ABSTRACT

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Preparedness for Heavy Oil Spills, More Focus on Mechanical Feeder Skimmers

Numerous spills over the years have demonstrated that mechanical response to heavy oil spills at sea is less than successful. Recently, after the 10,000 m3 ERIKA Spill in France, less than 5% was recovered before the oil reached the coast. The weather played an important role, but the selection of equipment and apparent response strategy did as well. Mainly weir skimmers were used.

Weir skimmers are due to their simplicity and reliability widely used in spills at sea. Probably because some of the well known brands are equipped with heavy oil transfer pumps, they are commonly used in heavy oil spills. But also high capacity units with light oil centrifugal transfer pumps are being used on heavy oil (ERIKA).

Weir skimmers start losing their efficiency when the viscosity of the oil exceeds certain limits. It gets too difficult for the oil to pass the weir lip and flow into the hopper, so that the pump can transfer it. For very heavy oils, which barely can float, the inlet weir is an even larger obstruction. 
A mechanical feeder skimmer lifts or drags the oil out of the water to a position above the water surface, and feeds or drops it into a collection tank or a transfer pump. The mechanical feeder principle may result in significantly increased performance regarding high viscosity, debris, and - in most cases - low water content.

Recent tests at SAIC/Environment Canada’s test facility in Ottawa, Canada, sponsored by the Canadian Coast Guard, demonstrated that floating bitumen with a viscosity of about 2 million cSt could be recovered by mechanical feeder skimmers, while a “high viscosity” weir skimmer had no effect. This puts the ERIKA Spill’s viscosity of “only” 200,000 cSt into perspective, and strongly point at mechanical feeder skimmers in the preparedness for heavy oil spills. 

F. Hvidbak - flemingCo environmental aps 

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