final ppta report

7/31/2019 Final Ppta Report

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PRODUCTION DEPARTMENT (OXPLANT)

U N I V E R S I T Y O F E N G I N E E R I N G & T E C H N O L O G Y , L A H O R E Page 1

(PRODUCTION DEPARTMENT)

SUBMITTED TO

MR. REHAN SIRAJ (Plant Manager OX PLANT)

SUBMITTED BY

MUHAMMAD ALI


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Acknowledgment

Before proceeding to the actual report, I would like to thank a few people

without whom this would never have been possible. Firstly, I am thankful to the

HUMAN RESOURCE DEPARTMENT LOTTEPPTA, for giving me a chance to have a

one of a kind work experience in this world renowned multinational organization. I

am also grateful to the MR.REHAN SIRAJ (PLANT MANAGER) for helping me in such

a nice way & also the following persons for showering their knowledge so

generously upon me, without them it wasnt possible. Thank You all for teaching

me that no one ever could.

MR. ASAD (Process Engg. Manager)

MR.M.AMIR SHEIKH (Senior Shift Manager)

MR.SARANG ABDULLAH (Process Engg.Support Manager )

MR.ZAEEM (Trainee Engineer)

MR.WAHEED (Trainee Engineer)

Regards,

Hafiz M. Ali

Department of Chemical Engineering University of Engineering & Technology, Lahore.


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PREFACE

Industrial models are exceptionally diverse than those

taught in classrooms. One strictly needs an industrialexposure in order to comprehend the way these ideal,

theoretical tools are applied on practical equipment.

This internship at Lotte Pakistan PTA limited, gained me a

head start toward my practical life. The report reflects

all the knowledge that I got from here.


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CONTENTS

TOPICS Page#

Introduction to LOTTE-PPTA 5

Safety, Health & Environment (SHE) 6-7

Process Description 8-11

TASK # 1 (Study of equipments in the plant) 12-28

TASK #2 (Understanding of Anti-surge control loop) 29-33

TASK #3 (Calculation of Efficiency of multistage compressor) 34-37

TASK #4 (Calculation of Efficiency of two stage Expander) 38-39

APPENDIX 1 - Excel sheet of Task 2 & 3 40

Special Thanks 41


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INTRODUCTION TO LOTTE-PAKISTAN PTA, LTD.

Lotte Pakistan PTA Limited is a world-class supplier of purified terephthalic acid, an essentialraw material having purity of 99.8%, used in the polyester industry. Lotte Pakistan PTA Limitedis the single largest foreign direct investment in Pakistans petrochemical industry. The plant,located at Eastern Industrial Zone some 50 kilometers from Karachi, was built using ICIs state-of-the-art technology. In 1995, ICI group invests in the local (Pakistan) petrochemical industry tocapture the growing local demand of PTA. In 1997 project construction started which was

commissioned in 1998. In 2000, PTA business de-merged from ICI Pakistan Limited intoPakistan PTA limited (PTA) and separately listed on all stock exchanges in Pakistan. In 2008,Akzo Nobel completed its acquisition of ICI, subsequently becoming the ultimate holdingcompany of Pakistan PTA Limited. In 2009, Lotte acquired majority shareholdings in PakistanPTA Limited (PPTA) making it an official member of the Lotte Worldwide Group.Subsequently, the name of the company was changed to Lotte Pakistan PTA Limited. It producesPurified Terephthalic Acid (PTA) an essential raw material for Pakistans textile and PET(Polyethylene terephthalate) packaging industries and forms the backbone of polyesters chainincluding Polyester Staple Fibre, Filament Yarn, and PET (bottle grade) resin.

Within a short time, PPTAs dedicated and highly motivated team of professional engineers proved that they could run this complex plant to world standards of safety, environmental care, product quality, and process efficiency. Since 2002, the plant has operated above its nameplatecapacity of 400,000 tons per annum. One of the goal of the company was to increase the capacityto 500,000 tons per annum which it achieved in 2009 through process improvements.

In future PPTA is planning for two projects.

To install a Catalyst Recovery Unit costing approximately US $5 million to optimize its production process. The project is on roll.

