Forced-Circulation Crystallizer

The most common use of this crystallizer is as an evaporative crystallizer with materials having relatively flat solubility or 

When the heat exchanger is used, it normally is one pass or two pass, and is designed for relatively low temperature rises of the solution pumped through the exchanger. This limits the supersaturation when heating materials of inverted solubility. In most applications, the steam-liquid AT is also limited so as to prevent mass boiling of the solution pumped through the tubes or vaporization at the tube wall. 

This type of crystallization equipment is probably the most widely used of any and is found in sizes ranging from 0.6 m for laboratory equipment up to over 12 m in diameter. Per pound of product produced, it is normally the least expensive type of equipment available, particularly when substantial amounts of evaporation are required. 

The FC crystallizer is recommended for the crystallization of a wide range of organic and inorganic compounds, such as NaCl, sodium sulfate, sodium carbonate monohydrate, citric acid, urea, sugar, etc. 

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Crystallizers with Fines Removal In Example 3, the product was from a forced-circulation crystallizer of the MSMPR type. In many cases, the product produced by such machines is too small for commercial use therefore, a separation baffle is added within the crystallizer to permit the removal of unwanted fine crystalline material from the magma, thereby controlling the population density in the machine so as to produce a coarser ciystal product. When this is done, the product sample plots on a graph of In n versus L as shown in hne P, Fig. 18-62. The line of steepest ope, line F, represents the particle-size distribution of the fine material, and samples which show this distribution can be taken from the liquid leaving the fines-separation baffle. The product crystals have a slope of lower value, and typically there should be little or no material present smaller than Lj, the size which the baffle is designed to separate. The effective nucleation rate for the product material is the intersection of the extension of line P to zero size. 

Forages, as ruminant feed, 10 863 Foraminifera, 17 690 Forastero cocoa beans, 6 353 Forced air cooling, of food, 21 560 Forced circulation crystallizer, 8 136 Forced-circulation evaporators, in sodium chloride solution mining, 22 803, 804 Forced convection, 13 245 Forced drainage experimental procedure, 12 12... 

The forced-circulation crystallizer is a simple unit designed to provide high heat-transfer coefficients in either an evaporative or a cooling mode. Figure 12 shows a... 

In DTB and DT crystallizers the circulation rate achieved is generally much greater than that available in a similar forced-circulation crystallizer. The equipment therefore finds application when it is necessary to circulate large quantities of slurry to minimize supersaturation levels within the equipment. In general, tliis approach is required to obtain long operating cycles with material capable of growing on... 

Forced circulation crystallization. Continuous crystallizer jn which agitation inside the vessel is created by external circulation of large quantities of liquid throngh a heater or cooler. 

A forced-circulation crystallizer operating at 3.38 h retention will make this sized product (Bennett and Van Buren 1969). 

Not all crystallizers are agitated with impellers in the vessel itself in agitated tank configuration. A common arrangement is to use a pump (or an axial flow impeller in an external pipe) to generate flow in a loop external to, but drawing from, and discharging to the main vessel. Such crystallizers are known as forced circulation crystallizers. These are widely used, for example, in sodium chloride crystallization (see Chapter 5, section... 

The parallel product flow configuration for a two-effect evaporative forced-circulation crystallizer is illustrated in Figure 9.16. The feed rate is maintained at a constant rate by feedback flow control. The level is controlled by varying the mother liquor return from downstream solid-liquid separation to the suction of a centrifugal pump. 

Figure 9.16 Schematic of a multi-effect forced-circulation crystallizer with parallel product flow.

Figure 9.17 Schematic of a multi-stage forced-circulation crystallizer.

The control strategy for the growth-type crystallizer would be the same as shown for the forced circulation crystallizers, but the hardware implementation for classification would differ. This hardware and control scheme could also satisfy the counterflow crystallization duty described above. 

Forced-circulation crystallizer with controlled solution supersaturation... 

Forced-circulation crystallizer with controlled solution supersaturation and controlled crystal bed (Oslo crystallizer)... 

Forced-circulation crystallizer with control of solution supersaturation, crystal phase and nucleation (Messo crystallizer... 

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