Abstract:
A device for the storage of compressed hydrogen gas comprises a plurality of glass capillary tubes each having a sealed extremity and an open extremity, wherein said plurality of glass capillary tubes is sheathed in an external tubular cover, and wherein the open end of a bundle of said tubular covers is housed in an adaptor, and wherein said adaptor is suitable to allow compressed hydrogen gas to be added to, and to prevent said hydrogen gas from escaping from, said glass capillary tubes.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a gas storage system and method. More particularly, the invention relates to a system comprising glass capillaries suitable to be inserted with gas in high pressure, contain it and allow its extraction. 
       BACKGROUND OF THE INVENTION 
       [0002]    Hydrogen is often used as a fuel substance. It is highly recommended since it is non-toxic and therefore it is safe to produce, store (even in large amounts), and transport. There are many other advantages to hydrogen such as the fact that it is lighter than air, carbon-free, exceptionally clean, can be produced from a variety of resources, and the only byproducts are water and heat. 
         [0003]    Hydrogen is often used in combination with fuel cells that are used all over the world. Stationary cells are often used for emergency power systems as a backup power supply system, and they are used in hospitals, nursing homes, office buildings, etc. Portable cells can supply power for cars, boats, submarines, spacecraft, etc. A fuel cell can also charge different kinds of batteries for a variety of electronic devices. 
         [0004]    A fuel cell that comprises hydrogen is an electrochemical cell which converts chemical energy into electric current. The chemical reaction is created when the hydrogen comes into contact with an oxidant. When using hydrogen fuel cells, it is less noisy than in other fuel systems, and most importantly—there is no emission of hazardous materials. 
         [0005]    Hydrogen must be stored in a suitable containing system, which can endure high pressure, resulting from containing compressed hydrogen. In order to deliver the hydrogen to different locations, the containing system should be portable. Nowadays, most containing systems that meet those requirements are built from metal materials, alloys and/or composites, and the use of such materials makes the containing system relatively heavy, and therefore limits its portability and range of uses. 
         [0006]    WO2011/080746 teaches a storage tank comprising a plurality of hollow micro-cylinders having each an end sealed with a plug made of an easily meltable alloy and heating coils wound around the micro-cylinder ends, which are heated to melt the plug and thereby to liberate the hydrogen gas from said array. This type of arrangement is complex and presents practical problems that prevent it from being a satisfactory industrial solution. 
         [0007]    Therefore, there is a need for a simple, efficient, refuelable and low-cost solution that would permit the storage of hydrogen gas in a relatively light-weight storage. It is an object of the invention to provide a system and method that overcome the drawbacks of the prior art. 
         [0008]    Other objects and advantages of the invention will become apparent as the description proceeds. 
       SUMMARY OF THE INVENTION 
       [0009]    A device for the storage of compressed hydrogen gas comprises a plurality of glass capillary tubes each having a sealed extremity and an open extremity, wherein said plurality of glass capillary tubes is sheathed in an external tubular cover, and wherein the open end of a bundle of said tubular covers is housed in an adaptor, and wherein said adaptor is suitable to allow compressed hydrogen gas to be added to, and to prevent said hydrogen gas from escaping from, said glass capillary tubes. 
         [0010]    In one embodiment of the invention the bundle of tubular covers is connected to the adaptor at the open end with gluing material. In another embodiment of the invention the gluing material is an epoxy resin. The device may further comprise sealing material. 
         [0011]    In one embodiment of the invention the adaptor is provided with a sealing valve, which may be integral with the adaptor or may be coupled thereto. 
         [0012]    The invention is also directed to a method for generating a capillary tube with one closed end, which is suitable for use with the device of the invention, comprising providing an open-ended capillary tube, applying a glass cupping to one open end and then melting the glass at said end. 
         [0013]    Further encompassed by the invention is a system for the storage of compressed hydrogen gas, comprising an array of two or more devices according to claim  1 , said two or more devices being connected to a common conduit for the addition of gas to, and withdrawal of gas from, the storage devices. 
         [0014]    Fuel cells comprising as the hydrogen-storage element one or more devices according to the invention, and their uses, also form part of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In the drawings: 
           [0016]      FIG. 1  is a perspective view of an MC (“multi-capillary” structure), according to one embodiment of the invention; 
           [0017]      FIG. 2  is a perspective view of a group of MCs-MMC (“multi multi-capillary” structure) of  FIG. 1 ; 
           [0018]      FIG. 3  is an array of MMCs, according to another embodiment of the invention; 
           [0019]      FIG. 4  is a diagram of a fuel-providing system comprising an array of MMC; and 
           [0020]      FIG. 5  is another diagram of a fuel-providing system further comprising a check valve and a release valve. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The invention relates to a gas-containing system and method. The following description refers to hydrogen gas, but obviously the system may be exploited to store additional and/or alternative gases, as long as the pressure of said gases does not exceed the maximum pressure that the system can accommodate. 
         [0022]    The gas is caused to flow into a thin glass tube, which will also be referred to herein as “capillary”. The cross-section of the capillary can be round or of any other geometrical shape, such as a hexagonal. 
