Optimization of a combined cooling, heating and power system using CO2 as main working fluid driven by gas turbine waste heat

Abstract

A combined cooling, heating and power system driven by marine gas turbine waste heat is proposed. The proposed CCHP system includes a supercritical CO2 (S-CO2) recompression cycle, two transcritical CO2 (T-CO2) refrigeration cycles and a steam generator. Comprehensive thermodynamic and exergoeconomic analyses are performed for the supercritical CO2 recompression cycle, transcritical CO2 refrigeration cycle and the overall system. Considering the importance of compactness and cost to the ship, the total product unit cost and total heat exchanger area per unit exergy output are proposed as the objective functions of the system optimization. Parametric analyses are conducted to study the effects of key operating parameters including the pressure ratio of air compressor, S-CO2 compressor inlet pressure, pressure ratio of S-CO2 cycle, split ratio of S-CO2 cycle and T-CO2 compressor outlet pressure on the total product unit cost and total heat exchanger area per unit exergy output. The optimum system parameters are obtained through the multi-objective optimization method based on the GA (genetic algorithm). The optimization result shows that the optimum values of total product unit cost and total heat exchanger area per unit exergy output are 10.0526 $/GJ and 0.1755 m2/kW, respectively. The result also indicates that by using the CCHP system, 4.9901 MW of power, 0.584 MW of heat capacity, and 0.627 MW of refrigeration capacity can be recovered from the exhaust gas (with the mass flow rate of 95.6102 kg/s, temperature of 466 °C and the major compositions of nitrogen 74.45%, oxygen 15.74%, carbon dioxide 4.77% and water 5.04% by mass). Furthermore, the superiority of the CCHP system is verified through comparative analyses from the viewpoints of exergoeconomic and compactness.