Abstract:
A vapor recovery and pressure management system for a vehicle refueling facility includes two rotary vane pumps and a hydrocarbon-stripping membrane between the pumps. One pump draws vapor from a storage tank as well as from refueling nozzles, while the other pump draws vapor from the membrane and discharges the vapor back into the tank. A controller controls both pumps to maintain a slight vacuum in the tank, thereby preventing leakage of hydrocarbons from the tank to the atmosphere. Clean air from the membrane is exhausted, preferably through a charcoal canister, and a hydrocarbon sensor monitors for the presence of undesirable hydrocarbons in the clean air exhaust. One or more liquid drop outs are provided for separating liquid from the hydrocarbon vapor and returning the liquid to the tank along with the vapor, preferably before the liquid is sent to the membrane, to thereby increase efficient fuel recovery and to protect the membrane from undesirable contact with liquid.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to filling stations, and more particularly to systems and methods for vapor recovery in filling stations and for managing pressure in storage tanks in filling stations. 
     BACKGROUND 
     As is familiar to drivers, filling stations typically enable people to dispense fuel from a storage tank (which can be buried underground) through nozzles that are inserted into the gas tanks of vehicles. As is also familiar, the nozzles often come equipped with boots, to trap otherwise polluting hydrocarbon vapors and thereby prevent the vapors from entering the atmosphere. The trapped vapors are then returned to the tank, i.e., are recovered, by a vapor recovery system. One such vapor recover system is disclosed in the present assignee&#39;s U.S. Pat. No. 5,484,000, incorporated herein by reference. 
     It happens that as vapor is returned to the tank, the pressure in the tank can become greater than atmospheric pressure. When this happens, pollutants can escape from the tank through small leaks. These leaks can be difficult to detect, particularly from underground storage tanks. 
     Accordingly, systems have been introduced to manage pressure in filling station storage tanks. One example of such a system is disclosed in Gilbarco&#39;s U.S. Pat. No. 5,464,466, incorporated herein by reference. In the Gilbarco system, a pump recirculates vapor from a storage tank through a membrane that separates clean air from hydrocarbon vapor, with clean air being exhausted to the atmosphere and hydrocarbon vapor being returned to the tank. The pump is operated to establish a desired pressure in the tank. 
     The present invention recognizes that several important improvements to the art can be made. First, the present invention recognizes that many commercial embodiments of pressure management systems require large, expensive compressors and/or vacuum pumps, some of which require three phase power. Three phase power, however, is not always readily available in many locations, and the size and expense of many pumps in use, and in particular positive displacement piston-type pumps, render such systems unduly complex and expensive to procure and maintain. As recognized herein, however, it is possible to provide a pressure management system that uses simple, inexpensive, yet effective pumps. 
     Another problem recognized by the present invention is that when membranes are used in existing systems, the membranes can be damaged by contact with liquid that might condense in the vapor lines. However, preventing formation of liquid in the vapor lines to promote membrane operation results in nothing but hydrocarbon vapor being returned to the storage tank. We have recognized that a disadvantage of returning only vapor to the storage tank is that the vapor is lost when the storage tank is accessed to refill the tank, an occurrence that can happen as frequently as twice a day in some locations. Understandably, filling stations operators would prefer to minimize the amount of fuel they lose as vapor, and environmentalists would likewise prefer to limit the amount of hydrocarbon vapors that escape from filling stations. Fortunately, we have recognized that is possible to both return liquid to storage tanks while preventing liquid from contacting membranes in the pressure management system. 
     Furthermore, we have recognized that is possible for membranes and other pressure management system components to fail, potentially leading to the release of hydrocarbons to the environment through the clean air exhaust line. Unfortunately, present systems do not seem to anticipate such failure and thus do not appear to provide for warning of such failure or for corrective action for such failure. We have recognized, however, that it is possible to address this shortcoming in an efficient and cost effective way. 
     SUMMARY OF THE INVENTION 
     A system is disclosed for managing pressure in a storage tank that contains hydrocarbons, with the system also returning vapor from fuel-dispensing nozzles that are in fluid communication with the tank. The system includes at least one vapor recovery system in fluid communication with the nozzles, and at least one pressure management system. The pressure management system includes at least one membrane that communicates with the vapor recovery system and the tank and that is arranged such that vapor from the vapor recovery system passes through the membrane before returning to the tank. The membrane separates hydrocarbon vapor from non-hydrocarbon vapor. 
