Vapour recovery apparatus

Abstract: Vapour recovery apparatus particularly applicable to a fuel dispenser (10) for fuelling motor vehicles comprises a vapour pump (36) for returning vapour from a nozzle (15) to fuel storage tank (12). Inlet and outlet pressure transducers (38, 40) on vapour pump (36) provide signals to a controller (50) from which the actual vapour flow rate through the vapour pump (36) is determined.

Description: The present invention relates to improvements in vapour recovery apparatus for liquid fuel dispensers, and an improved method for recovering vapour in liquid fuel dispensers, both particularly, but not exclusively, applicable in the dispensing of fuel to a motor vehicle. Many fuel dispensers for the fuelling of vehicles are now equipped with means for recovering vapour displaced by the fuel entering the vehicle tank. Such dispensers are becoming more prevalent with the growing appreciation of the need to reduce environmental pollution, and indeed many existing non-"vapour recovery" dispensers are being retro-fitted with vapour recovery systems. Vapour recovery essentially comprises extracting the vapour emanating from the vehicle tank as the fuel is dispensed and returning this vapour via a vapour recovery line to an underground tank, normally with the aid of a pump. It is known that the rate of flow of the vapour in the vapour recovery portion of the system should be selected to avoid two undesired conditions. First, a vapour flow rate which is too low will not retrieve all of the vapour, thus permitting pollution to go on. A vapour recovery flow rate which is too high will pull in air, along with the vapour. The oxygen component of the air, if allowed to build to a relatively high level, can cause a dangerously explosive mixture to exist in the fuel reservoir. Accordingly, the vapour flow rate is of critical concern. Several prior endeavors have focused on calculating what the desired flow rate ought to be. For example, U.S. Patent No. 5,040,577 to Pope, the disclosure of which is hereby incorporated by reference, describes a vapour recovery system in which the speed of the vapour recovery pump is set by a microprocessor so its volumetric flow rate matches the volumetric flow rate of the liquid dispenser. In one embodiment, the volumetric flow of the vapour recovery pump is modified so as to maintain an expected pressure at its input. In European Patent Application Number 92306271 there is disclosed a system in which the vapour flow rate is modified from the liquid flow rate, to account for thermal expansion or contraction of the vapour caused by heat exchange with the liquid. U.S. Patent No. 5,038,838 to Bergamini et al discloses a system in which the vapour pump is continuously controlled to draw in a volumetric quantity of a vapour/air mixture equal to the volumetric quantity of fuel delivered, plus a possible excess of air. However, none of the aforementioned systems disclose or suggest how to monitor the actual flow rate through the vapour pump. This is a problem for, unlike a liquid, the vapour is compressible and therefore the volume displaced, for example by a positive displacement pump, is not dependent only on the operation of the pump, but will deviate depending on conditions extemal to the pump. Such deviations may be introduced by various aspects of the vapour recovery fuel dispenser system, and may vary from one installation to another. Variations in components such as hose length, the presence of liquid in the vapour line, or dirt/particle deposits on the inside of the vapour lines influence the inlet vacuum and/or discharge pressure. This influence increases or decreases the vacuum and/or discharge pressure, which in turn affects the amount of vapour flow through the vapour recovery system. Other components of the system which might influence the pressure differential across the pump and its resultant flow rate are the presence of hose breakaways, smaller size vapour return piping, and the like. Accordingly, there remains a need in the art for an apparatus and method for monitoring the flow rate through the vapour pump and correcting for any discrepancies between a desired and ascertained flow rate. According to a first aspect of the present invention there is provided vapour recovery apparatus for pumping recovered vapour in a vapour recovery liquid fuel dispenser including a vapour passage and a vapour pump arranged to pump vapour from the vapour passage through a vapour pump inlet to a vapour pump outlet and having a characteristic that the flow rate through the vapour pump at a given vapour pump operating speed is determinable from the difference between the vapour pump inlet and outlet pressures. Sensors associated with the inlet and outlet are provided to generate signals representative of the inlet and outlet pressures. A controller for the vapour pump is arranged to receive the pressure signals and a desired vapour pump flow rate datum and is adapted to adjust the vapour pump operating speed to reduce any discrepancies between a vapour pump flow rate derived from the pressure signals and the desired vapour pump flow rate datum. By employing the present invention it is possible to derive the vapour flow rate without the need for any additional moving components in the system. The use of pressure sensors also avoids any problems with inertia that may be a problem with mechanical flow sensors. In a preferred embodiment, the vapour pump has a characteristic that the flow rate through the vapour pump at a given operating speed is inversely