internship pdf

SUMMER PRACTICE 2010

FAIZAN MIR MIDDLE EAST TECHNICAL UNIVERSITY NORTHERN CYPRUS CAMPUS INTERNSHIP REPORT(MECH 400) 1586692

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TABLE OF CONTENTS INTRODUCTION………………………………………………………………….04 -05

SAFETY AND QUALITY CONTROL.......................... CONTROL........................................ ............................ ......................06-0 ........06-08 8 EQUIPMENTS Centrifugal Pumps……………………………………………………… ..09 Heat Exchanger (with figure) .. ………………………………………10-11 Furnace…………………………………………………………………… ..12

Burner (with figure) ……………………………………………. ……….. 13 Soot Blower…………..…………………………………………………….13

Stack, Insulation & Cooling towers (with figure)…………………..... 14 Fractionating Column (with figure)………………………………… 15-16 Electric Desalter……..……………………………………………………..17

UTILITIES Boiler(with figure) ………………………………………………………… ..18 Electric Generator (with figure) ………………………………………….19 Instrumental Air……..……………………………………………………...19

QUALITY CONTROL (with table) ………………………………………………...20-22 STORAGE FACILITIES(with table) ………………………………………………23-24 PROCESS FLOW…………………………………………………………………... 25-35

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SUMMER PRACTICE 2010 MAINTAINENCE DEPARTMENT………………………………………………….36 CONCLUSION………………………………………………………………………… 37 ABBRIVIATIONS……………………………………………………………………… 38 REFERENCES………………………………………………………………………… 39

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INTRODUCTION The aim of doing internship in the Bosicor company limited was to experience the work environment of a mechanical engineer in an oil refinery. Following is a brief profile of the company:

Profile: COMPANY NAME

Bosicor Pakistan Limited (MKP-1)

OWNED BY

BOSICOR GROUP

ESTABLISHED

January 1995

REVAMP

Sept – Oct 2003

ADDRESS

PLANT ADDRESS Mouza Kund Plant, Sub Tehsil Gadani, Near Hub Power Company

Ltd.

Power

plant (HUBCO),

District

Oil Marketing

Unit 6th

Lasbela,Balouchistan . MANAGING OFFICE Bosicor

Pakistan

Limited

Floor,Business Plaza, Mumtaz Hassan Road, Karachi Phone: 021-111-222-081 (EXT: 519) email: [email protected] STATUS

Bosicor Pakistan Ltd is the fifth Oil refinery in Pakistan.

DEPARTMENTS

EHS(Environment, Health and Safety) Laboratories(7 chemicalcengineers, 12 technicians)

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SUMMER PRACTICE 2010 Maintainence(8 machenical engineers, 20 technicians) Operation(10 chemical engineers, 25 technicians) Oil Moment(3 engineers, 5 technicians ) Decanting and Shipping(no engineers or technicians) CRUDE TYPE

Imported (QATAR MARINE CRUDE OIL) Q M C O. Collected from Ships at ZOT(PSO),Port Qasim

PRODUCTS

-Naphtha - Gasoline

- HSD

- LPG

- Kerosene PLANT CAPACITY

30,000-35,000 barrels per day

% CONTRIBUTION

5% to the total Crude Production of Pakistan

STATISTICS

Sales(2007)

9999 Million Rs

Net profit(2007) 633 FUTURE PROJECTS

Million Rs

1. Additional Storage Facility 2. Sub-Sea Pipeline Project 3. Isomerization Unit

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SAFETY AND QUALITY CONTROL Safety: Safety is generally interpreted as implying a real and significant impact on risk of death, injury or damage to property. Safety measures are activities and precautions taken to improve safety (i.e.reduce risk related to losses).

Safety against fire: The biggest danger which BOSICAR can face is fire. As it is an oil refinary which deals with the fuel which in any condition can burn steadily and can destroy the plant area and even the workers working there.

Types of fire: There are four types of fire: Solid /Combustible Liquid/Flammable Gas/ Electric Metal Quenching the fire: Following are the ways through which we can remove the fire: Smothering Starvation 6

SUMMER PRACTICE 2010 Cooling Few types of equipment are used which help us controlling fire: Dry chemical Powder Carbon dioxide Foam Water Safety department: Byco has it department for safety called EHS (Environment, Health and Safety). The work of this department is to monitor all the plant area and take all precautions to protect the plant and even to protect all the workers at the plant .More than that it is also capable of tackling any emergency situation at the plant area or at the whole covered area. The objectives of this department are as follows: 

To ensure there is no fire at the plant area, and taking it out if any.



To ensure that fire extinguishers are placed at the plant in good and working condition where ever it is needed.



To ensure no body is carrying anything which can burn or can help in burning. (e.g match boxes, lighters mobile phones or batteries).



To provide electronic equipments with IS(intrinsically Safe ) batteries.

