Drop sizes during turbulent mixing of toluene-heavy oil fractions in water

The properties of heavy oil emulsions produced in heavy oil extractions processes often fluctuate, thus making treatments difficult. We investigated whether oil-phase ratios and flow conditions might influence these emulsions. We studied turbulent mixing effects on droplet sizes in real time, using a fully baffled stirred tank with a Rushton turbine in bench-scale batch experiments. Breakup/coalescence of various volume fractions of toluene diluted heavy oil in model process water was measured at four mixing speeds. The range of oil volume fractions was 0.01 to 0.3, where 0.01 is the Kolmogorov limit and 0.3 the upper limit for oil-in-water (O/W)emulsions. Results showed that size distributions depended on mixing time, rpm, and oil fractions. Breakage dominated at low oil fraction 0.01 and high mixing intensities produced bimodal distributions. The persistence of finer droplets was attributed to reduced coalescence. Steady state was not reached. The middle range oil fractions (0.05, 0.1) approached steady state more quickly and followed a first-order breakage model at 800 rpm. The size distributions narrowed before the end of the mixing time. The highest oil fractions and lowest mixing speeds produced the largest droplet sizes. Plots of d(32) vs. rpm for 75 min mixing showed that as the volume fraction of oil phase increased the shapes of the curves changed from concave to linear to convex. The d(32) vs. energy dissipation curves suggested that turbulent dampening reduced breakage. However, drop coalescence from erosive collisions as well as droplet surface elasticity were factors affecting droplet sizes. (c) 2006 American Institute of Chemical Engineers.