bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wärme‐ und Stoffübertragung in der Wirbelschicht
Authors: Martin Holger 
Published: December 2004

AbstractHeat and mass transfer in fluidized beds. Methods of calculation are presented which enable reasonably accurate prediction of heat and mass transfer coefficients in fluidized beds. Some well established equations already given in the literature could be used for estimating the range of existence of the fluidized bed and for calculating maximum fluidization velocities, bed expansion, and particle‐to‐fluid heat and mass transfer. However, a new model had to be developed for the wall‐to‐bed heat transfer from solid surfaces immersed in fluidized beds. This model makes use of some basic ideas adopted from the kinetic theory of gases in order to describe the mechanism of energy transfer through the moving particles. Predictions with this new model are in good agreement with most of the experimental observations, particularly regarding the effects of particle diameter, temperature, pressure, physical properties of gas and particles, and gas velocity.
Herstellung von Synthesegas aus Braunkohle
Authors: Franken Gerd , Adlhoch Wolfgang , Koch Werner 
Published: December 2004

AbstractProduction of synthesis gas from lignite. The production of methanol synthesis gas from lignite is explained for the high‐temperature Winkler process. The influence of experimental factors on the economics of the overall process is indicated, and the production of methanol synthesis gas from lignite, residual oil, and natural gas is compared. The article concludes by presenting further developments of the high‐temperature Winkler process.
Über die Auswahl von Polymerisationsreaktoren
Authors: Gerrens Heinz 
Published: December 2004

AbstractChoice of polymerization reactors. Industrial syntheses of polymers always yield a highly complex product whose adequate characterization often requires application‐oriented tests in addition to chemical and physical parameters. In contrast to the synthesis of low‐molecular mass substances subsequent corrections, e. g. by distillation or crystallization, are usually impossible. Extremely detailed reaction control is of paramount importance.Polyreactions can be classified according to kinetic aspects (monomer linkage with and without termination reaction, linkage of polymers). Apart from homogeneous bulk polymerization, there are the heterogeneous processes of precipitation‐, bead‐, and emulsion‐polymerization. The polymerization reactors can be assigned to the known ideal types (batch reactor, continuous plug flow reactor, series of stirred tanks, and continuous stirred tank reactor). High viscosity often thwarts thorough mixing in bulk polymerization and segregation may occur.The article surveys the variants of the reactor types used for various polyreactions and polymerization processes in industry and examines the reasons for this choice. Most commonly used is the batch reactor, followed by the cascade of stirred tanks. Continuous polymer‐linkage (polycondensation, polyaddition) is frequently performed in a series of several different kinds of reactors.
Fortschritte bei der mechanischen Flüssigkeitsabtrennung durch Filtration
Authors: Bender Wolfgang , Redeker Dettmar 
Published: December 2004

AbstractTrotz der gestiegenen Kosten für den apparativen Aufwand ist die mechanische Flüssigkeitsabtrennung immer noch ein relativ billiger Verfahrensschritt. Bei geringem Energieaufwand lassen sich selbst feindisperse Feststoffe um mehr als eine Zehnerpotenz, oft sogar noch einstufig, aufkonzentrieren. Aus der breiten Palette der verfügbaren Apparate gewinnt in der Chemischen Industrie das gasdicht gekapselte Filter aufgrund arbeitshygienischer und sicherheitstechnischer Gesichtspunkte zunehmend an Bedeutung. Für die Teilvorgänge Filtrieren, Auswaschen und Entfeuchten der Kuchenfiltration wurden mehrere Modellansätze vorgeschlagen. In der Praxis genügt jedoch meist die einfache, näherungsweise Beschreibung der Kuchenbildung mit Hilfe der Darcy‐Gleichung. Bei stark zur Entmischung neigenden Feststoffen und bei kompressiblem Kuchen ist die Annahme einer homogenen Kuchenstruktur aber nicht mehr zulässig. Die Filterkuchenentfeuchtung durch Trockenblasen oder Trockensaugen ist wegen der beim Schrumpfen oft eintretenden Rißbildung nur im begrenztem Maße möglich. Gelingt es nicht, die Rißbildung zu unterdrücken, so ist das Trockenschleudern in Zentrifugen oder das mechanische Auspressen die günstigere Methode. Abluftprobleme werden bei diesen beiden Entfeuchtungsmethoden vermieden. Die zur Beurteilung erforderlichen Stoffeigenschaften können in Laborversuchen ermittelt werden. Die erarbeiteten Grundlagen erlauben es, die Dimensionierung der Betriebsmaschinen mit größerer Sicherheit durchzuführen als bisher. Diese Grundlagen sind auch dann notwendig, wenn die Steuerung des Verfahrens mit Prozeßrechnern beabsichtigt ist.Mit der sog. dynamischen Filtration ist eine Möglichkeit eröffnet, strukturviskose, schwerer filtrierbare Suspensionen kontinuierlich in geschlossenen Apparaten bis an die Grenze ihrer Fließfähigkeit aufzukonzentrieren und zu waschen.
Anlagen zum Ultrahocherhitzen von Lebensitteln — Stand der Technik und Optimierung
Authors: Reuter Helmut 
Published: December 2004

