Testing dispersants in ice-cold water BSEE uses Ohmsett test tank to evaluate the likely effectiveness of oil dispersants in an Arctic offshore oil spill response Alan Bailey Petroleum News
The Bureau of Safety and Environmental Enforcement has used its Ohmsett test facility in New Jersey to test the effectiveness of dispersants in dealing with an offshore oil spill in Arctic conditions, according to the spring issue of an Ohmsett newsletter. The idea was to determine whether various dispersants would be suitable for Arctic use, the newsletter said.
Dispersants work in a similar manner to soap, breaking an oil slick into minute oil particles that can disperse through the water column, thus accelerating the rate at which microbes in the water consume and destroy the oil. Although controversial as a consequence of questions over the potential toxicity of the dispersants and of the oil droplets that the dispersants create, dispersants can form part of the arsenal of tools used to combat an oil spill.
But the increased viscosity of oil in cold water may inhibit the action of a dispersant, while the dispersant itself may behave differently in cold conditions from the way in which it acts in relative warmth, the newsletter says.
The Ohmsett facility consists essentially of a large, long water tank, with equipment for creating waves to simulate ocean conditions. Researchers tested four different dispersants by applying each dispersant to an oil slick composed of North Slope crude oil, floating on water in the Ohmsett tank. The tests were carried out in cold winter conditions, augmented by a chiller system, with the water temperature maintained just above the freezing point for salt water, the newsletter says.
Breaking waves Dispersants require a mixing action, perhaps from waves or the wash of a vessel, to spread the oil droplets through the water. So, the researchers conducted the Ohmsett testing by spraying dispersant onto the slick and exposing the treated slick to breaking waves generated in the test tank. Three identical test runs were carried out for each type of dispersant. In addition, three control runs, in the same conditions but without dispersant, were carried out at the beginning, in the middle and at the end of the test sequence, to provide a baseline against which the effectiveness of the dispersants could be measured.
Samples of oil recovered after each test were analyzed for water content, to correct for the effects of emulsification and for the natural water content of the oil, the newsletter says. And during the tests a laser and flourometer system measured the nature of the dispersed oil droplets. These instruments enabled the quantification of the performance of each dispersant, showing how much oil was diluted into the water and the sizes of the oil droplets that the dispersants created, the article says. Droplets more than a certain size will tend to resurface to form a new slick, rather than remaining suspended in the water, the newsletter says.
The newsletter article does not describe the results of the testing but says the results will provide oil spill response organizations and government regulators with information for making decisions on dispersant use.
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