Abstract:
An object of the present invention is to provide a catalyst carrier suitable for use of three-phase alternating current. In the present invention, three catalyst foils are spirally wound and surface contact among the catalyst foils is prevented thereby allowing the catalyst carrier to be connected to a three-phase alternating current source. Each of the catalyst foils is a strip-shaped conductive foil formed of a heat-resistant alloy, and a wavy shape is imparted to the foil. Further, an insulating layer and a catalyst-carrying layer are formed on a surface of the catalyst foil.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a catalyst carrier which can be electrified in order to effect heating. 
     Conventionally, there have been known various types of catalyst carriers, such as those for use with single-phase alternating current and those for automobile exhaust gas. When a large catalyst apparatus, such as a deodorizing apparatus is produced, there arises a d e s ire for use of three-phase alternating current, which is widely used in large machinery. However, to the best of the present inventor&#39;s knowledge, no conventional catalyst carrier for use with single-phase alternating current or for automobile exhaust gas is designed for consideration of use of three-phase alternating current. In order to use three-phase alternating current, at least three catalyst foils are required; one for each of the three phases of a power source. However, if catalyst foils, each having a wavy longitudinal cross section and a straight lateral cross section are merely rolled, formation of a large number of uniform channels serving as gas passages is difficult. Further, catalyst apparatuses for automobile exhaust gas are designed to be driven by power sources producing a voltage as low as 12 volts. Thus, insulation for catalyst foils is complete only in a small number of catalyst apparatuses. Therefore, these catalyst apparatuses are not considered suitable for use with a three-phase alternating current power source that provides a standard voltage (200 V). 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a catalyst carrier capable of being electrified in order to effect heating, in which three catalyst foils, having a predetermined shape, are spirally wound and surface contact among the catalyst foils is prevented to thereby allow the catalyst carrier to be connected to a three-phase alternating current source, thus enabling use of a three-phase alternating current source as well as enabling an increase in a size of a catalyst apparatus. 
     The present invention provides a catalyst carrier capable of being electrified in order to effect heating, in which three catalyst foils are spirally wound, namely meshed with each other while surface contact among the catalyst foils is prevented, to thereby allow the catalyst carrier to be connected to a three-phase alternating current source. Each of the catalyst foils is a strip-shaped conductive foil formed of a heat-resistant alloy and having a wavy shape, that is, a wave contour with a wave direction generally in a longitudinal direction of the strip-shape, is imparted thereto. Further, an insulating layer and a catalyst-carrying layer are formed on the surface of the catalyst foil. 
     Imparting a wavy shape to the strip-shaped metal foil refers to forming the metal foil such that the metal foil has a wavy, uneven cross section including periodical crests and valleys formed in a widthwise direction of the strip-shaped foil. The crests and valleys are provided in a herringbone shape, for example, in which the crests and valleys have acute angles, for instance, and are repeated periodically. Three catalyst foils to which the above-described wavy shape have been imparted are wound in a state in which surface contact does not occur among the catalyst foils. Therefore, the catalyst foils are not superposed in a state in which the wavy portions of adjacent catalyst foils fit into each other. Thus, a large number of channels for gas passages are formed between the adjacent catalyst foils. The prevention of surface contact among the catalyst foils is achieved by employment of a configuration in which the catalyst foils are wound in a state in which a phase difference is produced between the periodic crest and valleys of adjacent catalyst foils. If a plurality of catalyst foils whose cross section are wavy only in a longitudinal direction, i.e., wavy in the longitudinal direction but straight in the widthwise direction, are wound, the wavy portions of the catalyst foils fit into each other, so that channels for gas passages are not formed properly. In order to avoid such a problem, the catalyst foils whose cross sections are wavy only in a longitudinal direction are wound in a state in which a flat foil, serving as a spacer, is interposed between the wavy foils. In the present invention such spacers are not required, accordingly, the number of foils required to form a rolled catalyst carrier is decreased. 
     Further, when a catalyst carrier is formed from six films including wavy films and flat films in order to allow use of three-phase alternating current, two foils, i.e., a spacer and a catalyst foil serving as a resistor, are connected to each line of a three-phase alternating current source. In other words, two conductors are connected in parallel. Therefore, the resistance of each line decreases. By contrast, in the present invention described described above, a single catalyst foil is connected to each line of a three-phase alternating current source, so that the resistance for each line is greater compared to the case where the spacer foil is required. Consequently, the catalyst carrier can be electrified with high efficiency even when three-phase alternating current is used. 
