Abstract:
A method and apparatus is provided which will provide over-pressure protection for an underground storage cavern by reducing the pressure of a pressurized gas stream originating from the an underground storage cavern to form a lower pressure gas stream, monitoring the pressure of a lower pressure gas stream and stopping the flow of the lower pressure gas stream to the pipeline should the pressure of the lower pressure gas stream exceed a threshold value.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method and apparatus for improving the operational safety in handling a pressurized gas originating from an underground storage cavern. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is known to store hydrogen, as well as other gases in salt caverns. These large storage sites help to provide a buffer in the event when customer demand exceeds normal production capacity or if production capacity is reduced below normal levels. For various reasons, the pressures within these large salt caverns can be very high, sometimes greatly exceeding the pressure of the pipeline to which the gas will be subsequently introduced. One method of controlling the pressure of the gas is to use a pressure control device, which is configured to safely reduce the pressure of the gas before it is introduced to the pipeline. However, if this device were to fail, the overall safety would be compromised. A solution known heretofore has been to include a pressure relief valve downstream the pressure control device, which allows for the system to depressurize to a vent or flare stack. Unfortunately, this solution requires a large capital expenditure as the vent or flare stack must be sized large enough to handle the entire volume of the underground storage cavern. 
       SUMMARY OF THE INVENTION 
       [0003]    Certain embodiments of the present invention relate to a method and apparatus for providing over-pressure protection for an underground storage cavern. 
         [0004]    In one embodiment, the method can include the steps of removing the pressurized gas from the underground storage cavern, reducing the pressure of the pressurized gas to form a lower pressure gas, monitoring the pressure of the lower pressure gas, and if the pressure of the lower pressure gas exceeds a first threshold value, sending a signal to a controller to close a set of isolation valves located upstream of a pressure relief valve. By including the set of isolation valves, the size of the vent or flare stack associated with the pressure relief valve can be reduced without compromising safety. 
         [0005]    According to other optional aspects of the invention: 
         [0006]    the pressurized gas is at a sufficiently high pressure within the underground storage cavern such that the method comprises an absence of an additional pressurization step between removing the pressurized gas from the underground storage cavern and introducing the lower pressure gas to the pipeline; 
         [0007]    the method further includes the step of venting at least a portion of the lower pressure gas to a vent or flare stack via a pressure relief valve if the pressure of the lower pressure gas exceeds a second threshold value; 
         [0008]    the first threshold value and the second threshold value are the same; 
         [0009]    the method further includes the step of removing moisture and/or impurities from the lower pressure gas in downstream equipment before the step of introducing the lower pressure gas to the pipeline; 
         [0010]    the downstream equipment is located downstream the isolation valves and upstream the pipeline; 
         [0011]    the downstream equipment comprises driers configured to remove moisture from the lower pressure gas; 
         [0012]    the downstream equipment comprises filters configured to remove solid particles from the lower pressure gas; 
         [0013]    the first threshold value is based on a pressure rating of the downstream equipment and/or the pipeline; and 
         [0014]    the pressurized gas is selected from the group consisting of nitrogen, natural gas, air, carbon dioxide, hydrogen, helium, argon, and combinations thereof; 
         [0015]    In another embodiment of the invention, the apparatus can include a pressure reducing device in fluid communication with the underground storage cavern, a pressure monitor configured to monitor the pressure of the lower pressure gas, at least one isolation valve in fluid communication with the pressure reducing device, and downstream equipment disposed downstream the pressure reducing device, the downstream equipment having a maximum operating pressure. In one embodiment, the pressure reducing device is configured to reduce the pressure of the pressurized gas received from the underground storage cavern to form a lower pressure gas. In another embodiment, the at least one isolation valve is configured to stop the flow of gas if the pressure monitor senses the pressure of the lower pressure gas exceeds a first threshold value. 
