Abstract:
A cryogenic fluid storage tank having a first conduit adapted for filling and extracting a cryogenic liquid from the tank and a second conduit adapted for filling and extracting a gas from the tank is disclosed, wherein heat originating from inlet and outlet conduits transferred to the tank is minimized.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to a cryogenic storage tank, and more particularly, to an improved cryogenic storage tank with a minimized 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. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to an anode of the fuel cell and oxygen is supplied as an oxidant to a cathode. 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 compress 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 under a vacuum. The interior of the tank, however, must include fluid communication, 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 a gas conduit adapted to be both an inlet and outlet. 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. At least a portion of each conduit is exposed to the ambient environment. The conduits bridge any insulation that is present between the inner and outer vessel and allow heat from the ambient environment to transfer into the inner vessel. 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 conduit. 
     It would be desirable to develop a cryogenic storage tank with a minimized heat transfer originating from inlet and outlet conduits. 
     SUMMARY OF THE INVENTION 
     Concordant and congruous with the present invention, a cryogenic storage tank with a minimized heat transfer originating from inlet and outlet conduits, has surprisingly been discovered. 
     In one embodiment, the cryogenic fluid storage tank comprises a tank adapted to store a cryogenic fluid; a first conduit penetrating said tank and having an outlet and an inlet disposed within said tank, said first conduit adapted to supply a cryogenic liquid to said tank through the outlet and extract the cryogenic liquid from said tank through the inlet; and a second conduit penetrating said tank and disposed within said tank adapted to selectively supply a gas to said tank and extract the gas from said tank. 
     In another embodiment, the cryogenic fluid storage tank comprises a tank adapted to store a cryogenic fluid; a first conduit penetrating said tank and having an outlet and an inlet disposed within said tank, said first conduit adapted to supply a cryogenic liquid to said tank through the outlet and extract the cryogenic liquid from said tank through the inlet, wherein the outlet is disposed substantially in a gaseous phase of said tank reservoir and the inlet is disposed substantially in a liquid phase of said tank reservoir; and a second conduit penetrating said tank and disposed within said tank adapted to selectively supply a gas to said tank and extract the gas from said tank, wherein the first aperture of said second conduit is disposed substantially in a gaseous phase of said tank reservoir. 
     In another embodiment, the cryogenic fluid storage tank comprises a tank adapted to store a cryogenic fluid; a first conduit penetrating said tank and having an outlet and an inlet disposed within said tank, said first conduit adapted to supply a cryogenic liquid to said tank through the outlet and extract the cryogenic liquid from said tank through the inlet, wherein the outlet is disposed substantially in a gaseous phase of said tank reservoir and the inlet is disposed substantially in a liquid phase of said tank reservoir; and a second conduit penetrating said tank and disposed within said tank adapted to selectively supply a gas to said tank and extract the gas from said tank, wherein the first aperture of said second conduit is disposed substantially in a gaseous phase of said tank reservoir; and a vacuum tube penetrating a sidewall of said tank, wherein a portion of said first conduit and a portion of said second conduit are disposed in the vacuum tube. 
    
    
     
       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 schematic sectional view of a cryogenic storage tank according to an embodiment of the invention; and 
         FIG. 2  is a schematic sectional view of a cryogenic storage tank according to another embodiment of the invention. 
     
    
    
     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. 
       FIG. 1  shows a storage tank  10  according to an embodiment of the invention. The storage tank  10  includes a reservoir  12 , a first conduit  14 , and a second conduit  16 . An inner vessel  18  forms the reservoir  12 . The inner vessel  18  is disposed in an outer vessel  20  forming an interstitial space therebetween. The space between the inner vessel  18  and the outer vessel  20  is filled with a multi-layered thermal vacuum insulation  22 . It is understood that the space between the inner vessel  18  and outer vessel  20  may be filled with any insulation, as desired, or the space can remain empty. 
