Slurry Settling

Slurry-settling characteristics Slurry-filtering characteristics... 

In the Jar Test , an initially uniform, homogeneous suspension of partieles slurries settles out under the foree of gravity into distinet zones, as illustrated in Figure 2.6. 

Figure 2.6 Sedimentation zones during slurry settling (The Jar Test ). A, initial uniform concentration, B, zone of increasing concentration, C, sediment or sludge, D, clear liquor...

Figure 2.7 Particle sedimentation rates in slurry settling (schematic)...

Coe and Clevenger method. Since the slurry settling rate R varies with concentration of solids in the thickener batch settling tests are used to determine R over the concentration range of operation F S) and the corresponding... 

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). 

Very stable operation was maintained for run MG-4 without magnesium sulfate addition with the total Mg2+ concentration stabilizing at about 356 ppm. The sulfate-to-sulfite ratio decreased to 2.0, the filter cake insoluble solids reached 53%, and the slurry settling rate was 2.2 cm/min. The results confirmed the base case solids quality and scrubber performance obtained from run MG-1. 

Cova (3 ) measured the solid concentration profiles of a Raney nickel catalyst with an average diameter of 15.7 ym in a h.6 cm id reactor, using water and acetone as the liquids. He developed a sedimentation diffusion model, assuming solid and liquid dispersion coefficients were equal, and slurry settling velocities were independent of solid concentration. The model was then applied to data for Raney nickel in 6.35 and kk.J cm id bubble columns, in both cocurrent and countercurrent flow. 

Slurry Settling Rate Quantification The settling rate measurements were conducted using a Beckman Coulter QuickSCAN Liquid Dispersion... 

Slurry settling in line. This is usually caused by a heavy slurry or low slurry pump speed. Check pump rpm and tighten V-belts if necessary. If a heavy slurry is causing the problem, dilute the slurry with mother liquor before pumping to the dewatering equipment. 

Equations 20 and 21 apply only to free, particulate separation not affected by flocculation or aggregation and for all particles having the same density. Under gravity field, few shear forces exist and have little effect on floes. Flocculation may be strong to change behavior of settling suspension to that of zone settling (i.e., all particles in slurry settle en masse at the same velocity irrespective of their size). 

Figure 18. Slurry settling velocity of 40-45-mesh Ottawa sand in 0.48% by weight hydroxypropylguar gum. (Reproduced with permission from reference 64. Copyright 1985 Society of Petroleum Engineers.)...

Flow of slurries in rotary drums depends on, among other factors, slurry settling characteristics. For the case of highly settling slurries flowing in a rotary drum with open-end and no lifters, these conclusions were obtained ... 

Figure 5.4 Coding the slurry settling characteristics (adapted from Purchas and Wakeman, 1986).

The duty specification, jar sedimentation and filtration tests enable the slurry settling and filtering characteristics to be broadly classified, and a selection problem to be specified through a series of letter codings. In order to select and rank equipment from this information it is necessary to provide charts and/or tables which relate equipment performance to the letter codings. Comparisons between the user defined specifications and the tables/charts enable the selection process. 

An alternative method for predicting slurry settling rates is based on the drag coefficient approach (already used above for single particles) has been reviewed by Di Felice (1994). Again, starting from the force balance and noting that the buoyancy is due to the suspension (i.e. particles and fluid), not just the fluid... 

Although the calculated reactivity additions associated with slurry settling were quite large, such additions would not occur instantaneously rather, they would be a function of time, the rate of reactivity addition being controlled by the rate at which the slurry settled. Settling data for slurries containing ItKX) or 500 g Th/liter correspond to rates of reactivity addition of less than 0.02% AAv/sec. These rates are well within permissible rates of reactivity addition however, if settling took place over a period... 

Flocculated slurries settle to a concentration at which the floes become... 

Brief studies made with thorium hydroxide indicated [33] that it is probably not a good source material for the production of slurry oxide. As precipitated from nitrate solution, the hydroxide formed a bulky precipitate which was hard to filter and wash, was amorphous to x-rays, and contained con.siderable nitrate impurity. Drying at 300 to 500°C yielded a crystalline oxide product which was difficult to slurry. Autoclaving a slurry of the hydroxide (without previous drying) at 250°C gave a bulky slurry (settled volume 300 to 500 g Th/liter) exhibiting a characteristic TI1O2 x-ray diffraction pattern. 

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