GB2471449A

GB2471449A - A vapour recovery unit having means to melt ice

Info

Publication number: GB2471449A
Application number: GB0910739A
Authority: GB
Inventors: Peter Davies; Tony Pinson
Original assignee: VR Technology Ltd
Current assignee: VR Technology Ltd
Priority date: 2009-06-22
Filing date: 2009-06-22
Publication date: 2011-01-05
Also published as: WO2010150005A1; GB0910739D0

Abstract

A vapour recovery unit 100 for recovering vapours from a petroleum vapour-bearing gas comprises a gas inlet 111, a gas outlet 113, a heat exchange module 130 to condense the vapour to form recovered petroleum liquid, and at least one liquid outlet 151, 155, 157 arranged to allow said recovered liquid to flow out from the unit. A heater device is provided for heating at least a portion of the unit in order to melt any ice formed inside the unit during its operation. The heat is provided by passing hot gases through the heat exchange module 130. Melted ice can flow out from the unit through at least one of the liquid outlets, preferably 151.

Description

APPARATUS AND METHOD OF VAPOUR RECOVERY

The present invention relates to a system for, and method of, converting volatile gasoline/petroleum vapours into liquid. In particular but not exclusively the invention relates to a system for, and method of, converting volatile gasoline/petroleum vapours into liquid during the supply, handling and distribution of petroleum products for use in road transport and in particular, but not exclusively, when these activities are performed at a petrol filling station. The system thereby assists in mitigating damage to the environment and reducing exposure of harmful vapours to individuals.

BACKGROUND

Typically, when a petrol delivery tanker carrying a load arrives at a delivery site, for example a commercial petrol vending site, the tanker is connected via an outlet port and hose to an underground fuel storage tank to allow transfer of petrol from the taker to the underground storage tank. Voiding is typically performed under gravity.

Petrol in the underground storage tank may subsequently be pumped via a separate set of dedicated conduits to pumping stations at a forecourt of the petrol vending site to allow customers/users to access the petrol.

A moderately busy petrol filling station comprising about six petrol pumps will receive at least one delivery of petrol per day whereas a larger, for example, motorway service station, may receive as many as five fuel deliveries per day. Accordingly, delivery, voiding from the tanker and filling individual vehicles with petrol is a constant 24/7 process.

There are three stages of vapour recovery. Stage 1A vapour recovery concerns the control and elimination of unwanted emissions of petrol vapour which occur at distribution terminals. Stage 1 B vapour recovery concerns the recovery of fumes which escape when fuel is delivered to storage tanks at retail petrol stations. Stage II vapor recovery systems collect petroleum/gasoline vapors from vehicles' fuel tanks while customers dispense petroleum products into their vehicles at petrol/gasoline dispensing facilities. The present invention is concerned with vapour recovery at Stage 1 B and Stage II. It is to be understood that some embodiments of the invention are suitable for use with stage 1 A vapour recovery systems.

It is to be understood that ullage space above the level of petroleum stored in the underground storage tank contains petrol vapours, sometimes to a saturated level.

Upon filling of underground storage tank with the delivery load, these vapours are necessarily displaced by the incoming liquid and are conventionally vented to the atmosphere via extended pipes in a so called vent stack arrangement.

The discharge of such vapours to the atmosphere is not only wasteful but is damaging to the environment and can create a risk of explosion. In addition, inhalation or other contact with petrol vapours can present a serious health hazard.

In order to mitigate this vapour release, in what is termed in the art as Stage 1 B" vapour recovery (vapour balancing) it is known to modify the petrol storage vent system so that the vapours displaced during unloading are returned to the delivery tanker. In petrol stations having Stage 1 B vapour recovery in place a hose is connected from a receptacle on the vent system of the filling station to a fitting on the tanker which is in turn connected to the ullage of the tanker. In theory, as the liquid is transferred to the underground tank, vapours are drawn into the ullage or empty space of the tanker. The tanker then returns to its terminal with, theoretically a consignment of petroleum vapour.

Once back at the terminal these vapours are expelled as the tanker is refilled and the vapours are passed through the terminal's own vapour recovery system. In practice this system is not very efficient.

The terminal vapour recovery units have massive power consumption so that the carbon footprint for this operation is substantially negative. A further disadvantage of the prior art vapour recovery Stage 1 B is that the tanker theoretically returns to the terminal with a cargo of highly explosive vapours.

In practice it is likely that a substantial amount of the vapours are dispersed from the tanker during the course of its return journey to the terminal through vents in the tanker body and thus contributes further to environmental pollution. It is also possible that due to the high vapour pressure of the petrol as it is transferred to the underground storage tank much of it will be discharged to atmosphere via a pressure and volume valve that is built into the conduit system.

