RE: THERMAL POWER PLANT
|| THERMAL POWER PLANT
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For the power generation with 2x110 MW and 3x210 MW of K.T.P.S. authorities are required to be operative to active full operation. The auxiliaries are basically operation either on L.T. System i.e. 415 V 3 Ø power supply is made available to the system after providing the station transformer of 3x50 MVA capacity with voltage 220 KV/ 7.2/7.2 KV & different service transformers of capacity 1.0 MVA , 1.5 MVA , 2.0 MVA , which are located near the load centre as the transformer having the voltage of 6.6 KV /415 V. The 6.6 KV power is distributed through 6.6 KV interconnected Bus System for all the five units with a control through DC of 220 V.
The 415 V power supply is done through a L.T. SWGR (Switchgear) which are located nearby the distribution transformer as well as the load centers. The all in -comers, which are breaker controlled , are having the control the L.T. SWGR are having the control system on 110/ 220 V AC. The 6.6 KV power supply which are either MOCB (Minimum Oil Circuit Breaker) of JYOTI MAKE or Air Circuit Breakers.
The 6.6 KV power supply to various draining equipment’s i.e. more is made through breakers which are either MOCB of Jyoti make air circuit breaker which are either of voltage makers as well as SF 6 of NGEF make. The LT supply is also controlled through air break circuit breaker which are either L&T make or English Electric Company of India. The various H.T. motors are switched on / started through on direct ON line (DOL) in order to inverse the availability of equipment at full efficiency without time gap.
Further , the 6.6 KV system which is normally in delta configuration and terms as an unearthed system so also to keep the running motor complete in operating condition in case of any one .phase of motor winding is earthed due to any one reason. Earthling is detected by an protection system with alarm facility to take remedial measures immediately and at the same time to maintain the generation level in the same condition, prior to occurring the earth fault the single phase earth fault is detected in due course till the motor is not earthed to other or another phase.
“PUBLIC ADDRESS SYSTEM” is available through in area of each unit which helps in fast communication for prompt remedial measure.
Soot Blowers are there in the boiler area on the furnace side or Zone which helps in blowing the soot / ash deposition regularly of the furnace wall / economizer tubes to keep heat transfer at the required parameter.
In April 1973, Central Electricity Authority prepared a Project Report for power station comprising of the two units of each of capacity 110 MW for RSEB subsequently in September 1975 this was revised by the Consultant Thermal Design Organization, Central Electricity Authority for invention of 2x110 MW units being manufactured by BHEL, Hyderabad in 1st Stage.
The planning commission cleared the project report in Sept 1976 for installation of two units each of 110 MW in first estimated cost of Rs. 143 Crores.
The Kota Thermal Power Station is ideally on the left bank of Chambal River at Up Stream of Kota Barrage . The large expanse of water reached by the barrage provides an efficient direct circulation of cooling system for the power station. The 220 KV GSS is within ½ Kms. from the power station.
Land measuring approx. 250 hectares was required for the project in 1976, For disposal of ash tank very near to power station is acquired which the ash in slurry form is disposed off through ash and slurry disposal plants.
Coal India limited owns and operates all the major coal fields in India through its coal producing subsidiary companies viz. Eastern Coal Fields Limited, Western Coal Fields Limited Coal India limited is supply coal from its coal mines of coal producing subsidiaries BCCL, SECL & ECL to Kota Thermal Power Station through railway wagons. The average distances of SECL, ECL & BCCL are 800, 950 and 1350 Kms. Respectively.
The source of water for power station is reservoir formed by Kota Barrage on the Chambal River. In case of large capacity plants huge quantities of coal and water is required. The cost of transporting coal and water is particularly high. Therefore, as far as possible, the plant must be located near the pit rather than at load centre for load above 200 MW and 375 MW . The transportation of electrical energy is more economical as compared to the transportation of coal.
The satisfactory design consists of the flowing steps.
Estimation of cost.
Selection of site.
Capacity of Power Station.
Selection of Boiler & Turbine.
Selection of Condensing Unit.
Selection of Electrical Generator.
Selection of Cooling System.
Design of Control and instrumentation system.
The design of steam power station requires wide experience as the subsequent operation and maintenance are greatly affected by its design. The most efficient design consist of properly sized component designed to operate safely and conveniently along with its auxiliaries and installation.
General Layout & Basic Idea
A control system of station basically works on Rankin Cycle. Steam is produced in Boiler is exported in prime mover and is condensed in condenser to be fed into the boiler again. In practice of good number of modifications are affected so as to have heat economy and to increase the thermal efficiency of plant.
The Kota Thermal Power Station is divided into four main circuits :
Fuel and Ash Circuit.
Air and Gas Circuit.
Feed water and Steam Circuit.
Cooling Water Circuit.
Fuel & Ash Circuit
Fuel from the storage is fed to the boiler through fuel handling device . The fuel used in KTPS is coal , which on combustion in the boiler produced the ash. The quantity of ash produced is approximately 35-40% of coal used. This ash is collected at the back of the boiler and removed to ash storage tank through ash disposal equipment.
Air and Gas Circuit
Air from the atmosphere is supplied to the combustion chamber of Boiler through the action of forced draft fan and induced draft fan. The flue gas gases are first pass around the boiler tubes and super heated tubes in the
furnace, next through dust collector (ESP) & then economizer. Finally, they
are exhausted to the atmosphere through fans.
