BY- ANKIT GUPTANIT JAMSHEDPUR

an overview of thermal power plant and hp and lp heaters

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INTRODUTIONThe TATA POWER Ltd. (Tata Power) is one of the oldest private power sector utilities in our country. Till recently called Tata Electric Companies (TEC) the Tata Power Group comprised three companies.

TATA POWER Set up in 1999Andhra Valley Set up in 1916TATA Hydro Set up in 1910

These Company manages around 3200 MW of generation, transmission, and distribution business at present and has set goals to take this level to 5000 MW by the year 2008. It also intends to diversity into related infrastructure business for further growth. The Company started its operations in Jharkhand with the acquisition of 67.5 MW coal based captive power unit of TATA STEEL in April 1997. Keeping in view the industrial development of Jharkhand and modernization expansion programmes in TATA STEEL, TATA POWER decided to add two more units of 120 MW capacity each at Jamshedpur in the year 1998. The first 120 MW unit began commercial operation in February 2001 followed by the second unit in February 2002. These two units constitute the first ever IPP in the state of Jharkhand. Situated in Jojobera on the outskirts of Jamshedpur amidst green surrounding, this division of TATA POWER today is one of the most efficient and reliable power generation utilities in the eastern region.The principal customer of TATA POWER is TATA STEEL with whom the transactions done on the power purchase agreement (PPA) basic. The entire power generated is sold to TATA STEEL, which in turn utilizes it for its use as well as for supplying it to the other local industries and township. TATA POWER earns its entire revenue for TATA STEEL.

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BASIC IDEA ON THERMAL POWER GENERATIONAs we know that CARNOT CYCLE is the mother of all basic cycle. This Schematic diagram of the Carnot power cycle shows that the water is heated in the boiler and is converted into steam then this high pressure steam and high temperature steam is used to rotate the turbine which is rigidly coupled the generator. Then the low energy steam goes to the condenser which is a heat exchanger and the steam is converted into water. Then again with the help of compressor the water is again pump to the boiler and thus making the cycle to be a closed cycle.

Compressor (Pump)

Turbine

1-2: Heat addition at constant temperature in the boiler2-3: Isentropic Work done on the turbine3-4: Heat rejection in the condenser at constant temperature4-1: Isentropic Work done by the pump

Boiler

Condenser

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Carnot cycle is having the maximum efficiency. But implementing the Carnot cycle in practical situation is but possible due to the following reasons:

i) The steam is not saturated at the inlet of the turbine. And the turbine cannot handle high moist content of steam because the water droplet can cause damage to the blades of the turbine.

ii) At the inlet of the pump it is a two phase system. And to manufacture a two phase pump is not practically feasible.

iii) Low work/ heat

Due to all these reasons the practical implementation of the Carnot Cycle in Power Plants is not possible.

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Rankine Cycle

1-2: Water is pump from the Hot Well to the Deaerator through CEP (CONDENSATE EXTRACTION PUMP).2-3-10: DEAREATOR removes air from the condensate water.3-4: BOILER FEED PUMP delivers the feed water from the deaerator to the boiler.4-5-6: Feed Water enters the ECONOMISER and then to BOILER.6-7: SUPERHEAT

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7-8: High pressure and high temperature steam enters the HIGH PRESSURE TURBINE which is rigidly coupled with the generator.8-9: Steam is REHEAT9-10-11: Steam enters INTERMEDIATED PRESSURE TURBINE AND LOW PRESSURE TURBINE.11-1: Steam is then converted into water in the CONDENSOR.

RESOURCES

The fuels used for power generation are: Coal

LDD(Light Diesel Oil)

WATER

COALThe primary fuel is coal, 60% of which is procured. The balance quantity is supplied by Mahanadi ‘Coalfields Limited. The specific Coal Consumption of the division is 0.76 Kg/kwh. The two types of coal used are

Middlling Coal

RESOURCES

COAL

WATER

OIL

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(Gross calorific value= 4500 kcal/kg) MLC Coal (Gross calorific value = 2500 kcal/kg)

LDO (LIGHT DIESEL OIL)

The secondary fuel used in the Plant is Light Diesel oil. It is sourced form Indian oil corporation or HPCL or BPCL. Specific LDO Consumption of the division is 0.71 ml/kwh.Calorific value of LDO is 9000 kcal/kg.

