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Mechanische Schaumzerstorer kommen zum Einsatz, wenn eine Zerstorung rnit chemischen Antischaummitteln nicht in Frage kommt. Verschiedene am Markt angebotene Gerate rnit unterschiedlichen Bauformen zeigen, daB ein groBer Bedarf fur eine wirksame mechanische Schaumzerstorung besteht. In der Praxis werden meistens Schaumzerstorer eingesetzt, die rnit rotierenden Einbauten arbeiten. Wir haben uns daher auf dieses Arbeitsprinzip beschrankt. In diesem Beitrag sollen die Grundlagen der Schaumzerstorung mit diesen Geraten behandelt werden. Ausgehend von dem Mechanismus, der fur die Zerstorung von Schaumen durch Rotoren verantwortlich ist, werden Angaben gemacht, die der Ingenieur fur eine Apparate-Auslegung benotigt. Der wichtigste Mechanismus ist das ZerreiBen einzelner Lamellen. Dazu ist eine Mindestschergeschwindigkeit erforderlich. Die Flache des Rotors kann berechnet werden, wenn man die zulassige Geschwindigkeit kennt, rnit der der Schaum in den Rotor eintreten darf. Weiterhin wird gezeigt, daB mechanische Schaumzerstorer dieser Bauart einen Schaum nicht vollstandig in Gas-und Flussigkeitsphase auftrennen konnen. Diese Schaumzerstorer sind deshalb nur Schaumverdichter. Der beim Zerstorungsvorgang entstehende feinblasige Sekundarschaum wird zu einem groBen Problem fur die Schaumzerstorung und kann die Ursache fur das Fluten des Apparates sein. Dieser EinfluB wird durch das Koaleszenz-Verhalten des entstehenden Feinschaumes berucksichtigt. Die einzelnen Aussagen werden in Form eines Flutpunktsdiagrammes zusammengefaBt. * Vortrag von B. Furchner auf dem Jahrestreffen der Verfahrens-Ingenieure, 25. bis 27. Sept. 1985 in Hamburg.

Air classification is a process for the dry separation of a disperse phase according to the particle size, particle shape, or density, or, more precisely, the settling velocity. The settling velocity results from the balance of forces between the mass force and the drag force for every single particle. In a vertical gravity classifier particles move to the fine fraction if their settling velocity is lower than the air velocity, and to the coarse fraction if their settling velocity is higher than the air velocity. Particles in a deflector wheel behave similarly. The settling velocity must be calculated with the centrifugal acceleration in this case. Coarse classification in the range of 0.2 – 10 mm particle size is performed by gravity classifiers. Fine classification is generally performed in classifiers with deflector wheels. The fineness is adjusted by means of the speed of the wheel; increasing speed increases the centrifugal force and settling velocity. Fineness values of deflector wheel classifiers range from 1 to 200 µm. A peripheral speed of up to 150 m/s is used for finest products. Air classification is widely used in many industries and for many applications from laboratory scale to large‐scale processing. 1. Introduction 2. General Principles 2.1. Equilibrium of Forces at Individual Particles 2.1.1. Classifying in the Gravitational Field 2.1.2. Classifying in a Centrifugal Field 2.2. Separation of Bulk Material 2.3. Energy Requirement for Air Classifying 3. Machines for Air Classification 3.1. Gravity Classifiers 3.2. Inertial Classifiers 3.3. Internal Recirculation Air Classifiers 3.4. Deflector‐Wheel Classifiers 3.5. Classifier Mills 4. Application Examples for Air Classification 4.1. Cement 4.2. Fillers 4.3. Protein Shifting 4.4. Toner

The first part of this paper presents a relationship for the minimum velocity of rotating installations for foam breaking. The derivation is based on equilibrium of inertia and surface forces. Inertia forces occur during the acceleration of foam bubbles and act mainly at the plateau borders. High and definite acceleration can be obtained with a defoamer composed of a rotor and a stator. The surface force is due to the dynamic surface tension because surface-active solutions react to a rapid change in surface area by altering their surface tension. The theoretical relationship is compared with experimental results of minimum velocities needed to break foams produced from aqueous solutions of detergents. The equation presented here explains why measured minimum velocities often range between 10 and 20 mis. The second part of the paper deals with condensation of continuously generated foam in a closed system. In the process of condensation, foam is not completely separated into liquid and gas phase but turns into foam with small bubbles and high density. The collapse of this condensed foam must be considered for the control of persistent foams in a closed system. The collapse of foams made of aqueous solutions of different surface-active agents has been investigated. Different highly surface-active agents show small variations in times of coalescence. A relationship for the lifetime is given, which is based on laminar flow along plateau borders. Recommendations are made with respect to the geometry of the foam breaker, scale-up and operating variables such as rotational speed of the foam breaker and gas flow rate.

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