Exergoeconomic analysis and optimization of a combined cooling, heating and power system based on organic Rankine and Kalina cycles using liquified natural gas cold energy

Abstract

With the increase of liquified natural gas trade, more and more attention has been paid to the liquified natural gas cold energy utilization. In order to better recover and utilize liquified natural gas cold energy, a novel combined cooling, heating and power system based on liquified natural gas cold energy utilization and exhaust gas waste heat recovery is proposed in this paper. The system consists of a three-stage organic Rankine cycle, a Kalina cycle and liquified natural gas direct expansion. To evaluate the performance of the combined cooling, heating and power system, a mathematical model was established, and through the thermodynamic analysis the net output power, thermal efficiency, and exergy efficiency of the system were 1257.708 kW, 43.43%, and 70.4%, respectively. The effects of the pump and compressor outlet pressure, n-hexane mass flow rate in the first Rankine cycle, turbine inlet temperature, and isentropic efficiency of the turbines on the system performance were analyzed. Moreover, exergoeconomic analysis is used to calculate the total product unit cost of the combined cooling, heating and power system, which was found to be 51.1 $/GJ. In addition, single- and multi-objective optimizations of the system were performed. The multi-objective optimization results show that the maximum exergy efficiency and minimum total product unit cost of this novel combined cooling, heating and power system were 80.49% and 48.04 $/GJ, respectively. This work shows a great potential in utilizing the liquified natural gas cold energy and waste heat of exhaust gas by a combined cooling, heating and power system.