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SECTION 1.0 1.1 1.2 1.2.1 1.2.2 1.2.3 1.2.4 1.3 2.0 2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.1.5 2.1.6 2.1.7 2.1.8 2.1.9 2.1.10 2.1.11 2.1.12 2.1.13 2.1.14 2.1.15 2.1.16 2.1.17 2.1.18 2.1.19 2.1.20 2.1.21 2.1.22 2.2 2.2.1 2.2.2
PROCESS STD 105A PAGE Contents-1 REV 10 DATE JULY 2002
TITLE
PAGE
INTRODUCTION
1
Objectives of this Standard Features and Characteristics of Fractionating Trays Sieve or Perforated Trays Valve Trays Bubble Cap Trays Specialty Traps Process Engineering Work Related to Fractionating Traps
1 1 1 2 2 3 3
DEFINITION AND DISCUSSIONS
4
General Tray Terminology Anti-Jump and Splash Baffles Bubbling or Active Area Calming Area Capacity Factor Downcomer Area Downcomer Backup Downcomer Clearance Downcomer Clearance Area or Area Under Downcomer Downcomer Seal Area Downcomer Residence Time Downcomer Width Flow Path Length Free Area Hole or Perforated Area and Hole Diameter Number of Tray Passes Tower Area Tray Materials of Construction Tray Spacing Unit Reference Number V-Load Weir Height Weir Length General Operation Features Downcomer Clearance Velocity Downcomer Residence Time, Downcomer Backup and Downcomer Width
4 4 4 5 5 5 5 5 6 6 7 7 7 7 7 8 8 8 9 9 10 10 10 11 11 11
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SECTION 2.2.3 2.2.4 2.2.5 2.2.6 2.2.7 2.2.8 3.0 3.1 3.2 3.3 4.0 4.1 4.2 4.3 5.0 5.1 5.2 5.3 6.0 6.1 6.2
7.0
PROCESS STD 105A PAGE Contents-2 REV 10 DATE JULY 2002
TITLE
PAGE
Dumping, Weeping and Entrainment Flooding and Percent Flood – Flood Factor Foaming Characteristics – System Factor Minimum and Maximum Vapor Velocity Criteria Pressure Drop Swaged Tower Sections
12 12 14 15 16 17
SIEVE TRAY CALCULATION METHODS
18
Hand Calculation Methods Computer Calculation Methods Recommendations
18 18 19
VALVE TRAY CALCULATION METHODS
20
Hand Calculation Methods Computer Calculation Methods Recommendations
20 20 21
BUBBLE CAP TRAY CALCULATION METHODS
22
Hand Calculation Methods Computer Calculation Methods Recommendations
22 22 23
PROCESS TRAY DATA
24
Tray Data Requisition Form (Form Number 135-110A) Guidelines for Providing Tray Data for Tray Data Requisition Form
24 24
CHECKING CHECKING VENDOR’S PROPOSALS
28
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APPENDIX APPENDIX NO.
TITLE
PAGE
I
Bubble Cap Tray Calculation Methods
29
II
Sieve Tray Calculation Methods
30
III
Tray Data Information
31
IV
Method for Estimating Percent Flood of Valve Trays
35
FIGURES NO.
TITLE
PAGE
I
Sieve and Valve Tray Details
40
II
Typical One Pass Sieve or Valve Tray Layout
40
III
Tray Design and Tray Layout Definitions
41
IV
Tray Flow Path Layouts
42
V
Outlet Weir Details
43
VI
Bubble Cap Details
44 TABLES
NO.
TITLE
PAGE
1.1
Tray Spacing Table and Maximum Number of Tray Passes
45
1.2
Minimum Downcomer Residence Time and Maximum Downcomer Backup
46
References
47
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1.0
PROCESS STD 105A PAGE 1 REV 10 DATE JULY 2002
INTRODUCTION A widely used method of separating separating and purifying purifying materials in the processing processing industries is fractional distillation. This operation is generally performed in fractionation towers, which contain internal devices to promote intimate contact between countercurrent vapor and liquid streams. The most common of such devices is the fractionating tray. Many forms of the fractionating trays have been devised over the years, but only three have achieved widespread commercial acceptance. These are the sieve or perforated tray, the valve tray, and the bubble cap tray. 1.1
Objectives of this Standard The purpose of this standard is to provide a source for the material most commonly used by the process engineer when specifying fractionating trays. It is intended as a summary of the various calculation methods and computer models that are currently available, and contains rules and guidelines that can be used for quickly checking a particular tray design. It should be noted that the rules and guidelines contained in Section 2.0 are intended as “rules of thumb” and any discrepancies between results obtained from the use of this section and the results obtained from other sources, such as a tray manufacturer, should be thoroughly investigated before any action is taken.
1.2
Features and Characteristics of Fractionating Trays 1.2.1
Sieve or Perforated Trays In this type of tray, th the e vapor-liquid contact is obtained through the perforations on the tray deck. Under stable operation, the liquid traveling across the tray contacts the vapor passing through the perforations in the tray deck. This type of tray design is economical since there are no moving parts and the tray decks can be fabricated (punched) in one operation. The efficiency of a well designed sieve tray is as good as any other type of tray in commercial practice. The flexibility is generally satisfactory for most services, but may be limited in some applications requiring high efficiency over a wide range of turndown. A typical sieve tray is shown in Figure 1.
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PROCESS STD 105A PAGE 2 REV 10 DATE JULY 2002
Valve Trays In this type of tray, the individual holes or orifices in the tray deck are covered with a cap that opens and closes with variation in vapor flow rate. As the vapor load increases, the cap will open to permit more vapor to pass through the orifice. As the vapor load decreases, the cap will tend to close. Since the peripheral area between the cap and the tray deck changes for different process loadings, the amount of liquid leaking downward through the orifices at turndown, or weeping, is minimized. For this reason, valve trays are widely used throughout the industry, since they will tend to handle a wider range of capacity variation (turndown) than do sieve trays. Valve trays can generally be designed for a pressure drop equivalent to sieve trays. Valve trays are manufactured by three main fabricators: Glitsch, Koch, and Nutter. Glitsch’s trademark for their valve trays is “Ballast Trays”. The various types of Ballast trays, with a description of each, are shown in the Glitsch Ballast Tray Design Manual Bulletin 4900. Koch’s name for their proprietary proprietary valve tray is the “Flexitray”. The Flexitray and Ballast Ball ast Trays are quite similar in design; both have circular orifices orif ices of approximately 1 1/2 inches in diameter. A third type of valve tray is the “Float Valve Tray”, manufactured by Nutter. These trays are similar to the Ballast Trays and Flexitrays, except that the openings in the tray deck and the caps are rectangular instead of circular. A typical valve unit unit is shown shown in Figure Figure II.
1.2.3
Bubble Cap Trays In this type of tray, the cap (bubble cap) is situated directly above a fixed riser extending up from the tray deck. The vapor flows up through the riser, changes direction, and flows down and out through the slot at or near the base of the bubble cap. The slots are submerged within the liquid on the tray, which is where the vapor-liquid contact occurs. This type of cap offers essentially infinite turndown, and can operate with peak efficiency at very low loads. Bubble cap trays are therefore used mostly mos tly where the vapor/liquid vapor/liquid (V/L) ratio is large, and where liquid li quid distribution on the tray tra y deck is a problem due to low liquid rates. FOSTER WHEELER ENERGY LIMITED 2002
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Two types of bubble caps, the FRI Bubble Cap and the conventional bubble cap, are shown in Figure VI. Until the late 1950's, this was the most widely used type of fractionating tray. Since that time, it has been replaced, almost completely, by other types of trays such as the valve tray, which offer higher capacities and higher efficiencies at a lower cost, with some sacrifice in tray flexibility. 1.2.4
Specialty Trays Through the years, other types of fractionating trays have been developed by various manufacturers for specific processing applications. The Linde MD (Multiple Downcomer) Tray designed by Union Carbide Corp., for example, can be used in revamps to debottleneck an existing tower when the liquid loading is controlling the upper operating limit. These trays resemble sieve trays except that there are multiple box type downcomer units, and the successive trays are rotated 90 degrees. While being effective in hydraulic performance, some sacrifice in tray efficiency is to be expected when Linde MD trays are used to replace other conventional types of trays. The Linde MD trays, however, can usually be installed with relatively small tray spacing.
