1. INDUSTRIAL TRAINING
REPORT
IOCL ( AOD )
DIGBOI REFINERY
REPORT SUBMITTED BY:
Rajan kumar choudhary
5TH
Semester
Scholar No. 091116012
Mechanical Engineering
Maulana Azad National Institute Of Technology
Bhopal, 462051
2. 2
DECLARATION
I hereby declare that this project is being submitted
in fulfillment of the VOCATIONAL TRAINING
PROGRAMME in IOCL (AOD) Digboi, and is the result
of self done work carried out by me under the
guidance of various Engineers and other officers.
I further declare that the structure and content of
this project are original and have not been submitted
before for any purpose.
SUBMITTED BY:
RAJAN KUMAR CHOUDHARY
SCHOLAR NO. 091116012
B.TECH. (5TH SEMESTER)
MAULANA AZAD NATIONAL INSTITUTE OF
TECHNOLOGY
BHOPAL (MADHYA PRADESH), 462051
3. 3
CERTIFICATE
This is to certify that Mr. Rajan kumar choudhary Of Maulana
Azad National Institute Of Technology, Bhopal has
undergone Vocational Training for a period of 14 days from
17.05.2011 to 30.05.2011 at Digboi Oil Refinery, IOCL
(AOD), and has made the project report under my guidance.
Project Guide
Mr. P. K. Bordoloi
4. 4
ACKNOWLEDGEMENT
A detailed report such as this one doesn’t become
possible without the contribution of several people who are
willing to help wholeheartedly. Through this training, I’ve
been lucky to have got the opportunity to learn so much
from the Engineers, Officers, and Staff members of IOCL
(AOD), Digboi who have always helped me through the
period of my training.
I would give thanks to the Training Department of IOCL
(AOD), Digboi as they have given me the chance of having
this wonderful learning experience.
I am also indebted to respected Officers and Engineers:
1) Mr. A. K. Kalita ( DM-Safety)
2) Mr. Debayan Sengupta
3) Mr. Ashutosh Pathak
4) Mr. Nani Gopal Deb
5) Mr. J. Pathak
5. 5
INTRODUCTION
The Digboi Refinery in North Eastern India is India's oldest refinery and
was commissioned in 1901. Originally a part of Assam Oil Company, it
became part of IndianOil in 1981. Its original refining capacity had
been 0.5 MMTPA since 1901. After modernization the capacity of the
refinery has been enhanced to to 0.65 MMTPA. The Digboi refinery
produces distillates, heavy ends and excellent quality wax from
indigenous crude oil produced at the Assam oil fields. The refinery
presently produces MS and HSD complying BS-III grade.
Petroleum products are supplied mainly to north-eastern India
primarily through road and by rail wagons. A new Delayed Coking Unit
was commissioned in 1999. A new Solvent De-waxing Unit for
maximizing production of micro-crystalline wax was installed and
commissioned in 2003. The refinery has also commissioned a
Hydrotreater and Hydrogen Plant in 2003 to improve the quality of
diesel. The MSQ Upgradation project has been completed. A new
terminal with state of the art facility is under construction and
expected to be completed by end of 2011.
The refinery is ISO-9001,ISO-14001 and OHSAS-18001 accredited, its
laboratory is NABL accredited and follows TPM.
Digboi Refinery manufactures conventional petroleum products
like LPG, Naphtha, Motor Spirit, Superior Kerosene (SKO), High
Speed Diesel (HSD), Furnace Oil (FO) and Raw Petroleum Coke. It
also produces one of the best quality of Paraffin Wax besides
6. 6
other products like Aromex, Jute Batching Oil (JBO), Mineral
Turpentine Oil (MTO), Solar Oil etc.
The refinery’s fuel requirement is met by refinery off-gases
generated from the
various process units and also the purchased natural gas from
M/s Oil India Limited.
The purchased natural gas is used in Captive Power Plant in Gas
Turbines to produce power while the refinery off-gases / natural
gas is used in the various furnaces of the process units and also
supplementary firing in HRSGs. Only in case of failure of Natural
Gas supply, HSD is used in Gas Turbines. The refinery is self-
sufficient in electrical power and does not have to import power
from the state grid for refinery operations. In fact, Digboi Refinery
has taken up to sell 5 MW of power to state grid.
7. 7
GENERAL SAFETY RULES
According to the regulations of the plant administration, every
employee & visitor in the plant has to adhere to the 11 point
General Safety Rules, as mentioned below:
Safety Shoe
Safety Helmet
Spark Arrestor (in exhaust of vehicles)
Photography Prohibited
Speed Limit in plant is 20 kmph
Smoking Banned
Incendiary Items ( matchbox,lighter,etc.) Banned
Use of VCD,VCR Prohibited
Use of Radio Devices Banned
Use Fire Safety Equipments like Extinguishers-
DCP,Foam,CO2.
