ne = Turbine generator engine efficiency
h1 and h2 = (see Equation 1)
he = Actual extraction or exhaust enthalpy, Btu/lb
nt = Turbine mechanical efficiency
ng = Generator efficiency
Engine efficiency is usually obtained from turbine generator manufacturers
or their literature. Therefore, it is not usually necessary to calculate engine
Typical turbine generator engine efficiencies are provided in Figure 18.
Actual Steam Rate. The actual steam rate of a turbine can be determined by
dividing the actual throttle steam flow rate in pounds per hour by the actual
corresponding kilowatts, at the generator terminals, produced by that amount of steam.
The resulting steam rate is expressed in pounds of steam per kWh. The actual steam rate
can also be determined by dividing the theoretical steam rate by the engine efficiency
of the turbine generator.
A.S.R. = T.S.R./ne
A.S.R. = actual steam rate of the turbine, lb/kWh.
Cogeneration in Steam Power Plants. Cogeneration in a steam power plant
affects the design of the steam turbine relative to the type of cycle used, the exhaust
or extraction pressures required, the loading of the steam turbine, and the size of the
steam turbine. Appendix C presents a further discussion on steam plant cogeneration.
Definition. In steam power plant practice, cogeneration normally describes an
arrangement whereby high pressure steam is passed through a turbine prime mover to
produce electrical power, and thence from the turbine exhaust (or extraction) opening to
a lower pressure steam (or heat) distribution system for general heating, refrigeration,
or process use.
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