WO1990006180A1 - An improvement in corona discharge arrangements for the removal of harmful substances generated by the corona discharge - Google Patents

An improvement in corona discharge arrangements for the removal of harmful substances generated by the corona discharge Download PDF

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Publication number
WO1990006180A1
WO1990006180A1 PCT/SE1989/000690 SE8900690W WO9006180A1 WO 1990006180 A1 WO1990006180 A1 WO 1990006180A1 SE 8900690 W SE8900690 W SE 8900690W WO 9006180 A1 WO9006180 A1 WO 9006180A1
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WO
WIPO (PCT)
Prior art keywords
electrode
corona
corona electrode
suction channel
target
Prior art date
Application number
PCT/SE1989/000690
Other languages
French (fr)
Inventor
Andrzej Loreth
Vilmos TÖRÖK
Original Assignee
Astra-Vent Ab
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Filing date
Publication date
Application filed by Astra-Vent Ab filed Critical Astra-Vent Ab
Publication of WO1990006180A1 publication Critical patent/WO1990006180A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/10—Preparation of ozone
    • C01B13/11—Preparation of ozone by electric discharge

Definitions

  • the present invention relates to an improvement in corona discharge arrangements for removing and render ⁇ ing harmless the potentially harmful gaseous products, in particular ozone and nitrogen oxides, that are pro- prised by a corona discharge.
  • a corona discharge arrangement of the kind to which the present invention pertains consists, in principle, of at least one corona electrode and at least one target electrode.
  • the corona and target electrodes are spaced apart, and each of the electrodes is connected to a respective pole of a d.c. source, and the configuration of the corona electrode and the pole voltage of the d.c. source are such as to generate a corona discharge on the corona electrode.
  • This corona discharge results in the generation of electrically charged air-ions of the same polarity as the corona electrode, and the air- ions migrate towards the target electrode, under the influence of the electric field, where they surrender their electric charge.
  • Corona discharge arrangements of the principle con ⁇ struction are found in many different forms in practice and are used for many different purposes.
  • corona discharge arrangements of this kind are used to a significant extent in air-purifying electrostatic precipitators.
  • the air ions generated by the corona discharge are operative to charge electri ⁇ cally the contaminants, particles and/or liquid droplets ⁇ , present in the air in the form of aerosols.
  • These electrically charged impurities are extracted from the air, by being attracted to and bound on col ⁇ lecting surfaces of opposite polarity.
  • Corona discharge arrangeusents of this kind are also used in air-trans- portati ⁇ ai systems in which air flows are driven with the aid of so-called electric ion or corona wind.
  • Vari ⁇ ous different designs of such air transportation sys ⁇ tems ares found described in the literature, for in- stance in international patent applications
  • corona discharge will generate chemical compounds, primarily ozone and nitrogen oxides, which are liable to cause an irritating effect and which may even be harmful ⁇ to people when the compounds are present in excessive quantities. It is also known that a corona discharge will give rise to strong and unpleasant odours, which persist even subsequent to termination of the cor ⁇ sna discharge process and subsequent to disper ⁇ sal of tftie ozone generated by said process.
  • odorous gaseous substances are not known at present, although it is reasonable to assume that they occur as a result of chemical changes in airborne organic compounds in the highly reactive plasma layer of the corona discharge.
  • the odorous substances genera ⁇ ted by the discharge may therefore be potentially very harmful. All of the undesirable, initiating or harmful substan ⁇ ces are created in the immediate vicinity of the corona electrode and spread to the ambient air.
  • the substances are produced at a rate which is contingent on the size of the electric corona current, and much higher levels of contaminating substances are produced by a negative corona discharge than by a positive corona discharge. The problem still exists, however, in the case of posi ⁇ tive corona discharges.
  • the object of the present invention is to provide an improved arrangement for recovering and rendering harmless the deleterious substances that are generated by the corona discharge of a corona discharge arrangement, this improved arrangement being based on the principle described in the international patent application PCT/SE87/00183, according to which the air present in the immediate vicinity of the corona elec ⁇ trode and carrying said harmful substances is removed continuously by suction, and which provides an effec ⁇ tive solution to the aforediscussed problem that remains when practising this known technique.
  • an additional electrode is mounted either within the suction channel or at a location adjacent the inflow orifice of the channel located in the proximity of the corona elec ⁇ trode, and the additional electrode is connected to a potential which, in relation to the potential of the corona electrode, has the same polarity as the polarity of the target electrode.
  • the additional elec ⁇ trode will function as an excitation electrode which facilitates and promotes the generation of the corona discharge on the corona electrode, such that a more effective and stabler corona discharge can be obtained with the aid of a smaller potential difference and/or a greater distance between the corona electrode and the target electrode.
  • Fig. 1 illustrates a first embodiment of the invention incorporated in an arrangement intended for the trans ⁇ portation of air with the aid of ion wind
  • Fig. 2 illustrates a second embodiment of the invention incorporated in an arrangement intended for the trans ⁇ portation of air with the aid of ion wind
  • Fig. 3 illustrates a third embodiment of the invention incorporated in an arrangement for the transportation of air with the aid of ion wind
  • Fig. 4 illustrates a fourth embodiment of the invention incorporated in an arrangement for the transportation of air with the aid of ion wind;
  • Fig. 5 illustrates a fifth embodiment of the invention incorporated in an arrangement for the transportation of air with the aid of ion wind;
  • Fig. 6 illustrates a sixth embodiment of the invention incorporated in an arrangement intended for the trans ⁇ portation of air with the aid of ion wind and simul ⁇ taneous cleansing of said air; and Fig. 7 illustrates a seventh embodiment of the inven ⁇ tion incorporated in a corona discharge arrangement intended for producing electrically charged air ions in an air flow which is driven by means of fan.
  • Fig. 1 illustrates schematically and in axial section an exemplifying arrangement which, with the aid of ion wind, is intended to drive an air flow through an air duct l, which in the illustrated case is assumed to have a rectangular cross-section.
  • the arrangement in- eludes, in a known manner, a corona electrode K in the form of a wire which extends transversely across the duct 1 in its central plane, and a target electrode M in the form of two, flat plate-like electrode elements which extend in mutual parallel relationship in the longitudinal direction of the duct 1.
  • the corona elec ⁇ trode K and the target electrode M are each connected to a respective pole of a d.c.
  • the arrangement may also include, in a known manner, an elongated screening electrode S, which is disposed parallel with and upstream of the corona electrode and which is connected to the same potential as said electrode.
  • an elongated screening electrode S which is disposed parallel with and upstream of the corona electrode and which is connected to the same potential as said electrode.
  • a suction channel or tube 4 which extends axially within the airflow duct 1 and which has an opening or orifice 4a located immediately downstream of and facing towards the corona electrode K.
  • the suction channel 4 is configured so that the orifice 4a thereof 10 facing the corona electrode K has an extension which corresponds to the extention of the corona electrode K.
  • an additio- nal electrode E Arranged within the suction channel 4, or at a location adjacent the inflow orifice 4a thereof, is an additio- nal electrode E, the extension of which preferably corresponds to the extension of the corona electrode K and which is connected to a potential which, in rela ⁇ tion to the potential of the corona electrode K, has the same polarity as the target electrode M.
