Abstract:
A hydrogen fuel system for a vehicle includes a fuel tank having a fuel inlet for receiving a borohydride fuel into a fuel holding portion of an internal cavity, and a waste inlet arranged to receive the waste liquid generated by an on-board hydrogen reaction process. The waste liquid is received into a waste liquid portion of the internal cavity. An expandable divider element is positioned within the tank to keep the fuel holding portion of the internal cavity separate from the waste liquid holding portion. The waste liquid holding portion can be positioned within the internal cavity so as to allow heat from the waste liquid to preheat the fuel stored in the fuel holding portion.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/339,183 filed Dec. 10, 2001. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention generally relates to hydrogen generation fuel systems for a motor vehicle, and more specifically, to a fuel delivery and storage arrangement for a hydrogen fuel system.  
           [0004]    2. Background Art  
           [0005]    Generally, fossil fuels, namely hydrocarbons, provide the fuel required to operate the majority of the world&#39;s combustion engines. However, the shortage of hydrocarbons have led to the development of engine arrangements that use alternative fuel sources.  
           [0006]    One alternative fuel source is hydrogen. Hydrogen is an attractive fuel source because it is the most abundant element in the universe and can typically fuel conventional engines with only minor modifications to the engines. Furthermore, hydrogen burns relatively pollution free, and a large weight percentage of the hydrogen can be converted to power engines as compared to, for example, gasoline. In addition to being used directly as a fuel in combustion engines, hydrogen can also be used in a variety of fuel cells through electrochemical oxidation.  
           [0007]    Several methods of storing and/or generating hydrogen have been developed. One such method teaches the physical storing of hydrogen as a compressed gas or as a low temperature liquid in high pressure cylinders. However, liquefying the hydrogen requires a substantial amount of energy, obtaining and maintaining extremely low temperatures on a vehicle is very difficult, and fuel is lost over time due to evaporation and boil-off. In addition, the high pressure cylinders themselves pose problems due to their bulk and limited storage capacity.  
           [0008]    In addition to the physical storage method described above, chemical methods of storing hydrogen have also been developed. One such chemical method includes reforming hydrogen containing fuels such as methanol or other hydrocarbons. However, this method requires a significant input of heat and does not solve the CO and CO 2  emission problem due to the presence of carbon. Another chemical method available is the storing of hydrogen in reversible hydrides. However, this method is expensive, has very low storage efficiency by weight of hydrogen, and may require thermal energy to separate the hydrogen and the hydride. A third method is the production of hydrogen through the use of alkali metal hydride reactions. However, this method is associated with difficulties in controlling such reactions.  
           [0009]    In order to overcome the problems of the above described methods for storing and producing hydrogen, it is currently known to utilize an aqueous solution to produce and store hydrogen. Using this approach, pure hydrogen is produced as required through the use of a catalytic reaction. The use of such an aqueous solution to store and generate hydrogen allows for the creation of a hydrogen powered fuel cell or combustion engine that operates in a safe and efficient manner and which can be easily refueled through the addition of more aqueous solution.  
           [0010]    The aqueous solution employed in this approach is alkaline sodium borohydride (NaBH 4 , tetrahydroborate). When solutions of aqueous NaBH 4  are reacted with metal or metal boride catalysts, these solutions hydrolyze to produce hydrogen gas and sodium borate which is water-soluble and environmentally safe. The overall reaction is:  
           NaBH   4          (   aq   )       +     2        H   2        O                   ς   catalyst                   4        H   2       +       NaBO   2          (   aq   )                             
 
           [0011]    The above reaction is inorganic and yields no products which might harm the operation of a fuel cell, such as sulfur, carbon monoxide, or aromatics.  
