Bei der Behandlung von Feststoffteilchen in einer Wirbelschicht kommt es oft zur gewollten oder ungewollten VergroBerung oder Verkleinerung dieser Partikel. Wahrend die VergroRerung durch Kornwachstum, Agglomeration 0. a. meist durch die ProzeBparameter bewuflt gesteuert wird, ist die Entstehung von kleinen Partikeln aus den Ausgangspartikeln oft unenviinscht. Die Wirtschaftlichkeit des Prozesses kann durch dieses Zerfallsverhalten entscheidend beeinflufit werden. Als Zerfallsverhalten wird dabei die Anderung der Par-tikelgroRe durch die Einwirkung der in der Wirbelschicht wirkenden Krafte iiber der fortschreitenden ProzeBzeit bezeichnet, Zur Abschatzung eines solchen Zerfallsverhaltens ist es empfehlenswert, bereits im Stadium der Verfahrensentwicklung die Partikeleigenschaften und den EinfluR der ProzeRbedingungen zu untersuchen. Ziel der Arbeit ist die Entwicklung eines Standardverfahrens rnit zugehoriger Apparatur zur Beurteilung des Zerfallsverhaltens verschiedenartiger Partikelzusammensetzungen und -formen, wobei die unterschiedlichen Betriebsbedingungen in Wirbelschichten nachgebildet werden konnen. Der Schwerpunkt liegt dabei auf der Entwicklung eines aus einfachen Versuchen bestehenden Verfahrens, daR die vorausschauende Beurteilung des Wirbelschichtverhaltens des zu untersuchenden Stoffsystems in relativ kurzer Zeit ermoglicht. Die Veranderung der KorngroRe als beschreibender Parameter des Zerfallsverhaltens ist dabei von besonderem Interesse. Zur Durchfiihrung der Testuntersuchungen stehen zur Verfiigung : -eine pneumatische Forderstrecke (DN 40) mit wahlweise moglicher Reibungs-und/oder Prallbeanspruchung, eine Kugelmuhlen-Testapparatur rnit unterschiedlicher Beanspruchung des Mahlgutes durch die Wahl der Mahlkorper und der Beanspruchungszeit und --eine Wirbelschichtversuchsanlage DN 150. Die pneumatische Forderstrecke erlaubt das Bruchund Abriebverhalten eines Bettmaterials nachzubilden und zu ermitteln. Die Partikel werden dabei mit Hilfe einer Dosierrinne in einen Injektor gefordert und von dort mittels eines eingestellten Druckluftstromes durch die Beanspmchungsstrecke transportiert und anschlieflend rnit einem Laserbeugungsspektrometer unter Einbeziehung der In-line-MeRzelle hinsichtlich der Partikelverteilung vermessen. Wahrend die Partikelprobe die Forderstrecke passiert, wird gleichzeitig die Partikelgeschwindigkeit gemessen. In einer nachgeschalteten Absaug-und Staubabscheideeinheit werden der Staub und die Partikelprobe abgeschieden. Erste MeBergebnisse experimenteller Untersuchungen mit unterschiedlichen Granulaten werdenvorgestellt und bewertet.
Communications for viscosities of 0.26 and 25 mPa s. The assumption of a constant diffusion coefficient is based on reference measurements with a comparable system. However, at the highest viscosity of 260 mPa s the measured and calculated values deviate considerably. The main reason for this is that Bravo et al. fitted their coefficients on measured data with much lower viscosity. Thus, of course, their model is applicable only to a limited extent for the measurements discussed here.The packing surface, which is also part of the model, is only useful to a certain extent in the high-viscosity range. This was confirmed by looking inside the column during the measurements with the high-viscosity liquids. The liquid drained very poorly from the packing. The useful surface area was certainly much lower than the value inserted in the model. At lower liquid viscosity the wetting of the packing is much better. ConclusionOn the basis of the investigations with a test column as described here, the following results can be stated: ± The efficiency decreases significantly with increasing viscosity. At a viscosity of 260 mPa s, only 20 % of the reference value was achieved. ± Flooding occurs at considerably lower loading.Distillation with structured packing in high-viscosity systems may be an economically interesting process option. If solvents or monomers must be removed from or exchanged in polymers, only a small number of theoretical stages are necessary. The results presented must be taken into consideration in the design of technical plants. There are some applications in this area at Bayer. Therefore, special liquid distributors and flash arrangements also need to be developed.This kind of development may help extend the application of distillation technology into the area of high-viscosity liquids. Especially in this area it is necessary to provide a better description of mass transfer by improving existing or developing new mass transfer correlations. ProblemThe use of an adsorbent can be advantageous for the gentle drying of temperature-sensitive products. The used adsorbent binds water vapor and causes a driving force for drying to equilibrium, so that drying is possible also at low temperatures in the range of atmospheric pressure. The literature provides comparatively few data on drying of wet, especially biological products.The expected effects should be verified by experimental investigations with model substances and selected biological products. At the same time test methods and a test equipment should be established in order to be able to investigate various products in connection with different adsorbing agents with relatively little effort.For a physically based mathematical modeling of adsorption drying at low temperatures the water vapor adsorption isotherms of the products to be dried and the adsorbing agents at corresponding temperatures must be known. Therefore, they were determined experimentally and modeled mathematically. Experimental Investigations Drying Tests with a Rotating DrumFor the experim...
Some special features of the fluidization technique, such as very good mixing behaviour, small-scale abrasive and thermical stress, permit an advantageous utilization in bioengineering. The use of the fluidization technique for fermentation, immobilization and working up and conditioning is investigated. Existing results with regard to using gas-fluidized beds in bioengineering are promising and have been investigated further. Brief Characterization of the Fluidization TechniqueA certain piling of solid particles is stored on a perforated plate and a gas or liquid streams through it. As the velocity of the fluid rises, flow-pressure loss Apscl, increases whereas the relative void space remains constant. After exceeding the point of fluidization the bed begins to expand. The particles are now moving with high intensity and large mixing efficiency ( Fig. 1). At the point of carrying upward the kinetic energy of the fluid is higher than the weight force of piling. The particles are carried upward by the fluid flow. The velocities of fluidization and carrying upward are determined by particle size. Therefore, the range of fluid-bed existence is determined between the fluidizing-point velocity of the largest particles and the carrying-upward velocity of the smallest particles of the packing. A homogenous or one of the different inhomogenous fluidized beds may be formed (Fig. 1). A clearly homogenous fluidized bed can be observed only with a liquid fluidizing matter. It is determined by a particle concentration independent of place and time. Most frequent a bubbling state arises. In the case of a gaseous fluidizing matter it is characterized by ascending bubbles. Some special features of the fluidization technique permit an advantageous utilization on an industrial scale: -The very good mixing behaviour of fluidized beds and the big relative velocity between the fluidizing matter and the solid particles lead to high mass and heat transfer coefficients and, thus, to reduced dimensions of the equipment in comparison with other contacting possibilities (Fig. 2).
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