Falling-film crystallization

Eig. 4. Falling-film crystallizer, semibatch. Tube length is 12.2 m tube diameter is 7.6 cm. 

FIG. 11-122 Evaporator types, a) Forced circulation, (h) Siibmerged-tiihe forced circulation, (c) Oslo-type crystallizer, (d) Short-tube vertical, (e) Propeller calandria. (f) Long-tube vertical, (g) Recirculating long-tube vertical, (h) Falling film, (ij) Horizontal-tube evaporators. G = condensate F = feed G = vent P = product S = steam V = vapor ENT T = separated entrainment outlet. 

Major evaporator designs include forced-circulation, long-tube vertical (both rising and falling film), and calandria-type evaporators. The economics of a particular process will dictate the evaporator style and model best suited to a particular application. Forced-circulation and calandria evaporators are required for processes where crystals are formed. These evaporators are designed to keep crystals suspended in solution to prevent scaling of the equipment. Long-tube vertical evaporators are used to concentrate a liquid that does not have solids present. 

Falling-film crystallization utilizes progressive freezing principles to purify melts and solutions. The technique established to practice the process is inherently cyclic. Figure 20-15 depicts the basic working concept. First a crystalline layer is formed by subcooling a liquid film on a vertical surface inside a tube. This coating is then... 

Commercial Equipment and Applications The falling-film crystallization process was invented by the MWB company in Switzerland. The process is now marketed by Sulzer Chemtech. Products successfully processed in the falling-film crystallizer are listed on Table 20-9. The falling-film crystallization process is available from the Chemtech Div. of Sulzer Canada Inc., 60 Worcester Rd., Rexdale, Ontario N9W 5X2 Canada. 

Sulzer A family of processes for purifying organic chemicals by melt-crystallization without using solvents. Two systems are in use static crystallization, and falling-film ciystalliza-tion. The latter is proprietary to Sulzer Chemtec, Switzerland. 

Figure 8.16. Some types of evaporators, (a) Horizontal tube, (b) Calandria type, (c) Thermocompressor evaporator, (d) Long tube vertical, (e) Falling film, (f) Forced circulation evaporator-crystallizer, (g) Three types of Oslo/Krystal circulating liquid evaporator-crystallizers.

Evaporation. The evaporator is normally needed to remove water from the AN solution. It must produce a solution with the required concentration at a temperature that avoids crystallization. The acceptable water content is normally below l percent for a prilled product and up to 8 percent for the feed to some granulation processes. Evaporators in commercial use include circulatory systems, shell and tube heat exchangers, and falling film-type evaporators.103... 

Falling films are also used for evaporation in which the film is both entirely or partially evaporated (juice concentration). This principle is also used in crystallization (freezing). 

The RO treatment removes salts and the concentrate is crystallized by a tube type of falling film evaporator and its condensate is recirculated back to the process. For example, when a stream at McKinley of approximately 660 m /day is RO treated it results in a permeate of about 490 m /day (1-1.3 m /t product). The salt removal is needed because the high conductivity levels dismrb the usability of the wet end chemicals [45,46]. 

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