GB2188558A

GB2188558A - Filter medium

Info

Publication number: GB2188558A
Application number: GB08608443A
Authority: GB
Inventors: N Twizell; A D Harris
Original assignee: Plenty Ltd
Current assignee: Plenty Ltd
Priority date: 1986-04-07
Filing date: 1986-04-07
Publication date: 1987-10-07
Also published as: GB8608443D0

Abstract

A filter medium comprises substantially spherical metal or metal alloy particles, suitably of copper nickel alloy or stainless steel, typically of 60 to 300 microns diameter. Such a medium is arranged as a bed in a plurality of compartments which are sequentially backwashed by a rotary means.

Description

SPECIFICATION Filter media This invention relates to filter media, particularfilter media for an automatic backwashing filter, and to a filter including such filter media.

In known backwashing filters, for example filters such as those shown in our prior U.K. Patent Specifications Nos. 1091933 and 2067087,filter media consist of wire mesh, felt or other closely woven material. In our co-pending European Patent Application No. 85306953.2 we proposed an automaticfilterwhich provided much finerfiltration than could be attained with wire mesh or surface filtration screens, the filter media being sand particulate material.

For such a filter to operate satisfactorily to give both efficientfiltration and backwashing properly, the filter media must have several fairly closely defined parameters, namely: (a) Size (b) Shape (c) Density(d) Bed Depth,(e) Compatabilitywiththe fluid to be filtered. Traditional particulate filter media would be silica sand or a combination of anthracite and garnet. However these materials tend to be of a large particle size and therefore require a much deeper bed (typically 1 metre thick) than can be used with a filter as proposed in our aforementioned European patent application.

It is an object of the present invention to provide an improved fine filtration filter media.

According to the present invention filter media for afiltercomprisesmetal or metal alloy particles. The particles are suitably less than 300 micron in size and preferably are in the range 60-150 microns.

Suitable metallic material is 70/30 copper nickel alloy or316 stainless steel. The use of metallic particles in a filter is surprising since conventional materials for a filter bedaregranularmineralsand yet several gradesofthese known mineral materials were tested without success. The use of metallic materials minimises weight and space requirements so that a much shallower bed is required. Particularly in a backwash filter, the bed needs to re-settle to a consistent pattern which does not always happen with irregularshapegrainsofsandorgarnet.This can give a variable flow path through the media which affects filtration efficiency and pressure drop particularly with much thinner bed depths.Hence the shape of the media particles affects the settling speed and pattern of the bed and consequently the filtration efficiency. Moreover the density or specific gravity of the particles is particularly important in backwash applications, since the wash rate must be vigorous enough to expand the bed and upliftthe contaminant removed by the filter, without lifting the media themselves. In addition the media must not disintigrate, corrode or be chemically incompatible with the fluid to befiltered.

Therefore in the preferred arrangement filter media for a filter comprise spherical or near spherical particles of a metal or metal alloy having a particle size less than 300 micron. The invention also includes a filter including such filter media.

Preferably the filter comprises a hollow supporting member, a plurality of compartments supported exteriorly of the supporting member and including metallic particulate filter media, rotatable backwash means disposed axially of the supporting member and having at least one duct arranged to registerwith apertures in the supporting member leading tothe filter compartments, and means for bringing the duct into registration with the apertures to permit backwashing thereof.

The filter media of the present invention are preferably used in a filter as shown in our co-pending European Patent Application 85306953.2 and the details in that specification are incorporated herein for a full disclosure of the preferred type offilter.

Ourtests have shown that a typical specification for particulate material in accordance with the invention would be: (a) Size-60-150 microns (b) Shape - Spherical or very nearly spherical (c) Specific gravity - 13 (d) Bed depth - 0.125 metres (e) Material - 70/30 Copper Nickel alloy or 316 Stainless Steel Such a material will remove particles down to 2 microns in size, and removal efficiency can be enhanced by chemical dosing such as polyelectrolytes and coagulantswhen the filtered fluid is water or sea water.

The use of metallic particles in accordance with the present invention is surprising since metallic particles would not be as economic nor sufficiently chemically inert and thus minerals have been the normal choice. We havefound with the present invention that the space-saving characteristics ofthe metallic particles outweigh the economic disadvantages and metallic particles, selected in accordance with the fluid to be filtered, can be adequately corrosion resistant.

1. Filter media for a filter comprising metal or metal alloy particles.

2. Filter media according to Claim 1 wherein the particles are less than 300 microns in size.

3. Filter media according to Claims 1 or 2 wherein the particles are in the range 60 to 150 microns in size.

4. Filter media according to any preceding claim wherein the particles are selected from copper nickel alloyorstainlesssteel.

5. Filter media for a filter, comprising spherical or nearspherical particles of a metal or metal alloy having a particle size less than 300 microns.

