Filtration leaf filters

A static leaf filter is used for cleaning machine tool coolants. These are used on the suction side of a pump circulating system, with the same pump employed for withdrawal of the filtrate as for backdushing the filter elements. SoHds in this case are removed from the sump by a scraper conveyor. 

Vertical Vessel, Horizontal Leaf Filters. These filters, like all horizontal leaf filters, are advantageous where the flow is intermittent or where thorough cake washing is required. Filtration areas are limited to about 45 m. ... 

Horizontal pre.s.sure leaf filters. In these filters the leaves may be rectangular leaves which run parallel to the axis and are of varying sizes since they form chords of the shell or they may be circular or square elements parallel to the head of the shell, and aU of the same dimension. The leaves may be supported in the sheU from an independent rack, individuaUy from the shell, or from a filtrate manifold. Horizontal filters are particiilarly suited to diy-cake discharge. 

Vertical pre.s.sure leaf filters. These filters have vertical, paraUel, rec tangular leaves mounted in an upright cylindrical pressure tank. The leaves usually are of such different widths as to aUowthem to conform to the curvature of the tank and to fill it without waste space. The leaves often rest on a filtrate manifold, the connec tion being sealed by an O ring, so that they can be lifted individuaUy from the top of the fil-... 

Pressure leaf filters are used to separate much the same lands of slurries as are filter presses and are used much more extensively than filter presses for filter-aid filtrations. They should be seriously considered whenever uniformity of production permits long-time operation under essentially constant filtration conditions, when thorough washing with a minimum of hquor is desired, or when vapors or fumes make closed construction desirable. Under such conditions, if the filter medium does not require frequent changing, they may show a considerable advantage in cycle and labor economy over a filter press, which has a lower initial cost, and advantages of economy and flexibility over continuous vacuum filters, which have a higher first cost. 

Vertical Pressure Leaf Filters are essentially the same as Horizontal Plate Filters except for the orientation of the filter elements which are vertical rather than horizontal. They are applied for the polishing slurries with very lov solids content of 1-5% or for cake filtration with a solids concentration of 20-25%. As with the horizontal plate filter the vertical leaf filters are also well suited for handling flammable, toxic and corrosive materials since they are autoclaved and designed for hazardous environments when high pressure and safe operation are required. Likewise, they may be readily jacketed for applications whenever hot or cold temperatures are to be preserved.The largest leaf filters in horizontal vessels have a filtration area of 300 m and vertical vessels 100 m both designed for an operating pressure of 6 bar. 

There are a variety of arrangements that operate in the same manner as the plate- and-frame filter. One is the leaf filter, which may consist of one or more frames that are covered by the filter medium and immersed in the slurry. These filtration devices, are often operated by means of a vacuum that draws the filtrate through the filter, with the cake collecting on the filter medium on the outside of the frame. 

A sample of the slurry was tested, using a vacuum leaf filter of 0.05 m2 filtering surface and a vacuum equivalent to a pressure difference of 71.3 kN/m2. The volume of filtrate collected in the first 300 s was 250 cm3 and, after a further 300 s, an additional 150 cm3 was collected. It may be assumed that cake is incompressible and the cloth resistance is the same in the leaf as in the filter press. 

As the filtration area of the full-size plant is 10 times that of the leaf filter then ... 

A slurry containing 40 per cent by mass solid is to be filtered on a rotary drum filter 2 m diameter and 2 m long which normally operates with 40 per cent of its surface immersed in the slurry and under a pressure of 17 kN/m2. A laboratory test on a sample of the slurry using a leaf filter of area 200 cm2 and covered with a similar cloth to that on the drum, produced 300 cm3 of filtrate in the first 60 s and 140 cm3 in the next 60 s, when the leaf was under pressure of 84 kN/m2. The bulk density of the dry cake was 1500 kg/m3 and the density of the filtrate was 1000 kg/m3. The minimum thickness of cake which could be readily removed from the cloth was 5 mm. 

In the leaf filter, filtration is at constant pressure from the start. 

A plate and frame press with a filtration area of 2.2 m2 is operated with a pressure drop of 413 kN/m2 and with a downtime of 21.6 ks (6 h). In a test with a small leaf filter 0.05 m2 in area,... 

Dumont s filter consists of a wooden box of j he form of a four-aided truncated pyramid with a double bottom. The inner bottom is a metallic plate pierced with numerous holes upon it a cotton cloth is kid, and coarse-grained animal charcoal moistened with water is then Bpread layer by layer each layer being rendered of uniform thickness, and packed or pressed closely together by means of a sort of trowel. When the bone-black has been thus formed into a compact bed or stratum of about fifteen or eighteen inches in thickness, and Within five to ten inches fi om the top of the box, it is covered with another cotton cloth, and with another metallic plate pierced with holes, The object of the second cloth and metallic cover Is to collect any substances which would otherwise obstruct the interstices of tho superior stratnm. of the bone-black—an inconvenient accident which is easily prevented by the use of such a cover, and this cover is readily exchanged for another, should it be no mo itself obstructed. The superior covir is only of use when the previously described filtration through the cotton bag or leaf filter is omitted. 

Figure 11.3. Laboratory test data with a vacuum leaf filter, (a) Rates of formation of dry cake and filtrate, (b) Washing efficiency, (c) Air flow rate vs. drying time, (d) Correlation of moisture content with the air rate, pressure difference AP, cake amount W Ib/sqft, drying time 6d min and viscosity of liquid Dahlstrom and Silverblatt, 1977).

Filtration leaf test results indicate that the filtration rate of a protein product is 50 dry lbs/(ft2 hr). What size production filter would be required to obtain 100 dry lbs of filter cake per hour ... 

Filtration. Filtration in Washington wineries is performed almost exclusively with plate-and-frame filter presses. In some cases, these filters have wide frames so that they are capable of performing diatomaceous earth filtrations. There is only one stainless steel, screened, diatomaceous earth, pressure-leaf filter in use in the Washington wine industry. Two major wineries have found they can utilize a paper septum over a medium pad in their plate-and-frame filters. This allows them to precoat and body feed with diatomaceous earth as the wine is filtered. This accomplishes both a coarse and medium filtration in one movement of the wine. 

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