Consider a cogeneration plant shown below consisting of a 150 MW gas turbine for

Question

Consider a cogeneration plant shown below consisting of a 150 MW gas turbine for electric power generation and a waste-heat recuperator (heat exchanger) producing useful hot water for district heating. The gas turbine plant has a thermal efficiency of 39%. The gas turbine exhaust gas and stack gas temperatures are 520 and 180 C, respectively, and its flow rate is 500 kg/s. The water supply and return temperatures in the district heating system are 110 and 70 C, respectively. Assume a specific heat of exhaust gas and water of 1.05 and 4.19 kJ/kg-K, respectively. Calculate the heating water flow rate [kg/s], the useful heat output [kJ/s], the heat to power ratio, and the energy utilization factor of the plant.

Explanation / Answer

a)heat loss by gas=heat gain by water 500(1.05)(520-180)=m(4.19)(110-70) mass flow rate of water=m=1065 kg/s b)efficiency=output/input=W/Qh= W=58.5 MW Qdt=178MW c) heat/power=178/58.5=3.04 d)energy utilization factor=Qh/Qdt=0.84

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