Use of Hydrant Water for other purposes is banned
Apart from the above mentioned rules, several other things must
also be kept in mind.
In case of an accident or hazard, there are MCP(Manual Call Point)
at regular intervals, which must be activated once a danger is
seen. If the danger Is very serious in nature, then the people are
required to assemble in the 3 Assembly Points provided for the
purpose, so that they may be safely escorted out.
In case of a DISASTER, a 3-Cycle siren is sounded, which is a
straight siren, sounding for 7 minutes.
8. 8
WORK PERMIT SYSTEM
For performing different types of jobs, particular permits have
to be acquired.
There are different permits which need to be taken, like:
1. Hot Permit – for hot jobs like welding, gas cutting, etc.
2. Height permit – to work at heights
3. Soil Excavation Permit
4. Cold Permit
PERSONAL PROTECTION
EQUIPMENTS
Hand Gloves
Goggles
Ear Plugs
Safety Net
Safety Belt
Scaffolding
Breathing Apparatus
Hard Helmet
9. 9
WHAT IS PETROLEUM?
Petroleum (L. petroleum, from Greek: petra (rock) + Latin:
oleum (oil) or crude oil is a naturally occurring, flammable
liquid consisting of a complex mixture of hydrocarbons of
various molecular weights and other liquid organic
compounds, that are found in geologic formations beneath
the Earth's surface. Petroleum is recovered mostly through
oil drilling. This latter stage comes after studies of structural
geology (at the reservoir scale), sedimentary basin analysis,
reservoir characterization (mainly in terms of porosity and
permeable structures). It is refined and separated, most
easily by boiling point, into a large number of consumer
products, from gasoline and kerosene to asphalt and
chemical reagents used to make plastics and
pharmaceuticals.[4] Petroleum is often attributed as the
"Mother of all Commodities" because of its importance in the
manufacture of a wide variety of materials.
The composition consists roughly of the follows:
– 83-87% Carbon
– 11-15% Hydrogen
– 1-6% Sulfur
• Paraffins – saturated chains
• Naphthenes – saturated rings
• Aromatics – unsaturated rings
11. 11
DESCRIPTION:
The crude oil which comes in the plant is stored in an offsite
tank through which it is taken to a Crude Oil Preheater(PH1)
through a pump.
Then the heated crude oil ( at 128*C, 10 kg/cm2) goes into
the DESALTER, which separates the effluents like water,
dissolved salts, metals, etc.
The Desalted Crude is then taken through a 6 stage
Centrifugal Booster Pump, with output pressure at 32
kg/cm2, which is split into 2 parts taken going into PH2 &
PH3, whre crude is heated to 250*C, pressure decreases to
25 kg/cm2.
Then a Fuel Gas Furnace heats it to 354*C, at 12 kg/cm2,
output goes into CDU( Crude Distillation Unit).
The temp in CDU column varies uniformly from 119*C at
1.019 kg/cm2 to 321*C at 1.519 kg/cm2.
The products of CDU are
Vapours
Raw Naphtha
Light Kero, Heavy Kero, Light Gas Oil, Heavy Gas Oil
– Together called High Speed Diesel(HSD)
Reduced Crude Oil(RCO), which is the bottom
residue.
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The Raw Naphtha obtained is unstable & is sent to
NSU(Naphtha Stabilization Unit) to get Motor Spirit. This is
sent to Motor Spirit Quality Upgradation Unit (MSQU) to
obtain petrol.
HSD is sent to Hydrotreating Unit (HDT) for further
upgradation.
The RCO at 330*C is heated in Vacuum Hater by Fuel Gas
firing at 40 mm Hg pressure to 396*C. Then its sent to
Vacuum Distillation Unit (VDU).
VDU gives :
Vacuum HSD
Pressurized Wax Distillate (PWD)
Heavy Wax Distillate (HWD)
Vacuum Residue (VR)
It is to be kept in mind that the Vacuum HSD is inferior in
quality than the HSD obtained in the CDU.
The Vacuum HSD is sent to HDT for upgradation.
PWD sent to Solvent Dewaxing Unit (SDU), then to Wax
Hydrofinishing Unit (WHFU) then used to manufacture wax.
HWD & VR are sent to Delayed Coking Unit (DCU), where
LPG, HSD & Coke are obtained.
