Settling slurry properties

Solid-liquid mixing involves the suspension, distribution, and the drawing down of solids by agitation. In addition to vessel geometiy, impeller variables include type, diameter, number, speed, and location. Process results include the desired level (quality) of suspension, such as just off-the-bottom, complete uniformity, or any intermediate condition. The slurry properties, density difference (solid/liquid), viscosity, and solids concentration all determine how difficult the task may be. As alternatives to stirred vessels, jets (see Section 9.10) can be used for light-duty suspension. Literature references deal mainly with settling solids as opposed to floating solids. We will try to address both conditions. 

Slurry properties. The suspension (slurry), usually aqueous, must be stable (not settle) and able to adequately coat the metallic substrate. To achieve this target, it is necessary to control the particle size of the catalyst, and to adjust pH (considering the isoelectric point (IFF) of the catalyst) and the viscosity of the slurry. 

Fig. 5. Effect of polymer dosage on different observed properties of flocculated slurry (40). Comparison of five parameters in a flocculation system (8%fluorite suspension + polyacrylamide Cyanamer P250). A, Rate of settling of floe boundary, in cm/s B, height of settled bed, cm C, height of consoHdated filter-cake, cm D, refiltration rate, arbitrary units and E, clarification, % optical transmission of 1 cm of supernatant Hquid after 3 min settling...

Ultraviolet spectrophotometry (DuPont 400 SO2 analyzer) was used to monitor the gas phase SO2 concentrations and SO2 removal efficiencies. The pH of scrubbing liquor in each reactor was measured hourly during pilot testing. Solid dewatering properties were characterized by hold tank slurry settling rate and filter cake insoluble solids concentration. Detailed descriptions of the test facilities and analytical procedures were reported earlier(S). 

The properties of coal slurries that are of most interest are 1) the viscosity/rheology, which controls the ease of pumping and atomization 2) the stability against settling, which controls the ability of the slurry... 

Solids Dewatering. Adipic acid does not significantly affect the settling and filtration properties of oxidized or unoxidized slurry solids, whereas magnesium does. 

Fracture geometry and extension during treatment depend largely on the rheological characteristics of the clean viscous fluid and suspensions or slurries prepared with viscous carrier fluids. Particle settling and distribution in the fracture also are affected significantly by suspension properties. 

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