Thermal Power Plants

Desai Harshad Suresh B050254EE

Thermal Power Plants contribute maximum to the generation of Power for any country.Thermal Power Plants constitute 75.43% of the total installed captive and non-captive power generation in India. In thermal generating stations coal, oil, natural gas, etc are employed as primary sources of energy.

Coalhopper

Burnerpulverizer

Turbine Generator

CondenserPre-heated air

Feed Water Pump

Steam

Feed Water

Stack

Cooling Tower

Step-up Transformer

BUS

Exhaust Gases

FurnacePre-heated

Pulverizer

Steam

Feed Water

Feed Water Pump

11 kV BUS

Stack

CoolingFurnace

Exhaust

1. Energy Source: Coal, Natural Gas, Diesel, Oil are the major sources of primary energy.

Coal fired thermal plants form 55.23% of total installed capacity. They formed almost 83% of installed thermal power generation. The prices of the fuel determines the economics of thermal power plants.

2. Boiler and Furnace: The fuel is burnt in the furnace to produce steam in the boiler.

Pulverized coal is burnt to produce steam.

Water from the feed pump, after pre-heating enters the boiler. This water may be obtained from a nearby river or lake. The condensed water from the cooling tower is re-used.

To increase the efficiency of the plant steam is generated at highest possible temperature and pressure. To further increase the efficiency steam is re-heated after it is partially expanded by an external heater.

3. Prime Movers: These depend on the fuel used.Coal fired plants use Steam Turbines.Gas fired use Gas Turbine Engines, which are similar to Turbo-Prop engines used in airplanes.Diesel fired use IC engines.

In case of coal fired plants steam produced in the boiler is passed through an axial flow turbine.

The turbine is coupled to the generator and thus energy conversion is achieved.

Gas fired are usually operated in combined cycle mode to attain maximum efficiency.

In these types in the 1st stage gas turbine engines are coupled to the generators.

In 2nd stage the hot gases exhausted from the gas turbines are passed through heat exchangers to generate steam which drives the conventional steam turbine.

Alternatively heat from the exchanger can be used for industrial purposes.

4. Generators: The prime movers are coupled to the generators to convert mechanical energy into electrical energy.

Modern practice is to design and build generating units having large MW generating capacity since their capital cost per kW decreases as the MW capacity is increased.

Increasing the unit capacity from 100MW to 250MW results in saving of about 15% in their capital cost per kW.Moreover units of this magnitude result in fuel saving of almost 8% per kWh.The cost of installation is also low for such units.

Presently the max capacity of turbo-generator sets being produced is nearly 1200 MW.

In India, super thermal power units of capacity 500 MW are being commissioned by BHEL.

Also many Ultra-Mega Power Plants are being sanctioned to achieve the government s goal of energy for all.

5. Condenser and Cooling Tower: The steam after passed through the turbines is condensed in a condenser. The water is then supplied to the cooling tower where it is cooled.The water is then fed to the feeder pump from where it is given to the boilers.

6. Precipitators and Chimneys: The waste gases from the boiler are first passed through precipitators to separate the solid dust particles. The fly ash is collected at these precipitators.The gases are then thrown out with the use of Chimneys.

7. Control Room and Switchyard :The control room monitors the overall

operation of the plant. It is provided with controls for real and reactive power flow.It is provided with safety relays and switchgears.

Switchyard is the place where voltage levels are stepped up using a step-up transformer. The supply from the generators is connected to the grid at the switchyard bus.The switchyard also has energy meters, SF6 gas breakers, protective relays and lightning arrestors.

Coal fired units form the majority of thermal power plants. However, for the same amount of power generated a combined-cycle gas fired station is environment friendly. The flue gases emitted by these stations contain almost zero SO2, 50% CO2 and 25% NOX as compared to those produced in coal fired.

Also the installation cost of gas fired is lower than coal fired.Gas fired units can be started quickly.The operating costs of Gas fired plants are high due to high fuel costs. As such these are used to supply peak load demand and for short periods.

The waste gases from thermal plants contain particles and gases like oxides of sulphur and NOX. This results in pollution of air.Thermal pollution also results in due to large amount of heat released via the condenser to the cooling water.

It is possible to increase the overall efficiency of a thermal power plant to 65% using the techniques of co-generation. In co-generation, electricity and steam or hot water is simultaneously made available for industrial use or space heating.

Power System Analysis, T.K. Nagsarkarand M.S. Sukhija.The figures are obtained from Central Electricity Authority s General Review 2005 report.

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