Abstract:
A system and method for removing, compressing, and storing excess air and vapors from a fuel dispensing facility fuel storage containment system during periods of over-pressurization without venting or processing the excess air and vapors. The stored air and vapors are subsequently returned back to the containment system during periods of under-pressurization that typically occur diurnally during periods of high fueling activity. The system may be used to compliment an ORVR compatible dispensing system that typically encounters over-pressurization problems when low or no refueling activity is occurring.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional patent application Ser. No. 60/361,352, filed on Mar. 5, 2002. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus and method for reducing volatile organic hydrocarbon (VOC) environmental pollution by controlling excess pressure in liquid fuel storage containment systems at gasoline dispensing facilities. 
     BACKGROUND OF THE INVENTION 
     Fuel storage containment systems at gasoline dispensing facilities (GDF&#39;s) (i.e. gasoline stations) suffer from over-pressurization caused by fuel vaporization and thermal expansion, especially with high volatility wintertime fuels. Over-pressurization can be the cause of polluting gaseous emissions of fuel components to the atmosphere, soil, and groundwater because the various parts of fuel storage containment systems at GDF&#39;s are rarely, if at all, perfectly tight. Most often leakage can occur through fueling nozzle valves, fittings, pipe junctions, relief valves, and seals. The problem can be exacerbated by the recent and ongoing proliferation of vehicles equipped with on-board refueling vapor recovery (ORVR) systems which can cause some types of existing fuel dispensers with vapor recovery capability to ingest excess air during vehicle refueling, thereby promoting more evaporation and pressurization in the containment system. 
     The problem is substantially reduced for fuel dispensers equipped with passive “balance” type vapor recovery systems. In this case, air and vapor ingestion is significantly restricted by the combination of a nozzle to vehicle fill pipe seal which exists during dispensing and the ORVR equipped vehicle vapor seal which exists within the ORVR system, thereby preventing return vapor or air flow back into the fueling nozzle and, therefore, the fuel storage containment system. Under these conditions liquid fuel is dispensed (removed) from the containment system and little or no fuel vapor or air is returned to the containment system so the vapor space increases without a corresponding increase in vapor and air mass. Therefore the pressure in the system tends to be reduced. This substantially alleviates the over-pressurization problem in the containment system. But when no or only a few ORVR vehicles are refueled over many hours, for instance, as typically can occur during nighttime at a GDF, the containment system can still become over pressurized as described above. 
     The problem is more severe for dispensers equipped with active “vacuum assist” type vapor recovery systems. In this case, when ORVR vehicles are refueled, there is no seal between the nozzle and the vehicle fill pipe. A dispenser vacuum pump creates a vacuum at the nozzle to draw in fuel vapors which, for non-ORVR vehicle refuelings, are normally expelled from the vehicle&#39;s tank. But for ORVR vehicle refuelings, vapors are not expelled from the vehicle. Therefore, ambient air is ingested into the fuel storage containment system in place of fuel-rich vapors. This air is returned by the vacuum pump and vapor piping to the containment system tank(s). The returned air promotes excessive liquid fuel vaporization within the tank(s), resulting in over-pressurization of the system. One improvement which can reduce this problem is disclosed in U.S. Pat. No. 5,782,275, Jul. 21, 1998, “Onboard Vapor Recovery Detection”, Gilbarco, Inc. Another is disclosed in U.S. patent application Ser. No. 2002/0000258 A1, Jan. 3, 2002, “Dispenser with Radio Frequency On-Board Vapor Recovery Identification”, Dresser Inc. This apparatus senses the absence of fuel vapors during refueling and shuts off the vacuum pump while refueling ORVR equipped vehicles. This significantly reduces the amount of air and residual vapors returned to the containment system during refueling. Therefore, an ORVR detection equipped vacuum assist dispenser affects the containment system in a similar manner as a balance type dispensing system, significantly reducing the over-pressurization problem. 
     Various other means have been disclosed in patents and are used in practice to effect similar outcomes in order to handle ORVR equipped vehicles without causing excessive over-pressurization of the fuel storage containment system. All of these types of apparatus and methods are considered to be various types of “ORVR compatible” systems. 