Practicing the capabilities: Apart from all the safety provided by the department, this department also tests there`s and worker`s skills at times: 

Fire drills are held time to time to train workers of different departments.



Safety alarms are rung to prepare workers for any emergency situation.



To check emergency equipments from time to time. 7


Precautions: Byco uses following sources or equipments for safety: PPE’s(Personal Protective Equipments) Safety shoes Safety Cover Gloves, Air Filters, Goggles, at sensitive areas Body Safety Harness at height (Above 6 feet). Work Permits (PTW) These permits are classified by the work that is required to be done: Hot Work Permits: This includes the work in which sparks are produced. Cold Work Permits: Activates involve working in plant areas. Excavation work Permits: Including civil work Confined Space Entry Certificate: Work inside Confined Spaces. Conditions: Following conditions should be maintained in order to have the confined permit. -

H2S level must

be

-

Oxygen level must be 20.9%

minimally.

- LEL (low explosive level) must be 0.00% maximally 8


EQUIPMENTS In this section the brief detail of some most important equipments, which act as a backbone of an oil refinery, without the knowledge of which, it is impossible to understand the processes. Centrifugal Pumps: A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure of the fluid. Centrifugal pumps are commonly used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits into the downstream piping system. Centrifugal pumps are used for large discharge through smaller heads. A centrifugal pump works by converting kinetic energy into potential energy measurable as static fl uid pressure at the outlet of the pump. This action is described by Bernoulli’s principle. With the mechanical action of an electric motor or similar, the rotation of the pump impeller imparts kinetic energy to the fluid through centrifugal force. The fluid is drawn from the inlet piping into the impeller intake eye and is accelerated outwards through the impeller vanes to the volute and the outlet piping. As the fluid exist the impeller, if the outlet piping is too high to allow flow, the fluid kinetic energy is converted into static pressure. If the outlet piping is open at a lower level, the fluid will be released at greater speed.

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Heat exchanger:

A heat exchanger is a device built for efficient heat transfer from one medium to another; both the medias are separated by a solid wall so that they never mix. They are extensively used in petroleum refineries over a wide range for various purposes, such as: •

Heating the crude streams up to desired temperature bef ore entering the

desalters. •

Cooling the product streams to ambient temperatures. e.t.c.

•

As a condenser for condensing the vapors.

•

As a re-boiler for maintaining the columns bottom temperature.

Shell & tube heat exchangers Shell and tube heat exchangers consist of a series of tubes. One set of these tubes contain the fluid that must be either heated or cooled. The second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required. A set of tubes is called the tube bundle and can be made up of several types of tubes : plain, longitudinally finned etc. Shell and tube heat exchangers are 10

SUMMER PRACTICE 2010 typically used for high pressure applications. This is because the shell and tube heat exchangers are robust due to their shape. There are several thermal design features that are to be taken into account when designing the tubes in the shell and tube heat exchangers Following are the few main parts of the heat exchanger: •

Shell

•

Tubes

•

Floating head

•

Channel head

•

Baffles

Condition that affects heat transfer: •

Proper Mixing o f Medium

•

Transfer Area

•

Evaporation of Medium

•

Arrangement of Shell and Tube

Fouling: Deposition of undissolved particles in the exchangers that reduces the flow is called fouling can be caused by: •

Frequent use of the Heat Exchanger.

•

Not cleaning the Heat Exchanger regularly.

•

Reducing the velocity of the fluids moving through the heat exchanger.

•

Over -sizing of the heat exchanger. 11


Furnace: An industrial furnace or direct fired heater is equipment used to provide heat for a process or can serve as reactor which provides heats of reaction, and is used in all petroleum refineries. Furnace is that part of petroleum refinery which controls the economics of whole plant. Efficient operation of furnace is vital. How it works is that, first, fuel flows into the burner and is burnt with air provided from an air blower. The flames heat up the tubes, which in turn heat the fluid inside in the first part of the furnace known as the radiant section or firebox. In this chamber where combustion takes place, the heat is transferred mainly by radiation to tubes around the fire in the chamber. The heating fluid passes through the tubes and is thus heated to the desired temperature. The gases from the combustion are known as flue gas. After the flue gas leaves the firebox, most furnace designs include a convection section where more heat is recovered before venting to the atmosphere through the flue gas stack. Following are some of the main parts of the furnace: •

Radiant Section: The radiant section is where the tubes receive almost all its heat by radiation from the flame.

•

Convection section: The convection section is located above the radiant section. Heat transfer takes place by convection here, and the tubes are finned to increase heat transfer.

