Abstract:
A passive pressure control method and system for controlling pressure in the ullage vapor space of a volatile liquid fuel underground storage tank (“UST”) temporarily, during periods of increasing ullage vapor space pressure, allows vapor to flow into an auxiliary vapor space of variable volume, defined at least in part by a resilient wall member, thereby to reduce the volume of vapor otherwise released to the environment.

Description:
[0001]    This application is a continuation-in-part of U.S. application Ser. No. 10/340,951, filed Jan. 3, 2003, now pending, which claims benefit of U.S. Provisional Application No. 60/347,698, filed Jan. 11, 2002, and U.S. Provisional Application No. 60/364,745, filed Mar. 15, 2002, both now abandoned. This application also claims benefit of U.S. Provisional Application No. 60/387,458, filed Jun. 10, 2002, now abandoned, U.S. Provisional Application No. 60/408,949, filed Sep. 5, 2002, and U.S. Provisional Application No. 60/428,018, filed Nov. 21, 2002. The complete disclosures of all of the applications listed above are incorporated herein by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This invention relates to underground gasoline storage tanks, and more particularly to systems for controlling escape of gasoline vapor from such tanks.  
         BACKGROUND  
         [0003]    During refueling of automobiles and other vehicles, liquid gasoline is delivered into the vehicle fuel tank, and a mixture of gasoline (or other fuel) vapor and air is displaced from the tank. To minimize escape of gasoline vapor into the atmosphere, gasoline dispenser nozzles are typically equipped (as often mandated by local environmental protection regulations) with vapor recovery vacuum systems to collect the displaced gasoline vapor, and air, and deliver it back into the ullage (i.e., vapor) space of the underground storage tank (“UST”). Preferably, a 1-to-1 ratio balance is sought between volume of liquid gasoline drawn from the underground storage tank, e.g. during vehicle refueling, to volume of gasoline vapor and air returned into the ullage space by the vapor recovery system. However, due to a variety of factors, including, e.g., differences in temperature, inefficiencies in the vapor recovery system, ingestion of excessive external air, etc., such a balance is difficult to achieve. As a result, some amount of gasoline vapor may be discharged, or air ingested, through the UST pressure/vacuum relief vent valve during any 24-hour period of operation.  
           [0004]    This problem has been addressed, in part, by design of ORVR (“onboard refueling vapor recovery”) equipped vehicles, in which gasoline vapor collecting in the ullage space of the vehicle tank is recovered onboard the vehicle, making it necessary for the fuel dispensing system to recover only a relatively smaller volume of gasoline vapor and air during refueling, e.g. as compared to non-ORVR vehicles. As a result of the differences between ORVR-equipped and non-ORVR-equipped vehicles, and the fact that both types of vehicles are in regular use, fuel dispensing systems must be designed to detect and accommodate different vapor recovery requirements.  
           [0005]    One such fuel dispensing system employs the Healy 800 Nozzle, from Healy Systems, Inc., of Hudson, N.H., assignee of the present application, which is embodied in my earlier U.S. Pat. No. 6,095,204, issued Aug. 1, 2000, the complete disclosure of which is incorporated herein by reference. However, during ongoing field-testing of the Healy 800 Nozzle for purposes of addressing a need to prevent return of too much air when refueling ORVR-equipped vehicles, a troubling phenomenon has been uncovered. A feature of the Healy 800 Nozzle is that it reduces the volume of air returned to the underground storage tank to approximately 25% of the liquid volume dispensed to an ORVR-equipped vehicle. It has been discovered that this can create a problem in a busy service station because ORVR refueling can cause the vapor space pressure to fall to −8.0 inches W.C. (“water column”), at which point the UST pressure/vacuum relief vent valve will open, thus introducing air into the UST. For example, calculations show that less than 600 gallons of gasoline dispensed to ORVR-equipped vehicles can reduce the UST pressure by +8.0 inches W.C. when the ullage space is 20,000 gallons. Additional fueling of ORVR-equipped vehicles beyond that point will then result in a one-to-one relationship of air returned to the UST versus liquid gasoline dispensed, as the Healy 800 Nozzle will continue to return air at a 25% rate while the pressure/vacuum relief vent valve will continue to reopen to allow inward air flow equal to 75% of the liquid gasoline dispensed. Later, when sales activity slows down in the evening and refueling of ORVR-equipped vehicles drops off, the large quantity of air previously ingested will promote evaporation of liquid gasoline into the air in the ullage space, as the enclosed system of gas and liquid moves toward an equilibrium of hydrocarbon concentration in the ullage space with the volume of liquid gasoline. The increasing concentration of gasoline vapor will cause the pressure in the UST to rise, potentially to a positive pressure of +3.0 inches W.C., which will cause the pressure/vacuum relief vent valve to reopen, releasing gasoline vapor into the environment. The problem is not apparent for service stations pumping an average of less than about 150,000 gallons per month; however, it can be very pronounced for larger sites, e.g. those that pump an average over about 500,000 gallons per month.  
