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Holdup extraction

The nonuniformity of drop dispersions can often be important in extraction. This nonuniformity can lead to axial variation of holdup in a column even though the flow rates and other conditions are held constant. For example, there is a tendency for the smallest drops to remain in a column longer than the larger ones, and thereby to accumulate and lead to a locali2ed increase in holdup. This phenomenon has been studied in reciprocating-plate columns (74). In the process of drop breakup, extremely small secondary drops are often formed (64). These drops, which may be only a few micrometers in diameter, can become entrained in the continuous phase when leaving the contactor. Entrainment can occur weU below the flooding point. [Pg.69]

Coalescence and Phase Separation. Coalescence between adjacent drops and between drops and contactor internals is important for two reasons. It usually plays a part, in combination with breakup, in determining the equiHbrium drop si2e in a dispersion, and it can therefore affect holdup and flooding in a countercurrent extraction column. Secondly, it is an essential step in the disengagement of the phases and the control of entrainment after extraction has been completed. [Pg.69]

The General Mills mixer—settler (117), shown in Figure 13b, is a pump—mix unit designed for hydrometaHurgical extraction. It has a baffled cylindrical mixer fitted in the base and a turbine that mixes and pumps the incoming Hquids. The dispersion leaves from the top of the mixer and flows into a shallow rectangular settler designed for minimum holdup. [Pg.75]

The sohd can be contacted with the solvent in a number of different ways but traditionally that part of the solvent retained by the sohd is referred to as the underflow or holdup, whereas the sohd-free solute-laden solvent separated from the sohd after extraction is called the overflow. The holdup of bound hquor plays a vital role in the estimation of separation performance. In practice both static and dynamic holdup are measured in a process study, other parameters of importance being the relationship of holdup to drainage time and percolation rate. The results of such studies permit conclusions to be drawn about the feasibihty of extraction by percolation, the holdup of different bed heights of material prepared for extraction, and the relationship between solute content of the hquor and holdup. If the percolation rate is very low (in the case of oilseeds a minimum percolation rate of 3 x 10 m/s is normally required), extraction by immersion may be more effective. Percolation rate measurements and the methods of utilizing the data have been reported (8,9) these indicate that the effect of solute concentration on holdup plays an important part in determining the solute concentration in the hquor leaving the extractor. [Pg.88]

Direction of extraction, whether from dispersed to continuous, organic hquid to water, or the reverse Dispersed-phase holdup Flow rates and flow ratio of the liquids... [Pg.1477]

In extraction column design, the model equations are normally expressed in terms of superficial phase velocities, L and G, based on unit cross-sectional area. The volume of any stage in the column is then A H, where A is the cross-sectional area of the column. Thus the volume occupied by the total dispersed phase is h A H, where h is the fractional holdup of dispersed phase, i.e., the droplet volume in the stage, divided by the total volume of the stage and the volume occupied by the continuous phase, in the stage, is (1-h) A H. [Pg.194]

Under changing flow conditions, it can be important to include some consideration of the hydrodynamic changes within the column (Fig. 3.53), as manifested by changes in the fractional dispersed phase holdup, h , and the phase flow rates, Ln and G . which, under dynamic conditions, can vary from stage to stage. Such variations can have a considerable effect on the overall dynamic characteristics of an extraction column, since variations in hn also... [Pg.195]

As explained in Sec. 3. 3. 1.11, the fractional holdup of the dispersed phase in agitated extraction columns will vary with changing phase flow rate. This dynamic variation in the holdup along the column will cause a dynamic velocity profile in both phases. [Pg.556]

Batch esterification, 10 478—480 Batch experimental reactor, 21 352 Batch extraction, 10 756 Batch extractor, holdup in, 10 764 Batch fermentation, 10 267 Batch filter cycles, 11 344, 345-346 Batch furnaces, 12 288—289 Batch gasoline blending, 12 413 Batch hydrogenation, 10 811 Batching, ceramics processing, 5 648 Batch injection analysis (BLA) technique, 9 586-587... [Pg.88]

If necessary, the implicit nature of the calculation may, however, be avoided by a reformulation of the holdup relationship into an explicit form. The resulting calculation procedure then becomes much more straightforward and the variation of holdup in the column may be combined into a fuller extraction column model in which the inclusion of the hydrodynamics now provides additional flexibility. The above modelling approach to the column hydrodynamics, using an explicit form of holdup relationship, is illustrated by the simulation example HOLDUP. [Pg.153]

The fractional holdup of the dispersed phase in agitated extraction columns varies as a function of flowrate. Under some circumstances it may be important to model the corresponding hydrodynamic effect. The system is represented below as a column containing seven agitated compartments or stages. [Pg.459]

Determination of CholesteroL For meat extraction, the procedures for determining the cholesterol of extracted lipid samples were described Chao et al. (2i). For edible beef tallow extraction, the preparation of samples for cholesterol content was based on the AOAC (22) method Section 28.110. The prepared sample was then injected into a Supelco SPB-1 fused silica capillary column of 30 meters x 032 mm i.d. in a Varian Model 3700 gas chromatograph equipped with dual flame ionization detectors. The initial holdup time was 4 min at 270°C and then programmed to a temperature of 300°C at a ramp rate of 10°C/min. Helium flow rate and split ratio were 13 ml and 50 1, respectively, while the injector/detector temperature was 310°C. [Pg.121]

The nonunifomiily of drop dispersions can often be important in extraction. This nonuniformity can lead to axial variation of holdup in a column even though the flow rates and other conditions are held constant,... [Pg.596]

Continuous glycerin washing of soap produced by saponification has been demonstrated in a countercurrent centrifugal extractor (38). The device achieves phase separation with as little as 0.02 specific gravity difference and accomplishes up to 10 theoretical stages of extraction. Some of the advantages over prior operations reportedly include flexibility in feed, low holdup, less waste due to more efficient separation, simple operation, rapid startup, and small space requirements. [Pg.68]


See other pages where Holdup extraction is mentioned: [Pg.544]    [Pg.544]    [Pg.160]    [Pg.544]    [Pg.544]    [Pg.544]    [Pg.160]    [Pg.544]    [Pg.65]    [Pg.74]    [Pg.207]    [Pg.1323]    [Pg.1476]    [Pg.1480]    [Pg.1490]    [Pg.67]    [Pg.198]    [Pg.545]    [Pg.270]    [Pg.24]    [Pg.28]    [Pg.476]    [Pg.333]    [Pg.211]    [Pg.293]    [Pg.310]    [Pg.325]    [Pg.346]    [Pg.476]    [Pg.484]    [Pg.565]    [Pg.55]    [Pg.68]    [Pg.69]    [Pg.229]   
See also in sourсe #XX -- [ Pg.434 ]

See also in sourсe #XX -- [ Pg.434 ]

See also in sourсe #XX -- [ Pg.434 ]




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Holdup

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