WO1998052676A1

WO1998052676A1 - A coalescing filter element

Info

Publication number: WO1998052676A1
Application number: PCT/GB1998/001455
Authority: WO
Inventors: Stephen Nicholas Smith
Original assignee: Domnick Hunter Limited
Priority date: 1997-05-21
Filing date: 1998-05-20
Publication date: 1998-11-26

Abstract

A coalescing filter element (6) for collecting liquid that is entrained in a gas stream has a hollow tubular configuration arranged for flow of the gas stream from the outside thereof to the inside. The element has an opening at its base to allow liquid that is coalesced by the element and that collects within the element on the downstream side of the wall thereof to drain. A sealing member (14) extends around the element towards its base to form a pressure-tight seal between the element and the side wall of a housing in which the element is located when in use.

Description

A COALESCING FILTER ELEMENT

This invention relates to a coalescing filter element for collecting liquid that is entrained in a gas stream, and to a filter assembly which includes such a coalescing filter element .

Coalescing filters are used to collect liquid that is entrained in a gas stream by causing aerosol droplets of the liquid to coalesce and collect as drops which can flow as a liquid. They generally comprise several layers of filter media. The density and thickness of the media layers are selected according to the flow rate of the gas stream, the level and nature of the impurities in the gas stream, the level of purity that is sought in the gas stream after filtration and so on.

Common filter element constructions comprise a tubular filter element mounted in a tubular housing. The gas to be filtered passes radially through the filter. Solid particles entering the filter housing are collected by the filter. Liquid droplets, possibly as aerosols, entrained in the gas are collected by the filter element and coalesce to form drops at the base of the surface of the filter element for drainage. Clean gas can then leave the filter.

Commonly, coalescing filter elements of this type are arranged so that gas to be filtered flows radially outwardly through the element: the gas is supplied to the cavity within the element and then passes outwardly through the element for discharge from the space between the outer surface of the element and the housing. Coalesced liquid that is collected by the element also collects and drains down the outer surface of the element. The filter is closed at its base to ensure integrity, preventing by-pass flow of the gas that is to be filtered. Liquid which coalesces in the element is collected in the base -of the housing. A valve arrangement is provided for discharge of the liquid in such a way that loss of gas pressure in the housing is minimised, and preferably avoided. Such coalescing filters are commonly referred to as "in-to-out" filters, reflecting the direction of flow of gas through the filter medium.

It can be desirable for some applications to arrange for the flow of gas through a tubular filter element to take place radially inwardly so that gas to be filtered is supplied initially to the space between the element and the housing. In known equipment, gas passes through the element and is discharged from the housing from the tubular cavity within the element. Liquid which coalesces as a result of the filtration of the gas flows down the internal surface of the element. The integrity across the element (preventing bypass flow of the gas that is to be filtered) between the incoming gas supplied to the space between the element and the housing and the cavity within it, is maintained by means of a closed base on the filter element. A drain tube is used to discharge accumulated liquid from within the element, communicating directly with the outlet from the housing. Seals are required between the element and the drain tube, and between the drain tube and the outlet from the housing, to prevent loss of pressure from within the housing. These seals must be maintained reliably. Failure of a seal can lead to loss of integrity in pressurised gas in which the liquid is suspended, leading to a reduction in operating efficiency. Furthermore, the large number of seals means that assembly of the assembly is complicated and increases the manufactured cost of the assembly.

The present invention provides a hollow coalescing filter element designed for flow of fluid from its outside to its Minside, which includes a sealing member extending around it towards its base to form a pressure-tight seal between the element and a housing in which the element is located when in use .

Accordingly, in one aspect, the invention provides a coalescing filter element for collecting liquid that is entrained in a gas stream, the element having a hollow tubular configuration arranged for flow of the gas stream from the 'outside thereof to the inside, the element having an opening at its base to allow liquid that is coalesced by the element and that collects within the element on the downstream side of the wall thereof to drain, and having a sealing member which extends around the element towards its base to form a pressure-tight seal between the element and the side wall of a housing in which the element is located when in use .

