Upload
praveen-kumar
View
47
Download
2
Tags:
Embed Size (px)
Citation preview
0
VOCATIONAL TRAININGREPORT
GAIL (INDIA) LTD. U.P PETROCHEMICAL COMPLEX PATA,
AURAIYA (U.P)
SUBMITTED TO-TRAINING DEPARTMENTGAIL - PATA
SUBMITTED BY-
1
Content PAGE NO ACKNOWLEDGEMENT 2 INTRODUCTION OF GAIL 3 HISTORY 5 IOP/S 6
a) Introduction of Boiler 7b) Utility Boiler 8c) Steam Turbine 17d) Protective Equipment 23
DOWN STREAM 25a) Description of HDPE 26b) Polymer formation diagram 27 c) Mechanical Seal 31d) Pump 32e) LLDPE 41
UP STREAM 45a. Gas Sweeting Unit 46b. Gas cracker Unit 52c. LPG 58
2
ACKNOWLEDGEMENT
I would like to thank Training Department for providing me the opportunity as a vocational trainee in such a huge plant equipped with modern technology.
I am deeply indebted to Mr. Santosh , Mr. Rakesh, Mr. Abhishek for his kind super vision and guidance in my training period.
Here I wish my sincere gratitude towards Mr. Ajay Tripathi (DGM, Mech.), Mr. R.C. Pandey , Mr. Joyonto Panging (Ch. Manager, Mech.) for their cooperation and kind supervision throughout.
Also I want to thank all the other Engineers of Service Building-2 (SB-2) , for patiently going through my innumerable questions and clearing my doubts.
3
INTRODUCTION
GAIL (India) Limited, is India's flagship Natural Gas company, integrating all
aspects of the Natural Gas value chain (including Exploration & Production,
Processing, Transmission, Distribution and Marketing) and its related services. In a
rapidly changing scenario, GAIL is spearheading the move to a new era of clean
fuel industrialisation, creating a quadrilateral of green energy corridors that
connect major consumption centres in India with major gas fields, LNG terminals
and other cross border gas sourcing points. GAIL is also expanding its business to
become a player in the International Market.
Today, GAIL's Business Portfolio includes
* 7,700 km of Natural Gas high pressure trunk pipeline with a capacity to carry
157 MMSCMD of natural gas across the country
* 7 LPG Gas Processing Units to produce 1.2 MMTPA of LPG and other liquid
hydrocarbons
* North India's only gas based integrated Petrochemical complex at Pata with a
capacity of producing 4,10,000 TPA of Polymers
* 1,922 km of LPG Transmission pipeline network with a capacity to transport
3.8 MMTPA of LPG
* 27 oil and gas Exploration blocks and 3 Coal Bed Methane Blocks
* 13,000 km of OFC network offering highly dependable bandwith for telecom
service providers
* Joint venture companies in Delhi, Mumbai, Hyderabad, Kanpur, Agra,
Lucknow, Bhopal, Agartala and Pune, for supplying Piped Natural Gas (PNG) to
4
households and commercial users, and Compressed Natural Gas (CNG) to the
transport sector
* Participating stake in the Dahej LNG Terminal and the upcoming Kochi LNG
Terminal in Kerala
* GAIL has been entrusted with the responsibility of reviving the LNG terminal
at Dabhol as well as sourcing LNG
* GAIL Gas Limited, a wholly owned subsidiary of GAIL (India) Limited, was
incorporated on May 27, 2008 for the smooth implementation of City Gas
Distribution (CGD) projects. GAIL Gas Limited is a limited company under the
Companies Act, 1956.
* Established presence in the CNG and City Gas sectors in Egypt through equity
participation in three Egyptian companies: Fayum Gas Company SAE, Shell CNG
SAE and National Gas Company SAE.
* Stake in China Gas Holding to explore opportunities in the CNG sector in
mainland China
* A wholly-owned subsidiary company GAIL Global (Singapore) Pte Ltd in
Singapore
5
HISTORY
GAIL (India) Ltd. (erstwhile Gas Authority of India Ltd), India's principal gas
transmission and marketing company, was set up by the Government of India in
August 1984 to create gas sector infrastructure for sustained development of the
natural gas sector in the country.
The 2800-km Hazira-Vijaipur-Jagdishpur (HVJ) pipeline became operational in
1991. During 1991-93, three LPG plants were constructed and some regional
pipelines acquired, enabling GAIL to begin its regional gas distribution in various
parts of India.
GAIL began its city gas distribution in Delhi in 1997 by setting up nine CNG
stations, catering to the city's vast public transport fleet.In 1999, GAIL set up
northern India's only petrochemical plant at Pata.GAIL became the first
Infrastructure Provider Category II Licensee and signed the country's first Service
Level Agreement for leasing bandwidth in the Delhi-Vijaipur sector in 2001,
through its telecom business GAILTEL. In 2001, GAIL commissioned world's
longest and India's first Cross Country LPG Transmission Pipeline from Jamnagar
to Loni.GAIL today has reached new milestones with its strategic diversification
into Petrochemicals, Telecom and Liquid Hydrocarbons besides gas infrastructure.
The company has also extended its presence in Power, Liquefied Natural Gas re-
gasification, City Gas Distribution and Exploration & Production through equity
and joint ventures participations. Incorporating the new-found energy into its
corporate identity, Gas Authority of India was renamed GAIL (India) Limited on
November 22, 2002.
6
INTREGATED OFFSITE PLANT
&
STORAGE
(IOP & S)
7
INTRODUCTION TO POWER PLANT
Power Plant in U. P. Petrochemical Complex comprises 3 Nos. Utility Boilers
each having Steam Generating Capacity of 120 TPH at MCR, at pressure 106
Kg/Cm2 (g) 510 oC.
The Steam Generated from all these boilers is utilised for production of
Electrical Power in 2 Nos. of Turbo Generators having Generating Capacity of
15.5 MW(Extraction type) & 25.6 MW(Condensing type) in addition to meeting
demand for process steam requirement in different section of the complex . The
high pressure steam (106 Kg/Cm2 (g) ) produced from all the 3 boilers is connected
to a common header from where steam is fed separately to 2 nos. of steam turbines
, serving as prime mover to rotate 2 nos. of generators.
Normally, these boilers are meant for producing steam at very high pressure (105
Kg/Cm2) but depending on process requirement this VHP steam is led down to
high pressure (40 Kg/Cm2) , Low medium pressure (8.0 Kg/Cm2) and Low pressure
at 4.0 Kg/Cm2.
8
UTILITY BOILER
A- Construction Details:
Make : M/s BHPV
Boiler Designation : 17.3 60
F VU 60 36
26 2
Where F- Stands for : Furnace
17.3 : Width of furnace in feet
26 : Length of furnace in feet
VU : Vertical Unit.
60 :I.D of upper drum in inch.
2 : Diameter of Bank tube in
inch
36 : ID. of Lower drum in inch
Location : Semi out Door
Boiler Type : Natural Circulation, BI-
Drum, Front Wall Fired
9
Forced Draft Furnace,
Radiant Closed Bottom
Suitable for Oil/Gas Firing
Fuel : Rich Gas
: Lean Gas
: Combination of Blended
fuel oil & Rich Gas.
10
GENERAL DESCRIPTION OF BOILER
The steam generator is a natural circulation water tube design arranged for forced
draft firing . Basically it is a two drum vertically bent tube arrangement with water
– cooled furnace walls combined with convective boiler bank surfface. The
furnace is specifically designed to suit for 10% excess air operation for gas firing .
The complete furnace section is of the welded wall type arranged as a gas and
pressure tight envelope which eliminates the problem of casing corrosion and
cumbersome refractory maintenance , besides this provides structural rigidity for
the unit . The complete steam generator is of the bottom supported design resting
on concrete pedestals .
