GB2222964A

GB2222964A - Air Filter

Info

Publication number: GB2222964A
Application number: GB8919345A
Authority: GB
Inventors: Dr Keith Sydney Robinson
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1988-09-16
Filing date: 1989-08-25
Publication date: 1990-03-28
Anticipated expiration: 2009-08-25
Also published as: GB2222964B; GB8919345D0; GB8821717D0

Abstract

An air filter (26) consists of an upright cylinder of corrugated or pleated filter fabric (30), joined at its upper end to a tubular right-angled elbow (34). The open end of the elbow includes an internal lip seal (36), so the elbow can be slid onto a horizontal spigot (28) in an air fitter unit (10). The filter (26) can be cleaned by subjecting the fabric (30) to a reverse pressure pulse from a nozzle (44). The construction facilitates removal of the filter (26) into a plastic bag secured round frame (17) behind door (16), when the unit is used to filter radioactive dust from air. <IMAGE>

Description

Air Filter The invention relates to an air filter which can be regenerated by subjecting the filter medium to a reverse pressure pulse.

If a dust-laden air stream is passed through a filter a cake of dust builds up on the up-stream surface of the filter medium. This cake produces an additional pressure drop, and it is known to regenerate the filter medium at intervals by subjecting it to a reverse pressure pulse.

This shakes the dust cake off the surface of the filter.

The filter medium is preferably upright, so that the dust cake falls off, to collect in a dust hopper below the filter. A known design of filter unit consists of a housing defining a hopper at the bottom, and divided by a horizontal plate or partition into a lower, dusty portion and an upper, clean portion, one or more filters being supported by the plate and arranged to filter air flow through respective apertures through the plate. Each filter might be a substantially rigid cylindrical tube of corrugated filter medium, closed at its lower end, sealed by a gasket onto the under surface of the plate, and clamped onto the plate by one or more bolts. Eventually it becomes necessary to remove and replace the filters.Where the dust includes radioactive particles it is preferable to enclose the filter in a plastic bag both during and after removal, and it has been found difficult to remove filters of the type described above when enclosed in a bag.

According to the present invention there is provided a regenerable air filter unit comprising a housing defining a dust hopper, an inlet port for a gas stream to be filtered and an outlet port for the gas stream after filtration, a partition within the housing to separate the filtered gas from the unfiltered gas and defining an aperture, and an open-ended duct extending from the aperture and defining a horizontally extending cylindrical spigot onto which can be fitted a filter having a right angled tubular elbow at its upper end, the open end of the elbow locating around the spigot and sealing thereto by a lip seal, and means for providing a reverse pressure pulse within the spigot.

The invention also provides a filter having a right angled tubular elbow at its upper end, the open end being adapted to locate around the spigot, and incorporating an internal lip seal to seal to the spigot.

The filter of the invention can readily be installed, or removed from the filter unit of the invention even if enclosed in a bag, as it merely needs to be pushed onto or pulled off the spigot. Preferably the filter unit includes a back pressure supply tube which extends horizontally through the spigot and has a downward-directed aperture aligned with the longitudinal axis of the filter when the filter is installed. This enables the filter to be regenerated by subjecting it to a pulse of compressed gas in the reverse flow direction, the dust cake falling down into the hopper. Desirably means are provided in addition to the spigot to support the weight of the filter when installed; this may comprise two parallel support rods arranged to bear against the outside surface of the tubular elbow when the filter is installed.

The invention will now be further described by way of example only and with reference to the accompanying drawings, in which: Figure 1 shows a sectional view in a vertical plane through a filter unit; and Figure 2 shows a sectional view on the line Il-Il of Figure 1.

