A partitioned dynamic ammonia injection strategy based on real-time NOx flux distribution characteristics in an SCR system

Abstract

To optimize the NOx/NH3 (Nitrogen Oxides/Ammonia) matching ratio for a SCR (Selective Catalytic Reduction) system, dynamic NH3 injection was achieved on the basis of the constructed control rules for critical AIG (Ammonia Injection Grid) branch-pipe valves via the determination of the basic NH3 injection amount and the secondarily distributed NH3 injection amount. Moreover, the real-time NOx flux distribution characteristics in each subzone were analysed on the basis of the operation data of the flue gas velocity and NOx concentration originating from multiple measuring points located in the flue cross-section which is in front of the AIG. The engineering application results of a 350 MW coal-fired unit revealed that 12 “critical” AIG branch-pipe valves achieved dynamic NH3 injection. With a maximum fluctuation in NOx flux of 433 mol/h in the subzone of the individual flue cross-section, the opening of this AIG branch-pipe valve was subsequently adjusted by 22° to optimize the NOx/NH3 matching ratio in the system in a timely manner. The ACRs (Ammonia Consumption Rates) of the A and B sides in the studied SCR system were reduced by approximately 26.70 % and 11.90 %, respectively. In addition, the average RSD (Relative Standard Deviation) of the NOx concentration at the outlet of the SCR reactor for sides A and B were approximately 11.9 % and 13.6 %, which were reduced by approximately 11.63 % and 15.47 %, respectively, owing to the application of the dynamic NH3 injection strategy.