The conservatively sized upper and lower drums are connected by the bank
tubes . The steam drum is provided with simple and efficient drum
internals ,resulting in high steam quality at all loads of boiler outputs . Unheated
downcomers are located in the boiler bank sides.
The boiler bank tubes are arranged in line for best heat absorption , minimum tube
draft loss and for easy inspection and cleaning . Required accessibility is provided
at the front & rear side of the boiler bank convective surface . Adequate peepholes
are also provided to watch the flame.
The feed water from economiser is fed into the steam drum. Circulation is
maintained in the boiler bank through the downcomers . From the bottom drum,
water flows through the heat absorbing furnace tubes and back into steam
drum .After separation of moisture in the steam drum the saturated steam flows
into the superheater . The superheater system has two sections. They are radiant
platen pendent section (arranged at the outlet of furnace) and the final superheater
adjacent to platen section. A desuperheater is provided in-between the two sections
11
in the connective links for controlling the superheater temperature over the wide
load range . The location and selection of superheater is so chosen that the
specified temperature of superheater achieved between 30 to 100% MCR load of
the boiler .
The firing system consists of 4 No. of burners designed for gas firing located in the
font wall . Gas igniters are provided for lighting the burner . The flame scanning
system is provided to monitor the main flame condition in the furnace.
1 No. Forced draft fan with dual drive (motor + steam turbine ) will supply
the complete combustion air at the required pressure for the boiler.
A bare tube in line economiser is provided as the last heat recovery section.
The complete integral piping , valves and fitting, air and gas ducting, all
refractory and insulation materials are provided.
Feed water is supplied to the steam drum from the feed storage tank through feed
line. The water side of the steam drum is connected with lower drum through
boiler bank tubes . Furnace side walls inlet headers are supplied with water from
lower drum through supply tubes. The steam water mixture generated in the side
walls are collected in the side wall outlet headers and from where it is discharged
into the drum through a system of riser tubes. Boiler water from the lower drum is
fed into the front walls through floor panels and discharged into steam drum as
steam water mixture . Likewise rear wall receives the boiler water from lower
drum and discharges to the steam drum.
B - ECONOMISER
12
The purpose of the economiser is to preheat the boiler feed water before it is
introduced into the steam drum, and to recover some of the heat from the fuel
gases leaving the boiler.
The economiser is located in the second pass of the boiler. Each section is
composed of a number of parallel tube circuits, arranged in horizontal rows. All
tube circuits originate from inlet header and discharge into outlet header. Feed
water is supplied to the economiser inlet headerfrom FEED CONTROL
STATION. The feed water flow is upward or downward through the economiser
that is in counterflow to the hot fuel gases . Most efficient heat transfer is thereby
accomplished . Any chance of steam generation within the economiser is
eliminated . From the outlet header the feed water is led to the drum.
Before starting up the boiler, the economiser should be inspected externally
and if necessary cleaned . Especially if the installation is new, accumulation of
erection material is not unusual. Large debris should be removed manually ,
followed by the washing down the economiser banks by means of hose and water.
All joints in the economiser casing should be examined occasionally for
tightness in order that air in filtration be kept to minimum. Insulation should be
kept in good condition.
C - SUPERHEATER
It is non drainable superheater , pendant type . The superheater coils are suspended
below the superheater header.
No. of coils in Primary Super Heater (PSH ) - 13
No. of coils in Final Super Heater (FSH ) – 47
13
D - DESUPERHEATER
Desuperheater are provided in the steam line between PSH & FSH to permit
reduction of steam temperature when necessary and to maintain the temperature at
design values within the limits.
Temperature reduction is accomplished by injecting spray water into the
path of the steam through a nozzle . The spray water source is from the boiler feed
water system. It is essential that the spray water be chemically pure to avoid
contamination of main steam.
E- BURNER
4 nos. of Dual Fuel Burner per boilers are mounted on common windbox . The
windbox is designed in such a manner that combustion air is uniformly distributed
to all the burners. The combustion air entry to the burner is through air register
which is controlled by pneumatically operated air cylinder. The dual Fuel Burner
is Fitted with 1 No. of oil gun with steam atomiser tip assembly and 8 Nos. of Gas
Poker Assembly.
The ignition system which is supplied along with burner is capable of
lighting liquid as well as gaseous fuel on giving light up command to ignitor . Pilot
flame presence indication will be giving to the Burner Management System .
In turn BMS will give a signal to open gas valve. Thereafter Main Gas Flame will
be detected by flame scanners system. The flame scanners system shall provide the
continuous monitoring of the flame inside the furnace which shall provide safety to
the boiler.
In the event of Flame outage of individual burner the flame monitoring system
shall give signal to open or to close gas valves together with other interlocks for
14
safe tripping of the burners isolation valves. In the event of all four burners flame
failure it will trip master fuel trip valve. The flame monitoring system is provided
with self check facility so that spurious signals are eliminated and reliable
performance of the burner is guaranteed.
FD FAN :
Centrifugal Single Suction Fans are being used to handle Clean Air . The spiral
Casing converts part of kinetic energy of the fluid into a Static Pressure . the Fan
output is usually controlled by adjustable inlet dampers or by varying the speed of
the Fan either by means of hydraulic couplings or by any suitable speed control
device .The fan is driven by motor/prime mover through coupling.
OPERATING PROCEDURES FOR BOILER
A - Preparation
1.Inspect the boiler prior to start.
Chack that (a) All foreign material has been removed.
(b) All doors are closed.
( c ) Starting equipments are ready.
(d) Interlocks are OK.
(e) Individual valves of burners are closed.
2.Close the Following Valves.
(a) Feed water regulating valve
(b)All drain valves of boiler, water walls and Economizer.
15
(c)Desuperheater control valves.
Open the Following Valves.
(a) Drum Air Vents.
(b)SH Air Vents.
(c)SH drain Valves
(d)Main steam line drain valve.
(e)Start up vent valve.
(f)Isolation valves on both sides of desuperheater
control valve.
(g)All instrument and control connections to the boiler.
3.Check the Following Eqts for adequate Lubrication & Cooling Water Flow.
(a)Boiler Feed Pump.
(b)FD Fan.
1. Put all automatic Control equipments on Manual Control.
2. Check that all Control equipments are ready for service.
Manually operate all sequential trips and see that the emergency fuel trips function
properly.
B- LIGHT UP.
a) Take water into Steam Drum and maintain Drum Level Normal.
16
b) Close Inlet vanes of FD Fan.
c) Open inlet damper of Air duct.
d) Open inlet damper of Chimney .
e) Start FD Fan.
f) Increase Air Flow more than 30% of MCR.
g) Light the Lower burner one at a time .
h) Close Drum Air vents when Drum pressure reaches 2 Kg/Cm2.
i) Take other Burners in line and raise the drum pressure slowly as per start up
curve
j) Connect the boiler with the Header when steam pressure is 105 kg/Cm2.
k) Close main steam drain and SH drains.
l) Inject Chemicals into D/A and drum to maintain
C- SHUT- DOWN
a) Start reducing boiler load gradually. Reduce the firing rate in line with
reducing the steam flow.
b) Shut-Down the Burners one at a time, Starting with the upper elevation .
c) All fires should be out when the boiler is off the line.
d) Run the Fans for at least 10 minutes after Shutting down.
e) Maintain the water level in drum .
f) When the drum pressure comes down to 2 Kg/Cm2.
17
STEAM TURBINE
A turbine is a rotary engine that extracts energy from a fluid flow and converts it
into useful work. The simplest turbines have one moving part, a rotor assembly,
which is a shaft or drum with blades attached. Moving fluid acts on the blades, or
the blades react to the flow, so that they move and impart rotational energy to the
rotor. Early turbine examples are windmills and water wheels.
