Drum Filter Productivity

TDF Drum Filter. This is a fairly conventional dmm filter housed in a vertical pressure vessel. Test data, obtained with the smallest model of only 0.75 m filtration area, is available (18). Larger models have also been announced, ranging up to the filtration area of 46 m and very large vessels. The operating pressures are moderate, up to 25 or 35 kPa, and the dmm speeds fairly conventional from 0.3 to 1.5 rpm. The range of dry cake production quoted is from 250 to 650 kg/m h for fine coal. 

Slurries of free-filtering sohds that are difficult to suspend are sometimes filtered on a top-feed drum filter or filter-diyer. An example application is in the production of table salt. An alternative for slurries of extremely coarse, dense solids is the internal drum filter. In the chemical-process industiy both top-feed and internal drums (which are described briefly by Emmett in Schweitzer, op. cit., p. 4-41) have largely been displaced by the horizontal vacuum filter (q.v). 

This type of filter can be used for removal of Penicillium and Streptomyces mycelia in the production of penicillin and streptomycin, respectively.5 In these processes the rotary drum filter is used with a pre-coated cloth filter with filter aid the filter cake is removed by a knife blade which scrapes the cake from the rotating drum. 

After precipitation is complete, the slurry is pumped to vacuum drum filters where a neady complete liquid—solids separation is accomplished. The liquid is dilute sodium sulfide solution, which is concentrated by evaporation to a flaked 60 wt % sodium sulfide product. The filter cake is a 60 wt % strontium carbonate soHd which is fed to a carbonate dryer. After drying, the strontium carbonate product is cooled, ground, and screened for packaging. 

Solvent Fractionation. This process is the most expensive because of solvent loss, solvent recovery equipment, much lower temperature requirement, and stringent safety features. The process involves the use of solvents such as hexane or acetone. The oil is first dissolved in the solvent followed by cooling to the desired temperatures to obtain the desired crystals. Cooling is effected by brine if very low temperature is required. The miscella containing the partially crystallized oil and solvent is then filtered under vacuum suction in an enclosed drum filter. The olein miscella and stearin miscella are then separately distilled to remove the solvent and recover the fractions. Yield of olein is about 80%. The solvent process nowadays is only viable in the production of high value products such as cocoa butter equivalent or other specialty fats. 

Precoated rotary vacuum drum filters (Fig. 6) are used by filtering a slurry of filter aid and water first, then subsequent product filtration. Difficult filtering materials, which have a tendency to blind, are removed with a doctor blade. Precoat is removed along with the slurry to expose a new filtration surface each cycle. 

Yet another improvement was of great influence on the economics of yeast production The separation of the yeast from the spent mash was performed by centrifugation and subsequent dehydration of the resulting yeast cream in a frame press. Only the application of frame presses allowed dry substance values of about 27% to be attained, this being the desired standard with respect to handling properties and shelf-life. Attempts to replace frame presses with rotating drum filters showed that such dry substance values were barely achievable. The problem was solved in an ingenious way by K. v. Rokitansky and E. Rustier. 

The efficiency of a rotary drum filter is expressed by the product of the average filtration rate and the ratio of filtrate volume to weight of filter aid spent. Efficiency reaches a maximum at different rates of knife motion and varies according to the properties of the specific filter aid. An increase in the thickness of a cake layer cut results in a ratio of filtrate volume to weight of filter aid spent. One should account for the volume weight of different filter aids since this parameter varies considerably even among different grades of the same material. 

Parts which do not come into contact with the product are made of steel and may also have an appropriate corrosion-resistant paint coating. For hght-duty applications, vacuum drum filters with main components made of plastic are also used. 

A rotary drum filter (area 3 m, 30 percent submergence internal pressure of 30 kN/m ) operates at 0.5 rpm. If the filter cake is incompressible and the filter cloth has a resistance equal to 1 nun of cake, find the rate of production of filtrate and the cake thickness. 

In many industrial processes, solid-liquid separation operations are combined with drying operations. Figure 50.1 illustrates a process combining drum filters, a rotary kiln, a centrifuge, a disk filter, a spray dryer, and a conveyor dryer. In this combined operation, the solid-liquid separation enhances the quality of the product and decreases the thermal energy of... 

In the dewatering of flotation concentrate slurries, produced during mineral dressing operations, and in similar processes, the objectives are to recover the maximum amount of solids, produce saleable products where possible, and thus increase plant capacity at the most economic cost. There has been a significant improvement in process efficiency in this application by the use of belt discharge drum filters in place of disc vacuum filters and string/scraper drums. 

Pressure drum filters are suitable for processing at high pressures and/or high temperatures. They are particularly suited for foodstuffs production, antibiotics, dyestuffs, agricultural chemistry, solvent refined coal products, waxes, oils and grease, paraffin and all high-viscosity solvents at normal temperature. They are particularly suited to applications where the liquid is easily vaporized and to filtration processes in protective gas atmospheres. 

Rotary disc vacuum filters have the advantage, compared with rotary drum filters, of giving a much larger filter area per unit of floor area. They are thus particularly suitable for the processing of bulk products, for example in coal preparation, ore dressing, pulp and paper processing, and so on. 

The turbo-tray dryer can handle materials from thick slurries [1 million (N s)/m (100,000 cP) and over] to fine powders. It is not suitable for fibrous materials which mat or for doughy or tacky materials. Thin slurries can often be handled by recycle of dry product. Filter-press cakes are granulated before feeding. Thixotropic materials are red directly from a rotary filter by scoring the cake as it leaves the drum. Pastes can be extruded onto the top shelf and subjected to a hot blast of air to make them firm and free-ffowing after one revolution. 

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