Patent Publication Number: US-2016237869-A1

Title: Energy-saving type dielectric barrier discharge plasma nox reduction device

Description:
CLAIM FOR PRIORITY 
     This application claims priority to Korean Patent Application No. 2015-0023940 filed on Feb. 17, 2015 and 2015-0035697 filed on Mar. 16, 2015 in the Korean Intellectual Property Office (KIPO), the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     Example embodiments of the present invention relate to a field of waste gas treatment, and more specifically, to an energy saving-type dielectric barrier discharge (DBD) plasma nitrogen oxide reduction device capable of efficiently treating waste gas including nitrogen oxides (NOx) and other pollutants. 
     2. Related Art 
     Along with rapid industrialization, energy has served as a fundamental means for industrial activities for satisfactory of human&#39;s need. However, as use of the energy is increased, generation of environmental pollution has become inevitable, and also the extent thereof has been getting larger. Since air pollutants are inevitably emitted in a combustion process of fossil fuel, which is the majority of energy source, such as oil, coal, natural gas, and the like, it is necessary for all of mankind to promote a balance between economic growth and environmental preservation to ensure sustainable growth. 
     Air pollution due to use of energy is classified into local pollution and international pollution according to an effective range and a responsible range. Damage to animals and plants and acid rain due to sulfur oxide, nitrogen oxide, and the like occur relatively locally, on the contrary, green-house gases, such as carbon dioxide, NOx, and the like, have become an international issue in the discussion on global warming. 
     Due to indiscriminate growth-oriented economic management, air pollution around domestic major cities and industrial complexes has already reached its critical point. Methodology for prevention of domestic air pollution, due to income increase caused by economic growth, and global warming being regulated by being internationally watched with interest and vision of air pollutants according to use of energy have been important issues. 
     Currently, in a situation in that that use of fluoride compound has been growing day by day as demand related to semiconductor display is increased, a catalytic method is today mainly used as techniques for handling NOx and solving a problem of regulation on total quantity due to large quantity emission of secondary pollutant (NOx) generated after the semiconductor process gas treatment, however, it is required to secure an alternative technique because of excessive use of energy during operation. Therefore, the alternative technique to solve existing problems is needed. 
     (Patent Document 1) Korean Laid-open Patent Application No. 10-2011-0065985 
     SUMMARY 
     Accordingly, example embodiments of the present invention are provided to substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     Example embodiments of the present invention provide a nitrogen oxide reducing-type plasma oxidizing device efficiently treating nitrogen oxides by limitedly emitting nitrogen oxide with a form of NO 2  by arranging a combustion unit, a wet processing unit, and a plasma oxidizing unit in a housing of the plasma nitrogen oxide reduction device in order. 
     In some example embodiments, an energy saving-type DBD plasma nitrogen oxide reduction device configured to treat waste gas includes a combustion unit combusting the waste gas; a wet treatment unit configured to receive the combusted gas from the combustion unit and perform wet treatment on the gas; and a plasma oxidizing unit arranged to insert plasma gas for treating nitrogen oxide included in the gas passing through the wet treatment unit. 
     The energy saving-type DBD plasma nitrogen oxide reduction device further includes a housing, wherein the combustion unit, the wet treatment unit, and the plasma oxidizing unit are arranged in the housing. 
     The energy saving-type DBD plasma nitrogen oxide reduction device further includes a main emission tube configured to emit the nitrogen oxide, treated by the plasma gas, to outside of the housing, wherein the plasma oxidizing unit is connected and mounted to a connection path connected to the main emission tube in the housing. 
     The plasma gas is O 3  generated through plasma discharge of the plasma oxidizing unit. The nitrogen oxide is converted into NO 2  by oxidizing with O 3  generated in the plasma oxidizing unit. 
     The converted NO 2  is treated through a reduction reaction in a wet treatment process which is a post treatment process. 
     The plasma oxidizing unit includes a rod-shaped internal electrode, a dielectric configured to surround the internal electrode, and an external electrode inserted and mounted into an outer part of the dielectric in a coil form, wherein the internal electrode and the external electrode are applied with alternating current power for generation of plasma. 
     The external electrode has a surface coated with thermal spraying. 
     An external surface of dielectric and an external surface of external electrode are formed at the same height. 
     The plasma oxidizing unit is configured to generate plasma using DBD plasma. 
     According to the present invention, the plasma nitrogen oxide reduction device may limitedly emit nitrogen oxide with a form of NO 2  at a final outlet of the plasma nitrogen oxide reduction device by arranging, in the housing, the plasma oxidizing unit arranged to insert plasma gas for treating the nitrogen oxide included in the gas passing through the combustion unit and the wet treatment unit. Also, the nitrogen oxide is treated by discharging the dielectric barrier discharge plasma of the plasma oxidizing unit made of a coil type electrode without additional equipment, thereby saving energy supplied to equipment. 
