Abstract:
The present invention relates to both a method and a device for removing Volatile Organic Compounds (VOC) from gaseous streams in conduits, chimneys and/or exhaust ducts. The method is especially useful in eliminating a large variety of pollutants, and especially organic odorous pollutants such as mercaptans and sulfurous compounds. The method is based on the principle of direct oxidation of the pollutants by ozone and the conversion of these pollutants into non-harmful products, and comprises the steps of: a) providing an electrical corona discharge reactor capable of producing ozone; b) supplying an electric current to the corona discharge reactor; and c) causing the gaseous effluents to flow through the reactor. With this method, the volatile organic compounds contained in the gaseous effluents are oxidised by the ozone produced by the corona discharge reactor. The present invention also relates to a device for reducing this method into practice, this device being a corona discharge reactor comprising two concentric electrodes producing ozone.

Description:
BACKGROUND OF THE INVENTION 
     a) Field of the Invention 
     The present invention relates to both a method and a device for removing ecologically noxious Volatile Organic Compounds (VOC) from gaseous streams in conduits, chimneys and/or exhaust ducts. The method is based on the principle of the direct oxidation of VOC by ozone and is especially useful in eliminating a large variety of organic odorous pollutants, such as mercaptans and others sulfurous compounds, by converting them into non-harmful, environmentally friendly products. 
     b) Description of the Prior Art 
     To carry out the elimination of Volatile Organic Compounds (VOC) and other organic compounds from gaseous effluents, it is known to adsorb them with activated carbon or with a fibrous bed. It is also a common practice to use aqueous solutions to scrub the gases and thereby remove the VOC. Another method is to bum and destroy the VOC by the action of heat, combined or not with metal catalysts, using a thermal incinerator. The problems related with these methods are numerous. The activated carbon adsorption method requires frequent regeneration (steam, hot nitrogen or thermal) and regular replacement of the activated carbon. The water scrubber method requires the separation of the solvents from the soiled water prior to their reintroduction into the scrubber while the thermal incineration requires the burning of fuel to maintain an appropriate temperature inside the incinerator. Accordingly, all of these known methods not only demand high capitalization costs but they are further very expensive to operate. 
     A simpler approach is the use of High Energy Corona (HEC) which permits the removal of ecologically noxious substances from gases at relatively low temperatures. U.S. Pat. Nos. 5,542,967 and 5,601,633 disclose respectively an apparatus and a method using an electrical precipitator wherein a stream of gases is subjected to micro plasma discharges. These electrical discharges break down the VOC into carbon and other by-products like a micro-incinerator. However, the method and apparatus described in these two patents are expensive to use due to their high energy demand. They are furthermore different from the present invention in that they require a power supply and a multi-stage Fitch generator in order to provide the very high voltage necessary to produce the electrical discharges. They also aim in producing highly active intermediate substituents other than ozone. 
     Recently, U.S. Pat. No. 5,573,733, disclosing an ozone generator was granted to the present inventor. The technology behind this ozone generator is innovative and could be used in the treatment of gaseous effluents. By creating a very oxidizing environment one could fully or partially break down the organic pollutants contained in gaseous effluents and transform these pollutants into more environmentally friendly products such as H 2 O, CO 2  and SO 2 . 
     Accordingly, there is thus a need for a simple, efficient and cheap reactor and method thereof which are based on the use of ozone for the treatment of polluted gaseous effluents. The present invention fulfils these needs and avoids or overcomes the various previously mentioned disadvantages of the prior art. The present invention also fulfils other needs as will be apparent to those skilled in the art upon reading the following specification. 
     SUMMARY OF THE INVENTION 
     A main object of the invention is to provide an efficient and economical method for the treatment and purification of gaseous effluents containing a large variety of pollutants such as those found in the effluents of many organic processing plants (petrochemicals, solvent manufacturing, solvent recycling, waste water lift stations, insecticides, pesticides, and food industries such as in the baking &amp; frying sectors). 
     The method according to the invention permits the purification of air or of any gaseous stream by the in situ oxidation of pollutants thereby removing the undesirable oxidation products. More specifically, a first object of the invention is to provide a method for the oxidation of volatile organic compounds contained in gaseous effluents, comprising the steps of:
         a) providing an electrical corona discharge reactor capable of producing ozone;   b) supplying an electric current to the corona discharge reactor in order to generate corona discharge; and   c) causing the gaseous effluents to flow through the corona discharge reactor;
 
