Study of the influence of static mixers of evaporation and distribution of injected Urea in SCR systems

Abstract

[EN] Nitrogen oxides are an important pollutant in industrialized countries. A widely used technology to reduce NOx emissions is Selective Catalytic Reduction (SCR) with ammonia as a reducing agent. SCR has been applied in power plant for several decades. Recently SCR has been established in heavy duty engines used in trucks. It is likely to become a key technology in passenger cars applications which may be unavoidable due to the latest Euro VI legislation. This miniaturization of SCR systems cause some additional problems. From among this difficulties one of the biggest is limited space and therefore time which is available to urea evaporation and decomposition. This obstacle is overcoming by using static mixers before SCR catalyst. Influence of mixers geometry is the aim of this thesis. During the study various types of geometry have been analyzed. For all of them influence of mixer construction on NH3 uniformity, pressure drop and wall film formation has been checked. Influence of mixer position (first geometry), trumpet construction and injector inclination (second geometry) has been also calculated. As a result of several modifications large improvement of system performance has been achieved. In first case trough base mixer modification NH3 uniformity has been increased by 12 percentage points and film formation has been decreased by half. Using the same mixer combined with changes in injector inclination helped to increase NH3 uniformity by 14p.p and film formation by more than half in second case.