AbstractAls Ultrahocherhitzungsverfahren gelten kontinuierliche Verfahren zum Haltbarmachen fließfähiger Lebensmittel durch Erhitzen auf 135 bis 150°C für die Dauer von einigen Sekunden. Die so sterilisierten Lebensmittel werden unter sterilen Bedingungen in sterile Packungen abgefüllt, die unter sterilen Bedingungen keimdicht verschlossen werden. UHT‐Verfahren werden heute besonders in der Milchverarbeitung zur Haltbarkeitsverlängerung von Milch, Sahne, Puddings, Desserts, aber von Suppen und Soßen angewendet. Gegenwärtig kommt die 3. Generation der UHT‐Anlagen auf den Markt. Nach Art der Wärmezufuhr unterscheidet man zwischen direkt arbeitenden Anlagen mit Dampfinjektion und indirekten Anlagen mit Wärmeaustauschern. Hochviskose Medien werden in Rieselfilmerhitzern direkt durch Dampf erhitzt. UHT‐Anlagen müssen in regelmäßigen Zeitabständen nach 6 bis 12 Betriebsstunden gereinigt werden, um die im oberen Temperaturbereich auf den Wärmeaustauschflächen gebildeten Ablagerungen zu entfernen. Von wirtschaftlicher Bedeutung sind daher die Standzeit der Anlagen, der durch Wärmeaustausch erzielbare Wärme‐Rückgewinn der Anlage, der für direkte Anlagen zwischen 40 bis 50%, für indirekte zwischen 60 bis 80% liegt, der Grad der Automatisierung, die Meß‐, Regel‐ und Sicherheitseinrichtungen sowie der Wartungs‐ und Reparaturaufwand. Eine Optimierung der Anlagen kann unter verschiedenen Zielvor‐stellungen erfolgen. Die für Lebensmittel allgemein bedeutsamste Zielgröße ist die Produktqualität, die vorrangig durch das Temperatur/Zeit‐Verhalten der Anlagen bestimmt wird. Zur Optimierung der thermischen Wirksamkeit der Anlagen können die in der Konserventechnik bewährten Sterilisationswerte,F‐ undC‐Werte, dienen. Durch eine reaktionskinetische Betrachung und bei Vorliegen bestimmter Voraussetzungen ist nach weisbar, dasF‐ undC‐Werte auch für den Temperaturbereich der UHT‐Verfahren anwendbar sind.
Zur frühzeitigen Erkennung gefährlicher Reaktionszustände in chemischen Reaktoren
Authors: Gilles Ernst Dieter , Schuler Hans 
Published: December 2004

AbstractUm Reaktoren mit stark exothermer Reaktion sicher betreiben zu können, sind Meßeinrichtungen erforderlich, die es gestatten, gefährliche Reaktionszustände bereits im Stadium ihres Entstehens zu erkennen. Nur dann können rechtzeitig geeignete Gegenmaßnahmen eingeleitet werden, um solche Zustände zu vermeiden. Im Rahmen dieses Beitrags wird gezeigt, daß die moderne Regelungstheorie mit ihren modellgestützten Meßverfahren Methoden anbietet, die in der Lage sind, einen entscheidenden Beitrag zur Lösung dieses Erkennungs problems zu leisten. Diese Methoden benutzen die in Form eines mathematischen Modells vorliegende a‐priori‐Information über das Prozeßgeschehen, um den gesamten Zustand einer Anlage aus denjenigen Größen zu rekonstruieren, die einer Messung unmittelbar zugänglich sind. Die Kenntnis des gesamten Prozeßzustandes erlaubt dann eine prädiktive Berechnung des zukünftigen Reaktionsablaufs und damit eine frühzeitige Erkennung gefährlicher Reaktionszustände. Die Möglichkeiten eines auf dieser Grundlage basierenden Konzepts zur sicheren Führung stark exothermer Reaktionen werden ausführlich anhand eines einfachen Batch‐Prozesses diskutiert.
Elektrostatische Trennung der Komponenten von Kali‐Rohsalzen
Authors: Bock Rudolf 
Published: December 2004

