WO1991006360A1

WO1991006360A1 - Filter bag for separating particles from a gas

Info

Publication number: WO1991006360A1
Application number: PCT/SE1990/000680
Authority: WO
Inventors: Odd Edgar BJARNØ
Original assignee: ABB Fläkt AB
Priority date: 1989-10-25
Filing date: 1990-10-19
Publication date: 1991-05-16
Also published as: SE466942B; SE8903534D0; SE8903534L; AU6634890A

Abstract

A filter bag for separating particles from a gas by screening, said filter bag being adapted to cooperate with an arrangement (7, 10) for expanding and supporting the filter bag (5), comprises longitudinal means (6) for fixingly receiving the arrangement (7, 10) arranged on its surface.

Description

1 FILTER BAG FOR SEPARATING PARTICLES FROM A GAS

Field of the Invention

The present invention relates to a filter bag for separating particles from a gas by screening. The filter bag is adapted to cooperate with an arrangement for expanding and supporting the filter bag. Description of the Prior Art

A common method of separating particles from a gas, for example flue gas from an incineration plant, is to let the gas pass through a bag filter. This usually contains a plurality of filter bags which are made of PTFE (poly- tetrafluoroethylene), fibre-glass or some other suitable filtering material. As the gas passes through the filter bag, its dust is deposited in the form of a dust cake on the inside or out¬ side of the filter bag, depending on whether the gas flows from the inside of the filter bag and outwards, or vice versa. In the first case, the gas pressure keeps the fil- ter bag expanded, but in the second case, it compresses the filter bag so as to collapse. During cleaning of the filter bag, the direction of gas flow therethrough is reversed, whereby the filter bag is subjected to the action of the gas in the opposite direction. This means that in both cases the filter bag must be supported so as not to collapse during operation or clean¬ ing. Fig. 1 illustrates an example of a conventional fil¬ ter cage 1 for supporting a filter bag 2. This cage com¬ prises nine rods 3 which are held together by holding means 4 and form, together with these, a rigid construc¬ tion. When the gas flows from the bag outside and inwards, the bag is kept expanded adjacent the rods 3, whereas between the rods it forms concave folds. The folds are extended during cleaning, when the direction of gas flow is reversed, and this motion of the folds breaks up and throws off the formed dust cake from the bag. 2

When the filter bag is supported by a cage, the posi¬ tion of which is not fixed, as is the case in Fig. 1, a certain sliding motion between the rods of the cage and the filter bag is obtained as the bag moves during clean- ing. Since there is always a small amount of dust between the rods and the bag, this sliding motion causes the bag to get worn, and eventually such wear results in open tears in the bag. The filter bags must then be exchanged, and in case this occurs frequently, the cost of main- tenance for the bag filter will be high.

The use of a cage, the position of which is not fixed, for supporting a filter bag can also result in the filtering material being unevenly distributed between the rods, i.e. in some places there will be big folds and, consequently, the filtering material will perform great motions and thus be subjected to considerable strain, whereas in other places there will be small folds and small motions and, thus, poor cleaning of the filtering material during the cleaning operation. To obtain a more even distribution of the filtering material between the rods, the cage can of course be pro¬ vided with further rods, which means however that the cage will be heavier and more expensive in manufacture. This especially applies to long filter bags. In this case, the cleaning will also be poorer, since the motions of the filtering material will be smaller because of the dimi¬ nished folds between the rods. Summary of the Invention Technical problem Since cages, the position of which is not fixed, subject the filtering material of the filter bag to high mechanical load, especially during cleaning, it consti¬ tutes in many applications a problem to find a filtering material of sufficiently high mechanical strength so as to make the life of the bag acceptable, at the same time as the chemical and thermal properties are those required for the application. The object of the present invention therefore is to provide a filter bag for separating particles from a gas by screening, which filter bag can cooperate in such manner with an arrangement for expanding and supporting the filter bag that the filtering material is not sub¬ jected to high mechanical loads during cleaning. Solution of the problem

According to the present invention, the above-men¬ tioned problems are solved by means of a filter bag which is of the type mentioned by way of introduction and which is^" characterised by means arranged on the surface of the filter bag, for fixingly receiving said arrangement.

