NO340323B1 - System for collecting pollutants floating on water - Google Patents

Description

Field of the invention

The present invention relates to equipment used for the collection and retrieval of pollution from seawater, and more specifically a system for storing collected pollution and separating the pollution such as oil spills and the like from the water.

Background

Oil spills are often collected from water using a V-shaped oil boom combined with a skimmer towed behind a vessel. At the tip of the skimmer part of the oil boom, a collection bag for the collected oil spill has been installed. The amount of oil spillage that can be collected in the bag is normally dependent on the towing speed of the vessel, which determines how much oil spillage is lifted above the normal water level. However, an oil boom must be towed at a speed low enough to prevent contamination from being mixed into the water. Dispersed oil will easily escape under the boom. When towing ceases, the oil spill will also normally easily escape from the bag.

NO 315 619 describes such a system. At the tip of the oil boom is a flexible open container or bag that acts as a pool for collected oil. At the entrance to the bag, there is a narrowing tunnel that increases the water pressure and raises the water level. This is how the oil spill is lifted into the bag. The water is released through a bottom valve, while the oil spill is caught in the bag.

A known problem with such oil spill collection systems is that the thickness of the oil layer inside the bag, when the bag is open to drain out water, depends on the density difference between oil and water and the height relative to the water line at the outlet of the oil boom to which the bag is connected to. The height depends on the speed at which the system is towed. For example, with a conventional crude oil from the North Sea having a density of 0.8 g/cm<3> and with a relative flow velocity between oil and water of approximately 2 knots (1 m/s), the maximum or greatest thickness of the oil inside in the bag be approximately 20-25 cm. Another known problem is that by supplying oil and water directly to the collection bag, turbulence and a front wave will be produced between the oil and the water inside the bag. This prevents the desired separation between oil and water and means that only a small volume of the bag is available for storing oil.

From WO2013/106681, a purely passive system for collecting oil spills is known, where a number of linked bilges and containers float freely in the water anchored to the seabed. Oil spills flow into the bilges via one-way openings and eventually run/slop into the containers.

From US5073261 a container for separating and storing oil and water is known. The container comprises several dividing plates which define an inlet chamber and several subsequent intermediate chambers. The chambers communicate via openings at the bottom of each partition plate. In the text, it is emphasized that one should try to avoid turbulence in the inlet chamber, so that oil starts to separate already here. The openings in the partitions are dimensioned so that turbulence is also avoided in the subsequent chambers. This system relies on a pump to bring the oil spill into the first chamber, and cannot handle viscous contamination either.

Other prior art appears in US5478480, US6341920, N0773442, US4381994, GB2074887 and WO2011/037479.

Summary of the Invention

One purpose of the present invention is to provide a system for collecting pollution floating on water, where the amount of collected pollution is almost independent of the density difference between pollution and water and/or the towing speed of the system.

It is another object of the invention to provide a system which is secure and will not allow collected contamination to escape even if the container is disconnected from the oil boom, or in the event the towing speed of the oil spill collection system is reduced to zero.

These purposes are fulfilled by a system as defined in the attached requirements.

More specifically, the system comprises a V-shaped oil boom for towing behind a vessel, where the open end of the oil boom is adapted to collect pollution and concentrate the pollution at a pointed end thereof, and where at the pointed end there is a channel leading directly to a container, the container comprising an upper wall, a lower wall, side walls, an inlet section and an end section, where a partition wall placed inside the container near the inlet section divides the container into an inlet part and an inner part, with a gap between the partition wall and the the lower wall allowing fluids to pass the dividing wall, and an outlet located in the lower wall in the inner part of the container. This arrangement will disperse the pollution into the water. The dispersion will easily flow under the partition wall to be trapped inside the container. This is in contrast to prior art methods which depend on using a plate to skim off the contamination from the water. According to various embodiments of the invention, the dividing wall can be vertical or angled, attached to the upper wall and the side walls, or hinged to the upper wall.

The container may also include a perforated tube along the upper wall, the tube being led out of the container and to a position above the waterline. The hose prevents air from collecting in the container. Such trapped air will lower the capacity of the container.

The container should preferably include an inlet pipe with a conical fitting to connect it to an oil boom. This arrangement allows a full container to be released from the oil boom, and to be replaced with an empty container. The full container can then be collected from the sea by another vessel.

In another embodiment, the container may include a level meter to detect the level of contamination inside said container, the level meter being arranged to issue a warning signal when the container is filled to a predetermined level. The purpose of this arrangement is to avoid the container being overfilled. If the container becomes too full, the contamination will flow straight through.

