METHOD AND A DEVICE FOR THE COLLECTION OF OIL SLICKS ON A WATER SURFACE

Abstract: A method for collection of oil slicks (20) on a water surface, using a barge (1) or similar, with a rectangular, transversal bow section (4) and which is towed by a towboat (5) and where there is at least one collection device (8) designed to lead oil in toward the bow section (4) of the barge (1). The water below the oil film (20) in front of the bow section (4) of the barge (1) is set in an upward flow, so that water is led up from the water surface, entraining the oil film (20) and across the forward, transversal bow edge (4) and into a tank room (3) in the barge (1). The water in the lower portion of the tank room (3) is led or flows freely into the surrounding water. A device for embodiment of the method comprises a barge (1) or similar, designed to be towed across the water. The barge has a rectangular transversal bow section (4) and there is mounted at least one long collection device (8) in the form of an oil boom. Outside the bow section (4) there is fastened a device, e.g. a rotating drum (12) or nozzles (20), directed in an upward slant, designed to produce an upward flow of the surrounding water immediately in front of the transversal bow section, sufficiently strong to accelerate the water in an upward slanting direction, which entrains oil from the oil film (14) across the transversal bow section (4).

Description: METHOD AND A DEVICE FOR THE COLLECTION OF OIL SLICKS ON A WATER SURFACE The present invention relates to a method and a device for the collection of oil slicks on a water surface, using a floating collection container in the form of a barge or similar with a receiving bow section and a collection device, such as an oil boom, designed to collect at least some portions of an oil slick. It seems inevitable that large quantities of oil leak from tankers, oil platforms and installations ashore, ending up in the sea and in lakes. Since oil is lighter than water, this will remain as a film on the water surface. Such a floating layer of oil may have an unfavourable influence on marine life and if it should drift toward land, it may spoil the shores in that the oil may foul up beaches, docks, fish farms, etc. Large oil spills at sea are considered catastrophies. Even minor oil spills at a dock or in a coastal region may be quite serious and may entail heavy costs. A number of different methods and devices have been proposed for the collection of oil on water. One known method is to block or capture an oil slick by means of so-called oil booms. An oil boom consists of a long floating member, e.g. a plastic pipe, which on its underside has a skirt with weights at its lower edge so that this hangs down in the water from the floating member. With sufficient lengths of such oil booms it is possible to limit the spread of an oil slick on the water under favourable weather conditions. However, practical use of oil booms have shown that even a moderate current with a speed of one knot will force the oil down under the skirt of the oil boom. Should there be waves of one meter or higher, the use of oil booms will represent great difficulties. There have also been proposed vessels for direct collection of oil slicks on the water surface. From German patent No. 3347988 there is known a vessel which has an open well at the bow, where a conveyor belt runs from a level under the water surface to a higher level, designed to transport oil inside a tank in the vessel. From European patent application No. 0357239 is known a similar device where the transport system consists of a conveyor belt with open mesh, on which is mounted equipment for supplying intensive heat to the transported oil for liquefaction of this so that the oil slides off the conveyor belt when it is led into the vessel. The latter publication points out an important problem for all collection of oil from the ocean surface. A major portion of the oil that ends up in the sea is crude oil, thus a very viscous oil. Such an oil will adhere extremely well to everything it comes into contact with. The known collection devices will therefore soon be covered with oil and will have such a thick layer that the devices scarcely will be able to function. In the European patent an attempt has been made to remedy this by heating the oil which has adhered to the collection devices, in order to transform this viscous oil to a more liquid kind, making it possible to remove it from the collection device. US patent No. 3.684.095 shows a barge-based collection system for an oil slick. The barge is used together with booms. US patent No. 3.726.406 shows a capturing system by using oil booms, as well as water nozzles which are located under the water surface in order to channel a captured oil slick across an edge for collection. Further examples of the state of the art are shown in US patent No. 3.662.891, US patent No. 3.847.815, DE-3.416.683, GB-2.064.971 A and SU-95 85 83. The purpose of the present invention is to give instructions for a method and a device for the collection of oil, also heavy, viscous oil, where the said drawbacks are avoided so that the collection device is not fouled up by heavy, viscous oil. According to the invention this is achieved by a method of the formerly mentioned art, which is characterized in that the collection container is located downstream of and adjacent to the collection device and the oil slick on the water surface is forced to move toward the receiving section of the bow and that a limited water layer immediately below the oil slick in front of the receiving bow section is set in a flow that is directed