Abstract:
A cryogenic system that off-loads cryogenic liquid from a delivery vehicle and pumps the cryogenic liquid to a storage tank includes an interlock that enables the pneumatic valves which control the flow of the cryogen. The interlock includes a pneumatic relay, a pneumatic line and a pressure sensing line. The pneumatic line transfers pressurized air to the pneumatic relay while the pressure sensing line pressurizes the pneumatic relay when hoses from a delivery truck are connected to the system. The pneumatic relay includes a housing that defines a chamber with a piston having an arcuate passage located therein. When a hose from the delivery truck is connected to the system, the pressure sensing line detects a change in pressure and pressurizes the pneumatic relay. The pressure displaces the piston of the pneumatic relay which aligns the arcuate passage of the relay with the pneumatic valve to allow pressurized air to travel to the pneumatic valve thereby opening the pneumatic valve.

Description:
CLAIM OF PRIORITY  
       [0001]    This application claims priority from U.S. Provisional Patent Application Serial No. 60/267,517, filed Feb. 8, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to systems for refilling the storage tanks of cryogenic liquid dispensing stations and, more particularly, to an interlock that prevents spills during off-loading of cryogenic liquid from a delivery vehicle to a cryogenic liquid dispensing station.  
         BACKGROUND OF THE INVENTION  
         [0003]    Liquid natural gas (LNG) is a cryogenic liquid that is plentiful, environmentally friendly and domestically available energy source and, therefore, is an attractive alternative to oil. As a result, LNG is increasingly being used as a fuel for vehicles. This is especially true for fleet and heavy duty vehicles.  
           [0004]    Due to the increased use of LNG, dispensing stations for refueling LNG-powered vehicles are becoming more common. LNG dispensing stations typically include at least an insulated tank containing a supply of LNG and a pump that dispenses the LNG to the vehicle or saturation/conditioning components.  
           [0005]    The dispensing station is periodically refilled by a delivery vehicle such as a tank truck. The delivery truck features a tank containing a supply of LNG as well as a liquid feed hose in communication with the liquid side thereof and a vapor return hose in communication with the vapor side thereof. LNG is off-loaded from the delivery truck tank by connecting the feed hose to a pump that is on-site and in communication with the dispensing station tank. The vapor return hose is placed in communication with the line between the pump and the dispensing station tank. Vapor from the head space of the dispensing station tank is returned via the vapor return hose to the vapor side of the delivery truck tank to relieve pressure build-up in the dispensing station tank. LNG is transferred from the delivery truck tank to the dispensing station tank when the pump is activated.  
           [0006]    It has become common practice in the industry to use the same pump to dispense and or condition the LNG and to off-load the LNG from the delivery truck. For example, the pump dispenses LNG from the tank for use. The pump also off-loads LNG from a transport truck to refill the tank. In such stations, automatic and pneumatically operated valves typically control the piping status so that the station may be configured in either the dispense mode or the delivery truck off-load mode. If by some error or failure the valves are improperly set, however, an upset condition may occur. For example, the station could be configured to off-load LNG when the delivery truck hoses are not connected to the station. In addition, even if the station valves were functioning properly, a delivery truck driver could drive away from the station with the delivery truck hoses still connected (known as a “drive off”) and the station still configured for off-loading LNG. In both situations, spillage of LNG could occur. Such an occurrence is undesirable from the standpoint that LNG is wasted and a hazardous condition for the delivery truck driver and environment could be created.  
           [0007]    Alternatively, a pump separate from the station dispensing pump may be used to off-load LNG from the delivery truck. With such an arrangement, the liquid feed and vapor return hoses of the delivery truck are also connected to the off-loading pump inlet and outlet sides, respectively. The valves in such a station are typically configured manually by the delivery truck driver. If the delivery truck driver incorrectly configures the valves, or if the delivery truck driver drives off without disconnecting the liquid feed and vapor return hoses, spillage of LNG may also occur.  