  • the addi- tional electrode E of the illustrated embodiment is connected to earth. It will be understood that although it is practical to connect the additional electrode E to earth from the aspect of ' Controlling the strength of the current applied to said electrode, such connection is not absolutely necessary.
  • a carbon filter in which the harmful sub ⁇ stances are extracted chemically from the contaminated airflow, or to a location in which the contaminated air can be released safely, e.g. to free atmosphere exter ⁇ nally of the building housing the arrangement, as des- cribed in the earlier mentioned international patent application PCT/SE87/00183. It has been found that the aforesaid harmful substances can be removed very effec ⁇ tively when proceeding in this manner, and are pre- vented from spreading to the airflow 3 passing through the duct 1.
  • the presence of the additional electrode E in the suction channel 4 is also operative to reduce the screening or disturbing effect of the suction chan ⁇ nel 4 on the corona electrode K.
  • the addi- tional electrode E may well have an excitation effect on the corona discharge, so as to enable this discharge to be sustained with a smaller potential difference or with a greater distance between the corona electrode K and the target electrode M.
  • the additional electrode E may be connected to the voltage source 2 or to earth as in the case of the illustrated embodiment, through a resistor 5 of suit- ably adapted resistance.
  • resistors of such large resistance values in view of the large potential differences, in the order of lOkV, and the small corona currents, in the order of lO ⁇ A, which are entailed, it may be necessary to use resistors of such large resistance values as to exclude the possibility of acquiring in practice resistors such as those whose resistance values can be adapted with the precision required.
  • This "resistance device” com ⁇ prises a closed container 6 which has a cylindrical form in the illustrated embodiment and which includes an electrically conductive outer cylindrical wall and electrically insulating end walls, and a wire-shaped corona electrode 7, hereinafter referred to as the contained corona electrode, which extends axially with ⁇ in the container.
  • the contained corona-electrode 7 is connected electrically to the additional electrode E, whereas the cylindrical wall of the container 6 is connected to earth.
  • the device 6, 7 thus functions as an accurately adjust ⁇ able, large resistor for determining the corona current from the corona electrode K to the additional electrode E, and also the potential of the additional electrode E.
  • the container 6 may be sealed hermetically, such as to prevent the harmful substances generated by the corona discharge on the contained corona-electrode 7 from escaping to the surroundings. It will be under ⁇ stood that in practice, of course, the inventive ar- rangement need not necessarily be provided with both a resistor 5 and the resistive device 6, 7, and that the inclusion in Fig. 1 of both the resistor 5 and the device 6, 7 as a means of connecting the additional electrode E to the voltage source 2 has been done mere- ly in order to illustrate two possibilities that are available in this regard.
  • Fig. 2 illustrates an arrangement for driving an air- flow through a duct 1 of circular cross-section with the aid of an ion wind.
  • the arrangement includes, in a known and previously described manner, a corona elec ⁇ trode K and a target electrode M which are spaced axially from one another in the duct 1 and each of which is connected to a respective pole of a d.c. vol ⁇ tage source 2.
  • the target electrode M of the Fig. 2 embodiment is ring-shaped, whereas the corona electrode K comprises two wire-like electrodes which intersect to form a cross, as is best seen from Fig. 2A.
  • the two electrode elements of the corona electrode K are attached directly to the open end 4a of a suction chan ⁇ nel or tube 4 of round cross-section, such as to extend across said open end 4a.
  • the additional electrode E of this embodiment is also ring-shaped and is arranged within the suction channel 4, which extends in the upstream direction, and is connected to earth in the manner before described.
  • the ion flow from the corona electrode K to the additional electrode E gives rise to an ion wind which generates an airflow through the open end 4a of the channel 4, in the manner indicated sche ⁇ matically by arows 8, and therewith past the corona electrode K, so that the harmful substances generated in the immediate vicinity of the corona electrode K are drawn by suction into the channel 4.
  • the channel may have moun ⁇ ted therein a carbon filter 9 which is capable of extracting the harmful substances carried by the air flowing through the channel 4.
  • a carbon filter 9 which is capable of extracting the harmful substances carried by the air flowing through the channel 4.
  • the additional electrode E and the main target elec ⁇ trode M of the arrangement according to Fig. 2 are located on mutually opposite sides of the corona elec ⁇ trode K, and consequently it is possible to obtain a very powerful and highly stable corona discharge on the corona electrode K, even when the potential difference between the corona electrode K and the main target electrode M is comparatively moderate and/or when the distance between said electrodes is relatively large.
  • Fig. 3 illustrates schematically and in section an air transportation arrangement which operates with ion wind and which has the general construction described and illustrated in international patent application PCT/SE88/00365 (Fig. 6, 7).
  • the housing or airflow duct 1 in which the arrangement is accommodated is rectangular in the plane perpendicular to the plane of the drawing and has a central inflow opening la for the airflow 3 generated by the ion wind, and two mutually opposing outflow openings, referenced lb, which extend substantially at right angles to the inflow opening la.
  • the wire-like corona electrode K, the two plate-like target electrodes M and the screening electrode S are arranged and connected to the d.c.
  • the rear wall Id of the housing 1 has formed therein a suction channel 4 which is located axially opposite the corona electrode K.
  • an additional electrode E mounted in the suction channel 4, or at a location adjacent the open end 4a thereof, is an additional electrode E which is connected to earth via a resistance in the form of a corona discharge device 6, 7, in the manner aforedes- cribed.
  • the air carrying the harmful substances and flowing through the suction channel 4 is caused to pass through a sorbent, e.g. a carbon filter 9, which adsorbs/absorbs the harmful substances, as illustrated schematically in the drawing.
  • a sorbent e.g. a carbon filter 9, which adsorbs/absorbs the harmful substances, as illustrated schematically in the drawing.
  • the corona electrode K can be positioned very close to the open end 4a of the suction channel 4, without obstruct ⁇ ing the "free view" from the corona electrode K to the target electrodes M.
  • Fig. 4 illustrates schematically and in longitudinal section a similar air transportation arrangement which operates with an ion wind.
  • the housing 1 accommodating the arrangement has a cylindri ⁇ cal configuration in the plane extending perpendicu ⁇ larly to the plane of the Figure, such as to provide a circular-symmetrical arrangement.
  • One wall of the hous ⁇ ing thus has provided therein a circular inflow opening la, and a peripheral, annular outlet opening lb through which the airflow 3 generated by the ion wind exits.
  • the target electrode M comprises a cylindrical net or grid which is mounted between the front wall and the rear wall Id of the housing 1.
  • the suction channel 4 formed centrally in the rear wall Id and having a cir ⁇ cular cross-section has a closed axial end in this particular case and, the cylindrical wall of said chan- nel is, instead, provided with a plurality of openings 4a.
  • Extending across the openings 4a is a wire-like corona electrode K, which encircles the suction channel 4.
  • the additional electrode E has the form of a net or grid disposed within the channel 4, such that the coro ⁇ na current from the corona electrode K to the additio ⁇ nal electrode E will give rise to an airflow 8 which is driven by an ion wind and which passes through the openings 4a and therewith in close relationship with the corona electrode K.
  • the suction channel 4 may include an outlet which incorporates a carbon filter 9 for extraction of harmful substances from the airflow 8.