The container can also include at least one coalescing element in the interior of the container, the element preferably including polypropylene split fibers which can be fixed to the dividing wall. Such a coalescence element will increase the speed of the separation of contamination from water, which means that the residence time in the container is reduced, which in turn allows the container to be designed more compactly.

The container may also have a double hull to prevent leakage of collected contamination if the outer fabric is accidentally punctured.

Brief description of the drawings

The invention will now be described in detail, by way of example only, with reference to the attached drawings, in which:

Figure 1 shows a cross-section of an embodiment of the container according to the invention,

Figure 2 is a perspective view of the container in Figure 1, and

Figure 3 shows the container installed in a system for collecting oil spills.

Detailed description

Figure 3 illustrates the intended use of the inventive system. The figure shows an oil boom (oil trawl) 15 which is to be towed behind a vessel (not shown). The open end of the oil boom will collect pollution floating on the water, such as oil spills, and concentrate the pollution at the tip. The boom 15 tapers towards a narrow channel at the tip. At the other end of the channel there is a container 1 for collecting pollution/oil spillage.

The oil spill collected by the oil boom will have a fairly high viscosity, in the range of 100-2000 cP. If the water is emulsified into the oil, the apparent viscosity can reach 300,000 cP measured at a shear rate of 1 sec"<1>. Note that the terms oil spill and contaminant as used herein can be any fluid, mixture of fluids, or emulsion of fluid in water or water in fluid, which has a density lower than water and is not miscible with water Oil can mean anything from thin oil, such as diesel, which floats on water to clumps of near-solid oil, which may incorporate solids such as sand/gravel/granulated materials or absorbent materials.

The container 15 is shown in detail in Figures 1 and 2. The container includes side walls 10, 11 and lower and upper walls 4, 5. The ends of the container include tapered sections. At the front end of the container, the tapered section is terminated in an inlet pipe 2. The inlet pipe 2 may be terminated in a conical coupling ring, for connection to a corresponding coupling device on the oil boom. At the rear end of the container (as seen in the towing direction) there is a tapered section 6 which closes the container.

Inside the container there is a dividing plate 6 near the inlet pipe 2 and an opening with an outlet pipe 7 near the rear end of the container. The dividing plate 8 can be attached to the walls of the container with a slot 9 near the bottom. The dividing wall 8 can be vertical or it can be angled as shown in the figures. The plate divides the container into an inlet part, the upstream plate and an inner part downstream of the plate.

The container may be constructed with rigid walls, for example from a fibre-reinforced plastic material, but is preferably made from a flexible material which allows the container to be completely collapsed for storage. The container may also have a double hull to prevent leakage of collected contamination if the outer fabric is accidentally punctured.

When a mixture of oil and water enters the container through the inlet pipe, it will be forced as an oil in water dispersion to flow down along the dividing plate, in the channel between the dividing plate and the front wall 4, and enter the inner chamber. When less than about 20%-30% oil spill is dispersed in the water, the dispersion will achieve a viscosity close to that of water alone (1 cP). This means that the contamination will flow easily under the partition wall and be trapped in the inner chamber. To achieve this effect, the speed of the water in the inlet section must generally exceed 1 knot. Waves are then formed in the contact between oil and water which disperse (mix) the oil into the water. Technically, for the system to work effectively, the velocity of the fluids in the channel between the dividing plate and the container wall should exceed the termination velocity of the oil droplets in the water.

When the dispersion has passed under the dividing plate and entered the inner chamber, the flow area is significantly enlarged, the velocity of the oil will be lowered and the turbulence reduced. This means that the linear velocity of the dispersion is reduced below the termination velocity of the oil droplets. The oil/contaminant will therefore begin to separate and accumulate on top of the water and become trapped between the walls of the container, the underlying water and the dividing plate. The dividing plate prevents the oil from flowing back through the inlet pipe.

The outlet of the container is arranged below the waterline at the bottom of the container, preferably near the rear section. The outlet can be a fixed opening, or a controllable (closable) outlet means arranged in the outlet pipe. The area of the outlet should be equal to or preferably greater than the smallest area of the inlet part of the container; this means either the inlet itself or the area of the opening into the inner chamber below the partition plate. When the area of the outlet is larger, the flow through the outlet will have the same or lower speed than the flow through the inlet.

Once it has entered the inner part with its calm conditions, the oil will separate from the water. To speed up the separation of oil and water, oleophilic coalescence elements can be installed inside the container. The coalescing elements should preferably be attached to the dividing plate on the side opposite the inlet. The elements can also be attached to a net or frame arranged between the dividing plate and the bottom of the container, the elements extending backwards coinciding with the water flow. The coalescing elements should have an oleophilic surface, a suitable material being polypropylene fibres.