WATER The division gets its supply of water from Raw Water pump House of TATA STEEL. The Specific water consumption of the division is 2.49 l/kwh. Raw water is treated in DM-Plant with pH limit of 5-7.5 , cond should be between 1-0.5 and silica should be upto 20 ppm.

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OVERVIEW OF JOJOBERA POWER

PLANT

1. Cooling tower. 2. Cooling water pump. 3. Transmission line (3-phase). 4. Unit transformer (3-phase). 5. Electric generator (3-phase). 6. Low pressure turbine. 7. Condensate extraction pump. 8. Condenser .9. Intermediate pressure turbine. 10. Steam governor valve. 11. High pressure turbine. 12. Deaerator . 13. Feedheater . 14. Coal conveyor. 15. Coal hopper. 16. Pulverized fuel mill. 17. Boiler drums. 18. Ash hopper. 19. Super

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heater. 20. Forced draught fan. 21. Reheater. 22. Air intake. 23. Economizer. 24. Air pre-heater. 25. Precipitator. 26. Induced draught fan. 28. Chimney Stack

PROCESS FLOW DIADRAM

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Power Generation of jojobera

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power plant is 547.5 mw UNITS COMMISSIONED CAPACITY

Unit#1 1997 67.5Unit#2 2000 120Unit#3 2001 120UNIT#4 2005 120UNIT#5 2009 120

Areas of operation Coal handling plant Boiler and turbine areas Transformer Yard Electrostatic Precipitator Switchyard

Fuel cycle

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The material used for power generation is coal, light diesel oil and water. Two types of coal are used for power generation at TATA power jojobera plant:

Middlig coal (from Bokaro ) having G.C.V of 4000 kcal.

IB valley coal (Mahanadi mines) having G.C.V of 25000 kcal.

Coal Handling Plant

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COAL HANDLING PLANT is responsible for procurement and supply of sized coal to the Coal Mill Bunkers so that supply of pulverized coal required for filling of Boiler for generation of power is maintained without interruption.

TATA POWER receives the coal through wagon.

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i) The

unloading of the coal is done through wagon trippler.

ii) Then through conveyer belt the coal goes to the primary crushing house, where the primary crushing of the coal is done.

iii)Then the uncrushed coal and the rejected coal are separated from crushed coal.

iv)Then the crushed coal goes form primary crushed to the secondary crusher through junction #5. The size of the crushed coal from the secondary crusher is about 25mm.

v) Then from junction #4 the crushed coal is stored in the crushed coal yard #1 and crushed coal yard #2.

vi)Then through reclaim hopper #1 and reclaim hopper #2 the crushed coal is again loaded into the conveyer belt. Through junction #2 #3 &#1 goes to the trippler floor.

vii) From the trippler floor the crushed coal enters into the bunker.

The uncrushed coals of irregular sizes are first initially crushed to the fineness of 25 mm^3 in the coal handling plant. From there it comes into bunkder through series of conveyer belts.Capacity of the plant : The designed capacity of CHP is 1176 TPH & the rated capacity is 1000 TPH.Conveyor System : Coal received from the Apron Feeder is processed and conveyed through a series of equipment which includes conveyors.

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FEEDER

The function of the feeder is to transfer the crushed coal from the bunker to the mill. The speed of the feeder can be monitored so that the amount of pulverized coal entering into the furnace can be controlled to meet the power production requirement at that particular time.

MILLThe mills are used to grid the crushed coal into fine pulverized coal which is then conveyed to the boiler’s furnace by the primary air. In Jojobera power plant ,XXP 783 Bowl Mills are usedWhere: X- frequency (3-phase 540Hz) R- Raymond, name of the inventor P – pressurized type with PA fan before78 – indicates the Bowl diameter in inches, 3 stands for the number of rollers.Five mills are provided for each unit.

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Bowl mills are medium speed (40-70 rpm) vertical mill. It has got three journal shaft assemblies and a Bull ring (bowl) which is used to pulverized the coal. It is rotated by a Planetary Gear Box,

WORKING

The mill receives the crushed coal from the feeder through the centre pipe. Then in trhe mill the coal is grinded by the combined effect of the bowl and the three journal shat arrangement which are at an angle of 120. The clearance between the journal shaft arrangements and the bowl should be about 200 BS Mesh (75 micron). Coal is fed to rotating bowl and thrown outward by centrifugal force to the rotating ring where it is pulverized by rolling under spring loaded rollers. Air sweeps by the bowl and removes the product to the classifier, from which large particles are returned for further grinding.

