Schematic Arrangement of Steam Power Plant
Though the main process in steam power station is the conversion of heat energy into electrical energy,it comprises of many steps for its proper working and good efficiency.The whole arrangement of a steam power station could be divided into following steps.The whole arrangement is shown in a schematic figure given below.
- Coal and ash handling arrangement
- Steam generating plant
- Steam turbine
- Feed water
- Cooling arrangement
1. Coal and ash handling plant
The coal is transported from different places to the station by means of rails or road and is stored in a coal storage plant.It is to use as a preserve at the time of scarcity.From coal storage plant it is transferred to coal handling plant for pulverisation.Pulverisation is the process by which large lumps of coal are broke to small pieces.
Why Pulverisation is done?
Pulverisation is done to increase the the surface of area of coal and thereby helping the easy combustion of coal with small intake of air.The pulverised coal is fed to the boiler by means of conveyor belt.The coal is burnt in the boiler and the ash so produced by burning is removed to the ash handling plant and finally to the ash storage plant for its disposal.This process is necessary since ash in the boiler furnace does not promote proper combustion.
2. Steam Generating Plant
The steam generating plant consist of boiler and its auxiliary equipments for the utilisation of flue gases.
The heat produced by the burning of coal in the boiler is used to produce steam at high temperature and pressure. The flue gases produced at the time of combustion is passed through the super heater,economiser,air- preheater and finally exhausted into the atmosphere through chimney.
2.2 Super Heater
The steam produced in the boiler has got moisture content so it is dried and superheated (ie steam temperature is increased above boiling point of water)by the flue gases on the way to chimney.Super heating ensures two benefits at first the overall efficiency of the system is increased and secondly the corrosion to the turbine blades due to condensation in later stages is prevented.The superheated steam from superheater is fed to steam turbine by means of a main valve.
Economiser is a feed water heater.It uses the heat produced by the flue gases for this purpose.The feed water is passed through the economiser before supplying it to the boiler and economiser absorbs a part of heat from the flue gas to increase the temperature of the feed water.
2.4 Air preheater
Air preheater increases the temperature of the air supplied to coal for combustion using flue gases.Air is drawn in using a forced draught fan and is passed through preheater before supplying it to the boiler.This process increases the thermal efficiency and steam capacity per square meter of the boiler surface.
The dry and super heated steam from superheater is fed to the turbine by means of a main valve.Due to the striking or reaction impact of the steam on the blades of turbine it starts rotating ie heat energy is converted to mechanical energy.After giving heat energy to the turbine the steam is exhausted to a condenser which condenses the exhausted steam by means of a cold water circulation.
The steam turbine is coupled to an alternator ,the alternator converts the mechanical energy into electrical energy.The electrical output is transferred to the bus bars through transformer,circuit breaker and isolators.
The condensed water produced in the condenser is used as feed water,some amount of water may be lost in the cycle but it is compensated using an external source and the cycle repeats and gives a better efficiency to the system.
6. Cooling Arrangement
Inorder to increase the efficiency of the plant the steam coming from the turbine is condensed using a condenser.The water circulation for cooling steam in condenser is take from a natural source like river,stream etc and the out coming hot water from condenser is discharged in some lower portion of the water source.In scarcity of water the water from the condenser is cooled and reused with the help of a cooling tower.