Slow-settling suspensions

For vessels greater than 38 m (10,000 gal), the economic attractiveness of side-entering impellers increases. For vessels larger than 380 m (100,000 gal), units may be as large as 56 kW (75 hp), and two or even three may be installed in one tank. For the suspension of slow-settling particles or the maintenance of uniformity in a viscous slurry of small particles, the diameter and rotational speed of a sideentering agitator must be selected on the basis of model tests or experience with similar operations. 

A simple test for wetting efficiency is to make up suspensions using the same concentration of powder but different wetting agents and allow the suspension to settle out. About a gram of powder dispersed in 10 ml of liquid is suitable. Slow settling, a clear interface between the clear liquid and the turbid lower layers and a small depth of sediment indicate the best... 

Some of these foods, principally tomato concentrates, are used to make other foods (e.g., sauces). The word suspension denotes that the insoluble solids settle rapidly, but in the aforementioned foods there is little or very slow settling such that they can be called either cohesive suspensions or dispersions. The aforementioned... 

The slow settling and consolidation after the suspension, reaching about 30% solids, have been attributed to the presence of unrecovered bitumen (Figure 9) (5) or to the presence of fine clays and amorphous materials, which either may hold amounts of water disproportionate to their concentration or may form an ordered floe structure at 30 wt% solids (4). One explanation emphasizes the possible role of soluble organic surfactants that modify the clay surfaces, the effect of strongly bound organic material on the minerals, asphaltenic components from... 

Many suspensions of solids in liquids are difiBcult to separate by gravitational, centrifugal, or vacuum techniques by reason of slow settling characteristics, poor fiherability, high solids content and other fectors. hi this circumstances, iiere large separating areas may prove necessary, the use of pressure filtration equipment is indicated. 

Solid suspensions are typically carried out in mechanically agitated or stirred vessels. Pumped liquid jets have also been used to suspend low concentrations of relatively slow settling solids. Although static mixers have been used to disperse fine solids into polymers, application of the technology is limited and beyond the scope of the present discussion. 

The DTB, crystallizer has a relatively slow-speed propeller agitator located within a draft-tube which draws a fine-crystal suspension up to a boiling zone of wide cross-sectional area, as shown in Figure 3.3(i). The fine-crystal magma then passes through an annular zone in which an additional baffle is located. Liquor flow continues upwards at low velocity while crystals settle out and fall to the base of the vessel. Liquor from the external pumped loop provides an up-... 

As a river or stream slows, it loses some of its ability to keep solids in suspension, and they begin to settle out. Heavier particles such as pieces of gravel and sand settle out first, and lighter particles, such as pieces of silt, settle out later. As a river or stream reaches a lake or ocean, it slows enough that essentially all of its suspended materials are deposited on the lake or ocean bottom. This process is referred to as sedimentation or siltation. A distinction is sometimes made between these two terms depending on the size of particles deposited, hut they are often used interchangeably. 

It only operates in continuous mode and uses catalyst particles of a slightly larger size than in BCR an upward flow of L maintains S in suspension, but the L velocity should be slower than the S settling velocity. Stability also requires a very narrow particle size distribution. Hydrodynamics and mass transfer depend on G/L flow ratio. G velocity is usually rather slow, with bubbles rising through a continuous L phase. Heat removal is restricted to use of wall exchangers. 

Variations in assay results can be avoided by the preparation of homogeneous, well-mixed, or non-settling fine particle suspensions (size 1-10 pm). Particle size reduction results in slow, more uniform settling rates. The bioavailability of drugs is improved by reducing the size of suspension particles. Furthermore, drug particles smaller than 20 pm produce less pain and tissue irritation when injected parenterally. However, fine particles may have a deleterious effect on chemical stability because of their high dissolution rate. 

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