension cords should be of the grounded type. Before each period of use, examine extension cords carefully for any failure of the outer insulation, particularly at terminal points where the cord enters a plug or a
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fixture.
g.
11.
3)
Lights and tools should not be disconnected from an extension cord while the other end of the cord is in a socket or receptacle.
4)
The ground cable with which each tool is equipped should be secured to a suitable ground before the tool is plugged into a source of electricity.
Miscellaneous 1)
Contact with electrical conductors should be avoided whether they are energized or not.
2)
Fenced substation areas should be entered only by authorized personnel.
3)
Faulty electrical equipment must not be used. Report it immediately.
4)
Before changing broken light bulbs, be certain the current is turned off.
5)
No employee should work within 15' of a high voltage power line except by special authorization of plant supervision.
Laboratory Safety a.
b.
Good Housekeeping 1)
Cleanliness and orderliness are absolutely essential to the safe operations of laboratories.
2)
A continuous program should be in effect to prevent the accumulation of rubbish, rags, partly-used samples, dismantled equipment, etc.
Equipment 1)
Inspect all gas hoses for leaks each day that they are used.
2)
Extinguish all gas burners when they are not in use.
3)
Glassware: a)
Discard all cracked, broken or damaged glassware.
b)
Fire-polish all chipped edges on burettes, breakers, graduates, etc.
c)
Avoid thermal shock with all glassware.
d)
Use only glass tubing with fire-polished ends.
e)
Before attempting to insert glass tubing in stopper holes, be certain that the holes are the proper size. Always moisten the stopper hole and the glass tubing with water, and rotate the glass tube as it is inserted pushing it away from the body. When rubber tubing or stoppers stick on glassware, cut them away.
f)
Do not eat or drink out of laboratory glassware.
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c.
d.
Storing and Identifying Chemicals 1)
Adequately label or mark bottles and containers to identify the chemical within.
2)
Keep chemicals stored in their proper place. Solvents should not be brought into laboratory in quantities greater than 5 gallons.
3)
Keep volatile combustible liquids in safety containers and away from direct flames or sources of heat.
Handling Chemicals 1)
When handling acids or caustic materials in quantities, always wear protective clothing and eye protection.
2)
Always pour acids and caustic materials into water, NEVER the reverse.
3)
If acids or caustic materials enter the eye, flush with plenty of water and report immediately for first aid treatment.
4)
Wash hands immediately after handling chemicals bearing poison labels. Wash hands after handling mercury and clean up mercury spills at once.
5)
Dispose of acids or caustic materials in a proper approved manner.
6)
Refer to vendor information and Material Safety Data Sheets for specifics on the safe handling of individual types of chemicals, and first aid steps for accidents involving them.
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SECTION III INSTALLATION AND ASSEMBLY
RECEIPT OF EQUIPMENT 1.
2.
3.
The desalter vessels are to be retrofitted in the field. a.
Two (2) vessels to be converted to EDD type desalters.
b.
Control panels shipped separate for site installation.
c.
Miscellaneous instruments, valves, and accessories shipped boxed for site installation.
Check the equipment on receipt* at site: (*NOTE: We recommend that a NATCO Service Technician be present to assist with the inspection and pre-commissioning.) a.
Confirm that all materials received are in agreement with the packing list and are in good condition.
b.
Check for any shipping damage. Immediately document any damage with a formal report and photographs. Claims for damages should be sent to the freight company.
Transformer and panel handling and storage should be performed with the factory supplied shipping pallet securely attached. Lifting lugs have been provided for the handling of tanks by over-head lift. Slings should be padded to protect painted surfaces. Particular care should be taken to avoid any damage to bushings and insulators. A cool, dry, and protected area should be used for the storage of electrical equipment. The temperature of storage areas containing liquid fi lled power supplies should not exceed 60 C. Electrical Schematics showing the terminal identification markings, are attached to the unit in an envelope. Please consult these schematics for connection instructions.
4.
The equipment should be checked for level and re-levelled if required.
5.
Open all manways, vent, clean, and sandblast vessel interior. (Check to make sure vessel is safe - free from vapors - before entering.)
INSTALLA TION PROCEDURE FOR VESSEL MODIFICATION 1.
Safety a.
If any field piping has been connected, make certain that the vessel is isolated with solid metal blinds. The isolation is necessary to prevent any possibility of dangerous gas or vapors from entering the vessel.
b.
Make certain that all electric power is locked "OFF".
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c.
Open the manways on each end of the vessel. We recommend placing a fan in one of the manways for forced ventilation. Test for breathable air inside the vessel before anyone is allowed to enter.
d.
Place a thermometer inside the vessel to monitor the temperature.
CAUTION:
2.
If the modification is made during the hot season, the temperature inside the vessel may become too hot for safe working conditions. We do not recommend working in the vessel at temperatures of 120 F or above. With hot working conditions, extreme care should be taken to maintain salt intake and avoid dehydration or heat stroke.
e.
At least two (2) people should be working together at all times. One (1) person who is certified for confined space operations should r emain out of the vessel.
f.
All relevant drawings shall be distributed to persons who are working on the modification work. Everyone involved should understand his responsibility and work content in addition to the modification time schedule. The drawings shall be referred to the drawing lists for mechanical assembly and transformers.
Installation of External Attachments and Supports Following procedure may be taken by the Client f or installation of internal piping part s and supports prior to installing electrode plates and channel rails. Transformer installation should be done according to the separate tr ansformer instructions. Exact steps and priority of the work should be determined by the Client. Following order is only for reference.
a.
Clean internal surface of the vessel.
b.
Make certain that all of the nozzle openings in the bottom of the vessel are covered to prevent entrance of nuts, bolts or debris.
c.
Remove insulation cover and materials at proposed locations for new nozzles.
d.
Make cutting lines on vessel surface.
e.
Remove or cut existing items as follows: 1) 2) 3) 4) 5)
Pipe inlet spreaders (remove) Pipes of trycocks (remove) Supports and lugs for electrode (cut/remove) Stilling well for level transmitter (remove) Supports for transformers (cut/remove)
f.
Clean internal surface again. If necessary, use handtools or sandblasting for cleaning.
g.
Cut vessel shell by gas arc cutter and smooth the cut surface by grinders. 1) 2)
6 nozzles for 6" entrance bushings 2 nozzles for 2" level transmitters
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3)
2 nozzles for 4" sludge drains
h.
Provide scaffolding or temporary steps in the vessel from one end to the other end.
i.
Attach following parts: Priority of hook-up and installation of parts should be determined by the Client and his subcontractors. 1) 2) 3) 4) 5) 6)
j.
Platforms and supports for transformers Lugs for electrode hangers Lugs for support angles Support angles for water injection headers Brackets for float switches Support angles for sludge drain headers
Following mechanical parts will be assembled prior to electrode assembly 1) 2) 3) 4) 5) 6) 7)
Sludge drain pipes Distribution header pipes Emulsion spreader housings Water injection header pipe Water injection lateral pipes Insulation hangers Channel rails with splicers
The steps from Item 6) above are referred to in detail on the drawings. 3.
Electrode Internals for EDD Desalter Vessels a.
Refer to NATCO Drawings D-92576 and D-28659 and B-90888 to B-90890.
b.
Inspect the internals for shipping damage. Identify the parts and materials according to drawings and check if their quantities are correct.
c.
Make certain that all of the nozzle openings in the bottom of the vessel are covered to prevent entrance of nuts, bolts, or debris.
d.
Carefully install the Teflon® insulators (Item 4) to electrode hangers inside the vessel.
e.
Lay out the four (4) channel rails (Item 1) and fasten the grid supporting strap (Item 2) to the channels as shown on drawing using the 3/8" channel studs and nuts (Items 5 and 7) making sure t hat they are 10" (254mm) apart on each rail and are staggered on 5" (127mm) centers. NOTE: The rail sections are spliced together with a 1" wide x 3mm thick flat bar about 150mm long. Check to be sure that splice bars have remained bolted in place.
f.
Install the channel (Item 1) on the Teflon insulator hangers (Item 4) using nuts, washers, and C-rail clamps (Item 3) provided with hangers. Check for true level. Make sure all hangers are free of any stress or binding. Check end clearance of the channels to allow minimum 6" (152mm) from vessel head. Adjust the level if necessary by raising or lowering the rail and C-rail clamps on the hangers (It ems 1 and 3).
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g.
Install the two (2) 8" OD float balls onto the float switch. Refer to the float switch assembly detail on Drawing No. [D-92577]. The float balls were shipped with the entrance bushings, adaptor flanges and other fittings for the transformer installation.
h.
Install the FRP electrode plates onto the support straps in accordance with the details on the drawing and the f ollowing instructions: 1) 2)
3) 4)
5)
6)
7)
8)
9)
Work from one end of the vessel toward the other end. Lay out electrode plates "A", "B", "C", "D", "E", "F", "G", and "H" into separate stacks. NOTE: The plates are fabricated from Fiber Reinforced Plastic (FRP). Care should be taken to avoid damage to the plates. The Type "C", "D", "E", "F", "G", and "H" plates are shorter for extending the electrode into the vessel head. Each vessel has three (3) type "A/B", "C/D", "E/F" and "G/H" plates. Note that the crimp and black strip on each plate will be all installed facing the same direction. Start with plate "H" (the shortest). Refer to the electrode plate assembly detail (Drawing No. [D-92577]) and hang the plate from the support strap. The support strap forms a clamp that attaches to the top ridge of the plate. The plate must be centered in the vessel. Refer to the "Electrode Plate Voltage Tie-Rod" detail (Drawing No. [D92577]). Each plate has one (1) 8" ID hole and 1/4" hole located 12" (304.8mm) from the center of the plate. The 1/4" hole is drilled through the conductive strip on the plate. Insert the 1/4" bolt (Item 14) through this hole in plate "H". Make sure that the "star" washer is located against the conductive strip. Install the steel "voltage tie-rod" (Item 13) on the 1/4" bolt. Slip the Teflon sleeve over the tie rod. Hang plate "G" on the next set of support straps. Note that plate "G" does not attach to the same rails as plate "H". Plate "G" and plate "H" will be 5" (127mm) apart center-to-center. A wooden block may be cut to 4-15/16" (154.4mm) to use as a gauge for setting the distance between plates. Adjust the location of the support straps as required to maintain the correct centers. Note that the 6" hole in plate "G" fits over the "tie rod" installed on plate "H". Insert the 1/4" bolt through the small hole in plate "G" for the next "tie rod". Make sure that the 1/4" star washer is located against the conductive strip. Install the steel "voltage tie-rod" (Item 13) on the 1/4" bolt. Slip the Teflon sleeve over the tie-rod. Install the 1/4" all-thread stud (Item 14) into the end of the tie-rod. NOTE: The tie-rod on plate "H" should be in the center of the 6" hole in plate "G". Hang plate "F" on the next set of support straps. Plate "F" will be attached to the same rails (Item 1) as plate "H". Confirm the 5" (127mm) center-tocenter spacing between the plates using the wood block gauge. Adjust the support straps as required. Note that the tie-rod from plate "H" will connect to plate "F". Install the star washer against the conductive strip. Install the 1/4" bolt with contact strip on the end of the tie-rod which is fixed on the "H" plate. Screw the previous tie-rod assembly with contact strap (Items 13, 14 and 17) onto the back of plate "F". Note that the tie-rod on plate "G" should be in the center of the 6" hole in plate "F". Provide next tie-rod on plate "F". Hang electrode plate "E" on the next set of support straps. Plate "E" will be attached to the same rails as plate "G". Confirm the 5" (127mm) center-to-
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10)
11)
12)
13)
i.
