Patent Publication Number: US-2016231049-A1

Title: Hydrogen liquefaction device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2015-0016990, filed on Feb. 5, 2015, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to a hydrogen liquefaction device, and more particularly, to a hydrogen liquefaction device using a dual tube type heat pipe, which utilizes cooling energy of a cryocooler via dual tube type heat pipe to liquefy gaseous hydrogen. A method of liquefying hydrogen is also disclosed herein. 
     Recently, hydrogen energy has emerged as a potential solution to air pollution and climate change caused by excessive use of fossil fuels. Utilizing fuel sources that are not hydrocarbon based can help reverse the problems of pollution and climate change that may otherwise continue unchecked. Hydrogen is advantageous because it can be obtained from water. In addition, unlike hydrocarbon fuels, when hydrogen energy is combusted it only creates water as a byproduct. No carbon dioxide is emitted, for example. 
     In order to effectively utilize hydrogen as energy source, it should be made convenient to transport and store. These goals may be achieved by, for example, reducing the volume of the hydrogen via a densification process. Among the methods for reducing a volume of hydrogen and storing hydrogen, a method of liquefying and storing the hydrogen in a liquid phase has the largest storage energy. 
     Among methods for liquefying gaseous hydrogen, the Linde-Hampson cycle, Claude cycle, and similar cycles are known. However, these liquefying cycles require large-scale hydrogen liquefaction systems that may not be suitable for liquefying and/or transporting smaller amounts of hydrogen. The ability to liquefy and/or transport small amounts of hydrogen is an important aspect of increasing hydrogen consumption in different sectors of the global economy. 
     As a result, a need exists for improving the performance and stability of hydrogen liquefaction processes. This is particularly true for those processes employing a cryocooler. 
     SUMMARY 
     In one example embodiment, a hydrogen liquefaction apparatus is disclosed. The apparatus includes an outer container; a liquefaction container positioned at least partially within the outer container; a heat pipe positioned within the liquefaction container. The head pipe includes a condensing portion, an evaporating portion, an inner tube portion containing a working fluid and operatively coupling the condensing portion to the evaporating portion, and an outer tube portion surrounding the inner tube portion and defining a dual tube region between the outer tube and the inner tube. Also included is a cryocooler in thermal communication with the liquefaction container and configured to cool the condensing portion of the heat pipe; a pre-cooling tube positioned at least partially within the dual tube region and comprising an inlet port for receiving gaseous hydrogen and an outlet port for discharging gaseous hydrogen into the liquefaction container; and an ortho-para converting part positioned at least partially within the pre-cooling tube, the ortho-para converting part comprising a catalyst configured to induce an ortho-para conversion of gaseous hydrogen within the pre-cooling tube. 
     In another example embodiment, a method of liquefying hydrogen is disclosed. The method includes, for example, providing a liquefaction container positioned at least partially within an outer container, and providing a heat pipe within the liquefaction container, the heat pipe including a condensing portion, an evaporating portion, an inner tube portion, and an outer tube portion, wherein the inner and outer tube portions for a dual tube region. The method includes introducing gaseous hydrogen into a pre-cooling tube positioned within the dual tube region; ortho-para converting the gaseous hydrogen within the pre-cooling tube; and collecting liquid hydrogen within the liquefaction container. 
     In yet another example embodiment, a heat pipe is disclosed having a condensing portion; an evaporating portion; an inner tube portion containing a working fluid and operatively coupling the condensing portion to the evaporating portion; an outer tube portion surrounding the inner tube portion and defining a dual tube region between the outer tube and the inner tube; a cryocooler in thermal communication with the condensing portion; a pre-cooling tube positioned at least partially within the dual tube region and comprising an inlet port for receiving gaseous hydrogen and an outlet port for discharging gaseous hydrogen into the liquefaction container; and an ortho-para converting part positioned at least partially within the pre-cooling tube, the ortho-para converting part comprising a catalyst configured to induce an ortho-para conversion of gaseous hydrogen within the pre-cooling tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic view showing an example structure of a hydrogen liquefaction apparatus using a dual tube type heat pipe. 
         FIG. 2  is a diagrammatic view of an example structure of a dual tube region of a heat pipe in a hydrogen liquefaction apparatus using a dual tube type heat pipe. 
