Abstract:
A plasma scrubber that forms a high temperature atmosphere in a reactor to effectively decompose and remove a non-biodegradable gas and reduce power consumption is disclosed. The plasma scrubber includes: a first reactor to which a non-biodegradable gas is supplied; an electrode installed in the first reactor and protruding in the flow direction of the non-biodegradable gas to generate plasma in the non-biodegradable gas supplied between the electrode and the first reactor by a discharge reaction in the first reactor; a second reactor connected to the first reactor to form continuous arc jets by anchoring the plasma to the electrode; and a third reactor connected to the second reactor to decompose the non-biodegradable gas by forming a reaction section of high temperature that contains electrons and chemical species of high reactivity in the second reactor and thereby increasing the stay time and reactivity of the non-biodegradable gas.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates generally to a plasma scrubber and, more particularly, to a plasma scrubber that enables decomposition of non-biodegradable gases with low cost. 
         [0003]    2. Description of the Related Art 
         [0004]    Gases that cause global warming include CO 2 , CH 4 , N 2 O, HFC, and per-fluorocompounds (PFC). The per-fluorocompounds (PFC) are gases mainly used in display manufacturing processes and semiconductor manufacturing processes and include CF 4 , C 2 F 6 , SF 6 , and NF 3 . 
         [0005]    Global warming gases have stable molecular structures and are not easily biodegraded, so they are referred to as non-biodegradable gases. A technology for decomposing non-biodegradable gases is necessary to prevent environmental contamination and global warming caused by such non-biodegradable gases. 
         [0006]    Methods for removing non-biodegradable gases include an oxidation method using combustion of gases, a method for chemically absorbing gases, and a decomposition method using plasma. The decomposition method using plasma is mainly used in removal of per-fluorocompounds. 
         [0007]    The decomposition method using plasma uses a plasma torch generating plasma of high temperature in a reactor, in which case several tens or hundreds of kilowatts of power is consumed only to treat several tens or hundreds of liters per minute. 
         [0008]    Non-biodegradable gases are decomposed in a reactor through thermal decomposition of the gases under a high temperature atmosphere or collisions of electrons of high energy and gas molecules. However, it is difficult to form in a reactor an expanded reaction section of high temperature in which electrons of high energy and chemical species of high reactivity are abundant. 
       BRIEF SUMMARY 
       [0009]    The present invention has been made in view of the above problems, and the present invention provides a plasma scrubber that enables effective decomposition and removal of non-biodegradable gases by forming an expanded reaction section of high temperature in which electrons of high energy and chemical species of high reactivity are abundant. 
         [0010]    The present invention also provides a plasma scrubber that enables effective decomposition and removal of non-degradable gases by forming a high temperature atmosphere in a reactor while reducing power consumption. 
         [0011]    In order to achieve the objects, the present invention provides a plasma scrubber including: a first reactor to which a non-biodegradable gas is supplied; an electrode installed in the first reactor and protruding in the flow direction of the non-biodegradable gas to generate plasma in the non-biodegradable gas supplied between the electrode and the first reactor by a discharge reaction in the first reactor; a second reactor connected to the first reactor to form continuous arc jets by anchoring the plasma to the electrode; and a third reactor connected to the second reactor to decompose the non-biodegradable gas by forming a reaction section of high temperature that contains electrons and chemical species of high reactivity in the second reactor and thereby increasing the stay time and reactivity of the non-biodegradable gas. 
         [0012]    The internal passage of the second reactor may become narrower as it goes from the first reactor to the third reactor. The third reactor may have an inner diameter larger than the maximum inner diameter of the second reactor. 
         [0013]    The electrode may include: an expansion section that becomes gradually expanded toward the inner surface of the first reactor as it goes from the first reactor to the second reactor; a maximum diameter section formed at an end of the expansion section; and a contraction section that becomes gradually contracted from the maximum diameter section. 
         [0014]    The first reactor may include first gas supply holes and the first gas supply holes face the expansion section of the electrode. The first gas supply holes may be inclined with respect to the normal direction of the first reactor. 
         [0015]    The electrode may include second gas supply holes connected to the outside and the second gas supply holes face the first reactor from the expansion section. The second gas supply holes may be inclined with respect to the normal direction of the electrode. 