center spacing. Note that the tie-rod on plate "G" connects to plate "E" with contact strip. Install the star washer against the conductive strip. Screw the previous tie-rod assembly onto the back of plate "E". Note that the tierod in plate "F" should be in the center of the 6" hole in plate "E". Refer to the "electrode plate end spacer" detail. Install the end spacer assembly (Items 14, 15, and 16) at the ends of plate "E". The spacer rod assembly is similar to the tie-r ods, except the spacers are made from FRP. Hang electrode plate "D" on the next set of support straps. Plate "D" will be attached to the same set of rails as plate "F". Check the spacing and note the tie-rod on plate "F" connects to plate "D". Install the star washer against the conductive strip and screw the next tie-r od assembly on the back of plate "D". Note that the tie-rod in plate "E" should be in the center of the 6" hole in plate "D". Install the end spacers at the end of plate "D". The distance between the end of plate "E" or "D" and the vessel shell should be the same on each end. Make a wood block gauge to check as each plate is hung in operation. Hang plate "C" on the next set of support straps. Plate "C" will be attached to the same rails (Item 1) as plate "E". Confirm the 5" (127mm) center-tocenter spacing between the plates using the wood block gauge. Adjust the support straps as required. Note that the tie-rod from plate "E" will connect to plate "C". Install the star washer against the conductive strip. Screw the next tie-rod assembly with contact strap onto the back of plate "C" with contact strap. Note that the tie-rod on plate "D" should be in the center of the 6" hole in plate "C".
Continue to install electrode plates alternating between plate "C" and "D". Remember that the tie-rods and spacers must be installed as each plate is hung. 1)
2)
3)
4)
Hang electrode plate "A" on the next set of support straps. Plate "A" will be attached to the same rails as plate "D". Confirm the 5" (127mm) center-tocenter spacing. Note that the tie-rod on plate "D" connects to plate "A". Install the star washer against the conductive strip. Screw the next tie-rod assembly onto the back of plate "A" with contact strip. Note that the tie-rod in plate "C" should be in the center of the 6" hole in plate "A". Refer to the "electrode plate end spacer" detail. Install the end spacer assembly at the ends of plate "A". The spacer rod assembly is similar to the tie-rods, except the spacers are made fr om FRP. Hang electrode plate "B" on the next set of support straps. Plate "B" will be attached to the same set of rails as plate "C". Check the spacing and note the tie-rod on plate "C" connects to plate "B". Install the star washer against the conductive strip and screw the next tie-r od assembly on the back of plate "B" with contact strap. Note that the tie-rod in plate "A" should be in the center of the 6" hole in plate "B". Install the end spacers at the end of plate "B". The distance between the end of plate "A" or "B" and the vessel shell should be the same on each end. Make a wood block gauge to check as each plate is hung in position.
j.
Continue to install electrode plates alternating between plate "A" and "B". Remember that the tie-rods and spacers must be installed as each plate is hung.
k.
When the installation of plates reaches the position in the vessel where the contact rods are installed: 1)
Note that the "contact rods" are each supported by two (2) plates and that
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2)
3)
l.
the contact rod assembly must be installed at the same time as the plates. One contact rod must be mounted on t wo (2) "A" plates and the other on two (2) "B" plates. The contact rods should be positioned as shown on the "side view" detail in Drawing No. D-92577 - 2/2. A deviation in the spacing of the plates from that shown from drawing will cause a deviation in the contact rod location. Some deviation (±1") is acceptable). An extension rod must be added to the top of the contact rod assembly in the "EDD" vessels. These extensions are shipped with the transformer hook-up fittings. Thread a 1/2" nut onto the contact rod and then screw on the extension. Tighten the 1/2" nut up against the extension to lock it in place. Check to be sure that the float switch makes contact with the rod extension.
After the contact rods have been installed, connect the entrance bushing to the contact rod as shown on Drawing D-92580. There must be enough cable inside the vessel to allow removal of the entrance bushing from outside the vessel. If necessary, extra cable may be loosely coiled around the contact rod. (Prior to attaching to entrance bushings.)
CAUTION:
Be certain that the cable between the entrance bushing and contact rod does not come near (within 6") of other metal parts. The system will not work if the cable is shorted t o ground or to the opposite electrode.
m.
Complete the electrode installation.
n.
Carefully clean all debris from inside the vessel and remove covers from nozzle openings in the bottom of the vessel.
o.
Replace the manway covers and do not allow entry until pre-commissioning activities start. Refer to the operation manual.
NOTE: We recommend that a NATCO specialist inspect and certify the electrode and transformer installation prior to commissioning.
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SECTION IV PRE-COMMISSIONING PRE-COMMISSIONING CHECKLIST 1.
Commissioning team and operators have read and are thoroughly familiar with the instruction manual.
2.
Equipment was inspected on receipt and checked against packing lists and all damage was documented and reported.
3.
Equipment is set level.
4.
Foundation bolts installed.
5.
Internal bolts are tight.
6.
Shipping supports/packing removed.
7.
Ladder, platform, handrails installed.
8.
All pipe spools and accessories are installed in accordance with the P&I and assembly drawings.
9.
The pneumatic hookup has been checked.
10.
Electrical wiring has been checked.
11.
Vessels, skid, and instrumentation are properly grounded.
12.
All piping and accessories have been checked for tightness.
13.
Customer field piping has been connected.
14.
Temporary strainers have been installed.
15.
Instrument air supply has been hooked up and regulators adjusted.
16.
Control panel installed.
17.
Field wiring checked.
18.
Control panel operation verified.
19.
LRC installed and operation verified.
20.
Chemical tank is clean and pump hooked up.
21.
Transformer and grid system check-out completed.
22.
Internal dilution water headers flushed on EDD units.
23.
Vendor literature in mechanical catalog has been reviewed and all instructions for precommissioning or adjusting valves and accessories have been followed.
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24.
Hydrotest/leak test completed.
25.
Sample lines and sample coolers checked.
26.
Chemical suppliers ready to run plant tests.
INSPECTION PROCEDURE FOR INTERNAL ASSEMBLY 1.
List of Items for Internal Installation a.
Check the voltage tie-rod installation. These are the metal rods near the center of the plates. 1) 2) 3) 4)
5)
2.
Make sure that the tie rods contact the graphite strip. Make sure that the contact strip is installed on every plate. Make sure that the tie rod is within 1-1/2" of the center of the holes where they pass through the alternating plates. Make sure that the Teflon sleeve that covers the steel tie rod is cut about 1/8" shorter than the tie rod. If the Teflon sleeve is too long, it will prevent the tie rod from making good contact to the conductive strip. Make sure that the "tie rods" are the Teflon sleeved steel rods and not the fiberglass rods that are used at the ends of the plates.
b.
Check the fiberglass electrode plate end spacers to be sure that none have separated and to be sure that fiberglass r ods were used and not the metal r ods that are to be used as tie rods.
c.
Check the electrode plate spacing. After the installation is complete, the spacing of the electrodes should be 5" (127mm) plus or minus 1/2" (12.7mm). This spacing should be maintained along the length of the plate at the top and the bottom. Check the spacing between the ends of the plates and the vessel shell to be sure it is not less than 4-1/2" (114mm).
d.
Check to be sure that the electrodes are all facing the same direction. The crimps should all face the same direction.
e.
The bottom of the plates should be located 8" (203mm) above the center line of the vessel (±1" or 25.4mm).
f.
Be sure that there are no cracked or broken plates.
g.
Check the installation of the contact rods. One contact rod should be attached to the "A" set of plates and one contact rod should be attached to the "B" set of plates. The voltage tie rod must attach to the contact rod assembly.
h.
Check the float switch assembly and clearance between the float switch and contact rod. Be sure that the float moves freely and nothing will cause the float to "hang up" in the vessel. When the float is in the UP position, there must be at least 5" (127mm) clearance to the contact rod.
i.
Clean and inspect the Teflon insulator hangers. These should be wiped with a clean, soft cloth dampened with clean kerosene.
List of Items for Electrical Connection
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3.
a.
Check the cable connection between the bottom of the entrance bushing and the contact rod. The connections must be tight and the cable must have at least 6" (152 mm) clearance to any ground or oppositely charged parts. Be sure that the cable weight has been installed and that the entr ance bushing can be removed without going inside the vessel.
b.
Disconnect the bushings inside the diode box on the transformer. Make sure that the wires are not near a ground then megger test the electrode assembly. Megger test between electrode set "A" and "B" and between "A" and ground and "B" and ground. This must be done with the floats up.
c.
Check to be sure that there is continuity through the length of the tie rods and from each tie rod to the conductive strip on the plates. Hook the megger at one end of the vessel and check the opposite end to be sure t he voltage is conducted the full length.
d.
Check to be sure that air is vented out of the top of the bushing housing.
e.