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Burner: The

burner

in

the vertical cylindrical

furnace is located in the floor and fires upward. The burner is made of high temperature refractory and is where the flame is contained in. Air registers are located below the burner. A furnace can be lit by a small pilot flame. Most pilot flames now a days are lit by an ignition transformer (much like a car's spark plugs). The pilot flame in turn lights up the main flame. When using liquid fuels, an atomizer is used, otherwise, the liquid fuel will simply pour onto the furnace floor and become a hazard.

Furnace draft: This draft or difference of pressure is caused by the difference between the weight of the vertical column of the hot flue gas in the furnace stack and the weight of the column of the cooler outside air of the same height. The cooler, outside air is heavier. As outside air enters the opening around the furnace burners, it’s greater

weight causes it to rush through these opening and push the lighter, hotter flue gases up the stack. In this manner the movement of air through the furnace becomes continuous.

Soot blower: Soot blowers are found in the convection section. As this section is above the radiant section and air movement is slower because of the fins, soot tends to accumulate here. Soot blowing is normally done when the efficiency of the convection section is decreased. 13

SUMMER PRACTICE 2010 Stack: The flue gas stack is a cylindrical structure at the top of all the heat transfer chambers. The breeching directly below it collects the flue gas and brings it up high into the atmosphere where it will not endanger personnel. Insulation: Insulation is an important part of the furnace because it prevents excessive heat loss. Refractory materials such as firebrick, castable, refractories and ceramic fiber, are used for insulation. Cooling towers: Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or rely solely on air to cool the working fluid to near the dry-bulb air temperature. It is an important part of any refinery it is used to cool hot water circulated from the refinery, which is re-used after cooling. In BOSICOR there two cooling towers: •

THE OLD TOWER: The old cooling tower consist of six fans and it is of counter

current type. •

THE NEW TOWER: The new tower consist of one fan which is cross flow type.

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SUMMER PRACTICE 2010 Fractionating column:

A fractionating column is an essential item used in the distillation of liquid mixtures so as to separate the mixture into its component parts, or fractions, based on the differences in their volatilities. In refineries, the crude oil feedstock is a very complex multi-component mixture that must be separated called fractions and that is the origin of the name fractional distillation or fractionation. All materials that enter the column as feed leave as products in either the make or tails this material balance is an application of the principle of conservation of mass.Conditions necessary to make distillation works are: •

The components in the system are chemically & thermally stable.

There is a significant difference between the boiling points & vapor pressures of the components to be separated. •

The components are miscible. 15

SUMMER PRACTICE 2010 •

The desired concentration of low boilers in the make & high boilers in the tails

are achieved through use of a practical number of separations (trays or stages) in the column. •

There are no solids formed in the system as high boilers are concentrated.

Temperature control: Head temperature is the lowest temperature in the column and is the boiling point temperature of the stream leaving the column. Therefore the head temperature is used to monitor the composition of the make. Head temperature is controlled through the reflux. Head temperature is a critical control in distillation process. The temperature profile across a distillation column operating at a fixed pressure represents the boiling points thus the concentration of components, up & down the column, on each tray. An increase in temperature at constant pressure represents an increase in high boiler concentration and decrease in temperature at constant pressure represents an increase in low boiler concentration. Reflux: The vapor velocity up the column can be stabilized at different feed rates by recycling a portion of the OH condensate. This in essence is a way to maintain a constant feed rate to the column. This stream is called the reflux and serves a second purpose of increasing low boiler concentration overhead by sending high boilers back down the column. Reflux is also a means of controlling the temperature profile in the column. Increasing the amount of reflux flow lowers the temperatures in the column. Decreasing the reflux flow raises the column temperature. Changing the temperature by reflux rate is simply the result of changing the concentration of high & low boilers.

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SUMMER PRACTICE 2010 Electrical desalter: An electrical desalter is a process unit on an oil refinery that removes salt from the crude oil by meals of electrical field. The salt is dissolved in the water in the crude oil, not in the crude oil itself.

Why desalt crude? •

The salts that are most frequently pr esent in crude oil are Calcium, Sodium and

Magnesium Chlorides. If these compounds are not removed from the oil several problems arise in the refining process. The high temperatures that occur downstream in the process could cause water hydrolysis, which in turn allows formation of hydrochloric acid. •

Sand, Silts, Salt deposit and Foul Heat Exchangers.

•

Water Heat of Vaporization reduces crude Pre -Heat capacity.

•

Sodium, Arsenic and Other Metals can poison Catalysts.

•

Environmental Compliance, i.e., By removing the suspended solids, which

might otherwise become an issue in flue gas opacity norms, etc., A typical desalter comprised of a vessel, electric transformer, oil outlet header, electrodes, inlet header, water effluent header, mud wash header and mixing valve .The vessel is a horizontal gravity settling vessel in which brine water is separated from the crude oil. Electrical desalting process consists of two steps. The first step consists of forming an emulsion of crude oil & water. Second step is a demulsification process in which the emulsion of crude oil & water formed in the first step is broken by means of an electrical field.

