Abstract:
An air purifying apparatus includes an air flow generating device for generating a flow of air, a nozzle spraying water to the air flowing through the air flow generating device, a plasma module performing a plasma reaction on the air containing the water sprayed from the nozzle, and oxidizing NOx in the air and converting it into NO 3 , an eliminator eliminating the NO 3  converted in the plasma module and the water contained in the air and passing pure air through the eliminator and out of the air purifying apparatus and a water tank storing the water received from the eliminator, thereby heightening the removal efficiency of NOx from the air.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Korean Patent Application 10-2008-0131936, filed on Dec. 23, 2008, the disclosure of which is hereby incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    (i) Technical Field 
         [0003]    The inventive concept relates to an air purifying apparatus and to an air purifying method thereof, and more particularly, to an air purifying apparatus capable of removing NOx from air by using a plasma reaction. 
         [0004]    (ii) Description of the Related Art 
         [0005]    There is currently ongoing research to prevent defects in wafer manufacturing processes and to increase the production yield of semiconductor devices as semiconductor technology rapidly advances. Consequently, as a result, it may be also necessary to increase the air purification level of a clean room due to the fact that the air purification level of a clean room may significantly influence the production yield of semiconductor devices. 
         [0006]    In conventional air purification processes air supplied into the clean room may be purified by removing diverse chemicals including dust in the atmosphere by using various kinds of air purifying apparatuses. For example, a water shower system in the conventional art is currently mainly used as an air purifying apparatus and is configured to contact chemicals, such as for example, NH 3 , SOx and NOx, with water and then filter these chemicals from the air. 
         [0007]    In addition, with the above-mentioned conventional air purification processes, the water supplied to remove the chemicals, NH 3 , SOx and NOx is managed through PH level. which indicates acidity or basicity. In examples of the relatively highest removal efficiency of air purification processes of the conventional art, a water-soluble level for NH 3  and SOx is relatively high and thus the removal efficiency therefor is high, but NOx has a low solubility and thus the efficiency thereof is checked as 10% or below. Therefore, NOx may be very difficult to remove by an air purifying apparatus of the conventional art and thus NOx may be supplied into the clean room thereby adversely affecting the air purification level of the clean room and the production yield of semiconductor devices. 
         [0008]    Thus, there is a need in the art for an air purifying apparatus and an air purifying method thereof capable of heightening the removal efficiency of NOx contained in air. 
       SUMMARY 
       [0009]    Some embodiments of the inventive concept may provide an air purifying apparatus and an air purifying method thereof capable of heightening a removal efficiency of NOx contained in air. 
         [0010]    In accordance with an embodiment of the inventive concept, an apparatus for purifying air is provided. The apparatus includes an air flow generating device for generating a flow of air, a nozzle spraying water to the air flowing through the air flow generating device, a plasma module performing a plasma reaction on the air containing the water sprayed from the nozzle, and oxidizing NOx in the air and converting it into NO 3 , an eliminator eliminating the NO 3  converted in the plasma module and the water contained in the air and passing pure air through the eliminator and out of the air purifying apparatus, and a water tank storing the water received from the eliminator. 
         [0011]    The plasma module may generate a low-temperature atmospheric-pressure plasma reaction, and may comprise a dielectric barrier reactor or a pulse corona reactor. 
         [0012]    The NO 3  may be collected by dissolving it in the moisture of the air. 
         [0013]    In accordance with another embodiment of the inventive concept, a method of removing NOx is provided. The method includes converting the NOx in air into NO 3  through a plasma reaction and then subsequently removing the NO 3  from the air. 
         [0014]    In accordance with another embodiment of the inventive concept, a method of purifying air is provided. The method includes generating a flow of air, spraying water to the air, performing a plasma reaction on the air containing the water, and oxidizing NOx in the air and converting it into NO 3  and eliminating the water and the NO 3  contained in the air and passing pure air. 
         [0015]    Accordingly, with embodiments of the inventive concept, air undergoes a plasma reaction, thereby efficiently removing NOx from the air. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The inventive concept will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration just, and thus are not limitative of the inventive concept, and wherein: 
           [0017]      FIG. 1  schematically illustrates an air purifying apparatus according to an embodiment of the inventive concept; 
           [0018]      FIG. 2  is a cross-sectional view of a dielectric barrier reactor; 
           [0019]      FIGS. 3A and 3B  are cross-sectional views illustrating a pulse corona reactor; 
           [0020]      FIG. 4  is a flowchart providing an air purifying method according to an embodiment of the inventive concept; 
           [0021]      FIG. 5  is a graph showing a removal efficiency of chemicals based on the PH of water; and 
           [0022]      FIG. 6  is a graph of comparing chemical removal efficiency before and after a plasma reaction. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]    Embodiments of the inventive concept now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the inventive concept are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
         [0024]    An air purifying apparatus and an air purifying method thereof according to an embodiment of the inventive concept are described as follows. 