  • the corona current from the corona electrode K to the main target electrode M is operative to drive the airflow 3 through the arrangement in a known manner.
  • the inlet opening la and the outlet opening lb of the arrangement are covered with an earthed net or grid 10, which serve as a guard against inadvertent body contact with the high-voltage corona and target electrodes K and M respectively.
  • Fig. 5 illustrates schematically and in axial section a further embodiment of an ion-wind driven air-transpor- tation arrangement.
  • the airflow duct 1 has a rectangular cross-section and includes two inlet openings la through which airflow 3 generated by an ion wind enters the duct 1.
  • the target electrode M com ⁇ prises a flat plate, which is positioned centrally in the duct l such as to be parallel with the longitudinal
  • the corona electrode K has the form of an elongated wire and is mounted in the inflow opening or orifice 4a of the suction channel 4.
  • the outlet end of the suction channel 4 is covered with a carbon filter 9, for the extraction of harmful substances from the air flowing therethrough.
  • the carbon filter 9 of this embodiment is also intended to function as an additional electrode E, which draws current flow from the corona electrode K, so as to create the ion wind which drives the airflow 8 through the opening 4a and past the corona electrode K.
  • said wall part 4c may be made electrically conductive or semi-conductive and connec ⁇ ted to earth or to the additional electrode E through a large resistance.
  • Fig. 6 illustrates schematically and in axial section an arrangement for transporting air with the aid of an ion wind, while simultaneously cleansing the air trans ⁇ ported through the arrangement.
  • the arrangement inclu ⁇ des an airflow duct 1 of circular cross-section.
  • Moun- ted in the duct 1 is a first corona discharge device which is operative to generate an ion wind for driving the airflow 3 through the channel 1.
  • This first corona discharge device is constructed principally in the same manner as the device described in the aforegoing with reference to Fig.
  • the Fig. 6 embodiment of the inventive arrangement also includes a second corona discharge device which is not intended for driving the airflow 3 through the channel 1, but solely to ionize the airflow so as to enable aerosol contaminants in the airflow to be charged elec- trically and therewith enable said contaminants to be extracted from said airflow in a capacitor separator.
  • This second corona discharge device includes a wire ⁇ like corona-electrode K2 which is ring-shaped and en ⁇ circles the suction channel 4 in the vicinity of the inlet end of the duct 1, and a cylindrical, target- electrode M2 which is located closely adjacent the inner surface of the wall of said duct 1 or which may optionally have the form of a coating applied to said inner surface.
  • This second corona discharge device is operative to generate an ion current which flows from the corona electrode K2 to the target electrode M2.
  • This ion current charges the aerosol contaminants in the airflow 3 electrically, with a polarity correspond ⁇ ing to the polarity of the corona electrode K2.
  • These electrically-charged impurities or contaminants are separated from the airflow 3 and precipitate onto the target electrode M2, under the influence of the elec ⁇ tric field prevailing between the target electrode M2 and a further, cylindrical electrode 11 mounted adja- cent to or on the outside of the suction channel or suction tube 4 and connected to a potential of opposite polarity in relation to the potential of the target electrode M2.
  • the target electrode M2 and the electrode 11 thus form together a so-called electrostatic capaci- tor separator for extraction of the impurities carried by the airflow 3.
  • the wall of the suction channel 4 is provided with a plurality of openings 4b, across which the corona electrode K2 is extending. Also moun ⁇ ted in the suction channel 4 is a further, ring-shaped additional electrode E2 which is operative to draw corona current from the corona electrode K2, such as to generate an ion wind for driving an airflow 8b through the openings 4b and past the corona electrode K2.
  • the harmful substances generated by the corona discharges on the two corona electrodes Kl and K2 are thus drawn by suction into the suction channel 4, through respec ⁇ tive openings 4a and 4b, and are thereby prevented from entering the airflow 3 passing through the duct 1.
  • the harmful substances can be removed from the air drawn through the suction channel 4, by means of a carbon filter 9 mounted in said channel, in the aforedescribed manner.
  • Fig. 7 illustrates schematically a corona discharge device for ionizing an airflow 3 which is driven through an airflow duct 1 by means of a fan 12 or some corresponding device.
  • This corona discharge device includes a target electrode M which has the form of a net or grid extending transversely across the duct 1, and further includes a wire-like, ring-shaped corona electrode K which encircles a suction channel or suc ⁇ tion tube 4 extending centrally and axially in the duct 1.
  • the end of the channel 4 facing towards the target electrode M is closed, and the cylindrical wall of the channel is provided, instead, with a plurality of open ⁇ ings 4a, over which the corona electrode K extends.
  • the suction channel 4 includes a ring-shaped additional electrode E, such as to obtain an airflow 8 through the openings 4a, for the removal of the harmful substances generated by the corona discharge on the corona electrode K.
  • These harmful substances are extracted from the airflow 8 by means of a carbon filter 9 mounted at the down- stream open-*end of the suction channel 4. Aerosol con ⁇ taminants present in the airflow will be charged elec ⁇ trically by the ions migrating from the corona elec ⁇ trode K to the target electrode M, and as a result of this electric charge will be driven by the electric field prevailing between said electrodes back to the target electrode M, i.e. against the direction of air ⁇ flow, and will precipitate onto the target electrode M. This results in cleansing of the airflow while prevent ⁇ ing, at the same time, dirtying of the corona electrode arrangement.
  • Fig. 8 illustrates schematically and in section an air transportation arrangement which operates with ion wind and which is of similar construction to the arrangement described in the aforegoing with reference to Fig. 4, although in this case the corona electrode has a dif ⁇ ferent configuration.
  • the corona electrode K has the form of a loop of thin wire which is supported by an electrically insu- lating holder 13.
  • the ring-shaped loop which functions as the actual corona element per se, is located at some distance upstream of the open end 4a of the suction channel 4.
  • the arrangement illustra ⁇ ted in Fig. 8 has essentially the same construction and the same modus operandi as the arrangement illustrated in Fig.
  • corona electrode K is con ⁇ figured and arranged in the manner illustrated in Fig. 8.
  • One advantage is that the corona electrode K is not in direct contact with the walls of the suction channel 4, which walls may become dirtied with airborne con ⁇ taminants, which can give rise to difficulties when the corona electrode is in direct contact with such dirtied walls.
  • the electrically insulated holder 13 supporting the corona electrode K of the Fig. 8 arrangement may alternatively be directed in the other direction, i.e. extend in through the inlet open ⁇ ing la of the arrangement.
  • the ring-shaped corona electrode K may comprise a plurality of wire ⁇ like elements each extending over solely a part of the periphery of said ring but which together form a com- plete ring. This electrode construction may be neces ⁇ sary in order to achieve the requisite mechanical sta ⁇ bility of a corona electrode K which is made of very fine wire.
  • a corona electrode K which has the configuration illustrated in Fig. 8 can also be used with many of the inventive embodiments described in the aforegoing, for instance with the embodiments illustrated in Figs. 2, 6 and 7.
  • the invention can be applied with corona discharge arrange ⁇ ments of the most widely varying designs and intended for many different purposes.
