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INDUSTRIAL TRAINING REPORT IOCL ( AOD ) DIGBOI REFINERY REPORT SUBMITTED BY: Rajan kumar choudhary 5 TH Semester Scholar No. 091116012 Mechanical Engineering Maulana Azad National Institute Of Technology Bhopal, 462051
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DIGBOI Rajan

Apr 12, 2017

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Page 1: DIGBOI Rajan

INDUSTRIAL TRAINING REPORT

IOCL ( AOD )

DIGBOI REFINERY

REPORT SUBMITTED BY:

Rajan kumar choudhary 5TH Semester Scholar No. 091116012 Mechanical Engineering Maulana Azad National Institute Of Technology Bhopal, 462051

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DECLARATION

I hereby declare that this project is being submitted

in fulfillment of the VOCATIONAL TRAINING

PROGRAMME in IOCL (AOD) Digboi, and is the result

of self done work carried out by me under the

guidance of various Engineers and other officers.

I further declare that the structure and content of

this project are original and have not been submitted

before for any purpose.

SUBMITTED BY:

RAJAN KUMAR CHOUDHARY

SCHOLAR NO. 091116012

B.TECH. (5TH SEMESTER)

MAULANA AZAD NATIONAL INSTITUTE OF

TECHNOLOGY

BHOPAL (MADHYA PRADESH), 462051

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CERTIFICATE

This is to certify that Mr. Rajan kumar choudhary Of Maulana

Azad National Institute Of Technology, Bhopal has

undergone Vocational Training for a period of 14 days from

17.05.2011 to 30.05.2011 at Digboi Oil Refinery, IOCL

(AOD), and has made the project report under my guidance.

Project Guide

Mr. P. K. Bordoloi

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ACKNOWLEDGEMENT

A detailed report such as this one doesn’t become

possible without the contribution of several people who are

willing to help wholeheartedly. Through this training, I’ve

been lucky to have got the opportunity to learn so much

from the Engineers, Officers, and Staff members of IOCL

(AOD), Digboi who have always helped me through the

period of my training.

I would give thanks to the Training Department of IOCL

(AOD), Digboi as they have given me the chance of having

this wonderful learning experience.

I am also indebted to respected Officers and Engineers:

1) Mr. A. K. Kalita ( DM-Safety)

2) Mr. Debayan Sengupta

3) Mr. Ashutosh Pathak

4) Mr. Nani Gopal Deb

5) Mr. J. Pathak

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INTRODUCTION

The Digboi Refinery in North Eastern India is India's oldest refinery and

was commissioned in 1901. Originally a part of Assam Oil Company, it

became part of IndianOil in 1981. Its original refining capacity had

been 0.5 MMTPA since 1901. After modernization the capacity of the

refinery has been enhanced to to 0.65 MMTPA. The Digboi refinery

produces distillates, heavy ends and excellent quality wax from

indigenous crude oil produced at the Assam oil fields. The refinery

presently produces MS and HSD complying BS-III grade.

Petroleum products are supplied mainly to north-eastern India

primarily through road and by rail wagons. A new Delayed Coking Unit

was commissioned in 1999. A new Solvent De-waxing Unit for

maximizing production of micro-crystalline wax was installed and

commissioned in 2003. The refinery has also commissioned a

Hydrotreater and Hydrogen Plant in 2003 to improve the quality of

diesel. The MSQ Upgradation project has been completed. A new

terminal with state of the art facility is under construction and

expected to be completed by end of 2011.

The refinery is ISO-9001,ISO-14001 and OHSAS-18001 accredited, its

laboratory is NABL accredited and follows TPM.

Digboi Refinery manufactures conventional petroleum products

like LPG, Naphtha, Motor Spirit, Superior Kerosene (SKO), High

Speed Diesel (HSD), Furnace Oil (FO) and Raw Petroleum Coke. It

also produces one of the best quality of Paraffin Wax besides

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other products like Aromex, Jute Batching Oil (JBO), Mineral

Turpentine Oil (MTO), Solar Oil etc.

The refinery’s fuel requirement is met by refinery off-gases

generated from the

various process units and also the purchased natural gas from

M/s Oil India Limited.

The purchased natural gas is used in Captive Power Plant in Gas

Turbines to produce power while the refinery off-gases / natural

gas is used in the various furnaces of the process units and also

supplementary firing in HRSGs. Only in case of failure of Natural

Gas supply, HSD is used in Gas Turbines. The refinery is self-

sufficient in electrical power and does not have to import power

from the state grid for refinery operations. In fact, Digboi Refinery

has taken up to sell 5 MW of power to state grid.

