Offshore oil spills could be contained using curtains of air bubbles that are effective even in the face of gale-force winds and strong tidal currents, according to Norwegian researchers.
A recent trial of the technology used a bubble curtain measuring 12m in length and 1.5m in width to contain a mock spill at the Trondheim Fjord in Norway.
‘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,’ said Grim Eidnes, a marine technology scientist at Norwegian research institute SINTEF.
The hardware consists 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 they rise to the surface, they drag the surrounding water with them. When this water reaches the surface, it creates a horizontal surface current that keeps the oil in place and prevents it from spreading further. This makes it easier to control and collect the oil spill.
In the trial, out of consideration for the environment, bark was used as a substitute for oil. The bubble curtain was shown to control the spill at current speeds of around 70cm per second, equivalent to a knot and a half, which compares with the 40-50cm/sec (one knot) that traditional oil booms can deal with.
Since the bubble curtain generator is actually submerged to a depth of a couple of metres, a boat can be run over it — an obvious advantage during oil-spill recovery operations.
‘In principle, there are no limits to the strength of the currents in which this equipment could operate. The more air that the compressor can force out of the hoses, the stronger the current it can tackle. But to double the effect of the bubble curtain on the current, we would have to increase the air by a factor of eight, so the limitation actually lies in the compressor power available,’ said Eidnes.