Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
1999-11-15
2001-09-25
Smith, Duane S. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S054000, C096S007000, C096S009000
Reexamination Certificate
active
06293996
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a system for reducing the discharge of pollutants from underground gasoline storage tanks. The system is arranged to discharge pollutant free air when the pressure within the system reaches a predetermined level. Air to be discharged is separated from gasoline vapor within the storage system prior to its discharge.
U.S. Pat. No. 5,464,466, to Nanaji et al., describes a fuel storage tank vent filter system where a filter or fractionating membrane is used to capture pollutants from the vapor vented from the system's fuel storage tanks. A property of the membrane is that it will capture or collect selected pollutants including hydrocarbons. The captured pollutants are drawn from the membrane as a liquid and returned to the fuel storage tanks. The fractionating membrane comprises a plurality of stacked and bound thin sheets. Each sheet has a hole formed in its center to form an aperture in the stack extending axially from end to end. A perforated removal pipe must be positioned in the axial aperture to enable the captured vapors to be drawn out of the membrane under a vacuum created by a vacuum pump. The throughput of the system is limited because pollutant molecules, as opposed to air molecules, must be pulled through the fractionating membrane in liquid form. U.S. Pat. No. 5,571,310 discloses the use of such a membrane in an organic chemical vent filter system. Harmful volatile organic compounds (VOC's) are drawn through the membrane by using a vacuum pump to create a pressure drop of one atmosphere across the membrane. The pump is positioned between the membrane and the tanks, as opposed to between the membrane and the atmosphere.
These prior art systems are inadequate, however, because, to achieve adequate throughput, a substantial pressure drop, e.g., one atmosphere, must be created across the fractionating membrane. Further, the fractionating membrane of these prior art systems, and the associated hardware, is typically too large and costly for many applications. The pumping and fluid transfer system is likely to be more costly and difficult to assemble because of the relatively high levels of vacuum created in the system. Finally, the prior art systems do not expel substantially pollutant free air to the atmosphere. Rather, pressure within the tanks is reduced by merely condensing the pollutant vapors to liquid and returning them to the tanks. Accordingly, there is a need for a compact fuel storage system vent filter assembly that provides improved filtering and throughput at a competitive cost.
BRIEF SUMMARY OF THE INVENTION
This need is met by the present invention wherein a fuel storage system vent filter assembly is provided that includes a fuel vapor duct defining a flow path extending from the filter input port to a primary filter output port. Air is drawn through an air-permeable partition and larger, less mobile, pollutant hydrocarbons or VOC's pass to an outlet duct essentially unobstructed by the partition.
In accordance with one embodiment of the present invention, a fuel storage system is provided comprising a storage tank, an exhaust port, a filter system, a primary pump, and at least one secondary pump. The storage tank includes a fuel delivery port, a fluid vent port, and a pollutant return port. The filter system comprises a filter input port coupled to the fluid vent port, a fuel vapor duct, and primary and secondary filter output ports. The fuel vapor duct defines a flow path extending from the filter input port to the primary filter output port. The primary filter output port is coupled to the pollutant return port. At least a portion of the fuel vapor duct forms a permeable partition designed to pass a non-pollutant component of fluid within the fuel vapor duct through the permeable partition and designed to inhibit passage of a pollutant component of fluid within the fuel vapor duct through the partition. The secondary filter output port is partitioned from the fuel vapor duct by the air-permeable partition and is coupled to the exhaust port. The primary pump is positioned to cause fluid to pass from the filter input port to the primary filter output port. The secondary pump is positioned to cause the non-pollutant component within the fuel vapor duct to pass through the permeable partition to the secondary filter output port and the exhaust port. The non-pollutant component may comprise, among other things, oxygen or water vapor. The system may further comprise a microwave unit arranged to direct microwave radiation at fluid released through the exhaust port.
The primary pump may have a characteristic pumping capacity capable of generating a first volumetric fluid flow rate. The secondary pump may have a characteristic pumping capacity capable of generating a second volumetric fluid flow rate through the permeable partition and the secondary filter output port to the exhaust port, and capable of generating, in combination with the primary pump, a third volumetric fluid flow rate through the primary filter output port. Preferably, the second volumetric fluid flow rate is greater than a characteristic average net fluid volume return rate of the fuel storage system. The second volumetric flow rate may be approximately two to eight times greater than the average net fluid volume return rate of the fuel storage system. For example, the second volumetric fluid flow rate may be between approximately 15 standard cubic feet per hour and approximately 150 standard cubic feet per hour. The secondary pump is preferably designed to be capable of creating a pressure drop of between about 25 to 100 kPa across the air-permeable partition. The fuel vapor duct and the primary pump are preferably arranged such that fluid passes from the filter input port to the primary filter output port with a negligible pressure drop.
The primary pump may have a characteristic pumping capacity capable of generating a fluid flow of between approximately 150 standard cubic feet per hour and approximately 1500 standard cubic feet per hour. The storage tank, the filter system, and the primary and secondary pumps are preferably arranged such that the storage tank and additional portions of the fuel storage system operate below atmospheric pressure.
The fuel storage system may include a plurality fuel vapor ducts. The plurality of fuel vapor ducts may define a plurality of flow paths therein extending from the filter input port to the primary filter output port. Each of the plurality of fuel vapor ducts may form separate portions of the air-permeable partition so as to pass and inhibit respective portions of the non-pollutant component and the pollutant component. Each of the plurality of fuel vapor ducts may be enclosed within a common fuel vapor duct enclosure. The filter input port, the primary filter output port, and the secondary filter output port may be formed in the common fuel vapor duct enclosure.
According to another embodiment of the present invention, a method of storing fuel is provided comprising the steps of: (i) providing at least one storage tank including a fuel delivery port, a fluid vent port, and a pollutant return port; (ii) providing an exhaust port; (iii) providing a filter system comprising a filter input port coupled to the fluid vent port, a fuel vapor duct defining a flow path extending from the filter input port to a primary filter output port, wherein the primary filter output port is coupled to the pollutant return port, and wherein at least a portion of the fuel vapor duct forms an air-permeable partition designed to pass an non-pollutant component of fluid within the fuel vapor duct through the permeable partition and designed to inhibit passage of a pollutant component of fluid within the fuel vapor duct through the air-permeable partition, and a secondary filter output port partitioned from the fuel vapor duct by the air-permeable partition and coupled to the exhaust port; (iv) positioning a primary pump to cause fluid to pass from the filter input port at a first volumetric fluid
Grantham Rodger P.
Walker Glenn K.
Killworth, Gottman Hagan & Schaeff LLP
Smith Duane S.
Vapor Systems Technologies, Inc.
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