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GENERAL SAFETY RULES

According to the regulations of the plant administration, every

employee & visitor in the plant has to adhere to the 11 point

General Safety Rules, as mentioned below:

Safety Shoe

Safety Helmet

Spark Arrestor (in exhaust of vehicles)

Photography Prohibited

Speed Limit in plant is 20 kmph

Smoking Banned

Incendiary Items ( matchbox,lighter,etc.) Banned

Use of VCD,VCR Prohibited

Use of Radio Devices Banned

Use Fire Safety Equipments like Extinguishers-

DCP,Foam,CO2.

Use of Hydrant Water for other purposes is banned

Apart from the above mentioned rules, several other things must

also be kept in mind.

In case of an accident or hazard, there are MCP(Manual Call Point)

at regular intervals, which must be activated once a danger is

seen. If the danger Is very serious in nature, then the people are

required to assemble in the 3 Assembly Points provided for the

purpose, so that they may be safely escorted out.

In case of a DISASTER, a 3-Cycle siren is sounded, which is a

straight siren, sounding for 7 minutes.

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WORK PERMIT SYSTEM

For performing different types of jobs, particular permits have

to be acquired.

There are different permits which need to be taken, like:

1. Hot Permit – for hot jobs like welding, gas cutting, etc.

2. Height permit – to work at heights

3. Soil Excavation Permit

4. Cold Permit

PERSONAL PROTECTION

EQUIPMENTS

Hand Gloves

Goggles

Ear Plugs

Safety Net

Safety Belt

Scaffolding

Breathing Apparatus

Hard Helmet

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WHAT IS PETROLEUM?

Petroleum (L. petroleum, from Greek: petra (rock) + Latin:

oleum (oil) or crude oil is a naturally occurring, flammable

liquid consisting of a complex mixture of hydrocarbons of

various molecular weights and other liquid organic

compounds, that are found in geologic formations beneath

the Earth's surface. Petroleum is recovered mostly through

oil drilling. This latter stage comes after studies of structural

geology (at the reservoir scale), sedimentary basin analysis,

reservoir characterization (mainly in terms of porosity and

permeable structures). It is refined and separated, most

easily by boiling point, into a large number of consumer

products, from gasoline and kerosene to asphalt and

chemical reagents used to make plastics and

pharmaceuticals.[4] Petroleum is often attributed as the

"Mother of all Commodities" because of its importance in the

manufacture of a wide variety of materials.

The composition consists roughly of the follows:

– 83-87% Carbon

– 11-15% Hydrogen

– 1-6% Sulfur

• Paraffins – saturated chains

• Naphthenes – saturated rings

• Aromatics – unsaturated rings

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GENERAL REFINERY

SCHEMATIC

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DESCRIPTION:

The crude oil which comes in the plant is stored in an offsite

tank through which it is taken to a Crude Oil Preheater(PH1)

through a pump.

Then the heated crude oil ( at 128*C, 10 kg/cm2) goes into

the DESALTER, which separates the effluents like water,

dissolved salts, metals, etc.

The Desalted Crude is then taken through a 6 stage

Centrifugal Booster Pump, with output pressure at 32

kg/cm2, which is split into 2 parts taken going into PH2 &

PH3, whre crude is heated to 250*C, pressure decreases to

25 kg/cm2.

Then a Fuel Gas Furnace heats it to 354*C, at 12 kg/cm2,

output goes into CDU( Crude Distillation Unit).

The temp in CDU column varies uniformly from 119*C at

1.019 kg/cm2 to 321*C at 1.519 kg/cm2.

The products of CDU are

Vapours

Raw Naphtha

Light Kero, Heavy Kero, Light Gas Oil, Heavy Gas Oil

– Together called High Speed Diesel(HSD)

Reduced Crude Oil(RCO), which is the bottom

residue.

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The Raw Naphtha obtained is unstable & is sent to

NSU(Naphtha Stabilization Unit) to get Motor Spirit. This is

sent to Motor Spirit Quality Upgradation Unit (MSQU) to

obtain petrol.

HSD is sent to Hydrotreating Unit (HDT) for further

upgradation.

The RCO at 330*C is heated in Vacuum Hater by Fuel Gas

firing at 40 mm Hg pressure to 396*C. Then its sent to

Vacuum Distillation Unit (VDU).

VDU gives :

Vacuum HSD

Pressurized Wax Distillate (PWD)

Heavy Wax Distillate (HWD)

Vacuum Residue (VR)

It is to be kept in mind that the Vacuum HSD is inferior in

quality than the HSD obtained in the CDU.

