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 hydrogen permeable coils surround a perforated output tube that draws in any hydrogen gas that diffuses through the hydrogen permeable coils. The presence and position of the output tube prevent any significant lateral movement of hydrogen gas within the diffusion cell.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of patent application Ser. No. 09/702,636, entitled HYDROGEN DIFFUSION CELL ASSEMBLY AND ITS METHOD OF MANUFACTURE, filed Nov. 1, 2000, which has issued U.S. Pat. No. 6,464,759. 
    
    
     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 types 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 coils of palladium tubing have many problems. One of the major problems is that of reliability as the hydrogen diffusion cell ages. 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 contracts, 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. 
     The problem of palladium tube cracking is amplified by the manner in which hydrogen gas is drawn out of the hydrogen diffusion cell. In a prior art hydrogen diffusion cell, hydrogen is typically drawn out of one end of the cell. This creates a one-way flow of hydrogen within the confines of the hydrogen diffusion cell as the hydrogen gas flows to one exit point within the cell. Depending upon how rapidly hydrogen gas is drawn from the hydrogen diffusion cell, the flow of hydrogen gas within the confines of the hydrogen diffusion cell can range from a constant mild flow to a sudden severe flow. 
     As hydrogen gas flows out of such a prior art hydrogen diffusion cell, the flowing hydrogen applies a biasing force to the palladium coils contained within the hydrogen diffusion cell. Over time, the biasing force of the flowing hydrogen physically deforms the palladium coils. The palladium coils become compressed at the end of the coils that are nearest the exit port within the hydrogen diffusion cell. This is because the flowing hydrogen gas biases the palladium coils in the direction of the flow. Likewise, the ends of the palladium coils that face away from the hydrogen gas exit port become stretched as the palladium coils are pulled away by the flowing hydrogen gas. As a result, the palladium coils become stressed in the areas where they are stretched. As the coils expand and contract when heated and cooled, the stressed areas of the palladium coils crack over time and begin to leak. Once a palladium coil begins to leak, the hydrogen diffusion cell is no longer functional. 
     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 deformation experienced by the palladium tubing caused by the flowing hydrogen gas. However, these techniques 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. Disposed in the center of the hydrogen permeable coils is an output tube that collects any hydrogen that diffuses through the hydrogen permeable coils as it flows between the supply tube and the drain tube. The output tube is at least as long as the hydrogen permeable coils and is perforated along its length. In this manner, hydrogen gas is drawn into the output tube throughout the center of the hydrogen diffusion cell. This prevents hydrogen gas from flowing laterally within the hydrogen diffusion cell and deforming the hydrogen permeable 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 selectively fragmented 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 , a drain tube  14  and an output tube  15 . The supply tube  12  supplies unpurified hydrogen gas to the hydrogen diffusion cell  10 . The drain tube  14  removes the unused, unpurified hydrogen gas from the hydrogen diffusion cell  10 . The output tube  15  removes purified hydrogen gas from the hydrogen diffusion cell  10 . The supply tube  12 , drain tube  14 , and output tube  15  are all made of stainless steel or another inert high strength alloy. The supply tube  12 , drain tube  14  and output tube  15  all pass through an end cap plate  16 . The supply tube  12 , drain tube  14  and output tube  15  are welded to the end cap plate  16  at the points where they 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 , drain tube  14  and output tube  15 . 
     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  corresponds 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, which has issued as U.S. Pat. No. 6,378,352, 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 a brazing flange  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  matches 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 not 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. 
     The output tube  15  extends down the center of the hydrogen diffusion cell  10 . The coils  24 ,  26  surround the output tube  15 . As such, the output tube  15  extends down the center of the concentrically disposed coils  24 ,  26 . The length of the output tube  15  is at least as long as the length of the coils  24 ,  26 . As such, the output tube is present along the entire length of the coils  24 ,  26 . 
     The output tube  15  is perforated along its length. The perforation enables purified hydrogen gas to pass into the output tube  15 . The holes  29  used to perforate the output tube  15  can have a constant diameter. However, in a preferred embodiment, the holes  29  increase in diameter along the length of the output tube  15 , as the output tube  15  extends away from the end cap plate  16 . In this manner, the draw of hydrogen gas into the output tube  15  through the various holes  29  remains relatively constant along the entire length of the output tube  15 . 
     Once the coils  24 ,  26  placed around the output tube  15  and are attached to both 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. 
     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 drawn into the output tube  15 . The remainder of the contaminated hydrogen gas is drained through the drain tube  14  for reprocessing. 
     Since the output tube  15  is located in the center of the coils  24 ,  26 , the flow of hydrogen gas from the coils  24 ,  26  to the output tube  15  does not act to laterally deform the coils  24 ,  26 . Rather, the flow of the hydrogen gas merely acts to move the coils radially inwardly. The shape of the coils  24 ,  26  naturally resist this force and the coils  24 ,  26  remain undeformed by the flow of hydrogen. 
     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  32 , 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  30  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. 
     A single output tube  40  is used in the hydrogen diffusion cell  30 . The output tube  40  has a length at least as long as the combined length L of the coil sets in the diffusion cell. The output tube  40  is perforated to receive the purified hydrogen gas emitted by the various coils. The holes  42  that create the perforations can be calibrated to create an even intake flow rate along the entire length of the output tube  40 . 
     To help even out the intake flow of gas along the length of the output tube  40 , baffle plates  44  can be placed in the hydrogen diffusion cell  30  in between different sets of concentric coils  37 ,  38 ,  39 . The baffle plates  44  can be solid obstructions. However, the baffle plates  44  are preferably partial obstructions that inhibit, but do not prevent the lateral flow of hydrogen gas outside the various sets of coils  37 ,  38 ,  39  in the hydrogen diffusion cell  30 . 
     The baffle plates  44  serve multiple functions. First, the baffle plates  44  help prevent hydrogen gas from flowing toward one end of the hydrogen diffusion cell  30 . Additionally, the baffle plates help the output tube  40  receive the purified hydrogen gas with a minimal lateral movement of the hydrogen gas around the various sets of coils  37 ,  38 ,  39 . Second, the baffle plates  44  reinforce the position and orientation of the supply tube  34 , the drain tube  36  and the output tube  40 . In this manner, the supply tube  34 , drain tube  36  and output tube  40  are less likely to vibrate. This minimizes stress on these components and the coils that are supported by these components. 
     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 be made. For instance, the length and diameter of the coils, supply tube, drain tube and/or output tube can be changed. The number of sets of concentric coils and baffle plates 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.