           [0012]    Stable NaBH 4  solutions do not produce hydrogen unless contacted with a catalyst. While various metal salts may be employed as a catalyst in this hydrogen producing reaction, it has been found that the environmentally safe element ruthenium (Ru) is able to liberate hydrogen from borohydride solutions most rapidly. The Ru catalyst is supported on ion exchange resin beads and allows the above hydrogen producing reaction to proceed when brought into contact with the NaBH 4  solution. This process allows hydrogen to be generated at close to ambient temperatures and is not plagued by the safety concerns of storing hydrogen through mechanical compression. In addition, because hydrogen is only produced as needed and because stabilized NaBH 4  solutions do not produce hydrogen when not in the presence of a catalyst, no hydrogen will be generated in the event of a spill and no hydrogen will be released in the event of a puncture. NaBH 4  solutions are nonflammable and can be easily stored in, for example, plastic containers. When NaBH 4  is exposed to the atmosphere or water, there is no possibility of dangerous reactions occurring.  
           [0013]    Borohydride solutions are also favored because they are able to satisfy the large energy demands of, for example, a motor vehicle. However, the use of borohydride solutions to supply hydrogen to power a motor vehicle also presents operating and design issues that must be addressed. For example, the conditions under which the hydrogen producing reaction takes place must be such that the temperature of the effluent is kept above a predetermined temperature so as to prevent precipitation. The predetermined temperature is approximately negative (−) 32° C. but varies slightly depending on molar concentration. Thus, a need exists for a vehicle fuel delivery arrangement capable of preventing the effluent of such a hydrogen producing reaction from precipitating under extreme ambient temperatures below negative 32° C.  
           [0014]    A further issue relating to the use of a borohydride solution as a source of hydrogen fuel is that a waste liquid of NaBO 2  remains after the catalytic operation. Such waste liquid is nonexplosive, and can be recovered and reprocessed into fresh borohydride solution. Thus, the fuel delivery system must account for storage of both the fresh borohydride fuel solution, as well as the resulting waste liquid. Such a requirement poses size and packaging problems when the system is used a fuel source for a motor vehicle.  
         SUMMARY OF INVENTION  
         [0015]    Accordingly, one aspect of the present invention is to provide a hydrogen fuel system for a vehicle capable of storing borohydride solution as well as recovering and holding waste liquid in a space efficient manner.  
           [0016]    In accordance with another object of the present invention, a hydrogen fuel delivery system is provided having a fuel tank capable of separately holding both a borohydride fuel and waste liquid so that the fuel can be supplied to a reaction process to produce hydrogen, and the waste liquid by-product of the reaction can be held for subsequent recovery and disposal or refining. In accordance with yet another aspect of the present invention, the tank can be formed with an expandable internal member capable of holding within the same tank one of the fuel or waste liquid separate from the other. In addition, the member can be positioned such that heat from the collected waste liquid can be used to preheat the fuel.  
           [0017]    Therefore, in accordance with these and other aspects, the present provides a fuel system for a vehicle having a reactor and separator system arranged to process a borohydride fuel mixture into hydrogen for use by a vehicle powerplant, the process also generating a waste liquid by-product. The fuel system includes a fuel tank coupled to the reactor and separator system, the fuel tank having a fuel inlet for receiving the borohydride fuel mixture into a fuel holding portion of an internal cavity, and a waste inlet arranged to receive the waste liquid into a waste liquid portion of the internal cavity. An expandable divider element is arranged to keep the fuel holding portion of the internal cavity separate from the waste liquid holding portion.  
           [0018]    The present invention will be more fully understood upon reading the following detailed description of the preferred embodiment(s) in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a schematic view of a first exemplary hydrogen fuel system in accordance with the present invention;  
         [0020]    [0020]FIG. 2 is a flow diagram illustrating a control logic for the fuel system of FIG. 1;  
         [0021]    [0021]FIG. 3 is a schematic view of a second exemplary hydrogen fuel system in accordance with the present invention;  
         [0022]    [0022]FIG. 4 is a flow diagram illustrating a control logic for the fuel system of FIG. 3;  
         [0023]    [0023]FIG. 5 is a cross-sectional block diagram of a main fuel storage tank in accordance with the present invention;  
         [0024]    [0024]FIG. 6 is a simplified view of an exemplary embodiment of the fuel tank;  
         [0025]    [0025]FIG. 7 is a simplified view of another exemplary embodiment of the fuel tank;  
         [0026]    [0026]FIG. 8 is a simplified view of still another exemplary embodiment of the fuel tank; and  
         [0027]    [0027]FIG. 9 is a simplified view of yet another exemplary embodiment of the fuel tank. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    [0028]FIG. 1 illustrates an exemplary vehicle hydrogen fuel system  10  for producing hydrogen fuel in accordance with the present invention. More specifically, hydrogen fuel system  10  includes a main fuel tank  12 , a mixer  14 , an electric heater  16 , a controller  18 , and a reaction and separation tank  20 .  
