Thermo-economic analysis of combined different ORCs geothermal power plants and LNG cold energy

Abstract

Thermo-economic analysis is applied to four combined liquefied natural gas (LNG) cold energy and (1) simple, (2) with internal heat exchanger, (3) regenerative and (4) dual-fluid ORCs. These power plants use geothermal fluid energy as low-grade heat source and cold energy of LNG as thermal sink. Also, after vaporization in the organic fluid condenser, natural gas expands in a turbine to generate power. The effects of operating parameters on energy and exergy efficiencies as well as total annual cost rate are studied for the proposed systems. The operating parameters considered include inlet pressure of the organic fluid and natural gas turbines, condensing temperature of organic fluid, minimum temperature difference in evaporator, inlet temperature and mass flow rate of geothermal fluid. Moreover, optimal values of operating parameters of the system are evaluated to maximize the energy and exergy efficiencies and minimize the total product unit cost. The results show that the highest energy and exergy efficiencies are obtained for regenerative system and for the system with internal heat exchanger, respectively, while the simple system has the lowest total product cost. Furthermore, the maximum net power output is obtained using dual-fluid system at the same operating condition. Also, the higher and lower total cost rate in optimum performance condition belong to dual-fluid and regenerative systems, respectively.