Focusing on geothermal heat extraction and utilization system: Scheme optimization and coupling coordination degree analysis

Abstract

The present work aims to probe the coupling mechanism of enhanced geothermal system (EGS) and power generation system (PGS), and to improve the techno-economic performance of whole geothermal system. To evaluate the overall performance of various scheme of power generation, the model of coupling coordination degree (CCD) is proposed. Furthermore, four types of EGS and three types of PGS are respectively combined to be the candidate geothermal system, and their performance are synthetically probed and compared. Eleven evaluation indexes are used to reveal the potential CCD of EGS and PGS from five aspects, including the production performance and life span of EGS, energy output, economic performance and energy conversion ability of PGS. Further, based on the grey relational theory, the major relation factors that affect the geothermal system performance are revealed. The results show that the single flash (SF) system has maximum heat supply and net revenue, double flash system has the optimal energy conversion performance and SF with organic Rankine cycle (SFORC) system has the lowest exergy loss and levelized cost of electricity. The production temperature and net exergy output of EGS have strong associations with the net generation, heat supply and exergy efficiency of PGS. The CCD between SFORC and various types of EGS is the highest, especially for the EGS with pinnate horizontal well. The optimization analysis proves that organic working fluid of R600 is the optimal choice for the ORC system. Using the recommended geothermal power scheme, the net generation per unit time is expected to 6874.9 kW, the maximum exergy efficiency reaches to 55.8 %, the LCOE can be reduced to 0.012 USD/kWh and the annual net revenue can rise up to 6.33 × 107 USD.