New ideas for dealing with oil spills
Improved efficiency of in-situ burning, the use of forward looking infrared and the use of sniffer dogs to locate oil can all help
The world of oil spill response is an evolving phenomenon, with people continuing to think up ingenious new ways of finding and dealing with renegade hydrocarbons. On Feb. 12 attendees at the Alaska Forum on the Environment heard about three developments, each with the potential to improve response effectiveness: increasing the efficiency of in-situ oil burning; the use of forward looking infrared, or FLIR, for the detection of oil; and the use of dogs to sniff out the locations of remnant oil hidden along a shore.
Burn efficiencyThe in-situ burning of spilled oil is a proven technique which has been used widely. But, while the complete burning of oil should result in the production of, essentially, water and carbon dioxide, in practice the burning in not complete and thus generates huge volumes of air-polluting soot, while also leaving an oily residue. Can the burning be rendered more efficient?
Ali Rangwala, a professor in Department of Fire Protection Engineering in the Worcester Polytechnic Institute, described research into why the burning is inefficient and, hence, how the efficiency may be improved. One interesting finding from the research is that all oil fires tend to burn at the same constant rate with the same flame height, regardless of the size of the burn. The researchers determined that soot from the fire limits the burn to that constant rate. In effect, the soot blocks the radiated heat from the fire reaching the burning oil, thus limiting the oil to an equilibrium temperature below the temperature required for rapid and more complete burning.
Flame refluxerTo counter the blanketing effect of the soot, the researchers have tried experimental oil burns with what is called a flame refluxer, a system of vertical metal rods protruding up through the fire: The metal conducts heat that would otherwise be lost from the upper part of the fire back down into the oil, hence increasing the temperature of the fire, and thus increasing the burn rate and efficiency. The researchers have tried this technique burning oil that has leaked from electrical transformers, North Slope crude oil, an oil slick and organic waste.
Adding 37 vertical metal rods to a test burn involving North Slope crude mixed with water, for example, increased the burn rate by a factor of more than two, while adding 59 rods increased the rate about six times, Rangwala said.
Offshore burnsThe challenge in the case of an offshore oil slick is the cooling effect of the water on which the thin layer of oil floats. To overcome this problem, the researchers tried placing a fine copper mesh on the slick and attaching copper coils rather than rods to the mesh to transfer heat into the burn. A burn in a test tank showed a six-fold improvement in the burn rate relative to a traditional burn approach, Rangwala said. The efficiency also improved: oily residue left after the burn dropped from 32 percent of the original oil to somewhere between 1.5 and 4 percent, with much less smoke and a reduction of 50 percent in the ratio of carbon monoxide to carbon dioxide generated.
There are many potential applications for this technique, Rangwala suggested.
Infrared oil detectionLee Majors, planning and development manager for Alaska Clean Seas, the North Slope oil spill response organization, talked about the use of forward looking infrared to detect spilled oil. Infrared detection involves the use of a camera designed for the sensing and imaging of infrared radiation, a form of radiated heat. The camera produces digital images similar to those from a conventional digital camera but using infrared radiation rather than visible light.
The infrared detection of oil depends on the fact that oil and water have different levels of heat emission, Majors explained. The slightly higher radiation from oil appears as light areas in an FLIR image. And the technology is sufficiently sensitive to even detect the level of the oil in an oil tank.
The technology can be used on many different platforms, including ships, aircraft and drones. There are also handheld FLIR devices. And FLIR cameras can be used in almost all spill response situations. Conditions to be evaluated when considering the use of FLIR particularly relate to visibility, with fog, rain or snow potentially detracting from the technology’s effectiveness, Majors said. With ice prevalent on the North Slope for around eight months of the year, ice conditions also must be considered when evaluating the potential for FLIR use on the Slope, he said.
Uses in ice and snowAlthough it is not possible to use FLIR to detect oil under ice, the technology is very effective at locating oil slicks on water between ice floes. On the North Slope FLIR can also detect warm, recently produced oil that has been spilled under snow - in a spill response the technology can prove invaluable in outlining the full extent of a spill in snow, beyond the area where the oil is immediately visible. And a FLIR image can be merged into a map of the spill.
However, FLIR cannot detect oil under snow, once the oil has cooled. The FLIR images also become unreliable in detecting a very thin, surface oil layer, Majors said. However, a FLIR image can be used to assess the thickness of an oil pool.
FLIR technology can also be used to detect marine mammals, because of the heat that the animals radiate. In fact, on the North Slope people use FLIR to detect polar bear dens. Majors showed an image of a den, with a sow and two cubs clearly visible.
Using trained dogsScott Pegau from the Prince William Sound Oil Spill Recovery Institute talked about an evaluation of the use of dogs to detect hidden, spilled oil on Prince William Sound beaches. This is relic oil from the Exxon Valdez oil spill that has been on the beaches for 25 years but that has not been degraded because it is not in direct contact with the sea or the atmosphere.
The idea is to retrain dogs that were originally intended for detecting unexploded bombs, to find oil instead. Pegau said that the dogs can be trained to recognize some specific threshold of oil concentration. The Prince William Sound evaluation involved determining if a suitably trained dog could find remnant oil by taking the dog to two different residual oil sites. Could the dog both locate oil and delineate the extent of an oil patch? If so, it could be possible to map out areas of contamination without having to dig ditches all across a beach.
The dog used for the Prince William Sound experiment was part of a team of six dogs being used to detect oil in streams as part of an oil spill cleanup in Saskatchewan, Pegau said.
A team effortThe oil search test involved a specialist dog handler, a dog trainer and a shoreline oil cleanup expert. The dog was fitted with a GPS collar, to enable the team to track the dog’s position. When the dog detected a target, it signaled an alert. The team placed a flag to mark each alert. It was found that for the most part the searches resulted in oil patch delineation, with the dog handler having to repeatedly move the dog out of an oil patch area, so that the dog could locate another edge of the patch, Pegau said.
In some cases the team buried an oil target, to see if the dog would find it.
Oil detectionIn the experiment, the dog made 52 alerts for oil, 19 of which were found to be associated with oil beneath the surface and nine of which were not associated with the presence of oil. It did not prove possible to verify whether 22 alerts were associated with oil. And two alerts were found to be a result of site contamination because people had just come from an oil impacted beach.
A reason for some false alerts may have been oil odors migrating up the shore before reaching the surface, or because of a very low oil concentration, Pegau said.
The result of the experiment was a determination that the dog could detect known locations of oil in the context of Prince William Sound, in areas where the oil is not always visible. The most valuable use of dogs could be determining which beaches are clear of oil, without having to dig pits in the beaches, Pegau suggested.