Abstract:
A hydrogen diffusion cell that is used to purify contaminated hydrogen gas. The hydrogen diffusion cell has a supply tube that supplies contaminated hydrogen gas into a confined area and a drain tube that removes contaminated hydrogen gas from the confined area. Hydrogen permeable coils are disposed between the supply tube and the drain tube. The coils include at least one small diameter coil. Concentrically surrounding the small diameter coil is at least one larger diameter coil. All coils are mounted in such a manner so that they maintain a constant radius of curvature along their entire lengths.

Description:
RELATED APPLICATIONS 
     This application is related to co-pending patent application Ser. No. 09/702,637, entitled METHOD AND APPARATUS FOR WINDING THIN WALLED TUBING. 
    
    
     REFERENCE TO DOCUMENT DISCLOSURE 
     The matter of this application corresponds to the matter contained in Disclosure Document 454147 filed Apr. 1, 1999, wherein this application assumes the priority date of that document. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     In general, the present invention relates to hydrogen diffusion cells. More particularly, the present invention relates to hydrogen diffusion cells that contain wound coils of palladium tubing. 
     2. Description of the Prior Art 
     In industry, there are many known techniques for separating hydrogen from more complex molecules in order to produce a supply of hydrogen gas. One such technique is electrolysis, wherein hydrogen gas is obtained from water. Regardless of how hydrogen gas is obtained, the collected hydrogen gas is typically contaminated with secondary gases, such as water vapor, hydrocarbons and the like. The type of contaminants in the collected hydrogen gas are dependent upon the technique used to generate the hydrogen gas. 
     Although contaminated hydrogen gas is useful for certain applications, many other applications require the use of pure hydrogen. As such, the contaminated hydrogen gas must be purified. One technique used to purify hydrogen is to pass the hydrogen through a hydrogen diffusion cell. A typical hydrogen diffusion cell contains a single coil of palladium tubing. The palladium tubing is heated and the contaminated hydrogen gas is directed through the palladium tubing. When heated, the palladium tubing is permeable to hydrogen gas but not to the contaminants that may be mixed with the hydrogen gas. As such, nearly pure hydrogen passes through the palladium tubing and is collected for use. 
     Prior art hydrogen diffusion cells that use a coil of palladium tubing have many problems. One of the major problems is that of reliability. As a coil of palladium tubing is repeatedly heated and cooled, it expands and contracts. The longer the wound tube is, the more the tube expands and contracts. As the palladium tubing expands and contacts, cracks occur in the tubing. Cracks are particularly prevalent at the ends of the tubing where the palladium tubing is welded to common piping. Once a crack occurs in the palladium tubing or the welded supports of the tubing, the hydrogen diffusion cell ceases to function properly. 
     One solution that has been attempted to increase the reliability of hydrogen diffusion cells is to decrease the length of the palladium tubing and/or the number of windings in the coil of palladium tubing. These techniques reduce the degree of expansion and contraction experienced by the palladium tubing but also greatly decrease the surface area of the palladium tubing and thus the output and efficiency of the hydrogen diffusion cell. 
     A need therefore exists for a new hydrogen diffusion cell that has increased reliability yet does not have decreased flow efficiency. This need is met by the present invention as it is described and claimed below. 
     SUMMARY OF THE INVENTION 
     The present invention is a hydrogen diffusion cell that is used to purify contaminated hydrogen gas. The hydrogen diffusion cell has a supply tube that supplies contaminated hydrogen gas and a drain tube that removes contaminated hydrogen gas. Hydrogen permeable coils are disposed between the supply tube and the drain tube. The coils include at least one small diameter coil. Concentrically surrounding the small diameter coil is at least one larger diameter coil. All coils are mounted in such a manner that they maintain a constant radius of curvature along their entire lengths. 
     As contaminated hydrogen passes from the supply tube to the drain tube through the various coils, purified hydrogen permeates through the material of the coils and is collected from a confined space that surrounds the coils. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the following description of exemplary embodiments thereof, considered in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view of a hydrogen diffusion cell in accordance with the present invention; and 
     FIG. 2 is a perspective view of an alternate embodiment of a hydrogen diffusion cell in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a first exemplary embodiment of a hydrogen diffusion cell  10  is shown in accordance with the present invention. The diffusion cell  10  contains a supply tube  12  and a drain tube  14 . The supply tube  12  and the drain tube  14  are both made of stainless steel or another inert high strength alloy. Both the supply tube  12  and the drain tube  14  pass through an end cap plate  16 . The supply tube  12  and the drain tube  14  are welded to the end cap plate  16  at the points where the supply tube  12  and the drain tube  14  pass through the end cap plate  16 . To prevent stresses caused by expansion and contraction, the end cap plate  16  is preferably made of the same material as is the supply tube  12  and the drain tube  14 . 
     On the supply tube  12  is located a clustered set of brazing flanges  20 . Each brazing flange  20  is a short segment of tubing that is welded to the supply tube  12 . The short segment of tubing is made of the same material as is the supply tube  12 . Within each clustered set of brazing flanges  20 , each brazing flange  20  is a different distance from the end cap plate  16 . Furthermore, each brazing flange  20  in the clustered set radially extends from the supply tube  12  at an angle different from that of any of the other brazing flanges  20  in that same clustered set. 
