Advanced exergy and exergoeconomic analysis for a polygeneration plant operating in geothermal cascade

Abstract

This paper presents an advanced exergy and exergoeconomic analysis applied to a polygeneration plant operating in a geothermal cascade arrangement. An organic Rankine cycle (ORC), an absorption chiller and a dehydrator are the main components of the plant. The energy and exergy analysis of the polygeneration plant were carried out operating under real, unavoidable and ideal conditions. Considering real conditions, the polygeneration plant is able to reach a power output of 40 kWe, a cooling effect of 175.8 kWf and 30 kWt of useful heat for dehydration. The conventional exergy analysis shows that the component with the highest destruction of exergy of the polygeneration plant is the main heat exchanger (HX-I) having 44.05 kW, followed by the ORC with 38.58 kW. The advanced exergy analysis also indicates that 10.61 kW and 2.28 kW of exergy destruction in the HX-I and in the ORC can be avoided by improving design variables of these components. In this same context, the thermally activated refrigeration (TAR) can avoid destroying endogenously 7.36 kW while interacting with the other components of the plant operating under ideal conditions. On the other hand, the conventional exergoeconomic analysis reveals a cost of electricity production of 8.54 $/h, a cost of cooling production of 7.78 $/h and a cost of useful heat production for dehydration of 3.52 $/h. Finally, the advanced exergoeconomic analysis indicates that the heat exchanger HX-II is the component of the plant where more opportunity for reducing exergy destruction can be found.