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Current literature relies almost exclusively on the power number to compare and characterize impellers. Industrial mixing requirements may rely on conditions far away from the impeller. A protocol is proposed to compare impellers designed for turbulent mixing on the basis of impeller hydrodynamic performance and mixing process objectives. A hydrofoil impeller (KPC), and a mixed‐flow impeller (45° down‐pumping PBT), each at two diameters, were used to test the protocol. Fourteen measures were considered. Five are recommended for full characterization: power number, momentum number, and peak rate of dissipation of turbulent kinetic energy to characterize conditions at the impeller; power at just‐suspended speed to compare the efficiency of solids suspension at the bottom of the tank; and point of air entrainment as a measure of turbulence penetration to the free surface. These five measures provide complete information about mixing performance and good differentiation between the impellers and geometries. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2573–2588, 2012

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The impact of mixing conditions on the removal of water and solids from high-water, poor-quality bitumen froth was explored. Naphtha diluent and a demulsifier were added to improve removal of water and solids from bitumen froth. The mixing and subsequent settling of this system were carried out in the confined-impeller stirred tank, a lab-scale mixing test vessel with well-characterized, relatively uniform mixing conditions. A protocol for finding the proper demulsifier dosage at which to study mixing effects was applied successfully. High mixing energy J and the predilution of demulsifier (characterized by its injection concentration IC) improved dewatering and solids removal performance, agreeing with earlier studies in diluted bitumen and bitumen froth of higher quality (Laplante et al. Fuel Process. Technol. 2015, 138, 361–367; Arora, N. Mechanisms of Aggregation and Separation of Water and Solids from Bitumen Froth Using Cluster Size Distribution, 2016). An unexpected finding was that dewatering was significantly delayed in poor-quality froth: it was not detectable until up to 45 min in some cases. This induction time was replicated and was clearly impacted by changes in the mixing conditions.

It has been known for years that the performance of a demulsifier in diluted bitumen dewatering improves up to a certain demulsifier bulk concentration. After this limit, the water removal deteriorates. This phenomenon is called overdosing. In this paper, the effects of mixing energy and demulsifier injection concentration on water removal are studied in systems with a high bulk demulsifier concentration. The experiments were conducted in a confined impeller stirred tank (CIST), which provides well-controlled mixing conditions with more uniform turbulence and flow than a conventional stirred tank. The results show that an increase in mixing energy and pre-dilution of the demulsifier may be able to overcome overdosing effects at a high bulk (mean) concentration. If the mixing conditions are well-designed, high local demulsifier concentrations at the feed point are avoided and the demulsifier can perform well, even at high bulk concentrations. The best demulsifier performance in an overdosed system was obtained with a combination of high mixing energy and low injection concentration, where over 80% of the water content was separated at a demulsifier bulk concentration that showed severe overdosing behavior at poor mixing conditions.

Mixing conditions were explored as a possible avenue for improvement of demulsifier performance in the solventdiluted bitumen dewatering process. The effects of demulsifier bulk concentration, demulsifier injection concentration, and mixing energy on water and solids removal from the oil phase were tested. All of the experiments were carried out in a confined impeller stirred tank, which provides well-characterized mixing conditions and relatively uniform flow and turbulence. Results showed that lowering the injection concentration and increasing the mixing energy both improve demulsifier performance, allowing a 50% drop in the bulk concentration of demulsifier. This result agrees well with an earlier study by Laplante et al. 1 in which a different demulsifier was investigated. In that study, it was shown that the product of mixing time and energy dissipation rate at the feed point (the mixing energy = J) provides an alternate mixing variable.