Optimization Of Ammonia-injection In Denitration System Of 600MW Power Plant Boiler

In recent years,the contradiction between economic development and environmental pollution has deepened.Among them,the large emission of NOx is one of the main causes of acid rain and ozone layer destruction.At the same time,the state's control over the emission of nitrogen oxides in power plants is becoming more and more stringent.In some areas,the requirement of "ultra-low" emission of nitrogen oxides in power plants has been put forward.So controlling the emission of NOx has become one of the important tasks of coal-fired power plants.In the actual operation of denitrification system,the flue gas distribution in denitrification system will be affected by the fluctuation of boiler load and the burning state in the furnace.If the flue gas distribution in denitrification system can not be changed in time,the ammonia concentration in the catalyst inlet will be changed accordingly.Distribution of NH3 does not match the distribution of NOx concentration,which increases the non-uniformity of ammonia-nitrogen mixing,affecting the denitrification efficiency of denitrification system,resulting in a series of problems such as blockage and corrosion of air preheater.In order to meet the new standard of NOx emission in power plants,improve the operation efficiency of denitrification system,reduce the deviation of NOx concentration at the outlet of the system,and reduce the amount of ammonia escaping,it is of great significance to study the optimization of ammonia injection in boiler denitrification system.The SCR denitrification system of a 600 MW coal-fired boiler in a power plant has some problems,such as low denitrification efficiency,excessive NOx and ammonia escape.Irrational ammonia injection is one of the main reasons for the above problems.In order to solve the problem,ammonia injection optimization adjustment test was carried out for SCR denitrification system.The flow velocity of flue gas inlet and outlet,concentration of NOx and ammonia concentration were measured by grid method.Relative standard deviations of NOx concentration at outlet A and B of denitrification reactor before ammonia injection adjustment test were 23.57%,20.21%.Distribution deviation did not meet the requirement of less than 20%.By adjusting the opening of ammonia spray valve several times,the deviation of NOx concentration at the outlets of side A and B of denitrification reactor decreased to 15.98%and 13.93%.the denitrification efficiency at side B of denitrification reactor increased to 85.3%,and the denitrification efficiency increased by 2.52%.In order to further improve the uniformity of ammonia distribution at the catalyst inlet and match the amount of injecting ammonia with the concentration distribution of NOx,thereby improving the denitrification efficiency and reducing the ammonia escape rate,the influence of the number of nozzles and the size of nozzles on the denitrification system concentration field was simulated and analyzed by FLUENT software on the basis of the experiment of ammonia injection adjustment.The results show that the uniformity of ammonia distribution can be improved by increasing the number of nozzles,and the deviation of NH3 concentration distribution first decreases and then increases with the increase of the size of grid nozzles.The concentration field was optimized and analyzed by more refined adjustment of ammonia injection zone.The nozzle velocity of each zone was adjusted several times to simulate,and the nozzle velocity of each zone was finally determined.The results show that the relative deviation of ammonia concentration above the first catalyst is reduced to 2.54%,and the denitrification efficiency is increased to 87.70%.The denitrification reaction in the catalyst is guaranteed to proceed uniformly with the more uniform distribution of the component concentration at the entrance section of the catalyst.