     The plasma oxidizing unit may include an internal electrode, a dielectric configured to surround the internal electrode, and an external electrode inserted and mounted to an outside of the dielectric in a coil form. A surface of the external electrode is coated with thermal spraying, and an external surface of dielectric and an external surface of external electrode are formed at the same height, thereby preventing dusts from adhering between the electrodes, and solving a problem of heat and arc generated between the dielectric and the electrode. 
     Effects of the present invention are not limited to the above-described effects and other unmentioned effects may be clearly understood by those skilled in the art from the following descriptions. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Example embodiments of the present invention will become more apparent by describing in detail example embodiments of the present invention with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic view illustrating a gas purifying system applied with a plasma oxidizing unit of the present invention; 
         FIG. 2  is a view illustrating a plasma nitrogen oxide reduction device applied with the plasma oxidizing unit of the present invention; 
         FIG. 3  is a perspective view illustrating the plasma oxidizing unit of the present invention; 
         FIG. 4  is a cross-sectional view illustrating the plasma oxidizing unit of the present invention; and 
         FIG. 5  is an enlarged view illustrating the plasma oxidizing unit of the present invention. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. In descriptions of the invention, when detailed descriptions of related well-known technology are deemed to unnecessarily obscure the gist of the invention, they will be omitted. 
     Hereinafter, embodiments will be described in detail by explaining exemplary embodiments of the invention with reference to the attached drawings. In descriptions of the embodiments with reference to the attached drawings, like reference numerals in the drawings denote like elements, and redundant description thereof will be omitted. 
     Generally, nitrogen oxides are generated by a stationary emission source, such as a thermoelectric power plant, and a mobile emission source, such as a vehicle. Nitrogen oxides generated in a semiconductor process are generated by a reaction between nitrogen and oxygen by a high temperature at the time of combustion in a combustion process in a scrubber through which various harmful gases pass to be safely treated before the gases are emitted into the atmosphere. 
     NO emitted into the atmosphere is oxidized into NO 2 , NO 3 , N 2 O 4 , by O 3 , O 2 , moisture, and the like in the air. Most of them are NO 2 , the NO 2  is dissolved into the air in an aerosol state to become acid rain or to form photochemical smog by sunlight. With extensive damage, the acid rain and the photochemical smog cause a respiratory disease and sight disability due to eye irritation, corrode metal, and affect growth of plants. 
     A thermal treatment device is used in a process of treating harmful gases, such as SiH 4 , NF 3 , used in a semiconductor process. The thermal treatment device is classified into a fuel-type, an electric heater type, and a plasma type. The thermal treatment devices in these types generate a large amount of nitrogen oxides (NO and NO 2 ) by a reaction between O 2 , H 2 O, and the like and N 2  during a treatment process. Particularly, the thermal treatment devices in the fuel type and the plasma type has a high operation temperature to generate NO of the nitrogen oxides at a high rate. 
     As another generation source, NH 3  and NF 3  of gases used in a semiconductor process generate a large amount of nitrogen oxide (mostly NO) by reacting a nitrogen factor (N+), decomposed from NH 3  and NF 3  in a decomposing or chemical reaction process, with O 2  or H 2 O in the air. 
       FIG. 1  is a view schematically illustrating a gas purifying system applied with a plasma oxidizing unit of the present invention, and  FIG. 2  is a view illustrating a plasma nitrogen oxide reduction device applied with the plasma oxidizing unit of the present invention. 
     Referring to  FIGS. 1 and 2 , a gas purifying system for treating waste gas including nitrogen oxides includes processes of inserting waste gas, used in main process equipment  100 , into a plasma nitrogen oxide reduction device  300  applied with a plasma oxidizing unit  330  through a vacuum pump  200 , treating the inserted waste gas by the plasma nitrogen oxide reduction device  300 , and emitting the waste gas into the atmosphere through a wet scrubber  400 , which is a post process, and a fan  500 . 
     Here, the plasma nitrogen oxide reduction device  300 , applied with the plasma oxidizing unit  330  according to the present invention, may be a point of use (POU) scrubber which is a thermal treatment device generally used to treat waste gas. A combustion unit  310  and a wet treatment unit  320  may be included in a conventional POU scrubber. However, in the plasma nitrogen oxide reduction device  300  according to the present invention, the housing  301  may include the plasma oxidizing unit  330  to insert plasma gas for treating nitrogen oxide included in gases passing through the wet treatment unit  320 , in addition to the combustion unit  310  and the wet treatment unit  320 . 