13. 13
MECHANICAL DEVICES
Used in an OIL REFINERY
1. PUMPS:
A pump is a device used to move fluids, such as liquids,
gases or slurries.
A pump displaces a volume by physical or mechanical
action. Pumps fall into three major groups: direct lift,
displacement, and gravity pumps. Their names describe the
method for moving a fluid.
Pumps based on their principle of operation are primarily
classified into:
• Positive displacement pumps (reciprocating, rotary pumps)
• Roto-dynamic pumps (centrifugal pumps)
14. 14
Positive Displacement Pumps
Positive displacement pumps, which lift a given volume for
each cycle of operation, can be divided into two main
classes, reciprocating and rotary.
Reciprocating pumps include piston, plunger, and
diaphragm types. The rotary pumps include gear, lobe,
screw, vane, regenerative (peripheral), and progressive cavity
pumps.
15. 15
Roto-dynamic pumps
Roto-dynamic pumps raise the pressure of the liquid by first
imparting velocity energy to it and then converting this to
pressure energy. These are also called centrifugal pumps.
Centrifugal pumps include radial, axial, and mixed flow
units.
A radial flow pump is commonly referred to as a straight
centrifugal pump; the most common type is the volute
pump. Fluid enters the pump through the eye of impeller,
which rotates at high speed. The fluid is accelerated radially
outward from the pump casing. A partial vacuum is created
that continuously draws more fluid into the pump if properly
primed.
In the axial flow centrifugal pumps, the rotor is a propeller.
Fluid flows parallel to the axis of the shaft. The mixed flow,
the direction of liquid from the impeller acts as an in-
between that of the radial and axial flow pumps.
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Centrifugal Pumps
The centrifugal pumps are by far the most commonly used
of the pump types. Among all the installed pumps in a
typical petroleum plant, almost 80–90% are centrifugal
pumps.
Centrifugal pumps are widely used because of their design
simplicity, high efficiency, wide range of capacity, head,
smooth flow rate, and ease of operation and maintenance.
The subsequent development of centrifugal pumps was very
rapid due to its relatively inexpensive manufacturing and its
ability to handle voluminous amounts of fluid.
However, it has to be noted that the popularity of the
centrifugal pumps has been made possible by major
developments in the fields of electric motors, steam
turbines, and internal combustion (IC) engines. Prior to this,
the positive displacement type pumps were more widely
used.
17. 17
The centrifugal pump has a simple construction, essentially
comprising a volute (1) and an impeller (2) (refer to Figure
1.16). The impeller is mounted on a shaft (5), which is
supported by bearings (7) assembled in a bearing housing
(6). A drive coupling is mounted on the free end of the shaft.
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Screw Pump
In addition to the previously described pumps based on the
Archimedes’ screw, there are pumps fitted with two or three
spindles crews housed in a casing.
Three-spindle screw pumps, as shown in Figure 1.14, are
ideally suited for a variety of marine and offshore
applications such as fuel-injection, oil burners, boosting,
hydraulics,
fuel, lubrication, circulating, feed, and many more. The
pumps deliver pulsation free flow and operate with low noise
levels. These pumps are self-priming with good efficiency.
These pumps are also ideal for highly viscous liquids.
Three-spindle screw pump – Alweiller pumps
19. 19
Reciprocating Pumps
Reciprocating pumps are positive displacement pumps and
are based on the principle ofthe 2000-year-old pump made
by the Greek inventor, Ctesibius.
Reciprocating pumps comprise of a cylinder with a
reciprocating plunger in it. The head of the cylinder houses
the suction and the discharge valves. In the suction stroke,
as the plunger retracts, the suction valve opens causing
suction of
the liquid within the cylinder. In the forward stroke, the
plunger then pushes the liquid out into the discharge
header.
The pressure built in the cylinder is marginally over the
pressure in the discharge.
The gland packings help to contain the pressurized fluid
within the cylinder. The plungers are operated using the
slider-crank mechanism. Usually, two or three cylinders are
placed alongside and their plungers reciprocate from the
same crankshaft. These are called as duplex or triplex
plunger pumps.
20. 20
Diaphragm Pumps
Diaphragm pumps are inherently plunger pumps. The
plunger, however, pressurizes the hydraulic oil and this
pressurized oil is used to flex the diaphragm and cause the
pumping of the process liquid.
Diaphragm pumps are primarily used when the liquids to be
pumped are hazardous or toxic. Thus, these pumps are
often provided with diaphragm rupture indicators.
Diaphragm pumps that are designed to pump hazardous
fluids usually have a double diaphragm which is separated
by a thin film of water.