The filter element of the invention can operate as an out-to- in filter in which the gas stream to be filtered is supplied to the space between the outer wall of the element and the housing in which the element is located, and then passes inwardly through the element for discharge from within the hollow space within the element. Coalesced liquid that is collected by the element collects and drains down the inner surface of the element. The element can be open at its base so that the collected liquid can be discharged directly from the base of a housing in which the element is located. The filter element of the invention has the advantage that liquid that has been collected from a gas stream by means of the element can be discharged from the housing in which the element is located by means of discharge arrangements such as are already known for use in connection with in-to-out filters. The element can therefore operate as an out-to-in filter with just a single discharge valve, that is without any requirement to incorporate separate drain valve elements, for discharge of liquid from within the filter element into the housing, and from the housing for disposal. This simplicity of construction means that the filter element of the present invention can be constructed more simply than existing filters, and can therefore be constructed and operated more reliably and economically. In particular, the simple construction of seal can maintain the integrity of the element reliably, preventing by-pass flow of the gas that is to be filtered. A further advantage of the filter element of the invention is that it can also be used as an out-to-in filter in a filter housing which has not been designed for use with multiple valves between the filter element and the housing, and for drainage from the housing, for example when a housing is to be converted from use with an in-to-out filter to use with an out-to-in filter.

The filter element of the invention can be used in apparatus from which filtered gas is to be collected centrally in a filter housing for discharge, generally to flow from the element through a central port, for example in a cap for the housing. Such constructions might be found for example in a regulator. Hitherto, such constructions have generally had be used with a filter for particulate material but which cannot provide the function of coalescing liquid in the gas to be filtered. The present invention provides a filter element which can coalesce liquid droplets for discharge and collect particulate contaminants, and which can be used in such applications with out-to-in flow of the gas to be filtered, for discharge of the gas through a central port. The use of a single filter element, especially using a micro- fibre filter medium, to achieve these objectives enables high operating efficiencies to be attained. Preferably, the seal defines a space in the base of the housing, around the outlet from the housing for collected liquid and between the filter element and the said outlet, in which liquid can collect for discharge. The space is defined at its lower end by the base of the housing and at its upper end by the element. Its side walls can be provided by any of (a) the side walls of the housing, (b) an upstanding portion of the housing, and (c) a downwardly extending projection on the base of the element, for example on an end cap on the element .

Accordingly, in another aspect, the invention provides a filter assembly for collecting liquid that is entrained in a gas stream, which comprises:

(a) a housing,

(b) a coalescing filter element located within the housing for collecting liquid that is entrained in a gas stream, the element having a hollow tubular configuration arranged for flow of the gas stream from the outside thereof to the inside, the element having an opening at its base to allow liquid that is coalesced by the element and that collects within the element on the downstream side of the wall thereof to drain, and having a sealing member which extends around the element towards its base to form a pressure-tight seal between the element and the housing,

(c) an inlet to the housing for the gas to be filtered through which the gas is supplied to the annular space between the element and the housing,

(d) an outlet for gas that has been filtered, in - communication with the interior of the element, and (e) an outlet from the housing for collected liquid that has been coalesced by the element,

the seal defining a space in the base of the housing, around the outlet from the housing for collected liquid and between the element and the said outlet, in which liquid can collect for discharge.

The sealing member can be provided on a bottom end cap on the element. The end cap might extend appreciably below the portion of the element provided by a filter medium through which the gas to be filtered passes, for example to engage the housing. It can be preferred for the sealing member is provided relative to the base of the element such that liquid not entrained with the gas which is to be filtered drains substantially directly through the element at its base to be discharged from within the element together with liquid that has been coalesced by the element. This has the advantage of avoiding substantial (and preferably all) accumulation of liquid upstream of the element between the element and the housing .

The seal can be provided by a component that is separate from both the element and the housing. It can be provided by a feature on the element or on the housing, or by features on the element and the housing in cooperation with one another. The element or the housing or both might be provided with formations for engaging a sealing member, for example in the form of one or more grooves or ridges.