     As shown in  FIG. 2 , an introducing tube  311  is connected to an upper part of the combustion unit  310  of the plasma nitrogen oxide reduction device  300  according to the present invention, such that the waste gas used in a semiconductor manufacturing may be introduced into the housing  301  through the introducing tube  311 . The waste gas introduced into the housing  301  is combusted by the combustion unit  310 , and the combusted waste gas is emitted to the wet treatment unit  320  by an emission tube  312  having a cross-section getting gradually narrower at a lower part of the combustion unit  310 . 
     The combustion unit  310  uses a method of treating the waste gas by making the waste gas including harmful components pass through flames. To increase fuel efficiency, O 2  and CH4 may be injected through a combustion gas injection port  313  provided on an upper part of the combustion unit  301 . 
     However, a large amount of nitrogen oxides (NO and NO 2 ) are generated by a reaction between O 2 , H 2 O, and the like and N 2  during a treatment process. Particularly, since an operation temperature is high at the time of combustion in the combustion process, the NO of the nitrogen oxides is generated at a high rate. 
     The waste gas treated in the combustion unit  310  passes through the wet treatment unit  320  to accumulate secondary by-product, dissolve soluble gases, and cool the high temperature combustion gas. 
     The wet treatment unit  320  may include a first injection nozzle  321 , a second injection nozzle  322 , a wet water tank  323 , a flow rate adjusting device  324 , a pump  325 , and a water supply tube  326  to receive the gas combusted from the combustion unit  310  and perform wet treatment on the gas. 
     The wet treatment unit  320  adsorbs and dissolves soluble waste gas and silicon dioxide (SiO 2 ) powders generated in the combustion unit  310  through injection of the injection nozzles  321  and  322 , and stores the treated materials, emitted from the combustion unit  310  and the injection nozzles  321  and  322 , and emits the treated materials using the wet water tank  323 . It is preferable that the first injection nozzle  321  and the second injection nozzle  322  be installed on an upper part of the wet water tank  323 . 
     The first injection nozzle  321  and the second injection nozzle  322  are connected to the water supply tube  326  to receive water from the wet water tank  323 , and the pump  325  may be mounted between the wet water tank  323  and the water supply tube  326  to supply, to the injection nozzles  321  and  322  on an upper part the wet water tank  323 , the water in the wet water tank  323  mounted at a lower part inside the housing  301 . Also, the flow rate adjusting device  324  may be mounted between the wet water tank  323  and the pump  325  to control the amount of water injected by the injection nozzles  321  and  322 . 
     In this way, the wet water tank  323 , the flow rate adjusting device  324 , the pump  325 , and the water supply tube  326  interwork with each other in the wet treatment unit  320  to be functioned as a water circulation means to continuously circulate water at an even temperature water in the wet treatment unit  320 . 
     A main emission tube  327  may be further included at a rear end of the wet treatment unit  320  to emit the treated waste gas to the outside of the housing  301  and then to a device for post-treatment process. 
     The main emission tube  327  is extended from the inside of the housing  301  to the outside thereof, and the main emission tube  327 , formed in the housing  301 , of the main emission tube  327  may be connected with the plasma oxidizing unit  330  by a connection path  328  connected to the main emission tube  327 . 
     That is, the plasma oxidizing unit  330  according to the present invention may be arranged along with the combustion unit  310  and the wet treatment unit  320  in the housing  301  of the plasma nitrogen oxide reduction device  300  to be formed as integrated single scrubber equipment. 
     Also, an alternating current power supply unit  340  may be further included in a lower part of the plasma oxidizing unit  330  to apply alternating current power to the plasma oxidizing unit  330 . 
     In this way, by arranging the plasma oxidizing unit  330  in the main emission tube  327  which is a rearmost end in the plasma nitrogen oxide reduction device  300 , the nitrogen oxide (NO) to be finally emitted to the outside of the housing  301  through the main the emission tube  327  may be limitedly emitted as NO 2 . 
     That is, O 3 , generated in the plasma oxidizing unit  330  through plasma discharge, and nitrogen oxide (NO) generated at the time of combustion in a combustion process are converted into NO 2  through oxidization, and the converted NO 2  is emitted through the main emission tube  327  to the outside of the housing  301 . The NO 2  emitted to the outside of housing  301  may efficiently treat the nitrogen oxide through a reduction reaction of the wet treatment process which is a post treatment process. 
       FIG. 3  is a perspective view illustrating the plasma oxidizing unit of the present invention,  FIG. 4  is a cross-sectional view illustrating the plasma oxidizing unit of the present invention, and  FIG. 5  is an enlarged view illustrating the plasma oxidizing unit of the present invention. 
     Referring to  FIGS. 3 to 5 , the plasma oxidizing unit  330  of the present invention may include an internal electrode  331 , a dielectric  332 , and an external electrode  333 . 
     The internal electrode  331  has a hollow rod shape and may be formed of a conductive material to apply an electric current. The discharge gas for the plasma discharge is inserted through a reactive gas inlet  336  at a lower part of the internal electrode  331 , the plasma gas generated through the plasma discharge may be emitted through a plasma gas outlet  337  at an upper part of the internal electrode  331 . Preferably, the discharge gas for the plasma discharge may be O 2 , and the plasma gas generated through the plasma discharge may be O 3 . 