  • the inven ⁇ tion in practice, it is relatively easy to adapt by trial and error the strength of the total corona cur- rent and its distribution on the main target electrode and the additional electrode respectively, and also the potential on the main target electrode and the addi ⁇ tional electrode in relation to the corona electrode, in the corona discharge arrangement applicable, so as to obtain the desired result.
  • the corona current from the corona electrode to the additional electrode used for removal of the harmful substances by suction should, in many instances, be equally as large, or in some cases even larger than the corona current from the corona electrode to the main target electrode.
  • the total corona current from the corona electrode will always be greater, and in many cases twice as great or still greater than in those instances when the invention is not applied.
  • this will result in an increase in the amount of harmful substances generated by the corona discharge, but since these harmful substances are effectively removed and rendered harmless by means of the inventive arrangement, this increase in the genera ⁇ tion of harmful substances will carry no disadvantage.
  • the airflow used for removing the harmful substances from the vicinity of the corona electrode into the suction channel which airflow is generated according to the present invention by the corona current or ion flow from the corona electrode to the additional elec ⁇ trode, may when necessary also be assisted by mechani ⁇ cal air transporting means, such as a fan or an air pump, connected to the suction channel.
  • mechani ⁇ cal air transporting means such as a fan or an air pump

Abstract

A corona discharge apparatus includes a corona electrode (K) and a target electrode (M) which is spaced from the corona electrode (K). The electrodes are connected to a d.c. source (2) having a voltage such as to produce a corona discharge on the corona electrode. For the purpose of removing the harmful or irritating gaseous substances generated by the corona discharge, there is provided a suction channel (4) which has an inflow opening or orifice (4a) located in the immediate vicinity of the corona electrode (K). The remainder of the suction channel is delimited in relation to the space (1) housing the corona electrode and the target electrode. Mounted in the suction channel (4) or at a location adjacent the channel opening (4a) is an additional electrode (E), which is connected to a d.c. potential which, in relation to the potential of the corona electrode (K), has the same polarity as the potential of the target electrode (M), so that an ion current will occur from the corona electrode (K) to the additional electrode (E), and therewith give rise to an airflow (8) past the corona electrode (K) and into the suction channel (4), through the channel opening (4a).

Description

AN IMPROVEMENT IN CORONA DISCHARGE ARRANGEMENTS FOR THE REMOVAL OF HARMFUL SUBSTANCES GENERATED BY THE CORONA DISCHARGE.
The present invention relates to an improvement in corona discharge arrangements for removing and render¬ ing harmless the potentially harmful gaseous products, in particular ozone and nitrogen oxides, that are pro- duced by a corona discharge.
A corona discharge arrangement of the kind to which the present invention pertains consists, in principle, of at least one corona electrode and at least one target electrode. The corona and target electrodes are spaced apart, and each of the electrodes is connected to a respective pole of a d.c. source, and the configuration of the corona electrode and the pole voltage of the d.c. source are such as to generate a corona discharge on the corona electrode. This corona discharge results in the generation of electrically charged air-ions of the same polarity as the corona electrode, and the air- ions migrate towards the target electrode, under the influence of the electric field, where they surrender their electric charge.
Corona discharge arrangements of the principle con¬ struction are found in many different forms in practice and are used for many different purposes. For example, corona discharge arrangements of this kind are used to a significant extent in air-purifying electrostatic precipitators. In this case, the air ions generated by the corona discharge are operative to charge electri¬ cally the contaminants, particles and/or liquid droplets^, present in the air in the form of aerosols. These electrically charged impurities are extracted from the air, by being attracted to and bound on col¬ lecting surfaces of opposite polarity. Corona discharge arrangeusents of this kind are also used in air-trans- portatiαai systems in which air flows are driven with the aid of so-called electric ion or corona wind. Vari¬ ous different designs of such air transportation sys¬ tems ares found described in the literature, for in- stance in international patent applications
PCT/SE85/00539, PCT/SE86/00548, PCT/SE87/00595 and PCT/SE8S/00365. Corona discharge arrangements of simi¬ lar principle construction ate also used in various other apparatus, as for instance electrostatic copying machines and laser printers.
A well Jεmown and not-readily solved problem encountered with the use of such corona discharge arrangements in spaces εr_r locations in which people are to be found, for insfcance in dwellings or working places, and also in ventilation systems and air treatment systems which communicate with such spaces or locations, is that the corona discharge will generate chemical compounds, primarily ozone and nitrogen oxides, which are liable to cause an irritating effect and which may even be harmful ϋto people when the compounds are present in excessive quantities. It is also known that a corona discharge will give rise to strong and unpleasant odours, which persist even subsequent to termination of the corαsna discharge process and subsequent to disper¬ sal of tftie ozone generated by said process. The nature of these odorous gaseous substances is not known at present, although it is reasonable to assume that they occur as a result of chemical changes in airborne organic compounds in the highly reactive plasma layer of the corona discharge. The odorous substances genera¬ ted by the discharge may therefore be potentially very harmful. All of the undesirable, initiating or harmful substan¬ ces are created in the immediate vicinity of the corona electrode and spread to the ambient air. The substances are produced at a rate which is contingent on the size of the electric corona current, and much higher levels of contaminating substances are produced by a negative corona discharge than by a positive corona discharge. The problem still exists, however, in the case of posi¬ tive corona discharges. This 'generation of harmful or irritating substances has seriously limited the pos- sibilities of using corona discharge arrangements in populated environments and has meant that the corona current used with such arrangements must be restricted. This limitation of the size of the corona current used, however, is in conflict with the intended purpose of such corona discharge arrangements, to wit the genera¬ tion of a large number of electrically charged air- ions.
One solution to this problem is described in interna- tional patent application PCT/SE87/00183, according to which the air located in the immediate vicinity of the corona electrode and carrying the undesired, harmful substances, is removed continuously, e.g. by suction, through a tubular channel element which has an inflow orifice located in the immediate vicinity of the corona electrode and through which the contaminated air remo¬ ved from the vicinity of the electrode is passed either to an air-filtering arrangement, in which the air is cleansed of its contaminant content, e.g. with the aid of sorbents, or alternatively to a location at which the air and the substances carried thereby can be released safely to the surroundings, i.e. to the open air. This solution to the problem in question is cor- rect in principle and can also be applied in practice. It is proposed in the aforesaid international patent application that the requisite flow of air passed the corona electrode and into the suction channel is gene¬ rated with the aid of a fan, an air pump or some cor- responding device connected to the suction channel. One drawback with this solution, however, is that the pro¬ vision of a fan, an air pump or the like for this pur¬ pose is both cost and space demanding, besides which the presence of such a fan, air pump etc., will add significantly to the noise generated by the system as a whole. It is also suggested in the aforesaid interna¬ tional patent application that the contaminated air could conceivably be guided through the inflow orifice of the suction channel with the aid of air which al- ready flows past the corona electrode and target elec¬ trode of the corona discharge arrangement, this airflow being sustained, for instance, by an external existing fan or being generated by the ion wind which flows from the corona electrode to the target electrode, and thus obviates the need for connecting a separate fan, air pump or corresponding device to the suction channel. This solution, however, requires the inflow orifice of the suction channel to be located immediately down¬ stream of the corona electrode, as seen in the direc- tion of the prevailing airflow, and also very close to the corona electrode, which in many instances would require an unacceptable structural configuration of the corona discharge arrangement. Generally speaking, in order to be able to remove through the suction channel a significant proportion of the harmful substances generated by the corona dis¬ charge, it is necessary for the airflow carrying the contaminating substances to pass very close to the corona electrode and from there rapidly through the inflow orifice and into said suction channel, since these contaminating substances are generated in the close proximity of the corona electrode and tend to disperse rapidly in the ambient air. In many cases, it is found that this is difficult to achieve in practice at the level of efficiency desired, when practising the method described in the afonssaid international patent application. It has also been found that the end of the suction channel, or tube, located in the close proxi¬ mity of the corona electrode has, in many instances, an unfavourable screening and disturbing effect on the corona electrode, such as to make it difficult to pro¬ duce and sustain the desired corona discharge without increasing the voltage difference between the corona and target electrodes or reducing the distance between these electrodes. Such increases in voltage difference or reductions in the distance between the electrodes, however, are not desirable, since the general endeavour is to produce the largest possible ion flow from corona electrode to target electrode with the aid of the lowe¬ st possible voltage and with significant spacing bet¬ ween the corona and target electrodes. This latter criterium is particularly important when the corona discharge arrangement is used to drive airflows with the aid of so-called ion wind.
