A new Experimental Rig for Oil Burning on Water – Results for Crude and Pure Oils

Abstract

A new experimental apparatus, the Crude Oil Flammability Apparatus (COFA), has been developed to study in-situ burning of crude and pure oils spilled on water in a controlled laboratory environment with large water-to-oil ratios. The parameters and phenomena studied for an asphaltic crude oil (Grane) and two pure oils (n-Octane and dodecane) with different initial oil layer thicknesses include burning efficiency, burning rate, regression rate, flame height and boilover. Pyrex glass cylinders (157 and 260 mm ID) placed on top of a steel foot in a water basin (1m x 1m x 0.5m) enabled free circulation of the water, which, along with the large water-to-oil ratios (up to 10,000) ensured that the oil burning barely increased the temperature of the surrounding water environment, which created more realistic offshore conditions than seen in many other laboratory studies. The burning efficiency was found to be nearly 100% for n-Octane and of dodecane, whereas the crude oil burning efficiency ranged between 35% and 65%. The main reason for this variation proved to be the onset of an extremely violent boilover, which occurs for oils with relatively high boiling temperatures when the water sub layer is superheated. When the initial crude oil layer thickness exceeded 20 mm the oil became solid and no boilover occurred. The heat-loss to the water sub-layer also had an effect on the burning efficiency and the regression rate was found to reach a constant value after increasing continuously as the oil was heated. Similar results were found regarding the flame height which reached a steady flame height. The pure fuels, n-Octane and dodecane, produced a much higher steady flame height than the crude oil, however they did not reach boilover, though dodecane showed boilover tendencies. Theoretical predictions with existing correlations and input data specific for the current oils generally compared well with the experimental data for both the time to boilover and the regression rates. As such, the COFA is envisioned to produce high-fidelity results in the future and thereby contribute to the further development of in-situ burning as an alternative response technique for oil spills on water.