GB2265556A

GB2265556A - An electrostatic filter device

Info

Publication number: GB2265556A
Application number: GB9205121A
Authority: GB
Inventors: Robert William Gibbs
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-03-10
Filing date: 1992-03-10
Publication date: 1993-10-06
Also published as: GB9205121D0

Abstract

A filter device comprising a filter medium 1, 2 for gas of dielectric material, a charge applying means 3 of electrically conductive material connectable to a supply of high voltage power and juxtaposed said filter material such that when said electrically conductive material is subject to a high voltage a charge is applied to said dielectric material over its surface area, and an earth or ground means 8, 20 juxtaposed said filter medium on a side of said filter medium opposite to said charge applying means. The filter medium may be a glass fibre matt, polypropylene, polystyrene or nylon. The charging and grounding means may be wire mesh 5, 11, 12. <IMAGE>

Description

A FILTER DEVICE The present invention relates to a filter device for removing particles from gas such as from air.

There is an ever increasing awareness of the need to remove undesirable particles, such as resulting from the smoking of tobacco, from the air in public places, such as offices and from domestic environments and it is an object of the present invention to provide an improved means for enabling such particle removal.

Simple mechanical filters are known but, unless they are of a particularly expensive type, such are not sufficiently efficient for the intended purpose and soon become clogged. In prior, known devices it is possible to remove and discard the contaminated filter media although the support frame which forms part of the filter device is also often contaminated - especially by tobacco smoke - and retains foul odours, such frame is not readily cleaned because all its components were permanently attached, usually by some form of hinge.

Thus even after replacement of the filter media, foul odours of such prior devices are still apparent on the framing and are subsequently emitted.

It is also known that particles are removed by ionisers which produce negatively charged ions which combine with other airborne particles in the air and are then attracted to walls and other surfaces inside and outside of the device. Electro static precipitators are also known which include a duct containing charge applying means which uses a high voltage corona discharge which charges airborne particles and then downstream thereof with respect to the flow of air, a plurality of electrically conductive metal baffle plates, which may be oppositely charged attract the charged particles (e.g. of .30 micron) which adhere thereto and to the subsequent downstream walls.Such devices are not particularly efficient and require very high DC potential which is also particularly expensive to produce and also produces ozone which can be dangerous to health and some such devices are banned in USA and Canada.

Electro-static filters are also known wherein a fan passes air through a filter material and such mechanical frictional action causes the filter material to be electrostatically charged so as to draw particles to such although such devices have a limited efficiency.

According to the present invention a filter device comprises a filter medium for gas of dielectric material, a charge applying means of electrically conductive material connectable to a supply of high voltage power and juxtaposed said filter material such that when said electrically conductive material is subject to a high voltage a charge is applied to said dielectric material over its surface area, and an earth or ground means juxtaposed said filter medium on a side of said filter medium opposite to said charge applying means.

The inventor has discovered that when a high voltage field is applied to a very low efficiency filter medium of dielectric material and providing such is nontackified, such will increase the capability of the filter medium to arrest particles many times beyond its original efficiency ratings. The preferred feature of the ground means on a side of the filter medium opposite to the charge applying means and preferably at least the downstream side relative to the air flow, increases efficiency and minimises the discharge of particles which may become charged in the filter medium. The ground means either will remove the charge or attract the particle.

Also according to the present invention a filter device comprises a filter medium for gas of dielectric material supported between a charge applying means of electrically conductive material connectable to a supply of high voltage power and an earth or ground means preferably in the form of a screen, of electrically conductive material with said charge applying means and ground means being electrically insulated from each other and such that when the high voltage power supply is connected a charge is applied to said filter material.

Preferably the charge applying means will be a sheet like material such as a metal gauze or wire mesh or perforated metal sheet of a like or grill of wires, and preferably two filter media will be provided each located on opposite sides of said charge applying means and preferably two ground means will be provided located at distal opposite sides of the two filter media with said ground means preferably in the form of a mesh of electrically conductant material.

In a preferred embodiment according to the invention a filter device comprises two sheets of filter medium for gas and of dielectric material located either side of a charge applying means in the form of an electrically conductive screen mesh or the like; Two earthing or ground means in the form of electrically conductive material sheets, such as a mesh, perforated screen or other wire like or the like arrangement, located at opposite distal surfaces of said filter sheets with the thus provided laminate arrangement being connectable together; said charge applying means being electrically insulated from the outer ground means which also each preferably have a peripheral frame forming a support or housing port for the composite arrangement.