Since said arrangement is received by means that are attached at fixed locations along the surface of the fil- ter bag, the position of the arrangement will be fixed relative to the filtering material. This means that there will be no sliding motion between the arrangement and the filtering material and no irregular formation of folds in the filtering material. Preferably, at least three means are arranged on the surface of the filter bag.

Preferably, 3 - 12, particularly 4 - 8, especially 4 means are arranged on the surface of the filter bag.

The means are preferably shaped as channels, grooves or rails extending along the inner surface of the filter bag in the longitudinal direction thereof, preferably in substantially the entire longitudinal direction thereof.

The channels are preferably made of the same material as the filter bag, whereas the grooves or rails are made of plastic, e.g. PTFE, or metal, e.g. aluminium. Description of a proposed embodiment

The invention will now be described in more detail with reference to the accompanying drawings.

Fig. 1 illustrates a conventional cage for supporting a filter bag. Fig. 2 is a schematic view of an embodiment of the filter bag according to the present invention.

Fig. 3 is a top plan view of the filter bag in Fig. 2. Fig. 4 is a schematic view of a further embodiment of the filter bag according to the present invention.

The filter bag 5 shown in Fig. 2 is in the form of a conventional, closed-end cylindrical hose having a length of 3-10 m, usually about 10 m, and a diameter of 100-300 mm, usually about 145 mm. The bag is provided with four parallel channels 6 which extend along the inner sur¬ face of the bag in the entire longitudinal direction thereof and have an inner diameter of 10-40 mm, usually about 20 mm. The channels are sewn on to the bag inner surface during manufacture thereof and are preferably made of the same material as the bag which is made of, for example, fibre-glass that withstands high operating tempe¬ ratures and has high chemical resistance to noxious sub¬ stances, such as sulphur, but has low mechanical strength. When manufacturing the bag, transverse stiffening means 7 are inserted in a given spaced-apart relationship, 0.5-2 m, usually about 1 m, into the channels 6 over the entire length thereof. The stiffening means are designed as a quadrangle in each corner of which an eye 8 is posi- tioned. One eye is inserted into each channel 6 via an opening 9 formed in the wall of the channel. The outer diameter of the eye is 10-40 mm, usually about 20 mm, whereas its inner diameter is 7-37 mm, usually about 17 mm. A rod 10 is inserted in each channel 6 and the eyes 8 thereof, and as appears from Fig. 3, the outer diameter of the rods, which is 5-35 mm, usually about 15 mm, is smaller than the inner diameter of the eyes 8. This means that during mounting and dismounting of the filter bag 5 in and, respectively, from a filter housing (not shown), it will be easy to insert and, respectively, pull out the rods 10 in and, respectively, from the eyes 8 placed in the channels 6. The rods 10 are preferably of the same length as the channels 6 and thus extend along the bag 5 in the entire longitudinal direction thereof. Consequent¬ ly, the eyes 8 of the stiffening means 7 fix, in coopera- tion with the channels 6, the position of the rods rela¬ tive to the filtering material of the bag, at the same time as they prevent, by their stiffening effect on the rods, excessive inward bending of the rods during opera¬ tion, as the dust-laden gas which is to be cleaned flows from the bag outside and inwards and exerts a considerable gas pressure upon the filtering material.

As is further apparent from Fig. 3, the channels are positioned symmetrically at the same distance from each other along the bag inner surface, which means that the folds of the filtering material that are formed between the rods 10 during operation are of the same size along the entire circumference of the bag. The appearance of the bag during operation is indicated by dashed lines in Fig. 3. During cleaning, as the gas flows from the bag inside and outwards, the bag instead assumes the shape indicated by full lines in Fig. 3.