Gas, steam, and water turbines usually have a casing around the blades that
contains and controls the working fluid. Credit for invention of the steam turbine is
given both to the British Engineer Sir Charles Parsons (1854–1931), for invention
of the reaction turbine and to Swedish Engineer Gustaf de Laval (1845–1913), for
invention of the impulse turbine. Modern steam turbines frequently employ both
reaction and impulse in the same unit, typically varying the degree of reaction and
impulse from the blade root to its periphery.
A steam turbine is a mechanical device that extracts thermal energy from
pressurized steam, and converts it into rotary motion. It has almost completely
replaced the reciprocating piston steam engine primarily because of its greater
thermal efficiency and higher power-to-weight ratio. The steam turbine is a form of
heat engine that derives much of its improvement in thermodynamic efficiency
through the use of multiple stages in the expansion of the steam, which results in a
closer approach to the ideal reversible process. There are several classifications for
modern steam turbine.
18
Type of Turbines-
(A)Based on operation
Impulse Turbines: It has fixed nozzles that orient the steam flow into high
speed jets. These jets contain significant kinetic energy, which the rotor
blades, convert into shaft rotation as the steam jet changes direction. A
pressure drop occurs across only the stationary blades, with a net increase in
steam velocity across the stage. As the steam flows through the nozzle its
pressure falls from inlet pressure to the exit pressure (atmospheric pressure,
or more usually, the condenser vacuum). Due to this higher ratio of
expansion of steam in the nozzle the steam leaves the nozzle with a very
high velocity. The steam leaving the moving blades is a large portion of the
maximum velocity of the steam when leaving the nozzle. The loss of energy
due to this higher exit velocity is commonly called the "carry over velocity"
or "leaving.
Reaction Turbines: In this the rotor blades themselves are arranged to form
convergent nozzles. This type of turbine makes use of the reaction force
produced as the steam accelerates through the nozzles formed by the rotor.
Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the
stator as a jet that fills the entire circumference of the rotor. The steam then
changes direction and increases its speed relative to the speed of the
blades. A pressure drop occurs across both the stator and the rotor, with
steam accelerating through the stator and decelerating through the rotor, with
no net change in steam velocity across the stage but with a decrease in both
pressure and temperature, reflecting the work performed in the driving of the
rotor.
19
(B)Based on Steam Supply and Exhaust Conditions
Noncondensing or backpressure turbines are most widely used for
process steam applications. The exhaust pressure is controlled by a
regulating valve to suit the needs of the process steam pressure.
Condensing turbines exhaust steam is in a partially condensed state,
typically of a quality near 90%, at a pressure well below atmospheric to a
condenser.
In a reheat turbine, steam flow exits from a high pressure section of the
turbine and is returned to the boiler where additional superheat is added.
The steam then goes back into an intermediate pressure section of the
turbine and continues its expansion.
In an extracting type turbine, steam is released from various stages of the
turbine, and used for industrial process needs or sent to boiler feedwater
heaters to improve overall cycle efficiency. Extraction flows may be
controlled with a valve, or left uncontrolled.
Induction turbines introduce low pressure steam at an intermediate stage to
produce additional power.
Principle of Operation
The motive power in a steam turbine is obtained by the rate of change in
momentum of a high velocity jet of steam impinging on a curved blade which is
free to rotate. This jet of steam impinges on the moving vanes or blades, mounted
on a shaft. Here it undergoes a change of direction of motion which gives rise to a
change in momentum and therefore a force. The interior of a turbine comprises
several sets of blades. One set of stationary blades is connected to the casing and
20
one set of rotating blades is connected to the shaft. The sets intermesh with certain
minimum clearances, with the size and configuration of sets varying to efficiently
exploit the expansion of steam at each stage.
Operation and Maintenance
When warming up a steam turbine in order to avoid slugging nozzles and blades
inside the turbine with condensate on start-up which can break these components
from impact. The blades were designed to handle steam, not water. The main
steam stop valves have a bypass line to allow superheated steam to slowly bypass
the valve and proceed to heat up the lines in the system along with the steam
turbine..
Steam Turbine Components
The components of Steam Turbine are:
Blades
Rotors
Casings
Seals
Nozzles.
Steam turbines consist of circularly distributed stationary blades called nozzles
which direct steam on to rotating blades or buckets mounted radially on a rotating
wheel. In a steam turbine nozzles apply supersonic steam to a curved blade. The
blade whips the steam back in the opposite direction, simultaneously allowing the
21
steam to expand a bit.Typically, the blades are short in proportion to the radius of
the wheel, and the nozzles are approximately rectangular in cross section.
STEAM TURBINE GENERATOR (STG # 1)
Vendor : M/s BHEL Hyderabad.
Type : EHNG 40/32 – 3.
Capacity : 15.5 MW.
No. of Stages : 17
HP (Impulse +Reaction) : 1 + 6
LP (Impulse +Reaction) : 1 + 9
Turbine Speed : 8500 rpm.
Reduction Gear Output Speed 3000 rpm.
Steam Pressure : 105 Kg/Cm2
Steam Temperature : 500 oC
Wheel Chamber : 75.8 Kg/Cm2
Extraction Pressure : 41.0 Kg/Cm2
Extraction Flow : 55 TPH
Exhaust Pressure : 5.00 Kg/Cm2
Exhaust Flow : 75 TPH
Maxm Steam Flow : 130 TPH
22
STG # 2
Vender : M/s BHEL
Type : Full Condensing
Capacity : 25.6 MW
No. of Stages : 48
Impulse : 1
Reaction : 47
Turbine Speed : 3000 rpm
Steam Pressure : 105 Kg/Cm2
Steam Temperature : 500 oC
Steam Flow : 91 TPH (for full Load)
23
PROTECTIVE EQUIPMENTS
(a)EMERGENCY STOP VALVE :
It is a protection eqt.The emergency stop valve is the fundamental shut off organ in
the live steam line . In event of a disturbance , it cuts off steam supply to the
turbine in a minm time . It will be in the closed position when the turbine is at stand
still position .
(b)OVER SPEED TRIP :
It is a protection system against un acceptable over speed . The over speed trip
shuts down the turbine when the permissible turbine speed is exceeded by more
than 5%.
If the turbine speed rises to the set tripping speed the centrifugal force of the
pin in the over speed trip bolt over comes the force of the compression spring . The
trip bolt moves a few mm out of the shaft , thereby striking the pawl of the
automatic trip. This opens the trip oil circuit so that the emergency stop valve and
control valves close, thus shutting down the turbine immediately
(c)EMERGENCY TRIPPING DEVICE :
It is a protection device . In the event of a disturbance , the emergency tripping
device serves for admitting emergency trip oil and causes closing of the ESV and
separation of the turbine from the steam supply .
(d)Control Valves
The control valves are opened and closed in order to adjust the through put of
steam to give the required power out put from the turbine . Depending on the
power required , the control valves are opened or closed in a specific sequence.
24
When the turbine is at rest, the springs keep the crossbar in its lowest and valves
are forced on to their seat by the pressure of steam . A control pulse from the
governor causes the actuator to pull the arm downwards , the raising the stems and
lifting the crossbar . The valves then lift in a sequence determined by the different
lengths of the spacer bushes in the crossbar .
POWERGENERATIONTHROUGH STGs-
Presently the Maximum requirement of Electrical power for the complex is around
32 MW.
This demand of 32 MW power requirement in met by 2 Steam Turbo Generators .
2 Nos. of Generators having capacity of 15.5 MW & 25.6 MW are separately
coupled with steam turbines, serving as prime movers.