Inside the container, behind the dividing plate, the contaminant will separate from the water, be trapped by the walls (and the plate) and slowly fill the container. As the outlet of the container is in the lower part, and preferably at the bottom, only water will drain out. When the container is filled, the surface of the water will drop until it is at the level of the outlet. Then the container is full, and pollution that enters the container will flow out again.

A level gauge 13 can be installed in the inner chamber. The dipstick will actually measure the level of the oil-water interface. The meter is designed to send out a warning signal if the oil level exceeds a predetermined value, i.e. when the container is full. The warning signal can be realized as an optical signal emitted by a lamp mounted on top of the container, or as a wireless signal sent to a device on the towing vessel or on an accompanying vessel or to a mobile phone.

If the oil boom is towed at speeds above about 1 knot, air will also be easily dispersed into the water and collected behind the dividing plate. This means that the container will float high in the sea and reduce the effective collection capacity of the container. The container will also be more exposed to waves in the surrounding sea. To prevent this effect, a perforated hose 16 has been provided from the upper part of the container to the connection to the oil boom. This air duct drains trapped air from the container. In the case that the container is made of a flexible material, the hose or drainage channel can be realized as an elongated pocket that conducts air from the inner chamber to the inlet of the container. Inside the pocket is a rope (not shown) that prevents the pocket from collapsing. The rope is secured in T-tabs at each end of the pocket.

A full container can be mounted by the oil boom and left floating in the sea for collection by another vessel. When the container is released from the oil boom, it is important that the collected oil spill remains inside the container. This is particularly important when a flexible container is used, which is to be lifted on board another vessel. The container is designed to avoid oil spillage from the container during this operation, with the dividing plate preventing backflow and by the water outlet being located at the bottom of the container. However, safety against loss of oil can be improved by several means. For example, the dividing plate can be arranged as a rotatable wing hinged to the upper wall. If the container is made loose from the oil boom, the plate can swing back towards the inlet and close the inlet. Another means is to manufacture the inlet pipe from a flexible hose and weight the coupling ring on the inlet. When the container is disconnected from the oil boom, the inlet pipe will lower and close the flexible hose. Finally, the outlet pipe can also be produced by a flexible hose. A rope may be attached to the end of this flexible outlet pipe. When the container is disconnected from the oil boom, the discharge pipe can be hinged in and raised above the waterline by pulling on this rope.

The container 1 shown in Figure 1 also includes an opening 12 for emptying, for example by using a suction nozzle. The container can thus be emptied when it floats in the sea.

Claims (11)

1. System for collecting pollution floating on water, comprising a V-shaped oil boom (15) for towing behind a vessel, wherein the open end of the oil boom (15) is adapted to collect pollution and concentrate the pollution at a pointed end of this, and where at the pointed end there is a channel leading directly to a container (1), the container (1) comprising an upper wall (5), a lower wall (4), side walls (10, 11), an inlet section and an end section (6), characterized wood single partition wall (8) located inside the container (1) near the inlet section which divides the container (1) into an inlet part and an inner part, with a gap (9) between the partition wall (8) and the lower wall (4) to allowing fluids to pass through the dividing wall (8), and an outlet located in the lower wall (4) in the inner part of the container. 2. System according to claim 1, where the dividing wall (8) is vertical or wound with its upper part closest to the inlet section. 3. System according to claim 1, where the dividing wall (8) is attached to the upper wall (5) and the side walls (10, 11). 4. System according to claim 1, where the dividing wall (8) is hinged to the upper wall (5). 5. System according to claim 1, further comprising a perforated hose (16) installed in the container along the upper wall (5), the hose being led out of the container (1) and into a position above the water line. 6. System according to claim 1, further comprising an inlet pipe (2) with a conical coupling (3) for connection to an oil boom. 7. System according to claim 1, further comprising a level meter (13) for detecting the level of pollution inside the container (1), the level meter (13) being arranged to issue a warning signal when the container (1) is filled to a predetermined level. 8. System according to claim 1, further comprising at least one coalescing element in the interior of the container. 9. System according to claim 8, wherein said at least one coalescing element includes polypropylene fibers. 10. System according to claim 9, where the polypropylene fibers are attached to the dividing wall. 11. System according to one of the preceding claims, where the container is made of a flexible material that allows the container to be folded together for storage, the outer walls being preferably double-layered.