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UTILITIES Utilities play an important role in process of any Industry. Following are few of the utilities used in BOSICOR.

Boiler:

The steam requirement of the industry is fulfilled by two boilers in BOSICOR. Types of both of them are: •

Fire Tube Boiler

•

Water Tube boiler

Water from reservoir is soften first by the help of chemical injection and all salts of

Mg+2 and Ca+2 which produce hardness are converted into the salts of

Na+ which don’t produce hardness. Then it is passed through Deaerator where salts of

PO4-3 and SO3-1 are injected where oxygen is removed from the water. After that it is injected to Economizer and then to the Boiler. Where water is converted into steam and then it is used further.

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SUMMER PRACTICE 2010 Electric generation: BPL has its own dependable electric power generation facility consist of 6 generators out of which 4 meets plant requirements, 3 in working condition ,1 stand-by. Each having 1.5 MW capacity producing 60Hz of electricity. Apart from that 2 for electrical official requirement ,1 in working 1 stand-by producing 500KVA 50Hz.

Instrumental air: Nearly all of the instruments are pneumatic. So pressurized air is required for there working. The air is supplied by the compressors one of which is in working condition and other is stand-by. The compressor has its capacity 650 m 3 /hr and its working pressure is 7.6 - 8.4 bar. The other standby is 345 m 3 /hr. It can produce 6.5 - 8.5 bar pressure

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SUMMER PRACTICE 2010 QUALITY CONTROL

Quality is controlled in the industry to make their products marketable. Standards are set and maintained which is an important thing. The quality is tested time by time and is reported to the engineers where they compare the results with the standard. If the result is not of the standard they take steps to maintain their standards. Following are the tests which are performed at the lab:

Materials

Tests

Specific Gravity Color Light Naphtha

Reid Vapor Pressure Doctor Test Distillation

Specific Gravity Color Heavy Naphtha

Doctor Test Reid Vapor Pressure

Specific Gravity Color High Speed Diesel Before

Flash Point

Injection

Cloud point Pour Point Distillation

Specific Gravity Color

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SUMMER PRACTICE 2010 High Speed Diesel After

Flash Point

Injection

Cloud point Pour Point Distillation Sulphur test

Specific Gravity Furnace Fuel Oil Before

Flash Point

Injection

Viscosity Pour Point

Furnace Fuel Oil After

Flash Point

Injection

Viscosity Pour Point

Alkalinity TDS(total dissolved solids test) Boiler Blown Down

pH

Water

Sulfite Phosphate Iron

Wash Water

pH Chloride

Boot Water

pH Specific Gravity

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SUMMER PRACTICE 2010 LPG

Cu Corrosion Weathering

pH TDS Zinc Iron Cooling Water

Free Chloride Cooling Water Alkalinity Hardness

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SUMMER PRACTICE 2010 STORAGE FACILITIES Tank farm: Tank farm area is basically the storage facility for the rundown streams coming continuously from plant area. There are 22 storage tanks in total and 4 LPG storage vessels. This area also serves for the pumping of products to shipping area for filling the bowsers when required. Further detail of area is given below.

PRODUCT

NUMBER OF TANK

MAX CAPACITY (barrels)

FURNACE OIL

4

48000

HIGH SPED DEISEL

6

38000

HEAVY NAPTHA

2

10000

LIGHT NAPTHA

1

50000

SOUR NAPTHA

1

5000

SWEET NAPTHA

1

15000

PMG(Petrol for vehicles)

5

25000

LPG(liquefied petroleum

4

3050

JP(Jet fuel)

2

10000

SLOP

1

5000

gas)

API separator & slop oil tank: The oil from different sampling points before every new sampling is drained from the lines which then through pipe lines go to the API separator, also any leakage of plant is forced to go to this separator. This separator is simply the tank where water is allowed to settle down under the gravity action and is drained to water pond located nearby through pump. The oil from top is then pumped to the slop oil tank wherefrom it goes to the booster pump through pipeline and mixed with the feed line of crude oil to plant. Also if any product becomes out of desired set points goes to this slop oil tank. 23

SUMMER PRACTICE 2010 This process takes place to separate oil from the drain so that the drain entering the sea is less harmfull to marine life.

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SUMMER PRACTICE 2010 PROCESS FLOW

This portion includes the brief discussion of ,process flow of BPL(MKP-1),nearly all the aspects are covered including the decantation up to shipping, detail of various equipments has been covered in the last portion, but further explanation of technicalities involved in process is also discussed wherever necessary. Also the PFD's of different unit's are given for better understanding of process. The whole process flow is divided into three segments. Pre-refining flow: In this division various operations, which are performed before refining area, are discussed. Decanting section: This section serves for unloading crude oil being transported through bowsers. Before receiving the crude oil bowsers are inspected for the crude level by dip rod for any loss during transportation. After inspecting the level bowsers are allowed to move towards oil gantries, where crude is pumped from bowsers to the storage tanks located nearby. There are 16 gantries, so at a time 16 bowsers are unloaded. Crude bowsers have nearly 50,000-60,000 Ltr. Capacity. It takes nearly 45 minutes to withdraw the crude from bowsers.