The Vacuum HSD is sent to HDT for upgradation.

PWD sent to Solvent Dewaxing Unit (SDU), then to Wax

Hydrofinishing Unit (WHFU) then used to manufacture wax.

HWD & VR are sent to Delayed Coking Unit (DCU), where

LPG, HSD & Coke are obtained.

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MECHANICAL DEVICES

Used in an OIL REFINERY

1. PUMPS:

A pump is a device used to move fluids, such as liquids,

gases or slurries.

A pump displaces a volume by physical or mechanical

action. Pumps fall into three major groups: direct lift,

displacement, and gravity pumps. Their names describe the

method for moving a fluid.

Pumps based on their principle of operation are primarily

classified into:

• Positive displacement pumps (reciprocating, rotary pumps)

• Roto-dynamic pumps (centrifugal pumps)

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Positive Displacement Pumps

Positive displacement pumps, which lift a given volume for

each cycle of operation, can be divided into two main

classes, reciprocating and rotary.

Reciprocating pumps include piston, plunger, and

diaphragm types. The rotary pumps include gear, lobe,

screw, vane, regenerative (peripheral), and progressive cavity

pumps.

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Roto-dynamic pumps

Roto-dynamic pumps raise the pressure of the liquid by first

imparting velocity energy to it and then converting this to

pressure energy. These are also called centrifugal pumps.

Centrifugal pumps include radial, axial, and mixed flow

units.

A radial flow pump is commonly referred to as a straight

centrifugal pump; the most common type is the volute

pump. Fluid enters the pump through the eye of impeller,

which rotates at high speed. The fluid is accelerated radially

outward from the pump casing. A partial vacuum is created

that continuously draws more fluid into the pump if properly

primed.

In the axial flow centrifugal pumps, the rotor is a propeller.

Fluid flows parallel to the axis of the shaft. The mixed flow,

the direction of liquid from the impeller acts as an in-

between that of the radial and axial flow pumps.

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Centrifugal Pumps The centrifugal pumps are by far the most commonly used

of the pump types. Among all the installed pumps in a

typical petroleum plant, almost 80–90% are centrifugal

pumps.

Centrifugal pumps are widely used because of their design

simplicity, high efficiency, wide range of capacity, head,

smooth flow rate, and ease of operation and maintenance.

The subsequent development of centrifugal pumps was very

rapid due to its relatively inexpensive manufacturing and its

ability to handle voluminous amounts of fluid.

However, it has to be noted that the popularity of the

centrifugal pumps has been made possible by major

developments in the fields of electric motors, steam

turbines, and internal combustion (IC) engines. Prior to this,

the positive displacement type pumps were more widely

used.

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The centrifugal pump has a simple construction, essentially

comprising a volute (1) and an impeller (2) (refer to Figure

1.16). The impeller is mounted on a shaft (5), which is

supported by bearings (7) assembled in a bearing housing

(6). A drive coupling is mounted on the free end of the shaft.

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Screw Pump In addition to the previously described pumps based on the

Archimedes’ screw, there are pumps fitted with two or three

spindles crews housed in a casing.

Three-spindle screw pumps, as shown in Figure 1.14, are

ideally suited for a variety of marine and offshore

applications such as fuel-injection, oil burners, boosting,

hydraulics,

fuel, lubrication, circulating, feed, and many more. The

pumps deliver pulsation free flow and operate with low noise

levels. These pumps are self-priming with good efficiency.

These pumps are also ideal for highly viscous liquids.

Three-spindle screw pump – Alweiller pumps

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Reciprocating Pumps Reciprocating pumps are positive displacement pumps and

are based on the principle ofthe 2000-year-old pump made

by the Greek inventor, Ctesibius.

Reciprocating pumps comprise of a cylinder with a

reciprocating plunger in it. The head of the cylinder houses

the suction and the discharge valves. In the suction stroke,

as the plunger retracts, the suction valve opens causing

suction of

the liquid within the cylinder. In the forward stroke, the

plunger then pushes the liquid out into the discharge

header.

The pressure built in the cylinder is marginally over the

pressure in the discharge.

The gland packings help to contain the pressurized fluid

within the cylinder. The plungers are operated using the

slider-crank mechanism. Usually, two or three cylinders are

placed alongside and their plungers reciprocate from the

same crankshaft. These are called as duplex or triplex

plunger pumps.

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Diaphragm Pumps Diaphragm pumps are inherently plunger pumps. The

plunger, however, pressurizes the hydraulic oil and this

pressurized oil is used to flex the diaphragm and cause the

pumping of the process liquid.