A pressure sensor senses the pressure of this water. In a
normal condition, the pressure on the process and oil sides
of the diaphragms is always the same and the pressure
between
the diaphragms is zero.
21. 21
Gear Pump
In gear pumps, two identical gears rotate against each other.
The motor provides the drive for one gear. This gear in turn
drives the other gear. A separate shaft supports each gear,
which contains bearings on both of its sides.
As the gears come out of the mesh, they create expanding
volume on the inlet side of the pump. Liquid flows into the
cavity and is trapped by the gear teeth while they rotate.
Liquid travels around the interior of the casing in the
pockets between the teeth and the casing. The fine side
clearances between the gear and the casing allow
recirculation of the
liquid between the gears.
The above diagram shows A Gear Pump in 3 stages of
operation. The left side is the INLET & the right side is the
OUTLET.
22. 22
Out of all the above pumps, the Centrifugal & Reciprocating
Pumps are the most widely used. There are a few advantages
& disadvantages for both the pumps, & they are used
according to specific need. The main characteristics of both
the pumps are:
1. Centrifugal Pump:
High Flow Rate
Low Discharge Pressure
Quiet & Smooth Operation
Leakage is not there.
There is a mechanical seal.
2. Reciprocating Pump:
Low Flow Rate
High Discharge Pressure
Leakage occurs after short time of
usage.
Noisy operation.
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2.COMPRESSORS:
A compressor is a device used to increase the pressure of a
compressible fluid. The inlet & outlet pressure are related,
corresponding with the type of compressor & its
configuration.
The types of Compressors can be classified by the following
chart:
24. 24
Reciprocating Compressors:
The reciprocating compressor is probably the best known
and the most widely used of all compressors. It consists of a
mechanical arrangement in which reciprocating motion is
transmitted to a piston which is free to move in a cylinder.
The displacing action of the piston, together with the inlet
valve or valves, causes a quantity of gas to enter the cylinder
where is in turn compressed and discharged, Action of the
discharge valve or valves prevents the backflow of gas into
the compressor from the discharge line during the next
intake cycle.
The discharge valve or valves prevents the backflow of gas
into the compressor from the discharge line during the next
intake cycle.
When the compression takes place on one side of the piston
only, the compressor is said to be single acting.
The compressor is double-acting when compression takes
place on each side of the piston.
Configurations consist of a single cylinder or
multiple cylinders on a frame. When a single cylinder is used
or when multiple cylinders on a common frame are
connected in parallel, the arrangement is referred to as a
single-stage compressor. When multiple cylinders on a
common frame are connected in series, usually through a
cooler, the arrangement is referred to as a multistage
compressor.
26. 26
CENTRIFUGAL COMPRESSORS:
The radial-flow, or centrifugal compressor is a widely used
compressor and is probably second only to the reciprocating
compressor in usage in the process industries.
The compressor uses an impeller consisting of radial or
backward-leaning blades and a front and rear shroud. The
front shroud is optionally rotating or stationary depending
on the specific design.
As the impeller rotates, gas is moved between the rotating
blades fro the area near the shaft and radially outward to
discharge into a stationary section, called a diffuser. Energy
is transferred to the gas while it is traveling through the
impeller. Part of the energy converts to pressure
along the blade path while the balance remains as velocity at
the impeller tip where it is slowed in the diffuser and
converted to pressure.
The fraction of the pressure conversion taking place in the
impeller is a function of the backward leaning of the blades.
The more radial the blade, the less pressure conversion in
the impeller and the more conversion taking place in the
diffuser. Centrifugal compressors are quite often built in a
multi-stage configuration.
28. 28
HEAT EXCHANGER:
A heat exchanger is a piece of equipment built for efficient
heat transfer from one medium to another. The media may
be separated by a solid wall, so that they never mix, or they
may be in direct contact.
Flow Arrangement: There are two primary classifications of
heat exchangers according to their flow arrangement. In
parallel-flow heat exchangers, the two fluids enter the
exchanger at the same end, and travel in parallel to one
another to the other side. In counter-flow heat exchangers
the fluids enter the exchanger from opposite ends. The
counter current design is most efficient, in that it can
transfer the most heat from the heat (transfer) medium.
Types of heat exchangers:
1. Shell And Tube Type
2. Plate Type
3. Fluid Heat Exchanger
4. Direct Contact Heat Exchanger
Out of these commonly used types, the Shell & Tube Type
Heat Exchanger is widely used in industries & the same is
being used at Digboi Refinery.
Shell and tube heat exchangers consist of a series of tubes.
