Abstract:

The mixing/separation characteristics of the two-component large-difference particle system composed of FCC catalyst (d_p =90 μm) and molecular sieve (d_p =1875 μm) in fluidized bed were investigated experimentally. The results show that in the dense phase bed,pressure drop in unit height at the dilute dense phase interface will rise sharply with the gradual increase of the initial proportion of large particles X₀. At low gas velocity,the mass fraction of large particles in the dense phase bed is uniformly distributed in the radial direction. At high gas velocity,a “U” shape distribution with a high sidewall and low center appears. The whole bed mixing uniformity is better when X₀<20.0%,and the uniformity will gradually decrease with the increase of apparent gas velocity u_g and X₀. In the dilute phase space,entrained large particles gradually increase with the increase of u_g,and decrease with the increase of X₀. When X₀=68.5%,entrainment meets maximum. The mass fraction of large particles in the dilute phase space,in the radial direction, appears “M” shape distribution,and the “M” shape distribution will gradually change to inverted “U” type distribution with the increase of height. Based on the experimental results,the empirical correlations for calculating the total mixing height and separation efficiency are proposed.

Key words: fluidized bed, large difference particles, particle classification, multiphase flow, mixing

摘要：

实验考察了FCC催化剂(d_p=90 μm)和分子筛(d_p=1875 μm)构成的双组分大差异颗粒体系在流化床内的混合/分离特性。结果表明，在密相床层，随着大颗粒初始比例X₀逐渐增加，床层稀密相界面处的单位高度压降逐渐上升。双组分混合颗粒完全流化时密相床层内大颗粒质量分数在径向上总体分布均匀，但随着表观气速的增加大颗粒在径向上呈现出边壁高中心低的“U”形分布。全床混合均匀性在X₀<20.0%时较佳，且均匀性会随着表观气速u_g增加和X₀的增加而逐渐减小。在稀相空间，被夹带到稀相空间的大颗粒随着表观气速u_g增加逐渐增大，随着X₀的增大先增大后减小，当X₀=68.5%时夹带量最大。稀相空间内大颗粒质量分数在径向上呈“M”形分布，并且随着轴向高度的增加逐渐由“M”形分布转变为倒“U”形分布。基于实验结果，给出了计算完全混合高度和分级效率的经验关联式。

关键词: 流化床, 大差异颗粒, 颗粒分级, 多相流, 混合