ABSTRACT
Recovery Devices and Pumping Techniques for High Viscosity Oil Spills
Numerous spills over the years have demonstrated that mechanical response to high viscosity oil spills at sea is less than successful. 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 even commonly attempted used in heavy oil spills. But also high capacity units with light oil centrifugal transfer pumps are being used on heavy oil (ERIKA). However, 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 becomes 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.
Tank tests at SAIC/Environment Canada’s test facility in Ottawa, Canada, sponsored by the Canadian Coast Guard, and tank tests since 1999 carried out by flemingCo, under contract with PDVSA/Bitor, have demonstrated that floating bitumen in the viscosity range of 2 to 3 million cSt could be recovered by several mechanical feeder skimmers, while a “high viscosity” weir skimmer had no effect. This puts the ERIKA Spill’s viscosity of 200,000 cSt, the Baltic Carrier’s 500,000 cSt, and the Prestige Spill’s 320,000 cSt into perspective, and strongly point at mechanical feeder skimmers in the preparedness for heavy oil spills. However, the same tests clearly demonstrated that the transfer pumps in the skimmers had difficulties transferring the extremely viscous product from pump inlet to pump discharge; meaning that feeding the product into the pump inlet showed difficult and/or the pressure/friction losses inside the pump itself could barely be overcome. It was therefore deemed necessary to test existing and newly developed techniques, which might improve these pumps’ ability to transfer high to extreme viscosity oil. This presentation will document that there as of today are skimming and pumping equipment and techniques available, which can be efficiently used in response to spills of even very viscous oil.
F. Hvidbak - flemingCo environmental aps
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