Abstract:
A carbon-based electrode device and a DDBD system for air purification and the production of ozone. The air treatment system is designed, in one embodiment thereof, to be operational in a double stage cycle involving the production of ozone-enriched air and the disintegration of air-borne pollutants, in a first stage; and the decomposition of residual ozone in the air, in a second stage. The multi-electrode crisscross array of the present invention features geometrical placement of the electrodes in triads to increase the efficiency of the system via two parameters, the close proximity of oppositely charged electrodes and the multiplicity of electrodes configured in triads, that is, crisscross arrays of three.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a non-thermal, double dielectric barrier discharge (DDBD) type air treatment system, and more particularly, to an ozone-generating and airborne pollutants purification system and a carbon-based, plasma reactor device for use therein.  
         BACKGROUND OF THE INVENTION  
         [0002]    The use of plasma and its application for treatment of air and for production of ozone has been widely known for the past couple of decades. The performance of the plasma-based reactor depends on the type of electrical discharge, specifically known as micro-discharges, but the two terms are used interchangeably hereinafter for the sake of simplicity. The electrical discharge itself depends on the shape of electrodes, on the nature of the inter-electrode region, and on the voltage and current waveforms used for producing the plasma.  
           [0003]    An electrical micro-discharge results in the flow of electrical current through a material that does not normally conduct electricity, such as air. On application of a high voltage source, the normally insulating air begins to exhibit conducting characteristics, and sparks, which are a form of electrical discharge, fly.  
           [0004]    Normally, air consists of neutral molecules of nitrogen, oxygen and other gases, in which electrons are tightly bound to atomic nuclei. On application of an electric field above a threshold level, some of the electrons are separated from their host atoms, leaving them as positively charged ions. The electrons and the ions are then free to move separately under the influence of the applied electric field. Their movement constitutes an electric current. This ability to conduct electrical current is one of the more important properties of plasma.  
           [0005]    Gas phase corona reactor (GPCR) technology enables the use of electrical discharges in order to excite electrons to very high energies, while the rest of the gas stays at ambient temperature. GPCRs of the DDBD type have historically been used to produce industrial quantities of ozone, which have been used in the air and water purification fields. This process also has wide application in the treatment of air-borne pollution.  
           [0006]    Generally, DDBD electrodes exhibit boundary problems. The abrupt, step-like, change of the electrical potential at the conductor edges of the electrodes will lead to the undesired effect of arcing and subsequently to the degradation of the electrode set-up.  
         SUMMARY OF THE INVENTION  
         [0007]    It would be desirable to achieve an improved, effective, DDBD type electrode which can be used to produce electrical discharges in a plasma reactor core for an efficient and cost-effective air treatment process.  
           [0008]    Accordingly, it is an object of the present invention to overcome the disadvantages of the prior art and provide a carbon-based electrode device and a DDBD system for air purification and the production of ozone. The air treatment system is designed, in one embodiment thereof, to be operational in a double stage cycle involving the production of ozone-enriched air and the disintegration of air-borne pollutants, in a first stage; and the decomposition of residual ozone in the air, in a second stage.  
           [0009]    In DDBD systems, the energy density at a given voltage is inversely proportional to the distance between pairs of electrodes of opposite polarity. There is a significant drop in energy density as spatial separation from a discharge point is increased, such that energy becomes significantly lower even at short distances away from a discharge point. In the multi-electrode crisscross array of the present invention, the geometrical placement of the electrodes in triads increases the efficiency of the system via two parameters, the close proximity of oppositely charged electrodes and the multiplicity of electrodes configured in triads, that is, crisscross arrays of three.  
           [0010]    Therefore, in accordance with a preferred embodiment of the present invention, there is provided a carbon-based electrode device comprising:  
           [0011]    a hollow tube, sealed at both ends, the seals comprising a bulk of dielectric material;  
           [0012]    a carbon filler material filling the hollow tube; and  
           [0013]    a metallic wire being embedded in the carbon filler material and extending outwardly through one sealed end of the hollow tube so as to be connectable to an electrical circuit in a DDBD reactor core.  
