Crystallizers circulating magma

Fig. 2. Forced circulation evaporators (a) submerged-tube, shown as circulating magma crystallizer (b) submerged-tube, shown as suspension type...

Circulating liquor crystallisers and circulating magma crystallisers are used for the large-scale production of a wide range of crystal products. 

Circulating magma Production of large-sized crystals. High throughputs Ammonium and other inorganic salts, sodium and potassium chlorides... 

Circulating liquor Production of uniform crystals (smaller size than circulating magma). High throughputs. Gypsum, inorganic salts, sodium and potassium nitrates, silver nitrates... 

This type of equipment is sometimes called the circulating-magma crystallizer. In this type, the uniformity of suspension of the product solids within the crystallizer is sufficient. It has been said that most commercial equipment satisfies this assumption. 

The circulating-magma design describes equipment in which crystals are intentionally transported with the liquor to the region where supersaturation is being created. Swenson-Walker, Wulff-Bock, and doublepipe crystallizers are examples of this type. Forced-circulation design is common. 

In a circulating-magma crystallizer the supersaturation created in the vapor head does not rise to point b, for it is being deposited on the crystals as it is formed by evaporation. Higher recirculation rates and/or magma densities permit operation at lower actual supersaturations, thereby decreasing spontaneous nucleation, but increasing the number of nuclei formed by attrition. 

Mixed-Suspension, Mixed-Product-Removal Crystallizers This type of equipment, sometimes called the circulating-magma... 

In this type both the liquor and growing crystals are circulated through the zone in which supersaturation occurs. Circulating magma crystallisers are probably the most... 

Mixed-Suspension, Mixed-Product-Removal Crystallizers This type of equipment, sometimes called the circulating-magma crystallizer, is by far the most important in use today. In most commercial equipment of this type, the uniformity of suspension of product solids within the crystallizer body is sufficient for the theory [Eqs. (18-34) to (18-36c)] to apply. Although a number of different varieties and features are included within this classification, the equipment operating with the highest capacity is the kind in which the vaporization of a solvent, usually water, occurs. 

Many of these classes are self-explanatory, but some require definition. For example, the term controlled refers to supersaturation control. The term classifying refers to the production of a selected product size by classification in a fluidized bed of crystals. In a circulating-liquor crystallizer the crystals remain in the crystallization zone only the clear mother liquor is circulated, e.g., through a heat exchanger. In the circulating-magma crystallizer the crystals... 

Newman, H.H. and Bennett, R.C. (1959) Circulating magma crystallizers. Chemical Engineering Progress, 55, (3), 65-70. 

In a crystallizer with a circulation pump or agitator, it has been shown that collisions between such a device and crystals in the circulating magma dominate nucleation resulting from other collisions. Consequently, it might be expected that a relationship of impact energy E to crystallizer variables must include the mass of the impact crystal M,., and the rotational velocity of the impeller available energy actually transmitted to the crystal, t, should also be included in the model ... 

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