Techno-economic assessment of the retrofit of a natural gas combined cycle for variable load operations

The increasing penetration of renewable energy sources is forcing fossil fuel power plants, where carbon capture and storage represents a key decarbonization pathway, into more frequent part-load operation, requiring greater operational flexibility. In this context, we assess the techno-economic viability of retrofitting an existing natural gas combined cycle power plant operating under variable load conditions, based on realistic hourly dispatch data, by integrating a post-combustion carbon capture system using a piperazine 20% wt. and methyldiethanolamine 10% wt. solvent blend. The thermodynamic performance of the retrofitted plant is assessed through process simulation in Aspen Plus, while the economic and investment viability is evaluated using MATLAB. Results demonstrate that the retrofitted plant achieves 90% CO 2 capture rate across all operating conditions, with a 6 percentage point efficiency penalty compared to the unabated baseline, maintaining a high global efficiency of 50%. From an economic perspective, the retrofitted configuration exhibits a levelized cost of electricity of 156 €/MWh and a CO 2 avoidance cost of 115 €/t CO 2 , avoid , both competitive with alternative low-carbon generation options. Net present value analysis confirms the economic feasibility of the retrofit under current European market conditions. Furthermore, with carbon prices expected to rise in line with decarbonization targets, investment profitability is projected to improve progressively.