           [0014]    There is further provided an air treatment system for the production of ozone-enriched air, the disintegration of air-borne pollutants, and the decomposition of residual ozone in the air, the air treatment system comprising:  
           [0015]    at least one air filter for filtering particulate matter;  
           [0016]    a DDBD reactor core for subjecting air to non-thermal plasma, wherein the DDBD reactor core comprises a plurality of carbon-based electrode devices configured in an array of oppositely charged electrodes, wherein each carbon-based electrode device comprises:  
           [0017]    a hollow tube, sealed at both ends, each seal comprising a bulk of dielectric material;  
           [0018]    a carbon filler material filling the hollow tube; and  
           [0019]    a metallic wire being embedded in the carbon filler material and extending outwardly through one sealed end of the hollow tube so as to be connectable to an electrical circuit in the DDBD reactor core;  
           [0020]    a plurality of ozone filters for decomposition of ozone in the air;  
           [0021]    a filter housing for mounting said plurality of ozone filters, wherein the filter housing provides diversion of inflowing air in one of two paths: a path through the plurality of ozone filters and a path directly through the at least one reactor core; and  
           [0022]    at least one blower for drawing air into and through the air treatment system.  
           [0023]    Additional features and advantages of the invention will become apparent from the following drawings and description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    For a better understanding of the invention with regard to the embodiments thereof, reference is made to the accompanying drawings (not to scale), in which like numerals designate corresponding sections or elements throughout, and in which:  
         [0025]    [0025]FIG. 1A is an axial, cross-section view of a carbon-filled hollow tube, comprising a double dielectric barrier discharge electrode, sealed with bulk glass material at both ends, and constructed in accordance with the principles of the present invention in a preferred embodiment thereof;  
         [0026]    [0026]FIG. 1B is an axial, cross-section view of another embodiment of the carbon-filled hollow tube of FIG. 1A;  
         [0027]    [0027]FIG. 2 is a cross-section view of an open-air DDBD reactor core constructed in accordance with a preferred embodiment of the present invention;  
         [0028]    [0028]FIG. 3 is a cross-section view of another embodiment of the device of FIG. 2, comprising a closed DDBD reactor core;  
         [0029]    [0029]FIGS. 4A and 4B are axial end views of an electrical wiring circuit for an array of five electrodes arranged in a cylindrically shaped, closed-air DDBD reactor core constructed in accordance with another embodiment of the present invention;  
         [0030]    [0030]FIGS. 5A and 5B are axial end views of another embodiment of the invention of FIG. 4;  
         [0031]    [0031]FIGS. 6A and 6B are pictorial flow diagrams of a two-phase system for air treatment in accordance with a preferred embodiment of the invention; and  
         [0032]    [0032]FIGS. 7A and 7B are pictorial flow diagrams of an alternate embodiment of the invention comprising a single air-blower system for ozone generation and air purification. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    [0033]FIG. 1A is an axial, cross-section view of a carbon-filled hollow tube, comprising a DBDD electrode device, sealed with bulk glass material at both ends, and constructed in accordance with the principles of the present invention in a preferred embodiment thereof.  
         [0034]    DDBD electrode device  10 , comprises a hollow glass tube  12  of length L and thickness δ which is sealed at a first end by a bulk dielectric material, such as bulk-glass  14  in a preferred embodiment of the invention, of length between 15δ and 20δ, (depending on the applied high-voltage), and filled with a carbon filler  16 . In the preferred embodiment illustrated in FIG. 1A, carbon filler  16  comprises granulated carbon, with granules preferably, but not necessarily, of cylindrical shape, but any spherical or multi-facet shaped grains in the dimensions of about 3-5 mm×1 mm diameter are usable.  
         [0035]    At the second end of hollow glass tube  12 , a metallic wire  18  is inserted, slightly penetrating the surface  20  formed by the carbon filler  16  while slightly extending outwardly from the second end of hollow glass tube  12  to provide for a connection to a lead wire connecting the electrode device  10  to an electric power source (not shown). The second end of hollow glass tube  12  is then completely sealed with a bulk dielectric material, such as bulk-glass  14  in a preferred embodiment of the invention, which is poured in a liquid state surrounding the extension of metallic wire  18  during air evacuation of the tubular volume.  
         [0036]    [0036]FIG. 1B is an axial, cross-section view of another embodiment of the carbon-filled hollow tube of FIG. 1A.  
         [0037]    In this embodiment of the invention, a hollow glass tube  12 , of length L and thickness δ, corked at a first end with a bulk dielectric material, such as bulk glass  14  in a preferred embodiment of the invention, is filled with carbon filler  16  to form a surface  20  inside hollow glass tube  12  which is then plugged with a first cork  22  made of any highly electrical insulating and flexible material, such as Teflon or Polyurethane. In the preferred embodiment of the invention illustrated here, first cork  22  is made of poured flexible Polyurethane.  
