Exergy and exergoeconomic assessments of an electricity production system in a running wastewater treatment plant

This study aims at presenting a detailed exergy and exergoeconomic analyses of a biogas engine powered electricity production system in a wastewater treatment plant located in Adana, Turkey. The overall system consists of a compressor, a turbine, a pump, four heat exchangers and a gas engine. The effect of the each system component on the exergy efficiency and exergoeconomic parameters is analyzed separately. The analysis indicates that major exergy destruction happens in the gas engine as 4055.31 kW, followed by the exhaust gas heat exchanger (EGHE) and lubrication oil heat exchanger (LOHE) as 99.86 kW and 92.64 kW, respectively. The second law efficiency of the compressor, turbine, pump, BGHE, LOHE, WHE, EGHE and gas engine are found as 76.50%, 78.43%, 6.49%, 13.40%, 11.56%, 60.44%, 67.36%, and 50.79%, respectively. The operating and maintenance costs, capital investment cost and total cost of the system are reckoned as 14.74 US$/h, 13.90 US$/h, and 28.64 US$/h, respectively to point out the exergoeconomic performance. The unit exergy cost and exergy cost of the fuel, which feeds the compressor, are reckoned as 4.88 US$/GJ and 141.12 US$/h. The exergy cost and electricity production unit exergy cost in the turbine are found as 4.87 US$/h and 11.32 US$/GJ.