Study On The Mixing Characteristics Of Flues In The SCR DeNox System With Built-in SV-type Static Mixing Elements

SCR Denox Technology is a kind of tail gas denox technology with high denox efficiency and mature technology.The performance of SCR Denitration System is affected by the performance of catalyst and many factors,including the mixing degree of Reactor Inlet reductant and NOx.It is an important measure to improve the out-of-stock effect of SCR system by adopting reasonable flue duct structure design and improving the mixing effect of reducing agent and NOx.In this paper,the SV type static mixing element is installed in the pre-mixed flue of catalyst layer in a large-scale flue gas denitrification system of a coal-fired power plant.Numerical simulation of flow velocity field,concentration field and pressure drop in the flue before catalyst layer of SCR denitration reactor was carried out by using the fluid mechanics software FLUENT,the influence of the arrangement of SV type static mixing elements,the number of components and the ratio of height to diameter on the gas mixing effect in rectangular flue and the influence of the arrangement of SV type static mixing elements on the gas mixing effect in the flue before catalyst layer of SCR reactor were studied.Firstly,the effects of the arrangement of SV type static mixing elements,the number of components and the ratio of height to diameter on the velocity field and concentration field in rectangular flue gas duct were studied by using the control variable method,the simulation results show that: 1 when the SV type static mixing elements are arranged in order,the air flow forms reverse vortices in the channel formed by the mixing elements,the velocity relative standard deviation coefficient is reduced by 20.33% and the pressure drop is reduced by 24.63% compared with the cross-row,although the relative standard deviation coefficient of ammonia concentration is slightly higher than that of forked arrangement,the relative standard deviation coefficient of ammonia concentration is less than 15% 2 the mixing effect of gas in the flue is improved gradually with the increase of the number of components,the RSD of velocity and concentration can be reduced to about 11%,but when the number of components increases from 10 to 30,the pressure drop of the system is increased by 55.45%.3 for the static mixing element with the height-diameter ratio from 0.5 to 1.25,the mixing effect in the flue is improved gradually with the increase of the distance from the outlet of the mixing element,the improvement effect is no longer obvious.When the distance from the exit of the mixing element is more than 200mm,the corresponding results of the height-diameter ratio are close.Secondly,based on the research results of the control variable method and the specific structure of the SCR system,the SV type static hybrid elements with 25high-diameter ratio of 0.5 are selected for the next research,the influence of the installation position of SV type static mixing element on the gas mixing effect in the flue of SCR reactor before Catalyst Layer is discussed,the gas velocity distribution and concentration distribution in the flue are better than those in the static mixer only in the front or back of the flue.The relative standard deviation coefficient of the main flow velocity is 14.54%,the relative standard deviation coefficient of the ammonia concentration is 5.36%,the pressure drop is only 26.75% higher than that of the static mixing element only arranged in the front part,and the mixing performance is better.In addition,the simulation results show that the pressure drop of the system is the largest when the mixing element is placed in the vertical flue section,which is 5.7 times higher than that when the mixing element is placed only in the front section of the first layer of catalyst.Therefore,on the premise of ensuring mixing effect,the excessive mixing elements should be minimized in the vertical flue design.