Thermal Power Plant Training Training Report-Aniket Kaushal

ANIKET KAUSHAL

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Acknowledgment

The tree of knowledge grows best when it has sturdy roots and the strength of them is clearly

dependent upon our intentions. During the journey of knowledge we meet certain people who

play a pivotal role in our development and it’s a privilege to thank them for the same. So I would

take this opportunity in expressing gratitude towards my mentor and guide in this period of

vocational training, Mr. Summit Chaurasia. It would have been extremely difficult to cover this

course without his able guidance. Then I’m obliged to thank Mr. Pawan Tiwari sir who took the

pains and interest in explaining the nicks of the thermal power plant.

I’m ever thank full to my parents and of course god. In fact, many people have contributed to

this report and I would love to express my gratitude to all of them, like Mr. Anil Awasthi, Mr.

Chandra Prakash, Mr. Bharat Patel and many more.

Aniket Kaushal

ANIKET KAUSHAL

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Abstract

A thermal power station is a power plant in which the prime mover is steam driven. Water is

heated, turns into steam and spins a steam turbine which drives an electrical generator. After it

passes through the turbine, the steam is condensed in a condenser and recycled to where it was

heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power

stations is due to the different fuel sources. Some prefer to use the term energy center because

such facilities convert forms of heat energy into electricity. Some thermal power plants also

deliver heat energy for industrial purposes, for district heating, or for desalination of water as

well as delivering electrical power. A large part of human CO2 emissions comes from fossil

fueled thermal power plants; efforts to reduce these outputs are various and widespread. At

present 54.09% or 93918.38 MW (Data Source CEA, as on 31/03/2011) of total electricity

production in India is from Coal Based Thermal Power Station. A coal based thermal power

plant converts the chemical energy of the coal into electrical energy. This is achieved by raising

the steam in the boilers, expanding it through the turbine and coupling the turbines to the

generators which converts mechanical energy into electrical energy.

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Contents

PROJECT ……………………………………………………………………………………1

OBJECTIVES……………………………………………………………………………......2

BRIEF HISTORY/INTRODUCTION OF ORGANIZATION……………………………...3

ORGANIZATIONAL CHART……………………………………………………………...5

PLANT LAYOUT…………………………………………………………………………...6

PRODUCTS AND SPECIFICATION………………………………………………………7

PRODUCT FLOW CHART…………………………………………………………………8

CHRONOLOGICAL TRAINING DIARY…………………………………………………11

PRODUCTION PROCESS…………………………………………………………………12

TURBINE……………………………………………………………………………………23

210 MW TURBINES IN PARICCHA………………………………………………………32

MARKETING STRATEGIES………………………………………………………………37

DIVERSIFICATION OR EXPANSION……………………………………………………38

SUGGESTIONS……………………………………………………………………………..39

CONCLUSION……………………………………………………………………………....40

REFFERENCES……………………………………………………………………………..41

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Project

To study the general concepts and working of

thermal power plant, and its components,

especially turbine.

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Objectives

• To learn the basic working of thermal power plants.

• To learn about various components of the same.

• To develop the understanding of the operation and maintenance of turbines.

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Brief history

This is a project run under Uttar Pradesh Rajya Vidhyut Utpadan Nigam Ltd.

UPRVUNL is wholly owned state thermal power utility with present generating capacity of 4082

MW, operating 5 Thermal Power Stations within Uttar Pradesh. Poised to contribute in the

growth of state, we're in the process of adding further 2000 MW capacity to our existing fleet by

year 2012.

The name of this power project is paricha thermal power project its foundation war laid

in 1979 and it started producing electricity in 1983. It is a state owned semi government

project. It has four units which are generating electricity. Two no of 250MW which are

likely to be completed tip to year 2011.

Total installed capacity of the plant at present is 640 mw. The total installed capacity of the plant

will be 1140 mw in the year 2011 presently it is thermal power project of UPRVUNL.

This project is thermal based power project in which combustion of coal is used to convert water

into steam and then steam is used to rotate the turbine the rotation of turbine drives an a.c.

generator, thereby producing a.c. power.

The entire thermal power project needs continuous supply of water and thus they are built near

Betwa river. A dam has been constructed for this purpose of collection of water, by the name of

paricha

dam.

Coal is also required for this project and it is supplied from mines of BCCL, ECL.

At present, four units of Parichha are generating 640 mw of electricity.

Uttar Pradesh Rajya Vidyut Utpadan Nigam Ltd. was constituted on 25 August 1980 under the

company’s act 1956 for construction of new thermal power projects in the state sector.

On 14th Jan 2000, in accordance to up state electricity reforms acts 1999, UP state electricity

board, till then responsible for generation, transmission and distribution of power within the state

of Uttar Pradesh, was unbundled and operations of the state sector thermal power stations was

handed over to UPRVUNL.

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PLANT LOCATION IT IS LOCATED IN DISTRICT JHANSI ABOUT 25 KM BEFORE JHANSI, ON KALPI-

JHANSI ROAD. JHANSI IS WELL CONNECTED BY AIR/RAIL AND ROAD ROUTE

FROM ALL MAJOR CITIES.