proportional to the difference between the vapour pump inlet and outlet pressures. Typically, the vapour pump is driven by an electric motor and the controller includes vapour recovery control electronics and motor drive electronics. The electronics receives the desired vapour pump flow rate datum, the pressure signals and a vapour pump speed signal and outputs a motor velocity modulation signal to the motor drive electronics. The motor drive electronics, in turn, outputs a voltage drive signal to the motor. The apparatus is useful in a liquid fuel dispenser apparatus adapted to dispense liquid fuel. A transducer associated with the dispenser apparatus generates a liquid fuel flow signal indicative of the rate of liquid fuel flow and applies the liquid fuel flow signal to the controller as the desired vapour pump flow rate datum. Alternatively, the liquid fuel flow signal may pass through an intermediate processor to determine the desired vapour pump flow rate datum. For example, the intermediate processor may modify the liquid fuel flow signal to compensate for thermal contraction or expansion of the vapour arising from temperature differences between the liquid fuel and the vapour. According to a second aspect of the invention a method is provided for pumping recovered vapour in a vapour recovery liquid fuel dispenser. The method includes providing a vapour pump having a characteristic that the flow rate through the vapour pump at a given vapour pump operating speed is determinable from the difference between the vapour pump inlet and outlet pressures and pumping vapour with the vapour pump from a vapour passage through a vapour pump inlet to a vapour pump outlet. The pressures at the inlet and outlet of the vapour pump are sensed, and the vapour pump speed is controlled in response to the sensed pressures and a desired vapour pump flow rate. In a presently preferred embodiment, the pump flow rate is inversely proportional to the pressure difference. The method preferably includes driving the vapour pump by an electric motor and the controlling step includes controlling the electric motor, such as by outputting a voltage drive signal to the motor. The method advantageously includes dispensing liquid fuel at a liquid fuel flow rate and using the liquid fuel flow rate as the desired vapour pump flow rate. Alternatively, the liquid fuel flow rate and the respective liquid fuel and vapour temperatures may be used to derive the desired vapour pump flow rate. The invention is useful for the dispensing of volatile liquids generally, where the recovery of the vapours of the liquids is desired. Therefore the invention should be deemed to include methods and apparatus for pumping recovered vapour in a dispenser for other volatile liquids, in addition to liquid fuels. One embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings of which: Figure 1 is a block diagram of a vapour recovery fuel dispenser according to a preferred embodiment of the invention; and Figure 2 is a graph of the vapour flow rate correlated with the pressure across the vapour pump used in the preferred embodiment. Referring now to Figure 1, which is a block diagram of the components of the present invention as installed in a vapour recovery liquid fuel dispensing system. A conventional liquid fuel dispenser 10 draws fuel from a reservoir 12 along a liquid inlet line 13 and discharges it through an outlet line 17, typically to a nozzle 15 adapted to fit into the filler pipe of a motor vehicle tank. Interposed between the lines 13 and 17 is a fuel flow transducer 14 which measures the liquid flow rate passing through the dispenser 10. This flow rate is conventionally used to determine the amount of fuel sold. However, in the present invention, a signal representing the volumetric liquid flow rate is also fed to a controller 50 along line 18. Vapour is retrieved through an orifice at the nozzle 15, shown schematically in Figure 1 as a vapour passage 30 through nozzle 15. The vapour line 34 from the vapour passage 30 generally parallels and juxtaposes, in practice, the fuel line 17, the two nozzles 15 shown schematically in Figure 1 in reality being a single nozzle. The vapour is induced to move along line 34 by a vapour pump 36 which pumps the vapour from the passage 30 to the reservoir 12 (shown schematically as a second reservoir, but in actuality, the same as the first-mentioned reservoir 12). Within reservoir 12 the vapour may be available for condensation and reuse. Upstream of the pump 36 is a vapour pump inlet 35 and downstream is a vapour pump outlet 37. The pressures at the inlet and outlet are measured by sensors such as inlet pressure transducer 38 and outlet pressure transducer 40. The signals from these sensors are passed along lines 60, 64 to the controller 50. Similarly, the temperature of the liquid fuel in the reservoir 12 is sensed by a temperature sensor 16 which passes a temperature signal along line 68 to the controller 50. Other sensor locations may be used, if desired. The temperature of the vapour is sensed by a temperature sensor 32, with a corresponding signal being passed along line 66 to the controller 50. The vapour temperature may, if desired, be approximated by measuring the ambient temperature. The vapour pump 36 is driven by shaft 44 of electric motor 42. Thus, the speed of the electric motor 42 is transmitted to the vapour pump and directly affects the vapour pump speed. A signal of that speed is passed along line 62 back to the controller 50. The controller 50 includes vapour recovery control