upward and downstream so that the water layer is raised from the surrounding water level, entraining the supernatant oil slick and transferring it over a threshold in the receiving bow section and down into the collection container. The water and the oil in the collection container is advantageously separated countinuously in an upper oil phase and a lower water phase which is continuously led out of the collection container after first having been mixed. The collection container and the collection device may be kept in a stationary position and the current in the water will advantageously produce a relative movement between the collection container and the surrounding water surface. Alternatively the surrounding water surface may be mainly without a current and the collection container and the collection device are towed across the water surface and produce the said relative movement between the collection container and the surrounding water surface. In conformance with the present invention there is also prepared a device of the art mentioned in the introduction which is characterized in that the collection container is placed downstream of and adjacent to the collection device in such a manner that the oil slick on the water surface is channelled toward the receiving bow section, and that in front of the bow there is placed a device substantially under the water surface, designed to produce a flow in an upward and downstream direction in a limited water level immediately below the oil slick in front of the receiving bow section. A threshold is placed in the receiving bow section over which threshold the flow of the limited water level is led, entraining the supernatant oil slick. The device for producing the directed flow may be one under the waterline operable paddle wheel with its rotation axis running across the longitudinal axis of the collection container, alternatively a number of water nozzles, positioned in a predetermined pattern and with regard to direction. The device for bringing about the directed flow is advantageously positioned in a house which is partly closed, which house has portions designed according to flow-dynamic principles and which has at least one slit through which a water layer created by the device is led for entrainment of the limited water layer and the supernatant oil slick. The collection container may advantageously include adjustable screen devices for adjusting the draught of the collection container. The receiving bow section may also advantageously have a number ofbaffles, which may be adjustable, and which divert the water current that does not move across the threshold, past the house. In the following the invention will be explained in more detail, with reference to the drawing, where Fig. 1 schematically shows an embodiment of the device according to the invention . Fig. 2 shows a top plan view of a barge to be used with the device, Fig. 3 shows a cross section through the barge in Fig. 2 along the line III-III. Fig. 4 shows a longitudinal section through a modified embodiment for a barge. Fig. 5 shows a top plan view of a second embodiment of the collection container or the barge according the invention, Fig. 6 shows a schematic side view of the barge according to Fig. 5, Fig. 7 shows a schematic side view of the barge according to Fig. 6 in an alternative embodiment, Fig. 8 shows a schematic side view and in large scale the receiving bow section of the barge, but not in operation, Fig. 9 shows the same side view as Fig. 8, but in operation, Fig. 10 shows an alternative embodiment of the receiving bow section shown in Fig. 8 and 9, Fig. 11 shows schematically a collection container towed by a vessel through its booms, Fig. 12 shows a stationary collection container positioned in a sound where there is a current and with the collection container anchored to the shore by means of its booms. The device shown in Fig. 1 - 4 for the collection of oil slicks on a water surface consists of a flat barge 1 with lateral tanks 2 and a central tank 3 which occupies most of the vessel. The bow consists of a straight transversal edge 4. The barge is towed by a towboat 5 across tow rope 6, 7. To e.g. tow rope 7 there may be fastened a transfer conveyor, for instance a pressure hose for the transfer of a hydraulic drive medium to the barge from the towboat. Between vessel 5 and barge 1 a collection oil boom is suspended, which transports any oil on the surface into the barge. This oil boom 8 is fastened to the bow section 4 on the port side. At the starboard side there is fastened an additional oil boom 9 which is towed by a smaller vessel 10. With the help of vessel 10 and boom 9 it is possible to collect oil all the way in to an uneven shore line 11. To bow portion 4 of the barge is fastened a device which accelerates water upwardly and rearwardly.In the embodiment according to Fig. 2 and 3 the device consists of a paddle wheel 12, rotating about an axis 13 which runs transversal to the longitudinal direction of the barge. The paddle wheel is run by a motor, not shown, for instance a hydraulic motor and is rotating in the direction of the arrow P. Thereby the paddle wheel will throw the water upwardly across transversal bow section 4 and will entrain oil slick 14 which is floating on the water surface. The water that is thrown over bow section 4 into the barge, i.e. into tank room 3, will rapidly separate from the water so that an upper oil slick 15 and a lower water level 16 are formed. As and when water and oil is fed, the water will automatically be forced out through a bottom opening 17 in the tank. As and when the oil slick 15 is increased