Abstract:
An ozone generating apparatus includes a base container for holding water, and a head assembly connected to the upper edge of the base container, the head assembly containing a plurality of ozone generating cells each having a dielectric tube and an electrode assembly coaxially disposed within the associated dielectric tube. The dielectric tubes and electrode assemblies are disposed and connected such that the tube and/or electrode assembly of each ozone generating cell can be accessed independently of all other ozone generating cells, and such that the possibility of cascade failure of all remaining ozone generating cells upon failure of a single cell is substantially eliminated. The base container is provided with a process back flood prevention structure to protect the ozone generating cells.

Description:
RELATED APPLICATION DATA 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/274,815, filed Aug. 21, 2009, by the same inventor/applicant, and under the same title. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to systems for generating and dispensing ozone, and in its preferred embodiments more specification relates to improvements in the physical design of ozone generating systems for producing ozone in a corona discharge field, and to functional improvements in such systems. 
     BACKGROUND 
     It has long been known that ozone is a very powerful oxidizer, and ozone is employed in a variety of processes for a variety of purposes. One of the most significant of those purposes is treatment of water, both in processes for production of potable water and in processes for the treatment of waste water. Ozone is effective as a water treatment agent for the reduction of BOD and COD, VOC&#39;s, and bacterial and viral pathogens, and is also beneficial in the removal of small particles and metal compounds. For a variety of reasons, including the fact that ozone can be efficiently generated at the treatment site, requiring only electricity and dry air, it is rapidly becoming the preferred water treatment agent for use at remote sites and/or in undeveloped regions. Ozone is also increasingly being used in established treatment facilities as a replacement for chlorine. 
     The majority of the ozone used in water treatment facilities is generated in what are referred to as corona discharge generators, in which dry oxygen is passed through a corona discharge field created by imposing a high voltage electrical potential on a conductive electrode that is disposed in proximity to a dielectric material imposed between the electrode and an electrical ground. Most commonly, dried air is the feedstock to the generator and ozone is created from the oxygen component of the air. Dried gas mixtures containing higher concentrations of oxygen, up to and including pure oxygen, may certainly be used, but the additional cost and complexity of that approach is usually not justified by the higher ozone output that can be achieved. For purposes of this application, the feedstock gas is referred to as air, and it is to be understood that other oxygen containing gas mixtures, or pure oxygen, could be used within the scope of the described invention. The high electrical potential difference allows a corona discharge field to form between the electrode and dielectric. As air is passed through that field, some of the molecular diatomic oxygen (O 2 ) is ionized, and some of the ions recombine in triplets as ozone (O 3 ). Most high capacity ozone generators are of the Kerag type, in which ozone is generated in a plurality of ozone generating cells that are contained within a generator enclosure. Each ozone generating cell comprises, typically, an elongate electrode that is suspended within the interior of, but not in contact with, an elongate hollow dielectric tube, typically of glass or ceramic. In ozone generators of the prior art, the dielectric tubes are supported at their upper, open ends, by a support plate or seal plate, with each dielectric tube extending through an aperture in the plate downward into a container of water. The water is used for cooling as well as being a grounded electrical conductor. In the prior art generators, each electrode is supported at its upper end by an electrode support plate which, like the dielectric tube support plate, is penetrated by a plurality of apertures in which the electrodes are positioned to extend through a lower chamber lying between those two supporting plates. Commonly, each electrode includes a fuse that extends upwardly from the electrode to an electrical contact plate through an upper chamber lying between the electrode support plate and the contact plate. Air is drawn into the upper chamber, into the interior of the electrodes, down the electrodes to their open bottoms, into the space between the electrode and dielectric tubes, up through the corona discharge field to produce ozone, and out the open upper end of the dielectric tubes into the lower chamber, from which the mixed air and ozone is withdrawn for use. 
     Corona discharge ozone generators of the prior art are effective at producing ozone, and are fairly reliable. However, the ozone generating process is a high energy process, and the high energy corona discharge field maintained within each ozone generating cell can have destructive effects on the generating cell components, requiring generating cell maintenance and occasional replacement. In an ozone generator of the prior art, any maintenance activity that requires access to one or more of the dielectric tubes requires an almost complete disassembly of the generator. An upper closure plate must first be removed, then the electrical contact plate, and then the electrode support plate and all electrodes supported from it, before the upper ends of the dielectric tubes are exposed. During the procedure of removing the electrode support plate and electrodes, and the reverse process of reinstalling them, the risk of damage to electrodes and dielectric tubes is high. 
     Operational failure of one or more ozone generating cells within an ozone generator of the prior art can also present significant problems in addition to the difficult and time consuming procedure necessary to gain full access to the cells. In the event of a cell failure arising from a dielectric tube fracture, cooling water will immediately enter the tube, electrically short the electrode to ground, and cause the fuse connecting the electrode to the high voltage source to fail. A more significant problem associated with a tube fracture, however, is the potential for flooding of the lower chamber to which all dielectric tubes of the generator open. Water entering that chamber will flood into all dielectric tubes and bring about a catastrophic, cascading failure of all generating cells. 