electronics 52 and motor drive electronics 54. The vapour recovery control electronics 52 receives the various input signals 60, 62, 64, 66, 68, 18 and outputs a velocity modulation signal 53 to the motor drive electronics 54 which suitably configures the motor velocity modulation signal as an output voltage drive signal 55 to the motor 42. For example, if the motor 42 is a stepper motor, the motor drive electronics 54 may modify a DC-type analogue signal to a pulse train. The exact configuration of the vapour recovery electronics 52 and motor drive electronics 54 may be selected by those of ordinary skill in the art according to the nature of the various input sensor signals and the motor type. In particular, the vapour recovery control electronics 52 compares the difference between the inlet and outlet pressure signals 60, 64 as a measure of the actual volumetric flow rate through the vapour pump 36 and compares the so-calculated vapour flow rate with a desired flow rate. The desired flow rate may be the actual liquid fuel flow rate represented by signal 18. Preferably, that flow rate is modified to take account of the differences in temperature of the vapour and liquid, as signalled to the vapour recovery control electronics 52 along lines 66, 68, in accordance with principles set forth in U.S. Patent No. 5,156,199 to Hartsell et al, the entire disclosure of which is hereby incorporated herein by reference. The desired vapour flow rate may, of course, be determined by other means, provided that it is compared with the ascertained actual flow rate, the actual flow rate being ascertained from the differences in the inlet and outlet pressures across the vapour pump 36. Referring now to Figure 2, a graph of a characteristic of a vapour pump 36 illustrates how the difference in the inlet and outlet pressures may be used to give a measure of the flow rate. The data recorded in Figure 2 is representative of characteristics of Blackmer Positive Displacement Pump Model VRG 3/4, operating at 2800 rpm. Two plots are shown. The ordinate of the graph shows the flow rate through the vapour pump in actual cubic feet per hour. The abscissa shows the outlet pressure, such as the signal on line 60, in inches of water. The upper plot shows a relationship of these two variables for a constant inlet vacuum of 1" of water, comparable to the signal along line 64. The lower plot shows the same relationship for a 10" inlet vacuum. As can be seen, for each inlet vacuum, the flow rate is almost linearly inversely proportional to the outlet vacuum. In practice, the relationship can be treated as linear. Thus, by ascertaining the inlet and outlet pressures (measured as vacuum levels or otherwise), the actual flow rate can be derived quite readily using known mathematical techniques. Since these characteristics will be characteristics of the vapour pump, measuring the inlet and outlet pressure will give a vapour pump flow rate measurement. That calculated measurement can be used to determine if there is a deviation from a desired vapour pump flow rate, and the speed of the motor 42 can be modified to reduce any such discrepancy. The discrepancies may arise from various temporary or permanent restrictions or obstructions along the lines 34, 39 from the vapour passage 30 back to the reservoir 12. Prior to the present invention, such aberrations could cause inappropriate vapour pump flow rates which could lead to the release of vapours to the atmosphere, dangerous buildup of oxygen in the reservoir 12, or decreases in the vapour recovery efficiency. In operation, when fuel is to be dispensed through the outlet nozzle 15, it is drawn from the reservoir 12 along line 13 and measured in the fuel flow transducer 14. The fuel flow rate in the transducer 14 is signalled along line 18 to the controller 50, along with an indication of the liquid temperature along line 68. At the same time, the vapour recovery component is started, so that the vapour pump 36 begins drawing vapour from the vapour passage 30 along lines 34, 39 back to the reservoir 12. The temperature of the vapour or the ambient is signalled along line 66 to the controller 50. The vapour recovery control electronics 52 of the controller 50 outputs to the motor drive electronics 54 a motor or velocity modulation signal 53, which is selected to have the vapour flow rate match the liquid flow rate through the transducer 14, as modified to compensate for thermal contraction or expansion of the vapour. If desired, the temperature compensation may be omitted, or other compensations may be included. The motor drive electronics 54, in turn, shapes that signal and applies a modified version 55 to the electric motor 42 so that the shaft 44 of the motor 42 drives the vapour pump 36 at the desired speed. The vapour recovery control electronics 52 also receives the inlet and outlet pressure signals along lines 60, 64, from which it can ascertain the actual vapour flow rate through the pump 36 and compare it with the desired vapour recovery flow rate. If the result of that comparison indicates that flow rate is insufficient, the motor velocity modulation signal 53 can be increased to speed up the electric motor 42 to compensate for such sensed deficiency in the vapour flow rate. The actual motor rate is sensed along line 62. If the flow rate through the vapour pump 36 is sensed as being too high, so that air is being pumped into the reservoir 12, the vapour recovery control electronics can retard the speed of motor 42, to reduce the flow rate through the vapour pump 36.

