VAPOUR RECOVERY SYSTEM

Abstract: An apparatus and method for recovering a volatile organic compound which arises in gaseous form during the transfer of a volatile organic liquid from a first to a second container, the method comprising feeding said gaseous volatile organic compound from said first or second container to a heat exchanger, feeding a cryogen to said heat exchanger to cause said gaseous volatile organic compound to condense and feeding said condensed volatile organic compound to a third container.

Description: Vapour Recovery System The present invention relates to a method and apparatus for recovering gaseous volatile organic compounds (NOCs) in liquid form for use particularly, but not exclusively in the petrochemical industry for recovering petroleum vapours from petroleum transport vehicles and/or containers and/or fixed site installations. Conventionally, when a petrol delivery tanker carrying a load arrives at a delivery site, for example a commercial petrol vending site, the tanker body is connected via an outlet port and hose so that petrol is voided from the tanker body. Voiding can be under gravity or it can be pressure assisted. Petrol passes through a conduit system to an underground storage facility or the like, from where customers/users can access the petrol at individual pumping stations. The space above the level of petroleum in the underground storage facility contains vapours, sometimes to a saturated level. Upon filling the storage facility with the delivery load, these vapours are displaced and vented to the atmosphere via extended pipes. When the tanker has transferred all its liquid contents to the storage facility, the tanker interior has petroleum vapours therein. Typically, the tanker would then make a return journey to its filling station/distribution depot for refilling. At the distribution depot the tanker is connected to a fill pipe and petrol is pumped from a storage reservoir into the empty tanker. As the petrol fills the tanker, the vapours inside the tanker are expelled via a vent pipe to atmosphere. When the tanker is filled, it is then ready to make another delivery. The vapours that are vented to atmosphere contain many potentially hazardous chemicals. These chemicals include benzene which, according to the International Agency for Cancer Research (IARC) classification system, is a class 1 carcinogen i.e. is proven to cause cancers in humans. International treaties and legislation seek to reduce benzene emission to a zero level and provide for heavy financial penalties and/or terms of imprisonment to those who do not comply. Some specialised distribution depots provide fixed facilities to compress the tanker interior vapours during filling the tanker in an attempt to recover some of the gaseous VOCs in liquid petroleum gas (LPGs) form. However, not all distribution depots are provided with such compression facilities. Moreover these types of facilities are expensive to install and maintain. In the instance of a compression recovery facility breakdown, it follows that no tanker can be filled and so delivery is interrupted indefinitely at some considerable cost to the delivery company and inconvenience to the consumer. Additionally, compression recovery facilities can only handle a limited number of tankers at one time. The recovery process takes between 20-40 minutes per tanker, depending on the tanker size, to complete. Consequently, tanker queuing is commonplace. Typically, between 40-60 litres of petrol can be recovered from a 33,000-litre carrying capacity tanker. Given that a tanker can make many trips per day then the volume of petrol recoverable is considerable. This volume of recovered petrol is commercially important since the vapours are a valuable duty paid product. Of perhaps more concern is that if the vapours are allowed to simply vent to atmosphere then the environmental pollution is overwhelming especially given the benzene content in petrol is in the range of several parts per million. A further problem associated with the prior art is that during a return journey from a delivery site, for example a commercial petrol vending site to the filling station/ distribution depot the tanker is carrying a load of gaseous VOCs. The load is thus potentially explosive and combustible during this transit period. A system that could provide rapid, safe, economical, reliable vapour recovery at a site of delivery and a site of filling, in addition to providing an inert tanker load on a return journey would offer immediate advantage to the industry, consumer and the environment. According to a first aspect of the invention there is provided an apparatus for recovering a volatile organic compound which arises in gaseous form during the transfer of a volatile organic liquid from a first to a second container, said apparatus comprising at least one heat exchanger unit, means for feeding said gaseous volatile organic compound from said first or second container to said at least one heat exchanger, a vessel for storing a cryogen, means for feeding said cryogen to said at least one heat exchanger so as to condense said gaseous volatile organic compound, means for feeding said volatile organic compound to a third container. Preferably, one of said first or second containers is a tanker vehicle. Preferably, said cryogen is stored on or with said tanker vehicle. Preferably, said heat exchanger is mounted on or provided with said tanker vehicle. Preferably, said apparatus comprises a plurality of heat exchangers. Preferably, said cryogen is liquid nitrogen or any other cryogen that is in liquid form, ideally