Optimization Simulation Research On Partition Ammonia Injection Of SCR Denitrification System In Coal-fired Power Plant

With our country’s increasing requirements for the control of nitrogen oxide emissions from coal-fired power plants,Selective Catalytic Reduction(SCR)flue gas denitrification technology has become the main choice for domestic coal-fired power plants.In view of the existing SCR denitrification system,there are generally problems such as large ammonia slip and large deviation of NOx concentration at the reactor outlet.In this paper,the optimization simulation study of the zoned ammonia injection of the SCR denitrification system of coal-fired power plants is carried out.The method of combining numerical simulation analysis and performance test is used to analyze the flow field and concentration field distribution,and the zoned optimized ammonia injection is simulated and calculated.According to the multi-point measurement system,the NOx concentration distribution at the outlet of the SCR can be obtained,then combine with the on-site debugging experience of ammonia injection valve,the simulation results can provide guidance for the optimization strategy of the SCR system’s zoned ammonia injection.In this paper,a 660 MW unit is used as the research object.First,the grid method is used to test the denitration performance of the SCR reactor.It is found that the system has problems such as the mismatch between the ammonia injection and the flue gas NOx,and the large deviation of the outlet NOx concentration distribution,it is necessary to optimize and adjust the partitioned ammonia injection system.The measured flue gas data based on the performance test is used as the simulated inlet boundary condition,and the CFD(Computational Fluid Dynamics)numerical simulation calculation is performed on the flue gas field of the SCR denitration system.Improve the accuracy and practicability of CFD simulation methods by modifying inlet uniformity assumptions and adding catalyst chemical reaction models.The flue gas flow fields under three typical loads(i.e.,100%,75% and 50%)are simulated and the patterns are analyzed,and the influential factors of 5 zones and 42 nozzles on ammonia concentration distribution in 18 zones of catalyst inlet section were obtained.According to the analysis and research of the above-mentioned on-site performance test and flow field simulation results,the distribution characteristics of the flue gas flow field and the ammonia nitrogen concentration field of the unit can be obtained.The simulation results show that the main reason for the uneven distribution of NOx concentration at the outlet of the SCR system is the unreasonable ammonia injection,resulting in an unideal ammonia-nitrogen mixing effect.Based on the ammonia-nitrogen molar ratio at the inlet of the catalyst and the NOx concentration distribution at the outlet,a matrix equation for solving the optimal ammonia injection amount is established based on the ammonia injection influential factor.The optimization results show that the quantitative solution of the optimized ammonia injection quantity based on the influential factor is suitable for different working conditions,and the calculation efficiency is high.After 42 nozzles were simulated and optimized,the relative deviation of NOx concentration at the outlet of three working conditions was reduced to 13.7%,15.3% and 17.6% respectively,and the uniformity was significantly improved,which is better than the optimization effect of 5 zones.Optimization of ammonia injection quantity can be combined with the multi-point measurement results of the NOx concentration at the outlet to provide guidance for on-site ammonia injection valve debugging.