AN ELECTROSTATIC FILTER

Abstract: An electrostatic filter includes a disposable sheet of conductive media to which an earthed or high voltage power supply is attached. The disposable filter is positioned adjacent a charged plate inside an insulated frame, so that an electrostatic field is generated without arcing. The disposable filter comprises a conductive media, such as unprocessed foiled paper, foil or film. The filter configuration is designed for ease of plate changing, so that it is cheaper and less complex than existing disposable cartridge type electrostatic air filters. The general configuration of the device may be re-sized so as to enable a very slim-line, relatively flat filtration system to be incorporated into other products, such as furniture, picture frames, mirrors, or wall and ceiling panelling.

Description: AN ELECTROSTATIC FILTER Technical Field The present invention relates to an electrostatic filter. It relates particularly, but not exclusively, to an electrostatic filter for filtering particulates from air. Background Art Presently available electrostatic or electronic air filters are cleaned by either washing collector plates, on which dust accumulates (precipitator type filters), or by opening a filter and removing and replacing individual pads or cartridges (charged media type filters). In cleaning these electrostatic filters, the collector plates are cumbersome and need to be cleaned professionally. The charged media type filters require expensive pads or cartridges. Published International Patent Application WO-A1-9105611 (Yamamoto) describes a cylindrical filtration device for filtering foreign particles from air. The device includes a pair of electrodes, between which there is a sufficient potential difference to avoid ionisation of foreign particles. The filtration device accepts a cartridge for filtering which is fitted, or retrofitted, into a housing for a filter unit. Another example of an electronic air filter is described in US Patent US 4 549 887 (Joannou). The device includes a frame arrangement which supports first and second fibrous pads through which air is drawn. Because the pads are polarised by a high voltage, particles are drawn towards them and are removed from the air. The device is complex and fibrous pads are expensive and difficult to clean. Another problem with existing air filters is that they offer no real flexibility in their construction, being too cumbersome to be easily integrated into the interior design of most indoor environments. An object of the present invention is to provide an electrostatic air filter in which a dust collecting media is disposable. Another objective is to provide an electrostatic filter in a unit which is flexible and can be sized according to its specific design requirements. Brief Description of Invention According to the present invention, there is provided an electrostatic filter for filtering particulates from a gas, comprising: first and second electrodes, there being in use, a potential difference between the electrodes; a removable, disposable surface, which in use is in electrical contact with one of the electrodes; and means for displacing the gas so that it flows adjacent said surface, thereby attracting particulates towards said surface so that they attach thereto and are filtered from the gas. Preferably the first electrode is in the form of a conductive clip which clips the disposable surface and conducts electricity thereto. It may, however, include a metal plate, which may be substantially planar, or tubular, or another shape. Preferably the second electrode is a plate, or rod, and also comprises a conductive material. The disposable surface may be in the form of a sheet of conductive media, such as foiled paper. Alternatively, the disposable surface may be a sheet of ordinary (unfoiled) paper or card. The disposable surface may act as a collector plate, and may be held inside the air filter device parallel to a permanent plate. Preferably the permanent plate is charged to a much higher voltage than the collector plate. This sets up an electrostatic field so that charged particulates that enter the field are directed towards the disposable surface. The disposable surface is hereinafter also referred to as a collector plate. The permanent plate is preferably profiled so that turbulence is induced in the airflow between the plates, thus increasing efficiency of particulate collection. Preferably a number of insulating spacers are mounted on the permanent plate, so that an adequate distance is maintained between the permanent and the disposable collector plates. Preferably an earthed or high voltage power supply makes a temporary contact with the disposable collector plate. Inlets of the filter are advantageously fitted with corona wires. The corona wires are preferably held in insulating frames which also act to maintain separation of the permanent plate from the disposable collector plate. Preferably the corona wires are held at the same voltage as the permanent plate and are used to charge the particulates that flow into the filter. In a preferred embodiment the electrostatic field is defined by