whereby the volatile organic compounds contained in the gaseous effluents are oxidised by the ozone produced by the corona discharge reactor.
       

     To improve its efficacy, the method of the invention further preferably comprises at least one of the additional steps of:
         d) causing the gaseous effluents to contact a metal catalyst whereby volatile organic compounds remaining in the gaseous effluents are further oxidised; and/or   e) subjecting the gaseous effluents to UV radiation, whereby volatile organic compounds remaining in the gaseous effluents are further oxidised.       

     Another object of the invention is to provide a device allowing to carry out the aforesaid method. Accordingly, the invention provides an electrical corona discharge reactor for the oxidation of volatile organic compounds contained in gaseous effluents, comprising at least two concentric spaced apart electrodes between which the gaseous effluents flow. An outer hollow cylinder incorporates a first electrode. The outer cylinder has an inner surface and an outer surface and forms an outer duct wherein the gaseous effluents flow. The outer surface of the outer cylinder incorporates the first electrode. An inner cylinder incorporates a second electrode and has an outer surface facing the inner surface of the outer cylinder. The inner cylinder is concentrically positioned inside the outer cylinder and also spaced apart and electrically insulated therefrom. When an electric current is supplied to the reactor, ozone is produced between the two electrodes, the ozone produced oxidises the volatile organic compounds contained in the gaseous effluents. 
     Advantageously, the outer surface of the inner cylinder is provided with a plurality of protrusions that may be coated with a metal catalyst. 
     Preferably the inner cylinder is hollow and forms an inner duct inside and insulated from the outer duct. It is then possible to flow a gas or a liquid inside the inner duct to regulate the temperature inside the reactor. Generally, a flow of a cooling gas or of a cooling liquid will circulate into the inner cylinder to lower the temperature into the reactor. 
     Steps a) to e) of the method of the invention may be advantageously reduced to practice using a device incorporating in a single reactor all the necessary elements. It is thus another object of the invention to provide an electrical corona discharge reactor for the oxidation of volatile organic compounds contained in gaseous effluents, comprising at least two concentric spaced apart electrodes between which the gaseous effluents flow, wherein:
         an outer hollow cylinder incorporates an electrode, the outer cylinder having an inner surface and an outer surface and forming an outer duct wherein the gaseous effluents flow. The outer cylinder is made of a dielectric and UV permeable material and its outer surface is coated with a material both UV permeable and electrically conductive;   a hollow inner cylinder incorporates a second electrode. The hollow inner cylinder has an outer surface facing the inner surface of the outer cylinder. The outer surface of the inner cylinder is preferably coated with a metal catalyst and comprises a plurality of protrusions. The inner cylinder is concentrically positioned inside the outer cylinder, spaced apart and electrically insulated therefrom. The hollow inner cylinder forms an inner duct wherein a gas or a liquid can flow inside in order to regulate the temperature into the reactor; and   at least one electric UV lamp capable of producing UV rays is positioned close to the outer surface of the outer cylinder.       

