INDUSTRIAL TRAINING REPORT

UNDER

INDIAN OIL CORPORATION LIMITED

(Assam Oil Division)

DIGBOI, ASSAM

Duration: 18.06.2024 – 17.07.2024

A final year project submitted in partial fulfillment of the requirement for

the Degree of Bachelor’s in Mechanical Engineering

Submitted By-
Kamal Das (212310002028)

Trideep Kurmi (222350002004)

Kalyan Jyoti Baruah (212310002027)

MECHANICAL ENGINEERING DEPARTMENT

GOLAGHAT ENGINEERING COLLEGE, GOLAGHAT, ASSAM

i
 DECLARATION

This is to declare that the industrial training report submitted by Kamal Das
(212310002027), Trideep Kurmi (222350002004), Kalyan Jyoti Baruah (212310002027)
in partial fulfillment of the requirements for the academic course of GOLAGHAT
ENGINEERING COLLEGE is the recoded of the candidates own work carried out by him
under my supervision. This report or a part of here has not been submitted elsewhere for any
degree or for any purpose previously.

I wish him a successful career and a prosperous life ahead.

Place: Digboi, Assam

Date: 17.07.2024

Mr. Bikash Mete

Senior Manager (Mechanical Maintainenece)

IOCL (AOD) Digboi, Assam

ii
 ACKNOWLEDGEMENT

It gives me immense pleasure to express my deepest sense of gratitude and sincere thanks to
our highly respected and esteemed guide Mr. Bikash Mete (Senior Manager, Mechanical
Maintainence, IOCL Digboi) and Mr. Puneet Agarwal ( General Manager, Learning &
Development Office) for his valuable guidance and encouragement along the training period
and in completing the project. His useful suggestions and co- operative behavior are sincerely
acknowledged.

I would like to express my sincere thanks to Mr. Debasish Gogoi (Head of the Department,
Mechanical Engineering), for giving me this opportunity to undertake this internship.

I would also like to extend my gratitude towards L&D department of IOCL Digboi for giving
me the opportunity to perform training at IOCL, Digboi.

At the end I would like to express my sincere thanks to all the staff, which have directly
or indirectly helped me in my project.

Kamal Das

Trideep Kurmi

Kalyan Jyoti Baruah

iii
 ABSTRACT

Mechanical maintenance in an oil refinery is critical for ensuring the smooth and efficient
operation of the facility. This type of maintenance involves the repair and upkeep of various
mechanical systems and equipment that are used to process crude oil into refined products.
One important aspect of mechanical maintenance is the inspection and maintenance of
process equipment, such as pumps, compressors, valves and turbines. These pieces of
equipment are subject to wear and tear, and regular maintenance is necessary to keep them
running at optimal efficiency. This may include cleaning, lubrication, and replacing worn
parts. Another important aspect of mechanical maintenance is the inspection and maintenance
of utility systems, such as cooling systems, heating systems, and power generators. These
systems provide the necessary support for the operation of the refinery, and any disruptions
can lead to costly downtime. Regular maintenance is necessary to ensure that these systems
are running smoothly and efficiently.

INDIAN OIL CORPORATION LIMITED (IOCL), Digboi has an annual production of 0.65
MMTPA as it is a very small industry. The production plant contains 13 number of each unit,
which are inter-related to each other. The various units are Atmospheric and Vacuum
Distillation Unit (AVU), Delayed Coking Unit (DCU), Catalytic Reforming Unit (CRU),
Motor Spirit Quality Up-gradation Unit (MSQU), Solvent De-waxing Unit (SDU), and many
more. The AVU is the mother of all plants which extract crude oil for OIL INDIA LIMITED
and distribute by-products to different other units. SDU is the most profitable unit of IOCL,
Digboi, as it produces the highest quality wax in the entire country.
The working of each plant is incomplete without the maintenance of the mechanical
equipment used in each of the units. The various mechanical equipment that we came across
in the plant are compressors (both reciprocating and centrifugal), various types of pumps
such as reciprocating, centrifugal, rotary, vane, heat exchangers, filters, valves, coupling,
types of bearing and many more. In our training period we learned the practical application of
the theory in academic syllabus.

iv
 CONTENTS

CHAPTER
TITLE PAGE No.
No.

Declaration ii
Acknowledgement iii
Abstract iv
Table of Contents v-vi

Table of Figures vii-viii

Abbreviation List ix
1
1 Introduction To IOCL, DIGBOI
2-3
2 Fire & Safety
4-8
3 Wax Sector

3.1 Solvent De-Waxing Unit/De-Oiling Unit

3.2 Wax Hydro-Finishing Unit

9-17
4 Hydro-Treater Block (HDTB)

4.1 Hydro-Treater Unit (HDTU)

4.1.1 Amine Treating Unit (ATU)

4.1.2 Amine Recovery Unit (ARU)

Wild Naptha
4.1.3
Stabilization Project
(WNSP)
4.2 Hydrogen Generation Unit (HGU)

4.3 Sulphur Recovery Unit (SRU)

4.4 Sour Water Stripper Unit (SWSU)

4.5 High Purity Nitrogen Unit (HPNU)

v
 18-25
5 Fuel Sector

5.1 Atmospheric Vacuum Unit (AVU)

5.2 Catalytic Reforming Unit (CRU)

5.3 Delayed Coking Unit (DCU)

5.4 Motor Spirit Quality Upgradation (MSQU)

26-39
6 Captive Power Plant (CPP)

6.1 Gas Turbine Generator

6.2 Cooling Tower

6.3 De-Mineralized Plant

6.4 Air Compressor House

40-67
7 Mechanical Equipment
68
8 Conclusion

vi
 TABLE OF FIGURES

FIGURE
FIGURE NAME PAGE No.
No.

Typical refining scheme for paraffin 4

Fig 3.1:
wax production
7
Fig 3.2: Wax Feedstock capacity table
12
Fig 4.1: LPG sweetening unit
13
Fig 4.2 Wild Naptha Stabilization process diagram
14
Fig 4.3: Flow chart of hydrogen generating unit
16
Fig 4.4: Sour Water Stripper Process
18
Fig 5.1: Classification of Fuel Sector
23
Fig 5.2: Semi-regenerative catalytic reforming unit
24
Fig 5.3: Delayed Coking Unit
27
Fig 6.1: Open loop Brayton Cycle
30
Fig 6.2: GT casing cross-section
32
Fig 6.3: Flow chart of GT unit in IOCL, Digboi
33
Fig 6.4: Cooling tower
34
Fig 6.5: Process flow diagram
41
Fig 7.1: Reciprocating Compressor
42
Fig 7.2: Working of Reciprocating Compressor
43
Fig 7.3: Single Stage Air Compressor
44
Fig 7.4: Double Stage Air Compressor
45
Fig 7.5: Rotary Vane Compressor
46
Fig 7.6: Screw Compressor
46
Fig 7.7: Working Principle Screw Compressor

vii
viii
 48
Fig 7.8: Construction of Centrifugal Compressor
50
Fig 7.9: Single Stage Compressor
50
Fig 7.10: Multistage Compressor
52
Fig 7.11: Construction of Piston Type Pump

Fig 7.12: Construction of Diaphragm Pump 54

55
Fig 7.13: Construction of Vane Pump
57
Fig 7.14: Working of Vane Pump
58
Fig 7.15: Construction of Centrifugal Pump
60
Fig 7.16: Construction of Jet Pump
62
Fig 7.17: Shell and Tube Heat Exchanger
64
Fig 7.18: Butterfly Valve
65
Fig 7.19: Non Return Valve
65
Fig 7.20: Gate Valve
66
Fig 7.21: Safety Valve
66
Fig 7.22: Globe Valve
67
Fig 7.23: Ball Valve
67
Fig 7.24: Plug Valve

viii
viii
 ABBREVIATION LIST

NAME FULL FORM

MMTPA Million Metric Tonnes Per Annum

LPG Liquefied Petroleum Gas
BS-IV Bharat Stage Emission Standards 4
MS Motor Spirit
HSD High Speed Diesel
HGU Hydrogen Generating Unit
PSA Pressure Swing Adsorption
SDU Solvent De-waxing Unit
PWD Pressable Waxy Distillate
WHFU Wax Hydro-Finishing Unit
CHP Combined Heat and Power
CDU Crude Distillation Unit
HWD Heavy Waxy Distillate
VDU Vacuum Distillation Unit
SRR Semi-Regenerative catalytic Reformer
MSQU Motor-Spirit Quality Upgradation
HDTU Hydro-Treater Unit
NSU Naptha Stabilizing Unit

ix
CHAPTER-1: INTRODUCTION TO DIGBOI REFINERY

The small town of Digboi in the remote north-eastern corner of the country is the birthplace of the
Oil Industry in India. Digboi Refinery, commissioned on 11th December 1901, is India's oldest
operating refinery and one of the oldest operating refineries in the world. The historic Digboi
Refinery has been termed as the "Gangotri of the Indian Hydrocarbon sector".

It was formerly a component of the Assam Oil Company Limited/ Burmah Oil Company until
joining Indian Oil Corporation Limited in 1981 by an Act of Parliament on 14th October 1981 and
become the Assam Oil Division of Indian Oil Corporation Limited. Digboi Refinery, with its vastly
modernized operations and facilities, is an ISO - 9001, ISO 14001 and BS OHSAS 18001 certified
Refinery, which implies that it uses all possible means to promote environment protection through
adoption of proactive pollution control measures. This refinery has significantly updated
operations and facilities.

The Digboi Refinery can process crude at a rate of 0.65 MMTPA. Waxy crude from oil fields
operating close to Digboi is processed there. It also started processing of Crude condensate in
2018. The end of the 1990s saw the commissioning of new CDU, DCU, and CRU at the Digboi
Refinery which was a step towards modernization. New units SDU, WHFU, HDTU, HGU, SRU,
and Captive Power Plant were commissioned in the early years of the twenty-first century. Later,
in 2010, Digboi Refinery launched the MSQU, NHT, and ISOM units. Additionally, the refinery
also features a unit for wax moulding and another for wax palletization, which produce finished
wax in slab and pellet forms, respectively. CRMB+ unit was also installed and commissioned by
IOCL, Digboi in 2018 which is used for production of Crumb Rubber Modified Bitumen using
IOCL R&D developed technology. Digboi Refinery's current product portfolio includes LPG, BS-
IV compliant MS & HSD, Fuel Oil, Sulfur, RPC and Wax.

Today, Indian Oil's Assam Oil Division prides in having some flagship CSR projects namely
IOCL (AOD) Hospital, Assam Oil School of Nursing, Shikshak Dakshta Vikas Abhiyan, Sarve
Santu Niramaya among many other regular socially committed initiatives. The oil heritage of
Digboi has been carefully preserved at the Digboi Centenary Museum suitably located around
India's first Oil Well (drilled in year 1889). This caring for heritage project tells the over 100 years
old story of Digboi through unique exhibits, equipment, plants and many other knick-knacks.

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CHAPTER-2: FIRE & SAFETY

Fire and safety department of Indian Oil Corporation Limited, Digboi is concerned about the fire
hazards and safety of the company employees and labors. Fire and safety officials train the
laborers in a daily manner. A person can enter the battery area if and only if he/she has a safety
pass. This safety pass is issued by the Fire and Safety Department officials only.

IMPORTANT TERMINOLOGIES:

 Safety: Safety is a condition which gives us freedom from hazards, risk accidents which
may cause injury, damage and loss of materials or properties or even death.
 Accident: It is an unexpected or unplanned event which may or may not result in injury or
damage or loss of property or death.
 Injury: It is defined as harmful conditions sustained by the body because of the accident.
 Hazards: Inherent properties of a substance or an occurrence which has the potential to
cause loss or damage to properties or life.
 Risk: It is the probability of the potential for loss or damage or injury.

