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VOCATIONAL TRAININGREPORT

GAIL (INDIA) LTD. U.P PETROCHEMICAL COMPLEX PATA,

AURAIYA (U.P)

SUBMITTED TO-TRAINING DEPARTMENTGAIL - PATA

SUBMITTED BY-

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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

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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.

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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

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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

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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.

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INTREGATED OFFSITE PLANT

&

STORAGE

(IOP & S)

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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.

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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

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Forced Draft Furnace,

Radiant Closed Bottom

Suitable for Oil/Gas Firing

Fuel : Rich Gas

: Lean Gas

: Combination of Blended

fuel oil & Rich Gas.

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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

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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

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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

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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

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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.

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(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.

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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.

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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.

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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.

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(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

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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

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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

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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)

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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.

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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.

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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.

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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

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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

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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:

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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

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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.