Comparative investigation on techno-economics of cascade supercritical CO2 combined cycles for waste heat recovery of typical gas turbines

Abstract

An advanced supercritical CO2 (sCO2) power cycle for recovering waste heat from the gas turbine (GT) is thought to be an effective way to improve energy utilization efficiency and achieve low-carbon power generation. To obtain the best techno-economic sCO2 cycle configurations at various capacity levels, eight cascade cycle configurations were designed for coupled power generation with typical gas turbines in the power range of 11.4–593 MW, with the number of heaters, the number of split flow branches, and inter-cooling process as variables. The techno-economics of cascade sCO2 combined cycles were assessed and compared using various engineering equations. The results show that adding a heater and inter-cooling process increases the levelized cost of electricity (LCOE) by about 0.53 $/(MWh) and 0.99 $/(MWh) on average, respectively, while adding a split flow branch can decrease the LCOE by about 1.3 $/(MWh) on average. In addition, the increase in installed capacity can lead to a lower LCOE. When the net power range of the combined cycle is 14.9–767.1 MW, the LCOE of the triple cascade cycle ranges from 56.45 to 32.52 $/(MWh). Compared to a conventional combined cycle, using a cascade sCO2 cycle as the bottom cycle can decrease the LCOE by approximately 12.1–16.2%. Sensitivity analysis reveals that natural gas price has the greatest effect on LCOE, followed by annual operating hours, and suggests efficient ways to decrease the LCOE. The triple cascade cycle is recommended at all capacity levels due to its lower LCOE. The specific cost (SC) and LCOE prediction equations for the combined cycle are proposed for the first time to aid in the design and techno-economic assessment of the cascade sCO2 combined cycles.