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Reactor Type (reactor + type)
Selected AbstractsOn the continuum approximation of large reaction mixturesAICHE JOURNAL, Issue 7 2010Teh C. Ho Abstract In analyzing a reaction mixture of very many components, treating the mixture as a continuum can produce results of generality. In many practical situations (e.g., hydrodesulfurization), it is highly desirable to predict the overall behavior of the mixture at large times (high conversions) with minimum information on the mixture property. For irreversible first-order reactions in a plug-flow reactor, it was previously shown that the continuum approximation cannot be valid at arbitrarily large times. This work is an investigation of the validity of the approximation for mixtures with complex kinetics. It is found that the approximation can be conditionally or universally valid, depending on kinetics, reactor type, pore diffusion, and mixture properties. The validity conditions for a variety of situations, nontrivial as they may seem, take a power-law form. Backmixing and pore diffusion widen the range of validity. The underlying physics and some dichotomies/subtleties are discussed. The results are applied to catalytic hydroprocessing in petroleum refining. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Fast pyrolysis kinetics of expanded polystyrene foamAICHE JOURNAL, Issue 6 2010Pravin Kannan Abstract Fast pyrolysis of polymers, biomass and other substances is of great interest in various applications. For example, in the lost foam casting process, kinetic information about expandable polystyrene (EPS) decomposition under extremely high-heating rate conditions is essential for further process development. A simple laboratory-scale fast pyrolysis technique has been developed and demonstrated for elucidation of EPS decomposition kinetics. Pyrolysis experiments were performed at different reaction temperatures. The cumulative gaseous yields were determined using a flame ionization detector (FID) connected in series with the fast pyrolysis reactor. The governing equations for a semibatch reactor type were modified and applied to obtain kinetic parameters (activation energies and the pre-exponential rate constants) for the EPS decomposition process. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Comparison, Combination and Validation of Measuring Techniques for Local Flow and Turbulence Analysis in Bubble Columns and Airlift ReactorsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Christophe Vial Abstract The applicability of velocimetry techniques based on the Doppler effect , such as laser and ultrasound Doppler velocimetry , for investigating local hydrodynamics in bubble columns and airlift reactors have been extended to non-coalescing media. Their limitations are highlighted, especially as a function of gas sparger and reactor type. The ultrasound technique was shown to be able to measure either bubble or liquid velocity. Differences in local hydrodynamics due to coalescence behaviour were used to support the analysis. Data validation was carried out both by mass balance and by comparison with other techniques, such as electrochemical probes, Pavlov tubes and optical probes. L'applicabilité des techniques de vélocimétrie laser Doppler et de vélocimétrie ultrasonore pour décrire l'hydrodynamique locale dans les colonnes à bulles et les airlifts est étendue aux milieux non-coalescents. On étudie leurs limitations, notamment en fonction du type de distributeur et de réacteur. On montre que la technique ultrasonore permet à la fois la mesure de la vitesse locale des bulles et du liquide. Les différences dues à l'aptitude à la coalescence du milieu sont démontrées. Les résultats sont validés par des bilans et par la comparaison avec d'autres techniques (sonde électrochimique, tube de Pavlov et sonde optique). [source] Nutzung biogener Festbrennstoffe in Vergasungsanlagen,CHEMIE-INGENIEUR-TECHNIK (CIT), Issue 7 2004S. Osowski Dipl.- Ing. Abstract Aufgrund der knapper werdenden fossilen Rohstoffe gewinnen Biomassen als regenerative Energiequellen zunehmend an Bedeutung. Daher ist es für die Umsetzung von Biomasseprojekten und den verstärkten Einsatz von Biomasseanlagen wesentlich, geeignete thermische Verfahren für den Biomasseeinsatz zu identifizieren. Vor diesem Hintergrund muss die Bewertung verschiedener Vergasungstechnologien hinsichtlich unterschiedlicher Randbedingungen und Einsatzstoffe erfolgen. Da die Zusammensetzung des Produktgases mit Art und Form des Brennstoffs sowie der Vergaserbauart variiert, wird im Folgenden die Eignung für die Biomassenvergasung in ausgesuchten Vergasungsreaktoren mit ihren Vor- und Nachteilen analysiert. Utilization of Biogenic Solids in Gasifiers As a result of shrinking fossil fuels biomass as a regenerative energy source gains in importance. To realize biomass projects it is essential to investigate convenient thermal procedures. On this evidence an analysis and evaluation of diverse gasification technologies with different boundary conditions and diverse biomasses is indispensable. Form and kind of the biomass as well as the type of the gasification plant cause different compositions of the product gas. The gasifiers show advantages and disadvantages concerning the biomass and the produced gas quality, depending on reactor type, kind of heat supply, gasification medium, and the pressure ratio in the reactor. As the ideal gasifier for different biomass is presently not available it will be shown which biomass is suitable for fixed bed or fluidised bed gasifiers. [source] Characterization of flow conditions in 2 L and 20 L wave bioreactors® using computational fluid dynamicsBIOTECHNOLOGY PROGRESS, Issue 1 2010Alper A. Öncül Abstract Characterization of flow conditions is of great importance to control cell growth and cell damage in animal cell culture because cell viability is influenced by the flow properties in bioreactors. Alternative reactor types like Wave Bioreactors® have been proposed in recent years, leading to markedly different results in cell growth and product formation. An advantage of Wave Bioreactors® is the disposability of the Polyethylenterephthalet-bags after one single use (fast setup of new production facilities). Another expected advantage is a lower shear stress compared to classical stirred-tank reactors, due to the gentle liquid motion in the rocking cellbag. This property would considerably reduce possible cell damage. The purpose of the present study is to investigate in a quantitative manner the key flow properties in Wave Bioreactors®, both numerically and experimentally. To describe accurately flow conditions and shear stress in Wave Bioreactors® using numerical simulations, it is necessary to compute the unsteady flow applying Computational Fluid Dynamics (CFD). Corresponding computations for two reactor scales (2 L and 20 L cellbags) are presented using the CFD code ANSYS-FLUENT®. To describe correctly the free liquid surface, the present simulations employ the Volume of Fluid (VOF) method. Additionally, experimental measurements have been carried out to determine liquid level, flow velocity and liquid shear stress, which are used as a validation of the present CFD simulations. It is shown that the obtained flows stay in the laminar regime. Furthermore, the obtained shear stress levels are well below known threshold values leading to damage of animal cells. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | ||||||||||