     In a preferred embodiment, the pressure management system includes a clean air outlet and a hydrocarbon sensor communicating with the clean air outlet. Further, a charcoal canister can be in fluid communication with the clean air outlet to further cleanse air being discharged to the environment. 
     As disclosed in greater detail below, a pressure pump in the pressure management system has a suction in fluid communication with the tank and a discharge communicating with the membrane. A membrane assembly holds the membrane, and the membrane assembly communicates with the clean air outlet and a hydrocarbon outlet. A vacuum pump has a suction in communication with the hydrocarbon outlet and a discharge communicating with the tank. 
     The preferred pressure management system also includes at least one liquid drop out device communicating with the discharge of the pressure pump, the tank, and the membrane. If desired, a second liquid drop out device can be disposed in fluid communication with the discharge of the vacuum pump and the tank. A vapor blocker can be disposed between the first liquid drop out device and the tank for impeding vapor flow through the vapor blocker. 
     To manage pressure in the tank, a controller is electrically connected to at least one motor that actuates the pumps, and the controller selectively energizes the motor to establish a predetermined pressure range in the tank. When the charcoal canister mentioned above is provided, at least one solenoid valve communicates with the canister, and the controller selectively operates the valve or valves to establish forward air flow through the canister, wherein air from the membrane assembly flows through the canister to the clean air outlet. To backflush the canister, the controller operates the solenoid valve or valves to establish reverse air flow through the canister, wherein air flows through the canister to the tank to flush the canister. 
     In another aspect, a system is disclosed for managing pressure in a storage tank containing hydrocarbons. The system includes at least one pressure pump having a suction in communication with the tank, and the pressure pump also has a discharge. At least one membrane assembly includes at least one membrane communicating with the discharge of the pressure pump, with the membrane assembly also communicating with at least one clean air outlet and at least one hydrocarbon outlet. At least one vacuum pump has a suction in communication with the hydrocarbon outlet and a discharge communicating with the tank, and at least one hydrocarbon sensor is in fluid communication with the clean air outlet. 
     In still another aspect, a system for a vehicle refueling station having at least one storage tank and plural vehicle nozzles communicating therewith includes first and second rotary vane pumps. The first pump has a suction for receiving vapor from at least some of the nozzles. A membrane is between the pumps, and the membrane is in fluid communication with the pumps. At least one liquid drop out is in fluid communication with at least one of the pumps to reduce liquid contact with the membrane. 
     In yet another aspect, a pressure control system includes at least one membrane to control service station storage tank pressure. In accordance with the present invention, the system includes at least one clean air discharge of the membrane and at least one hydrocarbon sensor communicating with the clean air discharge for generating a failure signal when at least one predetermined concentration of hydrocarbons is present in the clean air discharge. 
     The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a high level block diagram of the present system; 
     FIG. 2 is a schematic piping diagram of the system; and 
     FIG. 3 is a flow chart showing the pump control logic. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to FIG. 1, a system is shown and generally designated  10  for managing pressure in a storage tank  12  that contains hydrocarbons, specifically petroleum-based fuel, and for returning to the tank  12  vapor from fuel-dispensing nozzles  14  that are in communication with the tank  12 . As shown, the system  10  includes a vapor recovery system  16  that is in communication with the nozzles  14 . In one preferred embodiment, the vapor recovery system  16  includes a vapor recovery pump  20 , also referred to as a “blower”, that is actuated by an electric, preferably single phase motor  22 , to which the pump  20  is coupled via a coupling represented by the line  24 . The vapor recovery pump can be a type GVR 313 pump made by Rotron. Also, the vapor recovery pump  20  is in fluid communication with the nozzles  14  via a fluid line  26 . Most vapor collected from the vehicle fuel tanks is returned to the tank  12  via a tank suction line  60 , described in further detail below. Excess vapor, on the other hand, is sent from the vapor recovery system  16  via a fluid line  28  to a pressure management system  30 , also described in further detail. As described below, the pressure management system  30  includes a membrane, not shown in FIG. 1 for clarity of disclosure but shown in FIG.  2 . 
     The pressure management system  30  preferably includes a pressure pump  32 , also referred to as a “compressor”, and a vacuum pump  34 . In the preferred embodiment, both the pressure pump  32  and vacuum pump  34  are identical type E10rotary vane pumps made by Blackmer, and both pumps  32 ,  34  are actuated by one single phase ac two horsepower motor  36 . In FIG. 1, the couplings between the motor  36  and pumps  32 ,  34  are represented by the lines  38 ,  40 , respectively. The couplings can be belt drive mechanisms known in the art. 
