| Chemical dispersants represent a potentially important response alternative for oil spills. Effective use of this countermeasure depends on understanding the factors that control the effectiveness of this process. Therefore, the objective of this research was to investigate several important factors, such as mixing energy, fluid dynamics, and the rheological and chemical properties of the oil, that are believed to control dispersion. Understanding the mechanisms involved during dispersion could allow us to formulate reliable predictive models which could be used by spills responders to decide whether dispersion would be an effective and prudent response tool.;Oil-dispersion experiments to investigate the effects of fluid flow and the specific energy dissipation rates were conducted in two bench-scale experimental systems: baffled flasks that were mixed on a gyratory shaker and baffled 1000-ml beakers that were mixed with a two-blade flat paddle. Dispersion effectiveness increased with increasing specific energy dissipation rate in both the mixing systems, and was found to be inversely related to the droplet size formed. Though important, the specific energy dissipation rate alone wasn't sufficient to characterize dispersion and at a minimum, the dynamics of fluid flow must be considered. To study the impact of physical properties of oil on dispersion, three crude oils covering a wide range of viscosities were used. The droplet size distributions were found to be multimodal for all three oils indicating multiple mechanisms causing droplet formation. Lower viscosity and interfacial tension favored formation of smaller droplets compared to highly viscous oil with high interfacial tension. To evaluate the effects of chemical composition on dispersion, the relative proportions of saturate (S), aromatic (A), resin (R) and asphaltenes (A) in the oil was systematically varied. Experiments showed that the dispersion process is not completely guided by the relative proportion of the SARA components but also what constitutes each of them separately. Finally, scaling laws were investigated to evaluate ways to predict at-sea performance from lab-scale results. Four dimensionless numbers---Weber (We), Reynolds (Re), Capillary (Ca) and Ohnesorge (Oh)---played a significant role in explaining the relative importance of different forces acting to control droplet size. |
