Optimization and applicability of compound power cycles for enhanced geothermal systems

摘要

Both thermodynamic performance and techno-economic analysis of compound power cycles for enhanced geothermal systems have been investigated in this study. Thermodynamic analysis were carried out for four power generation systems: single-flash (SF) system, double-flash (DF) system, flash-ORC (FORC) system; and double-flashORC (DFORC) system. By choosing the maximum net power output as an objective function, optimization is done based on comparisons among the four systems with a goal of increasing the net power output by 20% under the condition that the SF is replaced by one of the compound systems (DF, FORC, and DFORC). As an original contribution, five maps useful for real applications have been generated for selecting optimum geothermal power cycles under different geofluid's conditions, with consideration of five ORC working fluids (R123, R152a, isobutane, n pentane and R245fa). The boundaries that determine whether the compound systems have advantages over the SF system are functions of the geofluid temperature, geofluid dryness, and the type of the working fluid used by the ORC. In the techno-economic study, Levelized Electricity Cost (LEC) and Payback Period (PBP) analyses were carried out. The results from the LEC and PBP studies show good agreement. For the three scenarios analyzed, each of the compound power systems has a better engineering economic performance than the SF system. For the "common" heat source condition investigated, comparison among the three compound systems shows that the DF system has a lowest levelized electricity cost and the shortest payback period; the FORC and DFORC show similar techno-economic performance and have advantages over the SF system.