Consequently, the object of the present invention is to provide an improved arrangement for recovering and rendering harmless the deleterious substances that are generated by the corona discharge of a corona discharge arrangement, this improved arrangement being based on the principle described in the international patent application PCT/SE87/00183, according to which the air present in the immediate vicinity of the corona elec¬ trode and carrying said harmful substances is removed continuously by suction, and which provides an effec¬ tive solution to the aforediscussed problem that remains when practising this known technique.
This object is achieved with the inventive arrangement defined in the following claims.
In accordance with the present invention, an additional electrode is mounted either within the suction channel or at a location adjacent the inflow orifice of the channel located in the proximity of the corona elec¬ trode, and the additional electrode is connected to a potential which, in relation to the potential of the corona electrode, has the same polarity as the polarity of the target electrode. This arrangement results in the migration of air ions from the corona electrode to the additional electrode, such as to generate an ion wind which flows from the corona electrode and into the suction channel, through the inflow orifice thereof located in the close proximity of the corona electrode. Since this airflow is driven by the air ions which migrate from the corona electrode to the target elec- trode, the airflow will pass very close to the corona electrode, and it is found possible when proceeding in this manner, to transport into the suction channel practically all of the deleterious or harmful substan¬ ces generated by the corona discharge on the corona electrode, such that only a negligible or a very small proportion of these substances will disperse directly to the surrounding atmosphere. It is also found that the additional electrode placed in the suction channel, or adjacent its inflow orifice, will eliminate the problem relating to the screening or disturbing effect that the suction channel has on the corona electrode. Instead, it has been found that the additional elec¬ trode will function as an excitation electrode which facilitates and promotes the generation of the corona discharge on the corona electrode, such that a more effective and stabler corona discharge can be obtained with the aid of a smaller potential difference and/or a greater distance between the corona electrode and the target electrode.
This will afford significant advantages in many instan¬ ces. It is true that, in this case, there is generated a larger corona current in total, which results in the production of larger quantities of harmful substances, but since these substances are removed effectively by means of the inventive arrangement, this constitutes no disadvantage. Thus, since the inventive arrangement is operative to eliminate the screening effect of the suction channel on the corona electrode, the inflow orifice of the suction channel can be located very close to the corona electrode to no detriment, which further enhances the efficiency of the arrangement.
The inventive arrangement may be given many different forms in practice, as will be understood from the fol lowing description of a number of exemplifying embodi¬ ments thereof, made with reference to the accompanying schematic drawings, in which Fig. 1 illustrates a first embodiment of the invention incorporated in an arrangement intended for the trans¬ portation of air with the aid of ion wind; Fig. 2 illustrates a second embodiment of the invention incorporated in an arrangement intended for the trans¬ portation of air with the aid of ion wind; Fig. 3 illustrates a third embodiment of the invention incorporated in an arrangement for the transportation of air with the aid of ion wind; Fig. 4 illustrates a fourth embodiment of the invention incorporated in an arrangement for the transportation of air with the aid of ion wind;
Fig. 5 illustrates a fifth embodiment of the invention incorporated in an arrangement for the transportation of air with the aid of ion wind;
Fig. 6 illustrates a sixth embodiment of the invention incorporated in an arrangement intended for the trans¬ portation of air with the aid of ion wind and simul¬ taneous cleansing of said air; and Fig. 7 illustrates a seventh embodiment of the inven¬ tion incorporated in a corona discharge arrangement intended for producing electrically charged air ions in an air flow which is driven by means of fan.
Fig. 1 illustrates schematically and in axial section an exemplifying arrangement which, with the aid of ion wind, is intended to drive an air flow through an air duct l, which in the illustrated case is assumed to have a rectangular cross-section. The arrangement in- eludes, in a known manner, a corona electrode K in the form of a wire which extends transversely across the duct 1 in its central plane, and a target electrode M in the form of two, flat plate-like electrode elements which extend in mutual parallel relationship in the longitudinal direction of the duct 1. The corona elec¬ trode K and the target electrode M are each connected to a respective pole of a d.c. voltage source 2 which has an intermediate, earthed tapping point, so that the corona electrode K and the target electrode M will have electrical potentials of mutually different polarities in relation to earth. Such an arrangement will have significance in practice, since it will reduce the maximum high-voltage potential of the arrangement in relation to earth. There occurs at the corona electrode K a corona discharge that gives rise to electrically charged air ions which migrate to the target electrode M, at which the ions surrender their electrical charge. This ion migration is operative to drive an air flow, so-called ion wind, through the duct 1 in the direction indicated by the arrow 3, in a manner known from, for instance, the international patent applications recited in the introduction. The arrangement may also include, in a known manner, an elongated screening electrode S, which is disposed parallel with and upstream of the corona electrode and which is connected to the same potential as said electrode. The presence of the scree¬ ning electrode will prevent ion-migration, and there¬ with undesirable ion-wind, in an upstream direction from the corona electrode K.
