Patent Publication Number: US-2007111077-A1

Title: Carbon dioxide remover for direct oxidation fuel cell and fuel cell system having the same

Description:
CLAIM OF PRIORITY  
      This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 from an application for CARBON DIOXIDE REMOVER FOR DIRECT OXIDATION FUEL CELL AND FUEL CELL SYSTEM HAVING THE SAME, earlier filed in the Korean Intellectual Property Office on the 17 of Nov. 2005 and there duly assigned Serial No. 10-2005-0110161.  
     BACKGROUND OF THE INVENTION  
      1. Technical Field  
      The present invention relates to a fuel cell system and, more particularly, to a fuel cell system employing a direct oxidation fuel cell scheme.  
      2. Related Art  
      A fuel cell is, as is well known, an electricity generating system for directly converting chemical reaction energy into electric energy through an electrochemical reaction between hydrogen contained in hydrocarbon materials and oxygen additionally supplied.  
      A fuel cell is mainly classified into a fuel cell with a reformer and used as a polymer electrolyte membrane fuel cell (PEMFC), and a direct oxidation membrane fuel cell without the reformer and used as a direct methanol fuel cell (DMFC).  
      The PEMFC includes a fuel cell body called a stack (hereinafter, referred to as a stack for the purpose of convenience). In the PEMFC, electric energy is generated through an electrochemical reaction between a hydrogen gas supplied from a reformer and air supplied by operating an air pump or a fan. The reformer functions as a fuel processing device which reforms a fuel, generates a hydrogen gas from the fuel, and supplies the hydrogen gas to the stack.  
      Unlike the PEMFC, in the direct oxidation fuel cell, an alcohol type fuel instead of hydrogen gas is directly provided, and electric energy is generated through an electrochemical reaction between hydrogen contained in the alcohol type fuel and oxygen additionally supplied.  
      In a fuel cell system employing a direct oxidation fuel cell scheme, the direct oxidation fuel cell discharges carbon dioxide, which is generated through a fuel oxidation reaction, and a non-reactive fuel remaining in the fuel cell. Thus, the fuel cell system needs to function as a recycling system which can remove the generated carbon dioxide and recycle the non-reactive fuel.  
      The recycling system includes a carbon dioxide remover which removes carbon dioxide while storing the non-reactive fuel and the carbon dioxide discharged from the fuel cell, and which recycles the non-reactive fuel as a fuel cell.  
      However, in this fuel cell system, a container is additionally required for storing the non-reactive fuel and the carbon dioxide discharged from the fuel cell. Thus, the overall structure of the fuel cell system is complicated due to the requirement for a container. Furthermore, the entire system is not compact because additional space is needed to install the container.  
     SUMMARY OF THE INVENTION  
      The present invention provides a carbon dioxide remover for a direct oxidation fuel cell which has a simple structure and does not require additional space for installation, and a fuel cell system having the same.  
      According to an aspect of the present invention, the carbon dioxide remover for a direct oxidation fuel cell removes carbon dioxide discharged along with a non-reactive fuel from a fuel cell body which generates electric energy through a fuel reaction and an oxygen reaction, includes a carbon dioxide removing element which is disposed in a passage through which the non-reactive fuel and the carbon dioxide pass, and which discharges the carbon dioxide through the passage.  
      In addition, the carbon dioxide removing element may include a filter member which separates the carbon dioxide from the non-reactive fuel, and which passes only the carbon dioxide.  
      According to another aspect of the present invention, the carbon dioxide remover for a direct oxidation fuel cell removes carbon dioxide discharged along with a non-reactive fuel from a fuel cell body which generates electric energy through a fuel reaction and an oxygen reaction, wherein the carbon dioxide remover includes: a channel member which has the shape of a pipe which allows the non-reactive fuel and the carbon dioxide to flow, which is connected to the fuel cell body, and which includes a plurality of vent holes for discharging the carbon dioxide; a filter member which is disposed in the channel member to block the vent holes, which separates the carbon dioxide from the non-reactive fuel, and which passes only the carbon dioxide to the vent holes; and one or more suction members which have porosity so as to suck the non-reactive fuel, and which are disposed inside the channel member.  