AbstractDie Entwicklung des elektrostatischen Trennverfahrens für die Mineralien von Kali‐Rohsalzen wird geschildert. Die wichtigsten Schritte waren die Entdeckung von wirksamen Konditionierungs‐Reagentien, die Berücksichtigung der atmosphärischen Feuchte und der Temperatur im elektrischen Feld sowie die Konstruktion eines leistungsfähigen Scheiders.
Möglichkeiten und Grenzen deduktiven Vorgehens bei der Entwicklung technischer Katalysatoren
Authors: Riekert Lothar 
Published: December 2004

AbstractWährend es für zahlreiche verfahrenstechnische Prozesse eine auf physikalischem Verstehen basierende Grundlegung gibt, die auch präzise Vorhersagen zuläßt, ist dies für den wichtigsten Bestandteil von Reaktionsapparaten, die darin enthaltenen festen Katalysatoren, nur in begrenztem Ausmaß der Fall. Es wird erörtert, wie sich die für die technische Durchführung eines Verfahrens wichtigen Leistungsdaten eines Reaktors auf die Kinetik der Vorgänge an der aktiven Komponente in einem porösen Kontaktkorn zurückführen lassen. Die chemische Kinetik der Reaktionen an der aktiven Komponente ist grundsätzlich nicht aus der Theorie vorausberechenbar. Daher sind empirische Methoden bei der Entwicklung technischer Katalysatoren nicht zu vermeiden. Das bedeutet aber nicht, daß ein rein empirisches Vorgehen der Sache allein angemessen wäre. So kann man z. B. den Einfluß der Morphologie des Kontaktkorns auf die Aktivität und die Selektivität genau vorhersagen. Ein auf Prinzipien der Reaktionstechnik gegründetes methodisches Vorgehen vermindert die Zahl der durch Versuche zu optimierenden Variablen.
Instationäre Prozeßführung kontinuierlicher Reaktoren
Authors: Renken Albert 
Published: December 2004

AbstractNon‐steady‐state operation of continuous reactors. The behaviour of continuous chemical reactors can be altered significantly by forced oscillation of the reactor parameters such as feed concentration of the reactants, flow rate, and temperature. In contrast to autonomous oscillations in unstable systems, the forced periodic disturbances are controlled and can be used as a further parameter for process optimization. The dynamic behaviour of individual steps of the overall reaction and of the reactor can be exploited to obtain performances and selectivities which cannot be accomplished in the traditional way on steady‐state operation under comparable conditions. This is shown in discussing some simple kinetic schemes published in theoretical studies and comparing them with experimental results for homogeneous and heterogeneous reactions. The physical and chemical causes for the predicted and observed advantages of periodic operation are discussed.
Citronensäure‐Fermentation — biotechnologische Probleme und Möglichkeiten der Rechnersteuerung
Authors: Siebert Diethelm , Hustede Helmut 
Published: December 2004

AbstractCitric acid fermentation – biotechnological problems and possibilities of computer control. Citric acid today is produced almost exclusively by fermentation with the mold Aspergillus niger according to the surface or submerged process. The application of complex raw materials, like molasses, gives rise to considerable waste water burdens as well as to problems with microbiological process control. In order to gain qualitative and quantitative ideas about the metabolic activities of the mold during citric acid fermentation according to the submerged process production fermentors were equipped with several measuring points for the acquisition of physico‐chemical changes in the medium and with devices for waste air analysis. The measured values were requested in rotation by an on‐line computer and converted to characteristic derivative data. Together with additional analytical laboratory values these data were appropriate for getting a deeper insight into the biochemical events during fermentation. In this way mathematical models could be prepared which supported a better control and optimization of the fermentation course. The knowledge derived from these investigations permitted the extension of the data acquisition and computer system for monitoring and control of all production fermentors.
Gepackte Aufstrom‐Blasensäulen
Authors: Hofmann Hanns 
Published: December 2004

