GB2218918A

GB2218918A - Filter cell

Info

Publication number: GB2218918A
Application number: GB8812290A
Authority: GB
Inventors: Roger John Temple
Original assignee: FLOWTECH FLUID HANDLING LIMITE
Current assignee: FLOWTECH FLUID HANDLING LIMITE
Priority date: 1988-05-24
Filing date: 1988-05-24
Publication date: 1989-11-29
Anticipated expiration: 2008-05-24
Also published as: GB2218918B; GB8812290D0

Abstract

An inward-flow filter cell of hollow, annular disc form, adapted to be stacked with other cells, comprises two filter sheets 2, 3 spaced apart by an internal support 6. At least the upper sheet 3, and possibly both sheets, is reinforced on its outer surface by a layer 14, which resists expansion of the cell if the pressure drop is reversed but does not substantially resist fluid flow. Layer 14 may be a random-fibre scrim of polyester, nylon or carbon fibres or stainless steel mesh, and it may be heat sealed to the filter sheet, which is of cellulosic fibres. A moulded peripheral seal 5 secures the various parts together. The cell may be used at the top of a stack of similar cells or of cells without reinforcement. <IMAGE>

Description

FILTER CELL This invention relates to filter cells.

Known filter cells comprise a pair of sheet-like filter elements, for example of square or circular shape, sealingly connected together at their outer edges, with a separator or spacer element enclosed between them.

The sheet material of the filter elements is typically made from a slurry of cellulosic fibre; the separator or spacer element can be moulded of a suitable plastics material. The spacer element has a central aperture which co-operates with central apertures in the filter elements to form a discharge passage. In use, the cell is received within a filter housing, either on its own or in a plurality of the cells assembled together into a vertical stack to make a filter cartridge. The fluid to be filtered passes from the outside of the or each cell through the filter elements, the filtrate being discharged through a fluid discharge tube communicating with the discharge passage of the cell or cells. Contaminants are deposited on the outside of the filter elements.

A stack of filter cells making a filter cartridge of this kind is normally used ih-line in a fluidtransfer system in which a fluid containing contaminants flows through the filter housing and the cartridge(s) within. Whilst such an arrangement usually functions perfectly satisfactorily when fluid is in the process of being transferred through the cartridge, certain problems can arise during start-up and shut-down of the transfer system. In particular, upon start-up, fluid is often introduced suddenly at significant pressure into the filter housing. This results in air inside the filter cartridge being unable to escape from the filter housing quickly enough through a vent provided for a build-up of air pressure within the cartridge to be avoided.This results in the filter elements, particularly the upper element of the upper cell of a stack, being subjected to abnormal loads and consequently being damaged. Similar damage may also occur after shut-down of the transfer system when the filter cartridge may be subjected to a considerable pressure head produced by fluid standing in pipework connected to the outlet side of the filter housing. These problems often occur when the fluid transfer system is installed in a brewery or winery where beer or wine, upon leaving the filter housing, is pumped to a higher level of the brewery or winery, for example for bottling. Although both problems can be avoided by correct use of valves and other devices in the transfer system, departure from such correct procedures often takes place in practice.

The known filter cells of the kind mentioned above also have the disadvantage that, when it comes to cleaning the cells of deposited contaminants, it is often quite difficult to rinse deposited contaminants a.

from the filter elements, to which contaminants tend to adhere, especially when the elements are formed from.

cellulosic fibre as mentioned.

The present invention provides a filter cell comprising first and second sheet-like filter elements, each comprising a layer of filter material, and a support element therebetween, at least one filter element having on its outer surface a support layer which overlies the filter material layer and provides support for the support layer against outward deformation thereof whilst providing no appreciable resistance to flow of fluid through the filter element.

A filter cell according to the invention will normally be used, with its support layer facing upwards, as the upper cell of a stack of cells making up a filter cartridge. In this way, the likelihood of damage to the filter cell in circumstances such as those described above can be very substantially reduced.

It has also been found that filter cells according to the invention are much more easily rinsed of deposited contaminants than known cells in which the contaminant is deposits on the filter material layer.

For this reason, cells according to the invention may advantageously have both their first and second filter elements formed with outer support layers as described and such cells, or cells with single support layers can advantageously be used at any position in a filter cell stack.

Conveniently, the filter elements of the cell are connected together at their outer peripheries by a moulded plastics seal, into which the filter material layers and the support layer are embedded. Cells of this type of construction are described in UK Patent Specifications 2185695A and 2185696A.

The support layer(s) may be formed of any suitable material having the stated properties. The layer(s) are however preferably of a plastics material having an openwork structure. A particularly preferred material is random-fibre scrim material. The plastics material may be, for example, polyester or nylon, or a carbonfibre scrim, suitably of 50 or 100 grams/sq. metre.

Advantageously, the support layer is bonded to its underlying filter material layer, preferably by heatsealing. A nylon reinforcing net with a suitable grid, for example, 1/8th inch grid, can instead be employed as the support layer.

For some applications of the filter cell, it is advantageous for the support layer(s) to be of metallic mesh, for example, of stainless steel. The mesh may have a sieve number, for example, in the range of 12 to 400. A filter cell with a metallic mesh support layer may be used in a pre-coat filtration system in which the support layer acts a substrate or septum for the deposited material forming the filtration medium. In such an arrangement, the filter material layer acts as a back-up filter for the pre-coat filter and traps any solid particles which may become loose in the liquid being filtered upon break-up of the deposited filter layer. In this way, the provision of a separate backup filter is avoided and savings in costs and materials can be made.

