Catalytic combustion for NOx abatement.

This paper describes concept and current status of development of catalytic combustion for NOx (nitrogen oxides) abatement. Catalytic combustion is an alternative technology, currently under development, which has been offering the potential of meeting SCR (Selective Catalytic Reduction of NOx) emission level and cost reduction. A conventional combustion process produces a peak temperature which is far into the thermal NOx formation region. In contrast, a catalytic combustion process maintains a peak temperature well below the NOx formation region without compromising combustion efficiency.Two types of the catalytic combustion concept have been proposed. One employs both homogeneous (gas phase) reaction and heterogeneous (catalyst surface) reaction to accomplish complete combustion within a honeycomb catalyst bed. It suggests that the catalyst temperature reaches the adiabatic temperature of fuelair mixtures and that the catalyst shoud withstand above 1300°C. The other employs only heterogeneous reaction, within a honeycomb catalyst bed, to reduce maximum catalyst temperature. And, complete combustion takes place in a post catalyst bed without a catalyst. The maximum catalyst temperature is maintained around 1000°C.Based on these concepts, several development programs for gas turbine applications have been conducted in USA and Japan. They demonstrated very low NOx emission performance (lower than 10ppmv). Despite the low NOx capability of catalytic combustion, further development efforts are needed in catalyst material, combustor design and control system.