Exergoeconomic analysis of a novel trigeneration system containing supercritical CO2 Brayton cycle, organic Rankine cycle and absorption refrigeration cycle for gas turbine waste heat recovery

Abstract

Poly-generation system is gaining more attentions recently due to its advantages of the effective promotion on energy utilization efficiency and deceleration of environmental pollution, as well as the security and reliable improvement on power supply. In this study, a novel trigeneration system composed of a gas turbine cycle (GTC), a regenerative supercritical carbon dioxide (sCO2) Brayton cycle, an organic Rankine cycle (ORC), and an absorption refrigeration cycle (ARC), is proposed. The waste heat exhausted from the GTC is firstly absorbed by sCO2 cycle and then utilized by ORC to generate power. The bottoming ARC is driven by the remaining heat to provide cooling capacity, while the hot water is provided by an intercooler in the GTC. The thermodynamic and exergoeconomic analyses are conducted to investigate the trigeneration system performance. Comparative study is carried out to evaluate the effects of ORC with different working fluids on the whole system performance. Besides, the performances of the proposed system are optimized and compared from the first law, second law of thermodynamics, and exergoeconomic viewpoints. Results show that the trigeneration system can generate 40.65 MW net power, 6.02 MW cooling capacity, and the 9.93 MW heating loads, with 20.17% overall exergoeconomic factor after the optimization on exergoeconomic aspect. Component combustion chamber presents the highest exergy destruction rate, while the subsystem GTC has the largest total exergy destruction and the highest total capital cost, successively followed by sCO2 cycle, ORC, and ARC. Compared with system using n-butane case, the total product unit costs increase by 0.27%, 1.09%, and 0.20% for fluids i-butane, n-pentane, and i-pentane cases, respectively, and the exergy efficiencies elevate correspondingly. However, the thermal efficiencies of above three cases decrease by 0.48%, 0.71%, and 1.06%, respectively. Moreover, combustion chamber is always the most important component for cost in the proposed trigeneration system optimized on the thermodynamic and exergoeconomic aspects, as well as the absorber being foremost in the bottoming ARC.