Performance optimization of static mixer in urea-SCR system considering flow and turbulence characteristics

• CFD analysis was conducted on static mixer model in 2 MW class diesel engine. • Impact of two different blades on flow characteristics and mixing efficiency studied. • Higher blockage ratios intensify swirl flow enhancing mixing performance. • Blade #1 deflects flow while Blade #2 intensifies turbulence for mixing. • Optimization of blade size and position reduces back pressure and improves mixing. The urea-Selective Catalytic Reduction (SCR) system is known to be the most proven technology among the various de-NO x technologies in diesel engines. Since hydrogen and ammonia fuel are focused on every thermal system for carbon neutral policy, thermal NO x by hydrogen, and fuel NO x by ammonia would be increased. In the urea-SCR system, the NO x reduction efficiency depends on the NH 3 concentration and velocity uniformity in the catalyst layer. Uniformity improves with longer flow lengths, but since the flow into the SCR is limited to 2.5 mbar back pressure, a static mixer is required to maximize uniformity while minimizing the length of the mixer to improve uniformity. The flow characteristics of blockage ratio (BR) were evaluated by the blade geometry of a static mixer used in the 2 MW class urea-SCR system. Mixing performances and flow by characteristics were investigated using numerical analysis. As a result, swirl flow was formed by the complex interaction between two blades (Blades #1 and #2) due to the geometry of the static mixer. Blade #1 increased uniformity index(UI) by 8.8 % compared to Blade #2, and Blade #2 increased turbulent intensity(TI) by 28.5 % compared to Blade #1. The influence of blade offset was analyzed. As blade offset increased, back pressure decreased by 37.5 % in all BRs, and the reactor’s inlet UI vel decreased by 5.9 %, 5.6 %, and 3.5 % in BR50, BR45, and BR40, respectively. The cases satisfying all constraints with the maximum mixing performance and back pressure were “BR40–1–0.9D” or “BR40–1–1.2D”.