GB2517500A

GB2517500A - Gas Filter

Info

Publication number: GB2517500A
Application number: GB1315128.7A
Authority: GB
Inventors: Peter Gardner
Original assignee: ACE FILTRATION Ltd
Current assignee: ACE FILTRATION Ltd
Priority date: 2013-08-23
Filing date: 2013-08-23
Publication date: 2015-02-25
Also published as: GB201315128D0

Abstract

A rigid gas filter body (20) comprises solid particles of filter material such as activated carbon, bonded together with an adhesive such as methyl cellulose to render the body integral and self-supporting. The body is preferably cylindrical with a central gas flow passage (22) and retained between a closed end cap (12) and an end cap (10) with a central opening (15). The end caps may be connected together by one or more thin rods or strips (25) which do not obstruct the flow of gas through the filter body between the central flow passage (22) and the surrounding atmosphere. The filter body may be enclosed by a textile material (18) but does not require any internal or external support walls, so that gas flow through the filter body can be greatly increased.

Description

GAS FILTER

[00011 Invention relates to a gas filter, for use for example in systems for odour removal, air purification or flue gas filtration. Such filters are used in many fields of activity including for example the hydroponics industry.

[0002] Gas purification systems use solid particulate filtration media such as activated carbon. One known type of gas filter comprises two coaxial perforated cylindrical retaining walls of stainless steel or the like between which a loose particulate filter material such as granular coal or coconut activated carbon is retained in a woven bag of textile material with a mesh size that allows the passage of gas while retaining the filter particles. The filter is closed by an end cap at one end and at the other end has an end cap with a central aperture to communicate with a gas passage with an extractor fan so that gas can be drawn radially inwards through the perforations in the outer and inner cylindrical walls, passing through the particulate material held between them and then axially into the gas passage.

[0003] One disadvantage of such a system is that the filter particles can be awkward to handle and packing the filter material between the inner and outer cylindrical walls and as carbon is impressed into the cylinder it can fracture.

Another is that a filtration system that may be subject to considerable vibration filter particles are packed in a filter that is usually horizontally mounted but can move relative to one ancaher and may settle in a downward direction leaving a void at the top of the body of filter material resulting in a filter body of uneven density and filtration properties. As time passes the loose carbon become more like powder and performance deteriorates further.

[0004] Positioning of perforated metal walls on each side of the filter body limits the gas flow through the walls to the perforations, resulting in an uneven flow of gas through the filter body.

[0005] The present invention provides a rigid gas filter body comprising solid particles of filter material bonded together with an adhesive to render the body integral and self-supporting, the filter body having within it a gas flow passage open at least one end.

[0006] The filter particles may suitably be of activated carbon. The filter body is preferably elongate, with a central elongate gas flow passage through it, and the preferred configuration is a cylindrical body having a coaxial cylindrical filter passage through it.

[0007) The invention further provides a gas filter comprising a filter body as defined above mounted between a pair of end caps, one said end cap having a central opening communication with the gas flow passage of the filter body.

In a preferred embodiment, a cylindrical filter body is fitted with circular end caps, one end of the filter passage being closed by a solid end cap and the other communicating with a central opening of an annular end cap. The end caps are preferably connected and held together by means that do not substantially obstruct the flow of gas into, through or out of the filter body. For example one or more connecting rods or strips may extend through the central flow passage from one end cap to the other. Between the end caps the filter body may be enclosed by a net or screen suitably of textile material, to prevent damage to the filter body while allowing relatively unobstructed flow of gases.

[0008] In use, the central flow passage is connected through an end cap to a flow duct of a filtration system. Gas may flow in either direction through the filter body. More usually the flow is radially inwards through the outer screen, through the filter body to the central flow passage and thereafter axially through the opening at one end of the filter. In some applications, however the gas flow may be in the opposite direction, flowing axially through the aperture in one end cap, through the central flow passage of the filter body and radially outwards through the filter body and outer textile screen. In this embodiment it may be desirable to provide a textile covering for the surface of the central flow passage. Because the filter body of the invention does not require rigid inner or outer supporting walls, air flow through the filter can be increased by up to 30% compared to the conventional filters described above.