Power Generated by these Generators is at 11 KV . It is further stepped up to 33
KV through transformers which is synchronised with the 33 KV grid.
This power at 33 KV is then stepped down through the transformers to 6.6 KV &
415 KV to run HT motors and L.T. motors of the complex.
25
DOWN STREAM
HIGH DENSITY POLY ETHYLENE
(HDPE)
&
LOW LINEAR DENSITY POLY ETHYLENE
(LLDPE)
26
BRIEF DESCRIPTION OF HDPE PROCESS
Catalyst system
To initiate any polymerization reaction, catalyst is necessary. The catalyst system
for Polyethylene is based on ‘Ziegler-Natta catalysts’. This system consists of a
catalyst-co catalyst pair. Main catalyst - Halides or other derivatives of transition
metals in group IV-VIII of periodic table. (In our plant it is the PZ catalyst which
is based on ticl4). Co catalyst - Alkyls of Group I-III metals. (In our plant it is
TEAL i.e. Try Ethyl Aluminum)
Polymerization
Raw materials
The raw materials used in the production of HDPE and their roles is as,
Ethylene – This is the basic monomer which forms the backbone of HDPE chain.
Catalyst – This initiates the polymerization reaction.
Hydrogen – This helps in termination of polymer chain. Hence this controls the
molecular weight. So Hydrogen is used to control MFR. The control of Hydrogen
feed is done based on Hydrogen / Ethylene ratio. This ratio varies as per grade
because each grade has different MFR.
Butene-1 / Propylene – These two are co-monomers. They take part in reaction
along with Ethylene and form side branches. The loading of co-monomer decides
density of polymer.
Hexane – This is inert reaction medium. This helps in removal of enormous
amount of heat of polymerization.
27
Polymer formation diagram-
Catalyst preparation
Polymerization
Separation & Drying
PelletizerHexane recovery
Low polymer handling
Flaker unit
Catalyst
(PZ, AT)
Catalyst soln
Raw material like C2, H2, Bu-1, Propylene
Polymer slurry
Mother
liquor
Mother liquor
recycle
Dry powder
Pure and dry
hexane
Crude hexane
from IOP
LP pitsLP wax to flaker
LP Flakes
G-Lex pellets for bagging
Molten wax
Recovered
hexane
28
Operation
The polymerization reaction is highly exothermic. It gives out enormous amount of
heat. This heat needs to be taken out immediately and effectively to avoid run
away reactions. The reactors have three modes of heat removal, Overhead coolers
– the un-reacted gas from reactor is taken to overhead cooler. The hexane content
in the gas is cooled and separated. The cooled gas is again bubbled from the
bottom of the reactor. Along with agitators, this helps in preventing the slurry from
settling. The condensed hexane is also fed back to the reactor. Slurry coolers – at
high loads, some portion of slurry is also taken out from the bottom of the reactors.
It is circulated through coolers and fed back to the reactors. Jackets - Each reactor
has jacket with cooling water running through it.
Feed of Hydrogen to the reactor is most critical part of the polymerization. It needs
to be accurately controlled. Each reactor is equipped with on line Process Gas
Chromatographs (PGC) for this purpose. A small sample of un-reacted gas from
the reactor is continuously fed to the PGC.
PGC analyses the Hydrogen and Ethylene content of the stream. Special programs
on the MAPS convert the % to ratio of Hydrogen to Ethylene.
Hydrogen valve opening is controlled by MAPS Programme
Separation
The polymer slurry, after degassing, is fed to the centrifuge. The centrifuge
separates the polymer powder from hexane. The wet cake of polymer is fed to
dryer. The hexane decanted contains some amount of low polymer formed
during polymerization and is called mother liquor. The wet cake is dried in
rotary dryer. Some portion of the mother liquor is recycled back to the reactors.
29
Remaining mother liquor is sent to hexane recovery section of purification of
hexane.
Drying
The wet cake from centrifuge is fed to rotary dryer. It has hexane content of
30% by weight. $Dryer uses two drying media, Low pressure steam running
through the inner pipe inside the dryer. This is indirect heating. Hot nitrogen fed
to the dryer coming in contact with powder. This is direct heating. $The hot
nitrogen coming from dryer is cooled and scrubbed with hexane to wash off any
entrained powder. It is again heated and fed back to dryer. The dry powder
(with hexane content of 0.2% wt or lower) is conveyed to hopper by nitrogen
30
Extruder
The dry powder from dryer is taken to a intermediate hopper. Before sending to
extruder, various additives are mixed with the powder. The blend of powder
and additives is melted in the extruder barrel. The melt is forced through a die
having number of holes to give thin noodle like strands. A cutter assembly,
rotating very close to the face of the die, cuts the strands to pellets. The pellets
are conveying by air to various storing silos. From silos, the pellets are sent for
bagging
Hexane recovery
The mother liquor decanted from centrifuge is fed to this section. The low polymer
in mother liquor is separated in a stripper. Pure hexane vapors from stripper top are
recovered, condensed and dehydrated. The pure hexane is stored in tanks and put
in re-use. The low polymer concentrate recovered from stripper bottom is
subjected to flashing to recover maximum hexane from it. The low polymer is then
dumped to pits. After solidification, low polymer blocks are cut out. These are
processed in flaker plant to form flakes.
Utilities
Various utilities / auxiliary services used in the plant are,
Brine system
HP steam
LP steam
Nitrogen
Process water
31
Instrument air
Cooling water
Electric power
Caustic soda
MECHANICAL SEAL-
General Classifications
Seals may be generally sub-divided into :
(A)Dynamic Seals
(B)Static Seals
The primary purpose of seals is to prevent ingress of unwanted contaminants and
to prevent egress of any internal sustance whether it be gas or liquid for
containment or lubrication. The majority of applications are in areas where the
substance retained is a lubricant and the purpose of the seal is to ensure that it stays
where it is put.
In simple terms, external seals have two main functions: to prevent lubricating oil
from leaking out, and, to prevent dust, water, and other contaminants from entering
the bearing. When selecting a seal, the following factors need to be taken into
consideration: the type of lubricant (oil or grease), seal peripheral speed, shaft
fitting errors, space limitations, seal friction and resultant heat increase, and cost.
Dynamic seals can be used with either rotary or reciprocating motions. A separate
group of dynamic seals comes under the heading “others”. These seals are indeed
statistically attached to the counterfaces and the limited motion is fully taken up by
the seal material itself. Examples of the latter would be bellows and the
diaphragms.
32
Apart from Static and dynamic, the Sealing devices for rolling bearings fall into
two main classifications:
(a)Contact Seals.
(b)Non-contact Seals.
a. Contact seals:
Contact seals accomplish their sealing action through the contact pressure of
a resilient part of the seal (the lip is often made of synthetic rubber) and the
sealing surface. Contact seals are generally far superior to non-contact seals
in sealing efficiency, although their friction torque and temperature rise
coefficients are higher.
b. Non-contact seals:
Non-contact seals utilize a small clearance between the shaft and the housing
cover. Therefore friction is negligible, making them suitable for high speed
applications.
PUMP
Pump is the machine that lifts liquids, moves them from place to
place,pressurizes them for a number of task converting mechanical energy
from a prime mover such a motor, turbine etc.
The reliability & availability & efficiency of the different type of pumps
depends a lot on the behavior of these machines.
Under this system, the pumps can be classified as:
• DYNAMIC TYPE
33
In which the energy is continuously added to increase the fluid passes
through a volute while increases the pressure.
• DISPLACEMENT TYPE
In which the energy is periodically added by application of force to one
or more moveable boundaries of any desired number of enclosed, fluid
containing volumes, resulting into direct increase in pressure upto the
valve required to move the fluid thru valves or ports into discharge line.