the amount of liquid nitrogen provided is in the region of 20-50 Kg and more ideally 25-40 Kg. Preferably, said apparatus additionally comprises a series of valves for controlling the flow of cryogen and/or gaseous volatile organic compound and/or condensed volatile organic compound recovered. The valve(s) may be expansion valves and operated by means of temperature and/or pressure and/or simple pneumatics. Preferably, said heat exchanger houses an elongate section of pipe that is configured so as to provide a large surface area for vapour contact. For example, the pipe may be configured so that it is bent, and ideally folded back upon itself, in flattened S/concertina fashion. In this way, the pipe surface area is maximised with respect to the volume it occupies within the heat exchanger. Accordingly a thin pipe can be bent back upon itself many times and provide a large surface area for vapour contact. The pipe is attached at one end to the cryogenic condenser, from which it transports liquid nitrogen to the heat exchanger. The pipe passes into a lower wall surface of the heat exchanger. Pipe inside the heat exchanger is configured so as to provide a large cold surface area for vapour contact. The pipe exits the heat exchanger at an upper wall surface into the tanker main body so that expanded gaseous nitrogen can fill the tanker and/or be vented to atmosphere. Preferably, said heat exchanger is provided with at least two ports. A first port being positioned at an upper area of a wall for allowing vapours into the heat exchanger, and a second port being positioned at a lower area of a wall for allowing liquid to exit said heat exchanger. Ideally, said second port is associated with said third container. In one embodiment of the invention the apparatus additionally comprises at least one refrigerant cooling unit, ideally said refrigerant cooling unit is sealed and is adapted to circulate a refrigerant such as glycol or the like. It will be appreciated that the apparatus of the invention is intended to be operate on, or as part of, a delivery tanker but that the system is equally suited as a portable stand-alone unit or can be used at a fixed installation site. Thus, vapours can be recovered during a filling operation from either the tanker itself or the underground storage facility or both and the condensed petrol left on site. The specifics of which are not intended to limit the scope of the application. In another embodiment of the invention the apparatus is provided as a kit of parts including at least one cryogen storage unit and at least one heat exchanger. According to a second aspect of the present invention there is provided a method for recovering a volatile organic compound which arises in gaseous form during the transfer of a volatile organic liquid from a first to a second container, the method comprising feeding said gaseous volatile organic compound from said first or second container to a heat exchanger, feeding a cryogen to said heat exchanger to cause said gaseous volatile organic compound to condense and feeding said condensed volatile organic compound to a third container. Preferably, said gaseous volatile organic compound is condensed during filling of said first or second container and may optionally be left on site. Thus, gaseous volatile organic compound(s) can be recovered in liquid form during the filling of a tanker and the condensate can be left on site. Additionally, or alternatively, gaseous volatile organic compound(s) can be recovered from an underground tank via a recovery pipe placed in connection with the tanker as the fuel load is discharged from said tanker. The recovery pipe is connected at one end to a vent pipe which is provided with a suction and pressure valve. At an opposite end, said recovery pipe is connected to a dedicated port provided on the tanker for vapour collection. Concentrated gaseous volatile organic compound(s) is/are then returned to a depot for processing as the tanker is being re-filled. In another embodiment of the invention the heat exchanger is connected in series with said recovery pipe and the gaseous volatile organic compound(s) are condensed to liquid form before reaching the tanker. Expanded gaseous cryogen, ideally nitrogen, is fed to the tanker interior so as to provided an inert atmosphere therein. A further advantage of the apparatus and method of the invention is in providing an atmospherically inert tanker interior so that transportation of a tanker, having unloaded its volatile organic liquid, is safer. Moreover volatile organic liquids are recovered form vapours and are not vented to atmosphere thus providing significant financial savings whilst concomitantly preventing environmental damage. The invention will now be described, by way of example only with reference to the following Figures, wherein: Figure 1 represents the vapour recovery system according to the present invention attached to a delivery tanker. Figure 2 represents the heat exchanger unit of the vapour recovery system of Figure 1 in greater detail. Figure 3 represents an alternative embodiment of a heat exchanger unit of the vapour recovery system according to the present invention. Figure 4 represents a further alternative embodiment of a heat exchanger unit of the vapour recovery system according to the present invention. Figure 5 represents a yet further alternative embodiment of a heat exchanger unit of the vapour recovery system according to the present invention. With reference to Figure 1 there is shown a vapour recovery system according to the present invention attached to a delivery tanker 13. The