Proposal and assessment of a new geothermal-based multigeneration system for cooling, heating, power, and hydrogen production, using LNG cold energy recovery

Abstract

Multigeneration systems (MGSs) driven by renewable sources are proved as cutting-edge technologies for multiple productions purposes to curb greenhouse gas emissions. With this regard, a novel geothermal-based MGS is proposed to produce multiple commodities of cooling, heating, power, and hydrogen, simultaneously, using liquefied natural gas (LNG) as cold energy recovery. The system is composed of an organic Rankine cycle (ORC), an ejector refrigeration cycle (ERC), an LNG power generation system, and a proton exchange membrane (PEM) electrolyzer system. To demonstrate the feasibility of the proposed MGS, energy, exergy, and exergoeconomic analysis are employed as the most effective tools for the performance assessment of the system. It is found that the proposed MGS can produce cooling capacity, heating capacity, net output power, and hydrogen of 1020 kW, 334.8 kW, 1060 kW, and 5.43 kg/h, respectively. In this case, the thermal efficiency, exergy efficiency and total SUCP (sum unit cost of the product) of the MGS are calculated 38.33%, 28.91%, and 347.9 $/GJ, respectively. Furthermore, condenser 2 is introduced as the main source of irreversibility of the proposed MGS by exergy destruction ratio of 58.98%. Moreover, a comprehensive parametric study is carried out and it is concluded that the SUCP of the system can be optimized based on the geothermal inlet temperature. In addition, it is demonstrated that a higher thermal efficiency can be obtained by increasing the turbine 2 expansion ratio, evaporator temperature, and geothermal temperature or decreasing of the generator terminal temperature difference, turbine 1 expansion ratio, pump 3 pressure ratio, and condenser temperature. In the same vein, a higher exergy efficiency can be attained at high turbine 1 expansion ratio, turbine 2 expansion ratio, evaporator temperature, and pump 3 pressure ratio or low generator terminal temperature difference, geothermal inlet temperature, and condenser temperature.