Abstract:
A liquid hydrogen storage system having minimized tanking losses. Hydrogen is discharged from a liquid hydrogen tank through connector piping of a filling connector to a discharge pipe and then to an external device, such as a fuel cell. As such, the connector piping is maintained at a cryogenic temperature substantially that of liquid hydrogen. During refilling of the tank through the already cryogenically cold connector piping there is substantially reduced evaporation of the liquid hydrogen provided by a liquid hydrogen tank station.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates generally to liquid hydrogen storage tanks and more specifically to a method of reducing gaseous hydrogen losses when a liquid hydrogen storage tank is refilled with liquid hydrogen.  
       BACKGROUND OF THE INVENTION  
       [0002]     Many systems require a hydrogen supply for operation as, for example, fuel cells. If the fuel cell system is in a motor vehicle, for example, the hydrogen utilized by the fuel cell system is stored in, preferably, liquid form in a liquid hydrogen storage system comprised of a liquid hydrogen storage tank and associated components such as, for example valves and pipes, located within the motor vehicle. In order to maintain the hydrogen in a substantially liquid form in the liquid hydrogen storage tank, the liquid hydrogen must be kept at cryogenic temperatures, temperatures below minus two hundred fifty degrees Celsius. When it is necessary to refill the liquid hydrogen storage tank located within the motor vehicle at, for example, a liquid hydrogen tank station, liquid hydrogen flows from the liquid hydrogen tank station to the liquid hydrogen storage tank through connector piping of a filling connector of the liquid hydrogen storage system connecting the liquid hydrogen storage tank to the liquid hydrogen tank station. At the start of the refilling process, the connector piping of the liquid hydrogen storage system connecting the liquid hydrogen storage tank to the liquid hydrogen tank station may be at higher temperature than the liquid hydrogen being transported from the liquid hydrogen tank station to the liquid hydrogen storage tank. The higher temperature of the connector piping causes a substantial portion of the liquid hydrogen being transported to evaporate. The gaseous hydrogen produced by evaporation prevents the liquid hydrogen storage tank from filling with liquid hydrogen and flows back to the liquid hydrogen tank station after passing through the liquid hydrogen storage tank. After a few minutes of refilling, the connector piping becomes cooled by the liquid hydrogen being transported to a temperature such that liquid hydrogen reaches the liquid hydrogen storage tank and the liquid hydrogen storage tank can then be filled with liquid hydrogen.  
         [0003]      FIG. 1  is an example of a prior art liquid hydrogen storage system  100  suitable for use with a fuel cell system in a motor vehicle. The liquid hydrogen storage system  100  is composed of liquid hydrogen storage tank  102 , cryo-block  104 , filling connector  104 ′, cryo-coupling valve  106 , heat exchanger  108 , shut-off valve  110 , safety valve  112 , and boil-off valve  114 . Liquid hydrogen storage tank  102  contains hydrogen; a portion  116  thereof in liquid form and a portion  118  thereof in gaseous form along with level sensor  120  and pipes  122 ,  124 . Cyro-block  104  consists of gas valve  126 , liquid valve  128 , filling valve  130 , and pipes  132 - 140 . For fuel cell system operation, gaseous and liquid hydrogen in discharge pipe  140  flows through energized heat exchanger  108  into pipe  144  through shut-off valve  110 , which is connected to a fuel cell system  146 . Filling connector  104 ′ consists of piping  145  in the form of pipes  138 ″ and  142  between cyro-block  104  and cryo-coupling valve  106 . Cryo-coupling valve  106  connects to a liquid hydrogen tank station (see  FIG. 3B ) to refill the liquid hydrogen storage tank  102 .  
         [0004]      FIG. 2A  depicts valves  110 ,  126 ,  128 , and  130  in the closed position whereas  FIG. 2B  depicts valves  110 ,  126 ,  128 , and  130  in the open position.  FIG. 3A  depicts the closed position of cryo-coupling valve  106  when the liquid hydrogen storage system  100  is not connected to a liquid hydrogen tank station; while  FIG. 3B  depicts the open position of cryo-coupling valve  106  when the liquid hydrogen storage system  148  is connected to a liquid hydrogen tank station via coupling  302 .  
         [0005]     Liquid hydrogen storage system  100  includes a discharge mode of operation and a refilling mode of operation, wherein when utilized in a motor vehicle the discharge mode of operation as two sub-modes, parked and driving modes. In parked mode, all valves  106 ,  110 ,  126 ,  128 , and  130  are closed and heat exchanger  108  is not energized.  