         SUMMARY  
         [0006]    According to one aspect of the invention, a passive pressure control method for controlling pressure in ullage vapor space of a volatile liquid fuel underground storage tank (“UST”) comprises the steps of: removing liquid fuel from the UST, including for delivery into a vehicle fuel tank, delivering into the ullage vapor space of the UST, to replace the volume of liquid fuel removed, a gaseous flow comprising at least one of: (a) fuel vapor and air, e.g. displaced from the fuel tank by delivery of the liquid fuel; and (b) air; and, during periods of increasing ullage vapor space pressure, allowing vapor to flow into an auxiliary vapor space of variable volume defined at least in part by a resilient wall member, the flow of vapor into the auxiliary vapor space causing deflection of the resilient wall member, thereby increasing the combined vapor storage volume of the ullage vapor space and the auxiliary vapor space.  
           [0007]    Preferred embodiments of this aspect of the invention may include one or more of the following additional features. The passive pressure control method comprises the further step of, during periods of decreasing ullage vapor space pressure, causing vapor to flow from the auxiliary vapor space under pressure of deflection of the resilient wall member. The passive pressure control method comprises the further step of treating the gaseous flow into the ullage vapor space to increase the concentration of fuel vapor in the gaseous flow, including toward saturation.  
           [0008]    According to another aspect of the invention, a passive pressure control system for controlling pressure in the ullage vapor space of a volatile liquid fuel underground storage tank (“UST”) comprises means for temporarily, during periods of increasing ullage vapor space pressure, allowing vapor to flow into an auxiliary vapor space of variable volume, defined at least in part by a resilient wall member.  
           [0009]    Preferred embodiments of this aspect of the invention may include one or more of the following additional features. The passive pressure control system further comprises means for temporarily, during periods of decreasing UST vapor space pressure, causing flow of vapor from the auxiliary vapor space into the ullage vapor space. The passive pressure control system further comprises means for treating a gaseous flow into the ullage vapor space in a manner to increase the fuel vapor concentration of the gaseous flow, including toward saturation.  
           [0010]    According to still another aspect of the invention, a passive pressure control system for controlling pressure in the ullage vapor space of a volatile liquid fuel underground storage tank (“UST”) comprises an underground storage tank defining a storage volume for storage of volatile liquid fuel with an ullage vapor space, an auxiliary tank defining an auxiliary vapor space in communication with the ullage vapor space, the auxiliary vapor space defined at least in part by a resilient wall member, the resilient wall member being adapted to deflect from an at-rest position in response to increasing vapor pressure in the auxiliary vapor space, thereby to increase the contained effective vapor storage volume of the auxiliary vapor space, and the resilient wall being adapted to return toward the at-rest position in response to decreasing vapor pressure in the auxiliary vapor space, thereby to decrease the contained effective vapor storage volume of the auxiliary vapor space.  
