Abstract:
A hydrogen tank system for collectably storing of excess hydrogen. The hydrogen tank system consists of a primary tank apparatus and a cryoadsorption hydrogen storage apparatus, as well as tubing, detectors, valves, and regulators required to manage the collection and storage of excess hydrogen gas generated during operation, as well as to manage distribution of hydrogen gas to one or more functional modules, such as a stationary fuel cell.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to the storage and manipulation of gases, and more particularly to the storage and control of excess hydrogen gas produced by boil-off and mass transfer losses from stationary storage and filling systems.  
       BACKGROUND OF THE INVENTION  
       [0002]     Hydrogen storage technology is a necessary prerequisite for the development of many advances in the area of alternative fuel sources. Hydrogen is the cleanest and most abundant of these energy sources. In particular, mobile applications, such as hydrogen-propelled vehicles, place a demand on the infrastructure to provide safe, efficient, and inexpensive delivery of hydrogen to the end user.  
         [0003]     A number of current storage technologies are available. Compressed gaseous hydrogen (CGH 2 ) involves storage of hydrogen gas under high pressures of for example between 35 and 70 MPa. Liquid hydrogen (LH 2 ) involves storage of liquefied hydrogen gas. These technologies involve several technical challenges, notably low storage densities, in the case of both methods, and hydrogen boil-off in the case of LH 2 .  
         [0004]     An alternative storage mechanism is provided by the physisorption of hydrogen molecules on high-surface materials like activated carbons, zeoliths, metal-organic frameworks (MOFs) or polymers of intrinsic microporosity (PIMs). Since the interaction of the hydrogen and the substrate material is quite weak, it is necessary to apply operating pressures from 10 to 50 bar and operating temperatures of about 25K to 150K.  
         [0005]     During the operation of the filling facility, particularly the refilling of LH 2  into a primary tank apparatus, some hydrogen can be lost to the environment. This occurs primarily because the associated pipes and machinery have to be cooled down toward 20K, but also for fundamental thermodynamic reasons. The losses from boil-off, tanking, and other mass transfer activities have to be minimized for commercial, safety, and environmental reasons.  
         [0006]     A customer might be required to pay for the lost hydrogen during re-filling. Alternatively, the operator of the station may be required to absorb these losses. Therefore, it is very attractive from a commercial standpoint to minimize these losses as much as possible.  
         [0007]     For safety reasons, hydrogen should not be released into the environment of a pump. Under certain conditions, this can create a fire or an explosive hazard. Hydrogen could react exothermically with oxygen to form water and to release large amounts of energy, as for example in a fire or in an explosion. From a safety standpoint limiting the amounts of hydrogen gas released will drastically reduce the oxygen reaction hazards.  
         [0008]     Hydrogen release may also have environmental effects. Hydrogen gas that is lost during refilling or as boil-off could reach the upper atmosphere. Here it could react via a complex chemical reaction with ozone to form water, thereby decomposing critical atmospheric ozone. This consequence would also be limited by preventing release of hydrogen.  
         [0009]     Another consideration in the construction of a stationary fueling application is the stability of the flow rate. Some of the stationary applications, such as a stationary internal combustion engine (ICE) or a stationary fuel cell, require a stable flow of hydrogen gas to operate effectively. Excess hydrogen gas generated through mass transfer and spot heating could disrupt the orderly flow of hydrogen gas to these applications.  
         [0010]     Some attempts have been made to remedy these effects. Re-liquefaction would help mitigate some of these factors but would be very expensive and require additional equipment. Compression would also be expensive and require additional equipment. Catalytic burning of the lost hydrogen has also been proposed, but this is wasteful since the resulting water cannot, itself, be used for energy generation.  
         [0011]     Therefore, what remains needed in the art is a means of controlling the excess hydrogen gas produced through its use as a fuel in stationary applications.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention is a hydrogen tank system designed to collect, store and transfer excess hydrogen gas that has been generated in the normal course of the operation of a hydrogen fueled stationary application. Within the framework of this invention, a cryoadsorption hydrogen storage apparatus is added to the conventional setup of a stationary hydrogen fueled application, such as a hydrogen filling station. The hydrogen tank system would serve as a hydrogen collection system, an intermediate hydrogen storage system, and a hydrogen transfer system to cope with the amount of excess hydrogen gas generated during the normal activities of hydrogen delivery, such as a hydrogen filling station for filling of LH 2  vehicles, during boil-off mode of the main LH 2  storage tank, etc. Further, the cryoadsorption hydrogen storage apparatus may serve as a reserve tank, which may be utilized in mobile as well as stationary applications.  
