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

• A partitioned dynamic ammonia injection strategy for optimization. • The real-time NO x flux distribution in front of ammonia injection grid was perceived. • The basic and secondary distribution NH 3 injection were introduced to control rules. • Less NH 3 consumption and more uniform outlet NO x distribution were achieved. To optimize the NO x /NH 3 (Nitrogen Oxides/Ammonia) matching ratio for a SCR (Selective Catalytic Reduction) system, dynamic NH 3 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 NH 3 injection amount and the secondarily distributed NH 3 injection amount. Moreover, the real-time NO x flux distribution characteristics in each subzone were analysed on the basis of the operation data of the flue gas velocity and NO x 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 NH 3 injection. With a maximum fluctuation in NO x 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 NO x /NH 3 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 NO x 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 NH 3 injection strategy.