June 18, 2001 University Park, Pa. --- Penn State researchers have shown in laboratory experiments that some open water oil spills previously thought to be incombustible potentially can be cleaned up via burning, the most efficient, rapid and environmentally friendly option.
Dr. Anil K. Kulkarni, professor of mechanical engineering, says, "Oil spill combustion can be a highly effective clean up measure for contained spills occurring on open water bodies, such as an oil spill on the ocean contained by booms or a spill surrounded by ice. When feasible, it is an inexpensive technique that can have a very high efficiency of removal, possibly greater than 99 percent. The burning is very rapid and any resulting ecological damage is less severe compared to conventional oil removal methods."
However, the window of opportunity for using burning is often limited by wave and wind conditions and by the proximity of the spill to populated areas. In addition, over time, oil spilled at sea becomes mixed with water forming an emulsion that is difficult or impossible to ignite.
Now, Penn State researchers have widened the applicability of burning by showing that diesel fuel emulsions up to 80 percent water and crude oil emulsions up to 35 percent water can be ignited. In laboratory experiments, they demonstrated that positioning an external radiant heat source near the spill facilitates ignition. In addition, they have developed simple charts for use as a quick reference to determine the minimum external heat source needed to facilitate burning.
Kulkarni points out, however, that an open water demonstration still needs to be done to show proof of concept.
The Penn State researcher detailed the findings at the Arctic and Marine Oil Spill Program meeting in Calgary, Canada, June 14 in a paper, "Combustion of Mixtures of Weathered Alaskan Crude Oils and Water under External Heat Flux." His co-author is A. .Y. Walavalkar, who recently earned his doctorate at Penn State; part of the work was the subject of Walavalkar's doctoral dissertation.
In the Penn State laboratory experiments, two electrically operated heating panels were used to supply an external radiant heat source. The panels were positioned over a pool of water about ten inches deep. The researchers poured oil and water emulsions to a desired thickness on the water and then applied the external heat source at a predetermined level.
After the surface temperature reached a certain preset value, an attempt was made to ignite the emulsion. Upon failure to cause ignition, the heat flux level of the panels was increased by a small amount. The process was repeated until sustained combustion was achieved and the minimum critical heat flux needed to ignite the sample was determined.
Kulkarni says that, in actual open water conditions, an external heat flux could come from an adjacent deliberately set fire. "A small fire will not produce sufficient heat flux, but if the fire's size is sufficiently large, it will provide the needed minimum heat flux for the surrounding emulsion to ignite and burn. As the emulsion ignites, the fire's size will grow, providing an even larger heat flux to the yet-unburned emulsion, causing it to ignite in a chain reaction that will continue until all of the emulsion is burned. In this way, a spill previously considered incombustible can be removed," he explains.
In subsequent experiments, the Penn State researchers found that he could correlate oils and emulsions with the same density with the radiant heat needed to facilitate their ignition. He says, "Using density measurements of a specific spill will make it easier for people who are managing the clean up to decide what to do. Rather than try to decide whether to attempt burning the spill based on the type of oil it is, for example Alaskan North Slope, Milne Point crude, or diesel, they can measure the spill's density and then consult the charts we've developed to determine how large a heat flux would be needed."
The research was supported by a grant from the National Institute of Standards and Technology.
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