Patent Publication Number: US-6901973-B1

Title: Pressurized liquid natural gas filling system and associated method

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a liquid natural gas filling system and, more specifically, to a natural gas filling system having a low pressure vessel for holding a bulk quantity of liquid natural gas, and a high pressure vessel, for filling a use vessel, such as a fuel tank on a vehicle. 
   2. Background Information 
   There are an increased number of vehicles that use liquid natural gas (LNG) as a fuel. As such there is an increased need for filling systems to refuel the LNG vehicles and a need for such filling systems to hold an increased amount of fuel. It is understood that the pressure and temperature of a fluid in an enclosed space are related and that a higher pressure corresponds to higher temperature and a lower pressure corresponds to a lower temperature. Hereinafter, the pressure of the LNG will be identified as “high” or “low”, it is understood that LNG at a lower pressure is also at a lower temperature. The fuel tank on an LNG vehicle is structured to hold the LNG at a pressure between about 75 psi to 125 psi. As used herein, this pressure shall be referred to as a “high” pressure. To contain the LNG, and any natural gas vapor, at such a high pressure, the LNG vehicle fuel tank is structurally robust. The manufacture of small vessels structured to contain LNG at a high pressure is not difficult or exceedingly expensive. 
   Presently, the filling systems for LNG vehicles include a bulk vessel that is structured to be coupled directly to the vehicle&#39;s LNG fuel tank. Because the bulk vessel is coupled directly to the fuel tank, the LNG in the bulk vessel must be maintained at a pressure similar to the pressure of the LNG fuel tank. As such, the bulk vessel must be constructed to hold a large quantity of LNG at a high pressure. Construction of such a vessel is not inexpensive. It is desirable to be able to store the bulk LNG at a lower pressure to reduce the cost of the bulk LNG vessel. 
   There is, therefore, a need for a LNG filling system that stores the bulk LNG at a lower pressure while delivering high pressure LNG to a vehicle. 
   There is a further need for a LNG filling system that stores the bulk LNG at a lower pressure while delivering high pressure LNG to a vehicle which may be used to fill multiple vehicles in rapid succession. 
   SUMMARY OF THE INVENTION 
   These needs, and others, are met by the invention which provides a liquid natural gas filling system having a first, low pressure vessel and at least one second, high pressure vessel. The low pressure vessel is, preferably a bulk vessel. The high pressure vessel is sized to fill the fuel tank on a LNG vehicle. The LNG in the low pressure vessel is transferred to the high pressure vessel where the pressure of the LNG is increased. Once the LNG is at a high pressure, the LNG is transferred to the vehicle fuel tank. 
   In a preferred embodiment, the liquid natural gas filling system is structured to deliver a small quantity of low pressure LNG to the vehicle fuel tank. This small quantity of low pressure LNG collapses the pressure head in the vehicle fuel tank and facilitates filling with the high pressure LNG. This also reduces the saturation temperature of the filled tank and allows for a longer hold time before venting is required. 
   In another embodiment, there is a third, high pressure vessel which is substantially similar to the second, high pressure vessel. In this system, LNG from the first, low pressure vessel is delivered to alternate high pressure vessels so that one of the high pressure vessels is ready to fill a vehicle even after the other high pressure vessel has just completed a fill operation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
       FIG. 1  is a schematic view of the filling system of the present invention. 
       FIG. 2  is a schematic view of the filling system of the present invention showing the fluid flow during a venting step. 
       FIG. 3  is a schematic view of the filling system of the present invention showing the fluid flow during a transferring step. 
       FIG. 4  is a schematic view of the filling system of the present invention showing the fluid flow during a pressurizing step. 
       FIG. 5  is a schematic view of the filling system of the present invention showing the fluid flow during a low pressure filling step. 