An embodiment of the invention will now be described by way of example with reference to the drawing, the sole figure of which is a partial crosssectional side view of a filter cell.

The filter cell shown in the figure comprises two filter elements in the form of annular filter discs 2, 3. The filter disc 2, shown as the lower disc in the drawing, is made from a slurry of cellulosic fibre, in which particulate filter material is included. The other filter disc 3 is made from two layers of material. The inner layer 12 is made from the same material as the filter disc 3, whereas the outer layer 14 is formed from random-fibre polyester scrim material which provides a support layer but presents no substantial resistance to fluid flow through the disc 3.

The filter discs 2, 3 have compressed flange portions 4 at their outer peripheral edges, at which the sheets are sealingly connected. This peripheral connection is effected by means of an edge seal 5 of plastics material, preferably polypropylene, which is moulded onto the compressed flange portions to hold them sealingly together. Both layers 12, 14 of the disc 3 are secured at the edge seal 5 in this way.

Trapped between the two filter discs 2, 3 is a spacer element 6 of generally annular form, with a central aperture corresponding to the central apertures 7 of the two filter discs. The spacer element is integrally moulded of suitable plastics material, for example, polypropylene, and comprises a plurality of radially extending ribs 9 connected together by spaced flat concentric connecting rings 10. The spacer element 6 prevents the inner faces of the filter discs 2, 3 from being forced together into contact in use of the cell, by excess external pressure, to avoid reduction of the effective filtering area.

To locate the spacer element 6 securely within the filter cell, the radial ribs 9 are connected at their outer ends by- a flat outermost connector ring 11 which extends radially outwardly beyond the ribs, and is received between the flange portions 4 of the filter discs 2, 3. The connector ring 11 or at least that part of it received between the filter discs can be quite thin, for example it may be about twenty thousandths of an inch in thickness. Preferably, the outer diameter of the connector ring 11 equals or approximates to that of the filter discs 2, 3 but it may exceed it, so that the connector ring is received in the seal edge 5 when this is moulded around the edges of the filter sheets.

The filter cell described above will usually be employed as the upper cell of a stack of cells making up a filter cartridge, the rest of the cells of which are formed by filter cells having both filter elements formed as the lower disc 2 shown in the drawing. One or more of the rest of the cells may however be as shown in the drawing; in other cartridges one or more of the cells may have both filter elements formed as the upper disc 3 shown in the drawing. Whatever the nature of the filter elements of the cells of the rest of the cartridge, the upper element of the upper cell will however normally be as the disc 3.

Cell elements which are as the disc 3 can have a much greater resistance to rupture or deformation as a result of build-up of internal gas of liquid pressure in use. Such elements can also much more easily rinsed of deposited contaminants than elements on which contaminants are deposited on the filter medium itself.

For both these reasons, it can be advantageous to have more than one filter element of the cartridge formed as the disc 3.

In a modified embodiment, the outer layer 14 of the filter disc 3 is bonded to the inner layer 12 by heat-sealing.

In a further modified embodiment, the outer layer 14 of the filter disc 3 is replaced by a sheet of stainless steel mesh which is secured to the edge seal 5 by being moulded into that seal. A filter cell of this modified embodiment can form an effective substrate or septum for a pre-coat filter comprising solid material deposited on the stainless steel mesh.

In such use, the inner layer 12 of the disc 3 acts as a back-up filter for entrapment of solid particles broken-off from the deposited layer.

Claims

1. A filter cell comprising first and second sheetlike filter elements, each comprising a layer of filter material, and a support element therebetween, at least one filter element having on its outer surface a support layer which overlies the filter material layer and provides support for the support layer against outward deformation thereof whilst providing no appreciable resistance to flow of fluid through the filter element.

2. A filter cell according to claim 1, in which both said filter elements have a said support layer on its outer surface.

3. A filter cell according to claim 1 or 2, in which the filter elements of the cell are connected together at their outer peripheries by a moulded plastics seal, into which the filter material layers and the support layer(s) is/are embedded.

4. A filter cell according to any preceding claim, in which the support layer(s) is/are of a plastics material having an openwork structure.

5. A 'filter cell according to claim 4, in which the plastics material is random-fibre scrim material.

6. A filter cell according to claim 5, in which the plastics material is polyester or nylon.

7. A filter cell according to any of claims 1 to 3, in which the support layer(s) is/are of carbon-fibre scrim material having an openwork structure.

8. A filter cell according to any of claims 1 to 3, in which the support layer(s) is/are formed by metallic mesh material.

9. A filter cell according to claim 1, in which the mesh is of stainles steel.

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10. A filter cell according to any claim 5 or 7, in which the srim material has a specific mass of 50 or 100 gum~2.

11. A filter cell according to claim 8 or 9, in which mesh has a sieve number of from 12 to 400.

12. A filter cell according to any preceding claim, in which the or each support layer is bonded to its underlying filter material layer.

13. A filter cell according to claim 12, in which the bonding is by heat sealing.

14. A filter cell substantially as hereinbefore described with reference to the drawing.

15. ' A filter stack comprising a plurality of filter cells, the upper cell of the stack being in accordance with any of claims 1 to 14 and the upper surface of the upper cell including a said support layer.