         [0038]    A metallic wire  18  is inserted at the end of hollow glass tube  12  so as to penetrate first cork  22  and slightly penetrate the surface  20  of the carbon filler  16  while extending outwardly from the hollow glass tube  12  and thus providing for a connection to a lead wire (not shown) enabling the electrode device device  11  to be connected in an electrical wiring circuit of a reactor core.  
         [0039]    A second cork  24 , made of any highly electrical insulating and hard material, is applied to surround and seal the metal wire  18  into position. In a preferred embodiment of the invention, second cork  24  is made of poured hard Polyurethane. Second cork  24  is poured directly into glass tube  12  from the liquid phase and, until it hardens, is prevented from leaking into carbon filler  16  by the presence of first cork  22 .  
         [0040]    [0040]FIG. 2 is a cross-section view of an open-air DDBD reactor core constructed in accordance with a preferred embodiment of the present invention.  
         [0041]    A plurality of the carbon-based electrode device  11  from FIG. 1B are shown in a cross-section view illustrating an arrangement of the electrodes in three, parallel rows with a center electrode device  11  being disposed in a reverse orientation in relation to the surrounding outer-disposed electrodes most closely adjacent to the center electrode device  11 . The plurality of electrode devices  11  are mounted and fixedly held in parallel to each other between two supporting bars  26 A and  26 B (hereinafter generally designated  26 A/B) which are manufactured with holes (not shown) to accommodate and support the ends of each of the plurality of electrode devices  11 . The resulting structure comprises a DDBD reactor core  44   a  constructed in accordance with a preferred embodiment of the invention.  
         [0042]    The supporting bars  26 A/B may be made of PVC, Teflon, ceramic material, or any other highly electrical insulating material, but in the preferred embodiment shown in FIG;  2 , the supporting bars  26 A/B are made of PVC. The supporting bars  26 A/B may be made in any appropriate shape to accommodate and support the plurality of electrode devices  11 , but in a preferred embodiment of the invention, are formed as rectangular blocks with tub-like recesses  28  provided in the outer facets of supporting bars  26 A/B, which face away from one another.  
         [0043]    The plurality of electrode devices  11  are mounted in an alternating array forming at least one triad, or group of adjacent, oppositely charged electrodes comprising DDBD reactor core  44 A, as illustrated by way of example in the cross-section view of FIG. 2. In actual practice, any number of triads of electrode devices  11  can be mounted in a fixed array to form a DDBD reactor core, the number depending on the scale of operation required for efficient and effective air treatment.  
         [0044]    In supporting bars  26 A/B, the inner facet is perforated by a crisscross arrangement of three holes (not shown) which exactly match the diameter of each, carbon-filled, hollow glass tube  12  (see FIG. 1) comprising the triad of electrode devices  11 . The holes accommodating the ends of electrode devices  11  bearing a protruding electrical wire  18  run through the entirety of bars  26 A/B, extending outward into the tub-like recess  28  formed in the outer facets of bars  26 A/B. The holes accommodating the bulk-glass  14  ends of the electrode devices  11  do not extend into the tub-like recesses  28  in the outer facets of bars  26 A/B, but rather are drilled only to the extent of providing mechanical support for the bulk-glass  14  ends.  
         [0045]    After mounting electrode devices  11  in supporting bars  26 A/B and wiring the electrode devices  11  to lead wires  30  and  32 , the tub-like recesses  28  in the supporting bars  26 A/B are filled with a liquid phase dielectric material which hardens in place filling the volume of the tub-like recesses  28 . It should be noted that the liquid phase filler material, in a preferred embodiment of the invention, comprises poured hard Polyurethane and is identical to the material used in second cork  24  already hardened and in place surrounding an extension of metallic wires  18  embedded in the carbon filler material  16  as described heretofore in reference to FIG. 1.  
         [0046]    Each of the metallic wires  18  that protrude from the outer-positioned electrode devices  11  of DDBD reactor core  44   a  extending into the tub-like recesses  28  of supporting bar  26 A are internally interconnected by conducting wires  19 , made of copper wire, to join like, electrically charged terminals to a lead cable. In general, the outermost electrode devices  11  are connected to a ground lead  30 , primarily for safety reasons. (The interconnecting wires  19  are arranged, in preferred embodiments of the invention, as shown in FIGS. 4 and 5, described hereinafter.) The metallic wire  18  in the electrode device  11  extending through supporting bar  26 B is internally connected directly to another cable, in this example, comprising a high voltage lead  32  connectable to a power supply (not shown).  
