Measuring and testing – Gas content of a liquid or a solid – By vibration
Utility Patent
1998-08-14
2001-01-02
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas content of a liquid or a solid
By vibration
C073S023310, C073S024010, C141S059000, C141S083000, C141S094000
Utility Patent
active
06167747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to vapor recovery systems used in connection with fuel dispensing apparatus, and, more particularly, to a method and system for monitoring the vapor emissions and adjusting the flow rate of pumped vapors in response to low levels of detected hydrocarbon.
2. Description of the Related Art
The fuel tanks of serviced vehicles contain both a liquid component corresponding to the fuel dispensed into the tank and a vapor component overlying the fuel level and corresponding to a volume of volatilized fuel vapors. Refueling the vehicle will result in fuel vapors being discharged into the atmosphere since any gasoline flowing into the fuel tank will displace an equivalent volume of the volatilized vapors and thereby force such displaced vapors out of the tank. Increased awareness of the adverse impact of vapor pollutants on the environment has prompted governmental authorities to require that fuel dispensing systems be designed to eliminate the release of vapors into the atmosphere, preferably by collecting the vapors for storage and possible recycling. The response of industry has been to develop various systems designed to collect and return the fugitive vapor emissions to a storage tank, such as the underground facility located on-site at the service station where the fuel supply is maintained. The recovered vapors may be further transported to a processing site where the vapors are returned to liquid form in a recycling operation.
One class of conventional vapor recovery systems utilizes a vacuum pump to assist in the collection of fuel vapors and their subsequent transfer to the storage tank. The vacuum pump draws fugitive vapors into an intake line and conveys the collected vapors back to the storage tank. The aspirating action generated by the vacuum pump is normally sufficient to capture the vapor emissions, thereby obviating the need for any sealing structure such as a bellows element, and only requiring that the inlet port of the vapor intake line be disposed in close proximity to the filler neck of the fuel tank from where the vapors emanate.
In all such vacuum-assist vapor recovery systems, it is critically important that the volume of vapor emissions being collected closely approximate the volume of vapor being displaced by the gasoline flowing into the fuel tank. Otherwise, if the volume of vapor being collected is less than that being displaced, the non-recovered portion will be discharged into the atmosphere. Conversely, if the volume of vapor being collected is greater than the volume being emitted from the tank, the excess volume will consist of atmospheric components that are recovered along with the vapors.
Several configurations have been proposed that focus upon making calculated adjustments to the flow rate generated by the vapor pump based upon measurements produced by sensing apparatus that monitor the fueling and vapor recovery operations. In one such representative configuration disclosed in U.S. Pat. No. 5,355,915 to Payne, there is provided a vapor recovery system including a vapor pump driven by an electric motor, and further including sensors to generate pulse train signals representative of the flow rate of both the liquid fuel pump and the vapor pump. A controller is provided to control the speed of the vapor pump based upon a comparison of the flow rates of the liquid fuel pump and vapor pump, as indicated by their respective pulse train signals. In particular, the operating speed of the vapor pump is adjusted so that the vapor pump flow rate is equalized with the liquid fuel flow rate. The overall purpose of tracking the vapor flow rate to the liquid fuel rate is to ensure that the volumetric quantity of retrieved vapor is the same as the volumetric quantity of vapor being displaced by the dispensed fuel. However, since adjustments to the vapor flow rate are made on the basis of measurements (i.e., volumetric flow rates) that are not specifically representative of the hydrocarbon concentration of the recovered vapors, the flow rate equalization process may not in fact be sufficiently accurate or reliable in its attempt to precisely regulate the composition of the recovered vapors.
In another prior art vapor recovery configuration disclosed in U.S. Pat. No. 5,507,325 to Finlayson, an array of sensors are provided to produce signals representative of the vapor-to-air ratio as measured at a variety of positions located proximate to the tank opening. A controller is provided to determine a baseline collection rate for the vapor pump based on the liquid fuel flow rate; the initial pump rate is then adjusted according to the signals generated by the vapor-to-air ratio sensors in order to minimize the amount of fuel vapors that escape into the atmosphere, and to minimize the amount of air contained in the gaseous mixture that is drawn along the vapor intake line.
The vapor recovery system of Finlayson is an advance over the systems described above because it provides a means by which the compositional content of the recovered emissions (i.e., vapor versus air) can be directly measured. This permits a more accurate evaluation of whether the vapor pump is inducing the proper volumetric flow of fugitive emissions into the recovery line. However, one significant problem attending the Finlayson system stems from the fact that the sensors are susceptible to a permanent condition of producing false readings in the event that vapor condensate settles onto the sensor surfaces. Vapor condensation within the intake line is a recurring problem that results when differentials in temperature and pressure throughout the vapor recovery system reach threshold conditions. The accumulation or even transient deposition of condensed fuel vapors on fuel-detecting sensors will produce false measurements of the fuel content in the monitored environment and lead to improper adjustment of the vapor pump rate.
What is therefore needed in the art is a system that monitors the fugitive vapor emissions displaced from a tank during refueling and that adjusts the vapor recovery rate based on direct measurements of the hydrocarbon concentration in the monitored environment. Such a system must also be capable of accommodating both vapor and liquid forms of the emissions in its measurement apparatus, and be able to remove condensate from its sensor elements to avoid false readings of the hydrocarbon content.
SUMMARY OF THE INVENTION
The present invention provides a vapor recovery system that monitors the vapor emissions emanating from a fuel tank during refueling and generates detection data indicating the hydrocarbon concentration in the vapor stream. This measurement of the hydrocarbon content is then used as the basis for appropriately adjusting the operating speed of the vapor pump. The sensing apparatus includes a crystal oscillator coated with a layer of material capable of interacting with hydrocarbon and which induces a shift in the oscillation frequency of the crystal in response to such interactions.
The invention comprises, in one form thereof, a system for recovering vapor emissions from a fuel receiving tank, comprising a vapor collection means, crystal oscillator means, and controller means. The vapor collection means, which is disposed in vapor communicating relationship with respect to the fuel receiving tank, controllably collects vapor emissions emanating from the fuel receiving tank. The crystal oscillator means, which is exposed for contact with vapor emissions from the fuel receiving tank and is adapted to exhibit a shift from its fundamental resonance frequency in response to the presence of hydrocarbon, generates a frequency shift signal having a frequency of oscillation representative of a hydrocarbon concentration within vapor emissions exposed to the oscillator means. The controller means, which is operatively coupled to the vapor collection means and to the oscillator means, controllably adjusts the rate of vapor collection by the vapor collection means in accordance with the freque
Brown Arthur R.
Koch Wolfgang H.
Knuth Randall J.
Larkin Daniel S.
Tokheim Corporation
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