SOCK Skimmer -- Performance and Field Tests
Authors: Fraser John P. , Clark L.M.C. 
Published: December 2007

The spilled oil cleanup kit (SOCK) skimmer has been developed to recover oil efficiently at sea under realistic sea conditions. It was designed to operate with typical oilfield work or supply vessels and to operate in seas with wave heights up to at least 8 ft [2.4 m]. Field tests offshore New Jersey in April 1980 confirmed conclusions from 3–1/2 months' operating experience in a major offshore oil spill in 1979. In addition, the field tests were able to define more quantitatively the performance characteristics and efficiency of operation of this skimmer.

Background

One of the major unresolved problems in control of oil spills has been the containment and recovery of oil spilled at sea. Most of the equipment developed in the past has been limited to use under very calm conditions and has had low efficiency. Even if the rate of oil recovery and the efficiency were good in calm seas, performance generally deteriorated rapidly with increasing wave height. In addition, the cost of the equipment has been high, especially if it involved a special purpose, dedicated skimming vessel. In 1975, development was begun on a new type of offshore oil spill recovery device. This device, the SOCK skimmer, was designed to be deployed and operated from typical oilfield work or supply vessels to reduce cost, and to operate in seas with wave heights up to 8 ft [2.4 m], which should allow it to operate most of the time in most parts of the world. The SOCK skimmer is now a tested and proven oil spill recovery device. Field experience over a 3–1/2 month period during 1979 showed that it can recover spilled oil at sea effectively under a wide variety of environmental conditions. Significant advantages of this skimmer over other open-seas skimming units include the following.The skimmer has mobility; it can travel easily to locations of oil accumulation.It may operate relatively independently of other equipment such as booms and support vessels.SOCK is able to operate efficiently under a variety of realistic weather conditions at sea, including seas with significant waveheight up to at least 6 ft [1.8 m]. (In the future, operation to 8-ft [2.4-m] significant wave height appears possible.)The device has good efficiency and oil-recovery rates. Recovery efficiencies of 95 to 100% at 200 to 250-bbl/hr [32 to 40-m3/h] oil phase recovery rate are possible with oil thickness of 2 mm and with oil phase viscosity up to 2,000 cSt [0.002 m2/s]. High throughput efficiencies are also possible. Oil with higher viscosity can be recovered at good efficiency but at some sacrifice in recovery rate.When weather conditions are too rough for skimming, the oil recovery unit can quickly be brought aboard the work boat for safe keeping. The unit can be deployed again as soon as the seasmoderate.

The SOCK Skimmer

The SOCK skimmer (Fig. 1) is essentially a covered boom towed alongside the tending vessel. The boom collects oil in much the same way as a conventional boom except that the cover damps out small waves within the drape of the boom and eliminates wave reflections, which would otherwise cause oil loss from the boomed area. The boom and its cover are made of oil-resistant fabric to allow the skimmer to conform to large waves and swells. Three prototypes of the fabric oil-recovery unit have been constructed: one of nylon-reinforced nitrile rubber, the second of polyester/nylon-reinforced polyvinyl chloride (PVC), and the third of polyester/nylon-reinforced polyvinyl chloride (PVC), and the third of polyester/nylon-reinforced polyurethane. The draft of the boom is 4–1/2 ft polyester/nylon-reinforced polyurethane. The draft of the boom is 4-1/2 ft [1.4 m] to allow accumulation of a large volume of oil before drainage. The fabric folds like an accordion for storage. Oil is recovered from within the boomed area from multiple suction points located in the top cover, some of which are 4 ft [1.2 m] forward of points located in the top cover, some of which are 4 ft [1.2 m] forward of the aft end; some are 7 ft [2.1 m] forward. In addition to the fabric oil-recovery portion, the skimmer kit includes a power package and a launching system. The power package consists of a diesel engine, a hydraulic power unit, and a positive-displacement pump driven by a hydraulic motor.

JPT

p. 451