Diaphragm pumps are primarily used when the liquids to be

pumped are hazardous or toxic. Thus, these pumps are

often provided with diaphragm rupture indicators.

Diaphragm pumps that are designed to pump hazardous

fluids usually have a double diaphragm which is separated

by a thin film of water.

A pressure sensor senses the pressure of this water. In a

normal condition, the pressure on the process and oil sides

of the diaphragms is always the same and the pressure

between

the diaphragms is zero.

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Gear Pump In gear pumps, two identical gears rotate against each other.

The motor provides the drive for one gear. This gear in turn

drives the other gear. A separate shaft supports each gear,

which contains bearings on both of its sides.

As the gears come out of the mesh, they create expanding

volume on the inlet side of the pump. Liquid flows into the

cavity and is trapped by the gear teeth while they rotate.

Liquid travels around the interior of the casing in the

pockets between the teeth and the casing. The fine side

clearances between the gear and the casing allow

recirculation of the

liquid between the gears.

The above diagram shows A Gear Pump in 3 stages of

operation. The left side is the INLET & the right side is the

OUTLET.

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Out of all the above pumps, the Centrifugal & Reciprocating

Pumps are the most widely used. There are a few advantages

& disadvantages for both the pumps, & they are used

according to specific need. The main characteristics of both

the pumps are:

1. Centrifugal Pump:

High Flow Rate

Low Discharge Pressure

Quiet & Smooth Operation

Leakage is not there.

There is a mechanical seal.

2. Reciprocating Pump:

Low Flow Rate

High Discharge Pressure

Leakage occurs after short time of

usage.

Noisy operation.

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2.COMPRESSORS:

A compressor is a device used to increase the pressure of a

compressible fluid. The inlet & outlet pressure are related,

corresponding with the type of compressor & its

configuration.

The types of Compressors can be classified by the following

chart:

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Reciprocating Compressors:

The reciprocating compressor is probably the best known

and the most widely used of all compressors. It consists of a

mechanical arrangement in which reciprocating motion is

transmitted to a piston which is free to move in a cylinder.

The displacing action of the piston, together with the inlet

valve or valves, causes a quantity of gas to enter the cylinder

where is in turn compressed and discharged, Action of the

discharge valve or valves prevents the backflow of gas into

the compressor from the discharge line during the next

intake cycle.

The discharge valve or valves prevents the backflow of gas

into the compressor from the discharge line during the next

intake cycle.

When the compression takes place on one side of the piston

only, the compressor is said to be single acting.

The compressor is double-acting when compression takes

place on each side of the piston.

Configurations consist of a single cylinder or

multiple cylinders on a frame. When a single cylinder is used

or when multiple cylinders on a common frame are

connected in parallel, the arrangement is referred to as a

single-stage compressor. When multiple cylinders on a

common frame are connected in series, usually through a

cooler, the arrangement is referred to as a multistage

compressor.

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Cross Section Of a Reciprocating Compressor

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CENTRIFUGAL COMPRESSORS:

The radial-flow, or centrifugal compressor is a widely used

compressor and is probably second only to the reciprocating

compressor in usage in the process industries.

The compressor uses an impeller consisting of radial or

backward-leaning blades and a front and rear shroud. The

front shroud is optionally rotating or stationary depending

on the specific design.

As the impeller rotates, gas is moved between the rotating

blades fro the area near the shaft and radially outward to

discharge into a stationary section, called a diffuser. Energy

is transferred to the gas while it is traveling through the

impeller. Part of the energy converts to pressure

along the blade path while the balance remains as velocity at

the impeller tip where it is slowed in the diffuser and

converted to pressure.

The fraction of the pressure conversion taking place in the

impeller is a function of the backward leaning of the blades.

The more radial the blade, the less pressure conversion in

the impeller and the more conversion taking place in the

diffuser. Centrifugal compressors are quite often built in a

multi-stage configuration.

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HEAT EXCHANGER:

A heat exchanger is a piece of equipment built for efficient

heat transfer from one medium to another. The media may

be separated by a solid wall, so that they never mix, or they

may be in direct contact.

Flow Arrangement: There are two primary classifications of

heat exchangers according to their flow arrangement. In

parallel-flow heat exchangers, the two fluids enter the

exchanger at the same end, and travel in parallel to one

another to the other side. In counter-flow heat exchangers

the fluids enter the exchanger from opposite ends. The

counter current design is most efficient, in that it can

transfer the most heat from the heat (transfer) medium.

