Abstract:
A cryogenic fluid delivery system includes a main tank system with a main tank adapted to contain a first supply of cryogenic liquid, and reserve tank system with reserve tank adapted to contain a second supply of cryogenic liquid. A pressure building circuit is adapted to delivery vapor to the head space of the main tank to build pressure in the main tank and a fuel delivery line supplies cryogenic fuel from either the main tank or the reserve tank to a use device. The reserve tank stores saturated cryogenic fuel that is delivered to the use device via the fuel delivery line while the cryogenic liquid in the main tank is being saturated. The fluid delivery system automatically switches to delivering cryogenic fuel from the main tank to the use device via the fuel delivery line upon saturation of the cryogenic liquid in the main tank.

Description:
REFERENCE TO PRIORITY DOCUMENT 
       [0001]    This application claims priority to co-pending U.S. Provisional Patent Application Ser. No. 62/004,477 entitled “LNG Delivery System with Saturated Fuel Reserve”, filed May 29, 2014. Priority to the aforementioned filing date is claimed and the provisional application is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to a system for delivering liquefied natural gas (LNG) from a storage tank to a use device, such as a natural gas powered vehicle engine. The disclosed devices and methods can be used in a variety of environments and are particularly suited for markets in which pre-saturation of the LNG fuel is not performed. The disclosed devices and methods may be used as a source of “trim heat” if the storage tank pressure falls below a pre-defined level. 
         [0003]    Many heavy-duty, natural gas fueled vehicle engines require that an intake pressure of natural gas be at a certain value, such as around 100 psig. In most markets, LNG is saturated, or heat is added, to a point at which its vapor pressure is roughly equal to the pressure required by the use device (i.e., the vehicle). This process of building saturation pressure is typically performed at LNG fueling stations. However, there exist some markets in which this saturation of the fuel before transferring it to the vehicle storage tank is not performed or is not performed to an extent great enough to achieve 100 psig saturated liquid in the vehicle tank after fueling. Thus, the storage tank may end up being filled with LNG well below the desired pressure. Additionally, some engines require pressures around 150 psig, which is not readily available, even at fuel stations that saturate the fuel before delivery. 
         [0004]    In one proposed solution, compressed natural gas (CNG) is used to add vapor pressure above LNG to deliver the fuel at an elevated pressure. However, this solution requires a second tank for CNG be mounted on the vehicle, which adds weight and occupies valuable space on the vehicle chassis. In another proposed solution, a specialized fuel station sequentially fills the storage tank with LNG then uses natural gas vapor to add additional heat to saturate the fuel in the storage tank. The vehicle fuel system is equipped with a special overflow tank into which excess LNG passes during the fill. However, this solution requires a special fuel station where the vehicle must be filled. 
         [0005]    Another proposed solution utilizes an overflow tank, but also uses special main tanks that remain hydraulically full to maintain sufficient pressure to the engine no matter the liquid&#39;s saturation pressure. However, the special fuel tanks add extra cost and complexity to the system. 
       SUMMARY 
       [0006]    Disclosed is an LNG delivery system that overcomes the aforementioned shortcomings of the prior art. In an embodiment the system uses a system of one or more main tanks along with a reserve tank wherein the tanks can be mounted on a movable vehicle. The main tanks may utilize a pressure building circuit of the type sometimes used on stationary cryogenic cylinders. This type of pressure building circuit utilizes a gravity to feed liquid cryogen into a vaporizer. Upon vaporization of the liquid, its volume expands and the evolved gas is routed to a vapor space above the cryogen in the main tank, building a head of vapor pressure above the liquid phase in the tank. Alternatively, gas from downstream in the fuel system (after the heat exchanger) can be pushed back to the vapor space by means of mechanical action. U.S. patent application Ser. No. 14/044,622 describes a related device and method for such a mechanical pressure building action and is incorporated herein by reference. 
         [0007]    Neither the traditional-style pressure building circuit nor the mechanical action pressure builder on a vehicle storage tank can alone maintain a constant supply of pressurized LNG. Since LNG vehicle tanks are used in mobile applications, any vapor pressure that is built above the liquid phase will quickly collapse as soon as the vehicle is in motion and the liquid and vapor phases mix. It may take an inconvenient amount of time, such as an hour, to add enough heat in this fashion to fully saturate the bulk of LNG in the tank. 
         [0008]    Therefore, in addition to a tank using a form of pressure-building, a reserve tank is used in the system that stores saturated liquid that the vehicle can use to drive while the main tank(s) are being saturated. Once the liquid in the main tanks is saturated, the main tank(s) fuel the vehicle with their now-saturated liquid and refill the reserve tank, which will be stored until next fill. 