      In the aforementioned aspect of the present invention, the filter member may be disposed on the outer circumferential surface of the channel member so as to block the vent holes.  
      The filter member may be disposed on the inner circumferential surface of the channel member so as to block the vent holes.  
      The filter member may have hydrophobicity, and may be buried in the vent holes so as to block the vent holes.  
      The filter member may have hydrophobicity, and may be provided in the form of a film. In this case, the filter member may be made of a fluorinated resin selected from the group consisting of PolyVinylidene-Fluoride, Fluoroethylene-Propylene, Polytetra-Fluoroethylene, FluorinatedEthylene-Propylene, PolyChloroTri-Fluoroethylene, and Fluoroethylene-Polymer.  
      The suction member may be made of a porous medium selected from among ceramic, foaming sponge, and metal foam.  
      The channel member may include a first region which is connected to the fuel cell body and which has vent holes, and a second region which excludes the first region. In this case, the suction member may block the channel passage, and may be disposed inside the second region.  
      According to another aspect of the present invention, a fuel cell system includes: a fuel cell body which generates electric energy through a fuel reaction and an oxygen reaction; a mix tank which stores a mixture fuel in which the fuel is mixed with water, and which supplies the mixture fuel to the fuel cell body; an oxygen supplier which supplies oxygen to the fuel cell body; and a carbon dioxide remover which is connected to the fuel cell body and the mix tank, which removes carbon dioxide discharged along with a non-reactive mixture fuel from the fuel cell body, and which supplies the non-reactive mixture fuel to the mix tank; wherein the carbon dioxide remover has the shape of a pipe forming a passage through which the non-reactive mixture fuel and the carbon dioxide pass, and includes a filter member which is disposed in the passage, which separates the carbon dioxide from the non-reactive mixture fuel, and which discharges the carbon dioxide out of the passage.  
      In the aforementioned aspect of the present invention, the carbon dioxide remover may include a channel member which includes: a plurality of vent holes for discharging the carbon dioxide, and which forms the passage; and a suction member which has porosity so as to suck the non-reactive fuel, and which is disposed inside the channel member.  
      The channel member may include a first region which is connected to the fuel cell body and has vent holes, and a second region which is connected to the mix tank and excludes the first region. In this case, the suction member may block the channel passage, and may be disposed inside the second region.  
      The filter member may be disposed on the channel member so as to block the vent holes. In this case, the filter member may have the shape of a film, and may be disposed on the outer circumferential surface of the channel member, may be disposed on the inner circumferential surface of the channel member, or may be buried in the vent holes so as to block the vent holes.  
      The suction member may be made of a porous medium selected from among ceramic, foaming sponge, and metal foam.  
      The oxygen supplier may include an air pump which sucks air and supplies the air to the fuel cell body. In this case, the non-reactive mixture fuel and the carbon dioxide may pass through the passage using pumping pressure of the air pump.  
      The mix tank may be connected to the fuel cell body, and may collect moisture discharged from the fuel cell body.  
      The fuel cell system may further include a fuel tank which is connected to the mix tank, which stores a pure fuel, and which supplies the pure fuel to the mix tank. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
       FIG. 1  is a block diagram schematically showing the structure of a fuel cell system according to an embodiment of the present invention;  
       FIG. 2  is an exploded perspective view showing the structure of the fuel cell body of  FIG. 1 ;  
       FIG. 3  is a partial perspective view schematically showing a carbon dioxide remover according to a first embodiment of the present invention;  
       FIG. 4  is a cross-sectional view of the carbon dioxide remover of  FIG. 3 ;  
       FIG. 5  is a cross-sectional view of a carbon dioxide remover according to a second embodiment of the present invention; and  
       FIG. 6  is a cross-sectional view of a carbon dioxide remover according to a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings such that the present invention can be easily put into practice by those skilled in the art.  
      However, the present invention is not limited to the exemplary embodiments, but may be embodied in various forms.  
       FIG. 1  is a block diagram schematically showing the structure of a fuel cell system according to an embodiment of the present invention.  
      Referring to  FIG.1 , a fuel cell system  100  according to an embodiment of the present invention may be formed using a direct oxidation fuel cell scheme such as a direct methanol fuel cell (DMFC), in which a fuel and an oxidant gas are directly provided, and electric energy is generated through an oxidation reaction of hydrogen contained in the fuel and through a reduction reaction of the oxidant gas.  