ABOUT GENERATING UNITS AT PARICHHA THERMAL POWER STATION ALL THE UNITS OF THIS STATION ARE COAL FIRED THERMAL POWER PLANTS,

HAVING A TOTAL GENERATING CAPACITY OF 640 MW AND CONSISTS OF

FOLLOWING UNITS -

STAGE UNITS

NO.

ORIGINAL

CAPACITY

MW

DERATED

CAPACITY

MW

DATE OF FIRST

COMMISSIONING

ORIGINAL

EQUIPMENTS

MANUFACTURERS

1 01 110 110 31.03.1984 BHEL

02 110 110 25.02.1985 BHEL

03 210 210 25.11.2006 BHEL

04 210 210 01.12.2007 BHEL

THE COAL TO ALL THESE UNITS IS FED FROM COAL MINES OF BCCL, ECL BY

MEANS OF RAILWAYS.

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Organizational chart

CIRCLE OPERATION AND MAINTENANCE

EXECUTIVE ENGINEER

…… ……….

ASSISTANT ENGINEER

…… ………...

JUNIOR ENGINEER

….

OPERATOR (TG 2)

….

Chief Engineer

Level 2(admin.)

Chief Engineer

level 2(O&M)

Chief Engineer, Level 1

Chief Engineer level

2 (construction)

SE SE SE SE SE (CIVIL) SE(HQ)

EE EE EE EE(CIVIL) EE

AE AE AE AE(CIVIL)

AE

JE JE JE

OPERATOR OPERATOR

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Plant Layout

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Products and Specifications

Following two are the main products in a thermal power plant:-

1) Electricity

Electricity is produced at approximately 15.5 KV after which it is stepped up to 220 KV

for reduction in losses due to transmission. Then it is connected to the grid for supply.

The main client for purchasing electricity of UPRVUNL is UPPCL which is UTTAR

PRADESH POWER CORPORATION LIMITED.

2) Ash:-

Ash is the byproduct of coal after its combustion. It can be categorized in two parts:-

1) Fly ash, which is sold to cement manufacturing organizations like Diamond and

Satna. Earlier they were given away to the same, but since posses certain value,

they’re now being sold to them which generates revenues up to twenty lakhs.

2) Ash slurry, it is a waste product which is generally provided to construction

companies for road-filling etc.

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Product Flow Chart

Procedure for production of electricity is based on modified Rankine cycle. The four process of

Rankine cycle as used in thermal power plants are as follows:-

1) Heat addition in boiler.

2) Adiabatic expansion in turbines.

3) Heat rejection in condenser and,

4) Adiabatic compression in boiler feed pumps.

This may seem to be a simple enough process, but every step employs various circuits to

accomplish the required conditions for the fore told steps. Certain circuits are as follows,

Fuel and Ash Circuit.

Air and Gas Circuit.

Feed water and Steam Circuit.

Cooling Water Circuit.

Various methods are employed to increase the efficiency of classical rankine cycle by

adding devices like air-preheater, economizer, superheater etc.

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MILLS

SUPER HEATED STEAM

ENERGY (MECHANICAL) ELECTRICITY

CW HW

Above is the flow chart of production of electricity in a thermal power plant.

The input at boiler is the DM water and pulverized coal with air. The DM water is prepared in

the water treatment plant facility where it is deionized and deareated. It prepared in the scale of

neutral liquid i.e. 7ph, although, slightly basic nature is used.

PULVERISED COAL DM WATER

BOILER FEED PUMP

BOILER

HP TURBNE IP TURBINE LP TURBINE

CONDENSER

WATER TREATMENT

PLANT

COAL TREATMENT

PLANT

ASH TREATMENT

PLANT

COOLING TOWER

GENERATOR TRANSFORMER

TRANSMISSION

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The coal is prepared at coal handling plant, where it first arrives in wagons. The coal is taken

out from wagons with the help of a machine known as wagon tippler. The coal is the picked and

sent to crushers, where it crushed and then to bunkers. From bunkers the coal moves on to mills

and is finely grounded to a pulverized form and the fed to the boiler. Then this coal is fed to the

boiler and combustion takes place. The energy of the combustion is helpful in transforming the

water into the steam. This steam is then used to drive the turbine, the turbine shaft drives the

generator. Hence electricity is developed.

The other product, which is ash, is fed into the ash treatment plant and flue gasses are

expelled in the atmosphere.

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Chronological training diary

22nd

June 2011 to 28th

June 2011

This week was dedicated to familiarization with power plant, a basic understanding was

developed of the flow of various elements in the production cycle, like flow of steam, DM water,

clarified cooling water, coal and flue gases.

29th

June 2011 to 5th

July 2011

This week was dedicated in the study of installed 210 MW turbines. Various concepts regarding

turbine were studied like axial shift, casing expansion, barring gear mechanism, synchronisation

of turbine during startup, etc.

6th

July 2011 to 12th

July 2011

We spent this week with familiarization with coal handling plant, learning flow of coal in it and

the methods and processes of converting large sized coal to a form of powder.

13th

July 2011 to 19th

July 2011

This time was spent in understanding the importance and working of ash handling plant and

water treatment plant.

