Fractionation, hydrocyclones

Time is a critical variable because the magnetite settles if the mixture is held too long in a static condition. Use of hydrocyclones makes possible the separation in a fraction of a minute (21). These devices impart centrifugal force to the system, thereby permitting a separation to be made at a specific gravity less than that required in static, heavy-Hquid separations. 

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... 

The second important piece in the process development is the separation scheme. Several methods were suggested, such as decanting, water extraction or fractional distillation, use of hydrocyclones, hydrophobic membrane filters, etc. In the early work at EBC, many of its patents refer to facilitating catalyst separation via immobilization, although no mention is given on how activity was impacted by that immobilization. Furthermore, there were no details on how immobilization was achieved and which were the preferred means and techniques. 

In the case of the multicomponent PET beverage bottles, once the labels are removed, the lighter HDPE fraction is separated from the heavier PET and aluminum pieces in a hydrocyclone system. It is at this stage that other reclamation methods often differ, using a separation step based on flotation methods Dittman suggests that the hydrocyclone system will be an improvement over the flotation methods. The HDPE chips are then dried and collected. 

The experimental results reported in this paper demonstrate the ability of a flat-bottom hydrocyclone to separate the coarse fraction of ammonium sulfate crystals from a slurry which contains crystals of a wide size range. It appears that the grade efficiency curve, which predicts the probability of a particle reporting to the underflow of the cyclone as a function of size, can be adjusted by a change in the underflow diameter of the hydrocyclone. These two observations lead to the suggestion to use hydrocyclone separation to reduce the crystal size distribution which is produced in crystallisers, whilst using a variable underflow diameter as an additional input for process control. 

Definitions. The performance of a hydrocyclone is generally characterised by means of a grade efficiency or Tromp-curve which is the fractional mass recovery expressed as a function of particle size. 

The effective density of separation depends on the particle size and aspect ratio. As the particle size and aspect ratio decreases, the separation becomes more efficient and the offset between separation density and hydrocyclone medium density decreases. This findings suggest that for efficient density separation closely sized fine plastic fractions are required. 

The A-starch slurry from the centrifugal decanter is screened and then refined either with hydrocyclones or with separators and decanters. Purification and concentration of A-starch is accomplished in multistage hydrocyclones, or the A-starch slurry is separated into A and B fractions in a nozzle-type centrifuge and the A-starch fraction is finally refined in a centrifugal decanter. The B-starch stream is passed through vibrating screens and concentrated in a decanter. Pentosans and other solubles are concentrated and either dried or co-fermented with the B-starch for ethanol production. 

FIGURE 4.18 (Continued) (c) Predicted particle volume fraction for 35% weight CaCOs powder in a 75-mm hydrocyclone, (d) Experimental and predicted size selectivity curves for 35% weight CaCOg powder in a 75-mm hydrocyclone (the interactions correspond to viscosity corrections made for the particle volume fraction distribuiuBi within the hydrocyclone). From Rcgamani and Mifai [48]. 

This is a batch size analyzer [33] (Figure 10.1). An extremely dilute sample of milled ore is introduced, at a constant flow rate, to a coarse separator in the form of a tangentially fed cylindrical screen. The coarse fraction is allowed to settle and the fine fraction is further separated with an efficient hydrocyclone into a fine and a very fine fraction. The very fine fraction is discarded and the fine fraction is allowed to settle. The ratio of the times taken to fill the coarse and fine fraction collection vessels to indicated levels can be related directly to the particle size distribution. The cyclosensor has a sensitivity whereby a change of 1.8% passing 100... 

CERPHOS process (Centre d Etudes et de recherche des Phosphates Mineraux) in the washing step the fine fraction, containing a particularly high impurity concentration, is separated in a hydrocyclone. Drying and calcining is carried out as in conventional calcium sulfate production. 

In the second stage, the suspension is concentrated in a thickener. Although gravity thickeners dominate the field, cross-flow filter thickeners, hydrocyclones, and electrophoretic devices can be also used. A large fraction of the liquid can be removed economically in thickeners, thereby leading to smaller units in the third stage. 

In fractionating towers, the trays are still incorporated in one vessel, i.e., part of one unit. In other cases, for example, cascades of hydrocyclones, gas centrifuges and-last not least-membrane modules, the unit itself will be the stage of the cascade. 

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