     In the embodiment shown in FIG. 1, there is only one clustered set of brazing flanges  20  on the supply tube  12  and that clustered set contains two brazing flanges  20 . Such an embodiment is merely exemplary. As will later be explained, multiple clustered sets of brazing flanges  20  can be present on the supply tube  12  and any plurality of brazing flanges  20  can be contained within each clustered set. 
     The drain tube  14  also contains clustered sets of brazing flanges  22 . The brazing flanges  22  are of the same construction as those on the supply tube  12 . The number of clustered sets of brazing flanges  22  on the drain tube  14  correspond in number to the number of clustered sets of brazing flanges  20  present on the supply tube  12 . Similarly, the number of brazing flanges  22  contained within each clustered set on the drain tube  14  correspond in number to the number of brazing flanges  20  in each clustered set on the supply tube  12 . 
     A plurality of concentric coils  24 ,  26  are provided. The concentric coils  24 ,  26  are made from palladium or a palladium alloy. The process used to make the coils is the subject of co-pending U.S. patent application Ser. No. 09/702,637, entitled METHOD AND APPARATUS FOR WINDING THIN WALLED TUBING, the disclosure of which is incorporated into this specification by reference. 
     The number of brazing flanges  20 ,  22  in each clustered set corresponds in number to the number of coils  24 ,  26 . One end of each coil  24 ,  26  extends into the brazing flanges  20  on the supply tube  12 . The opposite end of each coil  24 ,  26  extends into a brazing flange  22  on the drain tube  14 . The concentric coils  24 ,  26  have different diameters so that they can fit one inside another. Furthermore, each coil has a slightly different length so that the ends of the coils align properly with the different brazing flanges  20 ,  22  on the supply tube  12  and the drain tube  14 , respectively. 
     In the embodiment of FIG. 1, there are two coils  24 ,  26 . As such, there are two brazing flanges  20  on the supply tube  12  and two brazing flanges  22  on the drain tube  14 . It will be understood that more than two concentric coils can be used. In any case, the number of supply brazing flanges  20  and drain brazing flanges  22  would match the number of coils used. 
     The coils  24 ,  26  have a nearly constant radius of curvature from one end to the other. As such, the coils  24 ,  26  do no contain any natural stress concentration points that may prematurely crack as the coils  24 ,  26  expand and contract. To further increase the reliability of the hydrogen diffusion cell  10 , the brazing flanges  20  on the supply tube  12  and the brazing flanges  22  on the drain tube  14  are treated. The brazing flanges  20 ,  22  are chemically polished prior to brazing. Such a preparation procedure produces high quality brazing connections that are much less likely to fail than brazing connections with untreated brazing flanges. 
     Once the coils  24 ,  26  are attached to the supply tube  12  and the drain tube  14 , the coils  24 ,  26  are covered with a cylindrical casing  28 . The cylindrical casing  28  is welded closed at the end cap plate  16 , thereby completing the assembly. An output tube  29  communicates with the interior of the cylindrical casing  28 . The output tube  29  can be located either in the end cap plate  16 , as is shown, or at any point in the cylindrical casing  28 . 
     To utilize the hydrogen diffusion cell  10 , the cell  10  is heated. Once at the proper temperature, contaminated hydrogen gas is fed into the supply tube  12 . The contaminated hydrogen gas fills the coils  24 ,  26 . Purified hydrogen gas permeates through the coils  24 ,  26  and is collected in the cylindrical casing  28 . The purified hydrogen gas is collected through the output tube  29 . The remainder of the contaminated hydrogen gas is drained through the drain tube  14  for reprocessing. 
     Referring to FIG. 2, an alternate embodiment of a hydrogen diffusion cell  30  is shown. In this embodiment, there are multiple clusters of brazing flanges  32  on both the supply tube  34  and the drain tube  36 . For each cluster of brazing flanges, there is a set of concentric coils. In the shown embodiment, there are three clusters of supply brazing flanges  32  and three clusters of drain blazing flanges (not shown). Accordingly, there are supplied three separate sets of concentric tubes  37 ,  38 ,  39 . Each set of concentric tubes  37 ,  38 ,  39  consists of multiple tubes of different diameters. The ends of the tubes are brazed to the corresponding clusters of supply brazing flanges  32  and drain brazing flanges. 
     The coils within the hydrogen diffusion cell have a combined length L, however, no one coil in the hydrogen diffusion cell  30  extends across that length. Since shorter coils are used in series, the amount of expansion and contraction experienced by any one coil is minimized. However, the effective combined length of the various coils can be made to any length. 
     The use of three separate sets of coils  37 ,  38 ,  39  in the embodiment of FIG. 2 is merely exemplary and it will be understood that any number of sets can be used. Furthermore, each set of coils can contain any number of concentric coils depending upon the design requirements of the hydrogen diffusion cell  30 . 
     There are many variations to the present invention device that can made. For instance, the length and diameter of the coils, supply tube and drain tube can be changed. The number of sets of concentric coils can be changed and the number of concentric coils in each set can be changed. It will therefore be understood that a person skilled in the art can make numerous alterations and modifications to the shown embodiments utilizing functionally equivalent components to those shown and described. All such modifications are intended to be included within the scope of the present invention as defined by the appended claims.