LFL estimates for crude oil vapors from relief tank vents



In 1970, the Alyeska Pipeline Service Company was formed to manage the design, costruction, operation and maintenance of the Trans-Alaska Pipeline System. The 800 mile long pipeline carries crude oil from Prudhoe Bay on the North Slope to Port Valdez on Prince William Sound. There are 11 pump stations located along the pipeline, each of which is equipped with a crude oil relief tank. Because of the potential flammable nature of the crude oil vapors being vented from the tanks, Alyeska wanted to determine the region surrounding the tanks within which the lower flammable limit (LFL) could be exceeded. Because numerical models cannot accurately model the flow near structures, especially for dense gases (as is the case here), wind tunnel modeling was conducted to provide more accurate distance to LFL estimates. The wind tunnel model simulations were also used to judge the effect of various modeling parameters (i.e., site specific configurations, release scenarios and meteorological conditions), and to assist in possible future refinements to numerical models. Field observations were also obtained at one of the pump stations for the purpose of validating the wind tunnel modeling. The project, wind tunnel scaling methods, experimental methods, concentration measurement results, distance to LFL estimates and comparison between the field and wind tunnel observations are described in this paper.