         [0013]     Other stationary applications of hydrogen fueling impose more stringent requirements in the management of excess released hydrogen gas. More involved stationary applications, such as those that include stationary internal combustion engines or stationary fuel cells, require a relatively stable flow of hydrogen gas. The intermediate storage system according to the present invention will smooth the flow rate of outgoing hydrogen and therefore will address this problem.  
         [0014]     The hydrogen tank system according to the present invention is designed in such a way as to minimize mass transfer losses of hydrogen from the system into the environment and to minimize heat transfer from the environment into the system.  
         [0015]     The hydrogen tank system consists of a primary tank apparatus and the above referenced cryoadsorption hydrogen storage apparatus, as well as tubing, detectors, valves, and regulators required to manage the collection, storage and transfer of the excess hydrogen gas.  
         [0016]     The primary tank apparatus consists of at least one liquid hydrogen (LH 2 ) storage tank, conventional in the art, as well as the required tubes, hoses, valves and regulators necessary to connect the primary tank apparatus to the cryoadsorption hydrogen storage apparatus. The LH 2  can be dispensed directly from the primary tank apparatus to an external tank, such as for example the fuel tank of a mobile hydrogen fueled device. In the operation of the hydrogen tank system, excess hydrogen gas will inevitably be produced; however, this excess hydrogen gas is collected by the cryoadsorption hydrogen storage apparatus.  
         [0017]     The cryoadsorption hydrogen storage apparatus can consist of a single cryoadsorption unit, or a group thereof configured in series, in parallel, or in a more general topological structure. The cryoadsorption units are connected by means of pipes or tubes and controlled via valves. Particular elements of the piping aid in the modulation of temperature in the cryoadsorption units.  
         [0018]     The hydrogen tank system additionally provides means to transfer hydrogen gas from the cryoadsorption hydrogen storage apparatus to external functional modules. These functional modules can be stationary hydrogen-fueled applications, such as for example stationary internal combustion engines, stationary fuel cells, other devices, such as re-liquifiers, compressors or other cryoadsorption units, or even mobile fuel tanks. Each of these functional modules is connected by means of pipes and tubes to the primary storage tank, the cryoadsorption hydrogen storage apparatus, or both.  
         [0019]     Accordingly, it is an object of the present invention to provide a means to collect, store and transfer excess hydrogen gas which evolves in the normal operation of stationary devices fueled by a hydrogen tank system.  
         [0020]     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  
       [0021]      FIG. 1  is a block diagram of a hydrogen tank system consisting of a primary tank apparatus and a cryoadsorption hydrogen storage apparatus, configured to supply hydrogen gas to functional modules.  
         [0022]      FIG. 2A  is a schematic representation of a configuration of valves and pipes for a single cryoadsorption unit to process excess hydrogen gas produced in normal boil-off and during fueling operations.  
         [0023]      FIG. 2B  is a schematic representation of the same system as seen in  FIG. 2A , wherein now the valves are set for de-fueling the cryoadsorption unit.  
         [0024]      FIGS. 3A and 3B  are topological diagrams showing two different topologies of a cryoadsorption hydrogen storage apparatus according to the present invention.  
         [0025]      FIG. 4  is a diagram showing an example of regulation of hydrogen gas flow from a cryoadsorption hydrogen storage apparatus to functional modules which require stable flow of hydrogen gas, according to the present invention.  
         [0026]      FIG. 5  is a block diagram showing a family of functional modules associated with a cryoadsorption hydrogen storage apparatus according to the present invention.  
         [0027]      FIGS. 5A and 5B  are schematic representations showing further detail of certain of the functional modules of  FIG. 5 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     Referring now to the Drawing,  FIGS. 1 through 5 B depict aspects of a hydrogen tank system  100  according to the present invention, which is configured to collect, store and transfer excess hydrogen gas that has been generated in the normal course of operation. The following description of the preferred embodiment is merely exemplary in nature and is not intended to limit the invention, its applications, or its uses.  
         [0029]     With reference to  FIG. 1 , the hydrogen tank system  100  consists of a primary tank apparatus  102  and a cryoadsorption hydrogen storage apparatus  104 , either of which being connectable to various functional modules  106 .  