     A similar problem can result in the event of a back flow of water from downstream in the treatment system of which the generator is a part. In a back flow situation, water will back up in the conduit carrying ozone to distribution, and into the lower chamber of the ozone generator, to which all dielectric tubes open. Water that enters that chamber will flow into all of the dielectric tubes and precipitate a complete failure of the entire ozone generator system by shorting all of the electrodes. 
     The problems and increased risk of failure associated with ozone generating systems of the prior art have not been effectively addressed, and contribute to reluctance to utilize ozone in water treatment operations, especially in circumstances in which generator failures can cause extended down time in the functioning of the treatment facility. There remains a need for an ozone generator system that avoids the disadvantages of the prior art and provides a much more reliable source of ozone. 
     SUMMARY OF THE INVENTION 
     The present invention provides an ozone generating system that addresses the disadvantages of the prior art and substantially eliminates the risk of complete generator failure related to process upset back flow. In the generating system of the invention all dielectric tubes and electrodes are independently accessible without requiring complete removal of an integrated electrode support and electrical contact plate and all electrodes, and the dielectric tubes are in a manner that minimizes the possibility that failure of a single dielectric tube can precipitate a cascading failure of the entire system. The system of the invention also provides an integrated cooling water level control to prevent flooding, and subsequent failure, of the ozone generator in the event of a downstream process water back flow. 
     The preferred structure and features of the generator system of the invention will be described below with reference to the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cut-away side elevation view of a preferred embodiment of the apparatus of the ozone generating system of the invention, showing the integration of components in a single enclosure. 
         FIG. 2  is a front elevation view of the system enclosure of  FIG. 1 . 
         FIG. 3  is a cut-away rear elevation view of the embodiment of  FIG. 1 . 
         FIG. 4  is a partially cut-away top plan view of the system apparatus as in  FIG. 1 , illustrating an array of ozone generating cells of the ozone generator component. 
         FIG. 5  is a side elevation isometric view of the ozone generator of the invention, with water seal assembly, weir assembly, and pressure relief valve, shown in a full visibility view. 
         FIG. 6  is a cut-away side elevation view of the upper portion of the preferred embodiment of the ozone generator of the invention and of the head assembly. 
         FIGS. 7   a  and  7   b  are cut-away side elevation views of a portion of the head assembly as shown in  FIG. 6 , providing greater detail of the structure of the illustrated components. 
         FIG. 8  is a longitudinally separated partial side elevation view of a preferred embodiment of an ozone generating cell, showing details of the electrode assembly. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     In its preferred embodiments the ozone generating system of the invention includes an ozone generator assembly  10  that is combined, as a packaged unit, with an incoming air sensor assembly  11 , an incoming air filter unit  12 , a transformer and electrical power conditioning and control assembly  13 , and a cooling fan unit  14 , all disposed within an enclosure or cabinet  15  that surrounds and protects the system components while providing easy access to them for inspection, maintenance, and the like. 
     The principal component in the ozone generating system of the invention is the ozone generator assembly  10 , in which ozone is produced by passing dry oxygen or a mix of oxygen with other gases through a corona discharge. Typically, the feedstock gas is dried air, but references to “air” in this description shall be taken to include pure oxygen or another oxygen containing gas mixture. Generator assembly  10  comprises a container body  16 , preferably formed as a cylindrical container with a side wall  17 , that has an upper edge  18 , and a closed bottom  19 . A drain aperture  20 , which is in indirect liquid flow communication with the interior of the container body, is disposed in the generator assembly at an elevation between the elevation of bottom  19  and the elevation of upper edge  18  of the container body. The generator assembly also includes a head assembly  21 , preferably also cylindrical like the container body but of slightly larger diameter, coaxially aligned with the container body so that the lower edge  22  of the head assembly is received against the upper edge  18  of the container body in closely fitting relation as the head assembly is releasably connected to the container body to form a water tight seal. It is contemplated that the upper edge  18  of the container body and lower edge  22  of the head assembly will be formed with mating flanges connected by bolts, and in the drawing figures the reference numbers  18  and  22  identify annular flanges around the top of the container body and the bottom of the head assembly. However, the specific manner of connection of the head assembly to the container body is not a significant feature of the invention, and any effective manner of releasably connecting those components may be used. 