One set of these tubes contains the fluid that must be either
29. 29
heated or cooled. The second fluid runs over the tubes that
are being heated or cooled so that it can either provide the
heat or absorb the heat required. A set of tubes is called the
tube bundle and can be made up of several types of tubes:
plain, longitudinally finned, etc. Shell and tube heat
exchangers are typically used for high-pressure applications
(with pressures greater than 30 bar and temperatures
greater than 260°C).[2] This is because the shell and tube
heat exchangers are robust due to their shape.
30. 30
VALVES:
A valve is a mechanical device used to start, stop, control or
regulate the flow of a fluid through a pipe.
The various types of valves widely used in Industries today
are as follows:
Gate Valve: A gate valve, also known as a sluice valve, is
a valve that opens by lifting a round or rectangular
gate/wedge out of the path of the fluid. The distinct feature
of a gate valve is the sealing surfaces between the gate and
seats are planar, so gate valves are often used when a
straight-line flow of fluid and minimum restriction is
desired.
32. 32
Pressure Safety Valve
(PSV): A Pressure safety
valve is a valve mechanism
for the automatic release of
a substance from a boiler,
pressure vessel, or other
system when the pressure or
temperature exceeds preset
limits.
Non Return Valve: Non-return valve or one-way
valve is a mechanical device, a valve, which normally
allows fluid (liquid or gas) to flow through it in only one
direction.
33. 33
FRACTIONATING COLUMN:
A fractionating column or fractionation column is an essential
item used in the distillation of liquid mixtures so as to
separate the mixture into its component parts, or fractions,
based on the differences in their volatilities. Fractionating
columns are used in small scale laboratory distillations as well
as for large-scale industrial distillations.
Fractional distillation is one of the unit operations of chemical
engineering. Fractionating columns are widely used in the
chemical process industries where large quantities of liquids
have to be distilled. Such industries are the petroleum
processing, petrochemical production, natural gas processing,
coal tar processing, brewing, liquefied air separation, and
hydrocarbon solvents production and similar industries but it
finds its widest application in petroleum refineries. In such
refineries, the crude oil feedstock is a very complex
multicomponent mixture that must be separated and yields of
pure chemical compounds are not expected, only groups of
compounds within a relatively small range of boiling points,
also called fractions and that is the origin of the name
fractional distillation or fractionation. It is often not worthwhile
separating the components in these fractions any further
based on product requirements and economics.
Distillation is one of the most common and energy intensive
separation processes. In a typical chemical plant, it accounts
for about 40% of the total energy consumption.[6] Industrial
34. 34
distillation is typically performed in large, vertical cylindrical
columns (as shown in Figure) known as "distillation towers" or
"distillation columns" with diameters ranging from about 65
centimeters to 6 meters and heights ranging from about 6
meters to 60 meters or more.
36. 36
MAIN SECTIONS OF A
REFINERY
A modern refinery consists of a number of sectors for
performing different functions. The Crude Oil is passed
through these sections in a specific order according to the
functions. These are:
1.ATMOSPHERIC & VACUUM UNIT
( AVU )
The AVU forms the most important part of the Fuel Sector of
the refinery. The intake of the AVU is CRUDE OIL & after
passing through the AVU the output is obtained in the form of
many products like:
Raw Naphtha
Light Kero
Heavy Kero
Light Gas Oil
Heavy Gas Oil
Vacuum HSD
Pressurized Wax Distillate (PWD)
Heavy Wax Distillate (HWD)
Vacuum Residue (VR)
38. 38
All these products are obtained in a series of steps which are
primarily performed in 3 Units of the AVU:
CRUDE DISTILLATION UNIT ( CDU ) :
Process Objective:
–To distill and separate valuable distillates (naphtha,
kerosene,diesel) and atmospheric gas oil (AGO) from the crude
feedstock.
•Primary Process Technique:
–Complex distillation
•Process steps:
–Preheat the crude feed utilizing recovered heat from the
product streams
–Desalt and dehydrate the crude using electrostatic enhanced
liquid/liquid separation (Desalter)
–Heat the crude to the desired temperature using fired heaters
–Flash the crude in the atmospheric distillation column
–Utilize pump-around-cooling loops to create internal liquid
reflux
–Product draws are on the top, sides, and bottom
40. 40
VACUUM DISTILLATION UNIT ( VDU ) :
Process Objective:
–To recover valuable gas oils from reduced crude via vacuum
distillation.
Primary Process Technique:
–Reduce the hydrocarbon partial pressure via vacuum and
stripping steam.