Clean and inspect the Teflon parts of the entrance bushings. These should be wiped with a soft, clean cloth dampened with clean kerosene.
f.
Perform the electrical checks on the transformer and diode box as listed in the procedure. These checks should be done at maximum available voltage. Lower voltages may result in not finding some high voltage breakdown points.
g.
Conduct megger checks from the ends of the electrode plate tie rods to the top of the entrance bushing to confirm that the cables, saddles, and tie rods have continuity.
Others a.
When all the other checks are complete, clean the screen in the strainer on the dilution water supply line and flush the overhead water header. Go inside the vessel with the water spray on and visually check to see that all of the small holes are clear.
PNEUMATIC CHECK-OUT PROCEDURE 1.
Turn on instrument air supply to the desalter skid. Maximum air pressure at skid edge should be 100 psig and a minimum of 50 psig.
2.
Blow down the instrument air header and piping to remove any dirt and scale.
3.
Refer to the "Mechanical Catalog" or "Vendor Equipment Booklet" and follow the detailed instructions for each pneumatic instrument and control valve.
4.
Adjust the instrument air regulators to set the supply pressure for each instrument.
5.
Check all connections and fittings for leaks by soap bubble test.
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6.
Stroke all valves from full open to full close several times to confirm functional operation.
ELECTRICAL INSTRUMENTATION CHECK-OUT PROCEDURE 1.
Hook up field wiring to junction boxes on the desalter skids and to the LRC. (Refer to drawings included in this manual.)
2.
Make continuity checks on all field wiring. (Refer to "BB" above.)
3.
Refer to the "Mechanical Catalog" and follow the detailed vendor instructions for each instrument.
4.
Turn on 24 VDC and 110 volt instrument power supply to desalter skids and functionally check each instrument for correct operation.
HIGH VOLTAGE ELECTRICAL SYSTEM CHECK-OUT PROCEDURE 1.
Before connecting line power, be sure all cables and wiring are installed and connected. The circuit breaker should be padlocked in the OFF position.
2.
Transformer, LRC, and vessel are grounded.
3.
Make sure electrodes are free hanging and no loose materials ground them to the vessel interior or to each other.
4.
Study the LRC manual and drawings (Appendix A).
5.
With the local disconnect at the transformer locked "OFF", load in the required operating parameters into the controller and perform the necessary calibrations as instructed in by the LRC manual.
6.
Using the following procedure, complete all steps of the electrode electrical check: Step #1 a.
Set the LRC to "manual mode" and with "secondary KV" displayed.
Step #2 a.
Make certain there are NO explosive gases in or around vessel.
b.
Make certain the disconnect is in the OFF position.
c.
Using wiring harness provided in the packing box, jumper across diode pack to effectively short it out. Refer to Sketch 1.
d.
Tie or block both level float switches in the UP position. Make sure there is no contact with the charged electrode or the upright connector rods.
e.
Make certain NO ONE is in or on the vessel,
f.
Close the circuit and following the instructions for the LRC in the manual mode, gradually increase the secondary voltage up to 20 KV.
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g.
Check the primary amperage. Amperage should be between 0-2 amps.
Step #3 a.
Open the circuit breaker and padlock it in the OFF position.
b.
Go back inside the vessel and release the float switches so that they contact the vertical high voltage connecting rods. Make sure each float is resting fully on the rod, remove the material previously used to tie the floats in the up position from the vessel interior.
c.
Make one more internal inspection to be sure the float switch is free to swing upward with fluid rise.
d.
Leave the vessel and make certain no one is in or on the unit.
f.
Close and bolt all vessel access manways.
g.
The circuit breaker MUST remain in the OPEN or OFF position from now until the electrodes are covered with oil.
h.
Remove the jumper wires from the high voltage diodes and replace original wiring before closing the junction box.
i.
The unit is now electrically prepared for start-up.
FLUSHING OF INTERNAL DILUTION WATER HEADERS FOR EDD UNITS There are many small holes in the internal distribution header and if they become plugged, t he efficiency of the operation will be reduced. Any dirt or grit that might have entered the dilution water piping must be flushed out before startup. 1.
Supply dilution water or other clean water through connection "4N" on the "EDD" assembly. A temporary strainer should be installed in the piping at skid edge.
2.
Go inside the vessel and remove the plug from the end of one of the distribution laterals.
3.
Start water flow at approximately 30 gpm and allow to run about five (5) minutes. Replace the plug in the end of the tube and repeat the process for each of the remaining laterals.
4.
During the flushing process, check to be sure that water is spraying from each of the small holes. If necessary, use a small wire to unplug any hole.
HYDROTEST AND LEA K TEST Both vessels and piping will require hydrotesting at the completion of modifications. These instructions were written with reference to assembly drawings and flow diagrams. The procedure is for one (1) train. Both trains are identical in operation and start-up procedure.
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Hydrotest water should be clean, potable, deoxygenated, with a corrosion i nhibitor. 1.
The customer must determine the extent of vessels and piping that will be hydrotested together. All of the components must be rated for the test pressure. It is recommended that the entrance bushings should be replaced with blind flanges during hydrotest.
2.
Isolate any component that may be damaged by exposure to water or the designated test pressure. Do not test demulsifier chemical lines with water.
3.
Isolate the vessels and piping to be tested by closing appropriate block valves or by using blinds.
4.
Close all vent, drain, purge and sample valves on the piping, vessels, and instruments.
5.
Make sure that all block valves, control valves, and bypass valves in the piping to be tested are open.
6.
Open isolation valves on relief valves, level switches, level transmitter, and level gauge. Close isolation valves on pressure gauges.
7.
Open high point vent valve(s) as necessary and begin to slowly fill the system with water. The vent valves on the top of the oil outlet piping from the first and second-stage desalters should be opened along with others depending on the extent of piping and equipment to be tested.
8.
Slowly fill the system until water begins to overflow the vents. Close the vent valves as each section or vessel is filled.
9.
When the system is full and before starting to increase the pressure, check the system to be sure that pockets of air have been eliminated. Open vent valves on level switches, level transmitters, and level gauges to vent trapped air. Open the drain valves under the safety relief valves. Open sample valves on vessels and piping.
10.
The system can now be slowly pressured up to the test pressure.
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SECTION V PROCESS DESCRIPTION DESIGN CONDITIONS Specified Crude Feedstock Maximum Crude Throughput (bpd-each) Crude Specific Gravity (60 C, 15.6 C) + /-0.015 Maximum Feed BS&W (%) Feed Salt Content - See "Guaranteed Performance" Maximum Viscosity (Cst) + /-15% @ 30 C @ 70 C Operating Temperature ( C) Operating Pressure (kg/cm2g) + /-1 Maximum Required Dilution Water (bpd)
Feed 1 50,000 0.8990 0.075
Feed 2 50,000 0.8866 0.05
500 50 135-145 11 3000
30 8.0 130-145 11 3000
0.3
0.2
** ** ** **
** **
0.2
0.15
** ** ** **
** **
Minimum Performance BS&W (%) in Product Salt (PTB NaCl) in Product @ Second Stage Outlet Feed Salt Content @ Second Stage Inlet 1.5 PTB NaCl 4 PTB NaCl 7 PTB NaCl 12 PTB NaCl Estimated Performance BS&W (%) in Product Salt (PTB NaCl) in Product @ Second Stage Feed Salt Content @ Second Stage Inlet 1.5 PTB NaCl 4 PTB NaCl 7 PTB NaCl 12 PTB NaCl
GENERAL DESCRIPTION Refer to drawing J9210140. This two-stage desalting process consists of two (2) consecutive steps of dilution and dehydration. The brine from the system as a whole is discharged from an existing AC first-stage desalter to disposal. The brine from the second-stage desalters is pumped through a recirculation loop and injected into both the incoming crude, ahead of the first- stage desalter heaters, and into the second stage feed. Fresh dilution water may be injected either or both of two places for each second-stage desalter. Part of the dilution water may be injected into the crude stream after the fi rst dehydration step, prior to entering the second-stage desalter vessels. The second "overhead" dilution water stream is injected inside the second-stage desalters through a connection in the top of the vessels.
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The heated crude is pumped to the inlet piping of the first-stage desalter where it is combined with the recycled brine. The dehydrated crude leaving the first stage desalter is split into two streams under flow control, and fed to each second-stage desalter through a manual mixing valve prior to entry into each desalter. The mixing valves serve to bring the dilution water into contact with the finely dispersed, highly concentrated salt water in the crude oil. The fluid stream enters each second-stage desalter near the bottom of the vessel. The stream is routed through inverted-trough metered orifice distributors which extend the entire length of the desalter for uniform distribution of the crude to the coalescing area. The trough type distributors are of open bottom design and water sealed t o force the oil upwards and at the same time allow free fall of the large water particles to the water section of each vessel. The water level in the desalter is controlled by a float-operated, oil-water interface controller. This control is an electric, proportional device which sends a 4-20 milliamp signal to the customer's control panel, which in turn directs a corresponding pneumatic signal to a diaphragm-operated water discharge valve. The oil rises into the electrode area where the remaining water particles are electrically coalesced from the oil. The coalesced water falls to the bottom of the desalter where it is discharged as previously described. The oil rises into the EDD electrode area where the overhead dilution water is electrically mixed and then coalesced from the oil. The coalesced water falls to the bottom of the desalter where it is discharged as previously described. The dehydrated oil then exits at the t op of the vessel through two (2) outlet connections and is combined into a single outlet header. The total dilution water injection rate is metered and controlled by a diaphragm operated valve. The overhead dilution water injection rate is controlled by a flow control valve. The internal design of the second-stage desalters is shown on: 1)
Drawings D-92576/77/78/79 and 80 (for VE-1A)
2)
Drawings D-92585/86/87 and 88 (for VE-1B). At this point in the system, the crude oil has been dehydrated.
