烧结烟气SCR脱硝系统流场模拟及导流结构优化

Sintered flue gas SCR denitrification system flow field simulation and inflow structure optimization

选择性催化还原(SCR)技术可以有效解决铁矿烧结烟气排放中NOx不达标问题,实现废气超低排放。SCR反应器内流场、温度、压力和氨氮浓度比等物理场分布的均匀性是决定脱硝效率的重要因素。基于某钢厂出现的脱硝效率低下及氨逃逸问题,考虑脱硝过程中反应器内气体的化学反应,采用FLUENT软件对流场进行了数值模拟,对比分析了SCR反应器内流场、温度、压力和氨氮浓度比等各物理场数值及分布均匀性。通过加装整流格栅和优化导流板结构,极大改善了物理场的均匀性,提高了脱硝效率。结构优化后,第一层催化剂上游烟气流速不均匀性偏差降低为8.48%,温度不均匀性偏差降低为4 K,氨氮浓度比不均匀性偏差降低为4.71%,满足了设计要求。此外,导流板结构的优化应综合考虑导流板数量、厚度、形状和布置间距等因素,且随着烟道上弯头处导流板数目的增加,第一层催化剂上游烟气流速不均匀性偏差逐渐降低,有效改善了反应器内气流分布的均匀性。

Selective catalytic reduction(SCR) technology can effectively effectively solve the problem of NOx non-compliance in iron ore sinter flue gas emissions and achieve ultra-low emissions of waste gases.The uniformity of the physical field distribution such as flow field,temperature,pressure and concentration ratio of ammonia-nitrogen in the SCR reactor are important factors in determining the denitrification efficiency.Based on the low denitrification efficiency and ammonia escape problem in a steel plant,the flow field was numerically simulated using FLUENT software to compare and analyze the values and uniformity of the distribution of each physical field such as flow field,temperature,pressure and concentration ratio of ammonia-nitrogen in the SCR reactor,considering the chemical reactions in the reactor during denitrification.The uniformity of the physical fields is greatly improved by adding a rectifier grille and optimizing the structure of the deflectors,and the denitrification efficiency is improved.After structure optimization,the deviation of flue gas flow rate inhomogeneity upstream of the first layer of catalyst is reduced to 8.48%,the deviation of temperature inhomogeneity is reduced to 4 K,and the deviation of concentration ratio of ammonia-nitrogen inhomogeneity is reduced to 4.71%,which satisfied the design requirements.In addition,the optimization of the deflectors structure should take into account the number,thickness,shape and spacing of the baffles,etc.With the increase of the number of deflectors at the elbow on the flue,the deviation of the flue gas velocity inhomogeneity upstream of the first layer of catalyst is gradually reduced,which effectively improves the uniformity of the airflow distribution in the reactor.