It will be understood that current practices of Stage 1 B are not completely satisfactory as vapour escape to atmosphere still occurs. Furthermore, it is especially unsatisfactory to the petrol filing station owner since the vapours recovered in liquid form are not returned to the purchaser but rather kept by the individuals involved in tanker distribution or the tanker owners at the terminal depots. Since there are very meager profit margins to be had at filling stations associated especially with large supermarket chains, any petrol that could be recovered by the filling stations themselves on site would offer an immediate

advantage over the prior art.

It will be appreciated that there are two other situations where vapour release occurs at the petrol vending stations. Firstly, vapour release occurs due to evaporation when petroleum is stored in the underground storage tank. During this passive or stand-by mode vapours in the storage tank are displaced to atmosphere by a build up of pressure in the underground storage tank (vapour pressure). Where a pressure and vacuum (P&V) valve is fitted to a venting system vapours will still be discharged to atmosphere whenever the vapour pressure exceeds the release setting of the P&V valve. To eliminate the possibility of underground storage tank overpressure the P&V valve is normally set to around 30mb. The vapour pressure of petrol under normal storage conditions is well in excess of this so there is a constant release to atmosphere of vapours.

In addition to Stage 1 B vapour recovery and the constant evaporation from the storage tank, there is a small amount of vapour loss each time a customer or user dispenses petrol from individual dispensers or pumps into their vehicle. The volume of vapour lost is estimated to be equal to or more than the volume of liquid fuel transferred. This is referred to as "Stage II" vapour loss and Stage II legislation (to be in force by 2010 for petrol stations selling more than around 106 I/year) will require that these vapours must be recovered and release of noxious vapour to the environment prevented.

Prior art Stage II systems typically consist of special nozzles and coaxial hoses at each petrol/gasoline pump that capture vapors from the vehicle's fuel tank and route them to the station's underground or aboveground storage tank(s) during the refueling process.

PCT/GB2008/050616 discloses removing vapours from gases at a petrol filling station by passing the gases through a heat exchanger unit and cooling the gases to condense the vapours to liquid form. The present inventors have recognized that this system suffers the disadvantage that during the course of operation blockages can occur in one or more conduits of the apparatus due to a build-up of ice. This can result in a situation that is potentially very dangerous since a vent pipe may become blocked resulting in overpressure of a petroleum storage tank.

There is therefore a need to provide an improved system and method of efficiently recovering petrol vapours and preventing their escape to atmosphere from a variety of sources especially at petrol filling stations.

Embodiments of the present invention provide an improvement to both Stage 1 B and Stage II vapour recovery in addition to vapour recovery from underground storage tanks in a passive stand-by' mode. Embodiments of the invention offer immediate benefit to the environment, the filling station proprietors and consumer alike.

There is also a need for a reliable system that can be installed easily at existing gasoline/petroleum dispensing outlets.

BRIEF SUMMARY OF THE DISCLOSURE

According to a first aspect of the invention there is provided a vapour recovery unit for recovering vapours from a vapour-bearing gas comprising: a gas inlet; a gas outlet; a cooler device for cooling a gas flowing through the unit from the gas inlet to the gas outlet thereby to condense the vapour to form recovered liquid; at least one liquid outlet arranged to allow said recovered liquid to flow out from the unit; and a heater device for heating at least a portion of the unit thereby to melt ice formed in the unit during operation of the unit, the unit being arranged to allow melted ice to flow out from the unit through at least one said at least one liquid outlet.

The unit is preferably arranged whereby cooling of gas flowing through the unit is terminated when the heater device heats the at least a portion of the unit.

Preferably the unit comprises a reservoir, the unit being arranged whereby said recovered liquid is collected in the reservoir.

Preferably the reservoir is provided with at least one liquid outlet.

Preferably the at least one liquid outlet is arranged to allow recovered liquid above a level of at least one liquid outlet to pass through the outlet thereby to be removed from the unit.

The at least one liquid outlet may comprise an aperture formed in a wall of the reservoir.

The aperture may be formed in a side wall of the reservoir.

The at least one liquid outlet may comprise an upstand portion, the outlet being arranged to allow liquid above a level of the upstand portion to pass through the outlet thereby to flow out from the unit.

Preferably the at least one liquid outlet is provided with a valve member arranged to allow a flow of liquid from the reservoir through the at least one liquid outlet to be controlled.