     In use, ozone is produced between the two electrodes of the reactor when an electric current is supplied thereto. The ozone produced oxidises the volatile organic compounds contained in the gaseous effluents flowing inside the said reactor, and the metal catalyst and the UV rays further oxidise the volatile organic compounds remaining in the gaseous effluents. 
     The present invention will be better understood with reference to the following non-restrictive description of several preferred embodiments of the invention, made with reference to the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a chimney incorporating an electrical corona discharge reactor according to the invention for treating the effluents with ozone. 
         FIG. 2  is a top plan view of an electrical corona discharge reactor capable of producing ozone according to a preferred embodiment of the invention, with an enlargement showing an end of an ozone producing tube through which the gaseous effluents flow. 
         FIG. 3  is a side elevational view of the inside of the electrical corona discharge reactor of  FIG. 2  provided with four ozone producing tubes and three UV lamps. 
         FIG. 4  is a longitudinal cross-sectional view taken along lines  4 — 4  of  FIG. 3  of the inside of the electrical corona discharge reactor, said view showing a portion of the inside of two ozone producing tubes. 
         FIG. 5  is a longitudinal cross-sectional view taken along lines  5 — 5  of FIG.  4 . 
         FIG. 6  is a top cross-sectional view of an ozone producing tube taken along lines  6 — 6  of FIG.  5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention aims to provide a simple, efficient and economical method for the oxidation of Volatile Organic Compounds (VOC), as well as other undesirable compounds such as H 2 S, NH 4 , mercaptans, and chlorinated solvents which can be present in gaseous effluents, by the use of ozone (O 3 ). Ozone is known to be an unstable, powerfully oxidizing agent with the ability to break down VOC, H 2 S and NH 4  into H 2 O, CO 2 , SO 2 , and other by- product(s) as depicted in this very simple equation: 
                        
 
     As documented in the prior art and depicted in the above equation, UV light, heat, and metal catalysts aid the oxidation of the VOC by accelerating the oxidation reactions and/or by oxidizing recalcitrant organic molecules which have not been entirely oxidized by O 3  alone. 
     The method of the invention comprises the use of an electrical corona discharge reactor capable of producing ozone. As it is well known in the art, during a corona discharge, a faint glow envelops a high-field electrode and is often accompanied by streamers directed toward a low-field electrode. Various types of corona reactors can be use according to the invention, with the provision that the reactors produce ozone in quantities sufficient to achieve the objects of the invention. 
     As shown in  FIG. 1 , the electrical corona discharge reactor  1  can be installed inside steam conduits, chimneys and/or exhaust ducts. A preferred configuration is an elongated, vertical and tubular chimney  2  having an inlet  21 , an outlet  23  and an intermediary portion  22  wherein the gaseous effluents to be treated flow. The chimney  2  may be of any appropriate size and configuration and can be made of any suitable material, preferably of either metallic or temperature resistant metallic material. The chimney  2  may comprise fan(s) or blower(s)  4  for helping in the introduction and circulation inside the chimney  2  of the gaseous effluents. 
     In use, the gaseous effluents will flow totally or partially into the corona reactor  1  and will be subjected to a high electrical voltage in the range of about 5 kV to about 50 kV. Under such voltages, the reactor  1  will produce ozone and other very active oxidizing species which will break down the VOC into H 2 O, CO 2  and SO 2  as depicted in the hereinabove mentioned equation. 
     According to the needs of the user, the chimney  2  may further comprise one or more of the following elements, the sequence into which these elements are installed being also subjected to the user&#39;s needs:
         a condenser  6 , the corona discharge reactor  1 , through which circulates a gas or a liquid. Such a condenser  6  will help to reduce the water content of the effluents by condensing the water into a first receiving container  7  before the gaseous effluents are directed through the reactor  1 ;   a filter  8 , upstream the corona discharge reactor  1 , for removing solid particles that may be present in the effluents before the effluents are introduced inside the reactor  1 ;   an injector  14  preferably upstream the reactor  1  for introducing into the duct one or more sprays of a gaseous catalyst such as ozone, and/or mist of an aqueous solution or of a suspension of a metal catalyst or salts thereof to further oxidize the VOC and/or other undesirable compounds and by-products which have not been totally oxidized by the corona reactor  1 ;   a lamp  10 , with an electromagnetic wave length between 189 and 254 nm, capable of producing UV rays in order to submit the gaseous effluents to a UV treatment;   a catalytic bed  12 , of either metal and non-metal material which is compatible with ozone, and comprising a catalyst such as PdCl 2 —MgO—Cu, Mn 2+ , Co, BiCu, CoCu, Ag, ZnO, Cu—Mn, V—Cu, Cu—Mn, VCu, Co 2+ , UO—MoO 3 —Cu, Ag, AgO, Mo, W, Ti, V, V 2 O 5 —K 2 SO 4 , Mo—V—P—Na, V—P, Mn—Co, a combination thereof or alloys containing them. The catalytic bed  12  will help to further oxidize the VOC and other undesirable compounds and by-products contained in the gaseous effluents downstream the reactor  1 ;   a spray  16  to introduce into the chimney  2  water or a mildly alkaline aqueous solution combined or not with a packing material such as Raschig rings or other bed packing material known to increase the surface contact between ozone and the VOC, and thereby scrub the gaseous effluents by dissolving the remaining undesirable compounds and/or by-products into a second container  17  before the gaseous effluents exit the duct  2 ; and   an ozone destruction unit  18  to convert residual ozone back to oxygen before the gaseous effluents exit the duct  2 .       