6. Afilter including filter media according to any preceding claim.

7. Afiltercomprising a hollow supporting member, a plurality of compartments supported exteriorly of the supporting member and including metallic particulate filter media, rotatable backwash means disposed axially of the supporting member and having at least one duct arranged to register with apertures in the supporting member leading to the filter compartments, and means for bringing the duct into registration with the apertures to permit

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Filter media This invention relates to filter media, particularfilter media for an automatic backwashing filter, and to a filter including such filter media. In known backwashing filters, for example filters such as those shown in our prior U.K. Patent Specifications Nos. 1091933 and 2067087,filter media consist of wire mesh, felt or other closely woven material. In our co-pending European Patent Application No. 85306953.2 we proposed an automaticfilterwhich provided much finerfiltration than could be attained with wire mesh or surface filtration screens, the filter media being sand particulate material. For such a filter to operate satisfactorily to give both efficientfiltration and backwashing properly, the filter media must have several fairly closely defined parameters, namely: (a) Size (b) Shape (c) Density(d) Bed Depth,(e) Compatabilitywiththe fluid to be filtered. Traditional particulate filter media would be silica sand or a combination of anthracite and garnet. However these materials tend to be of a large particle size and therefore require a much deeper bed (typically 1 metre thick) than can be used with a filter as proposed in our aforementioned European patent application. It is an object of the present invention to provide an improved fine filtration filter media. According to the present invention filter media for afiltercomprisesmetal or metal alloy particles. The particles are suitably less than 300 micron in size and preferably are in the range 60-150 microns. Suitable metallic material is 70/30 copper nickel alloy or316 stainless steel. The use of metallic particles in a filter is surprising since conventional materials for a filter bedaregranularmineralsand yet several gradesofthese known mineral materials were tested without success. The use of metallic materials minimises weight and space requirements so that a much shallower bed is required. Particularly in a backwash filter, the bed needs to re-settle to a consistent pattern which does not always happen with irregularshapegrainsofsandorgarnet.This can give a variable flow path through the media which affects filtration efficiency and pressure drop particularly with much thinner bed depths.Hence the shape of the media particles affects the settling speed and pattern of the bed and consequently the filtration efficiency. Moreover the density or specific gravity of the particles is particularly important in backwash applications, since the wash rate must be vigorous enough to expand the bed and upliftthe contaminant removed by the filter, without lifting the media themselves. In addition the media must not disintigrate, corrode or be chemically incompatible with the fluid to befiltered. Therefore in the preferred arrangement filter media for a filter comprise spherical or near spherical particles of a metal or metal alloy having a particle size less than 300 micron. The invention also includes a filter including such filter media. Preferably the filter comprises a hollow supporting member, a plurality of compartments supported exteriorly of the supporting member and including metallic particulate filter media, rotatable backwash means disposed axially of the supporting member and having at least one duct arranged to registerwith apertures in the supporting member leading tothe filter compartments, and means for bringing the duct into registration with the apertures to permit backwashing thereof. The filter media of the present invention are preferably used in a filter as shown in our co-pending European Patent Application 85306953.2 and the details in that specification are incorporated herein for a full disclosure of the preferred type offilter. Ourtests have shown that a typical specification for particulate material in accordance with the invention would be: (a) Size-60-150 microns (b) Shape - Spherical or very nearly spherical (c) Specific gravity - 13 (d) Bed depth - 0.125 metres (e) Material - 70/30 Copper Nickel alloy or 316 Stainless Steel Such a material will remove particles down to 2 microns in size, and removal efficiency can be enhanced by chemical dosing such as polyelectrolytes and coagulantswhen the filtered fluid is water or sea water. The use of metallic particles in accordance with the present invention is surprising since metallic particles would not be as economic nor sufficiently chemically inert and thus minerals have been the normal choice. We havefound with the present invention that the space-saving characteristics ofthe metallic particles outweigh the economic disadvantages and metallic particles, selected in accordance with the fluid to be filtered, can be adequately corrosion resistant. CLAIMS

1. Filter media for a filter comprising metal or metal alloy particles.

6. Afilter including filter media according to any preceding claim.

7. Afiltercomprising a hollow supporting member, a plurality of compartments supported exteriorly of the supporting member and including metallic particulate filter media, rotatable backwash means disposed axially of the supporting member and having at least one duct arranged to register with apertures in the supporting member leading to the filter compartments, and means for bringing the duct into registration with the apertures to permit backwashing thereof.

8. Afilter bed for a filter comprising substantially spherical particu late materia 1 60 to 150 microns in size to a depth of about 0.125 metres, the particulate material being selected from particles of copper nickel alloyorstainlesssteel.

9. Filter media substantially as hereinbefore described.