SAFETY MEASURES:

Different safety measures are taken to reduce the chances of hazards. Mobiles, laptops, pen- drives
and cameras are prohibited inside the battery area. Cars which are allowed to enter the battery area
are provided with spark arrestors. Cigarettes, alcohol and other inflammable objects are not
allowed inside the battery area. Fire alarms and Fire Extinguishers are present within a
considerable distance inside the refinery. Workers are always advised to use their PPES.

PERSONAL PROTECTIVE EQUIPMENT OR PPE:

Personal Protective Equipment is provided for the workers. This equipment is as follows:

 Safety shoes/Gumboots for protection of feet.

 Safety helmet for protection of head.

 Face shield for protection of face.

 Ear plugs and earmuffs for protection of ears.

 Hand gloves for protection of hands.

 Apron for protection of body.

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  Dust mask for protection of nose.

 Safety goggles for protection of eyes.

 Safety belts for working at height.

The major types of siren codes are:

 A continuous test siren is sounded every morning at 7 am for 2 minutes.

 Small fire- no siren.

 Major fire- a wailing siren for 2 minutes.

 Disaster- 3 times wailing siren for 2 minutes at intervals of 1 minute in between (8

minutes in total).

FIRE EXTINGUISHER:

Three types of fire extinguishers are there:

 Dry chemical powder (DCP)-for control of any type of fire.

 CO2 gas extinguisher-for control of electrical fire hazards.

 Foam for control of liquid/oil fire hazards.

Red and Green tag system is therefore marking of an object. Workers are always advised not to
use the red gas objects as they cause an accident. There are also 3 assembly points in the refinery.
All employees and workers are advised to assemble there in case of a siren.

The aim of Indian Oil Corporation Limited is Zero Accident and Fire and safety department plays
an important role in that.

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CHAPTER-3: WAX SECTOR

Introduction:

From early 50s to late 80s, Assam Oil was the sole exporter of Paraffin wax from India. The first
step in making the paraffin wax is to remove the oil (de-oiling or de-waxing) from the slack wax.
The oil is separated by crystallization. Most commonly, the slack wax is heated, mixed with one or
more solvents such as ketone and then cooled. As it cools, wax crystallizes out of the solution,
leaving only oil.

Fig 3.1: Typical refining scheme for paraffin wax production

There are three different categories of wax that are being produced from this refinery:

 Wax Type – 1 (As per IS 4654) – Food/ Pharmaceutical grade wax. This is known as
one of the best waxes in the world.
 Paraffin Wax Type – 2 & 2A (As per IS 4654) – Used for candle manufacturing,
polishes, sealant and various other applications including the manufacture of artifacts.
 Paraffin Wax Type – 3 (As per IS 4654) – Used in non-critical areas like Match
and Tarpaulin industries.

Paraffin Wax from Digboi refinery is a specialty product of Indian Oil which is used in many
items of our daily use: Candles, decorative candles, scented candles. Wrapper in food items like
bread, biscuits, Cosmetics like lipstick, face creams, moisturizing toiletries, Pain balms, Vaseline,
Cable industry, tire industry, Tarpaulin, polishes etc.

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 3.1- SOLVENT DE-WAXING UNIT/ DE-OILING UNIT (SDU):

Introduction:

The Digboi refinery has built a solvent de-waxing/de-oiling (SDU) system to replace its antiquated
wax extraction unit and wax sweating stove unit and boost both the quality and quantity of its
output. Wax production increased to roughly 49,000 TPA with the installation of the SDU unit, up
from 33,000 TPA with the previous wax extraction unit. Additionally, extra production of around
11,000 TPA of microcrystalline wax is achievable, something that was not possible with the
previous unit. These would result in a substantial increase in value for the refinery's product
pattern. SDU is capable of 210,000 TPA. The feedstock to the unit is press-able waxy distillate
(PWD,370°C-480°C) and heavy waxy distillate (HWD,480°C-530°C) from vacuum distillation
unit, the wax to be produced will have an oil content of 0.2wt. % and 0.5wt.% for PWD and HWD
feed respectively. The unit has blocked operations for PWD and HWD. Provisions have also been
kept for processing USRD distillate through this unit. The unit is designed for 8000 hours of
operation per year out which 80 % (168,000 TPA) is for PWD {total output equivalent to 636
MT/day; turnout to 254 MT/day (39%) and 20% (42.800 TPA) for HWD {Total output equivalent
to 605 MT/day; turndown to 242 MT/day (40%)} operation.

To produce finished wax, WHFU will receive the SDU de-oiled wax. The dewaxed oil will either
be used as feedstock for NDCU or added to the HSD pool. Oil is extracted from the waxy
feedstock using a solvent called methyl isobutyl ketone (MIBK).

Equipment Used:

i) Rotary vacuum drum filter:

The rotary vacuum drum filter used in Digboi refinery is Dorr Oliver type of design.
The filter has the following components:

• Vapour tight tank & hood

• Internal rotating drum
• Master control valve
• Cake washing pipe
• Wax deflector
• Wax discharge scroll
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ii) Filter and scroll drive:

Rotational power for the drum is supplied by electrical motor connected to shaft-mounted gear
reducer. Power for the discharge scroll is supplied by a second electric motor through a foot
mounted gear reducer.

iii) Cake discharge deflector and clean flush out system:

A double edge, nonabrasive beveled Teflon blade is used to guide cake into discharge scroll. The
blade can be turned to be second edge when the first edge is worn, doubling the effected life of the
blade. A wash header flush system is mounted behind the deflector blade to clean wax which may
build up under the blade. If left un-cleaned, wax accumulation may push the blade away from the
drum surface, decreasing production or forcing unscheduled downtown.

iv) Hydraulic hood lifting mechanism:

The hydraulic hood lifting mechanism accurately aligns the hood on the tank gasket quickly and
easily and during closing. This mechanism eliminates the necessity of using crane to suspend the
hood.

v) Chillers:

In simple words, chillers basically are a type of heat exchangers. PWD before going to the rotary
drum filter needs of wax to take place. Now, wax that gets crystallized in the chiller must be cont.
scrapped from the walls or it may block the chiller pipe. So, the chiller used is scrapped surface
heat exchanger. The coolant flowing in the outer pipe is either glycol or filtrate. The flow
arrangement is counter type to be cooled down to a particular temperature for crystallization. The
scrapped surface heat exchanger consists of a rotating shaft with scrapper blade attached to it. The
crystal which mainly builds up on the pipe wall during cooling are scrapped off by the scrapper
blades of the continuously rotating scrapper shaft.

vi) Drive System:

The scrapper shaft runs using a chain drive. Excellent lubrication of the heavy-duty roller chain is
assured by an oil splash lubrication system arranged in the bottom part of the drive housing, which
prolongs the chain service life. In order to avoid fouling of the oil bath and for reasons of accident
prevention the chain drive is enclosed in oil and dust tight housing.

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3.2- WAX HYDRO-FINISHING UNIT (WHFU):

Introduction:

The wax hydro finishing machine was installed to refine the de-oiled wax that SDU provided by
hydrogenating it in the presence of a catalyst to remove colour, colour stability, and sulphur
content. By de-sulphurizing and denitrifying the wax, the catalyst and chosen operating conditions
enable hydrogenation of aromatic compounds as well as the removal of sulfur and nitrogen.
Following hydrogenation, any oxygenated chemicals that may be present in the feed will be
removed. The machine can handle 60,000 MTPA of wax feedstock of different grades, according
to design.

Wax Feedstock Capacity (TPA)

Paraffin Wax Type 1 10,000

Paraffin Wax Type 2 35,000

Paraffin Wax Type 3 5,000

Table 3.2 – Wax Feedstock capacity table

Process
Description:

Reaction Section –

• Storage tanks at WHFU are used to store de-oiled wax from SDU.
• After being preheated in the HE by the bottom output of the vacuum dryer, liquid wax
feedstock is delivered into the reaction section by the feed booster pump from storage tanks

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at a temperature of around 750 c.

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• The KOD and the make-up gas compressor are used to introduce the H makeup into the
device. The combined gas is then added to the liquid feed stock after it has been combined
with gas from a recycle gas compressor.
• The hard valve on the discharge of makeup gas compressor takes care of preventing back
pressure during tripping as well as on-line isolation of the compressor.
• This valve is operated in case of tripping of the feed pump.
• The resultant steam is preheated in exchanger by the reactor effluent to about 2250c.
• The steam passes through a 3-way temperature control valve.
• Reactor skin temperature is maintained through DCS by the electrical heater as per
operational requirements.
• However, tripping conditions are set for safety of the heater and the unit as well as trip the
heater during -

Low feed flow to the heater

High heater outlet temperature of 3650c

High heater skin temperature of 4250c

• The effluent in the reactor is cooled down in the exchanger and is flashed in HP hot
separator
• A by-pass of the feed controls its temperature.

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CHAPTER – 4: HYDRO-TREATER BLOCK (HDTB)

Introduction:
Hydro-treating is used for a variety of hydrocarbon streams ranging from naphtha to vacuum tower
residue. The emphasis is typically on the removal of contaminants such as sulfur and nitrogen to
avoid poisoning downstream catalysts. Petroleum refineries transform crude oil into useful fuels
and products while satisfying technical, government, and safety requirements. In addition, they
must comply with environmental policies that increasingly limit the amount of sulfur and other
impurities in fuels. Hydro-treating is a well-established and industrially acceptable process to
refine the crude petroleum and production of transportation fuels. In this process, a high volume of
hydrogen gas is used for the removal of the undesired impurities (e.g., sulfur, nitrogen, oxygen,
etc.) in crude petroleum to reduce the emission of pollutant gases (e.g., SOx and NOx) during its
consumption, and also for enhancing the quality of various fuels (e.g., diesel and gasoline) by
increasing the cetane number.

Now to remove the impurities from crude oil we need hydrogen. Hydrogen gas is one of the most
important elements in the production of de-sulphurized fuels. For hydro-treating, the hydrogen
stream must be extremely pure (>99%) and have no humidity. The stream should have a low
hydrocarbon content, as well as low mercaptan and hydrogen sulfide levels (<0.1%).

To fulfill this hydrogen demand IOCL, Digboi imports natural gas from Oil India Limited,
Duliajan. Only about 15–30% of the hydrogen demand of the refinery is produced internally by
processes such as catalytic reforming of naphtha; the rest is supplied by external producers.

The Hydro-Treater Block (HDTB) of IOCL, Digboi mainly comprises of the following units:

Hydro-Treater Block (HDTB)

Hydrogen Sulphur Sour Water High Purity
Hydro-treater
Generation Unit Recovery Unit Treater Unit Nitrogen Unit
Unit (HDTU)
Amine (HGU) (SRU) (SWSU) (HPNU)
Treating Unit
(ATU)

AMine
Recovery
Unit (ARU)
Wild Naptha
Stabilization
Project
(WNSP)

10 | P a g
e
4.1 - HYDRO-TREATER UNIT (HDTU):

During the Second World War, the oil field produced almost 7000 barrels of crude oil per day. It
was pushed to produce so much with little regard to the reservoir management, with the result that
the production started dropping towards the end of the war. To overcome these technological
problems, a modernization project was undertaken by the company. This was a major attempt to
refurbish and modernize the refinery. The refinery installed Hydro-treater to improve the quality of
diesel. As a result, its refining capacity increased from a meagre 0.5 MMTPA (million metric tons
per annum) to the present capacity of 0.65 MMTPA. Due to such continuous efforts, the refinery
has been awarded the ISO - 14001 and OHSMC certificate.