CHEMICAL TESTING A ND SELECTION Chemical testing, selection, or supply is beyond NATCO's scope of supply. This section is included only for Customer information. Preliminary selection of demulsifier chemical is a necessary part of the pre-commissioning process. Selection of the proper demulsifier is much different than selection or specification of other commodities that may be used in the operation or maintenance of equipment. The selection/specification of a demulsifier is complicated because the chemical is a blend of two, three, or more base compounds out of a possible selection from hundreds of compounds. The oil/water solubility of each base compound may be quite different and two or more solvents may be required in the formulation in order to maintain a stable solution. A chemist must consider
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many factors in preparing a formulation including solubilities, pour points, and volatility. The selection process begins by requesting several (at least three) reputable chemical suppliers to send a representative to visit each plant site to become familiar wi th the process and equipment and to run preliminary "bottle tests". Bottle tests on a fresh representative sample of the production to be treated constitute a fair ly reliable method for chemical suppliers to screen possible formulations. Bottle tests on aged samples may be very unreliable and give misleading results. If the chemical supplier has experience in the same field and formation with similar production equipment and methods, the bottle testing may not be required. Each supplier should be able to propose one or t wo demulsifier formulations based on his preliminary work. The chemist will select the base compounds and make a formulation to fit a specific application. Each oil field, each formation i n the field, each location, and sometimes each well, will produce an emulsion with characteristics that are different from any others. The variations in the emulsions are due to the chemical and physical characteristics of the crude oil and water including: 1.
Chemical composition (the amount of paraffins, asphaltenes, and natural surfactants have a great effect on the emulsion).
2.
Amount and type of solids produced.
3. 4.
Oil gravity. Water gravity (salt content and composition).
5.
Amount of gas.
6.
Production temperature/pressure.
Other factors affecting the emulsion and chemical selection include: 1.
Method of production (flowing wells, surface pump, downhole pump, water flood, chemical flood, steam flood, fire flood, etc.).
2.
Pressure drops.
3.
Length of flow lines.
4.
Retention time in vessels or tanks (age of emulsion).
5.
Other chemicals (water and corrosion).
6.
Type of pumps.
For refinery applications, other factors which enter into chemical selection include the following: 1.
The variation of the expected crude oil slate. Chemicals must often perform over the total range of oil types to be processed.
2.
The length of each crude oil run. Short runs will make chemical changes between oils impractical.
3.
Conditions of storage in the tank farm. If tanks tend to stratify before processing, wide swings in suspended solids may be experienced as the tank is drawn down.
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4.
Slop oil recycle. The quantity and type of slop oil recycled can have a great influence on the influx of suspended solids, stable emulsion, and precipitated hydrocarbons.
5.
Compatibility of the oils being processed. Incompatible oils can result in the precipitation of asphaltenes and other semi-soluble hydrocarbon fractions.
Final demulsifier selection should be based on competitive full scale plant tests. The "optimum" demulsifier should allow the process to meet the required product specifications at the lowest total operating costs. Total operating costs include chemical, fuel, maintenance, and plant upsets. The cheapest chemical may not always be "optimum" when all factors are considered. Other considerations include condition of oil and water inter faces, buildup of interface sludge, water quality, and availability of qualified service personnel.
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SECTION VI START-UP PROCEDURES The desalting system is a two-stage process consisting of one single first stage desalter and two smaller parallel second stage desalters. The first stage desalter is outside the scope of this instruction. It should be started using the procedures supplied by the original supplier, and which have been followed in the past. This instruction is concerned with start-up of the second stage desalters. The two second stage units can operate independently of each other. Therefore it is not necessary to start each of them simultaneously; it is acceptable to start one completely, then start the other. However, it is recommended that each step of start-up be completed for both units before proceeding to the next step, and in that way, that both units be brought on-stream approximately together.
FILL Before steady state flow can be established, it is necessary to fill the desalter vessels with water (to the interface level) and oil. According to the start-up master plan the vessels (and entire piping system) will be empty at the beginning of the fill process. With all water discharge and drain valves closed, open block valves in desalter feed line allowing oil to fill vessel. Open block valves in desalter discharge line. The vessels must be filled with oil to displace all air before any electrical power is turned on to the electrodes and flow proven.
In an alternate plan if the desalters begin the filling process full of hydrotest water, the water must be displaced with oil. As oil is fed to the desalter at a slow rate, the water outlet valves are opened allowing water to discharge. Open the by-pass around the pump, and the by-pass around the control valve CV-L102 or CV-L103. The water should be routed to the "Pump out" drain. The drains can also be opened to speed up the water discharge rate, then closed before the oil-water interface reaches the desired control level. As the level approaches the control point, close the bypass around the control valve, and put the control valve and level control loop into operation. (Refer to instructions for the individual components.) When the vessel is full of oil above the interface, open the vents to bleed air from the high points of the vessel such as entrance bushing connections.
ESTABL ISH CRUDE OIL FLOW 1.
With the desalters full of oil the feedstock charge rate may be set at the full design rate. After establishing satisfactory operation, adjust the Flow Control Valves CV-F101 and 102 as required to balance the flow to each of the two second stage desalters. Each vessel should have a flow of 50,000 bpd of raw feedstock (at standard conditions).
2.
Start the injection system for chemical additives. The dosages should be those determined during chemical testing.
ESTABLISH PRESSURE CONTROL Establish a back pressure on the desalters by adjusting Pressure Controller s IC-P101 and 102. The pressure should be between 10 and 12 kg/cm 2 to avoid vaporization of any components of
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the crude.
ESTABL ISH TEMPERATURE CONTROL Establish a steady operating temperature for the feedstock of between 130 and 145oC for Arabian oil, and between 135 and 145 oC for the Chinese oil.
START ELECTROSTATIC SYSTEM OPERATION 1.
Observe flow to ensure steady rate. Observe pressures and temperatures for operation within the recommended limits. The electrostatic system can be energized whenever the operating temperature is above 90 oC. Ensure chemical injection is functioning properly.
2.
Using the procedures given in the Load Responsive Controller (LRC) operating instructions, program the controller for operation in the manual mode. Install the following starting set points into the LRC: For Feed #1 Crude:
For Feed #2 Crude:
Settle Voltage (KV) 12 Mix Voltage (KV) Settle Time (Sec) Disperse Time (Sec) 1 Mix Time (Sec) 5 Coalesce Time (Sec) 5 Settle Voltage (KV) 20 Mix Voltage (KV) Settle Time (Sec) Disperse Time (Sec) 0.7 Mix Time (Sec) 1 Coalesce Time (Sec) 0.7
20 1
20 0.7
3.
Ensure power is turned on at main swithgear (main breakers, contactors, etc.)
4.
Energize the desalter electrodes by pushing the LRC "ON" switch. Calibrate the screen values for voltage and amperage feedback. Operate the transformer for 8 hours at the above settings.
5.
At the end of the 8 hours, begin a series of incremental increases in the Mix Voltage setting, increasing 5 KV each hour until the Mix Voltage reaches 35 KV, or until the voltage is limited by high current.
ESTABL ISH OIL/WATER INTERFACE With the electrical system operating, water can be introduced into the vessel to create a water layer and establish an oil/water interface. This water should be added through the desalter internal (overhead) water injection line. As the interface level rises to the desired level, open the water discharge block valves and the block valve in the bypass around the recycle pumps, and put the interface level control system into operation by adjusting IC-L102/103 until control valves CVL102/103 are throttling the water outlet stream and the interface is stabilized. The design normal interface level is 826mm (32.5") below the vessel centerline.
START THE DILUTION AND RECYCLE PROCESS
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The dilution water can be injected into the second stage desalters at two different points. The first is the overhead dilution injection, the second is injection into the feed line ahead of the mixing valve and/or preheat train for a single or first stage desalter. Dilution can be accomplished through either of these points, or through both at the same time. Thus second stage dilution is possible in the following ways: 1. 2. 3.
Overhead dilution directly into the second stage desalter vessel. Injection of wash water into second stage feed stream, ahead of mixing valve. Both overhead injection plus second stage feed stream injection.
Effluent water from the second stage desalters can be routed in three directions. First, it can be discharged for disposal. Second, it can be recycled back to the feed of the first stage desalter (inter-stage recycle). One or the other of these options will be required, and both options require that discharge be made under interface level control from the second stage desalter. A third option for the second stage effluent water, used in combination with one of the other two, is to recycle it back to the feed of the second stage (internal recycle). Thus the following combinations are possible for the second stage effluent water: A. B. C. D.
Second stage water discharge to disposal. Inter-stage recycle of second stage effluent water. Second stage discharge to disposal plus a portion internally recycled. Inter-stage recycle plus a portion internally recycled.
In all cases the water from the first stage desalter will have to be discharged to disposal. Any of wash water options 1, 2 or 3 can be combined with any of the effluent options A, B, C or D as desired. These variations give great flexibility for meeting a wide variation of conditions and needs. Generally the most efficient use of available dilution water is expected using option 1 in combination with option D. Start-up is initiated with option 1 and option A, using the following steps: 1.
When the desalter is stabilized in crude flow, pressure, and temperature, the dilution process may be initiated. Ensure that wash water heaters are operating, and that any necessary chemical additives to the wash water are supplied, and injectors working.
2.
With fresh water pumps running, open valves to allow fresh water to overhead injection line only. Adjust overhead fresh water flow controller such that the control valve throttles the flow to about 1000 bpd (6.6 m3/hr).
3.
Close the block valve in the pump discharge line upstream of the level control valve. Open the block valves in the pump suction and the main recycle lines. Start water discharge pump. Make any necessary adjustments to the interface control settings.
4.
If not already operating, put the first stage desalter into operation at this time.
5.
Open the internal recycle line and adjust the flow control valve to obtain a flow of about 1500 bpd (9.9 m 3/hr). The mixing valve should be wide open to start with.
Once these steps have been completed, the basic systems of the desalters have been started. Yet without optimization good desalting is unlikely, so now with all systems operating i n a stable manner, proceed to that phase of the start -up.
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OPTIMIZE PROCESS This step in the start-up involves adjusting operating parameters so as to obtain the most efficient operation for the feedstock being processed. When feedstocks are changed, the parameters may have to be altered for optimum performance. Optimization begins with certain initial settings, then empirically tests each setting for its effect on performance. After a change is made, sufficient time must be allowed for the effects of the change to come to steady state. This usually requires at least 2-3 theoretical exchanges of oil downstream of the point of application of the change for oil phase equilibrium t o be reached. Water phase equilibrium will require an even longer time. The desalter should be operating at full flow capacity to minimize fluid displacement time. Performance with each changed variable is tested by measuring the inlet and outlet salt contents and BS&Ws. When the optimum settings are found for all parameters, they are recorded for future reference when processing that feedstock. Use the following procedure for optimization: Optimization of Electrical Parameters 1.
