Patent Document

FIELD OF THE INVENTION 
     The invention relates generally to a cryogenic storage tank, and more particularly, to a cryogenic storage tank including a thermal shield that minimizes heat transfer to the cryogenic fluid originating from inlet and outlet conduits. 
     BACKGROUND OF THE INVENTION 
     Electric vehicles and internal combustion engine powered vehicles may be powered by a number of different fuels. Internal combustion engine powered vehicles may be powered by various fuels including gasoline, diesel, ethanol, methane, or hydrogen, for example. Fuel cells have been proposed as a power source for electric vehicles, and other applications. Such a fuel cell system is disclosed in commonly owned U.S. patent application Ser. No. 10/418,536, hereby incorporated herein by reference in its entirety. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied as a fuel to an anode of the fuel cell and oxygen is supplied as an oxidant to a cathode of the fuel cell. A common technique for storing large quantities of hydrogen is to cool and compress hydrogen via liquefaction techniques, and to store the liquid phase hydrogen in a cryogenic storage tank. Hydrogen gas liquefies at −253° C. and can be stored at about 70 g/L in the liquid phase. The amount of energy required to cool down hydrogen gas into a liquid is very high, and currently may use as much as 40% of the energy obtained from the hydrogen fuel. Thus, it is advantageous to keep the liquid phase hydrogen insulated to militate against liquid evaporation. 
     Any transfer of heat to the innermost portion of the cryogenic storage tank affects the natural evaporation rate of the cryogenic vessel. The more heat that is transferred, the faster the rate of boil-off of the liquid hydrogen, or the higher the natural evaporation rate. In order to maintain the hydrogen in a liquid state, heat transfer from the ambient environment to the cryogenic liquid must be kept to a minimum. Cryogenic storage tanks generally consist of an inner storage vessel encapsulated with an outer vessel or shell. The space between the inner vessel and the outer vessel is commonly well insulated and maintained under a vacuum. An interior of the inner vessel, however, must include fluid communication means, typically in the form of inlet and outlet conduits, for the filling and extraction of liquid and gaseous hydrogen. 
     A typical storage tank includes a liquid inlet conduit, a liquid outlet conduit, and an inlet and outlet gas conduit. The liquid inlet conduit and the liquid outlet are sometimes combined into a single conduit. Further, additional conduits are sometimes included to provide a path for cables to sensors or heaters that may be included in the inner vessel. The three conduits typically penetrate a sidewall of the storage tank through three separate apertures, or together in a common vacuum tube penetrating the sidewall of the inner vessel. At least a portion of each conduit is exposed to the ambient environment. The conduits bridge an insulation that is present between the inner vessel and the outer vessel, and allow parasitic heat from the ambient environment to transfer into the inner vessel. 
     The use of a vacuum tube is a typical method employed to mitigate the heat transfer from the ambient environment to the inner vessel. A vacuum tube is provided that extends into the inner vessel creating a tubular cavity. The inlet and outlet conduits pass through the vacuum tube before penetrating the inner vessel. The cavity in the vacuum tube is maintained colder than the inlet and outlet conduits contained therein. The colder temperature in the cavity cools the inlet and outlet conduits, and reduces the heat transfer by the inlet and outlet conduits from the ambient environment into the inner vessel. 
     The use of the vacuum tube has some shortcomings. The vacuum tube reduces a storage volume of the inner vessel. Further, testing the inner vessel for vacuum tightness once welded closed is difficult and any repairs to welds or conduits at a far end of the vacuum tube are not possible. Accordingly, there is a need for an improved cryogenic liquid storage tank and particularly, one that minimizes heat transfer originating from the inlet and outlet conduits and maximizes the storage volume and serviceability of the inner vessel. 
     It would be desirable to develop a cryogenic storage tank with a minimized heat transfer originating from the inlet and outlet conduits and maximized storage volume and serviceability of the inner vessel. 
     SUMMARY OF THE INVENTION 
     Compatible and attuned with the present invention, a cryogenic storage tank with a minimized heat transfer originating from the inlet and outlet conduits and maximized storage volume and serviceability of the inner vessel, has surprisingly been discovered. 
