In filters of the type in which a cake of solids deposited from a liquid slurry thereof on a generally horizontal filter medium is subjected to treatment involving passage of liquid through the cake while on the filter medium, means is provided for increasing the drainage rate of the formed cake by causing the cake to form on the medium from the slurry fed thereto by gravity settling in the liquor of the slurry and by removing liquor of the slurry from above the cake while the liquor still contains unsettled fine particles.
The washing efficiency of removal of cooking and bleaching chemicals from cellulose paper pulp on horizontal belt washing filters is improved by disrupting the filter mat adjacent the belt intermediately of soft, displacement wash liquor applications to the filter mat topside. The objective may be achieved by directing a line of low volume, high pressure jets of filtrate or wash liquor against the belt underside. Alternatively, sonicly vibrated foils extended transversely of and adjacent to the belt are effective to disrupt the filler mat pursuant to the invention objective.
Tilting filter pans is disclosed having generally parallel leading and trailing sidewalls which are sloped at an angle to permit increased filtration rates for a predetermined filtering efficiency, and also to permit increased filtering efficiency where the feed rate is constant. The feed is a slurry from which the liquid is removed, and the filter cake being dumped by rotation of each filter pan at a predetermined point of movement of the filter pan along a cyclical path. Hold-down devices having a reduced volume are also used in combination with the improved pan design, so that an increased filtration rate is possible due to decrease in the required filter cake height. A cam arrangement is provided for turning the pans with minimum stress in a minimum length of pan travel, while avoiding collisions between adjacent pans and while permitting washing of each pan.
The present invention features a filtration plate for use in a filter pan comprising a corrugated sheet having a series of alternately upwardly and downwardly opening channels and a reinforcing material bonded to surfaces of the downwardly opening channels. The reinforcing material is effective for strengthening the sheet and retaining heat in a manner effective to slow cooling of the filtration plate during washing and to reduce heat losses from the filtration plate during filtering. According to a preferred aspect of the invention, the corrugated sheet is a monolithic sheet of structural metal having a smooth upper filtration surface. The invention also provides a filter pan configured for use in filtration of a filtrate from solid particles. The filter pan comprises a filtration plate including a corrugated, monolithic sheet of structural metal having a series of alternately upwardly and downwardly opening channels. The filtration plate has an upper filtration surface that is smooth and unbroken by welds or joints, and the upwardly opening channels thereof have a width effective for channeling liquid. The invention also provides a method for making a filtration plate for use in a filter pan, comprising the steps of stamping a sheet of a structural metal to form it into a corrugated sheet having a series of alternately upwardly and downwardly opening channels. The upwardly opening channels have a width effective for channeling a filtrate and the downwardly opening channels include a reinforcing material bonded thereto for strengthening the sheet. The reinforcing material is effective for retaining heat in a manner effective to slow cooling of the filtration plate during washing and for reducing heat losses from the filtration plate during filtering.
