Gas separation: apparatus – Apparatus for selective diffusion of gases
Reexamination Certificate
1999-03-26
2001-01-16
Spitzer, Robert H. (Department: 1724)
Gas separation: apparatus
Apparatus for selective diffusion of gases
C096S111000, C096S144000, C095S050000
Reexamination Certificate
active
06174351
ABSTRACT:
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'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'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
Gray John M.
McDowell Robert W.
Delaware Capital Formation Inc.
Dinsmore & Shohl LLP
Spitzer Robert H.
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