AbstractPacked upflow bubble columns. Packed upflow bubble columns are used in the chemical industry, in biotechnology, and in waste‐water purification. They are usually operated in the co‐current mode and have various advantages, but also disadvantages, compared with empty bubble columns. This survey reports the current state‐of‐the‐art in fluid dynamics (flow states, pressure drop, holdup and dispersion, bubble size and bubble rise velocity, interfacial area), mass and heat transfer (mass transfer coefficients at the gas/liquid and liquid/solids interface, heat transfer coefficients for fluid/solids and fluid/wall interfaces, effective thermal conductivity of the bulk solids through which flow occurs), flow models (continuum models, stage models, zone models), and other aspects of this type of multiphase reactor; gaps in our knowledge are also indicated.
Neues zur mathematischen Modellierung von Flüssig/Flüssig‐Extraktionskolonnen
Authors: Steiner Ladislav , Hartland Stanley 
Published: December 2004

AbstractRecent results in mathematical modelling of liquid/liquid extraction columns. Flow in extraction columns is so complicated that it defies exact description. Methods have to be found for approximating the actual state, which can be accomplished by modelling. Approximations should be sought which closely approach reality, and yet can be formulated mathematically and solved by expenditure of a reasonable amount of effort. The development of models proceeded from the plug flow assumption via the theory of back‐mixing to mechanistic models, which should also correctly describe the fundamentals of the various processes. It is now also possible to simulate complicated processes, such as parameter changes along the height of the column. The models described in this article can be readily solved numerically. Only standard procedures are used which can be managed by minicomputers.
Turbulenter Wärme‐ und Stoffaustausch
Authors: Jischa Michael 
Published: December 2004

AbstractTurbulent heat and mass transfer. Turbulent heat and mass transfer is inseparably connected with turbulent momentum transfer. Thus we again find the same problems as those encountered in the description of turbulent momentum transfer. Moreover, further difficulties arise because of the temperature and concentration fluctuations in addition to the velocity and pressure fluctuations. The problems are essentially experimental ones. It is much simpler to measure correlations of velocity fluctuations like the turbulence energy or the Reynolds shear stress than correlations of other fluctuating quantities. This is why attempts were made at an early stage to reduce the turbulent heat and mass transfer to the comparatively well understood turbulent transfer of momentum. Therefore the basic ideas concerning the modelling of the turbulent momentum flux are discussed at first. A brief introduction to concepts of the statistical theory of turbulence is also given. Finally some proposals to describe the turbulent heat transfer based on modelling assumptions are presented for example of turbulent tube flow. Turbulent mass transfer is only briefly touched upon because of the far greater experimental gaps opposing reliable modelling.
Lebensmittel‐Gefriertechnik mit kryogener Kälte
Authors: Dinglinger Günter 
Published: December 2004

AbstractFood freezing with cryogenic techniques. Typical for this freezing technique is the immediate contact of the goods to be frozen with the refrigerant. While in the past only nitrogen which boils at – 196°C at atmospheric pressure was seen as a cryogenic coolant, the refrigerating agents CO2 and difluorodichlormethane (R 12) are nowadays also included in this category because some criteria of these processes correspond to those of the original cryogenic freezing technique. The principles of the cryogenic freezing technique are explained, and differences between the various processes and the refrigerants mentioned are detailed. Different types of apparatus were developed to take the conditions of the product and of the refrigerant into consideration. Here above all the physical properties of the refrigerants are important but so are the kind and the dimensions of the goods to be frozen. With reference to recently‐published literature, apparatus are described which utilize the spray or dip technique. However, some apparatus works only with low temperatures without allowing the refrigerant to boil at the surface of the material to be frozen. An economics study gives information about the conditions under which the cryogenic freezing technique is able to compete with traditional freezing techniques.
Herstellung, Stabilität und Spaltung multipler Emulsionen
Authors: Kriechbaumer Alois , Marr Rolf 
Published: December 2004

AbstractProduction, stability, and breaking of multiple emulsions. The production, stability and breaking of multiple emulsions are dependent on many factors, some of which are definable theoretically, some empirically. The stability of an emulsion is characterized by the interplay and superposition of interparticular interactive forces and rheological properties of the continuous phase. Interface‐active substances are adsorbed at the phase boundary and form an interfacial film, whose mechanical properties exert a strong influence on the stability of the droplets. Repulsive forces and interfacial film form an energy barrier. If this is overcome by increasing the thermal energy, by increasing the mobility of the particles or by external energy influences, the film breaks and the droplets coalesce. These processes are demonstrated theoretically and practically with the aid of individual methods of demulsification.
Zur Bewegung feiner Partikeln, die in turbulent strömenden Medien suspendiert sind
Authors: Ebert Fritz 
Published: December 2004