         [0006]     In driving mode, if the pressure in liquid hydrogen storage tank  102  is above a predetermined pressure, gaseous hydrogen  118  flows into pipes  122  and  132  through open gas valve  126  into pipe  132 ′ and discharge pipe  140  to energized heat exchanger  108 . After passing through energized heat exchanger  108 , gaseous hydrogen flows into pipe  144  and through open shut-off valve  110  to the fuel cell system  146 . Valves  106 ,  128  and  130  are in the closed position during this time.  
         [0007]     Otherwise, in driving mode, if the pressure in liquid hydrogen storage tank  102  is below a predetermined pressure, liquid hydrogen  116  flows into pipes  124 ,  136 , and  134  through open liquid valve  128  into pipe  134 ′ and discharge pipe  140  to energized heat exchanger  108 . After passing through energized heat exchanger  108 , gaseous hydrogen flows into pipe  144  and through open shut-off valve  110  to the fuel cell system. Valves  106 ,  126  and  130  are in the closed position during this time.  
         [0008]     In refilling mode, there will either be a small amount or no liquid hydrogen  116  in liquid hydrogen storage tank  102 . Hence, liquid hydrogen storage tank  102  will contain substantially gaseous hydrogen  118 . A liquid hydrogen tank station  148  is connected to open cryo-coupling valve  106  via coupling  302  as depicted in  FIG. 3B . Liquid hydrogen flows from the liquid hydrogen tank station  148  into the filling connector  104 ′ through the connector piping  145  via pipe  138 ″, through pipe  138 ′, through open filling valve  130 , and through pipes  138 ,  136  and  124  to the liquid hydrogen storage tank  102 . Gaseous hydrogen  118  flows into pipes  122  and  132  through open gas valve  126  through pipe  132 ′, into the filling connector  104 ′ through the connector piping  145  via pipe  142 , and through cryo-coupling valve  106  into coupling  302  back to the liquid hydrogen tank station. Heat exchanger  108  is de-energized and shut-off valve  110  is closed during this mode.  
         [0009]     At the start of the refilling process, the connector piping  145  (pipes  138 ″ and  142 ) of the filling connector  104 ′ are at a higher temperature than the liquid hydrogen being transported from the liquid hydrogen tank station to the liquid hydrogen storage tank  102 . The higher temperature of the connector piping causes a substantial portion of the liquid hydrogen being transported to evaporate. The gaseous hydrogen produced by evaporation flows through pipes  138 ″ and  138 ′, open filling valve  130 , and through pipes  138 ,  136  and  124  and enters the liquid hydrogen storage tank  102  as gaseous hydrogen  118  and prevents the liquid hydrogen storage tank from filling with liquid hydrogen, whereupon the gaseous hydrogen returns to the liquid hydrogen tank station as previously described. After a few minutes of refilling, the connector piping  145  (pipes  138 ″ and  142 ) are cooled sufficiently by the hydrogen being transported so as to be at a cryogenic temperature such that liquid hydrogen reaches the liquid hydrogen storage tank  102  as previously described and the liquid hydrogen storage tank can then be filled with liquid hydrogen.  
         [0010]     The gaseous hydrogen produced through evaporation of the transported liquid hydrogen from the liquid hydrogen tank station due to the temperature of the connector piping  145  flowing back to the liquid hydrogen tank station, as previously described, may be recovered or just vented to the atmosphere. If the gaseous hydrogen is recovered, energy must be expended to re-liquefy the gaseous hydrogen. If the gaseous hydrogen is vented to the atmosphere, it is lost. Hence, if the amount of gaseous hydrogen produced by the refilling process through evaporation can be reduced, a significant amount of energy and hydrogen can be saved.  
         [0011]     Accordingly, what is needed in the art is a method of reducing gaseous hydrogen losses when the liquid hydrogen storage tank is refilled with liquid hydrogen.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention is an apparatus and method of reducing gaseous hydrogen losses when a liquid hydrogen storage tank is refilled with liquid hydrogen. The gaseous hydrogen losses are produced by the refilling process through evaporation of the transported liquid hydrogen from a liquid hydrogen tank station to a liquid hydrogen storage system due to the temperature of the connector piping of the filling connector of the liquid hydrogen storage system which connect to the liquid hydrogen tank station being substantially greater than the temperature of the transported liquid hydrogen from the liquid hydrogen tank station to the liquid hydrogen storage system.  