     As described further below, the pressure and vacuum pumps  32 ,  34  respectively push and pull vapor through a membrane that separates clean air from hydrocarbon vapor. The clean air is exhausted to atmosphere through a clean air outlet  42 , whereas the hydrocarbon vapor is returned to the tank  12  through a hydrocarbon return line  44 . With the above introductory disclosure in mind, the skilled artisan will appreciate that excess vapor from the vapor recovery system  16  passes through the membrane in the pressure management system  30  before returning to the tank  12 . 
     As also discussed further below, the pressure management system  30  can include one or more solenoid valves and one or more sensors, and the pump motors  22 ,  36  and solenoid valves are electrically connected to a controller  46 . In accordance with the detailed discussion below, the controller  46  is responsive to the system sensors for selectively energizing the motor  22  and for selectively actuating the solenoid valves. In one preferred embodiment, the controller  46  is implemented by discrete logic on a circuit board for undertaking the sequence of operations described below. It is to be understood, however, that the controller  46  can be a PC or other computer that is programmed with a software application to undertake the present logic. 
     Now referring to FIG. 2, in which fluid flow direction is indicated by various arrows, the vapor recovery pump  20  has a suction port  48  that communicates with the nozzles  14  to evacuate hydrocarbon vapor away from the nozzles  14 . A vapor recovery pressure switch or sensor  50  communicates with the suction port  48  of the vapor recovery pump  20  for generating an electrical signal that is sent to the controller  46 . The electrical signal is representative of the pressure at the suction port  48  of the vapor recovery pump  20 . When the signal indicates that the vapor recovery pump  20  is not functioning (e.g., when no vacuum exists at the suction  48 ), the controller  46  stops the motors  22 ,  36  and, if desired, activates an audible or visual alarm. 
     Hydrocarbon vapor is discharged through a discharge port  52  of the vapor recovery pump  20 . As shown in FIG. 2, the discharge port  52  of the vapor recovery pump  20  communicates with a suction port  54  of the pressure pump  32 . Additionally, a bypass line  56  establishes a separate path for fluid communication from near the suction port  48  of the vapor recovery pump  20  to near the discharge port  52  of the pump  20 , and a bypass element  58  partially occludes the bypass line  56 . In one preferred embodiment, the bypass element  58  is established by a vacuum regulator that includes a vertical pipe having a weight movably disposed therein, with the weight being movable to a closed position in which fluid communication through the bypass line  56  is blocked. When the vacuum at the suction port  48  of the vapor recovery pump  20  becomes sufficiently large, the weight lifts and allows vapor from the discharge port  52  to bypass the pump  20  and recirculate back to the suction port  48 . Alternatively, the element  58  can be established by an orifice plate having two quarter-inch diameter holes formed therein. In any case, the bypass element  58  is configured as appropriate to establish a desired constant air to liquid flow rate ratio (A/L) to promote efficient and effective operation of the membrane of the present invention. 
     Continuing with the description of the preferred piping system shown in FIG. 2, a tank suction line  60  establishes a path for fluid communication from the tank  12  to the suction  54  of the pressure pump  32  as shown. If desired, a tank suction line particulate filter  62  can be disposed in the suction line of the pressure pump  32  to filter particles out of the vapor from the tank  12  that is evacuated by the pressure pump  32 . In one preferred embodiment, the tank suction line particulate filter  62  is a particulate filter made by Cim-Tek Filtration. Also, for purposes to be shortly disclosed, a tank suction line three-way solenoid valve  64  is disposed in the tank suction line  60 , it being understood that the valve  64  is electrically connected to the controller  46 . During normal operation, the tank suction valve  64  is configured to establish communication between the suction line  60  and the pressure pump  32 , whereas during the below-described backflush procedure the suction valve  64  is configured to establish communication between the pressure pump  32  and a backflush return line  65 . 
     The pressure pump  32  discharges fluid through a discharge port  66  to a condenser  68 . The condenser  68  condenses vapor in the discharge of the pressure pump  32  to liquid. As envisioned herein, the condenser  68  can be implemented by a conventional heat exchanger such as an air cooler/radiator. Alternatively, we have found that the condenser  68  can be established by an uninsulated segment of the piping line, or indeed by a length of rubber tubing that can be disposed in the piping line. 