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Production process

Diagram of a typical coal-fired thermal power station

In a coal based power plant coal is transported from coal mines to the power plant by railway in

wagons or in a merry-go-round system. Coal is unloaded from the wagons to a moving

underground conveyor belt. This coal from the mines is of no uniform size. So it is taken to the

Crusher house and crushed to a size of 25mm. From the crusher house the coal is either stored in

dead storage( generally 20 days coal supply) which serves as coal supply in case of coal supply

bottleneck or to the live storage(8 hours coal supply) in the raw coal bunker in the boiler house.

Raw coal from the raw coal bunker is supplied to the Coal Mills by a Raw Coal Feeder. The Coal

Mills or pulverizer pulverizes the coal to 200 mesh size. The powdered coal from the coal mills

is carried to the boiler in coal pipes by high pressure hot air. The pulverized coal air mixture is

burnt in the boiler in the combustion zone.

Generally in modern boilers tangential firing system is used i.e. the coal nozzles/ guns form

tangent to a circle. The temperature in fire ball is of the order of 1300 deg.C. The boiler is a

water tube boiler hanging from the top. Water is converted to steam in the boiler and steam is

separated from water in the boiler Drum. The saturated steam from the boiler drum is taken to

the Low Temperature Superheater, Platen Superheater and Final Superheater respectively for

superheating. The superheated steam from the final superheater is taken to the High Pressure

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Steam Turbine (HPT). In the HPT the steam pressure is utilized to rotate the turbine and the

resultant is rotational energy. From the HPT the out coming steam is taken to the Reheater in the

boiler to increase its temperature as the steam becomes wet at the HPT outlet. After reheating

this steam is taken to the Intermediate Pressure Turbine (IPT) and then to the Low Pressure

Turbine (LPT). The outlet of the LPT is sent to the condenser for condensing back to water by a

cooling water system. This condensed water is collected in the Hotwell and is again sent to the

boiler in a closed cycle. The rotational energy imparted to the turbine by high pressure steam is

converted to electrical energy in the Generator.

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Principal

Coal based thermal power plant works on the principal of Modified Rankine Cycle.

Components of Coal Fired Thermal Power Station:

Fuel preparation system

In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into

small pieces and then conveyed to the coal feed hoppers at the boilers. The coal is next

pulverized into a very fine powder. The pulverizers may be ball mills, rotating drum grinders, or

other types of grinders.

Air path

External fans are provided to give sufficient air for combustion. The forced draft fan takes air

from the atmosphere and, first warming it in the air preheater for better combustion, injects it via

the air nozzles on the furnace wall.

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The induced draft fan assists the FD fan by drawing out combustible gases from the furnace,

maintaining a slightly negative pressure in the furnace to avoid backfiring through any opening.

Boiler furnace and steam drum

Once water inside the boiler or steam generator, the process of adding the latent heat of

vaporization or enthalpy is underway. The boiler transfers energy to the water by the chemical

reaction of burning some type of fuel.

The water enters the boiler through a section in the convection pass called the economizer. From

the economizer it passes to the steam drum. Once the water enters the steam drum it goes down

the downcomers to the lower inlet waterwall headers. From the inlet headers the water rises

through the waterwalls and is eventually turned into steam due to the heat being generated by the

burners located on the front and rear waterwalls (typically). As the water is turned into

steam/vapor in the waterwalls, the steam/vapor once again enters the steam drum. The

steam/vapor is passed through a series of steam and water separators and then dryers inside the

steam drum. The steam separators and dryers remove water droplets from the steam and the

cycle through the waterwalls is repeated. This process is known as natural circulation.

The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot blowers,

water lancing and observation ports (in the furnace walls) for observation of the furnace interior.

Furnace explosions due to any accumulation of combustible gases after a trip-out are avoided by

flushing out such gases from the combustion zone before igniting the coal.

The steam drum (as well as the superheater coils and headers) have air vents and drains needed

for initial startup. The steam drum has internal devices that removes moisture from the wet steam

entering the drum from the steam generating tubes. The dry steam then flows into the superheater

coils.

Superheater

Coal based power plants can have a superheater and/or reheater section in the steam generating

furnace. Nuclear-powered steam plants do not have such sections but produce steam at

essentially saturated conditions. In a coal based plant, after the steam is conditioned by the

drying equipment inside the steam drum, it is piped from the upper drum area into tubes inside

an area of the furnace known as the superheater, which has an elaborate set up of tubing where

the steam vapor picks up more energy from hot flue gases outside the tubing and its temperature

is now superheated above the saturation temperature. The superheated steam is then piped

through the main steam lines to the valves before the high pressure turbine.

Reheater

Power plant furnaces may have a reheater section containing tubes heated by hot flue gases

outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go inside the

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reheater tubes to pickup more energy to go drive intermediate or lower pressure turbines. This is

what is called as thermal power.

Fly ash collection

Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag

filters (or sometimes both) located at the outlet of the furnace and before the induced draft fan.

The fly ash is periodically removed from the collection hoppers below the precipitators or bag

filters. Generally, the fly ash is pneumatically transported to storage silos for subsequent

transport by trucks or railroad cars.

