Crystallizer residence time

The CSD from the continuous MSMPR may thus be predicted by a combination of crystallization kinetics and crystallizer residence time (see Figure 3.5). This fact has been widely used in reverse as a means to determine crystallization kinetics - by analysis of the CSD from a well-mixed vessel of known mean residence time. Whether used for performance prediction or kinetics determination, these three quantities, (CSD, kinetics and residence time), are linked by the population balance. 

It has been shown that an increase in crystallizer residence time, or decrease in feed concentration, reduces the working level of supersaturation. This decrease in supersaturation results in a decrease in both nucleation and crystal growth. This in turn leads to a decrease in crystal surface area. By mass balance, this then causes an increase in the working solute concentration and hence an increase in the working level of supersaturation and so on. There is thus a complex feedback loop within a continuous crystallizer, illustrated in Figure 7.11. 

Reid MR, Coath CD (2000) In situ U-Pb ages of zircons from the Bishop Tuff No evidence for long crystal residence times. Geology 28 443-446... 

Sr Crystallizer residence time y Solution viscosity v Frequency factor in rate equation p Density a Interfacial tension ip Interfacial contact angle i// Dielectric constant... 

By allowing some clear liquor to overflow from the crystallizer Figure 9.7b) the crystal residence time can be increased and rendered independent of the liquor residence time, i.e. WjP If required, the liquor overflow can be... 

Theoretical considerations (Saeman, 1956) suggest that the true crystal residence time, t, i.e. the age of a product crystal in a classifying crystallizer, is four times the over-all residence time (draw-down time), T. Thus from point (6) above t is about 8 h. 

Crystals Residence Time (ps) Diffusion Coefficient (10" mVsec) ... 

Thus as t), 5J.. In other words a change in crystallizer residence time has a corresponding but opposite effect on the level of supersaturation. 

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