AbstractMotion of fine grained particles, suspended in turbulent flow. This article considers the motion of particles, suspended in turbulent flow. If the particles are sufficiently small to respond to turbulence, their motion includes stochastic components. Concerning processes like air classification or separation of fine powders the stochastic contribution – characterized by the conception of a particle diffusivity – the particle motion exhibits a detrimental influence. Sharpness of cut and separation efficiency are reduced. The paper aims to present the state of the art in particle diffusion. First, theoretical investigations are reported, attention being focused on the equation of motion of the particle which is the link between the motion of the fluid and the motion of the particle. Then, experimental results are reviewed. The following tendencies can be seen: Particles which response to turbulence of fluid flow show increasing diffusivity with increasing inertia. Field forces like gravity or electrical field forces exhibit a damping effect on diffusivity.
Verhalten von (Schwer‐) Metallen bei der Verbrennung kommunaler Abfälle
Authors: Vogg Hubert 
Published: December 2004

AbstractBehaviour of (heavy) metals on incineration of municipal wastes. Incineration technology is being used to a growing extent for the disposal of municipal wastes. In order to make this technology less harmful to the environment, steps must be taken to counteract the emission of HCl and SO2 and NOx as well as of some metals, above all mercury. For this purpose the pollutant inventory must be known more reliably than was previously the case. Care must also be taken that the problems connected with pollutants are not merely transposed from the air to water or solids. If necessary, the fractions that are soluble in a slightly acid medium must be removed from the fly ash, reacted chemically, and immobilized as compact materials. The actual incineration must be performed in such a way that inert slag is formed so that reusability is assured. The slag may also have to undergo chemical treatment.
Maßnahmen zur Verbesserung des Wärmeübergangs bei der Kondensation
Authors: Renz Ulrich 
Published: December 2004

AbstractMeasures to improve heat transfer for condensation.In the search for measures to improve the heat transfer for condensation, one has to differentiate between condensation of pure vapours and that of mixtures of vapours. For pure vapours a considerable proportion of the heat transfer resistance is associated with the condensed film. The heat transfer can therefore be improved either by reducing the film thickness or by increasing the heat transport across the film. For mixtures of vapours the heat transfer coefficient at the phase interface is often decisive, and one has to investigate the vapour behaviour rather than the condensed film. The present article surveys the options available to improve the heat transfer for film condensation of pure vapours on vertical surfaces, and as well in vertical or horizontal passed pipes as on pipes in a transverse stream.
Leistungskennwerte verschiedener Gegenstrom‐Extraktionskolonnen
Authors: Pilhofer Theo , Schröter Jürgen 
Published: December 2004

AbstractPerformance indices of various countercurrent extraction columns. The permissible working range and the separation efficiency achievable therein are characteristic indices for the performance of extraction columns. An introductory account of the design principles, especially of columns supplied with mechanical energy, is followed by an illustrative discussion of the influence of operational and constructional parameters and of material properties on the loading range and the separation efficiency attainable therein. Then follows a section comparing the efficiencies of various columns as a function of loadability for a variety of material systems. These comparisons are valid only for certain parameters. Hence, the changes occurring on variation of these parameters are also considered qualitatively. In conclusion, the separation efficiencies of two newly developed columns are examined with a view to establishing whether the dependence upon loading has changed relative to conventional columns.
Betriebs‐Analysenmeßgeräte als Meßumformer
Authors: Gundelach Volkmar 
Published: December 2004

AbstractOn‐line analyzers as transducers. The term transducer is employed frequently by manufacturers and users of measuring instruments and measuring systems. It is generally understood to be an element of a measuring chain which is loaded by as many functions as possible in order to set the rest of equipment free for other tasks. If demands associated with this are not mutually compatible, compromises must be sought. The article starts from the definition of the term transducer, compares this with the results of a discussion on the characteristics such instruments display in practice, and finally, using characteristic examples from on‐line analyzers, outlines the ideas and assessments which stem from such an analysis.
Auslegungsgrundlagen von Kristallisatoren
Authors: Mersmann Alfons , Kind Matthias 
Published: December 2004

AbstractDesign 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.