Análise do escoamento água, óleo e gás em padrão disperso

Abstract

The effect of the insertion of a bubble swarm on the separation of finely dispersed oil droplets in a liquid flow was investigated experimentally and numerically. The generation of gas bubbles and oil droplets in a liquid flow allowed the analysis on the efficiency of offshore separation processes (gravitational separators - primary oil processing). Those processes have shown to be strongly dependent on hydrodynamic forces and on the physical interactions of the dispersed phases in flows governed by viscous dissipation as well as hydrodynamic effects when inertia forces dominate. In this context, it is noteworthy that the efficiency of the flotation equipment can be improved by a better understanding of the interactions between bubbles and droplets, which depend on factors such as the bubble and droplet sizes, the population, and velocity fields along runoff. Despite their importance, studies in this field are scarce and a lack of information about the physics of the problem persists. The goal of this study is to ascertain which of these phenomena govern the separation kinematics. To achieve this objective, the high-speed shadowgraph technique was used to determine the trajectories of the dispersed phases, equivalent diameters, and their rising velocity. The numerical simulation, by its turn, complemented the experimental work, allowing the analysis of flow details not supplied by the lab experiments, such as the secondary flow of the continuous phase, among others. The experiments, in contrast to the simulations, suggested that the presence of the bubble swarm enhances the separation of the oil droplets from the liquid because of the increased gravitational effects associated to the liquid-induced flow. Furthermore, the insertion of the bubbles reduced the random circulation of the droplets inside the bubble column. Buoyancy effects were increased, leading to a smaller retention time of the droplets. Thence, the hydrodynamic interactions promoted by the insertion of the bubbles govern the separation of droplets from the liquid stream, leading to an enhanced separation process.