Understanding Steam Power Plants: Components and Operation

Posted on Apr 2, 2025 in Technology

Steam Power Plant

• The major components of this power plant are: (i) boiler, (ii) steam turbine, (iii) condenser, (iv) water feed pump, (v) electrical generator, (vi) cooling tower, etc.
• In a steam power plant, thermal energy is converted to electric energy.
• Water is supplied to the boiler through a feed water pump (1) from the water tank.
• The water in the boiler (4) is heated by transferring heat from the combustion of fossil fuel in the furnace. The boiler consists of an economizer (6) and a superheater (5).
• Coal received in the coal storage yard of the power station is transferred to the furnace by a coal handling unit. Heat produced by burning coal is utilized in converting water contained in the boiler drum into steam at a suitable pressure and temperature.

• From the super-heater, the high-pressure, high-temperature steam strikes the turbine (7) blades at high speed, causing the turbine blades to rotate rapidly. Here, the pressure energy of the steam is converted into mechanical energy. Steam turbines are of various types, but mainly these are divided into impulse and reaction turbines.
• A generator is coupled with the turbine rotor. As the turbine rotates, the generator also rotates at the same speed, and the mechanical energy of the turbine is converted into electrical energy.
• After hitting the turbine blades, the steam loses most of its energy and leaves the turbine as low-pressure steam.
• This low-pressure steam enters the condenser (8). Cold water circulates in the condenser from the cooling tower (9). In the condenser, the low-pressure steam is converted into condensate, i.e., water. There are basically two types of condensers: jet condensers and surface condensers.
• This condensed water is then fed back to the boiler through the economizer. Finally, the feed water enters the boiler via a feed water pump to repeat the cycle. The feed pump increases the pressure of the water (condensate) to the boiler pressure.

Steam Power Plant Operation Circuits

The working of a steam power plant can be explained in four circuits:

1. Coal and Ash Circuit

• This includes coal delivery, preparation, coal handling, boiler furnace, ash handling, and ash storage. Coal from coal mines is delivered by ships, rail, or trucks to the power station. This coal is sized by crushers, breakers, etc. The sized coal is then stored in a coal storage (stock yard). From the stock yard, the coal is transferred to the boiler furnace by means of conveyors, elevators, etc.
• The coal is burnt in the boiler furnace, and ash is formed. Ash coming out of the furnace will be hot, dusty, and accompanied by some poisonous gases. The ash is transferred to ash storage. Usually, the ash is quenched to reduce temperature, corrosion, and dust content.
• There are different methods employed for the disposal of ash, such as hydraulic systems, water jetting, ash sluice ways, pneumatic systems, etc. In large power plants, hydraulic systems are used. In this system, ash falls from the furnace grate into a high-velocity water stream and is then carried to the slumps. A line diagram of the coal and ash circuit is shown separately in the figure.

2. Air and Flue Gas Circuit

• It consists of a forced draught fan, air pre-heater, boiler furnace, super heater, economizer, dust collector, induced draught fan, chimney, etc. Air is taken from the atmosphere by the action of a forced draught fan and passed through an air pre-heater. The air is pre-heated by the flue gases in the pre-heater. This pre-heated air is supplied to the furnace to aid the combustion of fuel. Due to the combustion of fuel, hot gases (flue gases) are formed.
• The flue gases from the furnace pass over boiler tubes and super heater tubes. (In the boiler, wet steam is generated, and in the super heater, the wet steam is superheated by the flue gases.) Then, the flue gases pass through the economizer to heat the feed water. After that, it passes through the air pre-heater to pre-heat the incoming air. It is then passed through a dust catching device (dust collector). Finally, it is exhausted to the atmosphere through the chimney.