| The appliance of dispersant is one of the emergency solutions to counter the effects of oil spill. Dispersed efficiency and oil-droplet size are key indicators to evaluate the effectiveness of dispersant. Current dispersant effectiveness tests are commonly performed with bench-scale testing apparatus, and the testing conditions are dramatically different with natural environment. In order to build the hydrodynamic conditions in the real sea environment, wave tank system is applied in the current study. Dispersed efficiency and oil-droplet size have been measured, and their influencing factors have also been analyzed respectively as well. The aim of this research is to provide guidance for the use of dispersant in practice.In this research, to disperse the 120# marine fuel oil dispersed efficiencies of GM-2 dispersant and Weipu bio-dispersant in different testing conditions have been analyzed by Infrared Oil Meter. The result shows that dispersed efficiency can be improved by increasing temperature or dispersant-oil ratio (DOR), and both of their effects are not linear. Contrast control group, using the GM-2 dispersants can increase the dispersion efficiency of about 1.3 to 4.7 times, Weipu dispersants from about 0.2 to 0.7 times. Since the range of 15℃ to 20℃ oil viscosity decreases rapidly, GM-2 Dispersant efficiency increased to 26% -37%, and increased by about 10% -14% at 20℃ to 25℃ range. Weipu dispersant’s figure increased by 10% -17% at former range, and the latter range figure increased by 3% to 9%. At 20℃, the ring growth of GM-2 dispersant efficiency is about 57% and 25% with the DOR change from 10% to 20% and from 20% to 30%, the ring growth of Weipu dispersant efficiency is about 18% and 7%. The presence of wave can enhance the dispersing ability. However, significant differences of final dispersed efficiencies in different wave frequency conditions have not been found. In addition, dispersed efficiency in different depths has also been tested. It illustrates that dispersed oil concentration in the depths of 3cm from the surface is about 1.2 to 1.5 times than it in the depths of 3cm from the surface during 10 to 30 minutes after the start of the experiment, and then the concentrations turn to be close after 30 minutes. Finally, the concentration in shallow depth is still slightly higher than the concentration in deeper depth.This paper also studies the dispersed distribution oil-droplets with using the GM-2 oil dispersant under different conditions, calculates the variance and the average particle size, the results indicate that 120# marine fuel oil final oil-droplet particle size is maintained at 20μm to 30μm with using no oil dispersant and maintained at 5μm to 10μm with the presence of oil dispersant in the DOR of 20% to 30%. After reaching the proper dosage (DOR>20%), increase dispersant dosage would not reduce the oil-droplets size significantly. Temperature is another important factor affecting the oil-droplets size, oil-droplet size decreases with increasing temperature, wherein the range of 15℃ to 20℃, since the oil viscosity decreases rapidly, the particle size decreases significantly faster. In addition, this study also demonstrated significant influence of wave conditions on the oil-droplets size, it shows that faster wave frequency can accelerate the process of reducing the oil-droplets size, comparative with it in no wave condition, the average particle diameter of the oil-droplets can be reduced from 20μm to 30μm down to 10μm or less. |
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