           [0008]    Prior art dispensing stations attempt to solve the above problems by providing a check valve in the station line running between the off-loading pump and the connection for the delivery truck liquid feed hose. As a result, one way flow of LNG from the delivery truck through the pump and to the station tank is ensured. A disadvantage of this approach, however, is that a pressure drop occurs across the check valve so that pump prime is adversely effected. Furthermore, a check valve may not be installed in the station line running between the station tank and the connection for the delivery truck vapor return line. As a result, this line may be a source of LNG spills even if a check valve is installed in the station liquid fill line.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention is directed to an apparatus for interlocking a cryogenic fluid dispensing station with a cryogenic fluid delivery vehicle. The dispensing station includes an off-loading port that is connected to a tank mounted on a fluid delivery vehicle. The off-loading port receives cryogenic fluid from the delivery vehicle. A pressure sensor is coupled to the off-loading port to sense the cryogenic fluid pressure at the port. A dispensing station valve is in fluid communication with the off-loading port. The dispensing station valve operates between an open position and a closed position wherein the dispensing station valve closes when the pressure sensor senses a fluid pressure at the port below a predetermined level.  
           [0010]    Another aspect of the invention is directed to a method of interlocking a cryogenic fluid dispensing station. The method of interlocking the cryogenic fluid dispensing station includes connecting a tank mounted on a fluid delivery vehicle to an off-loading port of the dispensing station. Cryogenic fluid is delivered from the fluid delivery vehicle to the dispensing station through the off-loading port. The off-loading port senses the fluid pressure of the cryogenic fluid. When the fluid pressure of the cryogenic fluid is below a predetermined level, a valve in communication with the off-loading port is closed.  
           [0011]    The following detailed description of embodiments of the invention, taken in conjunction with the accompanying drawings, wherein like characters identify identical parts, provide a more complete understanding of the nature and scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a schematic diagram of a prior art dispensing station to which a delivery truck is connected for off-loading LNG;  
         [0013]    [0013]FIG. 2 is a schematic diagram of the dispensing station and delivery truck of FIG. 1 where the dispensing station is equipped with an embodiment of the interlock for cryogenic liquid off-loading system of the present invention;  
         [0014]    [0014]FIG. 3A is a more detailed schematic diagram of the embodiment of the interlock for cryogenic liquid off-loading system of the present invention illustrated in FIG. 2, set in the enabled mode;  
         [0015]    [0015]FIG. 3B is a more detailed schematic diagram of the embodiment of the interlock for cryogenic liquid off-loading system of the present invention illustrated in FIG. 2, set in the safe mode;  
         [0016]    [0016]FIG. 4 is a schematic diagram of a second prior art dispensing station to which a delivery truck is connected for off-loading LNG; and  
         [0017]    [0017]FIG. 5 is a schematic diagram of the dispensing station and delivery truck similar to FIG. 4 but where the dispensing station is equipped with a second embodiment of the interlock for cryogenic liquid off-loading system of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    A portion of a typical prior art dispensing station is indicated in general at  10  in FIG. 1 and includes a storage tank  12  as well as a pump  14  positioned within a jacket-insulated sump  16 . Cryogenic liquids, such as liquid natural gas (LNG), have a boiling point below −150° F. at atmospheric pressure. As a result, storage tank  12  of the dispensing station is vacuum insulated via a jacket  22 . The storage tank  12  contains a supply of LNG  24 . The components of the dispensing station illustrated in FIG. 1 are positioned within a containment pit  23 . Containment pit  23  prevents leaked LNG from flowing away from the dispensing station.  