           [0011]    Preferred embodiments of this aspect of the invention may include one or more of the following additional features. Deflection of the resilient wall member from the at-rest position in response to increasing pressure in the auxiliary vapor space increases the combined contained effective vapor storage volume of the ullage vapor space and the auxiliary vapor space, allowing vapor to flow from the ullage vapor space into the auxiliary vapor space. Return of the resilient wall member toward the at-rest position in response to decreasing pressure in the auxiliary vapor space decreases the combined contained effective vapor storage volume of the ullage vapor space and the auxiliary vapor space, causing vapor to flow from the auxiliary vapor space toward the ullage vapor space. The passive pressure control system further comprises a pressure relief vent valve in communication with the ullage vapor space and configured to open while pressure of vapor within the ullage vapor space exceeds a predetermined maximum pressure, thereby to permit release of vapor into the environment, wherein deflection of the resilient wall member of the auxiliary vapor space from the at-rest position in response to increasing pressure within the auxiliary vapor space serves to reduce the volume of vapor released to the atmosphere during normal operation. The passive pressure control system further comprises a vacuum pressure relief vent valve in communication with the ullage vapor space and configured to open while pressure of vapor within the ullage vapor space is below a predetermined minimum pressure, thereby to permit ingestion of air into the ullage vapor space, wherein return of the resilient wall member of the auxiliary vapor space toward the at-rest position in response to decreasing pressure within the auxiliary vapor space serves to reduce the volume of air ingested into the vapor space during normal operation. The auxiliary tank comprises a flexible bladder, e.g. a thin wall flexible urethane bladder, defining the resilient wall member. The bladder is disposed within a storage tank, preferably mounted about an inlet defined at an upper end of the storage tank. The vacuum relief vent valve defines an orifice sized to limit flow of air into the auxiliary vapor space at a predetermined rate, thereby to limit rise of ullage vapor space pressure due to ingestion of excessive volumes of air. The vacuum relief vent valve defines an orifice sized to limit flow of air into the auxiliary vapor space to a ratio of about 2.5 gallons per minute. For use with a balance-type vapor recovery system, the vacuum relief vent valve is set to near atmospheric pressure and the pressure relief vent valve is set to near atmospheric pressure.  
           [0012]    In preferred embodiments of each of the aspects of the invention described above, the gaseous flow may be treated or conditioned, e.g. by passing it through a liquid fuel mist chamber or through a fuel-wetted mesh, or by causing the gaseous flow to maintain extended flowing contact with liquid-gasoline-wetted surfaces, or by placing the gaseous flow in extended, close proximity or contact with liquid gasoline, e.g. by entraining the gaseous flow with a flow of liquid gasoline and/or by bubbling the gaseous flow through a body of liquid gasoline, e.g. in a liquid reservoir or in the UST itself. Controls may be provided, e.g., to actuate delivery of liquid fuel to the conditioning apparatus when gaseous flow is detected, and/or to ensure that the vacuum/pressure relief valve is not opened for flow of air until a flow of liquid fuel to the conditioning apparatus is confirmed. Effective vapor storage volume may also be increased by removal of vapor from the vapor space, e.g. for treatment.  
           [0013]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0014]    [0014]FIG. 1 is a somewhat diagrammatic representation of a typical prior art fuel storage and delivery system.  
         [0015]    [0015]FIG. 2 is a somewhat diagrammatic side section view of a passive pressure control system for temporary storage of vapor from the UST vapor space, e.g., during periods of increased pressure, including a tank containing a bladder; and  
         [0016]    [0016]FIG. 3 is a somewhat diagrammatic enlarged side section view of the bladder support assembly for the passive pressure control system of FIG. 2. 
