GB2110561A - Fluid filter - Google Patents

Abstract

A fluid filter or filter element comprising at least one layer of cellular material (10, 12) the cells of which are filled or partially filled with activated carbon granules or particles (14) and are closed at their ends by air-permeable layers (16, 22) bonded to the cellular material through the intermediary of metal grilles (18, 20, 24) coated with a synthetic plastics bonding material, in which the cellular material is surrounded by an L-section metal frame (8) which permits at least one air-permeable layer (22) to be removed from the filter or filter element once the bond between the said layer and its respective grille (20) has been melted or otherwise broken or softened so that the carbon granules or particles can be removed from the cells when the granules or particles have lost their capacity to absorb noxious substances contained in fluid passing through the cells and be replaced by fresh activated carbon granules or particles. <IMAGE>

Description

SPECIFICATION Fluid filter This invention relates to fluid filters.

In a number of prior British Patents - for example, Patents Nos. 1,180,888; 1,225,751; and 1,505,843 -- I have described filters for filtering air and other gases having one or more filter elements each comprising one or more layers of cellular material the cell of which contain particles or granules of activated carbon so as to remove toxic gases and other toxic substances from air or other gas flowing through the filter. The ends of the cells are closed by layers of airpermeable material such as a woven fabric which is bonded to the ends of the cells by the use of grilles, mesh or other openwork layers formed of metal and coated with a synthetic plastics bonding material. In most commercial arrangements, these layers are formed of crisscrossing metal rods or wires which are welded to one another where they cross.

During manufacture of such filters, the metal grilles are heated and then dipped in a synthetic thermoplastic powder with the result that powder adheres to the hot metal and melts. While the plastics material is still in a molten condition, the grille is placed against one face of the cellular material so as to be bonded to that face once the plastics material has set. With the plastics material still molten, a layer of woven material or foam material is applied to the grille, thereby closing one end of each cell.

The other ends of the cells have a second plastics-coated metal grille applied to them. In order to ensure that no air or other gas can pass through the filter without being subjected to the scrubbing action of the activated carbon granules or particles, the plastics coating on the second metal grille serves to bond the layer of cellular material to a second layer of cellular material with the cells of one layer axially out of line with the cells of the other layer. The outer open ends of the cells in the second layer are then closed by a third metal grille and by a further layer of woven material. A metal casing is generally used to surround the above-described filter element or elements.

The present invention constitutes a development of the form of filter described above in that it relates to a filter or filter unit the construction of which allows the carbon granules or particles to be replaced once they reach the stage where they can no longer absorb noxious substances.

The present invention is accordingly directed to a filter element, or to a fluid filter having one or more such filter elements, comprising at least one layer of cellular material the cells of which are filled or partially filled with activated carbon granules or particles and which are closed at their ends by air-permeable layers which are bonded to the cellular material through the intermediary of metal grilles coated with a synthetic plastics bonding layer, wherein the cellular material is surrounded by an L-section metal frame which permits at least one air-permeable layer and the grille to which it is bonded to be removed once the bond has been melted or otherwise broken or softened so that the carbon granules or particles can be removed from the cells when the granules or particles have lost their capacity to absorb noxious substances contained in fluid passing through the cells and be replaced by fresh activated carbon granules or particles.

After the filter element or filter has been regenerated through the replacement of the "spent" carbon by fresh activated carbon, each grille removed from the filter element or filter is re-bonded to the cellular material by bringing the synthetic plastics coating on the grille, or each grille, to a molten or tacky condition through the application of heat from infra-red heat lamps.

Fresh synthetic plastics material in powder form can, of course, be applied to each grille should that be necessary. A fresh layer of air-permeable woven material is then pressed on to the grille, while the plastics material is still tacky, so as to close the ends of the freshly-filled cells.

The invention also extends to a method of regenerating a filter or filter element of the above construction.

An example of a filter element in accordance with the invention is shown in the accompanying drawing, the main figure being a vertical section through part of the filter element. The filter element comprises a rectangular L-section metal frame or casing 8 within which are arranged, one on top of each other, two layers 10 and 12 of cellular material the cells of which contain activated carbon granules or particles 14. In actual practice, the cells are very tightly packed with such granules having regard to the highly toxic nature of the substances which the filter is designed to remove from an air or gas stream.

So as to ensure that no air or other gas can pass upwards or downwards through the filter without being subjected to the action of the activated carbon granules or particles, the cells of one layer 10 are axially out of line with the cells of the other layer 12.

The lower ends of the cells in the layer 10 are closed by an air-permeable layer 16 of woven material, preferably woven glass fibres or woven wire. This is bonded to the said ends of the cells 10 by the interposition of a grille 18 made of crisscrossing metal rods or wires which are welded together where they cross.

During manufacture of the filter element, the grille 18 is coated with a molten layer of thermoplastics material. This can be applied either by heating the thermoplastics material so that it melts and then applying it to the grille, or else by heating the grille and then dipping it in thermoplastics powder so that the latter melts and forms a molten layer on the grille. Whichever method is used, the grille 18 is applied to one side face of the cellular layer 10 with the plastics material still in its molten state so as to bond the grille to that face once the plastics material has set.Immediately after application of the grille to the cellular layer 10, the air-permeable layer 16 of woven material is spread across the grille 18 with the plastics material still molten so that, when the plastics material sets, the layer 16 will have been bonded to the grille 18 which, in turn, will have become bonded to the said face of the cellular layer 10.