in thickness, this may be transferred over to an accompanying vessel or to lateral tanks 2 by means of a pump 8. In Fig. 4 is shown a modified embodiment, in that the paddle wheel 12 is replaced by a slanting plate 19 on whose overside is mounted, upward directed, slanting nozzles 20 to which water is fed from a pump, not shown. These water flows will, simular to the embodiment according to Fig. 3, throw the water with the oil film 14 across the edge of the bow 4 and into tank 3. A principal advantage with the invention is that no mechanical parts come into contact with the oil film in order to channel this into the vessel's tank. The paddle wheel 12 or the nozzles 20 only produce a flow in the water which causes the water and oil to be thrown across the edge of bow 4 and into the tank of the barge. Fig. 5 shows an alternative embodiment of the collection container or barge 1 where the receiving bow section 4 is telescoped somewhat into barge 1. Fig. 6 shows a side view of barge 1 and shows the new positioning of paddle wheel 12 in relation to receiving party 4. The paddle wheel 12 is mounted in a partly enclosing house 33 which transfers water from the surrouding area in toward the paddle wheel 12. The receiving bow section 4 terminates in an edge or a threshold 35 whose height is a bit above the water surface. The reference number 37 shows schematically a wing or a foil with its adjusting organs so that the wing may be turned or tipped. Wing 37 is used to adjust the draught of the barge. Fig. 7 shows an alternative embodiment to the one shown in Fig. 6. Instead of paddle wheel 12 a number of water nozzles 20 are used. These are positioned in a predetermined pattern in order to create a favourable fluid motion. House 33 is also designed with due regard to flow-dynamics in order to create a favourable current. House 33 is only partly closed to allow entrance of the surrounding water. As illustrated in Fig. 5, 6 and 7, barge 1 is kept either in a stationary position or is towed across the water by means of booms 8. The traction force may advantageously be transferred in a lower line or wire 8, which gives a lower point of application in barge 1. In addition the wire may be fastened to the lower skirt of the boom so that the boom will not easily give way and allow the oil to get through. In other words, this is a great help in forcing the oil film toward the receiving bow section of barge 4. The height of boom 8 may also be designed in such a way that the highest point is near barge 1 and the lowest near the shore connection or the towboat. This is because the oil slick is concentrated toward barge 1 and is expected to be increasingly thicker as it approaches barge 1. The water force will be substantial and barge 8 need not withstand greater force than strictly necessary, hence this possibility of decreasing boom height upstream. Fig. 8 shows the receiving bow section 4 in larger scale and not in operation. As illustrated in Fig. 8, house 33 forms an upwardly directed slit 36 through which water shall escape. Fig. 9 illustrates how the water and the oil slick behave during rotation of paddle wheel 12. Paddle wheel 12 draws water in and leads the water as illustrated by the arrows. The water is channelled through slit 36 and forms an inner water layer 31. This slit 36 is placed in such a way as to entrain a thin water slick 30 and which in turn entrains oil slick 14 over threshold 35. As can be seen, the oil scarcely comes into contact with the equipment. If plastic bags, cans, bits of wood, etc., should float on top of the oil film, this is of no importance; everything is transported across threshold 35 without any problems. Fig. 10 shows the alternative embodiment in a larger scale. Here a number of nozzles 20 are placed on a portion 34 of house 33, designed according to flow-dynamic principles. As illustrated by the arrows, these nozzles send a flow of water toward slit 36, similar to the embodiment shown in Fig. 8 and 9. In operation the result will be the same as shown on Fig. 9. As indicated on the figure, the threshold height h from the water surface may be in the order of 150 - 250 mm in a practical embodiment. Slit 36 may for instance be located approx. 50 mm below the water surface. To prevent too much brake effect from the receiving bow section, the latter is designed with baffles which send substantial quantities of water past house 33, both latterally and below. In a practical embodiment paddle wheel 12 and house 33 are designed as small as possible, which means that the draught is as shallow as possible, and as mentioned, will be designed with baffles in the front, so that no large frontal wave will be formed in front of barge 1. Thus it should be understood that only water layer 30 is led over threshold 35, and the remaining quantity of water must be led past house 33 in the best possible flow-technical manner. With regard to water separation inside barge 1, this will function in the same manner as in the embodiment shown in Fig. 1 - 4. Fig. 11 and 12 show two different applications of the device for collection of oil slicks. In Fig. 11 barge 1 is towed by vessel 25 and booms 8 are each fastened to cantilever booms 26. This type of collection is used when there is no substantial current in the water. When there is current in the water, which often is the case in a sound, stationary equipment as shown in Fig. 12 is used. Here barge 1 is stationary and fastened via booms 8 to shore connections 27. Such a system may also be used when tidal water is present; however, the boom must then be turned around regularly as and when the tidal water is changing direction.