         [0029]    The main fuel tank  12  receives solid NaBH 4  through a fill valve  22  at an NaBH 4  fill point  24 . Tank  12  can be insulated to facilitate temperature control of the fluids held therein. The temperature of the main fuel tank  12  is monitored by a fuel temperature sensor  26 . The fuel temperature sensor  26  can be activated by the controller  18  when the ambient temperature reaches a predetermined critical point. The ambient temperature is measured using an ambient temperature sensor  32 . The fuel temperature sensor  26  also monitors the temperature of the effluent contained in a flexible accumulator  48  which is disposed within the main fuel tank  12 . The flexible accumulator can be insulated separately from the main tank.  
         [0030]    From the main fuel tank  12 , NaBH 4  flows to the mixer  14 . At the mixer  14 , the NaBH 4  is mixed with water from a reservoir or fuel cell stack  27 . From the mixer  14 , a mixture of NaBH 4  and water passes through a solenoid control valve  28  and a pump  29 . If the ambient and fuel temperatures are at or above a predetermined temperature, as detected by sensors  26  and  32 , the controller  18  routes the mixture to the reaction and separation tank  20 . In one application, the predetermined temperature is approximately negative 32° C. If the fuel temperature is below the predetermined temperature, the controller  18  activates the electric heater  16  as well as a heater/return flow valve  30 . The heater/return flow valve  30  causes the mixture to return to the mixer  14 . Once the fuel temperature is at or above the predetermined temperature, the mixture is allowed to pass through the heater/return valve  30  to the reaction and separation tank  20 . The heated mixture keeps the effluent warm.  
         [0031]    At the reaction and separation tank  20 , a catalyst (not shown) preferably in the form of a ruthenium catalyst is added to the water/NaBH 2  fuel mixture to initiate a reaction yielding hydrogen and a waste fluid of sodium metaborate (NaBO 2 ). From the reaction and separation tank  20 , hydrogen is output as needed to the vehicle&#39;s engine and/or a fuel cell stack  34 . As the hydrogen flows from the reaction and separation tank  20 , it is monitored by a hydrogen flow sensor  36  and a hydrogen pressure sensor  38 . The hydrogen flow sensor  36  transfers hydrogen flowrate information to the controller  18 . In the same manner the hydrogen pressure sensor  38  transfers information as to the pressure of the hydrogen to the controller  18 . To ensure that a supply of hydrogen is present to immediately comply with a request from the fuel cell controller, a hydrogen buffer valve  40  can be opened so as to fill a hydrogen buffer  42  with hydrogen.  
         [0032]    As noted above, in addition to hydrogen, the reaction which takes place in the reaction separation tank  20  also yields a waste fluid in the form of NaBO 2 . The NaBO 2  travels from the reaction separation tank  20  to a NaBO 2  solenoid control valve  43 . The opening and closing of the NaBO 2  solenoid control valve  43  is controlled by the controller  18 . From the NaBO 2  solenoid control valve  43  the NaBO 2  can be selectively drained through a drain valve  44  to a drain port  46 . NaBO 2  which is not diverted to drain valve  44  returns to the flexible accumulator  48  of main fuel tank  12 .  
         [0033]    In FIG. 2 illustrates an exemplary control logic in accordance with one aspect of the present invention. The method is entered at block  100  by a fuel cell/engine controller which makes a command request for additional hydrogen fuel to the controller  18 . The methodology proceeds to block  102  where the controller  18  employs a control signal to ensure that the NaBH 4  fill point  24  and the NaBO 2  drain port  46  are closed. The methodology next proceeds simultaneously to blocks  104  and  106 . At block  104  the NaBH 4  solenoid valve  42  is opened, while at block  106  the hydrogen buffer valve  40  is opened to allow instant flow of hydrogen to the engine/fuel cell  34 . At block  108 , the concentrated fuel and water is mixed from a reservoir or fuel cell stack in the mixer  14 . At block  110  the NaBO 2  solenoid valve  42  is opened. The methodology next simultaneously proceeds to blocks  112  and  114  to activate pump  29  to operate at normal speed, as well as a separator in the reaction separation tank  20 , if required.  