     In one embodiment, the cryogenic fluid storage tank comprises a tank having an outer wall and adapted to store a cryogenic fluid; a first conduit penetrating the tank at a penetration point; and a thermal shield disposed adjacent the penetration point of the first conduit to thermally shield the conduit from ambient temperatures. 
     In another embodiment, the cryogenic fluid storage tank comprises a dual wall tank having an inner tank wall, an outer tank wall, and an interstitial space formed therebetween; a first conduit penetrating the outer wall and the inner wall of the tank; and a thermal shield disposed in the interstitial space to thermally shield the conduit. 
     In another embodiment, the cryogenic fluid storage tank comprises an outer vessel; an inner vessel disposed in the outer vessel forming an interstitial space therebetween, the inner vessel and the outer vessel cooperating to store a cryogenic fluid; a first conduit penetrating the outer wall and the inner wall of the tank, the first conduit adapted to vent and extract a gas from the tank; a second conduit penetrating the outer wall and the inner wall of the tank, the second conduit adapted to supply the cryogenic liquid to the tank; a third conduit penetrating the outer wall and the inner wall of the tank, the third conduit adapted to extract the cryogenic liquid from the tank; and a thermal shield disposed in the interstitial space between the first, second, and third conduits and the outer vessel to thermally shield the first, second, and third conduits. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
         FIG. 1  is a sectional side view of a cryogenic storage tank according to an embodiment of the invention; 
         FIG. 2  is a sectional top view of the cryogenic storage tank shown in  FIG. 1 ; 
         FIG. 3   a  is an enlarged fragmentary schematic sectional top view of a portion of the cryogenic storage tank shown in  FIG. 2  generally depicted by circle  3  and illustrating a thermal shield; 
         FIG. 3   b  is an alternate embodiment of the thermal shield shown in  FIG. 3   a;    
         FIG. 3   c  is an alternate embodiment of the thermal shield shown in  FIG. 3   a ; and 
         FIG. 3   d  is an alternate embodiment of the thermal shield shown in  FIG. 3   a.    
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. 
       FIGS. 1 and 2  show a cryogenic fluid storage tank  10  according to an embodiment of the invention. The storage tank  10  includes a reservoir  12 , a first conduit  14 , a second conduit  16 , a third conduit  18 , and a thermal shield  13 . An inner vessel  20  forms the reservoir  12 . The inner vessel  20  is disposed in an outer vessel  22  forming an interstitial space therebetween. The space between the inner vessel  20  and the outer vessel  22  is filled with a multi-layered thermal vacuum insulation  24 . It is understood that the space between the inner vessel  20  and outer vessel  22  may be filled with any insulation, as desired, or the space can remain empty. It is also understood that the cryogenic fluid may be any fluid such as hydrogen, oxygen, nitrogen, argon, neon, krypton, xenon, and helium or compounds thereof, for example, as desired. 
     In the embodiment shown, the first conduit  14  includes a first portion  26  and a second portion  28 . The first conduit  14  extends through a first penetration  30  of the storage tank  10  to provide fluid communication between the reservoir  12  and a consumer of cryogenic fluid (not shown) such as a fuel cell stack, an internal combustion engine, or a waste tank, as desired. The first penetration  30  is formed by a series of apertures in the outer vessel  22 , insulation  24 , and inner vessel  20  that provide a channel adapted to receive a portion of the first conduit  14 . The first portion  26  includes an outlet (not shown) formed at a distal end thereof. The second portion  28  is substantially L-shaped and includes an aperture  32  adapted to be an inlet. The aperture  32  is disposed substantially near a top of the storage tank  10 , above a cryogenic liquid  100  and in a gas  102 . It is understood that the second portion  28  may be curvilinear, helical, and otherwise shaped, as desired. 
     The second conduit  16  includes a first portion  34  and a second portion  36 . The second conduit  16  extends through a second penetration  38  of the storage tank  10  to provide fluid communication between the reservoir  12  and a source of cryogenic fluid (not shown) such as a refueling source, another source of liquid, or a source of gas, as desired. The second penetration  38  is formed by a series of apertures in the outer vessel  22 , insulation  24 , and inner vessel  20  that provide a channel adapted to receive a portion of the second conduit  16 . The first portion includes an inlet (not shown) formed at a distal end thereof. The second portion  34  is substantially L-shaped and includes an aperture  40  adapted to be an outlet. The aperture  40  is disposed substantially near a top of the storage tank  10 , above the cryogenic liquid  100  and in the gas  102 . It is understood that the second portion  36  may be curvilinear, helical, and otherwise shaped, as desired. 