Storage tanks: There are four storage tanks for crude oil having the total storage capacity of 200000 bbl (approx.). The settling time of 3-4 hr. is provided for settling the water down by gravity, after which water is drained out through drainage line. After this mixer is turned on for homogenizing the crude mixture & mixing the sludge (mainly the heavier particles of crude), which settle down at bottom during settling time.

Booster pumps: Crude oil from storage tanks flows into the suction of crude booster pumps. These pumps provide part of necessary head required to move the crude oil through the crude charge system. 25

SUMMER PRACTICE 2010 Refining: This section includes various operations & processes performed with crude. This section is further sub-divided into different sections.

CDU: This unit performs the basic distillation process and seperates the crude feed into different fractions. This section includes mainly desalters, PF tower, furnace,distillation column, naphtha splitter& strippers. After fractionation the different fractions goes to different units for further processing.

Chemical injection: Two chemicals are injected into crude oil line ahead of crude charge pumps by PD pumps, for diverse purposes. Chemicals & their relative details are given in the table.

CHEMICAL NAME

PURPOSE

FEED RATE/RATIO

Caustic solution

Controlling the pH

10-20 ppm

Demulsifier

Breaking the emulsion.

0-10 ppm

Charge pumps: The crude pumped by booster pumps divided into two streams ahead of crude charge pumps & then flows separately into the suction of crude charge pumps. These pumps provide remainder necessary head required to move the crude oil through the crude charge system. Crude from the discharge of charge pumps then separately flows into heat exchanger trains (named old & new), for recovering the heat (energy) from hot product streams & attaining the temperature necessary for desalting & again exchanging heat separately with various streams for achieving the temperature necessary for pre-flash tower operation. (Note: exchanger trains are sub-classified as A & B on the basis of pre-desalter & postdesalter streams)

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SUMMER PRACTICE 2010 Old train(a): Crude from charge pump divided into two parallel streams, one flowing to the tube side of crude & other flowing to the the tube side of heat exchanger both streams leaving the exchangers recombine and flows to tube side of crude & then flow to the tube side of crude exchanger.The stream from here goes to the desalter 2.

New train(a): Crude from discharge of charge pump divided into two streams, one flowing through shell side of crude v/s TPA exchanger & the other flowing through crude v/s HSD exchanger, the two streams leaving the exchangers recombine & then again splitting into two stream, one flowing through tube side of crude v/s kero exchanger & other flowing through crude v/s FFO exchanger.The two streams then recombine and flowing to the tube side of crude v/s TPA exchanger. This stream then goes to desalter 1.

Desalters: Streams from old & new exchanger trains separately flows to desalter-2 & desalter-1 respectively. At the inlet of desalters fresh water is injected at the rate of 4-5%vol. of crude into these two streams, which then passes along with crude through the static mixer to form the emulsion. In the desalters the water with salts is separated from crude oil, drawn up from vessels by means of interface level controllers and then flows through the shell side of desalter water exchanger where it is cooled, by exchanging heat with fresh water inlet stream of desalters, and sent to oily sewer.

Old train(b): Crude from desalter-2 enters the shell side of crude v/s HSD exchanger and than passes from tube side of crude v/s HSD exchanger, then splitting into two streams one flowing through the tube side of crude v/s FFO exchanger & other flowing through tube side of crude v/s exchanger. The two streams then combine and then flow through HE & goes to pre-flash tower.

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SUMMER PRACTICE 2010 New train(b): Crude from desalter-1 enters the tube side of crude v/s HSD exchanger then splitting into two streams, one flowing through the shell side of HE& other flowing through the tube side of crude v/s HSD exchanger. The two streams then recombine and pass through shell side of crude v/s FFO exchanger and then goes to pre-flash tower.

Pre-flash tower: Crude through new train & old train by a PCV-680 & PCV-670 combines andenters at the tray#16 of pre-flash tower .Pre- flash tower recover most of the light ends and a part of the light naphtha. PF tower OH via fan cooler goes to PF OH drum. Where uncondensates (gases) are removed from top & from bottom naphtha is obtained, a part of which returns back to the tower as a reflux & remaining part is sent to the naphtha splitter. PF tower bottom is pumped by the pump, then divided into two streams, one flowing through PF bottom v/s HSD exchanger & the other flowing through PF bottom v/s FFO exchanger, the two streams then combine and again splitted into two streams, one flowing through shell side of HE & the other flowing through tube side of HE. The two streams then combine and goes to born heater.

