Synergetic mechanism of organic Rankine flash cycle with ejector for geothermal power generation enhancement

Abstract

With the decrease of installed capacity, the problem of high working fluid pump power and low system efficiency is serious in organic Rankine cycle (ORC), and meanwhile, the matching between heat source and system also deteriorates. In this study, an organic Rankine flash cycle with ejector (EORFC) is proposed to eliminate the pump at the condenser outlet, thereby improving the above problem. A parametric study of the effects of the evaporating temperature, flashing temperature, evaporator outlet dryness and entrainment ratio on the thermodynamic and techno-economic performance of the organic Rankine flash cycle (ORFC) and EORFC are investigated. A comparative analysis for the two systems is further carried out, and meanwhile, R601, R601a, R245ca and R123 are comparably examined. The results show that when the net power output is the optimal, the net power output, thermal efficiency and exergy efficiency of the EORFC are averagely 3.26%, 6.96% and 1.96% higher than that of ORFC. The heat exchanger is the main component that increase the investment cost and exergy destruction, and the introduction of ejector can effectively improve them. Considering the two systems at the same operating conditions, the EORFC always has better thermal efficiency and levelized energy cost, while has higher net power output and exergy efficiency at high entrainment ratio and low pump isentropic efficiency. The multi-objective optimization indicates that the EORFC has better performance on the exergy efficiency and levelized energy cost, and R601 is suggested as the working fluid for the EORFC and ORFC.