      The fuel cell system  100  functions as a recycling system in which carbon dioxide generated through a fuel oxidation reaction is removed when the direct oxidation fuel cell operates, and in which moisture generated through an oxygen reduction reaction and a non-reactive fuel remaining in the fuel cell after the reaction is completed can be recycled.  
      In the present embodiment, the fuel is a highly concentrated alcohol type liquid fuel such as methanol or ethanol. Hereinafter, a pure fuel combined with water is defined as a mixture fuel. The fuel cell system  100  may use oxygen stored in an additional storage element as an oxidant gas, or may use air containing oxygen. Hereinafter, the latter case will be exemplified.  
      The fuel cell system  100  includes a fuel cell body  10  formed as a direct oxidation fuel cell, a mix tank  30  for storing the mixture fuel, a fuel tank  50  for storing the pure fuel mentioned above, an oxygen supplier  70  for supplying oxygen to the fuel cell body  10 , and a carbon dioxide remover  90  for removing carbon dioxide discharged along with a non-reactive mixture fuel from the fuel cell body  10 .  
      The fuel cell body  10  is connected to the mix tank  30  and the oxygen supplier  70 , respectively. Furthermore, the fuel cell system  100  includes an electricity generator  11  composed of cells to which the mixture fuel is supplied from the mix tank  30  and air is supplied from the oxygen supplier  70  so as to generate electric energy through an oxidation reaction of hydrogen contained in the fuel and through a reduction reaction of oxygen contained in the air.  
      The fuel cell body  10  may include a plurality of the electricity generators  11 . The fuel cell body  10  may have a stack structure which is constructed by sequentially disposing the plurality of electricity generators  11 .  
       FIG. 2  is an exploded perspective view showing the structure of the fuel cell body  10  of  FIG. 1 .  
      Referring to  FIG. 2 , as described above, the fuel cell body  10  according to the present embodiment includes a plurality of the electricity generators  11 . Each electricity generator  11  may include a membrane electrode assembly (MEA)  12  and separators  13 , each disposed in close contact with both surfaces of an MEA  12 .  
      The MEA  12  includes anode and cathode electrodes disposed on both sides thereof, and an electrolyte membrane interposed between the two electrodes.  
      The anode electrode decomposes hydrogen contained in a mixture fuel into electrons and hydrogen ions. The electrolyte membrane moves the hydrogen ions to the cathode electrode. The cathode electrode generates moisture by reacting the electrons and the hydrogen ions received from the anode electrode with oxygen supplied from the separators  13 .  
      The separators  13  supply the mixture fuel to the anode electrode of the MEA  12 , form a channel through which the mixture fuel and air are supplied to the cathode electrode of the MEA  12 , and connect the anode and cathode electrodes of the MEA  12  in series.  
      Furthermore, the fuel cell body  10  includes a first injection hole  15  for supplying the mixture fuel to the electricity generators  11 , a second injection hole  16  for supplying the air to the electricity generators  11 , a first discharge hole  17  for discharging carbon dioxide generated through a fuel oxidation reaction performed by the electricity generators  11  and a mixture fuel remaining after the reaction is completed in the electricity generators  11 , and a second discharge hole  18  for discharging moisture generated through an oxygen reduction reaction performed by the electricity generators  11  and air remaining in the electricity generators  11  after the reaction is completed.  
      As shown in  FIG. 1 , the mix tank  30  is a sealed tank having an internal space for storing the mixture fuel. In the mix tank  30 , a highly concentrated pure fuel stored in the fuel tank  50  is mixed with water so as to supply the mixture fuel to the fuel cell body  10  after adjusting the concentration of the pure fuel to appropriate concentration required for operating the fuel cell body  10  effectively.  
      The mix tank  30  is connected to the first injection hole  15  of the fuel cell body  10  through a pipeline. Thus, the mixture fuel stored in the mix tank  30  is supplied to the electricity generators  11  of the fuel cell body  10 . The mix tank  30  is connected to the fuel tank  50  through a pipeline, and selectively receives the pure fuel stored in the fuel tank  50 . Also, the mix tank  30  is connected to the carbon dioxide remover  90 , and receives a non-reactive mixture fuel after carbon dioxide is removed by the carbon dioxide remover  90 . Furthermore, the mix tank  30  is connected to the second discharge hole  18  of the fuel cell body  10  through a pipeline, and receives moisture discharged from the second discharge hole  18  of the fuel cell body  10 .  