Preferably, the sealing member that is provided around the periphery of the element is arranged so that the seal to a housing in which the element is located is enhanced as a result of exposure to the differential pressure applied by the gas being filtered. For example, the sealing member might be outwardly deformable to enhance the seal between the housing and the element. The outward deformation might be caused by pressure applied by the gas being filtered, especially into contact with the internal wall of the housing. The face of the sealing member that is exposed to the pressurised gas to be filtered is preferably not convex when viewed in cross-section. For example, the said face might be substantially flat when viewed in cross-section. Preferably, it is concave. The sealing member might therefore comprise two limbs defining a channel between them. In use, one of the limbs might contact (and possibly be connected to) the element with the other limb being directed outwardly to contact the wall of the housing. With such a sealing member, pressure applied by the gas being filtered can force the limbs apart so as to tend to open the channel, forcing the limbs into tighter contact with the element and the housing respectively.

Tighter sealing might also be provided by forcing a sealing member into a tapering space between the element and the housing, especially under the pressure applied to the element by the gas that is to be filtered. For example, the internal wall of the housing into which the element is fitted might be tapered inwardly (at least in the region in which the seal is formed) towards the end towards which the element is inserted .

An advantage of using a sealing member which presents a concave face to the pressurised gas when in normal use is that the seal can be released by causing back flow of gas through the filter assembly. Thus a seal which presents two limbs to the gas, which are forced apart by the gas, will be released when a back pressure is applied involving closing of the two limbs towards one another, away from the internal - surface of the housing or the element or both. This can protect the element from back flow conditions which can damage the element.

Other forms of sealing member might be used. For example, the sealing member might be provided by a gasket with a closed cross-section. The sealing member might be hollow or solid. For example, it might be provided by an O-ring.

The material that is selected for the sealing member will depend on factors such as the nature of materials to which the member is exposed during use, the material of the filter medium, the pressures to which it will be exposed and so on. Polymeric materials will often be preferred for the sealing member, in particular for their resilience in deformation. Examples of suitable materials include polyolefins, especially polyethylene, polypropylene and ethylene-propylene copolymers, polysulphones, and butyl rubber, polychloroprene rubber, nitrile rubber, polyurethane, silicone, and fluoro- polymers (such as fluorosilicones and fluoroelastomers) .

Preferably, the sealing member is formed as a closed loop, of an appropriate size to fit over the element. This has the advantage of maximising the effectiveness of the seal that the member provides, minimising axial leak paths. The sealing member can be attached to the element. It might be attached mechanically, for example by means of interfitting formations (such as tongue and groove formations), or otherwise such as by means of an adhesive. It might also be formed integrally with the element or a part thereof, for example with an end cap part of the element.

The sealing member can be formed by a moulding process. This is particularly preferred when the sealing member is formed as a closed loop and when it is formed integrally with the element or a part thereof. It can also be formed by processes such as extrusion. A continuous length of material can be formed by extrusion which can be cut to an appropriate length. The cut length can be formed into a closed loop, and held in that configuration if desired by an appropriate bonding technique, or by attached to the element around its periphery. Techniques such as moulding and extrusion are preferred when the sealing member is formed from certain polymeric materials.

It can be preferred for the sealing member to be provided at about the bottom of the section of the element through which the gas stream flows . This has the advantage of providing a path for drainage of liquid that separates from the flowing gas upstream of the element. That liquid can drain through the element and then from the element together with liquid that has been coalesced by the element for discharge.

The filter element itself will be selected according to the nature of the gas that is being filtered, the nature of contaminants (liquid droplets, aerosols and solid particles) to be filtered from the gas, the pressure differential across the filter and so on. Examples of media materials which can be used in the filter include foamed polymers (such as poly- urethanes and polyesters), glass and borosilicate fibre materials, polymeric materials such as polyolefins (especially polyethylene and polypropylene) especially in the form of fibres, paper based materials and so on. Examples of suitable features for the filter element of the invention can be found in filter elements sold for use in in-to-out filters by Domnick Hunter Limited under the trade mark OIL-X.

The filter element of the invention can be used to separate contaminants, especially liquid carried as aerosol droplets, in a pressurised gas medium. The filter element can be used in particular to separate compressor oil droplets from compressed gas, for example in refrigeration equipment.

