Techno-economic optimization of a geothermal multi-product layout composed of a CO2 trans-critical Rankine-LNG system integrated with ejector cooling system and HDH desalination unit

Abstract

This current research introduces and examines a new multi-product configuration based on geothermal energy, using energy, exergy, and exergy-economic perspectives. The configuration under consideration aims to maximize the use of geothermal energy. A cascading trans-critical CO2 Rankine cycle (TCRC)/LNG subsystem functions as the primary system, and a cascading ejector cooling system (ECS)/humidification-dehumidification (HDH) desalination unit functions as the secondary system. The LNG subsystem's output power is transferred to an alkaline electrolyzer for the manufacture of hydrogen once the output power is retrieved from the TCRC. The HDH system and ECS provide the necessary cooling and freshwater. Thus, the suggested plan is transformed into a poly-generation scheme. The addressed research gap lies in the integration of these subsystems to create a novel poly-generation arrangement that simultaneously produces electricity, hydrogen, cooling, and freshwater using geothermal energy—a configuration not yet explored in existing studies. The novelty of this work lies in optimizing this unique system through a comprehensive exergy-economic approach. In the parametric analysis section, geothermal heat source temperature, the hot side temperature difference of TCRC heater, upper pressure of TCRC, and lower temperature in the TCRC are chosen for sensitivity analysis. In conclusion, when taking into account exergy efficiency and the payback period as two opposing objective functions, they are determined to be 16.99 % and 0.616years, respectively, in the optimization process. At this stage, the suggested configuration is capable of generating 435.9 kW of power, 251.5 kW of cooling, 3.68 kg/h of hydrogen, and 0.0493 kg/s of freshwater.