Claims: Vapour recovery apparatus for pumping recovered vapour in a vapour recovery liquid fuel dispenser comprising a vapour passage (39), a vapour pump (36) arranged to pump vapour from said vapour passage through a vapour pump inlet (35) to a vapour pump outlet (37) and having a characteristic that the flow rate through the vapour pump (36) at a given vapour pump operating speed is determinable from the difference between the vapour pump inlet and outlet pressures, sensors (38, 40) associated with said inlet and outlet to generate signals representative of the inlet and outlet pressures, and a controller (50) for said vapour pump arranged to receive the pressure signals and a desired vapour pump flow rate datum and adapted to adjust the vapour pump operating speed to reduce any discrepancies between a vapour pump flow rate derived from the pressure signals and the desired vapour pump flow rate datum. Apparatus as claimed in claim 1 wherein said vapour pump has a characteristic that the flow rate through the vapour pump at a given operating speed is inversely proportional to the difference between the vapour pump inlet and outlet pressures. Apparatus as claimed in claim 1 or 2 wherein the controller (50) receives a signal indicative of the speed of an electric motor (42) of the vapour recovery pump (36) and controls the speed of the pump dependent on the desired flow rate datum, the pressure signals and the vapour recovery pump speed signal. Apparatus as claimed in any preceding claim wherein the desired vapour pump flow rate datum is derived from an electrical signal from a liquid fuel dispenser (10) with which the vapour recovery apparatus is associated, the signal being a liquid fuel flow signal indicative of the rate of liquid fuel flow in the dispenser. Apparatus as claimed in claim 4 wherein said controller further comprises means for receiving at least one signal indicative of any temperature differences between the liquid fuel and the vapour, and wherein the controller modifies the liquid fuel flow signal to take account of any such differences in temperature. A fuel dispenser comprising vapour recovery apparatus as claimed in any preceding claim. A fuel dispenser as claimed in claim 6 wherein the controller controls the vapour pump operating speed, such that any discrepancies between the vapour pump flow rate derived from the pressure signals and the liquid fuel flow rate of the dispenser are reduced. A method for pumping recovered vapor in a vapor recovery liquid fuel dispenser comprising providing a vapor pump (36) having a characteristic that the flow rate through the vapor pump at a given vapor pump operating speed is determinable from the difference between the vapor pump inlet and outlet pressures, pumping vapor with the vapor pump from a vapor passage (39) through a vapor pump inlet (35) to a vapor pump outlet (37), sensing the pressures at the inlet and outlet of the vapor pump, and controlling the vapor pump speed in response to the sensed pressures and a desired vapor pump flow rate to reduce any discrepancies between a vapor pump flow rate derived from the sensed pressures and a desired vapor pump flow rate. A method as claimed in claim 8 wherein the providing step includes providing a vapor pump that has the characteristic that the flow rate through the vapor pump at a given operating speed is inversely proportional to the difference between the vapor pump inlet and outlet pressures. A method as claimed in claim 8 or 9 further comprising determining the speed of the motor in dependence on the sensed pressure, the desired vapour pump flow rate and the determined speed of the motor. A method as claimed in claim 8, 9 or 10 further comprising dispensing liquid fuel at a liquid fuel flow rate and using the liquid fuel flow rate as the desired vapour pump flow rate. A method as claimed in any one of claims 8 to 10 further comprising determining any difference between the temperature of the liquid and the temperature of the vapour and using the respective liquid fuel and vapour temperatures to derive the desired vapour pump flow rate.

Inventors: HARTSELL HAL C JR, NANAJI SEIFOLLAH S, PAYNE EDWARD A, POPE KENNETH L, HARTSELL, HAL C.JR., NANAJI, SEIFOLLAH S., PAYNE, EDWARD A., POPE, KENNETH L.
Applicants: GILBARCO INC, GILBARCO INC.
Application year: 1993
Main classification: B67D5
IPC codes: B67D7