Preferably a high voltage power supply or means for supplying a high voltage to said charge applying means e.g. a voltage multiplier device, will be mounted on one of the frames forming support means. A connecting insulated manner with the charge applying means which is otherwise insulatedy supported within their arrangement.

The filter medium is preferably a known filter material in sheet form preferably a non-woven random disposition mat preferably of glass fibres possibly bonded with urea formaldehyde or other, or may be polypropylene, polystyrene or nylon and is non tackified.

A preferred filter preferably automatic earthing or ground means will be provided and operable such that upon separation of one ground means screen or the like, the charge applying means is grounded for safety purposes.

In preferred embodiments of the invention, all components are detachable so that each can be removed from the other and may be immersed in a cleaning solution for the purpose of removing any film which may emit a foul odour.

It will be appreciated that in the present invention the high voltage charge is applied to the filter medium and not to airborne particulate. Any particle that picks up a charge and becomes ionised within the filter would discharge itself on the grounded (earthed) ground means upon leaving the filter medium and then return to the space in a neutral condition and therefore remain in suspension to be recycled by the air fans of the building or the like. Such suspended particles could then be returned to the filter for collection by the filter medium. It is to be appreciated that the charge applying means which is preferably in the form of a metal screen or mesh supported by a frame is electrically insulated from any of the electrically conductive components with the supporting housing which may be formed by the outermost ground means. To achieve this stand-off insulators may be provided at its corners to provide a snug fit within outer frames and the space from any vertically conducted material. Preferably the high voltage to the charge applying means is disconnected automatically as any ground means is removed.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is an exploded perspective view of a filter device forming a preferred embodiment according to the invention; Fig. 2 is a front elevation of a filter device of similar construction to that of Fig. 1; Fig. 3 is an underneath plan of the device of Fig. 2; Fig. 4 is a vertical transverse section through the device of Fig. 2; Fig. 5 is a vertical transverse section through the central inner screen, and Fig. 6 is a partial elevation of the inner or central screen of Fig. 5; member of electrically insulating material so as to prevent such frame and mesh from abutting against any undesired electrically conductive material.Two spaced apart and apertured locating strips 7 of electrically insulating material extend from the bottom frame 4 to facilitate assembly of the whole device - as will be described subsequently.

A first earthed or ground means 8 comprises a rectangular metal frame which also functions as a housing and support of the device and is formed from four rectangular aluminium extrusions 9 interconnected by plastic corner pieces (with connecting lugs such as illustrated in Figs. 7, 7a and 7b) and is of the type as is used, for example, for forming framed meshes for protection against mosquitoes. A rectangular wire mesh 11 is located within frame 9 in the same manner as said mosquito protection devices and as is illustrated in Fig.

8A wherein the wire mesh sheet has its edges forced and folded into channel sections 12 running around the periphery of each side of the frame 9 whereupon a resilient retaining bead 13 is pressed into the recess and against the screen edges 11' to hold such in place.

Two spaced apart locating pins 14 are provided extending from the bottom side of the frame 9.

A device 15 for providing a high voltage supply is detachably mounted on the top of frame 8 and comprises a coaxially pinned socket 16 enabling the device to be connected to a power supply e.g. a 24 volt battery or power source, and said device 15 includes a series of voltage multipliers so as to provide a high voltage output for example, in the region of 7,500 volts DC which is led out of the device by a wire conductor 17 which has an insulating sheath 18 along most of its length although a free end of the wire extends therebeyond and is folded over at a position so that the top edge portion of frame 4 of the charge applying means 3 may abut thereagainst when in position of use.A resilient and deflectable earth wire member 19 extends from the upper part of a frame 9 downwardly and outwardly away from the frame 8 as shown in Fig. 1 and is angled such that in the assembled condition of the whole device a second earthed or ground means 20 has an upper frame portion which abuts thereagainst to deflect the wire 19 against its resilient action and out of contact with charge applying means 3.

The second earthing or ground means 20 comprises a rectangular metal frame 21 formed of hollow extruded aluminium section in the same manner as frame 9 and has a wire mesh 22 extending between the sides thereof and located in the same manner as frame 9 as shown in Fig. 8.