         [0019]    Sump  16  communicates with tank  12  via fill line  26  and overflow line  28  so that it remains filled with LNG. As a result, pump  14  is submerged in LNG. This prevents cavitation in the pump and allows dispensing to begin without the pump cool down period that would otherwise be required. Pump  14  pumps the LNG in sump  16  through line  32  to the user device. Alternatively, line  32  may lead to a saturation arrangement (not shown) so that the LNG is conditioned prior to dispensing. An example of a LNG dispensing station featuring such a saturation arrangement is presented in U.S. Pat. No. 5,682,750 to Preston et al., which is owned by the assignee of the present application. Lines  26 ,  28  and  32  feature pneumatically operated valves  46 ,  48  and  42 , respectively. Alternatively, valves  46 ,  48  and  42 , and the others described herein, could be operated with hydraulics or electrical relays. During the dispensing or saturation of LNG  24 , valves  46 ,  48  and  42  are open while the remaining valves illustrated in FIG. 1 are closed.  
         [0020]    In addition to dispensing, pump  14  is commonly used to refill tank  12  by off-loading LNG from a delivery vehicle such as a tank truck, indicated in general at  52  in FIG. 1. Tank truck  52  features an insulated tank  54  containing a supply of LNG  56 , liquid feed hose  58  and vapor return hose  62 . During off-loading, as illustrated in FIG. 1, the liquid side of the delivery tank truck  52  is connected via liquid feed hose  58  and hose connector  66  to a line  64 , which leads to sump  16 . Similarly, the vapor space of the delivery tank truck  52  is connected via vapor return hose  62  and hose connector  72  to line  74 , which leads to a line  76 . The outlet of pump  14  communicates with the head space of tank  12  via the line  76 .  
         [0021]    Line  64  features manually operated valve  75  and pneumatically operated valve  77 . Line  74  includes manually operated valve  82  and pneumatically operated valve  84 . Line  76  includes pneumatically operated valve  86 . During off-loading, these valves are all opened. In contrast, valves  42 ,  46  and  48  are closed. As a result, sump  16  does not receive LNG from tank  12  and the outlet of pump  14  is isolated from the dispensing or saturation portion of the station. Instead, LNG flows from delivery tank truck  52  to sump  16  via hose  58  and line  64  and is pumped by pump  14  through line  76  to dispensing station tank  12 . As a result, tank  12  is refilled. Vapor from the head space of station tank  12  returns to the delivery truck tank via line  76 , line  74  and hose  62  to relive pressure build-up in the tank  12  prior to activation of pump  14 .  
         [0022]    As illustrated in FIG. 1, line  64  features a check valve  92  which prevents LNG from flowing back towards the delivery truck. As a result, LNG spills are prevented in the event that valves  75  and  77  are open when the feed hose  58  is not attached to connector  66 . Such a situation could occur if there was an error or failure in the valve control system or if the delivery truck driver drove off without disconnecting the feed hose  58 . The resulting LNG spill would be worse if any of valves  86 ,  48  or  46  were also open. Even with check valve  92  present, however, LNG spills could still occur through line  74  if the vapor return hose  62  was not attached to connector  72 . This could occur if valves  82 ,  84  and  86  were open.  
         [0023]    [0023]FIG. 2 illustrates the pneumatic and electronic control system for the valves connected to the dispensing station of FIG. 1. A source  93  of air communicates under the direction of electronic controller  95  with all of the pneumatically operated valves of FIG. 1 except manually controlled valves  75  and  82 . Controller  95  is programmed to open the valve  46  via line  96 , valve  48  via line  97  and valve  42  via line  98 , so that the station tank is configured for the dispensing/saturation mode. Controller  95  is also programmed to close valves  46 ,  48  and  42  open valve  77  via line  103 , valve  84  via line  107  and valve  86  via line  99 , so that the station tank is configured for the off-load mode.  