     High and low safety shut off pressure switches  70 ,  72  communicate with the discharge  66  of the pressure pump  32  for detecting the discharge pressure thereof. In one presently preferred embodiment, when the discharge pressure drops below 15 psig, the low pressure switch  72  generates a low pressure signal, and the signal is sent to the controller  46  to activate an alarm and/or to deenergize the pumps of the present invention. In contrast, when the discharge pressure exceeds 25 psig, the high pressure switch  70  generates a high pressure signal, and the signal is sent to the controller  46  to activate an alarm and/or to deenergize the pumps of the present invention. 
     Fluid from the condenser  68  flows through a liquid drop out device  74 , as shown in FIG.  2 . As intended by the present invention, the liquid drop out device  74  separates liquid in the fluid from vapor, with the liquid passing through a liquid return line  76  to the tank  12 . In one preferred embodiment, the liquid drop out device  74  is a type SEP  10  or  25  cyclone separator. Other equivalent devices, however, can be used in lieu of a cyclone separator, including a drop out pot, a dryer, a small diameter pipe to large diameter pipe transition that turns vertical, stainless steel wool or batting, or a combination of one or more of such devices. 
     A vapor blocker, such as pressure activated valve or float switch  78 , can be disposed in the liquid return line  76  to impede vapor from passing through the liquid return line  76 . Other equivalent vapor-blocking devices can be used in lieu of the pressure activated valve or float switch  78 , such as, e.g., a float drain check valve, an orifice, or a poppet-implemented drain trap. 
     In contrast to the path that liquid takes from the liquid drop out device  74 , vapor passes through a particulate filter  80  to a membrane assembly  82 . A membrane, represented by the line  84  in FIG. 2, separates hydrocarbon vapor from clean air. It may now be appreciated that the liquid drop out device  74  not only advantageously returns, as liquid, some of vapor from the nozzles  14 , but also reduces or eliminates liquid contact with the membrane  84 , which would otherwise be deleterious to the performance of the membrane  84 . 
     In the preferred embodiment, the membrane  84  is made by Membrane Technology and Research (MTR) of Menlo Park, Calif., model # 340-4120 LPI. Other membranes can be used, including those in U.S. Pat. Nos. 5,199,962 and 5,089,033, incorporated herein by reference. 
     As can be readily appreciated in reference to FIG. 2, after passing through the membrane  84  the hydrocarbon vapor is evacuated through a hydrocarbon outlet line  86  from the membrane assembly  82  by the vacuum pump  34 , which pumps the vapor back to the tank  12  via the hydrocarbon return line  44 . If desired, the hydrocarbon return line  44  can join the return line  76  as shown, to minimize openings into the tank  12 . Also, if desired a second condenser  88  or a second liquid drop out device can be disposed in the hydrocarbon return line  44  to further separate liquid from vapor and thereby increase the amount of hydrocarbons in the liquid phase that are returned to the tank  12 . In any case, a suction port  90  of the vacuum pump  34  is in communication with the hydrocarbon outlet of the membrane assembly  82 , while a discharge port  92  of the vacuum pump  34  communicates with the tank  12 . 
     Having described the vapor and liquid hydrocarbon return paths to the tank  12 , attention is now directed to the clean air exhaust path. As shown in FIG. 2, clean air from the membrane assembly  82  is exhausted through a clean air check valve  94  and the clean air exhaust  10  line  42  to atmosphere. To ensure that the clean air being exhausted to the environment does not contain an amount of hydrocarbon vapor that exceeds regulatory limits, a hydrocarbon sensor  96  communicates with the clean air exhaust  42 , and the hydrocarbon sensor  96  generates a signal that is sent via an electrical line or wireless network to the controller  46  (FIG.  1 ), which deenergizes the motors  22 ,  36  when a hydrocarbon limit is reached. 
     To further cleanse hydrocarbons from the air that is exhausted to the environment, a charcoal canister  98  can be disposed between the membrane assembly  82  and clean air exhaust  42  as shown. As the air passes through the canister  98 , hydrocarbons are removed from the air. 
     When the charcoal canister is provided, the present invention recognizes that it might be desirable to backflush the canister from time to time, to refresh the activated material in the canister. To facilitate this, a three-way solenoid backflush valve  100  that is controlled by the controller  46  is disposed in the clean air outlet line upstream of the charcoal canister  98 . During normal operation, the backflush valve  100  is configured to establish communication between the membrane assembly  82  and the charcoal canister  98 . During backflush, however, the backflush valve  100  is configured to establish communication between the membrane assembly  82  and a  25  backflush line  102 . A canister discharge check valve  104  is disposed downstream of the charcoal canister  98  in the clean air exhaust line  42 , and a check valve bypass line  106  interconnects the upstream and downstream sides of the check valve  104  as shown. An orifice  108  is disposed in the bypass line  106  to establish a backflush flow rate. 