[0009] Preferred embodiments of the invention will now be described with reference to the accompanying drawings, wherein, Figure 1 is a perspective view of a filter assembly in accordance with an embodiment of the present invention; Figure 2 shows the individual parts of the filter assembly of Figure 1 and; Figure 3 is a cross-section of the line III to III of Figure 1, showing gas flow through the filter assembly.

[0010] Referring first to Figure 1. A filter assembly comprises a first end cap 10 and a second end cap 12 both of which may suitably be made of metal such as stainless steel or aluminium, or of a rigid plastics material.

[0011] The first end cap 10 is annular with a central axial projection 14 defining an opening 15 to a central gas flow passage of the filter as will be described in more detail below. Three screw holes 28 are spaced circumferentially around the projection.

[0012] As can be seen in Figure 2, the second end cap 12 is also circular and defines a closed end of the assembly.

[0013] Between the end caps 12 is a cylindrical sleeve of open-weave textile material 18, surrounding the filter body of the invention as will be described in more detail below.

[0014] Figure 2 shows a filter body 20 in accordance with the invention, comprising particulate filter material such as activated carbon the particles bonded together with an adhesive material which may suitably aqueous-based. The filter body has a coaxial passage 22 extending throughout its length. End cap 12 has, secured to its main inner surface three elongate connecting strips 25 suitably of metal or rigid plastics material, having mounting flanges 23 at their lower ends end turned at right angles to the longitudinal extent of the strips. The strips are each secured at one end to the main inner surface of end cap 12, suitably by spot welding screws through the mounting flanges. Alternatively the strips could be provided at their ends with screw-threaded bushes. The strips are positioned inwardly of a peripheral rim 24 of the end cap 12, their planes tangential to an imaginary circle concentric with the end cap, the diameter of which is slightly less than the diameter of the passage 22 to the filter cartridge 20.

[00151 An annular gasket 26 made suitably of elastomeric material such as neoprene rubber, is secured to the inner surface of the end cap 12 surrounding the connecting strips spaced radially inwards from the rim 24 of the end cap.

Such gaskets could alternatively be provided on each end of the filter body. For clarity, only a small part of the surface structure of the cartridge is shown, the rest being indicated schematically.

[0016] The cylindrical filter cartridge 20 is shaped and dimensioned to fit neatly over the three connecting strips 25, one end of the cartridge being accommodated snugly within the rim 24 of end cap 12 with the annular end face of the cartridge abutting gasket 26.

[0017] The filter cartridge 20 can be positioned in end cap 12, with the textile outer covering 18 fitted around its outer surface, the ends of the covering extending to within the rim 24. The end cap 12 can then be fitted over the top end of the filter cartridge 20 and textile covering 18 as shown in Figure 2, and secured with screws through screw holes 28 in the end cap and screw holes 23 at the upper ends of the connecting strips 25 to complete the assembly.

[0018] The assembled filter is shown in cross-section in Figure 3. In a filter system, the filter will usually be mounted horizontally as shown in this figure. Arrows in this figure show the direction of flow of air or other gas radially inwardly through the textile cover 13 and filter body 20 and into the coaxial filter passage 22, and then axially towards the outlet opening 15. It can be seen that because the filter body 20 is self-supporting its inner cylindrical surface can he made entirely free of any covering such as the perforated inner walls used in conventional filters. Furthermore, its outer surface is covered only by textile covering that can be of a loose weave with a high degree of gas permeability. Overall gas flow through the system can therefore be substantially increased.

[0019] As has already been indicated above, in some applications the direction of gas flow through the filter could be reversed, with the gas entering through opening 15 then passing radially outwardly from passage 22.

[Q020] The filter body may be of any suitable dimensions.

Typically it may be from 200 to 1200 mm in length and external diameter of 150 to 600 mm, the internal diameter of the flow passage being preferably 125 to 200 mm, with the radial thickness of the filter material being from 30 to 60 mm, more preferably 40 to 50 mm.

[0021] The filter particles may suitably have a mesh size in the range from 1 to 6 mm, preferably 2 to 4 mm. The total surface area is preferably in a range of 500 to 1500 m2/g, as measured by the BET N2 test method. A preferred range is 800 to 1200 m2/g.

[0022] The binder for the filter particles is preferably an aqueousbased material, suitably a methyl cellulose such as hydroxypropylmethylcellulose.