Born heater: Crude from bottom of PF tower after exchanging heat in various heat exchangers flows to the born heater which provides the temperature necessary for desired distillation. Crude before entering the heater divided into two streams, the flow of both streams is controlled by FCV-604 & FCV-605. These two streams enter the convection section of heater, where it is heated by the hot flue gases. Saturated steam also enters the convection section & gets superheated, which is in turn use for injecting into crude tower. Crude oil from convection section then enters into tubes located in radiation section and heated up to temperature of 350~360 oC. after attaining the required temperature the crude streams leave the heater and combines then goes to crude tower. crude oil entering the crude tower has the vapor-liquid composition of 60% &40% respectively. Heater has 10 burners and is dual fired thus having the both options of firing with fuel oil or fuel gas, or with both at a time. fuel oil comes through PCV------& 28

SUMMER PRACTICE 2010 fuel gas through PCV-118. Atomizing steam is also provided for proper dispersion of fuel oil which is necessary for good & complete combustion of fuel oil, otherwise fuel will not burn completely &falls on floor. For proper atomizing the SH steam & FO mixture in the ratio of 1.5:1 is good choice.

Crude tower: The vapor liquid mixture of crude oil from crude heater enters the flash zone of crude tower for desired distillation. Also the SH steam is injected at the bottom of tower for stripping (removing) the lighter ends from reduced crude.above the designed capacity steam feed rate will add to the heat liad of the tower. Steam rate below the designed rate will allow excessive amount of middle distillates to be included in the reduced crude from the bottom of tower.

Crude tower top reflux: The top reflux controls the tower top temperature. The crude tower OH vapors along with stripping steam is condensed first in HE, then in air cooler and finally in trim cooler & then accumulated in OH reflux drum. Pressure in reflux drum is controlled 8 - 10 psig. The liquid hydrocarbon from OH reflux drum are pumped by reflux pumpas top reflux to tower. Top reflux flow controls the tower top temperature. The remaining liquid from drum under level controller is sent as feed to naphtha splitter.

Top pump around reflux(tpa): To provide reflux for the middle / upper section of the tower, a hot stream from plate#08 is taken out. TPA pumps pumps this stream to shell side of crude v/s TPA exchanger & then passes through shell side of HE where it preheats the crude, TPA is further cooled in air cooler. The cooled TPA returns to crude tower plate#06.

Naphtha splitter: Naphtha from PF tower & crude tower OH system through pumps respectively is pumped to PF tower. Both the streams combine ahead of splitter tower to form a single stream. Which then flows through the tube side of splitter feed v/s bottom reboiler and 29

SUMMER PRACTICE 2010 through the tube side of hot oiv/s naphtha feed reboiler temperature of feed is controlled through TCV- 262 by controlling the hot oil flowing through the reboiler . the stream then enter the splitter tower. In which light & heavy naphtha fractions are seperated . light naphtha from OH flows to the fan cooler & then through the trim cooler and ultimately goes to reflux drum . The reflux drum is installed in vertical position and is operated at maximum liquid level to avoid separation of LPG from liquid. Light naphtha from including LPG from reflux drum os drawn off by pump. part is sent back to splitter as reflux, and remaining portion is sent as a feed to LPG unit for the separation of LPG. an independent stream is drawn from the bottom of the splitter. It passes through the shell side of splitter reboiler where it is heated by hot oil passing through the tube side of reboiler, hot oil flow is controlled by TCV-233 to control splitter bottom temperature. Reboiler stream is flashed back into splitter. The flashed hot liquid vaporizes the light ends from the heavy naphtha flowing down in splitter. Heavy naphtha from the bottom of splitter is pumped by pump to shell side of HE where it is cooled by splitter feed. The heavy naphtha is further cooled in air cooler and then in trim cooler wherefrom it is sent to HDT feed tank. This can be routed to merox unit for sweetening.

Strippers: All side streams drawn from crude tower first flow through the strippers for the removal of lighter ends from respective streams.steam is injected at the bottom of strippers for stripping the lighter ends. There are two strippers in function at present. One stripper strips the lighter ends from kero. Kero.is drawn from the tray#19 of crude tower. The second stripping column strips the lighter ends from HSD, HSD is drawn from tray#24, the lighter ends removed from HSD are returned back to tray#26. HSD obtained from the bottom of column is sent to storage. While kero. is sent to merox unit for sweetening

Lpg separation unit: This unit separates the LPG from light naphtha, simply by removing propane & butane from L/N & thus this unit also serves as naphtha stabilizing unit. L/N from the top of naphtha splitter is the feed of this unit, which comes to LPG feed tank 21-T-1, 30