         [0047]    In another embodiment of the present invention (not illustrated) the middle electrode and the respective holes are of a different (smaller/greater) diameter than the outer electrodes and their respective holes. The thickness of each of the carbon-filled, hollow glass tubes  12  comprising the plurality of electrode devices  11 , as indicated generally by the symbol δ (as in FIG. 1), is identical. The ratio between the diameter of the middle electrode and the outer electrodes is determined by the gap distances between adjacent and oppositely poled electrodes with respect to given applications.  
         [0048]    The gap distance between adjacent and oppositely poled electrodes is itself set in accordance with the respective application. For ozone generation, the gap is set between 1 mm and 2 mm. On the other hand, for gas, or air purification treatment, the gap is set between 2 mm and 6 mm.  
         [0049]    [0049]FIG. 3 is a cross-section view of another embodiment of the device of FIG. 2, comprising a closed DDBD reactor core constructed in accordance with the principles of the present invention.  
         [0050]    The internal elements of the reactor core  44   b  are essentially identical to those shown in FIG. 2, but the array of electrode devices  11  are enclosed in a cylindrically-shaped, sealed glass jacket  34  to accommodate the entry of air or gas for treatment. The glass jacket  34  is provided with an inlet  36  and outlet  38  comprising glass nozzles for feeding source gases, such as air, pure oxygen or a contaminated air stream, as the case may be. The circulating gas serves also as a coolant for cooling the DDBD reactor core  44   b.    
         [0051]    The diameter of glass jacket  34  is chosen so as to maintain the same gap distance between its inner diameter and the nearest surface of the most outwardly disposed carbon-based electrode devices  11  surrounding the centrally disposed electrode device  11 . The thickness of the glass jacket  34  is identical to that of each of the carbon-filled, hollow glass tubes  12  comprising each of the electrode devices  11 .  
         [0052]    The extension of metallic wire  18  from the middle positioned electrode device  11  in supporting bar  27 A is internally and directly connected to a first lead wire  32 , whereas the extensions of metallic wires  18  from the outwardly positioned electrode devices  11  extending into the tub-like recess  28  of supporting bar  27 B are internally interconnected by conducting wires  19 , made of copper wire and joined to a second lead wire  30 . The first lead wire  32  and the second lead wire  30  are then connectable to a power source (not shown) for operation of the DDBD reactor core  44   b.    
         [0053]    In an alternate embodiment of the invention of FIG. 3 (not shown), the glass jacket  34  is covered with an external conductive layer  40 , as shown in the wiring circuit in FIG. 5B, which is electrically connected to a ground  30  as shown in FIG. 5B.  
         [0054]    [0054]FIGS. 4A and 4B are axial end views of an electrical wiring circuit for an array of five electrodes arranged in a cylindrically shaped, closed-air DDBD reactor core constructed in accordance with another embodiment of the present invention.  
         [0055]    Referring now to FIG. 4A, there is shown an axial end view of an arrangement for the interconnection of wires  19  among four carbon-based electrode devices  11  constructed in accordance with the principles of the invention and described in reference to FIG. 1B. Carbon-based electrode devices  11  are disposed in an array within a glass enclosure  34  forming a cylindrically shaped, closed air DDBD reactor core  44   b  provided with gas inlet  36  and outlet  38 . Four of the carbon-based, electrode devices  11  are further interconnected to a ground lead  30  by connecting wires  19 .  
         [0056]    The four outwardly positioned, carbon-based electrode devices  11  are interconnected by connecting wires  19  and supported in a circular end cork generally defined by the inner walls of glass enclosure  34 . The circular end cork is formed from poured liquid phase Polyurethane that hardens to a concave shape filling the volume within the glass enclosure  34  above the inlet  36  and outlet  38  of the glass enclosure  34 . The poured dielectric material embeds the connecting wires  19  while providing support to maintain fixed gaps between the four outwardly positioned electrode devices  11  and a centrally positioned electrode device  11  (see FIG. 4B). FIG. 4B is an axial view of the opposite end of DDBD reactor core  44   b  of FIG. 4A, illustrating the electrical connection for a high-voltage lead  32  extending from a fifth, centrally positioned electrode device  11  in the array of five, in accordance with a preferred embodiment of the invention. The electrode device  11  in FIG. 4B is disposed in a reverse end orientation and is of opposite polarity in respect to that of the four surrounding electrode devices  11  shown in FIG. 4A.  