Different feeds oils from diverse sources, whether straight-run or cracked products, are treated by
the HDT unit. The feed consists of a variety of items with unsaturated, aromatic, sulfur, and
nitrogen constituents. Nitrogen and sulfur concentrations vary depending on the crude. The DHDS
Unit's function is to hydro treat a mixture of straight run gas oil and cracked gas oil in order to
produce HSD (High Speed Diesel) with a sulfur level of less than 500 ppm wt. A continuous
absorption procedure utilizing 25 weight DEA (Di-ethanolamine) solutions is used to remove the
H2S Gas that is released during the hydrodesulphurization reaction. Desulfurization happens along
with nitrification and the saturation of unsaturated molecules. The hydrogen unit is where the
hydrogen is obtained. From the Amine Regeneration Unit, lean amine for absorption is obtained
(ARU). ARU receives rich amine that has been exposed to H2S for amine regeneration.

Purpose of the unit:

• To meet the requirements of environmental regulations for greener fuels by producing low
sulfur (500 ppm), high cetane (48.5) HSD, and high smoke point (21mm) kerosene.
• Middle distillate is in higher demand in emerging economies.
• Effective utilization of bottom of the barrel.

The Hydro-Treater Unit (HDT) is further subdivided into 3 categories:

• Amine Treating Unit (ATU)

• Amine Recovery Unit (ARU)
• Wild Naptha Stabilization Project (WNSP)

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4.1.1- Amine Treating Unit (ATU):

The objective of the Amine Treating Unit is to remove H2S, CO2 and mercaptan compounds from
various gas streams, such as recycled gas in hydro-treating and hydro-cracking processes,
hydrogen plant feed, and fuel gas systems. The H2S recovered is used as feed for the Sulfur
Recovery Unit (SRU). Gas containing hydrogen sulfide (H2S) is generated as a result of the
hydro-treating process. Amine is used for selective removal of H2S often referred to as “Acid
Gas”. Acid gas is introduced to the bottom of the absorber (contact tower) while an amine/water
combination is introduced at the upper section of the contactor. As the streams circulate and come
into contact with one another, the amine removes the acid gas by absorption. The rich amine is
then fractionated to Amine Recovery Unit (ARU) to separate and remove the hydrogen sulfide.
The lean amine, which is stripped of the hydrogen sulfide, is recycled back to the contact tower.

Absorption Temperature:

A lower lean amine temperature affords better H2S removal, usually between 80–105º F (27–41º C)

Amine Concentration:

• 15–20% amine concentration for MEA (mono-ethanolamine)

• 20–30% amine concentration for DEA (di-ethanolamine)
• 35–45% amine concentration for MDEA (mono di-ethanolamine)

Optimum amine concentration allows H2S removal with the lowest heat requirement.

Variables that Induce Corrosion:

• High Temperature
• High Acid Gas Loading
• High Amine Concentration
• High Contaminants

4.1.2- Amine Recovery Unit (ARU):

The amine solution, now ‘rich’ in hydrogen sulfide, is routed to the regenerator, where the
hydrogen sulfide and carbon dioxide are driven off, known as ‘acid gas’, and the lean amine can be
reused in the absorber unit. The H2S recovered is used as feed for the Sulfur Recovery Unit
(SRU). The rich amine leaves at the bottom of the LLE, while the sweet LPG leaves at the top.
Following this, any absorbed hydrocarbons are removed in a flash drum. The rich amine is then

11 | P a g e
fed to the top

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of the stripper column after being heated in the rich/lean amine heat exchanger. H 2S and CO2 are
stripped from the rich amine as it flows down the column, leaving the lean amine at the bottom. It
is then recycled to the top of the absorber where it passes through a lean/rich exchanger and
repeats the cycle.

Fig 4.1: LPG sweetening unit

4.1.3- Wild Naptha Stabilization Project (WNSP):

Naphtha is a flammable liquid hydrocarbon mixture. Generally, it is a fraction of crude oil, but it
can also be produced from natural-gas condensates, petroleum distillates, and the fractional
distillation of coal tar and peat. Wild Naptha is nothing but unstabilized naphtha stream, which
comes from stripper overhead in hydro-treaters and comprises of light gases in it, mainly C1
(methane) & C2 (ethane), in it. A naphtha stabilizer is a type of distillation column equipment used
in IOCL Refinery, Digboi to separate and remove light hydrocarbons such as ethane, propane,
butane, and pentane from naphtha, which is a mixture of hydrocarbons with carbon numbers
typically in the range of C5 to C12.

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The primary purpose of a naphtha stabilizer is to produce a stabilized naphtha product with a
specific vapor pressure and composition that meets the desired specifications for various
downstream applications. By removing the lighter hydrocarbons, the naphtha stabilizer helps to
prevent excessive vapor pressure in the naphtha, which is important for ensuring safe storage,
transportation, and further processing of the naphtha.

Stabilized naphtha is commonly used as a feedstock in petrochemical plants for the production of
various chemicals and plastics, as well as in the production of gasoline and other fuels. The
removal of light hydrocarbons through the naphtha stabilizer helps to improve the quality and
consistency of the naphtha product, making it suitable for these applications.

Fig 4.2: Wild Naptha Stabilization process diagram

4.2- HYDROGEN GENERATION UNIT (HGU):

As the name suggests this unit generates Hydrogen for the refining purpose. Hydrogen gas is one
of the most important elements in the production of de-sulphurized fuels. This unit separates
hydrogen gas from natural gas that is supplied from OIL, Duliajan by processing through several
methods. The final hydrogen stream provided by this unit is 99.9% pure and has no humidity

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content. The stream also has a low hydrocarbon content, as well as low mercaptan and hydrogen
sulfide levels (<0.1%). The Hydrogen Generation Unit (HGU) consists of high-temperature shift
conversion, desulfurization, reforming, and process gas cooling to increase the hydrogen content
of the process gas. PSA Unit is used for purification. Natural gas serves as the hydrogen unit's
feedstock.

Fig 4.3: Flow chart of hydrogen generating unit

The Hydrogen plant is divided into six main sections:

• Feed treatment consists of feed Compression and desulphurization

• Reforming
• Heat Recovery
• High-Temperature Shift Reaction
• Product purification using the PSA unit
• The steam system consists of water conditioning

To meet the hydrogen, need in the feed treatment section, some hydrogen is recycled there,
while the reforming section's purge gas from the PSA unit is used as fuel.

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4.3- SULPHUR RECOVERY UNIT (SRU):

Sulfur Recovery Unit (SRU), converts hydrogen sulfide (H2S), also known as sour gas or acid gas,
into sulfur. Sulphur recovery refers to the conversion of hydrogen sulphide (H2S) to elemental
sulphur. Hydrogen sulphide is a by-product of processing natural gas and refining high- sulphur
crude oils. There are many sulphur recovery technologies available for different applications.
However the most common conversion method used is the Claus process. Approximately 96
percent of recovered sulphur is produced by the Claus process. The Claus process typically
recovers 95 to 98 percent of the hydrogen sulphide feed stream.

Clause Process:

There are three catalytic converters, a main combustion chamber (also known as a reaction
furnace), and heat recovery equipment in the Claus portion. The burner in the main combustion
chamber receives a mixture of sour gas and acid gas as feed. The burner is made to ensure
thorough mixing of air and feed gas for the oxidation of all hydrocarbons, residual sulphur
compounds (such mercaptans if any), ammonia, and a notional one-third of hydrogen sulphide of
feed gas is converted to S02 without the usage of ammonia combustion. After the Claus Section,
the last catalytic converters exhaust gases are handled in the incineration Section. All sulphur
species that are present in the tail gas are burned to produce sulphur dioxide. Gas from a refinery is
utilized as fuel for an incinerator. Liquid sulphur is transported to the sulphur pit via the sulphur
seal pot and sulphur look pot, where it is piped to the sulphur yard for solidification.

4.4- SOUR WATER STRIPPING UNIT (SWSU):

Sour water stripping is used to remove ammonia (NH3) and hydrogen sulfide (H2S) from sour
water streams coming from many unit (such as catalytic cracking units, hydrocrackers, flare seal
drums, etc) operations to condition it for discharge or reuse within the refinery. In IOCL, Digboi
refinery most of the sour water comes from distillation, fluid catalytic cracking, catalytic
reforming, coker and acid gas removal units, with many other operations contributing to the
balance. The different streams are collected in a surge tank for centralized processing via a heat
exchanger and a single stripper column, or two in series. A combination of pH control and heat,
from direct injection steam or reboiler drives off the ammonia and hydrogen sulfide. The presence
of solids and hydrocarbons (‘oils’) are major contaminants that cause heat exchanger, stripper
column, and
16 | P a g e
reboiler fouling. The impact is loss of SWS capacity that may bottleneck refinery production rates,
drive the need for unscheduled SWS shutdowns and cleanouts leading to additional production
losses, high maintenance costs and increased worker safety issues from exposure to the highly
volatile H2S in the sour water system.

Oil contamination of the stripper also leads to a range of problems downstream. One is oil
carryover in the acid gas stream heading to the sulfur plant, leading to sulfur plant reliability issues
and increased risk of fires from oil coking of the reactor beds. Another is excess oil in the stripped
water to the water treatment plant creating an overload condition resulting in environmental risk
and/or the need to reduce refinery capacity.

Normally, refinery SWS are designed for a feed concentration in the range of 500 to 15000 ppm
wt. of both NH3 and H2S.

Fig 4.4: Sour Water Stripper Process

4.5- HIGH PURITY NITROGEN UNIT (HPNU):

As the name suggests this unit is designed to extract nitrogen from pure air that is present in our
atmosphere for various purposes within the refinery. However, according to the rules of Govt. of
India IOCL, Digboi is allowed to extract nitrogen from pure air only to fulfill its requirements
within the refinery. Economic selling of this extracted nitrogen outside the refinery is not allowed.

The production of nitrogen from the air is carried out mainly by three methods: cryogenic
distillation, pressure swing adsorption (PSA), and membrane separation. The selection of a
suitable technique is primarily based on the required production rate, load profiles, utilization (e.g.
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operating

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hours per week), and purity level of the product gas. While the operation of cryogenic air
separation units (ASUs) is the most efficient method if large amounts of high-purity nitrogen are
demanded, the utilization of membranes would be in preference when the requirement for either
quantity or purity is lower. Currently, the PSA technology for nitrogen generation is commercially
established in the intermediate area, for product flow rates up to several thousand Nm3/h (at 0 °C,
1 bar abs) and product purity levels up to 10 ppm of the residual oxygen concentration. The
process allows the kinetic separation of oxygen from nitrogen which is possible by taking
advantage of the remarkably faster sorption rate of oxygen over nitrogen in PSA-plants equipped
with carbon molecular sieves (CMS). High selectivity is attainable due to the sieving effect in
intentionally narrowed micro pore mouths. The simplicity of the plant operation, together with
multiple process variables and cycle organization strategies, makes the PSA a technology of choice
due to an opportunity for customizing the system to individual requirements. However, any
modification of the cycle organization or slight alteration of process conditions influences the
distribution of driving forces as a function of time within the production and regeneration steps.

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CHAPTER- 5: FUEL SECTOR

Introduction:

Petroleum refineries are large scale industrial complexes that produce saleable petroleum products
from crude oil. Actual refinery operations are very complicated, but the basic functions of the
refinery can be broken down into three categories.

The first process is known as distillation. In this process, crude oil is heated and fed into a
distillation column. As the temperature of the crude oil in the distillation column rises, the crude
oil separates itself into different components, called “fractions.” The fractions are then captured
separately. Each fraction corresponds to a different type of petroleum product, depending on the
temperature at which that fraction boils off the crude oil mixture.