1.3
Process Engineering Work Related to Fractionating Trays In general, FW process engineers are not required to develop detailed designs of fractionating trays. For valve trays such designs are provided by tray vendors who also will give performance guarantees. For sieve trays and bubble cap trays, both of which are less frequently used than valve trays, it may be necessary for the process engineer to develop a detailed design using in-house computer programs and hand calculation methods. In all cases the process engineer is required to issue a tray loading data sheet and a process vessel sketch for all fractionating towers. These sketches are invariably required, by other specialty groups, well before final data is available from tray vendors. It is required that the number of trays, their diameters, spacing, and the number of passes specified is not expected to significantly change so that revision to the basic design is minimized. One of the purposes of this standard is to provide the necessary background and calculation methods for this work.
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DEFINITIONS AND DISCUSSIONS 2.1
General Tray Terminology This section contains an alphabetical listing of the terms most frequently used when designing a fractionating tray. It is intended to be used as a glossary. It also contains important design criteria that can be useful when designing a new fractionating tray or checking an existing tray for new loadings. Figures II and IV should be used in conjunction with Section 2.1. 2.1.1
Anti-Jump and Splash Baffles Operation at high vapor rates requires that anti-jump baffles be added at the center downcomer of two pass trays, and off-center downcomers of multipass trays. The anti-jump baffle runs parallel to the outlet weir and is located over the center of the downcomer. This vertical baffle is usually approximately 15" high. The purpose of the anti-jump baffle is to direct the liquid into the downcomer at very high rates. By observation, vapor expansion at the outlet weir pumps the liquid over the weir. At sufficiently high vapor rate, the trajectory carries the liquid completely over the downcomer and onto the opposite side of the tray. The tray then floods prematurely due to increased liquid hold-up caused by the cycling of the liquid across one side of the tray and back to the other. Anti-jump baffles deflect the liquid into the downcomer, as does the tower shell when the flow is towards the side. Splash baffles are normally recommended for low liquid flowrates in order to maintain an even distribution of liquid on the tray and to prevent the liquid from being blown off the tray. Splash baffles may be picket fence type, or may be solid metal extending shell to shell. The solid baffle is parallel to, and located just before, the overflow weir.
2.1.2
Bubbling or Active Area Bubbling area is the area enclosed by the tower walls, the outlet weir and inlet edge of the tray. The bubbling area is also referred to as the active area, as this is the area in which the vapor-liquid contact occurs. The bubbling area is equal to the tower area minus the sum of the downcomer area plus the downcomer seal area.
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2.1.3
PROCESS STD 105A PAGE 5 REV 10 DATE JULY 2002
Calming Area The calming area is included within the bubbling area on a tray. The purpose of the calming area is to allow the vapor to disengage from the tray liquid before it enters the downcomer. The calming area is usually a two or three inch wide strip of unperforated active area parallel to the outlet weir, extending the entire length of the outlet weir.
2.1.4
Capacity Factor The capacity factor is used in the method outlined in the Glitsch Ballast Tray Design Manual Bulletin 4900 to establish the minimum active area on a tray. The vapor capacity factor is an indication of the vapor rate through a tray at the point of incipient flooding by massive entrainment.
2.1.5
Downcomer Area The downcomer area is the area necessary to allow the liquid to flow from one tray to the one below. Normally, the area at the top of the downcomer is equal to the area at the bottom of the downcomer, that is, the downcomer is straight (vertical) Sloped or stepped downcomers are used to increase the tray active area without increasing the tower diameter when the tower diameter is vapor controlled. Weir rate considerations may require that the top downcomer area be larger than the downcomer area required by downcomer residence time requirements. Therefore, the bottom downcomer area can be less than the top downcomer area, provided the minimum downcomer residence time requirements are satisfied. Since the downcomer seal area is equal to the bottom downcomer area, the active area is increased by the difference between the top and bottom downcomer areas.
2.1.6
Downcomer Back Up The pressure drop through the tray or constrictions in the downcomer may cause the aerated liquid to partially fill or back up the downcomer. If the level of aerated liquid in the downcomer rises to the level of the outlet weir on the above tray, the liquid flow discharging into the downcomer will back up and cause flooding.
2.1.7
Downcomer Clearance The downcomer clearance is the vertical distance from the tray deck of the tray below to the bottom of the downcomer of the tray FOSTER WHEELER ENERGY LIMITED 2002
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above. For most designs, it is set at 1.5” to 2", but should never exceed the height of the outlet weir. The downcomer clearance is generally ¼” to ½” less than the outlet weir height in order to provide a liquid seal on the tray outlet. In designs where the downcomer back up exceeds the allowable percentage of the tray spacing, a curved downcomer outlet can be used to reduce the head loss under the downcomer, thereby reducing the downcomer back up. 2.1.8
Downcomer Clearance Area or Area Under Downcomer The downcomer clearance area is defined as the downcomer clearance multiplied by the wall to wall distance of the downcomer. For straight downcomers, the wall to wall distance of the downcomer is equal to the outlet weir of the tray above. The sloped downcomers, the wall to wall distance of the downcomer would be somewhat less than the outlet weir length.
2.1.9
Downcomer Seal Area The downcomer seal area is the area below the bottom of the downcomer and is used to seal the downcomer and distribute the liquid to the tray. In some designs, the downcomer seal area is recessed below the tray deck to reduce downcomer back up and provide a positive liquid seal for all operating conditions.
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2.1.10 Downcomer Residence Time The minimum required residence time in the downcomer in order that the vapor be allowed to disengage from the liquid. This value is dependent on the froth characteristics of the downcomer liquid, and if not met will cause the passage of a two-phase mixture through the downcomer. 2.1.11 Downcomer Width The width in inches of either the side, center, or off center downcomer, measured at the top of the downcomer, with relat ion to the tower centerline. 2.1.12 Flow Path Length The flow path length is defined as the distance from the inlet edge of the tray to the outlet weir or outlet edge of the bubbling area (see Figure I). The minimum flow path length is approximately 17 inches if internal manways are required. FRI Studies indicate no change in tray performance when the flow path length is varied from 15 inches to 70 inches. Normally the flow path length should not exceed 100-120 inches. 2.1.13 Free Area The free area is defined as the area on the tray that is available for vapor flow. The free area is equal to the tower area minus the maximum area at the top of the downcomer. 2.1.14 Hole or Perforated Area For most services where pressure drop is not a controlling design consideration, a hole area of 8 to 10 percent of the bubbling area will be satisfactory. This range of hole areas will also provide the maximum flexibility. For services where downcomer back-up or pressure drop is limiting a hole area of up to 15 percent of the bubbling area can be used. Hole areas less than 8 percent will entrain excessively. Hole areas greater than 15 percent will weep excessively. A hole diameter of 0.5 inches is typically the best selection for most services. Larger holes will have a higher pressure drop and cause a higher entrainment rate. Smaller holes may plug or foul, however, they should be considered for vacuum services since the pressure drop and entrainment rate will be less.
