Steam is mainly required for power generation, process heating and pace heating purposes. The capacity of the boilers used for power generation is considerably large compared with other boilers.
Due to the requirement of high efficiency, the steam for power generation is produced at high pressures and in very large quantities. They are very large in size and are of individual design depending the type of fuel to be used.
The boilers generating steam for process heating are generally smaller in size and generate steam at a much lower pressure. They are simpler in design and are repeatedly constructed to the same design. Though most of these boilers are used for heating purposes, some, like locomotive boilers are used for power generation also. In this chapter, some simple types of boilers will be described.
A steam generator popularly known as boiler is a closed vessel made of high quality steel in which steam is generated from water by the application of heat. The water receives heat from the hot gases though the heating surfaces of the boiler. The hot gases are formed by burning fuel, may be coal, oil or gas. Heating surface of the boiler is that part of the boiler which is exposed to hot gases on one side and water or steam on the other side. The steam which is collected over the water surface is taken from the boiler through super heater and then suitable pipes for driving engines or turbines or for some industrial heating purpose. A boiler consists of not only the steam generator but also a number of parts to help for the safe and efficient operation of the system as a whole. These parts are called mountings and accessories.
STEAM PRIME MOVERS
The prime mover convert the natural resources of energy into power or electricity.
The prime movers to be used for generating electricity could be diesel engine, steam engine, steam turbines, gas turbines, and water turbine.
Since we know that, a power plant generated a flow of mechanical or electrical energy by means of generators. When coupling runs the generator, then the generator is a prime mover.
In case of steam power plant, the prime movers is steam engine or steam turbine, which is called, steam prime movers. Presently, the steam turbine has totally replaced steam engine. The steam is gener-ated in a boiler and is then expanded in the turbine. The output of the steam turbine is utilized to run the generator. The fuel used in the boiler is coal or oil.