| 摘要 |
An upwash, upflow or downflow, graded sand bed dust collector has a reusable imperforate or slightly porous diaphragm on the top of the graded filter media and an inlet for pressurized gas above the diaphragm for inflating the diaphragm against the media during dust removal stage. The dust collector housing can be flared upwardly and outwardly at selected portions to reduce the velocity of upflowing gas during wash stage for improved grading of the filter media. A natural foraminous layer may be self-grading at the top of the filter media, allowing a circumferential or side outlet for filtrate. A layer of fine, dense filter media may also be used to increase the size range of media particles in the dust collector. Special diaphragms may be composed of individual leaflets that rise above the filter media but not to the level of the gas exit during the wash stage, and which settle on top of the filter media during the filter stage. To improve the fluidization of the filter media during the wash stage and the sand bed can be vibrated or oscillated. An alternate design has a moveable screen above the filter media to compress the media during the dust collection stage. Performance is improved by providing immediately below the screen a layer of material which is coarser than the layer of material below that top layer.
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