         [0016]    The plasma scrubber may further include an insulator mounted to the first reactor to electrically insulate and seal the electrode and the first reactor. 
         [0017]    The first reactor may include: an inner cylinder into which the electrode is inserted; and an outer cylinder coupled to the outer side of the inner cylinder on the opposite side to the second reactor. 
         [0018]    A supply line for supplying the non-biodegradable gas may be connected to the outer side of the outer cylinder, a gas chamber may be formed inside the outer cylinder, and first gas supply holes for supplying the non-biodegradable gas supplied to the gas chamber toward the electrode may be formed in the inner cylinder. 
         [0019]    The electrode may include: an expansion section that becomes gradually expanded toward the inner surface of the first reactor as it goes from one side to the other side of the inner cylinder; a maximum diameter section formed at an end of the expansion section; and a contraction section that becomes gradually contracted from the maximum diameter section. 
         [0020]    The plasma scrubber may further include an insulator mounted to the outer cylinder to electrically insulate the electrode and the inner cylinder and seal the outer cylinder and the electrode. 
         [0021]    The non-biodegradable gas may be a per-fluorocompound gas. The non-biodegradable gas may be one of CF 4 , C 2 F 6 , SF 6 , and NF 3 . 
         [0022]    A cooling water supply passage and a cooling water discharge passage that supply cooling water into the electrode, and circulate and discharge the cooling water may be formed in the electrode. 
         [0023]    The cooling water supply passage and the cooling water discharge passage may be dually formed and the cooling water supply passage may be formed inside the cooling water discharge passage. 
         [0024]    The electrode includes: a supply passage formed in the interior thereof to supply one of water, an oxidizing agent, a fuel and an inert gas into the first reactor; and a porous section connected to the supply passage. 
         [0025]    The first reactor may include a first nozzle for supplying one of water, an oxidizing agent, a fuel, and an inert gas into the first reactor. 
         [0026]    The second reactor may include a second nozzle installed in a jet hole formed in the second reactor to supply one of water, an oxidizing agent, a fuel, and an inert gas into the second reactor. 
         [0027]    The third reactor may include a third nozzle installed in a third reactor to supply one of water, an oxidizing agent, a fuel, and an inert gas into the third reactor. 
         [0028]    According to the present invention, plasma can be generated by a discharge between an electrode and a first reactor by supplying a non-biodegradable gas into a first reactor in which the electrode is installed. 
         [0029]    Further, the contact property between a reactant, i.e., a non-biodegradable gas and plasma can be improved by a gradually contracted shape of a second reactor connected to the first reactor. 
         [0030]    Furthermore, the stay time of the non-biodegradable gas in a reactive expanded volume of high temperature can be increased by a gradually expanded shape of a third reactor connected to the second reactor, thereby expediting decomposition of the non-biodegradable gas. 
         [0031]    Furthermore, when an inflammable gas and an oxidizing gas are supplied to the non-biodegradable gas, chemical species such as radicals necessary for decomposition of a per-fluorocompound (PFC) gas can be supplied to form a high temperature atmosphere inside a reactor and reduce power consumption. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
           [0033]      FIG. 1  is a schematic view of a non-degradable gas decomposing apparatus including a plasma scrubber according to the first embodiment of the present invention; 
           [0034]      FIG. 2  is an exploded perspective view of the plasma scrubber according to the first embodiment of the present invention; 
           [0035]      FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 2 ; 
           [0036]      FIG. 4  is a cross-sectional view taken along line IV-IV of  FIG. 3 ; 
           [0037]      FIG. 5  is a cross-sectional view of a plasma scrubber according the second embodiment of the present invention; 
           [0038]      FIG. 6  is a cross-sectional taken along line VI-VI of  FIG. 5 ; 
           [0039]      FIG. 7  is a cross-sectional view of a plasma scrubber according to the third embodiment of the present invention; and 
           [0040]      FIGS. 8 and 9  are cross-sectional views of electrodes applied to the plasma scrubber of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. However, the present invention may be realized in various forms and is not limited to the embodiments. In the drawings, elements that are not relevant to the description of the embodiments of the present invention are omitted to make the present invention clear. The same or similar elements are endowed with the same reference numerals throughout the specification. 