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For valve trays, Glitsch specifies a 1-17/32 inch diameter orifice for their Ballast Units. There are usually a maximum of 12 to 14 Ballast Units per square foot of bubbling area. The number of Ballast Units on a tray can vary depending on turndown and pressure drop requirements. 2.1.15 Number of Tray Passes The number of passes on a tray refers to the number of liquid flow paths. For a design where the liquid rates are high, the diameter of the tower may have to be increased substantially in order to obtain the length of weir or downcomer area needed to satisfy liquid flow requirements. In these cases where the tower diameter is controlled by the liquid rate, the number of tray passes should be increased, until the smallest diameter is found where both vapor and liquid flow criteria have been satisfied. Most tray designs incorporate the one or two-flow trays. Four flow trays are used in designs where the liquid rates are extremely high, and the vapor rates are relatively low. Three flow trays are not used in Foster Wheeler designs, due to difficulties in controlling liquid flow equally to each pass. A diagram indicating the flow paths for one through four flow trays is shown in Figure IV. The maximum number of tray passes for various diameters is shown in Table I. The maximum number of tray passes that can physically fit into a given diameter is largely a function of tray manway and minimum flow path length requirements. 2.1.16 Tower Area The tower area is the total cross-sectional area within the tower shell. The tower area is equal to the sum of the downcomer area, bubbling area, and downcomer seal area, or the sum of the free area plus the downcomer area. 2.1.17 Tray Materials of Construction For sieve trays, the decks and downcomers can be specified as either carbon steel or stainless steel. However, some plugging of holes may result if carbon steel decks are used with a hole diameter much less than ½”. For valve trays, the decks and downcomers can be specified as either carbon steel or stainless steel. Ballast units are almost always specified as stainless (12 chrome) to avoid the problem of FOSTER WHEELER ENERGY LIMITED 2002
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the valves corroding shut on the tray decks. 2.1.18 Tray Spacing The tray spacing, or vertical distance between tray decks, will affect the capacity and entrainment of fractionating trays. Tray spacing does not affect the lower operating limit. An increase in tray spacing will increase the operating range of a tray, up to a limiting value. The tray spacing is often varied in different sections of the column. Table 1.1 lists the minimum tray spacing for various tower diameters. The minimum tray spacing is set by the desire to have a crawl (3) space across each tray. (This would not normally apply to “welded-in” or “cartridge” trays.) This space should be about 14 inches high. The presence of major and minor beams, of bentdown plate, and of tray hardware (caps or valve assemblies), establishes the minimum spacing. Table 1.1. shows the minimum spacing increasing in 6-inch increments. In borderline cases, 3inch increments should be considered. In any case, these dimensions are a guide, subject to thoughtful review in specific cases, and subject to tray vendor information. 2.1.19 Unit Reference Number (U.R.N.) (7) The Unit Reference Number appears in the Glitsch Ballast Tray Computer Program printout. The Unit Reference Number is defined as the percent of Ballast Units that are partially open. The following guidelines can be used for design to predict performance at turndown: Number of Tray Passes
Minimum U.R.N.
1
40
2
60
4
80-90
The Unit Reference Number is actually an indication of the minimum vapor rate for a particular tray design. The U.R.N. should be approximately equal to 100 at design rates. When the U.R.N. approaches 200, entrainment flooding could begin to be a problem and should be checked. It should be noted that these guidelines apply to a pressurized system, and do not strictly apply to a vacuum system where pressure drop is much more critical. FOSTER WHEELER ENERGY LIMITED 2002
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2.1.20 V-Load This term appears in the Glitsch Tray Program Printout, and in the Glitsch Tray Design Manual, Bulletin 4900. It is used by Glitsch to establish a minimum active area and is a function of vapor volumetric flow and vapor and liquid densities. 2.1.21 Weir Height A weir height of 2" is used in most services. Exceptions are those services having a low pressure drop specification. A weir height as low as ½” has been used in vacuum columns but a ¾” minimum weir height is normally recommended. A weir height up to 6" can be used where a high liquid residence time is necessary, for example, where a chemical reaction is involved. If the weir height is greater than 15% of the tray spacing, the effective tray spacing for purposes of calculating percent of flood should be reduced by the excess of the weir height over 15% of the tray spacing. Pressure drop will increase with increasing weir height. Weeping and entrainment will increase slightly with increasing weir height. V-notch or rectangular notched weirs (see Figure V) are normally recommended under the following conditions: (4) 0.6 GPM (Hot) Inch of Outlet Weir
Total GPM (Hot) from Tray 9.0 x (Tower Diameter, F t)
A notched weir or splash baffle insures good distribution of liquid on the tray deck at low liquid rates. In the cases where v-notches or rectangular notches are specified, the weir height shall be measured from the bottom of the notch to the tray deck. 2.1.22 Weir Length The weir length establishes the rate of travel of the liquid across the tray. The rate of liquid flow over the weir is referred to as the weir rate. The weir rate is generally used to calculate the tray pressure drop, and in the case of sieve trays, the weir rate is used to establish other important design criteria, such as minimum hole area. A swept-back weir (see Figure V) is used to decrease the weir rate for the purposes of improving tray hydraulics and lowering the tray pressure drop without increasing either the tower diameter or FOSTER WHEELER ENERGY LIMITED 2002
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downcomer area. A swept-back weir does not change either the active area or effective downcomer area, or the capacity of the trays, except in small diameter towers. 2.2
General Operation Features Below are valve tray criteria which can be used to quickly check the tray design as offered by the various valve tray vendors. These criteria are intended only to be used to quickly evaluate tray designs or spot check inadequacies, with the final check, as required, based on the more rigorous procedures. 2.2.1
Downcomer Clearance Velocity Downcomer clearance velocities should be less than 1.0 ft/sec, calculated by the following equation
Q Ax
DC v = 0.00223
where
DCV =
downcomer clearance velocity, ft/sec
Q
=
total liquid rate into downcomer, gpm at operating temperature
Ax
=
downcomer clearance area, ft 2
The downcomer clearance area, Ax, is the cross-sectional area available to the liquid as it exits the downcomer (see Section 2.1.7). For multi-pass trays, the downcomer clearance velocity should be checked individually. 2.2.2
Downcomer Residence Time, Downcomer Back-Up and Downcomer Width As the liquid flows over the weir and into the downcomer, it exists as a froth. Time must be allowed for the vapor portion of the froth to disengage before the liquid enters the downflow clearance area and flows to the next tray. Also, any foam that is created by the liquid turbulence in the downcomer must be allowed to collapse and dissipate. As a guideline for checking vendor designs, Foster Wheeler has established 5 seconds as the minimum downcomer residence time, with not more than 50% of the downcomer to be backed up. Glitsch, however, prefers to use the downcomer FOSTER WHEELER ENERGY LIMITED 2002
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design velocity criteria shown in the Glitsch Ballast Tray Design Manual Bulletin 4900 to size downcomers. Using the method developed by Foster Wheeler, the downcomer residence time is calculated by the following equation:
V D Q
R = 449
where
R
=
residence time, seconds
VD
=
downcomer volume, ft 3
Q
=
total liquid rate into downcomer, GPM at operating temperature
If the downcomer residence time calculated for a particular design is less than 5 seconds, the volume of the downcomer must be increased until the minimum downcomer residence time requirement is satisfied. The Minimum Downcomer Width is determined by the following relationship O wo > 1.0 hi t O wi > 1.7 hi t
Where
2.2.3
T
=
Tray spacing inches
Owo
=
Allowable width of outside downcomer, inches
Owi
=
Allowable width of inside downcomer. (multiple pass trays), inches
hi
=
height of liquid above the outlet weir, inches
Dumping, Weeping, and Entrainment This topic will be issued for review later.
2.2.4
Flooding and Percent Flood - Flood Factor The term “Flooding” is used quite often when referring to the upper FOSTER WHEELER ENERGY LIMITED 2002
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operating limit of fractionating trays. A fractionating tower can flood due to excessive liquid or vapor rates, or when the ultimate capacity of the system is reached. A brief description of each type of flooding is included below: A.
System Limitation. Each system has a limiting or ultimate capacity at a constant diameter which cannot be exceeded by changing the tray design or by increasing the tray spacing. This phenomenon is associated with the interaction between the vapor and liquid spray in the intertray space and is not related to the hardware used on the tray. This occurs when there is substantial net upward flow of liquid relative to the total liquid flow, and is a function of the terminal velocity of the liquid drops populating the intertray space.