The first variables to be tested are the settings of the Load Responsive Controller (LRC). Initial settings are as given in a previous section. Take samples of the second stage desalter feed and oil outlet, and measure for salt content and, in the outlet, BS&W.
2.
Variables for adjustment in the LRC include: SETTLE VOLTAGE MIX VOLTAGE SETTLE TIME (duration of settling segment of the cycle) DISPERSE TIME MIX TIME COALESCE TIME Generally, higher MIX VOLTAGE and longer MIX TIME results in better contact of the salt by the dilution water; and lower SETTLE VOLTAGE and longer COALESCE and SETTLE TIMES result in better water removal. There are limits to how high and how low to go, determined by the oil itself. For example a very high MIX VOLTAGE may mix so hard that it creates a dispersion of the dilution water which cannot be removed in the subsequent dehydration. Or high MIX VOLTAGE may cause short circuiting, and therefore require lower voltage for operation. This is often typical of very conductive oils. There is a limit to how low to set the SETTLE VOLTAGE also. Usually voltages below about 10 KV are less effective at coalescing dispersed water droplets in crude oil. The durations of each of the four segments of the modulation cycle depend on properties of the oil. Generally lighter oils desalt best with short cycle times of 2-3 seconds, while more viscous oils typically need a longer period of up to 10-12 seconds.
3.
Study the salt and BS&W figures from the first set of samples to determine whether to increase or decrease either the MIX VOLTAGE or the SETTLE VOLTAGE, or to change the time settings. While generalities such as those given above are helpful, this is basically a "trial and error" procedure. At full crude flow rate changes made to the LRC should reach oil phase equilibrium after about 20-25 minutes. Only change one parameter at a time in order to best discern the effect of each.
4.
"Optimum" performance may, in fact, be a compromise between those conditions which produce lowest salt, and those which produce lowest BS&W. The two subprocesses which make up the desalting process, mixing and dehydration, may not optimize at the same conditions. It will then be necessary to make a decision about the best operating
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conditions. Record the optimum values for LRC operation. Optimization of Mixing Valve 5.
For initial setting, adjust the manual mixing valve such that the pressure drop through the valve is 15 psi. This should produce satisfactory (but not optimum) desalting performance. To optimize the mixing valve may require more attention than is available during start -up. When time permits, the mixing process can be optimized using the following procedure. Check the outlet crude BS&W and salt content. Adjust the mixing valve to increase the pressure drop across the mixing valve by 5 psi over the initial 15 psi setting. After an interval 30-45 minutes of operation at the new condition again check BS&W and salt. If an improvement was observed, increase pressure drop by an additional 5 psi, and check. Now reduce the pressure drop to 5 psi lower than the initial setting, and check performance. If improvement was observed, decrease another 5 psi and check again. It may be helpful to repeat this sequence more than once. The resulting performance as a function of mixing valve pressure drop can be plott ed on a graph.
6.
Select the best performance point on the pressure drop graph and set mixing valve accordingly.
Optimization of Dilution and Recycle Rates 7.
With the crude throughput at design capacity, and the optimum electrical settings and mixing valve setting installed, the dilution and recycle rates can be optimized. Generally, the greater the amount of water used, the higher will be the salt removal efficiency. This rule, however, is often limited by dilution water availability, or by conductivity of the water and oil mixture.
8.
Set the internal recycle at a flow rate of 2500 bpd (16.6 m3/hr), or 5% of the crude flow rate. The internal recycle is completely independent of the dilution water rate, so this rate can be varied as desired within the capacity r ange of the water pump.
9.
Adjust the dilution water going to the desalter overhead to a flow rate of 1000 bpd (6.6 m3/hr), 2% of the oil rate. Equilibrium in the water phase may take several hours, but conditions close enough to steady state in the oil phase can be attained in about an hour. Measure salt and BS&W content of samples, as before.
10.
Readjust the dilution water rate to the desalter to 1500 bpd (9.9 m3/d), 3% of oil rate, stabilize, and measure results again. Repeat this for increased dilution rates up to the maximum available, or until the electrostatic system draws excessive current and loses its voltage field, whichever comes first. If desired, the effects of changing the internal recycle rate can be measured by repeating steps 8-10 for other recycle rates of, say 3% and 7%.
11.
12.
Once the data is complete for dilution and recycle operation, select the best operating conditions and install those values for the corresponding parameters. Record all optimized settings.
Optimization of Other Parameters 13.
If any variation in chemical demulsifier is to be tested, that can be done at this time. Likewise, if dilution water pH or other treatment is to be tested, it can be done by making changes, allowing for equilibrium, then sampling and analysis.
14.
Variation of the oil-water interface is not normally necessary. The allowable variation is
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relatively small, from the normal interface level (NIL) of 826 mm (32.5") below vessel centerline, up or down about 6". Changing the level by more than that can impair fluid distribution. Variation of the interface level can affect the electrical field flux, the amount of interface sludge tolerated, and the phase retention times slightly. Variation from NIL should only be made if an operational difficulty suggests such change might be beneficial. After completion of these steps, the performance of the unit should be well known over a range of parameter values. Whenever this feedstock is processed, these settings should be installed. Remember that each time the feedstock is changed, the operating conditions may need to be changed to reflect the parameters determined to be optimum for that particular oil.
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SECTION VII NORMAL OPERATION Once the desalter is started up and optimized the operation is not maintenance intensive. So long as operating parameters remain constant, performance will be consistent. Normal operation is that which involves no unintentional changes of operating parameters. Should unexpected changes occur with operation or performance. consult Section X TROUBLESHOOTING. During normal operation a degree of attention to the prevention of operational problems is prudent. This is found in Section IX MAINTENANCE.
MONITORING PROCESS PERFORMANCE The performance of the desalters should be monitored during normal operation to ensure that operation is, indeed, normal. The following items should be monitored. Frequency of monitoring is suggested. However, frequency should be modified to suit the needs of the particular circumstances. Monitoring should be more frequent initially after start-up, and then can become less frequent as conditions warrant. Crude Salt and BS&W Depending on the consistency of the feedstock and other experience based factors, the salt and BS&W of the desalter outlet should be checked anywhere from every couple of hours to once daily. Sampling and testing methods may be whatever is standard practice in the refinery. If short-cut procedures are used for routine monitoring, r esults should be compared to those obtained using procedures given in Section VIII PROCESS PERFORMANCE TESTING AND GUARANTEE. Electrostatic System Voltage and Current The voltage and current of the electrostatic system should be observed on a bi-hourly basis. High current and low voltage can signal a problem which should be diagnosed using troubleshooting procedures from Section X. Interface Sludge Accumulation If interface rag builds into too thick a layer, it will be detected by the interference it causes to the operation of the electrostatic system. However before that occurs, the build-up can be detected by interface sampling. If interface sludge is discovered to be a problem, it should them be addressed by special chemical treatment, or by draining the int erface sludge away for segregated treatment.
Operating Conditions Using the Distributed Control System, all basic process operating conditions such as flows, temperatures, pressures and levels should be observed regularly. Unexpected changes should be investigated immediately, of course. Effluent Water Quality The oil and solids content of effl uent water from all desalter vessels should be checked at least monthly to detect problems such as corrosion or bacterial growth. Such checks should be performed during normal operations, and not at times when mud-washing is occurring or when
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interface sludge is being discharged from the water outlet.
SWITCHING FEEDSTOCKS After start-up when the operating parameters are optimized, a standard set of conditions should be developed for each feedstock. Later, if new feedstocks are introduced, optimization and standardization should be repeated for the new oils. When a switch of feedstocks is made, the standard (optimum) conditions for that particular oil are installed in the operation. Assuming that crude oil flow is uninterrupted during switching, the following order for changes is suggested for minimizing transition upset. 1.
Alter demulsifier type and dosage as needed. This should be done immediately when the oil switch is made.
2.
Alter operating temperature if different. Adjust the control set point as soon after switching oils as practical.
3.
Adjust the mixing valve pressure drop in the second stage feed approximately 30 minutes after the new feedstock is introduced. Make necessary adjustments in the rate of flow for any feed stream dilution or internal recycle.
4.
Switch program variables in LRC. The LRC can store several different sets of operating parameters, so that it is necessary only to retrieve the set corresponding with t he particular feedstock being brought on-stream. These changes to the second stage desalters should be made about 40 to 50 minutes after the new feedstock has been introduced.
5. At about the same time as number 4 above, adjust the second stage overhead internal fresh water injection rate as required.
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SECTION VIII PROCESS PERFORMANCE TESTING AND GUARANTEE ANA LYSIS PROCEDURE To determine the performance of the desalting pr ocess it is necessary to accurately measure the amount of salt in the process feed stream, and both salt and BS&W in the product stream. This requires representative sampling of each stream, followed by analysis of the samples. It also requires a periodic measurement of feedstock properties and of process operating parameters to ensure operation is within the guaranteed conditions. Sampling Sampling method for salt and BS&W analysis is important. Samples should be withdrawn from designated sample points which incorporate sample cooling prior to pressure r elease across the sample valve. The sample should ideally be extracted from the center of the flow line through a stinger (extension of the sample tube into the line). Alternately samples should be taken from the side of horizontal lines, or from vertical lines away from elbows. Analysis should be done as soon as possible after samples are taken. It is essential that the samples lines should be adequately purged before collecting the sample to insure that fresh, representative liquids are collected. Analysis for Salt Analysis of both inlet and outlet samples for salt content should be accomplished with a procedure incorporating hot water extraction, followed by some method of ion measurement. Such a method measures both crystalline and aqueous phase salts, which are the objective of the desalting process. It will not measure ions which are organically bonded. These ions, if they exist, are not water extractable, and are not covered in the process guarantee. One client’s standard method utilizes UOP Method 579-64T. This salt measurement procedure is acceptable for performance evaluation, either for proving the Process Performance Guarantee, or for routine process monitoring. Analysis for BS&W Guaranteed BS&W is based on the ratio of separable water to total fluid at the process operating conditions. At elevated temperatures some oils exhibit a solubility for significant amounts of water. Water which is present in the oil in true solution cannot be removed by a desalter. When a sample of oil is withdrawn for BS&W measurement, cooling prior to pressure letdown is imperative to avoid vaporization of all water. However when this cooling takes place, soluble water in the oil will come out of solution and exist as dispersed water. Even if the desalter removed all dispersed water at operating temperature, cooling of the sample will l iberate dissolved water, resulting in a relatively high content of dispersed water. In order to avoid this inaccuracy the solubility of the water in the oil must be considered in sample analysis. To account for dissolved water, the water solubility as a function of temperature in the particular oil being processed can be determined. With such a functional relationship defined, either centrifugal separation (ASTM D96 or equal), or titration by Karl Fischer method (ASTM D1744 or equal) can be used for water measurement. Results obtained must then be corrected by subtracting out the dissolved water, obtained from t he solubility-temperature function.
