(335c) Experimental Research on the Structural Parameter of the Coupling Apparatus of Granular Bed with Cyclone

Abstract: Dust in the flue-gas turbine is a key bottleneck restricting the long-time operation of the fluid catalytic cracking units(FCC). Developing a high efficiency/low pressure drop cyclone is quite essential. Dust carried in the flue gas containing many kinds of metallic elements influences on the subsequent reaction performance and fluidization characteristics. Small particles(<3μm) accumulate on the pressure-side surface of rotors, while large particles(>20μm) induce erosion at the trailing edge of rotors. As the conventional dust removal equipment in FCC unit—cyclone, however, cannot separate particles less than 5μm. The design of this apparatus is based on the idea of combining different dust removal mechanisms including the centrifugal separation, the inertial collision and the interception. A gas-solid separator coupling cyclone and cross-flow particle bed was investigated. Reasonable coupling with different separation mechanisms makes up for the inherent disadvantages of the third cyclone and achieves the purpose of collaborative strengthening. The goal of this study is to evaluate the effects of the main structural parameters—swirling space ratio on the performance of fine dust; by analyzing the flow field distribution on the built-in granular bed surface, the separation mechanisms in different regions of the separator were studied. It was found that: (1) the pressure drop decreased with an increasing swirling space ratio as expected while the separator with large swirling space ratio has a desired operation stability; (2) when their total separation efficiency exceeded 99%, cyclone shell in the large swirling space ratio apparatus contributions more to the total separation efficiency which reduced the load of built-in particle bed effectively; (3) the variation of swirling space ratio strengthened the division characteristics between granular bed and cyclone shell, the separation efficiency of the particles less than 5μm improved significantly in the large swirling space ratio; (4) according to different separation mechanisms, the apparatus was divided into two regions along the axial direction, the cross-flow diffusion region and the entrainment effect region. Regionalization of granular bed provided theoretical basis for establishing the dust removal model for the coupling apparatus.