Slurries hindered settling rates

This diameter should have no effect on slurry hindered-settling rate certainly up to 400 g Th/kg H2O concentration and possibly even higher. 

Fig. 4 20. Effect of angle of container inclination on TI1O2 slurry hindered settling rate. Slurry concentration 300 g Th/kg H2O, container diameter 1.63 in.

Roorn-tefnperature sedimentation characteristics. The room-temperature hindered-settling rates (for a given slurry concentration), critical concentrations, and. settled concentrations of thorium oxide slurries (unpumped) all increased with increasing firing temperature up to 1000°C of the oxide. In addition, the hindered-settling rates also increased with decreasing slurry concentration (see Fig. 4-7) [53]. It should be noted in Fig. 4-7 that all slurries are in compaction in the 500 to 800 g Th/kg H2O concentration range. 

Fig. 4-12. Effect of thorium sulfate on hindered settling rates of oxide slurries.

Fig. 4-12. An abnormal increase in the hindered-settling rate in the temperature region of 150 to 200 C was obtained upon the addition of between 500 and 1000 ppm of sulfate (based on Th02) and again at about 5000 ppm of sulfate. The concentration region of 2000 to 3000 ppm of sulfate appears to be one of a relatively low settling rate and good temperature stabihty. It is of interest to note that in the operation of a high-temperature loop, abnormal pump power demands at 200°C were observed when piunping slurry containing 1000 ppm, and that increasing the sulfate concentration to between 2000 and 3000 ppm removed the difficulty and permitted operation at 300°C [54].

If the feed rate exceeds the maximum of the design, particulate matter are unable to settle out of the normal clarification zone. Hence, there is an increase in the solids concentration, resulting in hindered settling. The result Is a corresponding decrease in the sedimentation rate below that observed for the feed slurry. 

When a particle is at a sufficient distance from the walls of the container and from other particles so that its fall is not affected by them, the process is called free settling. Interference is less than 1% if the ratio of the particle diameter to the container diameter is less than T.200 or if the particle concentration is less than 0.2 vol % in the solution. When the particles are crowded, they settle at a lower rate and the process is called hindered settling. The separation of a dilute slurry or suspension by gravity settling into a clear fluid and a slurry of higher solids content is called sedimentation. 

Hindered-settling systematics. The hindered-settling velocity of slurries may be expressed as a coefficient times the Stokes law settling rate. Table 4-12 summarizes [120] typical coefficients obtained in theoretical and empirical investigations. A plot of these coefficients versus porosity showed that they are substantially in agreement. Steinour [121] introduced the concept of immobilized water in his treatment of flocculated suspensions and showed that by defining... 

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