GIANT fuel tankers spewing oil into the sea are an all too familiar sight. But the damage caused by such disasters could be dramatically reduced if a recovery vessel could follow behind and mop up the slick.
For every thousand barrels of crude oil transported around the world, one is spilt in the sea, says Omar Chaalal, an engineer at the United Arab Emirates University in Al-Ain. So he designed a tanker to recover the lost oil, which not only helps to reduce any environmental damage but also produces a sellable product.
On board the recovery ship is a large tank, which is completely filled with seawater before the ship leaves the dock. When the ship approaches an oil slick, it opens a series of holes in the bottom of the hull to connect the water in the tank to the water outside. Just like a pint glass full of water that is upturned in a filled sink, the water in the tank does not flood out as long as the holes remain submerged.
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As the ship moves along, its specially designed hull shape forces any oil it encounters underneath the boat past the holes (see Graphic). Because oil is less dense than seawater, it rises up through the holes to the top of the tank. As the oil builds up in the tank, it gradually displaces the seawater until it contains nothing but oil. The holes are closed and the ship returns to dock to unload its catch.
Chaalal and his colleague Mamdouh Ghannam demonstrated the technique using a scale model 60 centimetres long in a tank containing a one-litre “slick” of crude oil. To simulate sea conditions, the team agitated the tank. In only a couple of minutes, the boat recovered 99 per cent of the oil (Fuel, vol 82, p 789).
The idea sounds feasible and would certainly be welcomed by the oil industry, says Will Hendry, operations supervisor for Briggs Environmental Services, a counter-pollution specialist based in Aberdeen, Scotland. There are currently no methods for recovering oil without also collecting water. “The basic principles haven’t changed in the last 30 years,” he says.
Perhaps one reason for the lack of innovation is that only a few countries permit oil to be spilt deliberately to test out new technologies in realistic conditions, says Kare Jorgensen, an advisor on operations for the Norwegen oil spill recovery organisation NOFO.
The standard way of mopping up oil spills starts by containing the slick using large floating booms and then the salvage team uses skimming equipment to scoop up the oil. The effectiveness of the technique depends on the type of oil. “The lighter they are, the easier they are to recover,” says Hendry. “But you always get a certain amount of water in.”
Recovered oil can be sent off to be refined again, but only if it is in good condition after being salvaged, Hendry adds. Often, it is destroyed and any oil left behind is dispersed with chemicals.
Chaalal’s tanker is now attracting interest from the oil industry. Jacque-Miguel Dujon, a French oil consultant also based in Al-Ain, is working with Chaalal and some oil companies to build a larger version of the tanker to test in open water.