     
    
       [0017]    Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0018]    Referring to FIG. 1, in a typical prior art fuel storage and delivery system  10 , e.g. at a gasoline fueling station, S, an underground storage tank (“UST”)  12  contains a volume of volatile liquid fuel  14 , e.g. gasoline, and a volume of a saturated or semi-saturated mixture of gaseous fuel vapor and/or air  16  in a vapor or ullage space, U, above the liquid fuel. The ullage space is connected to the atmosphere via conduit  20 , controlled by a UST pressure/vacuum relief vent valve  22 , which typically is set to open at −8.0 inches W.C. to permit intake of air into the ullage space and to open at +3.0 inches W.C. to permit release of gaseous vapor from the ullage space, thereby to avoid dangerous buildup of pressure or vacuum within the UST  12 .  
         [0019]    During refueling of a vehicle, C, as liquid fuel, L, is delivered via conduit  27  from the UST  12  into the vehicle tank  28 , fuel vapor, V, displaced from the vehicle tank by the liquid fuel is recovered (typically in a mixture with air) by vacuum drawn by pump  30  in the fuel dispenser  26  and returned to the ullage space, U, via conduit  32 . If the vehicle, C, is an ORVR-equipped vehicle, the vacuum return is set at a relatively lower volume ratio of air ingested to liquid removed for delivery into the vehicle tank, e.g. at a volume ratio of about 0.26 to 1.00 (air to liquid).  
         [0020]    Referring now to FIGS. 2 and 3, the phenomena of increasing pressure in the ullage space, U, during off-peak, evening hours, due to the enclosed system of evaporation of liquid gasoline  14  into the ullage space, U, as the system of vapor  16  and liquid  14  moves toward an equilibrium state, is addressed by a passive pressure control system  40 . The system includes a storage tank  42 , e.g. a 400 gallon steel storage tank, connected to the vent pipe  20 , which, in turn, is in communication with the vapor space, U, of a UST  12  (FIG. 1). The vapor space is controlled by the pressure/vacuum relief valve  22  set to open to ingest air into the ullage space, U, in response to vapor space vacuum below −8 inches W.C., and to open to release vapor from the ullage space, U, in response to vapor space pressure over +3 inches W.C. The storage tank  42  contains a thin wall flexible urethane bladder  44  defining an auxiliary vapor space volume  46  in communication with the UST vapor space, U. The flexible bladder  44  and the storage tank wall  48  also together define an air space  50  in communication with the atmosphere through an air relief/air ingestion valve  52  set to open at +¾ inch W.C. to release air from the air space  50  and to open at −¾ inch W.C. to ingest air into the air space  50 , as described in more detail below. This is a passive system not requiring electrical components. As a result, installation costs are relatively low.  
         [0021]    In FIG. 2, the tank  42  is shown mounted in vertical position upon a concrete tank slab  66  (other suitable methods for installation and mounting may be employed). The flexible bladder  44  is suspended within the air space volume  50  of the tank  42  from the bladder support assembly  68  (FIG. 3). The support assembly includes a flange  70 , secured to neck  71  at an aperture  72  into the tank volume by bolts  98  with lock washers  100  and nuts  102 , sealed by o-rings  103 , from which extends a pipe nipple  74  supporting a circumferential bladder flange  76 . A clamp ring  78  bolted ( 79 ) to the bladder flange secures and seals the bladder opening. A tap  80  defines an inlet/outlet  81  to a first, axial vapor passageway  83  into the bladder volume  46  by way of pipe nipple  82  terminating in a pipe barb  84  and a siphon tube  85  that extends to the lower end of the bladder  44  within the tank  42 . A tee-fitting  86  (to which tap  80  is mounted) defines an inlet/outlet  87  to a second, annular passageway  88  through the space between coupling  90  and pipe nipple  74  and the outer wall of pipe nipple  82 . The inlet/outlets  81 ,  87 , as well as condensate drain  92  from the base of the tank air space  50 , are connected to vent pipes  20  by 1-inch connection piping  94 . Flow through the connection piping  94  is controlled by ball valves  95 , which should be padlock-secured against tampering. The air relief/air ingestion valve  52  is connected to a pipe nipple  53  (FIG. 2) mounted to the flange  70  at an aperture  96  in communication with the air space  50  about the bladder  44  in tank  42 .  