     The dielectric  332  is configured to surround the internal electrode  331  from one end to the other end thereof at a predetermined distance, and has the same rod shape as the internal electrode  331 . The dielectric  332  is arranged between the internal electrode  331  and the external electrode  333  to prevent arcing generated between the electrodes by a high voltage applied to the electrodes. 
     The external electrode  333  may be formed in a coil-type electrode structure having a coil shape, and may be inserted and mounted into an outer surface of the dielectric  332 . A coil may be inserted at regular intervals. In a cross-section of the coil, a gap between a groove formed in the dielectric  332  and the coil when the coil is inserted into the dielectric  332  is not allowed. The cross-section of the coil may have a rectangular shape so that the external surface  334  of dielectric and the external surface  335  of external electrode are formed at the same height. However, the shape of the cross-section of the coil may be variously changed depending on users. 
     Alternating current power is applied to the internal electrode  331  and the external electrode  333  by the alternating current power supply unit  340  mounted to a lower part of the plasma oxidizing unit  330 . For example, a voltage is applied to the internal electrode  331 , and the external electrode  333  is grounded. Or, polarities of the internal electrode  331  and the external electrode  333  may be changed. High voltages may be applied to both of the two electrodes depending on the alternating current power supply unit  340 . That is, a high voltage WI is applied to any one of the internal electrode  331  and the external electrode  333 , and the other one is grounded. Or, when a positive electrode is applied to any one of the internal electrode  331  and the external electrode  333 , a negative electrode may be applied to the other one. 
     Also, the internal electrode  331  and the external electrode  333 , which are the conductive materials including metal, may be made of any one among aluminum (Al), stainless steel (STS), titanium (Ti), nickel (Ni), chrome (Cr), copper (Cu), tungsten (W), and titanium (Pt) that have strong corrosion resistance, or an alloy thereof. Preferably, hastelloy mainly made of nickel having excellent moldability and corrosion resistance may be applied. 
     The dielectric  332  may be applied with any one material among MgO, Al 2 O 3 , TiO 2 , and SiO 2  that are an oxide ceramic with high dielectric constant. 
     A surface of the external electrode  333  formed in a coil form may be coated with thermal spraying, and the external electrode  333  may be inserted and mounted to an outer part of the dielectric  332 . Also, the external surface  335  of external electrode inserted into the dielectric  332  may be arranged at the same height as the external surface  334  of dielectric. 
     Like this, the surface of the external electrode  333  is coated with thermal spraying, and the external surface  335  of external electrode is arranged at the same height as that of the external surface  334  of dielectric, thereby preventing dusts from adhering between the electrodes, and solving a problem of heat and arc generated between the dielectric  332  and the electrode. 
     The plasma oxidizing unit  330  may be implemented in various sizes depending on users. However, in a preferable size of the internal electrode  331  according to the present invention, a height from one end to the other end is set to 1.5 m. In the dielectric  332 , a height from one end from the other end is set to 1.2 m. Also, in the external electrode  333  in a coil form, a height from one end from which a coil start to the other end of the coil is set to 0.95 m. Thicknesses of the coil and the dielectric  332  are, as shown in  FIG. 4 , set to 2 mm and 7 mm, respectively. 
     A dielectric barrier discharge (DBD) plasma device using the coil-type electrode structure is applied with a high frequency and a high voltage to additionally form an induced electric field in an electric field, generated between the two electrodes, by Faraday&#39;s Law of Induction, thereby maximizing the strength of electric field. Therefore, consumption of power is remarkably reduced, and plasma with excellent performance may be generated. 
     As described above, a the plasma oxidizing unit  330  according to the present invention generates plasma using the dielectric barrier discharge plasma, and O 2  is converted into O 3  by generation of the plasma, and thus the O 3  is emitted to the main emission tube  327  through the connection path  328 . The O 3  emitted to the main emission tube  327  performs oxidation and ionization treatment with pollutant in the main emission tube  327 . For example, NO and CO are oxidized into NO 2  and CO 2 , THC is oxidized and ionized, and HF or dust is coarsened. 
     Therefore, the nitrogen oxide generated during a combustion process in the plasma nitrogen oxide reduction device  300  by the plasma generated in the plasma oxidizing unit  330  according to the present invention is treated by reacting with O 3  generated through the plasma discharge, thereby limitedly emitting nitrogen oxide with a form of NO 2  at the final outlet of the plasma nitrogen oxide reduction device  300 . 
     A reaction mechanism in which the nitrogen oxide is oxidized by the plasma oxidizing unit  330  is as follows. 
       NO+O 3 ≧NO 2− +O 2  
 
