Crystallization equipment scale

The constant may depend on process variables such as temperature, rate of agitation or circulation, presence of impurities, and other variables. If sufficient data are available, such quantities may be separated from the constant by adding more terms ia a power-law correlation. The term is specific to the Operating equipment and generally is not transferrable from one equipment scale to another. The system-specific constants i and j are obtainable from experimental data and may be used ia scaleup, although j may vary considerably with mixing conditions. Illustration of the use of data from a commercial crystallizer to obtain the kinetic parameters i, andy is available (61). 

Coefficient of Variation One of the problems confronting any user or designer of crystallization equipment is the expected particle-size distribution of the solids leaving the system and how this distribution may be adequately described. Most crystalline-product distributions plotted on arithmetic-probability paper will exhibit a straight line for a considerable portion of the plotted distribution. In this type of plot the particle diameter should be plotted as the ordinate and the cumulative percent on the log-probability scale as the abscissa. 

Figure 9.4 Experimental set-up Bench-scale multi-purpose batch crystallizer equipped with an in situ ATR FTIR probe. Reprinted from Fevotte (2002)43 with permission from Elsevier.

Both batch and continuous crystallization equipment are available at industrial scale, although batch operation is normally favored for pharmaceutical products where batch integrity must be maintained for quality control reasons. Continuous crystallization is suited to higher throughputs and enables more energy efficient operation. 

A tank crystallizer is the simplest type of industrial crystallizing equipment. Crystallization is induced by cooling the mother liquor in tanks, which may be agitated and equipped with cooling coils or jackets. Tank crystallizers are operated batch-wise and are generally used for small-scale production. 

Ciystallization has been the most important separation and purification process in the pharmaceutical industry throughout its history. Many parallels exist in the fine chemicals industry as well. Over the past several decades the study of crystallization operations has taken on even higher levels of importance because of several critical factors that require increased control of the crystallization process. These levels of control require better understanding of the fundamentals as well as of the operating characteristics of crystallization equipment, including the critical issue of scale-up. 

The second stage of the hybrid-process is essentially a crystallization capable of crystallizing all solids dissolved in the feed resp. the brine of the RO stage. Parts of these substances tend to heavy scaling and, therefore, the choice of the crystallization equipment is limited. A proven solution is, of course, the agitated thin film evaporator. However, this type of equipment must lead to high specific treatment costs for two reasons ... 

Choose the type of crystallizer that best meets the requirements for (a) product size, (b) product quality, (c) process economics, and (d) scale of operation. See Table 5.1 for a list of the general characteristics of crystallization equipment. 

Boiler Deposits. Deposition is a principal problem in the operation of steam generating equipment. The accumulation of material on boiler surfaces can cause overheating and/or corrosion. Both of these conditions frequentiy result in unscheduled downtime. Common feed-water contaminants that can form boiler deposits include calcium, magnesium, iron, copper, aluminum, siUca, and (to a lesser extent) silt and oil. Most deposits can be classified as one of two types scale that crystallized directiy onto tube surfaces or sludge deposits that precipitated elsewhere and were transported to the metal surface by the flowing water. 

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. 

Answer An electronic temperature monitor could be equipped with a bar-code liquid crystal display which could be read by a portable bar-code reader. These devices have a memory so several readings may be taken before they are readout over a telephone modem to a data logging computer. The simplest way to read the acid type would be to post a label that is bar-coded to indicate the acid type. Tire acid quantity could be indicated by an acid level gage using a bar-code display of the level. The aluminum quality could be indicated by displaying a label in bar-code. The amount of aluminum could be determined by weight using a bar-code readout on the scales. 

Many of these treatments can be straightforwardly scaled-up to industrial quantities by adding steam to calcination furnace atmospheres and carrying out various forms of solution ion exchange or chemical treatment and/or acid extractions in suitable powder and granule contacting equipment. The products vary in stability and catalytic properties because the treated materials are no longer freshly crystal-... 

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