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PERFORMANCE TEST PROCEDURE The tests conducted to prove conformance with the Process Performance Guarantee shall be performed in compliance with the following instructions: 1.
Desalting equipment and all related equipment and systems shall be maintained in good working condition prior to and during the performance tests.
2.
NATCO shall be contacted at least two weeks prior to performance testing. A NATCO engineer shall be allowed access to the entire desalting process for observation and consultation at least one week prior to and during validity testing period.
3.
Laboratory facilities and procedures shall conform to the instructions set forth in ANALYSIS PROCEDURE above. NATCO's engineer shall be given access to observe laboratory analysis.
4.
The desalter shall be operated strictly within the Performance Design Conditions defined below. Sufficient measurement of operating conditions and feedstock properties shall be made to ensure that operation remains wit hin the limits of these conditions throughout testing. For expected and guaranteed performance refer to PROCESS GUARANTEE.
5.
NATCO's engineer reserves the right to request evidence of demulsifier performance. Alternately NATCO will be assisted in conducting tests of their own to verify that chemical destabilization of the crude oil i s being accomplished.
6.
The desalter will be operated in a normal manner during tests. The feedstock to be tested shall be processed through the desalters for at least two days prior to commencement of the formal test period. Recommendations made by NATCO's engineer for changes in process variables just prior to and during testing shall be accommodated if at all possible.
7.
The test for each feedstock shall cover a 24 hour period. Each feedstock shall be tested separately. Performance testing shall commence at least 30 hours prior to a crude change. While the test is underway the density and viscosity of the feedstock shall be measured at the beginning of the test and at 12 and 24 hours into t he test.
8.
All process related variables shall be recorded on the attached DATA LOG SHEET once every four hours. The client must output the operating conditions from the data logger printer of the DCS every four hours regarding operating parameters of the desalters. On the same schedule, inlet and outlet samples shall be taken for each of the two parallel second stage desalters separately, or for the pair acting as a unit. At the end of the 24 hour period, the arithmetic average of all six outlet samples and all six inlet samples for both second stage desalters shall be compared against the guarantee figures to ascertain if guaranteed performance was met.
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NATCO“ CLIENT”
PROCESS PERFORMANCE GUARANTEE NATCO offers a Process Performance Guarantee that each EDD desalter supplied by NATCO (used in conjunction with process components supplied by others, but necessary for operation) will reduce the salt content and limit the BS&W content of the specified oils in accordance with "Guaranteed Performance" when operated within the "Performance Design Conditions" set forth below. Performance Design Conditions Specified Crude Feedstock Maximum Crude Throughput (bpd-each) Crude Specific Gravity(60 F, 15.6 C) +/-0.015 Maximum Feed BS&W (%) Feed Salt Content-See "Guaranteed Performance" Maximum Viscosity (Cst) +/-15% @30 C 500 @70 C 50 Operating Temperature ( C) Operating Pressure (kg/cm2g) +/-1 Maximum Required Dilution Water (bpd)
Feed 1 50,000 0.8990 0.075
Feed 2 50,000 0.8866 0.05
30 8.0 135-145 11 3000
130-145 11 3000
**
**
** ** ** **
** **
Guaranteed Performance BS&W (%) in Product Salt (PTB NaCl) in Product @ Second Stage Outlet Feed Salt content @ Second Stage Inlet 1.5 PTB NaCl 4 PTB NaCl 7 PTB NaCl 12 PTB NaCl
Estimated Performance (Not part of the Process Guarantee) BS&W (%) in Product
0.2
0.15
** ** ** **
** **
Salt (PTB NaCl) in Product @ Second Stage Feed Salt content @ Second Stage Inlet 1.5 PTB NaCl 4 PTB NaCl 7 PTB NaCl 12 PTB NaCl
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SECTION IX MAINTENANCE OF EQUIPMENT MAINTENANCE OF THE DESALTING SYSTEM POWER SUPPLY Maintenance of the desalting system involves a program of upkeep for the individual components. However, most of the components are typical process hardware which is maintained in accordance with well established manufacturers procedures or company practice. This chapter will address some considerations in the maintenance of the high voltage Transformer/Reactor, which is a specialty item in NATCO's desalting system. General Specifications Primary
AC voltage to match power source, single phase, 50 or 60 Hz
Secondary
16.5/23.0 KV
Tertiary
100V
Temperature Rating
55 C Rise, 50 C Ambient
Insulation Class
Class A
Construction
Fluid filled outdoor enclosure
Enclosure
Walls - 7 or 10 gauge hot rolled, pickled and oiled steel sheet per ASTM A569 Lid - 10 gauge hot rolled, pickled and oiled steel sheet per ASTM A569 Bottom - 25" gauge hot rolled steel plate per ASTM A569 Lids fastened with alloy clamps torqued to 240 in lbs Enclosure designed to withstand 7 psig; completed units pressure tested at 4 psig with nitrogen and shipped with 1/2 psig residual pressure of nitrogen
Insulating Fluid
Exxon Univolt 60, 61 or equivalent (Cross Oil)
Component Description
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The power supply consists of three major components - t ransformer, reactor, and rectifiers, mounted in an oil filled enclosure. The transformer and reactor are designed to provide the necessary voltage transformation, and to provide 100% system reactance. Both are constructed of laminated grain oriented silicon steel cores. The reactor is air gapped to prevent saturation. Low voltage windings are aluminum or copper strip, high voltage windings are copper wire. All windings are suitably braced to withstand stresses caused by short circuit stresses. Winding insulation materials are thermally upgraded by vacuum varnish process to increase service life. All input connections for transformer and reactor are made in air filled low voltage terminal chamber. Rectifiers are RC compensated, have a PIV rating of 90KV, and are sized for two (2) times highest normal operating current. Rectifier assembly is located in the oil filled high voltage termination chamber. Maintenance Information All maintenance work must be performed with power off. All power sources should be locked out/tagged out in compliance with OSHA Standards 1910.213, 1910.218, 1910.261, and 1926.400, as well as applicable state, county and municipal requirements. Periodic maintenance should be performed at least once each six months, more often when used in contaminating atmosphere and/or unusual loading conditions exist. The following procedure should be used. 1)
Outside Cleaning: Remove accumulation of dust and other foreign matter from bushings, gauges and tank. Accumulation of matter on bushings can cause arcing to ground. Dirt on the tank can decrease the heat dissipation of the tank and result in the unit overheating.
2)
Check Oil Level: Inspect the oil level in the tank. If it is necessary to refill the unit, use only the type of oil specified by NWL. Fill through the filling hole on the cover. Do not allow the unit to stand without liquid. After filling, allow the unit to stand for at least eight (8) hours to allow entrapped air to escape from the winding. Then operate the transformer under a "noload" condition for at least one (1) hour before placing in regular service at full voltage. (This can be achieved by disconnecting the wire from t he diode assembly to the entrance bushing. Observe proper electrical hazards operating instructions by eliminating all power sources while disconnecting and connecting wiring.)
3)
Deposit Check Inside the Tank: The amount of deposit that accumulates in the oil is of great importance. If a sample of oil from the bottom of the apparatus indicates that the oil is badly discolored or contains sediment, an internal inspection should be made for sludge deposits. Proper disposal of oil is the responsibility of the owner/operator. Should there be a deposit on any surface of the tank, filt er the oil, and thoroughly clean the core and coil structure and tank by forcing clean, dry oil through the ducts and against all surfaces. Suitable pressure for this operation can be obtained from a filterpress pump. When oil is found to be in very bad condition, filtering may remove most of the sludge, but badly sludged oil, even after filtering, may soon form a new deposit of sludge. When such conditions occur, it is usually more economical to obtain new oil or to reclaim the old oil. If it is necessary to untank the unit, contact NATCO.
4)
Check on Dielectric Strength: Oil should be sampled and tested every six (6) months or so. The recommended time between inspections and tests depends on local climatic conditions, the load on the apparatus and the importance of minimizing service interruptions. Intervals between tests should be one year or greater depending on the above considerations. Accurate records of these tests should be kept. If at any time, the oil tests below 22 KV at
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room temperature, use a filter press or oil purifier to restore the dielectric strength to 26 KV or more. 5)
Sampling and Testing: It is recommended that the American Society for Testing Materials' standard methods for sampling (latest revision of D-923) and testing (latest revision of D-117) be followed when sampling and testing electrical insulating oils. The accuracy of results may be seriously affected if the samples are not correctly obtained, handled, and tested. The following are a few important points which experience has indicated as essential.
5.1)
Sampling Procedure: Use glass receptacles if possible, so that if any water is present it may readily be observed. Chemically cleaned one-quart, clear glass, screw-cap sample bottles are recommended. If metal containers are used, be sure they are free from rust, solder and other contaminants.
5.2)
Rinse sample containers with dry non-leaded gasoline, Stoddard solvent, or dry water-white kerosene until they are entirely clean. Always wear appropriate approved personal protective equipment when using hydrocarbon solvents. Make sure ventilation is adequate and proper fire prevention standards are followed. Invert and drain to remove excess solvent, and then wash them with strong soapsuds, rinse t horoughly with water, and dry in an oven at 105 C to 110 C. After drying, store them unstoppered in a dry, dust-free cabinet or compartment at a temperature of not less than 38 C (100 F). If they are not stored in a hot cabinet, cork and cap the containers immediately after drying.