B.
Downcomer Back-Up. During normal operation, the liquid in the downcomer should only rise to a level of approximately 50% of the tray spacing. When the downcomer fills with aerated liquid or foam to a higher % of the tray spacing, not all the liquid can be accommodated by the downcomer, and the tray may become flooded by the liquid accumulating in the bubbling area.
C.
Jetting or Massive Entrainment. With an adequate downcomer design, flooding of fractionating trays may be caused by massive entrainment, or jetting of liquid spray from tray to tray. The amount of vapor required to flood a tray due to the massive entrainment mechanism will vary substantially with tray design, tray spacing and system properties.
D.
Blowing. Opposite to flooding - Liquid is blown into fine spray leaving the tray essentially dry. Blowing occurs at very high V/L ratios. A weir loading of at least 5 GPM/ft should be maintained to avoid blowing.
The term FF, or Flood Factor, is used in the Glitsch Ballast Tray Design Manual Bulletin 4900 for purposes of estimating the minimum active area and minimum downcomer area. This term is the “design percent of flood” expressed as a fraction. A value of not more than 0.77 is normally used for vacuum towers and a value of not more than 0.82 is used for other services. These values are intended to limit entrainment to approximately 10% entrainment. Higher flood factors may result in excessive entrainment and/or a column sized too small for effective FOSTER WHEELER ENERGY LIMITED 2002
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operation. The “actual percent of flood” should be determined once the final tray design has been completed. The “actual percent of flood” should be in the range of 75 to 85 percent, at maximum design rates. These values may vary, however, depending on the particular application. In a revamp, for example, a higher percent of flood than would typically be used for normal designs may be allowed in order to permit the use of existing trays or an existing fractionating tower. In all cases, the actual percent of flood should be established in conjunction with or approved by the Chief Process Engineer/Manager or the Process Supervisor. The percent of flood for sieve and bubble cap trays can be determined by the appropriate hand or computer calculation methods outlined in Sections 3.0 and 5.0, respectively. The percent of flood for valve trays should be determined from the appropriate tray manufacturer’s design manuals, several of which are outlined in Section 4.0. A generalized flooding calculation procedure, included in Appendix IV, can be used to estimate the percent flood of valve trays if the appropriate tray manufacturer’s tray design manual is unavailable. A sample hand calculation is also included in Appendix IV. 2.2.5
Foaming Characteristics - System Factor System factors are used in the Glitsch Ballast Tray Design Manual Bulletin 4900 to represent the degree of foaming for a particular system. The system factor is actually a safety factor applied to downcomer velocities to prevent premature flooding by downcomer backup. It is also used in conjunction with the Capacity Factor (Section 2.1.4) for sizing columns and calculating the percent flood of a given tower diameter. A table listing the system factors that should be used for various systems is shown in the Glitsch Ballast Tray Design Manual Bulletin 4900. Other tray vendors use other values.
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2.2.6
Minimum and Maximum Vapor Velocity Criteria Establishing the hole area for sieve trays, slot area for valve trays, or slot area for bubble cap trays is generally the responsibility of the tray vendor. The amount of perforated area on a tray deck is a function of turndown and pressure drop requirements. Also, the size and arrangement of the perforations can influence the rate of entrainment and flooding. The tray vendor has conducted extensive research in these areas, and will generally guarantee tray flexibility. In the past FW has, on occasion, designed sieve trays and bubble cap trays using in house hand calculation methods and/or computer programs. This, however, has not been the case in recent years. It should be noted, however, that some clients insist upon using their own tray design computer programs for all applications rather than vendor designs. This section contains guidelines for quickly checking a vendor’s design for new loading, or to determine if an existing tray in a revamp, for example, is acceptable with new loadings. a.
Sieve Trays - At present there is no quick guideline for determining the minimum and maximum hole velocity for sieve trays. There are equations in the FRI Tray Design Handbook relating tray geometry and loading to the minimum and maximum hole velocity, but they require some knowledge of tray design methods and are cumbersome to use. As an initial estimate, the valve tray guidelines can be applied to sieve trays.
b.
Valve Trays - The maximum slot velocity in feet per second can be determined from the following equation: V maximum =
15.0
(Ft)
(Vapor Density) ( Sec )
The minimum slot velocity in feet per second can be determined from the following equation: V minimum =
6.5
(Ft)
(Vapor Density) ( Sec )
Vapor density = lbs/cu. ft. The minimum slot velocity calculation is based on minimum FOSTER WHEELER ENERGY LIMITED 2002
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vapor flow and the area of the opening around the valve periphery (fully opened). As a rule, the slot area for Koch and Glitsch valves is equal to approximately 0.012 sq. ft. per valve; but this should be checked with the vendor particularly for Nutter Trays. Where different weighted valves are specified for a single deck, the minimum velocity should be tested for the minimum vapor flow using the slot area for the lighter valves plus the area of the fixed opening (valves having a dimple to keep it off the deck) of the heavier valves. c.
Bubble Cap Trays - The maximum slot velocity in feet per second can be determined by the following equation: (8) V maximum =
12.1
(Ft)
(Vapor Density) ( Sec )
The minimum slot velocity in feet per second can be determined by the following equation: (8) V minimum =
5.0
(Ft)
(Vapor Density) ( Sec )
NOTE 1. Although the Davies article (8) recommends 3.4, a value of 5.0 is used by Foster Wheeler. Vapor density = lbs./cu. ft. 2.2.7
Pressure Drop The following table is to be used as a guide f or specifying the tray pressure drop. The allowable pressure drop can be increased or decreased depending upon flexibility requirements or system pressure drop limitations.
P/Tray, PSI, in
P/Tray, mm Hg, in (3)
Pressure Service
Vacuum Service
0.1 to 0.20
1 to 2
Bubble Cap (5)
0.15 to 0.20
2.5 to 3.5
Valve
0.10 to 0.20
3.5 to 4.5
Tray Type Sieve (4)
(2.5 for V-4 trays) (3.0 to 3.5 for V-1 trays) (3.5 to 4.5 for A-1 trays) FOSTER WHEELER ENERGY LIMITED 2002
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2.2.8
PROCESS STD 105A PAGE 17 REV 10 DATE JULY 2002
Swaged Tower Sections When a tower has several feeds and/or several pump around sections, the vapor and liquid loadings may be substantially different in each section. The tower diameter should therefore be adjusted to compensate for these changes in process loadings, i f no other internal adjustment such as tray spacing and type, will allow the diameter to remain constant. Rules for deciding which sections of the tower to swage vary depending on diameter, materials of construction, and tower height. A guideline obtained from the FWEC Vessel Engineering Group is that it becomes economic to decrease the diameter, if the decrease in diameter is greater than one foot. Also, the section with the decreased diameter should be at least 20 feet in length.
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3.0
PROCESS STD 105A PAGE 18 REV 10 DATE JULY 2002
SIEVE TRAY CALCULATION METHODS This section serves as a summary of a few of the methods now available to the process engineer to design and rate sieve trays. The user manuals for all of the computer programs are available in the Process Design Library unless otherwise noted. The sieve tray vendor shall provide the final design. 3.1
Hand Calculation Methods The design methods most often used to rate sieve trays by hand calculations are:
3.2
A.
FRI, “The Fractionation Tray Design Handbook”, No. 3, Volume I, Section 5.0. This is available in the Process Design Library.
B.
“Process Design of Diffusional Equipment - Recommended Procedures”, FWEC, Volume I, 1 December, 1960. This is available from the Process Design Services group and from various Chief Engineers and Managers.
C.
“Sieve Tray Calculation Methods”, included in Appendix II. This is included for reference only.
Computer Calculation Methods The following computer programs are now available: A.