Process steps:
–Heat the reduced crude to the desired temperature using fired
heaters
–Flash the reduced crude in the vacuum distillation column
–Utilize pump-around-cooling loops to create internal liquid
reflux
42. 42
NAPHTHA STABILIZATION UNIT ( NSU ) :
Process Objective:
To convert the unstable Raw Naphtha obtained from CDU to
stabilized naphtha which can be used to make motor spirit.
The Naphtha Stabilization Unit is set up after the CDU to obtain
usable Naphtha which is very important for further motor fuel
synthesis.
Process Technique:
Unstable naphtha (also known as light naphtha) consists of the
light components of a crude oil distillation which have not yet
had the C4 components removed from it.
Unstable naphtha is fed to a tall distillation column
(approximately 20-30 trays) known as a debutanizer where all
C4 components (and any lighter boiling point components) are
removed. The bottom product of a debutanizer is stabilized
naphtha.
43. 43
DELAYED COKING UNIT ( DCU )
Process Objective:
–To convert low value residue to valuable products (naphtha
and diesel) and coker-gas oil.
•Primary Process Technique:
–Thermo-cracking increases H/C ratio by carbon rejection in a
semi-batch process.
•Process steps:
–Preheat residue feed and provide primary condensing of coke
drum vapors by introducing the feed to the bottom of the main
fractionator
–Heat the coke drum feed by fired heaters
–Flash superheated feed in a large coke drum where the coke
remains and vapors leave the top and goes back to the
fractionator
–Off-line coke drum is drilled and the petroleum coke is
removed via hydro-jetting ( By water jet at pressure
120kg/cm2)
45. 45
CATALYTIC REFORMING UNIT ( CRU )
Process Objective:
–To convert low-octane naphtha into a high-octane reformate
for gasoline blending and/or to provide aromatics (benzene,
toluene, and xylene) for petrochemical plants.
-Reforming also produces high purity hydrogen for hydro-
treating-processes.
•Primary Process Technique:
–Reforming reactions occur in chloride promoted fixed catalyst
beds; or continuous catalyst regeneration (CCR) beds where
the catalyst is transferred from one stage to another, through a
catalyst regenerator and back again.
Desired reactions include:
Dehydrogenation of naphthenes to form aromatics;
isomerization of naphthenes;
Dehydro-cyclization of paraffins to form aromatics; and
isomerizationof paraffins.
Hydrocracking of paraffins is undesirable due to
production of increased light-ends.
46. 46
•Process steps:
–Naphtha feed and recycle hydrogen are mixed, heated and
sent through successive reactor beds
–Each pass requires heat input to drive the reactions
–Final pass effluent is separated with the hydrogen being
recycled or purged for hydro-treating
–Reformate product can be further processed to separate
aromatic components or be used for gasoline blending
CRU Formation Of Toluene
48. 48
CAPTIVE POWER PLANT
The Captive Power Plant in the refinery has a rated generating
capacity of 45.5 MW electricity, which is used to run the plant
as well as supplied to the IOCL township.
The Power Generation is done by 4 Gas Turbines – 3 GTs of 8.5
MW each, & 1 GT of 20 MW. It is wholly a Gas Turbine operated
Power Plant.
WORKING:
In a gas turbine power plant, air is used as the working fluid.
The air is compressed by the Gas Booster Compressor is lead
to the combustion chamber where heat is added to air, thus
raising its temperature. Heat is added to the compressed air
either by burning fuel in the chamber or by the use of air
heaters. The hot and high pressure air from the combustion
chamber is then passed to the gas turbine where it expands
and does the mechanical work. The gas turbine drives the
alternator which converts the mechanical energy into electrical
energy.
49. 49
Advantages
1. It is simple in design as compared to steam power station
since no boilers and their auxiliaries are required
2. it is much smaller in size as compared to steam power
station of same capacity.This is expected since gas
turbine power plant doesnot require boiler,feed water
arrangements etc
3. The initial and operating costs are much lower than that
of equivalent steam power station
4. It requires comparatively less water as no condenser is
used
5. The maintenance charges are quite small
6. Gas turbines are much simpler in construction and
operation than steam turbines
7. It can be started quickly from cold conditions
Disadvantages
1. There is a problem for starting the unit. It is because
before starting the turbine, the compressor has to be
operated for which power is required from some external
source. However once the unit starts, the external power
is not needed as the turbine itself supplies necessary
power to the compressor.
2. Since a greater part of the power developed by the
turbine is used in driving the compressor, the net output
is low
50. 50
3. The overall efficiency of such plants is low(about 20%)
because of the exhaust gases from the turbine contain
sufficient heat
4. The temperature of combustion chamber is quite
high(3000 deg.F)so that its life is comparatively reduced.
