Thermodynamic Assessment of a Combined Cycle Gas Turbine with Post-Combustion Carbon Capture and Exhaust Gas Recirculation Under Part-Load Operation

Applying post-combustion Carbon Capture (CC) is a solu- tion to reduce CO2 emissions from Combined Cycle Gas Turbine (CCGT) power plants. However, its deployment is hindered by its high CAPEX as well as the high OPEX linked with the energy re- quired for the solvent regeneration process, reducing the global plant efficiency. Performing Exhaust Gas Recirculation (EGR) has the potential to lower the CC cost: indeed, the flue gas flow rate is reduced, while its CO2 content is increased significantly, leading to a lower CC penalty. However, knowing that CCGTs will operate most of the time under part-load conditions to back- up renewable production, the impact of using EGR during part- load CCGT operating conditions is still unclear. Therefore, the objective of this work is to investigate different operating strate- gies for the application of EGR under full and part-load CCGT operations. To this end, an Aspen Plus model has been built and validated using data from Thermoflow, to which an EGR loop has been added. The results show that keeping the turbine inlet temperature constant is the operating strategy that maxi- mizes CCGT performance when EGR is applied. In contrast, working with a constant turbine exhaust temperature degrades performances. Therefore, maintaining the same turbine exhaust temperature setpoints for the load control strategy with and with- out EGR reduces the CCGT performance when EGR is applied. Finally, EGR provides flue gas characteristics more favourable to carbon capture in terms of size, performance and flexibility.