     Head assembly  21  includes an upper, air chamber  23  and a lower, ozone chamber  24  immediately below the air chamber, both surrounded by a head assembly side wall  25 . An upper closure plate  26  extends across the upper edge  27  of the head assembly side wall  25 , and is preferably releasably connected thereto, so that the upper closure plate may be removed to provide access to the interior of the head assembly without removing the head assembly from the container body. Again, it is contemplated that upper edge  27  of side wall  25  will be formed as an annular flange to which the outer perimeter of the upper closure plate is connected, but any effective manner of connection may be used. Intermediate the upper and lower edges of side wall  25 , an annular ledge  28  extends from the inner surface of side wall  25  inwardly a sufficient distance to provide a stable support for a contact plate support ring  29  at the transition between the upper and lower chambers of the head assembly. Ring  29  is an annular ring with an outer edge  30  at the perimeter of the ring, and an inner edge  31 . In the preferred embodiment of ring  29 , a notch is formed around the ring at the intersection of edge  30  and the lower surface  32  of the ring, providing a ledge  33  to be received upon ledge  28  so as to suspend the contact plate support ring in the interior of the head assembly. Similarly, a notch is formed at the inner edge  31 of ring  29  at the intersection of that inner edge with ring upper surface  34 , providing an annular ledge  35  extending around the inner edge of contact plate support ring  29 . Ring  29  is formed of an insulating material, preferably but not limited to ceramic or plastic, to electrically isolate components that are in direct contact with the ring but not in contact with each other. Further, ring  29  is sealed against ledge  28  by, preferably, O-ring gasket  36  extending fully around the intersection between ledge  33  of the ring and ledge  28  of the head assembly to form an air tight and water tight seal. The connection of ring  29  to ledge  28  may be made by any convenient conventional means within the scope of the invention. Ring  29  may be formed as a continuous body, or maybe divided into two or more segments, if desired, within the scope of the invention. 
     A contact plate  37 , configured and dimensioned so that the perimeter edge portion  38  of the contact plate is received on ledge  35  of support ring  29  with the contact plate extending fully across and filling the space surrounded by ring  29 . An air tight and water tight seal is formed between ledge  35  and contact plate  37  by an O-ring gasket  39  extending fully around ledge  35 . The connection of the contact plate to the support ring may be made by any convenient conventional means, so long as the components remain electrically isolated. The combination of ledge  28 , support ring  29 , and contact plate  37  defines the bottom of upper chamber  23  of the head assembly and divides the upper chamber from lower chamber  24 . Contact plate  37  is formed of an electrically conductive material, preferably stainless steel, and functions to electrically connect electrodes of corona discharge ozone generating cells, described below, to transformer assembly  13  through high voltage lead  40 , connected to contact plate  37  by terminal  41 . 
     As an alternative to connecting high voltage lead  40  directly to contact plate  37 , contact may be made through an electrical conductor disposed within support ring  29 , that makes contact with the contact plate when the contact plate is connected to the support ring. In this embodiment an insulated channel is formed in support ring  29  and an electrical conductor is disposed in and through the channel to one or more electrical contacts within, e.g., ledge  35  formed at the inner edge of ring  29 . When the contact plate  37  is received upon ledge  35  and connected to ring  29 , an electrical connection between the ring and the contact plate is established. In this embodiment, a conductor establishing contact between ring  29  and the exterior of the head assembly is disposed within an insulated tower that extends from contact with ring  29  through either upper closure plate  26  of the head assembly or through side wall  25  in sealed relation therewith. High voltage lead  40  is connected to the conductor at the outer end of the insulated tower. 
     To provide a passageway for the flow of air from the upper chamber of the head assembly to ozone generating cells, described below, contact plate  37  is penetrated by a plurality of apertures  42 . Apertures  42  are spaced through the central portion of the contact plate inward from the perimeter portion  38  so that none of the apertures penetrate the portion of contact plate  37  that overlies ledge  35  of support ring  29 . Apertures  42  are grouped in sets, and the sets of apertures are disposed in a selected pattern across the contact plate. 
     The lower end of head assembly  21 , opposite upper closure plate  26 , is closed by seal plate  43 , which extends fully across the lower end of the head assembly between side wall  25 , adjacent to lower edge  22  of the head assembly, and generally defines the bottom of lower chamber  24  of the head assembly. Seal plate  43  may be removably connected to side wall  25 , and/or lower edge  22 , may be permanently connected to the sidewall and/or lower edge, or may be integrally formed with lower edge  22  as a blank flange plate that extends fully across the lower end of the head assembly and is connected to the lower end of the side wall. Although convenient, removability of the seal plate is not necessary to provide access to the internal components of the ozone generator of the present invention. The specific structure of upper and lower closures for the generator head assembly is not critical to the invention, and variety of designs in addition to those mentioned above may be used within the scope of the invention. 
     Seal plate  43  is penetrated between upper face  44  and lower face  45  by a plurality of apertures  46 , disposed in a selected pattern across the seal plate. The pattern of disposition of apertures  46  is the same as the pattern of disposition of the sets of apertures  42  in contact plate  37 , so that each aperture  46  will be positioned directly below a set of apertures  42  in the final alignment and connection of head assembly components. Each of apertures  46  extends into seal plate  43  from upper face  44  the majority of the distance to lower face  45  at a first diameter, and then narrows to a second, smaller diameter through the remainder of the distance to lower face  45 , forming an annular ledge  47  at the transition between the two diameters. The larger diameter portion of each aperture  46  above ledge  47  is threaded. 
