The Methodology to Improve the Performance of a Selective Catalytic Reduction System Installed in HRSG Using Computational Fluid Dynamics Analysis

The effective methods to increase nitrogen oxides (NOx) removal efficiency of a commercial-scale selective catalyst reduction (SCR) system can be achieved through improving ammonia (NH₃) concentration distribution at the catalyst layer using computational fluid dynamics (CFD) analysis. This methodology was suggested and applied to the commercial-scale heat recovery steam generator (HRSG), and the flue gas mass flux distribution passing through the ammonia injection grid (AIG) was computed by CFD analysis with porous media assumption. The optimal NH₃ injection rate for individual AIG in the group(s) was determined according to the flue gas mass flux distribution. The experimental results and CFD analysis results have shown that the NOx removal efficiency of the commercial-scale SCR system was improved from 54.4 to 74.8% as NH₃ concentration deviation at the catalyst layer was reduced from 23 to 8.6%. This clearly indicated that the increase of NH₃ concentration homogeneity at the catalyst layer contributes to improve the performance of the commercial-scale SCR system not only for NOx removal efficiency but also for minimizing NH₃ slip.