OIL SPILL RESPONSE Speedily deployed oil collector passes first major test

Top view of the hydrodynamic circus when permanently installed. A Gothenburg engineering consultancy has devised a novel solution for combating oil spills in waters with strong currents. After several years of development, the system has lately undergone extensive trials, and was unexpectedly put to the test in Sweden last December.

"Circus" performs in waters too turbulent for conventional boom systems

A Gothenburg engineering consultancy has devised a novel solution for combating oil spills in waters with strong currents. After several years of development, the system has lately undergone extensive trials, and was unexpectedly put to the test in Sweden last December.

Captain Blomberg's Hydrodynamic Circus, invented by Erling Blomberg Offshore, is designed to work in severe conditions close to shore or in rivers. In action, water and oil are ushered via an oil boom to the inlet of the circus, which is basically an artificial lagoon placed alongside the rescue vessel.

Water and oil are then guided through an opening in the side of the circus into a rotation chamber. There floating oil is recovered, whilst the water is taken out of the side opening by means of a downward displacement current, flowing under the boom.

The circus can be built into a vessel permanently, or simply secured alongside for offshore sweep operations. It can also be deployed from very small work boats for sweeping, collecting and recovering oil which can then be stored in special bags. It could also be used to prevent spread of oil along a coastline.

At the end of 1994 the system in its current form was called into action for the first time when 900 litres of diesel fuel from a road tanker spilled directly into the Bruzaan River in Sweden. Conventional oil booms proved ineffective in the strong river currents, so the local fire brigade in Eksjo asked for the circus to be sent out from the Municipal Rescue Services Unit in Karlskrona, 220 km away.

Five hours later, the system and its booms were deployed in the river, and oil was recovered from the circus using a conventional Sala vacuum pump.

Development of the circus stretches back several years, with heavy involvement from the Swedish Coast Guard which has supplied personnel and vessels to the project as well as advice. Another active and more recent participant is the Swedish Rescue Services Board (SRSB).

Early in 1994, a roadside accident led to a tank vehicle spilling its load of diesel fuel into a river near the town of Karlskamn. A prototype circus was tested at the spill: the results persuaded SRSB to join a subsequent project to develop a model of the circus suited to the needs of municipal rescue services.

A system was adapted for deployment from small workboats which would be easily transportable, and which would also act as a complete oil spill response (OSR) system, capable of control, recovery, transfer/transport and storage. Project work was performed at Karlskrona, where SRSB has a regional OSR depot.

The circus has been put through various trials and test methods at Karlskrona to determine optimal performance and handling. For instance, a sinker with great water resistance (drag), line and float was employed to observe how water flow entered and left the circus, and how vertical fields of flow acted inside it.

By adjusting the draught of the boom in relation to the opening in the circus' side it is possible to regulate incoming water volumes, thereby also permitting sweep speed to be adjusted. Trials showed that a sweep speed of roughly 2.5 to three knots is appropriate in calm waters.

Trials with high speed sweeping revealed the need to complement the Circus with an oil-collector mounted in the centre of the vortex, in order to create calm water and concentrate the oil for recovery. This scenario could be applied to work boats too small to handle a skimmer.

The oil-collector is an open, adjustable pipe or tube mounted vertically in the centre of the circus, with an opening for the oil to enter into. A shallow draught boom between the circus wall and the inner tube guides the oil into the collector's aperture. At a sufficient sweeping speed, the oil layer builds up, allowing it to be pumped out with a minimum water content.

Specially designed containment systems, or bags, can be attached to hold oil pumped directly from the circus, with excess water sent out through an evacuation hose fitted to the bag. When full, the bag is easily sealed and fastened to the boat by a specially designed fitting.

Cost of a complete circus system would be far lower than any other conventional recovery system such as skimmers, claim the designers, with minimal maintenance requirements. The next test for the system will be on a river delta in a developing country where there are several oil terminals, and heavy tanker traffic. Numerous circuses will be deployed from existing river boats.

For more information contact Erling Blomberg, Erling Blomberg Offshore: Tel (46) (31) 299-553 or Fax (46) (31) 299-599

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