         [0042]      FIG. 1  is a schematic view of a non-biodegradable gas decomposing apparatus including a plasma scrubber according to the first embodiment of the present invention. 
         [0043]    Referring to  FIG. 1 , the non-biodegradable gas decomposing apparatus includes a plasma scrubber  200  installed inside a body  100  to decompose a non-biodegradable gas, a wet scrubber  300  preventing recombination of the gas decomposed by the plasma scrubber  200 , and a collector  400  collecting particles contained in the gas that has passed through the wet scrubber  300  to discharge the decomposed gas. 
         [0044]    The non-biodegradable gas is a gas that causes global warming, and includes a per-fluorocompound (PFC) gas. For example, per-fluorocompound gases include CF 4 , C 2 F 6 , SF 6 , and NF 6  that are used in a display manufacturing process or a semiconductor manufacturing process. 
         [0045]    A supply line  101  supplying a per-fluorocompound gas and a discharge line  102  discharging the gas obtained by decomposing the per-fluorocompound gas is connected to the body  100 . The plasma scrubber  200 , the wet scrubber  300 , and the collector are installed inside the box  100  and are disposed between the supply line  101  and the discharge line  102 . 
         [0046]    The plasma scrubber  200  is connected to the supply line  101  to decompose and remove the non-biodegradable gas supplied to the supply line  101  using plasma reaction. 
         [0047]    The wet scrubber  300  injects water to the gas decomposed by the plasma scrubber  200  or forces the gas to pass through a liquid space filled with water to restrain and remove recombination of the decomposed gas. For example, HF is diluted and retrieved. 
         [0048]    The collector  400  may be a cyclone collector, and removes silicon particles such as SiH4 from the gas supplied from the wet scrubber  300 . The collector  400  is connected to the discharge line  102  and the decomposed gas is discharged outside the box  100 . 
         [0049]    The wet scrubber and the collector  400  are well known in the art, and a detailed description of the illustrated nozzle  301  and the cyclone collector will be omitted. 
         [0050]      FIG. 2  is an exploded perspective view of the plasma scrubber according to the first embodiment of the present invention.  FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 2 . 
         [0051]    Referring to  FIGS. 2 and 3 , the plasma scrubber  200  includes a first reactor  10 , a second reactor  20 , and a third reactor  30  that are sequentially disposed in the box  100 , and an electrode  40  installed inside the first reactor  10 . 
         [0052]    A non-biodegradable gas is supplied to the first reactor  10  so that a discharge operation is carried out between the first reactor  10  and the electrode  40  to generate plasma. One side of the first reactor  10  is opened and the other side thereof is closed so that the plasma generated between the first reactor  10  and the electrode  40  can flow in the flow direction of the supplied non-biodegradable gas. 
         [0053]    The electrode  40  is installed inside the first reactor  10  and protrudes in the flow direction of the non-degradable gas. A discharge is generated between the electrode  40  and the first reactor  10  by an AC or DC voltage applied to both the electrode  40  and the first reactor  10 , and the inert gas and non-biodegradable gas supplied to the first reactor  10  and the electrode  40  generate plasma. 
         [0054]    Considering flow of a non-biodegradable gas and generation of plasma, the electrode  40  changes the distance between the electrode  40  and the first reactor  10 . The electrode  40  may include an expansion section, a maximum diameter section  42 , and a contraction section  43  that are smoothly connected to each other. 
         [0055]    The expansion section becomes gradually expanded toward the inner surface of the first reactor  10  as it goes from the first reactor  10  to the second reactor  20 . Accordingly, the distance between the expansion section  41  and the first reactor  10  becomes gradually smaller as the expansion section  41  goes toward the maximum diameter section. 
         [0056]    The contraction section becomes gradually contracted as it goes from the maximum diameter section  42  to the second reactor  20 . Accordingly, the distance between the contraction section  43  and the first reactor  10  becomes gradually larger as the contraction section  43  becomes far away from the maximum diameter section  42 . 
         [0057]    The expansion and contraction structure of the electrode  40  installed inside the first cylindrical reactor  10  enables repetition of creation and termination of a discharge between the first reactor  10  and the electrode  40  during application of an AC or DC voltage. 
