Patent Application
20150159336
The present invention relates to equipment used for collection and retrieval of pollution from sea water, and in particular a container for storing collected pollution and separating the pollution such as oil spills and the like, from water.
Oil spills are often collected from water by means of a V-shaped oil boom combined with a skimmer towed behind a vessel. At the apex of the skimmer section of the all boom there is installed a collection bag for the recovered oil spills. The amount of oil spills that may be collected in the bag is normally dependent on the towing speed of the vessel, which determines how much the all spills are lifted above the normal water level. However, an oil boom must be towed at a speed which is low enough to prevent the pollution from being entrained into the water. Dispersed oil will easily slip out below the boom. Also, when the towing ceases, the oil spills will normally easily escape from the bag.
NO 315 619 discloses such a system. At the apex of the oil boom there is a flexible open container or bag acting as a basin for collected all. At the entrance to the bag there is a tapered tunnel increasing the water pressure and lifting the water level. Thus, the oil spills are lifted into the bag. The water is released through a bottom valve, while the oil spills are trapped in the bag.
A known problem with such oil spill collecting 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 in relation to the waterline at the outlet of the oil boom whereto the bag is connected. The height depends on the speed in which the system is towed. For instance with a conventional crude oil from the North Sea having density of 0.8 g/cm3 and with a relative flow speed between the oil and water of about 2 knots (1 m/s), the maximum or greatest thickness of the oil inside the bag will be about 20-25 cm. Another known problem is that by supplying oil and water directly to the collection bag, turbulence and a front wave between the oil and water is created inside the bag. This prevents the desired separation between oil and water and renders only a small volume of the bag available for oil storage.
An object of the present invention is to provide a container for collecting pollution floating on water, wherein the amount of collected pollution is nearly independent of the density difference between pollution and water and/or the tugging speed of the system.
It is yet another object of the invention to provide a container which is safe and will not allow collected pollution to escape even if the container is disconnected from the oil booms, or in case the tugging speed of the oil spill collecting system is reduced to zero.
These objects are met by a container as defined in the appended claims.
In particular the container comprises an upper wall, a lower wall, side walls, an inlet section and an end section, wherein a partition wall located inside the container near the inlet section divides the container in an inlet part and an interior part, with a slot between the partition wall and the lower wall admitting fluids to pass the partition wall, and an outlet located in the lower wall in the interior part of the container.
This arrangement will disperse the pollution into the water. The dispersion will easily flow beneath the partition plate to become entrapped inside the container. This is in opposition to prior art methods, which depend on using a plate to skim off the pollution from the water.
According to different embodiments of the invention, the partition wall may be vertical or inclined, fastened to the upper wall and the side walls, or hinged to the upper wall.
The invention allows oil slips to be concentrated and transferred directly from an oil boom to the container without using pumps. The oil is mechanically dispersed into the water such that the viscosity of the mixture will correspond to the viscosity of seawater. This is obtained by designing the inlet of the container to obtain sufficient turbulence in this area (the relative velocity between the oil and water must exceed 1 knot). The oil boom, the design of the container inlet and the flow of the mixture that includes less than 20-30% by volume oil in water (dependent on the viscosity of the oil) provide for a proper dispersion of oil in water, and which will pass the partition wall with as little friction as possible. It is important that this mixture is kept in dispersion until it has passed the partition wall. The separation of oil from water will occur inside the container behind the partition wall. The oil may be transferred to the pulling ship for storage by simply hoisting the container from the water, or optionally, by pumping the oil to a storage tank on board.
The container may also include a perforated hose along the upper wall, the hose being conducted out of the container and into a position above the waterline. The hose prevents air from being entrapped within the container. Such entrapped air will lower the capacity of the container.
The container should preferably include an inlet tube with a conical coupling for connection to an oil boom. This arrangement allows a full container to be released from the oil boom, and to be replaced by an empty container. The full container may then be collected from the sea by another vessel.
In another embodiment, the container may include a level meter for detecting the level of the pollution inside said container, the level meter being adapted to issue a warning signal when the container is filled to a predetermined level. The purpose of this arrangement is to avoid the container from becoming overfilled. If the container becomes too full, the pollution will flow straight through.
The container may also include at least one coalescent element in the interior of the container, the element preferably including polypropylene split fibers that may be fastened to the partition wall. Such a coalescent element will speed up the separation of pollution from water, which means that the retention time in the container is diminished, again allowing the container to be designed more compact.
The container may also have a double hull to prevent leakage of collected pollutant if the outer fabric is accidentally punctured.
The invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:
The oil spill collected by the oil boom can have a quite high viscosity, in the range of 100-2000 cP. If water is emulsified into the oil, the apparent viscosity may reach 300 000 cP measured at a shear velocity of 1 sek−1. Note that the terms oil spill and pollution as used here may be any fluid, mixture of fluids or emulsion of fluid in water or water in fluid, that have a density lower than water and being immiscible with water. Oil may mean anything from thin oil, such as diesel, floating on the water to lumps of nearly solidified oil, possibly incorporating solids such as sand/pebbles/granulated materials or absorbing materials.