     In the embodiment shown, the first conduit  14  includes a first portion  28 , a second portion  30 , and an extraction conduit  29 . The first conduit  14  extends through a first penetration of the storage tank  10  to provide fluid communication between the reservoir  12  and a source of fluid (not shown). It is understood that the first conduit  14  may also be in fluid communication with another storage tank (not shown), a fuel cell stack (not shown), or an internal combustion engine (not shown), as desired. The first penetration  31  is formed by a series of apertures in the outer vessel  20 , insulation  22 , and inner vessel  18  that provide a channel adapted to receive a portion of the first conduit  14 . The first portion  28  includes an inlet (not shown) formed at a distal end thereof in communication with the source of fluid. The second portion  30  is substantially v-shaped and includes an outlet  24  formed at a distal end thereof and an inlet  26  formed intermediate the outlet  24  and the first penetration. In the embodiment shown, the inlet  26  has a diameter less than a diameter of the outlet  24 . It is understood that the dimensions of the diameters may be equal or the diameter of the outlet  24  may be less than the diameter of the inlet  26 , as desired. It is further understood that the outlet  24  and inlet  26  may also be adapted to be both an inlet and an outlet, as desired. The outlet  24  is disposed substantially near a top of the storage tank  10 , above a cryogenic liquid  40  and in a gas  42 . The inlet  26  is disposed substantially near a bottom of the storage tank  10 , in the cryogenic liquid  40 . It is understood that the first conduit  14  may have any shape with the outlet  24  in the gas  42  and above the cryogenic liquid  40  and the inlet  26  in the cryogenic liquid  40 , such as a substantial u-shape, or substantial semi-circular shape, as desired. As shown, the extraction conduit  29  penetrates the insulation  22  and outer vessel  20  and is in fluid communication with the source of fluid. It is understood that the extraction conduit  29  may be disposed anywhere on the first conduit  14 , as desired. It is also understood that the cryogenic liquid  40  and gas  42  may be any fluid such as hydrogen, oxygen, nitrogen, and helium, for example, 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  33  of the storage tank  10  to provide fluid communication between the reservoir  12  and the source of fluid. The second penetration  33  is formed by a series of apertures in the outer vessel  20 , insulation  22 , and inner vessel  18  that provide a channel adapted to receive a portion of the second conduit  16 . The first portion  34  includes an inlet (not shown) and an outlet (not shown), each formed at a distal end thereof. It is understood that the inlet of the first portion  34  may be in communication with the refueling source, another source of liquid, or a source of gas, as desired. It is understood that the outlet of the first portion  34  may be in communication with a fuel cell stack, an internal combustion engine, or a waste tank, as desired. The second portion  36  terminates at an aperture  32  adapted to be an inlet and outlet. The aperture  32  is disposed substantially near a top of the storage tank  10 , above the cryogenic liquid  40  and in the gas  42 . It is understood that the second portion may be curvilinear, helical, and otherwise shaped, as desired. 
     During a filling operation, the cryogenic liquid  40  is caused to flow through the first conduit  14  into the reservoir  12  of the storage tank  10 . The cryogenic liquid flows through the outlet  24  and through the gas at the top of the storage tank  10  before flooding to the bottom of the storage tank  10 . As the cryogenic liquid  40  passes through the gas  42  at the top of the storage tank  10 , the gas  42  is cooled. Simultaneously, a portion of the cryogenic liquid may flow through the inlet  26  into the bottom of the reservoir  12 . The rate of flow of the cryogenic liquid  40  through the inlet  26  is typically less than the rate of flow of the cryogenic liquid  40  through the outlet  24  due to the difference of the inlet  26  and outlet  24  diameter sizes. It is understood that the inlet  26  may have a seal, a gasket, a valve, or other means of regulating flow so that during a filling operation flow through the inlet  26  is militated against. Simultaneously with the cryogenic liquid  40  filling, the gas  42  may be extracted from the storage tank  10  through the second conduit  16  to relieve the pressure in the reservoir  12  and to facilitate a filling of the storage tank  10  with the cryogenic liquid  40 . 
     During an extraction operation, the cryogenic liquid  40  is caused to flow through the inlet  26  of the first conduit  14 , through the extraction conduit  29 , and out of the storage tank  10 . Before liquid extraction may occur the cryogenic liquid  40  must first flow through the inlet  26  to flood the first conduit  14 . Typically, the level of the liquid  40  in the first conduit  14  will be equal to the level of the liquid  40  in the reservoir  12 . Simultaneously, if desired, the gas  42  may be caused to flow through the aperture  32  of the second conduit  16  and into the storage tank  10  or the gas  42  may be caused to flow through the aperture  32  out of the storage tank  10 , as desired. The difference in size of the diameters of the inlet  26  and outlet  24  facilitates regulation of the flow through the inlet  26  according to a desired extraction rate. 