     Ozone generator assembly  10  also includes a plurality of ozone generating cells  48 , within each of which a corona discharge is created and ozone is generated from air that is flowing through the corona discharge within the cell. Each generating cell in a typical corona discharge type ozone generator basically comprises an electrode and a dielectric tube within which the electrode is suspended and from which the electrode is electrically separated. When the electrode is connected to a high voltage source, the high potential difference across the dielectric allows the creation of a corona discharge field between the electrode and the dielectric. When dry air or oxygen is passed through the corona discharge field, the incoming oxygen, which is in the O 2  molecular form, is ionized and a portion of the ions recombine as O 3 , known as ozone. 
     Each generating cell  48  includes as necessary operational components an insert  49 , a dielectric tube  50 , and an electrode assembly  51 . Insert  49  comprises a hollow body, formed of an insulating material, with an open upper end  52  and an open lower end  53 . The height of insert  49  between upper and lower ends is less than the height of the lower chamber of the head assembly between contact plate  37  and seal plate  43 . The edge of insert  49  at upper end  52  is preferably formed with a plurality of notches or slots extending into the insert from upper end  52 , to provide gas outlet passages through the wall of the insert at its upper end. The preferred number of slots is four, but the number may vary within the scope of the invention. Intermediate the upper and lower ends, insert  49  is functionally divided into two portions; a lower, outside threaded cylindrical portion  54  and an upper, preferably non-threaded, portion  55 , in which the slots referred to above are formed. In addition to providing passages from the interior of insert  49  to the exterior, the slots formed in portion  55  are designed to be engaged by a insertion and removal tool that is used to rotate the insert around its longitudinal axis. Alternatively, Portion  55  may be formed with a polygonal cross-sectional configuration, to allow that portion of the insert to be engaged by a conventional wrench for insertion and removal, so long as provision is made for the passage of gasses from the interior of insert  49  to the lower chamber of the head assembly. In assembly of the ozone generator, the lower portion of insert  49  is threaded into one of apertures  46  in seal plate  43  from the upper face of the seal plate until the lower end of the insert is received on ledge  47  near the lower face of the seal plate. An O-ring gasket  56  is disposed between the lower end of the insert and the ledge, to form a gas and liquid tight seal. 
     Each of dielectric tubes  50  comprises an elongate cylindrical tube with an open upper end  57  and a closed lower end  58 . It is preferred that tubes  50  be formed of glass, but other dielectric materials, such as a ceramic material, may be used within the scope of the invention. The outside diameter of tube  50 , especially at its upper end  57 , is slightly less than the inside diameter of the lower portion of the insert  49 , so that the upper portion of the tube may be extended fully through aperture  46  without interference, and inserted into the interior of insert  49  through lower end  53 . As insert  49  is tightened in aperture  46 , O-ring  56  will expand across the space between the outer surface of the dielectric tube and the inner surface of the insert to seal that space as well as sealing between the lower end of insert  49  and ledge  47 . In a variation, or alternative approach, a packing ring or sleeve  59  may be disposed between the outer surface of the dielectric tube and the inner surface of the insert, above the lower end of the insert, in addition to O-ring  56 . In addition to providing a secondary seal, the use of packing  59  between the tube and insert would also provide at least a mild frictional connection between them. 
     Electrode assembly  51  comprises an elongate hollow electrically conductive electrode tube  60 , preferably metallic, with an open upper end  61  and an open lower end  62 . An electrically conductive bayonet tube  63 , of smaller diameter than tube  60 , extends partially through the upper end  61  into tube  60  in coaxial alignment with the electrode tube. Connection between the bayonet tube and the electrode tube is made by an annular connector  64 , which is disposed in, and fills, the space between the outer surface of the bayonet tube and the inner surface of the electrode tube, so that gas flowing down the bayonet tube is allowed to flow into and down the interior of the electrode tube but not through the connection between the bayonet tube and the electrode tube. Annular connector  64  also establishes electrical contact between bayonet tube  63  and electrode tube  60 . The upper end of bayonet tube  63 , which extends outwardly from connector  64 , is received into the interior of electrode insulator  65  through its lower end  66 , and is releasably connected therein such that the bayonet tube, plug, and electrode tube are all suspended from and supported by the electrode insulator. An O-ring gasket  67  is disposed around the bayonet tube between the lower end  66  of the electrode insulator and the upper end of electrode tube  60 , to seal the connection between them. 
     Electrode insulator  65  comprises an elongate hollow member with an upper end  68  opposite lower end  66 . The portion of insulator  65  adjacent to upper end  68  is formed as a hollow support block  69 , which has an outside diameter generally equal to the outside diameter of insert  49 . The lower portion of the electrode insulator, from block  69  to lower end  66 , is of the same diameter as lower and  66 . The configuration and dimensions of electrode insulator  65  allow the lower end  66 , with the connected bayonet tube and electrode tube suspended below it, to be inserted through insert  49  and into the interior of dielectric tube  50  until further movement is arrested when support block  69  is received on the upper end of insert  49 . In order for an ozone generating cell to operate, an electrical connection must be established between the electrode tube, through the bayonet tube, and a high voltage source. The electrical path is completed by contact spring  70  and fuse  71 . Spring  70  is disposed in the interior of electrode insulator  65  with its lower end in contact with bayonet tube  63 , and fuse  71  is disposed above spring  70 , with the lower end  72  of the fuse in contact with spring  70  and the upper end  73  extending outwardly above support block  69 . 