SUMMER PRACTICE 2010 wherefrom it is pumped to depropanizer column . In this column propane is removed from L/N. one side stream is drawn from the top side which after passing through HE goes to reflux drum where one stream is drawn from the bottom and pumped by pump, a part of this stream goes back to the top of the column, Top flow is controlled by FCV11, and remaining part is sent to storage which is propane. One stream is drawn from the bottom which goes to kettle type reboiler, where it is heated by hot oil circulation. Two streams are drawn from reboiler, one goes back to the column for maintaining the column bottom temperature, and the other stream is sent as feed todebutanizer. In this column butane is removed. One stream is drawn from the top side which after passing through HE goes to reflux tank, the bottom stream is pumped by (21-P-5-A/B), a part of this stream goes back as reflux & remaining part is the butane which is sent to LPG storage. The stream drawn from the bottom of debutanizer column passes through reboiler from where a part is sent back as boilup and reamaining part after passing through HE is sent to light naphtha merox unit for sweetening.

Merox unit: Merox is an acronym for mercaptan (RSH is a mercaptan, R signifies an organic group such as a methyl, ethyl, e.t.c) oxidation. It is a catalytic chemical process used in oil refineries and natural gas processing plants to remove mercaptans from LPG, propane, butanes, light naphtha, kerosene and jet fuel by converting them to liquid hydrocarbon disulfides. The Merox process requires an alkaline environment which is provided by an aqueous solution of sodium hydroxide (NaOH), a strong base, commonly referred to as caustic. The catalyst is impregnated onto charcoal granules. Processes within oil refineries or natural gas processing plants that remove mercaptans and/or hydrogen sulfide (H2S) are commonly referred to as sweetening processes because they results in products which no longer have the sour, foul odors of mercaptans and hydrogen sulfide. the overall oxidation reaction that takes place in converting mercaptans to disulfides is: 4 RS H + O 2

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2RSSR + 2H2O

SUMMER PRACTICE 2010 lpg merox: The LPG feedstock through LCV-13 enters the prewash vessel and flows upward through a batch of caustic which removes any H2S that may be present in the feedstock. The coalescer at the top of the prewash vessel prevents caustic from being entrained and carried out of the vessel. The feedstock then enters the mercaptan extractor and flows upward through the contact trays where the LPG intimately contacts the downflowing Merox caustic that extracts the mercaptans from the LPG. The sweetened LPG exits the tower and flows through: a caustic settler vessel to remove any entrained caustic, a water wash vessel to further remove any residual entrained caustic and a vessel containing a bed of rock salt to remove any entrained water. The dry sweetened LPG exits the Merox unit. The facilities for sweetening of light naphtha, heavy naphtha & kerosene are also present. there merox units are nearly same for all these with few alterations.

Reformer unit: This unit accounts for increasing the octane rating of gasoline and HOBC(reformate) is the product of this unit. this unit consist of following units. HYDRODESULFURIZATION: The hydrodesulfurization reaction takes place in a fixed-bed reactor at elevated temperatures ranging from 300 to 400 °C and elevated pressures ranging from 30 to 130 atmospheres of absolute pressure, typically in the presence of a catalyst consisting of an alumina base impregnated with cobalt and molybdenum. Hydrogenation is a class of chemical reactions in which the net result is the addition of hydrogen (H). Hydrogenolysis is a type of hydrogenation and results in the cleavage of the C-X chemical bond, where C is a carbon atom and X is a sulfur, nitrogen (N) or oxygen (O) atom. The net result of a hydrogenolysis reaction is the formation of C-H and H-X chemical bonds. Thus, hydrodesulfurization is a hydrogenolysis reaction. Using ethanethiol (C2H5SH), a sulfur compound present in some petroleum products, as an example, the hydrodesulfurization reaction can be simply expressed as

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Ethanethiol + Hydrogen

Ethane + Hydrogen sulfide

C2H5SH + H2

C2H6 + H2S

The liquid feed is pumped by pump up to the required elevated pressure and is joined by a stream of hydrogen-rich recycle gas, the pressure of gas is controlled by PCV-340 The resulting liquid-gas mixture is preheated by flowing through a heat exchanger. The preheated feed then flows through a fired heater where the feed mixture is totally vaporized and heated to the required elevated temperature before entering the reactor and flowing through a fixed-bed of catalyst where the hydrodesulfurization reaction takes place. The hot reaction products are partially cooled by flowing through the heat exchanger where the reactor feed was preheated, then flows through fan cooler and then flows through a trim cooler. The resulting mixture of liquid and gas enters the gas separator vessel at about 35 °C and 3 to 5 atmospheres of absolute pressure. Most of the hydrogen-rich gas from the gas separator vessel is recycle gas which is routed through an amine contactor for removal of the reaction product H2S that it contains. The pressure of gas is controlled by PCV-235. The H2S-free hydrogen-rich gas is then recycled back for reuse in the reactor section. Any excess gas from the gas separator vessel joins the sour gas from the stripping of the reaction product liquid. The liquid from the gas separator vessel flows to the suction of pump routed through a reboiled stripper distillation tower. The bottoms product from the stripper is the final desulfurized liquid product from hydrodesulfurization unit.