Frame 21 has two oppositely pivotally mounted clips or clamp members 23 and 23' which are displaceable parallel to the plane of the wire mesh 22 and each has a U-shaped portion with limbs which engage a side of frame 21 and around the distal opposite face of frame 9 so as to holdthe whole device in assembled condition. The lower side of frame 21 has two apertures 24 aligned so as to receive pins 14 for location purposes.

The two frames 9 and 21 are of the same size and shape as each other. The two sheets of filter material 1 and 2 are of the same size and shape as each other but slightly smaller than frames 9 and 21 so as to be clampable therebetween with the edges preferably abutting or even slightly overlapping the inner peripheral edges of frames 9 and 21 so as to ensure air passing through meshes 11 and 22 also passes through filter material.

The frame 4 is smaller than the inner periphery defined by the frame members 9 and 21 and the meshes 11 and 22 are located towards the distal sides of the frames 9 and 21 and almost flush with the end faces so as to provide oppositely facing cavities for the receipt of the filter material 1 and 2 and the charge applying means 3 therewithin. The frames 9 and 21 are clampable together in abutting relationship by pivoting of devices 23 and 23' toward the frame members to interengage frame 21 with frame 9 - the pins 14 extending through the apertures in strip 7 and into apertures 24. the corner members 6 of insulating material will be such as to, as mentioned, prevent the screen 4 and wire 5 from contacting any other metal surface and will preferably also space the mesh 5 equally between meshes 11 and 22.

To assemble the device, sheet 2 is located in the cavity defined by frame 9 and with the top edge of sheet 2 in a space between output electrode 17, 18 and wire screen 11 so that wire conductor 17 thus extends on the side of sheet 2 adjacent charge applying means 3 which is then juxtaposed sheet 2 with wire 19 abutting against the frame 4 of means 3. Pins 14 extend through the apertures in plastics material strips 7. Subsequently sheet 1 is applied against the surface of mesh 5 remote from sheet 2 and then frame 21 with devices 23 and 23' pivoted away from the frame applied thereagainst and the whole laminate assembly clamped together by devices 23 and 23' with the upper crosspiece of frame 21 abutting against the upper portion of wire 19 to further deflect such and away from and out of contact with charge applying means 3.

When power is supplied to the socket 16 and air passed through the filter a particularly efficient filter device and operation is achieved. Means 8 and 20 are grounded and thus means 20 if on the downstream- and air exit side, acts to attract and/or neutralise any charged particles exiting from the filter media.

Upon removal of devices 23 and 23' and the frame 21, the wire 19 springs against charge applying means 3 to earth such for safety.

The device of Figs. 2 - 6 are very similar to Fig. 1 - the only significant difference being that instead of clamps 22 and 23, inverted keyhole shaped slots 25 and 26 and connecting bolt heads 27 and 28 are provided for the interconnection.

The high voltage power supply to the inner screen 4 and 5 is disconnected automatically as the outer screen is dropped in its slots for disassembly. Before the two outer screens 11 and 22 can be opened but after the high voltage has been disconnected, a ground (earth) pin will touch the inner screen discharging it to ground (earth) and therefore prevent any danger to maintenance personnel. The high voltage power supply is fixed to one of the outer panels by the same slot and bolt configuration used on the outer screens, allowing it and in the previous embodiment to be easily removed so that both outer screens can be submerged independently for cleaning. There is considerable advantage here achieved by the outer screens being detachable from each other for cleaning.

It will be appreciated that the inner screen 4 and 5 is not in any way attached to the outer screens but rather is held in place by stand-off insulators at its corners and because of its snug fit to the outer frames is able to hold the two pieces of filter media and itself in place as soon as the holding bolts (or connecting devices 23 and 23') are operated in the former instance by being slipped into their respective slots on the outer frame.

The high voltage supply means 15 of Fig. 1 is detachably connected to frame 9.

Various possible modifications may be effected without departing from the scope of the present invention. For example, frames 9 and 21 may be hinged together along their long vertical side edges and clamping device(s) 22 provided only on one side. Other securement means are possible. Alternatively, a metal hinge or plate may be provided in connecting the bottom sides of frame 9 and 21 (pins 12 and 14 being omitted) and a semi resilient interconnection being provided. The charge applying frame means may have corner pieces with resiliently and outwardly deflectable portions which abut against the inner periphery of the outer frame members to hold such inner frame in position. A single sheet of filter material may be provided. The filter device may be used to adapt existing precipitator devices wherein the "ionising device thereof is switched off and the filter device of the invention located across the air port.