     The soiled aqueous solutions which have accumulated in the first  7  and second containers  17  can be treated with a treatment unit  19  for removing any pollutant therein. These solutions may be subsequently used by the spray  16  or sent to the sewers. 
     Referring now to  FIGS. 2  to  6 , there is shown a particularly preferred embodiment of the invention combining, in a single module, many of the different oxidation reaction steps listed hereinabove. The electrical corona discharge reactor  1  consists of a circular vessel  24 , devised to be installed inside a chimney, and comprises at least one, preferably a plurality, of vertically aligned corona tubes  30  having a length varying from few inches to several feet. Similar corona tubes producing ozone are described in detail in U.S. Pat. No. 5,573,733 which is incorporated herein by reference. Each tube  30  comprises two electrodes  40 , 50  incorporated respectively into concentric spaced apart outer and inner cylinders  42 , 52  forming a gap  45 , having from few millimeters to several centimeters, through which the gaseous effluents to be treated flow. If necessary, the tubes  30  can be adapted to allow direct injection of ozone or of another catalyst, directly into the gap  45 . 
     As best shown in  FIGS. 3 and 5 , upper and lower covers  32  assemble together the cylinders  42 , 52  and also carry the high voltage current to the inner electrode  50 . Accordingly, covers  32  are preferably made of an electrically insulating material such as CPVC, PVDF, Teflon™, and ceramic, to electrically insulate from each other the electrodes  40 , 50  and also electrically insulate the said electrodes from the main body of the vessel  24 . The covers are further provided with a plurality of holes  34  which allow the effluents to flow between the outer  40  and inner  50  electrodes. The electric current may be distributed in reactor  1  by a pair of electrical wires  36  linking together the electrodes of each tube  30  and connecting them to an electrical source (not shown) producing high voltage AC, DC, Pulsed AC, Pulsed DC or a combination of these currents. Alternatively, the voltage may be distributed to the electrodes by connecting the power supply to a lid  25  composed of an electrically conductive material such as stainless steel. 
     In use, all of the gaseous effluents will flow through the holes  34  into the gap  45  formed by the two concentric electrodes  40 , 50  and the pollutants and oxygen contained in the effluents will be subjected to high electrical voltage in the range of about 5 kV to about 50 kV. Electric arcs will form between the two electrodes and begin to break down the VOC while simultaneously producing ozone and other very active oxidizing species which will further break down the VOC into H 2 O, CO 2  and other by-products as depicted in the above-mentioned equation. Preferably, the temperature inside will be controlled within the range of about 50° C. to about 200° C. 
     As best shown in  FIGS. 4 ,  5  and  6 , the outer cylinder  42  is hollow. It has an inner surface  43  and an outer surface  44  and it forms an outer duct wherein the gaseous effluents flow. The outer cylinder  42  may be made of glass, ceramic, composites, quartz or of any ozone compatible dielectric material. 
     As mentioned previously, the outer cylinder  42  incorporates a first electrode  40 . In a preferred embodiment, the outer cylinder  42  is coated with a transparent electrically conductive material such as tin-oxide, tin-indium oxide, or a very thin layer of gold or platinum layer thereby forming the first electrode  40 . Electric current is distributed to this electrode  40  with a plurality of spring-like electrically conductive wires  60  distributed around the outer surface  44  of the outer cylinder  42 . Such spring-like wires are also useful in diffusing heat from the outer cylinder  42  to ambient air. As best shown