Catalytic reforming: Before entering the reactors two chemcials are injected into the feed: •

PERC

•

Methanol The purpose of there chemicals is to maintain the chloride level and to support metallic reactions thus increase the rate of reaction. 33

SUMMER PRACTICE 2010 Following reaction takes place in the Reformer Unit : • Naphtene Dehydrogentaion • Naphtene Isomerisation • Paraffins Dehydrogentaion • Paraffins Isomerisation • Hydrocracking •

Demethylation • Aeromatic Dealkylation

The liquid feed from hydrodesulfurization unit is pumped through pump - up to the reaction pressure (5 to 45 atm) and is joined by a stream of hydrogen-rich recycle gas. The resulting liquid-gas mixture is preheated by flowing through a HE. The preheated feed mixture is then totally vaporized and heated to the reaction temperature in fired heater before the vaporized reactants enter the first reactor. As the vaporized reactants flow through the fixed bed of catalyst in the reactor, the major reaction is the dehydrogenation of naphthenes to aromatics which is highly endothermic and results in a large temperature decrease between the inlet and outlet of the reactor. To maintain the required reaction temperature and the rate of reaction, the vaporized stream is reheated in the second fired heater before it flows through the second reactor. The temperature again decreases across the second reactor and the vaporized stream is again be reheated in the third fired heater before it flows through the third reactor. As the vaporized stream proceeds through the three reactors, the reaction rates decrease and the reactors therefore become larger. At the same time, the amount of reheat required between the reactors becomes smaller. Usually, three reactors are all that is required to provide the desired performance of the catalytic reforming unit. The hot reaction products from the third reactor are partially cooled by flowing through the heat exchanger where the feed to the first reactor is preheated and then flow through a fan cooler & then through water-cooled heat exchanger.this cooled stream goes to the gas separator. Most of the hydrogen-rich gas from the gas separator vessel returns to the suction of the recycle hydrogen gas compressor and the net production of hydrogen-rich gas from the reforming reactions is exported for use in hydrodesulfurization. The liquid 34

SUMMER PRACTICE 2010 from the gas separator vessel is routed into a fractionating column called a stabilizerThe overhead off gas product from the stabilizer contains the byproduct methane, ethane, propane and butane gases produced by the hydrocracking reactions as explained in the above discussion of the reaction chemistry of a catalytic reformer, and it may also contain some small amount of hydrogen. That offgas is routed to the refinery's central gas processing plant for removal and recovery of propane and butane. The residual gas after such processing becomes part of the refinery's fuel gas system. The bottoms product from the stabilizer is the high-octane liquid reformate that will become a component of the refinery's product gasoline.

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SUMMER PRACTICE 2010 MAINTENANCE DEPARTMENT The following jobs were observed during my stay in this department. 

Oil caustic dosing pump was removed and relocated in tank farm area for jet fuel graduation.



Seals of the pumps were to be rectified because they had leakage problem in them.



Gland leakages for the pumps were to be rectified due to the abnormal sound.



Mechanical seals of the pump to be changed which are also normally called couplings.



Burner flexible hose pipe to be changed.



Oil cooling tower to be boxed up(Make it ready for service).

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SUMMER PRACTICE 2010 Conclusion In the end I would like to appreciate the helpfulness of all the department heads and the engineers under them, who helped me in understanding the most important department in the oil refinery. I would also like to appreciate the help of my supervisor, Mr Muzaffer Malik, who introduced me to the department heads and explained me everything which I couldn’t understand. The refinery experience gave me a lot of practical knowledge in the

field of operations and maintenance and would help me in taking my decision to choose my career path.

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ABBREVIATIONS

• • • • • • • • • • • • • • • • • • • • • • • • • • • •

API: American petroleum Institute BPA: Bottom Pump Around BPL: Bosicor Pakistan Limited BS&W: Base Sediments and Water CDU: Crude distillation Unit FCV: Flow Control Valve FFO: Furnace Fuel Oil FO: Furnace Oil HDT: Hydro Theater HE: Heat Exchanger HOBC: High Octane Blending Component HSD: High speed Diesel JP: Jet Fuel Kero: Kerosene L/N: Light Naphtha LCV: Level Control Valve LPG: Liquid Petroleum Gas OH: Over Head Reflux PCV: Pressure Control Valve PD Pump: Positive Displacement Pump PFD: Process Flow Diagram PMG: Premier Motor Gasoline PR tower: Pre- flash tower SH: Steam Super Heated Steam TCV: Temperature Control Valve TDS: Total Dissolved Salt TPA: Top Pump Around RON: Research Octane Number

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internship pdf

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