Steam Power Plant Arrangement
General. Small units utilize the transverse arrangement in the turbine
generator bay, while the larger utility units are very long and require end-to-end
arrangement of the turbine generators.
Typical Small Plants. Figures 15 and 16 show typical transverse small plant
arrangements. Small units less than 5,000 kW may have the condensers at the same level
as the turbine generator for economy, as shown in Figure 15. Figure 17 indicates the
critical turbine room bay clearances.
Heat Rates. The final measure of turbine cycle efficiency is represented by
the turbine heat rate. It is determined from a heat balance of the cycle, which
accounts for all flow rates, pressures, temperatures, and enthalpies of steam,
condensate, or feedwater at all points of change in these thermodynamic properties.
Heat rate is an excellent measure of the fuel economy of power generation.
Heat Rate Units and Definitions. The economy or efficiency of a steam power
plant cycle is expressed in terms of heat rate, which is total thermal input to the
cycle divided by the electrical output of the units. Units are Btu/kWh.
a) Conversion to cycle efficiency, as the ratio of output to input energy,
may be made by dividing the heat content of one kWh, equivalent to 3412.14 Btu by the
heat rate, as defined. Efficiencies are seldom used to express overall plant or cycle
performance, although efficiencies of individual components, such as pumps or steam
generators, are commonly used.
b) Power cycle economy for particular plants or stations is sometimes
expressed in terms of pounds of steam per kilowatt hour, but such a parameter is not
readily comparable to other plants or cycles and omits steam generator efficiency.
c) For mechanical drive turbines, heat rates are some times expressed in
Btu per hp-hour, excluding losses for the driven machine. One horsepower hour is
equivalent to 2544.43 Btu.