Direct numerical simulation of flow and surface reaction in de-NOx catalyst

Selective catalytic reaction is a very efficient method to reduce NO_x emissions from thermal power plants and is widely used in Japan. To develop a higher performance de-NO_x system and optimize its maintenance schedule, it is important to understand the NO_x reduction mechanism in the honeycomb channel which supports the de-NO_x catalysts. In this study, the effects of duct channel flow behavior on the de-NO_x reaction at the catalyst surface were investigated using a direct numerical simulation (DNS). The DNS computations were performed for three inflow conditions, one laminar and two turbulent. The results show that although the flow transitions from turbulent to laminar flow as the flow moves downstream for the turbulent inflow conditions, de-NO_x reaction rates for the turbulent inflow conditions are higher than that for the laminar inflow condition even in the downstream region. This is because of the remaining cross-sectional fluid motions caused by the inflow turbulence. As a result, de-NO_x efficiencies for the turbulent conditions are higher than that for the laminar case. For both laminar and turbulent inflow conditions, de-NO_x reaction is suppressed in the corner regions due to the flow stagnation.