Design Performance Simulation of a Supercritical CO2 Cycle Coupling With a Steam Cycle for Gas Turbine Waste Heat Recovery

Abstract

This study presents a train of thought and method for flue gas energy utilization management by connecting an optimized supercritical carbon dioxide (S-CO2) Brayton cycle with a selected steam/water Rankine cycle to recover the turbine exhaust gas heat with promising flue gas coupling capacity. Better performance over the currently used steam/water bottoming cycle is expected to be obtained by the combined bottoming cycle after the S-CO2 cycle is coupled with the high-temperature flue gas. The performances of several S-CO2 cycles are compared, and the selected steam/water cycle is maintained with constant flue gas inlet temperature to properly utilize the low-temperature flue gas. Aspen Plus is used for simulating the cycle performances and the flue gas heat duty. Results show that the recompression S-CO2 cycle with the reheating process is most recommended to be used in the combined bottoming cycle within the research scope. The suggested combined bottoming cycle may outperform most of the triple reheat steam/water cycles for the turbine exhaust temperature in the range of 602–640 °C. Subsequently, it is found that the intercooling process is not suggested if another heat recovery cycle is connected. Moreover, the specific work of the suggested S-CO2 cycles is calculated, and the bottoming cycle with the preheating cycle with the reheating process is found to be more compact than any other combined bottoming cycles.