GB2389326A

GB2389326A - High temperature gas filter

Info

Publication number: GB2389326A
Application number: GB0211732A
Authority: GB
Inventors: Frederick Ian Wood
Original assignee: Fenchurch Environmental Group Ltd
Current assignee: Fenchurch Environmental Group Ltd
Priority date: 2002-05-22
Filing date: 2002-05-22
Publication date: 2003-12-10
Anticipated expiration: 2022-05-22
Also published as: GB0211732D0; GB2389326B

Abstract

A filter (6) comprises a filter element (11) located between an inlet (9) and outlet (10) of a housing (8); wherein the filter element is formed from a body of fibrous material sandwiched between two sheets of mesh. The body of fibrous material has a graduated density increasing from the inlet towards the outlet. The element is folded to define pleats, wherein the mesh supports and compresses the fibrous material and holds adjacent pleats apart. The filter is capable of withstanding temperatures up to 350{C. Preferably the fibrous material is made from two layers - the first layer, on the inlet side, having a graduated density and made from compressed long stranded glass fibre; and the second being manufactured from fine glass cloth. The mesh is preferably a copper wire mesh. The filter is particularly suitable for treating high temperature gases produced by automotive drying ovens.

Description

A FILTER

The present invention relates to a filter which may be used, particularly but not exclusively, for treating high temperature gases produced by automotive drying ovens. Motor vehicles have traditionally been coated with a cellulose paint. The coated vehicle then passes through a large oven where the air has been heated to approximately 300 C in order to dry the coating. To minimise energy use and the cost of heating the air to such temperatures, the air is re-circulated and passed through a filter, or series of filters, to remove dust and paint particles. The term 'high temperature gases' will be used herein to refer to gases of the kind typically encountered in the gas filtration system of automotive drying ovens at a temperature of approximately 250 to 350 C. The removal of particles from such gases is essential to prevent them adhering lo the next 'wet' vehicle, which may require the vehicle to be passed through the coating and drying process again. The particles may be of dust or paint for example.

A conventional filter system used in most ovens of this type consists of a series of planar filter panels of high temperature glass fibre. The panels are self-supporting and are housed in a steel or aluminium mesh support frame. Each panel is typically manufactured from compressed long stranded glass fibre and has a thickness of approximately 15 to 20mm. The filter panels are installed in a V-formation with the edges of adjacent panels in abutment to provide the filter area necessary to deal with the relevant air volume at acceptable levels of resistance to airflow.

The recent trend away from cellulose-based coatings towards water-based coatings has presented some motor manufacturers with air filtration problems. In particular, conventional filters used in conjunction with water-based coatings become blocked quickly, e.g. within seven days. Blocked filters must be replaced or insufficient air is supplied to the oven to dry the vehicle. This results in unacceptable downtime as production must cease while the filters are changed.

One solution to the above problem would be to increase the surface area presented to the air flow by the filter, thereby reducing the need for filter replacement. This would required the installation of a greater number of filter panels as detailed above but i unfortunately the available space is rarely sufficient to have additional filters of the conventional type. It should also be noted that filter systems in this type of application are required to operate effectively at temperatures of up to 350 C throughout their working lives which limits the options available to filter designers.

Filter systems are known which incorporate glass fibre of graduated density, the fibre density increasing from the inlet side of the filter to the outlet side of the filter. In some applications a graduated density structure can be advantageous as relatively I large particles accumulate adjacent the inlet side of the filter whereas relatively smal] 2 particles accumulate adjacent the high density side of the filter. Thus dust build up (known as "dust load") is distributed through the body of filter material, ensuring that the filter does not become blocked as a result of a rapid build up of material immediately adjacent the inlet side of the filter. The density of the conventional filters used in motor manufacturing paint ovens as described above is not known in detail. However, even if the conventional filters are of uniform density, merely adopting a graduated density structure would not be sufficient to achieve an acceptable working life. i An object of the present invention is to obviate or mitigate the aforementioned problems. According to a first aspect of the present invention there is provided a filter comprising a housing defining a cavity located between inlet and outlet apertures' and a filter element received within the cavity such that fluid flow between the inlet and outlet must be through the element, wherein the filter element is formed from a body of fibrous material sandwiched between two sheets of mesh, the body of fibrous; material being of graduated density such that the density increases from the inlet towards the outlet, the body and sheets of mesh being folded to define pleats, the

mesh having sufficient structural strength to compress the fibrous material and hold the fibrous material of adjacent pleats apart, and the filter being capable of withstanding temperatures up to 350 C Providing a filter in this way allows the surface area of the filter to be increased over conventional filters whilst not increasing the overall space required to accommodate the filter.

