Thermodynamic Assessment of a Combined Cycle Gas Turbine With Exhaust Gas Recirculation Under Part-Load Operation Toward Carbon Capture Penalty Reduction

Performing Exhaust Gas Recirculation (EGR) is a solution to reduce the negative impact of applying Post-Combustion Carbon Capture (PCCC) on Combined Cycle Gas Turbine (CCGT) power plant. 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 operation is still unclear. Therefore, the objective of this work is to investigate different operating strategies for the application of EGR under full and part-load CCGT operations. To this end, an Aspen Plus model of the CCGT has been built and validated using data from Thermoflow, to which an EGR loop has been added. The PCCC unit is not modelled in this work and will be addressed in future work. The results show that keeping the turbine inlet temperature constant is the operating strategy that maximizes CCGT performance when EGR is applied. In contrast, working with a constant turbine exhaust temperature degrades performance. Therefore, the load control strategy currently used for heavy-duty gas turbines, which follows a fixed turbine exhaust temperature profile, will induce a performance reduction when EGR is applied. A strategy based on a turbine inlet temperature, rather than an exhaust temperature setpoint, would improve performance. Finally, EGR provides flue gas characteristics more favourable to carbon capture in terms of size, performance, and flexibility.