Reconsider Prob. 18-94. The space heating provided by this cogeneration plant will replace natural gas heating. How much money does this plant make by selling geothermal heat at a discount rate of 25 percent with respect to natural gas. The efficiency of natural gas furnace is 85 percent and the price of natural gas is $1.3/therm (1 therm 5 105,500 kJ). Assume a winter operation period of 4200 h under these average conditions.
Prob. 18-94.
Consider a binary geothermal cogeneration plant like that in Fig. P18-94 using geothermal water at 165oC with isobutane as the working fluid. The mass flow rate of geothermal water is 175 kg/s and the net power output is 6.9 MW. It is determined that geothermal water leaves the plant at 85oC (state 6) and leaves the heater at 65oC (state 7). The fresh liquid water, heated to 75oC (state 9), is used for space heating and returns to the cogeneration plant at 50oC (state 8).