Classification of pumps -
34
Centrifugal pump (dymamic type)
CONSTRUCTION FEATURES
Centrifugal pump essentially consists of:
– Impeller
– Shaft with sleeve
– Casing ( Volute / diffuser)
– Support bearings & bearing housings
– Wear rings
– Pump sealing (gland packing / mech seal)
– Coupling
– Prime movers (Electric motor / turbines / engines)
Liquid flow path inside a centrifugal pump
A centrifugal pump has two main components:
I. A rotating component comprised of an impeller and a shaft
II. A stationary component comprised of a casing, casing cover, and bearings.
35
General components of Centrifugal Pump
Stationary Components
1. Casing
Casings are generally of two types: volute and circular. The impellers are fitted
inside the casings.
1. Volute casings build a higher head; circular casings are used for low head and
high capacity.
A volute is a curved funnel increasing in area to the discharge port. As the
area of the cross-section increases, the volute reduces the speed of the
liquid and increases the pressure of the liquid.
One of the main purposes of a volute casing is to help balance the hydraulic
pressure on the shaft of the pump .Double- volute casings are used when
the radial thrusts become significant at reduced capacities.
36
2. Circular casing have stationary diffusion vanes surrounding the impeller
periphery that convert velocity energy to pressure energy. Conventionally, the
diffusers are applied to multi-stage pumps.
The casings can be designed either as solid casings or split casings. Solid
casing implies a design in which the entire casing including the discharge
nozzle is all contained in one casting or fabricated piece. A split casing
implies two or more parts are fastened together.
2. Suction and Discharge Nozzle
The suction and discharge nozzles are part of the casings itself. They commonly
have the following configurations.
1. Side suction/Top discharge - The suction nozzle is located at the end of, and
concentric to, the shaft while the discharge nozzle is located at the top of the case
perpendicular to the shaft. This pump is always of an overhung type and typically
has lower NPSHr because the liquid feeds directly into the impeller eye.
2. Top suction Top discharge nozzle -The suction and discharge nozzles are
located at the top of the case perpendicular to the shaft. This pump can either be an
overhung type or between-bearing type but is always a radially split case pump.
3. Side suction / Side discharge nozzles - The suction and discharge nozzles are
located at the sides of the case perpendicular to the shaft. This pump can have
either an axially or radially split case type.
3. Seal Chamber and Stuffing Box
Seal chamber and Stuffing box both refer to a chamber, either integral with or
separate from the pump case housing that forms the region between the shaft and
casing where sealing media are installed. When the sealing is achieved by means
of a mechanical seal, the chamber is commonly referred to as a Seal Chamber.
37
When the sealing is achieved by means of packing, the chamber is referred to as a
Stuffing Box
Gland: The gland is a very important part of the seal chamber or the stuffing
box. It gives the packing or the mechanical seal the desired fit on the shaft
sleeve. It can be easily adjusted in axial direction. The gland comprises of
the seal flush, quench, cooling, drain, and vent connection ports as per the
standard codes like API 682.
Throat Bushing: The bottom or inside end of the chamber is provided with
a stationary device called throat bushing that forms a restrictive close
clearance around the sleeve (or shaft) between the seal and the impeller.
Throttle bushing refers to a device that forms a restrictive close clearance
around the sleeve (or shaft) at the outboard end of a mechanical seal gland.
Internal circulating device refers to device located in the seal chamber to
circulate seal chamber fluid through a cooler or barrier/buffer fluid reservoir.
Usually it is referred to as a pumping ring.
Mechanical Seal is a type of seal utilized in rotating equipment, such as
pumps and compressors. When a pump operates, the liquid could leak out of
the pump between the rotating shaft and the stationary pump casing. Since
the shaft rotates, preventing this leakage can be difficult.
4. Bearing Housing
The bearing housing encloses the bearings mounted on the shaft. The bearings
keep the shaft or rotor in correct alignment with the stationary parts under the
action of radial and transverse loads. The bearing house also includes an oil
reservoir for lubrication, constant level oiler, jacket for cooling by circulating
cooling water.
38
Rotating Components
1. Impeller
The impeller is the main rotating part that provides the centrifugal acceleration to
the fluid. They are often classified in many ways.
Based on major direction of flow in reference to the axis of rotation
Radial flow
Axial flow
Mixed flow
Based on suction type
Single-suction: Liquid inlet on one side.
Double-suction: Liquid inlet to the impeller symmetrically from both sides.
Based on mechanical construction
Closed: Shrouds or sidewall enclosing the vanes.
Open: No shrouds or wall to enclose the vanes.
Semi-open or vortex type
Impeller types
Impeller type
39
Closed impellers require wear rings and these wear rings present another
maintenance problem. Open and semi-open impellers are less likely to clog,
but need manual adjustment to the volute or back-plate to get the proper
impeller setting and prevent internal re-circulation. Vortex pump impellers
are great for solids and "stringy" materials but they are up to 50% less
efficient than conventional designs. The number of impellers determines the
number of stages of the pump. A single stage pump has one impeller only
and is best for low head service. A two-stage pump has two impellers in
series for medium head service.
A multi-stage pump has three or more impellers in series for high head service.
Wear rings: Wear ring provides an easily and economically renewable
leakage joint between the impeller and the casing. Clearance becomes too
large the pump efficiency will be lowered causing heat and vibration
problems.
Shaft: The basic purpose of a centrifugal pump shaft is to transmit the
torques encountered when starting and during operation while supporting
the impeller and other rotating parts. It must do this job with a deflection
less than the minimum clearance between the rotating and stationary parts.
Shaft Sleeve: Pump shafts are usually protected from erosion, corrosion,
and wear at the seal chambers, leakage joints, internal bearings, and in the
waterways by renewable sleeves. The sleeve shall be sealed at one end. The
shaft sleeve assembly shall extend beyond the outer face of the seal gland
plate.
Coupling: Couplings can compensate for axial growth of the shaft and
transmit torque to the impeller. Shaft couplings can be broadly classified
into two groups: rigid and flexible. Rigid couplings are used in applications
40
where there is absolutely no possibility or room for any misalignment.
Flexible shaft couplings are more prone to selection, installation and
maintenance errors. Flexible shaft couplings can be divided into two parts-
Elastomeric couplings use either rubber or polymer elements to
achieve flexibility. These elements can either be in shear or in
compression. Tire and rubber sleeve designs are elastomer in shear
couplings; jaw and pin and bushing designs are elastomer in
compression couplings.
Non-elastomeric couplings use metallic elements to obtain
flexibility. These can be one of two types: lubricated or
nonlubricated.
POSITIVEDISPLACEMENT PUMP (RESIPROCATING TYPE)
WORKING PRINCIPLE
In a reciprocating pump, a piston / plunger makes reciprocating motion inside
a cylinder. The pump functions by sucking the fluid through suction valves
into the cylinder during the backward stroke of the piston / plunger. The
kinetic energy of the fluid is increased during the subsequent forward stroke
of the piston / plunger. The fluid is then delivered to the high pressure
discharge manifold when the desired pressure values (discharge pressure) are
attained.
Reciprocating pumps are either single acting or double acting and they are
also run in parallel (many pumps are operated in one crank shaft) to increase
the quantity at the same pressure.
41
LLDPE
REACTION AREA
Solvent (SH) is recycled to the reaction area from the reflux drum of the HB
Column in the Solvent Recovery Area. The temperature of this solvent stream is
approximately 175oC and is cooled to 31oC by a series of heat exchangers which
includes the Process Exchanger and the Recycle Coolers. First, cooling in the
Process Exchanger will reduce the recycle solvent temperature to approximately
155oC. The heat from this stream is used to warm the feed to one of the distillation
columns thereby increasing the energy efficiency of the operation. Further cooling
is provided with a Recycle SH Air Cooler in series with a Recycle SH water
Cooler. The use of Recycle SH Air Cooler minimizes cooling water demand.