     The nitrogen oxide oxidized by the plasma oxidizing unit  330  and emitted as NO 2  through the main emission tube  327 , as shown in  FIG. 1 , is finally treated through a reduction reaction in a wet treatment process of the wet scrubber  400  which is a post treatment process. Also, in the wet scrubber  400 , THC ionized in the pretreatment process is absorbed, remaining O 3  is reduced, and HF is treated other than the nitrogen oxide. 
     A main reaction mechanism in which the nitrogen oxide is reduced by the wet scrubber  400  is as follows. 
       NO 2 +(Na 2 S+α)=N 2 +Na 2 SO 4  
 
     In this way, the nitrogen oxide generated in the plasma nitrogen oxide reduction device  300  during combustion may be efficiently treated through an oxidation process, caused by the plasma oxidizing unit  330 , and a reduction process of the wet scrubber  400 . 
     EXPERIMENTAL EXAMPLE 1 
     To evaluate a process performance of equipment to which the plasma oxidizing unit of the present invention is mounted, a conversion efficiency test in which the nitrogen oxide is converted into NO 2  by the plasma discharge of the plasma oxidizing unit is performed. 
     A table 1 and a table 2 are results of the test of the equipment to which the plasma oxidizing unit of the present invention is mounted. 
     As conditions according to an experimental example 1, a concentration of plasma O 3  of an oxidation stage is set to 40 ppm, and a reference air volume is set to 2 CMM. Under conditions of a superficial velocity of 1 m/s and a residence time of 2 sec., NO 2  conversion efficiency of nitrogen oxide at the time of plasma OFF and plasma ON is given in the table 1, and results of an oxidation rate test according to a change in time is given in the table 2. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 PLASMA OFF 
                   
