GB2480858A - An oil spill recovery system - Google Patents

Abstract

The invention relates to an oil spill recovery system, comprising a collection device and a separation device. The collection device includes a suction mechanism and the separation device also stores the recovered oil. The suction mechanism may be a propeller 6 or a pump. The collection device may be a pontoon kept afloat by floats 3. A funnel 8 may form the inlet to the collection device and may form a weir. The separating device may be a gravity settling tank arranged to allow sea water (16 figure 3) to flow from the base of the tank, whilst the recovered oil remains (15 figure 3) in the tank. The separation device may have a removable cover (17 figure 3).

Description

Oil Spill Recovery System This invention relates to a collector and separation device for collecting and separating oil from water in the event of an oil spill.

Although the majority of oil pollution occurs on land, every year there are many oil spills in the ocean or similar navigable waters. Spills and leaks often occur from transportation vessels, underwater pipelines, or offshore oil rigs.

The response to the incident typically focuses on minimising the overall environmental impact. The environmental impact is influenced by the nature of the oil, the rate of spillage, the sea and weather conditions, the sensitivity of the environment, and the proximity to the shore.

A large marine spill is considered to constitute the release of over 700 tonnes of oil into the environment. In the years 2000 to 2009 there were an average of 3.3 large spills per year. This is lower than in previous decades, which is encouraging given that in the same decade there has been an overall increase in oil movements. The vast majority of oil spills are smaller. In the same decade there were 160 oil spills of between 7 and 700 tonnes of oil (figures are taken from The International Tanker Owners Pollution Federation Ltd website, accessed 26 May 2010, at http://www.itopf.com!information-services/data-and-statistics/statisticsf) . It is likely that oil spills will continue to be a concern for the foreseeable future.

Known methods for responding to an oil spill include the use of dispersants, burning the oil, the use of booms and mechanical recovery (in the form of skimmers, for example), or alternatively doing nothing. There are advantages and disadvantages to each approach, and the effectiveness of each solution depends on the circumstances. The choice of clean-up method is usually determined by the same factors that influence the environmental impact, i.e. the sea and weather conditions, the rate of spillage, and the location of the spill.

The use of dispersants remains controversial, as dispersants can be as toxic as the oil itself if used in close proximity to the shore. Dispersants act to encourage natural degradation of the oil, especially when combined with wind and wave action. Burning the oil on the surface of the sea produces toxic fumes; therefore this method is only used in open water. In addition, in order to ignite the oil the slick must be at least 3mm thick, and relatively fresh, as the volatile components tend to evaporate rapidly. Both methods do not recover the spilt oil.

As hydrocarbon resources become depleted and oil production costs increase over time, it would be advantageous to recover the spilt oil for re-use.

Recovery of the oil would also reduce the environmental impact of the spill.

Mechanical recovery methods are known, for example, skimmers are commonly used in conjunction with a boom. Mechanical recovery methods are usually regarded as expensive, labour intensive and inefficient. A successful clean-up operation would typically recover just 10% of the spilt oil. There are numerous types of skimmer available, some of which collect the oil for further processing, and some which are based on sorbent systems. The sorbent systems are designed to retain oil and reject water. These systems often involve towing lengths of sorbent material behind a vessel. This method is capable of recovering up to 70 tonnes of oil an hour (see for example, OPEC Offshore Emergency Oil Skimmer Force 7', details of which can be found online at http://www.opec.co.uklproducts_opro5.html). Booms may also be constructed from sorbent materials. Both of these methods have the disadvantage however, that the oil is not recovered for reuse and typically the sorbent materials are disposed of in a land fill.

Alternative skimmers include weir skimmers, drum skimmers, belt skimmers, vacuum skimmers and rotating disc skimmers, which allow for the collection of oil for re-use. The choice of skimmer depends on the conditions and the type of oil to be collected, but calm waters are usually required for skimmers to be effective. Rotating disc skimmers are considered the most effective, but this is only the case for certain types of oil. If the oil is too thin it will not adhere to the discs. These types of skimmer have slower oil recovery times, typically processing 20 to 40 tonnes of oil an hour.

Other mechanical methods include oil spill recovery vessels designed to collect oil from the open ocean. One such example is a vessel with a hinged split hull which opens and acts as two collecting arms to funnel the oil into the vessel.

This system has the advantage of being complete with significant on-board storage capacity. A vessel such as this is expensive, however, prohibiting widespread use.

The object of the current invention is to provide an alternative method of concentrating large quantities of spilt oil from the surface of the sea, quickly and at a reduced cost in comparison with known mechanical recovery methods.

According to the present invention, there is provided an oil spill recovery system, comprising a collection device and a separation device; where the collection device includes a suction mechanism and where the separation device is also a containment system.

The collector comprises a floating pontoon or raft under which is suspended a shallow funnel which is held just below the surface of the water. The funnel is designed to form a weir at the oillliquid interface, the height of the weir being adjustable. In the lower, narrow portion of the funnel a propeller is fitted to draw the water/oil mixture through the funnel and into an outlet pipe. The propeller is driven by an engine which is fixed to the top of the pontoon or raft.