The body of fibrous material is preferably comprised of first and second layers of filter material with the second layer on the outlet side of the first layer. The first layer may be manufactured from a graduated density fibre, such as glass fibre, to provide high dust-holding capacity combined with low initial resistance to air flow.. The I glass fibre may be compressed long stranded glass fibre, or the like.

Preferably the first layer has an uncompressed thickness of approximately 40-60mm and more preferably approximately 45-50mm.

The second layer may be manufactured from a fine cloth, such as fine glass cloth, to provide the required filtration efficiency.

Preferably at least one mesh sheet is a wire mesh and may be manufactured from copper. The housing preferably comprises at least one support to which the filter element is attached. The or each support may be a mesh screen and the filter element may be attached to the support using steel wire.

A pre-filter may be supported within the housing and may be supported therein by a retaining clip.

According to a second aspect of the present invention there is provided a method of manufacturing a filter comprising sandwiching a body of fibrous material between

two sheets of mesh to form a filter element, folding the element into pleats and locating the element within a cavity defined by a housing.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a prior art filter for high temperature gases produced

by automotive drying ovens shown partially cut away; Figure 2 is a perspective view of a filter according to the present invention; Figure 3 is a cross sectional view of part of a filter medium used in the manufacture of a filter in accordance with the present invention; Figure 4 is a perspective view of a filter support framework for receiving fillers of the type shown in Figure 2; Figure S is a schematic end view of a pleated filter formed from the filter medium shown in Figure 3; and Figure 6 is a graph of air resistance as a function of air volume using results obtained for a filter according to the present invention as described with reference to Figures 2 to 5. Figure 1 shows a conventional filter 1 for use with high temperature gases produced by automotive drying ovens. The filter I is composed of a series of individual planar filter panels 2 supported within a steel or aluminium mesh framework 3 in a V-

formation. The filter I is arranged such that gases pass through the filter I in the direction of arrow A. Each filter panel 2 is formed of a thin sheet of glass fibre 4. Due to the manner in which the panels 2 are manufactured each one has a thin layer of high-density glass _ i

fibre on its rear face which forms a backing layer 5. this backing 5 helps retain the structural integrity of the panel 2 and increases its filtration performance. In spite of these benefits, the backing 5 suffers from the disadvantage that it is brittle and the panels 2 cannot be folded. Thus individual panels 2 are positioned in edge-to-edge abutment. Referring now to Figures 2 and 3, a filter 6 embodying the present invention is composed of a filter medium which is pleated to follow the path generally indicated by line 7 and is supported within a housing 8 having a front gas inlet face 9 and a rear gas outlet face 10. The filter medium is formed as a flexible sheet 11 (Figure 3) having an inner composite core 12 located between two outer layers 13 of copper wire. The inner core 12 is composed of a layer of glass fibre 14 (uncompressed thickness approximately 50mm) and a number 20 fine glass cloth 15. The sheet 11 is folded into pleats and is supported within the housing 8 by steel wire stitching (not shown) between the apex 16 of each pleat and front and rear wire mesh screens 17, 18. The screens 17, 18 may be formed of the same mesh as the layers 13, e.g. a mesh defining square openings of dimensions in the range 25Tnm to 50mm. A layer of adhesive (not shown) is applied to the top edge and bottom edgel9 of the sheet 11 to secure it to opposed top and bottom walls 20, 21 of the housing 8.

The housing 8 comprises opposed upright sidewalls 22, 23 connected by the opposed top and bottom walls 20, 21. The front 9 and rear faces 10 of the housing are open to facilitate passage of gases through the filter 6 in the direction of arrow B. The housing 8 also comprises a header unit 24 around the front face 9 of the housing 8. The header unit 24 is slightly wider and taller than the housing 8 and can be used to accommodate a prefilter (not shown) if desired. A W-shaped retaining clip 25 is hingedly connected to the header unit 24 to retain the pre-filter in place when one is in use. A 6mm high temperature seal 26 is located at the rear of the header unit 24. This is used to secure the filter 6 within a conventional support framework 27 such as that shown in Figure 4. The framework 27 is designed to support a plurality of filters 6 in the correct location relative to the high temperature gases produced by the drying ovens.