       FIG. 6  is a schematic view of the filling system of the present invention showing the fluid flow during a high pressure filling step. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown in  FIG. 1 , a liquid natural gas filling system  10  includes a first, low pressure vessel  12 , at least one second, high pressure vessel  14 , a nozzle  16  structured to be coupled to a LNG vehicle fuel tank, a plurality of conduits  18  coupling, and providing fluid communication between, the first, low pressure vessel  12 , the at least one second, high pressure vessel  14 , and the nozzle  16 . The first, low pressure vessel  12  is structured to hold a cryogenic liquid saturated at a pressure between about 10 and 100 psi, and more preferably at about 20 psi. The first, low pressure vessel  12  is also structured to hold a bulk quantity of cryogenic liquid, preferably between about 13,000 and 20,000 gallons of cryogenic liquid, and more preferably about 16,000 gallons of cryogenic liquid. The at least one second, high pressure vessel  14  is structured to hold a cryogenic liquid saturated at a pressure between about 90 and 125 psi, and more preferably at about 100 psi. The at least one second, high pressure vessel  14  is also structured to hold a limited quantity of cryogenic liquid, preferably between about 100 and 500 gallons of cryogenic liquid, and more preferably about 220 gallons of cryogenic liquid. 
   Each of the conduits in the plurality of conduits  18  has a valve  20  thereon. Each valve  20  is structured to be moved between a first, closed position and a second, open position. When a valve  20  is in the first, closed position, fluid does not pass through the conduit associated with the valve  20 . Conversely, when a valve  20  is in the second, open position, fluid may pass through the conduit associated with the valve  20 . As set forth below, each valve  20  will be identified individually by the reference number “ 20 ” followed by a letter. For example, valve  20 A is coupled to, and controls fluid flow through, the first, low pressure vessel liquid outlet conduit  30 . 
   The plurality of conduits  18  include at least the following conduits; a first, low pressure vessel liquid outlet conduit  30 , a second, high pressure vessel liquid outlet conduit  32 , and a second, high pressure vessel liquid inlet conduit  34 . The first, low pressure vessel liquid outlet conduit  30  and the second, high pressure vessel liquid outlet conduit  32  are, preferably, coupled, and in fluid communication, thereby forming a nozzle conduit  36 . The nozzle  16  is disposed at, and is in fluid communication with, the distal end of the nozzle conduit  36 . The second, high pressure vessel liquid inlet conduit  34  extends between, and is in fluid communication with both, the nozzle conduit  36  and the second, high pressure vessel  14 . The valves  20 A,  20 B,  20 C, and  20 D are associated with the following respective conduits; the first, low pressure vessel liquid outlet conduit  30 , the second, high pressure vessel liquid outlet conduit  32 , the second, high pressure vessel liquid inlet conduit  34 , and the nozzle conduit  36 . 
   The a liquid natural gas filling system  10  also includes a pressure building means  22  structured to raise the saturation pressure of the cryogenic liquid from the pressure of the first, low pressure vessel  12  to the pressure of the second, high pressure vessel  14 . The pressure building means  22  may be, but is not limited to, a device such as a vessel heater attached to the second, high pressure vessel  14 . However, in the preferred embodiment, the pressure building means  22  is a vaporizer  24 . A vaporizer conduit  38 , having valve  20 E thereon, extends between, and is in fluid communication with both, the nozzle conduit  36  and the vaporizer  24 . A second, high pressure vessel vapor inlet conduit  40 , having valve  20 F thereon, extends between, and is in fluid communication with both, the vaporizer  24  and the second, high pressure vessel  14 . 
   A second, high pressure vessel vapor outlet conduit  42  may extend between, and be in fluid communication with both, the second, high pressure vessel  14  and the first, low pressure vessel  12 . Valve  20 G is associated with the second, high pressure vessel vapor outlet conduit  42 . 
   The liquid natural gas filling system  10  also includes a pump assembly  26 . The pump assembly  26  is disposed on, and in fluid communication with, the nozzle conduit  36 . The pump assembly  26  is, preferably, disposed upstream of the juncture of the nozzle conduit  36  and the vaporizer conduit  38 . The pump assembly  26  is structured to accelerate the speed of the fluid flow through the nozzle conduit  36 . 