For the purpose of removing and rendering safe harmful substances which are generated adjacent the corona electrode K by a corona discharge thereon, there is provided a suction channel or tube 4 which extends axially within the airflow duct 1 and which has an opening or orifice 4a located immediately downstream of and facing towards the corona electrode K. The suction channel 4 is configured so that the orifice 4a thereof 10 facing the corona electrode K has an extension which corresponds to the extention of the corona electrode K. Arranged within the suction channel 4, or at a location adjacent the inflow orifice 4a thereof, is an additio- nal electrode E, the extension of which preferably corresponds to the extension of the corona electrode K and which is connected to a potential which, in rela¬ tion to the potential of the corona electrode K, has the same polarity as the target electrode M. The addi- tional electrode E of the illustrated embodiment is connected to earth. It will be understood that although it is practical to connect the additional electrode E to earth from the aspect of'Controlling the strength of the current applied to said electrode, such connection is not absolutely necessary. As a result of the pre¬ sence of the additional electrode E, a proportion of the air ions generated by the corona discharge on the corona electrode K will migrate to the additional elec¬ trode and therewith generate an ion wind which flows from the corona electrode K to the additional electrode E and into the suction channel 4. The airflow 8 created by this ion wind will pass immediately adjacent the corona electrode K and into the suction channel 4, through its inflow orifice 4a, whereby practically all of the harmful substances generated in the immediate vicinity of the corona electrode K will be removed therefrom and carried through the suction channel or suction tube 4. These harmful substances are conducted through the channel 4 either to an air filtering de- vice, e.g. a carbon filter in which the harmful sub¬ stances are extracted chemically from the contaminated airflow, or to a location in which the contaminated air can be released safely, e.g. to free atmosphere exter¬ nally of the building housing the arrangement, as des- cribed in the earlier mentioned international patent application PCT/SE87/00183. It has been found that the aforesaid harmful substances can be removed very effec¬ tively when proceeding in this manner, and are pre- vented from spreading to the airflow 3 passing through the duct 1. The presence of the additional electrode E in the suction channel 4 is also operative to reduce the screening or disturbing effect of the suction chan¬ nel 4 on the corona electrode K. In fact, the addi- tional electrode E may well have an excitation effect on the corona discharge, so as to enable this discharge to be sustained with a smaller potential difference or with a greater distance between the corona electrode K and the target electrode M.
For the purpose of adapting the strength of the corona current delivered to the additional electrode E, partly in terms of absolute values and partly in relation to the size of the corona current delivered to the target electrode, and also for the purpose of adjusting the potential of the additional electrode E to appropriate values, the additional electrode E may be connected to the voltage source 2 or to earth as in the case of the illustrated embodiment, through a resistor 5 of suit- ably adapted resistance. However, in view of the large potential differences, in the order of lOkV, and the small corona currents, in the order of lOμA, which are entailed, it may be necessary to use resistors of such large resistance values as to exclude the possibility of acquiring in practice resistors such as those whose resistance values can be adapted with the precision required. Consequently, it may be advantageous to con¬ nect the additional electrode E to the voltage source 2 via a resistance in the form of a corona discharge path, as illustrated schematically in Fig. 1 as an alternative embodiment. This "resistance device" com¬ prises a closed container 6 which has a cylindrical form in the illustrated embodiment and which includes an electrically conductive outer cylindrical wall and electrically insulating end walls, and a wire-shaped corona electrode 7, hereinafter referred to as the contained corona electrode, which extends axially with¬ in the container. The contained corona-electrode 7 is connected electrically to the additional electrode E, whereas the cylindrical wall of the container 6 is connected to earth. By adapting the size of the con¬ tainer 6, and therewith the distance between the con¬ tained, central corona-electrode 7 and the outer wall of the container 6, said outer wall functioning as a contained target-electrode, it is possible to adjust accurately the corona current between the contained corona-electrode 7 and the outer wall of the container 6, and therewith the equally as large current between the corona electrode K and the additional electrode E. The device 6, 7 thus functions as an accurately adjust¬ able, large resistor for determining the corona current from the corona electrode K to the additional electrode E, and also the potential of the additional electrode E. The container 6 may be sealed hermetically, such as to prevent the harmful substances generated by the corona discharge on the contained corona-electrode 7 from escaping to the surroundings. It will be under¬ stood that in practice, of course, the inventive ar- rangement need not necessarily be provided with both a resistor 5 and the resistive device 6, 7, and that the inclusion in Fig. 1 of both the resistor 5 and the device 6, 7 as a means of connecting the additional electrode E to the voltage source 2 has been done mere- ly in order to illustrate two possibilities that are available in this regard.
Fig. 2 illustrates an arrangement for driving an air- flow through a duct 1 of circular cross-section with the aid of an ion wind. The arrangement includes, in a known and previously described manner, a corona elec¬ trode K and a target electrode M which are spaced axially from one another in the duct 1 and each of which is connected to a respective pole of a d.c. vol¬ tage source 2. The target electrode M of the Fig. 2 embodiment is ring-shaped, whereas the corona electrode K comprises two wire-like electrodes which intersect to form a cross, as is best seen from Fig. 2A. The two electrode elements of the corona electrode K are attached directly to the open end 4a of a suction chan¬ nel or tube 4 of round cross-section, such as to extend across said open end 4a. The additional electrode E of this embodiment is also ring-shaped and is arranged within the suction channel 4, which extends in the upstream direction, and is connected to earth in the manner before described. The ion flow from the corona electrode K to the additional electrode E gives rise to an ion wind which generates an airflow through the open end 4a of the channel 4, in the manner indicated sche¬ matically by arows 8, and therewith past the corona electrode K, so that the harmful substances generated in the immediate vicinity of the corona electrode K are drawn by suction into the channel 4. As illustrated schematically in the Figure, the channel may have moun¬ ted therein a carbon filter 9 which is capable of extracting the harmful substances carried by the air flowing through the channel 4. Naturally, the ion flow from the corona electrode K to the main target elec- trode M maintains, at the same time, a flow of air which is driven by the ion wind through the duct 1 in the direction of the arrow 3.
The additional electrode E and the main target elec¬ trode M of the arrangement according to Fig. 2 are located on mutually opposite sides of the corona elec¬ trode K, and consequently it is possible to obtain a very powerful and highly stable corona discharge on the corona electrode K, even when the potential difference between the corona electrode K and the main target electrode M is comparatively moderate and/or when the distance between said electrodes is relatively large.
Fig. 3 illustrates schematically and in section an air transportation arrangement which operates with ion wind and which has the general construction described and illustrated in international patent application PCT/SE88/00365 (Fig. 6, 7). The housing or airflow duct 1 in which the arrangement is accommodated is rectangular in the plane perpendicular to the plane of the drawing and has a central inflow opening la for the airflow 3 generated by the ion wind, and two mutually opposing outflow openings, referenced lb, which extend substantially at right angles to the inflow opening la. The wire-like corona electrode K, the two plate-like target electrodes M and the screening electrode S are arranged and connected to the d.c. voltage source 2 in the manner described in the aforesaid international patent application and give rise to an airflow 3 through the housing 1 of said arrangement in a manner similar to that described in the specification of said international application. For the purpose of extract¬ ing harmful substances generated in the vicinity of the corona electrode K, the rear wall Id of the housing 1 has formed therein a suction channel 4 which is located axially opposite the corona electrode K. Mounted in the suction channel 4, or at a location adjacent the open end 4a thereof, is an additional electrode E which is connected to earth via a resistance in the form of a corona discharge device 6, 7, in the manner aforedes- cribed. The air carrying the harmful substances and flowing through the suction channel 4 is caused to pass through a sorbent, e.g. a carbon filter 9, which adsorbs/absorbs the harmful substances, as illustrated schematically in the drawing. In the case of an air transportation arrangement of this configuration, the corona electrode K can be positioned very close to the open end 4a of the suction channel 4, without obstruct¬ ing the "free view" from the corona electrode K to the target electrodes M.