     In the complete ozone generator of the invention, the number of inserts, dielectric tubes, and electrode assemblies is the same, and is equal to the number of apertures  46  in seal plate  43  and to the number of sets of apertures  42  in contact plate  37 . An insert, dielectric tube, and electrode assembly is installed in each aperture  46  as described above. When the contact plate is positioned during assembly of the generator, the outer edges of hollow support blocks  69  are brought into contact with the lower surface of the contact plate around apertures  42  and the upper end of fuse  71  is brought into electrically conductive contact with the contact plate. An O-ring gasket  74  is disposed between the upper end of support block  69  and the lower surface of contact plate  37  to prevent gas flow from apertures  42  into the lower head assembly chamber  24 . To accommodate any dimensional variations and to assure that the electrode insulator and O-ring  74  remain firmly seated against the contact plate, a wave spring  75  is disposed between the upper end of insert  49  and the lower end of support block  69 , with a washer  76  between the wave spring and the surface against which the spring force is applied. 
     In an assembled unit of the generator of the invention, dielectric tubes  50 , connected to seal plate  43  with inserts  49 , extend into the interior of the container base where they are surrounded by cooling water. The lower ends  58  of tubes  50  may be received upon a supporting structure or pad near the bottom of the container base, or the tubes may be hung freely without support, as desired, within the scope of the invention. The cooling water in the container base absorbs heat created by the corona discharge in the generator cells, and is continuously exchanged during operation of the generator to remove the excess and potentially damaging heat. Heated water from the generator may be circulated in a closed loop with heat exchange to cool the water before returning it to the generator, the water may be discharged and replaced with fresh, cooler water, or a combination of those two approaches may be used. The manner in which cooling water is used within the system of the invention is not significant to the scope of the invention, and will be determined by specific conditions and water availability at each site where the generator system is used. 
     Electrode assemblies  51 , which, like dielectric tubes  50 , are suspended by inserts  49  and also supported by seal plate  43 , extend from insert  49  downward into the dielectric tubes, and upward through the lower, ozone chamber of the head assembly to make electrical contact with contact plate  37 . Contact plate  37 , and the components supporting it in the head assembly, separate the upper, air chamber of the generator head assembly from the lower, ozone chamber, and it will be understood that the design of the ozone generator of the invention avoids positioning any of the generator cell components in the upper, air chamber of the head assembly. It is also to be understood, as can be seen from the drawing figures, that insert  49  extends upwardly above seal plate  43  through the majority of the height of the lower, ozone chamber of the head assembly in which it is disposed, and that the ozone containing gas exiting from the generator cell exits through the top of insert  49 . 
     It will be seen and understood that the structure of the ozone generator of the present invention eliminates the need for an electrode support plate that, in prior art devices, divides the upper, air chamber of a head assembly from the lower, ozone chamber of the head assembly, and to which all electrode supports and insulators are connected. In the prior designs the dielectric tubes are supported by a plate, similar to seal plate  43 , that closes the bottom of the head assembly, and prior art electrode assemblies are suspended from the additional electrode support plate. The electrode assemblies extend within the dielectric tubes but remain completely physically independent of the tubes as well as electrically isolated from them. In the structure of the ozone generator of the present invention, each generator cell comprises an electrode assembly and dielectric tube assembly that are physically connected but electrically isolated from each other, and each is independent of the other cells. With the prior art designs, it is necessary to remove the electrode support plate and all electrode assemblies, after the contact plate is removed, in order to gain access to any of the dielectric tubes. If the electrode support plate and electrodes are removed together, great care must be used in lifting the support plate and electrodes so that the plate and electrodes are lifted straight up, without rotation, to avoid destroying electrodes and/or dielectric tubes. Alternatively, each electrode in a prior art device may be individually removed from the support plate and lifted from the associated dielectric tube before the electrode support plate is removed to provide access to the dielectric tubes. With the generator of the present invention, however, removal of the contact plate allows each electrode assembly and each dielectric tube assembly to be accessed individually. A single electrode assembly can be easily and quickly replaced by removing that electrode assembly from its dielectric tube, which is accomplished by lifting the electrode insulator and suspended electrode from the dielectric tube, and sliding a replacement electrode assembly into place. Similarly, each dielectric tube can be individually accessed and replaced by removing the electrode assembly from that tube and then unscrewing the insert and suspended tube from the seal plate. A new dielectric tube and insert can be installed just as easily and quickly as the old one was removed. The improved accessibility to the ozone generator components provided by the present invention will very significantly reduce the down time associated with generator maintenance in comparison to the prior art, with directly resulting reductions in labor costs and lost operational time. 
