Tube Baffle DTB Crystallizer

Control of the population of fine particles by the mother liquor pumped from the baffle zone permits crystallization of products such as ammonium sulfate, KCl, and (NH4)2HP04 in the range of 6-20 mesh. 

This type of equipment is especially useful in multiple-stage cooling crystallizer applications where the cooling of the feed solu- 

The reactants can be mixed in the circulation piping of an FC-type crystallizer or in the draft tube of a DTB-type crystallizer where a large volume of slurry is mixed continuously with the reactants so as to minimize the driving force (supersaturation created by the reaction). Removal of heat is conveniently done by vaporizing water or other solvents as in a conventional evaporative-type crystallizer. 

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Special devices for classification of crystals may be used in some applications. Figure 14 shows a draft-tube-baffle (DTB) crystallizer that is designed to provide preferential removal of both fines and classified product. As shown, feed is introduced to the fines circulation line so that any nuclei formed upon introduction of the feed can be dissolved as the stream flows through the fines-dissolution heat exchanger. The contents of the crystallizer are mixed by the impeller, which forces the slurry to flow in the indicated direction. A quiescent zone is formed between the... 

FIG. 18-72 Draft-tube-baffle (DTB) crystallizer. Swenson Process Equipment Inc.)... 

The third, (c), is clear liquid overflow recycling to an elutriating leg which prevents undersized particles from escaping prematurely. Draft tube baffle (DTB) crystallizers contain elutriation legs, but DTB units are more commonly evaporative rather than cooling crystallizers. 

FIGURE 51.8 A draft-tube baffled (DTB) crystallizer. (Reprinted from Mersmann, A., Ed., Crystallization Technology Handbook, Marcel Dekker, New York, 1995. With permission.)... 

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