in  FIGS. 5 and 6 , in an other preferred embodiment the outer cylinder  42  comprises a plurality of electrically conductive strips  62  extending longitudinally on its outer surface  44 . The electric current may be distributed to these strips  62  with spring-like electrically conductive wires  60  as explained previously or with a supplementary strip (not shown) extending perpendicularly and connecting together the longitudinal strips  62 . The strips  62  and the spring-like electrically conductive wires  60  are preferably made of an electrically conductive such as copper, plated copper, brass, aluminum and stainless steel. 
     Now referring to  FIGS. 4 ,  5  and  6 , it is shown that the inner cylinder  52  incorporates the inner electrode  50 . The inner cylinder  52  is concentrically positioned inside the outer cylinder  52  and it is spaced apart and electrically insulated therefrom by the covers  32  as explained previously. The inner cylinder  52  has an outer surface  54  facing the inner surface  43  of the outer cylinder  42 . The inner cylinder  52  extends through the tube  30  and through the covers  32 . Advantageously, the inner cylinder  52  is made of electric and heat conductive material selected from the group consisting of conductive composite, graphite, steel, stainless steel, brass, copper, tungsten, molybdenum, aluminum, and alloys thereof. 
     In the preferred embodiment shown in  FIGS. 4 ,  5  and  6 , the inner cylinder  52  is hollow and forms an inner duct  55 . Advantageously, the inner duct  55  is connected with other components such that a flow of a gas or of a liquid circulates inside the inner duct  55  permitting thereby to regulate accordingly the temperature inside the corona tube(s)  30 . Preferably, a flow of a gaseous refrigerant such as compressed air, ammonia, carbon dioxide, nitrogen or of a cooled dielectric fluid such as high voltage transformer oils, circulates within the inner cylinder  52  in order to lower the temperature inside the tube(s)  30  and the reactor  1 . 
     Preferably, the outer surface  54  of the inner cylinder  52  is provided with a plurality of protrusions  56  obtained by chemical etching or electroforming of the outer surface  54 . In a preferred embodiment, the protrusions  56  are obtained by machining the outer surface  54  with two sets of parallel grooves having a low depth and a “V” shaped cross-section therefore resulting in square based pyramids wherein the tips define a plurality of points. The protrusions  56  may be distributed throughout the outer surface of the inner cylinder or limited to specific zones  57  as shown in  FIGS. 4 and 5 . The protrusions  56  create turbulence in the flow of gas circulating into the gap  45 , thereby increasing the pathway of the flow and the oxidation of the volatile compounds. 
     The outer surface  54  of the inner electrode  50  and/or the protrusions  56  may be further coated by any appropriated means known in the art with a metal catalyst that will not be affected by ozone or the corona environment. Of course, the choice of the catalyst will vary with respect to the nature of the pollutants to be eliminated. Such a catalyst may be selected from the group consisting of PdCl 2 —MgO—u, Mn 2+ , Co, BiCu, CoCu, Ag, ZnO, Cu—Mn, V—Cu, Cu—Mn, VCu, Co 2+ , UO—MoO 3 —Cu, Ag, AgO, Mo, W, Ti, V, V 2 O 5 —K 2 SO 4 , Mo—V—P—Na, V—P, Mn—Co, a combination thereof or alloys containing them. The metal catalyst will help in further oxidizing the VOC and other undesirable compounds remaining in the gaseous effluents. 