         [0057]    [0057]FIGS. 5A and 5B are axial end views of another embodiment of the invention of FIG. 4.  
         [0058]    In this embodiment of the invention, an electrically conductive coating  40  is applied over the insulating jacket  34  of the cylindrical, closed-air DDBD reactor core  44   c . In FIG. 5B the ground lead  30  is also connected to the layer of conductive coating  40  making it part of the electrical wiring circuit and increasing the output of micro-discharges along the length of the glass enclosure  34  when the reactor core  44   c  is connected to a power supply (not shown). Other like-numbered elements in the embodiment of the invention shown in FIG. 5 are substantially as described in reference to FIG. 4.  
         [0059]    [0059]FIGS. 6A and 6B are pictorial flow diagrams of a two-phase system for air treatment in accordance with a preferred embodiment of the invention.  
         [0060]    [0060]FIG. 6A is a pictorial flow diagram of the first, ozone-generating phase in the air treatment system, and FIG. 6B is a pictorial flow diagram of the second, ozone-decomposition phase in the system of air treatment of FIG. 6A.  
         [0061]    In FIG. 6A, the first, ozone-generating phase of the air treatment system, normal air, indicated by a series of horizontal arrows depicting an air stream, is drawn through a dust filter  42  for filtering out particulate matter in the entering air for efficient operation of the air treatment system. The filtered air is then passed through a DDBD reactor  44 , examples of which were described heretofore. The DDBD reactor  44  is constructed in accordance with the principles of the present invention so as to efficiently produce ozone-enriched air. A first, standard type, air blower  46   a  is used to draw air into the air treatment system and to pull the air through DDBD reactor  44 .  
         [0062]    [0062]FIG. 6B is a pictorial flow diagram of the second phase of operation of the air treatment system of FIG. 6A. A second air blower  46   b  pulls the ozone-enriched air (arrows indicate the air flow) through a dust filter  42  and towards a filter housing  48   a  where the dust-filtered air is pulled through a plurality of catalytic ozone filters  47  mounted in the filter housing  48   a . The filter housing  48  is provided with a sealed baffle  51  so that incoming air is directed through multiple passages in ozone filters  47  to maximize the catalytic action. The treated air is then exhausted from the air treatment system by action of a second air blower  46   b.    
         [0063]    [0063]FIGS. 7A and 7B are pictorial flow diagrams of an alternate, preferred embodiment of the invention comprising a single air-blower system for ozone generation and air purification. Because there is only one air blower  46  required, this alternate embodiment of the invention is much more economical to operate, although it functions in two cycles for complete air treatment.  
         [0064]    In FIG. 7A, depicting the ozone-generating, first cycle of operation, normal air (shown by horizontal arrows representing an air stream) is drawn into a dust filter  42  and directed into a filter housing  48   b  which supports a plurality of ozone filters  47 . The entering air passes directly through a filter housing  48   b  whose front flap  49  is in an open position. Thus the air is not in contact with or treated by the plurality of ozone filters  47 . The normal air is pulled by blower  46  through a DDBD reactor  44  constructed and operated in accordance with the principles of the invention as hereinbefore described, producing ozone-enriched air.  
         [0065]    In FIG. 7B, depicting the air purification, second cycle of operation, the ozone-enriched air from the first cycle of operation shown in FIG. 7A, indicated by the horizontal arrows, is then recycled by being passed through dust filter  42  until the air encounters the front flap  49  of filter housing  48   b  which is now in a closed position so as direct the air stream into a plurality of ozone filters  47  which are activated. The dust-free, incoming ozone-enriched air stream (shown by multidirectional arrows) is forced to pass through many contact points within the active catalytic elements of the ozone filters  47  before being drawn out of the air treatment system by air blower  46 . Incidental to being exhausted from the air treatment system, the exhausted air passes through the DDBD reactor  44  which is in line, but now set to an off operating status, since it is not needed in this second cycle of operation.  
         [0066]    Having described the present invention with regard to certain specific embodiments thereof, it is to be understood that the description is not meant as a limitation, since further modifications may now suggest themselves to those skilled in the art, and it is intended to cover such modifications as fall within the scope of the described invention.