Gasoline vapor recovery system

Details Gasoline vapor recovery system Gasoline vapor recovery system

1999-12-22

2001-06-05

Young, Lee (Department: 3751)

Fluent material handling, with receiver or receiver coacting mea

Diverse fluid containing pressure filling systems involving...

Filling with exhausting the receiver

C141S007000, C141S095000

Reexamination Certificate

active

06240982

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally as indicated to a gasoline vapor recovery system and more particularly to a gasoline vapor recovery system wherein the volume of air/fuel vapor delivered to the storage tank takes into account potential saturation within the storage tank after delivery.
BACKGROUND AND SUMMARY OF THE INVENTION
An automobile or car is typically fueled at a service station by a gasoline dispensing apparatus which transfers a volume of liquid gasoline (V
liquid
) from a storage tank into the car's fuel tank. When the volume of liquid gasoline (V
liquid
) is dispensed into the car's fuel tank, it displaces the same volume of fuel/air vapor within the car's fuel tank (V
car
). A gasoline recovery system is usually provided to prevent the excessive release of this fuel/air vapor into the atmosphere at the vapor. This recovery system transfers fuel/air vapor released from the car's fuel tank back to the storage tank. The storage tank is usually situated underground and includes a vent for releasing vapor and introduced air to equalize the pressure of the storage tank.
In a typical gasoline dispensing apparatus, a fuel hose extends from the storage tank to a nozzle that may be selectively triggered to dispense the liquid gasoline into the car's fuel tank. The same fuel hose is also commonly used to transport the displaced air/fuel vapor back to the storage tank. A pump is provided to transport the liquid gasoline through the fuel hose and a liquid flow meter is provided to measure the volume of the liquid gasoline (V
liquid
) delivered to the car's fuel tank. A suction pump is provided to transport the displaced air/fuel vapor through the fuel hose and the flow rate of this suction pump is controlled by the gasoline recovery system to achieve the desired flow rate. For example, if a variable speed suction pump is being used, the speed of the pump may be modulated. Alternatively, if a constant speed suction pump is being used, the position of appropriately placed dampers or valves may be changed.
The escape or release of fuel vapor into the atmosphere is referred to as “emission” and is usually expressed in terms of the percentage volume of pure gasoline vapor relative to the volume of dispensed liquid gasoline (V
liquid
). “Nozzle emission” occurs if the volume of air/fuel vapor (V
car
) transported back to the storage tank is less than the volume of displaced air/fuel vapor (V
liquid
). “Vent emission” occurs if the storage tank becomes over pressurized and its vent is opened to release excess vapor. “Total emission” refers to the sum of nozzle emission and the vent emission.
As was indicated above, the liquid gasoline and the displaced air/fuel vapor are usually transported by the same fuel hose and these fluids are usually in a heat-exchanging relationship relative to each other as they counter flow through the fuel hose. For example, a fuel hose may include a central passageway through which the liquid gasoline is transported to the car's fuel tank and an outer annular passageway through which the displaced air/fuel vapor is transported to the storage tank. Assuming that the car's fuel tank is at the ambient temperature and the storage tank is situated underground, there will usually be a temperature differential between the car's fuel tank and the storage tank (T
car
≠T
storage
) whereby a heat transfer will occur between the counter flowing fluids. Consequently, the volume of the air/fuel vapor withdrawn from the car's fuel tank will be different than the volume of the air/fuel vapor introduced into the storage tank (V
car
≠V
storage
).
In winter conditions, the temperature of the car is less than the temperature of the storage tank (T
car
<T
storage
) and the volume of the vapor expands as it transferred from the car's fuel tank to the storage tank (V
car
<V
storage
). To eliminate nozzle emission, the recovery rate may be set so that the volume of vapor removed from the car's fuel tank (V
car
) is the same as the volume of liquid gasoline dispensed thereinto. (V
car
=V
liquid.
) However, this would result in volume of vapor delivered to the storage tank (V
delivered
) being greater than the volume of liquid gasoline removed from the storage tank (V
liquid
). (The volume of the liquid gasoline (V
liquid
) remains essentially unchanged since its thermal expansion coefficient is only about 0.0001/° C.)
The percentage increase in the volume of the vapor as it is transported from the car to the storage tank (V
delivered
−V
car
) due to thermal expansion is equal to the absolute temperature ratio (t=T
storage
/T
car
>1). To eliminate excess volume due to thermal expansion, the volume of vapor removed from the car's fuel tank (V
car
) may set to compensate for thermal expansion (V
car
=t V
liquid
). Since the volume of air/fuel vapor recovered (V
car
) is not less than the volume of air/fuel vapor displaced in the car's fuel tank (V
liquid
), nozzle emission is eliminated. However, since the volume of air/fuel vapor recovered (V
car
) is greater than the volume of air/fuel vapor displaced in the car's fuel tank (V
liquid
) excess air must be added to the recovery vapor.
When the excess air in the recovery vapor reaches the storage tank, it saturates with “fresh” gasoline vapor. This causes the just-delivered volume of air/fuel vapor to expand by a saturation factor of (1+&Dgr;p/p
ambient
) wherein &Dgr;p is the difference between the saturation pressure of the fuel vapor of the storage tank conditions (p
sat
(storage)) and the fuel vapor pressure at the car's fuel tank (p
vapor
(car)). Thus, the saturation of vapor in the storage tank results in excess vapor volume in the storage tank (V
liquid
t&Dgr;p/p
ambient
). This excess volume is released via the storage tank vent causing a vent emission equal to the released excess vapor volume times the relevant saturation factor (p
sat
(T
storage
)/p
ambient
)).
By way of specific example, suppose that the fuel vapor is pentane (C
5
H
12
), the temperature of the car is 290° K (T
car
) and the temperature of the storage tank is 300° K (T
storage
). If volume of vapor removed from the car's fuel tank (V
car
) is set to account for thermal expansion (1.033 V
liquid
), there would be an approximately 34% percent (1.34 V
liquid
) volume excess in the tank due to saturation expansion. The excess vapor volume released through the storage tank's vent would cause a storage emission, in percentage of the volume of dispensed liquid gasoline (V
liquid
), of about 25% pentane. Thus, while nozzle emission is eliminated, storage emission is relatively high whereby total emission is also relatively high.
The present invention includes the appreciation that, during winter conditions, total emission may be minimized by taking into account the saturation expansion of the air/fuel vapor delivered to the storage tank. To this end, the present invention provides a gasoline vapor recovery system wherein, during winter conditions, the volume of the air/fuel vapor delivered to the storage tank (V
delivered
) is less than the volume of liquid gasoline (V
liquid
) but that will expand upon saturation in the storage tank to be approximately equal to the volume of the liquid gasoline (V
liquid
).
Preferably, the volume of vapor delivered to the storage tank (V
delivered
) is based on the fuel vapor saturation pressure at the temperature of the storage tank (p
sat
(T
storage
)). More preferably, the volume of vapor delivered to the storage tank (V
delivered
) is based on the equation:
V
delivered
=V
liquid
/ (1+
&Dgr;p/p
ambient
)
wherein &Dgr;p=p
sat
(storage)−p
vapor
(delivered);
wherein p
sat
(storage)=saturation vapor pressure for the fuel at the temperature of the storage tank ; and
wherein p
vapor
(delivered)=vapor pressure at the rate-controlling device.
The saturation vapor pressure (p
sat
(storage)) is preferably determined by measuring the

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