         [0058]    The first reactor  10  has first gas supply holes  11  connected to the outside to introduce the non-biodegradable gas. The non-biodegradable gas is injected toward the expansion section of the electrode  40  through the first gas supply holes  11 . 
         [0059]    The first reactor  10  may include an inner cylinder  12  and an outer cylinder  13 . The electrode  40  is installed inside the inner cylinder  40 . In other words, a discharge space is formed between the electrode  40  and the inner cylinder  12 . The outer cylinder  13  is coupled to the outer side of the inner cylinder  12  opposite to the second reactor  20 . 
         [0060]    The outer cylinder  13  coupled to the inner cylinder  12  includes a gas chamber  14  therein. A supply line  101  supplying a non-biodegradable gas is connected to the outer side of the outer cylinder  13 . 
         [0061]    The inner cylinder  12  includes first gas supply holes  11  for supplying the non-biodegradable gas supplied to the gas chamber  14 . The first gas supply holes  11  supply the non-biodegradable gas supplied to the gas chamber  14  toward the electrode  40 . 
         [0062]    In this case, the expansion section  41  of the electrode  40  becomes gradually expanded toward the inner surface of the inner cylinder  12  to the maximum diameter section  42  as it goes from one side of the inner cylinder  12  to the opposite side thereof. The contraction section becomes gradually contracted from the maximum diameter section  42 . 
         [0063]      FIG. 4  is a cross-sectional view taken along line IV-IV of  FIG. 3 . 
         [0064]    Referring to  FIG. 4 , the first gas supply holes  11  are inclined with respect to the normal direction of the first reactor  10  or the inner cylinder  12 . Accordingly, the non-biodegradable gas supplied to the first gas supply holes  11  forms swirls between the electrode and the first reactor  10  or between the electrode and the inner cylinder  12 , forming plasma swirls. 
         [0065]    The swirls of the non-biodegradable gas induce uniform discharge between the electrode  40  and the inner cylinder  12  and enable efficient utilization of the interior space of the inner cylinder  12 . The plasma swirls form tighter arc swirls in the second reactor  12 . 
         [0066]    An insulator  50  is installed in the first reactor  10  or the outer cylinder  13  on the opposite side of the second reactor  20 . The insulator  50  may be variously formed according to the structure of the first reactor  10  or the outer cylinder  13 . 
         [0067]    In other words, the insulator  50  is mounted to the first reactor  10  on the opposite side of the second reactor  20 , and electrically insulates and seals the first reactor  10  and the electrode  40 . The insulator  50  may be made of ceramics of high heat-resistance. 
         [0068]    More particularly, the insulator  50  is mounted to the outer cylinder  13  on the opposite side of the second reactor  20 , and electrically insulates and seals the electrode  40  and the inner cylinder  12 . 
         [0069]    Bolts  51  are inserted through through-holes  52  formed in the insulator  50  and are screw-coupled to coupling holes  13 b formed in a flange  13 a of the outer cylinder  13  of the first reactor  10  and corresponding to the through-holes  52 , whereby the insulator  50  and the outer cylinder  13  of the first reactor  10  are connected to each other. The insulator  50  and the first reactor  10  may form a simple structure (not shown) using welding of an insulator case (not shown) to the first reactor. 
         [0070]    A discharge may occur between the electrode  40  to which an AC or DC voltage is applied and the first reactor  10  or between the electrode  40  and the inner cylinder  12  due to insulation of the insulator  50 , whereby a plasma reaction space is formed to decompose the non-biodegradable gas. 
         [0071]    The second reactor  20  is connected to the first reactor  10  to form an arc jet by increasing the density of plasma. The internal passage of the second reactor  20  becomes gradually narrower as it goes from the first reactor  10  to the third reactor  30 . A jet hole  21  is formed at an end of the second reactor  20 . 
         [0072]    Bolts  15  pass through through-holes  12   b  formed in a flange  12   a  of the inner cylinder  12  of the first reactor  10  and through-holes  23  formed on a flange  22  of the second reactor  20  and are screw-coupled to nuts  16  to connect the inner cylinder  12  of the first reactor  10  and the second reactor  20 . 