SPECIFICATIONTYPE BOWL XRP

783MADE BY BHELCAPACITY MAX36.5TP

HMIN8TPH

AIR FLOW MAX 50.5 TPH

DRIVE INDUCTION MOTOR

KW 3000RPM 966

VOLTAGE 6.6KV

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FURNANCEThe pulverized coal is then carried by the primary air from the mill to the furnace. It is conveyed to the furnace through four tables which fired the pulverized coal from each corners of the furnace.

I. There are fiver elevations A, B, C, D, E, from each mill through which each pulverized coal is fired.

II. There are the three elevations AB BC CD DE through which the oil (LDO) is fired in the initial start up time or in some emergency.

III. The firing of the pulverized coal is done at such an angle that FIRE BALL is created in the furnace. To get efficient operation three T’s – time temperature and turbulence is maintained.

IV. The furnace is made up of water walls.

CONDENSATE CYCLECONDENSATION SYSTEMThe water cycle that’s starts from the condenser hot well to the deaerator is known as condensate cycle. In the cycle the steam that is condensed in the condenser is stored in the hot well. It is then pumped by the CEP to SJAE, Gland Steam Condenser, Drain cooler, LPH1 ,LPH 2 .LPH 3 and then finally to the deaerator.

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HOT WELLAfter the condensation of steam in the condenser, the condensate water enters into the hot well. As the power plant is closed cycle, but there are some water losses due to some leakage or other factors, the level of hot well decreases. So in order to maintain the level of water in the hot well, DM water is being added as makeup of the system by water loss. This is known as HOT WLL MAKE UP.

HOT WELL Make UP PumpTwo numbers of hot well make up pump are provided to maintain hot well level, indirectly it supplies DM water to the system to make up the losses.CONDENSATE STORAGE TANK

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It serves as a storage tank for the demineralized water. It receives the DM water from the DM plant. The function of CST is :

i) CST is used for the hot well make up to maintain the hot well level.

ii) It is used to fill the boiler drum in the initial startup condition through the boiler fill pump.

iii)It is also used to fill the ACW tank through the boiler fill pump.

CONDENSATE EXTRACTON PUMP (CEP)It is seven stage pump. It is submerged in the water to provide Net Positive Suction Head (NSPH). The function of CEP is to evacuated condensate water from the hot well and supply it to the deaerator at rated pressure which is at height of 22.5m.

Serial No.

General

1. Manufacturer BHEL2. Model No. EN7H323. No. of pump 24. Type of Pump Vertical, bowl type,

multi stage5. Stages 76. Type of Suction Double suction at

first stage7. Type of coupling Flexible, spacer

type8. Type of seal Mechanical9. Type of thrust bearing Tilting pad

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type(between pump and motor)

10. Type of shaft flexible

The design capacity of the pump is 360 m^3/hr.

SJAE AND GLAND STEAM CONDENSERIt is a heat exchanger that is used to increase the condensate water temperature through the steam that these equipment uses for their functioning.

DRAIN COOLERIt also acts as a heat exchanger that is also used to increase the condensate water temperature. The drip of the LPH3 flows to LPH2 and from there it flows to LPH1. The drip is then flows to the drain cooler then it flows to LP flash tank and then to condenser. The temperature of the drip of the heaters in the drain cooler is higher than the condensate water. So the drain cooler acts as horizontal heaters for the condensate water.

LP HEATERSLow pressure heaters are a heat exchanger. In Jojobera power plant LPH are shell and tube type heaters. The function of LP heater is to extract steam from the turbine end heat the feed water to take a plant fuel efficient. Generally three LP heaters are used to

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raise the temperature of condensate water from the CEP outlet temperature to the required Deaerator inlet temperature. Thus it increases the efficiency of power plant. LPH is a horizontal tube and shell type heat exchanger which is attached with the condenser itself. Whereas LPH2 & LPH3 are vertical shell and tube type heat exchanger. The water passes through the tubes and steam flows through the shell. The extraction of LPH1 is from 7th stage of LPT.The extraction of LPH2 is from 5th stage of LPT.The extraction of LPH3 is from 3rd stage of LPT.Generally a LP heater has 2 sections.