                 PLASMA ON 
                   
               
               
                   
                 (ppm) 
                   
                 (ppm) 
                 EFFICIENCY 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 NO 
                 45 
                 NO 
                 7 
                 84% 
               
               
                 NO 2   
                 22 
                 NO 2   
                 55 
               
               
                 NOx 
                 67 
                 NOx 
                 62 
               
               
                 O 3   
                 40 
                 O 3   
                 1.4 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 PLASMA OFF 
                 PLASMA(O 3 ) ON 
                 NO 2   
               
               
                   
                 (ppm) 
                 (ppm) 
                 CONVERSION 
               
            
           
           
               
               
               
               
               
               
            
               
                 TIME 
                 NO 
                 NO 2   
                 NO 
                 NO 2   
                 EFFICIENCY 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 0.1 
                 min 
                 45 
                 22 
                 8 
                 55 
                 82% 
               
               
                 0.5 
                 min 
                 45 
                 22 
                 7 
                 55 
                 84% 
               
               
                 10 
                 min 
                 48 
                 22 
                 7 
                 55 
                 85% 
               
               
                 15 
                 min 
                 48 
                 22 
                 7 
                 55 
                 85% 
               
               
                 20 
                 min 
                 45 
                 22 
                 7 
                 55 
                 84% 
               
               
                 25 
                 min 
                 43 
                 22 
                 7 
                 55 
                 84% 
               
               
                 30 
                 min 
                 43 
                 22 
                 7 
                 55 
                 84% 
               
               
                 35 
                 min 
                 46 
                 22 
                 7 
                 55 
                 85% 
               
               
                 40 
                 min 
                 47 
                 22 
                 7 
                 55 
                 85% 
               
               
                 45 
                 min 
                 48 
                 22 
                 7 
                 55 
                 85% 
               
               
                 50 
                 min 
                 45 
                 22 
                 7 
                 55 
                 84% 
               
               
                 55 
                 min 
                 46 
                 22 
                 7 
                 55 
                 85% 
               
               
                 60 
                 min 
                 47 
                 22 
                 7 
                 55 
                 85% 
               
               
                 65 
                 min 
                 45 
                 22 
                 7 
                 55 
                 84% 
               
               
                 70 
                 min 
                 46 
                 22 
                 7 
                 55 
                 85% 
               
               
                 75 
                 min 
                 46 
                 22 
                 7 
                 55 
                 85% 
               
               
                 80 
                 min 
                 45 
                 22 
                 7 
                 55 
                 84% 
               
               
                 90 
                 min 
                 50 
                 22 
                 7 
                 55 
                 86% 
               
               
                 100 
                 min 
                 47 
                 22 
                 7 
                 55 
                 85% 
               
               
                 110 
                 min 
                 43 
                 22 
                 7 
                 55 
                 84% 
               
               
                 120 
                 min 
                 45 
                 22 
                 7 
                 55 
                 84% 
               
               
                   
               
            
           
         
       
     
     As shown in the table 1 and the table 2, it is confirmed that the nitrogen oxide may be efficiently converted into NO 2  according to whether energy of the plasma is applied. 
     EXPERIMENTAL EXAMPLE 2 
     In an experimental example 2, to evaluate a process performance of equipment to which the plasma oxidizing unit of the present invention is mounted, a conversion efficiency test in which the nitrogen oxide is converted into NO 2  by the plasma discharge of the plasma oxidizing unit after continuous operation for 80 min. is performed. 
     Tables 3 to 6 are test results of the experimental example 2 for the equipment to which the plasma oxidizing unit of the present invention is mounted. 
     As conditions of the experimental example 2, a concentration of plasma O 3  of an oxidation stage is set to 40 ppm, and a reference air volume is set to 2 CMM, so the conditions are the same as those of the experimental example 1. The test is performed in the same method as that of the experimental example 1 under condition of a superficial velocity of 1 m/s and various residence times. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 SUPERFICIAL VELOCITY: 1 m/s, 
               