Bottom ash collection and disposal

At the bottom of the furnace, there is a hopper for collection of bottom ash. This hopper is

always filled with water to quench the ash and clinkers falling down from the furnace. Some

arrangement is included to crush the clinkers and for conveying the crushed clinkers and bottom

ash to a storage site.

Boiler make-up water treatment plant and storage

Since there is continuous withdrawal of steam and continuous return of condensate to the boiler,

losses due to blowdown and leakages have to be made up to maintain a desired water level in the

boiler steam drum. For this, continuous make-up water is added to the boiler water system.

Impurities in the raw water input to the plant generally consist of calcium and magnesium salts

which impart hardness to the water. Hardness in the make-up water to the boiler will form

deposits on the tube water surfaces which will lead to overheating and failure of the tubes. Thus,

the salts have to be removed from the water, and that is done by a water demineralising treatment

plant (DM). A DM plant generally consists of cation, anion, and mixed bed exchangers. Any

ions in the final water from this process consist essentially of hydrogen ions and hydroxide ions,

which recombine to form pure water. Very pure DM water becomes highly corrosive once it

absorbs oxygen from the atmosphere because of its very high affinity for oxygen.

The capacity of the DM plant is dictated by the type and quantity of salts in the raw water input.

However, some storage is essential as the DM plant may be down for maintenance. For this

purpose, a storage tank is installed from which DM water is continuously withdrawn for boiler

make-up. The storage tank for DM water is made from materials not affected by corrosive water,

such as PVC. The piping and valves are generally of stainless steel. Sometimes, a steam

blanketing arrangement or stainless steel doughnut float is provided on top of the water in the

tank to avoid contact with air. DM water make-up is generally added at the steam space of the

surface condenser (i.e., the vacuum side). This arrangement not only sprays the water but also

DM water gets deaerated, with the dissolved gases being removed by an air ejector attached to

the condenser.

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Steam turbine-driven electric generator

Rotor of a modern steam turbine, used in a power station

The steam turbine-driven generators have auxiliary systems enabling them to work satisfactorily

and safely. The steam turbine generator being rotating equipment generally has a heavy, large

diameter shaft. The shaft therefore requires not only supports but also has to be kept in position

while running. To minimise the frictional resistance to the rotation, the shaft has a number of

bearings. The bearing shells, in which the shaft rotates, are lined with a low friction material like

Babbitt metal. Oil lubrication is provided to further reduce the friction between shaft and bearing

surface and to limit the heat generated.

Barring gear

Barring gear (or “turning gear”) is the mechanism provided to rotate the turbine generator shaft

at a very low speed after unit stoppages. Once the unit is “tripped” (i.e., the steam inlet valve is

closed), the turbine coasts down towards standstill. When it stops completely, there is a tendency

for the turbine shaft to deflect or bend if allowed to remain in one position too long. This is

because the heat inside the turbine casing tends to concentrate in the top half of the casing,

making the top half portion of the shaft hotter than the bottom half. The shaft therefore could

warp or bend by millionths of inches.

This small shaft deflection, only detectable by eccentricity meters, would be enough to cause

damaging vibrations to the entire steam turbine generator unit when it is restarted. The shaft is

therefore automatically turned at low speed (about one percent rated speed) by the barring gear

until it has cooled sufficiently to permit a complete stop.

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Condenser

Diagram of a typical water-cooled surface condenser

The surface condenser is a shell and tube heat exchanger in which cooling water is circulated

through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is

cooled and converted to condensate (water) by flowing over the tubes as shown in the adjacent

diagram. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous

removal of air and gases from the steam side to maintain vacuum.

For best efficiency, the temperature in the condenser must be kept as low as practical in order to

achieve the lowest possible pressure in the condensing steam. Since the condenser temperature

can almost always be kept significantly below 100 °C where the vapor pressure of water is much

less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-

condensible air into the closed loop must be prevented. Plants operating in hot climates may have

to reduce output if their source of condenser cooling water becomes warmer; unfortunately this

usually coincides with periods of high electrical demand for air conditioning.

The condenser generally uses either circulating cooling water from a cooling tower to reject

waste heat to the atmosphere, or once-through water from a river, lake or ocean.

Feedwater heater

In the case of a conventional steam-electric power plant utilizing a drum boiler, the surface

condenser removes the latent heat of vaporization from the steam as it changes states from

vapour to liquid. The heat content (joules or Btu) in the steam is referred to as enthalpy. The

condensate pump then pumps the condensate water through a Air ejector condenser and Gland

steam exhauster condenser. From there the condensate goes to the deareator where the

condenstae system ends and the Feedwater system begins.

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Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore

improves the thermodynamic efficiency of the system.This reduces plant operating costs and also

helps to avoid thermal shock to the boiler metal when the feedwater is introduced back into the

steam cycle.

Deaerator

A steam generating boiler requires that the boiler feed water should be devoid of air and other

dissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal.