     In the operation of the system of the invention, produced ozone will be drawn from the generator by the suction created in an ozone distribution unit, which mixes ozone containing gas with, e.g., wastewater, in the course of treatment. The ozone distribution unit develops an inlet suction that reduces the pressure within the ozone generator to below the ambient air pressure external to the generator, and draws air into and through the generator, along with the produced ozone. Dry air is supplied to the system apparatus from an outside source, and is drawn through air filter unit  12  at a controlled flow rate measured by sensor assembly  11 , and into the upper chamber of the generator head assembly. In addition to the flow rate sensor, assembly  11  also preferably includes a dew point sensor to monitor the moisture content of the air entering the generator. From the upper chamber the dry air is drawn through apertures  42  in contact plate  37 , into and through the hollow interior of electrode insulator  65 , and into the interior of electrode tube  60 , to which a high voltage electrical potential is applied. 
     Electrical power requirements of the system of the invention are satisfied by drawing upon a source of electricity outside the boundaries of the system of the invention, and utilizing transformer assembly  13  to create a high voltage potential difference between opposite poles. A power conditioning unit, for smoothing variations and fluctuations in the electrical supply, may be provided between the electrical supply and the transformer assembly if desired or deemed appropriate. One side of the high voltage potential is connected to contact plate  37  through high voltage lead  40 , through any intervening conductors, and is separated from ground by the air space between the electrode tubes  60  and dielectric tubes  50  and by the dielectric tube material itself. Ground, relative to the high voltage supply, is established through the generator body and the cooling water in the container body surrounding the dielectric tubes. The high potential difference that exists across the gap between and along the surfaces of the tubular electrode and the dielectric tube creates a corona discharge within the gap. 
     Air drawn into the generator cell is drawn down the interior of the tubular electrode and back up the dielectric tube between the outside surface of the electrode tube and the inside surface of the dielectric tube, through the corona discharge. As the air passes through the field, diatomic molecular oxygen is split into oxygen atoms and ionized. Some of the oxygen ions recombine in triplets to form ozone, and the remainder recombine into diatomic molecular oxygen. The ozone containing gas is drawn to the top of the dielectric tube, into the lower chamber of the head assembly through the notches or other gaps between the upper end of insert  49  and the lower surface of support block  69  of the electrode insulator, and from the lower chamber of the head assembly through an ozone exit port  77  and through a water seal assembly  78  to the ozone distribution unit. 
     The use of a water seal in ozone generators is known in the prior art, but in the prior art these assemblies are separate from the ozone generator and may be disposed at some distance from it. In the present invention, water seal assembly  78  is a part of the ozone generator itself, a unique configuration that provides certain advantages and benefits that have not been accomplished by the prior art. In the generator of the invention, ozone containing gas exits from the lower chamber of the head assembly through exit port  77 , formed in head assembly side wall  25 , and into a plenum  79  that is formed as a part of the head assembly. The specific disposition and configuration of plenum  79  is not critical, but it is preferred that the bottom closure  80  of the plenum be in generally the same plane as seal plate  43 . Bottom closure  80  may be integral with seal plate  43 , or may be a separate component. 
     Water seal assembly  78  includes an elongate open ended outer tube  81 , that is connected at its upper end  82  to bottom closure  80  of plenum  79 , around an aperture  83  that penetrates bottom closure  80 . Tube  81  extends downwardly from bottom closure  80  to its lower end  84  within a drain chamber  85  disposed within, or adjacent to and in water flow communication with, generator container body  16 . In the preferred embodiment, drain chamber  85  is formed within container body  16 , either as an integral part or as a separate component that is connected within the container body. Drain aperture  20  connects directly to the interior of drain chamber  85 , rather than to the major portion of the interior of the container body. Drain aperture  20  is disposed and connected to drain chamber  85  above the lower end  84  of outer tube  81 , so that when water is added to the drain chamber the lower end of the outer tube will be submerged before the water level reaches the drain aperture and is allowed to exit drain chamber  85  through that aperture. The bottom of drain chamber  85  is closed, either by bottom  19  of the container body if the chamber extends fully to the bottom of the container body, or by a separate bottom closure, so that the only connection between the interior of drain chamber  85  and the interior of the container body is at upper edge  86  of the drain chamber. An ozone tube  87 , for conveying ozone containing gas from the ozone generator system, extends from the exterior of the generator head assembly, preferably through the top closure, through plenum  79 , and through plenum bottom closure  80  in the interior of and in concentric, coaxial relationship with outer tube  81 . Ozone tube  87  is of smaller cross-sectional dimension than outer tube  81 , leaving an annular space  88  between the outer surface of the ozone tube  87  and the inner surface of the outer tube  81 . Ozone tube  87  extends below bottom closure  80  a shorter distance than outer tube  81 , so that the lower, open end  89  of ozone tube  87  is above the lower end  84  of tube  81 , and is also above the level of drain aperture  20 . 