51. 51
The three main sections of a Gas Turbine are the Compressor,
Combustor and Turbine. The gas turbine power plant has to
work continuously for long period of time without output and
performance decline. Apart from the main sections there are
other important Auxiliaries systems which are required for
operating a Gas Turbine Power Plant on a long term basis.
52. 52
Air Intake System
Air Intake System provides clean air into the compressor.
During continuous operation the impurities and dust in the air
deposits on the compressor blades. This reduces the efficiency
and output of the plant. The Air Filter in the Air Intake system
prevents this.
A blade cleaning system comprising of a high pressure pump
provides on line cleaning facility for the compressor blades.
The flow of the large amount of air into the compressor
creates high noise levels. A Silencer in the intake duct reduces
the noise to acceptable levels.
Exhaust System
Exhaust system discharges the hot gases to a level which is
safe for the people and the environment. The exhaust gas that
leaves the turbine is around 550 °C. This includes an outlet
stack high enough for the safe discharge of the gases. Silencer
in the outlet stack reduces the noise to acceptable levels.
Starting System
Starting system provides the initial momentum for the Gas
Turbine to reach the operating speed. This is similar to the
starter motor of your car. The gas turbine in a power plant
runs at 3000 RPM (for the 50 Hz grid - 3600 RPM for the 60
Hz grid). During starting the speed has to reach at least 60 %
53. 53
for the turbine to work on its on inertia. The simple method is
to have a starter motor with a torque converter ( Which is
actually a FLUID COUPLING) to bring the heavy mass of the
turbine to the required speed. For large turbines this means a
big capacity motor. The latest trend is to use the generator
itself as the starter motor with suitable electrics. In situations
where there is no other start up power available, like a ship or
an off-shore platform or a remote location, a small diesel or
gas engine is used.
Fuel System
The Fuel system prepares a clean fuel for burning in the
combustor. Gas Turbines normally burn Natural gas but can
also fire diesel or distillate fuels. Many Gas Turbines have dual
firing capabilities.
A burner system and ignition system with the necessary safety
interlocks are the most important items. A control valve
regulates the amount of fuel burned . A filter prevents entry of
any particles that may clog the burners. Natural gas directly
from the wells is scrubbed and cleaned prior to admission into
the turbine. External heaters heat the gas for better
combustion.
For liquid fuels high pressure pumps pump fuel to the
pressure required for fine atomisation of the fuel for burning.
54. 54
OTHER IMPORTANT SYSTEMS:
1. Apart from the gas turbines, the exhaust of the turbines
is fed to a HRSG ( Heat Recovery Steam Generator) which
has a capacity of generating 100 Tonnes of steam per
hour. This steam is used for various processes
throughout the plant.
2. For supply of De-mineralised Water to the HRSG, an
offsite DEMINERALISED WATER PLANT is setup from where
the DM Water is pumped to the HRSG.
3. GAS BOOSTER COMPRESSORS are there to supply
compressed air to the Gas Turbine at pressure of about
13 kg/cm2.
4. GENERATOR is mounted on the turbine shaft & produces
electricity by Electromagnetic Induction.
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SOLVENT DEWAXING UNIT
Solvent treating is a widely used method of refining lubricating
oils as well as a host of other refinery stocks. Since distillation
(fractionation) separates petroleum products into groups only
by their boiling-point ranges, impurities may remain. These
include organic compounds containing sulfur, nitrogen, and
oxygen; inorganic salts and dissolved metals; and soluble salts
that were present in the crude feedstock. In addition, kerosene
and distillates may have trace amounts of aromatics and
naphthenes, and lubricating oil base-stocks may contain wax.
Solvent refining processes including solvent extraction and
solvent dewaxing usually remove these undesirables at
intermediate refining stages or just before sending the product
to storage.
Solvent dewaxing is used to remove wax from either distillate
or residual basestock at any stage in the refining process.
There are several processes in use for solvent dewaxing, but all
have the same general steps, which are:
(1) mixing the feedstock with a solvent,
(2) precipitating the wax from the mixture by chilling, and
(3) recovering the solvent from the wax and dewaxed oil for
recycling by distillation and steam stripping.
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Usually MIBK ( Methyl Iso-butyl Ketone), which dissolves the oil
and maintains fluidity at low temperature(4-7 deg.C), is used
as solvent. Other solvents that are sometimes used include
benzene, methyl ethyl ketone, toluene, propane, petroleum
naphtha, ethylene dichloride, methylene chloride, and sulfur
dioxide. In addition, there is a catalytic process used as an
alternate to solvent dewaxing.
