The present invention relates to a gas filter apparatus of the reverse pulse type and more particularly to such an apparatus having an improved construction of bag cage.

Gas filter apparatus is used to remove particulate matter from gas streams. In this apparatus dust laden gas is ducted to the apparatus where it is filtered by filter medium bags or tubes which, in turn, are periodically purged of the collected particulate material. The removal of the collected particulate material may be accomplished in a variety ^" of ways and generally this characterises the type of gas filter apparatus. In gas filter apparatus of the reverse pulse type bags are used which are open at the top and closed at the bottom. The gas flow is from the outside of the bag to the inside and clean gas leaves at the top where the bag is connected to an overhead tube plate which separates a dust laden gas section of the apparatus from a clean gas section. The bags are mounted on cages to prevent their collapse and they are cleaned by admitting pulses of compressed air into the bags against the direction of the gas flow. The pulses of compressed air produce a Shockwave which travels down the bag, momentarily stopping the gas flow, and backwashing the fabric from which the bag is made. Such gas filter apparatus are described in Australian patent specification 520545.

The present invention relates to an improved construction of gas filter apparatus having an improved bag cage construction.

According to the present invention in a gas filter apparatus of the reverse pulse type, having a housing including a dust laden gas section with an inlet thereto and a clean gas section with an outlet therefrom, a tube

sheet mounted in said housing separating the dust laden gas section from the clean gas section and having a plurality of apertures, a filter medium bag depending into the dust laden gas section of the housing from each aperture in the tube sheet, each bag opening into the clean gas section of the housing, and a bag cage disposed within each filter medium bag to prevent collapse thereof under an applied gas pressure, the improvement wherein at its upper _. end one, the or each, bag cage is connected to a cap member which includes an element or elements extending outwardly over the upper edge of the associated filter medium bag and engages with the upper face of the tube sheet.

In a further embodiment the present invention consists in a bag cage for a gas filter apparatus of the reverse pulse type in which the cage is connected at its open end to a cap member which includes an element or elements extending outwardly and adapted, in use, to extend over the upper edge of an associated filter medium bag and engage with the upper face of a tube sheet from which the bag is suspended.

The cap member is preferably annular and is of substantially inverted U-section, having a substantially vertical inner annular wall element and a substantially vertical outer annular wall element which wall elements are joined by a substantially horizontal annular intermediate element.

The inner annular wall element is preferably _, so -dimensioned that it engages the inner face of the bag adjacent its upper end and urges it into contact with the edge of the tube plate surrounding the aperature in which the said bag and cage are disposed. This feature ensures that there is a good seal between the bag and the tube plate, and thus prevents dust laden gas flowing into the clean gas section of the housing without passing through

the filter bag, without the necessity for the use of screws, clamps, O-rings or other means to maintain an appropriate seal.

The outer annular wall element is preferably of such a depth that its free edge rests upon the upper face of the tube sheet without the cap member exerting any downward force on the upper end of the associated bag. If desired the cap member may act to physically support the cage so that the bag does not carry any of the weight of the cage or alternatively the load may be shared between ^' the bag which will normally have a degree of elasticity, and the cap member, or in a further alternative the weight of the cage may be substantially carried by the bag with the lower edge of the outer wall element just touching the upper surface of the tube plate.

The cap member is preferably, as ?has been indicated above, annular and continuous, however many of the advantages of the invention may be achieved if the cap member consists of an array of arcuate legs extending from the cage outwardly over the upper end of the bag and engaging the upper face of the tube sheet with the free ends of the legs. The advantages of the cap member are:-

(a) it may help position and secure the bag in its aperture in the tube sheet as has been described above,

(b) it can carry the weight of the cage as has also been described above,

(c) it can, if continuous, prevent abrasion of- the upper end of the bag by the pulses of reversely flowing air, (d) it can allow maintainance personel to walk around in the clean gas section of the housing without damaging the integrity of the seal between the bag and the tube plate, and

(e) it is very easy to replace the filter medium bags if required.

