THERMODYNAMIC OPTIMIZATION OF LOAD-FOLLOWING OPERATION IN A DECARBONIZED COMBINED CYCLE POWER PLANT UNDER NET-ZERO SCENARIOS

Post-combustion capture (PCC) by means of monoethanolamine (MEA) and hydrogen co-firing, combined with exhaust gas recirculation (EGR), were applied to a typical 2x1 combined cycle (CC) with the goal of reaching net-zero CO2 emissions. The novelty lies in integrating decarbonization solutions into the daily operation of the CC, when power generation is adjusted according to fluctuations in electricity demand, throughout two representative days in summer and winter. More specifically, off-design thermodynamic modelling was adapted to incorporate a multivariable optimization problem to find the maximum power plant efficiency as a function of the following decision variables: - load of each gas turbine (GT), spanning from minimum turndown to full load; - EGR rate, in a range that depends on the fuel type: [0; 0.4] for 100% natural gas (NG) vs. [0; 0.55] when hydrogen is fed to the combustor; with the constraint of net power output equal to electricity demand, for given environmental conditions. Suggestions were made to mitigate the energy penalty due to decarbonization in the load-following operation mode, taking the integration of MEA CO2 capture into the NG-fired CC as a benchmark. The solution in which EGR combines optimally with hydrogen in the fuel mixture, with the addition of PCC to abate residual CO2 emissions, has proven to be the most efficient way to provide dispatchable clean energy, especially in cold climates. Keywords: combined cycle; hydrogen; carbon capture; load following; dispatchable zero-carbon generation