Thermo-economic assessment and optimization of a geothermal-driven tri-generation system for power, cooling, and hydrogen production

Abstract

A tri-generation layout is proposed in the paper, which is composed of a novel cascade power generation system, a transcritical CO2 compression refrigeration system (CCRS) with LiBr–H2O absorption refrigeration system (ARS) after-cooler, and a proton exchange membrane electrolyzer (PEME). The performance of the system is evaluated and optimized based on the thermodynamic and exergoeconomic principles. The cascade system consists of a modified Kalina cycle (MKC), an organic Rankine cycle (ORC), and a liquefied natural gas (LNG) subsystem, which is driven by a geothermal heat source. Employing the MKC in such cascade systems and using the absorption subcooling method for the CCRC in a tri-generation system have not been investigated in previous studies. The cooling system and PEME are correspondingly fed by the output power of the ORC and MKC while the output electricity is generated in the LNG subsystem. An optimum point was selected from two scenarios of tri-objective optimization using a hybrid Genetic-Fgoalattain algorithm. The optimization of the proposed system revealed an exergy efficiency of 26.5%, which is much higher than the values reported for the similar tri-generation systems in the literature. At the optimal point, the net output power, cooling rate, and hydrogen rate produced by the system are 451.8 kW, 297.8 kW, and 2.274 kg⋅h−1, respectively. Moreover, the payback period of the system is obtained as 2.385 years.