Claims: P a t e n t C l a i m s 1. A method for the collection of oil slicks on a water surface, using a floating collection container in the form of a barge or similar with a receiving bow section (4) and a collection device (8) , such as an oil boom, designed to capture at least parts of an oil slick, in that there should preferably be relative movement between the collection container and the surrounding water surface, c h a r a c t e r i z e d i n t h a t the collection container is located downstrem of and adjacent to the collection device and the oil slick (14) on the water surface is forced and concentrated toward the receiving bow section (4) and a limited water level (30) immediately below the oil slick (14) in front of the receiving bow section (4) is set in a flow that is directed upward and downstream so that this water level is raised from the surrounding water level, entraining the supernatant oil layer (14) , and is transferred across a threshold (35) in the receiving bow section (4) and into the collection container. 2. A method according to claim 1, c h a r a c t e r i z e d i n t h a t the water and the oil in the collection container, after first having been mixed, continuously separate into an upper oil phase and a lower water phase which are continuously led out of the collection container. 3. A method according to claim 1 or 2, c h a r a c t e r i z e d i n t h a t the collection container and the collection device are kept in a stationary position and the flow in the water creates the relative movement between the collection container and the surrounding water surface. 4. A method according to claim 1 or 2, c h a r a c t e r i z e d i n t h a t the surrounding water surface is principally without a current and the collection container and the collection device are towed across the water surface and create said relative movement between the collection container and the surrounding water surface. 5. A device for the collection of oil slicks on a water surface, comprising a floating collection container in the form of a barge (1) or similar, with a receiving bow section (4) and a collection device, such as an oil boom (8) , designed to capture at least parts of an oil slick, and for the use of the device there should preferably be a relative movement between the collection container and the surrounding water surface, c h a r a c t e r i z e d i n t h a t the collection container is placed downstream of and adjacent to the collection device (8) so that the oil slick (14) on the weater surface is led toward the receiving bow section (4) , and that a device (12,19) is placed in front of the bow section (4) , substantially under the water surface, designed to bring about an upwards and downstream directed flow in a limited water level (30) immediately below the water level (14) in front of the receiving bow section (4) , and a threshold (35) in the receiving bow section (4) over which threshold (35) the flow of the limited water level (30) is led, entraining the supernatant oil slick (14) . 6. A device according to claim 5, c h a r a c t e r i z e d i n t h a t the equipment for the creation of the directed flow is one under the waterline operable paddle wheel (12) with its rotation axis (13) running across the longitudinal axis of the collection container. 7. A device according to claim 5, c h a r a c t e r i z e d i n t h a t the device for the creation of the correct flow is a number of water nozzles (20) which are placed in a predetermined pattern and with regard to direction. 8. A device according to claim 6 and 7, c h a r a c t e r i z e d i n t h a t the equipment for producing the correct flow is positioned in a house (33) which is designed according to flow-dynamic principles and which has at least one slit (36) through which a water layer (31) , produced by the device, is led for entrainment of the limited water layer (30) and the supernatant oil slick (14) . 9. A device according to one or several of claims 5 - 8, c h a r a c t e r i z e d i n t h a t the collection container comprises adjustable foil equipment (37) for adjustment of the draught of the collection container. 10. A device according to one or several of claims 5 - 9, c h a r a c t e r i z e d i n t h a t the receiving bow section (4) has a number of baffles, adjustable if necessary, which diverts the flow of water, which does not cross the threshold, past house (33) .

Inventors: PETTERSEN ODD, PETTERSEN, ODD
Applicants: PETTERSEN ODD, PETTERSEN, ODD
Application year: 1992
Main classification: E02B15
IPC codes: B63B35, E02B15