There are two reactor modes which are normally used.
1) #1 Reactor mode
2) 3→1 Reactor mode
The polymerization reaction is highly exothermic, releasing approximately 93.7
MJ of heat per kg mol of monomer or comonomer reacted. All reactor modes
operate adiabatically and therefore there is a substantial increase in the temperature
of the reaction mixtures through the reactor system.
RECYCLE AREA
The solvent and steam condensed in the Solvent Vapour Condenser from the
overhead of the Stripper is collected in a Decanter. In order to facilitate water
removal from the solvent, the Decanter is designed with a coalescer. Solvent
leaving the Decanter is relatively dry, containing dissolved water but no separate
liquid water phase. The saturation level for water in SH at 35oC is about 100 ppm
42
by weight. This stream is pumped to the LPS Hold Up Tank (HUT) in the LPVR
area.
Polymer formation flow diagram
EXTRUSTION \FINISHING AREA
43
Polymer from the bottom of the LPS is fed directly into the feed hopper of the
Main Extruder. The function of the Main Extruder is to pressurize the polymer and
feed it to the Melt Cutter or Pelletizer, which produces uniform pellets of the
polymer.
In the feed section of the Main Extruder, there is a tendency for gas to build up at
the rear of the first extruder screw flite. On low MI resins, at high screw speeds,
the vapour pocket formed Solid additives can be added to the main extruder with
the aid of the satellite extruder.
The Melt Cutter consists of a die plate on which rotates a set of knife blades which
cut the emerging polymer strands into uniform sized pellets. A flow of water
circulates through the cutter housing to first quench and then convey the cut pellets
away from the cutter.
From the melt cutter, the pellets are conveyed to a Delumper that segregates large
lumps of polymer into a waste hopper. Generally, large lumps are produced only
during startup of the extruder/cutter system. The Melt Cutter consists of a die plate
on which rotates a set of knife blades which cut the emerging polymer strands into
uniform sized pellets.
BUTENE-1
process can be divided into following areas:
1. Catalyst section. 2. Reaction section. 3. Evaporation section.
4. Distillation section. 5. Storage section.
FLOW DIAGRAM OF BUTENE-1
44
45
UPSTREAM
GAS PROCESS UNIT
(GPU)
&
GAS CRACKER UNIT
(GCU)
GAS SWEETENING UNIT
46
‘Sweetening’ means removal of acid from gases like H2S & CO2. The HVJ gas is
received from ONGC contains CO2 (5.52% by volume) & H2S (4ppm). The gas
forms the feedstock to the C2-C3 recovery unit where cryogenic conditions prevail
& if the CO2 component of the gas is not received. It will freeze at such a low
temp.
Gas sweetening plant uses DEA (Di Ethanol Amine) as a solvent for removing
CO2 in the natural gas by chemical absorption.
ABSORPTION SECTION
Natural gas coming from HVJ is treated in two parallel high pressure absorbers.
The gas is fed to the absorber column at a pressure of 52 kg/cm2 & temp 30 C.
This gas is counter currently treated with DEA solvent (40% by weight) which is
fed from the top of the column. The absorber column contains 30 valve trays. The
treated gas leaves from top of the column at 45 C & contains less then 50 ppm of
CO2.
TREATED GAS WATER WASH & COOLING
The treated gas from absorber column is counter currently washed with water in
water wash column equipped with ball rings to remove the DEA carried over the
gas. The DEA solution in water is removed from the bottom of this column & sent
to the rich amine flash drum. The treated gas is cooled to 40 C & leaves the unit at
pressure 50 kg/cm2.
RICH AMINE CIRCUIT:
47
The rich amine from the absorber bottom & the water wash column are sent to rich
amine flash drum. The rich amine flash drum is operated at 6.5 kg/cm2 & 70 C.
Most of the hydrocarbons are co-absorbed in DEA solution is removed in this
drum & sorted to the plant fuel gas system.
AMINE REGENERATION:
The rich amine solution from the flash drum enters the regenerator column through
the rich lean amine exchanger at 110 C. In the regenerator the solvent DEA is
stripped off CO2 using low pressure steam in the column reboilers. The column
has 21 valve trays. The top two trays are used to minimize DEA carryover with the
CO2. This column operates at 2kg/cm2. The top temp is 97 C & the temp at the
bottom is around 126 C. The lean amine is withdrawn from bottom of the column
& is sent to storage after being cooled to 45 C in rich lean amine exchanger & then
by cooling water.
Vapors from the top of the regenerators are condensed in the regenerator overhead
condenser & taken in to Regeneration reflux drum. The uncondensed gases mainly
CO2 are vent to atmosphere at a safe location & the condensed liquid is pumped
back as reflux to the column.
AMINE STORAGE:
The lean amine from regenerator is sent to amine storage tank from where it is
pumped to the absorbers. The amine tank is blanketed with N2 to prevent solvent
degradation with O2.
AMINE FILTERATION:
48
A stream of stored amine solution is continuously sent to the filteration package by
amine filteration pump. DEA solvent filteration is required to remove all the
dissolved hydrocarbons, scales & solvent degradation products that can cause
corrosion & foaming.
Levels of filteration may be as-
a) Precoat filter consisting of cellulose
b) Activated carbon filter which removes corrosion products
c) Cartridge filter which removes any carbon particles
ANTIFOAM INJECTION PACKAGE:
Antifoam facilities are provided to overcome foaming problems in the absorber.
The antifoam solution is an aqueous solution of silicon oil. This is injected to the
suction of amine charge pumps.
AMINE DRAIN RECOVERY:
All the solvent drains are removed in an underground amine sump pump.
C2/C3 RECOVERY UNIT
C2/C3 Recovery plant has been designed by Engineers India Limited. In this plant
C2/C3 fraction of the feed gas is recovered under cryogenic conditions by Turbo
Expander process. The C2/C3 product from this unit forms the feedstock of the gas
cracker unit.
The process comprises of the following section:
FEED GAS COMPRESSION:
49
The sweetened gas is recovered from the Gas Sweetening Unit at 50 kg/cm2 and
40 C in the field gas Knock Out Drum where the entrapped liquids are removed.
The gas is now compressed to 55 kg/cm2 in feed gas Expander compressor.
FEED GAS DRYING/REGENERATION:
The compressed gas is cooled down to 37 C using cooling water in Feed Gas
Compressor discharge cooler and further down to 18 C by the outgoing lean gas in
the feed/lean gas exchanger. The condensed moisture from the gas is removed in
moisture separator. The gas is now saturated with water that is removed in a dryer
to a water dw point of -100 C using molecular sieves as desiccants.
There are two dryers out of which one is in drying mode and the other is either
a standby or in regeneration mode. The drying period is around 12 hours and the
regeneration is also 12 hours.
A part of the lean gas from the first stage discharge of the lean gas compressors is
heated to 320 C in a gas fired heater and this hot gas is used for regeneration of the
dryers.
FEED GAS CHILLING/SEPARATION:
The feed gas enters the feed gas chiller #1 where it is cooled down to -32 C by the
separator 1 & 2 liquids and the lean gas. The gas is further chilled down to -38 C in
the demethaniser side reboiler.
The gas is again chilled in feed gas chiller 1 to about -55 C to -60 C. The
partially condensed feed gas at this stage is taken to the separator 1 where the
condensed liquid is separated and sent to chiller 1 for cold recovery. The liquid is
then fed to the demethaniser column.
