internship pdf

SUMMER PRACTICE 2010

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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..............................................................06-08

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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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

Lasbela,Balouchistan .

MANAGING OFFICE

Bosicor Pakistan Limited Oil Marketing Unit 6th

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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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 Million Rs

FUTURE PROJECTS 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


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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.


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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


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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 fluid 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 before 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


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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 of 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.


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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.


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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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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.


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• 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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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 present 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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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 m3/hr and its working

pressure is 7.6 - 8.4 bar. The other standby is 345 m3/hr. It can produce 6.5 - 8.5 bar

pressure


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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

Light Naphtha

Specific Gravity

Color

Reid Vapor Pressure

Doctor Test

Distillation

Heavy Naphtha

Specific Gravity

Color

Doctor Test

Reid Vapor Pressure

High Speed Diesel Before

Injection

Specific Gravity

Color

Flash Point

Cloud point

Pour Point

Distillation

Specific Gravity

Color


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High Speed Diesel After

Injection

Furnace Fuel Oil Before

Injection

Flash Point

Cloud point

Pour Point

Distillation

Sulphur test

Specific Gravity

Flash Point

Viscosity

Pour Point

Furnace Fuel Oil After

Injection

Flash Point

Viscosity

Pour Point

Boiler Blown Down

Water

Wash Water

Boot Water

Alkalinity

TDS(total dissolved solids test)

pH

Sulfite

Phosphate

Iron

pH

Chloride

pH

Specific Gravity


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LPG

Cu Corrosion

Weathering

Cooling Water

pH

TDS

Zinc

Iron

Free Chloride

Cooling Water

Alkalinity

Hardness


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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

gas)

4 3050

JP(Jet fuel) 2 10000

SLOP 1 5000

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.


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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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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.


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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 & post-

desalter streams)


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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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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 350~360oC. 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------&


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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


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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,


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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 FCV-

11, 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 2RSSR + 2H2O


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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.


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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


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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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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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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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REFRENCES

Books:

Petroleum refinery engineering by W.I.Nelson.

Petroleum processing hand book by William. F. Bland.

Unit Operations of Chemcial Engineering by Warren L.

Mc. Cabe.

Process technology by Thomas. D .Felder.

Web-sites:

• WWW.WIKIPEDIA.COM.

• WWW.API.COM

• WWW.AMSWERS.COM

• WWW.BOSICOR.COM.PK

• WWW.GOOGLE.COM

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