Under the announced approvals, PPTA will also invest in a captive 40MW Gas poweredCogeneration Power Plant, amounting to approximately US $40 million. 30MW will beused by this plant and remaining surplus power will be sold to KESC.


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SAFETY HEALTH & ENVIRONMENT

Pakistan PTA is a responsible organization, governed by a safety, health and environment (SHE)

policy. This accords the highest priority to the safety and health of their employees and the

public. The global policy inherited from IMPERIAL CHEMICAL INDUSTRIES (ICI) also

pledges them to an environment policy that conforms to international requirements and ensures

their operations are acceptable to their local community.

EMPLOYEES SAFETY:

The main equipment provided to each and every employee includes;

Safety shoes

Safety goggles

LEP (Light Eye Protect)

Ear plugs.

The whole plant has certain lined criteria, where these PPEs are to be used.

YELLOW lines are for PLANT AREA. GREEN and WHITE lines are for GOGGLE AREA. RED AND WHITE is the high noise area so its for EAR PLUGS. Parallel RED & GREEN lines are for HAZARDOUS AREA.


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The other equipments, that are not common but are provided for specific tasks, include;

Safety harness

PVC Gloves

PVC suit

Leather gloves

Face shield

Dust mask

Respirator/BA sets

Hearing protection

EXTRA SAFETY:

Smoking is not allowed in any area, particular area is allocated for smoking.

No battery-operated device is allowed in the plant area like mobile, radio, torch,

Camera, Calculator etc, as it may cause ignition because a slight spark couldcause fire.

Assembly points are established for employees in case of fire conditions.

Toxic refuges are there.


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PROCESS DISCRIPTION

PTA is made by the oxidation of Paraxylene, using Acetic Acid as a solvent. Air is blowninto a stirred reactor vessel containing a mixture of Paraxylene, Acetic Acid and a catalyst.Crude terephthalic acid is formed, crystallised out and dried. In a second, purification stage, thecrude terephphalic acid (TCA) is redissolved in hot water, co-products are removed byhydrogenation and pure terephthalic acid is again crystallized out and dried. This ensures that the99.98% purity required for the manufacture of polyester products is achieved. During themanufacturing process various ancillary stages are required to ensure waste recovery and raw

material efficiency.

The process requires nitrogen gas, hydrogen gas which is supplied by a nearby gascompany; BOG Gases on long contract.

A large quantity of fresh water is also needed. The need is satisfied by a freshwater lake,the water of which is supplied through an approximately 50 Km long pipeline.

Third and the most significant is electrical power. PPTA is supplied by 220KV of power from Bin Qasim KESC thermal power station. Still it owns three diesel generators for emergency backup purposes.

The plant is divided in three parts

Oxidation Plant

Purification Plant

Utilities Plant


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OXIDATION PLANT(BRIEF) :

The oxidation plant produces crude terephthalic acid is summarized in following steps

Reaction

Catalyst + solvent

PX + O2 CTA

Crystallization Filtration and solvent recovery Off gas drying and treatment Thermal oxidizer for catalyst recovery

BLOCK DIAGRAM :


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PURIFICATION PLANT(BRIEF) :

The purification plant produces pure terephthalic acid is summarized in following steps

Reaction

Catalyst + Solvent

CTA + H2 PTA

Product separation

Drying and product handling

Bagging

BLOCK DIAGRAM :


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UTILLITIES PLANT(BRIEF):

Utilities plant facilitates core plant by providing services to it such as

Raw material storage system

Raw water system

Effluent treatment plant

Two fire tube boilers

Three generators

Instrument air compressor

Raw material pumping station


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TASK NO. 1

Study of Equipments in OXPlant


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EQUIPMENT USED IN OX-PLANT

The following are the major equipments used in the oxidation plant:

Process air compressor

Feed mix drum

Oxidation reactor

Horizontal & vertical condensers

Degasser

Absorption columns

Crystallizers

ROVAC filters

Knockout drums

Pumps

Dryers

Scrubbers

Ejector

DH Column

Reboilers

Filters

Thermal Oxidizer Gas cooler


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PURPOSE OF EQUIPMENTS USED

PROCESS AIR COMPRESSOR

It is used to compress air so that air can be effectively used in

Oxidation reactor as a source for O 2(reactant In main reaction)

In crystallizers to improve quality by further conversion of intermediates to TA.