   The liquid natural gas filling system  10  also includes an electronic control system  28 . The electronic control system  28  is coupled to a plurality of sensors  29  as well as each of the valves  20 . The sensors  29  are, preferably, disposed on each vessel  12 ,  14  and are structured to monitor temperature and pressure. The electronic control system  28  is further structured to control the position of each valve  20  and thereby control the flow of fluid through the liquid natural gas filling system  10 . 
   There may also be a third, high pressure vessel  14 A. The third, high pressure vessel  14 A is substantially similar to the second, high pressure vessel  14  in size and structure. The third, high pressure vessel  14 A includes a third, high pressure vessel liquid outlet conduit  32 A, the third, high pressure vessel liquid inlet conduit  34 A. The third, high pressure vessel liquid outlet conduit  32 A is coupled to, and in fluid communication with, the second, high pressure vessel liquid outlet conduit  32 . Similarly, the third, high pressure vessel liquid inlet conduit  34 A is coupled to, and in fluid communication with, the second, high pressure vessel liquid inlet conduit  34 . The third, high pressure vessel  14 A preferably includes a third, high pressure vessel vapor inlet conduit  40 A. The third, high pressure vessel vapor inlet conduit  40 A is coupled to, and in fluid communication with, the second, high pressure vessel vapor inlet conduit  40 . The third, high pressure vessel  14 A also preferably includes a third, high pressure vessel vapor outlet conduit  42 A. The third, high pressure vessel vapor outlet conduit  42 A is coupled to, and in fluid communication with, the second, high pressure vessel vapor outlet conduit  42 . 
   The operation of the filling station  10  occurs as follows. As shown in  FIGS. 3 ,  4 , and  6 , there are at least three steps to a filling operation; a transfer step  50  ( FIG. 3 ), wherein fluid is transferred from the first low, pressure vessel  12  to the second, high pressure vessel  14 , a pressurizing step  52  ( FIG. 4 ), wherein the pressure of the cryogenic liquid in the second, high pressure vessel  14  is raised from the low pressure to a high pressure, and a filling step  56  ( FIG. 6 ) wherein the high pressure cryogenic liquid is transferred to an external vessel, such a vehicle fuel tank  1 . The following optional steps may also occur. As shown in  FIG. 2 , the second, high pressure vessel  14  may be vented  58  to reduce the internal pressure. As shown in  FIG. 5 , a small amount of cryogenic liquid from the first, low pressure vessel  12  may be transferred to the external vessel during a low pressure filling step  60 . 
   These steps are performed as follows. It is assumed for the sake of this example that all valves  20  are initially in the first, closed position and that the nozzle  16  is coupled to a vehicle fuel tank  1 . If the second, high pressure vessel  14  has recently been used, the second, high pressure vessel  14  may still contain residual cryogenic liquid and vapor at the high pressure. Thus, as shown in  FIG. 2 , the second, high pressure vessel vapor outlet conduit valve  20 G is opened to allow the high pressure vapor to be vented  58  to the first, low pressure vessel  12 . Once the pressure in both the first, low pressure vessel  12  and the second, high pressure vessel  14  have reached equilibrium, the second, high pressure vessel vapor outlet conduit valve  20 G is closed. Due to the relative size of the vessels  12 ,  14  the pressure at equilibrium will be substantially close to the nominal pressure of the first, low pressure vessel  12 . 
   Once the pressure in the second, high pressure vessel  14  has been reduced, cryogenic liquid is transferred  50  from the first, low pressure vessel  12  to the second, high pressure vessel  14 . That is the first, low pressure vessel liquid outlet conduit valve  20 A is opened and allows low pressure cryogenic fluid to flow though the first, low pressure vessel liquid outlet conduit  30 , the nozzle conduit  36 , the second, high pressure vessel liquid inlet conduit  34 , and into the second, high pressure vessel  14 . The flow may be accelerated by the pump assembly  26  at the nozzle conduit  36 . Once the second, high pressure vessel  14  is sufficiently filled with low pressure cryogenic liquid, the first, low pressure vessel liquid outlet conduit valve  20 A is closed. 
