SUMMER TRAINING REPORT AT UTTPAR PRADESH RAJAY VIDUAT UTPADAN

NIGAM LIMITED ANPARA SONEBHADRA

ON

“THERMEL POWER PLANT”

Submitted for partial fulfillment of award of

BACHELOR OF TECHNOLOGY

IN

MECHANICAL ENGINEERING

UNDER THE SUPERVISION OF:- COLLEGE INCHARGE:- ER.SAMIR BHATNAGAR DR. B D SAHOO (EXECUTIVE ENGINEER B.M.D. I) (H.O.D OF ME DEPARTMENT)

SUBMITTED BY:- RAGHWENDRA KU. PATHAK B.TECH ME 3rd YEAR REGD. NO. 1101320106

Acknowledgment

The result of all engineering efforts whatever from they take a direct outcome of not just

an individual’s thinking but represents the organization. The same view holds good this

seminar report.

I extended my sincere gratitude towards Er. SAMIR BHATNAGAR SIR (EXECUTIVE

ENGINEERING B.M.D.I, BTPS) for giving us invaluable knowledge & Technical guidance.

I would like to thanks Er. SAMIR BHATNAGAR SIR (EXECUTIVE ENGINEER B.M.D.I, BTPS) for

giving me their kind co-operation & inspiration to do my seminar work.

I also thanks all the staff members and my friends for their endless Help and support.

NAME OF THE STUDENT:-

RAGHWENDRA KU. PATHAK

REGD.NO. 1101320106

BRANCH:-ME 3rd YEAR

Certificate

This is certified that RAGHWENDRA KU. PATHAK student of Mechanical Engineering from

Aryan Institute of Engineering & Technology, Bhubaneswar has carried out his summer

training work during “7 MAY 2014 to 6 JUNE 2014” presented in this report entitled

“(THERMAL POWER PLANT)” under my supervision of Er. SAMIR BHATNAGAR (EXECUTIVE

ENGINEER B.M.D.I BTPS) and his entire team.

Er. SAMIR BHATNAGAR

(EXECUTIVE ENGINEER B.M.D.I BTPS)

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.

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

Project To study the general concepts and working of thermal power

plant, and its components, especially turbine.

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 4082MW, 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 parichadam. 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.

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:- A) 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. B) Ash slurry, it is a waste product which is generally provided to construction companies for road-filling etc.

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.

R.Pathak

Typewritten Text

5

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. 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.

Chronological training diary

7th May 2014 to 13thMay 2014 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. 14th May 2014 to 20thMay 2014 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, synchronization of turbine during startup, etc.

21th May2014 to 27thMay 2014 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. 28th May2014 to 6thjune 2014 This time was spent in understanding the importance and working of ash handling plant and water treatment plant.

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 formatngent 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 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 hot well 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.

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. 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 down comers to the lower inlet water

wall headers. From the inlet headers the water rises through the water walls and is eventually

turned into steam due to the heat being generated by the burners located on the front and rear

water walls (typically). As the water is turned into steam/vapor in the water walls, 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 water walls 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 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 blow down 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 de aerated, with the dissolved gases being removed by an air ejector attached to the condenser.

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 minimize 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.

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.

Feed water 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 Feed water system begins. Preheating the feed water

reduces the irreversibility’s 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 feed water 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 aeration

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.

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.

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. De mineralized 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.

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.

TURBINES A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, converts it into rotary motion. Its modern manifestation was invented by sir Charles 1884. It has almost completely replacegreater thermal efficiency and hirotary motion, it is particularly suitedall electricity generation in the worl

TYPES

Schematic operation of a steam turbine generator system

l device that extracts thermal energy from pressurized steam, n. Its modern manifestation was invented by sir Charles

almost completely replaced the reciprocating piston steam engine primarily because of it greater thermal efficiency and higher power-to-weight ratio. Because the turbine generates

motion, it is particularly suited to be used to drive an electrical generatorelectricity generation in the world is by use of steam turbines.

Schematic operation of a steam turbine generator system

l device that extracts thermal energy from pressurized steam, and n. Its modern manifestation was invented by sir Charles Parsons in

d the reciprocating piston steam engine primarily because of it weight ratio. Because the turbine generates

enerator-about 80% of

Steam turbines are made in a variety o f sizes ranging from small <1 hp (<0.75 kw) units (rare)

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

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

classifications for modern steam turbines.

Steam supply and exhaust conditions

These types include condensing, non condensing, reheat, extraction and induction. None 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.

Mounting of a steam turbine produced by Siemens

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.

Turbine efficiency

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

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 steam turbines use a mixture of the reaction and impulse steam turbines use a mixture of the reaction and impulse design; each stage behaves as either one or other, but the overall turbine uses both. Typically, higher pressure sections are impulse type and lower pressure stages are reaction type.

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

REACTION 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.

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

system along with the steam turbine. Also, a turning gear is engaged when there is no 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 disengaged and steam is admitted to the turbine, first to the astern

blades then to the ahead blades slowly rotating the

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

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

go and punching straight through the casing. It is, however, essenti

with dry steam –that is, superheated steam

into the steam and is blasted on to the blades (moisture carryover, rapid impingement and

erosion of the blades can occur leading to i

entering the blades this, 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.

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 is no steam to the

turbine to slowly rotate the turbine to ensure even heating to prevent uneven expansion. After first

turning gear, allowing time for the rotor to assume a straight plane (no

bowing) , then the turning gear is disengaged and steam is admitted to 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 are and maintenance requirements are relatively small. Any

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

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

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

into the steam and is blasted on to the blades (moisture carryover, rapid impingement and

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

entering the blades this, 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,

ains are installed in the steam piping leading to the turbine.

When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass

to heat up the lines in the

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

turbine to slowly rotate the turbine to ensure even heating to prevent uneven expansion. After first

turning gear, allowing time for the rotor to assume a straight plane (no

bowing) , then the turning gear is disengaged and steam is admitted to the turbine, first to the astern

slowly warm the turbine.

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

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

al that the turbine be turned

liquid water content. If water gets

into the steam and is blasted on to the blades (moisture carryover, rapid impingement and

mbalance and catastrophic failure. Also, water

entering the blades this, 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,

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 over speed 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 apart,

often 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.

The 210 MW Turbine of 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 design, 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.

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 connects 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 turbine are designed with integrally milled T-roots and shrouds. The last stages of lp turbine 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 root sand riveted 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. 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 clearances.

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 electro hydraulic 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 electro hydraulic 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.

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. Auxiliary 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.

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.

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.

Suggestions The plant is working fine with not many hindrances, but the main concern is the cleanliness of plant. The plant, especially 110X2 units 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 break downs. 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.

Conclusion From all the study it can be concluded that the Pariccha thermal power project of 210X2 units 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 requirementsmay proves hazardous to the turbine. Another interesting yet worrying fact is the quantity of coal consumed which approximately10800 tone 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 in reducing 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 awesme to see how all the components work in a synchronized manner.