The unit is advantageously arranged to open the valve member thereby to allow a flow of liquid from the reservoir when a level of liquid in the reservoir reaches a prescribed level.

Preferably the unit comprises first and second liquid outlets, the first outlet being arranged to allow liquid above a first level to be removed from the reservoir, the second outlet being arranged to allow liquid above a second level to be removed from the reservoir, the second level being higher than the first level.

Preferably the unit is arranged to allow recovered liquid to flow through the second liquid outlet when a level of recovered liquid in the reservoir reaches a prescribed level above the level of the second liquid outlet.

The unit may be arranged to allow a flow of recovered liquid through the second liquid outlet until the level of liquid in the reservoir corresponds to the level of the second liquid outlet.

Preferably the unit is arranged to close the valve member once the level of liquid in the reservoir corresponds to the level of the second liquid outlet.

Preferably the unit is arranged to open and close the valve member in order to allow recovered liquid to flow through the second liquid outlet to the level of the second liquid outlet once the liquid level reaches said prescribed level.

The unit may be arranged to measure an amount of recovered liquid passed through the second outlet aperture by measuring a number of times the second outlet valve is opened thereby to allow a level of liquid in the reservoir to change from the prescribed level to the level of the second liquid outlet.

The unit is preferably arranged to allow liquid to pass through the first outlet when required.

The unit may be arranged to open a valve member coupled to the first outlet upon receipt of a control signal when a level of liquid in the reservoir is at or below the level of the second liquid outlet.

The cooler device may comprise a conduit through which a cooled gas may be passed thereby to cool a surface of the cooler device exposed to vapour-laden gas passing through the unit.

The heater device preferably comprises a conduit through which a heated gas may be passed.

Alternatively or in addition the heater device may comprise an electric heating element.

Preferably the heater device and the cooler device are provided by the same device.

The cooler device is advantageously arranged to be removable from the unit.

The cooler device may be arranged to be removable from the unit by sliding and without a requirement to raise the device by means of a hoist.

In a second aspect of the invention there is provided a method of recovering vapour from a gas comprising: providing a petroleum vapour recovery unit; collecting gas containing petroleum vapour; passing the gas through the unit from a gas inlet to a gas outlet whereby a cooling device of the unit is arranged to condense the vapour to form recovered liquid; allowing recovered liquid to flow out from the unit through at least one liquid outlet; heating by means of a heater device at least a portion of the unit to melt ice formed inside the unit during operation of the unit; and allowing the melted ice to flow out from the unit through at least one liquid outlet.

Preferably cooling of gas flowing through the unit is terminated when the heater device heats the at least a portion of the unit.

Preferably the method comprises collecting said recovered liquid in a reservoir of the unit.

Preferably the reservoir is provided with the at least one liquid outlet.

Preferably the method comprises the step of allowing recovered liquid above a level of the at least one liquid outlet to pass through the outlet thereby to flow out from the unit.

Preferably the at least one liquid outlet is provided with a valve member arranged to allow a flow of recovered liquid from the reservoir through the at least one liquid outlet to be controlled.

Preferably the method comprises the step of opening the valve member thereby to allow a flow of recovered liquid from the reservoir when a level of liquid in the reservoir reaches a prescribed level.

The method preferably further comprises the step of opening a second valve member coupled to the second liquid outlet to allow recovered liquid to flow through the second liquid outlet when a level of recovered liquid in the reservoir reaches a prescribed height above the level of the second liquid outlet.

Preferably the method comprises the step of allowing a flow of recovered liquid through the second liquid outlet until the level of recovered liquid in the reservoir corresponds to the level of the second liquid outlet.

Preferably the method further comprises the step of closing the second valve member once the level of recovered liquid in the reservoir corresponds to the level of the second liquid outlet.

Advantageously the method comprises the step of measuring an amount of recovered liquid passed through the second outlet aperture by measuring a number of times the second valve member is opened thereby to allow a level of liquid in the reservoir to change from the prescribed level to the level of the second liquid outlet.

Preferably the method comprises the step of allowing liquid to pass through the first outlet when required.

Preferably the method comprises the step of opening a first valve member coupled to the first liquid outlet upon receipt of a control signal when a level of liquid in the reservoir is at or below the level of the second liquid outlet.

The cooler device may comprise a conduit through which a cooler gas may be passed, the method comprising passing the cooler gas through the conduit thereby to cool a surface of the cooler device exposed to vapour-laden gas passing through the unit, the cooler gas passing through the cooler device being provided in fluid isolation from the vapour-laden gas.

The heater device may comprise a conduit through which a heated gas may be passed.

Preferably the heater device comprises an electric heating element.

