GB2091575A - Filter press - Google Patents

Abstract

In a filter press each alternate filter plate 12 has passage means 22, 23 therein to deliver compressed air after the normal filtering operation to compress the filter cake 14 and possibly to pass through the filter cake to displace residual moisture. As shown all the plates are covered with filter cloth 18, 20, rendered impervious over restricted portions 24, 26, but in an alternative press the plates 10 carry filter cloth and the alternate plates 12 carry impervious membranes in place of cloths. These membranes are inflated to squeeze the cake but there is then no air flow through the cake. <IMAGE>

Description

SPECIFICATION Improvements in or relating to filter presses The present invention concerns improvements in or relating to filter presses.

The invention is concerned especially with filter presses comprising a stack of separable filter plates, each having a recess on each face so that when the plates are clamped together with their peripheral regions in sealing contact the facing recesses of adjacent plates define chambers to which the slurry to be filtered can be supplied under pressure. The faces of the filter plates are covered with filter cloths or any other suitable filter medium which are spaced from the face of the plates by suitable protrusions such that filtrate passing through the filter cloths can drain away.

Filter presses of the type described in this paragraph will be referred to hereinafter as "plate filter presses".

Normally, slurry is supplied to the chambers of such a filter press until they are filled with compressed filter cake at which time the plates are separated to allow removal of the cake. In many applications it is desirable that the filter cake has the minimum moisture content therein and this cannot be achieved without the aid of some additional means. One prior proposal has been to interpose a resilient diaphragm between the face of the filter plate and the filter cloth such that after the normal filtration operation described above has taken place compressed fluid can be supplied between the diaphragm and the filter plate so that the volume of the chamber is reduced and the cake is compressed.Whereas these prior arrangements have given a more compressed filter cake the filter press is much more complicated in construction and consequently more expensive and is more prone to damage through failure of the diaphragm.

It is an object of the present invention to obviate or mitigate these disadvantages.

According to the present invention there is provided a plate filter press of the type defined in which each alternate filter plate is provided with passage means connectable to a source of compressed gas and leading to the filter chamber so that compressed gas can be supplied to the chamber to compress filter cake thereon and/or pass through the filter medium carried by the said plate and the filter cake to remove moisture from between the cake particles.

Preferably the filter medium is a cloth which is impervious at its periphery, in those regions of the filter chamber of reduced thickness, and in the area of the passage for supplying slurry to be filtered to the chamber.

Alternatively the cloth on said alternate plates may be impervious over its entire area.

Further according to the present invention there is provided a filter plate for a plate filter press, the plate being provided with a sheet-like filter medium and a passage connectable to a source of compressed air leading to a face of the plate defining the filter chamber.

The filter plate may have a central feed hole for slurry to be filtered, the filter medium in the region of this feed hole, at the periphery of the plate and in those regions of the filter chamber of reduced thickness being impervious. Those areas of the filter cloth which are impervious may carry a coating of a plastics or rubber material.

According to another aspect of the present invention there is provided a process for reducing the moisture content of a filter cake in a plate filter press after a normal filtering operation has been concluded by supplying compressed gas between the filter plate and the sheet-like filter medium of every alternate filter plate such that said gas compresses the filter cake and/or passes through the filter medium and the filter cake towards the neighbouring plate to remove moisture from between the cake particles.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing which shows a sectional elevation of part of a filter press showing two adjacent plates defining a filter chamber.

A filter press comprises a horizontal stack of separable filter plates, two of which 10, 12 are shown in the drawing. Means (not shown) are provided for clamping the plates together and as each plate has a recess in each face a filter chamber 14 is defined between the plates. Each plate is provided with a central feed hole 16 so that slurry to be filtered can be fed to the chamber 14 which is lined with filter cloths 18, 20 which cover the facing faces of each plate 10, 12.

In operation, after the stack of plates has been clamped together slurry is supplied to the chamber 14 under pressure and as the filter cloths 18, 20 are held away from the filter plates 10, 12 by cylindrical protrusions or ribs 21 defining channels, filtrate from the slurry passes through the cloth 18, 20 and is removed from the press through filtrate passages, not shown in the drawing.

