Power Plant Engineering

FUNDAMENTAL OF POWER PLANT 19

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.

1.16 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.

1.17 Steam Condensers

Thermal efficiency of a closed cycle power developing system using steam as working fluid and
working on Carnot cycle is given by an expression (T 1 – T 2 )/T 1. This expression of efficiency shows that
the efficiency increases with an increase in temperature Tl and decrease in temperature T 2. The maxi-
mum temperature T 1 of the steam supplied to a steam prime mover is limited by material considerations.
The temperature T 2 (temperature at which heat is rejected) can be reduced to the atmospheric tempera-
ture if the exhaust of the steam takes place below atmospheric pressure. If the exhaust is at atmospheric
pressure, the heat rejection is at 100°C.

Low exhaust pressure is necessary to obtain low exhaust temperature. But the steam cannot be
exhausted to the atmosphere if it is expanded in the engine or turbine to a pressure lower than the
atmospheric pressure. Under this condition, the steam is exhausted into a vessel known as condenser
where the pressure is maintained below the atmosphere by continuously condensing the steam by means
of circulating cold water at atmospheric temperature.

A closed vessel in which steam is condensed by abstracting the heat and where the pressure is
maintained below atmospheric pressure is known as a condenser. The efficiency of the steam plant is
considerably increased by the use of a condenser. In large turbine plants, the condensate recovery be-
comes very important and this is also made possible by the use of condenser.

The steam condenser is one of the essential components of all modern steam power plants.

Steam condenser are of two types:

1. Surface condenser. 2. Jet condensers