Feed Water and Steam Circuit
The condensate leaving the condenser is first heated in low pressure (LP) heaters through extracted steam from the lower pressure extraction of the turbine. Then its goes to dearator where extra air and non-condensable gases are removed from the hot water to avoid pitting / oxidation. From deaerator it goes to boiler feed pump which increases the pressure of the water. From the BFP it passes through the high pressure heaters. A small part of water and steam is lost while passing through different components therefore water is added in hot well. This water is called the make up water. Thereafter, feed water enters into the boiler drum through economizer. In boiler tubes water circulates because of density difference in lower and higher temperature section of the boiler. The wet steam passes through superheated. From superheated it goes into the HP turbine after expanding in the HP turbine. The low pressure steam called the cold reheat steam (CRH) goes to the reheater( boiler). From reheater it goes to IP turbine and then to the LP turbine and then exhausted through the condenser into hotwell.
Cooling Water Circuit
A large quantity of cooling water is required to condense the steam in condenser and marinating low pressure in it. The water is drawn from reservoir and after use it is drained into the river.
ELECTRICITY GENERATOR AT K.T.P.S.
Thermal power station burns the fuel and use the resultant heat to raise the steam which drives the turbo-generator. The fuel may be “Fossil” ( Coal , Oil and Natural Gas) whichever fuel is used the object is same to convert the heat into mechanical energy to electrical energy by rotating a magnet inside the set of winding. In a coal fired thermal power station other raw materials are air and water. The coal is brought to station by train or other means travels from the coal handling system.
i) By conveyer belts to coal bunkers from where it is fed to pulverizing mills.
ii) Mills grind it fine as face powder.
iii) Then this powdered coal mixed with preheated air is blow into boiler by a fan known as primary air fan (PA fan).
iv) When it burns more like a gas as solid in conventional domestic or industrial grate with additional amount of air called secondary air supplied by “Forced Draft Fan”.
As the coal has been grinded so resultant ash is also as fine as powder. Some of its fine particles blinds together to form lumps which falls into the ash pit at the bottom of furnace.
v) The water quenched ash from the bottom of furnace is carried out boiler to pit for subsequent disposal.
vi) Most of ash still in fine particles form is carried out to electrostatic precipitators where it is trapped by electrode charged with high voltage electricity. The dust is then conveyed to the disposal area or to bunkers for sale.
vii) Now after passing through ESP few gases are discharged upto chimney by “Induced Draft Fan”.
Meanwhile the heat reloaded from the coal has been absorbed by kilometers long tubes which lies in boiler walls inside the tubes “ Boiler Feed Water” which is transferred into turbine blades and makes them rotate.
To the end of the turbine rotor of generator is coupled, so that when turbine rotates the rotor turns with it. The rotor is housed inside the stator having coil of copper bars in which electric is produced through the movement of magnetic field created by rotor.
The electricity passes from the stator winding to the transformer which steps up the voltage so that it can be transmitted effectively over the power line of grid.
The steam which has given up its heat energy in changed back into a condenser so that it is ready for reuse. The cold water continuously pumped in condenser. The steam passing around the tubes looses heat and rapidly change into water. But these two types of water ( boiler feed water and cooling water ) must never mix together. The cooling water is drawn from the river but the Boiler Feed Water must be pure than potable water ( DM Water).
Now the question arises why do we bother to change steam from turbine to
water when it is to be heated up again immediately ?
Laws of Physics gives the answer which states that the boiling point of water is related to pressure. The lower the pressure lower the boiling point temperature. Turbine designer wants boiling point temperature as low as possible because it can only utilize the energy from steam when change back to water, he can get no more work out at it. So there is a condenser which by rapidly changing the steam into water a vacuum. The vacuum results in a must power at lower boiling points which in turn mean it can continue getting out of steam will below 1000C at which it would change into water.
To condense volume of cooling water is huge and continuous volume of cooling water is essential. In most of the power stations , the same water is to be used over and over again, so the heat which the water extract from the steam in the condenser is removed by pumping water out of cooling tower. The cooling tower is simple concrete shell acting of air. The water is sprayed out at top of tower and as it falls into pond beneath it cooled by the upward draft of air. The cold water in the pond is then re-circulated by pumps to condensers. Invariably however some of the water drawn upwards as vapor by the draft .
220 KV System
Two 220 KV bus bars have been provided in switch yard and are inter- connected through a bus coupler. Each of the two 110 MW generator is connected to this system through a step up of 125 MVA 240/ 11 KV yard generator transformer. There are two step down transformer each feeding 6.6 KV system (Station Switchyard ) viz. BS-IS & SB-IB. Each station transformer has two windings one secondary side and is rated for 50/25/25 mva , 270/7/7.2 kva four feeder take off from 220 switch yard, two to SKATPURA ,GSS and other to HEERAPURA , Jaipur GSS. Each of four feeder are provided with bypass isolators which is connected across line breaker and breaker isolator. By closing bus coupler between 220 KV buses and putting line feeders whose breaker required maintenance of any one bus through by pass isolators and all other line feeders whose breaker is by passed is then transformed to bus coupler breaker. A brief description of equipments of 220 KV system is as follows.
Each of generator transformer, station transformer, line feeder and bus coupler is provided with minimum oil circuit breaker of BHEL make. It is rated for 245 KW, 2500 A and 13400 MVA circuit breaker is used to break the circuit either in load condition or in no load condition.
All the isolators are provided in 220KV switchyard and are motor operated. Triple pole double breaker type and power switch yard L&T make these and are rates for 245 KV and 1250 A. The four isolators are provided with earth switch.