         [0013]     In the practice of the present invention, the temperature of the connector piping of the filling connector of a liquid hydrogen storage system which connect to a liquid hydrogen tank station are operationally maintained at a cryogenic temperature substantially that of the transported liquid hydrogen from the liquid hydrogen tank station to the liquid hydrogen storage system. During operation, gaseous and liquid hydrogen within a liquid hydrogen storage tank are conveyed through the connector piping of the filling connector even while the liquid hydrogen storage system is not connected to the liquid hydrogen tank station for refilling so as to thereby maintain the connector piping at a cryogenic temperature substantially that of liquid hydrogen, and thereby substantially reducing evaporation of transported liquid hydrogen from the liquid hydrogen tank station to the liquid hydrogen storage system when the liquid hydrogen storage system is connected to a liquid hydrogen tank station to refill the liquid hydrogen storage tank. As such, the present invention may be retrofitted into prior art liquid hydrogen storage systems through modification of prior art liquid hydrogen storage systems to incorporate the present invention.  
         [0014]     Accordingly, it is an object of the present invention to provide the temperature of the connector piping of a filling connector of a liquid hydrogen storage system at cryogenic temperature during operation so that at the time of refilling, the temperature of the pipes of the filling connector are substantially at liquid hydrogen temperature.  
         [0015]     This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is an example of a prior art liquid hydrogen storage system suitable for use in a motor vehicle.  
         [0017]      FIG. 2A  is a depiction of a first valve of  FIG. 1 , and applicable to  FIG. 4 , in a closed position.  
         [0018]      FIG. 2B  is a depiction of a first valve of  FIG. 1 , and applicable to  FIG. 4 , in an open position.  
         [0019]      FIG. 3A  is a depiction of a cryo-coupling valve of  FIG. 1  in a closed position.  
         [0020]      FIG. 3B  is a depiction of a cryo-coupling valve of  FIG. 1  in an open position.  
         [0021]      FIG. 4  is an example of a liquid hydrogen storage system according to the present invention.  
         [0022]      FIG. 5A  is a depiction of a cryo-coupling valve of  FIG. 4  in a closed position.  
         [0023]      FIG. 5B  is a depiction of a cryo-coupling valve of  FIG. 4  in an open position. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]      FIG. 4  is an example of a liquid hydrogen storage system  400  according to the present invention. The example of  FIG. 4 , by way of exemplification, retrofits the present invention into the prior art liquid hydrogen storage system  100  of  FIG. 1  through modifying the prior art liquid hydrogen storage system of  FIG. 1  to incorporate the present invention, wherein like parts are shown with like reference numerals.  
         [0025]     The liquid hydrogen storage system  400  is composed of liquid hydrogen storage tank  102 , cryo-block  404 , filling connector  406 , cryo-coupling valve  106 , heat exchanger  108 , shut-off valve  110 , safety valve  112 , and boil-off valve  114 . Liquid hydrogen storage tank  102  contains hydrogen; a portion  116  thereof in liquid form and a portion  118  thereof in gaseous form along with level sensor  120  and pipes  122 ,  124 . cyro-block  404  consists of gas valve  126 , liquid valve  128 , filling valve  130 , and pipes  132 ,  132 ′,  134 ,  136 ,  138 ,  402 , and discharge pipe  440 .  
         [0026]     To operatively deliver hydrogen from the liquid hydrogen storage tank  102  to an external device such as a fuel cell system  146 , gaseous and liquid hydrogen flows through connector piping  410  of the filling connector  406  via, by way of example, pipes  442  and  408 , then through discharge pipe  440 , through energized heat exchanger  108 , and into pipe  144  through shut-off valve  110 , which is connected to the fuel cell system  146 . The filling connector  406  is located between cyro-block  144  and cryo-coupling valve  106 , and connects to a liquid hydrogen tank station  148  (see  FIG. 3B ) to refill the liquid hydrogen storage tank  102  through the connector piping  410  of the filling connector  406 .  
         [0027]      FIG. 2A  also serves as a depiction for  FIG. 4 , where the valves  110 ,  126 ,  128 , and  130  are in the closed position; whereas  FIG. 2B  also serves as a depiction for  FIG. 4 , where the valves  110 ,  126 ,  128 , and  130  are in the open position.  
         [0028]      FIG. 5A  depicts the closed position of cryo-coupling valve  106  when the liquid hydrogen storage system  400  is not connected to a liquid hydrogen tank station; while  FIG. 5B  depicts the open position of cryo-coupling valve  106  when the liquid hydrogen storage system  400  is connected to a liquid hydrogen tank station  148  via coupling  302 .  
         [0029]     Liquid hydrogen storage system  400  includes a discharge mode of operation and a refilling mode of operation, wherein when utilized in a motor vehicle the discharge mode of operation as two sub-modes, parked and driving modes. In parked mode, all valves  106 ,  110 ,  126 ,  128 , and  130  are closed and heat exchanger  108  is not energized.  