Figs. 11 to 13 illustrate a unit with fan and air inlet and outlets for wall or floor support and receiving a filter device of the invention via a hinged front flap.

Figs. 14 and 15 illustrate a unit with fan and air inlet and outlets for ceiling mounting and having a lower hinged flap for receiving the filter device.

Claims

1. A filter device comprising a filter medium for gas of dielectric material, a charge applying means of electrically conductive material connectable to a supply of high voltage power and juxtaposed said filter material such that when said electrically conductive material is subject to a high voltage a charge is applied to said dielectric material over its surface area, and an earth or ground means juxtaposed said filter medium on a side of said filter medium opposite to said charge applying means.

2. A device as claimed in claim 1, in which the filter medium is of non-tackified dielectric material.

3. A device as claimed in claim 1 or 2, in which the ground means is on a side of the filter medium opposite to the charge applying means and preferably at least the downstream side relative to the air flow.

4. A filter device comprises a filter medium for gas of dielectric material supported between a charge applying means of electrically conductive material connectable to a supply of high voltage power and an earth or ground means of electrically conductive material with said charge applying means and ground means being electrically insulated from each other and such that when the high voltage power supply is connected a charge is applied to said filter material.

5. A device as claimed in claim 4, in which the ground means is in the form of a screen.

6. A device as claimed in claim 4 or 5, in which the charge applying means is a sheet like material (such as a metal gauze or wire mesh or perforated metal sheet of a like or grill of wires).

7. A device as claimed in any of claims 4 to 6, in which two filter media are provided each located on opposite sides of said charge applying means.

8. A device as claimed in claim 7, in which two ground means are provided located at distal opposite sides of the two filter media with said ground means preferably in the form of a mesh of electrically conductant material.

9. A filter device comprising two sheets of filter medium for gas and being of dielectric material located either side of a charge applying means in the form of an electrically conductive screen mesh or the like; two earthing or ground means in the form of electrically conductive material sheets located at opposite distal surfaces of said filter sheets with the thus provided laminate arrangement being connectable together; said charge applying means being electrically insulated from the outer ground means.

10. A device as claimed in claim 9, in which the electrically conductive sheets are a mesh, perforated screen or other wire like or the like arrangement.

11. A device as claimed in claim 9 or 10, in which the outer ground means each preferably have a peripheral frame forming a support or housing port for the composite arrangement.

12. A device as claimed in any of claims 9 to 11, in which a high voltage power supply or means for supplying a high voltage to said charge applying means, e.g. a voltage multiplier device, is mounted on one of the frames forming support means in connecting insulated manner with the charge applying means which is otherwise insulatedly supported within the arrangement.

13. A device as claimed in any of claims 1 to 12, in which the filter medium is a known filter material in sheet form such as a non-woven random disposition mat.

14. A device as claimed in claim 13, in which the sheet is of glass fibres possibly bonded with urea formaldehyde or other, or may be polypropylene, polystyrene or nylon and is non-tackified.

15. A device as claimed in any of claims 1 to 14, wherein automatic earthing or ground means are provided and operable such that upon separation of one ground means screen or the like, the charge applying means is grounded for safety purposes.

16. A device as claimed in any of claims 1 to 15, in which all components are detachable so that each can be removed from the other and are such as may be immersed in a cleaning solution for the purpose of removing any film which may emit a foul odour.

17. A device as claimed in any of claims 1 to 16, in which the charge applying means, which is preferably in the form of a metal screen or mesh supported by a frame, is electrically insulated from any of the electrically conductive components with the supporting housing which may be formed by the outermost ground means.

18. A device as claimed in claim 17, in which the electrical insulator is provided by stand-off insulators provided at its corners of the frame, to provide a snug fit within outer frames and be spaced from any electrically conductive material.

19. A device as claimed in any of claims 1 to 18, in which the high voltage to the charge applying means is disconnected automatically as any ground means is removed.

20. A filter device as claimed in any of claims 1 to 19, used to adapt an existing precipitator device wherein the ionising device thereof is switched off and the filter device of the invention located across the air port.

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