The second and third processes are known as cracking and reforming. The heaviest fractions,
including the gas oils and residual oils, are lower in value than some of the lighter fractions, so
refiners go through a process called “cracking” to break apart the molecules in these fractions.
This process can produce some higher-value products from heavier fractions. Cracking is most
often utilized to produce gasoline and jet fuel from heavy gas oils. Reforming is typically utilized
on lower-value light fractions, again to produce more gasoline. The reforming process induces
chemical reactions under pressure to change the composition of the hydrocarbon chain.

The fuel sector is comprised of 4 major sub-units:

• Atmospheric and Vacuum Unit (AVU)

• Catalytic Reforming Unit (CRU)
• Delay Coking Unit (DCU)
• Motor Spirit Quality Unit (MSQU)

ATMOSPHERIC VACCUM UNIT (AVU)

CATALYTIC REFORMING UNIT (CRU)

FUEL SECTOR
DELAYED COKING UNIT (DCU)

MOTOR SPIRIT QUALITY UPGRADATION

(MSQU)

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Fig 5.1: Classification of Fuel sector

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5.1- ATMOSPHERIC AND VACCUM UNIT (AVU):

Introduction:

The atmospheric and vacuum distillation unit of Digboi refinery is designed to process 0.65
MMTPA of crude oil blend comprising Digboi, Duliajan and Kharsang crude oils. It is called the
mother plant of the refinery because the final products of this plants are used as feed for other
plants like DCU, NSU, CRU, MSQU, SDU etc.

CDU/VDU is integrated unit having no battery limit segregation. The entire unit is divided into 3
sections, as discussed below.

a) Crude distillation unit

b) Naphtha stabilizer unit
c) Vacuum distillation unit

Products obtained from CDU during normal case of operation are-

 Light Kerosene (LK)

 Heavy Kerosene (HK)
 Light Gas Oil (LGO)
 Heavy Gas Oil (HGO)
 Reduced Crude Oil (RCO)
 Raw Naptha

5.1.1- Crude Distillation Unit:

CDU separates crude oil into overhead vapors (fuel gas & stabilized naphtha), light kero, heavy
kero, LGO, HGO & RCO. It is further subdivided in to following sections:

• Crude preheat train:

Crude oil preheat train is basically two heat exchanger trains which are the parts of desalter
where the crude is preheated. Crude is charged into the unit by crude charge pump 01 PA-00-
001 A/B which takes suction from offsite crude pump 40PACF-802-A/B. The crude oil is
heated in preheat exchanger train to achieve desalting temperature & heat recovery by
successive heat
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exchange with HSD product. In this section crude is heated from the storage temperature to
desalting of 128°C. Desalting is done at 128.5°C and 10kg/cm2 pressure.

• De-salter:

Crude oil brings along with it salt, particularly those of sodium etc. metals like arsenic,
vanadium etc. and mud. Although these are present only in small amounts, their presence can
result in serious problems in downstream equipment like heat exchanger, heater and columns.
Hence the need for their removal is important before processing. A small quantity of caustic is
pumped to the desalter water with the help of single acting and single stage reciprocating
compressor for an alkaline medium in desalter that helps in settling the demulsifier added,
which helps in reducing the water carry over with crude and oil carry down neutralizing any
acid that may be formed at the operating temperature.

• Crude preheat train-II & III:

Desalted crude overflows to suction of crude booster pumps (01-PA-002 A/B, cap 112.5
Cu.m/Hr. and differential head- 342.1m. Desalted crude is pumped through preheat exchanger
in two parallel trains i.e. train-II and train-III. The crude oil after preheating in the respective
exchangers in the path is further heated up in atmospheric heater (01-FF-001) and fed to the
atmospheric distillation column (01-CC-001) for separation of various products.

• Atmospheric Heater:

The heater is a cylindrical type furnace having two parallel passes on the crude oil side. Flow
in each pass can be controlled by individual pass flow controllers. It is a dual fired furnace, i.e.
either fuel gas or fuel oil or both can be used as fuel. However, since fuel oil is not used in
Digboi refinery, these facilities have now been rendered redundant.

• Combustion Air System:

Atmospheric and vacuum heaters have a combined air preheating system to supply the
combustion air requirement of respective heater burners. The combustion air required for
atmospheric and vacuum heaters is supplied by two forced draft fans.

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 • Atmospheric Column:

The crude oil after final heating in atmospheric heater is fed to the atmospheric column for
separation of products. The atmospheric column contains 54 trays. The column has a stripping
section at the bottom. In order to maximize heat recovery and balance the tower loading for
maintaining temperature profile across the column four pump around system (PA) are
provided. These PA are down from their respective product draw off trays and are routed for
heat recovery before entering again back to the column. LK, HK, LGO, HGO are distillate
streams that are drawn as side cuts from the atmospheric column.

5.1.2- Naptha Stabilizing Unit:

Naphtha obtained in overhead naphtha reflux drum also contains light ends, the hot product
naphtha after preheating the feed to stabilizer is cooled down in stabilized naphtha cooler and sent
to storage or slop under flow control. This naphtha is feed naphtha stabilizer where C3 and part of
C4 hydrocarbons are removed from naphtha. The feed to stabilizer is first heated up to 100°C in
feed stabilizer bottom exchanger by exchanging heat with stabilized naphtha product stream from
stabilizer bottom.

5.1.3- Vacuum Distillation Unit:

Vacuum distillation unit (VDU) separates Reduced Crude Oil (RCU) into vacuum diesel, PWD,
HWD, Slop & vacuum residue. It essentially consists of a vacuum heater, vacuum column, product
stripper and product rundown cooling arrangement.

• Vacuum Furnace:

Reduced crude oil (RCO) from the bottom of the atmospheric distillation column at 337°C
mixed with other products enters the vacuum furnace. Flow controller controls the flow of
RCO. Provision for advanced control furnace Flow features is given for better efficiency of
heater. RCO feed coming from the vacuum heater enters the column in the flash zone where
the RCO is partially heated in vacuum and sent to VDU.

• Vacuum Distillation Unit:

The partially vaporized stock from vacuum furnace is fed to vacuum column. The vacuum
column has two sections of different diameter, top section is of 4750m, and bottom section is
of 4200m dia.

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 The RCO feed coming from the vacuum heater enters the column in flash zone below the slope
draw off chimney tray. The vaporized portion rises up the tower and is fractionated into four
side stream products; the liquid residue is withdrawn as vacuum residue by VR quench pump.
It is cooled in crude preheat exchanger train and circulated back to the column bottom as
quench stream and sent as run down.

5.2- CATALYTIC REFORMING UNIT (CRU):

Introduction:

The catalytic reformer unit is one of the most important units of the refinery. The catalytic
reforming is a major conversion process that transforms low octane naphtha feed stock to high
octane reformate for use as gasoline blending component to make lead free petrol. Due to the
presence of contaminants, naphtha is first hydrotreated and then fed to catalytic reforming unit.
Feed stock of catalytic reformer is hydro-treated naphtha received from HDTU.

The Catalytic Reformer Unit (CRU) in IOCL had been installed to meet the demand of unleaded
motor spirit in the North-eastern region. The design capacity of the CRU unit is based on the total
potential of 90-160°C TBP cut naphtha availability by processing 0.65 MMTPA of Assam crude
oil mix.

The IOCL, Digboi CRU consists of the following units:

i. Naptha Stabilization Unit (NSU)

ii. Hydro-treater Unit (HDT)
iii. Catalytic Reformer Unit (CRU)

The full range naphtha cut from CDU is split in the Naphtha Splitter Unit to produce special cut
naphtha. This naphtha is then treated in hydro-treater unit (HDT) to remove impurities viz.
Sulphur, nitrogen and other metals to form the feed stock for reformer unit.

In the reformer unit, the naphtha feed after adequate hydro treatment is passed over a bi functional
catalyst in three reactors in the presence of hydrogen. The reformate obtained is then stabilized and
routed for blending into MS pool. The hydrogen rich gases produced in the reformer are recycled
partly to reformer and balances to the naphtha hydro treatment section

Various products from CRU unit are:

1. Light Naptha
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 2. Gasoline or stabilized reformate
3. Hydrogen rich gas
4. LPG rich off gas

Light naphtha and stabilized reformate are blended into motor spirit. Hydrogen rich gas is sent to
waxy hydro finishing unit and fuel gas system LPG rich off gas is sent to LPG recovery unit.

Fig 5.2: Semi-regenerative catalytic reforming unit

5.3- DELAYED COKING UNIT (DCU):

Introduction:

The unit uses conventional delayed Coking technology with operation of two coke ambers to
upgrade feed mix consisting of vacuum residue and heavy waxy distillate and foots oil, LPG, fuel
gas, naphtha, kero, LDC, CFO, Coker residue and coke. DCU unit is an economically viable and
competitive process to upgrade the heavy residuals from refinery to more valuable distillate
products and premium grade coke.

The DCU unit of Digboi refinery has been designed for an output of 1,70,000 metric tons per year
of blend consisting of:

i. Heavy wax distillate

23 | P a g e
 ii. Short residue ex VDU
iii. Foots oil ex SDU

The unit is also designed to process long residue and pressable waxy distillate (PWD), if
necessary.

In Delayed Coking Process furnace, two coke drums, a fractionator, and a stripping section are all
part of the process. Vacuum residue reaches the distillation column's flash zone at the bottom or
immediately below the gas oil tray. The leftover oil is delivered to the coking furnace after
fractions that are lighter than heavy gas oil is flashed off.

To stop the furnace from prematurely coking, steam is introduced. Heat is applied to the feed to
the Coker drums to just above 482 °C (900 F). As it exits the furnace, the liquid-vapour mixture
travels to one of the coking drums. During the time that the other drum is being decoked and
cleaned, coke is placed in this drum for 24 hours. The liquid feed cools hot vapours that are
coming from the coke drum. The bottom of the fractionator receives vapours from the top of the
coke drum. Steam and the by-products of the thermal cracking reaction make up these vapours
(gas, naphtha and gas oils). The fractionator's quench trays allow the vapours to rise through them.
The top of the gas oil stripper returns steam and vaporized light ends to the fractionator. The
typical number of trays utilized between the gas oil draw and the naphtha draw or column top is
eight to ten.

Fig 5.3: Delayed Coking Unit

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5.4- MOTOR SPIRIT QUALITY UPGRADATION (MSQU):

Introduction:

The MSQU unit is a recently commissioned unit, used to further refine the Motor Spirit after it
comes out as a final product from the Hydro-treater unit (HDT). Initially the motor spirit output
from HDT was used as the final product and released in the market. But after 2010 the
commissioning subjected to further treatment in the MSQU of BS-II (Bharat Stage-II) the motor
spirit is being subjected to further treatment in the MSQU. The purpose of MSQU is to improve the
octane number of the light naphtha feed before blending it into pool of gasoline. The process of
motor spirit quality upgradation comprises of the following steps:

• Naptha Stabilizer unit (NSU)

• Hydro-treater unit (HDU)
• Isomerization unit

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CHAPTER- 6: CAPTIVE POWER PLANT (CPP)

Introduction:

Captive power plant (CPP), the heart of refinery, is basically a power generating plant which
provides the need for the required power responsible for the operations of different units inside the
refinery. The plant has a total installed power generating capacity of 45.5 MW provided by the
three gas turbines each having a capacity of 8.5 MW and a fourth one having capacity of 20MW,
manufactured by M/S BHEL (Bharat Heavy Electricals LTD.). The four turbines can run with the
help of natural gas as well as with the help of high-speed diesel which serves as a backup fuel.

An average of 20 MW power is required for the operation of refinery plants and 7-8 MW power is
exported to ASEB (Assam State Electricity Board) for distribution in Digboi Township and
generation of revenue.

