Filtration horizontal plate filter

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. 

FIGURE 58.5 Horizontal plate filter. (From Shirato, M. etal.. Filtration—Principles and Practice, eds. M.J. Matteson andC. Orr, Marcel Dekker, New York, pp. 299-423, 1987. With permission.)... 

The horizontal plate filter is a pressure filter with a number of horizontal circular drainage plates in a stack in a cylindrical shell. A filter cloth or paper is placed on each plate. Filter aid may be applied if necessary. Filtration is continued until the cake capacity of the unit is reached or the filtration rate becomes too slow owing to cake resistance. Pressure drop across the filter medium is generally designed for SO lb,/in.. Cake may be washed or air-blown prior to manual removal. This type of filter is flexible and easily cleaned or sterilized, but it has a high labor requirement. 

Disk or plate filters are very similar to horizontal plate pressure filters used in cake filtration. A paper... 

Industrial filtration units can be either batch or continuous in operation. In addition to the plate and frame filter press of Figure 14-1, there are leaf filters that also function in the batch mode. Figure 14-5 shows both a vertical leaf filter and the filter leaf itself. Other leaf filters include a Niagara type (Figure 14-6), which uses a horizontal leaf filter, and the Sweetland type (Figure 14-7), which consists of two half-cylinders that allow the bottom half to be opened downward to access vertical disk-shaped leaves. 

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°. 

Leaf and plate filters are mostly relatively simple pressure-driven filters made up of fiat filtration elements, although they can also be vacuum driven. The overall configuration of the filter may be horizontal or vertical, and the basic choice between them is often made according to the space available in the factory. They are mainly used for batch-operated solids recovery, although in combination with precoat they can also be employed for clarification and decontamination duties. 

Filtration systems have been a mainstay of fine and other exhaust gas cleaning for many years. The traditional baghouse (also called a fabric filter) uses an array of filter elements supported on cages and suspended from a horizontal plate inside the filter housing. This plate divides the dirty gas from the clean side of the filter, and is perforated with a regular pattern of holes to each of which a filter element is fixed. The gas flow may be from inside out (with dust collected inside the bag), or from outside in (with solids collecting on the outside surface) - the two systems having very different methods of solids removal. 

Nutsche Filter. The nutsche filter (Fig. 8) is simply an industrial-scale equivalent of the laboratory Buckner funnel. Nutsche filters consist of cylindrical or rectangular tanks divided into two compartments of roughly the same size by a horizontal medium supported by a filter plate. Vacuum is apphed to the lower compartment, into which the filtrate is collected. It is customary to use the term nutsche only for filters that have sufficient capacity to hold the filtrate from one complete charge. The cake is removed manually or sometimes by reslurrying. 

The vertical recessed plate automatic press is shown schematically in Figure 15. Unlike the conventional filter press with plates hanging down and linked in a horizontal direction, this filter press has the plates in a horizontal plane placed one upon another. This design offers semicontinuous operation, saving in floor space, and easy cleaning of the cloth, but it allows only the lower face of each chamber to be used for filtration. 

Plate pr esses. Sometimes called sheet filters, these are assemblies of plates, sheets of filter media, and sometimes screens or frames. Thev are essentially modified filter presses with practically no cakeholding capacity. A press may consist of many plates or of a single filter sheet between two plates, the plates may be rectangular or circular, and the sheets may lie in a horizontal or vertical plane. The operation is similar to that of a filter press, and the flow rates are about the same as for disk filters. The operating pressure usually does not exceed 138 kPa (20 psig). The presses are used most frequently for low-viscosity liqmds, but an ordinaiy filter press with thin frames is commonly used as a clarifier for 100-Pa s (1000-P) rayon-spinning solution. Here the filtration pressure may be 6900 kPa (1000 psig). 

Normally the filter strueture consists of a stack of plates attached to a hollow shaft which are mounted inside a pressure vessel with eaeh plate eovered with a suitable filter medium. The slurry is fed under pressure into the vessel and the eake, which is retained by the filter medium, forms on the top of eaeh plate whilst the filtrate passes through the hollow shaft further to the proeess. Filter sizes may vary but generally the maximum is 60 m area and designed for a 6 bar operating pressure. Each circular plate in the staek is eonstructed with radial ribs that are welded to the bottom and support a horizontal eoarse mesh screen whieh is eovered with a fmer woven metal screen or filter cloth to retain the cake. The bottom of the plate slopes towards the hollow eentral shaft whieh lets the filtrate flow freely through circumferential holes and further down the shaft to the filtrate outlet. The elearanee between the plates is maintained by speeial spacers... 

This family of filters consist of a vertical pressure vessel with a horizontal filter plate at the bottom. The filtrate from this equipment flows out a nozzle on the bottom of the filter. These devises are usually used for slurries where large amounts of solids are being collected. Variations of this equipment include equipment with removable lower heads for easy cake removal, ability to pressure or vacuum filter, ability to wash the filter cake, an agitator to break-up and rewash the filter cake, and heating or cooling jackets for the whole vessel. The Nutsche filter is the industrial version of the well known laboratory scale Buchner Funnel with the exception that it is designed to operate under either on vacuum or pressure. 

Pressure filters are worth noting. These are usually set up in the form of steel cylinders positioned vertically. Another variation consists of using horizontal filtration groups. This has the drawback that the surface loading is variable in the different layers of the filter bed moreover, it increases with greater penetration in the filter bed (the infiltration velocity is lowest at the level of the horizontal diameter of the cylinder). The filter bottom usually consists of a number of screens or mesh sieves that decrease in size from top to bottom or, as an alternative, perforated plates supporting gravel similar to that used in the filter bottoms of an open filter system. 

Figure 2. (Top) Detail of the MULVFS pump unit and filter-holder assembly. The filter holder consists of three stages. The upper two plates are baffles necessary to prevent particles from being redistributed on the filters during recovery. The next plate supports the 53-gm mesh Nitex prefilter, and the bottom plate supports the pair of 1-pm micro quartz-fiber filters and seals to the pump intake. (Bottom) Pressure vs. flow rate curves for the MULVFS and LVFS pump units. Horizontal bars indicate operating ranges of the two systems during filtration.

Horizontal Diaphragm Presses This is similar to the diaphragm press except the filter plates lay horizontally (while in diaphragm press, the filter plates are operated vertically). The press can be a singlechamber unit, or multiple chambers can be stacked to achieve greater filtration area. 

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