Abstract:
A warming system for a high pressure hydrogen gas storage tank in a motor vehicle for maintaining the temperature of the gas within the tank and the gas flow control components associated with one or more boss at the tank ends above the lower design temperature tolerance limit of the tank and components associate with the utilizing the Joule-Thomson effect in gas flowing from the tank to recycles the mechanical energy of heat compression in high pressure hydrogen fuel to warm the gas within the tank as the high pressure gas is utilized.

Description:
FIELD OF THE INVENTION 
     The present invention relates to warming high pressure hydrogen gas storage tanks by utilizing the Joule-Thomson effect. Warming compensates for thermal and mechanical stresses caused by a low temperature resulting from (1) gas decompression in the tank as the gas is depleted from the tank and (2) environmental exposure of the tanks in low temperature climate conditions. The present invention warms the gas stored within the tank and ameliorates mechanical stresses to the tank and the component parts of the tank caused by the thermal conditions of the tank environment and thermal changes in gas temperature associated with the depletion of high pressure gas from the tanks by utilizing the energy stored in the gas as a result of the refilling/pressurization process. The invention is useful in on board storage tanks in hydrogen powered (fuel cell and internal combustion) vehicles 
     BACKGROUND OF THE INVENTION 
     Fuel cell and internal combustion engine vehicles powered by hydrogen gas may include on board high pressure gas fuel tanks that may include gas absorbing materials within the tank interior. In previous applications for United States Letters patent, I have described that during driving, gas remaining in a tank becomes cold when tank pressure decreases as gas is consumed by the vehicle power plant and the tank decompresses. In cold climates, the tank internal gas temperature can drop to −60° C. or below, a temperature that may be below the permissible operating temperature of O-rings, or other rubber seals, or gas flow controls in the tank assembly. An excessively low temperature in the tank may upset design tolerance limits for the seals and flow controls and cause the stored gas to leak as a result of temperature caused stresses in the tank system assembly. For example, when the ambient temperature is −20° C., the reduction of internal tank temperature by an additional −40° C. due to gas decompression effects will result in an internal temperature in the gas tank of −60° C. or below. Expansion and contraction of the tank and the component parts of the gas flow system associated with the tank may produce adverse mechanical stress effects. 
     Hydrogen gas generates heat when the pressure of gas maintained under high pressure decreases to a level approximating the lower pressure in a gas flow line. This phenomenon is known as the Joule-Thomson effect, singular to hydrogen and helium, and is used in the invention to recycle the mechanical energy of heat compression in the hydrogen fuel stored in a tank during the refill process to warm the gas and/or the tank assembly as the decompression energy stored in the gas is utilized during the driving condition of a vehicle. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide a warming system for high pressure hydrogen gas storage tanks. Warming will reduce the risk of a fuel gas leak in cold climate driving conditions caused by excessively low tank and/or gas temperatures. Utilizing the Joule-Thomson effect, the decompression energy stored in the gas is utilized to warm the tank system. 
     The invention is described more fully in the following description of the preferred embodiment considered in view of the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a diagram showing the calculation of the heat recovery available for gas warming utilizing the Joule Thompson effect as hydrogen stored within the tank is decompressed while used for vehicle operation. 
         FIG. 2  is a chart of gas and valve temperatures of the tank plotted against a time axis depicting relative temperatures of the gas within the tank and the metal boss elements during the vehicle conditions of driving and parking. The cooling of the metal components after driving is shown wherein valve temperatures are below the lower tolerance limit after driving. 
         FIG. 3  is a side view of a tank structure using a heat exchanger internal to the tank heating the hydrogen gas output during tank depletion using the Joule Thomson energy of the hydrogen gas outflow during the decompression of the tank as the vehicle is driven. 
         FIG. 4  is a side view of a warming system of the invention wherein the heat exchange of Joule Thomson energy occurs within a metal tank boss that houses embedded tank flow control devices. 
         FIG. 5  is a side view of a tank structure using a heat exchanger external to the tank heating the gas through an internal heat exchanger using the stored Joule Thomson energy of hydrogen decompression as an energy source for heating in the gas flow system. 
         FIG. 6  illustrates a temperature control system utilized when the invention is combined with a supplemental warming system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In brief, the invention provides a warming system for a high pressure hydrogen gas storage tank utilizing Joule Thompson energy in vehicles powered by powered by hydrogen gas. Environmentally, a typical ambient temperature is approximately 20° C. In cold climates, the internal gas temperature in a vehicle tank can drop to −60° C. or lower, a temperature that may be below the permissible operating temperature range of O-ring and/or other rubber or polymer seals used in the tank and the port inlet and outlet metal part assemblies that control the inflow and outflow of gas to and from the storage tank. Below the acceptable temperature range, variances allowable for seals, valves, control devices, and the like, may be exceeded by thermally caused mechanical variations in the tank and associated assemblies. Leakage of the stored gas may result. The invention provides a solution that warms the storage tank system by recovering the energy stored in hydrogen consumed when the H 2  gas is refilled to a high pressure, such as 30-35 MPa. When the gas is decompressed to 1 MPa during use, Joule Thomson energy is recovered as heat for warming the remaining gas and/or tank assembly components. 
