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, post-combustion capture (PCC) by means of mono-ethanolamine (MEA), exhaust gas recirculation (EGR) and hydrogen co-firing were applied to a 2 × 1 combined cycle (CC), chosen as representative of existing power plants, 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 (ηCC,n) when applying different decarbonization solutions such as: 1) addition of PCC unit, 2) addition of PCC unit with EGR, when the fuel supply is 100% natural gas (NG) or 65% vol hydrogen co-firing. The multivariable optimization problem, with ηCC,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, in the range from minimum turndown to full load; - EGR rate, in a range that depends on the fuel type: [0; 0.4] for 100% NG vs. [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 ultimate goal is to identify the most efficient solution to decarbonize a CC under the assumption of flexible generation. 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.