Generally, power stations use a deaerator to provide for the removal of air and other dissolved

gases from the boiler feedwater. A deaerator typically includes a vertical, domed deaeration

section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler

feedwater storage tank

Cooling tower

A cooling tower is a heat rejection device, which extracts waste heat to the atmosphere though

the cooling of a water stream to a lower temperature. The type of heat rejection in a cooling

tower is termed “evaporative” in that it allows a small portion of the water being cooled to

evaporate into a moving air stream to provide significant cooling to the rest of that water stream.

The heat from the water stream transferred to the air stream raises the air’s temperature and its

relative humidity to 100%, and this air is discharged to the atmosphere. Evaporative heat

rejection devices such as cooling towers are commonly used to provide significantly lower water

temperatures than achievable with “air cooled” or “dry” heat rejection devices, like the radiator

in a car, thereby achieving more cost-effective and energy efficient operation of systems in need

of cooling.

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The cooling towers are of two types: -

1. Natural Draft Cooling Tower

2. Mechanized Draft Cooling Tower

i. Forced Draft cooling tower

ii. Induced Draft cooling tower

iii. Balanced Draft cooling tower

Auxiliary systems

Oil system

An auxiliary oil system pump is used to supply oil at the start-up of the steam turbine generator.

It supplies the hydraulic oil system required for steam turbine’s main inlet steam stop valve, the

governing control valves, the bearing and seal oil systems, the relevant hydraulic relays and other

mechanisms.

At a preset speed of the turbine during start-ups, a pump driven by the turbine main shaft takes

over the functions of the auxiliary system.

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Generator heat dissipation

The electricity generator requires cooling to dissipate the heat that it generates. While small units

may be cooled by air drawn through filters at the inlet, larger units generally require special

cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, is used because it has the

highest known heat transfer coefficient of any gas and for its low viscosity which reduces

windage losses. This system requires special handling during start-up, with air in the chamber

first displaced by carbon dioxide before filling with hydrogen. This ensures that the highly

flammable hydrogen does not mix with oxygen in the air.

The hydrogen pressure inside the casing is maintained slightly higher than atmospheric pressure

to avoid outside air ingress. The hydrogen must be sealed against outward leakage where the

shaft emerges from the casing. Mechanical seals around the shaft are installed with a very small

annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to prevent the

hydrogen gas leakage to atmosphere.

The generator also uses water cooling. Since the generator coils are at a potential of about 22 kV

and water is conductive, an insulating barrier such as Teflon is used to interconnect the water

line and the generator high voltage windings. Demineralized water of low conductivity is used.

Generator high voltage system

The generator voltage ranges from 11 kV in smaller units to 22 kV in larger units. The generator

high voltage leads are normally large aluminum channels because of their high current as

compared to the cables used in smaller machines. They are enclosed in well-grounded aluminum

bus ducts and are supported on suitable insulators. The generator high voltage channels are

connected to step-up transformers for connecting to a high voltage electrical substation (of the

order of 115 kV to 520 kV) for further transmission by the local power grid.

The necessary protection and metering devices are included for the high voltage leads. Thus, the

steam turbine generator and the transformer form one unit. In smaller units, generating at 11 kV,

a breaker is provided to connect it to a common 11 kV bus system.

Other systems

Monitoring and alarm system

Most of the power plant operational controls are automatic. However, at times, manual

intervention may be required. Thus, the plant is provided with monitors and alarm systems that

alert the plant operators when certain operating parameters are seriously deviating from their

normal range.

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Battery supplied emergency lighting and communication

A central battery system consisting of lead acid cell units is provided to supply emergency

electric power, when needed, to essential items such as the power plant’s control systems,

communication systems, turbine lube oil pumps, and emergency lighting. This is essential for a

safe, damage-free shutdown of the units in an emergency situation.

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TURBINES

A steam turbine is a mechanical device that extracts

and converts it into rotary motion. Its modern manifestation was invented by

Parsons in 1884.

It has almost completely replaced the

greater thermal efficiency and higher

motion, it is particularly suited to be used to drive an

electricity generation in the world is by use of steam turbines.

TYPES

Schematic operation of a steam turbine generator system

Steam turbines are made in a variety of sizes ranging from small <1

used as mechanical drives for pumps, compressors and other shaft driven equipment, to

2,000,000 hp (1,500,000 kW) turbines used to generate electricity. There are several

classifications for modern steam turbines.

23

is a mechanical device that extracts thermal energy from pressurized

and converts it into rotary motion. Its modern manifestation was invented by Sir Charles

It has almost completely replaced the reciprocating piston steam engine primarily because of its

greater thermal efficiency and higher power-to-weight ratio. Because the turbine generates

, it is particularly suited to be used to drive an electrical generator – about 80% of all

electricity generation in the world is by use of steam turbines.

Schematic operation of a steam turbine generator system

Steam turbines are made in a variety of sizes ranging from small <1 hp (<0.75 kW) units (rare)

nical drives for pumps, compressors and other shaft driven equipment, to

kW) turbines used to generate electricity. There are several

classifications for modern steam turbines.

pressurized steam,

r Charles

primarily because of its

. Because the turbine generates rotary

bout 80% of all

kW) units (rare)

nical drives for pumps, compressors and other shaft driven equipment, to

kW) turbines used to generate electricity. There are several

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Steam supply and exhaust conditions

These types include condensing, non condensing, reheat, extraction and induction.

