Thermodynamic analysis and system design of the supercritical CO₂ Brayton cycle for waste heat recovery of gas turbine

The supercritical CO₂ cycle is regarded as a potential replacement of steam on concentrated solar power, new generation nuclear reactor, fossil combustion power, waste heat recovery, and so on. It has advantages in high energy flux density, compact equipment, higher cycle efficiency, product modularization. In this paper, the thermodynamic analysis of supercritical CO₂ Brayton cycle for the waste heat recovery of the LM2500 gas turbine is discussed with the energetic and exergetic analyses via a system simulation program. The efficiency of waste heat utilization should be considered as the prior target in the system design and optimization. As regards the basic cycle, there are huge energy/exergy losses from the boiler due to the high temperature exit gas and the temperature gap between the exhausted gas and the supercritical CO₂. Besides, in the recuperator, the exergy loss is also significant due to the temperature difference on both sides. Therefore, an energy classification utilization cycle (the advanced cycle) is designed and analyzed. In both the energetic and exergetic analyses, the advanced cycle shows good system performances. Through the optimization, the advanced cycle can output the maximum net power as 8.81-MW higher 2.35MW output than the basic cycle, with the efficiency of waste heat utilization of 25.10% and the efficiency of exergy of 64.78% increased by 6.7% and 17.28% compared to the basic cycle, respectively.