气固流化床内费托铁基催化剂的流化特性

Flow behaviors of FT catalyst in gas-solid fluidized bed

为研究费托(Fischer-Tropsch, FT)催化剂在气固流化床内的流动过程,分析了催化剂的主要物性参数,在不同直径流化床内测量了各表观气速下FT催化剂的流动特性,并与广泛应用的流化催化裂化(Fluid Catalytic Cracking, FCC)催化剂的流态化行为进行了对比。结果表明,同为A类颗粒,相较于FCC催化剂,由于FT催化剂的休止角较小(约为FCC催化剂的75%),其临界流化速度较小、床层膨胀高度和气节高度较小;两种催化剂在流化床内流化过程基本相似,随表观气速增大依次出现膨胀、鼓泡、湍动等流型,但各流型转变时的临界速度差异较大。催化剂物性参数对流化特性影响较大,FT催化剂在各阶段流化过程均相对稳定,有利于催化剂在流化床内均匀分布,其气固接触效果优于FCC催化剂;不同催化剂床层高径比下气节高度变化的转折点与流型存在对应关系,可将气节高度随表观气速的变化关系作为判断湍动流化区内流型临界速度的依据。

To study the flow process of the Fischer-Tropsch(FT)catalyst in the gas-solid fluidized bed, the main physical parameters of the catalyst were analyzed firstly. And then the flow behaviors of the FT catalyst in different superficial gas velocities in the fluidized bed with different diameters were measured. Finally the flow behaviors of the fluid catalytic cracking(FCC) catalyst, which was widely used in the field of catalytic cracking of petrochemical industry, were compared with that of the FT catalyst. It was found that, although the FT catalyst and the FCC catalyst were both Geldart-A particles, the FT catalyst had smaller stagnation angle(almost 75% of that of the FCC catalyst). This caused that the FT catalyst had lower minimum fluidization velocity, less expansion height, less surge height. The fluidization process of the two catalysts in the gas-solid fluidized bed were basically similar,including the expansion, bubbles, turbulent and other flow patterns,which appeared successively with the increasing superficial gas velocity. However, the critical velocities during the transitionbetween different flow patterns were quite different. The results showed that the physical parameters of the catalysts affected the flow characteristics considerably. Comparing with the FCC catalyst, the FT catalyst was much stable in each step during the fluidization process, which was benefit to the uniform distribution of the catalyst in the gas–solid fluidized bed. Consequently, the contact performance of the FT catalyst was better than that of the FCC catalyst.Furthermore, with different ratios of bed height to diameter, the turning points of the surge height were related with the flow patterns. Therefore, the relationship between the surge height and the superficial gas velocity could be the estimation basis of the critical velocity in different flow patterns of the turbulent fluidized region.