The 4E emergy-based analysis of a novel multi-generation geothermal cycle using LNG cold energy recovery

Abstract

Over the last decade, the increasing demand for sustainable energy sources has led to the development of innovative approaches in geothermal power plant cycles. In this study, a novel combined geothermal power plant cycle (GTPPC) that integrates the Kalina cycle, transcritical Carbon Dioxide (T-CO2) cycle, with the injections of the Liquid Natural Gas (LNG) stream and geothermal water (GTW) stream is proposed in order to provide cold and hot sources of the system. The performance of the system is evaluated using emergy analysis, an evaluation factor based on thermodynamic principle and solar energy with the aid of emergoeconomic and emergoenvironmental factors. The injection of LNG stream leads to significant improvements: enhancing the net output power and overall emergoeconomic and emergoenvironmental efficiencies of the cycle. By conducting improvement priority and parametric studies, crucial stream points and the system's performance's optimization is identified. Our results indicate that the Kalina sub-cycle has a greater impact on performance, and the exergy destruction in the LNG stream will be minimized. At the optimal point, the GTPPC achieves high thermal efficiency and emergy-based metrics, indicating its sustainability and viability as a geothermal power generation solution. By the injection of LNG stream, the net output power, and overall emergoeconomic and emergoenvironmental efficiencies of the cycle, improved by 1.79 MW, 14 %, and 16 %, respectively. According to the obtained results, the performance of the Kalina sub-cycle has more effect than the Carbon Dioxide sub-cycle, and destructing exergy in the LNG stream will have irreparable effects on the operation of the GTPPC. At the optimum point of the system performance, the GTPPC will operate with the thermal efficiency, ψ, and φ of 15.4 %, 94.3 %, and 98.5 %, respectively.