1. Condensing section: where the steam is condensing.2. Sub Cooled section : section where the steam is

converted into waterWater path: The feed water enters into the heaters and then into the tubes. First is goes to the sub cooled section and into the condensing section. It exchanges heat as it flows thus increasing the feed water temperature.

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Steam path: The steam is extracted form IP & LP turbine and enters into the condensing section. As the steam goes further it reduces its enthalpy and thus its temperature, hence enters into subcooled region. The extracted steam is converted into drip. The drip of the LP heater goes form the high pressure (HP) heater to the LP heater. The drip of the LPH3 goes and then to LPH, from here the drip finally goes into the condenser.

FEED WATER CYCLE

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The water from the deaerator to the economizer is known as Feed water cycle. The feed water from the deaerator is stored in feed water storage tank(DFWS tank). Then it goes to the boiler Feed pump, which pump the water through HPH5 & HPH6 to the inlet of the Economizer header.

DEAERATOR

Economizer

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It is a feed water heater which derives heat from the flue gases. The flue gas leaving the LTSH is at higher temperature and has higher enthalpy. So, economizer is present in second pass to increase the plant efficiency. It is an arrangement of tubes through which fed water flows from BFP at high pressure and flue gas passes over the tubes ,thus raising the temperature of feed water. The use of economizer reduces per hour coal consumption to a great extent.

STEAM CYCLE

Hp – lp bypass system

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This by-pass system has been provided to allow the steam to build up, during startup, matching the parameters of the turbine. The steam generated is dumped into the condenser, thus avoiding loss of boiler water. The by-pass system has two sections: HP & LP. The HP bypass system diverts the main steam to the cold reheat CRH line. HP bypass system also reduced the rated steam parameters of the incoming steam from the superheaters to the steam conditions expected in the CRH line.The LP by-pass system diverts the incoming steam from the hot reheat HRH line to the condenser after reducing the HRH steam parameters to the condition approximately to that of LP turbine exhaust steam.

Gland steam condenser

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The turbine is lifted with a set of glands. Three glands are provided to reduce steam leakage to a minimum and to prevent any air ingress into the turbine. Steam leakage leads to the requirement of increased makeup. This increases the load on the feed and boiler water treatment chemicals and to a deterioration of the working environment surrounding the power plant. Air ingress leads to a loss of vacuum and hence reduction in plant efficiency and caused problems of thermal stressing around the gland as well as increases oxygen content of the exhaust steam.

HP TURBINE AND IP TURBINE GLANDSThe pressure in the HPT & LPT is quite high in comparison with the atmospheric pressure. And the clearance between the rotating shaft and the casing cannot be practically zero. This would lead to the steam leakage from the HPT& LPT. This leakage is minimized by using glands. The glands have many narrow sections. So by expanding or throttling the pressure is reduced and thus reducing the possibility to escape from the turbine. In initial start up of the unit the steam from the APRDS system is used to compensate the air pressure.

LP turbine glands.The pressure at the last stage of LP turbine is less than the atmospheric pressure. So the air can ingress from the surrounding to the turbine casing which can damage the turbine sacing due to the moisture content in the air and can also reduce the efficiency of power plant. To minimize this glands are provided, but they are not efficient enough to stop the air form entering the turbine. So, excess steam that leaks

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out to the IPT & LPT is applied from inside of LPT to compensate the effect of atmospheric air.

Steam jet air ejectorSJAE is used to maintain the vacuum in the condenser. Here in Jojobera power plant unit #1,#4 has ejector whereas rest all have vacuum pump.

WorkingThis is a simple diagram of SJAE. Here the steam of 18 from the APRDS enters into the inlet of the SJAE. SJAE has two converging and diverging nozzle where a low pressure zone is developed between the both sections.