An identical metal grille 20 and an airpermeable woven layer 22 are used in exactly the same way to close the upper ends of the cells in the cellular layer 12. Between the two cellular layers 10 and 12 there is a third metal grille 24 which is bonded to the two cellular layers through the use of thermoplastic material on the grille 24 which is brought to a molten condition.

Before the upper ends of the cells in the two cellular layers 10 and 12 are closed, the cells are filled with granules or particles of activated carbon. Then, once the respective grilles and woven layers have all been bonded to the cellular layers, a self-adhesive flexible sealing band or tape 26 is applied to the entire perimeter of the frame or casing 8 so as to seal the cellular layers within the frame. The band or tape 26 is prefarably made of a sealing material like felt, and can have, say, a width of between 2 and 10 cm. It is applied to the frame in such a way that it forms an L-section seal at the upper end of the filter element as it is shown in the main figure of the accompanying drawing.

After such a filter element has been in use for some time, the activated carbon will have become "spent" in that it is no longer capable of extracting noxious substances from the air or other fluid passing through the filter. Hitherto it has been the practice to throw the filter element away at that stage, but the filter element of the present invention allows the spent carbon to be replaced by fresh activated carbon granules or particles. It also permits the air-permeable woven layers to be replaced at the same time. In other words, the filter element of the present invention can be regenerated.

The method of regeneration is quite simple.

First of all, the felt sealing tape or band 26 is peeled off, whereupon the woven layer 22 and the grille 20 are exposed to heat from one or more infrared lamps or heaters. This soften the thermoplastics bond between the woven layer 22 and the grille 20 so that the woven layer 22 can be pulled away. Tis exposes the carbon granules or particles in the cellular layers so that the granules can be poured into a bag through the grille 20. The grille 20 is now heated up again by the infra-red lamp(s) or heater(s). Its bond with the upper cellular layer 12 is thereby released, with the result that the grille 20 may be removed to allow fresh activated carbon granules or particles to be poured into the empty cells of the two cellular layers.Once the cells have been re-filled, the grille 20 is re-heated to bring the thermoplastics coating thereon to a molten or tacky condition, whereupon the grille is re-applied to the upper side of the cellular layer 12 and becomes bonded thereto as the coating cools. At the same time, a fresh woven layer 22 is applied to the grille 20 and becomes bonded to the latter.

If desired, or if necessary, fresh thermoplastics material in powder form can be applied to the grille 20 prior to its re-application to supplement the thermoplastics coating already on it.

It will therefore be seen that the invention provides, at very little expense, an activated carbon filter element which can easily be regenerated. The fact that the frame 8 is of L-section and that an easily-removable sealing band or tape 26 is used means, in particular, that no difficulty is encountered in removing the woven layer 22 and the grille 20 during the regeneration operation.

Claims (9)

1. A fluid filter or filter element comprising at least one layer of cellular material the cells of which are filled or partially filled with activated carbon granules or particles and are closed at their ends by air-permeable layers bonded to the cellular material through the intermediary of metal grilles coated with a synthetic plastics bonding material, in which the cellular material is surrounded by an L-section metal frame which permits at least one air-permeable layer to be removed from the filter or filter element once the bond between the said layer and its respective grille has been melted or otherwise broken or softened so that the carbon granules or particles can be removed from the cells when the granules or particles have lost their capacity to absorb noxious substances contained in fluid passing through the cells and be replaced by fresh activated carbon granules or particles.

2. A fluid filter or filter element according to claim 1, in which the cellular layer or layers is, or are, sealed within the frame by one or more lengths of a self-adhesive flexible sealing band or tape applied to the entire periphery of the frame, the band or tape being removable by peeling so as to permit the said one air-permeable layer to be removed from the frame.

3. A fluid filter or filter element according to claim 1 or claim 2, in which the respective grille to which the removable air-permeable layer is bonded is likewise removable from the filter or filter element to facilitate the pouring of fresh activated carbon granules or particles into the cells.

4. A fluid filter or filter element according to any one of claims 1-3, in which the air-permeable layers are made of a woven material, while the metal grilles comprise criss-crossing metal rods or wires which are welded to one another where they cross.

5. A fluid filter or filter element according to any preceding claim having two layers of cellular material with the cells of one layer axially out of line with the cells of the other layer.

6. A fluid filter or filter element according to claim 2 or any claim appendant thereto, in which the self-adhesive flexible sealing band or tape is made of a sealing felt having a width of between 2 and 10 cm, the band or tape being applied to the frame in such a way that it forms an L-section seal at one side of the filter or filter element.

7. A fluid filter or filter element substantially as described herein with reference to the accompanying drawing.

8. A method of regenerating a fluid filter or filter element as claimed in claim 2 or any claim appendant thereto, which method comprises peeling off the sealing tape or band from the frame, exposing the upper air-permeable layer and its respective grille to heat from one or more infrared lamps or heaters to soften the synthetic plastics bond between them, pulling away the airpermeable layer from the frame to expose the carbon granules or particles in the cellular layer or layers, pouring the granules from the latter into a bag or other container through the grille, heating the grille so that its bond with the upper cellular layer is released, removing the grille from the frame, pouring fresh activated carbon granules or particles into the empty cells of the cellular layer or layers, re-heating the grille to bring the synthetic plastics coating thereon to a molten or tacky condition, re-applying the grille to the upper side of the cellular layer so that it becomes bonded thereto as the coating cools and, at the same time, applying a fresh air-permeable layer to the grille so that it becomes bonded to the latter.

9. A method according to claim 8, in which fresh thermoplastics material in powder form is applied to the grille prior to its re-application to supplement the thermoplastics coating already on it.