The above stated power generation is done by using two turbines, one of 20 MW capacity and the
other of 8.5 MW capacity. The rest two turbines, each having a capacity of 8.5 MW, are always
kept in standby to be used in case of emergency if any one of the running turbines gets tipped. The
exhaust of the gas turbine is used to run three HRSG (Heat Recovery Steam Generator) of 37- 5
TPH capacities and another one of 100 TPH capacity. Three gas turbines are of frame-III type (8.5
MW) and one is of frame-V type (20 MW). In general frame-V GT is always tried to be kept
running so as to reduce the load on frame-V turbine.

6.1- GAS TURBINE GENERATOR (GTG):

Gas Turbine Working Principle:

Gas turbine engines derive their power from burning fuel in a combustion chamber and using the
fast-flowing combustion gases to drive a turbine in much the same way as the high-pressure steam
drives a steam turbine. A simple gas turbine is comprised of three main sections: a compressor, a
combustor, and a power turbine. The gas turbine operates on the principle of the Brayton cycle,
where compressed air is mixed with fuel and burned under constant pressure conditions. The
resulting hot gas is allowed to expand through a turbine to perform work.

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Need of Gas Turbine:

Gas turbine is preferred for power generation over steam turbine and hydraulic turbine
because -

 The efficiency of the gas turbines is much higher than that of steam turbine due to the high
inlet temperature when other things being equal in both turbines.

 The non-availability of raw materials required for the operation of steam and hydraulic
turbines in the region.

 In steam turbine plants, water is used for cooling purposes; hence there are chances of
freezing in winter nights.

 Steam turbine requires coal to be burned as fuel for the generation of steam. Since there is
minimum production of coal in the north-eastern region, steam turbine is not a feasible
option.

 Also, hydraulic turbine requires a large head of water which is not available in the nearby
areas. So hydraulic turbines are not considered as an option for power generation.

Basic Principle of GT:

Fig 6.1: Open Loop Brayton Cycle

The gas turbine basically works on the Brayton cycle from principle of thermodynamics. As shown
in the diagram the processes can be described as:

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 Process 1-2: The air compressor takes the atmospheric air, and it compresses the air to high
pressure by using the power developed by the prime mover such as IC engine, Motor initially and
then utilizing the power generated by the turbine (as the compressor and the turbine share the same
shaft.

Process 2-3: With high pressure the air enters into combustion chamber then fuel is injected into
air after complete mixture of air and fuel the charge is ignited. The gases expand with increase in
temperature and entropy, while pressure remains constant.

Process 3-4: The energy of high-pressure working gas is converted into the rotating energy of the
blades, making use of the interaction between the gas and the blades. After isentropic expansion
the high pressure of the working gas is reduced to ambient pressure. The mechanical energy
produced, is further converted to electrical energy.

Process 4-1: The exhaust gases produced by the combustion chamber are released into the
atmosphere or it can be reused by providing heat exchangers which in return increases efficiency
and reduces pollution. The cycle repeats.

GT are of two types of Open cycle and Closed cycle. Basic components of both types are the air
compressor, a combustor, and the turbine. In open cycle the gas is released from the turbine to the
surrounding, whereas in the closed cycle the working fluid which is the exhaust from the turbine is
cooled in a cooler and is returned to the compressor.

In IOCL, Digboi open cycle GT is used in addition with a HRSG.

Basic Components of GT

Each GT unit consists of:

1. Diesel engine:

Prime mover is an initial source of motive power designed to receive and modify force and motion
as supplied by some fuel and apply them to drive machinery. In the case of a GT, a 4-cylinder IC
engine serves as a prime mover.

2. Torque Convertor

A torque converter is a type of fluid coupling which transfers rotating power from a prime mover.
It is used to provide for transmitting torque from the engine running at a relatively constant speed
to the turbine-generator shaft to accelerate it from zero speed, or a very low speed, through firing
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and acceleration to self-sustaining speed. When the torque convertor increases the speed,

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which is 60% of the RPM of GT and it overcomes its inertia force. the prime mover is then
disengaged.

3. Accessories Gear Box:

The RPM obtained from the diesel engine is very high and is used to drive the Fuel pump, lube
pump, main hydraulic oil pump, cooling water pump.

4. Fuel pump, Lube Pump, Main Hydraulic Oil Pump, Cooling Water Pump:

As the name says the fuel pump is used to pump the fuel to the combustion chamber. MOP is used
to circulate the lube oil to various parts of the GT. CWP is used to circulate water for cooling
purposes.

5. Atomizing air compressor:

For the turbine to work, the pressure in the combustion chamber needs to be higher than ambient
pressure. To increase the pressure compressor are necessary.

The types of compressors commonly used are: Centrifugal and Axial flow compressors. Early gas
turbines employed centrifugal compressors, which are relatively simple and inexpensive. They are,
however, limited to low pressure ratios and cannot match the efficiencies of modern axial-flow
compressors. Accordingly, centrifugal compressors are used today primarily in small industrial
units.

The axial flow compressor comprises of various rotor stator stages. The rotor comprises of series
of blades the move relative to a series of stationary blades called the stator. The rotor blades
transmit mechanical energy to pressure energy. Compression is accomplished in both rotor and
stator by continually diffusing it from high velocity to lower velocity with a corresponding rise in
static pressure.

6. Combustion chamber:

Air leaving the compressor must first be slowed down and then split into two streams. The smaller
stream is fed centrally into a region where atomized fuel is injected and burned with a flame held
in place by a turbulence generating obstruction. The larger, cooler stream is then fed into the
chamber through holes along a “combustion liner” (a sort of shell) to reduce the overall

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temperature to a level suitable for the turbine inlet. Combustion can be carried out in a series of
nearly cylindrical

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elements spaced around the circumference of the engine called cans, or in a single annular passage
with fuel-injection nozzles at various circumferential positions.

8. Speed reduction gearbox:

The shaft of the gas turbine is then coupled with the speed reduction gear box which reduces the
RPM of the turbine shaft to match the required RPM of the alternator.

9. Generator:

They include a rotor with a hollow core that rotates around a stator. The stator is typically a
powerful magnet, while the coils that carry electricity are wound around the rotor. In some
generators, the coils are wound around the stator and the rotor is magnetized. It doesn't matter.
Either way, electricity will flow. The rotor has to spin for electricity to flow, and that's where the
input of mechanical energy comes in. The current produced is alternating current.

Fig 6.2: GT casing cross-section

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Working of GT in IOCL:

The process involves:

➢ A diesel engine coupled to the main shaft of the gas turbine through a torque converter
housed in the accessory gear system is used as prime mover. The engine runs at 2600 RPM and
provides motive power to the accessory gear box.

➢ Accessory gear box drives the lube pump, fuel pump, main hydraulic oil pump and
atomizing air compressor

➢ The compressor sucks air at a pressure of 1kg/sq.cm through air filters which filter the air
and remove any kind of solid impurities present in the air before sending it to the compressor.
Then the air is compressed and sent to the combustion chamber at a rate of 6.5-kg/sq.cm.

➢ Air from the compressor enters the combustion chamber to facilitate combustion of fuel
and production of flue gases. The gas turbine has a dual fuel system and is capable to run either or
both
on Natural gas and High-speed diesel which is a product of IOCL. Natural gas received from Oil
India Ltd. is compressed to a pressure of 12kg/sq.cm through 910 kW capacity gas booster
compressors.

➢ Flue gases generated in combustion chamber are then sent into the turbine at a very high
velocity. The frame-III GT is a two-stage turbine with 1st set of blades running at a speed of 7100
RPM and 2nd set of blades running at a speed of 6500 RPM. The frame-V GT is a single stage
turbine with blades running at 5100 RPM.

➢ The turbine shaft is connected to the alternator shaft through the gear box which then
produces current. Since the maximum speed of alternator shaft for frame-III is 1500 RPM and for
frame-V is 3000 RPM, a speed reduction gear box is connected between turbine shaft and
alternator
shaft, and hence power is produced by the alternator which is used for different refinery operations

➢ Once the turbine overcomes its inertia of speed, the diesel engine is uncoupled from the
torque converter and the unit continues to run on its own.

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 Fig 6.3: Flow chart of GT unit in IOCL, Digboi

Lubrication system:

The lubrication requirements for the gas turbine are furnished by a common forced lubrication
system. The lubrication system completes with reservoir at the turbine base, pumps, coolers,
filters, valves, and various control and protection devices, furnishes normal lubrication and absorb
heat. MOP (main oil pump) supplies lubrication oil for normal operation and AOP (auxiliary oil
pump) & EOP (emergency oil pump) are required for startup, shutdown etc. EOP is driven by
battery.

Cooling water system:

Cooling water supply is maintained from the DRMP cooling tower in a closed loop. However, two
nos. of black start cooling tower including pump are available for black start conditions or any
emergency. The cooling water system circulates water, which is the cooling medium to the gas
turbine and maintains the lubricating fluid at acceptable temperature levels. The heat from the
lubrication system is absorbed through heat exchangers.

Fuel systems:

The gas fuel system is designed to deliver gas fuel to the turbine combustion chambers at the
proper pressure and flow rates to meet all the starting, acceleration and loading requirements of
gas turbine operation. The major components of gas fuel system are the gas stop/ratio and control
valve located in the accessory area. Associated with this gas valve is the necessary inlet piping and
strainer, fuel vent line, control servo valves pressure gauges and the distribution piping to the six
combustion fuel nozzles.

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Hydraulic system:

Hydraulic fluid at high pressure is provided by the hydraulic supply system, to operate the control
components of the gas turbine. High-pressure hydraulic oil furnishes the means of operating the
gas stop/ratio and control valve assembly, the second-stage nozzle control unit, and starting stage
clutch controls. Low pressure oil directly obtained from the lube bearing header is the hydraulic oil
supply for this system.

6.2- COOLING TOWER:

A cooling tower is a heat rejection device that rejects waste heat to the atmosphere through the
cooling of a water stream to a lower temperature. 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,
in the case of closed-circuit dry cooling towers, rely solely on air to cool the working fluid.
Common applications include cooling the circulating water used in oil refineries and other
chemical plants, thermal power stations, nuclear power stations and HVAC systems for cooling
buildings. The classification is based on the type of air induction into the tower: the main types of
cooling towers are natural draft and induced draft cooling towers. Cooling towers vary in size
from small roof-top units to very large hyperboloid structures that can be up to 200 meters (660 ft)
tall and 100 meters (330 ft) in diameter, or rectangular structures that can be over 40 meters (130
ft) tall and 80 meters (260 ft) long. The hyperboloid cooling towers are often associated with
nuclear power plants, although they are also used in some coal-fired plants and to some extent in
some large chemical and other industrial plants.

The above Fig 6.4 shows different parts of the cooling tower.

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6.3- DE-MINERALIZATION WATER PLANT:

Introduction:

Demineralization is the process of removing the mineral salts from water by ion exchange.
Impurities that remain dissolving in the water dissociate to form positive and negative charged
particles known as ions. These impurities or compounds are called electrolytes. Generally, all
natural water has electrolytes in varying concentrations. An ion exchange vessel holds ion-
exchange resins of required type through which water is allowed to pass. The selective ion in the
water are exchanged with ions or radicals loosely held by the resin. In this way water is passed
through several vessels or a mixed bed vessel so that both positive and negative ions are removed
and water is demineralized. Demineralization water is used in oil refineries, petrochemicals and
fertilizers, power stations, heavy chemical factories, paper and semiconductors and in
metallurgical and other industries for various uses like production of steam to generate power and
drive machinery and for processes such as distillation and reforming unit etc. since the cost resin
constitutes a major part of the total cost of DM plants, due consideration to be given to the proper
design and selection of resins to obtain optimum results and minimize operating cost.