The present invention also provides a filter assembly which incorporates the filter element discussed above. Accordingly, in another aspect, the invention provides a filter assembly for collecting liquid that is entrained in a gas stream, which comprises:

(a) a housing,

(b) a coalescing filter element of the kind discussed above located within the housing, the sealing member forming a seal between the element towards its base and the internal wall of the housing,

(d) an outlet for gas that has been filtered, in communication with the interior of the element, and

(e) an outlet from the housing for collected liquid that has been coalesced by the element .

The assembly can include a valve which enables pressure within the housing to be substantially maintained while liquid is discharged. For example, the assembly might include a two- or three-way valve. Such a valve might be operated by means of a pilot line fed with pressured gas from within the vessel. Examples of such a valve are disclosed in EP-A-81826. The valve will generally be provided at or near to the outlet for collected liquid from the housing. Preferably, the housing has an inwardly extending formation towards its base in the region in which it is contacted by the sealing member. The sealing member might be made to deform towards the formation as a result of the pressure differential across the element when in use. The formation can be in the form of, for example, an inwardly extending ridge when provided on a side wall of the housing, or an upwardly extending ridge when provided on its base. It can also be provided by an inwardly tapered portion of the wall of the housing. A formation can provide the advantage of enhancing the seal between the housing and the sealing member. It can also tend to hold the sealing member axially within the housing, reducing the tendency for the sealing member to be forced axially along the housing as a result of the pressure differential across the element. This can be important when the sealing member is not attached to the element, whether mechanically, by means of an adhesive, or in some other way.

The sealing member will generally be provided on a side wall of the filter element, especially when it is to engage the housing on a side wall thereof. However, the sealing member might be provided on a downwardly facing surface of the element in a construction in which the element is to engage the base of the housing.

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which :

Figure 1 is a side elevation, partially in section, through a filter assembly according to the invention.

Figure 2 is an enlarged view of the sealing member of the filter assembly shown in Figure 1. Figure 3 is an enlarged view of the outlet for liquid that has collected in the housing of the filter assembly shown in Figure 1, by the element.

Referring to the drawings, Figure 1 shows a filter assembly 2 which comprises a cylindrical housing 4 (for example formed from an aluminium alloy by a casting process, or from a polymeric material by a moulding process such as injection moulding) and a hollow cylindrical filter element 6 positioned in the housing, coaxially therewith. The housing is closed at its top and bottom ends. It has an inlet 8 in a side wall for a gas that is to be filtered. The gas is supplied through the inlet to the annular space between the filter element and the internal wall of the housing. The housing has an outlet 10 at its top end for the gas that has been filtered, through which the gas can leave the filter assembly after passing through the filter element, in a radially inward direction. The inlet and outlet are provided in an end cap for the housing, in which the top of the filter element can be located, and which provides appropriate flow paths for the gas to be filtered, from the inlet through the filter element to the outlet. The inlet and outlet are shown substantially in-line in the drawing. They might be arranged in other ways, for example offset from one another, or the outlet might be directed say upwardly from the filter element .

The filter element 10 comprises filter media such as one more layers of polymeric foam materials, and one or more layers of glass or borosilicate fibre based materials. The filter media will generally be arranged on a support cylinder, for example formed from a stainless steel or a polymeric material. The filter element includes top and bottom end caps 12a, 12b. They can be formed from a polymeric material, especially by moulding. The support cylinder might be formed as a single component with one or both of the end caps. The filter element has openings in the end cap at its base.

The housing has an outlet 18 at its lower end through which liquid collected by the element can be drained from the housing. The liquid that has been collected by the element drains from it through the openings in the base end cap into the space between the bottom of the element and the base of the housing. In the illustrated embodiment, the space extends across the entire cross-section of the housing. However, when the seal between the element and the housing is to the base of the housing (for example through a downwardly extending projection on the end cap or through an upwardly extending projection on the housing) , the space may extend across less than the entire cross-section of the housing. The outlet from the housing will generally include a valve. The valve can be controlled manually. Preferably, however, the valve is controlled in response to signals from sensors within the housing for the level of accumulated liquid, as known. An upper level sensor can generate a signal which opens the valve when the level of liquid reaches a predetermined level. A lower level sensor can generate a signal to close the valve when the level of liquid reaches a lower level. The movement of the valve between its open and closed positions in response to these signals might be controlled by compressed gas in a pilot line.