Non condensing or back pressure 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. These are commonly found at refineries, district heating units, pulp and paper plants,

and desalination facilities where large amounts of low pressure process steam are available.

Condensing turbines are most commonly found in electrical power plants. These turbines

exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well

below atmospheric to a condenser.

Reheat turbines are also used almost exclusively in electrical power plants. 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.

Extracting type turbines are common in all applications. In an extracting type turbine, steam is

released from various stages of the turbine, and used for industrial process needs or sent to

boiler feed water 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.

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Mounting of a steam turbine produced bySiemens

Casing or shaft arrangements

These arrangements include single casing, tandem compound and cross compound turbines.

Single casing units are the most basic style where a single casing and shaft are coupled to a

generator. Tandem compound are used where two or more casings are directly coupled together

to drive a single generator. A cross compound turbine arrangement features two or more shafts

not in line driving two or more generators that often operate at different speeds. A cross

compound turbine is typically used for many large applications.

Principal of design and operation

An ideal steam turbine is considered to be an isentropic process, or constant entropy process, in

which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving

the turbine. No steam turbine is truly “isentropic”, however, with typical isentropic efficiencies

ranging from 20%-90% based on the application of the turbine. The interior of a turbine

comprises several sets of blades, or “buckets” as they are more commonly referred to. One set of

stationary blades is connected to the casing and 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.

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Turbine efficiency

Schematic diagram outlining the difference between

To maximize turbine efficiency the steam is expanded, doing work, in a number of stages. These

stages are characterized by how the energy is extracted from them and are known as either

impulse or reaction turbines. Most st

designs: each stage behaves as either one or the other, but the overall turbine uses both.

Typically, higher pressure sections are impulse type and lower pressure stages are reaction type.

26

Schematic diagram outlining the difference between an impulse and a reaction turbine



impulse or reaction turbines. Most steam turbines use a mixture of the reaction and impulse



an impulse and a reaction turbine



eam turbines use a mixture of the reaction and impulse



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Impulse turbines

An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets

contain significant kinetic energy, which the rotor blades, shaped like buckets, 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 has 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 loss".

Types of turbine blades

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REATION TURBINES

In the reaction turbine, 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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Operation and maintenance

When warming up a steam turbine for use, the main steam stop valves (after the boiler) 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. Also, a turning gear is engaged when there

steam to the turbine to slowly rotate the turbine to ensure even heating to prevent uneven

expansion. After first rotating the turbine by the turning gear, allowing time for the rotor to

assume a straight plane (no bowing), then the turning gear is d

the turbine, first to the astern blades then to the ahead blades slowly rotating the turbine at 10 to

15 RPM to slowly warm the turbine.

A modern steam turbine generator installation

Problems with turbines are now rar

imbalance of the rotor can lead to vibration, which in extreme cases can lead to a blade letting go

and punching straight through the casing. It is, however, essential that the turbine be turned with

dry steam - that is, superheated steam with a minimal liquid water content. If water gets into the

steam and is blasted onto the blades (moisture carryover), rapid impingement and erosion of the

blades can occur leading to imbalance and catastrophic failu

will result in the destruction of the thrust bearing for the turbine shaft. To prevent this, along

with controls and baffles in the boilers to ensure high quality steam, condensate drains are

installed in the steam piping leading to the turbine.

Speed regulation

The control of a turbine with a governor is essential, as turbines need to be run up slowly, to

prevent damage while some applications (such as the generation of alternating current electricity)

require precise speed control. Uncontrolled acceleration of the turbine rotor can lead to an

overspeed trip, which causes the nozzle valves that control the flow of steam to the turbine to

close. If this fails then the turbine may continue accelerating until it breaks apa

29

turbine for use, the main steam stop valves (after the boiler) have a


lines in the system along with the steam turbine. Also, a turning gear is engaged when there



assume a straight plane (no bowing), then the turning gear is disengaged and steam is admitted to


15 RPM to slowly warm the turbine.

A modern steam turbine generator installation

Problems with turbines are now rare and maintenance requirements are relatively small. Any



that is, superheated steam with a minimal liquid water content. If water gets into the


blades can occur leading to imbalance and catastrophic failure. Also, water entering the blades



g leading to the turbine.



Uncontrolled acceleration of the turbine rotor can lead to an


close. If this fails then the turbine may continue accelerating until it breaks apart, often

turbine for use, the main steam stop valves (after the boiler) have a


lines in the system along with the steam turbine. Also, a turning gear is engaged when there is no



isengaged and steam is admitted to


e and maintenance requirements are relatively small. Any



that is, superheated steam with a minimal liquid water content. If water gets into the


re. Also, water entering the blades





Uncontrolled acceleration of the turbine rotor can lead to an


rt, often

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spectacularly. Turbines are expensive to make, requiring precision manufacture and special

quality materials. During normal operation in synchronization with the electricity network,

power plants are governed with a five percent droop speed control. This means the full load

speed is 100% and the no-load speed is 105%. This is required for the stable operation of the

network without hunting and drop-outs of power plants. Normally the changes in speed are

minor. Adjustments in power output are made by slowly raising the droop curve by increasing

the spring pressure on a centrifugal governor. Generally this is a basic system requirement for all

power plants because the older and newer plants have to be compatible in response to the

instantaneous changes in frequency without depending on outside communication.