Fig 6.5: Process flow diagram

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Impurities in water:

Water in its natural form may contain various impurities in suspended and dissolved state. The
major part of clarified water is classified into three major groups:

1. Ionic and dissolved impurities

2. Non-ionic and un-dissolved impurities

3. Gaseous impurities

Ionic and dissolve impurities may be cations and anions. Normally cations present in water are
calcium magnesium and sodium while anions mainly are chlorides, sulphates bicarbonates, and
silica, with lower concentration of nitrates, phosphates etc.

Types of De-mineralization:

The process of demineralization consists of the conversion of salts like:

NaCl, Ca(HCO3)2, MgSO4, etc. to their corresponding acids like HCl, H 2SO3, H2SO4, by cation
exchange resin (in hydrogen form) and removal of these acids by anion exchange resins (in
hydroxide form) thereby removing all dissolved ionic impurities from water and supplying water
in the purest form.

Ion-exchange resin:

Ion-exchange resins used in DM water plant are synthetic organic compounds made by co-
polymerization various organic compounds; most commonly used are Styrene & Divinyl benzene,
to supply the basic resin bed. These beds are further subjected to the process of sulphonation to
make cation resin, chloromethylation and amination to form anion resins.

Cation resin:

The exchange capacity of a cation resin such as INDION 225 H operating in H+ form depends on
the regenerant used. The factors affecting are regeneration level, sodium content, total cationic
load and the alkalinity of water

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Anion resin:

The exchange capacity of an anion resin such as INDION FFIP depends on the sulphate, the total
mineral acid content and silica content of the water, the regeneration level and regeneration
temperature. It is also affected by exhaustion time if less than 8 hours.

Deionization:

1. Two-bed deionization:

The two-bed deionizer consists of two vessels- one containing a cation-exchanger resin in the in
the hydrogen(H+) form and the other containing an anion resin in the hydroxyl(OH+) form. Water
flows through the cation column, whereupon all the cations are exchanged for hydrogen ions. To
keep the water electrically balanced, for every monovalent cation, e.g. Nat, one hydrogen ion is
exchanged and for every divalent cation, e.g. Ca2+, or Mg2+ two hydrogen ions are exchanged.
The same principle applies when considering anion-exchange. The decationised water then flows
through the anion column. This time, all the negatively charged ions are exchanged for hydroxide
ions combine with the hydrogen ions to form water ( H2O).

2. Mixed-bed deionization:

Inmixed-bed deionization the cation-exchange and anion-exchange resins are intimately mixed &
contained in a single pressure vessel. The through mixture of cation exchangers and anion
exchangers in a single column makes a mixed-bed deionizer equivalent to a lengthy series of two-
bed plants. As a result water quality obtained from a mixed-bed deionizer is appreciably higher
than that produced by a two bed plant. Although more efficient in purifying the incoming feed
water, mixed bed plants are more sensitive to impurities in the water supply and involve a more
complicated regeneration process. Mixed bed deionizer are normally used to polish the water to
higher level of purity after it has been initially treated by a two bed-deionizer.

6.4- AIR COMPRESSOR HOUSE:

In Digboi refinery, the compressed air is mainly used for two purposes:

Instrument air: This air, which is free from dust, moisture, lubricating oil of compressors is
used for operation of pneumatic valves within the refinery. A continuous supply of this air is

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essential to

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avoid malfunctioning and distortion in normal operations of instruments. The dew point, which is
the measure of the quality of instrument air should be less than -40°C.

Plant air: It is also known as service air or industrial air. This type of air is directly taken from
compressors and is used for operation of pneumatic tools and tackles loading of catalyst,
production of nitrogen, sand blasting and general cleaning and flushing in plant. The continuity of
this supply is not very essential and can be stopped if the need arises.

Instrument air requirement:

Instrument air pressure: 80-120 PSIG

Instrument air flow: 35 SCFM

DRMP air compressor house of the Digboi refinery is having four CENTAC Air compressors to
cater the air requirement of about 4000 NM3/Hr. It consists of two centrifugal air compressors of
3656 NM3/Hr. capacity each and two compressors of 4170 NM 3/Hr. capacity each. Besides these
four compressors, it is also having one HP air compressor (30kg/Sq.cm) of IR make. In addition to
the compressors there are two-

LP vessels and two HP

vessels: Old LP vessel: 6.5 m3

New LP vessel: 6.6 m3

Old HP vessel: 27.3 m3

New HP vessel: 30.8 m3

Details of CENTEC compressor:

The CENTEC compressor is a centrifugal air compressor driven by electric motor. The
compressor and the motor are directly coupled and the entire unit is mounted on a common base
plate with its own lube system and auxiliaries. The compressor contains compression stages
consisting of an impeller mounted on its own shaft, enclosed within a common cast iron casing.
Each rotor consists of an integral pinion gear driven at an optimum speed by a common bull
gear. The bull gear is

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directly driven by the main driver. An intercooler is mounted between each stage. A moisture
separator and removal system is supplied after each cooler to remove condensate.

Lubrication system:

The lubrication system for the compressor is completely self-contained and mounted on the base
plate. Oil is drawn from the oil reservoir located in the base plate and passes through the oil pump.
Two oil pumps are provided: a pre lube and a main oil pump. The pre lube oil pump serves to
prime the main oil pump and flood the compressor bearing and main oil lines before the
compressor starts. The pre lube pump starts when the control panel is energized and runs until the
compressor is up to speed and main oil pump increases oil pressure. It is shut down automatically
by a pressure transmitter that stops the pump after the main oil pump is supplying the required
system pressure.

When the unit trips on shutdown cycle, the pre lube pump starts immediately, and will continue to
run until the panel is de-energized. After the compressor is shut down, the pre lube oil pump
should be allowed to run 20 to 30 minutes to cool down the compressor bearings.

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Advantages and Disadvantages of DM Plant:

Advantages:
 Variety of cost effective in standard models.
 Improve aesthetics and rugged design.
 User friendly, low maintenance and easy to install.
 Simpler distribution and correction system.
 Quick availability
 Pre-dispatched assembly check
 De-multiport valves are top mounted as well as side mounted with the necessary
high pressure rating PVC piping
 Single valve operation as compared to the six valves in conventional filters.

Disadvantages:

 Operation cost is high.

 The ion exchange beads have to be regularly replaced, which can be costly.

 The process consumes large amount of energy, which can make it expensive to run.

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 CHAPTER- 7 MECHANICAL EQUIPMENTS

I. COMPRESSOR:

It is a device that increases the pressure of a compressible fluid.

1. Positive Displacement Compressor:

Positive displacement is a method of forcing air in a chamber where the volume is decreased
to increase the pressure. Most commonly used positive displacement compressor in IOCL
refinery, Digboi are:

1.1 Reciprocating compressor:

A reciprocating compressor has a piston that moves downwards thus reducing pressure in its
cylinder by creating a vacuum. This difference in pressure forces the suction chamber valves

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open and bring gas or air in. When the cylinder goes up, it increases pressure thus forcing
the gas or air out of the cylinder through a discharge chamber.

Working Principle:

In the reciprocating air compressor, the piston moves to BDC and air is sucked into a
cylinder from the atmosphere and moves it to the TDC. The compression of air starts and
increasing and pressure is also increasing. After reaching the limit of the pressure the
discharge valve is open and the compressed air is flowing through to the storage tank.

Construction:

Fig. 7.1- Reciprocating compressor:

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Working of Reciprocating Compressor:

Fig. 7.2: Working of Reciprocating compressor

Reciprocating Compressor works on the following ways:

➢ The reciprocating air compressor is powered by an electric motor or by diesel/gas

engines.
➢ When the power in on, the electric motor starts rotating and rotates the crankshaft which
attached to it and the piston starts moving the to and fro motion inside a cylinder.
➢ The piston is moved downward the air from the atmosphere enters into the cylinder
chamber.
➢ After reaching to BDC the piston start moving upward and the compression of air starts
and its pressure tends to increase.
➢ After reaching the set pressure the discharge valve is open and through it, the compressed
air is transfer to a storage tank where it can be used.

Different types of Reciprocating Air Compressor:

a. Single Acting.

b. Double Acting.

c. Single-stage Air Compressor.

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 d. Double stage air Compressor.

a. Single Acting:

The single-acting reciprocating air compressor has only a single side of the piston and it is used
for compression of air and another side is connected to the crankcase and it is not used for
compression.

b. Double Acting:

In the double-acting type of reciprocating compressor, the sides of the piston are used for
compression of air. On the one side, there is suction and compression takes place on the other
side. Both the suction and compression take place on every stroke of the piston.

c. Single Stage air Compressor:

The single-stage reciprocating air compressor, the compression of air takes place in a single cylinder. In
this, the air sucks from the atmosphere are first stroke and in the second stroke, it compresses the air and
delivers it to the storage tank.

Fig. 7.3 Single Stage air Compressor

d. Double stage air Compressor:

In the double stage air compressor, the compression takes place in two stages. In the first stage,
the air is compressed in one cylinder and after that, it transferred to the second cylinder for the
next compression. And in the end, the compressed air is stored in a tank.

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 Fig. 7.4 Double Stage air Compressor

1.2 Rotary VANE compressor:

A rotary vane compressor always compresses the gas to the design pressure defined by the
manufacturer, regardless of the pressure in the system in which the compressor is discharging.
This is a positive-displacement pump that consists of vanes mounted to a rotor that rotates inside
a cavity. The vane-type compressor consists of a cylindrical rotor with longitudinal slots in
which radial sliding vanes are fitted. The rotor is positioned eccentrically within a cylindrical
housing. The spaces between adjacent vanes form pockets of decreasing volume from a fixed
inlet port to a fixed discharge port. Compressor inlet and discharge valves are not employed in
the design.

Working Principle of Rotary Vane Compressor:

Rotary compressors are another type of famous compressor. It uses two Asymmetrical rotors that
are also called helical screws to compress the air. The rotors have a very special shape and they
turn in opposite directions with very little clearance between them. The rotors are covered by
cooling jackets. Two shafts on the rotors have been placed that transfer their motion with the
help of timing gears that are attached at the starting point of the shafts/compressor (as shown in
the image). Air sucked in at one end and gets trapped between the rotors and gets pushed to
another side of the rotors. The air is pushed by the rotors that are rotating in the opposite
direction and compression is done when it gets trapped in clearance between the two rotors.
Then it pushed towards the pressure side. Rotary screw compressors are of two types oil-injected
and oil-free. Oil-injected is cheaper and most common than oil-free rotary screw compressors.

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 Fig.7.5- Rotary Vane Compressor

1.3 Screw Compressor :

A screw compressor is a type of rotary compressor which compresses air due to screw
action. The main advantage of using this compressor is that it can supply compresses air
continuously with minimum fluctuation in delivery pressure. It is usually applied for low
pressure applications up to 8 bars.

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Construction:

Fig. 7.6- Screw Compressor

Working principle:

In a screw compressor one of the shafts is driving shaft and the other is driven shaft. The
driving shaft is connected to the driven shaft via timing gears which help to match speeds of
both the shafts. The driving shaft is powered by an electric motor generally. The two shafts
are enclosed in an airtight casing.

Fig.7.7- Working principle of Screw Compressor

The working cycle of the screw compressor has three distinct phases as following:
(i) Suction process
(ii) Compression process
(iii) Discharge process
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Suction process:

As the rotors rotate, air is drawn through the inlet opening to fill the space between the male
lobe and the female flute. As the rotor continues to rotate, the air is moved past the suction
port and sealed in the interlope space.

