GB2024040A - Rotating drum filter for air - Google Patents

Abstract

In a rotating drum filter for cleaning large amounts of air, the filter material web (7) is stretched peripherally round the drum over an air-previous support by a winding roller (32) which is secured to such support and enables retightening to be performed at any time. Also, the filter drum can be formed from a number of axially adjacent similar such units each corresponding in width to one filter web (7), the webs (7) being stretched over sealing rings disposed between the units to provide sealing tightness between the edges of the webs (7) <IMAGE>

Description

SPECIFICATION Rotating drum filter for intaking large quantities of air The invention relates to a drum air filter in which a removable filter material is stretched over an air pervious support surface, and which is capable of handling large throughputs of air.

In the context of the present invention, "large" throughputs through the filter denote filter throughptits of at least some 7000 m3/h, more particularly from 20000 to 170000 m3/h. Filters of this kind are of use typically for cleaning the air discharged from textile undertakings and from other industries, e.g. the asbestos and tobacco industries.

The air to be purified passes through filters of this kind from the outside towards the inside, the separated substance being deposited on the filter material which is usually a woven textile fabric; the separated material is usually removed from the filter material surface by a dust extractor moving periodically over the filter material forming the generated surface of the drum.

For satisfactory cleaning of the filter material, relatively high negative pressures are required at the extractor nozzle to remove the dirt. If filter material is not be be drawn excessively into the nozzle orifice, with the resulting formation of folds and premature damage of the filter material, the material must be stretched tightly over the external surface or envelope of the drum. Also, the filter material must for the same reason be periodically retightened.

The usual practice in conventional filters of this kind is to introduce a resilient means at an edge of the filter material as a retaining and tightening device to the resilient material.

It is relatively difficult with such known constructions to achieve uniform stretching or tightening of the filter material over the whole length of the generated surface of the filter drum, and repeated retightening-i.e., when the filter material has in the course of time been stretched beyond its elasticity limit-is virtually impossible.

It is therefore the object of the invention to improve the initial tightening and retightening of the filter material of filters of the kind described and more particularly to make retightening possible when the filter material has lost much of its elasticity after prolonged use, as a result of excessive stretching, and has become elongated.

Accordingly the present invention provides a rotating drum air filter having a removable filter material stretched over an air-pervious support casing, in which at least one winding roller is provided extending along a generatrix of the support surface and recessed therein arranged to act as a stretching means for the filter material.

The winding roller, which is arranged to be rigid over the length of the generated surface of the drum, ensures that the filter material is stretched uniformly over the whole of the length. Another possibility is that the filter material can be stretched in measured steps if the roller is rotated in fractions of a revolution, e.g. by means of a ratchet wheel and associated pawl. Since the roller can basically take up any desired length of surplus filter material, there is sufficient provision for re-adjustment even in the case of overstretched filter material.

In contrast to the known construction in which different degrees stretching can occur over the length, the uniform stretching provided over the entire length of the generated surface by the winding roller in the device embodying the invention may lead to difficulties in the case of filter materials which, as considered over the length of the generated surface of the filter, are composed of a number of webs and are, for instance, sewn or bonded along the periphery. This is because when treated the web distorts as a whole and/or regions arise whose thickness so differs from the thickness of the undistorted web, uniform winding becomes almost impossible.

According to another aspect of the invention, to obviate these disadvantages caused by the winding roller being rigid over the whole length of the generated surface, the filter drum comprises at least two axially adjacent basic units whose module length is the width of a web of the filter material, the webs not being joined in the axial direction. The edges of the discrete webs are stretched peripherally over a sealing ring; and the discrete filter webs are stretched by separate devices.

The width of the basic unit depends, for instance, upon the commercially available woven widths of woven filter fabrics or upon the panel width of foam materials used e.g. as the filter material.

In order to promote a fuller understanding of the above and other aspects of the present invention, an embodiment will now be described, by way of example only, with reference to the accompanying drawings, in which:~ Figure 1 is a side view of a drum filter fitted in a filter chamber (not shown in greater detail) of an extraction system, e.g. of a textile works; Figure 2 is a section on the line Il-Il of Fig.

1; Figure 3 is a view to an enlarged scale of a part A of Fig. 1; Figures 4 and 5 are sections on the lines IV-IV and V-V, respectively, of Fig. 3; Figure 6 is a view to an enlarged scale of a portion B of Fig. 1, and Figures 7 and 8 are sections on the lines VIl-VIl and VIlI-VIlI respectively.

A connecting ring 2 of sheet metal is, in known manner per se, rigidly secured in a side# wall of a filter chamber 1 (Fig. 1). A suction duct 3 which extends from the right is connected to the ring 2; and purified gases are conveyed through line 3 by means of a rotatable filter drum 6 to further processing.

In chamber 1 ring 2 is connected via flanged 5, 11 to the filter drum 6; the flange 11 on drum 6 serves as strengthening flange for a ring 9 whose purpose will be described hereinafter. Sealing between the stationary wall ring 2 and the drum 6 is provided by means of a resilient sealing element 13 which is secured to the ring 2 and which, urged by its own elasticity, slides on flange 11 of ring 9.

Drum 6 has stretched over it discrete webs 7 of a filter material, for example in the form of a woven textile material, or of a foam material having a woven textile reinforcement; the drum 7 is built up on the unit construction or module system from a number of discrete identical basic units 14. The module length is the width of a filter web 7 and is the width thereof without sticking or sewing together, e.g. the woven width of a textile material. Based on this dimension, the unit 14 comprises an air-pervious outer envelope or casing 8 which in the example shown is a wire lattice but which can be a screen or a perforate plate. The casing 8 is adapted in width to the web 7 and is connected at both ends to support on bearing rings 10 braced by struts or arms 12 or the like (Fig. 2).