P1096 FRI Sieve Tray Rating With given specific sieve tray design, vapor and liquid loading conditions and physical properties, the program evaluates the usual design parameters for one and two pass trays only, utilizing procedures given in the FRI Design Handbook. The program will accept either English or Metric (SI) units. This is the program distributed to FRI members. This program can be run with cards (batch) and is also available on TSO. P1096 can also be accessed via PDQ.
B.
P1115 FRI Multipass Sieve Tray Rating Program This program, issued and licensed by FRI, evaluates sieve tray designs of one-pass to four-passes of liquid. The program evaluates conditions for each flow path of a multipass design, based on vapor and liquid distribution determined from tray and downcomer hydraulic considerations. This program can only be run batch. FOSTER WHEELER ENERGY LIMITED 2002
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C.
PROCESS STD 105A PAGE 19 REV 10 DATE JULY 2002
Glitsch Sieve Tray Rating Program This program, issued by Glitsch, can be used to design one-pass to four-pass trays, or to rate existing one-pass to four-pass tray designs for a given set of process conditions. This is the same program which is used by Glitsch for their design work. At present, this block mode program can be accessed only on the Lear-Siegler ADM-31 CRT Terminal, available from the Process Design Services group. At this time, the input manual and program access procedure is available only through the Process Design Services group, since use of this program at FWEC is relatively new.
3.3
Recommendations The procedure shown in the FRI Fractionation Tray Design Handbook (Section 3.1A) is the recommended hand calculation method. The FRI Handbooks contain the latest technology available to design and rate sieve trays. The P1096 FRI Sieve Tray Program (Section 3.2A) or the Glitsch Sieve Tray Rating Program (Section 3.2C) can both be used to design and rate one or two pass trays. Quick results can be obtained from either program, via the TSO or the CRT. For critical designs, the FRI program should be used. The Glitsch Sieve Tray Rating Program and the P1115 FRI multipass Sieve Tray Rating Program (Section 3.2B) can both design & rate three or four pass trays. If quick results are required, the Glitsch program should be used, as the results appear directly on the CRT. As with the one and two pass tray designs, critical three and four pass trays should be designed using the FRI Program. The final selection should be made in conjunction with or approved by the Chief Process Engineer/Manager or the Process Supervisor. Avoid three-pass trays. It should be noted that the Glitsch calculation methods can only be used to determine the basic hydraulic parameters used in tray design, such as percent flood, downcomer backup, and pressure drop. If additional detailed design information is required, such as weep points, dump points, entrainment values or tray efficiencies, the FRI calculation method must be used.
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4.0
PROCESS STD 105A PAGE 20 REV 10 DATE JULY 2002
VALVE TRAY CALCULATION METHODS This section serves as a summary of a few of the methods now available to the process engineer to use for design and rate valve trays. The valve tray vendor shall provide the final design. 4.1
Hand Calculation Methods The design methods most often used to rate valve trays by hand calculations are: A.
The “Ballast Tray Design Manual”, Bulletin 4900, published by Glitsch. Be sure to use the latest printing available for the most upto-date criteria. This is probably the most widely used tray design manual within the Process Design and Development Department. Copies of this manual can be obtained from the Process Design Services Group.
B.
The “Flexitray Design Manual” published by Koch Engineering Company. This manual illustrates the design and rating procedures for the Koch Flexi-Tray.
C.
The “Float Valve Tray Design Manual” published by Nutter Engineering Company. This manual illustrates the design and rating procedure for the Nutter Float Valve Tray.
All of these design manuals are in the Technical File, Index No. 442.112. 4.2
Computer Calculation Methods The following computer programs are now available. A.
Glitsch Valve Tray Rating Program This program issued by Glitsch to FWEC can be used to design onepass to four-pass trays, or to rate existing one-pass to four-pass tray designs for a given set of process conditions. This is the same program which is used by Glitsch for their design work. At present this block mode program can be accessed only on the Lear-Siegler ADM-31 CRT Terminal, available from the Process Design Services group. At this time, the input manual and program access procedure is available only through the Process Design Services group, since use of this program at FWEC is relatively new.
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Note that the “Glitsch Tower Sizing Program, P1118”, is superseded by this program and should no longer be used. B.
P1067 Tower Sizing This program sizes fractionating towers using the approximate method outlined in the Glitsch Ballast Tray Design Manual, Bulletin 4900. The program calculates approximate tower diameters for a range of tray spacings and tray layouts for 1,2, and 4 pass trays. This program can only be run batch. Results may vary from the above rigorous program.
4.3
Recommendations The hand calculation method that should be used depends upon the type of valve unit under investigation. Normally, the Glitsch Ballast Tray Design Manual (Section 4.1A) is used for most new Foster Wheeler designs. The design manuals for the other proprietary trays mentioned in Sections 4.1B and 4.1C should be used if those particular types of trays are being checked for new loadings as in a revamp. See Section 1.2.4 for additional information on additional proprietary trays. The Glitsch Valve Tray Rating Program (Section 4.2A) is the recommended computer calculation method. P1067 (Section 4.2B) can be used to quickly spot-check a design, but should not be used for the final design calculations. The valve tray vendor shall provide the final design.
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5.0
BUBBLE CAP TRAY CALCULATION METHODS This section serves as a summary of a few of the methods now available to the process engineer to design and rate bubble cap trays. The bubble-cap tray vendor shall provide the final design. The user manuals for all of the computer programs are available in the Process Design Library unless otherwise noted. The procedure required to access these programs, either on batch or TSO, including PDQ, can be found in the Process Design Department Computer Users Manual. 5.1
Hand Calculation Methods The design methods most often used to rate bubble cap trays by hand calculations are:
5.2
A.
FRI, The “Fractionation Tray Design Handbook” No. 3, Volume I, Section 3.0. This is available in the Process Design Library.
B.
“Bubble Cap Tray Calculation Methods”, included in Appendix I. This is included for reference only.
,
Computer Calculation Methods The following computer programs are now available: A.
P1080 FRI Bubble Cap Tray Rating This is the FRI rating program to rate bubble cap trays of one or two pass design, with no cascading of trays. Output is in either English or metric (SI) units. This program can only be run batch.
B.
Glitsch Bubble Cap Tray Rating Program This program, issued by Glitsch to FWEC, can be used to design one-pass to four-pass trays, or to rate existing one-pass to four-pass tray designs for a given set of process conditions. This is the same program which is used by Glitsch for their design work. At present, this block mode program can be accessed only on the Lear-Siegler ADM-31 CRT Terminal, available from the Process Design Services group. At this time, the user manual and program access procedure is available only through the Process Design Services group.
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This program is identical to the Glitsch Valve Tray Rating Program (see Section 4.2A), except that the “Bubble Cap Tray” option is utilized. 5.3
Recommendations The procedure shown in the Fractionation Tray Design Handbook (Section 5.1A) is the recommended hand calculation method. The FRI Handbooks contain the latest technology available to design and rate bubble cap trays. The Glitsch Bubble Cap Tray Rating Program (Section 5.2B) or the P1080 FRI Bubble Cap Tray Rating Program (Section 5.2A) can be used as computer methods to design bubble cap trays. If quick results are required, the Glitsch Bubble Cap program should be used, as the results appear directly on the CRT. If the design is critical, the FRI Bubble Cap program should be used, as the FRI method appears to be more rigorous than the Glitsch method. The final selection should be made in conjunction with or approved by the Chief Process Engineer/Manager or the Process Supervisor. It should be noted that the Glitsch calculation methods can only be used to determine the basic hydraulic parameters used in tray design, such as percent flood, downcomer backup, and pressure drop. If additional detailed design information is required, such as weep points, dump points, entrainment values or tray efficiencies, the FRI calculation methods must be used.