     But all of these systems suffer from a common problem. When there is little or no refueling activity, evaporation and thermal expansion can still occur, causing over-pressurization and subsequent slow leakage of polluting containments into the environment. The California Air Resources Board (CARB) has promulgated regulations addressing this general problem. The regulations appear under the general title of Enhanced Vapor Recovery (EVR) system requirements. In part, they require that the containment system pressures remain below certain levels relative to ambient atmospheric pressure to limit the amount of slow leakage of pollutants into the environment. 
     An existing solution to the problem is to add a “vapor processor” onto the containment system to remove excess air from the containment system (“membrane separators”) or excess fuel vapors and air (“combustion systems”). But these methods are generally intended as high capacity, primary systems with capability beyond the needs of this residual over-pressurization problem and are expensive, complicated, and of limited reliability. They also emit low levels of pollution themselves during normal operation and have the potential to emit high levels of pollution under failure mode conditions. An example of such a device is shown in U.S. Pat. No. 5,985,002, Nov. 16, 1999, “Fuel Storage System with Vent Filter Assembly”. 
     The disclosed invention solves this residual over-pressurization problem for ORVR compatible, vapor recovery dispensing systems by controlling and limiting excess containment system pressures during periods of low fueling activity. It does this in a simple, low cost, reliable manner and in normal operation, no pollutants are emitted by the apparatus. It is applicable to all the types of vapor recovery equipped dispensing systems described above. 
     OBJECT OF THE INVENTION 
     It is therefore an object of the present invention to provide a method and system for reducing excess positive pressure relative to ambient atmospheric pressure at a fueling facility for the purpose of reducing fuel storage containment system leakage of VOC&#39;s which are a type of air, soil, and groundwater pollution. 
     It is another object of the present invention to provide a method and system for compressing and storing in a small pressure vessel, excess vapor and air from a fuel storage containment system during limited periods of low or no refueling activity when fuel evaporation and thermal expansion are likely to raise the pressure in the containment system above ambient atmospheric pressure. 
     It is yet another object of the present invention to provide a method and system to take advantage of normally occurring periods of decreasing pressure in fuel storage containment system at a GDF with ORVR compatible dispensers by returning stored liquid and/or vapor and air back into the containment system without causing excessive positive pressures in the system. 
     It is still another object of the present invention to provide a method and system for reducing excess positive pressure relative to ambient atmospheric pressure within a fuel storage containment system at a GDF by using a compressor and storage system which emits no VOC pollution itself. 
     It is still a further object of the present invention to provide a low cost and reliable method and system for reducing excess positive pressure within a fuel storage containment system at a GDF with ORVR compatible dispensers by providing just enough capacity and capability to handle the very limited amounts of excess vapor which are slowly generated in such systems. 
     SUMMARY OF THE INVENTION 
     The invention provides a way to temporarily remove, compress, and store excess air and vapors from a GDF fuel storage containment system during periods of over-pressurization without venting or processing them. The system then returns the stored air and vapors back to the containment system during periods of under-pressurization which typically occur diurnally during periods of high fueling activity. It may be used to compliment an ORVR compatible dispensing system by providing a remedy to the low—or no—refueling activity period over-pressurization problem; however, the system can be used in systems that are not ORVR compatible or compliant. 
     In ORVR compatible systems, the invention relies on the ORVR compatible characteristics of the dispensing system, which produce low-pressure conditions during periods of high vehicle refueling activity so that it may periodically return the stored air and vapors without causing over-pressurization of the containment system. 