         [0023]    The glass tubes are made of a material having high tensile strength a  20  and low mass density ρ. For example, materials that meet the condition σ/ρ&gt; — 1700 MPa-cm3/g are suitable for the glass tubes. Examples of materials suitable for the capillary tubes include, but are not limited to, borosilicate glass, MgAlSi glass, S-2 Glass™, R-glass available from Saint-Gobain Vetrotex Textiles, T-Glass available from Nitto Boseki Co., Ltd. (Nittobo), fused quartz, polymers (e.g., Kevlar™, 25 TwaronXM), etc. 
         [0024]    Generally, the glass tubes can have any desired length. The external diameter of the glass tubes can be in the range of about 1 micrometer to about 500 micrometers. A number of the capillary glass tubes in one MMC (see  FIG. 2 ) can, for example, be in the range of 50 to 1,000,000. These dimensions of the capillaries are strongly dependent on pressure resistance, possibility of easy manufacturing etc. whereas the dimensions of the arrays (various number of MMC) are dependent on the manufacturing process, opening procedure and the actual application. 
         [0025]    Methods for fabrication of hollow microcylinders (i.e., capillary glass tubes) and microcylindrical array structures are known per se. In particular, various microcylindrical (capillary) arrays made from glass and/or plastics are widely used in x-ray optics and photonics. Generally, the process of fabrication of microcylindrical arrays is divided into three main stages: (i) drawing capillaries with relatively large diameter, (ii) re-drawing them 10 into a bundle of capillaries with smaller diameter, and (iii) sintering capillaries into the array. Existing technology enables one to produce vast arrays with a capillary diameter down to 1 micron or even less, and a wall thickness-to-diameter ratio less than 5%. For example, capillary arrays suitable for the purpose of the present invention can be obtained from Paradigm Optics, Inc.; 9600 NE 126th Ave, Suite 2540 Vancouver, Wash. 15 98682 USA; Hilgenberg GmbH, Strauchgraben 2, D-34323 Malsfeld, Germany; INCOM 294 Southbridge Road, Charlton, Mass. 01507; etc. 
         [0026]    A group of capillaries is attached together to form a “multi-capillary” structure (MC). The MC outer cover also has a tubular shape.  FIG. 1  shows an MC  101  with a hexagonal cross-section, according to one embodiment of the invention. One end of the MC  101  is sealed by a glass cupping element, which in this example is shaped as a half sphere  102 , hereinafter—“half-sphere”. For better orientation, the end that comprises a half-sphere is designated as the bottom. The connection between a tube and a half-sphere is performed by melting the glass while applying pressure on both parts, one against the other. 
         [0027]    As shown in  FIG. 2 , a number of MCs can be attached and form an even larger storage system—“multi-multi-capillary” (MMC). An MC or a group of MCs—MMC are connected to an adaptor at the open (top) end of the capillaries—a unit which allows the addition and release of a gas into and from each tube. A valve can be provided in the adaptor or connected thereto, to prevent gas from escaping from the storage.  FIG. 2  shows an MMC  201  connected to an adaptor  202 . The attachment of an MC or an MMC to an adaptor can be performed for example by a glue such as epoxy resin. If necessary after the attachment of the adaptor to the MC/MMC, an additional sealing material can be used. One example of a suitable adaptor is one that is made of stainless steel 1.4301 and designed to securely hold the glass-steel connection at pressure up to 40 MPa. 
         [0028]    An exemplary adaptor made of SS 1.4301 has a wall thickness of 0.75 mm and is suitable to store gas at a pressure of up to 40 MPa, it is glued for a length of the glass sheath of 53 mm using Loctite 9483 A&amp;B. The resin is cures at 30° C. for 24 hours. 
         [0029]    As shown in  FIG. 3 , another form of storage system can be an array of MMCs, according to another embodiment of the invention. Every MMC  301  is connected to its own adaptor  302 , and every adaptor is connected to a conduit  303 . When all of the MMCs in the array are connected to one or more conduits, it provides for a convenient addition and extraction of gas into and from the storage system, and thus the procedure is performed only once for every group of MMCs connected to the same conduit  303 . 
         [0030]      FIG. 4  is a diagram of a fuel-providing system comprising an array of MMC. The fuel cell  401  is where the chemical reaction occurs, but the gas used in the process needs to enter the fuel cell  401  at a relatively low pressure, for example 0.2 MPa, and since it leaves the MMCs  402  at a pressure of up to 20 MPa, in this illustrative scheme a pressure regulator  403  is provided between the fuel cell  401  and the MMCs  402 . A fast coupling  404  can also be provided. 
         [0031]      FIG. 5  is another diagram of a fuel-providing system further comprising a check valve  501  and a release valve  502 . The additional two components are provided in this specific embodiment of the invention for safety reasons. The check valve  501  can detect hazardous situation relaying on pressure values measured by said valve  501 . If the pressure in the system is too high, the release valve  502  is operated by check valve  501 , for pressure release and regulation. 
         [0032]    All the above description has been provided for the purpose of illustration and it is not meant to limit the invention in any way except as provided for by the appended claims.