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6.0
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PROCESS TRAY DATA 6.1
Tray Data Requisition Form (Form Number 135-110A) This section includes instructions for use of Form No. 135-110A, Tray Data Requisition Form, which accompanies the process vessel sketch for towers. This data sheet contains 51 numbered lines of data that are required to allow the tray vendor to satisfactorily design a fractionating tray. These data sheets are issued by Process Engineering to the Vessel Engineering group, whose function is to complete the data sheet and subsequently coordinate purchase of the trays. In addition, the data sheets should be sent directly to the tray manufacturer by the Process Design and Development Department to confirm the results obtained by using the in-house computer methods.
6.2
Guidelines for Providing Tray Data for Tray Data Requisition Form This section includes guidelines for completing the Tray Data Requisition Form. A copy of a completed Tray Data Requisition Form has been included in Appendix III for reference. A line by line description of the information required to complete the form has been included here. Tray data is either furnished by the client or generated by the process engineer using a process simulation computer program, Foster Wheeler’s version of which is the P1086 Process Simulator. A sample of the type of data generated by the FW P1086 program has been included in Appendix III for reference. Should the tray data be generated by another program, and the vapor and liquid physical properties are not available, they should be obtained from other sources such as the FW Design Data Books, the API Technical Data Books, or the NGPSA Engineering Data Book. If the required data is unavailable in these sources, consult with the Technical Data Supervisor. When sections of a tower are given, specify the maximum and minimum loading points of the section. Should the P1086 computer program be employed to simulate the tray loads, these points are readily identified in the tray loading table under the heading V Load. In specifying the top tray, and for trays involving transition from fractionation to pump around service, data for both the vapor to/liquid from and vapor from/liquid to those particular section should be given. This also applies to selected towers such as strippers, in which case the maximum traffic in the top of the tower lies somewhere between the rates calculated as entering the top stage, and the rate calculated as leaving the tower. FOSTER WHEELER ENERGY LIMITED 2002
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The heat duty for pump around trays should be supplied as an additional item. The maximum vapor and liquid rates may not occur at the same point. Rather than specifying both sections, pick the maximum vapor loading and specify that section with the corresponding liquid load. As a footnote, inform the vendor to assure that the downcomers are guaranteed to handle the maximum liquid rate, unless the maximum liquid rate is very different from the rate corresponding to the Max V Load point, such as pump around design rates. If so, complete loadings for both should be supplied. Title Box - Fill in the client name, contract number, site and date. Also include the name and item number of the tower you are supplying data for where “Tray Data For” is noted. The requisition number and the vessel drawing number are left blank. They will be provided later by the Vessel Engineering group. The boxes marked C1 through C6 refer to the dates of future process revisions of the data sheet. Lines 1 and 2 - Indicate the operating case that you are providing tray data for. These may include different tower feeds, or different tower operations. Where a tower has many different operating cases, only those cases that will control tray design should be included. These cases should be selected in conjunction with or approved by the Chief Process Engineer/Manager. Line 3 - Indicate the tray numbers of the section that you are providing data for. This can be the entire tower, in the case of a stripper, or any particular section of a tower. Typical sections are those between different feed locations or between pump around sections, or where there is any other abrupt change in loadings, such as a liquid or vapor drawoff tray. Trays are usually numbered consecutively from bottom to top, and should be so indicated as in “1 (bottom) to 7” Line 4 - Indicate which tray number or loading point you are providing data for. This loading point should agree with the tray numbers shown in Line 3. Line 5 - Indicate the type and number of trays in the section noted in Line 3. Line 6 - Indicate the tower diameter of the section noted in Line 3. Line 7 - Indicate the tray spacing of the section noted in Line 3. Line 8 - Indicate the number of tray passes of the section noted in Line 3. FOSTER WHEELER ENERGY LIMITED 2002
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Line 9 - Indicate the maximum allowable pressure drop for the entire section noted in Line 3. The value specified in Line 9 should only be for the fractionating trays, the pressure drop for other internals such as mist eliminators or packed sections should not be included here. Lines 10 and 11 - These lines can be used to supply any additional information that would be helpful to the tray vendor. NOTE:
The data required for Lines 12 through 32 correspond to the loading point indicated in Line 4.
Line 12 - The direction of the vapor flow is indicated here. Normally, trays are designed for the vapor load entering the tray, therefore the word “(from)” should be crossed out. Lines 13 through 19 - The vapor flowrate and properties are indicated in Lines 13 through 19. These values can be obtained from Table II-E in the P1086 printout. A sample printout has been included in Appendix III. Line 20 - The direction of the liquid flow is indicated here. Normally, trays are designed for the liquid load leaving the tray, therefore the word “(to)” should be crossed out. Lines 21 through 27 - The liquid flowrate and properties are indicated in Lines 21 through 27. This liquid flowrate should correspond to the same loading point for which the vapor flow is specified in line 13. Do not specify the maximum vapor rate along with the maximum liquid rate within the section if they are not for the same loading point Note that there are two possible units of liquid viscosity that can be used in Line 24. Be sure to cross out the inappropriate unit. Line 28 - This line can be used to supply any additional information that would be helpful to the tray vendor. Line 29 - The minimum downcomer area is normally left blank. Line 30 - Select the proper System Factor, for example, the ones given in Tray Design Manual Bulletin 4900 (see Section 2.2.5). The selection should be based on past designs for the same type tower, and should be approved by the Chief Process Engineer/Manager. Lines 31 and 32 - The maximum and minimum operating range is FOSTER WHEELER ENERGY LIMITED 2002
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indicated in lines 31 and 32, respectively. These values normally are selected in conjunction with the client; typical values are 100% for the maximum operating range and 50% for the minimum operating range. Final selection of the minimum and maximum operating ranges should be approved by the Chief Process Engineer/Manager. Lines 35 through 46 - Mechanical Design and Tray Requisition Information. These lines are normally left blank. Lines 47 through 51 - These lines are used to provide any additional referenced notes that may be required. State whether a water-rich liquid phase “will be”, or “might be” present on the tray during normal operat ion. This will help in choice of materials of construction for the tray. Bottom Line on Data Sheet - The originating Process Engineer’s nam e or initial should appear where indicated. P.O. No. and Supplier are left blank.
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7.0
PROCESS STD 105A PAGE 28 REV 10 DATE JULY 2002
CHECKING VENDOR’S PROPOSALS It is the responsibility of the Process Engineer to insure that a proposal submitted by a tray vendor for supplying fractionating trays is technically correct. Some tray vendors will supply a computer printout of the tray rating program used to design the trays. When checking a vendor’s design, the following points should be examined. 1)
Check that the input used by the vendor to design the trays is correct. This input can include any or all of the following: a)
Vapor and liquid flowrates and physical properties
b)
Tower diameter and tray type
c)
Tray spacing
d)
Number of tray passes
e)
System Factor
f)
Turndown requirements
g)
Tray metallurgy
These data are normally specified on the Foster Wheeler Tray Data Requisition Form 135-110A. 2)
Other hydraulic parameters such as the Downcomer Clearance, Weir Height and Flow Path Length are normally not specified by Foster Wheeler on the Tray Data Requisition Form, but should be checked to insure that the criteria outlined in the corresponding sections are met. For Glitsch designs, the Unit Reference Number should also be checked.
3)
All of the hydraulic parameters outlined in Section 2.2 referring to tray design should be checked.
4)
Ensure that a statement appears in the proposal that the tray vendor will guarantee hydraulic performance for the operating ranges specified in Lines 31 and 32 on the Tray Data Requisition Form.
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PROCESS STD 105A PAGE 29 REV 10 DATE JULY 2002
APPENDIX I BUBBLE CAP TRAY CALCULATION METHODS
This appendix cites an old calculation method developed within Foster Wheeler to design Bubble Cap Trays. This method has been included for historical interest, as the more recent design methods and computer models listed in Section 5.0 are available and should be used instead. For the old bubble cap tray calculation method, see the old Process Standards, Volume I, Section 200 (Towers), pages 3 through 30.