two conductive frames that are fixed together by an insulated hinge arrangement. This allows the device to be opened to enable easy access to the disposable collector so that it can be removed and replaced. On closure of the frame (with a sheet of disposable collector in place) an electrical connection is made, thus enabling the electrostatic field to be created, only when the frames is closed. This is an important safety feature as the high voltage supply is automatically isolated when the filter is opened. The nature of the hinged plates and the simplicity of the disposable collector impose minimum constraints on the size of the surface area of the charged plates. This allows the filter to be easily incorporated as a relatively flat panel into other products, such furniture wall or ceiling panels, or other fitting or fixtures such as mirrors, pictures or signs. The flexible sizing of the planar dimensions of the device also enable it to be easily retrofitted into existing air handling systems. The filter preferably comprises: a frame which supports a disposable sheet, which in use is in contact with an electrode; a hinged parallel electrode configuration, whose size can be varied; a high voltage power supply adapted to be mechanically and electrically connected to first and second electrodes; means for displacing gas through the filter; said first electrode being profiled to induce air turbulence along a flowpath; and, a frame of corona wires arranged to ionise particulates which are drawn into the filter, so that, in use, they are collected on the disposable sheet. Preferably the filter is used with an automatic grounding switch which discharges the high voltages (positive or negative) on the electrodes when the filter is opened. The air filter may be connected in tandem with other filters. The arrangement may be powered by a single high-voltage power supply. An infra-red control system may be optionally included. In an alternative embodiment there is provided an insulated channel, which in use receives a disposable sheet; an electrode is located within the channel; a high voltage supply connected to the electrode and disposable sheet; an ionisation grid is positioned at an entrance to the channel and means for displacing gas through said channel is provided for displacing gas past said ionisation grid so that particulates are ionised; said ionised particulates being drawn towards and attach to said disposable sheet. Preferably said channel is tubular. Connection between the sheet and said high voltage supply may be by way of a conductive spring clip, which is connected to the supply. A number of embodiments of the invention will now be described, by way of example only, with reference to the Figures, in which:- Brief Description of the Figures Figure 1 shows a plan view of a filter, in part cutaway sections, showing the general position of control electronics, a fan and the frames containing corona wires; Figure 2 shows a cross sectional view of the filter of Figure 1 showing in detail a disposable plate; a permanent plate and corona wires; Figure 3 shows an overall view of the filter of Figures 1 and 2, showing both the permanent and the disposable charging plates; Figures 4a and 4b are partial cross-sectional views of the filter of . Figure 1, showing diagrammatically the action of a grounding switch when the permanent and disposable plates are separated; Figures 5 a and 5b show a possible application of the filter of Figure 1 within a tabletop; Figures 6a and 6b show a possible application of the filter as a picture or poster frame; Figure 7 shows a side view of the exterior of the general configuration of the disposable collector plate, according to a second embodiment of the invention; and Figure 8 shows a cross section of the general configuration of the disposable collector plate of Figure 7, with the central electrode. Detailed Description of Embodiment of the Invention Referring to Figures 1 and 2, in a first embodiment of the invention, there is provided a front cover 1 formed from an insulating material, and a back cover 2. The two covers are connected by hinges 3, which are located along one edge of the filter. A fan 4 is mounted on an inside surface of front cover 1. The fan 4 draws air into the filter via slots 5 which are located along sides of the filter. The slots 5 define corona wire housings and are formed from insulating material which is injection moulded in modular lengths. Corona wires 6 are located in the housings. Slots 5 act as finger traps, which prevent a objects, such as fingers being placed inside the filter. Corona wires 6, in use, are held at the same voltage as permanent plate 8. Plate 8 is made from a conductive material which is capable of holding charge. The plate 8 is shaped with a surface profile 9, which helps to induce turbulence in air as it flows through the filter. The permanent plate 8 and the slotted corona wire housings 5 are glued or bonded onto the inside surface of the front cover 1. If desired, the front cover 1 and back cover 2 can be coloured or covered with any material which could enable it to blend into its intended surroundings. For