Horizontal belt vacuum filters

Vacuum filters include the nulschc filter, enclosed agitated vacuum fillers, the vacuum leaf filter, the tipping pan filter, horizontal rotating pan filters, horizontal belt vacuum fillers, rotary vacuum drum lilters. and rotary vacuum disk filters. 

The vacuum is created behind the filter medium, which causes the atmospheric pressure in front of the filter medium to drive the slurry through the medium, filtering out suspended solids in the process. Types of vacuum filters include belt, horizontal pan, vertical disc, and dmm varieties. 

Horizontal filter surfaces also allow a high degree of control over cake formation. Allowances can be made for changed feeds and/or different cake quality requirements. This is particularly tme of the horizontal belt vacuum filters. With these units the relative proportions of the belt allocated to filtration, washing, drying, etc, as well as the belt speed and vacuum quality, can be easily altered to suit process changes. 

Fig. 11. Schematic diagram of a horizontal belt vacuum filter.

Horizontal belt filters are well suited to either fast or slowly draining soHds, especially where washing requirements are critical. Multistage countercurrent washing can be effectively carried out due to the sharp separation of filtrates available. Horizontal belt vacuum filters are classified according to the method employed to support the filter medium. 

Another type of horizontal belt vacuum filter uses reciprocating vacuum trays mounted under a continuously traveling filter cloth. The trays move forward with the cloth as long as the vacuum is appHed and return quickly to their original position after the vacuum is released. This overcomes the problem of friction between the belt and the trays because there is no relative movement between them while the vacuum is being appHed. The mechanics of this filter are rather complex, and the equipment is expensive and requires intensive maintenance. A range of solvents can be used. Widths up to 2 m and areas up to 75 m are available. The cloth can be washed on both sides. 

Some horizontal belt vacuum filter designs incorporate a final compression stage for maximum mechanical dewatering. This is achieved by another compression belt which presses down on the cake formed in the preceding conventional filtration stage. 

The endless-belt percolator (Wakeman, loc. cit.) is similar in principle, but the successive feed, solvent spray, drainage, and dumping stations are hnearly rather than circulany disposed. Examples are the de Smet belt extractor (uncompartmented) and the Lurgi frame belt (compartmented), the latter being a kind of linear equivalent of the Rotocel. Horizontal-belt vacuum filters, which resemble endless-belt extractors, are sometimes used for leaching. 

On a horizontal belt filter, the equivalent sections extend across the filter in narrow strips. Therefore, changes in vacuum do occur rapidly and may be considered as happening at a particular point along the length of the filter. 

Horizontal Vacuum Filters These filters are generally classified into two broad classes rotaiy circular and belt-type units. Regardless of geometiy, they have similar advantages and limitations. They pro-... 

Horizontal belt pressure filters, 11 379 Horizontal belt vacuum filter, 11 354-355 Horizontal box heaters, 19 511 Horizontal current classifiers, 16 619 Horizontal Feret s Diameter (HFD), 16 147 Horizontal injection wells, 16 613 Horizontal leaf filters, 11 366-367 Horizontal magnetic field-type (HMC), 23 857... 

Reciprocating vacuum trays, with horizontal belt filters, 77 355 Reciprocity... 

Horizontal Belt Vacuum Filter The final piece of equipment is the horizontal belt filter, in which the nnderflow from the hydroseparator (basically gypsum diluted with process liquor) will be filtered to produce marketable gypsum of -12% moisture. The filter cake will be washed to reduce the amount of dissolved solids and will be conveyed to a prodnct gypsnm storage area. Filtrate from this filter will be disposed of as an aqneons pnrge stream. 

Figure 11.11. Continuous horizontal vacuum filters especially suited to free settling and draining solids, (a) Principle of the conveyor belt filter units may operate up to 0.S m/sec with a cycle time up to 10 min and produce cake thicknesses up to 15 cm. (b) Showing the construction of a grooved rubber belt support for the filter cloth of the belt filter (Purchas, 1981). (c) Rotating horizontal vacuum filter the unit has readily accessible piping and is amenable to thorough washing of free draining solids (Dorr-Oliver Inc.).

The calcinate was quenched in water to produce a pumpable slurry. Carbon washing was carried out on a horizontal belt vacuum filter which reduced the salt content to 4 to 5%. To further reduce the salt content, if needed, additional slurrying and washing on the belt filter was required. In commercial operation the filtrate containing potassium salts could be processed to reconstitute the KOH for recycle. 

TABLE 11.12. Sizes of Commercial Continuous Vacuum Filters (a) Horizontal Belt Filters ... 

A popular variant of the rotating drum vacuum filter has been widely applied especially for the palm oil industry. The Florentine vacuum filter uses a horizontal stainless steel perforated belt with vacuum applied under the belt. This design includes a recycle from the first filter section, which is said to allow the first layer of stearine to act as a continuous precoat (25). 

Horizontal- lt Filter This filter consists of a slotted or perforated elastomer drainage belt driven as a conveyor belt carrying a filter fabric belt (Fig. 18-141). Roth belts are supported by and pass across a lubricated support deck. A vacuum pan, aligned with the slots in the elastomer belt, forms a continuous vacuum surface which may include multiple zones for cake formation, washing and final dewater-... 

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