POWER PLANTS

MAIN SOURCES OF ELECTRICAL ENERGY

The energy requirement is increasing with the growth of the world's population.The demand of electrical energy is  doubling every ten years.Therefore it has become essential to harness more energy resources with utmost economy so as to keep pace with the requirement of the world's population.

The main sources of generating power on large scale are as follows:
1.Thermal 
2.Hydro 
3.Nuclear

The thermal and Nuclear source of energy come under the category of non-renewable energy sources while the hydel energy is grouped under the renewable energy source.other significant forms of electrical energy sources include the following:
1.Solar energy 
2.wind energy 
3.Tidal energy 
4.Geothermal energy
5. Magneto-hydrodynamic (MHD)generation 
6. Ocen thermal energy conversion (OTEC)
7. Wave energy 

THERMAL POWER PLANTS

conventionally the thermal power plants can be classified as follows:
(a)Conventional coal-fired steam turbine based,
(b)Oil or gas-fired steam turbine based,
(c)Oil/gas fired diesel generator set
(d)Oil/gas fired gas turbines with waste heats recovery and steam turbine units.

SALIENT FEATURES OF A MODERN COAL-FIRED STEAM POWER PLANT

In a coal fired steam power plant,coal is burned in a furnace.The combustion products heat water in a boiler which converts water into steam.The steam drives a turbine which is mechanically coupled to an alternator.
coal is taken from storage.It is then crushed into small pieces and fed to a  pulveriser to make it into fine powdered form.It is mixed with preheated air and blown into the furnace,where it is burned.The modern large-size boiler are all water-tube boilers. In these boilers water flows inside the tubes and hot flue gases flow outside them.The circulation of water through the tubes of the boiler is forced circulation through the action of pumps.
The common equipment used in modern coal-fired steam power plants to increase the thermal efficiency are economizers, super heaters and preheaters.

The combustion in the boiler requires supply of sufficient quantity of air and removal of exhaust gases.Air is taken from the atmosphere by the action of forced and induced draft fans.The air is preheated in the preheater by the heat of flue gases before being supplied to the furnace.
An economiser is used to heat the feed water on its way to boiler by utilizing heat from the flue gases.Steam generated in the boiler is further super heated in a super heater.A superheater raises the temperature of steam to about 620 °C. This superheated  steam is supplied to the turbine which acts as a prime mover.After expansion through the turbines,the steam goes to the condenser. In order to improve the power plant efficiency,sufficiently low pressure(vacuum)is maintained in the condenser.

CIRCULATING WATER PUMPS 

circulate cooling water through the condenser tubes and condense the exhaust steam into water which is pumped back to the boiler.The same water is used over and over again in the boiler.
Water flowing through the tubes gets heated and is cooled again. A condenser needs huge quantity of water to condense the exhaust steam. Modern power plants use larger size of cooling towers(more than 100 m high) for cooling water coming out from the condenser. After cooling in the cooling towers,cooled water is recirculated through the condenser tubes.