     High pressure tanks are typically cylindrical having semi spherically shaped dome ends and are formed from a composite shell, a mixture of resin and carbon fiber embedded therein. Tanks may also include supplemental shells such as an outer shell and an interior liner, and other layers. With reference to  FIG. 1 , a typical high pressure gas storage tank  10  having an interior volume  12  for the storage of hydrogen is shown with sidewall structure  14 , including a boss  11  at one end. A gas inlet and a gas outlet are shown at boss  11  as  11  in and  11  out. Depending on design preference, the tank may include additional bosses or bosses with configurations differing from that shown. Driving and parking temperature conditions in the vehicle tank system are charted in  FIG. 2 . During driving, the gas temperature may exceed the lower tolerance limit of the tank system by the temperature difference shown as  25 . In a typical parking condition,  FIG. 2  illustrates that with time, the temperature  20  of the valve system cools to a difference  26  such that, in the period shortly after parking  21 , the valve temperature  20  cools below the lower acceptable limit of the system temperature tolerance. 
       FIG. 3  depicts the structure of an example of a Joule Thomson warming system: a tank  14 , formed from a carbon fiber resin composite shell  14   a  and liner  14   b , an interior volume for gas storage  12 , boss  11 , and gas outflow conduit  11  out. In the example of  FIG. 3 , the gas stored under high pressure, 30-35 MPa, in the tank volume flows through conduit GF to pressure regulator PR and internal heat exchanger  31 , where the Joule Thompson heat energy is released into the tank gas as the hydrogen is depleted from the tank. Heat flow is shown by the arrows            
     In  FIG. 4  an example of the warming system of the invention at a tank boss  41  at one end of the tank is shown in a side view. In this example, gas flow outlet conduit GF leads from the tank interior  41 , where initial pressure is 35 MPa through pressure regulator PR, also embedded in the tank boss, for heat exchange between the decompressed gas and the boss, nut, port, or tank, as the pressure regulated 1 MPa gas flows to the vehicle power plant. 
     In  FIG. 5 , an external heat exchanger and an internal heat exchanger are utilized in a further example of the warming system of the invention. Gas flow outlet conduit GF  5  leads from the tank interior volume  12 , where initial pressure is 35 MPa, and flow is directed in the conduit through boss  51  to external pressure regulator PR. After pressure regulator PR hydrogen gas flowing to the vehicle power plant has a pressure of 1 MPa. Intermediate in the gas flow conduit GF  5 , between the regulator PR and the gas outlet to the vehicle  52  is a heat transfer system, including heat exchange device  53 , conveying heat captured from GF  5  to the tank interior  12  where the heat captured is radiated to the remaining high pressure gas stored therein. The recovered/captured Joule Thomson heat is conveyed from HEX  53  through a heat pipe, coolant circulator, or like heat transfer conduit, HTC, to internal radiator (or HEX)  54  wherein the recovered heat is radiated and warms the remaining gas stored in the tank. 
     Thus, the system of the invention recycles heat recovered from the mechanical energy of gas compression stored in the gas during the refill process for use as a warming agent for gas remaining in the tank as the gas is consumed. The system of the invention may be used with a supplemental heating system such as described in my co-pending applications for patent S ELECTIVE  W ARMING AND  H EAT  I SOLATION FOR  O N  B OARD  H IGH  P RESSURE  S TORAGE  T ANKS  I NSTALLED ON  G AS  F UELED  V EHICLES , Ser. No. 11/935,637 filed on Nov. 6, 2007; I NDUCTION  H EATING  S YSTEM FOR  F IBER  C OMPOSITE  G AS  S TORAGE  C YLINDERS  [to be filed] and C ARBON  F IBER  W ARMING  S YSTEM FOR  F IBER  C OMPOSITE  G AS  S TORAGE  C YLINDERS  [to be filed]. 
     In an example incorporating both Joule Thomson heating and a supplemental warming system, a temperature power control system as is shown in  FIG. 6  may be utilized for overall temperature monitoring and regulation. In the example in  FIG. 6 , sensors measure T 1 =Boss Temperature; T 2 =Gas Temperature; T 3 =Ambient Temperature; and T 4 =Surface Proximity Temperature. The sensed temperatures are input into the power control system  200  that regulates power input into the supplemental system and thereby regulates overall gas and tank temperature such that the Control Temperature, generated by Joule Thomson heating and the supplemental warming system, regulated by the control processor system  200 , is: T 1 , T 2 &gt;Lower Tolerance Limit of the tank and valve components. Control system  200  regulates the energy flow from the warming power source  65  input into the supplemental warming system. The supplemental warming may be provided either an electrical system or a fluid system, interconnected to the tank at regulated power energy input connectors  61  and  62 . With reference to  FIG. 2  showing temperatures in various operating modes, the control system  200  maintains the system temperatures such that the differentials shown as  25  and  26  are eliminated and the lower tolerance limit of the system is not exceeded. 
     Having described the invention in detail, those skilled in the art will appreciate that, given the present description, modifications may be made to the invention without departing from the spirit of the inventive concept herein described. Therefore, it is not intended that the scope of the invention be limited to the specific and preferred embodiments illustrated and described. Rather, it is intended that the scope of the invention be determined by the appended claims.