Granular-bed filtration assisted by filter-cake formation 5. Treating a liquid in a panel bed with pulseback renewal of liquid-entry granular-bed faces

A “panel bed” of granular solid, held in place by louvers, can serve to filter “dirt” from a liquid (the filtration assisted by filter-cake formation) or to place the liquid in countercurrent contact with the solid. A sharp “reverse” pulse of liquid, at sufficient intensity and not too long duration, produces a body movement of the solid capable of causing it to spill in a substantially uniform amount from each liquid-entry face of the granular solid. The paper reports experiments elucidating the physical behavior of the granular solid during “pulseback” and casting light, as well, upon the behavior of a “sand” during puffback of a panel bed gas filter. In both puffback and pulseback, the quantity of spilled solid is a function of “active time” (time during which a reverse pressure gradient across the panel bed exceeds a value just capable of producing a spill). Puffback quickly achieves a maximum attainable spill rate (a function of louver geometry); accordingly, spill quantity is linear in active time. In pulseback, however, spill rate increases gradually, achieving at last a maximum attainable spill rate (whereupon spill quantity becomes linear in active time).