         [0024]    An embodiment of the interlock system of the present invention includes a pneumatic relay  101  positioned on the pneumatic line  103  that runs between the electronic controller  95  and pneumatically operated valve  77 . This preferred interlock embodiment also includes a pneumatic relay  105  positioned on the pneumatic line  107  that runs between the electronic controller  95  and pneumatically operated valve  84 . Pressure sensing line  111  provides communication between pneumatic relay  101  and connector  166 , or port, while pressure sensing line  113  provides communication between pneumatic relay  105  and connector  172 , or port. Connectors  166  and  172  may be, for example, standard three inch Compressed Gas Association (CGA) connectors for LNG. As will become apparent, the check valve  92  illustrated in FIG. 1 is unnecessary when the interlock of the present invention is installed and, therefore, it has been omitted from FIG. 2.  
         [0025]    As illustrated in FIG. 3A, the pneumatic relay  101  includes a housing  115  within which a sliding piston  117  is positioned. A two ended, preferably arcuate passage  118  is formed in the piston  117 . A compression spring  119  or other mechanical biasing means, such as a helical spring or a leaf spring, is disposed in the housing on one side of the piston  117  and biases the cylinder  117  to a lower position. An open chamber  123  exists on the opposite side of the piston  117 .  
         [0026]    As illustrated in FIG. 3A, when the delivery truck liquid feed hose  58  is attached to connector  166 , such as during an off-loading scenario, the chamber  123  of pneumatic relay  101  is pressurized via pressure sensing line  111 . As a result, the piston  117  is lifted so that arcuate passage  118  is in alignment with pneumatic line  103 . As such, when the interlock is in this enabled mode, valve  77  may be opened under the direction of controller  95  (FIG. 2).  
         [0027]    Pressures in the range of  2  psi to  20  psi within pressure sensing line  111  and chamber  123  are typical when feed hose  58  is attached to connector  166 . The pneumatic relay  101  may be adjusted to activate the enabled mode when the pressure within the pressure sensing line  111  reaches a predetermined level. As such, the interlock embodiment may be fine tuned depending upon the desired application or sensitivity. For example, if the pneumatic relay  101  was set to activate the enabled mode at too low a pressure, the pressure of LNG exiting line  64  through connector  166  when a drive off occurs could be enough to falsely indicate the presence of the delivery truck feed hose  58  to the pressure sensing line  111  and pneumatic relay  101 .  
         [0028]    As illustrated in FIG. 3B, the interlock goes into safe mode when the delivery truck feed hose  58  of FIG. 3A is removed. Under such circumstances, pressure sensing line  111  is at atmospheric pressure and chamber  123  of pneumatic relay  101  is not pressurized. As a result, as illustrated in FIG. 3B, piston  117  is pushed down by compression spring  119  so that arcuate passage  118  is moved out of alignment from pneumatic line  103 . Air from pressurized air source  93  (FIG. 2) is therefore unable to reach pneumatically operated valve  77  which closes as its default configuration.  
         [0029]    The interlock embodiment therefore automatically closes valve  77  when the delivery truck feed hose  58  is not attached to connector  166  so that LNG does not flow through line  64  and cause a spill regardless of the configuration of valve  75 , or any of the other station valves. As such, the interlock protects against LNG spills in the event of drive offs, controller error or failure in the configuration of the station valves.  
         [0030]    The pneumatic relay  105  and pressure sensing line  113  of FIG. 2 operate in a similar fashion with regard to pneumatic line  107 , pneumatically operated valve  84 , connector  172  and vapor return hose  62 . When the vapor return hose  62  is attached to the connector  172 , the pneumatic relay  105  is pressurized via pressure sensing line  113 . As a result, the interlock embodiment is enabled and the pneumatically operated valve is opened. Additionally, spills via line  74  are also avoided in the event of drive offs, controller error or failures when the vapor return hose is not attached to connector  172 .  
         [0031]    It should be noted that the specific structure of the pneumatic relay  101  illustrated in FIGS. 3A and 3B is presented as an example only. As is known in the art, alternative types of pneumatic relays may be substituted. Suitable pneumatic relays may be obtained from, for example, Airtrol Components, Inc. of New Berlin, Wis. or Clippard Europe S.A. of Belgium.  
