Power Plant Engineering

18 POWER PLANT ENGINEERING

1.13.7 Formula Summary

1. Rankine efficiency
   = (H 1 – H 2 )/(H 1 – Hw 2 )


2. Efficiency ratio or Relative efficiency
   = Indicated or Brake thermal
   efficiency/Rankine efficiency


3. Thermal efficiency = 3600/m(H 1 – Hw 2 ), m = steam flow/kw hr
   4. Carnot efficiency = (T 1 – T 2 )/T 1

1.14 Fuels and Combustion

The working substance of the energy conversion device viz., prime-mover (which convert the
natural resources of energy into power or electricity) is called fuel. The most common fuel is fossil fuel
viz., Coal, petrol, diesel or water gas in the case of steam power plants, I.C. Engines, gas turbines, and
hydro-electric power plants. Uranium 235(1U^235 ) as fissionable and 1U^238 as fertile fuel in the case of
fission reactors of nuclear power plant and hydrogen as fuel in the case of fusion nuclear reactor. While
fission reactor is conventional fusion reactor is supposed to be non-conventional due to its uncontrolled
reaction rate; and it is believed that Russian’s have developed it but keeping the whole world silence. In
the case of non-conventional power plants the fuels are according to their characteristics viz., Thermo-
electric material (Bi 2 Te 3 , bismuth telluride, lead telluride etc.); thermionic materials (Na, K, Cs, W etc.);
hydrogen or hydrocarbon or coal in the case of fuel-cells and further water and methane etc in the recent
development of the sources of energy.

Combustion of the fuel is a must in any energy conversion device. It is defined as rapidly pro-
ceeding chemical reaction with liberation of heat and light. This phenomenon incurved in the case of
thermal power plants especially in I.C. engines and gas turbines. But in the case of fuel cell it is of the
nature of chemical reaction i.e., transfer of ions, similarly in the case of thermo-electric generator it is
conduction of electron and holes, in the case of MHD power plant it is drifting of positive and negative
ion etc.

1.15 Steam Generators

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