         [0030]     With reference to  FIG. 2A , a hydrogen tank system  100 ′ is shown which is configured for managing boil-off or tanking (filling) hydrogen losses, and has a cryoadsorption hydrogen storage apparatus  104  in the form of a single cryoadsorption unit  112  cooled to approximately 20K by hydrogen gas from the primary tank apparatus  102 . An inlet pipe  114  runs selectively between the primary tank apparatus  102  and the cryoadsorption unit  112 , a cooling jacket  118  of the the cryoadsorption unit, and the functional modules  106 . In this regard, the inlet pipe  114  branches into three parts, a first supply pipe  114   a  for the cooling jacket  118  of the cryoadsorption unit  112 , a second supply pipe  114   b  for the cryoadsorption unit  112 , and a third supply pipe  114   c  that runs directly to the functional modules  106 . Each of these supply pipes is regulated individually by means of supply valves, namely a first supply valve  126   a  for the cooling jacket  118 , a second supply valve  126   b  for the cryoadsorption unit  112 , and a third supply valve  126   c  for the functional modules  106 .  
         [0031]     The first supply valve  126   a  to the cooling jacket  118  and the second supply valve  126   b  to the cryoadsorption unit  112  are both open and the third supply valve  126   c  to the functional modules  106  is closed. The cooling jacket  118  is vented by means of an outlet pipe  128  connected to the functional modules  106 . The cryoadsorption unit  112  is connected to the functional modules  106  by means of a outlet pipe  130  regulated by a functional module control valve  132 , which is closed. Further in this configuration of the hydrogen tank system  100 ′, hydrogen gas released from the storage tank apparatus  102  is routed to the cryoadsorption unit  112  and to the cooling jacket  118 . Direct flow to the functional modules  106  is prevented.  
         [0032]     With reference to  FIG. 2B , the hydrogen tank apparatus  100 ′ is now configured to de-fuel the cryoadsorption unit  112 . The only difference between this and the cryoadsorption hydrogen storage apparatus  104  of FIG.  2 A which is configured to manage boil-off and other excess hydrogen gas generation, is the settings of the valves. In this case, the first and second supply valves  126   a,    126   b  for the cooling jacket  118  and the cryoadsorption unit  112 , respectively, are now both closed, while the third supply valve  126   c  (between the inlet pipe  114  and the functional modules  106 ) and the functional module control valve  132  are now both open. In this configuration of the hydrogen tank apparatus  100 ′, hydrogen gas released from the primary tank apparatus  102  and the cryoadsorption unit  112  is released to the functional modules  106 . Flow of hydrogen gas from the primary tank apparatus  102  to the cooling jacket  118  or the cryoadsorption unit  112  is prevented.  
         [0033]     Hydrogen gas is released from the cryoadsorption units by applying heat via, for example, an electrical heater of a heat exchanger with the external environment, by reducing the operating pressure, or a combination of both. The materials used, the structural design, and techniques of operation of the cryoadsorption units of the cryoadsorption hydrogen storage apparatus are exemplified in U.S. patent application Ser. No. 11/348,107, filed on Feb. 6, 2006, which disclosure is hereby herein incorporated by reference.  
         [0034]     In order to increase the hydrogen collection capacity of the hydrogen tank system according to the present invention, additional cryoadsorption units may be added. With reference to  FIG. 3A , a plurality of cryoadsorption units (CAU)  112   a,    112   b,    112   c  are configured in series by means of tubing or pipe to each other singly in the direction of the flow of the hydrogen gas. In  FIG. 3B , a group of cryoadsorption units (CAU)  112   a ′ and  112   e ′ are connected in series with a parallel arrangement of cryoadsorption units  112   b ′,  112   c  and  112   d ′ by means of pipes or tubes. More complicated topologies for arranging the cryoadsorption units may be used according to the present invention. The cryoadsorption units may be insulated individually, as a group, or share insulation with the primary tank apparatus  102 . The insulation may be multi-layer super insulation, powder vacuum insulation and have a liquid nitrogen active cooling shield.  
         [0035]     Certain types of the functional modules  106  require a carefully regulated flow of hydrogen gas. With reference to  FIG. 4 , a cryoadsorption unit  112  is connected by means of an outlet tube  130  to a functional module  106 . The flow of hydrogen is controlled by a feedback system  134  conventional in the art. The feedback system  134  regulates the flow of hydrogen gas by adjustments to the functional module control valve  132 , to compensate for deviations from the target flow rate as detected by a hydrogen gas flow sensor  136 .  
         [0036]     With reference to  FIG. 5 , a family of functional modules  106  shows a range of device types that may be included in the present invention. This may include hydrogen fueled stationary applications, such as stationary internal combustion engines  106   d  and stationary fuel cells  106   c.  This may further include a functional module  106   b  which recycles hydrogen gas to the primary tank apparatus  102  including a re-liquefier  138 , as shown at  FIG. 5A . This may also include an alternate means of hydrogen dispensing  106   a  including compressor  140  tied to a compressed hydrogen gas (CGH 2 ) dispenser  142 , as shown at  FIG. 5B .  
         [0037]     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.