This invention concerns filters and more particularly filters of the type adapted to remove suspended solids from liquids, such as for dewatering or desludging applications.
Such applications usually involve large volumes of liquid to be filtered, and large filtering areas are necessitated. Typically, pressurized flow is necessary to provide adequate flow rates, and a high degree of automation of the filter operations is highly desirable.
A known arrangement for conducting filtration for such applications is a vertically stacked pressurized chamber filter arrangement. A typical arrangement of this type is shown in U.S. Pat. No. 4,346,003. In this arrangement, a plurality of filter housings are mounted in a vertical array, with each filter housing defining a filter chamber which is pressurized with the liquid to be filtered. The filter flow passes through a filter media taking the form of an endless belt which has a segment passing into each filter chamber, and out around rollers and back into the next filter chamber, and so on, through the vertical array. Each filter consists of separable housing members which are simultaneously moved apart vertically to allow advancement of the belt segments from within the filter housing. This movement is necessary to remove the accumulated filtered solids and clean the belt as the filtration process proceeds.
The necessity for separating the filter housings requires a complex and very sturdy mechanism which must withstand the enormous forces involved with large area filtration under pressurized conditions.
In related application Ser. No. 405,524, filed Aug. 5, 1982, now U.S. Pat. No. 4,430,231, there is disclosed an arrangement for sealing openings into a filter housing by means of inflatable hose seals, such that the housing members may be permanently closed and only the inflatable sealing apparatus operated to enable the filter belt and accumulated solids to be periodically moved out of the filtering cavities and for disposal.
This arrangement eliminates the need for the complex mechanical appratus for opening and closing the housing components.
However, a relatively complex belt drive mechanism is required since each segment of the endless belt is passed into and out of each housing successively into a next succeeding housing in the vertical array. Thus, a very great length of filter belt is involved, and a complex roller and drive arrangement necessitated to advance all of the belt segments simultaneously.
An effective sealing of the filter belt edges in the arrangement described in the aforementioned patent application is more difficult since flow around and under the edges of the filter is more likely. Any build-up of sludge will of course necessitate disassembly of the unit for periodic clean out. This would be highly disadvantageous. In the separable housing-type filters, complete sealing of the belt lateral edges may be achieved by sealing engagement of the housing.
An alternative approach to the endless belt has involved the use of individual rolls of a disposable flexible sheet filter media, which are individually associated with each housing in the vertical array. Since the media is disposable, it need not be circulated back into a succeeding filter chamber, and may pass therethrough for collection and disposal on the opposite side of the housing chamber. However, the cost of such disposal media may become substantial for typical high volume applications of the sort described.
Additionally, the disposable media is typically of much lighter weight and is less easily driven through the housing, particularly when loaded with the accumulated filtered solids. If the media passes atop a perforated plate or grid, filtration pressure forces the disposable media into openings in the support plate, and a high pulling force is necessary. This has led to difficulties in reliably powering the movement of the filtering media out of the filtration chamber, in addition to incurring the cost of the filter media material.
Another problem has been encountered in such vertically stacked pressure filter units when filtering liquids containing very fine solids. A significant accumulation of very fine solids passing through the media may occur in the collection chambers associated with the filter unit. Accumulation of these solids in the collection chambers may necessitate dismantling and disassembling of the entire apparatus in order to clean out the accumulated fine solid materials.
A further problem has been encountered in pressurized chamber filters using a flexible sheet media. That is, the media must be supported on a plate which provides support for the filter media to resist the pressure differentials required for filtration.
The solid areas of the support plate reduces the area of the permeable filter media available for filtering flow since the media tends to be sealed against such solid areas. On the other hand, a reduction in the solid areas weakens the support plate, and at relatively higher pressures, the structural integrity of the support plate may be threatened.
Accordingly, it is an object of the present invention to provide a filter of the type including an endless belt member which passes into a filtration chamber, but which does not require a complex belt drive arrangement.
It is a further object of the present invention to provide such filters in which a plurality of units may be stacked in a vertical array to establish independently operated filter belt drive arrangements.
It is still a further object of the present invention to provide an edge sealing arrangement for the filter of the type described in which the belt passes into the interior of the filter chamber of a permanently assembled filter housing through selectively sealed openings.
It is yet another object of the present invention to provide an arrangement for collecting the filtered liquid flow which allows for clean-out of the collection space, without disassembly of the filter apparatus, particularly in a stacked vertical array of the filter units.
It is another object of the present invention to provide a support plate configuration which allows for maximum filtering flow area but which provides sufficient structural integrity to resist the stresses induced by high pressure differential filtration, yet which is relatively low in cost to manufacture.