Figure 5 is a sectional view through part of the pleated filter of Figures 2 to 4. The wire mesh layers 13 provide sufficient structural support to keep the adjacent pleats apart, opening up a large surface area and yet providing a much greater volume of filter material to capture contaminants. Providing gaps 28 are maintained between adjacent pleats air can flow freely to all parts of the filter. The distance between the two planes defined by the crests 16 of the pleats is 292mm.

A series of tests were carried out to determine the performance of a set of filters according to the present invention. The graph shown in Figure 6 illustrates that, as desired, air resistance increased linearly as a function of air volume. Air velocity through the filter was measured as 0. 125 to 0.16 m/s compared to 2 to 2.5 m/s for a conventional filter. A lower air velocity is preferred since this increases contact time with the filter, thus enabling more unwanted matter to be filtered from the air passing through the filter. Surface area calculations were carried out for a set of conventional V-formation filters (as shown in Figure l) and a set of filters according to the present invention having similar overall dimensions. The set of conventional filters was composed of 30 panels (see panels 2 of Figure 1), each measuring 480 x 480 x 1 Omen, and had a total surface area of 6.91m2. The set of filters according to the present invention was composed of eight full size filters (each measuring 592 x 592 x 292mm) and two half size filters (each measuring 592 x 287 x 292mm) and had a total surface area of 33.92m2, which represented an increase of over 490% compared to the set of conventional filters.

Trials of a set of filters according to the present invention have been carried out and have shown that the operational lifetime of a set of such filters is up to eight times longer than that of a set of conventional filters. This is believed to be due to the large increase in surface area which results from using a compressed layer of graduated density glass fibre material that, in its uncompressed state, is approximately three times thicker than in conventional filters and a filter material which is sufficiently flexible to allow it to be pleated within the filter housing. Such increases in operational lifetime reduce downtime and increase production efficiency.

It will be understood that numerous modifications can be made to the embodiment of the invention described above without departing from the underlying inventive concept and that these modifications are intended to be included within the scope of; the invention. For example, the housing may take any convenient size and/or shape and any suitable filter materials can be used to suit the particular application.

Claims

1. A filter comprising a housing defining a cavity located between inlet and outlet apertures, and a filter element received within the cavity such that fluid flow between the inlet and outlet must be through the element, wherein the filter element is formed from a body of fibrous material sandwiched between two sheets of mesh, the body of fibrous material being of graduated density such that the density increases from the inlet towards the outlet, the body and sheets of mesh being folded to define pleats, the mesh having sufficient structural strength to compress the fibrous material and hold the fibrous material of adjacent pleats apart, and the filter being capable of withstanding temperatures up to 350 C.

2. A filter in accordance with claim 1, wherein the body of fibrous material is comprised of first and second layers of filter material with the second layer being positioned on the outlet side of the first layer. i 3. A filter in accordance with claim 2, wherein the first layer is manufactured from a! graduated density fibre.

4. A filter in accordance with claim 3, wherein the fibre is glass fibre.

S. A filter in accordance with claim 4, wherein the glass fibre is compressed long stranded glass fibre. I 6. A filter in accordance with any one of claims 2 to S. wherein the first layer has an uncompressed thickness of approximately 40-60mm.

7. A filter in accordance with any one of claims 2 to S. wherein the first layer has an uncompressed thickness of approximately 45-SOmm.

8. A filter in accordance with any one of claims 2 to 7, wherein the second layer is manufactured from a fine cloth.

9. A filter in accordance with claim 8, wherein the second layer is fine glass cloth.

10. A filter in accordance with any preceding claim, wherein at least one mesh sheet is a wire mesh.

11. A filter in accordance with claim 10, wherein the wire mesh is manufactured from copper. 12. A filter in accordance with any preceding claim, wherein the housing comprises at least one support to which the filter element is attached.

13. A filter in accordance with claim 12, wherein the or each support is a mesh screen.

14. A filter in accordance with claim 12 or 13, wherein the filter element is attached . usmg wire.

15. A filter in accordance with any preceding claim, wherein a pre-filter is supported within the housing.

16. A filter in accordance with claim 15, wherein the pre-filter is supported within the housing by a retaining clip.

17. A method of manufacturing a filter comprising sandwiching a body of fibrous material between two sheets of mesh to form a filter element, folding the element into pleats and locating the element within a cavity defined by a housing.

18. A filter for removing particulates from high temperature gases substantially as hereinbefore described with reference to figures 2 to 6 of the accompanying drawings.

19. A method of manufacturing a filter for removing particulates from high temperature gases substantially as hereinbefore described with reference to figures 2 to 6 of the accompanying drawings.