HIGH-PRESSURE REACTION AND EMISSIONS CHARACTERISTICS OF CATALYTIC REACTORS FOR GAS-TURBINE COMBUSTORS

The reaction and emissions characteristics of catalytic reactors compr ising noble metal catalysts were investigated using homogeneous mixtur es of natural gas and vitiated air at pressures up to 2.9 MPa. The mix ture temperatures at inlet ranged from 500 to 700 degrees C and the fu el-air ratio was increased till the exit gas temperature reached about 1200 degrees C. Values of combustion efficiency greater than 99.5% an d nitrogen oxides emissions for all catalytic reactors tested were les s 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 ef ficiency decreased with increasing pressure in the heterogeneous-react ion 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 perfor mance were evaluated at conditions typical of stationary gas turbine c ombustor operations. About 80% reduction in NOx emissions levels compa red with flame combustion was attained at 1 MPa pressure and 1180 degr ees C exit gas temperature, together with complete hydrocarbon combust ion.