Steam Power Plant
Steam power plant is also known as Thermal power plant. It is the power plant which generates electricity from the energy of steam. In this plant water is heated and turned into steam, the steam rotates the steam turbine which drives an electrical generator and electricity is produced. The steam power station works on the Rankine cycle
In Steam generating station a fossil fuel such as coal is burned to produce heat. This heat is then used to boil the water and convert it into the super-heated steam. The super-heated steam is passed into a steam turbine. The Steam turbine are rotated due to the pressure of the steam. The Steam is mechanically coupled with the rotor of the alternator/ generator. with the rotation of steam turbine, the rotor of the alternator also rotates, Electrical energy is produced.
Circuits of Steam Power Plant
The Modern steam power plant consists four circuits.
- Coal and Ash circuit
- Air and gas Circuit
- Feed water and Steam flow circuit
- Cooling water circuit
- Cooling water circuit
Coal from coal yard is supplied to the boiler furnace by means of conveyors, elevators etc. where its combustion takes place and ash is produced which is taken out form back of the boiler.
2. Air and Gas Circuit
The air from atmosphere is supplied to combustion chamber of boiler by forced draught fan (FD fan) and induced draught fan (ID Fan). The air is heated by flues gases in air pre-heater before entering the combustion chamber to aid in the combustion of fuel.
3. Feed Water and Steam Flow
The Steam from the boiler is supplied to the turbine, from turbine it is given to condenser for condensation. The condensate is preheated by the flue gases in the economizer. the preheated water is then supplied to boiler.
4. Cooling Water Circuit
The exhaust steam from the turbine is condensed in condenser. In the condenser, cold water is circulated to condense the steam into water. The steam is condensed by losing its latent heat to the circulating cold water. Thus the circulating water is heated. This hot water is then taken to a cooling tower, in cooling tower, the water is sprayed in the form of droplets through nozzles. The atmospheric air enters the cooling tower from the openings provided at the bottom of the tower. This air removes heat from water. Cooled water is collected in a pond (known as cooling pond). This cold water is again circulated through the pump, condenser and cooling tower. Thus the cycle is repeated again and again. Some amount of water may be lost during the circulation due to vaporization etc. Hence, make up water is added to the pond by means of a pump. This water is obtained from a river or lake.
Components of Steam / Thermal Power Plant
- Coal Mill: Coal mills grind the coal into fine powder, and the air entering the mill dries and drives the coal into the combustion chamber.
- Boiler: It converts the water into steam at high temperature and pressure. The mixture of pulverized coal and air (usually preheated air) is taken into boiler and then burnt in the combustion chamber. The heat produced due to combustion of coal converts the water in the tubes of boiler into steam at high pressure and temperature. The flue gases from the boiler make their way through super-heater, economizer, air pre-heater and finally get exhausted to the atmosphere from the chimney.
\;\;\;Super-heater: Super-heater converts the steam produced in a boiler into super-heated saturated steam. The super-heated saturated steam is then fed to high prssure turbine. For converting steam into super-heated steam super – heater takes heat from flue gases.
\;\;\;Economizer: it is feed water heater which heats the water before entering into boiler. The heater required for heating the water is taken from flue gases.
\;\;\;Air Pre-heater: The air taken from atmosphere by Forced draught fan is heated by air pre-heater by taking heat from flue gases before entering the combustion chamber of boiler.
3. Steam Turbine: The super-heated steam at high pressure and temperature is fed to the high pressure steam turbine. in The turbine steam cause the turbine to rotate, thus converting heat energy of steam into mechanical energy. The steam after leaving the high pressure steam turbine losses temperature and pressure. The steam at low pressure is fed to low pressure turbine. The steam before entering the low pressure turbine is heat again by Re-heater. Re-heater takes heat from the flue gases.
4. Condenser: The exhausted steam after leaving the low pressure turbine is condensed in the condenser by means of cold water circulation. The steam loses it’s pressure and temperature and it is converted back into water. Condensing is essential because, compressing a fluid which is in gaseous state requires a huge amount of energy with respect to the energy required in compressing liquid. Thus, condensing increases efficiency of the cycle.
5. Alternator: The steam turbine is coupled to rotor of an alternator / Generator. When the turbine rotates the rotor of the alternator, electrical energy is generated. This generated electrical voltage is then stepped up with the help of a transformer and then transmitted where it is to be utilized.
6. Feed water Pump: The condensate from the condenser is used as feed water to the boiler. Some water may be lost in the cycle which is suitably made up from external source. The feed water on its way to the boiler is heated by water heaters and economiser. This helps in raising the overall efficiency of the plant.
7. Electrostatic Precipitator: An electrostatic precipitator (ESP) is a filter device that removes fine particles, like dust and smoke, from a flue gases using the force of an induced electrostatic charge. Electrostatic precipitators are used for air pollution control, particularly for removing harmful particulate matter from flue gases. Such particulates reduce visibility, can contribute to climate change, and lead to serious health problems in humans, including lung damage and bronchitis.
8. Chimney: It is used to release theflue gases or smoke from the furnace to the environment at appropriate height. The height of the tower is very high such that it can easily throw the smoke and exhaust flue gases at the appropriate height. And it cannot affect the population living near the steam power plant.
9. Cooling Towers: It is a tower which contains cold water. Cold water is circulating to the condenser for condensing the steam leaving from steam turbine.
Salient Features of Steam Power Plant
- Generally located near the load center but other factor like transportation of fuel, enough water for cooling the condensate, cost of land are kept in mind.
- initial cost is lower than other thermal plants (e.g. Solar etc)
- Cost of fuel is high as compared to nuclear and hydro-electric power plant
- Maintenance cost is also higher than hydro-electric and diesel but comparable as compared to nuclear power plant.
- Running cost is high as compared to hydro and nuclear
- Generally used to supply base load.
Advantage of Steam Power plant
- Less initial cost as compared to other power plants
- It can be installed at any place irrespective of the existence of coal. The coal can be transported to the site of the plant by rail or road.
- It requires less space as compared to the hydroelectric power station.
- The cost of generation is lesser than that of the diesel power station.
Disadvantages of Steam Power Plant
- It pollutes the atmosphere due to the production of large amount of smoke and fumes.
- It is costlier in running cost as compared to hydroelectric plant.
- Starting up the plant and bringing into service takes more time.
- Ash handling is a big problem.