Dimensionierung von Kristallisatoren

Current status of crystallizer design . This paper surveys current knowledge in designing large scale crystallizers. The volume of a crystallizer depends on the desired mean crystal size, the suspended magma density and the permissible supersaturation, the latter determining the growth velocity and the nucleation rate. Different techniques for measuring the rate of crystal growth are outlined, as are also the methods used in its calculation, which are based upon various models of crystal growth. In designing a large scale crystallizer the phenomena of fluid dynamics and heat transfer must be taken into consideration. The paper deals with these two areas in detail and discusses problems associated with the control of population balance in the slurry.     

Entwicklung von Kristallisatoren

Development of crystallizers . The control of the crystallization kinetics and the spatial variation of the crystal mass are of decisive importance for the operation of industrial crystallizers. The influence of micro- and macro-attrition is demonstrated with particular reference to collisions with impeller blades and to breakage of crystals between impeller and draft tube. Spatial variations of supersaturation and crystal mass within the crystallizer have been shown to influence crystal size distribution. These variations are described by physical and mathematical models. Crystal size distributions measured in both pilot and industrial crystallizers show that simulation with the proposed models is very reliable. A model approach provides valuable support for the development of industrial crystallizers and also for the development of control using microprocessors.     

Auslegungsgrundlagen von Kristallisatoren

Design principles of crystallizers . Numerous processes in the chemical, heavy chemical, and food industries involve a crystallization step. Most commonly, a crystalline product is to be obtained from solution. Crystallizers are designed with the aim of cost-effective isolation of the product in the desired quality, i.e. in the necessary particle size and purity, while minimizing encrustation.     

Auslegung und Maßstabsvergrößerung von Kristallisatoren

Design and scale-up of crystallizers . Industrial scale crystallizers have to be designed in such a way that the crystalline product has the design particle size distribution, crystal form, and purity. Data on multiphase flow, solubility, balances of mass, energy, and number of crystals, kinetics (crystal growth rate and nucleation rate), and heat transfer are required. The present article discusses problems of kinetics in greater detail than other aspects. Multiphase flow is considered only briefly and heat transfer not at all. Familiarity with the terms homogeneous and heterogeneous (primary) and secondary nucleation [1, 2] is also assumed. This contribution is based on evaluation of available literature.     

Flüssigphasenoxydation von Cyclohexen in Gegenwart von Kombinationen von Verbindungen verschiedener Metalle

The Liquid Phase Oxidation of Cyclohexene in Presence of Combinations of Compounds of Different Metals The oxidation of cyclohexene ( 1 ) with molecular oxygen in chlorobenzene solution at 80°C has been studied using cobalt, manganese and copper compounds, respectively in combination with molybdenum complexes. The selectivity has been determined of cyclohex-2-en-1-hydroperoxide ( 2 ), epoxycyclohexane ( 3 ), cyclohex-2-en-1-ol ( 4 ), cyclohex-2-en-1-one ( 5 ), 2,3-epoxy-cyclohexane-1-ol ( 6 ) and cyclohexane-1,2-diol ( 7 ), formed from reacted 1 . Investigation of the consecutive reactions showed that 3 and especially 4 can react in different ways and moreover 4 inhibits the oxidation of 1 . From these results conclusions were drawn on the mechanism of oxidation of 1 .     

Die Herstellung von Kakaoerzeugnissen unter Anwendung von Pflugscharmischern

Manufacture of Cocoa Products Using Plough Share Mixers Various problems arise during mixing and thermal treatment of powdered material in the production and further processing cocoa powder. Means for solving such problems are shown. An effective process of mixing and the plough share mixers used for the same are described; these nearly automatic mixers are widely applicable. A further development of these mixers, the so-called DRUVATHERM-units, enable the combination of several mechnical processes, such as mixing, pulverizing of agglomerates, moistening, coating, tempering, cooling, drying and carrying out reaction processes under pressure or vacuum and at higher temperature. These new type of units can compete with conventional driers and roasters. They open new economical paths in the conventional treatment of products in cocoa industry as well.