Curtains of air-bubbles are being trialled as a new method of fighting oil spills in Norway by a team of scientists.
The bubbles gather up the oil efficiently, even in winds and strong currents, and keep the oil together in a “pool”. The technology has been developed by SINTEF scientists with financial support from the Research Council of Norway and the oil industry.
Trials have been carried out in severe gale force winds in Skarnsundet in the Trondheim Fjord and the scientists are now planning to develop the system for the commercial market.
The bubble curtain is 12 metres long and 1.5 metres wide, and takes the form of a large grating covered in perforated rubber air-hoses that release bubbles generated by a compressor. The grating is submerged to a depth of a couple of metres, where it releases a dense “wall” of bubbles.
As the bubbles rise to the surface, they drag the surrounding water with them. When the water reaches the surface it creates a horizontal surface current that keeps the oil in place and prevents it from spreading further, which makes it easier to control and collect the oil-spill.
“We already knew that the bubble curtain works in still water, and that it actually has a calming effect on waves. What we wanted to test in this field trial was the maximum current strength that our equipment could deal with,” says senior scientist Grim Eidnes of SINTEF’s Department of Marine Environmental Technology.
In the trial, out of consideration for the environment, bark was used as a substitute for oil. While traditional oil-booms manage to prevent oil-spills from spreading in currents of up to 40 – 50cm per second, the bubble curtain could control the spill at current speeds of around 70cm per second, equivalent to a knot and a half. Eidnes says this opens up new prospects for dealing with oil-spills in areas of strong currents.
The scientists say the bubble curtain is an efficient way of closing off a vulnerable area to prevent an oil-spill from entering it, limits the spread of a spill, and improves prospects of collecting the oil. Since the bubble curtain generator is submerged to a depth of a couple of meters, a boat can also go over it.
Statoil, which has been one of the project’s industrial partners, says it will consider whether the company should support the next stage – commercialisation – when it sees the final report.
Statoil scientist Cecilie Fjeld Nygård says: “So far, it appears that the bubble curtain could act as a barrier in coastal areas that would prevent oil-spills from spreading into or out of a fjord, for example.” And says the bubble curtain will not replace, but rather complement, traditional oil-booms.