Types of heat exchangers:

1. Shell And Tube Type

2. Plate Type

3. Fluid Heat Exchanger

4. Direct Contact Heat Exchanger

Out of these commonly used types, the Shell & Tube Type

Heat Exchanger is widely used in industries & the same is

being used at Digboi Refinery.

Shell and tube heat exchangers consist of a series of tubes.

One set of these tubes contains the fluid that must be either

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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 typically used for high-pressure applications

(with pressures greater than 30 bar and temperatures

greater than 260°C).[2] This is because the shell and tube

heat exchangers are robust due to their shape.

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VALVES:

A valve is a mechanical device used to start, stop, control or

regulate the flow of a fluid through a pipe.

The various types of valves widely used in Industries today

are as follows:

Gate Valve: A gate valve, also known as a sluice valve, is

a valve that opens by lifting a round or rectangular

gate/wedge out of the path of the fluid. The distinct feature

of a gate valve is the sealing surfaces between the gate and

seats are planar, so gate valves are often used when a

straight-line flow of fluid and minimum restriction is

desired.

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A GATE VALVE

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Pressure Safety Valve

(PSV): A Pressure safety

valve is a valve mechanism

for the automatic release of

a substance from a boiler,

pressure vessel, or other

system when the pressure or

temperature exceeds preset

limits.

Non Return Valve: Non-return valve or one-way

valve is a mechanical device, a valve, which normally

allows fluid (liquid or gas) to flow through it in only one

direction.

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FRACTIONATING COLUMN:

A fractionating column or fractionation 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. Fractionating

columns are used in small scale laboratory distillations as well

as for large-scale industrial distillations.

Fractional distillation is one of the unit operations of chemical

engineering. Fractionating columns are widely used in the

chemical process industries where large quantities of liquids

have to be distilled. Such industries are the petroleum

processing, petrochemical production, natural gas processing,

coal tar processing, brewing, liquefied air separation, and

hydrocarbon solvents production and similar industries but it

finds its widest application in petroleum refineries. In such

refineries, the crude oil feedstock is a very complex

multicomponent mixture that must be separated and yields of

pure chemical compounds are not expected, only groups of

compounds within a relatively small range of boiling points,

also called fractions and that is the origin of the name

fractional distillation or fractionation. It is often not worthwhile

separating the components in these fractions any further

based on product requirements and economics.

Distillation is one of the most common and energy intensive

separation processes. In a typical chemical plant, it accounts

for about 40% of the total energy consumption.[6] Industrial

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distillation is typically performed in large, vertical cylindrical

columns (as shown in Figure) known as "distillation towers" or

"distillation columns" with diameters ranging from about 65

centimeters to 6 meters and heights ranging from about 6

meters to 60 meters or more.

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A FRACTIONATING TOWER of a REFINERY

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MAIN SECTIONS OF A

REFINERY

A modern refinery consists of a number of sectors for

performing different functions. The Crude Oil is passed

through these sections in a specific order according to the

functions. These are:

1. ATMOSPHERIC & VACUUM UNIT ( AVU )

The AVU forms the most important part of the Fuel Sector of

the refinery. The intake of the AVU is CRUDE OIL & after

passing through the AVU the output is obtained in the form of

many products like:

Raw Naphtha

Light Kero

Heavy Kero

Light Gas Oil

Heavy Gas Oil

Vacuum HSD

Pressurized Wax Distillate (PWD)

Heavy Wax Distillate (HWD)

Vacuum Residue (VR)

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All these products are obtained in a series of steps which are

primarily performed in 3 Units of the AVU:

CRUDE DISTILLATION UNIT ( CDU ) :

Process Objective:

–To distill and separate valuable distillates (naphtha,

kerosene,diesel) and atmospheric gas oil (AGO) from the crude

feedstock.

•Primary Process Technique:

–Complex distillation

•Process steps:

–Preheat the crude feed utilizing recovered heat from the

product streams

–Desalt and dehydrate the crude using electrostatic enhanced

liquid/liquid separation (Desalter)

–Heat the crude to the desired temperature using fired heaters

–Flash the crude in the atmospheric distillation column

–Utilize pump-around-cooling loops to create internal liquid

reflux

–Product draws are on the top, sides, and bottom

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FLOW CHART OF CDU:

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VACUUM DISTILLATION UNIT ( VDU ) :

Process Objective:

–To recover valuable gas oils from reduced crude via vacuum

distillation.

Primary Process Technique:

–Reduce the hydrocarbon partial pressure via vacuum and

stripping steam.

