烧结烟气脱硫-除尘-脱硝系统流场模拟及结构优化

Flow field simulation and structure optimization on desulfurization-dust removal-denitrification system of sintering flue gas

烧结烟气作为钢铁行业污染物的主要排放源,对其进行有效治理是实现超低排放的关键。为改善某钢厂烧结烟气脱硫-除尘-脱硝系统的流场分布,提高系统的运行效率,利用计算流体力学商业软件ANSYS-Fluent对该系统流场进行数值模拟,分析一体化模拟的可行性与计算成本,通过速度、浓度、温度分布及其偏差系数对流场均匀性进行定性与定量评估。在此基础上,设计4因素3水平多指标正交试验,分析不同结构参数的脱硫塔渐扩管、除尘段入口区域、导流片和静态混合器等对系统流场均匀性的影响,并得到结构优化的最佳组合方案。结果表明:一体化模拟与单体模拟相比更贴近工程实际,能更准确地分析除尘段与脱硝段的流场。一体化模拟网格数约为1600万,并行计算时间约为60 h,计算成本在可接受范围之内。改进方案中通过减小脱硫塔渐扩管角度、将除尘段进口直管改为渐扩管以及增设弧度为75°的导流片和格栅间距为400 mm的静态混合器,系统的流场均匀性显著提高。脱硫段主床高度1/2处无量纲流速在0.5~1.5的区域明显增多。除尘段中心剖面的速度分布偏差系数分别降低了7.6%与9.6%。脱硝段第1层催化剂上侧1000 mm处浓度与温度分布偏差系数均降至10%以下。

Sintering flue gas is the main pollutant emission source in the steel industry and its effective treatment is the key to achieving ultra-low emission.In order to improve the flow field distribution of the sintering flue gas desulfurization-dust removal-denitrification system in a steel factory and the operating efficiency of the system,a numerical simulation of flow field of the system was carried out by means of computational fluid dynamics software,ANSYS-Fluent.The feasibility and cost of integrated simulation were analyzed.Flow field uniformity was evaluated qualitatively and quantitatively by the velocity,concentration,temperature distribution and their deviation coefficient.A four-factor three-level multi-index orthogonal test was designed to analyze the effects of the gradual expansion tube of desulfurization tower,the inlet section of dust removal,deflector and static mixer with different structural parameters on the flow field uniformity of the system.The results show that the integrated simulation is closer to the actual situation of the project than the single simulation and it can accurately analyze the flow field of the dust removal section and the denitrification section.The number of integrated simulation grids is about 16 million,the parallel computing time is about 60 h and the calculation cost is within the acceptable range.The improvement plan is to reduce the gradually expanding tube angle of the desulfurization tower,change the inlet straight tube of the dust removal section to a gradually expanding tube,add a deflector with an arc of 75°and a static mixer with a grid spacing of 400 mm.Flow field uniformity is significantly improved.The area of the dimensionless flow rate with 0.5-1.5 is significantly increased at 1/2 of the main bed height in desulfurization section.The deviation coefficient of velocity in the center plane of the dust removal section is reduced by 7.6%and 9.6%.The deviation coefficient of concentration and temperature distribution at 1000 mm above the first layer of catalyst is decreased to less than 10%in denitrification section.