      A first pump P 1  is installed in the pipeline which connects the mix tank  30  to the first injection hole  15  of the fuel cell body  10 . The first pump P 1  sucks the mixture fuel stored in the mix tank  30 , discharges the mixture fuel from the mix tank  30 , and delivers the mixture fuel to the first injection hole  15  of the fuel cell body  10 . A second pump P 2  is installed in the pipeline which connects the mix tank  30  to the fuel tank  50 . The second pump P 2  sucks the pure fuel stored in the fuel tank  50 , discharges the pure fuel from the fuel tank  50 , and delivers the pure fuel to the mix tank  30 .  
      A heat exchanger (not shown) may be installed in the pipeline which connects the mix tank  30  and the second discharge hole  18  of the fuel cell body  10 . Such a heat exchanger condenses the moisture discharged from the second discharge hole  18  in the form of vapor.  
      as shown in  FIG. 1 , the oxygen supplier  70  for supplying oxygen to the fuel cell body  10  sucks air. In order to deliver the air to the fuel cell body  10 , the oxygen supplier  70  includes an air pump  71 . The air pump  71  and the second injection hole  16  of the fuel cell body  10  may be connected through a typical pipeline. The oxygen supplier  70  of the present embodiment is not limited to include the air pump  71 , and may include a typical blower.  
      As shown in  FIG. 1 , the carbon dioxide remover  90  removes carbon dioxide while flowing the non-reactive mixture fuel discharged through the first discharge hole  17  of the fuel cell body  10  and the carbon dioxide, and supplies the non-reactive mixture fuel to the mix tank  30 . The carbon dioxide remover  90  maybe disposed between the fuel cell body  10  and the mix tank  30 , and may be connected to the first discharge hole  17  of the fuel cell body  10  and the mix tank  30 . The carbon dioxide remover  90  according to an embodiment of the present invention will be described in detail with reference to  FIGS. 3 and 4 .  
      Since the fuel cell system  100  of the present embodiment includes the air pump  71  for supplying oxygen to the fuel cell body  10 , the moisture generated through the oxygen reduction reaction performed by the electricity generators  11  and the air remaining in the electricity generators  11  after the reaction is completed can be discharged through the second discharge hole  18  of the fuel cell body  10  using pumping pressure of the air pump  71 .  
       FIG. 3  is a partial perspective view schematically showing a carbon dioxide remover according to a first embodiment of the present invention, and  FIG. 4  is a cross-sectional view of the carbon dioxide remover of  FIG. 3 .  
      Referring to  FIGS. 3 and 4 , the carbon dioxide remover  90  of the present embodiment includes a passage  91   b  for passing the non-reactive mixture fuel and the carbon dioxide discharged from the fuel cell body  10 . The carbon dioxide remover  90  separates the non-reactive mixture fuel and the carbon dioxide passing through the passage  91   b,  so that the carbon dioxide is discharged out of the passage  91   b  and the non-reactive mixture fuel is supplied to the mix tank  30  (see  FIG. 1 ) through the passage  91   b.    
      includes a channel member  91  which forms the passage  91   b  and which is connected to the fuel cell body  10  and the mix tank  30 , and a carbon dioxide removing element  93  which is formed on the channel member  91 .  
      The channel member  91  is constructed in the shape of a pipe forming the passage  91   b . The channel member  91  has a predetermined cross-sectional area through which the non-reactive mixture fuel and the carbon dioxide discharged from the fuel cell body  10  can pass. One end of the channel member  91  is connected to the first discharge hole  17  of the fuel cell body  10 , and the other end of the channel member  91  is connected to an inflow portion (not shown) of the mix tank  30 . The channel member  91  may be constructed in the shape of a pipeline having a rectangular or circular cross-section.  
      The carbon dioxide removing element  93  is formed on the passage  91   b  of the channel member  91 . The carbon dioxide removing element  93  separates the non-reactive mixture fuel and the carbon dioxide passing through the passage  91   b,  and discharges the carbon dioxide out of the passage  91   b.    
