Power Plant Engineering

1.13.6 REHEAT-REGENERATIVE CYCLE
In steam power plants using high steam
pressure reheat regenerative cycle is used. The ther-
mal efficiency of this cycle is higher than only re-
heat or regenerative cycle. Fig. 1.8 shows the flow
diagram of reheat regenerative cycle. This cycle
is commonly used to produce high pressure steam
(90 kg/cm
2
) to increase the cycle efficiency.
Steam
Turbine
Condenser
Feed water
pump
Mercury
Boiler
STEAM SUPERHEATER
Murcury
Turbine
Generator
Heat
Exchanger
Fig. 1.7
Fig. 1.8

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18
POWER PLANT ENGINEERING
1.13.7 FORMULA SUMMARY
1. Rankine efficiency
= (H
1
– H
2
)/(H
1
– H
w2
)
2. Efficiency ratio or Relative efficiency
= Indicated or Brake thermal
efficiency/Rankine efficiency
3. Thermal efficiency = 3600/m(H
1
– H
w2
), 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.