Tests to Determine the Limits to In Situ Burning of Thin Oil Slicks in Brash and Frazil Ice

摘要

The purpose of the study was to investigate the minimum ignitable thickness, combustion rate, residue amount and the effects of waves on thin oil slicks burned in situ on frazil or slush ice typical of freeze-up and brash ice typical of break-up. The study consisted of a literature review, small-scale burns in a chilled wave tank in Ottawa and mid-scale burns in an outdoor wave tank at Prudhoe Bay. A total of 114, 40-cm burns and 42, 170-cm burns were completed. The experimental variables were: (1) Oil type (Alaska North Slope, Endicott, Northstar and Pt. McIntyre crudes); (2) Ice type (brash and frazil); (3) Initial oil thickness on ice (3mm slicks and thinner); (4) Mixing energy (calm and low waves to simulate natural mixing of an ice field); and (5) Degree of oil evaporation. The small-scale tests involved: (1) Minimum ignitable thickness tests for three degrees of weathering for each crude on open water, ice cubes (representing brash) and crushed ice (pulverized ice cubes representing frazil); and (2) Burn rate and removal efficiency tests in calm and low wave conditions with 3-mm thick slicks spread out on top of the ice for three degrees of weathering for each crude on open water, ice cubes and crushed ice. The mid-scale tests mimicked the small-scale matrix and involved burn rate and removal efficiency tests in calm water and low waves conditions with 3-mm thick slicks spread out on top of open water, brash ice (growth in a nearby pit from brackish Purdhoe Bay water) and frazil, or slush, ice (simulated by using snow in water) for selected degrees of weathering of the various crudes. The paper focuses on the methods and results of the mid-scale tests and the rules-of-thumb proposed.