     In normal operation of the system  10 , forward air flow is established through the canister  98 , wherein air from the membrane assembly  82  flows through the canister  98  to the clean air outlet  42 . When the controller  46  determines that the canister  98  should be backflushed based on, e.g., the elapse of a predetermined time period between backflushes, or a high hydrocarbon signal from the hydrocarbon sensor  96 , or based on other criteria including a manually input “backflush” command signal, the controller  46  establishes a backflush configuration of the system  10 . To do this, the controller  46  signals the tank suction valve  64  to establish communication between the suction  54  of the pressure pump  32  and the backflush return line  65 . Also, the controller  46  signals the backflush valve  100  to establish communication between the charcoal canister  98  and the backflush line  102 . 
     In the backflush configuration, the pressure pump  32  takes a suction through the backflush return line  65  on the inlet side  110  of the canister  98 . The discharge of the pressure pump  32  flows through the membrane  84  as described before, but instead of passing in the normal direction through the canister  98 , the air is directed by the backflush valve  100  into the backflush line  102 . From the backflush line  102 , air passes through the bypass line  106  and then passes through the canister  98  in the reverse direction, thereby flushing the canister  98 . As mentioned above, the contaminated backflush air is then drawn through the backflush return line  65  into the pressure pump  32 , and discharged into the membrane assembly  82  to clean the air. When backflushing is complete, the controller  46  reconfigures the three way valves  64 ,  100  for normal operation. To avoid overpressurizing the storage tank  12 , backflushing can be undertaken incrementally by cycling the system  10  between the backflush configuration (to cleanse the canister  98 ) and normal configurations (to reduce pressure in the tank  12 ) several times, e.g., twenty times, until the canister  98  has been completely backflushed. 
     Completing the description of FIG. 2, on and off pressure switches  112 ,  114  communicate with the tank  12  for generating respective pressure signals. In the preferred embodiment, the on pressure switch  112  generates a signal when the tank  12  internal pressure is between 0.1″ W.C. and 1.0″ W.C. (i.e., when the tank  12  has a slight internal overpressure). In contrast, the off pressure switch  114  generates a signal when the tank  12  internal pressure is between −0.5″ W.C. and −1.0″ W.C. (i.e., when the tank  12  has a slight internal vacuum). These signals are sent to the controller  46 , which energizes the motor  36  upon receipt of an “on” signal from the on pressure switch  112  and which deenergizes the motor  36  upon receipt of an “off” signal from the off pressure switch  114 . 
     The above-described logic (omitting charcoal canister backflush operations for clarity) can be further appreciated in reference to FIG. 3, which shows the logic in flow format for disclosure purposes. It is to be understood that the logic can also be thought of in terms of state logic. 
     Commencing at decision diamond  116 , the controller  46  determines whether the hydrocarbon level in the clean air exhaust is high, as indicated by the signal from the hydrocarbon sensor  90 . If it is, the controller  46  deactivates one or more of the pumps of the present invention at block  118 . In the preferred embodiment, the pumps must be manually reset to resume normal operation. Otherwise, i.e., if the test at decision diamond  116  is negative, the logic moves to decision diamond  120 , wherein the controller  46  determines whether the vacuum in the tank  12  is high. If it is, the logic moves to block  118 , but otherwise proceeds to decision diamond  122  to determine whether the pressure in the tank  12  is high. A negative test result causes the logic to loop back to decision diamond  116 . In contrast, a positive test result at decision diamond  122  causes the controller  46  to activate the pumps at block  124 . As indicated above, however, the present logic need not flow from decision diamond to decision diamond, but instead can assume “on” and “off” states and await the various signals described herein to change state appropriately. In any case, the controller selectively energizes the pump motor  36  to establish a predetermined pressure range in the tank  12 . 
     While the particular PRESSURE MANAGEMENT AND VAPOR RECOVERY SYSTEM FOR FILLING STATIONS as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to the elements of the above-described preferred embodiment that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. For example, multiple two-way solenoid valves can be used in lieu of each three-way solenoid valve where appropriate, or a single pressure sensor can be used in lieu of two pressure switches where appropriate. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for”.