Referring to Figure 1, a filter unit 10 comprises a rectangular housing 12 with a square funnel-shaped hopper portion 14 at the bottom with a removable hatch 15, a large loosely hinged door 16 on one side held to the housing 12 by pivoted bolts (not shown), and a right-angled internal partition 18 near one upper edge of the housing 12 opposite the door 16. The door 16 covers an external spigot 17 which has two peripheral grooves for a bagging-out bag (not shown), and on the inside of the door 16 is a bracket 19 which provides a pocket to support the bag, so it does not trail into the housing 12.The partition 18 divides the volume of the housing 12 into two parts 20 and 21; a dusty air stream is supplied by a duct 22 to the part 20, and the filtered air stream leaves the part 21 through a duct 24, the air having passed through a filter 26, and then through an open-ended spigot 28 extending from an aperture in the upright part of the partition 18 (see arrows F).

The filter 26 consists of a filter medium 30 defining a cylinder whose longitudinal axis is upright (so the surfaces of the filter medium are upright), the lower end of the filter 26 being closed by a plate 31 and the upper end being provided with an annular p late 32. The filter

medium 30 may comprise corrugated NomexXnyTon fibre fabric coated with polytetrafluoroethylene, or more preferably high strength HEPA (high efficiency particulate/air) glass fibre filter paper which has been pleated. The latter consists of both woven glass fibres and glass fibre filter paper, so it is strong and can withstand changes in pressure drop, and is intrinsically a highly efficient filter medium, even before a filter cake has built up.A tubular elbow 34 connects the filter 26 to the spigot 28, one end of the elbow 34 being fixed to the upper surface of the annular plate 32 and the other end (which is of larger diameter) fitting over the spigot 28 and being sealed to it by a lip seal 36. Referring also to Figure 2, most of the weight of the filter 26 and the elbow 34 is supported by two support rods 38 which protrude from the upright part ofthe partition 18 below the spigot 28, and which bear against parts of the undersurface of the larger-diameter part of the elbow 34. The support rods 38 extend to beyondthe far side of the filter 26, and at the end remote from the partition are linked by a removable latch 40 which prevents accidental removal of the filter 26 and the elbow 34 from the spigot 28.A tube 42 passes through the wall of the housing 2 into the part 21, and extends axially through the spigot 28 to within the elbow 34, and has an open downward-facing end 44 aligned with the axis of the filter 26.

The filter unit 10 operates in a conventional fashion, the dusty air stream entering through the duct 22, the dust building up a cake on the filter medium 30, and the cleaned air stream leaving through the duct 24. At intervals a pulse of high pressure air is supplied through the tube 42 so the filter medium 30 is subjected to a reverse pressure pulse. Much of the dust cake falls off to collect in the hopper 14, from where it can if necessary be removed by opening the hatch 15. When it is desired to replace a filter 26 the air flow is stopped, the door 16 is opened, and the latch 40 removed. The old filter 26 along with its elbow 34 can then be slid off the spigot 28, and the new filter 26 with its elbow 34 pushed on in its place. This is easy to do, since precise alignment is not required, even when these operations have to be performed through a plastic bag.

Claims

1. A regenerable air filter unit comprising a housing defining a dust hopper, an inlet port for a gas stream to be filtered and an outlet port for the gas stream after filtration, a partition within the housing to separate the filtered gas from the unfiltered gas and defining an aperture, and an open-ended duct extending from the aperture and defining a horizontally extending cylindrical spigot onto which can be fitted a filter having a right angled tubular elbow at its upper end, the open end of the elbow locating around the spigot and sealing thereto by a lip seal, and means for providing a reverse pressure pulse within the spigot.

2. An air filter unit as claimed in Claim 1 wherein the pressure pulse means comprises a back pressure supply tube extending horizontally through the spigot and having a downward-directed aperture aligned with the longitudinal axis of the filter when the filter is installed.

3. An air filter unit as claimed in Claim 1 or Claim 2 also comprising means in addition to the spigot to support the weight of the filter when installed.

4. A filter for use in an air filter unit as claimed in any one of Claims 1 to 3, the filter having a right angled tubular elbow at its upper end, the open end of the elbow being adapted to locate around a spigot, and incorporating an internal lip seal to seal to the spigot.

5. A regenerable air filter comprising a cylindrical filter medium of pleated high strength HEPA glass fibre filter paper.

6. A regenerable air filter unit substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.