Retrofitting an Existing Combined Cycle Gas Turbine With Post-Combustion Carbon Capture: Assessment of Solvent Selection Impact on Performance

Abstract Amine(s)-based post-combustion Carbon Capture (CC) is the most mature and applicable technology to retrofit existing Combined Cycle Gas Turbine (CCGT) assets into low-carbon power plants. However, its deployment is hindered by high CAPEX as well as high OPEX, linked with the energy requirement for the solvent regeneration process, reducing the global plant efficiency. Hence, CC energy penalty reduction is necessary. Next to performing Exhaust Gas Recirculation (EGR), efficient heat integration is a key strategy, involving the extraction of steam from the most suitable location in the steam cycle to supply the CC solvent regeneration heat. The choice of extraction location depends on the required steam quality for solvent regeneration, which, in turn, is influenced by the specific solvent used in the carbon capture process. Therefore, it is imperative to evaluate the different integration strategies for individual solvents and analyse their influence on the overall performance of the plant. In this study, we investigate the use of two distinct solvents: monoethanolamine (MEA), the conventional choice, and a blend of methyldiethanolamine (MDEA) and piperazine (PZ) for CC application to a CCGT. The objective is to conduct a comprehensive comparison between both solvents, examining their heat integration and impact on plant performance for the retrofitting of an existing CCGT with post-combustion carbon capture. To this end, a thermodynamic analysis of a typical CCGT plant equipped with EGR and coupled with an amine(s)-based CC plant has been performed using specific simulation models in Thermoflex and Aspen Plus. Different heat integration strategies are presented and compared for both solvents. Results show that, by extracting steam from the Intermediate Pressure/Low Pressure (IP/LP) crossover, using MDEA/PZ instead of MEA allows to increase the electrical efficiency by 0.5 absolute percentage points, representing an efficiency reduction associated to the CC of 6.2 abs.%. However, extracting steam of higher quality, before the Intermediate Pressure (IP) steam turbine, leads to a more significant performance degradation, with an efficiency penalty of 8.3 abs.%. Consequently, the optimal option for retrofitting existing CCGT with MDEA/PZ-based CC is to extract steam from the IP/LP crossover under full-load operation. Future works will focus on part-load operation of the integrated CCGT-CC.