Alternatively, a pump or suction device could be used in place of the propeller.

The outlet pipe is fixed to the bottom of the funnel and connects the funnel to the separation device. In the separation device (the store) the oil/water mixture is separated using the difference in specific gravity. The store consists of a large diameter container, with an upper rim protruding at least 1 metre above the surface of the water. Under the surface of the water the walls of the store extend by at least 1 metre, preferably more, in order to create laminar flow conditions in which the oil and water can separate. Internal baffles, inclined plates or other coalescence techniques may be also be used within the store to improve the rate of coalescence and to reduce turbulent flow in the settling zone.

The store could be manufactured from steel, aluminium or an oil resistant plastic. Floats or buoyancy aids are fitted around the perimeter of the ring and spaced equidistantly. Optionally, the walls of the container can be made of a buoyant material, or formed with integral buoyancy aids. Flexible plastic sheeting could be used if supported on a suitable frame.

Once the oil layer in the store has reached sufficient depth, or after sufficient time has passed, a vessel can be deployed to collect the oil for further processing. The collection and separation system is easily scalable, with the advantage that both high and low capacity units can be produced.

The collector and store can be easily repositioned as they are designed to float on the surface of the ocean. The floating raft or pontoon of the collection device could be fitted with a sail, a motor, or be left to drift within the desired area. The pontoon does not have to be manned.

The collector and store offer many advantages over the prior art. This system is relatively simple to manufacture, with few moving parts (low maintenance), it is effective, mobile, relatively cheap, and capable of processing large quantities of oil/water mixture in a short time frame.

Examples of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a schematic showing a vertical cross-sectional view of the collector device.

Figure 2 shows an aerial view of the store.

Figure 3 is a schematic showing a vertical cross-sectional view of the store.

Referring first to Figure 1, the collector device is illustrated in cross-section.

The pontoon (1) or raft is kept afloat above the sea level (2) using floats (3). On the pontoon is an engine (4), connected to a gear box (5), for example, a bevel gear box, which drives a propeller (6) through a shaft (7). The propeller (6) is positioned in the lower, narrow end of the funnel (8). Bearing brackets (9) are also illustrated. The oil/water mixture (10) is drawn through the outlet pipe (11). The position of the pontoon in relation to the funnel is variable. Element (12) is arranged to reduce cavitation at the centre of the funnel, and can also be used to adjust or control the flow into the fimnel. The funnel need not be circular in shape. A pump could be used as an alternative to the propeller. The pontoon or raft could be substituted for any other floating vessel, and the collector device need not be situated directly below the vessel.

Figure 2 illustrates an aerial view of the store (13). The store is kept afloat using floats (14) spaced equidistantly along the perimeter. Alternatively the walls of the store could be formed from a buoyant material or include buoyant air cavities. The circular (cylindrical) shape is not essential and other configurations could be used.

The store is illustrated in greater detail in Figure 3. The oiL/water mixture (10) enters the store through the outlet pipe (11). The outlet pipe is positioned so as to optimise the recovery of oil and prevent the oil leaving through the bottom of the tank. As the oil and water separates due to the difference in specific gravity, an oil layer (15) accumulates at the surface of the store, and the concentration of oil is increased compared to the original slick. Sea water (16) is free to leave from the bottom of the tank. Smaller models of the store may include a cover (17) for the upper surface of the store, to reduce weathering and evaporation, as well as to prevent ingress of water from waves. These covers would be easily removable or fitted with ports through which the oil can be collected.

Claims (15)

1. Claims 1. An oil spill recovery system, comprising a collection device and a separation device; where the collection device includes a suction mechanism; and where the separation device is suitable for storing recovered oil.
2. 2. The system of Claim 1, where the suction mechanism is a propeller.
3. 3. The system of Claim 1, where the suction mechanism is a pump.
4. 4. The system of any preceding claim, where the collection device comprises a funnel.
5. 5. The system of any preceding claim, where the collection device is suspended from a floating vessel.
6. 6. The system of any preceding claim, where the collection device is suitable for forming a weir.
7. 7. The system of any preceding claim, where the separation device can be arranged to selectively retain oil.
8. 8. The system of any preceding claim, where the separation device is a gravity settling tank, arranged to allow fluids to flow from the base of the tank.
9. 9. The system of any preceding claim, where the separation device further comprises buoyancy aids arranged to suspend the separation device at or near the surface of the water.
10. 10. The system of any preceding claim, where the walls of the separation device protrude at least about 1 metre above the surface of the water.
11. 11. The system of any preceding claim, where the walls of the separation device extend at least about 1 metre below the surface of the water.
12. 12. The system of any preceding claim, where the walls of the separation device extend at least about 2.5 metres below the surface of the water.
13. 13. The system of any preceding claim, where the walls of the separation device are made froni oil resistant plastic, steel or aluminium.
14. 14. The system of any preceding claim, where the separation device further includes a removable cover.
15. 15. A method of separating oil from water through the use of a collection device and a separation device, where the oil and water is drawn into the collection device, transported to a separation device, separated, and the oil is subsequently stored in the separation device.