         [0022]    When the service station, S, is actively refueling ORVR-equipped vehicles, C, the Healy 800 Nozzle, N, reduces the volume of air returned to the UST  12  to approximately 25% of the delivered gas volume. This shortfall causes vapor pressure in the UST to go negative. At −¾ inch W.C., the ±¾ inch W.C. air relief/air ingestion valve  52  opens to ingest air into the space  50  between the 400-gallon steel tank  42  and the flexible bladder  44 , thus causing the internal volume of the bladder  44  to be transferred into the vapor space, U, of the UST  12 . This transfer will continue as long as the −¾ inch W.C. pressure is maintained, and until the bladder  44  is fully collapsed. The vapor space pressure may then continue to drop until reaching −8 inches W.C., at which point the pressure vacuum relief valve  22  will open to allow air to enter the ullage space, U.  
         [0023]    When the gasoline service station activity slows down and/or when the station closes for the night, the UST pressure will begin to rise as the system of vapor  16  and liquid gasoline  14  in the ullage space, U, moves toward equilibrium, with liquid gasoline in the UST  12  changing to vapor. At +¾ inch W.C., the air relief/air ingestion valve  52  will open to release air from the space  50  between the wall  48  of the 400-gallon steel tank  42  and the bladder  44 , allowing the bladder to expand as it receives vapor  16  from the UST vapor space, U, thus to maintain the UST vapor space pressure at a maximum pressure of +¾ inch W.C. After the flexible bladder  44  is fully expanded, with most or all of the air expelled from the air space  50 , the vapor space pressure may continue to rise until reaching +3 inches W.C., at which point the pressure vacuum relief valve  22  will open for release of vapor  16  from the ullage space, U. The storage tank  42  thus provides an additional capacity of 400 gallons for receiving vapor before the relief valve  22  is caused to open.  
         [0024]    The system  40  can also act to limit the rise of UST vapor space pressure due to ingestion of excessive volumes of air when a faulty Stage I fuel drop occurs. For example, the air relief valve portion of the air relief/air ingestion valve  52  valve may be provided with an orifice sized to limit flow of air into the bladder  44 , e.g. to a rate of 2.5 gallons per minute, when the UST vapor space pressure, U, is at +3 inches W.C., causing the P/V vent valve  22  to expel relatively large amounts of excess volume and thus preserve available bladder volume for use in reducing the UST vapor space pressure to +¾ inch W.C. when the fuel drop is completed.  
         [0025]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the passive pressure control system  40  described above may be used in combination with a gaseous flow conditioning apparatus for treatment of air return/air intake to the ullage space, U, of the UST  12  to increase the degree of saturation of the gaseous flow. Several embodiments of suitable gaseous flow conditioning apparatus are described in my earlier-filed provisional applications (Serial No. 60/347,698, filed Jan. 11, 2002; Serial No. 60/364,745, filed Mar. 15, 2002; and Serial No. 60/387,458, filed Jun. 10, 2002), all as mentioned and incorporated above.  
         [0026]    The system  40  may also be employed to control UST vapor space pressure with so-called “balance-type” vapor recovery systems by suitably reducing the air ingestion control portion of the air relief/air ingestion valve  52 , e g. from −¾ inch W.C. to near atmospheric pressure, and also suitably reducing the air relief control portion of the air relief/air ingestion valve  52 , e.g. from +¾ inch W.C. to near atmospheric pressure. The system  40  may also be employed without control of a functioning air relief/air ingestion valve  52 , e.g. in “real world” situations of tank systems  10  having significant air leakage.  
         [0027]    The system  40  may also be installed on top of the gasoline service station canopy ( 60 , FIG. 1) using a horizontal tank  62 , with the 1-inch vapor space connection (not shown) made to existing vapor return piping  32 .  
         [0028]    Accordingly, other embodiments are within the scope of the following claims.