Design And Application For Measuring The Denitration Outlet Flue Gas Parameters Based On The Flow Field Optimization And Equal Flow Sampling

NOx is one of the main pollution sources in the atmosphere,and the coal-fired power plants are the main source of NOx.In 2015,the ultra-low emission requirement of NOx in flue gas was put forward,that is,the emission concentration of NOx should not be more than 50 mg/m3.In order to meet the requirements of the national ultra-low emission standard,comprehensively improving the denitrification performance,further improving the denitrification efficiency,reducing the ammonia escape rate and the air preheater clogging are performed in the thermal power plants.Among them,the accurate measurement of NOx at the SCR outlet has become an important technology to optimize and control NOx emission.The accurate measurement of NOx concentration at SCR denitration outlet involves the optimization of denitrification flow field,optimization of ammonia spray,and optimization of sampling design.This article gives a solid and thorough analysis on the whole upgrading and renovation process in Tengzhou Xinyuan Redian Co.,Ltd.,which was aimed at improving the NOx measure precision for de-nitration SCR outlets in its No.3 boiler.Flow field optimization is the foundation for accurate measurement and the efficient and stable operation of de-nitration systems.This article starts with the CFD simulation of the SCR de-nitration flow field.After optimizing the design of the de-nitration system based on the flow field simulation results,the NOx distribution at the SCR outlets is still uneven during operation,and we therefore made optimization efforts to improve the ammonia injection of the flue gas de-nitration device at the No.3 boiler and thus the uniformity of the NOx concentration at the optimized de-nitration outlets.The relative standard deviation of the uniformity of the NOx concentration was reduced from 16%to 7%on the A side.On the B side,the number was reduced from 17%to 12%,and the ammonia usage was relatively reduced by about 14.7%.In the ammonia injection adjusting optimization test,it was found that the DCS online ammonia escape and NOx measurement point indication values with little fluctuation,was significantly lower than the experimental values.These data cannot reflect the actual ammonia escape and NOx concentration changes,and thus cannot give effective guidance to the operating staff,resulting in excessive ammonia injection adjustment.Therefore,optimization efforts were taken to optimize the de-nitration outlet grid method and rearrange the NOx measuring point at the No.3 boiler,and a full-section equal-flow multi-point flue gas sampling device is developed based on the results of calculation.During unit maintenance,the device was install for actual application at the production site.The results show that the device performance is excellent.The response time of the NOx measuring point at the de-nitration outlets for the ammonia injection adjustment at the de-nitration inlets is comprehensively improved.To provide operating staff with timely and accurate adjustment information,the total amount of ammonia injection was reduced dramatically,and the ammonia escape rate was significantly reduced,which fully met the requirements for operation monitoring and environmental protection,and is worth a wide application.