颗粒床过滤器除尘特性数值模拟研究

Numerical Study on the Dust Removal Characteristics in Granular Bed Filter

运用CFD和DEM方法,建立三维随机填充固定床颗粒层除尘过滤模型,颗粒之间的接触采用"搭桥法"进行处理。数值计算得到的压降结果与实验值、关联式吻合较好,压降与床层厚度近似呈线性关系。在此基础上,数值研究了除尘效率与颗粒床床层厚度、气体流速、粉尘粒径、气流温度及流动方向的关系。粉尘粒径大于5μm时,增加床层厚度,增大气体流速,均可以有效地增加除尘效率。而粉尘粒径大于5μm时,在圆筒壁面恒热流密度冷却的条件下,气流温度越高,除尘效率越低。流动方向与重力方向相同时,可提高除尘效率。并拟合了分级除尘效率与St数的关系式,当St<0.009时,分级除尘效率为一定值,当St≥0.009时,分级除尘效率随着lg(St)的增加呈线性增加的趋势。

In this paper, a three-dimensional randomly packed granular bed model was built using computational fluid dynamics（CFD） and discrete element method（DEM）. The bridges method was introduced to optimize the grids near the contact points between the granules. The simulation data of pressure drop matched well with the experimental results and empirical formula. And the pressure drop approximately linearly correlated with the granular bed depth. The influences of granular bed depth, gas velocity, particle diameter, gas temperature and flow direction on the grade collection efficiency was also investigated. The results indicated that the increase of granular bed depth and gas velocity can improve the collection efficiency of the particles with diameter greater than 5 μm.Additionally, the increase of the gas temperature could lead to the decrease of the collection efficiency under the constant wall heat flux cooling condition. Besides, when the gas flow direction and the gravity direction were the same, the grade collection efficiency could be improved. The relation formula of the grade collection efficiency and the Stokes number（St） was obtained. The grade collection efficiency kept a stable value when St〈0.009, then the grade collection efficiency increased linearly with the lg（St） when St≥0.009.