         [0073]    Actually, the first reactor  10 , the second reactor  20 , and the third reactor  30  may be simply manufactured by welding in a process of manufacturing the non-biodegradable gas decomposing apparatus according to the embodiment of the present invention. 
         [0074]    The shape of the second reactor  20  having an inner diameter D 20  that becomes gradually narrower enables the continuously generated arcs to pass through the jet hole  21  formed at a connection point of the second reactor  20  and the third reactor  30 . Accordingly, the contact property of the non-biodegradable gas with the plasma region increases while the non-biodegradable gas passes through the jet hole  21 , increasing reaction efficiency. 
         [0075]    The third reactor  30  is connected to the second reactor  20  to provide an expanded reaction space of a reactive high temperature atmosphere. The third reactor  30  is connected to the jet hole  21  of the second reactor  20  and has an inner diameter larger than the maximum inner diameter D 20  of the second reactor  20 . 
         [0076]    Bolts  31  pass through through-holes  25  formed in another flange  24  of the second reactor  20  and through-holes  33  formed in a flange  32  of the third reactor  30  and are screw-coupled to nuts  34 , whereby the second reactor  20  and the third reactor  30  are connected to each other. 
         [0077]    The third reactor  30  is connected to the jet hole  21  and has a rapidly expanded shape, in which case an expansion section of high temperature is formed. Accordingly, the time for staying a reactant, i.e., the non-biodegradable gas, stays in the expansion section increases, expediting decomposition of the non-biodegradable gas. 
         [0078]    If discharge of the first reactor  12  starts, a plasma arc is continuously generated by the reactor characteristics and flow characteristics of the first reactor  12  while passing through the jet hole  21 . The plasma arc is expanded in the third reactor  30  to form a condition advantageous in plasma reaction. In this case, the plasma arc is stably discharged with the arc not being detached from the electrode  40  but being anchored to the electrode  40 . 
         [0079]    In this state, the temperatures of the reaction spaces of the first, second, and third reactors  10 ,  20 , and  30  increase up to a temperature suitable for decomposition of the non-biodegradable gas, with the heat of the gaseous reactant being easily transferred. 
         [0080]    An inflammable gas and an oxidizing agent may be used to decompose the non-biodegradable gas. In this case, the inflammable gas and the oxidizing agent are supplied through the first gas supply holes  11  through which the non-biodegradable gas is supplied. 
         [0081]    When the non-biodegradable gas contains the inflammable gas and the oxidizing agent, the high temperature state formed by oxidation optimizes the plasma characteristics, improving transfer of heat into the interior spaces of the first, second, and third reactor  10 ,  20 , and  30 . 
         [0082]    If the reaction region is maintained at a low density with high temperature, the average number of collisions of electrons increases due to the low density. The increased average number of collisions of electrons induces acceleration of electrons, thereby generating a large number of electrons having high energy and expediting decomposition of the non-biodegradable gas. 
         [0083]    Reactive radicals necessary for removal of the non-biodegradable gas are produced in the oxidation of the inflammable gas and the oxidizing agent or the decomposition of the inflammable gas and the oxidizing agent, expediting decomposition of the non-biodegradable gas. 
         [0084]    For example, during decomposition of CF 4 , i.e., a per-fluorocompound (PFC), CF 4  is contained in nitrogen gas to be injected to rotating arc, in which case the decomposition ratio of CF 4  is low, being in the range of from several to several tens of percent at several kilowatts with respect to the flow rate of 5 to 10 Nm 3 /hr. 
         [0085]    However, if CF 4  and O 2 , i.e., an inflammable gas and an oxidizing agent, are supplied as a partial oxidation condition, the decomposition ratio of CF 4  increases up to 80 to 90% at the same power value. 
         [0086]    Recombination of the decomposed gas is restrained by the wet scrubber  300  and it is discharged through the discharge line  102 , resolving and removing HF formed in the decomposition process and removing particles through the collector  400 . 
         [0087]    Hereinafter, other various embodiments of the present invention will be illustrated. The other embodiments of the present invention are similar to the first embodiment of the present invention. Accordingly, description of the same or similar parts will be omitted and different points will be mainly described in detail. 
