Energy, exergy and economic analysis of different integrated systems for power generation using LNG cold energy and geothermal energy

This paper constructs four integrated power generation systems using liquefied natural gas (LNG) cold energy and geothermal energy. These systems contain a geothermal single flash cycle, LNG expansion process and organic Rankine cycle (ORC). Different mathematical models are established to simulate the systems under steady-state conditions respectively. The influences of key working parameters on energy efficiency, exergy efficiency and levelized cost of energy (LCOE) are analyzed, and the comprehensive performances are estimated. The results show that increasing separator pressure, LNG turbine and Rankine turbine inlet pressures could increase the energy and exergy efficiencies. Also, a higher LNG turbine outlet pressure leads to a higher LCOE. To achieve the best system performance, single- and multi-objective genetic algorithm (GA) based optimizations are performed respectively. By single-objective optimization, GSF-TSORC and GSF-TPORC can reach the highest energy and exergy efficiencies of 34.80% and 52.61% respectively, and GSFC has the lowest total cost rate of 0.326 M$·year−1. After using multi-objective optimization, the energy and exergy efficiencies of GSF-TPORC are 29.56% and 51.29% respectively, which are superior to the other three systems, from the thermodynamic point of view. From an economic perspective, GSF-ORC has the lowest LCOE of 0.028 $·kWh−1, implying that it is the best system.