In catalytic combustion unit

As a conveying gas

FEED MIX DRUM

Here feed (paraxylene), solvent (acetic acid) and catalyst (aqueous solution of cobalt,manganese acetates with hydrobromic acid) are mixed.

Agitation here ensures a homogenous mixture. Mixing here is very important for better efficiency in the oxidation reactor.

Components are continuously metered to feed mix drum.

Under running conditions of plant recycled solvents streams are used instead of fresh solvent & correct feed ratio is maintained by feed ratio control.


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OXIDATION REACTOR

Here Oxidation reaction takes place here at an operating pressure of 16 bar and atemperature of approximately 200 0C.

Air is charged under flow control with combined feed from feed mix drum and reactiontakes place.

Product T A is formed with some by products like 4-CBA, along with methyl acetate,solvent acetic acid , water & some unconverted paraxylene.

In this reactor, slinger are used which through the recycled stream from reactor condensers & separating drums to the walls of the reactor to remove solids on the reactor wall.

Agitator here serves to disperse the air evenly within the reactor, providing good mixing& hence better efficiency of the reaction.

Product formed is sent to the crystallizers.

CONDENSORS

Condensers used in the OX plant can be broadly classified as:

Reactor condensers

Crystallizer condensers

Vacuum vapour condenser

DH column condenser


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Reactor condensers

Due to the exothermic nature of reaction in reactor, solvent, water, air, other by products,impurities & unconverted paraxylene get vapourized and sent to horizontal reactor condenser.

Vapour/gas stream here is cooled to 170 0C and condensation occurs.

Due to heat transfer in this SHELL & TUBE condenser (vapour/Gas stream on tube side& water on tube side) , 6 barA steam is produced.

Uncondensed vapours from horizontal condenser pass to 1 st vent condenser wherecooling of vapours occurs to 130 0C.

2nd vent condenser cools the vapours to 80 0C.

Separation of solvent from gas & uncondensed vapours occurs in FI-304, FI-305 &FI- 306 separators.

Part of condensate(solvent) is sent back to oxidation reactor and part of condensate arecombined and sent to the solvent DH column.

Vent gases are sent to HP absorber via gas cooler which cools the gas to 50 0C makingconditions more favorable for absorption.

Crystallizer condensers

After flashing in 1 st crystallizer, vapours of acetic acid and water are sent to 1 st TAcrystallizer condenser where vapours are condensed to 110 0C.

Gas stream is further cooled to 50 0C In 1 st TA Crystallizer vent condenser.

After each condenser there are separating units(F1-430 & F1-431) attached.

Condensate streams from F1-430 & F1-431 are combined & sent to DH column.

Vacuum vapour condenser

After the ROVAC, mother liquor separator separates the mother liquor & vapours whichare condensed in vacuum vapour condenser under vacuum action.

DH column condenser

Vapours from DH column(majorly water vappours) are condensed here in air cooledcondenser.


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ABSORBERS

Two absorbers are being used in OX plant.

1. HP absorber

2. Atmospheric absorber

HP Absorber

Here vent gases from reactor are scrubbed

1st with cold acetic acid to recover paraxylene & methyl acetate.

Then with cold demin water to recover residual acetic acid.

Part of spent air stream is dried & used on TA and PTA plant as low grade inert gas, onthe powder pneumatic conveying systems.

Remaining part passes to expander which is coupled to process air compressor.

Atmospheric absorber(D1-508)

Vent gasses from the drier recirculating system, together with all vent streams are sent toatmospheric absorber via vent header.

Here Residual acetic acid is scrubbed from gas with recirculated bottoms fromatmospheric absorberD1-508 & fresh demin water.

Excess liquid is purged on level control in D1-508, from the delivery of atmosphericabsorber circulation pump to stripper stillpot.

The clean vent gas is then vented to atmospheric via the atmospheric absorber vent stack.


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CRYSTALLIZERS

There are three crystallizers in series in OX plant.

The slurry product after the reactor is sent to 1 st crystallizer where crystallization occurs by the application of reduction of pressure(Flashing).