         [0034]    At block  116  the methodology next determines the ambient temperature and fuel temperature using the fuel temperature sensor  26  and the ambient temperature sensor  32 . If the temperatures are deemed acceptable then the methodology proceeds to block  124 . However, if the ambient and fuel temperatures are deemed unacceptable, the methodology proceeds to block  118 . At block  118  the electric heater  16  is engaged to warm the tank interior by circulating aqueous NaBH 4  between the heater  16  and the mixer  14  (contained within fuel tank  12 ). After the electric heater  16  is engaged, the methodology proceeds to block  120  where the heater return valve is opened. From block  120 , the methodology returns to block  116  to again sense the temperatures. If the temperatures are again outside an acceptable level, the methodology repeats the steps of blocks  118  and  120 . If the temperatures are deemed to be acceptable, the methodology proceeds to block  124 .  
         [0035]    At block  124  hydrogen flow and pressure values are monitored using the hydrogen flow sensor  36  and the hydrogen pressure sensor  38 . If the flow and pressure of the hydrogen is determined to be too low, the methodology proceeds to block  126 . At block  126 , the methodology increases the pump speed and the flowrate. However, if the hydrogen flow and pressure is determined to be too high, the methodology proceeds to block  128 . At block  128  the pump speed and flowrate are decreased.  
         [0036]    Once proper flow and pressure control is obtained at blocks  124 ,  126 , and  128 , then as denoted at block  130 , the hydrogen flow rate information is sent back to the vehicle fuel cell controller, the hydrogen flow is monitored using the flow sensor  36 , the hydrogen pressure is monitored using the pressure sensor  38 , and the fuel tank temperature is monitored using the fuel temperature sensor  26 . From block  130  the methodology proceeds to block  132 . At block  132  the hydrogen buffer valve  40  is closed, but only if hydrogen production is sufficient and if the hydrogen buffer is refilled. From block  132  the methodology again returns to block  116  where the ambient and fuel temperatures are monitored.  
         [0037]    As described above, the fuel input into the vehicle is the form of a concentrated fuel. However, those skilled in the art will readily appreciate that the teachings of the present invention are equally applicable for input of a solid fuel or aqueous/liquid fuel (e.g., a pre-mixed liquid form). Where fuel is utilized in a liquid form, system  10  would not need mixer  14 . The liquid fuel would be input into main tank  12 , and subsequently pumped as needed. In addition, block  108  is omitted as the aqueous fuel need not be further mixed with water. At block  118  the electric heater  16  is engaged to warm the tank by circulating aqueous NaBH 4  between the heater  16  and the fuel tank  12 . The heater/return valve is closed by the controller to allow the warmed aqueous fuel to flow into the hydrogen generator system.  
         [0038]    Turning now to FIGS. 3 and 4, a hydrogen fuel system  60  is shown in accordance with a second embodiment of the present invention. System  60  is substantially similar to system  10  described above with the exception that system  60  utilizes heat produced by hydrogen combustion rather than by an electric heater. For this reason, common reference numbers are used to identify substantially identical elements or steps in FIGS. 3 and 4.  
         [0039]    [0039]FIG. 3 depicts a hydrogen fuel system  60  to generally include a fuel tank  12 , a mixer  14 , a controller  18 , a reaction and separation tank  20 , a small catalyst and separation tank  50 , and a combustor  52 .  