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APPENDIX II SIEVE TRAY CALCULATION METHODS
This appendix cites an old calculation method developed within Foster Wheeler to design sieve trays. This method has been included for historical interest, as the more recent design methods and computer models listed in Section 3.0 are available and should be used instead. For the old sieve tray calculation method, see the old Process Standards, Volume I, Section 200 (Towers), pages 31 through 40.
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APPENDIX III TRAY DATA INFORMATION
This appendix contains a sample of a completed Tray Data Requisition Form 135-110A. Also contained in this appendix are P1086 sample computer printouts of the Tray Loading Table, Table II-E and Stage Liquid Properties, Table II-B.
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APPENDIX III (Cont’d) TRAY LOADING TABLE TABLE II-E II-E. TRAY LOADING TABLE VAPOR ENTERING STAGE P, PSIA
COMP Z
FT3/S
LIQUID LEAVING STAGE
STAGE
M LB/HR
MOL WT
T,DEG F
LB/FT3
DEN**.5
VL,FT3./S
M LB/HR
HOT SG
T,DEG F
HOT GPM
MOL WT
1
81.783
43.01
105.14
211.00
0.7942
12.044
1.886
0.2597
3.13
52.014
0.4782
99.39
217.22
43.01
2
82.795
43.25
107.16
211.22
0.7938
12.153
1.892
0.2614
3.18
53.027
0.4739
105.14
223.44
43.38
3
82.813
43.51
109.53
211.43
0.7936
12.116
1.899
0.2618
3.17
53.044
0.4740
107.16.
223.50
43.80
4
82.796
43.83
112.39
211.65
0.7934
12.070
1.905
0.2622
3.16
53.028
0.4745
109.53
223.20
44.31
5
82.775
44.22
115.78
211.86
0.7932
12.017
1.913
0.2625
3.16
53.006
0.4753
112.39
222.73
44.93
6
82.773
44.66
119.57
212.08
0.7929
11.962
1.922
0.2629
3.14
53.004
0.4763
115.78
222.23
45.63
7
82.810
45.12
123.55
212.29
0.7926
11.909
1.932
0.2632
3.13
53.041
0.4775
119.57
221.84
46.40
8
82.889
45.58
127.45
212.51
0.7923
11.862
1.941
0.2636
3.13
53.121
0.4786
123.55
221.64
47.16
9
82.995
46.00
131.04
212.72
0.7919
11.823
1.950
0.2639
3.12
53.227
0.4797
127.45
221.61
47.86
10
83.102
46.36
134.19
212.94
0.7916
11.792
1.958
0.2642
3.12
53.333
0.4806
131.04
221.64
48.46
11
83.184
46.65
136.88
213.15
0.7914
11.767
1.964
0.2644
3.11
53.416
0.4814
134.19
221.62
48.96
12
83.227
46.88
139.16
213.37
0.7912
11.746
1.968
0.2645
3.11
53.458
0.4821
136.88
221.47
49.36
13
83.223
47.06
141.12
213.58
0.7911
11.726
1.971
0.2646
3.10
53.454
0.4827
139.16
221.16
49.66
14
83.172
47.20
142.86
213.80
0.7910
11.706
1.974
0.2645
3.10
53.403
0.4833
141.12
220.66
49.91
15
83.077
47.31
144.51
214.00
0.7910
11.685
1.975
0.2644
3.09
53.308
0.4840
142.86
219.96
50.11
16
88.501
47.50
145.79
214.30
0.7904
12.397
1.983
0.2648
3.28
132.530
0.4847
144.51
546.03
50.31
17
89.009
47.73
147.36
214.60
0.7896
12.412
1.992
0.2656
3.30
133.037
0.4842
145.79
548.74
50.46
18
89.589
48.02
149.35
214.90
0.7888
12.428
2.002
0.2665
3.31
133.617
0.4837
147.36
551.72
50.67
19
90.301
48.40
151.53
215.20
0.7879
12.448
2.015
0.2676
3.33
134.330
0.4832
149.35
555.23
50.94
20
91.213
48.90
155.22
215.50
0.7867
12.476
2.031
0.2688
3.35
135.242
0.4827
151.93
559.55
51.29
21
92.398
49.55
159.32
216.1
0.7853
12.517
2.051
0.2704
3.38
136.426
0.4822
155.22
565.02
51.75
22
93.924
50.34
164.17
216.10
0.7836
12.577
2.074
0.2722
3.42
137.952
0.4817
159.32
571.98
52.31
23
95.821
51.26
169.58
216.40
0.7816
12.661
2.102
0.2744
3.47
139.850
0.4810
164.17
580.62
52.96
24
98.036
52.25
175.21
216.70
0.7795
12.768
2.133
0.2768
3.53
142.065
0.4802
169.58
590.81
53.66
25
100.424
53.25
180.65
217.00
0.7773
12.890
2.164
0.2792
3.60
144.453
0.4793
175.21
601.93
54.36
26
102.760
54.17
185.59
217.30
0.7753
13.013
2.194
0.2816
3.66
146.789
0.4782
180.65
613.00
55.01
27
104.833
54.97
189.82
217.60
0.7735
13.121
2.219
0.2837
3.72
148.862
0.4773
185.59
622.88
55.57
28
106.510
55.61
193.34
217.90
0.7720
13.203
2.241
0.2854
3.77
150.539
0.4766
189.82
630.80
56.03
29
107.753
56.12
196.25
218.20
0.7709
13.259
2.257
0.2867
3.80
151.782
0.4761
193.34
636.68
56.39
30
108.588
56.50
198.78
218.50
0.7701
13.290
2.270
0.2876
3.82
152.618
0.4758
196.25
640.60
56.66
31
109.060
56.80
201.30
219.00
0.7693
13.284
2.280
0.2884
3.83
153.089
0.4757
198.78
642.66
56.88
32
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
44.029
0.4759
201.30
184.78
57.08
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VESSELS TOWERS-TRAYS
PROCESS PLANTS DIVISION
APPENDIX III (Cont’d) STAGE LIQUID PROPERTIES TABLE II-B II-B. STAGE LIQUID PROPERTIES CRIT TEMP, DEG F
CRIT PRESS, PSIA
PSEUDO
PSEUDO
DRY API
UOP K
HOT LB/BBL
VISC CP
SR. TENS DYNE/CM
SP HEAT IDEAL
SP HEAT RATIO
43.013
142.48
14.388
167.620
201.46
202.21
646.62
651.36
0.2753
0.088
0.0
0.3913
1.1338
2
43.384
141.86
14.377
166.122
203.54
204.69
642.99
650.25
0.2755
0.089
4.975
0.3962
1.1306
3
43.801
141.03
14.358
166.135
205.84
207.57
639.43
650.29
0.2757
0.090
4.961
0.3986
1.1284
4
44.310
139.88
14.327
166.302
208.69
211.13
635.58
650.79
0.2759
0.092
4.955
0.4009
1.1259
5
44.925
138.39
14.283
166.590
212.19
215.43
631.29
651.24
0.2761
0.095
4.954
0.4034
1.1231
6
45.634
136.62
14.229
166.961
216.32
220.36
626.61
651.16
0.2763
0.097
4.955
0.4060
1.1201
7
46.396
134.68
14.169
167.368
220.88
225.62
621.78
650.26
0.2766
0.100
4.955
0.4087
1.1170
8
47.155
132.71
14.106
167.767
225.55
230.84
617.14
648.55
0.2768
0.103
4.953
0.4114
1.1141
9
47.858
130.86
14.046
168.128
230.03
235.71
613.04
646.33
0.2769
0.105.