     Use of the first conduit  14  and the second conduit  16  to perform all liquid and gas filling and extraction operations minimizes the overall number of conduits in the storage tank  10 . By minimizing the number of conduits, the number of penetrations in the storage tank  10  into the reservoir  12  is minimized. Furthermore, the number of welds between the conduits  14 ,  16  and the storage tank  10  is also minimized which minimizes potential stress failures. Heat entry into the storage tank  10  and boil-off of the cryogenic liquid  40  is also minimized. Furthermore, by minimizing the number of conduits, the material costs, production costs, weight, and maintenance of the storage tank  10  is minimized. 
       FIG. 2  shows a storage tank  10 ′ according to another embodiment of the invention. The storage tank  10 ′ includes a reservoir  12 ′, a vacuum tube  13 ′, a first conduit  14 ′, and a second conduit  16 ′. The reservoir  12 ′ is formed by an inner vessel  18 ′. The inner vessel  18 ′ is disposed in an outer vessel  20 ′ forming an interstitial space therebetween. The space between the inner vessel  18 ′ and the outer vessel  20 ′ is filled with a multi-layered thermal vacuum insulation  22 ′. It is understood that the space between the inner vessel  18 ′ and outer vessel  20 ′ may be filled with any insulation, as desired, or the space can remain empty. 
     The vacuum tube  13 ′ is a conduit surrounding the first conduit  14 ′ and the second conduit  16 ′. The vacuum tube  13 ′ includes insulation  38 ′ that surrounds the first conduit  14 ′ and the second conduit  16 ′. It is understood that the vacuum tube  13 ′ may be any conventional vacuum tube, as desired, and maybe be a double walled insulated vacuum tube, or may be filled with a multi-layered thermal vacuum insulation, as desired. The vacuum tube  13 ′ is disposed through a first penetration  31 ′ of the storage tank  10 ′. The first penetration  31 ′ is formed by a series of apertures in the outer vessel  20 ′, insulation  22 ′, and inner vessel  18 ′ that provide a channel adapted to receive a portion of the vacuum tube  13 ′. It is understood that the vacuum tube  13 ′ may share a vacuum with the insulation  22 ′, as desired. 
     In the embodiment shown, the first conduit  14 ′ includes a first portion  28 ′, a second portion  30 ′, and an extraction conduit  29 ′. The first conduit  14 ′ extends through the vacuum tube  13 ′ to provide fluid communication between the reservoir  12 ′ and a source of fluid (not shown). It is understood that the first conduit  14  may also be in fluid communication with another storage tank (not shown), a fuel cell stack (not shown), or an internal combustion engine (not shown), as desired. The first portion  28 ′ includes an inlet (not shown) formed at a distal end thereof in communication with the source of fluid. The second portion  30 ′ is substantially v-shaped and includes an outlet  24 ′ formed at a distal end thereof and an inlet  26 ′ formed intermediate the outlet  24 ′ and the first feed-through. In the embodiment shown, the inlet  26 ′ has a diameter less than a diameter of the outlet  24 ′. It is understood that the dimensions of the diameters may be equal or the diameter of the outlet  24 ′ may be less than the diameter of the inlet  26 ′, as desired. It is further understood that the outlet  24 ′ and inlet  26 ′ may also be adapted to be both an inlet and an outlet, as desired. The outlet  24 ′ is disposed substantially near a top of the storage tank  10 ′, above a cryogenic liquid  40 ′ and in a gas  42 ′. The inlet  26 ′ is disposed substantially near a bottom of the storage tank  10 ′, in the cryogenic liquid  40 ′. It is understood that the first conduit  14 ′ may have any shape with the outlet  24 ′ in the gas  42 ′ and above the cryogenic liquid  40 ′ and the inlet  26 ′ in the cryogenic liquid  40 ′, such as a substantial u-shape, or substantial semi-circular shape, as desired. As shown, the extraction conduit  29 ′ is disposed through the insulation  22 ′ and outer vessel  20 ′ and in fluid communication with the source of fluid. It is understood that the extraction conduit  29 ′ may be disposed anywhere on the first conduit  14 ′, as desired. It is also understood that the cryogenic liquid  40 ′ and gas  42 ′ may be any fluid such as hydrogen, oxygen, nitrogen, and helium, for example, as desired. 