A sealing member 14 is provided around the periphery of the element at its base. The sealing member is provided by a gasket which is approximately V-shaped in cross-section so as to define two limbs 14a, 14b. The sealing member is connected to the bottom end cap 12a of the filter by a first one 14a of the limbs, and is orientated so that the open face 16 of the gasket faces upwardly. The second one 14b of the limbs is directed towards the internal wall of the housing. The orientation of the gasket ensures that pressure acting against it arising fr-om the pressure differential across the element forces the limbs apart, against the element and the internal wall of the housing respectively.

The sealing member is provided in the base end cap of the filter element, close to the bottom of the filter medium through which gas to be filtered passes. Any liquid not entrained with the gas which is to be filtered will collect on the sealing member and drain substantially directly through the element at its base to be discharged from within the element together with liquid that has been coalesced by the element .

Claims

CLAIMS :

1. A coalescing filter element for collecting liquid that is entrained in a gas stream, the element having a hollow tubular configuration arranged for flow of the gas stream from the outside thereof to the inside, the element having an opening at its base to allow liquid that is coalesced by the element and that collects within the element on the downstream side of the wall thereof to drain, and having a sealing member which extends around the element towards its base to form a pressure-tight seal between the element and the side wall of a housing in which the element is located when in use.

2. A filter element as claimed in claim 1, in which the sealing member is arranged so that the seal to a housing in which the element is located is enhanced as a result of exposure to the pressure applied by the gas being filtered.

3. A filter element as claimed in claim 2, in which the sealing member is outwardly deformable to enhance the seal between the housing and the element under pressure applied by the gas being filtered.

4. A filter element as claimed in claim 2 or claim 3, in which the sealing member comprises two limbs defining a channel between them, one limb being connected to the element and the other limb being directed outwardly to contact the wall of the housing.

5. A filter element as claimed in any one of claims 1 to 4, in which the sealing member is provided on a side wall of the element.

6. A filter element as claimed in claim 5, which is open at its base.

7. A filter element as claimed in claim 5 or claim 6, in which the sealing member is provided relative to the base of the element such that liquid not entrained with the gas which is to be filtered drains substantially directly through the element at its base to be discharged from within the element together with liquid that has been coalesced by the element.

8. A filter assembly for collecting liquid that is entrained in a gas stream, which comprises:

(a) a housing,

(b) a coalescing filter element as claimed in any one of claims 1 to 6 located within the housing, the sealing member forming a seal between the element towards its base and the internal wall of the housing,

(e) an outlet from the housing for collected liquid that has been coalesced by the element.

9. An assembly as claimed in claim 8, in which the housing has an inwardly extending formation towards its base in the region in which it is contacted by the sealing member, against which the sealing member is urged when the assembly is in use as a result of the pressure differential across the element .

10. An assembly as claimed in claim 9, in which the formation is provided on a side wall of the housing.

11. An assembly as claimed in claim 10, in which the formation is provided by an inwardly tapered portion of the side wall of the housing.

12. A filter assembly for collecting liquid that is entrained in a gas stream, which comprises:

(a) a housing,

(d) an outlet for gas that has been filtered, in communication with the interior of the element, and (e) an outlet from the housing for collected liquid that has been coalesced by the element,

13. An assembly as claimed in claim 12, in which the seal is provided on a side wall of the element.

14. An assembly as claimed in claim 12, in which the sealing member is provided at about the bottom of the element such that liquid which collects upstream of the element can drain through the element at its base to be discharged from within the element together with liquid that has been coalesced by the element.

15. An assembly as claimed in claim 12, in which the sealing member is arranged so that the seal to the housing is enhanced as a result of exposure to the pressure applied by the gas being filtered.