A Comparative Thermodynamic and Exergoeconomic Scrutiny of Four Geothermal Systems in Single- and Double-Flash Configurations with the Application of Humidification-Dehumidification Subsystems

Abstract

Geothermal heat sources are renowned as one of the most abundant renewable energy sources across the globe, available in approximately every location enriched with subterranean geofluid, among which water is mainly recognized. The present study proposes four systems powered by geothermal sources, thereby introduced as geothermal systems. System D demonstrated the most promising results among all systems after being analyzed by thermodynamic laws and performing exergoeconomic investigations, all of which were performed using EES software. The evaluated parameters are sum unit cost of products, net generated power output, energetic and exergetic efficiencies, for which the extracted numerations are 4.532$/GJ, 106.8kW, 45.83%, and 51.53%, respectively. In order to generate overplus power and further exploit waste heat, thermoelectric generators are implemented in the systems as substitutions for the condensers. The findings suggest an extra sum of 10.112kW generated power and exergetic improvement by 1.15% taking event in system D due to the application of two units of thermoelectric generators. The results further indicate exergy destruction for system D as a total value of 151.3kW. The most significant proportion of exergy destruction occurs in the low-pressure steam turbine by 25.1kW, which allocates 16.6% of the integral exergy destruction associated with system D. Moreover, multi- and single-objective optimizations aim to maximize energetic and exergetic performances and minimize the sum unit cost of products, given the geofluid intake temperature, the figure of merit, and intake pressure of the first and second flash chambers as decision variables. W1=1 is allocated to the single-objective thermal efficiency mode as the weight coefficient for energy efficiency, and the findings suggested the values for the sum unit cost of products, exergetic, and energetic efficiency as 4.523$/GJ, 48.91%, and 50.15%, respectively. Given W2=1 as the weight coefficient for exergy performance, the single-objective exergy efficiency mode yielded 4.519$/GJ, 54.34%, and 48.35% for the sum unit cost of products, exergy, and energy efficiency, respectively.

Keywords: Geothermal System, Thermoelectric generator, Humidification-Dehumidification Desalination, Steam Turbine, thermodynamic analysis, exergoeconomic analysis