5.3)
Take samples when the oil is at least as warm as the surrounding air. Insulating oil is not hygroscopic, but cold oil may condense enough moisture from a humid atmosphere to seriously affect its insulating properties. Take samples from outdoor apparatus on a clear day only, and guard against contamination by wind-blown dust, etc..
5.4)
Before taking a sample from apparatus, carefully clean the valve and allow enough oil to run out so that any contamination that may have collected in the valve will be removed. Take the sample from the small valve provided for that purpose. If no valve is supplied, use a sample thief device.
5.5)
Rinse the container several times with the same oil as the sample to remove any contamination that may have collected in the container. Do not mix these rinsings with the oil samples.
5.6)
Carefully seal the containers to prevent leakage or exposure of the oil to the atmosphere. Use glass stoppers, clean corks or screw caps to seal the glass receptacles. If corks are used or if the screw caps contain cork disk inserts, the cork should be covered with a tin or aluminum foil. Composition-cork gaskets covered by tin or aluminum foil should be used when the oil samples are placed in metal containers. Testing for Dielectric Strength: For testing the dielectric strength of oil, the technique as specified by the American Society for Testing Materials in the test method entitled, "Test for Dielectric Strength of Insulating Oil", Method D-877, should be followed. A 35 KV, 2 KVA test set is available and may be purchased from the General Electric Company or Westinghouse Electric Company. The following precautions and modifications must be observed: a) b)
c)
Set the spacing of the two 1-inch diameter, flat disk electrodes at 0.100 inch. Wipe the test cup and electrodes clean with dry, calendared tissues or clean, dry chamois; and thoroughly rinse with clean, non-leaded gasoline, Stoddard solvent or water-white kerosene. Fill the cup with a sample of the cleaning fluid and apply the voltage at the rate of 3
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d)
e)
f)
g)
i)
KV per second until breakdown occurs. If the breakdown voltage is less than 26 KV, clean the cup again with cleaning fluid and retest. After a satisfactory result, empty the cup immediately and rinse with oil sample to be tested. Then proceed with the test at once. The temperature of the oil, when tested, should be the same as that of the room which should be between 20 C and 30 C (68 F and 86 F). Testing at oil temperatures appreciably lower than room temperature is likely to give variable results and may be misleading. In order that representative test specimens may be obtained, the oil sample container should be gently inverted and the oil swirled several times before each filling of the test cup. The purpose is to thoroughly mix any impurities present with the oil. Too rapid agitation is undesirable, as it introduces an excessive amount of air into the mixture. Immediately after mixing, pour the oil slowly from the container so that no air bubbles will form. Fill the cup to overflowing. Gently rock the test cup a few times and allow three minutes for entrapped air to escape from the oil before applying voltage. When making the test, apply the voltage at the rate of 3 KV per second. Make only one test per cup filling and fill the cup at least five times. Average the results to get the breakdown voltage for the sample. Since the oil is the major insulation of the apparatus in which it is used, its dielectric strength must be kept up to definite standards as specified previously. If the oil fails to withstand the minimum breakdown KV specified, it is a sign that impurities, particularly moisture, have entered it. In this event the oil is no longer safe for use as an insulating medium and must be filtered to remove the impurities and bring it back to its original condition. Acidity (Neutralization): The acidity test is one of the most satisfactory indicators of oxidation in the oil. This is true because some of the oxidation products are of an acid nature and thus may be detected by measuring the acidity of the oil. The main hazard of oxidation is the deposition of sludge. Sludge occurs after the oxidation products held in solution finally saturate the oil and any additional products formed settle out in solid form. The acidity test indicates fairly accurately how far oxidation has progressed.
Oil Specifications (Cross Oil now) PROPERTY
UNIVOLT N60, N61
Physical Properties Aniline Point, C Color Flash Point, C Interfacial Tension @ 25 C, dynes/centimeter Pour Point, C Specific Gravity @ 15 C/15 C Viscosity, SSU/cST @ 100 C 40 C 0 C Visual Appearance
34/2.4 57/9.5 256.5/42.8 Clear and Bright
Chemical Properties Approved antioxidant content, wt % Corrosive sulfur Moisture, ppm Neutralization number, mg KOH/g of oil
0.05, 0.30 Non-corrosive 25 0.01
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76 10.5 160 46 -56 0.879
Oxidation stability Method A (acid/sludge test) 72 hours sludge, wt % Neutralization value, mg KOH/g 164 hours sludge, wt % Neutralization valve, mg KOH/g Method B (rotary bomb oxidation test) Electrical Properties Dielectric breakdown voltageat 60 hertz Disc electrodes, KV VDE electrodes, KV @ 0.040-in gap or @ 0.080-in gap Dielectric breakdown voltage impulse, 25 C, KV Needle (negative)-to-sphere (grounded) @ 1-in gap Power Factor at 60 Hertz, % at: 25 C 100 C
0.025, 0.016 0.150.08 0.06, 0.023 0.38, 0.03 215, 260
35 32 60 175 0.01 0.09
INSPECTION AND MA INTENANCE OF VESSEL INTERNALS General maintenance of vessel internals is limited to shutdowns. When a scheduled shutdown is planned, the agenda should include inspection and upkeep of desalter internals, especially those which are part of the electrostatic system. Inspection may be performed for two reasons. It can be conducted as part of a routine turnaround, scheduled and planned in advance, or it may be conducted because of a problem found in the system, and isolated to the vessel interior. If a problem is suspected, refer to Section X TROUBLESHOOTING for procedures for diagnosing and isolating the cause. In some cases the solution may require vessel entry. This is not common, but is possible. CAUTION - Refer to Section II SAFETY for safety infor mation pertaining to vessel entry and high voltage equipment maintenance. The following general guidelines are recommended: 1. In accordance with the safety instructions, ensure that all sources of electrical power to the vessel interior are turned and locked off. 2. Clean and purge the empty vessel of all hydrocarbon liquids and vapors, as described in the safety instructions. 3. Wipe all Electrode Insulators clean with a soft, non-abrasive rag soaked with a hydrocarbon solvent. In the same way clean the high voltage Entrance Bushings. These Teflon parts should be closely inspected after cleaning for surface damage or impenetrable deposition. If any is found, the part should be replaced. 4. Inspect the Electrode Plates for damage such as deformation, delamination, swelling or cracking. If such damage is found, and if it is severe, the affected plate(s) should be replaced. Minor delamination will not adversely affect performance and is acceptable. 5. Inspect electrical Entrance Cables (internal-from bushing to electrode), Contact Rods, and Low Level Float Switches for corrosion, movement, and mechanical soundness.
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6. Inspect internal overhead Dilution Water Distributor. Check holes to ensure they are not plugged. 7. Check vessel walls for corrosion, particularly at or below the oil/water interface. Check the internal structures for corrosion or damage, and repair if necessary.
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SECTION X TROUBLESHOOTING GENERAL GUIDELINES Trying to isolate the cause of a problem in a desalting process requires a systematic approach of studying the symptoms, applying the basic principles of desalting, and narrowing the possible causes. Then the possible causes must be checked out to isolate the one or more which are responsible for t he trouble. Desalting basically consists of two sub-processes: mixing and dehydration. Understanding this simple principle will aid in isolating problems with the desalting process. When the water content of the desalted crude is within specification, but the salt content is high, that indicates a problem with the mixing process. If, on the other hand, the water content as well as the salt is high, poor dehydration is indicated. Following is a cause-and-effect approach to troubleshooting the problems associated with the desalting process, presented under these headings: Desalting Process Malfunctions Electrical System Malfunctions Water Quality Problems The basic symptoms and manifestations of a problem may be process related. Yet the cause is frequently traceable to a mechanical or operational problem such as many of those listed in the following outline. Or the cause may be a problem with the function of the electrical system. If so, the search moves from the first section to the second section, "Electrical System Malfunctions". Details for checking the electrical system are included. In the following outlines, the basic symptoms and general cause are listed under the capital letter as a main heading. Specific causes are listed under further outline breakdown.
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DESALTING PROCESS MA LFUNCTIONS A. High salt content in outlet due to off-spec feedstock 1. Feedstock with different salt or water content than system was designed for. Check material balance. 2. Change in feed characteristics due to variation in conditions. a. Blended recycled (slop) oil b. Field contaminants such as frac sand, drill mud, acid c. Unusual emulsion stabilizing factors B. High salt content in outlet due to inadequate dilution. This can be identified when the high outlet salt is accompanied by low BS&W in the outlet.
1. Insufficient dilution water. Pump capacity problems a. b. c. d. e. f. g.
pump rotation reversed foreign material in pump air in water at suction pump suction cavitation wrong pump speed supply line scaled up strainer plugged
2. Insufficient mixing of dilution with entrained water a. b. c. d.
pressure drop across mixing valve too low dilution water temperature too low crystalline salt present in oil (ElectroDynamic systems only) mixing voltage too low or mixing cycle duration too short
3. Dilution water salinity too high (where other than fresh water is used) C. High salt content in outlet due to inadequate dehydration. This is identified when both the salt and BS&W of the outlet are high. 1. Emulsion not destabilized chemically a. b. c. d. e. f. g. h.
loss of power to injector sticking or worn check valve in chemical pump broken or plugged chemical line no chemical in tank pump airlock chemical rate set too low; adjust stroke or speed new chemical formulation needed chemical injected too near desalter inlet; no reaction time
2. Low operating temp a. heating system control point set too low b. control system malfunction - 216 -
c.
required duty higher than available duty
3. Abnormally high emulsion stability a. mixing valve pressure drop too large b. feedstock off-spec or abnormally agitated 4. Flow rate of crude too high a. rate higher than design b. average rate OK, but flow surging 5. Interface sludge build-up a. chemical dosage or formula not optimized for sludge treatment b. low operating temperature c. sludge not being effectively drained 6. Level problems a. interface level control or valve malfunction b. low level of oil due to rapid water or sludge draw-off; usually temporary condition c. high interface due to water outlet plugged with sand 7. Electrical system malfunction - see below 8. Voltage not optimized (ElectroDynamic system only) a. if salt in outlet is acceptable, only BS&W is high, then reduce mixing voltage b. if salt and BS&W too high, increase voltage of mixing cycle, or duration of coalescing cycle
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ELECTRICAL SYSTEM MALFUNCTIONS A. Loss of electrical power. The symptoms are no pilot light, no voltage, no current, decreased dehydration 1. Circuit breaker open 2. Master switch open 3. Master fuse open B. Short in high voltage (secondary) circuit due to process upset. Symptoms are pilot dim, voltage low and unsteady, current high but unsteady (See "Desalting Process" above) 1. 2. 3. 4. 5.