      The carbon dioxide removing element  93  includes a plurality of vent holes  91  a formed in the channel member  91  and a filter member  95  formed in the channel member  91  to block the vent holes  91   a.    
      From between the non-reactive mixture fuel and the carbon dioxide passing through the passage  91   b  the vent holes  91   a  discharge the carbon dioxide out of the passage  91   b.    
      The vent holes  91   a  may be formed over the entire area of the channel member  91 . The vent holes  91   a  are formed in a first region A, and the first region A is defined as a portion connected to the first discharge hole  17  of the fuel cell body  10 . On the other hand, a second region B is defined as a portion which is connected to the mix tank  30  and excludes the first region A of the channel member  91 .  
      In order to block the vent holes  91   a,  the filter member  95  is attached to the outer circumferential surface of the channel member  91 , that is, the outer circumferential surface of the first region A.  
      The filter member  95 , which separates the non-reactive mixture fuel and the carbon dioxide passing through the channel member  91 , functions as a vapor-liquid filter through which the non-reactive mixture passes and the carbon dioxide cannot pass. That is, the filter member  95  disposed on the outer circumferential surface of the channel member  91  blocks the vent holes  91   a  so as to prevent the non-reactive mixture fuel from discharging out of the passage  91   b  through the vent holes  91   a.  Thus, only carbon dioxide is discharged out of the passage  91   b  through the vent holes  91   a.    
      The filter member  95  is provided in the form of a film having hydrophobicity which cannot pass the non-reactive mixture fuel and a porosity which can pass the carbon dioxide. The filter member  95  may be made of a fluorinated resin selected from the group consisting of PolyVinylidene-Fluoride, Fluoroethylene-Propylene, Polytetra-Fluoroethylene, FluorinatedEthylene-Propylene, PolyChloroTri-Fluoroethylene, or Fluoroethylene-Polymer.  
      Furthermore, the carbon dioxide remover  90  of the present embodiment includes a suction member  97  which has porosity and which is disposed inside the channel member  91 . The suction member  97  sucks the non-reactive mixture fuel, and temporarily stores the non-reactive mixture fuel.  
      The suction member  97  has a plurality of air vents  97   a  for sucking the non-reactive mixture fuel. In order to block the passage  91   b  of the channel member  91 , the suction member  97  is disposed inside the channel member  91 . In the embodiment, the suction member  97  is disposed inside the second region B of the channel member  91 .  
      The suction member  97  may be made of a typical porous medium such as ceramic, limestone, activated carbon, foaming sponge, or metal foam.  
      The suction member  97  sucks the non-reactive mixture fuel cell while blocking the passage  91   b  of the channel member  91 . That is, the suction member  97  temporarily stores the non-reactive mixture fuel in the air vents  97   a  by sucking the non-reactive mixture fuel passing through the first region A of the channel member  91 , and prevents the carbon dioxide from passing through the second region B due to the non-reactive mixture fuel stored in the air vents  97   a.    
      As a result, since the carbon dioxide existing in the first region A of the channel member  91  is blocked by the suction member  97 , the carbon dioxide cannot pass through the second region B. Instead, the carbon dioxide is guided toward the vent holes  91   a,  and is thus discharged through the filter member  95 . The non-reactive mixture fuel sucked by the suction member  97  passes through the air vents  97   a  of the suction member  97  using the pumping pressure of the air pump  71  (see  FIG. 1 ), and is supplied to the mix tank  30  (see  FIG. 1 ) via the second region B.  
      The operation of the fuel cell system having the aforementioned structure according to an embodiment of the present invention will now be described in detail.  
      The mixture fuel stored in the mix tank  30  is supplied to the first injection hole  15  of the fuel cell body  10  by operating the first pump PI. The mixture fuel is then supplied to the electricity generators  11  through the first injection hole  15  of the fuel cell body  10 . The pure fuel stored in the fuel tank  50  may be supplied to the mix tank  30  by operation the second pump P 2  so as to adjust concentration of the mixture fuel stored in the mix tank  30 .  