The heater device and the cooler device may be provided by the same device.

Preferably the cooler device is arranged to be removable from the unit.

The method may comprise removing the cooler device from the unit by sliding in a substantially horizontal direction without a requirement to raise the device by means of a hoist.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Reference herein to a "petrol filling station" is intended to include a garage or petrol station, commercial or otherwise where a road vehicle or the like can receive petrol or fuel from a storage unit.

Reference herein to a "heat exchanger" is intended to include any device which is capable of transferring heat through a conducting wall from one fluid to another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 shows a through section of a vapour recovery unit according to an embodiment of the invention; FIGURE 2 shows a lower portion of the VRU of FIGURE 1; and FIGURE 3 shows a VRU according to an embodiment of the invention installed at a petroleum filling station.

DETAILED DESCRIPTION

The system of the present invention may be installed at a petrol filling station and comprises two main components, a Vapour Recovery Unit (VRU) 100 and a power control unit. The VRU 100 is typically installed adjacent to a remote fill point where a tanker would park to make a delivery. The VRU 100 advantageously has no mains voltage electrics. The power and control unit operating the VRU 100 is installed away from the "Zone 0" area in a suitable location and requires as little as a single phase mains electrical supply, with modification it is capable of operating using a low voltage AC or DC supply.

The area known as the "Zone 0" on a petrol station forecourt is the area where individuals dispense petrol into vehicles and where a delivery tanker may make its delivery.

The apparatus and method of the present invention has been designed to recover petrol vapours displaced from an underground storage tank when a tanker delivers fuel to the underground storage tank, and vapours generated and vapours displaced when a dispensing pump of the filling station dispenses fuel into a further storage tank such as that of a motor vehicle.

For vapour recovery when a tanker delivers fuel to an underground or other storage tank, the VRU 100 is connected to the (existing Stage 1 B) vapour recovery fitting on the petrol station venting system. Vapour-laden gas (such as air) displaced as the underground storage tank is filled passes directly through an inlet 111 of the VRU 1 00 and along a header tube 121 within an inner chamber 101 of the VRU 100. The inner chamber 101 of the VRU is thermally insulated from an external environment of the VRU 100. The inner chamber 101 may be thermally insulated by means of an air gap, a foam or any other suitable insulation medium.

The header tube 121 is disposed below a heat exchange module 130. The header tube 121 has a plurality of apertures 123 formed therein arranged to allow a flow of vapour-laden gas therethrough whereby the header tube 121 may be provided in fluid communication with the heat exchange module 130. The heat exchange module 130 is arranged to cool vapour-laden gas flowing therethrough such that the vapour condenses to form a liquid and subsequently falls into a sump 150.

The heat exchange module 130 has an inlet 131 through which ref rigerant flows into the heat exchange module 130 and an outlet 133 through which refrigerant flows out from the heat exchanger, whereby the module 130 is cooled.

Gas that is substantially free of vapour following cooling of the gas to condense the vapour passes from the heat exchange module 130 and out from the VRU 100 via gas outlet 113.

The header tube 121 is provided with a deflector plate 125 above the apertures 123 in order to prevent ingress of liquid into the header tube via the apertures 123.

A diffuser plate 129 is provided above the header tube 121 between the header tube 121 and the heat exchange module 130. The presence of the diffuser plate enhances a uniformity of flow of vapour-laden gas through the heat exchange module 130 thereby enhancing an efficiency of cooling of the gas.

A flame arrestor plate 159 is provided below the header tube 121.

The sump 150 has three upstanding pipe members therein. A first pipe 151 protrudes a relatively small distance up into the sump 150 to a first level 171 and provides a water outlet.

A second pipe 155 protrudes a larger distance up into the sump 150 to a second level 172 and provides a liquid petroleum outlet.

A third pipe 157 protrudes up into the sump 150 to a third level 173 being a maximum level at which liquid is permitted to build up in the sump 150 and provides an overflow member 157.

The first pipe 151 is typically coupled to a waste fluid collection storage facility of the filling station via a valve 152 whilst the second pipe 155 may be coupled to the filling station's storage tank (which is typically situated underground as discussed above) via a valve 156. Thus, liquid fuel recovered from vapours passing through the VRU 100 is returned to the filling station storage tank. The third pipe 157 may also be coupled to the filling station's storage tank. In some installations no valve is provided in the third pipe 157 since the purpose of the third pipe 157 is to eliminate the risk of a buildup of fuel to a dangerous level in the VRU 100.

A liquid level measuring device 158 is provided for measuring a level of liquid in the sump 150.