The ring 9 is screwed, by means of screw fasteners distributed over the periphery, to the outer periphery of the rings 10 (Figs. 6 to 8) with the interposition of a spacing strip 15.

Ring 9 serves as a lateral seal between the discrete filter webs 7 of the basic units 14, the webs being arranged consecutively along the drum axis. The strip 15, whose thickness corresponds at least substantially to the thickness of the wire used for the outer casing 8, serves to cover annular apertures which extend peripherally between the rings 9 and 10 and into which the casings 8 are introduced when the drum is assembled. The end support elements formed by the rings 9 and 10 receive a casing 8 on one side whereas the intermediate elements 9, 10 interconnecting two units 14 each have a casing 8 on both sides.

The arms or struts or the like 12 connect the various rings 10, which are arranged axially of the drum 6, to a central tube 16 which extends through the filter over the whole of its length and which is rotatably mounted at both ends. One bearing for the tube 16 is supported by an upright 17 mounted on the floor of the chamber 1 and the other bearing is mounted on a beam or bearer or the like 18 which extends horizontally through the ring 2. The drum 6 is driven by an electric motor 19 which is secured to the bottom of ring 2 and which drives a wheel 20, the wheel 20 rolling in the outermost right-hand ring 10 (Fig. 1) and rotating the drum 6 by friction drive.

The filter material is cleaned by means of an extractor facility 21 which is shown in very schematic form and is moved by a drive (not shown) along a generatrix of the rotating drum 6, the facility 21 being suspended from a guide bar or rail or the like 22.

In the example shown each main unit 14 has its own stretching and winding-on facility 25 which is disposed in the casing 8. Of course, all of the main units or a number thereof can have a common stretching facility.

The facility 25 is received in a housing 26 which is shown in Figs. 3 to 5 and it is recessed in the casing 8 and is secured in substantially air-tight fashion on both sides to a support construction 9, 10. The rings 9, 10 adjacent the housing 26 are reduced in width to the width of the strip 15. In the curve of the periphery of the casing 8 the housing 26 merges on both sides into support ledges or the like 27 for the casing 8, the casing being open along a generatrix. Covers 28 are secured to the members 27 by means of screws 29 having spacer sleeves (not shown) to space the two members 27 and 28 apart from one another. The resulting gap between the members 27 and 28 receives the casing 8 at assembly in just the same way as the casing 8 is received between the rings 9 and 10.The width of the slot therefore corresponds at least substantially to the width of the wire lattice used for the casing 8.

Also, the covers 18 are bent to relatively large radii of curvature to the housing 26 so that the filter material can enter the facility 25 without having to pass over sharp edges and be damaged.

One end of the filter material is in the form of a loop which receives a tube 30 having a good resistance to bending which is mounted in housing 26 and retained by two plates 31 welded to the two axial side walls of the housing 26 spaced from one of the covers 28 by a distance such that the web 7 can pass freely through the resulting aperture but the tube 30 is retained. The tube 30 forms one attachment for the stretching of the filter material shown in Fig. 5.

The other end of the web 7 is secured, for instance, by means of a Velcro-strip, to a winding roller 32 rotatably mounted in the axial side walls of the housing 26. The roller 32 has at one end a ratchet wheel 33 releasably engageable by a pawl 34 mounted for rotation in 26; consequently, when the web 7 is being stretched the roller 30 can be angu larly retained at fractions of a revolution.

Each roller 32 provided for a web 7 has at its periphery, at the ends remote from the ratchet wheel 33, angularly spaced turningbar holes 35 for receiving a lever (not shown) serving to rotate the roller 32 and stretch the web 7; stretching can be adjusted and increased in relatively fine steps corresponding to the number of teeth of the ratchet wheel 33.

Since the roller 32 can take up a relatively large amount of filter material, the possibility of retightening or restretching the web 7 after stretching of the material beyond the limit of its elasticity is virtually unlimited, since more web can be wound on.

Claims (9)

1. A rotating drum air filter having a removable filter material stretched over an airpervious support casing in which at least one winding roller is provided extending along a generatrix of the support surface and recessed therein arranged to act as a stretching means for the filter material.

2. A filter as claimed in Claim 1, in which the winding roller carries a ratchet wheel and a pawl is provided to releasably engage the roller so as to retain it is a selected one of a plurality of angular positions.

3. A filter as claimed in Claim 1 or 2, comprising at least two axially adjacent such units whose axial length module is the width of the associated web of filter material, the webs not being joined in the axial direction, in which the edges of the discrete webs are stretched peripherally over a sealing ring in the support surface, and the discrete filter webs are provided with respective separate winding rollers.

4. A filter as claimed in Claim 3, in which the support casing of each such unit is separate.

5. A filter as claimed in Claim 4, in which the support casings are interconnected and supported by support rings which are stiffened by struts or the like and to which said sealing rings are also secured.

6. A filter as claimed in Claim 5, in which the support rings co-operate with the sealing rings to define peripheral slots to receive the edges of the respective support casings.

7. A filter as claimed in Claim 5 or 6, in which the support rings are carried on a common central tube which extends over the axial length of the drum.

8. A filter as claimed in any one of the preceding Claims comprising at least one suction nozzle for removing impurities separated from air by the filter from the filter material, the nozzle being arranged to traverse the axial length of the filter.

9. A filter substantially as herein described with reference to the accompanying drawings.