Fig. 4 illustrates schematically and in longitudinal section a similar air transportation arrangement which operates with an ion wind. In this case, however, the housing 1 accommodating the arrangement has a cylindri¬ cal configuration in the plane extending perpendicu¬ larly to the plane of the Figure, such as to provide a circular-symmetrical arrangement. One wall of the hous¬ ing thus has provided therein a circular inflow opening la, and a peripheral, annular outlet opening lb through which the airflow 3 generated by the ion wind exits. The target electrode M comprises a cylindrical net or grid which is mounted between the front wall and the rear wall Id of the housing 1. The suction channel 4 formed centrally in the rear wall Id and having a cir¬ cular cross-section has a closed axial end in this particular case and, the cylindrical wall of said chan- nel is, instead, provided with a plurality of openings 4a. Extending across the openings 4a is a wire-like corona electrode K, which encircles the suction channel 4. The additional electrode E has the form of a net or grid disposed within the channel 4, such that the coro¬ na current from the corona electrode K to the additio¬ nal electrode E will give rise to an airflow 8 which is driven by an ion wind and which passes through the openings 4a and therewith in close relationship with the corona electrode K. Similar to the manner afore- described the suction channel 4 may include an outlet which incorporates a carbon filter 9 for extraction of harmful substances from the airflow 8. At the same time, the corona current from the corona electrode K to the main target electrode M is operative to drive the airflow 3 through the arrangement in a known manner. The inlet opening la and the outlet opening lb of the arrangement are covered with an earthed net or grid 10, which serve as a guard against inadvertent body contact with the high-voltage corona and target electrodes K and M respectively.
Fig. 5 illustrates schematically and in axial section a further embodiment of an ion-wind driven air-transpor- tation arrangement. In this case, the airflow duct 1 has a rectangular cross-section and includes two inlet openings la through which airflow 3 generated by an ion wind enters the duct 1. The target electrode M com¬ prises a flat plate, which is positioned centrally in the duct l such as to be parallel with the longitudinal
extension of said duct, and further comprises two elon¬ gated rods Ma. The rods Ma extend in the upstream direction of the plate, parallel with said plate. The corona electrode K has the form of an elongated wire and is mounted in the inflow opening or orifice 4a of the suction channel 4. The outlet end of the suction channel 4 is covered with a carbon filter 9, for the extraction of harmful substances from the air flowing therethrough. The carbon filter 9 of this embodiment is also intended to function as an additional electrode E, which draws current flow from the corona electrode K, so as to create the ion wind which drives the airflow 8 through the opening 4a and past the corona electrode K. In order to prevent a build-up of static electricity in that part 4c of the channel wall located nearest the corona electrode K and the inflow opening 4a, such build-up having a screening or disturbing influence on the corona discharge, said wall part 4c may be made electrically conductive or semi-conductive and connec¬ ted to earth or to the additional electrode E through a large resistance.
Fig. 6 illustrates schematically and in axial section an arrangement for transporting air with the aid of an ion wind, while simultaneously cleansing the air trans¬ ported through the arrangement. The arrangement inclu¬ des an airflow duct 1 of circular cross-section. Moun- ted in the duct 1 is a first corona discharge device which is operative to generate an ion wind for driving the airflow 3 through the channel 1. This first corona discharge device is constructed principally in the same manner as the device described in the aforegoing with reference to Fig. 2, and thus includes a ring-shaped target electrode Ml, a corona electrode Kl, in the form of two mutually crossing wires arranged over the open end 4a of the suction tube or channel 4, and a ring- shaped additional electrode El which is mounted within the suction channel 4, for the purpose of generating the airflow 8a in through the open end 4a of the suc¬ tion channel and past the corona electrode Kl.
The Fig. 6 embodiment of the inventive arrangement also includes a second corona discharge device which is not intended for driving the airflow 3 through the channel 1, but solely to ionize the airflow so as to enable aerosol contaminants in the airflow to be charged elec- trically and therewith enable said contaminants to be extracted from said airflow in a capacitor separator. This second corona discharge device includes a wire¬ like corona-electrode K2 which is ring-shaped and en¬ circles the suction channel 4 in the vicinity of the inlet end of the duct 1, and a cylindrical, target- electrode M2 which is located closely adjacent the inner surface of the wall of said duct 1 or which may optionally have the form of a coating applied to said inner surface. This second corona discharge device is operative to generate an ion current which flows from the corona electrode K2 to the target electrode M2. This ion current charges the aerosol contaminants in the airflow 3 electrically, with a polarity correspond¬ ing to the polarity of the corona electrode K2. These electrically-charged impurities or contaminants are separated from the airflow 3 and precipitate onto the target electrode M2, under the influence of the elec¬ tric field prevailing between the target electrode M2 and a further, cylindrical electrode 11 mounted adja- cent to or on the outside of the suction channel or suction tube 4 and connected to a potential of opposite polarity in relation to the potential of the target electrode M2. The target electrode M2 and the electrode 11 thus form together a so-called electrostatic capaci- tor separator for extraction of the impurities carried by the airflow 3.
For the purpose of removing the deleterious or harmful substances generated by the corona discharge on the corona electrode K2, the wall of the suction channel 4 is provided with a plurality of openings 4b, across which the corona electrode K2 is extending. Also moun¬ ted in the suction channel 4 is a further, ring-shaped additional electrode E2 which is operative to draw corona current from the corona electrode K2, such as to generate an ion wind for driving an airflow 8b through the openings 4b and past the corona electrode K2. The harmful substances generated by the corona discharges on the two corona electrodes Kl and K2 are thus drawn by suction into the suction channel 4, through respec¬ tive openings 4a and 4b, and are thereby prevented from entering the airflow 3 passing through the duct 1. The harmful substances can be removed from the air drawn through the suction channel 4, by means of a carbon filter 9 mounted in said channel, in the aforedescribed manner.
Fig. 7 illustrates schematically a corona discharge device for ionizing an airflow 3 which is driven through an airflow duct 1 by means of a fan 12 or some corresponding device. This corona discharge device includes a target electrode M which has the form of a net or grid extending transversely across the duct 1, and further includes a wire-like, ring-shaped corona electrode K which encircles a suction channel or suc¬ tion tube 4 extending centrally and axially in the duct 1. The end of the channel 4 facing towards the target electrode M is closed, and the cylindrical wall of the channel is provided, instead, with a plurality of open¬ ings 4a, over which the corona electrode K extends. In the manner described in the aforegoing, the suction channel 4 includes a ring-shaped additional electrode E, such as to obtain an airflow 8 through the openings 4a, for the removal of the harmful substances generated by the corona discharge on the corona electrode K. These harmful substances are extracted from the airflow 8 by means of a carbon filter 9 mounted at the down- stream open-*end of the suction channel 4. Aerosol con¬ taminants present in the airflow will be charged elec¬ trically by the ions migrating from the corona elec¬ trode K to the target electrode M, and as a result of this electric charge will be driven by the electric field prevailing between said electrodes back to the target electrode M, i.e. against the direction of air¬ flow, and will precipitate onto the target electrode M. This results in cleansing of the airflow while prevent¬ ing, at the same time, dirtying of the corona electrode arrangement.