         [0030]     In driving mode, if the pressure in liquid hydrogen storage tank  102  is above a predetermined pressure, gaseous hydrogen  118  flows into pipes  122  and  132  through open gas valve  126  into pipe  132 ′, then through the connector piping  410  of the filling connector  406  via pipes  442  and  408 , and then through discharge pipe  440  to energized heat exchanger  108 . After passing through energized heat exchanger  108 , gaseous hydrogen flows into pipe  144  and through open shut-off valve  110  to the fuel cell system. Valves  106 ,  128  and  130  are in the closed position during this time.  
         [0031]     Otherwise, in driving mode, if the pressure in liquid hydrogen storage tank  102  is below a predetermined pressure, liquid hydrogen  116  flows into pipes  124 ,  136 , and  134  through open liquid valve  128  into pipe  134 ′, through the connector piping  410  of the filling connector  406  via pipes  442  and  408 , and then through discharge pipe  440  to energized heat exchanger  108 . After passing through energized heat exchanger  108 , gaseous hydrogen flows into pipe  144  and through open shut-off valve  110  to the fuel cell system. Valves  106 ,  126  and  130  are in the closed position during this time.  
         [0032]     In refilling mode, there will either be a small amount or no liquid hydrogen  116  in liquid hydrogen storage tank  102 . Hence, liquid hydrogen storage tank  102  will contain substantially gaseous hydrogen  118 . In refilling mode, the liquid hydrogen tank station is connected to open cryo-coupling valve  106  via coupling  302  as depicted in  FIG. 5B .  
         [0033]     With simultaneous reference to  FIGS. 4 and 5 B, liquid hydrogen flows from the liquid hydrogen tank station  148  through the coupling  302  through cryo-coupling valve  106 , into the connector piping  410  of the filling connector  406  via pipe  408 , through pipe  402 , open filling valve  130 , and through pipes  138 ,  136  and  124  to the liquid hydrogen storage tank  102 . Gaseous hydrogen  118  flows into pipes  122  and  132  through open gas valve  126  into pipe  132 ′ into the connector piping  410  of the filling connector  406  via pipe  442 , through cryo-coupling valve  106  into coupling  302  back to the liquid hydrogen tank station  148 . Heat exchanger  108  is de-energized and shut-off valve  110  is closed during this mode.  
         [0034]     Because the flow of hydrogen during driving mode includes passage through the connector piping  410  of the filling connector  406 , at the start of the refilling process the connector piping (pipes  442  and  408 ) are at a cryogenic temperature substantially that of the liquid hydrogen being transported from the liquid hydrogen tank station  148  to the liquid hydrogen storage tank  102 . The already cryogenically low temperature of the connector piping substantially decreases evaporation of liquid hydrogen being transported from the liquid hydrogen tank station  148  to the liquid hydrogen storage system  400  in comparison to prior art liquid hydrogen storage systems, for example as depicted in  FIG. 1 . The significantly reduced gaseous hydrogen, compared to prior art liquid hydrogen storage systems, for example as depicted in  FIG. 1 , produced by evaporation of liquid hydrogen being transported from the liquid hydrogen tank station  148  to the liquid hydrogen storage system  400  flows through pipes  408  and  402 , open filling valve  130 , and through pipes  138 ,  136  and  124  and enters the liquid hydrogen storage tank  102  as gaseous hydrogen  118 , whereupon the gaseous hydrogen returns to the liquid hydrogen tank station as previously described. The connector piping  410  of the filling connector  406  are further cooled by the liquid hydrogen being transported from the liquid hydrogen tank station  148  to the liquid hydrogen storage system  400 , in a substantially shorter time of refilling, compared to prior art liquid hydrogen storage systems, for example as depicted in  FIG. 1 .  
         [0035]     The substantially decreased gaseous hydrogen produced through evaporation, compared to prior art liquid hydrogen storage systems, for example as depicted in  FIG. 1 , of the transported liquid hydrogen from the liquid hydrogen tank station  148  to the liquid hydrogen storage tank  102  may be recovered or just vented to the atmosphere. Because of the already precooled cryogenically low temperature of the connector piping  410  in the filling connector  406  due to the flow of cryogenic (near liquid hydrogen) temperature hydrogen flowing there through to the fuel cell system  146  during operation (ie., during drive mode as described above), much less energy must be expended to re-liquefy the gaseous hydrogen and much gaseous hydrogen is lost if it is vented to the atmosphere, compared to prior art liquid hydrogen storage systems, for example as depicted in  FIG. 1 . Hence, the present invention substantially reduces the amount of gaseous hydrogen produced by the refilling process through evaporation thereby saving a significant amount of energy and hydrogen.  
         [0036]     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.