Interface sludge accumulation High influx of stable off-spec emulsion Foreign material in desalter High interface level Wax or paraffin accumulation in electrical section
C. Short in high voltage circuit due to component malfunction. Symptoms are pilot out, voltage low or zero, current high but steady 1. Entrance bushing malfunction a. burned wire b. surface tracking of current c. corona deterioration 2. Electrode insulating hanger malfunction a. surface tracking b. corona deterioration 3. Rectifier malfunction 4. Transformer short in secondary coil a. dirty or wet insulating oil b. transformer operating too hot 5. Low crude oil level causing internal switches to ground secondary circuit a. malfunction of flow or level control system b. temporary condition due to rapid water or sludge draw-off D. Open circuit in high voltage circuit (unlikely but possible). Symptoms are pilot on, voltage high, current low, decreased dehydration efficiency 1. Rectifier malfunction 2. Entrance bushing wire burn-through 3. Transformer burn-out E. Open tertiary (meter) circuit. Symptoms are pilot off, no voltage, normal current, dehydration normal 1. Blown fuse in low voltage Junction Box - 218 -
2. Circuit breaker shuts off when energized F. Short in primary circuit 1. Short in transformer primary coil 2. Short in power feed wiring G. Breaker problem. Symptoms are circuit breaker shuts off intermittently, or on hot days 1. Breaker malfunction 2. Breaker too small for load
Electrical System Checkout Procedures Use the following procedures to check out electrical system malfunctions. Before attempting to isolate electrical problems read the section of this manual on SAFETY. Only qualified electricians experienced in high voltage equipment should attempt to perform these procedures: A. To isolate a short in the high-voltage circuitry, take the following steps: 1) Disconnect and padlock the transformer circuit breaker in the "OFF" or "OPEN" position. Be CERTAIN that power is not reaching the transformer. 2) Remove the top flange from the entrance bushing housing and visually inspect the interior. Look for signs of arcing (burn spots on insulation, wires, or contact rods) and/or discoloration of the insulating oil. Oil which has been subjected to arcing will often have a sharp, acrid odor and will look dark in color or have an opaque appearance. Fresh oil should be clear and relatively colorless. If possible, take a sample of oil and have its dielectric value measured. Discolored oil should be replaced with fresh oil. Clean oil with low dielectic value may be reconditioned by filtering. Take precautions to minimize exposure of the oil to airborne dust or moisture. 3) If all appears normal, isolate the transformer from the vessel by disconnecting the high voltage connections inside the entrance bushing housing. Always discharge the circuit before touching the conductors. Be sure that all conductors are well away from the high-voltage connections. 4) Restore power to the transformer and observe the symptoms. If high voltage is restored and the primary current is low, the problem is in either the connection wires or conductors in the entrance bushing housing, in the vessel entrance bushings, or inside the vessel. Also observe whether voltage cycling of the LRC is occurring. 5)
If the problem appears to be in the vessel entrance bushings, try connecting them one at a time to isolate which bushing is the problem. To do this, first DE-ENERGIZE THE TRANSFORMER AND SECURE IT “OFF”, re-connect one of the entrance bushings, and restore transformer power. Repeat the process on the other bushing. Refer to the maintenance instructions for bushing replacement, if necessary.
6)
If no problem is found in Step 4 above (that is, the condition of low voltage and high current persists), DE-ENERGIZE THE TRANSFORMER AND SECURE IT “OFF”, remove the cover from the high voltage junction box (diode compartment), and visually inspect the components and the oil as in Step 2 above including sampling the oil and measuring it s dielectric value.
7)
If no problems are evident from the visual inspection, temporarily secure the lid on the high-voltage junction box, diconnect the connections between the diode pack and transformer - 219 -
output bushings, and restore power to the transformer and observe the symptoms. 8) If readings return to normal (high voltage and low current), the transformer output bushings are faulty. 9) If power readings still show low voltage and high current, turn off power to the transformer and padlock the circuit-breaker in the "OFF" position. 10)Disconnect the diode pack fr om the high voltage AC bushing which is located on the wall of the diode compartment adjoining the main transformer tank. Be sure to discharge the circuit before touching the leads. Make sure leads are away from the diode pack and other high voltage wiring. 11) Temporarily secure the lid on the high-voltage junction box and restore power to the transformer and observe the symptoms. 12)If the readings now show high voltage and low current, the diode pack, transient suppression circuit, or associated wiring is shorted to ground and must be replaced or repaired. B. If it is determined that the short is inside the vessel (either entrance bushings or internal electrical components), the following procedure should be observed: 1) Reaffirm that the symptoms are NOT the result of process irregularities covered in the check list. They could appear as an electrical short inside the unit. 2) Turn OFF all electrical power to unit. All power sources should be locked out/tagged out in compliance with OSHA Standards 1910.218, 1910.261 and 1926.400, as well as applicable state, county and municipal requirements. 3) Remove the production from the system and depressurize the unit. 4) Disconnect and remove the entrance bushings and visually check for burned appearance (tracking). Be sure the bushings are clean. Sulfides or sediment buildup over the length of the bushing can cause shorting. If there are no visible signs of damage, a more complete determination can be made with a "megger" t o determine if there is any conductivity between the wire conductor and the pipe. Conductivity here may indicate a bad bushing. 5) If the bushings are good, drain the vessel and remove manway cover. 6) Before entering the vessel, once again be sure the power is "OFF" and the circuit breaker switch is locked in the "OFF" position. Also, be sure the vessel has proper ventilation. Provisions of the OSHA proposed standard for work in confined spaces should be f ollowed to ensure appropriate worker protection. 7) Visually inspect the insulating hangers that support the electrode assembly. Burned or otherwise damaged insulators should be replaced. 8) Check the electrodes for any foreign material that may be touching either electrode and ground. Also, check for proper spacing (at least 6") between the vessel wall and the electrodes and between electrodes themselves. 9) Inspect the safety float and shorting assembly. Be sure the float assembly moves freely without binding, also that the float has not leaked and filled with liquid preventing it from lifting off the contact rod when the vessel is filled. - 220 -
10) If a visual inspection has not revealed the problem, a more complete check will be necessary. With the float assembly lifted away from the contact rod assembly, a "megger" may be used to check conductivity between each electrode and ground, and each other. Any conductivity will indicate that one or more of the insulating hangers are bad. To determine which insulators are causing the problem it may be necessary to remove t he insulators one at a time and check individually. Any conductivity across an insulator indicates a bad insulator. C. To check for an open circuit in the high voltage circuit: 1) A simple check for this problem may be accomplished without draining the vessel by raising the interface level in the coalescing section. As the interface approaches the grid section, current should increase drastically if the high voltage circuitry is good. If it does not, an open does exist in the high-voltage circuitry. Appropriate precautions should be taken to prevent carryover of water or sludge out the oil discharge, particularly with refinery desalters. Note: The high voltage diode pack should be checked out in accordance with following. D. To check out the rectifier package and other high voltage circuits: Circuits that are designed to operate on high voltage will sometimes develop problems that cannot be detected with normal low voltage test equipment. Although an ohmmeter is a useful tool, it can deceive you. A conductor that is shorted with high voltage applied may appear normal with low voltage. Thus an ohmmeter would not detect this type of high voltage short circuit. An insulation tester, or "megger", is a better testing device for troubleshooting high-voltage circuits. Listed below are two methods for checking out t he high-voltage diode packs on the Dual Polarity unit. Use of Insulation Tester "Megger" Step 1 Disconnect and padlock transformer circuit breaker in the "OPEN" or "OFF" position. Be certain that power is NOT reaching the transformer. Follow all applicable requirements of OSHA Standards 1910.213, 1910.218, 1910.261 and 1926.400, as well as relevant state, county and municipal standards. Step 2 Remove the lid on the high-voltage junction box and isolate the diode pack by disconnecting the high-voltage entrance bushing leads and the transformer secondary lead. Step 3 Connect the "Line" lead from the megger to the diode pack input terminal (center) and connect the "Ground" lead to the positive terminal on the diode pack. Activate the megger. It should read high. Move the "Ground" lead from the positive terminal to the negative terminal on the diode pack. Again activate the megger and note the reading. It should read low. Step 4 Disconnect "Line" lead of the megger from the input terminal of the diode pack and connect the "Ground" lead to the diode input terminal. Connect the "Line" lead to the positive terminal on the diode pack. Activate the megger. The reading should be low. Move the "Line" lead from the positive terminal to the negative terminal on the diode pack. Again, activate the megger. The reading should be high. CAUTION:
Discharge voltage from megger after each reading. If readings do not correspond with those described, diode package is faulty.
CAUTION:
NEVER connect a “megger” to the transformer primary leads. This action could result in destruction of the transformer. - 221 -
WATER QUALITY PROBLEMS A. Gross oil carryover with effluent water (>5000 ppm) 1. oil "sucked" out with water 2. vortexing at water outlet a. No anti-vortex provision b. Interface level too low 3. Interface sludge layer being carried out with the water a. Incompatibility in feed-stocks precipitating asphaltenes or wax. b. High suspended solids load in feedstock (tank bottom carry-over, etc.) B. High oil carryover with effluent water (500 - 5000 ppm) 1. 2. 3. 4.
Insufficient water phase retention time Water rate higher than design Interface too low Dehydrator/Desalter vessels fouled with solids deposition. (If extreme, could result in gross carryover)
C. Inadequate demulsification 1. 2. 3. 4.
Chemical demulsifier not optimum for water quality. Chemical dosage too high or low Chemical not injected far enough upstream of desalter. Additional chemicals, such as wetting agents, may be required.
D. Incompatibility between produced and dilution water. Emulsion stabilized by precipitate E. High solids content in effluent water. Solids accumulation in bottom of vessel or suspended in water phase 1. 2. 3. 4.
Sand or produced solids Incompatibility of produced water and dilution water forming precipitate. Severe corrosion in system (example: iron sulfide) Sample taken during mud-wash operation.
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