         [0088]      FIG. 5  is a cross-sectional view of a plasma scrubber according the second embodiment of the present invention. 
         [0089]    A non-biodegradable gas is supplied from outside of the electrode  40  in the first embodiment, but is supplied to the interior of the electrode  240  in the second embodiment of the present invention. 
         [0090]    In  FIG. 5 , a non-biodegradable gas is supplied from outside of an electrode  240  and is also supplied through the interior of the electrode  240 . For convenience sake, additional structures will be described in detail in the second embodiment of the present invention. 
         [0091]    The electrode  240  includes second gas supply holes  241  connected to the outside. The second gas supply holes  241  are formed toward the inner cylinder  12  of the first reactor  10  at the expansion section of the electrode  240  formed inside the electrode  240 . 
         [0092]      FIG. 6  is a cross-sectional taken along line VI-VI of  FIG. 5 . 
         [0093]    Referring to  FIG. 6 , the second gas supply holes  241  are inclined with respect to the normal direction of the expansion section  41  of the electrode  240 . Accordingly, the non-biodegradable gas supplied to the second gas supply holes  241  forms swirls between the electrode  240  and the first reactor  10  or between the electrode  240  and the inner cylinder  12 , forming plasma swirls. 
         [0094]    The ends of the second gas supply holes  241  and the ends of the first gas supply holes  11  cross each other between the first reactor  10  and the electrodes  40  and  240 . Accordingly, the swirls of the non-biodegradable gas supplied through the second gas supply holes  241  makes the swirls of the non-biodegradable gas supplied through the first gas supply holes  11  stronger. 
         [0095]      FIG. 7  is a cross-sectional view of a plasma scrubber according to the third embodiment of the present invention.  FIGS. 8 and 9  are cross-sectional views of electrodes applied to the plasma scrubber of  FIG. 7 . 
         [0096]    Referring to  FIGS. 7 and 8 , a cooling water supply passage  341  and a cooling water discharge passage  342  that discharge cooling water after cooling water is supplied into the interior of an electrode  340  to be circulated are formed in an electrode  340 . 
         [0097]    The cooling water supply passage  341  and the cooling water discharge passage  342  are dually formed. For example, the cooling water supply passage  341  is formed inside the cooling water discharge passage  342 . 
         [0098]    Accordingly, cooling water of low temperature is supplied to the cooling water supply passage  341  to cool the electrode  340  heated by a plasma discharge, and is discharged through the cooling water discharge passage. Therefore, the electrode  340  can be prevented from being overheated. 
         [0099]    Referring to  FIG. 9 , a supply passage  441  formed inside the electrode  440  to directly supply an additive, i.e., one of water, an oxidizing agent, a fuel, and an inert gas into the interior of the first reactor  10  and a porous portion  442  connected to the supply passage  441  are formed in the electrode  440 . 
         [0100]    The additive supplied through the supply passage  441  is supplied between the electrode  440  and the first reactor  10 , making a continuous arc jet due to a plasma discharge stronger. 
         [0101]    Referring now to  FIG. 7  again, the first reactor  10  includes a first nozzle N 10 . An additive, i.e., one of water, an oxidizing agent, a fuel, and an inert gas is supplied through the first nozzle N 10  into the interior of the first reactor  10 . 
         [0102]    The second reactor  20  includes a second nozzle N 20 . An additive, i.e., one of water, an oxidizing agent, a fuel, and an inert gas is supplied through the second nozzle N 20  into the interior of the second reactor  20 . 
         [0103]    The third reactor  30  includes a second nozzle N 20 . An additive, i.e., one of water, an oxidizing agent, a fuel, and an inert gas is supplied through the third nozzle N 30  into the interior of the third reactor  30 . 
         [0104]    The first, second, and third nozzles N 10 , N 20 , and N 30  may be used in one plasma scrubber  300  all together or may be selectively used. 
         [0105]    The additive supplied to the first, second, and third nozzles N 10 , N 20 , and N 30  makes a continuous arc jet due to a plasma discharge stronger in the first, second, and third reactors  10 ,  20 , and  30 . 
         [0106]    While the invention has been shown and described with respect to the exemplary embodiments, it will be understood by those skilled in the art that the system and the method are only examples of the present invention and various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.