Compression process:

As the main rotor turns, the air trapped in the interlope space is moved both axially and
radially. The air is compressed by direct volume reduction as the enmeshing of the lobes
progressively reduced the flute volume and compression occurs.

Discharge process:

At a fixed point where the leading edge of the flute and the edge of the discharge port co-inside,
compression ceases and the air is discharged into the delivery line, until the flute volume has
been reduced to zero. The reason behind this is that the efficiency of any compression process
will be highest if it is carried out isothermally in comparison to adiabatically or polytropically.
Thus to maintain the temperature of air during compression, the heat developed is continuously
exchanged with flowing water.

2. DYNAMIC COMPRESSORS:

Dynamic compressors are rotary continuous-flow machines in which the rapidly rotating element
accelerates the air as it passes through the element, converting the velocity head into pressure,
partially in the rotating element and partially in stationary diffusers or blades.

2.1 Centrifugal Compressor:

Principle:
The compression principle of centrifugal compressor is quite different from that of reciprocating
or rotary type compressor.
When the air passes through the rotating impeller it experiences force or work which is
performed by centrifugal forces. The work input takes place as an increase in pressure and
velocity or speed of the air flow through the impeller. The air flow loosesit’s velocity after
entering in the diffuser section. The diffuser is actually a fixed or static component that escorts
47 | P a g e
the air flow when it leaves the impeller. This loss in velocity eventually results in an additional
increase of pressure. The impeller and the diffuser contributes about 65% and 35% of the total
pressure developed or produced in the compressor.

Construction:
A centrifugal compressor generally consists of four components named inlet, impeller, diffuser
and collector.

Fig. 7.8- Construction of Centrifugal Compressor

1. Casing and inlet:

The above mentioned components are usually protected or guarded by a casing or housing . A
case house consists of number of bearings in order to provide radial and axial support of the
rotor. The case also contains nozzles along with inlets and discharge flow connections in order to
introduce and extract flow from the compressor. A case is generally build of castironor steel.

2. Impellers:

The impellers are assembled or mounted on a steel shaft and this assembly is known as
compressor rotor (mostly in multi stage compressors). The rotor provides velocity to the gas with
blades that are attached to a rotating disc. These blades can be forward-leaning, radial or
backward-leaning depending upon the desired output. Most of the multistage compressors use
backward-leaning blades as they provide the widest range of efficiency.

3. Diffuser:
The impeller extracts the gas with great velocity into a diffuser passage. The diffuser usually
compromise two walls which form a radial channel. Because of this arrangements the velocity of
the gas decreases and dynamic pressure is converted into static pressure. The diffuser passages
are small space between adjacent diaphragms which generally turns the gas flow 180° in order to
direct it towards the next impeller.
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4. Collector:

Following the last stage impeller the gas must be collected and delivered to the discharge
flange. The component used to collect the gas discharged through the diffuser is called as
collector. It may also be termed as volute or scroll. The collector may also contain valves
and other instrumentation in order to control the compressor.

5. Coupling:

The coupling transmits power from driver to the compressor. Coupling can be direct or through a
speed increasing gear. Usually, toothed couplings are used with force-feed or filling lubrication.
The couplings with force-feed lubrication are designed for high speed of rotation and for the
most part they only are used in compressors. Another type of couplings is sealed, generally with
lubricating grease to be filled every so often; these couplings are used only on slower speed
drive shafts.
6. Shaft:
The shaft is a stiff section usually made of 40NiCrMo7 material. It is machined and impellers
and spacers are mounted on the central part, bearings and seals are mounted on both ends.
7. Bearings:
In a compressor the rotor is held in position axially by a thrust bearing and it rotates on two
journal bearings. The journal bearing are located at both end of the rotor and the thrust bearing is
mounted outside of the journal bearing and on the side opposite to the coupling.
Two types of bearings are generally used Thrust bearing and Journal bearing.

8. Shaft seal:
Seals at two shaft ends, where the shaft comes out of the casing, are used:
(a) To minimize leakage of process gas (which is being compressed), from inside to out of
compressor.
(b) To prevent outside air or oil vapour get into compressor and mix with process gas.

Types:
a. Single stage centrifugal compressor.

b. Multi stage centrifugal compressor.

a. Single stage compressor:

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Single stage compressors consist of only a single impeller and it is use for moving the air or
other gases up to 3 to 1 compression ratio for either pressure or vacuum duty. These types of
compressors are considered to have a beam design or an overhung impeller arrangement. In this
type of arrangement the impeller is at the non-driving end of the shaft. One major advantage of it
over the multistage compressor is that it provides high efficiency and the delivered gas is totally
oil and surge free.

Fig.7. 9- Single stage compressor

b. Multistage Compressor:

Multistage compressors consist of 1-10 impellers and it can be arranged in a variety of flow path
configurations. Throughout each and every stage the temperature and the compression ratio are
assumed to be constant. Multistage compressor can be arranged in straight-through, compound,
and double flow configurations. Multistage compressor are also considered to have beam-type
design but the impellers are located between the radial bearings.

Fig.7.10- Multistage compressor

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II.PUMPS:
A pump is a mechanical device that moves or transports fluids. This works by mechanical action
converted from electrical energy into hydraulic energy.

1. Positive Displacement Pump:

It is a type of pump that moves fluid by displacing it with a rotating or reciprocating piston or
other mechanisms. This action creates a vacuum that sucks fluid into the pump. Positive
displacement pumps are called so because of no fluid comes back to its casing during pumping
out. A locking is formed by meshing gears, sliding vanes that act like a seal and whole amount
of fluid goes through delivery line. This amount is called positively displaced amount and that’s
why it is called positive displacement pump.

Most commonly used positive displacement pumps in Digboi Refinery are:

1.1 Piston Type Pump:

It is a reciprocating pump, a positive displacement pump where certain volume of liquid is

collected in enclosed volume and is discharged using pressure to the required application.
Reciprocating pumps are more suitable for low volumes of flow at high pressures.

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Construction:

Fig.7.11- Construction of Piston type pump

a. Suction Pipe:
Suction pipe connects the source of liquid to the cylinder of the reciprocating pump. The liquid is suck by
this pipe from the source to the cylinder.

b. Suction Valve:
Suction valve is non-return valve which means only one directional flow is possible in this type
of valve. This is placed between suction pipe inlet and cylinder. During suction of liquid it is
opened and during discharge it is closed.

c. Delivery Pipe:

Delivery pipe connects cylinder of pump to the outlet source. The liquid is delivered to
desired outlet location through this pipe.
d. Delivery Valve:
Delivery valve also non-return valve placed between cylinder and delivery pipe outlet. It is in
closed position during suction and in opened position during discharging of liquid.

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e. Cylinder:
A hollow cylinder made of steel alloy or cast iron. Arrangement of piston and piston rod is
inside this cylinder. Suction and release of liquid is takes place in this so, both suction and
delivery pipes along with valves are connected to this cylinder.

f. Piston and Piston Rod:

Piston is a solid type cylinder part which moves backward and forward inside the hollow
cylinder to perform suction and deliverance of liquid. Piston rod helps the piston to its linear
motion.

g. Crank and Connecting Rod:

Crank is a solid circular disc which is connected to power source like motor, engine etc. for
its rotation. Connecting rod connects the crank to the piston as a result the rotational motion
of crank gets converted into linear motion of the piston.

h. Strainer:

Strainer is provided at the end of suction pipe to prevent the entrance of solids from water
source into the cylinder.

Working of Reciprocating Pump:

The working of reciprocating pump is as follows:

• When the power source is connected to crank, the crank will start rotating and
connecting rod also displaced along with crank.

• The piston connected to the connecting rod will move in linear direction. If crank
moves outwards then the piston moves towards its right and create vacuum in the
cylinder.
• This vacuum causes suction valve to open and liquid from the source is forcibly
sucked by the suction pipe into the cylinder.

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 • When the crank moves inwards or towards the cylinder, the piston will move
towards its left and compresses the liquid in the cylinder.

• Now, the pressure makes the delivery valve toopen and liquid will discharge through
delivery pipe.

• When piston reaches its extreme left position whole liquid present in the cylinder is
delivered through delivery valve.

• Then again the crank rotate outwards and piston moves right to create suction and
the whole process is repeated.

• Generally the above process can be observed in a single acting reciprocating pump
where there is only one delivery stroke per one revolution of crank. But when it
comes to double acting reciprocating pump, there will be two delivery strokes per
one revolution of crank.

1.2 Diaphragm Pump:

A diaphragm pump is a PD or positive displacement pump. It is also called as a membrane

pump. This pump works with using a blend of the reciprocating action of a rubber, Teflon
diaphragm otherwise thermoplastic & appropriate valves on any face of the diaphragm to push a
liquid.

Construction:

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 Fig. 7.12- Construction of Diaphragm Pump

Diaphragm pumps have a reciprocating diaphragm in a liquid chamber in place of

reciprocating piston inside a cylinder to produce the pumping action of the reciprocating
positive displacement pump. The arrangement of valves and their functioning is same as
that in the piston or plunger pumps. The liquid chamber is formed of the fixed body of the
pump and the diaphragm is fitted to one side of the chamber. The diaphragm is coupled to
an actuating part which moves the diaphragm.

Working:

By the action of the actuators the diaphragm bulges in and out of the liquid chamber. When the
diaphragm bulges out of the liquid chamber the volume of the chamber increases and pressure
inside the chamber decreases, this opens the inlet valve and liquid is taken inside the chamber.
When the diaphragm bulges in the chamber the volume of the chamber decreases and the
pressure increases which opens the outlet valve and the liquid is pumped out of the chamber. The
diaphragm does not have any frictional motion with the chamber, thus, there is no need of any
seal or liner. The movement of the diaphragm can be obtained either by hydraulic plunger or by
air pressure. Based on the type of actuation of the diaphragm the diaphragm pumps are of two
types, hydraulically operated or Air Operated Diaphragm Pumps.

1.3 Vane Pump:

A vane pump is a positive displacement pump that delivers a constant flow rate under different
pressure conditions. It is a self-priming pump. It is known as a “vane pump” because it
pressurizes the fluid due to the impact of the vanes.

Construction:

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 Fig.7.13- Construction of Vane Pump

a. Casing

This is an outer part of the rotary vane pump. It provides safety to all the internal components
of the pump. It prevents the internal parts, such rotor, shaft, sliding vanes etc., from any
damage due to the external source.

b. Inlet Port

This port uses to suck the fluid into the pump. It works as a one-way valve.

c. Outlet Port

After pressurizing the fluid, the pump discharges the fluid through the outlet port. It also
works as a one-way valve.

d. Shaft

A shaft of the pump is connected with an electric motor. This motor delivers power to the
shaft and rotates the shaft. This shaft further connects with the rotor.

e. Rotor

It is the most important part of the pump, which play a big role in fluid suction and
pressurization. It connects with the shaft. The rotor rotates according to the rotation of the
shaft. It has multiple vanes. When the rotor rotates it creates a vacuum inside the pump due
to that pump sucks fluid.

f. Vanes

The vanes of the vane pump are mounted on the rotor. The main objective of the vanes is to
convert the kinetic energy of the fluid into its speed. These vanes have a rectangular shape.
Sliding Vanes are present in the slots of the rotor.

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g. Cam Ring

This Ring is installed on the inner wall of the pump housing.

Working of Vane Pump:

Fig.7.14- Working of Vane Pump

A vane pump works in the following way:

• First of all, the power is delivered to the shaft through an electric motor or engine.
• The shaft is connected with the rotor, which rotates according to the rotation of the shaft.
• This rotor has multiple vanes which rotate as the rotor rotates.
• As the rotor rotates, a vacuum generates inside the pump; due to that, it sucks external
water into the pump.
• As the water enters the rotor area, the rotor blades move the water outward due to the
centrifugal force.
• When the water hits the vanes, these vanes convert the K.E of the water into speed and
send it toward the diffuser or volute casing area.
• The volute casing has a reducing area; due to that, it converts the speed of the water into
pressure and increases the pressure according to the requirements.
• After pressurizing the water, the water discharges and delivers to the desired area.

