Particle capture and plugging in packed-bed reactors

Fine particles in the liquid feed to packed-bed reactors can be trapped in the catalyst bed, which eventually leads to excessive pressure drop. The fine particles can include coke, corrosion products, days, and other minerals. The catalyst bed functions as a granular filter to remove particles much smaller than the size of the pores between the catalyst pellets. The efficiency for trapping the particles in the packed bed depends on the flow fields and the attractive forces between the packing and the fine particles, In order to understand the capture of fine particles from nonaqueous media, we studied a model system of carbon black in kerosene. Columns packed with glass beads and a catalyst were operated over a range of flow velocities to Reynolds numbers from 0.1 to 2.3, on the basis of the diameter of the packing in the bed. Plow was in the upward and in the downward direction. The filter coefficient and efficiency were sensitive to liquid velocity. Trapping was slightly more efficient with downward flow at low velocity. The pressure drop increased along the entire length of the packed bed, but the extent of increase at a given amount of deposit depended on the liquid velocity. Microscopy showed that the particles tended to deposit onto other particles, rather than smoothly coating the bed packing. At low velocities, more particles were deposited in the pores between the packing, giving a larger increase in pressure drop than that at high velocity, A model is presented far calculating pressure drop due to this type of deposition.