      In this process, the air pump  71  sucks air, and supplies the air to the second injection hole  16  of the fuel cell body  10 . Thereafter, the air is supplied to the electricity generators  11  through the second injection hole  16  of the fuel cell body  10 .  
      Accordingly, the fuel cell body  10  can output electric energy having a predetermined capacity through the fuel oxidation reaction and the oxygen reduction reaction performed by the electricity generators  11 .  
      discharges carbon dioxide generated through the fuel oxidation reaction and a non-reactive mixture fuel remaining in the electricity generators  11  after the reaction is completed through the first discharge hole  17 .  
      The non-reactive mixture fuel and the carbon dioxide discharged through the first discharge hole  17  of the fuel cell body  10  are supplied to the carbon dioxide remover  90  using the pumping pressure of the air pump  71 , and then pass through the first region A of the channel member  91 .  
      In this process, the non-reactive mixture fuel is sucked by the suction member  97  and is temporarily stored in the air vents  97   a  of the suction member  97 , thereby preventing carbon dioxide from passing through the suction member  97 . The carbon dioxide existing in the passage  91   b  of the first region A is blocked by the non-reactive mixture fuel sucked by the suction member  97 , and thus cannot pass through the passage  91   b  of the second region B. Instead, the carbon dioxide is guided toward the vent holes  91   a  of the first region A, and is discharged to an additional collector or to the air through the filter member  95 .  
      Meanwhile, the non-reactive mixture fuel sucked in the suction member  97  passes through the air vents  97   a  of the suction member  97  using the pumping pressure of the air pump  71 , and is supplied to the mix tank  30  through the second region B.  
      In the process of generating electric energy, the fuel cell body  10  discharges moisture in the form of vapor, generated through the oxygen reduction reaction performed by the electricity generators  11  and air remaining in the electricity generators  11  after the reaction is completed, through the second discharge hole  18 .  
      The moisture having a relatively high temperature and the non-reactive air discharged through the second discharge hole  18  of the fuel cell body  10  are processed by the heat exchanger (not shown). The moisture is condensed into water by the heat exchanger, and is collected in an internal space of the mix tank  30 . The air is collected in the additional collector so as to be recycled to the fuel cell body  10  or discharged to the air.  
       FIG. 5  is a cross-sectional view of a carbon dioxide remover according to a second embodiment of the present invention.  
      Referring to  FIG. 5 , the carbon dioxide remover  190  of the present embodiment basically employs the structure of the previous embodiment. The carbon dioxide remover  190  may include a filter member  195  which blocks a plurality of vent holes  191   a  of a channel member  191  and is disposed on internal walls of the channel member  191 .  
      The filter member  195  is attached to the internal walls of the channel member  191 , that is, internal walls of a first region A, and passes carbon dioxide existing inside the first region A through the vent holes  191   a  of the channel member  191 .  
      The structure and operation of the carbon dioxide remover  190  of the present embodiment are the same as in the previous embodiment except as described above, and thus a detailed description thereof will be omitted.  
       FIG. 6  is a cross-sectional view of a carbon dioxide remover according to a third embodiment of the present invention.  
      Referring to  FIG. 6 , the carbon dioxide remover  290  of the present embodiment basically employs the structure of the previous embodiment. The carbon dioxide remover  290  may include a filter member  295  which is buried in a plurality of vent holes  291   a  of a channel member  291 .  
      That is, the filter member  295  is inserted into the vent holes  291   a  of the channel member  291 , and discharges carbon dioxide, existing inside first region A, through the vent holes  291   a  of the channel member  291 .  
      The structure and operation of the carbon dioxide remover  290  of the present embodiment are the same as in the previous embodiment except as described above, and thus a detailed description thereof will be omitted.  
      According to the present invention, an additional container for storing a non-reactive mixture fuel and carbon dioxide discharged out of a fuel cell body is not required since a carbon dioxide remover having the shape of a pipe, such as a pipeline, is used. Therefore, the overall system structure is simplified.  
      According to the present invention, the entire system can be compact since additional space to install the system is not necessary.  
      Although exemplary embodiments of the present invention have been described, the present invention is not limited to the embodiments, but may be modified in various forms without departing from the scope of the appended claims, the detailed description, and the accompanying drawings of the present invention. Therefore, it is natural that such modifications belong to the scope of the present invention.