(36d) A Shear and Sedimentation Test Cell (SSTC) for Measuring the Effect of Mixing On the Performance of Chemical Additives

Mixing has an important role to play in the effectiveness of additive chemicals, but this interactions is poorly characterized in the literature. A uniform mixing environment is needed to test the effectiveness of demulsifiers and determine the mixing requirements of the process. To reach this objective, a mixing tank was developed: the SSTC (shear and sedimentation test cell). The SSTC is a narrow and tall tank (T=7.6 cm, H=3T) running with sets of multiple impellers. Three different impellers types were tested: A310, Rushton and Intermig. Sets of five (Rushton and A310) or six (Intermig) impellers of a relatively large diameter (D=T/2 for Rushton and A310 and D=2T/3 for Intermig) were used. Two fluids were used in the tank: water and triethylene glycol; to check the effect of the fluid viscosity. The power consumption of all sets of impellers was determined over a range of Reynolds numbers. Mean and rms velocities were measured throughout the tank using a Laser Doppler Velocimeter. Rushton impellers had the highest power consumption, followed by Intermig and A310. In all cases the set of impellers consumed less power than the same number of impellers operating separately. As the impeller to tank diameter ratio was large, the ratio between the maximum local dissipation and the bulk dissipation was smaller than the ratio obtained in a regular mixing tank. The maximum local energy dissipation was located in the impeller discharge stream for all configurations. The SSTC was able to provide a more uniform mixing for the bitumen extraction operation and is proposed as a test cell for additive chemicals in a wide range of applications.