   As shown in  FIG. 4 , to pressurize the second, high pressure vessel  14 , the pressure building means  22  is actuated. To accomplish this, during the step of pressurizing  52  the second, high pressure vessel  14 , the second, high pressure vessel liquid outlet conduit valve  20 B, the vaporizer conduit valve  20 E, and the second, high pressure vessel vapor inlet conduit valve  20 F are opened. Thus, a portion of the low pressure cryogenic liquid in the second, high pressure vessel  14  may flow through the second, high pressure vessel liquid outlet conduit  32 , the nozzle conduit  36 , the vaporizer conduit  38 , and into the vaporizer  24 . The flow may be accelerated by the pump assembly  26  at the nozzle conduit  36 . Within the vaporizer  24 , the low pressure cryogenic liquid is evaporated and becomes a vapor. The vapor is transferred through the second, high pressure vessel vapor inlet conduit  40  into the second high pressure vessel  14 . Preferably, the vapor is bubbled up through the low pressure liquid within the second high pressure vessel  14  to effect a transfer of heat. The introduction of the high pressure vapor to the second high pressure vessel  14  raises the pressure of the cryogenic liquid within the second high pressure vessel  14 . Once the fluid within the second, high pressure vessel  14  is at or about the high pressure, the second, high pressure vessel liquid outlet conduit valve  20 B, the vaporizer conduit valve  20 E and the second, high pressure vessel vapor inlet conduit valve  20 F are closed. 
   As shown in  FIG. 5 , a small quantity of low pressure cryogenic liquid from the first, low pressure vessel  12  may be transferred to the vehicle fuel tank  1 . As used herein, a “small quantity” shall mean between about 5 and 10 gallons of cryogenic liquid. The low pressure cryogenic liquid in the vehicle fuel tank  1  will cause the pressure head within the vehicle fuel tank to collapse. This facilitates filling the vehicle fuel tank  1  with the high pressure cryogenic liquid from the second, high pressure vessel  14 . During the low pressure filling step  60  the first, low pressure vessel liquid outlet conduit valve  20 A and the nozzle conduit valve  20 D are opened. Low pressure cryogenic liquid may then flow though the first, low pressure vessel liquid outlet conduit  30 , the pump assembly  26 , the nozzle conduit  36  and the nozzle  16  into the vehicle fuel tank  1 . Once a sufficient quantity of low pressure cryogenic liquid has been transferred to the vehicle fuel tank  1 , the first, low pressure vessel liquid outlet conduit valve  20 A and the nozzle conduit valve  20 D are closed. The flow may be accelerated by the pump assembly  26  at the nozzle conduit  36 . 
   As shown in  FIG. 6 , during the filling step  56 , cryogenic liquid at a high pressure is transferred from the second, high pressure vessel  14  to the vehicle fuel tank  1 . This is accomplished by opening the second, high pressure vessel liquid outlet conduit valve  20 B and the nozzle conduit valve  20 D. This allows the high pressure cryogenic liquid from the second, high pressure vessel  14  to flow through the second, high pressure vessel liquid outlet conduit  32 , the nozzle conduit  36 , the nozzle  16  and into the vehicle fuel tank  1 . After the vehicle fuel tank  1  is filled, the second, high pressure vessel liquid outlet conduit valve  20 B and the nozzle conduit valve  20 D are closed, thereby returning the system to the original configuration. 
   When the liquid natural gas filling system  10  includes the third, high pressure vessel  14 A, different steps of the filling procedure may occur simultaneously, or alternately, with respect to the different high pressure vessels  14 ,  14 A. That is, for example, the third, high pressure vessel  14 A may be vented  58  while the second, high pressure vessel  14  is being pressurized  52 . Thus, the third, high pressure vessel  14 A may be filled and pressurized and ready to fill another vehicle fuel tank  1  while the second, high pressure vessel  14  is in use. By charging the high pressure vessels  14 ,  14 A alternately, there is always one high pressure vessel  14 ,  14 A ready to be used. 
   While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. For example, the filling system  10  has been described as having vessels  12 ,  14 ,  14 A structured to hold LNG. The filling system  10  may also be used with other cryogenic liquids. Additionally, it is understood that the filling system  10  includes addition pressure relief valves, burst disks, and other safety devices disposed on each vessel, conduit, or other component. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.