Abstract:
A compressed gas storage system with an incorporated pressure relief device is disclosed. The compressed gas storage system comprises a tank for storing a compressed gas, a battery in the direct surroundings of the tank, and a relief valve in communication with the tank. The relief valve is configured to be responsive to electrical current generated by the battery. The battery is configured to define an electrically active state when it reaches a temperature above a maximum safe operating temperature of the compressed gas storage system The electrically active state of the battery is characterized by the generation of sufficient electrical current to open the relief valve which permits gas to escape from the tank. In another embodiment, a thermocouple in combination with a conducting metal may be substituted for the battery.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to a pressure relief device and, in particular, relates to a pressure relief device system for a compressed gas storage system. 
       BRIEF SUMMARY OF THE INVENTION 
       [0002]    It is a feature of the embodiments of the present invention to increase the safety of a compressed gas storage system by the incorporation of an improved pressure relief device system. Other features of the embodiments of the present invention will be apparent in light of the description of the invention embodied herein. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0003]    The following detailed description of specific embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
           [0004]      FIG. 1  illustrates a compressed gas storage tank according to an illustrative embodiment of the present invention; 
           [0005]      FIG. 2  illustrates an interface point of a tank with the environment and an incorporated pressure relief device of a compressed gas storage system according to an illustrative embodiment of the present invention; and 
           [0006]      FIG. 3  illustrates a foil-type battery in thermal communication with a tank of a compressed gas storage system according to an illustrative embodiment of the present invention. 
       
    
    
       [0007]    The embodiments set forth in the drawings are illustrative in nature and not intended to be limiting of the invention defined by the claims. Moreover, individual features of the drawings and the invention will be more fully apparent and understood in view of the detailed description. 
       DETAILED DESCRIPTION 
       [0008]    In the following detailed description of exemplary embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration, and not by way of limitation, specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present invention. 
         [0009]    Referring initially to  FIG. 1 , a compressed gas storage tank  10  is illustrated. The tank  10  may comprises a hollow body  30  for the storage of a gas under pressure. Hydrogen is an example of a typical gas that might be stored in the tank, but other gases may be stored as well such as, for example, natural gas. The hollow body  30  is defined by a liner  40 , or gas permeation barrier, which seals the tank  10 . The liner  40  may be comprised of a high molecular weight polymer material such as, for example, high density polyethylene (HDPE). A composite material  50  surrounds the liner  40  helping to maintain the gas under pressure. The composite material  50  may be comprised of a carbon composite shell such as, for example, carbon fibers plus resin. The tank  10  can typically store gases under pressure of approximately 10,000 psi, or 700 bar. An interface point  20  between the hollow body  30  of the tank  10  and the outside environment allows for the filling and removing of gas from the tank  10 . 
         [0010]      FIG. 2  illustrates the interface point  20 . The interface point  20  may extend into the hollow body  30  of the tank  10  as illustrated in  FIG. 2  or may extend only through to the liner  40 . In most cases, the interface point  20  and the tank  10  are made of different materials. The temperature at the interface point  20  can vary over an operational temperature gradient. For example, for hydrogen, when filling the tank  10  the temperature may rise to approximately 80° C. and when hydrogen is removed from the tank  10  the temperature may fall to approximately −80° C. This operational temperature gradient is a function of the tank  10  volume as well as the configuration of the compressed gas inlet and outlet plumbing at the interface point  20 . The operational temperature gradient represents the temperature swing the tank  10  undergoes from empty to full to empty and extends from a minimum operating temperature to a maximum operating temperature. 
         [0011]    Within the interface point  20 , there is a pressure relief device  60  that vents the gas in the hollow body  30  of the tank  10  to the environment. The pressure relief device  60  closes one of the connections between the interior of the tank  10  and the outside. The pressure relief device  60  is designed to be activated (i.e., opened) by external heat in the close proximity, or direct surroundings, of the tank  10 . 