     
    
    
     DETAILED DESCRIPTION 
     Hydrogen liquefaction device and methods of liquefying hydrogen are disclosed herein. In some example embodiments, the hydrogen liquefaction device utilizes a dual tube type heat pipe as described in detail below with reference to the accompanying drawings. While the present disclosure is shown and described in connection with example embodiments, various modifications can be made without departing from the spirit and scope of the invention. 
       FIG. 1  a diagrammatic view showing an example structure of a hydrogen liquefaction apparatus using a dual tube type heat pipe and  FIG. 2  is a diagrammatic view of an example structure of a dual tube region of a heat pipe in a hydrogen liquefaction apparatus using a dual tube type heat pipe. 
     Referring to  FIGS. 1 and 2 , an example embodiment of a hydrogen liquefaction apparatus is depicted. The hydrogen liquefaction apparatus utilizes a dual tube type heat pipe design. The device may include, for example, an external container  10 , a liquefaction container  20 , a cryocooler  30 , a heat pipe  40 , a pre-cooling tube  50 , and an ortho-para converting part  51 . 
     The external container  10  is configured to contain the liquefaction container  20 , heat pipe  40 , pre-cooling tube  50 , and ortho-para converting part  51 . The external container  10  may take any form, but as shown in  FIG. 1  has a cylindrical shape with an open upper end to enable another element such as the liquefaction container  20  and the like to be received therein. The open upper end of the external container  10  may be hermetically covered with an upper cover  12 . 
     A cryocooler  30  may be installed on the upper cover  12  or on the external container  10  directly. Cryocooler  30  may be a standalone cooler, such as, for example, a Stirling-type cooler, a Gifford-McMahon-type cooler, a pulse-tube refrigerator, or a Joule-Thomson-type cooler. Any other suitable type of cooler may be used, and the disclosure herein is not intended to be limited to a particular type of cryocooler. Cryocooler  30  may supply cooling energy to the heat pipe  40  placed in the liquefaction container  20 . The cryocooler  30  may supply the cooling energy which is sufficient to cool the liquefaction container  20  to a temperature of 20K or less. 
     A heat insulating layer  11  and/or a multi-layer insulating material (not shown) may be included between the external container  10  and the liquefaction container  20  to reduce heat invasion generated in the radial direction caused by the environment external to the external container  10 . 
     Additionally, the space between the external container  10  and the liquefaction container  20  may be provided in a vacuum state to form the heat insulating layer  11 . The heat insulating layer  11  performs a function of blocking convective heat transfer otherwise caused by air as well as conductive heat transfer to/from the external container  10 . A multilayered heat insulating material layer can be formed by overlapping the heat insulating material surrounding the liquefaction container  20  and, for example, performs the function of reducing heat radiation to/from the liquefaction container  20  and the external container  10 . 
     The liquefaction container  20  is a cylindrical container provided in the external container  10 , an upper end of the liquefaction container is fixed to the upper cover  12  or to a support (not shown) connecting a bottom surface of the external container  10  and a bottom surface of the liquefaction container  20  to each other. In order to reduce heat invasion in the axial direction from the upper cover  12 , the liquefaction container  20  may be provided with a blocking layer formed therein or a heat insulating layer disposed thereon and may be then fixed to the upper cover  12 . According to another embodiment, in addition, it is possible to install the liquefaction container through a separate support acting as a medium. 
     The heat pipe  40  may be positioned in the liquefaction container  20  for receiving the extremely low temperature cooling energy from the cryocooler  30 . In the embodiments of  FIGS. 1 and 2 , the heat pipe  40  includes a condensing part  41 , an evaporating part  42 , an outer tube  43 , and an inner tube  44  provided between the condensing part  41  and the evaporating part  42  in the form of a dual tube. 
     The condensing part  41  of the heat pipe  40  is in contact with the cryocooler  30  to transfer the cooling energy of the cryocooler  30  to the evaporating part  42  of the heat pipe  42  through working fluid acting as a medium. The evaporating part  42  liquefies gaseous hydrogen, which flows into the liquefaction container  20 , with the cooling energy transferred from the condensing part  41  by means of the working fluid. Cooling fins  41   a  and  42   a  are provided in the condensing part  41  and the evaporating part  42 , respectively, to promote the heat transfer in the heat pipe  40 . 