Process steps:

–Heat the reduced crude to the desired temperature using fired

heaters

–Flash the reduced crude in the vacuum distillation column

–Utilize pump-around-cooling loops to create internal liquid

reflux

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Flow Chart of VDU

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NAPHTHA STABILIZATION UNIT ( NSU ) :

Process Objective:

To convert the unstable Raw Naphtha obtained from CDU to

stabilized naphtha which can be used to make motor spirit.

The Naphtha Stabilization Unit is set up after the CDU to obtain

usable Naphtha which is very important for further motor fuel

synthesis.

Process Technique:

Unstable naphtha (also known as light naphtha) consists of the

light components of a crude oil distillation which have not yet

had the C4 components removed from it.

Unstable naphtha is fed to a tall distillation column

(approximately 20-30 trays) known as a debutanizer where all

C4 components (and any lighter boiling point components) are

removed. The bottom product of a debutanizer is stabilized

naphtha.

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DELAYED COKING UNIT ( DCU )

Process Objective:

–To convert low value residue to valuable products (naphtha

and diesel) and coker-gas oil.

•Primary Process Technique:

–Thermo-cracking increases H/C ratio by carbon rejection in a

semi-batch process.

•Process steps:

–Preheat residue feed and provide primary condensing of coke

drum vapors by introducing the feed to the bottom of the main

fractionator

–Heat the coke drum feed by fired heaters

–Flash superheated feed in a large coke drum where the coke

remains and vapors leave the top and goes back to the

fractionator

–Off-line coke drum is drilled and the petroleum coke is

removed via hydro-jetting ( By water jet at pressure

120kg/cm2)

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Flow Chart of DCU

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CATALYTIC REFORMING UNIT ( CRU )

Process Objective:

–To convert low-octane naphtha into a high-octane reformate

for gasoline blending and/or to provide aromatics (benzene,

toluene, and xylene) for petrochemical plants.

-Reforming also produces high purity hydrogen for hydro-

treating-processes.

•Primary Process Technique:

–Reforming reactions occur in chloride promoted fixed catalyst

beds; or continuous catalyst regeneration (CCR) beds where

the catalyst is transferred from one stage to another, through a

catalyst regenerator and back again.

Desired reactions include:

Dehydrogenation of naphthenes to form aromatics;

isomerization of naphthenes;

Dehydro-cyclization of paraffins to form aromatics; and

isomerizationof paraffins.

Hydrocracking of paraffins is undesirable due to

production of increased light-ends.

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•Process steps:

–Naphtha feed and recycle hydrogen are mixed, heated and

sent through successive reactor beds

–Each pass requires heat input to drive the reactions

–Final pass effluent is separated with the hydrogen being

recycled or purged for hydro-treating

–Reformate product can be further processed to separate

aromatic components or be used for gasoline blending

CRU Formation Of Toluene

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CAPTIVE POWER PLANT

The Captive Power Plant in the refinery has a rated generating

capacity of 45.5 MW electricity, which is used to run the plant

as well as supplied to the IOCL township.

The Power Generation is done by 4 Gas Turbines – 3 GTs of 8.5

MW each, & 1 GT of 20 MW. It is wholly a Gas Turbine operated

Power Plant.

WORKING:

In a gas turbine power plant, air is used as the working fluid.

The air is compressed by the Gas Booster Compressor is lead

to the combustion chamber where heat is added to air, thus

raising its temperature. Heat is added to the compressed air

either by burning fuel in the chamber or by the use of air

heaters. The hot and high pressure air from the combustion

chamber is then passed to the gas turbine where it expands

and does the mechanical work. The gas turbine drives the

alternator which converts the mechanical energy into electrical

energy.

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Advantages

1. It is simple in design as compared to steam power station

since no boilers and their auxiliaries are required

2. it is much smaller in size as compared to steam power

station of same capacity.This is expected since gas

turbine power plant doesnot require boiler,feed water

arrangements etc

3. The initial and operating costs are much lower than that

of equivalent steam power station

4. It requires comparatively less water as no condenser is

used

5. The maintenance charges are quite small

6. Gas turbines are much simpler in construction and

operation than steam turbines

7. It can be started quickly from cold conditions

Disadvantages

1. There is a problem for starting the unit. It is because

before starting the turbine, the compressor has to be

operated for which power is required from some external

source. However once the unit starts, the external power

is not needed as the turbine itself supplies necessary

power to the compressor.