     Since a typical GDF fuel storage containment system with high volatility fuels operates in an over-pressure (nighttime), under-pressure (daytime) diurnal cycle, the removal of vapor and air mixture during the over-pressure portions of the cycle and return of mixture during the under-pressure portion of the cycle solves the over-pressure problem. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: 
         FIG. 1  is a schematic view of a fuel dispensing and fuel storage containment system with vapor recovery dispensers and a pressure controlling apparatus in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic view of a pressure controlling apparatus showing components of the apparatus in accordance with an embodiment of the present invention; 
         FIG. 3A  is a flowchart diagram of the operation of one embodiment of the invention; and 
         FIG. 3B  is a flowchart diagram that is an extension of the flowchart diagram in FIG.  3 A. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the invention is described in connection with  FIG. 1 , which shows a fuel dispensing and fuel storage containment system with a vapor recovery dispenser and a pressure controlling apparatus  500  for use in a liquid fuel gasoline dispensing facility  10  (GDF). The GDF  10  may include a station house  100 , one or more fuel dispenser units  200 , a fuel storage containment system  300 , means for connecting the dispenser units  200  to the main fuel storage system  400 , and a pressure controlling apparatus  500 . The main fuel storage system  400  can be used interchangeably with fuel storage containment system  300  for the purpose of measuring pressure as described for the present invention since the vapor return pipe  410  is fluidly coupled to the fuel storage containment system  300 . 
     The fuel dispenser units  200  may be provided in the form of conventional “gas pumps.” Each fuel dispenser unit  200  may include one or more fuel dispensing points typically defined by the nozzles  210  and hoses  212 . The fuel dispenser units  200  may include one hose  212 , one coaxial vapor/liquid splitter  260 , one vapor return passage  220 , and one fuel supply passage  230  per nozzle  210 . 
     The vapor return passages  220  may be joined together before connecting with a common vapor return pipe  410 . The vapor return passages  220  may optionally include a single vacuum assist pump  250  per dispensing point. Vapor recovery dispensers  200  with vacuum assist pumps  250  are typically called “vacuum assist dispensers”. Vapor recovery dispensers  200  without vacuum assist pumps  250  are typically called “balance dispensers”. 
     When the vapor return passages  220  include optional vacuum assist pumps  250 , they may also optionally include a single On-board Refueling Vapor Recovery (ORVR) vehicle detection device  240  per dispensing point. Each detection device  240  may be electrically connected to a vacuum assist pump  250  by an electrical connector  242 . The detection device  240  controls the vacuum assist pump  250  by deactivating it during vehicle refueling activity when an ORVR vehicle is detected by the detection device  240 . The purpose of this detection and control is described below. 
     The fuel storage containment system  300  may include one or more fuel storage tanks  310 . It is appreciated that the storage tanks  310  may typically be provided underground; however, underground placement of the tank is not required for application of the invention. It is also appreciated that the storage tank  310  shown in  FIG. 1  may represent a grouping of multiple storage tanks tied together into a storage tank network. Each storage tank  310 , or a grouping of storage tanks, may be connected to the atmosphere by a vent pipe  320 . The vent pipe  320  may terminate in a pressure relief valve  330 . 
     A basic premise of the system  10  is that it includes a vapor storage system  550  which is the operative part of the pressure controlling apparatus  500  connected with a single pipe  555  to the vent pipe  320  intermediate of the storage tank  310  and the pressure relief valve  330 . A pressure sensor  520  which is also part of the pressure controlling apparatus  500  may be operatively connected to the vent pipe  320 . Alternately, it may be connected directly to the storage tank  310  or the vapor return pipe  410  below or near to the dispenser  200  since the pressure is normally substantially the same at all these points in the vapor containment system. 
     A controller  510  which is also part of the pressure controlling apparatus  500  may be located in the station house  100  or alternatively (not shown) in or near the vapor storage system  550  housing. The controller  510  may be a tank monitoring device, such as the Veeder-Root TLS-350, or may be a point-of-sale controller, such as the G-Site® manufactured by Gilbarco Inc. The controller  510  may be electrically connected to the pressure sensor  520  by an electrical connector  522  and may be electrically connected to the vapor storage system  550  by electrical connectors  562  and  572 . 
     The storage tank  310  may also include a fill pipe and fill tube  370  to provide a means to fill the storage tank  310  with fuel and a submersible pump  380  to supply the dispensers  200  with fuel from the storage tank  310 . 
