Page 246 - Low Temperature Energy Systems with Applications of Renewable Energy

Geothermal energy in combined heat and power systems 233

Fig. 6.9 Optimum hourly revenues for CHP plant as a function of the H-factor.

consideration for using such plants in conjunction with a direct heat application is the
availability of liquid geofluid as a byproduct of the power operation. On the one hand,
for the relatively rare dry steam plants, such as at Larderello and The Geysers, Califor-
nia, U.S., there is very little condensate and nowadays it is fully reinjected to help
maintain the reservoir. On the other hand, the vast majority of geothermal fields pro-
duce low-quality liquid-vapor mixtures, where the steam is separated for use in the tur-
bine and the liquid is either reinjected or flashed a second time to produce low-pressure
steam that drives a low-pressure turbine. The liquid that remains after separation or
flashing is usually reinjected. Thus, in the case of flash-steam plants there is an oppor-
tunity to add direct heat uses, subject to certain constraints related to the potential for
chemical precipitation and scaling.
The process flow diagrams for single- and double-flash plants and their correspond-
ing thermodynamic state diagrams are shown in Figs. 6.10e6.13 [4]. For both types of

Fig. 6.10 Schematic flow diagram for single-flash geothermal power plant [4]. See Nomen-
clature list.