4.949
0.4138
1.1115
10
48.465
129.21
13.992
168.443
234.10
240.01
609.68
644.02
02770
0.108
4.944
0.4159
1.1093
11
48.962
127.79
13.944
168.717
237.64
243.69
607.13
641.97
0.2771
0.110
4.941
0.4175
1.1076
12
49.356
126.57
13.903
168.962
240.67
246.80
605.31
640.40
0.2771
0.111
4.941
0.4188
1.1063
13
49.663
125.54
13.867
169.191
243.27
249.45
604.10
639.36
0.2770
0.113
4.945
0.4198
1.1053
14
49.906
124.63
13.835
169.415
245.55
251.80
603.35
638.82
0.2769
0.114
4.953
0.4204
1.1045
15
50.110
123.81
13.806
169.645
247.65
253.99
602.87
638.74
0.2768
0.116
4.965
0.4209
1.1039
16
50.305
123.00
13.778
169.900
249.72
256.20
602.50
639.10
0.2767
0.117
4.983
0.4213
1.1034
17
50.463
122.80
13.774
169.708
250.68
257.03
601.06
636.80
0.2768
0.118
4.952
0.4226
1.1027
18
50.668
122.50
13.768
169.527
251.93
258.14
599.35
634.16
0.2769
0.119
4.921
0.4241
1.1018
19
50.939
122.04
13.756
169.356
253.59
259.64
597.28
630.98
0.2769
0.120
4.885
0.4258
1.1008
20
51.295
121.39
13.738
169.189
255.80
261.63
594.75
627.06
0.2771
0.122
4.844
0.4278
1.0995
21
51.751
120.51
13.712
169.019
258.65
264.19
591.71
622.20
0.2772
0.124
4.795
0.4302
1.0979
22
52.310
119.39
13.677
168.830
262.16
267.32
588.16
616.27
0.2773
0.126
4.736
0.4329
1.0961
23
52.958
118.07
13.636
168.603
266.26
270.92
584.22
609.31
0.2775
0.128
4.665
0.4360
1.0941
24
53.658
116.63
13.589
168.322
270.73
274.76
580.12
601.61
0.2777
0.130
4.583
0.4393
1.0920
25
54.359
115.17
13.542
167.988
275.24
278.57
576.14
593.68
0.2778
0.133
4.494
0.4425
1.0900
26
55.010
113.81
13.497
167.623
279.50
282.11
572.57
586.16
0.2779
0.135
4.404
0.4455
1.0882
27
55.574
112.61
13.456
167.292
283.27
285.20
569.61
579.57
0.2780
0.136
4.324
0.4482
1.0866
28
56.034
111.58
13.421
167.054
286.47
287.81
567.36
574.22
0.2780
0.138
4.261
0.4503
1.0854
29
56.392
110.72
13.391
166.876
289.15
290.01
565.79
570.19
0.2780
0.139
4.212
0.4519
1.0845
30
56.664
109.96
13.364
166.770
291.44
291.95
564.85
567.41
0.2780
0.140
4.178
0.4531
1.0838
31
56.878
109.25
13.338
166.748
293.58
293.84
564.43
565.75
0.2779
0.141
4.157
0.4539
1.0833
32
57.076
108.48
13.311
166.798
295.88
296.03
564.37
565.11
0.2777
0.142
4.146
0.4545
1.0829
STAGE
MOL WT
1
TRUE
TRUE
Z CRIT
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PROCESS STD 105A PAGE 35 REV 10 DATE JULY 2002
APPENDIX IV METHOD FOR ESTIMATING PERCENT FLOOD OF VALVE TRAYS
This appendix contains a sample hand calculation using the method presented by Glitsch for estimating the flood point of valve trays. A sample computer output sheet of the Glitsch Valve Tray Rating Program (Section 4.2A) for the same tray design used for the sample hand calculation has also been included for comparative purposes.
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VESSELS TOWERS-TRAYS
PROCESS STD 105A PAGE 37 REV 10 DATE JULY 2002
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PROCESS STD 105A PAGE 38 REV 10 DATE JULY 2002
APPENDIX IV (Cont’d) METHOD FOR ESTIMATING PERCENT FLOOD OF VALVE TRAYS
Sample Output of Glitsch Valve Tray Rating Program (Section 4.2A). Sample Run for C 3/C4 Splitter Tray Loads with Glitsch Design Tray Number
40 (Top)
21
1 (BTM)
20 (Feed)
Vapor Lbs/Hr
82795
83077
109060
88501
12.2
11.7
13.3
12.4
Vapor Density
1.8920
1.9750
2.2800
1.9830
Vload
3.179
3.092
3.834
3.285
Liquid Lbs/Hr
53027
53308
153089
132530
Gallons per Min
223.7
220.2
643.3
546.6
Liquid Density
29.56
30.19
29.67
30.23
Tray Spacing
24.00
24.00
24.00
24.00
Vload/AA Operating
0.1686
0.1639
0.2033
0.1742
Capacity Factor (Caf)
0.3648
0.3637
0.3597
0.3636
Percent Flood Eq. 13
51.46
50.26
71.83
60.77
DC Loading 0/0 of Allow
28.35
27.63
81.95
68.56
DCBU-Inches Clear Liquid
6.17
6.11
8.88
8.04
D C Baffle Factor
2.07
2.12
1.39
1.63
DC Baffles Advisable
NO
NO
NO
YES
GPM/MFW
1.73
1.70
4.97
4.23
GPM/Weir Length (side(s))
2.17
2.14
6.25
5.31
76
75
92
80
VH2 DV/DL
1.33
1.26
1.91
1.42
Dry Tray Drop
1.66
1.62
1.78
1.65
Height Over Weir (Ave.)
0.60
0.60
1.22
1.10
Pressure Drop, Inch Liq.
3.07
3.02
3.80
3.55
Pressure Drop, MM HG
2.72
2.74
3.38
3.22
Vapor Cu Ft/Sec
Vload/AA Entrainment
Unit Reference
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VESSELS TOWERS-TRAYS
PROCESS PLANTS DIVISION
APPENDIX IV (Cont’d) Diameter
72.800
Approx. No. of Units
209
Side DC Width
10.650
Pitch
2.50 by 3.00 PFV
Center DC Width
9.500
Hole Area
2.66
Ballast Units
16 GA V-1 S.S.
Off Center DC Width Area DC Side
5.244
DC Clearance
1.50
Area DC Center
4.803
Tray Floor
10 GA S.S.
System Factor
0.85
Area DC Off Center Active Area
18.859
Weir Length Side(s)
102.91
Flow Path Length
21.000
Weir Height
2.00
Not Required
Number of Flow Paths
2
Packing
Specified by Customer Pressure Drop
MM HG/Tray
Downcomer Area
Sq. Ft.
Weir Height
Inches
Downcomer Clearance
Inches
Max Operating Rate
Percent
Min Operating Rate
Percent
Results The value of the percent flood obtained by the hand calculation method is in reasonable agreement with the value obtained by using the Glitsch Valve Tray Rating Program.
Percent Flood
Hand Calculation Method
Glitsch Valve Tray Rating Program
80
72
The discrepancy between the two methods is attributed to the simplified equation used in the hand calculation method for establishing flow path length. FPL =
Tower Diameter * 9 Number of Passes
The rigorous program optimizes the flow path length in order to either provide equal active area, or equal downcomer widths, depending on customer preference. This frequently generates a FPL different from that calculated by hand. In any event, the hand calculation method gives a good estimate of the tower diameter.
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PROCESS STD 105A PAGE 40 REV 10 DATE JULY 2002
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VESSELS TOWERS-TRAYS
PROCESS STD 105A PAGE 41 REV 10 DATE JULY 2002
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PROCESS STD 105A PAGE 42 REV 10 DATE JULY 2002
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PROCESS STD 105A PAGE 43 REV 10 DATE JULY 2002
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TABLE 1.2 MINIMUM DOWNCOMER RESIDENCE TIME AND MAXIMUM DOWNCOMER BACKUP(4) Frothiness
Example Service
Residence Time (Sec.)
Maximum Downcomer Backup (%)
Very low
Butane, Propane
4
60
Low
Gasoline, heptane
5
55
Moderate
Crude oil towers, Abs. oil strippers
6
50
High
Mineral oil absorbers, Vacuum towers
7
40
Very high
Amines, Glycols & unknown system
10-12
30-35
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