Acetic acid & water is vapourized and the vapours are condensed in 1

st

TA Crystallizer condenser.

The gas stream is further cooled in 1 st crystallizer TA vent condenser and separationoccurs in integral separating drums FI-430 & F1-431.

Now slurry from 1 st crystallizer is sent to 2 nd crystallizer where again flashing is done byreduction in pressure and vapors are directly sent to DH column.

Slurry from 2 nd crystallizer is then sent to 3 rd crystallizer where flashing occurs withreduction in pressure to 0.55barA vacuum. Vapors then are sent to the 3 rd crystallizer condenser.

Vacuum here is required so that all vapors are removed here and corrosion at ROVACfilter is avoided.

Pressure in 1 st & 2nd crystallizer is maintained by throttling the vapor exit streams.

Third crystallizer vacuum is achieved by single stage ejector.

Secondary oxidation reaction takes place in the crystallizers by addition of oxygen inthem. In this way maximum efficiency of reaction is achieved.


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ROVAC FILTER

Slurry from 3 rd crystallizer is sent to filter feed drum and then to ROVAC filter.

It separates the slurry feed from the FILTER FEED DRUM into cake containingless than 15% moisture, and MOTHER LIQUOR containing less than 0.3%solids.

A Vacuum is applied to the inside of a hollow rotating drum.

Slurry is picked up by the drum and MOTHER LIQUOR passes through thefiltration cloth into the inside of the drum whilst solids remain outside forming thecake.

The TA solids on the outside of drum are washed with fresh solvent as the drumrotates and then dried with gas drawn through the cake.

OPTIMIZATION

The quality of the slurry being feed to the filter is very important and the level of impurities affect the performance.

The drum speed is variable and is used to control the throughput of the filter.Higher thespeed, the greater the filtration rate but less effective the wash and drying phases.

A low pressure inside the drum is desirable.

The amount that the drum is submerged in the slurry has a large effect on the fraction of area of cloth which is picking up the cake.

A high temperature in the 3 rd crystallizer is avoided as MOTHER LIQUOR will flashacross the cloth.

Effecting cake washing is essential to displace MOTHER LIQUOR from the cake.


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KNOCKOUT DRUMS

Knockout drums are actually vapour-liquid separator, In OX-PLANT they are in:

OFF-gas Recovery section(F1-150)

Vacuum pump knockout drum(F1-417)

OFF-GAS RECOVERY SECTION The feed reactor off-gas is passed via knockout drum to the preheator.

Here the gas-liquid mixture is separated.

VACUUM PUMP KNOCKOUT DRUM

Inert gas plus vapour from MOTHER LIQUOR separator after the ROVAC vacuum

vapour condenser and vacuum pump are sent to VACUUM PUMP KNOCKOUTDRUM.

Here the gas is separated from liquid.

EJECTOR

Above the 3 rd crystallizer, there is an ejector responsible to create a vacuum required in 3 rd crystallizer so that all vapours are removed here and no flashing would occur in ROVAC.


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PUMPS

Pumps are the mechanical devices used for the transportation of incompressible fluidfrom low pressure/energy region to high pressure/energy region by maintaining a

pressure difference across themselves.

They are also used to increase flow rate of any stream.

So, from one equipment to other a pump is most likely to be there . so each and every pump cant be discussed.

Mostly SUNDYN PUMPS are used in the plant.

SUNDYN PUMPS are basically the centrifugal pumps. Movement of fluid from theimpeller is governed by the centrifugal action.

OBSERVATION

Suction line of every pump is greater than the discharge line. Thinking about this think and using my previous theoretical knowledge and after

confirming from seniors here I conclude that this is done to make the NPSH availablemore so that cavitation & other problems could be avoided

VALVES

Valves are the devices used for controlling as well as for regulating the flow.

There are many kinds of valves in OX-PLANT. So, there function, working etc is discussedseparately.


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DRYERSThere are two dryers in the OX-PLANT.

TA dryer

OFF-GAS dryer

TA DRYER

Wet cake from ROVAC Filter is sent to TA dryer through different screws.

This is a rotary steam tube dryer in which residual acetic acid is removed in a circulatingstream of inert gas.