     According to the present invention, it is further possible to combine the ozone producing tubes  30 , the metal catalyst and the UV lamp  10  into a single device (viz. the corona discharge reactor  1 ) instead of installing these elements in series as shown in FIG.  1 . According to this preferred embodiment which is best shown in  FIGS. 3  to  5 , the reactor  1  further comprises at least one UV lamp  10  capable of producing UV rays with an electromagnetic wave length comprised preferably between about 189 and about 254 nm. More preferably a plurality of UV lamps  10  are positioned between the longitudinal tubes  30  and close to the outer surface  44  of the outer cylinder  42 . The UV rays produced by the lamp(s)  10  will further oxidize the compounds contained in the effluents flowing between the electrodes  40 , 50 . Accordingly, the outer cylinder  40  will be made of a material providing a UV transparency. Advantageously, the outer cylinder  40  is made of a dielectric and UV permeable material such as quartz and it is coated with a transparent electrically conductive material such as tin-oxide, tin-indium oxide or very thin layers of gold, chrome or other precious/semi-precious metals. 
     In view of the above, it can be appreciated that according to a most preferred embodiment of the invention, the gaseous effluents and the VOC contained therein flow into the reactor  1  where they are subjected to a high voltage corona producing ozone and simultaneously to a UV treatment and a metal catalyst oxidation. This creates a highly oxidative environment wherein it is possible to break down VOC, H 2 S, NH 4 , mercaptans and chlorinated solvents into CO 2 , H 2 O, SO 2 , and other by-products. The undesirable by-products or compounds not entirely oxidized may be removed before exiting the chimney using a spray of water or of mildly alkaline solution as explained previously, or they can be treated by other methods known in the art. Moreover, some of the oxidation reactions are exothermic and therefore contribute to increase the temperature of the treated gaseous effluent which may be a desirable factor for catalyzing the decomposition of some organic pollutants. Furthermore, the temperature inside the reactor  1  of the present invention may be regulated as explained previously. A person skilled in the art will be able to safely operate the present invention outside the low and high explosion limits to avoid any risks of explosions or fire hazards. 
     The flow rate treated by invention is a function of several parameters such as the size of the chimney  2 , the size of the corona reactor  1 , the number and length of the tubes  30  and of the gaseous flow speed. For instance, given a chimney measuring 60 cm in diameter and a VOC stream comprising mainly of short chain alkanes such as gasoline, the reactor and method of the present invention could treat 100 ppm of VOC to 10 000 ppm of VOC at a flow rate of 700 m 3 /hr to 7 m 3 /hr respectively. As aforesaid, the principle asset of the reactor  1  of the invention is that it is quite easy to build and repair and further relatively inexpensive to operate. Further, since the reactor  1  operates at a relatively low temperature (50° C.-200° C.), as compared to the closest known competitive technologies which must function at much higher temperatures (700° C.-800° C.), the reactor of the invention requires less than ⅓ to ¼ of the energy which is necessary by the other technologies known in the art to achieve the same results. A lower temperature of oxidation also reduce greatly the amount of noxious NO x  which are generally produced during the reaction. 
     In summary, the main advantages of the corona reactor  1  of the invention are as follows:
         Based on the corona discharge principle;   Modular design;   Can be air or liquid cooled;   Works with low and high frequency to extend the life of dielectric and power supply;   Produces high ozone concentrations: each corona lamp can produce from about 5-20 g/hour with air feed, and about 10-50 g/hour with oxygen feed;   Has a low power consumption;   Can be compact and fully automated;   Easy maintenance;   Interface with existing installations;   Variable output from 10% to 100% of nominal output;   Rugged and reliable; and   Skid mounting is possible.       