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The 210 MW Turbine of Parichha Thermal Power Project

Since I got specially assigned to the turbine department, I had the privilege of understanding

turbines more closely. Apart from the kind of turbine employed, its specifications, I came across

various concepts regarding the steam turbines like axial shift, casing expansion and learnt about

the same.

The turbine used for electricity generation is a three cylinder- reheat- condensing turbine. This

name means that the turbine assembly is made of three turbines, namely:-

1) HP turbine (high pressure turbine)

2) IP turbine (intermediate pressure turbine)

3) LP turbine (low pressure turbine)

The term reheat is used to imply that the steam, after passing the hp turbine and before entering

the ip turbine, is reheated by passing it through the boiler again.

Since the previous introduction we are well aware of the importance of a turbine and its working

in a power plant. There are various other aspects like axial shift, casing expansion, bearings,

turbine lubrication etc.

Turbine requires perfect conditions to work efficiently. The manufacturer of turbine is BHEL

which is abbreviation of BHARAT HEAVY ELECTRICALS LTD. The turbine is based on

KWU desigh, which stands for KRAFT WORKS UNION. The given manufacturer as specified

certain condition for turbine working and certain specification of the same, which are as follows.

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TECHNICAL SPECIFICATION OF 210 MW STEAM TURBINE

SL.NO DESCRIPTION PARAMETER

1 RATED CAPACITY 210 MW

2 PRESSURE AT STOP VALVE 150 KG/CM2

3 TEMPERATURE AT STOP VALVE 535 C

4 MAX. STEAM FLOW AT S.V 641 TONNES /HR

5 REHEAT/NON REHEAT REHEAT

6 TYPE OF GOVERNING THROTLLE CONTROL

7 TURBINE SPEED 3000 RPM

8 EXHAUST PRESSURE 76 MM HG.ABS

9 NUMBER OF CYLINDERS

H.P-1,DOUBLE FLOW

IP-1,DOUBLE FLOW

LP-1

10 NUMBER OF STAGES

HP-25, IP-20 +20,LP-

8+8

11 HEIGHT OF LAST STAGE BLADE 676 MM

12 LAST STEAGE MEAN DIA 2132 MM

13

SPECIAL FEATURE

-DOUBLE SHELL HP

WITH BARREL TYPE

OUTER SHELL -

DOUBLE SHELL

DOUBLE FLOW IP -

HYDRAULIC BARRING

- ELECTRO-

HYDRAULIC

GOVERNING

14 WEIGHT OF TURBINE 425 TONNES

15 LENGTH OF TURBINE 14.1 METERS

16 TYPE OF TURBINE REACTION

17 COLLABORATOR SIEMENS, GERMANY

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Construction

The turbine is a tandem compound machine which separates the hp, ip and lp sections. The hp

section is single flow while ip & lp are dual flow. The turbine rotor and generator rotor are

connected by rigid couplings.

The hp turbine is throttle controlled, the steam is entered ahead of blades via combination of two

stop and control valves. A swing check valve is installed between the exhaust and the reheater, to

prevent the flow of hot steam back into the hp turbine. The steam coming from reheater is passed

to ip turbine via combination of two reheat stop and control valves. Cross around pipes connect

the ip and lp cylinders. Connections are provided at several point of turbine for feed water

extraction.

HP TURBINE

The outer casing of turbine is of barrel type, which has neither axial nor a radial flange. This

prevents mass concentration which would cause high thermal stresses. The inner turbine is

axially split, which is accommodate thermal expansion.

IP TURBINE

The ip turbine is a dual flow turbine, with horizontally split casings. This is to facilitate thermal

movement of inner casing within outer casing.

LP TURBINE

The lp turbine is dual flow. It has a three shell design which are horizontally split and are of rigid

welded construction. The innermost shell, which carries first row of stationary blades, is

supported, so as to allow the thermal expansion of inner shell within intermediate shell.

BLADING

The entire turbine provided with reaction blading. The moving blades of hp and ip turbine

and the blades of front rows of lp trurbine are designed with integrally milled T-roots and

shrouds. The last stages of lp turpine are fitted with a twisted drop-forged moving blades with

firtree roots engaging in corresponding grooves in rotor.

Highly stressed guide blades of hp and ip parts have inverted T roots and shrouding are

machined from one piece like the moving blades. The other guide blades have inverted L roots

and rivetted shrouding. The last three stages of lp turbine have fabricated guide blades.

BEARINGS

The HP rotor is supported on two bearings, a journal bearing on its front end and a combined

journal and thrust bearing immediately next to the coupling of the ip rotor.

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The ip and lp rotors have journal bearings at each of their rear ends. The combined journal and

thrust bearings incorporates a journal bearing and a thrust bearing which takes up residual thrust

from both direction. The bearing metal temperatures are measured by thermocouples directly

under the babbit lining. The temperature of the bearing is measured in the two opposite thrust

pads on each side.

