Compatibility investigation and techno-economic performance optimization of whole geothermal power generation system

Abstract

Appropriate compatibility between exploitation and utilization systems is of critical importance to geothermal electricity. However, few research works focused on the optimal dynamic matching between subsurface heat extraction system and surface power generation system according to the dynamic process of enhanced geothermal system (EGS). In present work, a potential EGS with pinnate horizontal well is proposed to generate electricity by incorporating three typical power generation systems, namely single-flash (SF) system, double-flash (DF) system and single-flash with organic Rankine cycle (SFORC) system. System coupling is achieved to explore the optimum operation strategy of surface power generation system by considering the dynamic characteristics of geothermal fluid temperature and flow rate. The reliability of numerical method and thermodynamic model used in present work are validated by the theoretical model. Furthermore, the response surface methodology is employed to optimize the operation strategy of proposed EGS. Based on the maximization of exergy efficiency and minimization of total cost, the optimum running strategies and techno-economic performance of proposed power generation systems are obtained, respectively. The results indicate that temperature drop of thermal reservoir is significantly affected by the combined effect of injection flow rate and reservoir permeability. The net output exergy is proportional to branch well length and reservoir permeability, and inversely proportional to the injection temperature and injection flow rate. Compared with the SF and DF systems, SFORC system is more compatible and economical to be applied in the proposed EGS. After 30 years of operating, the net revenue of SFORC system can reach to 2.66 × 108 USD, which are 2.30 and 1.02 times more than those of SF and DF systems, respectively. The corresponding flash temperature of SFORC is the same as production temperature of the EGS. Meanwhile, the evaporation temperature of n-pentane will drop in four steps from 405.15 K to 399.15 K.