         [0009]    In one aspect, there is disclosed a cryogenic fluid delivery system comprising: a main tank system, the main tank system including a main tank adapted to contain a first supply of cryogenic liquid, the main tank including a head space adapted to contain a vapor above cryogenic liquid stored in the main tank; a reserve tank system, the reserve tank system including a reserve tank adapted to contain a second supply of cryogenic liquid, the reserve tank including a head space adapted to contain a vapor above cryogenic liquid stored in the reserve tank; a pressure building circuit adapted to delivery vapor to the head space of the main tank to build pressure in the main tank; a fuel delivery line that supplies cryogenic fuel from either the main tank or the reserve tank to a use device; wherein the reserve tank stores saturated cryogenic fuel that is delivered to the use device via the fuel delivery line while the cryogenic liquid in the main tank is being saturated, and wherein the fluid delivery system switches to delivering cryogenic fuel from the main tank to the use device via the fuel delivery line upon saturation of the cryogenic liquid in the main tank 
         [0010]    Other features and advantages should be apparent from the following description of various embodiments, which illustrate, by way of example, the principles of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows an example of a prior fuel delivery system. 
           [0012]      FIG. 2  shows an example embodiment of a fuel delivery system with a reserve tank and a main tank. 
           [0013]      FIG. 3  shows another embodiment of the fuel delivery system with a main tank using a traditional style pressure building loop. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Before the present subject matter is further described, it is to be understood that this subject matter described herein is not limited to particular embodiments described, as such may of course vary. It is also to be understood that the terminology used herein is for the purpose of describing a particular embodiment or embodiments only, and is not intended to be limiting. Unless defined otherwise, all technical terms used herein have the same meaning as commonly understood by one skilled in the art to which this subject matter belongs. 
         [0015]      FIG. 1  shows an example of a fuel delivery system such as the type described in U.S. patent application Ser. No. 14/044,622, which is incorporated herein by reference. A cryogenic tank  22  contains cryogenic product, such as LNG, that includes liquid cryogen  26  with vapor space  36  above the liquid cryogen. A liquid line  24  communicates with the bottom region of the tank  22  where the liquid  26  is contained. As used herein, a “line” can be any type of tubing or piping through which fluid can flow. A product withdrawal line  28  connects the liquid line  24  to the gas use device such as a vehicle engine. A heat exchanger or vaporizer  32  is located in a withdrawal line  28  to vaporize the cryogen before it is delivered to the use device. A valve  10  in the withdrawal line  28  represents, for example, an automatic valve. 
         [0016]    With reference still to  FIG. 1 , an economizer circuit  34  includes a vapor line or tube  40 , which communicates with the vapor space  36 . The vapor tube  40  includes an economizer regulator  38 , which is set at a predetermined pressure threshold. A liquid line  24  communicates with liquid  26  in the tank  22 . When the pressure in tank  22  exceeds the pressure set point of regulator  38 , vapor  36  may be withdrawn through the vapor line  40  and to the use device through the withdrawal line  28 . This results in a lowering of the pressure in the tank  22 . Due to the horizontal nature of LNG vehicle fuel tanks, there is often sufficient hydrostatic pressure to cause liquid  26  to be withdrawn even when the regulator  38  is open. Therefore, a biasing relief valve  42  is included in the liquid line  24  to cause the economizer circuit  34  to be the path of least resistance out of the tank  22  when the regulator  38  is open. A small orifice  44  is located in parallel with relief valve  42  to allow back flow to the tank during transient periods of high to low use. 
         [0017]    As shown in  FIG. 1 , an active pressure building circuit  55  can be used to build head pressure in tank  22 . The pressure building circuit  55  includes an inlet line  51 , which branches off withdrawal line  28  downstream of the vaporizer  32 . A flow inducer  52  causes vaporized gas to flow from the inlet line  51  to an outlet line  53  leading back to the tank  22 . The outlet line  53  returns the gas to the vapor line  40  through a check valve  54 . 
         [0018]      FIG. 2  shows an example embodiment of a fuel delivery system with a reserve tank  62  and a main tank  22 . The tank  22  and  62  may be constructed, for example, of a single outer vessel with one or more insulated inner vessels. A vacuum space is located between the vessels within the outer vessel. Other configurations of the tanks  22  and  62  are possible. 
         [0019]    In the embodiment of  FIG. 2 , the system includes a pressure building circuit  55  as described with respect to  FIG. 1 . The reserve tank  62  includes all of the same components as tank  22  (described above with reference to  FIG. 1 ) and connects to the use device in parallel via a fuel line  75 . For example, the reserve tank  62  includes liquid  66  and the vapor space  76  located above the liquid  66 . 
         [0020]    The reserve tank  62  includes an economizer circuit  44  a vapor line or tube  80 , which communicates with the vapor space  76 . The vapor tube  80  includes an economizer regulator  78 , which is set at a predetermined pressure threshold. A liquid line  64  communicates with liquid  66  in the tank  62 . When the pressure in tank  62  exceeds the set point of regulator  78 , the vapor  76  may be withdrawn through the vapor line  70  and to the use device through the fuel line  75 . This results in a lowering of the pressure in the tank  62 . A biasing relief valve  82  is included in the liquid line  64  to cause the economizer circuit  74  to automatically be the path of least resistance out of the tank  62  when the regulator  78  is open. A small orifice  84  is located in parallel with the relief valve  72  to allow back flow to the tank during transient periods of high to low use 
         [0021]    With reference still to  FIG. 2 , a line  73  is the fill line for the tank  62  and tees into the withdrawal line  28 . A check valve  71  in the line  73  prevents flow back from tank  62  into the main tank  22  system. 