         [0025]    Function and operation according to an embodiment of the inventive concept are first described more in detail referring to  FIGS. 1 to 6 , as follows. 
         [0026]      FIG. 1  schematically illustrates an air purifying apparatus according to an embodiment of the inventive concept. As shown in  FIG. 1 , in the air purifying apparatus according to an embodiment of the inventive concept, air containing NOx is plasma reacted in a plasma module  30  and thus the NOx is converted into NO 3  having a high water-solubility, thereby removing it. At this time, air flowing in a given pressure from an air flow generating device such as, for example, a fan  10  is passed through water  60  sprayed from a nozzle  20 , thereby eliminating NH 3  and SOx therefrom. The nozzle  20  may be referred to as a water shower system, and spray water  60  as a fog type spray to the air. At this time, the air may have very high humidity through increased moisture. Therefore, the surface area of the water  60  sprayed through the nozzle  20  may be relatively large, thereby causing the melting and the removal of SOx and NH 3  having a relatively high water-solubility from the air. However, NOx may be hardly removed because of a relatively low water-solubility. 
         [0027]    NOx in air mostly exists as nitrogen monoxide and nitrogen dioxide. The above-mentioned components of NOx are pollution materials of the air generated when nitrogen in the air reacts with oxygen at a relatively high temperature in a device such as an automobile engine. Nitrogen monoxide is mainly generated through combustion and then is discharged into the atmosphere and oxidized into nitrogen dioxide. Nitrogen dioxide may be very harmful to the lungs and organs of the human body. Therefore, air supplied into a clean room should be provided after removing NOx therefrom. 
         [0028]    Accordingly, in the air purifying apparatus according to an embodiment of the inventive concept, NOx is excited into a plasma state and converted into NO 3  by using the plasma module  30 , and then melts in moisture of air and thus is produced into HNO 3  and then removed. 
         [0029]    In the plasma module  30 , air of the atmosphere undergoes the plasma reaction at relatively low-temperature (e.g. a normal temperature) and atmospheric-pressure. The plasma module  30  may be largely classified as a dielectric barrier reactor  30   a  or a pulse corona reactor  30   b.    
         [0030]      FIG. 2  is a cross-sectional view of a dielectric barrier reactor  30   a . In the dielectric barrier reactor  30   a , a dielectric  31  is installed in one or all of a plurality of discharge electrodes  32  having a given gap therebetween. When ionization occurs at one position point, transported-charges may be built up on the dielectric  31 . A uniform glow discharge  33  may be obtained by substantially increasing the efficiency of the voltage applied by alternate current through the use of a charge build-up effect of the dielectric  31 . 
         [0031]    Electrical fields caused by such charges may reduce an electrical field induced between the plurality of electrodes  32 , and after a lapse of several nanoseconds, a flow of current may be cut off. A current pulse duration time depends upon pressure and an ionization characteristic of gas and a characteristic of the dielectric  31 . The dielectric  31  may have two functions. In the dielectric  31 , a decided charge amount may be controlled by using a microdischarge and the microdischarge is dispersed entirely in the electrode  32 . An atmospheric-pressure plasma reaction has a density of a radical higher by about 100 to about 1000 times than an existing vacuum plasma, and has a relatively low temperature of normal temperature to about 150° C. 
         [0032]    One of significant characteristics in such mechanism is that there exists a microdischarge through a streamer with a relatively high current density locally in a space of the discharge. The streamer is used in an ozonator generating a large amount of ozone that oxidizes NOx of air in the atmosphere. Ozone can be generated by oxygen of air, and can oxidize NOx and convert it into NO 3  having a relatively high water-solubility. 
         [0033]    Therefore, in the air purifying apparatus according to embodiment of the inventive concept, NOx is oxidized by using ozone generated in the dielectric barrier reactor  30   a  and thus NO 3  having a relatively high water-solubility is produced and then the NO 3  can be removed through the eliminator. 
         [0034]      FIGS. 3A and 3B  are cross-sectional views illustrating a pulse corona reactor  30   b . In the pulse corona reactor  30   b , a high voltage iron-core electrode  34  receiving applied-high voltage power is provided in a center of ground electrode  36  having a tube shape. When a high voltage of several KVs is applied to the high voltage iron-core electrode  34 , a faint light emission effect can be shown on the periphery thereof, and this indicates a discharge occurrence. That is, an electrical field is generated on a surface of the high voltage iron-core electrode  34  and a pulse corona discharge  37  begins. 
         [0035]    The pulse corona discharge  37  is directed from the high voltage iron-core electrode  34  toward ground electrode  36  and so the intensity of the electrical field is rapidly lowered, and positive ions generated on the surface of the high voltage iron-core electrode  34  are directed to the ground electrode  36  and move at a relatively low speed. At a portion the ions move, ionization or an excitation reaction of molecules is generated, and most of them have a light emission between the electrodes  36 . Therefore, NOx is excited to positive ions and combined with oxygen and then can be changed into NO 3  based on a high water-solubility. 