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COOLING TOWER

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Cooling tower is very important in power plants. It is basically a heat exchanger. The primary task of the cooling tower is to reject heat to the atmosphere. The Steam that comes from the LP turbine is condensed in the condenser, so a heat exchanger is necessary in the condenser. And this is possible by using cool circulation water into the condenser, which also gain heat and becomes hot and this hot water from the condenser is sent back to cooling tower. There is loses its heat into the atmosphere.The above diagram shows the schematic diagram of the cooling water circulation. The cooling water enters into the condenser and rom there it interacts there and hot water goes to the cooling tower through the riser and from there it releases its heat into the environment and is collected into the water basin beneath the cooling tower and then goes to the CW pump and

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then the pump circulates the water back into the condenser. Thus makes the cycle a closed one. All though it is a closed one but there are some losses associated to it i.e evaporation loses or some leakage.Types of cooling towerCooling tower falls in two main categories:

i) Natural Draft: This type of cooling tower uses very large concrete chimneys. Air flow through this tower is produced by the density differential that exists between the heated air inside the stack and the relatively cool ambient air outside the tower.

ii) Mechanical Draft: Mechanical Draft towers utilize large fans to force or such air through circulated water. The water falls downward over fill surfaces, which help increase the contact time between the water and the air – this helps maximize heat transfer between the two.

Mechanical draft towers can be further sub-divided into the following types on the basis of the airflow arrangements:

Counter flows induced draft Counter flows forced draft Cross flow induced draft

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FEEDWATER HEATERA feedwater heater is a heat exchanger designed to preheat boiler feedwater by means of condensing steam extracted (or bled) from a steam turbine. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system.

RELATION TO POWER PLANT CYCLE.

The heating process by means of extraction steam is referred to as being regenerative. The feedwater heaters are an integral portion of the power plant thermodynamic cycle. Normally, there are multiple stages of feedwater heating. Each stage corresponds to a turbine extraction point. These extraction points occur at various stages of the expansion of steam through the turbines. The presence of the heaters in the cycle

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enhances the thermal efficiency of the power plant. The greater the number of extraction stages, the lower the amount of thermal energy required to generate a given amount of electrical energy. A beneficial by-product of the energy extracted by the heaters is the reduced rate of rejection of energy to the environment.

Regenerative Rankine cycleThe regenerative Rankine cycle is so named because after emerging from the condenser (possibly as a subcooled liquid) the working fluid is heated by steam tapped from the hot portion of the cycle. The process of extracting steam from the turbine at certain points during its expansion and using this steam for heating for feed water is known as Regeneration or Bleeding of steam.

The regeneration is perform in regenerator. A regenerative heat exchanger, or more commonly a regenerator, is a type of heat exchanger where heat from the hot fluid is intermittently stored in a thermal storage medium before it is transferred to the cold fluid. To accomplish this the hot fluid is brought into contact with the heat storage medium, then the fluid is displaced with the cold fluid, which absorbs the heat.

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The orientation of heaters can be horizontal or vertical(Channel Up or Down). The orientation oh heater in TATA POWER is vertical.Vertical heaters conserve less area but installation and removal is difficult than for horizontal heaters.

ZONES Zones are separate areas within the shell in a feedwater heater. Condensing Zone: All feedwaters have this zone. All of the steam is condensed in this area, and any remaining non condensable gases must be removed. A large percentage of the energy added by the heater occurs here. Subcooling Zone: The condensed steam enters this zone at the saturation temperature and is cooled by convective heat transfer from the incoming feedwater. Desuperheating Zone: The incoming steam enters this zone, giving up most of its superheat to the feedwater exiting from the heater.

In thermal power plant two type of regenerators are used.1) Low Pressure Regenerator/Heater2) High Pressure Regenerator/Heater.

Low pressure heater-It is commonly known as LP heaters. These heaters are a kind of Heat Exchanger which is used to transfer the heat energy from one fluid to another. In LP heater extracted steam, which

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is used to heat the feedwater, is from low pressure turbine. Therefore it is known as low pressure heater. LP Feed water Heater’s pressure ratings range between 30 to 100 kg/cm2.LP heater is located between the condensate pump and Deareator.The flow diagram of LP heater is shown in figure-

High pressure heater-It is generally called LP heaters. H.P. heater is installed after Boiler feed pump and it heats the feed water by exchanging heat with the steam that is extracted from the H.P. Turbine from different stages at different pressure.HP Feed water heater’s pressure ratings range from 100 to 300 kg/cm2.