Fig. 8 illustrates schematically and in section an air transportation arrangement which operates with ion wind and which is of similar construction to the arrangement described in the aforegoing with reference to Fig. 4, although in this case the corona electrode has a dif¬ ferent configuration. In the case of the Fig. 8 embodi¬ ment the corona electrode K has the form of a loop of thin wire which is supported by an electrically insu- lating holder 13. The ring-shaped loop, which functions as the actual corona element per se, is located at some distance upstream of the open end 4a of the suction channel 4. In other respects, the arrangement illustra¬ ted in Fig. 8 has essentially the same construction and the same modus operandi as the arrangement illustrated in Fig. 4. It has been found that significant advan¬ tages are afforded when the corona electrode K is con¬ figured and arranged in the manner illustrated in Fig. 8. One advantage is that the corona electrode K is not in direct contact with the walls of the suction channel 4, which walls may become dirtied with airborne con¬ taminants, which can give rise to difficulties when the corona electrode is in direct contact with such dirtied walls.
It will be understood that the electrically insulated holder 13 supporting the corona electrode K of the Fig. 8 arrangement may alternatively be directed in the other direction, i.e. extend in through the inlet open¬ ing la of the arrangement. Furthermore, the ring-shaped corona electrode K may comprise a plurality of wire¬ like elements each extending over solely a part of the periphery of said ring but which together form a com- plete ring. This electrode construction may be neces¬ sary in order to achieve the requisite mechanical sta¬ bility of a corona electrode K which is made of very fine wire. It will also be understood that a corona electrode K which has the configuration illustrated in Fig. 8 can also be used with many of the inventive embodiments described in the aforegoing, for instance with the embodiments illustrated in Figs. 2, 6 and 7.
It will be understood from the aforegoing that the invention can be applied with corona discharge arrange¬ ments of the most widely varying designs and intended for many different purposes. When applying the inven¬ tion in practice, it is relatively easy to adapt by trial and error the strength of the total corona cur- rent and its distribution on the main target electrode and the additional electrode respectively, and also the potential on the main target electrode and the addi¬ tional electrode in relation to the corona electrode, in the corona discharge arrangement applicable, so as to obtain the desired result. It has been found that the corona current from the corona electrode to the additional electrode used for removal of the harmful substances by suction should, in many instances, be equally as large, or in some cases even larger than the corona current from the corona electrode to the main target electrode. Thus, the total corona current from the corona electrode will always be greater, and in many cases twice as great or still greater than in those instances when the invention is not applied. As beforementioned, this will result in an increase in the amount of harmful substances generated by the corona discharge, but since these harmful substances are effectively removed and rendered harmless by means of the inventive arrangement, this increase in the genera¬ tion of harmful substances will carry no disadvantage.
The airflow used for removing the harmful substances from the vicinity of the corona electrode into the suction channel, which airflow is generated according to the present invention by the corona current or ion flow from the corona electrode to the additional elec¬ trode, may when necessary also be assisted by mechani¬ cal air transporting means, such as a fan or an air pump, connected to the suction channel.

Claims

1. An improvement in arrangements for removing harmful gaseous substances that are generated by corona dis¬ charge in corona discharge apparatus of the kind which include at least one corona electrode (K) , at least one target electrode (M) , and a d.c. voltage source (2) which is connected between said corona electrode and said target electrode and which has a voltage such as to produce on the corona electrode a corona discharge which will result in the generation of air ions which migrate from the corona electrode to the target elec¬ trode, said arrangement including a suction channel (4) which is restricted relative to the space (1) contain¬ ing the corona electrode (K) and the target electrode (M) and which has located in the immediate vicinity of the corona electrode (K) an inflow opening (4a) from said space (1), and which channel (4) is operative to conduct the harmful substances to a device (9) for rendering said substances harmless, or to evacuate said harmful substances from said apparatus, said improve¬ ment being characterized in that said arrangement in¬ cludes at least one additional electrode (E) which is connected to a d.c. potential which, in relation to the potential of the corona electrode (K) , has the same polarity as the potential of the target electrode (M) and which is mounted in said suction channel (4), or at a location adjacent said opening, such that an ion current will flow from the corona electrode (K) to the additional electrode (E) and give rise to an airflow (8) past the corona electrode (K) and into the suction channel (4) through said channel opening (4a).
2. An improvement according to Claim 1, characterized in that the device (9) mounted in the suction channel (4) comprises a filter element (9) which includes mate¬ rial capable of adsorbing/absorbing the harmful sub- stances carried by said airflow.
3. An improvement according to Claim 1, characterized in that the suction channel (4) communicates with an environment, for instance outdoor atmosphere, in which the harmful substances can be released safely.
4. An improvement according to any one of Claims 1-3, characterized in that the corona electrode (K) compri¬ ses one or more wire-like electrode elements which extend across said opening (4a) of the suction channel (4).
5. The improvement according to any one of Claims 1-3, characterized in that the corona electrode (K) compri- ses a thin wire-ring which is positioned opposite the suction-channel opening (4a), at a slight distance from said opening, in a plane which is substantially paral¬ lel with the plane of said opening.
6. The improvement according to any one of Claims 1-5, characterized in that the part of the suction channel (4) located nearest the corona electrode (K) has the form of a tube provided with an open end (4a).
7. The improvement according to any one of Claims 1-3, characterized in that the part of the suction channel (4) located nearest the corona electrode (K) has the form of a tube having a closed end and provided in the cylindrical wall thereof with one or more openings (4a); and in that the corona electrode (K) extends across said openings.
8. The improvement according to any one of Claims 1-7, characterized in that the part (4c) of the suction- channel wall located nearest the opening (4a) is at least slightly conductive electrically, and is connec¬ ted to a potential of the same polarity in relation to the corona electrode (K) as the additional electrode (E).
9. The improvement according to Claim 2, characterized in that the filter element ("9) also forms the additio¬ nal electrode (E).
10. The improvement according to any one of Claims 1-9, in which the corona electrode (K) and the target elec¬ trode (M) are connected respectively to the positive and negative poles of the d.c. source (2a), and in which the voltage source has an earthed intermediate tapping point, characterized in that the additional electrode (E) is connected to earth potential through a large resistance.
11. The improvement according to Claim 10, characteri¬ zed in that said resistance is formed by a corona dis¬ charge device which includes an airtight chamber (6), the walls of which are at least partially conductive electrically and are earthed; and a contained corona electrode (7) located within the chamber (6) and con¬ nected to the additional electrode (E) .
12. The improvement according to Claim 11, characteri¬ zed in that said chamber (6) is cylindrical and has a conductive, earthed cylindrical wall and electrically insulated end walls, and in that the contained corona electrode (7) comprises a wire-like electrode arranged axially in the chamber.
PCT/SE1989/000690 1988-12-08 1989-11-29 An improvement in corona discharge arrangements for the removal of harmful substances generated by the corona discharge WO1990006180A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE8804447-4 1988-12-08
SE8804447A SE462739B (en) 1988-12-08 1988-12-08 DEVICE OF A CORONA DISCHARGE DEVICE FOR THE REMOVAL OF THE DAMAGE ADDITION CREATING HARMFUL SUBSTANCES

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SE8804447L (en) 1990-06-09
CA2004828A1 (en) 1990-06-08
DD297868A5 (en) 1992-01-23
SE8804447D0 (en) 1988-12-08
SE462739B (en) 1990-08-27
AU4645789A (en) 1990-06-26
CN1043590A (en) 1990-07-04
US5180404A (en) 1993-01-19
JPH04503422A (en) 1992-06-18
EP0447418A1 (en) 1991-09-25

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