     EXAMPLE 1 
     Working tests to demonstrate the efficiency of the device and of the method of the invention were done using a prototype similar but simpler to the chimney shown in FIG.  1 . The prototype comprised four major elements, namely a multi-section duct having an inlet and an outlet and having therein a corona reactor according to the invention, a catalytic bed and a scrubbing water spray. The VOC studied was regular unleaded gasoline. Test results obtained with this prototype are shown in Table 1. 
     Materials and Methods 
     The first section of the prototype consisted of a 4-inch diameter PVC duct measuring 5 feet in height. A 100 cfm nominal fan (Minebea Co. Ltd., model number 4715FS-12T-B50) was located at the inlet of the duct and served to evaporate the VOC (regular unleaded gasoline) from either a saturated cotton pad placed above the fan or from a small hemi-spherical reservoir with a capacity of 600 ml placed below the fan. A constant VOC concentration was maintained at the inlet by feeding either the cotton pad or the reservoir with gasoline at the same rate as it was being evaporated. The fan was controlled using a potentiometer (KB Electronics, model KBWC-15™). This in turn controlled the speed of evaporation of the VOC and ultimately set the VOC concentration at the inlet of the duct. The flow rate of the VOC stream under each set of conditions was determined by measuring the time required to fill a 1 ft 3  plastic bag placed at the ducts outlet. The inlet VOC concentration inside the duct was measured by placing a MINI-RAE™ handheld VOC monitor at the outlet of the duct prior to turning on the corona reactor. This measurement is referred to as VOC in in Table 1. 
     A corona discharge reactor according to the invention and having a single corona lamp, was installed inside the duct. The VOC stream was directed vertically through the corona reactor such that the low pressure VOC laden air flowed between the outer and inner electrodes of the corona lamp. For this experiment, two types of corona lamps were studied, namely a 30 inch lamp (about 76 cm) producing about 2 to 3 gram of ozone per hour and a 15 inch lamp (about 38 cm) producing about 0.5 to 1 gram of ozone per hour with regular non-dried air feed. The corona lamps were powered by a 60 Hz low frequency power supply (Ozomax, model number TRANSFORMER-LT™) operating at maximum power yielding a secondary voltage of 14 kV when using the 15 inches corona lamp and 18 kV when operating the 30 inches corona lamp. Tests were carded out first using the 15 inch corona lamp which was later removed and replaced with the 30 inch corona lamp. 
     A second section of the prototype was mounted above the first section comprising the corona reactor described above. This second section consisted of a 90° elbow (Chemkor, PVC schedule 40, 4 inches diameter) and an upper aluminum duct measuring 23 inches long and 4 inches in diameter. A honeycomb structured solid catalytic converter measuring 4 inches in diameter and 3 inches high was installed into the aluminum duct. The catalytic converter comprised two types of platinum-palladium-rhodium based Engelhard catalysts which were evaluated separately, namely a Type 1 catalyst oxidizing VOC into water and carbon dioxide and a Type 2 catalyst reducing nitrous oxides into nitrogen and oxygen. The catalytic unit was placed halfway inside the aluminum duct and the duct section covering the catalytic unit was removed and replaced with adhesive copper foil in order to increase the efficiency of heat transfer when heating the catalyst. The catalyst was heated by placing a 125 W heating coil (Omega, model No FGR-030) on the outside of the copper foil. Tests were performed at both room temperature 20° C. and at 100° C. The temperature was measured by placing a thermocouple (Type K, chrome anode, aluminum cathode) on the outside of the copper foil and allowing the temperature to reach its steady state value. 
     Finally, in some experiments, the oxidation products were removed from the gaseous effluents by using a fine atomized water spray. A 90° full cone spray nozzle (Spray Systems Co., IIIISJ9013) was used and water was supplied therein at a flow rate of 1.5 gpm and 30 psi. 
     VOC measurements were taken at the prototype duct outlet using a MINI-RAE™ handheld monitor. These measurements are referred to as VOC out in Table 1 below. The efficiency of each set of conditions was evaluated by calculating the VOC % destruction as per the following equation. It is desired to maximize this ratio. 
         %   ⁢           ⁢   destruction     =       [         VOC   ⁢           ⁢   in     -     VOC   ⁢           ⁢   out         VOC   ⁢           ⁢   in       ]     ×   100         
 
