Performance analysis and optimization of a combined cooling and power system using low boiling point working fluid driven by engine waste heat

This paper develops a combined cooling and power system, which consists of a carbon dioxide Brayton cycle, a dual-pressure organic Rankine cycle and an ejector refrigeration cycle, to recover waste heat from exhaust gas and jacket water in internal combustion engines. Thermodynamic models of the system are performed and exergoeconomic methods are used to calculate the levelized exergy cost of the component products. Effects of seven parameters, including Brayton cycle turbine inlet temperature and inlet pressure, organic Rankine cycle turbine high-pressure side and low-pressure side inlet temperature and ejector primary inlet pressure, are evaluated. Single-objective optimization is carried out by means of genetic algorithm to obtain the minimum levelized exergy cost of system product. Results show that the increase of pressure at Brayton cycle turbine inlet and high-pressure and low-pressure side of the organic Rankine cycle turbine inlet contributes to the decrease of levelized exergy cost of the system product. Optimization results show that minimum levelized exergy cost for system product is 53.25 $ (MWh)⁻¹. When system product levelized exergy cost is minimum, system net power output, cooling capacity and exergy efficiency are 374.37 kW, 188.63 kW and 37.31%, respectively.