Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/28—Plant or installations without electricity supply, e.g. using electrets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/02—Plant or installations having external electricity supply
  • B03C3/04—Plant or installations having external electricity supply dry type
  • B03C3/14—Plant or installations having external electricity supply dry type characterised by the additional use of mechanical effects, e.g. gravity
  • B03C3/155—Filtration

Definitions

• the present invention relates to a device in connection with a filter, especially an active electret filter for air cleaning, said filter comprising an ionisation portion and a precipitator portion.
• Prior Art Electret filters for air cleaning are previously known, said filters comprising a filter material that consists of a filter material having relatively coarse fibres arranged in a relatively open pattern.
• the fibres in the filter material are subjected to a charging, said charging having the effect that although the filter is relatively open small particles may be separated.
• a prerequisite for this is that the particles have a weak charging. Since the filter is open the pressure drop across the filter is low.
• a disadvantage in connection with known electret filters is that the charging of the fibres and also the separating ability of the filter decline after a time.
• This filter consists of an electrically non-conductive material, preferably polypropylene having the characteristic that its fibres includes molecules that are easily polarised or oriented of a field directed towards the filter. This in its turn has the effect that charges are induced on the surfaces of the filter fibres and hence an electric field is created within the filter material.
• the particles passing through the filter, said particles being charged in the ionisation portion, are attracted and repelled respectively of the charged fibres, said particles normally adhere to a fibre having the opposite charging compared to the particles.
• the filter material must include fibres that in its turn includes molecules that are easily polarised from an applied electric field.
• the aim of the present invention is to define an active electret filter of the type defined above, said filter having' a freedom of choice as regards the filter material that is essentially improved compared to the device according to
• Figure 1 schemetically shows how a device according to the present invention is designed
• Figure 2 shows in section an embodiment of a filter in accordance with the principle of the present invention
• Figure 3 shows a section along III-III in figure 2.
• the device according to the invention includes an ionisation portion 10, said portion including a high voltage source 12 and a corona electrode 14 connected to said source 12, said corona electrode for instance being in the shape of a point, a brush or a wire.
• the device according to figure 1 includes also a precipitator portion 18, said portion 18 in its turn including a filter 20 that consists of a pre-filter medium and a layer ⁇ ' 22 of an electrically conductive material, said layer 22 being located downstream of the filter 20, seen in the direction 16 of the air flow.
• the layer constitutes of a grid 22.
• the pre-filter medium that constitutes the filter 20 may consist of a number of different materials.
• foamed materials having open pores should be mentioned, e.g. polyester or other synthetic materials.
• pre-filter medium be understood a filter having a fibre diameter down to about 20 ⁇ m and a spacing between the fibres of 200-400 ⁇ m.
• a material named CM 355 and marketed by the company Camfill has turned out to be a suitable material.
• it has turned out empirically that a large number of different filter materials may be used as filter material in the filter 20.
• the velocity of the air flow indicated by the arrow 16 depends on the coarseness of the filter. In connection with a pre-filter an air velocity of 0.2 m/s is suitable while in connection with a fine filter an air velocity of about 0.5 m/s is possible. The principle is that the more fine the filter is the higher air velocity.
• the grid 22 consists preferably of a metallic material. It has turned out to be important for the function of the device that the grid 22 closely abuts the filter 20. Within the scope of the invention it is also feasible that the grid consists of a non-metallic material that is electrically conductive, e.g. a plastic material. Nor is it necessary to have a grid but the corresponding function may for instance be achieved by an electrically conductive paint that is applied to the downstream side of the filter.
• the primary characteristic feature of the present invention is that the layer/grid 22 has an absolute potential that is lower than the potential of the corona electrode.
• absolute potential should in this connection be understood the magnitude of the potential regardless if it is negative or positive.
• the corona may for instance have a negative potential of 6-7 kV while the grid 22 has a positive potential- of 1 kV.
• the grid 22 is grounded, this being marked by a symbol in figure 1. In case the grid 22 is not grounded it must be connected to a voltage source .
• the device schematically shown in figure 1 functions in the following way.
• a charging is effected of the particles in the air flow that will be separated, this being pointed out above.
• the filter 20 will be charged due to the fact that the charged particles emit their charges to the filter 20 when they collide with the fibres in the filter 20.
• the particles thus adhere to the fibres, i.e. the air is cleaned from said particles.
• a charging of the fibres of the filter also takes place due to the fact that ions generated at the corona electrode 14 are transported, via the electric field, to the filter where said ions adhere to the fibres of the filter.
• the ionisation source 10 includes a negative corona.
• a positive corona it is fully feasible within the scope of the invention to use a positive corona, on condition that the problems of ozone generation are solved.
• positive ions will of course be generated at the corona electrode.
• the corresponding reasoning as regards charging of the filter 20 and separation of particles from the air are valid also in such a case.
• the device 1' in figure 2 and 3 an application of the invention in the shape of an air cleaner is shown.
• the device 1' according to figures 2 and 3 includes a casing 24, said casing 24 in its upper portion having an opening 26 where an axial fan 28 is mounted.
• the right part of the casing 24 in figure 2 and 3 has an ionisation portion 10', i.e. a corona electrode 14' in the shape of a wire is mounted in said part of the casing 24, said wire having an extension in the axial direction of the fan 28.
• the casing 24 has an essentially curved shape in the part constituting the precipitator portion 18', said filter 20' and said grid 22' constituting a part of the casing 24.
• the curved shape makes the distance between the corona electrode 14' and the filter 20' more uniform.
• the curved shape also facilitates e proper contact between the filter 20' and the grid 22'.
• the device 1' functions in principally the same way as has been described in connection with figure 1.
• the air symbolised by the arrow 30, is supplied to the casing by means of the fan 28.
• the air thus supplied is ionised by the wire- shaped corona electrode 14', i.e. particles that are to be separated are charged and free ions are supplied to the air.
• the air thus ionised is forced, by the fan 28, out through the filter 20', said air transport being symbolised by the arrows 32.
• the corona electrode 14' has a higher absolute potential than the grid 22', said grid 22' preferably being grounded.
• the separation process i.e. the cleaning of the air, takes place in a corresponding way as has been described in connection with the device according to figure 1. Empirically, it has turned out that the device according to figures 2 and 3 give a purification of 90%.
• a still further feasible application of the present invention is to use the principles of the invention in connection with so called supply air terminal device, i.e. where the ventilating duct emerges into spaces.
• a device may be used that principally corresponds to the device according to figures 2 and 3, the difference being that the fan 28 is deleted since the air flow emerging from the ventilating duct already has a certain, relatively low velocity.

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (3)

Cited By (2)

Citations (3)

• 1997
  • 1997-04-16 SE SE9701410A patent/SE522210C2/sv not_active IP Right Cessation
• 1998
  • 1998-04-08 AU AU70915/98A patent/AU7091598A/en not_active Abandoned
  • 1998-04-08 WO PCT/SE1998/000646 patent/WO1998046358A1/sv active Application Filing

Patent Citations (3)

Non-Patent Citations (3)

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