Dry solid product is discharged to TA Feed hopper through screws and valves bycontinuous conveying using a portion of the dried reactor off-gas stream.

OFF-GAS DRYER

Part of the spent air streams from OFF-GAS SCRUBBER is dried in OFF-GASDRYER.

This dried gas is used as a low grade inert gas, principally for pneumatically conveyingTA and PTA powders, but also for powder aerators in silos.

GAS COOLER

To make the conditions favorable for absorption, gas must be cooled. Gas cooler coolsthe gas from reactor condensers and hence efficiency of the absorber is improved.

Efficiency of absorber in turns increases the efficiency of the whole process. Its a modification to the plant.


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SCRUBBERS

Scrubbers used in the OX-PLANT are;

TA drier scrubber

DH Column vent scrubber

OFF-gas scrubber

TA DRIER SCRUBBER

Gas and vapour from the rotary drier pass to TA drier scrubber, where acetic acid isremoved by counter current scrubbing with cold acetic acid solvent.

Entrained solids are knockout by a spray of recirculated mother liquor from MOTHER LIQUAR DRUM.

DH COLUMN SCRUBBER

The non-condensable from Solvent Dehydration Column Condenser are directed to DHColumn Scrubber.

Here methyl acetate and paraxylene are scrubbed from the gas with the cooledcondensate from DH Column Condensate Cooler (E1-611).

OFF-GAS SCRUBBER

After cooling in Combustor Cooler, the cooled gas is scrubbed in this scrubber, whereHBr and Br2 are absorbed by recirculating a dilute solution of caustic and sodiumcarbonate around two packed beds.


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DH COLUMN

Water produced in oxidation reactor, together with that added in HP & AtmosphericAbsorber is removed from acetic acid by fractionation in solvent dehydration column.

Overhead distillate from column contains water containing 0.1% w/w acetic acid and bottom product of acetic acid containing approximately 5% w/w water.

There are five streams to the DH Column.

One feed stream is a vapour from SOLVENT STRIPPER.

Others are the liquid from First Crystallizer, flash vapour from Second Crystallizer, theliquid from HP Absorber.

And from the process condensate stream from the Reactor Vent Condenser System.

The overhead vapours are condensed and sub cooled in Solvent Dehydration ColumnCondenser.

Bottom product are sent to DH Solvent Drum. From this drum this is sent to Feed MixDrum.

THERMAL OXIDIZER

It is acting as a catalyst recovery unit.

Its an old technology in which metals are burnt and ash is produced.

Catalyst is recovered,

Now it is going to be replaced by CRU (Catalyst Recovery Unit).


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REBOILERS

Reboilers used in plant are:

DH COLUMN REBOILER

STRIPPER REBOILER

DH COLUMN REBOILER

Boil up is provided by solvent dehydration column reboiler.

It is an external vertical thermosyphon reboiler using 6 barA Steam.

STRIPPER REBOILER

Heat of vapourization for stripper stillpot is provided by this suppressed vapourizationreboiler,

This reboiler operates with high tube side velocity to avoid fouling.

METHYL ACETATE RECOVERY COLUMN This column is a 15- tray column.

Excess water from DH column reflux drum overflows into this column.

Waste water through methyl acetate heater come into the column.

The column is designed to distill methyl acetate producing an overhead productcontaining 97% w/w methyl acetate and bottom stream containing 0.2% w/w methylacetate.

In this way methyl acetate is recovered.


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VALVES (GENERAL)

TYPES

Mostly used valve in the industry are:

Gate valve

Globe valve

Ball valve

Butterfly valve

GATE VALVE

Gate valves are so named because the part that either stops or allowthrough the gate act somewhat like the opening and closing of agate.

These valves are used when a straight-line flow and minimumrestriction is desired.

These valves have an extended use in the petrochemical industrydue to the fact that they can work with metal-metal sealing.

Advantages

High capacity Tight shutoff Low cost Little resistance to flow

Poor control


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GLOBE VALVE

A globe valve is a type of valve used for regulating flow in a pipeline,

consisting of a movable disk-type element and a stationary ring seat in agenerally spherical body.