Working of LP/HP Heaters-As the heat exchanger used is counter flow, shell

and tube type heat exchanger both fluid(extracted

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steam and feed water) enter in regenerator from opposite side.

Extracted steam is at high temperature and pressure than feedwater, heat transfer takes place between steam and feedwater.

Feedwater absorbs the heat rejected by steam and then go to next heater or towards their destination.

Extracted steam after rejecting heat condenses which is known as drip.

Drip goes in opposite direction of feedwater.Ex. If extracted steam rejects heat in LP3 heater then drip will go to LP2 heater, because the temperature or enthalpy of drip of LP3 is more than LP2 heater. Therefore drip of LP3 heater rejects some heat to feedwater passing through LP2 heater.

Drip of LP3 Drip of LP2LP2 Heater

LP1 HeaterTo condenser

Drip of HP6 Drip of HP5HP5

Heater

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Feedwater from CEP passes through LP heaters then BFP to HP heaters and then in economiser.

The by-pass is present in case we have to stop the working of any heaters. All by-pass are shown in flow diagram.

Drain Coolers are employed because of heat consumption improvement in case of drain introduction into the lower heater through the control valve. These types of HP Feed water Heaters have been developed to meet the increasingly severe operating conditions in large turbo generator plants. These may include high heat rates, sudden load variations and frequent start-ups and shut–downs in case of peak-load power plants.

DEAREATORHP flash tank

Condensor

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Regenerators or Heat ExchangerHeat exchangers are devices that facilitate the exchange of heat between two fluids that are at different temperature while keeping them from mixing with each other. Heat transfer in a heat exchanger usually involves convection in each fluid and conduction through the wall separating the two fluids. The rate of heat transfer between the two fluids at a location in a heat exchanger depends on the magnitude of the temperature difference at that location, which varies along the heat exchanger hence LMTD is convenient to work with.Shell and Tube type heat exchangers are used in heaters.

THE OVERALL HEAT TRANSFER COEFFICIENT A heat exchanger typically involves two flowing fluids separated by a solid wall. Heat is first transferred from the hot fluid to the wall by convection, through the wall by conduction, and from the wall to the cold fluid again by convection. Any radiation effects are usually included in the convection heat transfer coefficients.The thermal resistance network associated with this heat transfer process involves two convection and one

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conduction resistances, as shown in Figure.

I-Inner surface, o- outer surfaceR –Radius, D- Diameterk- Thermal conductivity of materialL-length of tubeA- Surface area

Total thermal resistance

Therefore heat transfer between fluids

where U is overall heat transfer coefficient

THE LOG MEAN TEMPERATURE DIFFERENCEFor counter flow heat exchanger

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CONCLUSIONTATA POWER Jojobera, Jamshedpur division was started in 1997 by acquiring the 67.5 MW captive plants (CCP) from TATA STEEL.TATA POWER, Jamshedpur division is certified to ISO 9000:2001. An ISO 14000 certifications which are a testimony to the excellent and the world class quality management and environment standards respectively, maintained by it. It is also certified by the organization Health and Safety management standards certificate, which is a standard for the safety and health on the person there.The primary fuel is coal of which 60% is obtained TATA STEEL and remaining is Mahanadi Coalfields Limited and West Bokaro. The verities of coal used in the TATA POWER are IB- Valley and Middling. The GCV (Gross Calorific Value) of valley is 27000-3300kcal/kg and ash percent is 39%. The water comes from the river Swarnarekha and is supplied by the JUSCO. The secondary fuel used is Light Diesel Oil and is outsources from the Indian Oil Corporation of JOCL or BPCL.The TATA POWER is a signatory to the UN global compact and its ten principles and countries to standby these principles and activity implements them within the scope of its business activities. It is committed to be a good corporate citizen not only in compliance with relevant laws and regulation but also by actively assisting in the improvement of quality of the people in communities in which it operates with the objective of making self-reliant.

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Such social responsibility would comprise to initiates and support community initiatives in the field of community health and family welfare, water management, vocational training education and literacy and encourage application of modern scientific and managerial techniques and expertise. This is reviewed periodically in consonance with regional priorities. The company doesn’t treat these activities as optional ones but strives to incorporate them as integral part of its business plan. The company also encourages volunteering among its employees and helps them to work in the communities.