Vacuum dryer

A 95% yield of pure anthraquinone was obtained. This is an almost quantitative yield based on the 100% content of the anthracene used. The cmde anthraquinone was then purified. To a jacketed steel kettie, provided with an agitator, was added cmde anthraquinone and nitrobenzene. Under agitation, the charge was heated at 130—140°C until a complete solution resulted. Under slow agitation, the solution was cooled to 30 °C and the resulting slurry of anthraquinone was filtered on a pressure filter. The cake was washed twice with nitrobenzene, then was reslurried on the filter with nitrobenzene, sucked dry, and transferred to a vacuum dryer where the nitrobenzene was distilled. The dried anthraquinone was discharged to suitable containers. A 99% yield of pure anthraquinone was obtained equal to a recovery of approximately 90% based on the cmde anthraquinone. 

The fatty acids that emerge from the top of the column contain entrained water, partially hydroly2ed fat, and the Zn—soap catalyst. This product stream is passed into a vacuum dryer stage where the water is removed through vapori2ation and the fatty acid cooled as a result of this vapori2ation process. The dried product stream is then passed to a distillation system. 

FIG. 12-74 Atypical vacuum dryer. (Blaw-Knox Vood [Pg.1213]

TABLE 12-28 Standard (Double-Cone) Rotating Vacuum Dryers ... 

The vacuum plate drwer is provided as pari of a closed system. The vacuum dryer has a cylindrical housing and is rated for fiill-vacuum operation (typical pressure range 3-27 kPa absolute). The exhaust vapor is evacuated try a vacuum pump and is passed through a condenser for solvent recovery. There is no purge-gas system required for operation under vacuum. Of special note in the vacuum-drying system... 

For example, in rotary vacuum dryers it is possible to prevent the formation of explosible dust-air mixtures by setting and monitoring a certain partial vacuum (negative pressure). This pressure value must be determined by experiment for each type of dust. With pressures of less than O.I bar, in general, hazardous effects of dust explosions need not be anticipated. If the vacuum system malfunctions, the partial vacuum must be released by inert gas and the instaUation shut down. 

Figure 6-23. Drying-special three-stage assembly serving two high vacuum dryers. By permission, C. H. Wheeler Mfg. Co.

The gas entering the filter must be kept above its dewpoint to avoid water-vapor condensation on the bags, which will cause plugging. However, fabric filters have been used successfully in steam atmospheres, such as those encountered in vacuum dryers. In these applications, the housing is generally steam-cased. 

When the temperature of the drying material must be kept as low as possible, vacuum drying is used, and one form of vacuum dryer is shown in Figure 16.18. The dried material is collected in two screw conveyors and carried usually to two receivers so that one can be filled while the other is emptied. 

Given that the introduction of solvent obviously produces wet granules, the wet granulation process includes a drying step. Drying typically occurs in a fluid bed dryer. But there are other options, such as microwave vacuum dryers. In 1994, White applied on-line NIRS to monitor moisture content and predict drying end point in two TK Fielder microwave dryers. The NIR spectral data were correlated to off-line Karl Fischer measurements which resulted in a standard error of prediction equal to 0.6% when the samples... 

J.G. White, Online moisture detection for a microwave vacuum dryer, Pharm. Res., 11(5), 728-732 (1994). 

Boeh-Ocansey O., Freeze-drying in a fluidized-bed atmospheric dryer and in a vacuum dryer evaluation of external transfer coefficients, /. Food Eng., 7 (1988) 127-146. 

Production scrap containing Ecoflex /PLA compound should be handled separately from PE-LD scrap. It has been proven that scrap from the dryblend could be repelletized using an underwater granulator, where the die face is externally water cooled. The repelletized pellets could be used after drying of the water using a spin dryer and, if necessary, a vacuum dryer. Drying conditions have to be adapted to the Ecoflex /PLA compound being used. 

VAC TRAX is different from other thermal desorption processes in that it is a vacuum dryer. By sealing the drying chamber and reducing the air pressure, a vacuum is created. The vacuum allows a much lower temperature to be used in the dryer, enabling the use of smaller, more transportable equipment. 

A detailed example of capital and operating costs of a jacketed vacuum dryer for a paste on which they have laboratory drying data is worked out by Nonhebcl and Moss (1971, p. 110). 

The molten dinitrotoluene is run into the vacuum dryer, and heated at 120°C at a pressure of 15 mm Hg for 5 hr. It is tested for moisture by heating a small amount in a test-tube and looked for condensation on the side of the tube. The material is made up into solid blocks or flakes. .. 

FIGURE 12. Popular vacuum dryers with a mechanical paddle. ... 

Soluble complexes are typically dried using a spray dryer, vacuum dryer or freeze dryer, because if they are dried in a conventional oven, a glass is formed. Spray drying, vacuum drying and/or freeze drying are also used for heat-labile and reactive compounds such as complexes of some acids. With prolonged heating, some compounds decompose or react with the cyclodextrin. However, the time of exposure to... 

Special flavor formation for crumb chocolate takes place in the plant shown schematically in Fig. 14.28, left. In this system, so-called Maillard reactions between amino acids and reducing sugars occur in 1 to 2 minutes at 130°C, producing the classic flavors usually found in Great Britain, Scandinavia, and Japan. The process requires a few percent of moisture, which is added separately and removed in the vacuum after the reaction. The ZSK process saves on expensive vacuum dryers requiring several hours residence time. 

Related Calculations. Figure 19.17 is valid for condensers of shell-and-tube design, employing cooling water at 85°F. This example is adapted from Vacuum Dryers, Chem. Eng., January 17,1977. 

Equipment commonly employed for the drying of solids is described both in this subsection in Sec. 12, where indirect heat transfer devices are discussed, and in Sec. 17 where fluidized beds are covered. Dryer control is discussed in Sec. 8. Excluding fluid beds this subsection contains mainly descriptions of direct-heat-transfer equipment. It also includes some indirect units e.g., vacuum dryers, furnaces, steam-tube dryers, and rotary calciners. 

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