The Role of Part-Load Control Strategies in Optimizing the Efficiency of a Decarbonized Combined Cycle Power Plant in Load-Following Mode

In pursuit of the goal of decarbonization, postcombustion capture (PCC) by means of mono-ethanolamine (MEA), exhaust gas recirculation (EGR), and hydrogen cofiring were applied to a 2 × 1 combined cycle (CC) under load-following operation in two typical summer/ winter days. Keeping the same electrical demand profiles as in a previous study by the same author, the main novelty is to determine the part-load gas turbine (GT) control strategy that can maximize the CC net electric efficiency (gCC,n) when applying different decarbonization solutions such as: addition of PCC unit and addition of PCC unit with EGR, when the fuel supply is 100% natural gas (NG) or 65% vol hydrogen cofiring. The multivariable optimization problem, with gCC,n as objective function, under the constraint of net power output (PCC,n) equal to electricity demand, has been updated to include the following decision variables: load of each GT; EGR rate, depending on the fuel type, i.e., [0; 0.4] for 100% NG versus [0; 0.55] for hydrogen blending; GT inlet air flow and fuel flow, in a range such that the GT outlet temperature is maintained within the limit of about 50 °C above the nominal value. The main finding is that the operating guidelines depend not only on the load but mainly on the environmental conditions. Under hot weather and part-load conditions, the recommendation is to rely on modulating the air/fuel flow at the GT inlet rather than applying EGR.