Discussion
 
     Table 1 below summarizes the results obtained using the prototype described above. 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Flow rate 
                 Water 
                 O 3   
                   
                 Catalyst 
                 VOC in 
                 VOC out 
                 Destruction 
               
               
                 (CFM) 1   
                 (GPM) 2   
                 (gr/hr) 3   
                 Catalyst 4   
                 Temp. (° C.) 5   
                 (PPM) 6   
                 (PPM) 6   
                 (%) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 0 
                 2-3 
                 type 1 
                 20 
                 3339 
                 2649  
                 21 
               
               
                 1 
                 0 
                 2-3 
                 type 1 
                 20 
                 3070 
                 2413  
                 21 
               
               
                 1 
                 0 
                 2-3 
                 type 1 
                 100  
                 1155 
                 215 
                 81 
               
               
                 1 
                 0 
                 2-3 
                 type 1 
                 100  
                 1155 
                 180 
                 84 
               
               
                 1 
                 1.5 
                 2-3 
                 type 1 
                 100  
                 1155 
                  23 
                 98 
               
               
                 1.5 
                 1.5 
                 0.5-1 
                 type 1 
                 20 
                  650 
                  65 
                 90 
               
               
                 1.5 
                 1.5 
                 0.5-1 
                 type 2 
                 20 
                  410 
                  80 
                 80 
               
               
                   
               
               
                   1 CFM = cubic feet per minute of VOC laden air  
               
               
                   2 GPM = gallons per min of water used during water spray scrubbing  
               
               
                   3 O 3  produced in grams/hour by the corona lamps of the reactor  
               
               
                   4 Type 1 = oxidizing catalyst  
               
               
                 Type 2 = reducing catalyst  
               
               
                   5 Catalytic unit steady state temperature  
               
               
                   6 VOC measurements were done using a MINI-RAE ™ handheld monitor.  
               
             
          
         
       
     
     As shown, the corona discharge reactor of the invention used alone (without catalyst and without spray) proved to be effective to destroy the VOC (21%). Indeed, at 20° C. the catalyst contained in the catalytic unit is ineffective and absence of catalyst would have given similar results. Increasing the temperature of the catalytic unit yielded a higher percentage of VOC destruction (81-84%). As expected, the oxidizing catalyst (Type 1) yielded a higher % VOC destruction than the reducing catalyst (Type 2). 
     It was also demonstrated that better results could be obtained when the reactor of the invention (with a 30 inches corona lamp) was combined with the Type 1 catalyst heated to 100° C., and a final water scrubbing carried out a flow rate of 1.5 gpm of water. Under these conditions 98% destruction of the VOC was achieved. Up to 90% VOC removal was observed when using a reactor having the shorter 15 inches corona lamp and a 1.5 gpm water spray. Two replicates of each experiment were performed and proved the results to be very reproducible. 
     Therefore the reactor of the invention was found to be versatile in that it may efficiently eliminate VOC from gaseous effluents under a variety of conditions, such as, with or without the use of a water spray, with or without a catalyst and under a range of ozone production rates. Thus, results of these experiments clearly demonstrate the efficiency of the method and of the corona discharge reactor of the invention which enhances, in an unexpected ratio, the destruction of pollutants. Furthermore, it is assumed that a reactor combining a plurality of corona lamps according to the invention would have given even more impressive results. 
     Of course, numerous modifications could be made to the present invention according to the preferred embodiments disclosed hereinabove without departing from its scope as defined in the appended claims.