example, front cover 1 may be adapted to receive publicity material or advertisements. The device can be locked shut by a simple lock 19 attached to the front cover 1. A disposable collector plate 10 is constructed from any conductive media such as aluminium foil, and is held in place by conductive clips 11. Clips 11 are held at a collector plate voltage and are mounted onto the back cover 2. Once the covers are closed together a high voltage supply is connected to the permanent plate 8 and collector plate 10. A disposable sheet is held in place by insulating spacers 12 and the slots 5. The insulating spacers 12 are connected to the permanent collector plate and may be randomly, or evenly, spaced. Spacers 12 can be designed to help to induce turbulence within the filter device. In Figure 3, the disposable collector plate 10, the conductive clips 11 and the insulating spacers 12 are shown in greater detail. Airflow is adjacent the disposable surface. This means that the pressure drop across the filter is substantially less and hence requires a less powerful fan. Spacers are used to maintain a set distance between repelling and collecting electrodes. This prevents unwanted arcing or charge drain. Spacers are not intended to entrap particulates. Electrodes are preferably readily detachable for easy maintenance or replacement. High voltage supply circuitry 13 (Figure 2) includes an insulating housing box 13a, and is connected to the inside of the front cover 1. Circuitry 13 includes a main step down transformer (which may be about 12 volts), a low power high-voltage generator (which may be between 4 and 12 KiloVolts) and an infra-red control circuit connected to an infra-red detector. The infrared detector 14 may be mounted on the front cover 1 in high supports the fan 4. The infra-red control system is optional. The high voltage circuitry 13 supplies a high voltage to the permanent collector plate 8 via discharging safety switch 14 (see Figures 4a and 4b). It is important that all the high voltage conductors and the earthed conductors are sufficiently insulated or spaced apart so that no electrical arcing takes place. Generally, electrostatic precipitators are expensive to construct. The present invention is simple and enables manufacture of a very cheap particulate cleaner. Insulating spacers are designed to promote easy flow of gas across the disposable collector plate or along a tube. Fins of the spacers help create localized turbulence in the airflow along the collector plate. The introduction of a spool of flexible collector plate (disposable media) at one edge of the air flow is possible, so that dirty collector plate(s) can be easily replaced by manually or electrically winding clean collector plate(s) into the filter. The dirty collector plate(s) may be fed onto another spool or torn off and disposed. This enables the filter to operate for extended periods of time before a new roll of filter material has to be mounted into the device. In an alternative embodiment the filter is housed in a tubular shaped cover. The tube length can be as long as necessary in order to achieve a higher level of filter efficiency. Figures 4a and 4b show a spring loaded discharging safety switch 14 in its two positions: when the housing is closed (Figure 4a) and when it is open (Figure 4b). The discharging switch 14 switches any residual charge from the permanent plate 8 (should the covers be opened) to earth. When the covers are closed, the switch 14 is pushed back by disposable plate 10 which moves sliding contact 16 onto high voltage outlet contact 17. When this occurs permanent plate 8 is switched into direct electrical contact with the high voltage circuitry 13. When the covers are opened, switch 14 is allowed to spring back and this moves sliding contact 16 onto the earthed contact 18. This allows the charge held on the permanent plate 8 to be drained away to a safe level. Switch 14 is formed from an insulting material, so that the high voltage circuitry 13 is not provided any electrical path to the earthed disposable plate 10. An activated carbon filter may be inserted around the fan inlet 23. This helps to reduce odours. Figures 5a and 5b show how the filter can be adopted for inclusion in a tabletop 20. This is one furniture application. However, the slim design of the filter (with no real constraints on the size of the collector plates) enables the device to be used in a myriad of applications. The electrostatic filter can be discreetly integrated into indoor environments. The tabletop may be finished in any material, such as a wood veneer. Figures 6a and 6b show how the filter could be wall mounted to become a mirror or picture/poster frame. There may be provided a second outer hmge 21 on the device, which holds the front clear cover 22 to the picture frame A second embodiment of the invention is illustrated in Figures 7 and 8. A roll of conducting media 101 is inserted in insulated tube 102 so that it contacts a flexible reed contact 103, that is connected to earth. Conducting rod electrode 104 is held substantially at the axis of the tube 102 by a number of insulating inserts 105. Conductive medium 