Mixing of Slurries Near the Ultimate Settled Solids Concentration

Author:

J.Y. Oldshue

This article examines the mixing, suspension, and blending of high-solids slurries, particularly in the 60–100% range of ultimate settled solids (UWPSS), with a focus on coal and other industrial slurries. It highlights how factors such as viscosity, particle size, fillet volume, and impeller design impact power consumption, slurry uniformity, and mixing efficiency. The study also compares measurement methods, discusses the effects of coarse versus fine particles, and emphasizes proper mixer design to handle various slurry types effectively.

Key Learnings

• High-solids slurries (60–100% UWPSS) require careful consideration of viscosity, particle size, and fillet volume for effective mixing and suspension.
• Power consumption increases dramatically as the slurry approaches 100% of ultimate settled solids, and mixer design must accommodate this.
• Fillet height and volume in tanks significantly affect mixing efficiency, with small fillets often reducing additional power requirements.
• The settling velocity of particles can be measured visually and expressed via drag coefficients, Reynolds number, and sphericity for accurate correlations.
• Impeller speed must be adjusted based on particle size and slurry viscosity to achieve uniform suspension of both coarse and fine solids.
• Devices like Stormer viscosimeters, which combine mixing and viscosity measurement, provide more representative data than standard Brookfield viscometers.
• Proper mixer design, including considerations for single vs. multiple impellers and tank ratios (Z/T, D/T), is critical for handling a wide range of slurries, including coal, alumina, pyrrhotite, and various metal concentrates.
• Understanding slurry rheology and mixing behavior can prevent equipment damage and optimize operational efficiency in high-solids slurry applications.