Pinning and cavity in two types of cross-flow moving beds

• A trapezoid moving bed with a multiple-grid discharge cone is presented.
• Compared with rectangular bed, trapezoidal bed improves the pining and cavity.
• A model is established to account for pinning behaviors in two types of beds.
• The critical pressure drops and thicknesses of pinning can be predicted by model.

The pinning, cavity and pressure drop were investigated in both trapezoidal and rectangular cross-flow moving beds via a large plexiglass cold model under different operating conditions. Experimental results indicate that the pinning appears before cavity. The critical pinning/cavity superficial gas velocities of the trapezoidal bed are considerably higher than those in the rectangular bed. Namely, the trapezoidal configuration improves the operating flexibility of the moving bed. On the other hand, it also shows that the dimensions of the pinning and cavity are both enlarged when the superficial gas velocity increases. However, the size variations of the pinning and cavity are not significant with the change of the particle mass flux. Besides, most gas passes through the bed in the horizontal direction. In the operating process, there is an undesirable phenomenon called channeling in the top of bed. Based on the force balance analysis as well as the experimental results, a mathematical model of pinning is proposed. The critical pressure drops and the pinning thicknesses can be predicted by using this model.

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