9.
The schematic of a single-flash geothermal power
plant with state numbers is given in Fig. 1 Geothermal
resource exists as saturated liquid at 230°C. The geothermal
liquid is withdrawn from the production well at a rate of 230
kg/s, and is flashed to a pressure of 500 kPa by an essentially
isenthalpic flashing process where the resulting vapor is sepa-
rated from the liquid in a separator and directed to the tur-
bine. The steam leaves the turbine at 10 kPa with a moisture
content of 10 percent and enters the condenser where it is
condensed and routed to a reinjection well
it is proposed that the
liquid water coming out of the separator be used as the heat
source in a binary cycle with isobutane as the working fluid.
Geothermal liquid water leaves the heat exchanger at 90°C
while isobutane enters the turbine at 3.25 MPa and 145°C
and leaves at 80°C and 400 kPa. Isobutane is condensed in an
air-cooled condenser and then pumped to the heat exchanger
pressure. Assuming an isentropic efficiency of 90 percent for
the pump, determine (a) the mass flow rate of isobutane in
the binary cycle, (b) the net power outputs of both the flash-
ing and the binary sections of the plant, and (c) the thermal
efficiencies of the binary cycle and the combined plant.