     The third conduit  18  includes a first portion  42  and a second portion  44 . The third conduit  18  extends through a third penetration  46  of the storage tank  10  to provide fluid communication between the reservoir  12  and the consumer of cryogenic fluid. The third penetration  46  is formed by a series of apertures in the outer vessel  22 , insulation  24 , and inner vessel  20  that provide a channel adapted to receive a portion of the third conduit  18 . It is understood that the first penetration  30 , the second penetration  38 , and the third penetration  46  can be formed as a single penetration adapted to receive the first conduit  14 , the second conduit  16 , and the third conduit  18 . The second portion  44  is substantially linear and includes an aperture  48  adapted to be an inlet. The aperture  48  is disposed substantially near a bottom of the storage tank  10 , below the gas  102  and in the cryogenic liquid  100 . It is also understood that the second portion  44  may be curvilinear, helical, and otherwise shaped, as desired. 
     Each conduit  14 ,  16 ,  18  is oriented to penetrate the storage tank  10  near a top surface of the outer vessel  22  and extend downwardly through the insulation  24 . The conduits  14 ,  16 ,  18  are adapted to penetrate the inner vessel  20  near the bottom thereof. It is understood that the conduits  14 ,  16 ,  18  may penetrate the inner vessel  20  at other locations as desired. Additionally, each conduit  14 ,  16 ,  18  is joined to the inner vessel  20  at the aperture in the inner vessel  20  by a bond  50  therebetween. The bond  50  is typically a welded joint between the inner vessel  20  and the conduit  14 ,  16 ,  18 , although other bonds can be used as desired. Additional or fewer conduits (not shown) penetrating the storage tank  10  can be provided as desired. The conduits can provide communication between one or more sensors or heaters (not shown) disposed within the storage tank  10  and an electrical source (not shown) remotely located from the storage tank  10 . Further, it is also understood that the pathway of the conduits  14 ,  16 ,  18  from the outer vessel  22  to the inner vessel  20  may have paths other than the substantially straight path shown in  FIG. 1 . The other pathways of the conduits  14 ,  16 ,  18  can be longer and follow a perimeter of the inner tank, for example, as desired. 
     The thermal shield  13  includes a metal plate adapted to form a generally u-shaped elongated tube with an open upper end  52  and a closed lower end  54 . The thermal shield  13  is bonded to the inner vessel  20  at the closed lower end  54  located near a bottom of the inner vessel  20 . The penetration points of the conduit  14 ,  16 ,  18  into the inner vessel  20  are encompassed by the thermal shield  13 . The thermal shield  13  extends upwardly toward the upper portion of the tank  10  within the interstitial space between the conduits  14 ,  16 ,  18  and the outer vessel  22  to form a shielding cavity  56  between the inner vessel  20  and the thermal shield  13 . 
     The thermal shield  13  as shown in  FIGS. 2 and 3   a  is generally u-shaped and forms the shielding cavity  56 . However, the thermal shield  13  can form differently shaped shielding cavities as desired. Some examples of other shaped shielding cavities are shown in  FIGS. 3   b ,  3   c , and  3   d  although other shapes can be used. Like structure repeated from  FIG. 3   a  includes the same reference numeral and a prime symbol (′) in  FIG. 3   b , a double prime symbol (″) in  FIG. 3   c , and a triple prime symbol (′″) in  FIG. 3   d .  FIG. 3   b  shows a substantially v-shaped thermal shield  13 ′.  FIG. 3   c  shows a substantially rectangular thermal shield  13 ″.  FIG. 3   d  shows a substantially planar thermal shield  13 ′″. It is understood that the thermal shield  13  can have other shapes to shield the conduits  14 ,  16 ,  18  on one or more sides. Further, it is understood that the thermal shield  13  can be adapted to surround a greater or lesser portion of the conduit than shown in  FIG. 3   d  without departing from the scope and spirit of the invention. 