The inventive container 15 is shown in detail in
Inside the container there is a partition plate B close to the inlet tube 2 and an opening with an outlet tube 7 near the aft of the container. The partition plate 8 may be fastened to the walls of the container leaving a slot 9 near the bottom. The partition wall 8 may be vertical or it may be inclined as shown in the figures. The plate divides the container into an inlet part upstream of the plate, and an interior part downstream of the plate.
The container may be designed with stiff walls, e.g. from a fiber-reinforced plastic material, but is preferably made from a flexible material allowing the container to be fully collapsed in storage. The container may also have a double hull to prevent leakage of collected pollutant if the outer fabric is accidentally punctured.
When a mixture of oil and water enters the container through the inlet tube, it will be forced as an oil in water dispersion to flow down along the partition plate, in the channel between the partition plate and the upfront wall 4, and enter the interior chamber. When less than about 20%-30% oil spill is dispersed into the water, the dispersion will obtain a viscosity near the viscosity of water alone (1 cP). This means that the pollution will flow easily below the partition wall and be trapped in the interior chamber. In general, to achieve this effect the velocity of the water in the inlet section must exceed 1 knot. Then, waves are formed in the oil-water contact dispersing (entraining) the oil into the water. Technically, for the system to work efficiently, the velocity of the fluids in the channel between the partition plate and the container wall should exceed the termination velocity of the oil drops in the water.
When the dispersion has passed under the partition plate entering the interior chamber, the flow area is substantially enlarged, the oil velocity lowered and the turbulence lowered. This means that the linear velocity of dispersion is reduced below the termination velocity of the oil drops. Thus, the oil/pollution will start to separate and collect on top of the water and be trapped between the walls of the container, the underlying water and the partition plate. The partition plate prevents oil reflux through the inlet tube.
The outlet of the container is arranged below the waterline at the bottom of the container, preferably near the aft section. The outlet may be a fixed opening, or a controllable (closable) outlet means arranged in the outlet tube. The area of the outlet should be equal to or preferably larger 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 interior chamber below the partition plate. When the area of the outlet is larger, the flow through the outlet will have equal or lower velocity than the flow through the inlet.
When inside the interior part with its quiet conditions, the oil will separate from the water. In order to speed the separation of oil and water, oleophilic coalescence elements may be installed inside the container. The coalescence elements should preferably be fastened to the partition plate on the side opposite the inlet. The elements may also be fastened to a net or frame arranged between the partition plate and the bottom of the container, the elements extending backwards co-currently with the water flow. The coalescence elements should have an oleophilic surface, a suitable material being polypropylene fibers.
Inside the container, behind the partition plate, the pollution will separate from the water, be trapped by the walls (and 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 be drained out. As the container is filled, the surface of the water will sink until it is at the level with the outlet. Then, the container is full and pollution entering the container will flow out again.
A level meter 13 may be installed in the interior chamber. The level meter will actually measure the level of the oil-water interface. The meter is adapted to emit a warning signal if the oil level exceeds a predefined value, i.e. when the container is full. The warning signal may be realized as an optical signal emitted by a lamp mounted on top of the container, or as a wireless signal transmitted to a device on the towing vessel or an accompanying vessel, or to a mobile phone.
If the oil boom is towed at speeds above approximately 1 knot, air will also easily become dispersed into the water and be collected behind the partition plate. This means that the container will float high in the sea reducing the effective collection capacity of the container. Also, the container will 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 channel drains entrapped air from the container. In case the container is made in a flexible material, the hose or draining channel may be realized as a longitudinal pocket conducting air from the interior chamber to the container inlet. Inside the pocket there is a rope (not shown) preventing collapsing of the pocket. The rope is fastened in T-flipps at each end of the pocket.
A full container may be dismounted from 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 essential that the collected oil spills stay inside the container. This is particularly important when a flexible container is used, and is to be lifted on board another vessel. The container is designed to avoid oil spills from the container during this operation, with the partition plate preventing reflux and the water outlet being located at the bottom of the container. However, the security against loss of oil may be improved by several means. For example, the partition plate may be designed as a rotatable flap hinged to the upper wall. If the container is detached from the oil boom, the plate may swing back towards the inlet and close the inlet. A second measure is to produce the inlet tube from a flexible hose and weighting the inlet coupling ring. When the container is detached from the oil boom, the inlet tube will sink and close the flexible hose. Lastly, also the outlet tube may be produced from a flexible hose. A rope may be fastened to the end of this flexible outlet tube. When the container is detached from the oil boom, the outlet tube may be hauled in and elevated over the waterline by pulling this rope.
The container 1 shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 20131621 | Dec 2013 | NO | national |
