Overflow, hydrocyclones

The vessel design features a Chinese hat-like conical core stopper above the underflow sump, which is there to prevent the vortex from reaching the latter and reentraining the settled soHds. The core stopper is also beheved to stabilize and locate the vortex flow in the vessel. Overflow from the vessel is through a wide cylindrical insert through the Hd, similar to a vortex finder in a hydrocyclone (16), and an optional provision can be made for collecting any floatables in a float trap. 

This process removes the coarser fractions in the hydrocyclones. Hydrocyclones basically operate within the sand region, and if there is material that is finer than sand (material that passes a 200 mesh screen), then approximately 100 percent of that material will pass out the top. The finer fractions and the wastewater that overflow from the hydrocyclone are not treated any further. The contaminants that reside on the finer fhactions adhere fairly well to such particles, therefore, it does not make any processing sense to try and remove them. The coarser fractions then subsequently move down into the next cells. The fluid movement from right to left and the solid... 

An emulsion separation method using hydrocyclones. The emulsion comprises a continuous phase, a discontinuous phase and fine solid particles. In the first step, the original emulsion is separated into an overflow emulsion and an underflow emulsion, in a first hydrocyclone. The overflow emulsion comprises portions of the continuous phase, the discontinuous phase and the fine solid particles. The overflow emulsion is inverted in which the continuous phase of the overflow emulsion is now a second discontinuous phase and the original discontinuous phase becomes a second continuous phase. Then, the inverted emulsion is directed to one or more subsequent hydrocyclones and the second continuous and discontinuous phases are collected. The fine solid particles remain in the second discontinuous phase. 

The energetics slurry is transferred from the energetics slurry feed tank into the anolyte feed tank through a hydrocyclone. The concentration of the energetics in the hydrocyclone underflow is nominally 40 weight percent. This underflow drains into the anolyte tank. The overflow, depleted in energetics, goes to a second hydrocyclone. The underflow from the second... 

A scoop that is positioned in the hydrocyclone vortex to obtain the desired particle size distribution in the overflow stream. 

The flow rate to the hydrocyclones for the full-scale SILVER II unit, based on a 14-mm vortex finder and a 6.4-mm underflow spigot, would need to be approximately 3.2 m3/hr at a pressure of around 3.5 bar. This flow rate should be sufficient to achieve the overflow flow rate of 1.8 m3/hr required to feed the SILVER II cells. As noted previously, the hydrocyclones used in the 12-kW energetics and agent simulant trials for EDS II handled solids at the planned design loading (AEA, 2001a). 

Near the top of the hydrocyclone there will be some short-circuiting of the flow between the inlet and the overflow, although the effects are reduced as a result of the formation of circulating eddies, often referred to as the mantle, which tend to act as a barrier. Within the secondary vortex the pressure is low and there is a depression in the liquid surface in the region of the axis. Frequently a gas core is formed, and any gas dispersed in the form of fine bubbles, or coming out of solution, tends to migrate to this core. In pressurised systems, the gas core may be very much reduced in size, and sometimes completely eliminated. 

Most studies of hydrocyclone performance for particle classification have been carried out at particle concentrations of about 1 per cent by volume. The simplest theory for the classification of particles is based on the concept that particles will tend to orbit at the radius at which the centrifugal force is exactly balanced by the fluid friction force on the particles. Thus, the orbits will be of increasing radius as the particle size increases. Unfortunately, there is scant information on how the radial velocity component varies with location. In general, a particle will be conveyed in the secondary vortex to the overflow, if its orbital radius is less than the radius of that vortex. Alternatively, if the orbital radius would have been greater than the diameter of the shell at a particular height, the particle will be deposited on the walls and will be drawn downwards to the bottom outlet. 

Figure 55 Typical size distributions by volume, for the feed flow and the overflow, if the hydrocyclone is operated for fines removal. The ordinate value is defined by volume percentage divided by interval width.

Liibberstedt [64] tested three different hydrocyclones for HeLa cell separation a 7 mm Bradley [67], a 10 mm Mozley (Richard Mozley Ltd., Redruth, UK), and a 10 mm Dorr-Oliver (Dorr-Oliver GmbH, Wiesbaden, Germany) (the dimension quoted here is the diameter of the cylindrical part of each hydrocyclone). The best results were obtained with the Dorr-Oliver hydrocyclone (Fig. 3), which produced a cell separation efficiency of 81 % when working at a pressure drop of 300 kPa and a flow rate of 2.8 L min When operating with two 10 mm Dorr-Oliver connected in series (the overflow of the first as feed for the second) at 200 kPa, the global efficiency of the arrangement was 94% [65]. These experimental values confirm the computational fluid dynamics (CFD) predictions that high levels of efficiencies for mammalian cells could be achieved with small diameter hydrocyclones [46]. 

Fig. 4. Influence of pressure drop on ceU viability in the underflow and overflow of the following hydrocyclones Dorr-Oliver (a),Mozley (b) and Bradley (c) with diameters of 10 mm, 10 mm and 7 mm, respectively [66]...

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