               
                   
                 RESIDENCE TIME: 2 sec 
               
            
           
           
               
               
               
               
               
            
               
                   
                 PLASMA OFF 
                   
                 PLASMA ON 
                   
               
               
                 CONDITION 
                 (ppm) 
                   
                 (ppm) 
                 EFFICIENCY 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 NO 
                 46 
                 NO 
                 2 
                 96% 
               
               
                 NO 2   
                 26 
                 NO 2   
                 68 
               
               
                 NOx 
                 72 
                 NOx 
                 70 
               
               
                 O 3   
                 40 
                 O 3   
                 1.38 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 SUPERFICIAL VELOCITY: 1 m/s, 
               
               
                   
                 RESIDENCE TIME: 1.5 sec 
               
            
           
           
               
               
               
               
               
            
               
                   
                 PLASMA OFF 
                   
                 PLASMA ON 
                   
               
               
                 CONDITION 
                 (ppm) 
                   
                 (ppm) 
                 EFFICIENCY 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 NO 
                 45 
                 NO 
                 2 
                 96% 
               
               
                 NO 2   
                 26 
                 NO 2   
                 68 
               
               
                 NOx 
                 71 
                 NOx 
                 70 
               
               
                 O 3   
                 40 
                 O 3   
                 1.38 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 SUPERFICIAL VELOCITY: 1 m/s, 
               
               
                   
                 RESIDENCE TIME: 1 sec 
               
            
           
           
               
               
               
               
               
            
               
                   
                 PLASMA OFF 
                   
                 PLASMA ON 
                   
               
               
                 CONDITION 
                 (ppm) 
                   
                 (ppm) 
                 EFFICIENCY 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 NO 
                 45 
                 NO 
                 2 
                 96% 
               
               
                 NO 2   
                 26 
                 NO 2   
                 68 
               
               
                 NOx 
                 71 
                 NOx 
                 70 
               
               
                 O 3   
                 40 
                 O 3   
                 1.38 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 SUPERFICIAL VELOCITY: 1 m/s, 
               
               
                   
                 RESIDENCE TIME: 0.5 sec 
               
            
           
           
               
               
               
               
               
            
               
                   
                 PLASMA OFF 
                   
                 PLASMA ON 
                   
               
               
                 CONDITION 
                 (ppm) 
                   
                 (ppm) 
                 EFFICIENCY 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 NO 
                 43 
                 NO 
                 2 
                 95% 
               
               
                 NO 2   
                 26 
                 NO 2   
                 68 
               
               
                 NOx 
                 69 
                 NOx 
                 70 
               
               
                 O 3   
                 40 
                 O 3   
                 1.38 
               
               
                   
               
            
           
         
       
     
     As the results measured at residence times of 0.5 to 2 sec. in the tables 3 to 6, it is confirmed that every treatment efficiency is 95% or more. 
     As described above, the plasma nitrogen oxide reduction device  300  may limitedly emit nitrogen oxide with a form of NO 2  at the final outlet of the plasma nitrogen oxide reduction device  300  by arranging, in the housing  301 , the combustion unit  310  combusting waste gas, the wet treatment unit  320  configured to receive the combusted gas from the combustion unit  310  and perform wet treatment; and the plasma oxidizing unit  330  arranged to insert plasma gas for treating the nitrogen oxide included in the gas passing through the wet treatment unit  320 . Also, the nitrogen oxide is treated by emitting the dielectric barrier discharge plasma of the plasma oxidizing unit  330  made of a coil type electrode without additional equipment, thereby saving energy supplied to equipment. 
     Meanwhile, the embodiments disclosed in this specification and drawings are only examples to help understanding of the invention and the invention is not limited thereto. It is clear to those skilled in the art that various modifications based on the technological scope of the invention in addition to the embodiments disclosed herein can be made.