Abstract:
A method to increase gas mass flow loading rates to a gas storage cavern includes using liquid natural gas (LNG) to cool natural gas in a natural gas flow line upstream of a compressor used to compress gas for storage in to a gas storage cavern.

Description:
FIELD 
       [0001]    The present invention relates to a method of increasing gas mass flow injection rates to gas storage caverns using LNG. 
       BACKGROUND 
       [0002]    Natural gas is traditionally stored in a gaseous form in large volume salt caverns and aquifers to meet peak demand and ensure a secure supply. The gas is added to storage by compression, resulting in an increment in cavern temperature and an increment in cavern pressure. These increments in pressure and temperature in the cavern decrease the rate at which gas can be added to the cavern. 
       SUMMARY 
       [0003]    A method to increase gas mass flow injection rates to a gas storage cavern, includes using liquid natural gas (LNG) to cool natural gas in a natural gas flow line upstream of a compressor used to compress gas for storage in to a gas storage cavern. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to in any way limit the scope of the invention to the particular embodiment or embodiments shown, wherein: 
           [0005]      FIG. 1  is a schematic diagram that depicts an embodiment of the teachings contained herein. 
           [0006]      FIG. 2  is a variation on the embodiment shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    The preferred method to increase mass flow gas injection rates will now be described with reference to  FIG. 1 . 
         [0008]    Gas is supplied from main pipeline stream  1 . The gas to storage is routed through line  2  to exchanger  30  where it is cooled by LNG. The cooler gas exits exchanger  30  via stream  3  to knock out drum  31 , to remove any condensate and debris present in the stream. The condensate is removed through stream  4 . The cold gas is routed through stream  5  to compressor  32  for injection into cavern  33  via stream  6 . LNG is supplied from tank  35  and is routed through line  8  to pump  36  where it is pressurized and routed through line  9 . The LNG is routed through line  10  to exchanger  30 , to cool the gas to storage and exits the exchanger through line  11 . The gas in stream  11  is colder than compressed gas in stream  6 . The gas can then be routed through valve  39  and line  12  to mix directly with stream  6  in mixer  41 , increasing the gas density of gas stream  7  to storage  33 . The option of routing stream  11  through valve  38  and line  13  directly to storage cavern  33  is available. The operating conditions for the cavern are monitored by pressure and temperature sensors  34 . The objective is to increase the gas injection rate of compressor  32  by lowering the temperature of the gas suction line to the compressor, making the gas denser, thus increasing the mass flow rate and also decreasing the compressor outlet temperature. The compressor outlet temperature can be further decreased by direct mixing of stream  12  with stream  6 . For every incremental decrease in the temperature of gas entering cavern  33 , the amount of gas cavern  33  is capable of storing increases. If it is desirable to further decrease the temperature of cavern  33 , the option of routing stream  11  through valve  38  and line  13  directly to storage cavern  33  is followed. 
         [0009]    A variation will now be described with reference to  FIG. 2 . 
         [0010]    Gas is supplied from main pipeline stream  1 . The gas to storage is routed through line  2  to exchanger  30  where it is cooled by LNG. The cooler gas exits exchanger  30  via stream  3  to knock out drum  31  to remove any condensate and debris present in the stream. The condensate is removed through stream  4 . The cold gas is routed through stream  5  to compressor  32 , where it is compressed and delivered through line  6  to exchanger  41  where it is cooled. The compressed and cooled stream  7  mixes with stream  11  and is stored through line  12  into gas cavern storage  33 . LNG is supplied from tank  35  and is routed through line  8  to pump  36  where it is pressurized and routed through line  9 . The LNG is routed to exchanger  30 , to cool the gas to storage and exits the exchanger through line  10 . The gas in stream  10  is colder than compressed gas in stream  6 . The gas stream  10  enters exchanger  41  to cool the compressor discharge gas. The gas can then be routed through valve  39  to mix directly with stream  7  to storage  33  through line  12 . The option of routing stream  11  through valve  38  and line  13  directly to storage cavern  33  is available. The operating conditions for the cavern are monitored by pressure and temperature sensors  34 . The objective is to increase the gas mass flow injection rate of compressor  32  by lowering the temperature of the gas suction line to the compressor, making the gas denser, thus increasing the mass flow rate whilst also decreasing the compressor outlet temperature. The compressor outlet temperature is further decreased by indirect mixing of stream  10  with stream  6  thus further improving the power requirements for compression. The described embodiment of  FIG. 3  provides the ability for gas cavern operators to increase the mass flow gas injection rates to cavern storage. 
         [0011]    The stored gas exits the cavern via stream  50  to meet demand. 
         [0012]    In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. 
         [0013]    It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiments without departing from scope of the Claims.