Globe valves are named for their spherical body shape with the two halvesof the body being separated by an internal baffle.

This has an opening that forms a seat onto which a movable plug can be screwed in to close (or shut) the valve. The plug is also called a disc or disk. In globe valves, the plug is connected to astem which is operated by screw action in manual valves.

Advantages

Efficient throttling Accurate flow control Available in multiple ports

Disadvantages

High pressure drop More expensive than other valves

BALL VALVE

The ball valve has a spherical plug as a closure member. Seal on ball valves isexcellent, the ball contact circumferentially uniform the seat, which is usuallymade of soft materials. Ball valves are mostly used in shutoff applications. Theyare not recommended to be used in a partially open position for a long time under conditions of a high pressure drop across the valve, thus the soft seat could tend toflow through the orifice and block the valve movement.


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Low cost & High capacity Low leakage and maintenance Tight sealing with low torque

Disadvantages

Poor throttling characteristics Prone to cavitation

BUTTERFLY VALVE

Butterfly valves are quite versatile ones. They can be used at multiples industrialapplications, fluid, sizes, pressures, temperatures and connections at a relative low cost.

The development of this type of valve has been more recent than other ones. A major conviction on saving energy in the installations was an advantage for its introduction, dueits head loss is small.

The head loss is small as the flow goes aerodynamically around the disc when valve is full open

Butterfly valve can be manufactured with metallic seats that can perform at high pressure andextreme temperatures.

Advantages

Low cost and maintenance High capacity Good flow control Low pressure drop

Disadvantages

High torque required for control Prone to cavitation at lower flows


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TASK NO. 2

Understanding of ANTI SURGE CONTROL LOOP


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ANTI SURGE CONTROL LOOP

Surging

Surging is a term used to denote an un-controlled flow process in the compressor, causing strongfluctuation in pressure cyclic reversal of the direction of flow.

This can be due to two reasons:

If minimum flow is not maintained corresponding to certain discharge pressure.

If discharge pressure exceeds certain limit.

Consequences

High vibrations, Thermal stresses.

Damage to various components(bearings ,seals, even to impeller and rotors).

Repair expenditure

Production loss

Even if no damage would occur, the service life & efficiency of compressor would beinfluenced.

ANTI SURGE CONTROL

To avoid surging there is a control system called ANTI SURGE CONTROL system.

In this system there are different controllers used:

FIC-090

FC-095

PC-095


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Function

FIC-090

One signal from FT-090 and one from FC-095 comes into FIC-090. It contains integratedcircuit. When flow corresponding to certain pressure reduces to minimum value, FC-095 send asignal to FIC-090 which will further send signal to MIN. SELECTOR. This SELECTOR compared the signal from PIC-095 pressure signal and sent to solenoid valve to operate.

FC-095

Integrated circuit is installed here which do calculations telling about the minimum flowrequired against different values of pressure. It send signal to FIC-090 when minimum flow isachieved.

PC-095

From PT-095 signal comes to PC-095(Pressure limit controller). Its set point is 22-barg.As soon as pressure increases beyond 22-barg, control line is touched and anti-surge valve isopened by the action of PC-095.


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ANTI SURGE CONTROL LOOP


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HOW ANTI SURGE CONTROL LOOP WORKS?

Signal from FT-090 Is transmitted to FIC-090 as well as to FC-095. On other side signalfrom discharge of 6 th stage compressor through PT-095 is sent to pressure limit controller PC-095.

If due to some reasons the flow reaches its minimum value corresponding to certain

pressure, signal from FC-095 is sent to FIC-090 which will sent it to MIN. selector. MIN.selector compared the signal with PC-095 and minimum signal is sent to SOV-090through FY-090. And the blow-off valve is operated.

If due to some reason pressure increases and exceeds the 22-barg limit then PT-095transmit signal to pressure limit controller PC-095 and signal from here is sent to MIN.selector which will sent the signal to SOV-090 And blow-off valve is opened and pressure isreleased.

The response time of such blow off valve is just 2 seconds. Though even small openingsof valves may be sufficient to ensure that the compressor is restored to reliable operation inthe stable range.