In use, with the first and second valves 152, 156 in a closed condition a level of liquid petroleum builds up in the sump 150 as vapour-laden gas passes through the VRU 100.

When the level of liquid petroleum reaches a critical prescribed level, being a level above that of the second pipe 155, valve 156 is opened to allow the level of liquid petroleum to drop to that of the second pipe 155. A controller of the apparatus maintains a log of the number of times the valve 156 is opened thereby to monitor the amount of liquid petroleum being recovered by the VRU 100.

Vapour-laden gas passing through the VRU 100 typically contains water vapour in addition to petroleum vapours. Some of the water vapour condenses in the heat exchanger along with the petroleum vapours.

The heat exchanger module 130 is arranged to cool the petroleum vapours to around - 200 to -400 and therefore the water vapour typically forms ice which builds up on the heat exchanger module 130. Some ice is also deposited in the sump 150.

When it is required to remove ice that may have formed in the VRU 100, in the present embodiment the heat exchanger 130 is heated by passing hot gases through the module 130. The effect of heating the heat exchanger 130 is that ice that has accumulated in the heat exchanger 130 is melted and any droplets of water produced thereby drain into the sump 150.

The VRU 100 is arranged whereby heat from the heat exchanger 130 is sufficient to cause melting of any ice that has formed or otherwise accumulated in the sump 150.

Thus a build-up of liquid water will occur in the sump 150.

The first valve 152 is then opened and water allowed to drain from the sump 150 through the first pipe 151. It is to be understood that before heating the heat exchanger 130 valve 156 is opened thereby to drain any liquid petroleum via the second pipe 155.

Subsequently, the second valve 156 is closed and the first valve 152 is opened to drain water from the sump 150 during or following heating of the heat exchanger 130.

It is to be understood that embodiments of the present invention enable a buildup of ice in the VRU 100 to a dangerous level to be avoided. Thus, a risk that the second pipe or overflow member 157 become blocked due to ice buildup may be eliminated. It is to be understood that such a situation could have highly dangerous consequences.

It has been found to be possible to recover at least around 35 -50 litres of reusable petrol from a delivery of 35,000 litres by this method.

FIG. 2 shows the configuration of the sump 150 in more detail. The liquid level measuring device 158 provides feedback to a controller arranged to control the operation of the first and second valves 152, 156.

In the embodiment of FIG. 1 the sump is around 0.495m x 0.625m in lateral dimensions and around 0.125m deep.

In the embodiment of the invention shown in FIG. 1 and FIG. 2 the first pipe 151 protrudes a distance hi of 10mm up into the sump 150. Thus, level 171 is 10mm above a base portion 1 50A of the sumpi 50.

The second pipe 155 protrudes a distance hi of 30mm up into the sump 150. Thus, level 171 is 30mm above the base portion 150A.

The third pipe 157 (overflow pipe 157) protrudes a distance h3 of 110mm up into the sump 150. Thus, level 173 is 110mm above the base portion 1 50A.

Other distances are also useful.

In some embodiments the sump is sized such that it can accommodate the maximum amount of liquid that could be collected from a delivery of the maximum quantity of fuel that a delivery might provide. This may be up to 75 litres.

In the course of normal operation, with vapour-laden gas passing through the VRU 100 and the heat exchanger in a cooled condition, once the level of liquid in the sump 150 reaches the level indicated C in FIG. 2, the second valve 156 is opened and liquid allowed to drain through the second pipe 155 until the liquid level reaches the level indicated D. At this point the second valve 156 is closed. The controller monitors the level of liquid and once it again reaches level C, the second valve 156 is opened until the level falls again to level D. In the embodiment shown level C corresponds to a liquid depth of 95mm whilst level D corresponds to a liquid depth of 35mm.

As discussed above, the controller measures the number of times the second valve opens to drain liquid from the sump 150. From a knowledge of the volume of liquid required to raise the level from level D to level C the amount of liquid recovered by the VRU 100 during a given period may be determined.

If the controller determines that the level of liquid in the sump 1 50 has increased to level B, an overflow warning is generated. Level B corresponds to a liquid depth of 105mm.

The liquid level should in principle not reach level B unless the second pipe 155 has become blocked.

If the liquid level exceeds level B and reaches the level of the overflow member 157, the liquid should then drain from the sump 150 through the overflow member 157. If the overflow member 157 is blocked for any reason and the liquid level reaches level A, a further alert is provided. Level A corresponds to a liquid depth of 115mm.

It is to be understood that other values of levels A to D and levels 171, 172, 173 are also useful.