Fig. 4 illustrates a filter bag 11 provided with four parallel longitudinal rails 12 which are positioned symme¬ trically at the same distance from each other along the bag inner surface. Each rail is formed with a longitudinal groove 13 facing the centre of the bag. The rails are made of PTFE or aluminium and are glued to the inner surface of the bag in the entire longitudinal direction thereof.

Four rods 14 are fixedly interconnected by stiffening means 15 which are arranged along the rods in a given spaced-apart relationship, 0.5 - 2 m, usually about 1 m, over the entire length thereof. The stiffening means are shaped as a star with four points which are each welded to a rod 14. When mounting the filter bag 11 in a filter housing (not shown), the rods 14 and the stiffening means 15 are consequently inserted into the bag 11 as an inte¬ gral unit, the rods 14 being inserted in the rails 12, whereas the stiffening means 15 are inserted in the grooves 13 of the rails. The rods 14 are preferably of the same length as the rails 12 and accordingly extend along the bag 11 in the entire longitudinal direction thereof. The position of the rods relative to the filtering mate¬ rial of the bag is in this case fixed by the rails only. They provide, however, sufficient fixing of the rods also during the cleaning operation. The filter bag 11 is, during operation and cleaning, of the same appearance as the filter bag 5.

Of course, the invention is not limited to the embo¬ diments described above but can be modified in various ways within the scope of the appended claims.

The channels 6 can, for example, be glued or welded instead of sewn on to the bag inner surface. The channels can also be integrated with the filter bag and then, con¬ sequently, need not be attached to the surface of the filter bag.

The rails 12 can, for example, be welded or sewn instead of glued to the bag inner surface.

The stiffening means 7 can, for example, be designed as the stiffening means 15, and vice versa, the eyes 8 being in the first case attached to the points of the star. The channels 6 or the rails 12 can, for example, be attached to the bag outer surface, instead of the inner surface thereof.

The stiffening means 7 can, for example, be provided with hooks instead of eyes, and of course the eyes need not be of circular shape.

The rods 10 and 14 can, for example, be composed of a plurality of short members, e.g. 3 members, instead of being made in one piece.

The stiffening means 15 can, for example, be inte- grated with the rods 14, instead of being welded thereto. The shape of the stiffening means and the number of rods and channels or rails of course vary with the appear¬ ance of the filter bag which is to be expanded and sup¬ ported. In the specification above, the term "transverse stiffening means" means that the stiffening means extend in the transverse direction of the filter bag, the angle between the stiffening means 7 and 15 and the channels 6 or the rails 12 of the filter bag not necessarily being 90°.

Claims

1. Filter bag for separating particles from a gas by screening, said filter bag (5; 11) being adapted to coope¬ rate with an arrangement (7, 10; 14, 15) for expanding and supporting said filter bag (5; 11), c h a r a c t e r ¬ i s e d by longitudinal means (6; 12) arranged on the surface of said filter bag (5; 11), for fixingly receiving said arrangement (7, 10; 14, 15).

2. Filter bag as claimed in claim 1, c h a r a c ¬ t e r i s e d in that at least 3 means (6; 12) are arranged on the surface of said filter bag (5; 11).

3. Filter bag as claimed in claim 2, c h a r a c - t e r i s e d in that 3 - 12, preferably 4 - 8, particu¬ larly 4 means (6; 12) are arranged on the surface of said filter bag (5; 11).

4. Filter bag as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that said means are shaped as channels (6) extending along the inner surface of said filter bag (5) in the longitudinal direction thereof, pre¬ ferably in substantially the entire longitudinal direction thereof.

5. Filter bag as claimed in claim 4, c h a r a c - t e r i s e d in that said channels (6) are made of the same material as said filter bag (5).

6. Filter bag as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that said means are shaped as grooves or rails (12) extending along the inner surface of said filter bag (11) in the longitudinal direction thereof, preferably in substantially the entire longitu¬ dinal direction thereof.

7. Filter bag as claimed in claim 6, c h a r a c ¬ t e r i s e d in that said grooves or rails (12) are made of plastic, e.g. PTFE, or metal, e.g. aluminium.