Technologies for gas turbine power generation with CO2 mitigation
A review of the state of the art gas turbine power plants designs with CO2 capture was performed to set up a list of technologies to be considered in a conceptual process superstructure. It has been found that the efficiency and economics of carbon dioxide capture in gas turbine combined cycle power plants can be remarkably improved by introducing Flue Gas Recirculation (FGR) so as to increase the CO2 concentration in the flue gas and to reduce the volume of the flue gas treated in a CO2 capture plant. Thus, this process was chosen as the main focus of the thermo-economic modeling and the combustion system related experimental testing. Combustion studies were performed to quantify the impact of reduced oxygen content (caused by flue gas recirculation) on combustion stability and emission characteristics (NO x, CO). Tests were performed with methane, methane/ethane (simulated natural gas), methane/hydrogen and natural gas (as distributed in Switzerland) at different FGR ratios. For all conditions the addition of ethane or hydrogen shows beneficial effects (restoration of flame reactivity) on flame stability and CO emission. Using PSI's high pressure test rig, it has been shown, that by redirecting up to 30% of exhaust gas volume back to the combustor, the CO 2 concentration in the exhaust can be increased to 8% vol. while keeping the flame temperature constant (Tad = 1750 K) and meeting the emission requirements (CO, NOx < 25ppm @ 15% O2). Benchmark tests of catalytic partial oxidation reactors were performed to determine whether sufficient H2 could be produced in situ by reaction of a slip stream of natural gas with extracted compressor oxidant. The work confirmed that FGR has the potential to significantly reduce the energy penalty connected with post-combustion carbon capture techniques and still meet the requirements on NOx and CO emissions.