         [0036]    Furthermore, the pulse corona discharge  37  may be inappropriate for a large quantity of chemical industrial production, but when using the pulse corona discharge  37 , ionic wind can be formed in air and molecular ions may be freely generated. By using such characteristic nature, particles floating in air can be charged to ions and may be integrated onto the high voltage iron-core electrode  34  by using high voltage. 
         [0037]    As a result, in the air purifying apparatus according to embodiments of the inventive concept, NOx is excited and oxidized by using the pulse corona reactor  30   b , thereby producing NO 3  and readily removing NOx from the air. 
         [0038]    On the other hand, moisture having soluble NO 3  in air is eliminated by eliminator  40 . The eliminator  40  can gather and eliminate NO 3  soluble in the moisture of the air. For example, the eliminator  40  may comprise a filter, bubbler or cooling plate. The filter may be a filtering net through which air is passed via air holes, and collects NO 3  contained in the air and water  60 . The bubbler collects NO 3  and water  60  by bubbling air. The cooling plate collects the moisture of the air into water drops during cooling the air. The cooling plate has a plurality of air holes through which the air is passed. The cooling plate may be formed of, for example, Teflon material dominantly resisting to corrosion from an oxide solution, such as for example, NO 3 . Thus, the water drops condensed from the moisture of the air in the eliminator  40  fall into a water tank  50 . 
         [0039]    An air purifying method in the air purifying apparatus according to an embodiment of the inventive concept is described as follows. 
         [0040]      FIG. 4  is a flowchart providing an air purifying method according to an embodiment of the inventive concept. 
         [0041]    As shown in  FIG. 4 , in air purifying method according to an embodiment of the inventive concept, a portion of air in the outside atmosphere flows by a given pressure of fan  10  in a step S 10 . The air contains various kinds of chemical components, such as for example, NH 3 , SOx and NOx, together with dust. Also, particles such as dust of air may be removed through a filter adaptable on the front or back of the fan  10 . 
         [0042]    Then, water  60  from a nozzle  20  is sprayed to air to remove NH 3 , and SOx in a step S 20 . The water  60  sprayed from the nozzle  20  is dispersed in a shower type spray, not only removing NH 3  and SOx, but also heightening the humidity of the air. Accordingly, the air contains just NOx by practically eliminating NH 3  and SOx. 
         [0043]      FIG. 5  is a graph showing a removal efficiency of chemicals based on PH of water  60 . As shown in the graph, the removal efficiency of the chemicals in the air becomes different according to the PHs of the water  60  sprayed from nozzle  20 . In  FIG. 5 , almost all of the chemicals can be readily removed by using water of weak alkalinity of approximately PH 6.5. NH 3    70  has a removal efficiency of approximately 70% by using water  60  containing a soluble acid component with relatively low PH. On the other hand, SOx  80  has a removal efficiency of approximately 70% by using water  60  containing a soluble alkali component with relatively high PH. However, NOx  90  has a removal efficiency of approximately 10% or below even though water  60  containing a soluble alkali component with relatively high PH is used. In other words, it may be difficult to remove NOx  90  in air simply by controlling a value of PH. Therefore, NOx  90  may be physically decomposed and oxidized in a subsequent process. 
         [0044]    Subsequently, NOx in air undergoes a plasma reaction and is converted into NO 3  in a step S 30 . The plasma reaction is to excite corresponding material into ions and electron state from gas, liquid or solid state under given conditions. During that, a portion of oxygen in air may be converted into ozone. Similarly, a portion of NOx may be separated into nitrogen and oxygen in the plasma state, or may be mostly combined with peripheral oxygen or ozone, and thus may be converted into NO 3 . NO 3  receives hydrogen from moisture contained in air and then is converted into HNO 3 , and thus is dissolved into the moisture. Accordingly, NOx is converted into NO 3  and is soluble in moisture of air. 
         [0045]      FIG. 6  is a graph of comparing chemical removal efficiency of before and after a plasma reaction, and NOx is processed by the plasma reaction. As illustrated in  FIG. 6 , the removal efficiency of NOx is increased by almost three times or more relatively when the NOx is processed by the plasma reaction. Further, SOx and NH 3  are processed by the plasma reaction, thereby minutely increasing the removal efficiency. Accordingly, NOx is processed by the plasma reaction in a wet removal using water  60 , thereby increasing the removal efficiency of the NOx. 
         [0046]    In a last process, NO 3  is removed through eliminator  40  and then just pure air is passed into clean room in a step S 40 . Air containing moisture having soluble NO 3  is cooled by the eliminator  40 , thereby removing the moisture and purifying the air. 
         [0047]    As a result, in the air purifying method according to an embodiment of the inventive concept, NOx is converted into NO 3  through the plasma reaction and becomes soluble in the moisture of the air and thus is removed. 
         [0048]    Having described the exemplary embodiments of the present invention, it is further noted that it is readily apparent to those of reasonable skill in the art that various modifications may be made without departing from the spirit and scope of the invention which is defined by the metes and bounds of the appended claims.