     The present invention further provides an embodiment having a catalyst carrier in which first ends of the three superposed catalyst foils are connected to a center rod. The catalyst foils are wound spirally around the center rod and second ends of the catalyst foils, located at the peripheral side of the spiral, and the center rod are connected to a three-phase alternating current source. In this case, since the catalyst foils form a star connection, which is generally used for connection with a three-phase alternating current source, a large-sized catalyst apparatus can be formed easily. 
     The present invention still further provides an embodiment of a catalyst carrier in which opposite ends of the three catalyst foils are mutually connected at connection portions to form an endless catalyst foil having a substantially equilateral-triangular cross section. Center portions of the catalyst foils, which constitute sides of the triangle, are moved uniformly toward a center of the triangular cross section. Subsequently, the connection portions are rotated about a vertical axis passing through the center in order to wind the catalyst foils. Further, the connection portions are located on a peripheral edge of the spiral and are connected to a three-phase alternating current source in order to establish a delta connection. In this case, since the catalyst foils form a delta connection, which is generally used for connection with a three-phase alternating current source, a large-sized catalyst apparatus can be formed easily. Further, unlike the case of the star connection, no center rod is required, so that the gas passage area of the catalyst carrier is increased. The center of the equilateral-triangular cross section denotes a center of gravity of the equilateral-cross section. 
     The present invention yet further provides an improvement of the catalyst carrier according to any of the above configurations in which the three catalyst foils are superposed and wound spirally in a state in which respective longitudinal sides of the catalyst foils are slightly offset from one another in the widthwise direction. In catalyst foils capable of being electrified, an insulating layer is provided on a surface of each catalyst foil in order to prevent occurrence of a short circuit between adjacent catalyst foils. However, since the insulating layer is difficult to form at side edge portions of the catalyst foils, when the catalyst foils are wound, a short circuit may occur, especially between the edges of the longitudinal sides of adjacent catalyst foils. The offset longitudinal sides prevent an occurrence of a short circuit, which would otherwise occur between the side edges of the longitudinal sides of adjacent catalyst foils when the catalyst foils are wound. Therefore, the catalyst carrier according to the present invention can be electrified efficiently in order to effect heating. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a catalysis apparatus according to an embodiment of the present invention. 
     FIG. 2 is a perspective view showing a state in which three catalyst foils are spirally wound and electrodes are provided for the catalyst foils. 
     FIGS.  3 ( a ) and  3 ( b ) are cut-away views showing states in which the catalyst foils are offset from one another. 
     FIG. 4 is a connection diagram showing a star connection. 
     FIGS.  5 ( a ) and  5 ( b ) show a diagrams of a manner of winding catalyst foils for formation of a delta connection. 
     FIG. 6 is a connection diagram showing a delta connection. 
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention is now be described. Referring to FIG. 1, a catalyst apparatus  1  for use with three-phase alternating current has a tubular casing  2  accommodating a catalyst carrier  6  composed of three catalyst foils  3 ,  4 , and  5 , which are wound spirally in an overlapped manner. Each of the catalyst foils  3 ,  4 , and  5  is formed from a strip-shaped metal foil of a heat resistant alloy. 
     Referring to FIGS. 2,  3 ( a ) and  3 ( b ), each of the catalyst foils  3 ,  4 , and  5  is formed to have a herringbone pattern. The metal foil is formed of a stainless-steel heat-resistant alloy containing aluminum (Fe-20%Cr-5%Al-0.08La). In each of the catalyst foils  3 ,  4 , and  5 , over an entire surface of the metal foil having the herringbone pattern, aluminum whiskers are generated, an insulating layer is formed, a washcoat is applied, and a noble metal serving as a catalyst is applied. Specifically, a metal foil of Fe-20%Cr5%Al-0.08La having a thickness of about 50 μm is heat-treated at 900° C. for 15 hours in order to form whiskers of aluminum oxide on the surface of the foil. The whiskers serve as anchors for increasing strength of close contact with the washcoat, crystallized glass, and noble metal (catalyst) applied onto the surface of the foil. The washcoat contains SiO 2  (95%) and ZrO 2  (5%) and is applied by use of a spray coater. The crystallized glass is applied by, for example, the method disclosed in Japanese Patent Application Laid-Open (kokai) No. 4-198039. Further, platinum is used as the noble metal serving as the catalyst. 