     The means for connecting the dispenser units  200  and the fuel storage containment system  400  may include one or more vapor return pipelines  410  and one or more fuel supply pipelines  420 . The vapor return pipelines  410  and the fuel supply pipelines  420  are connected to the vapor return passages  220  and fuel supply passages  230 , respectively, associated with multiple fuel dispensing points  210 . As such, a “vapor return pipeline” designates any return pipeline that carries the return vapor of two or more vapor return passages  220 . 
     Operation of the pressure controller apparatus  500  is described in connection with  FIG. 2 , which shows the components of the vapor storage system  550 . The flowchart diagrams in  FIGS. 3A and 3B  show the operation of the controller  510  in connection with the components of the vapor storage system  550  illustrated in FIG.  2 . 
     Turning to the flowchart diagrams in  FIGS. 3A and 3B  with respect to  FIG. 2 , the process starts (step  1000 ), and the controller  510  frequently and periodically measures containment system  300  pressure relative to ambient atmospheric pressure using a pressure sensor  520  (step  1002 ). Under conditions of low or no dispensing activity, and with high volatility fuels, fuel storage containment systems  300  will generally experience slowly rising pressures due to evaporation and/or thermal expansion of vapors. When this occurs and the pressure exceeds a first predetermined threshold of approximately +0.6 inches of water column (″wc), the controller  510 , which may be electrically connected to a compressor pump  560  motor by an electrical connector  562 , activates the compressor pump  560  motor (decision  1004 ). The pump  560  draws the vapor and air mixture from the containment system  300  via a single connecting pipe  555  (step  1006 ). The single connecting pipe  555  may be connected to any convenient point of the containment system  300  with access to the vapor space including a vent pipe  320 , a tank access port in the tank  310 , vapor space manifold piping  410  between multiple tanks  310 , return vapor piping  410  from the dispenser(s)  200 , or vapor return piping  220  within a dispenser  200 . 
     The pump  560  compresses the vapor and air mixture from the containment system  300  and feeds the compressed mixture into a small pressure storage vessel  590  of approximately 1 or 2 cubic feet (cu-ft) capacity (step  1008 ). As the mixture is drawn from the containment system  300 , the pressure in the system will typically drop. When the pressure, as measured by the pressure sensor  520 , drops below a second predetermined threshold of approximately +0.2″ wc (decision  1010 ), the controller  510 , which is electrically connected to the compressor pump  560  motor by the electrical connector  562 , deactivates the compressor pump  560  motor (step  1012 ). The compressed mixture remains temporarily stored within the pressure storage vessel  590  at high pressure up to approximately 100 or 200 or more pounds per square inch (psi). If the compressor pump  560  does not include an inherent means to prevent back flow at high pressure, an optional check valve  565  may be added in series with the pump  560  to prevent back flow through the pump  560  while it is off. 
     The process of compressing the vapor and air mixture may cause some condensation of vapor into a liquid state. In this case both vapor and liquid are pumped into the storage vessel  590 . 
     ORVR compatible dispensers  200  will generally produce low pressure conditions in the containment system  300  during periods of high vehicle refueling activity. When this occurs and the fuel storage containment system  300  pressure drops below a third predetermined threshold of approximately −0.6″ wc (decision  1014  from FIG.  3 B), the controller  510 , connected to a solenoid operated drain valve  570  by an electrical connector  572 , activates the drain valve  570  which bypasses the compressor pump  560  and allows controlled return flow of stored liquid and/or vapor from the pressure storage vessel  590  back into the containment system  300  via the single connecting pipe  555  (step  1016 ). The flow is driven by the difference in pressure between the storage vessel  590  and the containment system  300 . 
     Since some liquid fuel may be present at the bottom of the storage vessel  590 , the vessel  590  is drained from the bottom rather than the top to allow its return in a liquid state. This can be effected by mounting the vessel  590  with the entry port at the bottom, or by using a fill/drain tube within the vessel (not shown), or other means. The storage and return process capacity is improved for a given vessel  590  size and working pressure limit by allowing the liquid to return to the containment system  300  in liquid rather than vapor form, which would take up much more space. Porting from the vessel  590  top would allow complete evaporation of the liquid as the pressure drops back near ambient atmospheric pressure levels. Some evaporation may occur even when liquid is fed to the drain valve  570 , depending upon the stored liquid temperature, due to the large pressure drop which occurs when the liquid is returned to the containment system  300 . 