     Cooling water is preferably introduced to the interior of the container body through an inlet disposed near container bottom  19 , and exits through aperture  20  after flowing from the container body into drain chamber  85 . The level of cooling water within the container body  16  is controlled and maintained by weir assembly  90 , disposed between the main container body  16  and drain chamber  85 , adjacent to upper edge  86  of that chamber. In the preferred embodiment, drain chamber  85 , and weir assembly  90 , are disposed outside the interior of container body  16  and connected to the outer surface of container body side wall  17 . In this embodiment weir assembly  90  includes a hollow weir box  91  with a closed bottom. The top of the weir box will underlie, and be effectively closed by, either flange  18  at the upper edge of the container body side wall, or flange  22 , at the lower edge of the head assembly side wall, depending upon design and construction decisions that are not critical to the scope of the invention. It is preferred that a transparent sight glass be disposed in the weir box to provide a view of the interior of the weir box and the level of the cooling water within the container body, but the sight glass could be omitted if desired. In the preferred embodiment, box  91  is connected to side wall  17  of the container body, around a substantially rectangular aperture  92  in the container body side wall that is open between the interior of the container body and the interior of the weir box. The upper edge  93  of aperture  92  is disposed below the upper edge  18  of side wall  17  a distance slightly greater than the distance across the air space to be maintained between upper edge  18  and the surface of the cooling water in the container body. In the preferred embodiment the distance through that air space is approximately two inches, and the upper edge  93  is disposed approximately one-eighth inch below the cooling water surface, but other dimensions could be used. It will be understood that weir box  91  may be formed in various ways and still accomplish the same function. Box  91  may be formed with two side walls disposed perpendicular to each other, with the outer edge of one side wall and an outer edge of the bottom closure connected to the container body side, and with the outer edge of the other side wall and the other outer edge of the bottom connected to the adjacent wall of the drain chamber. Box  91  may also be formed with three side walls and a bottom, leaving one open side, and connected to side wall  17  by connecting the free edges of the two opposing side walls and the free edge of the bottom to the container body side wall. In a third approach, box  91  may be formed with four connected side walls and a bottom, and connected to sidewall  17  by placing one of the weir box side walls against the container body wall and connecting the two walls to each other. In this alternative structure, an aperture matching aperture  92  is formed in the weir box side wall connected to the container body wall and aligned with aperture  92 . 
     In a design in which the drain chamber is disposed within the container body, weir assembly  90  is also disposed with the container body, and aperture  92  is formed in one of the side walls of weir box  91  rather than in side wall  17  of the container body  16 , since in this configuration cooling water enters the weir box without passing through the container body side wall. 
     In both of these design approaches, weir assembly  90  includes a weir  94 , over which water may flow from the interior of the weir box into the interior of the drain chamber. In the illustrated embodiment, weir  94  is formed by cutting a slot in the side wall or walls separating the interior of the weir box from the interior of the drain chamber. In a construction in which the weir box interior and the drain chamber interior are separated by two walls received against and connected to each other, the slot for weir  94  is sealed around the three edges of the slot so as to prevent water from entering any space between those walls. The upper edge  95  of weir  94  is positioned at the elevation at which the level of cooling water in container body  16  is to be maintained, which is slightly above the upper edge of aperture  92 . If the space between the surface of the cooling water and the upper edge  18  of the container body side wall is approximately two inches, the upper edge  95  of weir  94  is the same approximately two inches below upper edge  18 , and approximately one-eighth inch above the upper edge of aperture  92 . 
     As the container body of the generator is filled with water and the water level reaches the elevation of the lower edge of aperture  92 , water will flow through aperture  92  and fill the weir box  91  while the remainder of the container body is filled. When the water level in the weir box reaches the upper edge  95  of weir  94 , the water will begin to flow over the weir into drain chamber  85 , within which the water level will rise until it reaches the level of drain aperture  20 . Any additional water flowing over weir  94  into the drain chamber will drain out through aperture  20 . It will be understood that, once drain chamber  85  is filled, the water level in the drain chamber is independent of the water level in container body  16 , so that if the cooling water level in the container body is allowed to drop there is no effect on the level of water in the drain chamber, and the flow of air and ozone through the generator may continue until the flow of cooling water is resumed, or until the generator is shut down. 
     Although ozone generators can operate for extended periods with relatively few operational problems, those of the prior art, especially, can be adversely affected by problems arising from both internal causes and external causes. The two problems of most concern are the internal failure of a generating cell, resulting from or involving fracture of a dielectric tube, and an external problem with an ozone distribution unit that causes a back flow of water into the ozone generator head assembly. 