     The catalyst carrier  6  is formed through an operation of spirally winding the three superposed catalyst foils  3 ,  4 , and  5  having a same width and length. Respective inner ends of the catalyst foils  3 ,  4 , and  5  are connected to a center rod  7  disposed at a center of the catalyst carrier  6 . Further, outer electrodes  8 ,  9 , and  10  are connected to outer ends of the respective catalyst foils  3 ,  4 , and  5 . Thus, a star connection is formed between the center rod  7  and the outer electrodes  8 ,  9 , and  10 . FIG. 4 shows the configuration of the star connection. Reference numeral  11  denotes a three-phase load; reference numeral  12  denotes a first phase; reference numeral  13  denotes a second phase, and reference numeral  14  denotes a third phase. Such a star connection simplifies the arrangement of electrodes, and also simplifies the overall design of the catalyst apparatus. 
     Referring to FIG. 1 again, an insulating coat material  15 , serving as insulating means, is applied on the inner surface of the tubular casing  2 . Further, paired right and left insulating stoppers  16  for positioning are disposed on a near side, and an insulating bar (unillustrated) is disposed on the far side. The insulating coat  15 , the insulating stoppers  16 , the insulating bar, and the like constitute the insulating means. The catalyst carrier  6  is accommodated within the tubular casing  2  via the insulating means. Reference numeral  17  denotes a thermocouple. 
     As shown in FIG.  3 ( a ), the three catalyst foils  3 ,  4 , and  5  are wound in a state in which a widthwise offset L is provided between a longitudinal side  18  of the catalyst carrier foil  3  and a longitudinal side  19  of the catalyst carrier foil  4 , as well as between the longitudinal side  19  of the catalyst carrier foil  4  and a longitudinal side  20  of the catalyst carrier foil  5 . 
     The three catalyst foils  3 ,  4 , and  5  have the same herringbone pattern. As shown in FIG. 2, the herringbone pattern includes crest portions  21  and valley portions  22 , which are wider than the crest portions  21 . Further, the superposed catalyst foils  3 ,  4 , and  5  are wound in a state such that their longitudinal sides are slightly offset from one another in a width direction. Therefore, when the superposed catalyst foils  3 ,  4 , and  5  are wound, the adjacent catalyst foils interfere with each other, so that a large number of channels C having an identical sectional shape are formed between the adjacent catalyst foils to thereby form gas passages. Further, as shown in FIG.  3 ( b ), the superposed catalyst foils  3 ,  4 , and  5  may be superposed and wound such that the pattern of the crest and valley portions,  21  and  22 , of the intermediate catalyst foil  24  is a mirror image of the pattern of the crest and valley portions,  21  and  22 , of the catalyst foils  23  and  25 , which sandwich the intermediate catalyst foil  24 . That is, a phase shift of a half period of the pattern is produced between the intermediate catalyst foil  24  and the outside catalyst foils  23  and  25 . This structure more effectively prevents close contact among the catalyst foils  23 ,  24  and  25 . 
     Referring to FIGS.  5 ( a ) and  5 ( b ), a catalyst carrier for a delta connection is formed having a manner of winding catalyst foils in order to form a delta connection. First, as shown in FIG.  5 ( a ), the longitudinal ends of three catalyst foils  31 ,  32 , and  33  having the same length and width are connected to one another in an endless manner, so that the catalyst foils  31 ,  32 , and  33  assume an equilateral-triangular cross section when viewed from the side. Subsequently, as shown in FIG.  5 ( b ), longitudinally center portions of the catalyst foils  31 ,  32 , and  33 , which constitute respective sides of the equilateral triangle, are moved toward a center (centroid) P of the equilateral triangle. Subsequently, connection portions  34 ,  35 , and  36  are rotated about a vertical axis, passing through the center P, in a direction of arrow X in order to spirally wind the catalyst foils  31 ,  32 , and  33 . Further, electrodes are provided at the connection portions  34 ,  35 , and  36  of the spirally wound catalyst carrier. Thus, a delta connection is established. FIG. 6 shows the configuration of the delta connection, wherein reference numeral  40  denotes a three-phase load; reference numeral  41  denotes a first phase; reference numeral  42  denotes a second phase, and reference numeral  43  denotes a third phase. As in the case of the above-described star connection, the catalyst carrier having a delta connection can be built into a tubular case so as to obtain a catalyst apparatus. Further, the catalyst foils may be wound such that longitudinal sides of the catalyst foils are shifted from each other in the widthwise direction, as described for the case of star connection. 
     As described above, the present invention enables use of three-phase alternating current and also enables easy provision of a large-sized catalyst apparatus. Further, in the case in which an electric heater is built into a catalyst apparatus located on a upstream side of the catalyst carrier in order to heat gas flowing into the catalyst carrier to thereby accelerate catalytic reaction, such a electric heater can be omitted, because the catalyst carrier itself is electrified. Therefore, space for installation of an electric heater can be eliminated.