GB2258621A

GB2258621A - Filter press operation

Info

Publication number: GB2258621A
Application number: GB9117526A
Authority: GB
Inventors: Ian Morton Young
Original assignee: Edwards and Jones Ltd
Current assignee: Edwards and Jones Ltd
Priority date: 1991-08-14
Filing date: 1991-08-14
Publication date: 1993-02-17
Anticipated expiration: 2011-08-14
Also published as: GB9117526D0; GB2258621B

Abstract

After forming filter cake in chambers 16 of a filter press, by filtering under upstream pressure and then squeezing the cake using inflatable diaphragms 18, the cake is further dried by applying suction to the filtrate outlet ducts 30, 32. The drying may be enhanced by heating the cake, possibly by using hot water to inflate diaphragms 18 or electric or fluid heating means in the press plates or residual heat from a previous washing step. Also some air may be bled into chambers 16 through slurry inlets 24, 26 and sucked through the cake. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO FILTRATION METHODS AND APPARATUS The present invention concerns improvements in or relating to filtration methods and apparatus, and especially but not exclusively filtration carried out on a filter plate press.

A filter plate press comprises a plurality of movable plates which, when pressed together, define a number of chambers into which material to be filtered can be fed. Each chamber has filtration means therein so that residue is retained within the chamber and filtrate is removed therefrom. The residue forms a filter cake and by various known means the moisture content of the cake can be reduced. When the filtration process is completed the plates are separated so that filter cake can be removed from the chambers. After cleaning and rearranging of the plates a further filtration operation can be carried out.

Once an initial filtration has been achieved by apparatus of this nature, to increase the efficiency of filtration it is necessary to employ one or more of a number of additional stages, one such stage involves applying pressure to the filter cake by lining the chamber with resilient diaphragms which can be forced into the chamber by applying pressure therebehind to reduce the chamber volume and thereby exert a further filtration pressure on the filter cake.

It is an object of the present invention to provide a filtration method and apparatus which increases the removal of moisture from the filter cake.

According to a first aspect of the present invention there is provided a method of filtration employing using a filter plate press to filter liquid and at the conclusion of the filtration process connecting the or each filter chamber defined by the filter plates to a source of reduced pressure to remove additional moisture from the cake.

Preferably the cake is heated prior to and/or during the connection of the chamber to the source of reduced pressure.

According to a further aspect of the present invention there is provided a filter plate apparatus including a plurality of filter plates defining filter chambers therebetween and means for connecting each filter chamber to a source of reduced pressure.

Preferably means are provided also to supply heat to each chamber.

Preferably each chamber incorporates a resilient diaphragm on one or both of its sides and means for supplying fluid at an elevated temperature between said diaphragm and the filter plate to which it is attached to apply heat to the filter cake in the chamber.

Preferably valve means are provided in the filtrate outlet from the filter press to connect said outlet to a source of reduced pressure after a normal filtration operation has taken place.

Preferably conduit means are provided in each filter plate to enable fluid at an elevated temperature to be circulatated between the plate and its associated diaphragm.

Preferably the fluid is water.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing which diagrammatically shows two filter plates of a filter plate press in cross-section.

For clarity the plates have been drawn thicker than is actually the case.

A plate filter press comprises a framework 10 which slidably mounts a plurality of separable filter plates 12.

Each of the plates 12, in the present embodiment, is provided with a mutually facing recess 14 so that when the plates are clamped together by means (not shown) they define a filter chamber 16 therebetween. To each. of the facing faces of the plates 10 there is fixed a resilient diaphragm 18 have protrusions 20 projecting into the chamber and on which rests a filter cloth 22.

A supply conduit 24 for fluid to be filtered extends through the filter plates and branches 26 feed such fluid into the chamber 16 where primary filtration takes place with residue remaining within the chamber 16 while filtrate is removed therefrom by branches 30 leading to a conduit 32.

The filtration effect can be enhanced by the supplying'fluid under pressure through lines 34 to the space between the filter plates 10 and the resilient diaphragm 18. The application of pressure causes the diaphragm to move into the chamber thereby compressing the cake therein and permitting further filtration to take place if required.

When a filter cake has been produced its moisture content can be further reduced according to the present invention by applying heat thereto and a reduced pressure thereacross. The heat is conveniently applied by utilising fluid at an elevated temperature to perform the diaphragm pressing operation. Heat from this fluid passes into the filter cake to cause its temperature to rise thereby increasing the rate by which moisture evaporates therefrom. This rate can be further advanced according to well known principles of physics by reducing the pressure in the filter cake.

According to the present invention this is achieved by, after draining the conduits and branches 30, 32 of filtrate connecting these to a source of reduced pressure, for example, a vacuum pump (not shown) so that further filtrate in the form of vapour is removed from the cake.

A limited amount of air may be bled into the chamber through the conduit 24 and branches 26 to cause a circulation of moisture purging gas at reduced pressure through the cake.

Various modifications can be made without departing from the scope of the invention. For example, a chamber may have only one diaphragm. The pressure fluid for deflecting the diaphragm could be heated air or any other suitable gas but is preferably water and desirably high temperature waste water, perhaps from a different process.

It is not essential that the filter press employs diaphragms but it is important that the chamber is connected to a source of reduced pressure and it is certainly helpful that heat is applied to enhance evaporation. The heat may be applied directly from the plates which could be provided with any suitable heating means, for example, electric elements, steam or hot water passages therein, etc. Alternatively, in view of the relatively high mass of the plates which are normally fabricated from metal, the washing operation following an earlier filtration step could employ high temperature water or steam thereby storing heat within the plates for use during the subsequent operation.

It has been predicted that in accordance with the present invention an additional thirty minutes processing time utilising water of around 600C is likely to cause a reduction in the water content of the filter cake remaining in the press by between 5 and 10.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

Claims:

1. A method of filtration employing using a filter plate press to filter liquid and at the conclusion of the filtration process connecting the or each filter chamber defined by the filter plates to a source of reduced pressure to remove additional moisture from the cake.

2. A method according to claim 1, in which the cake is heated prior to and/or during the connection of the chamber to the source of reduced pressure.

3. A filter plate apparatus including a plurality of filter plates defining filter chambers therebetween and means for connecting each filter chamber to a source of reduced pressure.

4. Apparatus according to claim 3, in which valve means are provided in the filtrate outlet from the filter press to connect said outlet to a source of reduced pressure after a normal filtration operation has taken place.

5. Apparatus according to claims 3 or 4, in which means are provided also to supply heat to each chamber.

6. Apparatus according to claim 5, in which each chamber incorporates a resilient diaphragm on one or both of its sides and means for supplying fluid at an elevated temperature between said diaphragm and the filter plate to which it is attached to apply heat to the filter cake in the chamber.

7. Apparatus according to claim 6, in which conduit means are provided in each filter plate to enable fluid at an elevated temperature to be circulatated between the plate and its associated diaphragm.

8. Apparatus according to claims 6 or 7, in which the fluid is water.

9. A method of filtration substantially as hereinbefore described with reference to the accompanying drawing.

10. Filter plate apparatus substantially as hereinbefore described with reference to the accompanying drawing.

11. Any novel subject matter or combination including novel subject matter disclosed in the foregoing specification or claims and/or shown in the drawings, whether or not within the scope of or relating to the same invention as any of the preceding claims.