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 2. Dynamic Pump:

It is a type of velocity pump in which kinetic energy is added to the fluid by increasing the flow
velocity. A dynamic pump contains a rotating impeller that creates a vacuum that helps in
moving fluids. In these pumps a small amount of fluid gets back into the casing due to its casing
even when delivery valve is fully closed without causing any damage to the pump. Most
commonly used dynamic pump in Digboi refinery is centrifugal pump.

2.1 Centrifugal Pump:

A Centrifugal pump is a mechanical machine that pumps the fluids by converting the mechanical
power (rotational energy) into the pressure energy of the fluid flow. This mechanical power
generally supplies by the electric motor or engine. A centrifugal pump uses a centrifugal force to
pump the fluids. Therefore, it is known as a centrifugal pump.

Construction:

Fig.7.15- Construction of Centrifugal Pump

The various main parts of a centrifugal pump are:

a. Impeller

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It is the rotating part of the pump. The impeller is mounted on a shaft and the shaft of impeller is
again connected with the shaft of an electric motor. It is rotated by the motor and consists of
series of backward curved blades.

b. Casing
It is an air tight passage which surrounds the impeller. The design of the casing is done in
such a way that it is capable of converting the kinetic energy of the water discharging from the
outlet of the impeller into pressure energy before it leaves the casing and enters into the delivery
pipe.

c. Volutes:
Designed to capture the velocity of the liquid as it enters the outermost diameter of the impeller.

d. Diffusers:
Diffusers have multiple vanes and are positioned so they begin close to the outer edge of the
impeller.

e. Suction Pipe with Foot Valve and Strainer

A pipe whose one end is connected with the inlet of the impeller and the other end is dipped into
the sump of water is called suction pipe. The suction pipe consists of a foot valve and strainer at
its lower end. The foot valve is a one way valve that opens in the upward direction. The strainer
is used to filter the unwanted particle present in the water to prevent the centrifugal pump from
blockage.
f. Delivery Pipe
It is a pipe whose one end is connected to the outlet of the pump and other end is connected to
the required height where water is to be delivered.

g. Seals:
Mechanical Seals and Gland packing’s act as a method of containing fluid within the pump.
They are installed within the ‘seal area’ or ‘stuffing box’. Gland packing is a rope-like material
cut into rings to wrap around the shaft sleeve. A mechanical seal allows the rotating shaft to pass
through a stationary housing. It allows the rotating shaft to ensure the ‘wet’ area of the pump,
without allowing fluid to escape.

h. Bearings:

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 The Bearing reduces friction on moving parts within the pump and supports the shaft to
rotate smoothly. They are commonly found in all pump types. There are commonly two types of
bearings used in centrifugal pumps,

➢ Roller bearings: use a cylindrical shape roller between moving parts. These reduce the
friction and support radial and axial load.
➢ Ball Bearings use balls to support the movement of parts, although simple in design they
are suitable for high speeds and are easy to maintain.
i. Coupling:
It connects shaft of the pump with the prime mover.

Working of Centrifugal Pump:

•As the electric motor starts rotating, it also rotates the impeller. The rotation of the impeller
creates suction at the suction pipe. Due to suction created the water from the sump starts
coming to the casing through the eye of the impeller.
•From the eye of the impeller, due to the centrifugal force acting on the water, the water starts
moving radially outward and towards the outer of casing.
•Since the impeller is rotating at high velocity it also rotates the water around it in the casing. The
area of the casing increasing gradually in the direction of rotation, so the velocity of the water
keeps on decreasing and the pressure increases, at the outlet of the pump, the pressure is
maximum.
•Now form the outlet of the pump, the water goes to its desired location through delivery pipe.
2.2 Jet Pump:

A jet pump is a mechanical machine that flows fluids by a driving nozzle that transforms the
pressure of the fluid into a high-speed jet. This jet from the nozzle continuously draws the fluid
from the inlet side of the jet pump. In the mixing tube, the trapped fluid absorbs some part of the
energy of the moving fluid. The diffuser of this pump retransforms the fluid velocity into the
pressure.

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A jet pump works by pulling the water toward the surface instead of pulling it like submersible
pump. It is a self-priming pump with no moving parts. This pump creates a fast jet of almost any
liquid and drives another liquid by driving the pressure recovery in the diffuser.

Construction:

Fig.7.16. Construction of Jet Pump

➢ Fig. shows an arrangement of a jet pump in a bore well.

➢ Each jet pump consists of a conventional radial flow pump with a jet nozzle at the
suction end.
➢ This helps to increase that suction lift beyond the normal limit of about 8 m of water
head.
➢ With the use of the jet assembly, it is possible to increase the suction lift up to 60 m.

Working:

➢ The suction side is completely filled with water also the pump is started.
➢ Some stream of high-pressure water from a specific delivery pipe of the pump remains
allowed to flow through that suction jet nozzle. Some pressure energy of water is
converted into kinetic energy due to which a local drop-in this pressure takes place. Due
to this pressure drop suction remains created including water is sucked from the bore
well. Here action ensures a considerably large supply from low pressure water.
➢ During the streams with different velocities mix (in this mixing zone) some pressure rise
takes place in some mixing zone.
➢ Behind the mixing zone, there is a diverging section where the further rise of pressure
occurs due to decrease in velocity.
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3. Heat Exchangers:

A heat exchanger is a device used to transfer heat between two or more fluids. The fluids can be
single or two phase and, depending on the exchanger type, may be separated or in direct contact.

Classification:

3.1 Shell and Tube Heat Exchanger:

A shell and tube heat exchanger, in simple words, is a type of heat exchanger where the two
working fluids exchange heat with the help of, as the name suggests, tubes and a shell.

Construction:

Fig.7.17- Shell and Tube Heat Exchanger

Shell-
The shell, sometimes also known as the housing, is the main mass or body of the heat exchanger
and it is built in the shape of a cylinder. It contains all the components of the heat exchanger. It’s
a pressure vessel, which means it’s going to be pressurized to match the fluid or the system
pressure that’s flowing through it. The shell acts as a container for the shell side fluid. It has a
circular cross-section and is manufactured by rolling a metal plate of desired dimensions. It
specifically acquires a cylindrical shape.
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Tube-
Tubes are the prominent part of shell and tube heat exchangers, which usually provide a heat
transfer surface between the fluid flowing across the outer surface of the tube and the other fluid
flowing inside the tube.

Tube sheets-

These are the component of the shell and tube exchanger which holds the tube. Specifically, the
tubes are inserted into the holes in tube sheets. These are either welded to the tube sheet or
expanded into grooves that cut down into the holes.

Shell side nozzles-

The shell side nozzles are specifically a part of the shell itself, the inlet and exit ports.
Tube side channel and nozzles-
The flow of tube-side fluid in the shell and tube heat exchangers is controlled through the tube-
side channel and nozzles. This helps in the flow of fluid into and out of the tubes.

Pass Dividers-
The shell and tube heat exchangers, which have two tube side passes, effectively need pass
dividers. These are needed in both bonnets and channels for an exchanger who is having two
passes.

Baffles-
Baffles are the parts of shell and tube heat exchangers that have numerous functionalities.
Baffles are used to provide a support structure for the tubes to lie in an accurate position.

Tie rods-
Sometimes, one can also observe tie rods which are used to connect the tube sheets and baffles
together. Again, this adds further support to strengthen the structure.

Connections-
There are a lot of connections or nozzles in the heat exchanger. This includes both inlets and
outlets since we have two fluids flowing into and out of the device.

Turbulators-
It can be observed that within these tubes, turbulators or tube inserts can be embedded. These
turbulators or tube inserts are pushed into every one of these tube holes in order to create a
turbulent flow.

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Working of shell and tube heat exchanger:
The specific idea behind the working of shell and tube heat exchangers revolves around the
passing of hot fluid through a cold fluid without getting mixed so that their heat is being
transferred.

➢ In the core structure of shell and tube heat exchangers, there are two inlets and two outlets
where each of the fluids gets in motion at their respective inlet and get out of the device at
their outlets.
➢ With the help of a tube bundle, the tube side flow passes and provides the desired
mechanism.
➢ Turbulent flow exists in the tubes. It helps to cater down the sediment depositing and also
helps in increasing the overall efficiency of the heat exchanger.
➢ These are secured by tube plates or tube sheets which act as a protective casing.
➢ When it comes to shell side flow, the liquid flow starts from the shell inlet and passes over
the tubes.
➢ Another part of the heat exchanger known as baffles helps maximize the amount of thermal
mixing that takes place in coolant pipes and shell-side fluid.
➢ After the whole process, it exits from the shell outlet.
➢ The presence of headers on both sides of the tube bundle helps construct a reservoir that
helps the tube side flow to be continuous.
➢ This can also be split into different sections as per the specific heat exchanger types.
➢ The shell side fluid is among the essential parts of this exchanger that keeps on working
around the baffles, which helps transfer energy.
➢ The working of shell and tube heat exchangers also depends on the number of phases,
whether single-phase or two phases.
➢ The single-phase exchangers are effective when there is a need for a constant fluid phase in
the whole process.
➢ In accordance with that, the two-phase exchanger will work as a phase change while the
process occurs.

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 4. VALVES

4.1 Butterfly Valve-

Fig.7.18- Butterfly Valve

➢ It shut off or releases the flow but not regulate the flow.
➢ In pipelines where instant shut off and release of flow is required, this valve is used.

4.2Non Return Valve-

Fig.7.19- Non Return Valve

 It belongs to check valve family and works only in one direction.

 It determines the action of release and shut off the flow when there is pressure drop
in either side of the disc.

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 4.3 Gate Valve-

Fig.7.20- Gate Valve

 It simply on/off the flow.

 It neither determines the flow variation nor do compensate pressure drop.

4.4 Safety Valve-

Fig. 7.21 : Safety Valve

 It saves the plant from any abnormalities which could happen.

 It senses the differential pressure acting on either side of the seat and release
them out instantly.

4.5 Globe Valve-

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 Fig.7.22- Globe Valve

 It controls the flow.

 Here, the flow direction is like English alphabet “S”.

4.6 Ball Valve-

Fig. 7.23: Ball Valve

 It on/off the flow.

 It is opened on quarter turn and closed on the same.

4.7 Plug Valve-

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 Fig.7.24- Plug Valve

 It controls the flow.

 The two port conical plug in a plug valve which allow the flow and shut flow
on quarter turn.

CHAPTER 8 CONCLUSION

It was indeed a gratifying experience for us to be a part of the INDIAN OIL CORPORATION
LIMITED (IOCL), ASSAM OIL DIVISIN (AOD) during the period of our summer training. It
was the real time to correlate the theoretical knowledge with practical. Being a part of the
refinery during that period we had the opportunity to visit various units.

The main objective of the refinery is to do distillation of the raw crude that is supplied from M/S
oil India limited, Duliajan and other sources. One interesting unit in this plant is the wax sector.
It is the only refinery in India which has wax production unit.

And it was quite a memorable and interesting to see all parts of pumps, compressor, heat
exchanger and other various mechanical equipment and being a student of mechanical
engineering, it will be very beneficial for our future. Briefly we visited the whole refinery and
grasped a little knowledge about the refinery equipment but its short span of time is not enough
to have an in-depth knowledge of the whole plant. But this tenure of stay at the refinery was of
immense beneficiary and knowledgeable enough to have a better linkage between theory and
practical.

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