Comparative analysis on design and off-design performance of novel cascade CO2 combined cycles for gas turbine waste heat utilization

To provide a higher energy conversion efficiency for gas turbines (GT), this paper proposes a novel twostage cascaded supercritical CO2 and transcritical CO2 (sCO2-tCO2) power cycle for waste heat recovery (WHR) of GT exhaust. A comparative study on system design and off-design performance is conducted between the typical GT-sCO2 cycles and the novel GT-cascaded CO2 (GT-CCO2) cycles based on the detailed steady-state mathematical models and self-built simulation platform. The simple layout (SSBC) and recompression layout (RSBC) are chosen to represent the typical sCO2 Brayton cycle configurations. The simulation results show that the SSBC-tCO2 cycle is more suitable than the RSBC-tCO2 cycle to work as the bottoming cycle for GT since the SSBC-tCO2 cycle can produce higher power with a simpler configuration. Compared with the traditional GT-RSBC and GT-SSBC, the optimal GT-CCO2 cycle (GTSSBC-tCO2) gains an improvement of 5.32% and 4.32% for the thermal efficiency, and a decrement by 4.08% and 2.42% for the Levelized cost of electricity respectively. The combined GT-CCO2 cycles show superior performance with the variable inlet guide vane modulation during the off-design conditions because this control strategy increases the GT exhaust gas temperature and thus brings about a large improvement of the bottoming cycle output power. These findings could provide references for high efficiently utilizing gas turbine exhaust and verify the commercial viability of the CO2 system. (c) 2022 Published by Elsevier Ltd.