Tipping Pan and Table Filters

The Nutsche filter is a vertical vessel, divided into two chambers by a horizontal perforated plate roughly at its mid-point. This plate may itself be the filter medium, or a sheet of finer medium may be laid onto the plate. In its simplest form, the upper chamber of the filter is an open feed chamber, into which the feed suspension is poured or pumped. The enclosed lower chamber is the filtrate receiver, to which the vacuum connection is made (at a level above that of the top of the batch of filtrate) to draw the filtrate through the filter medium, leaving the suspended solids from the feed as a cake on the upper surface of the filter medium. This cake will then be dug out of the filter, or lifted out on a removable filter medium, or tipped out by turning the whole filter unit through 180°. 

The washing of a Nutsche filter cake must be done carefully to avoid the creation of channels through what is usually quite a thin cake, and also to avoid the mixing of filtrate and wash liquor if that is undesirable. 

The tipping (tilting) pan filter obviously, and the rotary table filter somewhat less obviously, are developments of the simple batch vacuum filter described in the previous chapter. The single lipping pan is a batch filter, just like the Nutsche, but other versions, including the table filter, are intended to allow more or less continuous operation. 

Feed is loaded into the pan and filtration takes place either by gravity or under vacuum, depending on the design of the unit and the filterability of the solids. Cake washing can be followed by air drying, if required, prior to removal of the cake by tipping the pan to empty out the solids. When the pans are in the inverted position, the filter fabric can then also be washed. 

Tipping pan filters are also available as multi-pan units, with the pans arranged in a horizontal circle, like a wheel, with the spokes of the wheel represented by the filtrate pipe connecting each pan to a central vacuum pipe and filtrate receiver. The pans are now trapezoidally shaped to fit together in the annular filtration zone. 

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A. Introduction 3B. Strainers 3C. Screens 3D. Nutsche filters 3E. Tipping pan and table filters 3F. Rotary drum filters 3G. Rotary disc filters 3H. Horizontal belt filters Centrifugal filters Pad and panel filters 3K. Bag, pocket and candle filters 3L. Cartridge filters... 

The Nutsche, tipping pan and table filters are intended only for solids recovery from liquid suspensions. The rotary drum filter is mainly used for that purpose, but has some applications in clarification as well as solids recovery. 

The rotary table filter is an extension of the multi-pan filter design. The pans are replaced by segments of the annulus, which still rotates around in a circle so that each segment in turn filters and washes. The segments do not tip, however, to discharge the solid, which is instead scraped off the surface of the filter medium by a screw conveyor, over a flexible outer containing wall. 

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