     The outer tube  43  is spaced from the inner tube  44  and surrounds the inner tube  44 . As a result, a dual pipe region  45  is formed in the space between the outer tube  43  and the inner tube  44 . In some embodiments, the dual pipe region  45  is filled, at least partially, with solid nitrogen. Solid nitrogen is a cooling material. To obtain solid nitrogen, gaseous nitrogen flows into and is cooled in this region so that the gaseous nitrogen is phase-changed to solid nitrogen (SN2) to at least partially fill this region. 
     The pre-cooling tube  50  is provided in the dual pipe region  45 . The pre-cooling tube  50  is spaced apart from the outer tube  43  and the inner tube  44  in the dual pipe region  45 , and is extended and wound around the inner tube  44  in the form of a coil. The pre-cooling tube  50  may be wound around the inner tube  44  in other orientations as well, depending on the implementation. The pre-cooling tube  50  is connected to the outer tube  43  via an upper inlet port  52  and a lower outlet port  54 . The upper inlet port  52  is connected to a gaseous hydrogen transferring tube  62  and the lower outlet port  54  is connected to a liquefaction guide tube  55 . 
     In the embodiments of  FIGS. 1 and 2 , the ortho-para converting part  51  is provided with a catalyst causing an ortho-para conversion is formed in the pre-cooling tube  50 . The ortho-para converting part  51  may be formed over an entire length of the pre-cooling tube  50  or may be formed over only a part of the pre-cooling tube. Due to the ortho-para converting part  51  formed in the pre-cooling tube  50 , when gaseous hydrogen passes through the pre-cooling tube  50 , gaseous hydrogen is simultaneously subjected to a pre-cooling and the ortho-para conversion. 
     The liquefaction guide tube  55  is extended toward an outer surface of the evaporating part  42  of the heat pipe  40  to guide gaseous hydrogen GH2 discharged through the liquefaction guide tube  55  to the evaporating part  42  of the heat pipe  40 . The orientation of liquefaction guide tube  55  shown in  FIG. 1  is merely an example orientation. Any orientation may be used to guide gaseous hydrogen to the evaporating part  42  of the heat pipe  40 . 
     A cooling material entering port  46  is formed on the outer tube  43  for allowing gaseous nitrogen to flow into the dual pipe region  45  between the outer tube  43  and the inner tube  44 . The cooling material entering port  46  is connected to a gaseous nitrogen transferring tube  64 . Gaseous nitrogen entered into the dual pipe region  45  is cooled and then phase-changed to solid nitrogen SN2, and the dual pipe region is at least partially filled with solid nitrogen. In some embodiments the dual pipe region is partially filled with solid nitrogen. In other embodiments the dual pipe region is fully filled with solid nitrogen. In yet other embodiments the dual pipe region is filled with a combination of solid, liquid, and/or gaseous nitrogen. 
     The inner tube  44  of the heat pipe  40  is filled with gaseous hydrogen acting as working fluid. For achieving the above, the heat pipe  40  may be provided with a working fluid entering passage for enabling gaseous hydrogen, which is the working fluid, to fill an inner space of the inner tube  44  or may be manufactured such that an inner space of the inner tube is hermetically filled with working fluid. 
     The gaseous hydrogen transferring tube  62  for transferring gaseous hydrogen from the outside to the liquefaction container  20  and the gaseous nitrogen transferring tube  64  for transferring gaseous nitrogen are extended in the liquefaction container  20 . 
     The gaseous hydrogen transferring tube  62  is connected to the upper inlet port  52  of the pre-cooling tube  50  and the gaseous nitrogen transferring tube  64  is connected to the cooling material entering port  46  to supply gaseous nitrogen to the dual tube region  45  between the outer tube  43  and the inner tube  44 . 
     Valves (not shown) may be installed on the gaseous hydrogen transferring tube  62  and the gaseous nitrogen transferring tube  64  for controlling transferring of gaseous hydrogen and gaseous nitrogen to the upper inlet port  52  and the cooling material entering port  46 . 
     Meanwhile, a liquid hydrogen transferring tube  68  is connected to a bottom surface of the liquefaction container  20  for transferring liquid hydrogen, which is liquefied in the liquefaction container  20 , to the outside. 
     An example process for liquefying hydrogen performed by, for example, the device of  FIGS. 1 and 2 , is described herein. 