It is to be understood that reference to liquid level is reference to a level of liquid above a lowest point of the sump 150 and is not a reference to a level of liquid over ice that may have formed in the sump 150.

In the embodiment shown the first pipe 151 is arranged to drain liquid (typically water) into an auxiliary collection tank 155 for later disposal.

Values of levels A to D and levels 171, 172, 173 may be chosen according to requirements for a given installation. In environments where a high level of water vapour is found in the atmosphere ice may build up more quickly than environments in which a relatively low level of water vapour is found in the atmosphere. Thus, it may be required to de-ice the VRU 100 by heating the heat exchanger more often in relatively humid environments compared with less humid environments.

The relative values of hi and h2 may be chosen to ensure that as little petroleum as possible is drained through the first pipe 151 and yet the value of h2 chosen such that it is unlikely that a level of water in the sump 150 will exceed level 172.

In some embodiments of the invention the heat exchanger module 130 is arranged to be removable by sliding laterally out from a housing of the VRU 100. This feature greatly facilitates maintenance of the apparatus since heat exchanger modules 130 are typically of relatively heavy construction.

FIG. 3 shows a VRU 100 according to an embodiment of the invention installed at a petrol filling station.

The filling station has a petrol dispensing pump 13 of standard or Stage Two type. A pump 13 of Stage Two type has means for recovering vapours generated during a process of dispensing petrol from the pump 13. In some installations the pump has a suction unit arranged to draw into a vapour return pipe 21 gases that are generated during dispensing of fuel. In the particular installation shown the vapour return pipe 21 runs inside a supply line 22 supplying fuel to the pump 13.

The fuel supply line is provided in fluid communication with liquid petroleum 24 stored inside an underground storage tank 23.

A tanker connection coupling 9 is also provided, the coupling being arranged to allow fuel to be dispensed from a tanker into the underground storage tank 23 through petroleum supply line 26.

The underground storage tank 23 has a petroleum vapour vent pipe 27 coupled between the underground storage tank 23 and the vapour recovery unit 100 by means of a manifold 5. The manifold 5 allows a plurality of vent pipes 27 from an underground storage tank farm to be coupled to a single vapour recovery unit 100.

The vent pipe 27 is also in fluid communication with the vapour return pipe 21 running from the dispenser 13. Thus, vapours from the dispenser 13 passing along the vapour return pipe 21 are arranged to pass into the vapour vent pipe 27 and from there to the vapour recovery unit 100.

Between the manifold 5 and the vapour recovery unit 100 an atmospheric vent pipe 15 is provided, in fluid communication with the manifold 5. If a pressure of gas in the manifold exceeds a prescribed pressure, a pressure relieve valve (PRV) 4 is arranged to open thereby to relieve the pressure via the atmospheric vent pipe 15.

The atmospheric vent pipe 15 is also coupled to a gas outlet of the vapour recovery unit 100 to allow cleaned gas passing out from the vapour recovery unit 100 to be vented to atmosphere.

The pressure drop (frictional loss) through the VRU 100 may be arranged to be less than the overpressure setting of the PRV 4 so that the PRV 4 will remain closed during normal operation.

It is to be understood that during a filling operation of an underground storage tank 23 by a tanker in which petroleum passes through petroleum supply line 26, vapour-laden gas in the underground storage tank 23 is displaced as the tank 23 is filled. The displaced gas passes along the vent pipe 27, through the manifold 5 and thereby to the inlet 111 of the vapour recovery unit 100.

In some embodiments the VRU 100 is capable of recovering vapours generated when petrol is dispensed from a dispensing pump 13 as well as when an underground storage tank is filled. In the case of filling an underground storage tank, up to 35000 litres of petroleum may be delivered during a period of around 20 minutes.

It is to be understood that petroleum is a volatile liquid and will typically begin to evaporate whilst in the underground storage tank 23. The rate of evaporation is dependent on temperature and other factors. In a sealed tank petrol will evaporate until a saturation vapour pressure is reached at which point the vapours saturate gas above the liquid petroleum. The pressure attained under saturation conditions is typically well in excess of that considered to be safe in underground storage tanks 23.

Thus, PRV valve 4 would in the absence of the vapour recovery unit 100 release pressure and therefore vent petroleum vapour to atmosphere long before saturation conditions were achieved in the underground storage tank 23.

Thus, in some embodiments of the invention the vapour recovery unit 100 may be arranged to recover vapour generated in the underground storage tank 23 even when a filling operation is not taking place in order to maintain below a prescribed pressure a pressure of gas above liquid petroleum in the storage tank 23.