50
The uncondensed vapor from the separator 1 are cooled to -18 C by the
outgoing lean gas in feed gas chiller 2. These vapours are now taken to Separator 2
where again the condensed liquid is separated. Cold from this liquid is recovered in
feed gas chiller 1. It is then mixed with the Separator 1 liquid and this is fed to the
demethaniser column on tray 18.
FEED GAS EXPANSION:
The overhead gas from separator-2 is expanded entropically in the feed gas
expander to around 22 kg/cm2 and the temp of the gas drops to -98 C. Due to this
chilling, there is further condensation of the gas. This vapour liquid mixture is fed
to the demethaniser column on the 8th day .The work available from the isentropic
expansion of the Separator-2 vapour is used to compress the feed gas.
FRACTIONATION:
The reaction consists of a demethaniser column which serves to recover C2-C3
product from (i) Separator 1 & 2 liquids received at -68 C and (ii) feed gas
expander overhead vapours received at -98 C.
This separates almost all the methane from the gas. It consists of 36 valve trays
and one chimney tray for supplying feed to side reboiler. The column reboilers
chill down the feed gas and in turn recover reboiler duty. The overhead vapours are
chilled from -98 C to -102 C and condensed in the demethaniser overhead
condenser by the cold gas from the demethaniser over expander outlet -117 C. The
demethaniser overhead vapour is expanded from 21.5 kg/cm2 to 12 kg/cm2 and
due to this gas is chilled to -117 C. This cold methane is the major source of
refrigeration in the unit.The bottom product from the demethaniser column is the
51
C2/C3 product, which is pumped as feed to cracker unit or sent to storage. The
recovery of C2 is around 90%.
LEAN GAS COMPRESSION:
The lean gas after giving away its cold to a series of exchanger (viz. Feed Gas
Chiller-2, Feed Gas Chiller-1, Feed/Lean Gas Exchanger) gets heated to 25 to 30 C
and is first compressed from 10kg/cm2 in the demethaniser overhead expander
compressor and is further compressed to 55 kg/cm2 in a 2-stage gas turbine driven
Lean Gas Compressor. It is cooled to 40 C and then sent back to HVJ pipeline.
About 36 ton/hr of lean gas is drawn from first stage discharge of the lean gas
compressor for dryer regeneration. This gas is then compressed to 55 kg/cm2 in a
steam turbine driven Residue Gas Compressor and is then sent to Lean Gas
Compressor discharge header.
A part of gas from the first stage Lean Gas Compressor discharge is also
taken for internal fuel consumption of the unit.
52
GAS CRACKER UNIT(GCU)
The Gas cracker unit is a part of the U.P.Petrochemical complex. The Gas Cracker
unit comprises of the Hot section (cracking furnace /cracked gas compressor) and
Cold section (The Ethylene recovery unit). The C2/C3 hydrocarbon is cracked and
compressed in Hot section and Ethylene, Hydrogen, Propylene, C4mix, C5+ are
separated (distilled) in Cold section. Ethylene and Hydrogen are main product,
where as Propylene, C4 mix and C5+ are separated as by products. The waste heat
from the cracker gas effluent is used to produce VHP steam at 105 Kg/cm2 and
510OC, which is subsequently used for running the turbine of gas compressors and
heat requirement of the GCU plant.The breaking of molecule to yield more useful
products is called cracking. Cracking requires high temperature to initiate it and is
endothermic. The heat is supplied by the direct firing of fuel gas in the furnace.
Gas cracker Plant mainly consist of following units
a) Furnace/ Quench Tower
b) Cracked Gas drying
c) Dispersed Oil Extraction process.
d) Demethaniser
e) Hydrogen unit (PSA)
f) De-ethaniser
g) C2 Hydrogenation
h) Ethylene Tower
i) Ethylene Product Distribution
j) DeButaniser
k) Propylene Stripper
53
FURNACES
The pyrolysis furnace area consists of four 24 W 144 type furnaces
for 300,000 MTA ethylene capacity based on 8000 hours / year. The
furnaces are both wall and floor fired and util ize gas fuels.As off-set
connection section recovers waste heat from the flue gases leaving
the radiant section of the furnaces. The fire gases are finally
discharged to atmosphere via an induced draft fan and a stub stack.
The cracked gases leaving the radiant coils are quenched in a series
of exchangers before being routed to the quench water tower.
The convection section of the pyrolysis furnaces contains the
following services:
a) Hydrocarbon (HC) Preheat - I .
b) Boiler Feed Water (BFW) Economizer.
c) HC Preheat II
d) High Pressure Superheated Steam (HPSS).
Hydrocarbon + Dilution Steam (HC + DS).
Process Description
FEED VAPORIZATION:
C2/C3is received from C2/C3 recovery unit of GPU at 0 C and 22 kg/cm2 abs. It is
flashed to around 10 kg/cm2 abs whereby it gets cooled at -26 C. It is then first
heated by the propylene refrigerant and then by quench water and LP steam to
around 80 C.
54
CRACKER FURNACE:
Dilution steam is mixed with C2/C3 vapor in the ratio of 0.3:1 and fed to
convection section of furnace.
The dilution steam has two functions:
a) Reduce the hydrocarbon partial pressure thereby increasing yield of
ethylene.
b) Reduce the rate of coke formation thereby increasing the furnace run length.
In the convection section of furnace the feed gets heated to around 650 C by heat
exchange with fuel gas. It is then fed to the radiant section of furnace where
cracking of C2/C3 takes place. There are 5 furnaces each having capacity of
1,00,00 TPA. Each furnace has 12 W type radiant coils having total length of 44m.
The temperature at the exit of the radiant coil is 850 C. the conversion per pass for
ethane is around 75% by weight while that for propane is 93%. The hot gases are
cooled to around 350 C by generating VHP steam in USX and TLX exchangers. It
is further cooled to around 200 C in TLX-2 by heating boiler feed water.USX and
TLX are heat exchangers.
QUENCH WATER AND DILUTION STEAM:
The hot gases are then quenched and cooled to around 40 C by direct contact with
water in quench tower. Some light fuel oil present in cracked gas gets condensed.
This is separated from water in oil water separator and pumped to off sites. The
steam, which gets condensed in quench tower, is pumped to process water
55
treatment unit to remove impurities such as oil and suspended solids. The treated
water is pumped to dilution steam is generated and used in the process.
CRACKED GAS COMPRESSION & DEHYDRATION:
The cooled cracked gas is compressed from 1.4 kg/cm2 abs to 26 kg/cm2 abs in a
4-stage steam turbine driven compressor having rated power of 18 MW. Inter
stage/after stage coolers and KOD are provided to cool the compressed gas and
separate the condensed liquid (fuel oil). H2S and CO2 present in cracked gas are
removed in caustic tower between 3rd and 4th stages of compression. The cracked
gas after the 4th stage is cooled by cooling water and propylene refrigerant and
then routed to dehydrators where the moisture in cracked gas is reduced to <1ppm
by volume
DEMETHANISER:
The dried gas is cooled in demethaniser section to around -100 C by different
levels of propylene and ethylene refrigeration. It is further cooled to -135 C by
vapors from expander compressor. The condensed liquids are fractioned in
demethaniser system. The C2+ liquids are sent to deethaniser while the vapors
(mainly CH4 and H2) are routed to expander where they are expanded from 21
kg/cm2 abs in a 3-stage machine. The vapors after giving cold in demethaniser
section are compressed and routed to fuel gas system.
The polybed Pressure Swing Adsorption (PSA) unit for hydrogen purification is
designed to deliver a constant and continuous flow of high purity hydrogen product
stream. PSA employs molecular sieve type adsorbent to purify the crude hydrogen
stream supplied from demethaniser system. The adsorber operates on an alternating
56
cycle of adsorption and regeneration with adequate beds always available for
service.
