Integrated research on power generation and heat extraction with an increasing-pressure endothermic process in a downhole heat exchanger

Abstract

There are plenty hot dry rock (HDR) resources in the range of 3-10 km underground. Seeking economical and efficient utilization scheme of using hot dry rock resources is an effective way to solve the shortage of energy supply. In this study, a novel power cycle, with an increasing-pressure endothermic process in the downhole heat exchanger (DHE) and CO2-based mixture as working fluid, has been developed for the geo-fluid temperature ranging from 100 °C to 200 °C. The adopted CO2-based mixture has a higher critical temperature and hence can be condensed under ambient temperature condition. It is has been found that the endothermic process in the DHE and exothermic process in the condenser have a better match with the temperature change of the heat source (geo-fluid) and that of the cooling water respectively, which reduces the heat transfer irreversibility. The maximum net power output has been chosen as an objective function in this study. The operation parameters of the power generation system and the structural size of the DHE have been optimized simultaneously. The thermodynamic performance of the proposed novel power cycle has been compared with flash-steam system and Organic Rankine Cycle (ORC) under same operation conditions.