The apertures are preferably oval or another elongate shape having arcuate ends of small radius, however other shapes may be used. The preferred elongate shape facilitates assembly of the bags into the tube sheet as compared with the conventional circular apertures. This preferred shape also provides an efficient engagement of the bag with the tube plate while the cage is being fitted within the bag. Once the cage is inserted into the bag the cap members preferably engages with the upper end of the bag and urges it more firmly into contact with the tube sheet. ^' Even light outward pressure across the flat sections of the bag is sufficient to maintain it firmly in position.

The selection of a preferred aperture shape, of course, sets the preferred shape for the cap member if it is of the preferred annular, configuration.

The filter medium bags may be of any conventional design. The lower end of the bag may be either sew_. closed or it may be closed by clamping, or otherwise connecting, the bag to a closure means such as a flanged plate. The upper end of the bag is preferably formed with a cuff containing a resiliently flexible metal band? The cuff may be formed by folding over the upper end of t bag to enclose the band or the band may be embed^^ into a flexible plastics cuff moulded integrally with th end of the bag.

The cage itself may be formed in any known ranner but is preferably formed of steel wire. The cage may be formed in one part or in two or.more lengths that are _. *- connected together on site during the installation of the bag and cage. _

Hereinafter given by way of example only is a preferred embodiment of the present invention described . with reference to the accompanying drawings in which: Fig. 1 is a plan view of a bag cage for a gas filter ,

apparatus of the reverse pulse type according to this invention in position in an aperture in the tube plate of the apparatus, and

Fig. 2 is a vertical sectional view of the bag cage, the associated filter medium bag and of the tube plate taken along A-A of Fig. 1.

The fabric filter apparatus 10 comprises a housing (not shown) which is divided by a tube plate 11 into a dust laden gas section below the tube plate 11 and a clean gas section above it. The dust laden gas is introduced into the housing through a gas inlet (not shown) integral with the dust laden gas section thereof and exits it through an outlet (not shown) integral with the clean gas section^thereof. The tube plate 11 is formed with a plurality of apertures 12 (only one of which is shown) . A filter medium bag 13 is suspended from each of the apertures 12 in che tube plate 11. Each bag 13 is formed at its upper end with a collar 14 which includes an annular resiliently flexible steel band 15. The outer surface of the collar 14 of each bag 13 is formed with a recess 16 which receives the edge of the tube plate 11 which surrounds the associated aperture 12. The resilient spring 15 urges the collar 14 outwardly into contact with the tube sheet 11. The collar 14 and the associated metal band 15 of each bag are essentially oval in plan view having a pair of opposed straight portions joined by a pair of arcuate portions of relatively small radius.

A bag cage 16 formed of steel wires 17 is disposed inside each of the filter medium bags 13. The cages 16 serve to prevent the collapse of the bags 13 when dust laden gasses are introduced into the dust laden gas section of the housing. The upper end of longitudinally extending wires 17 are welded to an annular cap member 18. Each cap member 18 is of a shape in plan view

corresponding to that of the collar 14 and aperture 12 and has a cross sectional shape which is that of an inverted-U. Each cap member 18 has an annular inner wall 19, an annular outer wall 21 and an annular connecting portion 22. Each inner wall 19 is connected to wires 17 and is of such dimensions as to urge the collar 14 into contact with the edge of tube sheet 11 around the associated aperture 12, or to at least prevent movement of the collar 14 away from the edge. The free edge of the outer wall 21 engages with the upper face of tube sheet 11 surrounding the respective aperture 12 and thereby totally or partially supports the cage 16.

Means are provided (not shown) to introduce reverse pulse air into the open mouth of bags 13 and to thereby clean the bags- in known manner.

In use the. bags 13 may be installed by dropping each bag 13 down through an aperture 12 and engaging the collar 14 with the edg& of an associated aperture 12. The overal shape of the collar has been found to facilitate this operation and to allow for rapid disconnection of the bag should it require replacement. The cage 16 is then lowered down into the bag until the inner wall 19 bears against collar 14. ^• urther light downward pressure on the cage 16 will '_._:ge the collar 14 outwardly and into tighter sealing engag ment with tube sheet 11. The outer wall 21 will then rest jn _.__e upper face of tube sheet 11 and support at least part of the weight of the cage 16 in the bag 13.

The cap member* 18 serves to prevent abrasion of the collar 14 by reverse flow gas and prevents inadvertent disengagement of collars 14 from the tube sheet 11 during maintenance of the apparatus 10.