     In the initial stage of operating the hydrogen liquefaction apparatus, the cooling energy is transferred from the cryocooler  30  to the condensing part  41  of the heat pipe  40 . Some of gaseous hydrogen transferred through the gaseous hydrogen transferring tube  62  is supplied to an inside of the inner tube  44  of the heat pipe  40  via a working fluid entering passage  48 . Gaseous hydrogen supplied to an inside of the inner tube  44  and acting as working fluid flows upward and downward in the heat pipe  40  and transfers the cooling energy of the cryocooler  30 , which was transferred to the condensing part  41 , to the evaporating part  42 . 
     Meanwhile, gaseous nitrogen transferred through the gaseous nitrogen transferring tube  64  is supplied to the dual pipe region  45  between the outer tube  43  and the inner tube  44  through the cooling material entering port  46 . Gaseous nitrogen entered into the dual pipe region  45  receives the cooling energy and is then phase-changed to solid nitrogen. 
     Gaseous hydrogen transferred through the gaseous hydrogen transferring tube  62  flows into the pre-cooling pipe  50  via the upper inlet port  52 . A time at which gaseous hydrogen flows into the pre-cooling tube  50  may be controlled by controlling a valve. While moving along the pre-cooling tube  50 , gaseous hydrogen entered into the pre-cooling pipe  50  is heat-exchanged with ambient solid nitrogen and then pre-cooled. Simultaneously, gaseous hydrogen passes through the ortho-para converting part  51 , is in contact with the ortho-para catalyst, and is converted to para hydrogen, which is an equilibrium state corresponding to approximately 77K, by performing the ortho-para conversion. Gaseous hydrogen is subsequently transferred to the liquefaction guide tube  55  through the lower outlet port  54 , and the liquefaction guide tube  55  guides gaseous hydrogen toward the evaporating part  42  of the heat pipe. Since gaseous hydrogen is in contact with the evaporating part  42  of the heat pipe after pre-cooled and converted to para hydrogen, gaseous hydrogen is rapidly liquefied to form a liquid hydrogen drop. 
     Liquid hydrogen obtained by a contact between gaseous hydrogen and the evaporating part  42  is fallen by its weight and is collected to a lower portion of the liquefaction container  20 , and the liquid hydrogen collected in the lower portion of the liquefaction container  20  is discharged to the outside through the liquid hydrogen transferring tube  68 . 
     As described above, according to the present invention, while passing through the dual tube region  45  filled with solid nitrogen via the pre-cooling tube  50 , gaseous hydrogen is heat-exchanged and passes the ortho-para catalyst so that gaseous hydrogen is pre-cooled and ortho-para converted, and is then in contact with the evaporating part  42  and is liquefied. As a result, gaseous hydrogen of room temperature of 300K is in direct contact with the cryocooler  30  to prevent a thermal load of the cryocooler from being rapid increased. In other words, the present invention is advantageous in that an initial thermal load of the cryocooler can be reduced. 
     In addition, even when an operation of the cryocooler  30  is halted, it is possible to retard the boil-off state in which liquid hydrogen in the liquefaction container  20  is gradually evaporated by a heat invasion from the outside until solid nitrogen with which the dual tube region  45  of the heat pipe  40  is filled is phase-changed to liquid nitrogen. 
     In some embodiments, the heat pipe and the ortho-para converting part are combined into one unit. 
     According to one embodiment, while passing through the pre-cooling tube placed in the dual tube region of the heat pipe, which is filled with solid nitrogen, and the ortho-para converting part, gaseous hydrogen is pre-cooled and ortho-para converted. For example, gaseous hydrogen is pre-cooled to a temperature of 77K and is ortho-para converted to an equilibrium state of 77K. Then, gaseous hydrogen is in contact with the evaporating part of the heat pipe and is liquefied to form liquid hydrogen. Due to the above, gaseous hydrogen having a temperature of 300K is in direct contact with the evaporating part of the heat pipe having a temperature of 20K to prevent a load of the refrigerator from being rapidly increased. As a result, an initial thermal load of the refrigerator can be reduced. 
     According to another embodiment, in the state where an operation of the cryocooler is halted, an evaporation of liquid hydrogen is retarded for the time during which solid nitrogen is phased-changed to liquid nitrogen. Thus, it is possible to enhance the liquid hydrogen storage performance of the hydrogen liquefaction apparatus. 
     It will be apparent to those skilled in the art that various modifications can be made to the above-described exemplary embodiments of the present disclosure without departing from the spirit or scope of the invention. Thus, it is intended that the present disclosure covers all such modifications provided they come within the scope of the appended claims and their equivalents.