Investigation of the geothermal flash cycle developed by a thermoelectric generator and PEMFC: 3E analysis and optimization

Abstract

Investigations have revealed that geothermal organic Rankine cycles (ORCs) have a low efficiency and high exergy destruction rate, especially in the heat exchangers network, which drastically reduces the whole system's performance. To tackle this problem, in the present research, the effects of employing thermoelectric generators (TEG) and proton exchange membrane fuel cell (PEMFC) on the performance of a geothermal ORC will be discussed from thermodynamic and economic points of view. In this study, three geothermal flash cycles are investigated. The first system, GFC, is a geothermal flash cycle. The second system is the GFC boosted by a TEG thermoelectric generator, which is applied instead of the condenser (GFTC). The third system is GFTC, developed using a PEMFC (GFTPC) before the evaporator. These systems are compared from energy, exergy, and economic perspectives. Parametric analysis is conducted for the system with the best performance and the effects of the evaporator temperature, evaporator quality, flash temperature, and PEMFC temperature on the system performance. Based on the results, the net power outputs of the GFTC and GFTPC are 10.21 % and 40.49 % higher than those of the GFC, respectively. GFTC and GFTPC have higher energy and exergy efficiencies and lower LCOE and payback period than GFC. In the GFTPC, a 32.86 % increase in the net power output, 20.81 % enhancement in the energy efficiency, and 0.22 % increase in the exergy efficiency are observed with an increase in the PEMFC temperature from 75 to 115 °C. Moreover, The PEMFC temperature increment reduces the LCOE and payback period of the GFTPC system. Also, the multi-objective optimization for GFTPC design with three decision variables has been done.