         [0040]    The operation of the second embodiment is substantially similar to operation of the first embodiment. The second embodiment differs from the first embodiment by the manner in which it controls the temperature of the effluent. In the second embodiment, once the controller  18  senses the ambient and fuel temperatures to be unacceptable, a signal is sent to open a heater return valve  30 . After the heater return valve  30  is opened, the controller  18  ignites combustor  52 . The heat produced by combustor  52  is then conducted to flexible accumulator  48  to insure that the temperature of the NaBH 4  effluent does not enter a frozen or precipitated state. Once the combustor is ignited, the controller activates the small catalyst and separation tank  50 . The small catalyst and separation tank  50  introduces Ru to the water/NaBH 4  mixture so as to initiate a reaction. The reaction of the small catalyst and separation tank  50  produces hydrogen to fuel the combustor  52  and releases NaBO 2  effluent to flexible accumulator  48 . In addition, a water byproduct valve  54  is opened to release water vapor produced by combustor  52  to a humidifier or atmosphere. The small catalyst evolves the hydrogen to be combusted, thus producing heat and warming the waste liquid NaBO 2 . Storing of the warmed NaBO 2  in the flexible accumulator  48  inside fuel tank  12  in turn warms the NaBH 4 .  
         [0041]    Once the controller senses the fuel temperature to be acceptable, the NaBH 4 /H 2 O mixture is allowed to proceed to the reaction and separation tank  20 . After the reaction at the reaction and separation tank  20  takes place, the hydrogen fuel system  60  operates in the same manner as the hydrogen fuel system  10  described above.  
         [0042]    [0042]FIG. 4 illustrates the control logic for heating the effluent by combustion. The methodology of blocks  100  through  116  and  124  through  132  is substantially the same as described above in connection with FIG. 2. However, controller  18  senses (as denoted at block  116 ) that the fuel temperature is unacceptable, the methodology proceeds to block  120  where the controller  18  opens the heater return valve  30 . The methodology next proceeds to block  119  where combustor  52  is ignited and the heat produced by the combustor  52  is conducted to heat the waste liquid/NaBO 2  reservoir stored in the flexible accumulator  48 . At this point, a small amount of water vapor is released from the combustor. Proceeding to block  121 , the methodology activates the small catalyst and separation tank  50 . The methodology next proceeds to block  123  where the water byproduct valve  54  is opened to allow water to flow to a humidifier or atmosphere. After block  123 , the methodology returns to block  116 . At block  116  the controller  18  senses the ambient and fuel temperatures. If the temperatures are again unacceptable, the methodology repeats the steps outlined in blocks  120 ,  119 ,  121 , and  123 . If the ambient and fuel temperatures are acceptable the methodology proceeds to block  124 .  
         [0043]    As with the first embodiment described above, the fuel can be supplied to the fuel tank in concentrated or liquid/premixed form. Again, those skilled in the art will readily appreciate that the teachings of the present invention are equally applicable for solid fuel or aqueous fuel. Where aqueous fuel is utilized, the system  60  would not require mixer  14 .  
         [0044]    A block diagram of fuel tank  12  is provided in FIG. 5. As shown, tank  12  is provided with an expandable bladder  160  supported within an internal cavity  162  of the tank. The tank further includes an inlet port  164  for receiving solid or liquid fuel into cavity  162 , and an inlet port  166  passing through the wall of tank  12  for coupling with bladder  160  to allow waste fluid to be received into the bladder. An outlet port  168  allows fuel to be pumped from cavity  162 , and an outlet pump  170  passes through the wall of tank  12  for coupling with the bladder  160  to allow fluid therein to be removed (such as for subsequent off-vehicle recycling/recharging).  
         [0045]    It will be appreciated that storage of the fuel in cavity  162  and the waste in bladder  160  is not to be construed as limiting, e.g., the fuel could be stored in bladder  160  and the waste fluid in cavity  162 . Thus, in accordance with the present invention, the internal, expandable bladder operates to allow tank  12  to separately and simultaneously hold both the initial fuel and the resulting waste liquid by-product as the fuel is depleted. With this arrangement, physical space requirements of the tank/fuel system are optimized.  