In some embodiments the vapour recovery unit 100 is arranged to operate intermittently, in order to reduce an amount of energy consumed by the vapour recovery unit 100.

In some embodiments a sensor in fluid communication with the underground storage tank 23 is arranged to cause the VRU 100 to be energised when a pressure of gas exceeds a prescribed value being a value below that at which PRV 4 is arranged to open.

Thus, vapours which would otherwise have been discharged to atmosphere via atmospheric vent pipe 15 pass through the VRU 100.

Once a pressure of gas in the underground storage tank 23 is reduced to a prescribed value (e.g. atmospheric pressure) the VRU 100 may be switched off. This process may in practice be fully automated.

Claims

CLAIMS: 1. A petroleum vapour recovery unit for recovering petroleum vapours from a petroleum vapour-bearing gas comprising: a gas inlet; a gas outlet; a cooler device for cooling a gas flowing through the unit from the gas inlet to the gas outlet thereby to condense the petroleum vapour to form recovered petroleum liquid; at least one liquid outlet arranged to allow said recovered liquid to flow out from the unit; and a heater device for heating at least a portion of the unit thereby to melt ice formed inside the unit during operation of the unit, the unit being arranged to allow melted ice to flow out from the unit through at least one said at least one liquid outlet.
2. A unit as claimed in claim 1 arranged whereby cooling of gas flowing through the unit is terminated when the heater device heats the at least a portion of the unit.
3. A unit as claimed in claim 1 or claim 2 comprising a reservoir, the unit being arranged whereby said recovered liquid is collected in the reservoir.
4. A unit as claimed in claim 3 wherein the reservoir is provided with the at least one liquid outlet.
5. A unit as claimed in claim 4 wherein the at least one liquid outlet is arranged to allow recovered liquid above a level of the at least one liquid outlet to pass through the outlet thereby to be removed from the unit.
6. A unit as claimed in claim 4 or claim 5 wherein at least one liquid outlet comprises an aperture formed in a wall of the reservoir.
7. A unit as claimed in claim 6 wherein the aperture is formed in a side wall of the reservoir.
8. A unit as claimed in any one of claims 5 to 7 wherein the at least one liquid outlet comprises an upstand portion, the outlet being arranged to allow liquid above a level of the upstand portion to pass through the outlet thereby to flow out from the unit.
9. A unit as claimed in any one of claims 4 to 8 wherein the at least one liquid outlet is provided with a valve member arranged to allow a flow of liquid from the reservoir through the at least one liquid outlet to be controlled.
10. A unit as claimed in claim 9 arranged to open the valve member thereby to allow a flow of liquid from the reservoir when a level of liquid in the reservoir reaches a prescribed level.
11. A unit as claimed in any one of claims 4 to 10 comprising first and second liquid outlets, the first outlet being arranged to allow liquid above a first level to be removed from the reservoir, the second outlet being arranged to allow liquid above a second level to be removed from the reservoir, the second level being higher than the first level.
12. A unit as claimed in claim 11 depending through claim 10 arranging to allow recovered liquid to flow through the second liquid outlet when a level of recovered liquid in the reservoir reaches a prescribed level above the level of the second liquid outlet.
13. A unit as claimed in claim 12 arranged to allow a flow of recovered liquid through the second liquid outlet until the level of liquid in the reservoir corresponds to the level of the second liquid outlet.
14. A unit as claimed in claim 13 arranged to close the valve member once the level of recovered liquid in the reservoir corresponds to the level of the second liquid outlet.
15. A unit as claimed in claim 14 arranged to open and close the valve member in order to allow recovered liquid to flow through the second liquid outlet to the level of the second liquid outlet once the liquid level reaches said prescribed level.
16. A unit as claimed in any one of claims 12 to 15 arranged to measure an amount of recovered liquid passed through the second outlet aperture by measuring a number of times the second outlet valve is opened thereby to allow a level of liquid in the reservoir to change from the prescribed level to the level of the second liquid outlet.
17. A unit as claimed in any of claims 11 to 16 arranged to allow liquid to pass through the first outlet when required.
18. A unit as claimed in claim 17 arranged to open a valve member coupled to the first outlet upon receipt of a control signal when a level of liquid in the reservoir is at or below the level of the second liquid outlet.
19. A unit as claimed in any preceding claim wherein the cooler device comprises a conduit through which a cooled gas may be passed thereby to cool a surface of the cooler device exposed to vapour-laden gas passing through the unit, the cooled gas passing through the cooler device being provided in fluid isolation from the vapour-laden gas.
20. A unit as claimed in any preceding claim wherein the heater device comprises a conduit through which a heated gas may be passed.
21. A unit as claimed in any preceding claim wherein the heater device comprises an electric heating element.
