Thermodynamic analysis and comparison of two new tri-generation (hydrogen, power, heating) systems using geothermal energy

In this study, two new multi-generation (hydrogen, power, heating) systems are thermodynamically analyzed and optimized. For the proposed cycles, the two systems are distinguished by the power generation cycle, so that the organic Rankine cycle and the Kalina cycle are used to produce power. Both systems also use domestic water heater for heating and proton exchange membrane electrolyzer for hydrogen production. After the thermodynamic simulation, a comprehensive study was performed for evaluating the parameters affecting hydrogen production, net output power, heating, thermal efficiency and exergy efficiency of two cogeneration systems and finally, an optimization was performed from an exergy efficiency point of view. According to the results of this study, for the organic Rankine cycle-based tri-generation system, when evaporator temperature increases exergy efficiency and hydrogen production show optimum values while for Kalina cycle-based tri-generation system, hydrogen production and exergy efficiency increase. Also, according to the study of various operating fluids for the organic Rankine cycle, the R152a as an organic Rankine cycle fluid produces more hydrogen. Furthermore, based on the optimized results for 120 °C heat source temperature, the Kalina cycle-based tri-generation system has more exergy efficiency and more hydrogen production than the organic Rankine cycle-based tri-generation system.