         [0016]    According to other optional aspects of the invention: 
         [0017]    the downstream equipment comprises a water removing device having a pair of desiccant driers configured in a permutable fashion such that one of the driers can be in operation while the other dryer is being regenerated; 
         [0018]    the downstream equipment comprises a particle removal device having a mechanical filtration system having a filter housing, wherein the mechanical filtration system is configured to allow for isolation of the filter housing; 
         [0019]    the particle removal system comprises a magnetic separation system configured to remove fine dust particles based on magnetic properties; 
         [0020]    the first threshold value is based on the maximum operating pressure of the downstream equipment; 
         [0021]    the apparatus further includes a pressure relief valve located downstream the isolation valve, the pressure relief valve configured to send at least a portion of the lower pressure gas to a vent or flare stack if the pressure of the lower pressure gas exceeds a second threshold value; and 
         [0022]    the first threshold value and the second threshold value are the same. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawing. It is to be noted, however, that the drawing illustrates only an embodiment of the invention and is therefore not to be considered limiting of the invention&#39;s scope as it can admit to other equally effective embodiments. 
           [0024]    The FIGURE shows a method and apparatus for providing over-pressure protection for an underground storage cavern in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalence as may be included within the spirit and scope of the invention defined by the appended claims. 
         [0026]    High pressure gases, including, but not limited to: nitrogen, air, carbon dioxide, hydrogen, helium, and argon, can be stored in caverns, whether leached in salt formations or created by hard rock mining. Additionally, the pressure of these gases exiting the cavern can be at very high pressures (e.g., 100-200 atmospheres), which can cause safety issues for downstream equipment and the mechanical integrity of the pipeline. 
         [0027]    Now turning to the FIGURE. The gas is withdrawn from pipeline  2  via line  4  and compressed in compressor  5  to a pressure that is sufficiently high enough such that the gas can be removed from underground storage cavern  10  without any mechanical means (e.g., pumps, etc. . . . ), preferably to a pressure of 10 atmospheres or higher, more preferably to 100-200 atmospheres. Following compression, the gas travels via line  6 . When pressure control device  14  is in a closed position, the gas is then directed into underground storage cavern  10 . The flow rate of the gas going in and out of underground storage cavern can be monitored by flow indicator  12 . 
         [0028]    When it is desired to use gas from underground storage cavern  10 , pressure control device  14  is opened, which allows for the gas to expand across pressure control device  14  before heading to downstream equipment  16 , which can include equipment for moisture removal and/or removal of any unwanted impurities (e.g., solid particles, magnetic particles, unwanted gases) before being introduced back to pipeline  2 . 
         [0029]    In one embodiment of the invention, an over-pressurization system can be installed should pressure control device  14  fail to safely control the pressure of the gas for the downstream equipment  16  and pipeline  2 . The pressure of the gas following pressure control device  14  can be monitored by pressure indicator  15 . Pressure relief valve  18  can be installed downstream pressure control device  14  in order to de-pressurizes the system to a vent or flare stack  19  in the event that the monitored pressure is too high. In the embodiment shown, isolation valves  8  are included, preferably both upstream and downstream of pressure control device  14 , which help to reduce the height of the vent or flare stack and provide additional safety protection. 
         [0030]    In one embodiment, isolation valves  8  would be closed if the pressure of the lower pressure gas (i.e., gas downstream of pressure control device  14 ) as measured by pressure indicator  15  is above a certain operational threshold (e.g., close to or just below the pressure rating of downstream equipment  16  and pipeline  2 ). In one embodiment, pressure indicator  15  is in electronic communication with isolation valves  8 , either directly or through a controller (not shown), such that pressure indicator  15  is configured to send a signal to isolation valves  8  to close. In one embodiment, pressure relief valve  18  and vent or flare stack can be included to provide over-pressure protection until isolation valves  8  are closed. In one embodiment, since the design of pressure relief valve  18  is primarily to provide over-pressure protection until the isolation valves are closed, pressure relief valve  18  can be smaller and the vent or flare stack height can be reduced due to the reduced thermal radiation. 
         [0031]    In one embodiment, the pressure of the gas in the cavern is maintained above the pipeline pressure. This advantageously allows for the absence of a mechanical device to help with movement of the gas to the pipeline (e.g., no need for an additional pump to move the gas from the storage cavern to the pipeline). 
         [0032]    While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, language referring to order, such as first and second, should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps or devices can be combined into a single step/device. 
         [0033]    The singular forms “a”, “an”, and “the” include plural referents, unless the context clearly dictates otherwise. 
         [0034]    “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”. 
         [0035]    “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary. 
         [0036]    Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur. 
         [0037]    Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range. 
         [0038]    All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.