     The second conduit  16 ′ includes a first portion  34 ′ and a second portion  36 ′. The second conduit  16 ′ is disposed through the vacuum tube  13 ′ to provide fluid communication between the reservoir  12 ′ and the source of fluid. The second conduit  16 ′ is disposed through the vacuum tube  13 ′ and adjacent the first conduit  14 ′. The first portion  34 ′ is substantially linear and includes an inlet (not shown) and an outlet (not shown), each formed at a distal end thereof. It is understood that the inlet of the first portion  34 ′ may be in communication with the refueling source, another source of liquid, or a source of gas, as desired. It is understood that the outlet of the first portion  34 ′ may be in communication with a fuel cell stack, an internal combustion engine, or a waste tank, as desired. The second portion  36 ′ is substantially v-shaped and includes an aperture  32 ′ adapted to be an inlet and outlet. The aperture  32 ′ is disposed substantially near a top of the storage tank  10 ′, above the cryogenic liquid  40 ′ and in the gas  42 ′. It is understood that the second portion  36 ′ may have any shape such as a substantial u-shape or substantial semi-circular shape, as desired. 
     During a filling operation, the cryogenic liquid  40 ′ is caused to flow through the first conduit  14 ′ into the reservoir  12 ′ of the storage tank  10 ′. The cryogenic liquid flows through the outlet  24 ′ and through the gas at the top of the storage tank  10 ′ before flooding to the bottom of the storage tank  10 ′. As the cryogenic liquid  40 ′ passes through the gas  42 ′ at the top of the storage tank  10 ′, the gas  42 ′ is cooled. Simultaneously, a portion of the cryogenic liquid may flow through the inlet  26 ′ into the bottom of the reservoir  12 ′. The rate of flow of the cryogenic liquid  40 ′ through the inlet  26 ′ is typically less than the rate of flow of the cryogenic liquid  40 ′ through the outlet  24 ′ due to the difference of the outlet  24 ′ and the inlet  26 ′ diameter sizes. It is understood that the inlet  26 ′ may have a seal, a gasket, a valve, or other means of regulating flow so that during a filling operation flow through the inlet  26 ′ is militated against. Simultaneously with the cryogenic liquid  40 ′ filling, the gas  42 ′ may be extracted from the storage tank  10 ′ through the second conduit  16 ′ to relieve the pressure in the reservoir  12 ′ and to facilitate a filling of the storage tank  10 ′ with the cryogenic liquid  40 ′. 
     During an extraction operation, the cryogenic liquid  40 ′ is caused to flow through the inlet  26 ′ of the first conduit  14 ′, through the extraction conduit  29 ′, and out of the storage tank  10 ′. Before liquid extraction may occur the cryogenic liquid  40 ′ must first flow through the inlet  26 ′ to flood the first conduit  14 ′. Typically, the level of the liquid  40 ′ in the first conduit  14 ′ will be equal to the level of the liquid  40 ′ in the reservoir  12 ′. Simultaneously, if desired, the gas  42 ′ may be caused to flow through the aperture  32 ′ of the second conduit  16 ′ and into the storage tank  10 ′ or the gas  42 ′ may be caused to flow through the aperture  32 ′ out of the storage tank  10 ′, as desired. The difference in size of the diameters of the inlet  26 ′ and the outlet  24 ′ facilitates regulation of the flow through the inlet  26 ′ according to a desired extraction rate. 
     Utilizing only the first conduit  14 ′ and the second conduit  16 ′ to perform all liquid and gas filling and extraction operations minimizes the overall number of conduits in the storage tank  10 ′. By minimizing the number of conduits, the number of penetrations disposed in the storage tank  10 ′ into the reservoir  12 ′ is reduced. Furthermore, the number of welds between the conduits  14 ′,  16 ′ and the storage tank  10 ′ is also minimized which minimizes potential stress failures. Heat entry into the storage tank  10 ′ and boil-off of the cryogenic liquid  40 ′ is also minimized. Furthermore, by minimizing the number of conduits, the material costs, production costs, weight, and maintenance of the storage tank  10 ′ is 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.