     During a filling operation, the cryogenic liquid  100  is caused to flow through the second conduit  16  into the reservoir  12  of the storage tank  10 . The cryogenic liquid flows through the aperture  40  and through the gas  102  at the top of the storage tank  10  before flooding to the bottom of the storage tank  10 . As the cryogenic liquid  100  passes through the gas  102  at the top of the storage tank  10 , the gas  102  is cooled. Simultaneously with the cryogenic liquid  100  filling, the gas  102  may be extracted from the storage tank  10  through the first conduit  14  to relieve the pressure in the reservoir  12  and to facilitate a filling of the storage tank  10  with the cryogenic liquid  100 . 
     During an extraction operation, the cryogenic liquid  100  is caused to flow through the aperture  48  of the third conduit  18  and out of the storage tank  10 . Simultaneously, if desired, the gas  102  may be caused to flow through the aperture  32  of the first conduit  14  out of the storage tank  10 , as desired. 
     When the storage tank  10  is in use, the distal ends (not shown) of the conduit  14 ,  16 ,  18  are generally exposed to the ambient environment and the second portions  28 ,  36 ,  44  are in contact with the liquid cryogenic fluid  100 . The typical cryogenic liquid is significantly colder than the ambient temperature, for example, hydrogen liquefies at a −253° C. The conduit  14 ,  16 ,  18  are a significant source of heat transfer from the ambient environment to the liquid cryogenic fluid  100  due to the significant temperature difference therebetween. The thermal shield  13  minimizes such heat transfer. 
     The thermal shield  13  is bonded to the inner vessel  20  placing it in thermal contact with the inner vessel  20 . The temperature of the thermal shield  13  is maintained at a temperature lower than the conduit  14 ,  16 ,  18  due to the low temperature of the cryogenic liquid  100  in the reservoir  12 . The conduit  14 ,  16 ,  18  are cooled as they pass through the shielding cavity  56  of the thermal shield  13  prior to penetrating the inner vessel  20 . The cooling of the conduit  14 ,  16 ,  18  minimizes the heat entry into the inner vessel  20  and boil-off of the cryogenic liquid  100 . Further, the thermal shield deflects the ambient environment thermal energy from the shielding cavity  56  facilitating the maintenance of the low temperature therein. 
     The thermal shield  13  facilitates a maximization of the volume of the reservoir  12  of the tank  10 . The prior art cryogenic tanks (not shown) typically employ a vacuum tube that extends into the reservoir of the tank. The vacuum tube occupies space within the reservoir that could otherwise be occupied with cryogenic fluid. The substitution of the vacuum tube with the thermal shield  13  maximizes the cryogenic fluid capacity of the reservoir  12 . 
     In the embodiment shown, the thermal shield  13  is provided on an exterior surface of the inner vessel  20  and is not subject to the pressure of the compressed cryogenic fluid  100  contained therein. The metal used for the thermal shield  13  can be thinner than the metal used for the inner vessel  20  since it is not a pressure containing structural member of the storage tank  10 . Further, the metal used for the thermal shield  13  does not need to be compatible with hydrogen and the welds bonding the thermal shield  13  to the inner vessel  20  do not need to be vacuum tight. The vacuum tube of the prior art on the other hand, is a member of the pressure containing portion of the tank and requires metal and welds capable of withstanding such pressures and a hydrogen atmosphere. The material costs, production costs, and weight of the storage tank  10  utilizing the thermal shield  13  are minimized. 
     As described above, the prior art cryogenic tanks typically employ a vacuum tube to cool the conduit that penetrate the tank. The tube is typically sized to accommodate the conduit with limited additional space therebetween. Further, the conduit penetrates the inner vessel at a far end of the vacuum tube. The structure restricts access to the vacuum tube welds and the welds bonding the conduit to the inner vessel once the inner vessel is closed. The structure of the storage tank  10  as illustrated in  FIG. 1  provides welds that are accessible from the exterior surface of the inner vessel  20 . The inner vessel  20  can be tested for vacuum tightness and the locations of any leaks are readily visible and accessible for repair. The production costs and repair costs of the storage tank  10  utilizing the thermal shield  13  are minimized. 
     From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.

Technology Category: f