101 is held against a flexible reed contact 106 which is connected to a high voltage supply (not shown). It is not essential that the conducting rod electrode 104 is centrally positioned in the tube. Electrode 104 may be situated off-centre, so long as the distance between the conducting media 101 and electrode 104 is of a sufficient size so as to prevent arcing. The high voltage of the central electrode 104 and the earthed collector plate 101 create an electπc field which acts to attract ionised particulates travelling along the tube. Connected to the central electrode 104 is an ionisation gπd 107 which contains a plurality of Corona-wires held within an insulating frame. The Corona-wires that are in contact with the central electrode 104, and hence, are at the same high voltage. As the air flows into the tube 101 it passes through the ionisation gπd 107, where the corona discharge charges air-borne particulates. Charged particles flow along the tube where they are urged onto the tubular collector plate 101 by the electπc field The tubular collector plate 101 composes a sheet of conductive media, such as foiled paper or film, and slotted into the tube via the gap between the ionisation gπd 107 and the tube walls 102. Alternatively, the rolled up sheet of conducting media could be inserted from the base of the tube 102, after the tube has been removed from the housing of the device. To remove the collector plate 101, the aforementioned process is reversed Insulating spacers 105 may be designed so that their fins are twisted. This helps to induce turbulence into the air flow in the tube 102 thereby improving precipitation. Any odours may be adsorbed by inclusion of an activated carbon filter 108, which may be placed just prior to the fan 109. Tube 102 may be formed from a clear material, such as plastic or glass, then the outer side of the collector plate 101 may have printed matter on and may be utilised as a form of advertising space. The invention has been described by way of a examples only and it will be appreciated that variation may be made to the embodiments without departing from the scope of the invention.

Claims: CLAIMS 1. An electro-static filter for filteπng particulates from a gas, compπsing: first and second electrodes, there being in use, a potential difference between the electrodes; a removable, disposable surface, which in use is in electπcal contact with at least one of the electrodes; and means for displacing the gas so that it flows adjacent said surface, thereby attracting particulates towards said surface so that they attach thereto and are filtered from the gas. 2. A filter according to claim 1 wherein at least one electrode compπses a metallic plate or metallic tube. 3. A filter according to claim 1 or 2 wherein at least one electrode includes a conductive clip. 4. A filter according to any preceding claim wherein the, or each, electrode has a profile which vanes along the gas path so as to induce turbulence in the gas flow between the electrodes. 5. A filter according to any preceding claim wherein corona wires are disposed so as to charge particulates. 6. A filter according to any preceding claim wherein the removable surface compπses a sheet of mateπal. 7 A filter according to claim 6 wherein the mateπal is paper. 8. A filter according to claim 6 wherein the material is a conductive sheet or foil. 9. A filter according to any preceding claim which is in the form of two frames, the frames being hinged together by an insulated hinge, thereby facilitating easy removal of the surface. 10. A filter according to claims 9 wherein a switch is arranged to isolate a high voltage when the frames are opened. 11. An electro-static filter preferably comprises: a frame which supports a disposable sheet, which in use is in contact with an electrode; a hinged parallel electrode configuration, whose size can be varied; a high voltage power supply adapted to be mechanically and electrically connected to first and second electrodes; means for displacing gas through the filter; said first electrode being profiled to induce air turbulence along a flowpath; and, a frame of corona wires arranged to ionise particulates which are drawn into the filter, so that, in use, they are collected on the disposable sheet. 12. An electro-static filter comprises an insulated channel, which in use receives a disposable sheet; an electrode is located within the channel; a high voltage supply connected to the electrode and disposable sheet; an ionisation grid is positioned at an entrance to the channel and means for displacing gas through said channel is provided for displacing gas past said ionisation grid so that particulates are ionised; said ionised particulates being drawn towards and attach to said disposable sheet. 13. A filter substantially as herein described with reference to the Figures. 14. A method of filtering particulates from a gas using the filter of claims 1 to 13.

Inventors: NEWBOULD PETER JAMES, NEWBOULD, PETER, JAMES
Applicants: NEWBOULD PETER JAMES, ROYAL COLLEGE OF ART, NEWBOULD, PETER, JAMES, THE ROYAL COLLEGE OF ART
Application year: 1999
Main classification: B03C3
IPC codes: B03C3