ETHYLENE RECOVERY UNIT:
In deethaniser, ethane/ethylene mixture gets separated from C3+. The
ethane/ethylene mixture (top product from deethaniser) is fed to C2 hydrogenation
section where acetylene is converted to ethylene/ethane by hydrogenation using
palladium catalyst. The affluent from C2 hydrogenation is routed to green oil tower
where green oil is removed by washing with cold ethylene. The overhead from
green oil tower after passing through secondary
dehydrator is fractioned in ethylene tower to separate ethylene and ethane.
Ethylene tower has 116 trays and operates at a pressure of around 18 kg/cm2 abs to
produce ethylene product of 99.8% by mole. A part of the ethylene (5%) is cooled
and sent to cryogenic storage. From the remaining 95% ethylene, cold is recovered
before sending it to downstream plant. The ethylene tower bottom supplies the
ethane recycled to the cracking furnace.
PROPYLENE RECOVERY:
The bottom of the deethaniser is sent to depropaniser, which operates at 7.2
kg/cm2. In depropaniser, propane and propylene are recovered in mixture form.
The propane/propylene mixture from the top of the depropaniser is fed to C3
hydrogenation system where methyl acetylene propadiene is converted to
propane/propylene. The reaction takes place at temp 9-44 C and pressure of 16.4-
17.4 kg/cm2 in C3 hydrogenation system. The propane/propylene mixture is then
fractioned in propylene tower to give chemical grade propylene as top product and
57
propane as bottom product. Propylene tower is maintained at a pressure of around
18 kg/cm2 and has 109 trays. The propane is recycled back to furnace.
BUTANE RECOVERY:
The bottom product from depropaniser is routed to debutaniser, which operates at 4
kg/cm2. The overhead product is C4 fractions and bottom product contains C5 and
heavier materials, which is sent to battery limit.
REFRIGERATION:
The plant has a 4-stage propylene refrigeration and 4-stage ethylene refrigeration.
Propylene refrigerant compressor is designed to supply propylene refrigerant at -
38.9 C, -24.4 C, -5.6 C and 7.2 C. The compressor is driven by condensing steam
turbine. Ethylene refrigerant compressor is designed to supply ethylene refrigerant
at four levels 100.6 C, -84.4 C, -67.8 C and -48.3 C respectively. The compressor
is driven by a condensing steam turbine.
PROPYLENE REFRIGERATION SYSTEM
The Propylene refrigeration system will be put in normal operation as the first one
of the three main compressors. C3R system will be utilized for cool down of the
Demethanizer and it will be the single source of process refrigeration until C2R
system start up. Propylene refrigeration system provides the initial chilling of gases
down to –38.90C. Propylene refrigerant at different pressure pickup the heat from
other streams generating propylene vapors at different pressures. Propylene
refrigeration compressor compresses these vapors with discharge pressure of 17.5
kg/cm2, at which the propylene is condensed using cooling water. The liquid
propylene is then flashed back, to provide chilling down to –39.2 0C in the circuit.
58
REFRIGERATION SYSTEM IN GCU
To get the desired products and by products of required purities from furnace
effluents, it is required to be passed through a series of distillation columns after
cracked gas is compressed and chilled adequately. The chilling is achieved by
refrigeration system.
Refrigeration system in GCU consists of Propylene refrigeration system (C3R) and
Ethylene refrigeration system (C2R). C3R compressor is driven by backpressure
cum condensing type turbine running using 105 kg/cm2g steam. C2R compressor
is driven by condensing type turbine using 40 kg/cm2g steam.
Four modes of operation for each of the refrigeration compressors were studied by
the licensor SWEC. There are 2 different feed cases, referred to as Case 1 and
Case2.There are 2 different chilled liquid ethylene product rates referred to as Case
A and Case B. These two chilled liquid ethylene product rates are 24000TPA and
155000TPA respectively.
59
LPG UNIT
The objective of this unit is to recover Liquefied Petroleum Gas (LPG) and
propane from Natural Gas (NG) and to provide C2/C3 feed stock to the existing
Gas Cracker Unit (GCU).
PROCESS DESCRIPTION:
Feed from GPU is fed at the 6th tray of C2/C3 column having 36 valve trays.
Column is operated at a pressure of 22 kg/cm2. The column is designed to operate
at a temp of 7.7 C at the top and 82.3 C at the bottom. Column top product is
mainly C2, C3 and some percentage of C4 at a temp of -3 C which is transferred to
C2/C3 storage or GCU by C2/C3 reflux and transfer pump and bottom product is
C3+ which goes into LPG column for further fractionation. Top product C2/C3
vapor from C2/C3 column is condensed in the condenser by propylene refrigerant.
LPG COLUMN:
Bottom product C3+ from C2/C3 column is fed at 14th tray of LPG column having
54 valve trays. Column is operated at temp of 150 C and 15.5 kg/cm2. Temp at the
top and bottom of column are 58 C and 130 C respectively. Operating pressure is
11 kg/cm2. Top product of the column is LPG vapor (C3, C4 and some C5), which
goes into condenser where it is condensed by cooling water, which is being
circulated in tubes. LPG product at 45 C is pumped to the LPG storage bullets by
reflux and transfer pumps. Heat load is provided by MP steam at 16 kg/cm2. Now,
bottom product goes into pentane column.
PENTANE COLUMN:
60
In pentane column, pentane and Spatial Boiling Point Solvent (SBPS) are
recovered. Feed enters at 15th tray of column having 19 valve trays. Column is
designed for a temp of 85 C and a pressure of 16.8 kg/cm2. It is normally operated
at a temp of 42 C at the top and 66 C at bottom and a pressure of 14.2 kg/cm2. Top
product of column is pentane vapor which goes into condenser where it is
condensed by cooling water and then it is stored in the storage tank and part of
condensed pentane is used as reflux in the column. Bottom product is SBPS, which
is like petrol. Head load is provided by LP steam at 5 kg/cm2.
PROPYLENE REFRIGERATION SYSTEM:
PRS has been provided in order to take care of chilling in LPG unit. Turbine,
which is driven by VHP steam, produces MP steam & LP steam. MP steam is used
in LPG bottom reboiler and LP steam is used in bottom reboiler of C2/C3 and of
propane column. Mechanical work produced in this process is used to run
compressor. Propylene liquid is used as cooling medium in C2/C3 over head
condenser to condense the C2/C3 vapor. Propylene gets vaporized during the
condensation process. Propylene vapor is fed to the Knock Out Drum (KOD-3).
From KOD-3, it is fed to the suction of compressor at 4.8 kg/cm2 and -7.0 C and
remaining propylene liquid is pumped into evaporator where it is converted into
vapor and then transferred to KOD-2 and some liquid which is not vaporized goes
into evaporator where it is converted into vapor and this vapor is fed to KOD-1.
Vapor from KOD-1 at 1.4 kg/cm2 and -41 C is feed for suction-1 and it comes out
from discharge-1 and D-1 goes into S-2 along with feed at 2.3 kg/cm2 and -28 C
coming from KOD-2. This compressed feed comes from D-2 and goes into S-3
along with the feed from KOD-3. Now this compressed vapor coming out from D-
3 is routed to S-4 along with vapor at 8.7 kg/cm2 and 13 C from KOD-4. Final
discharge from compressor is routed to condenser where propylene vapor is
61
condensed by cooling water and then it is fed into accumulator at 40 C and 16.9
kg/cm2. From accumulator, it is routed to KOD-4 and then it is sent back to the
C2/C3 condenser. Make up refrigerant is also provided because of loss in
propylene during operation. Antisurge valves are provided to each KOD to avoid
back flow.