[0023] The binder is preferably mixed with the filter particles in an amount from 2 to 6% by weight. In this way the particles can be rigidly bound together whilst still leaving ample surface area available for filter activity.

[0024] when this filter is used within the hydroponics industry, it works in conjunction with the fan assisted extraction system. The air is extracted away from the growing area, unpleasant odours are filtered out from the air stream before it is dispersed into the atmosphere. The filter will remove odours mainly created by human intervention with the use of pesticides and nutrient foliage sprays. Other odours created by rotting foliage or entrapped non flowing water will also be absorbed and removed from the air stream by installing this filter.

Examples

[0025] A number of cylindrical filter bodies made as follows, using the hydroxypropylmethylcellulose binder described above.

[0026] Activated carbon particles were soaked in water overnight to saturate them. The saturated particles had a water content of approximately 30% by weight. These were then mixed with hydroxypropylmethylcellulose adhesive, in an amount of 40g of adhesive per 1kg of wet carbon particles.

The mixture was then baked in a mould and dried at 80°C.

Filters were made up using the resulting filter bodies, each filter comprising a single filter body or two such bodies arranged coaxially end to end.

[0027] The dimensions and properties of the filters are set out in the following table.

-Internal External Length Wall Volume Number Carbon Compressed (-20% on 50) (40g/kg wet) Diameter Diameter mm thickness m3/hour of Volume m3 Wet carbon/kg (-30% on 40) Hydroxy- mm mm mm sections Baked dry propylmethyl-I Weight/kg cellulose -__________ __________ _______ _________ ________ ________ ___________ ______________ _____________ Weight/kg 1 125 205 250 40 300 1 0.0052 5.2 3.64 0.21 1 150 230 210 40 285 1 0.0068 6.8 4.75 0.28 3 150 230 420 40 720 2 0.0102 10.2 7.14 0.41 4 200 300 220 50 655 1 0.0086 8.6 6.88 0.35 S 200 300 440 50 1160 2 0.0173 17.3 13.84 0.70

Claims

CLAIMS: 1. A rigid gas filter body comprising solid particles of filter material bonded together with an adhesive to render the body integral and self-supporting, the filter body having within it a gas flow passage open at at least one end.
2. A filter body according to claim 1 wherein the filter particles are of activated carbon.
3. A filter body according to claim 1 or claim 2 wherein the filter particles have a mesh size in the range from 1 to 6 mm.
4. A filter body according to any preceding claim wherein the filter particles have a specific surface area of 500 to 1500 m2/g as measured by the BET N2 method.
5. A filter body according to any preceding claim wherein the filter particles are mixed with the adhesive in an amount from 2 to 6% by weight of adhesive, based on the total composition.
6. A filter body according to any preceding claim wherein the adhesive is a water-based adhesive.
7. A filter body according to claim 6 wherein the adhesive comprises a methyl cellulose.
B. A filter body according to claim 7 wherein the adhesive comprises hydroxypropylmethylcellulose.
9. A filter body according to any preceding claim which is of cylindrical shape with a coaxial filter passage therein.

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10 - 10. A filter body according to claim 9 wherein the central flow passage is cylindrical and extends one end of the filter body to the other.
11. A method of making the filter body according to any preceding claims which comprises the steps of soaking the filter particles in water to saturation, mixing an adhesive with the particles, moulding the mixture of particles and adhesive to the desired shape of the filter body with a gas flow passage therein, baking the filter body in the mould and drying the resulting shaped body.
12. A method according to claim 11 wherein the filter particles are soaked to a water content of 25 to 40% weight.
13. A method according to claim 11 or claim 12 wherein the filter body is dried at a temperature of 60 to 120°C.
14. A gas filter comprising a filter body as claimed in any one of claims 1 to 10 mounted between a pair of end caps, one said end cap having a central opening in communication with the gas flow passage of the filter body.
15. A gas filter according to claim 14 wherein the filter body is cylindrical with a coaxial gas flow passage therethrough, one end of the filter passage being closed by a solid end cap and the other communicating with a central opening of an annular end cap.
16. A filter according to claim 14 or claim 15 wherein the end caps are connected together by one or more elongate rods or strips extending through the central flow passage from one end cap to the other. 11 -
17. A filter according to any one of claims 14 to 16 wherein the outer surface of the filter body is covered with an open weave fabric.