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TASK NO.3

Calculation of Efficiency Of Multistage Compressor


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EFFICIENCY OF MULTISTAGE COMPRESSOR

There are three processes used for the calculation of compressor work.

Isothermal process

Isentropic process

Polytropic process

ISOTHERMAL PROCESS

An isothermal process is a thermodynamic process in which the temperature of the systemremains constant. The heat transfer into or out of the system typically must happen at such aslow rate that the thermal equilibrium is maintained .

For such a process, PV = Constant

ISENTROPIC PROCESS

When a process takes place in a thermodynamic system in such a way that heat exchange between the system and surroundings does not take place and the process is reversible too, then

such a process is called isentropic process.

For such a process , PV k = Constant

POLYTROPIC PROCES

A type of process in which neither the temperature nor heat are held constant. And the processis irreversible too, then the process is called a polytropic process.

For such a process , PV n = Constant

where n & k are the constants dependent on the process.


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POLYTROPIC PROCESS (MINIMIZING THE WORK)

To minimize the compressor work, one way is to reduce the friction, turbulence losses etc. Butthis way of reducing compression work would not be economical.

Economical way is to reduce the temperature during compression of gas as specific volume is proportional to the temperature.

Isentropic process involves no cooling.

Isothermal process involves maximum cooling.

Polytropic process involves some cooling .

This graph explains the above maintained points. So for an actual process, polytropic isconsidered. Moreover, the intercoolers minimizes the compression ratio and hence increasing theefficienc y.


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HOW I CALCULATE THE EFFICIENCY?

Pressure and temperatures at suction and discharge of each stage of 6 stage compressor (In barg and in degree celcius respectively) was taken from the data sheet.

To make the unit consistent for further calculation, pressure and temperature units wereconverted in SI of units (pressure in kPa and temperature in degree Kelvin).

Polytropic efficiency can be found by calculating compression work at each stage byequation below and then adding. This will give the total compression work .

Wcomp. =( nRT 1/n-1)*((P 2/P1)n-1/n -1))

where n = ln (P 2/P1)/ ln (D 2/D1)

So to calculate n, density at suction and discharge of each stage must be calculated.

Density at suction and discharge of each stage is calculated using

D = PM/RT

Where D denotes density in kg/m 3, P Denotes pressure in kPa, M denotes for molecular weight which is taken as 29 kg/mol, R value is taken as 8.314 and T denotes temperaturein degree Kelvin.

After density calculation, n is calculated using above formula.

After that compression work for each stage is calculated using above mentioned formula.

This will give us the theoretical work required. Multiply with mass flow rate andconsisting the units would give u the theoretical power required.

The following formula would give u the efficiency of MULTISTAGE COMPRESSOR.

= theoretical power calculated / actual power required * 100


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TASK NO.4

Calculation of the Efficiency of two stage Expander


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EFFICIENCY OF EXPANDER & POWER SHARING

OFF Gasses from the plant are utilized by installing a two stage expander which will thencontribute to save a considerable amount of power required by the compressor.

This process too is an polytropic process, so work delivered by expander was calculatedin the similar method as compression work for compressor.

Negative sign indicates the expansion process.

As its a two stage expander, so work delivered by the expander was calculated for bothstages using same formula as for compressor and hence power was calculated by justmultiplying the work by mass flow rate.

For efficiency, formula is just inverted as

= actual power delivered / theoretical power delivered * 100

Power sharing or contribution can be easily calculated as;

Power required by a compressor with expander, divided by power required if compressor works without expander and then multiplied by 100

This will give the % of power required by the compressor And hence power sharing of turbine was calculated by subtracting from 100.

Rest of the process of calculation is same as that for the multistage compressor.


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SPECIAL THANKS

There are other people other than the people I Acknowledged in the acknowledgment & whom Iwant to thank for their time and guidance in my internship.

MR.ZAHID

MR.ANAS

MR ALI KAMRAN

MR.ATIF

MR.WAQAS

MR.ALI ZULIFQAR

And all the other staff of LOTTE-PPTA for giving me comfortable environment during myinternship. Thanks to all of you.

Regards,

Hafiz M. Ali

Department of Chemical Engineering University of Engineering & Technology, Lahore.

final ppta report

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