Optimization and Comparison of Two Combined Cycles Consisting of CO2 and Organic Trans-Critical Cycle for Waste Heat Recovery

摘要

CO2-based trans-critical and supercritical cycles have received more and more attention for power generation in many applications such as solar and nuclear energy due to the desirable thermal stability and properties of CO2 and the high efficiency and compact size of the plant. In this study, two combined cycles driven by the flue gas exhausted from the LM2500+ gas turbine, CO2-TC+OTC (organic trans-critical cycle) and CO2-TC/OTC, which can achieve a good trade-off between thermal efficiency and utilization of the waste heat, are investigated. Parameters optimization is carried out by means of genetic algorithm to maximize the net power output of the combined cycle and the effects of the key parameters on the cycle performance are examined. Results show that the exergy efficiency of CO2-TC+OTC is about 2% higher than that of CO2-TC/OTC. In CO2-TC+OTC, the recuperation process of CO2 causes the largest exergy loss; in CO2-TC/OTC, the largest exergy loss occurs in the heat recovery vapor generator, followed by the intermediate heat exchanger due to the larger variation of the specific heat capacity of CO2 and organic fluid in the heat addition process.