         [0022]      FIG. 3  shows another embodiment of the fuel delivery system with a main tank  22  and a reserve tank  62  as described above with reference to  FIG. 2 . The system of  FIG. 3  includes a traditional style pressure-building loop or circuit  27 , which is used to build pressure within the main tank  22 . In this embodiment, a withdrawal line  23  extends downwardly from the liquid  26  in the tank  22 . The withdrawal line  23  includes a vaporizer  25 . The liquid  26  exits the withdrawal line  23  via a gravity feed. The exiting liquid  26  passes through the vaporizer  25 , where it is changed to a vapor, and returns to the vapor space  36  through a check valve  54 . In this manner, the pressure building circuit  27  increases pressure within the main tank  22 . 
         [0023]    In use, the reserve tank(s) retain a supply of previously saturated liquid. When the use device is filled, only the main tank(s) is filled with cold liquid. The reserve tank contains enough fuel to drive the use vehicle until the main tank becomes saturated. Pursuant to one method, the reserve tank is maintained in a normally empty state such that the reserve tank is empty upon arrival to the fuel station. Upon arrival at a fuel station, the liquid in the main tank is manually emptied into the reserve tank. The main tank is then filled with cold liquid at the fuel station. The use device uses fuel from the reserve tank while the main tank is saturated. When the reserve tank is nearly empty, the system switches to using fuel from the main tank for the use device. The use device can then operate until the main tank is nearly empty. 
         [0024]    In an alternate process, the reserve tank is maintained in a normally full state such that the reserve tank is full of liquid upon arrival to a fuel station. The main tank is then filled with cold liquid fuel station. The main tank is saturated while the use device uses fuel from the reserve tank. When the reserve tank is nearly empty, the use device switches to using fuel from the main tank. As the main tank becomes fully saturated, the reserve tank refills with liquid from the main tank. When the reserve tank is full, the feeling of the reserve tank is stopped and the use device continues while only using fuel from main tank. This device can then drive until the main tank is nearly empty. 
         [0025]    An example setup and operation of the described system for fueling an engine is now described using numerical values as non-limiting examples. In an example embodiment, the system for fueling an engine needs 10 barg inlet pressure. The economizer  38  has a set pressure of 12 barg and the economizer  78  has a set pressure of 11 barg. When the truck arrives at the fuel station, the reserve tank is −90% full of liquid saturated at 11 barg and the main tanks are nearly empty, but the liquid that remains is saturated at 11 barg. The main tanks are filled with cold liquid saturated at, for example, 4 barg. After the fill, all tanks are full; the main tank is full of liquid saturated at just above 4 barg, and the reserve tank is full of liquid saturated at 11 barg. The valve  10  is in a closed state and the valve  50  is in an open state. 
         [0026]    Continuing the example, the truck can operate using the liquid in the reserve tank  62  for the first 30 minutes or 1 hour of driving. During this time, the pressure building system  55  or  27  is acting on the main tank alone to build pressure and saturate the liquid in the main tank to 11 barg. By the time the reserve tank  62  is nearly empty, the main tank has sufficient pressure to be able to provide a constant source of high pressure to the engine. The control valve  10  will then open and the valve  50  will close. Then the pressure building system will build pressure up to 12 barg. When the liquid level in the main tank  22  falls to a predetermined threshold (such as, for example 60-70%), then the valve  50  will open and the valve  10  will close. This causes the reserve tank  62  to refill from the main tank  22  while providing high pressure gas to the engine. When the reserve tank  62  is full, the valve  50  will close and the valve  10  will open and the pressure building system will only maintain 11 barg. Then the vehicle will drive for the remainder of the fuel in the main tanks. 
         [0027]    In an embodiment, further control can be provided to keep the reserve tank pressure down while driving by strategically switching to use the reserve tank and also keep it filled to a desired level. In this embodiment, the system includes a control system that takes inputs on the fill levels and pressure levels of each of the main tank  22  and the reserve tank  62 . Additionally, to provide further control, the pressure building system of the main tank can strategically build pressure to different amounts depending on the level in the reserve tank. For example, immediately after fueling, it is undesirable for the main tank to build pressure greater than that of the reserve tank because then the reserve tank can begin to fill with perhaps cold liquid. Instead, it is desirable for the main tank to only build pressure to just less than the reserve tank until the reserve tank is nearly empty. Thereafter, it builds pressure to a higher setpoint and later fill the reserve tank as mentioned above with primarily saturated liquid. This level of control is easily attainable with standard pressure sensors, level sensors and solenoid valves known in the art. 
         [0028]    In any of the embodiments, multiple main tanks can be connected in parallel, sharing a fill connection, sharing return gas line  53 , and sharing withdrawal line  28 . 
         [0029]    Although embodiments of various methods and devices are described herein in detail with reference to certain versions, it should be appreciated that other versions, embodiments, methods of use, and combinations thereof are also possible. Therefore the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.