     An optional pressure regulator  575  can be included in the drain piping in series with the drain valve  570  to regulate and limit the pressure of the draining liquid and/or vapor to prevent excessive pressures in the single connecting pipe  555  and any part of the fuel storage containment system  300  during the draining period. 
     When or if the fuel storage containment system  300  pressure increases above a fourth predetermined threshold of approximately −0.2″ wc (decision  1018 ), the controller  510  deactivates the solenoid operated drain valve  570  which halts the flow of liquid or vapor and air back into the containment system  300 , preventing further increase in containment system  300  pressure and leaving it at a reasonably low level (step  1020 ). Additionally, since the storage vessel  590  may drain completely before the containment system  300  pressure reaches the fourth threshold, a predetermined timeout is implemented in the controller  510  to also deactivate the drain valve  570 . Alternately, an optional second pressure sensor (not shown) can be used by the controller  300  to measure the storage vessel  300  pressure and shut off the drain valve  570  when pressure reaches a lower threshold signifying an empty vessel  590 . 
     An over-pressure safety shutoff switch  580 , which may be connected to the compressor pump  560  motor by an electrical connector  582 , senses pressure within the high pressure side of the piping between pump  560  (or if present, optional check valve  565 ) and drain valve  570  and storage vessel  590 . If or when the pressure exceeds a predetermined upper working limit, the safety shutoff switch  580  opens, which by means of the electrical connector  582 , disconnects power from the compressor pump  560  motor which deactivates the pump  560  preventing excessive pressure from building up inside the storage vessel  590  and related components. Although safety shutoff defeats use of the apparatus  500  in keeping containment system  300  pressures from exceeding the first pressure threshold limit, it is expected that this is a rare and abnormal condition which will not materially affect long term averages of positive containment system  300  pressures. Since CARB requirements are generally based on weekly or monthly long-term averages, no adverse consequences will likely occur. 
     Since fuel vapor and air mixtures pose a flammability safety hazard, all the electrical components, including compressor pump  560  motor, solenoid activated drain valve  570 , pressure sensor  520 , pressure switch  580 , and associated electrical connectors,  582 ,  522 ,  562 ,  572  are designed as either intrinsically safe circuits and devices or are enclosed in explosion proof housings as appropriate to ensure safety. 
     The capacity of the pressure storage vessel  590  and the maximum working pressure capability of the vessel  590  and other components  560 ,  565 ,  580 ,  570  of the vapor storage system  550  determine the maximum volume of vapor and air mixture which may be removed from the containment system  300  during any one over-pressure, under-pressure cycle of the containment system  300 . For instance, if the vessel  590  capacity is 1 cu-ft and maximum working pressure capability of the components is 150 psi (about 10 atmospheres), then up to about 10 cu-ft of vapor and air mixture can be removed from the containment system  300  before some or all of the compressed mixture must be retuned to the system  300 . Based on measurements taken from multiple GDF fuel storage containment systems  300  over long periods of time, the maximum volume of vapor and air mixture which must be removed from the systems  300  to remain within CARB required pressure limits is approximately 10 or 20 cu-ft. Since some of the fuel vapor may be reduced to liquid form, actual storage capacity will be larger than that described in the above example. 
     Also, the storage system  550  piping, fittings, and structural members may be arranged in such a manner as to provide easy add-on connection means to connect and mount additional pressure storage vessels  590  so that storage capacity may be increased if needed at any particular GDF. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the construction and configuration of the foregoing embodiments of the invention without departing from the scope or spirit of the invention. For example, the specific pressures disclosed for triggering the operation of the pressure controller apparatus  500  may be varied without departing from the intended scope of the invention. Furthermore, the size, shape, location, capacity, powering, and monitoring of the pressure controller apparatus  500  may be varied without departing from the intended scope of the invention.