2. Since a greater part of the power developed by the

turbine is used in driving the compressor, the net output

is low

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3. The overall efficiency of such plants is low(about 20%)

because of the exhaust gases from the turbine contain

sufficient heat

4. The temperature of combustion chamber is quite

high(3000 deg.F)so that its life is comparatively reduced.

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The three main sections of a Gas Turbine are the Compressor,

Combustor and Turbine. The gas turbine power plant has to

work continuously for long period of time without output and

performance decline. Apart from the main sections there are

other important Auxiliaries systems which are required for

operating a Gas Turbine Power Plant on a long term basis.

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Air Intake System

Air Intake System provides clean air into the compressor.

During continuous operation the impurities and dust in the air

deposits on the compressor blades. This reduces the efficiency

and output of the plant. The Air Filter in the Air Intake system

prevents this.

A blade cleaning system comprising of a high pressure pump

provides on line cleaning facility for the compressor blades.

The flow of the large amount of air into the compressor

creates high noise levels. A Silencer in the intake duct reduces

the noise to acceptable levels.

Exhaust System

Exhaust system discharges the hot gases to a level which is

safe for the people and the environment. The exhaust gas that

leaves the turbine is around 550 °C. This includes an outlet

stack high enough for the safe discharge of the gases. Silencer

in the outlet stack reduces the noise to acceptable levels.

Starting System

Starting system provides the initial momentum for the Gas

Turbine to reach the operating speed. This is similar to the

starter motor of your car. The gas turbine in a power plant

runs at 3000 RPM (for the 50 Hz grid - 3600 RPM for the 60

Hz grid). During starting the speed has to reach at least 60 %

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for the turbine to work on its on inertia. The simple method is

to have a starter motor with a torque converter ( Which is

actually a FLUID COUPLING) to bring the heavy mass of the

turbine to the required speed. For large turbines this means a

big capacity motor. The latest trend is to use the generator

itself as the starter motor with suitable electrics. In situations

where there is no other start up power available, like a ship or

an off-shore platform or a remote location, a small diesel or

gas engine is used.

Fuel System

The Fuel system prepares a clean fuel for burning in the

combustor. Gas Turbines normally burn Natural gas but can

also fire diesel or distillate fuels. Many Gas Turbines have dual

firing capabilities.

A burner system and ignition system with the necessary safety

interlocks are the most important items. A control valve

regulates the amount of fuel burned . A filter prevents entry of

any particles that may clog the burners. Natural gas directly

from the wells is scrubbed and cleaned prior to admission into

the turbine. External heaters heat the gas for better

combustion.

For liquid fuels high pressure pumps pump fuel to the

pressure required for fine atomisation of the fuel for burning.

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OTHER IMPORTANT SYSTEMS:

1. Apart from the gas turbines, the exhaust of the turbines

is fed to a HRSG ( Heat Recovery Steam Generator) which

has a capacity of generating 100 Tonnes of steam per

hour. This steam is used for various processes

throughout the plant.

2. For supply of De-mineralised Water to the HRSG, an

offsite DEMINERALISED WATER PLANT is setup from where

the DM Water is pumped to the HRSG.

3. GAS BOOSTER COMPRESSORS are there to supply

compressed air to the Gas Turbine at pressure of about

13 kg/cm2.

4. GENERATOR is mounted on the turbine shaft & produces

electricity by Electromagnetic Induction.

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SOLVENT DEWAXING UNIT Solvent treating is a widely used method of refining lubricating

oils as well as a host of other refinery stocks. Since distillation

(fractionation) separates petroleum products into groups only

by their boiling-point ranges, impurities may remain. These

include organic compounds containing sulfur, nitrogen, and

oxygen; inorganic salts and dissolved metals; and soluble salts

that were present in the crude feedstock. In addition, kerosene

and distillates may have trace amounts of aromatics and

naphthenes, and lubricating oil base-stocks may contain wax.

Solvent refining processes including solvent extraction and

solvent dewaxing usually remove these undesirables at

intermediate refining stages or just before sending the product

to storage.

Solvent dewaxing is used to remove wax from either distillate

or residual basestock at any stage in the refining process.

There are several processes in use for solvent dewaxing, but all

have the same general steps, which are:

(1) mixing the feedstock with a solvent,

(2) precipitating the wax from the mixture by chilling, and

(3) recovering the solvent from the wax and dewaxed oil for

recycling by distillation and steam stripping.

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Usually MIBK ( Methyl Iso-butyl Ketone), which dissolves the oil

and maintains fluidity at low temperature(4-7 deg.C), is used

as solvent. Other solvents that are sometimes used include

benzene, methyl ethyl ketone, toluene, propane, petroleum

naphtha, ethylene dichloride, methylene chloride, and sulfur

dioxide. In addition, there is a catalytic process used as an

alternate to solvent dewaxing.

