Exhaust gas recirculation in gas turbines for reduction of CO2 emissions.: Combustion testing with focus on stability and emissions.

Exhaust gas recirculation can be applied with the intention to reduce the CO2 emissions. When a fraction of the exhaust gas is injected in the entry of a gas turbine, the amount of CO2 in the exhaust gas not being recirculated will be higher and less complicated to capture. However, with this change in combustion air composition, especially the reduced concentration of oxygen, the combustion process will be affected. The lower oxygen concentration decreases the stability and the increased amount of CO2, H2O and N-2 will decrease the combustion temperature and thus, the NO, emissions. Testing has been performed on a 65 kW gas turbine combustor, to investigate the effect of adding N-2, CO2 and O-2 in the combustion process, with focus on stability and emissions of NOx. Results show that adding N-2 and CO2 decrease the NOx emissions, whereas O-2 addition increases the NOx emissions. The tests have been performed both in a diffusion flame (pilot burner) and a premixed flame (main burner), and for additives being injected with the fuel or with the air stream. Addition into the fuel stream is proven to affect the NOx emissions most. The stability limits of the flames are indicated with respect to massbased additive-to-fuel ratios.