     When an ozone generating cell fails, with fracture of the dielectric tube, cooling water is allowed to enter the dielectric tube and short circuits the associated electrode, causing the fuse that connects the electrode to the contact plate to open and removing power from the failed generating cell. Other generating cells that are not affected by the initial failure and electrical short will continue to function and the generator may continue in service if flooding of the generator head assembly can be avoided. If the suction that draws air and ozone through the generator is sufficiently high and the pressure within the lower chamber of the head assembly is sufficiently below the ambient, external pressure, cooling water that enters the fractured dielectric tube will be drawn upward into the lower, ozone, chamber of the head assembly. From that chamber, water may flow into intact dielectric tubes of other generating cells through the ozone exit path, and cause an immediate failure of each such cell. The entry of even a small amount of liquid water or water vapor into a generating cell can cause cell failure, or, even if the dielectric tube does not fail, will cause a significant reduction in ozone production and a significant increase in the creation of very undesirable nitrogen oxides and acids. 
     The generator of the present invention addresses this problem in several ways. In the preferred manner of operation of the generator of the invention, the pressure differential between the interior of the lower chamber of the head assembly and the atmosphere around the generator is relatively low. A pressure differential of about two inches of water is preferred, though other values could be used. The selected pressure differential will be sufficient to maintain the flow of air/oxygen and ozone through the generator for effective operation of the generator, and to supply ozone to meet downstream processing needs, without being sufficiently high to draw water into the head assembly of the generator of the invention. In the generator of the invention, the level of the cooling water in the base container is maintained at a distance below the bottom of the seal plate of the head assembly, and the ozone outlet of each insert connected to the seal plate is disposed relatively high above the seal plate and near the contact plate that divides the lower chamber of the head assembly from the upper chamber. In the ozone generator of the invention, the pressure differential with which the generator operates is insufficient to draw cooling water up a dielectric tube over the distance of the gap between the cooling water level and the outlet from the dielectric tube in almost all circumstances, and the entry of water into the lower chamber of the head assembly is very unlikely. Even if water does enter that chamber, it would be necessary for the water to essentially fill the chamber before reaching the level of the ozone outlet from the generating cells and entering the dielectric tubes. As an additional measure to prevent cooling water from being drawn into the head assembly, the generator of the invention further includes a pressure relief valve  96 , disposed in an aperture  97  that forms a gas flow passageway between the lower chamber of the head assembly and the water seal drain chamber or the container body below the seal plate. If the pressure differential between the lower chamber of the head assembly and the interior of the container body, which is in communication with and thus at the same pressure as the drain chamber, exceeds the threshold pressure for the pressure relief valve, the valve will open and the pressure differential between the two spaces will be reduced. When the pressure differential is reduced to below the pressure relief valve threshold value, the valve will close. The pressure relief valve will maintain the pressure differential within a selected range that is sufficient to draw gas through the generator, but not so high as to draw cooling water into the lower chamber of the head assembly. 
     Flooding of the generating cells can also occur in the event of a back flow of water from an ozone distribution unit because of problems downstream from the ozone generator. In ozone generator designs of the prior art, ozone is drawn directly from the lower chamber of the generator head assembly, typically through an outlet port in the side wall of the head assembly, and any back flow of water from downstream enters directly into that chamber. Water under sufficient back flow pressure to enter the generator head assembly will almost certainly flood that chamber and flow, more or less simultaneously, into all dielectric tubes in the generator and precipitate a catastrophic generator failure. 
     During normal operation of the generator, the suction produced by the downstream ozone distribution unit draws the ozone produced in the generating cells into the lower chamber of the head assembly, through aperture  83  in plenum bottom closure  80  through the interior of outer tube  81 , into the lower end of ozone tube  87 , and through that tube to the distribution unit. In the event of a downstream upset that forces water to flow back upstream to the ozone generator, the back flow water will enter the generator through ozone tube  87  and be released from the lower end  89  of the ozone tube. If the conduit carrying ozone from the generator were connected directly to the lower chamber of the head assembly, water back flow to the generator would, as noted above, be forced directly into that lower chamber. In the ozone generator of the invention, however, water back flowing from downstream into the integrated generator system will be confined within ozone tube  87  as it passes through the ozone generator head assembly, and none of the water will be released into the head assembly. Instead, the water will be released from the lower end of ozone tube  87  into outer tube  81 , from which it flows from the open bottom of tube  81  into drain chamber  85 , from which it then exits the generator structure through drain aperture  20 . Because water back flowing into the ozone generator passes through the water seal assembly only, and not into any portion of the generator head assembly or container body outside the drain chamber, the only effect on the generator of the invention is a cessation of ozone production. No damage will be done to the ozone generator, and the generator can be returned to service immediately when the downstream problem causing the back flow is corrected, saving both generator repair or replacement cost and processing time that would otherwise be lost. Integration of the water seal structure with the generator in the same enclosure facilitates monitoring and coordinated control of the ozone generator and the protective flow control systems to a degree not available in the prior art. 
     The foregoing description of the ozone generator system of the invention is intended to be illustrative and not limiting. It is contemplated that others of skill in the art may devise additional alternative embodiments and variations on the basis of that illustrative disclosure, all within the scope of the invention in accordance with the following claims.