The MIBK is cooled by passing it through a heat exchanger

with Ethylene Glycol, which takes away its heat. The Ethylene

Glycol, in turn, is cooled by exchanging its heat with

propylene, which changes into vapour readily & thus can easily

ake a lot of heat. The propylene which is converted into gas is

again converted to liquid by spraying it through a nozzle which

brings down its temp due to sudden expansion & it liquefies.

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The De-waxing / De-oiling Unit of WAX SECTOR consists of

following six sections:

a) Chilling Section

b) Filtration Section

c) De-waxed Oil Solvent Recovery Section

d) Slack Wax Solvent Recovery Section

e) Refrigeration Section

f) Inert Gas System

(a) Chilling Section

In Chilling Section, the feed obtained from storage is

first heated in order to dissolve any precipitated

waxes which may be present. The feed heating is

done in the LP Steam Heater where the feed is

heated to 70-800C. This is followed by controlled

cooling and chilling of the feed in the subsequent

exchangers.

During feed chilling, dilution solvent is added at

various points along the DP exchanger/ chiller trains

to reduce the viscosity of the charge mix and hence

the pressure drop in the chilling trains.

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(b) Filtration Section

The wax crystals are separated from the chilled feed by

primary filters. The re-pulp or secondary filter

performs the second stage filtration in order to

further reduce the oil content in wax to the desired

level. The liquid to solid ratio of the feed to primary

and secondary filters is adjusted by filtrate

recirculation to promote easier filtration.

The primary filtrate is pumped by the primary filtrate

pump to the chilling section for cold recovery. The

wax cake formed on the filter cloth is washed with

chilled solvent as it emerges from the liquid slurry

(c) De-waxed Oil Solvent Recovery Section

The de-waxed oil (DWO) solvent recovery section

consists of flashing followed by steam stripping.

The primary filtrate from feed mix chilling section is

sent to DWO solvent recovery section to recover

solvent from the de-oiled wax. The de-waxed oil

from the stripper bottom called Foots Oil is sent to

storage tank through DWO stripper bottom pump

after heat recovery and cooling in the DWO Mix/

Foots Oil exchanger and finally to Foots Oil Cooler

respectively.

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(d) Slack Wax Recovery Section

The slack wax solvent recovery section consists of

single stage flashing followed by steam stripping.

The last traces of solvent are recovered in the

stripper by steam stripping. The wet solvent vapours

from stripper top are routed to solvent cooler and

then to solvent separator for further processing. The

wax product obtained from stripper bottom is sent

to storage through wax stripper bottom pump after

being cooled in tempered water cooler.

(e) Refrigeration Section

The typical refrigeration cycle serves as a utility to

provide the chilling medium for the feed-stock and

the solvent.

(e) Inert Gas Section

The inert gas is primarily used for filtration and

remains in circulation in a closed loop comprising of

primary and secondary filters, Primary and

Secondary Filtrate Receivers, Inert gas pot and inert

gas vacuum compressor. Inert gas is also used for

blanketing purposes in filters, solvent tanks etc.

This prevents solvent losses as well as fire hazards

by eliminating the contact of solvent with air. In

Digboi, NITROGEN gas is used for this purpose.

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WAX HYDRO-FINISHING UNIT

Process Objective

The objective of the hydro-finishing unit is to obtain Paraffin

Wax from the wax extract.

Process Details

This is a component of the refining process reserved for more

premium Petroleum basestocks.

Hydrofinishing uses a catalyst bed through which hydrogen

and heated oil are passed.

As these components pass through the bed, unstable

components such as sulfur and nitrogen are removed. Clay

treatment uses a different method to achieve a similar

outcome.

Both of these refining processes improve oxidation stability,

thermal stability and color of the lubricant basestocks.

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WAX RUN-DOWN SHED

The WRDS is the last step of the Wax Sector. The Paraffin Wax

obtained in the WHFU is finally sent there for solidification in

the form of slabs which are then sent dispatched for

marketing.

The molten wax is allowed to stand in long shallow containers

with slab-sized holes. A system is provided to take out each

individual wax slab after solidification.

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CONCLUSION

In the end, it has been a very good learning &

enlightening experience to do this Vocational Training

in the Digboi Refinery. Coming here, I understood a lot

about the processes taking place in an Oil Refinery.

The practical exposure has been unbelievable, & this

visit will stay with me as a good memory for years to

come.

THE END