Crystallizers tank crystallizer

Tank crystallizers. Tank crystallization is an old method still used in some specialized cases. Saturated solutions, in tank crystallization, are allowed to cool in open tanks. After a period of time the mother liquid is drained and the crystals removed. Nucleation and size of crystals are difficult to control. Typically, labor costs are very high. 

The plate is removed from the tank, the position of the solvent front marked, and the solvent allowed to evaporate from the plate. If the components of the mixture are coloured, the separation is obvious if colourless, they must be located either by viewing under U.. or by standing the plate in a closed dry tank containing crystals of iodine, whose vapour makes brown spots show i p. 

The reactor effluent, containing 1—2% hydrazine, ammonia, sodium chloride, and water, is preheated and sent to the ammonia recovery system, which consists of two columns. In the first column, ammonia goes overhead under pressure and recycles to the anhydrous ammonia storage tank. In the second column, some water and final traces of ammonia are removed overhead. The bottoms from this column, consisting of water, sodium chloride, and hydrazine, are sent to an evaporating crystallizer where sodium chloride (and the slight excess of sodium hydroxide) is removed from the system as a soHd. Vapors from the crystallizer flow to the hydrate column where water is removed overhead. The bottom stream from this column is close to the hydrazine—water azeotrope composition. Standard materials of constmction may be used for handling chlorine, caustic, and sodium hypochlorite. For all surfaces in contact with hydrazine, however, the preferred material of constmction is 304 L stainless steel. 

India, Goa and Bombay two plants built ca 1950 batch-type open-hearth roasters ceUs are operated discontinuously, the KMnO is crystallized separately in agitated tanks 1,200 114... 

Fig. 5. Fermentative production of amino acids (140). A, pure culture B, inoculation C, boiler D, air compressor E, air filter F, seed tank G, ammonia water for pH control H, fermenter I, sterilizer , culture media K, preparation tank L, centrifugal separator M, ion-exchange column N, crystallizing...

The manufacture of silver nitrate for the preparation of photographic emulsions requires silver of very high purity. At the Eastman Kodak Company, the principal U.S. producer of silver nitrate, 99.95% pure silver bars are dissolved in 67% nitric acid in three tanks coimected in parallel. Excess nitric acid is removed from the resulting solution, which contains 60—65% silver nitrate, and the solution is filtered. This solution is evaporated until its silver nitrate concentration is 84%. It is then cooled to prepare the first crop of crystals. The mother Hquor is purified by the addition of silver oxide and returned to the initial stages of the process. The cmde silver nitrate is centrifuged and recrystallized from hot, demineralized water. Equipment used in this process is made of ANSI 310 stainless steel (16). 

The product stream from the kilns is collected in storage bins. Black ash from the bins is fine-ground in a ball mill and fed to a leacher circuit, which is a system of stirred tanks, where it is dissolved in water and the muds are separated by countercurrent decantation. The solution from the decantation is passed through filter presses the muds are washed, centrifuged, and discarded. The filtered product, a saturated solution containing 12—13 wt % strontium sulfide, is sent to an agitation tank where soda ash is added to cause precipitation of strontium carbonate crystals ... 

In the Sulser-MWB process the naphthalene fractions produced by the crystallisation process are stored in tanks and fed alternately into the crystalliser. The crystalliser contains around 1100 cooling tubes of 25-mm diameter, through which the naphthalene fraction passes downward in turbulent flow and pardy crystallises out on the tube walls. The residual melt is recycled and pumped into a storage tank at the end of the crystallisation process. The crystals that have been deposited on the tube walls are then pardy melted for further purification. Following the removal of the drained Hquid, the purified naphthalene is melted. Four to six crystallisation stages are required to obtain refined naphthalene with a crystallisation point of 80°C, depending on the quaHty of the feedstock. The yield is typically between 88 and 94%, depending on the concentration of the feedstock fraction. 

A stable crystalline form for chocolate depends primarily on the method used to cool the fat present in the Hquid chocolate. To avoid the grainy texture and poor color and appearance of improperly cooled chocolate, the chocolate must be tempered or cooled down so as to form cocoa butter seed crystals (31). This is usually accompHshed by cooling the warm (44—50°C) Hquid chocolate in a water jacketed tank, which has a slowly rotating scraper or mixer. As the chocolate cools, the fat begins to soHdify and form seed crystals. Cooling is continued to around 26—29°C, during which time the chocolate becomes more viscous. If not further processed quickly, the chocolate will become too thick to process. 

Liquid citric acid is commercially available in a variety of concentrations with 50% w/w being most common. Grades are available that vary in appearance, purity, and color. Packaging is usually in dmms, tank tmcks, or rail cars. Liquid citric acid should be kept above 0°C to prevent crystallization. 

Batch Crystallization Batch crystalhzation has been practiced longer than any other form of ciystaUization in both atmospheric tanks, which are either static or agitated, as well as in vacuum or pressure vessels. It is still widely practiced in the pharmaceutical and fine chemical industry or in those applications where the capacity is veiy small. The integrity of the batch with respect to composition and history can be maintained easily and the inventoiy management is more precise than with continuous processes. Batch ciystalhzers can be left unattended (overnight) if necessary and this is an important advantage for many small producers. 

Process equipment function changes with different steps in process sequence (e.g., same vessel used as feed tank, reactor, crystallizer pump... 

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