The MIBK is cooled by passing it through a heat exchanger
with Ethylene Glycol, which takes away its heat. The Ethylene
Glycol, in turn, is cooled by exchanging its heat with
propylene, which changes into vapour readily & thus can easily
ake a lot of heat. The propylene which is converted into gas is
again converted to liquid by spraying it through a nozzle which
brings down its temp due to sudden expansion & it liquefies.
57. 57
The De-waxing / De-oiling Unit of WAX SECTOR consists of
following six sections:
a) Chilling Section
b) Filtration Section
c) De-waxed Oil Solvent Recovery Section
d) Slack Wax Solvent Recovery Section
e) Refrigeration Section
f) Inert Gas System
(a) Chilling Section
In Chilling Section, the feed obtained from storage is
first heated in order to dissolve any precipitated
waxes which may be present. The feed heating is
done in the LP Steam Heater where the feed is
heated to 70-80
0
C. This is followed by controlled
cooling and chilling of the feed in the subsequent
exchangers.
During feed chilling, dilution solvent is added at
various points along the DP exchanger/ chiller trains
to reduce the viscosity of the charge mix and hence
the pressure drop in the chilling trains.
58. 58
(b) Filtration Section
The wax crystals are separated from the chilled feed by
primary filters. The re-pulp or secondary filter
performs the second stage filtration in order to
further reduce the oil content in wax to the desired
level. The liquid to solid ratio of the feed to primary
and secondary filters is adjusted by filtrate
recirculation to promote easier filtration.
The primary filtrate is pumped by the primary filtrate
pump to the chilling section for cold recovery. The
wax cake formed on the filter cloth is washed with
chilled solvent as it emerges from the liquid slurry
(c) De-waxed Oil Solvent Recovery Section
The de-waxed oil (DWO) solvent recovery section
consists of flashing followed by steam stripping.
The primary filtrate from feed mix chilling section is
sent to DWO solvent recovery section to recover
solvent from the de-oiled wax. The de-waxed oil
from the stripper bottom called Foots Oil is sent to
storage tank through DWO stripper bottom pump
after heat recovery and cooling in the DWO Mix/
Foots Oil exchanger and finally to Foots Oil Cooler
respectively.
59. 59
(d) Slack Wax Recovery Section
The slack wax solvent recovery section consists of
single stage flashing followed by steam stripping.
The last traces of solvent are recovered in the
stripper by steam stripping. The wet solvent vapours
from stripper top are routed to solvent cooler and
then to solvent separator for further processing. The
wax product obtained from stripper bottom is sent
to storage through wax stripper bottom pump after
being cooled in tempered water cooler.
(e) Refrigeration Section
The typical refrigeration cycle serves as a utility to
provide the chilling medium for the feed-stock and
the solvent.
(e) Inert Gas Section
The inert gas is primarily used for filtration and
remains in circulation in a closed loop comprising of
primary and secondary filters, Primary and
Secondary Filtrate Receivers, Inert gas pot and inert
gas vacuum compressor. Inert gas is also used for
blanketing purposes in filters, solvent tanks etc.
This prevents solvent losses as well as fire hazards
by eliminating the contact of solvent with air. In
Digboi, NITROGEN gas is used for this purpose.
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WAX HYDRO-FINISHING UNIT
Process Objective
The objective of the hydro-finishing unit is to obtain Paraffin
Wax from the wax extract.
Process Details
This is a component of the refining process reserved for more
premium Petroleum basestocks.
Hydrofinishing uses a catalyst bed through which hydrogen
and heated oil are passed.
As these components pass through the bed, unstable
components such as sulfur and nitrogen are removed. Clay
treatment uses a different method to achieve a similar
outcome.
Both of these refining processes improve oxidation stability,
thermal stability and color of the lubricant basestocks.
61. 61
WAX RUN-DOWN SHED
The WRDS is the last step of the Wax Sector. The Paraffin Wax
obtained in the WHFU is finally sent there for solidification in
the form of slabs which are then sent dispatched for
marketing.
The molten wax is allowed to stand in long shallow containers
with slab-sized holes. A system is provided to take out each
individual wax slab after solidification.
62. 62
CONCLUSION
In the end, it has been a very good learning &
enlightening experience to do this Vocational Training
in the Digboi Refinery. Coming here, I understood a lot
about the processes taking place in an Oil Refinery.
The practical exposure has been unbelievable, & this
visit will stay with me as a good memory for years to
come.
THE END