tanker 13 is connected to an underground petroleum storage tank 12 by a pipe 8 so as to deposit liquid petroleum 14 into the storage tank 12 positioned below man chamber 11. As the level of liquid petroleum 14 rises, vapours in space 15 are directed via pipe 16 under pressure and suction under the control of valve 10. Connection along pipe 16 to vapour collection pipe 5 is controlled by valve 9. In the instance of valve 9 being opened, vapours pass through pipe 5 into heat exchanger 1. In heat exchanger 1 vapours contact the cold shell of the undulated pipe-work infrastructure 17. Liquid nitrogen from cryogen storage unit 2 flows through the undulated pipe- work infrastructure 17 via control valve 6. The pipe-work 17 is shaped so as to provide a large surface area for vapours to contact so that the efficiency of recovery is maximised. Vapours that have condensed upon contact with the cold surface of cryogenic containing pipework 17 are decanted into a tank 3 provided with a vent 7. Expanded gaseous nitrogen is directed to ullage 18 of tanker 13 via pipe 4. During this process the liquid nitrogen boils, giving up both its sensible heat and its latent heat of evaporation. Provision for additional nitrogen, which is not necessary for the thermal reaction, is made by means of control valve 6 and a by-pass connection via pipe 49 into pipe 4. It will therefore be appreciated from the foregoing that the vapour recovery system of the present invention involves no moving parts other than control valves, and that the system is powered by liquid nitrogen. No additional energy is required to complete the recovery of VOCs. Thus the system provides a means for recovering commercially important and environmentally damaging VOCs, at sites of delivery or sites of filling. Moreover the system can be fitted retrospectively to tankers or can be provided as a kit of parts or can be provided as an integral part of a delivery tanker or can be provided as a stand-alone portable apparatus for use with a tanker or fixed site installation. The system offers flexibility and is cost effective in saving time for recovery as compared to conventional recovery systems. A further significant advantage of the vapour recovery system of the present invention is that the tanker is inert for its return load in that the contents of ullage 18 is gaseous nitrogen. Gaseous nitrogen can be safely vented to atmosphere without any deleterious effects to the environment since the earth's atmosphere is predominantly nitrogen (80%). With reference to Figure 2 there is shown the heat exchanger 1 of Figure 1 in greater detail. Pipe 6 carrying liquid nitrogen enters heat exchanger 1 at position 21 of wall 19. The pipe is bent back upon itself so as to maximise the surface area available for vapour contact within the defined space 25 of the heat exchanger. Pipe 6 is continuous and exits the heat exchanger at an upper position 23 of wall 20. Vapour enters the heat exchanger via port 22 provided at an upper region of wall 19, and condensed petrol/ liquid exits via port 24 provided at a lower region of wall 20. In the embodiment depicted in Figure 3 there is shown a two-stage condenser. With reference to Figure 3 there is shown a pair of adjacent heat exchangers 1 A and IB, linked at an upper region by a bridge 27 of continuous closed lop circuit 26. Heat transfer fluid such as glycol is circulated around pipe circuit 26 by means of a pump 28. In this embodiment liquid nitrogen enters heat exchanger 1 A at port 29 and exits in gaseous form from port 30. Vapours enter adjacent heat exchanger IB at port 31 and exit in liquid form via port 32 to be collected in vessel 33. The embodiment of Figure 4 is suited to instances where there is a large temperature difference (ΔT) whereby sublimation of vapours could occur. This embodiment allows for the collection of frozen recovery product(s) after completion of a cycle. With reference to Figure 4 there is shown a single heat exchanger 1 positioned at an upper region 34 of a vessel 35. Liquid nitrogen enters at region 36 and exits in expanded gaseous form at region 37. Vapours enter the vessel at port 38 and pass over the heat exchanger 1 whereby they are condensed to liquid form and are directed by plates 40 so as to collect in vented 7 vessel 35 as pool 41. This embodiment is intended for use as a combined condenser and condensate storage tank. Finally, with reference to Figure 5 there is shown a yet further embodiment of the invention as depicted in Figure 4. In the embodiment of Figure 5 the vapour recovery system of the invention uses conventional refrigeration technology as the heat exchange medium. The system is additionally provided with an expansion valve, a compressor 43 and the coil 44 is air-cooled. Thus it will be appreciated from the foregoing that the vapour recovery system of the present invention offers a flexible and economical system for recovering gaseous VOCs and condensing them to liquid form. P32012.1