         [0012]    The purpose of the pressure relief device  60  is to relieve the pressure of the tank  10  before the structure of the tank  10  is significantly damaged by the nearby heat. The pressure relief device  60  can be, for example, an electrically activated valve that opens in response to a electrical current generated from a battery. In one embodiment, the valve may be activated by a thermobattery  100 . In another embodiment, a combination of thermocouples attached to a good heat conducting metal foil such as, for example, aluminum, and an electronic circuit (not illustrated) may activate the valve. 
         [0013]    In one embodiment and in the case of increasingly high temperatures, the thermobattery  100  may become electrically activated by the increasing heat. As the thermobattery  100  becomes electrically active, it, in turn, starts generating electrical current. When the temperature in the direct surroundings of the tank  10  exceeds a maximum temperature of the tank  10 , a sufficient level of electrical current may be generated by the thermobattery  100 . If the maximum safe operating temperature of the tank  10  is exceeded significantly, the thermobattery  100  is activated and the pressure relief device  60  opens. As soon as the pressure relief device  60  opens, the gas within the tank  10  is vented to the environment in order to relieve the pressure within the tank  10 . 
         [0014]    In another embodiment, increasingly high environmental temperatures result in an increased thermoelectric voltage output from the combination of thermocouples. This increased thermoelectric voltage output, in turn, electrically activates the pressure relief device  60  causing the pressure relief device  60  to open venting the gas within the tank  10  to the environment and relieving the pressure within the tank  10 . 
         [0015]      FIG. 3  illustrates one embodiment of a thermally activated thermobattery  100  that may trigger the opening of the pressure relief device  60 . The thermally activated battery  100  comprises a cathode  110  and anode  120  which are separated by an electrolyte  130 . The battery  100  is placed in close proximity to the tank  10  and is reactive to temperatures outside the tank  10 . The electrolyte  130  is not ionically conductive and is frozen under normal environmental conditions (i.e., temperatures between about −25° C. to about 50° C.) and therefore, not ionically conductive. When the electrolyte  130  is frozen, the battery  100  is electrically inactive and, therefore, does not show an electric discharge. 
         [0016]    In the case of a fire, or other increasing high temperatures, in close proximity of the tank  10 , the tank  10  becomes hotter resulting in the battery  100  also becoming heated which in turn causes the electrolyte  130  to melt. As the electrolyte  130  melts, the battery  100  gradually becomes electrically active. As the battery  100  becomes electrically active, an electrical current is produced. At a threshold point, the electrically active battery  100  produces electrical current to open the pressure relief valve  60  and relieve the gas pressure in the tank  10  by releasing the gas from the tank  10  into the environment. 
         [0017]    In one embodiment, a foil-type battery  100  is attached to the impact shield located below the tank  10 . The impact shield may be fiberglass reinforced plastic or any other material known in the art. In another embodiment, the foil-type battery  100  is wrapped around the tank  10 , as illustrated in  FIG. 3 , and can be triggered by spot heat sources that could relieve pressure before an explosion or structural damage to the tank  10  occurs. In both embodiments, the battery  100  covers a significant portion of the surface of the tank  10 . By covering more surface area, the tank  10  can be more completely protected against high heat sources. 
         [0018]    In another embodiment, the combination of thermocouples and metal foil arrangement is attached to the impact shield located below the tank  10 . In yet another embodiment, the combination of thermocouples and metal foil arrangement is wrapped around the tank  10 . The thermocouple embodiment provides the same protection against external heat sources as the thermobattery  100  by electrically activating the pressure relief device  60  before the tank  10  becomes damaged by the external heat. 
         [0019]    It is noted that terms like “preferably,” “commonly,” and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention. 
         [0020]    For the purposes of describing and defining the present invention it is noted that the term “device” is utilized herein to represent a combination of components and individual components, regardless of whether the components are combined with other components. 
         [0021]    For the purposes of describing and defining the present invention it is noted that the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term “substantially” is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
         [0022]    Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it