22. A unit as claimed in any preceding claim wherein the heater device and the cooler device are provided by the same device.
23. A unit as claimed in any preceding claim wherein the cooler device is arranged to be removable from the unit.
24. A unit as claimed in claim 23 wherein the cooler device is arranged to be removable from the unit by sliding and without a requirement to raise the device by means of a hoist.
25. A method of recovering vapour from a gas comprising: providing a petroleum vapour recovery unit; collecting gas containing petroleum vapour; passing the gas through the unit from a gas inlet to a gas outlet whereby a cooling device of the unit is arranged to condense the vapour to form recovered liquid; allowing recovered liquid to flow out from the unit through at least one liquid outlet; heating by means of a heater device at least a portion of the unit to melt ice formed inside the unit during operation of the unit; and allowing the melted ice to flow out from the unit through at least one liquid outlet.
26. A method as claimed in claim 25 whereby cooling of gas flowing through the unit is terminated when the heater device heats the at least a portion of the unit.
27. A method as claimed in claim 25 or claim 26 comprising collecting said recovered liquid in a reservoir of the unit.
28. A method as claimed in claim 27 wherein the reservoir is provided with the at least one liquid outlet.
29. A method as claimed in claim 28 wherein the at least one liquid outlet is arranged to allow recovered liquid above a level of the at least one liquid outlet to pass through the outlet thereby to be removed from the unit.
30. A method as claimed in claim 28 or 29 comprising the step of allowing recovered liquid above a level of the at least one liquid outlet to pass through the outlet thereby to flow out from the unit.
31. A method as claimed in any one of claims 28 to 30 wherein the at least one liquid outlet is provided with a valve member arranged to allow a flow of recovered liquid from the reservoir through the at least one liquid outlet to be controlled.
32. A method as claimed in claim 31 comprising the step of opening the valve member thereby to allow a flow of recovered liquid from the reservoir when a level of liquid in the reservoir reaches a prescribed level.
33. A method as claimed in any one of claims 28 to 32 wherein the unit comprises first and second liquid outlets, the first outlet being arranged to allow liquid above a first level to be removed from the reservoir, the second outlet being arranged to allow liquid above a second level to be removed from the reservoir, the second level being higher than the first level.
34. A method as claimed in claim 33 comprising the step of opening a second valve member coupled to the second liquid outlet to allow recovered liquid to flow through the second liquid outlet when a level of recovered liquid in the reservoir reaches a prescribed height above the level of the second liquid outlet.
35. A method as claimed in claim 34 comprising the step of allowing a flow of recovered liquid through the second liquid outlet until the level of recovered liquid in the reservoir corresponds to the level of the second liquid outlet.
36. A method as claimed in claim 35 comprising the step of closing the second valve member once the level of recovered liquid in the reservoir corresponds to the level of the second liquid outlet.
37. A method as claimed in any one of claims 34 to 36 comprising the step of measuring an amount of recovered liquid passed through the second outlet aperture by measuring a number of times the second valve member is opened thereby to allow a level of liquid in the reservoir to change from the prescribed level to the level of the second liquid outlet.
38. A method as claimed in any of claims 33 to 37 comprising the step of allowing liquid to pass through the first outlet when required.
39. A method as claimed in claim 38 comprising the step of opening a first valve member coupled to the first liquid outlet upon receipt of a control signal when a level of liquid in the reservoir is at or below the level of the second liquid outlet.
40. A method as claimed in any one of claims 25 to 39 wherein the cooler device comprises a conduit through which a cooler gas may be passed, the method comprising passing the cooler gas through the conduit thereby to cool a surface of the cooler device exposed to vapour-laden gas passing through the unit, the cooler gas passing through the cooler device being provided in fluid isolation from the vapour-laden gas.
41. A method as claimed in any one of claims 25 to 40 wherein the heater device comprises a conduit through which a heated gas may be passed.
42. A method as claimed in one of claims 25 to 41 wherein the heater device comprises an electric heating element.
43. A method as claimed in any one of claims 25 to 42 wherein the heater device and the cooler device are provided by the same device.
44. A method as claimed in any one of claims 25 to 43 wherein the cooler device is arranged to be removable from the unit.
45. A method as claimed in claim 44 comprising removing the cooler device from the unit by sliding in a substantially horizontal direction without a requirement to raise the device by means of a hoist.
46. A unit substantially as hereinbefore described with reference to the accompanying drawings.
47. A method substantially as hereinbefore described with reference to the accompanying drawings.