Claims: Claims 1. An apparatus for recovering a volatile organic compound which arises in gaseous form during the transfer of a volatile organic liquid from a first to a second container, said apparatus comprising at least one heat exchanger unit, means for feeding said gaseous volatile organic compound from said first or second container to said at least one heat exchanger, a vessel for storing a cryogen, means for feeding said cryogen to said at least one heat exchanger so as to condense said gaseous volatile organic compound, means for feeding said volatile organic compound to a third container. 2. An apparatus according to Claim 1 wherein one of said first or second containers is a tanker vehicle. 3. An apparatus according to either preceding claim wherein said cryogen is stored on or with said tanker vehicle. 4. An apparatus according to any preceding claim wherein said heat exchanger is mounted on or provided with said tanker vehicle. 5. An apparatus according to any preceding claim comprising a plurality of heat exchangers. 6. An apparatus according to any preceding claim wherein said cryogen is liquid nitrogen or any other cryogen that is in liquid form. 7. An apparatus according to Claim 6 wherein the amount of liquid nitrogen provided is in the region of 20-50 Kg 8. An apparatus according to Claim 7 wherein the amount of liquid nitrogen provided is 25-40 Kg. 9. An apparatus according to any preceding claim further comprising a series of valves for controlling the flow of cryogen and/or gaseous volatile organic compound and/or condensed volatile organic compound recovered. 10. An apparatus according to Claim 9 wherein the valves are expansion valves operated by changes in temperature and/or pressure and/or by simple pneumatics. 11. An apparatus according to Claim 1 wherein the heat exchanger houses an elongate section of pipe that is configured so as to provide a large surface area for vapour contact. 12. An apparatus according to Claim 11 wherein the pipe is bent and folded back upon itself in flattened S/concertina fashion. 13. An apparatus according to either Claim 1 1 or 12 wherein one end of the pipe is attached to the cryogenic condenser, from which it transports liquid nitrogen to the heat exchanger. 14. An apparatus according to any of Claims 11-13 wherein one end of the pipe exits the heat exchanger at an upper wall surface into the tanker main body so that expanded gaseous nitrogen can fill the tanker and/or be vented to atmosphere. 15. An apparatus according to any preceding claim wherein the heat exchanger is provided with at least two ports. 16. An apparatus according to Claim 15 wherein a first port is positioned at an upper area of a wall for allowing vapours into the heat exchanger, and a second port is positioned at a lower area of a wall for allowing liquid to exit said heat exchanger. 17. An apparatus according to either Claim 15 or 16 wherein the second port is associated with said third container. 18. An apparatus according to Claim 1 further comprising at least one refrigerant cooling unit. 19. An apparatus according to Claim 18 wherein the refrigerant cooling unit is sealed and is adapted to circulate a refrigerant such as glycol or the like. 20. An apparatus according to any preceding claim wherein the apparatus operates on, or as part of, a delivery tanker or alternatively as a portable stand-alone unit or at a fixed installation site. 21. An apparatus for recovering a volatile organic compound which arises in gaseous form during the transfer of a volatile organic liquid from a first to a second container comprising a kit of parts including at least one cryogen storage unit and at least one heat exchanger. 22. A method for recovering a volatile organic compound which arises in gaseous form during the transfer of a volatile organic liquid from a first to a second container, the method comprising feeding said gaseous volatile organic compound from said first or second container to a heat exchanger, feeding a cryogen to said heat exchanger to cause said gaseous volatile organic compound to condense and feeding said condensed volatile organic compound to a third container. 23. A method according to Claim 22 wherein said gaseous volatile organic compound is condensed during filling of said first or second container. 24. A method according to either Claim 22 or 23 wherein the gaseous volatile organic compound(s) is/are be recovered in liquid form during the filling of a tanker and the condensate is left on site, additionally, or alternatively, gaseous volatile organic compound(s) is/are recovered from an underground tank via a recovery pipe placed in connection with the tanker as the fuel load is discharged from said tanker. 25. A method according to any of Claims 22-24 wherein the recovery pipe is connected at one end to a vent pipe which is provided with a suction and pressure valve and at an opposite end said recovery pipe is connected to a dedicated port provided on the tanker for vapour collection whereby vapour recovery is controlled. 26. A method according to any of Claims 22-25 wherein concentrated gaseous volatile organic compound(s) is/are then returned to a depot for processing as the tanker is being re-filled. 27. A method according to any of Claims 22-26 wherein the heat exchanger is connected in series with said recovery pipe whereby gaseous volatile organic compound(s) are condensed to liquid form before reaching the tanker. 28. A method according to any of Claims 22-27 wherein expanded gaseous cryogen is fed to the tanker interior so as to provided an inert atmosphere therein. 29. A method according to any of Claims 22-28 using the apparatus of Claim 1 and any one or more of the features of Claims 2-21. 30. A volatile organic liquid produced by the method of Claim 22 and optionally further including any one or more of the preferred features of Claims 23-29 and/or produced using the apparatus of Claim 1 and optionally further including any one or more of the features of Claims 2-21.

Inventors: BOOTHROYD DAVID LAWRENCE, BOOTHROYD, DAVID, LAWRENCE
Applicants: ADVANCED CRYOGENIC SYSTEMS LIM, BOOTHROYD DAVID LAWRENCE, ADVANCED CRYOGENIC SYSTEMS LIMITED, BOOTHROYD, DAVID, LAWRENCE
Application year: 1999
Main classification: B01D5
IPC codes: B01D53