High-pressure reaction and emissions characteristics of catalytic reactors for gas turbine combustors

The reaction and emissions characteristics of catalytic reactors comprising noble metal catalysts were investigated using homogeneous mixtures of natural gas and vitiated air at pressures up to 2.9 MPa. The mixture temperatures at inlet ranged from 500 to 700 degrees C and the fuel-air ratio was increased till the exit gas temperature reached about 1200 degrees C. Values of combustion efficiency greater than 99.5% and nitrogen oxides emissions for all catalytic reactors tested were less than 0.2 g NO2/kg fuel (2 ppm (15% O-2)) for all reactors at reactor exit gas temperatures higher than about 1100 degrees C. Combustion efficiency decreased with increasing pressure in the heterogeneous-reaction controlled region, though a pressure increase favored homogeneous, gasphase reactions. Appreciable reactivity deterioration by aging for 1000 h at 1000 degrees C was observed at lower mixture temperatures. A two-stage combustor comprising a conventional flame combustion stage and a catalytic stage was fabricated and its NOx emissions and performance were evaluated at conditions typical of stationary gas turbine combustor operations. About 80% reduction in NOx emissions levels compared with flame combustion was attained at 1 MPa pressure and 1180 degrees C exit gas temperature, together with complete hydrocarbon combustion.