PARTICLE CAPTURE AND PLUGGING IN PACKED-BED REACTORS

Fine particles in the liquid feed to packed-bed reactors can be trappe d in the catalyst bed, which eventually leads to excessive pressure dr op. The fine particles can include coke, corrosion products, days, and other minerals. The catalyst bed functions as a granular filter to re move particles much smaller than the size of the pores between the cat alyst 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 car bon 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. P low was in the upward and in the downward direction. The filter coeffi cient and efficiency were sensitive to liquid velocity. Trapping was s lightly more efficient with downward flow at low velocity. The pressur e drop increased along the entire length of the packed bed, but the ex tent of increase at a given amount of deposit depended on the liquid v elocity. Microscopy showed that the particles tended to deposit onto o ther particles, rather than smoothly coating the bed packing. At low v elocities, more particles were deposited in the pores between the pack ing, giving a larger increase in pressure drop than that at high veloc ity, A model is presented far calculating pressure drop due to this ty pe of deposition.