SHAFT SEAL ANF BLADE TIP SEALING

All shaft seals, which seal the steam from the outer atmosphere are axial flow labyrinth type

seals. They consists of a large number of thin strips of seals which, in hp and ip turbine are

caulked alternately into the grooves in the shafts and the surrounding seal rings. In the lp turbine,

the seals are caulked only into seal rings. Seal strips of similar design are also used to seal the

radial blade tip clearences.

VALVES

The hp turbine is fitted with two main stop and control valves. One main stop valve and control

valve with stems arranged at right angles to each other, are combined in the common body. The

main stop valves are single seat spring action valves. The control valves are also single seat

valves but use diffuser a reduce the pressure losses.

The ip turbine has two reheat stop valves and control valves. The reheat stop valves are single

seat spring action valve, while the control valves are single seat valves loaded with diffusers. The

control valves operate in parallel and are completely open in the upper load range.

The main, reheat and control valves are supported free to move in thermal expansion. All the

valves are operated by individual hydraulic servomotors.

TURBINE CONTROL SYSTEM

The turbine has an electrohydraulic control system backed up with hydraulic governing system.

An electric system measures the speed and output and controls them by operating the control

valves hydraulically via controller electrohydraulic converter. The electro hydraulic controller

ensure controlled acceleration of the turbine generator up to the rated speed and prevents the

over shooting of speed in case of sudden load rejections. The linear power frequency droop

characteristics can be adjusted in fine steps even when the turbine is running.

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TURBINE MONITORING SYSTEM

In addition to measuring and display instruments for pressure, temperatures, valve lifts and speed

etc.. the monitoring system also includes the instruments for measuring and indicating the

following parameters:-

• Absolute expansion measured at the front and rear bearing pedestal of the hp turbine.

• Differential expansion of hp and ip turbines.

• Rotor expansion measured at the rear bearing pedestal of the lp turbine.

• Axial shift measured at the hp-ip pedestal.

• Bearing pedestal vibration, measured at all turbine bearings.

• Shaft vibration measured at all turbine bearings.

Turbine Stress Controller is provided to monitor thermal stresses in vital turbine components.

OIL SUPPLY SYSTEM

A single oil supply system lubricates and cool the bearings, governs the machine, operates the

hydraulic actuators and the safety and the protective devices and the drives the hydraulic timing

gear. The main oil pump is driven by turbine shaft and draws oil from main oil tank. Auxillary

oil pumps maintain the oil supply on start-up and shut down, during turning gear operation and

when the main oil pump is faulted.

When the turning is started a jacking oil pump forces high pressure oil under the shaft journals

the prevent boundary lubrication. The lubricating and cooling oil is passed through oil coolers

before entering the bearings.

AXIAL SHIFT

The axial shift is the measure of axial displacement of the shaft within the thrust bearing. Axial

shift is set at zero when thrust is at the center of the axial clearance at the thrust pads. Axial shift

towards generator is positive and towards generator is negative. Alarm and tripping is provided

when the axial shift reading exceeds the set value.

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MARKETTING STRATEGIES

The UPRVUNL, is the sister organization of UPPCL, hence all of the electricity generated is

sold to UPPCL at a fixed rate which is decided by UP State Electricity Regulatory Authority.

The other by product, which is fly-ash, is sold to various cement factories like Diamond factory

and cement factory of Satna.

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Diversification or Expansion

The Parichha thermal power project is in a constant state of expansion in context to the power

produced. Earlier the plant was of the capacity of 110X2 MW only.

Its power output was increased to the capacity of 640MW by installation of 210X2 MW units.

The development is not stopped yet, there is installation 250X2 MW units underway and are

expected to be operational with in some time.

Due to aggressive policy of government in power sector, the power sector is going to show

aggressive growth in the coming years.

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Suggestions

The plant is working fine with not many hindrances, but the main concern is the cleanliness of

plant.

The plant, especially 110X2 unit building of the plant is not clean enough. What I believe is that

cleaner environment might help in improving of productivity and decrease the rate of

breakdowns.

This might improve the efficiency of the unit as lesser number of foreign elements will be

present which prevent the proper functioning of the unit. If the efficiency increases, the coal

consumption will be reduced for the same load and that would provide a better profit to the

organization.

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Conclusion

From all the study it can be concluded that the Pariccha thermal power project of 210X2 unit is a

fairly organized unit with the latest machinery available.

The turbine is a very sophisticated assembly of machinery which requires specific conditions of

steam temperature and pressure to work efficiently. Any alteration of the specific requirements

may prove hazardous to the turbine.

Another interesting yet worrying fact is the quantity of coal consumed, which approximately

10800 tonne per day. The level of pollution is always controlled according the established norms,

but still I consider it to be quite enough. Well, efforts are always underway inreducing the

pollution and improving the efficiency of the plant.

All in all, a thermal power project is very large establishment with many components and it awes

me to see how all the components work in a synchronized manner.

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References

• Steam turbine for power generation NPTI.

• Wikipedia

• indianpowersector.com

• www.uprvunl.com

Documents

Thermal Power Plant Training Training Report-Aniket Kaushal