Performance enhancement and contribution analysis of dual-pressure evaporation organic Rankine cycle coupled with magnetic levitation turbine for geothermal power generation

Low-to medium-temperature geothermal energy, reliable, sustainable, and abundant, will play a key role in future. However, the efficiency enhancement of a conventional geothermal power generation scheme is limited by poor temperature matching in heat absorption and low turbine conversion efficiency. To address these bottlenecks, a dual-pressure evaporation organic Rankine cycle (DPORC) coupling with magnetic levitation turbines (MTs) is designed, and a conventional single-pressure evaporation ORC (SPORC) and a conventional turbine (CT) are selected as comparison benchmarks. Optimal system schemes and performance of four system combinations (SPORC/DPORC + CT/MT) are obtained by single- and multi-objective optimizations, respectively. The enhancement effects of DPORC + MT are quantitatively evaluated at different geothermal temperatures. The individual contributions of DPORC and MT to enhancement are quantified by a linear mixed-effects model. The exergy performance characteristics of DPORC + MT are also revealed. Results indicate that DPORC + MT can achieve 10.87 kWh∙t⁻¹ in electricity generation per ton of geothermal water and 13.38% in power generation efficiency. Compared with SPORC + CT, the advantages of DPORC + MT increase as the geothermal temperature rises, with the maximum enhancements of 49.53% and 9.16%, respectively. DPORC dominates the performance variations (accounting for over 60%), but will produce an opposite effect on power generation efficiency, while MT can fully compensate for the degradation, resulting in a good complementary effect. As the weight of electricity generation per ton of geothermal water increases, the critical temperature of the optimal working fluid becomes lower. Reducing the exergy losses of low-pressure turbine and condenser is the key to further enhancing the efficiency of DPORC + MT.