         [0046]    [0046]FIG. 6 depicts a simplified view of another exemplary fuel tank  12  embodiment. In this embodiment, fuel tank  12  is of a cylindrical shape containing an inner cylindrical cavity  210  and an outer cylindrical cavity  220 . The inner cylindrical cavity  210  holds the NaBH 4  fuel while the outer cylindrical cavity  220  holds the NaBO 2  waste effluent. The terms inner and outer are used to describe the exemplary application. Importantly, the larger volume cavity holds the NaBH 4 . Disposed within the inner cylindrical cavity  210  is the ruthenium catalyst and separator tank  20 , and the mixer  14  (if needed). The barrier between the inner cylindrical cavity  210  and the outer cylindrical cavity  220  may be flexible so as to accommodate varying volumes and to provide added crashworthiness of the fuel tank  12 .  
         [0047]    [0047]FIG. 7 depicts still another embodiment of the fuel tank  12 . In this embodiment, fuel tank  12  has a cube shape and is divided into two cavities. The first cavity  310  stores the NaBH 4  fuel while second cavity  320  stores the NaBO 2  waste effluent. Disposed within the first cavity  310  is the mixer  14  (if needed). The ruthenium catalyst and separation tank  20  are disposed within the tank. Preferably, the barrier between the first cavity  310  and the second cavity  320  is flexible so as to accommodate varying volumes and to provide added crashworthiness of the fuel tank  12 .  
         [0048]    [0048]FIG. 8 depicts yet another embodiment of the fuel tank  12 . In this embodiment, fuel tank  12  is a square shape divided into two cavities. An inner cavity  410  holds the NaBH 4  fuel and an outer cavity  420 , which surrounds the inner cavity  410 , holds the NaBO 2  waste effluent. The barrier between the inner cavity  410  and the second cavity  420  is preferably flexible so as to accommodate varying volumes and to provide added crashworthiness of the fuel tank  12 . Disposed within the outer cavity  420  is the mixer  14  (if needed) and the ruthenium catalyst and separation tank  20 .  
         [0049]    With the fuel tank embodiments of FIGS. 6 and 8, the NaBO 2  waste effluent surrounds the NaBH 4  fuel. This advantageously reduces the heating requirements for the NaBH 4  fuel because the NaBO 2  waste effluent naturally enters the accumulator  48  in a warmed state. By surrounding the inner cavity  210 ,  310  or  410 , the associated “warmed” second cavity  220 ,  320  or  420  serves to pre-heat the NaBH 4  fuel. In addition, when using a fuel concentrate/water mixing arrangement, the water used to create aqueous NaBH 4  could be pre-heated to further reduce fuel heating needs prior to hydrogen separation. Likewise, such an arrangement may assist in preventing the water from freezing in ambient environments at or below 0° C.  
         [0050]    More specifically, preheating the water required to create aqueous NaBH 4  may be accomplished by heating the water stored in reservoir  27 . One skilled in the art would understand that the water may be heated by using an electric heater, heat generated by the combustion of hydrogen, waste heat from the vehicle system, or by some other means. However, it may also be accomplished by storing the water in a separate chamber within the heated fuel tank.  
         [0051]    Accordingly, FIG. 9 depicts a simplified view of a fuel tank  12  embodiment which stores water in a separate chamber within the fuel tank. More specifically, in this embodiment fuel tank  12  is divided into  3  cavities. A first cavity  510  holds the fuel NaBH 4 , and a second cavity  515  holds de-ionized water used for creating the aqueous NaBH 4 . A third cavity  520 , which contains the waste effluent NaBO 2 , surrounds both the first cavity  510  and the second cavity  515 . The barriers between both the first cavity  510  and the second cavity  515 , and the third cavity  520 , are preferably flexible so as to accommodate varying volumes and to provide added crashworthiness of the fuel tank  12 . Disposed intermediate the first cavity  510  and third cavity  520  is the ruthenium catalyst and separation tank  20 . Disposed within the third cavity  520 , and between the first cavity  510  and the second cavity  515 , is the mixer  14 .  
         [0052]    In this embodiment, warm effluent NaBO 2  surrounds both the de-ionized water and the fuel NaBH 4 , thereby pre-heating both. In the event either or both the fuel NaBH 4 , and the de-ionized water require additional heating, heater  16  of the first embodiment circulates aqueous NaBH 4  back through a connection to the mixer  14 .  
         [0053]    While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the description of the appended claims.