When the normal filtering operation described above has been completed a cake of residue remains in the chamber 14. It is an object of the present invention to further compact this cake such that residual filtrate therein is at least partially removed. To achieve this the plate 12 is provided with an inlet passage 22 connectable to a source of compressed air and leading into the chamber 14. It will be realised that provided the pressure of the air supplied to the passage 22 is sufficiently high it will cause a further compression of the cake in the chamber and will also be forced to permeate through filter cloth 20, the cake and the filter cloth 18 carrying with it moisture and hence reducing the cake moisture content to a lower level than normally achieved. The drawing shows that the plate 12 has an additional passage 23 for supplying compressed air to the adjacent chamber.

Means are provided for varying the pressure of the compressed air which can be supplied to the chamber for varying lengths of time. It will be realised, of course, that compressed air is supplied to alternate plates of the press so that there is an unidirectional flow of the air through the cake in each chamber.

To ensure that the compressed air does not "short circuit" that is it is constrained to compress the cake and/or to pass through the cake at or near its areas of increased thickness, certain areas of the filter cloth 20 on the plate 12 are made impervious. These areas 24, 26 are around the periphery of the cloth and in those areas of the cloth covering a band at the periphery of the recess where the chamber is of reduced thickness and also around the central feed hole. it is intended that the compressed air causes the impervious area of the cloth to seal against the cake. Conveniently, the cloth 20 is made impervious by coating it with a continuous film of rubberised or plastics material.

The embodiment described above is particularly advantageous when used to de-water granular materials such as coal fines.

It will be realised that a standard plate filter press can readily be modified simply by providing for the introduction of compressed air to each chamber and making certain areas of the filter cloth impervious.

Various modifications can be made without departing from the scope of the invention, for example, the impervious areas of the filter cloth can be altered depending upon the location of the slurry feed passage. Additional impervious areas would be provided in the region of any stay bosses 28 outstanding from the plate faces.

In a further modification where it is desired only to compress the filter cake the cloth on the plate 12 could be impervious over its entire area. Thus filtration would take place only through the cloth 18 and after the supply of slurry has been cut off compressed air is supplied through passage 22 so that the impervious cloth 20 pushes the cake towards the plate 10, thus compressing it.

As the present invention enables removal of filtrate from the cake after "normal" filtration by the filter medium has taken place it is possible to treat cakes which are thicker than would normally be tolerated in view of their relatively high moisture content, the action of the compressed air removing excess filtrate from the cake. Thus the thickness of the filter chamber can be increased which results in a greater chamber volume and greater throughput.

Chamber thickness in excess of 60 mm are possible.

Claims (10)

1. A filter press of the type defined in which each alternate filter plate is provided with passage means connectable to a source of compressed gas and leading to the filter chamber so that compressed gas can be supplied to the chamber to compress filter cake therein and/or pass through the filter medium carried by the said plate and the filter cake to remove moisture from between the cake particles.

2. A filter press as claimed in claim 1, in which the filter medium is a cloth which is impervious at any one or more of the following regions, its periphery, in those regions of the filter chamber of reduced thickness, and in the area of the passage for supplying slurry to be filtered to the chamber.

3. A filter press as claimed in claim 1, in which the filter medium on each alternate filter plate is impervious over its entire area.

4. A filter press as claimed in claim 1, in which the chamber thickness is upwards of 60 mm.

5. A filter plate for a filter press of the type defined, the plate being provided with a sheet-like filter medium and a passage connectable to a source of compressed air leading to a face of the plate defining the filter chamber.

6. A filter plate as claimed in claim 5, including a central feed hole for slurry to be filtered, the filter medium in the region of this feed hole, at the periphery of the plate and in those regions of the filter chamber of reduced thickness being impervious.

7. A filter plate as claimed in claim Sin which those areas of the filter medium which are impervious carry a coating of a plastics or rubber material.

8. A process for reducing the moisture content of a filter cake in a filter press of the type defined after a normal filtering operation has been concluded by supplying compressed gas between the filter plate and the sheet-like filter medium of every alternate filter plate such that said gas compresses the filter cake and/or passes through the filter medium and the filter cake towards the neighbouring plate to remove moisture from between the cake particles.

9. A filter press substantially as hereinbefore described with reference to the accompanying drawing.

10. A filter plate substantially as hereinbefore described with reference to the accompanying drawing.

1 A process for reducing the moisture content of a filter cake, substantially as hereinbefore described with reference to the accompanying drawing.