         [0032]    Alternatively, the valves in the present invention may also be controlled hydraulically by a pressurized liquid. The valves of the present invention could also be controlled electrically by a number of electrical relays.  
         [0033]    [0033]FIG. 4 illustrates in general at  130  a portion of a dispensing station that does not use the same pump for dispensing and off-loading. Such an arrangement allows dispensing or saturation to occur simultaneously with off-loading from a delivery truck  52  so that interruptions in station operation are prevented.  
         [0034]    Similar to the dispensing station illustrated in FIGS. 1 and 2, a pump  132  for dispensing or transferring LNG to a dispensing, saturation or conditioning arrangement via line  133  is positioned within a jacket-insulated sump  134 . Sump  134  receives LNG via fill line  136  and overflow line  138  from a storage tank  135 . Storage tank  135  is vacuum insulated via a jacket  141 . Valves  143  and  145  are used to isolate the sump  134  from the storage tank  135  so that the sump  134  may be drained for maintenance operations on the pump  132 .  
         [0035]    A dedicated off-loading pump  151  communicates with the head space of storage tank  135  via line  153  and a connector  156  via line  158 . A vapor return hose  62  attaches to the station via connector  162  and communicates with line  153  via line  164 . During off-loading of LNG  56  from tank  54  of delivery truck  52 , manually operated valves  167 ,  169  and  171  are opened. Check valve  173  prevents LNG from flowing through line  158  and spilling in the event that feed hose  58  is not present.  
         [0036]    While the valves of the station of FIG. 4 are manually operated, the interlock embodiment of the present invention may be provided by adding a source of pressurized air  181 , as illustrated in FIG. 5. The source of pressurized air communicates with pneumatically operated valves  184  and  186  via lines  187  and  189 , respectively. Valves  184  and  186  are configured to be open when placed in communication with the source of pressurized air  181 .  
         [0037]    Pneumatic relay  183  is positioned within line  187  while pneumatic relay  185  is positioned within line  189 . Pneumatic relays  183  and  185  may feature the same construction as pneumatic relay  101  illustrated in FIGS. 3A and 3B. Pneumatic relay  183  communicates with connector  190  via pressure sensing line  191  while pneumatic relay  185  communicates with connector  194  via pressure sensing line  193 .  
         [0038]    The embodiment of the interlock of the present invention illustrated in FIG. 5 operates in a manner similar to the embodiments illustrated in FIGS. 2, 3A and  3 B. That is, when the delivery truck feed hose  58  is attached to connector  156 , pressure sensing line  193  pressurizes pneumatic relay  185  of the interlock so that the pneumatic relay  185  is set to an enabled mode. Pressurized air source  181  is therefore permitted to communicate with valve  186  via line  202 . As a result, pneumatically operated valve  186  is opened. Similarly, when vapor return hose  62  is attached to connector  162 , the pneumatic relay  183  of the interlock is pressurized via pressure sensing line  191  so that air is permitted to travel from pressurized air source  181  to pneumatically operated valve  184 . As a result, valve  184  is opened.  
         [0039]    If either the feed hose or vapor return hose of FIG. 5 is disconnected from the station, the appropriate pressure sensing line and pneumatic relay are exposed to atmospheric pressure thereby closing the associated pneumatic valve. This prevents a LNG spill regardless of the setting of the remaining station valves.  
         [0040]    In an alternative embodiment, one interlock would be in communication with the both the valve controlling the feed hose and the valve controlling the vapor return hose. The interlock would open the valves once the pneumatic relay of the interlock is pressurized via the corresponding pressure sensing line.  
         [0041]    It is to be understood that while the present invention is described above in terms of liquid natural gas (LNG) dispensing stations, dispensing systems for alternative types of fuels and/or cryogenic liquids represent additional applications for the invention. Furthermore, while illustrated above, the present invention may also be used with dispensing systems that do not feature a pump in a sump.  
         [0042]    While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention.