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Fluidized Bed. (fluidized + bed)
Selected AbstractsTheoretical performance analysis of the multi-stage gas,solid fluidized bed air preheaterINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2001Sang Il Park Abstract The multi-stage fluidized bed can be used to preheat the combustion air by recovering the waste heat from the exhaust gas from industrial furnaces. The dilute-phase fluidized bed may be formed to exclude the excessive pressure drop across the multi-stage fluidized bed. But, in this case, the solid particles do not reach to the thermal equilibrium due to relatively short residence time in each layer of fluidized bed. In this study, a theoretical analysis on the dilute phase multistage fluidized bed heat exchanger was performed. A parameter related to the degree of thermal equilibrium between gas and solid particles at the dilute-phase fluidized beds was derived. Using this parameter, a relatively simple expression was obtained for the thermal efficiencies of the multi-stage fluidized bed heat exchanger and air preheater. Copyright © 2001 John Wiley & Sons, Ltd. [source] Experimental and numerical research for fluidization behaviors in a gas,solid acoustic fluidized bedAICHE JOURNAL, Issue 7 2010Changqing Cao Abstract The effects of sound assistance on fluidization behaviors were systematically investigated in a gas,solid acoustic fluidized bed. A model modified from Syamlal,O'Brien drag model was established. The original solid momentum equation was developed and an acoustic model was also proposed. The radial particle volume fraction, axial root-mean-square of bed pressure drop, granular temperature, and particle velocity in gas,solid acoustic fluidized bed were simulated using computational fluid dynamics (CFD) code Fluent 6.2. The results showed that radial particle volume fraction increased using modified drag model compared with that using the original one. Radial particle volume fraction was revealed as a parabolic concentration profile. Axial particle volume fraction decreased with the increasing bed height. The granular temperature increased with increasing sound pressure level. It showed that simulation values using CFD code Fluent 6.2 were in agreement with the experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Experimental validation of CFD simulations of a lab-scale fluidized-bed reactor with and without side-gas injectionAICHE JOURNAL, Issue 6 2010Jian Min Abstract Fluidized-bed reactors are widely used in the biofuel industry for combustion, pyrolysis, and gasification processes. In this work, a lab-scale fluidized-bed reactor without and with side-gas injection and filled with 500,600 ,m glass beads is simulated using the computational fluid dynamics (CFD) code Fluent 6.3, and the results are compared to experimental data obtained using pressure measurements and 3D X-ray computed tomography. An initial grid-dependence CFD study is carried out using 2D simulations, and it is shown that a 4-mm grid resolution is sufficient to capture the time- and spatial-averaged local gas holdup in the lab-scale reactor. Full 3D simulations are then compared with the experimental data on 2D vertical slices through the fluidized bed. Both the experiments and CFD simulations without side-gas injection show that in the cross section of the fluidized bed there are two large off-center symmetric regions in which the gas holdup is larger than in the center of the fluidized bed. The 3D simulations using the Syamlal-O'Brien and Gidaspow drag models predict well the local gas holdup variation throughout the entire fluidized bed when compared to the experimental data. In comparison, simulations with the Wen-Yu drag model generally over predict the local gas holdup. The agreement between experiments and simulations with side-gas injection is generally good, where the side-gas injection simulates the immediate volatilization of biomass. However, the effect of the side-gas injection extends further into the fluidized bed in the experiments as compared to the simulations. Overall the simulations under predict the gas dispersion rate above the side-gas injector. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Characterization of flow regime transition and particle motion using acoustic emission measurement in a gas-solid fluidized bedAICHE JOURNAL, Issue 5 2010Wang Jingdai Abstract Particle motion is a major determinant of the dynamical performance of a fluidized bed. It plays an important role in determining and optimizing the complex correlation of fluidization condition between particle-particle and particle-environment in a system. A passive acoustic emission (AE) technique is applied to monitor, characterize, and control the fluidization condition of polyethylene particles in a gas-solid fluidized bed. Experimental results show that AE signals are very sensitive to the particle movements by analyzing energy distribution, which can help to understand the status of the system. The AE energy temporal analysis is further used to identify the transition of flow regimes. Moreover, the activity of particle motion can be quantitatively determined by using a combination of granular temperature and AE spatial energy analysis. This work provides valuable insights into the dynamic behavior of particles in a gas-solid fluidized bed based on AE technique. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Synthesis of multiwalled carbon nanotubes on Al2O3 supported Ni catalysts in a fluidized-bedAICHE JOURNAL, Issue 1 2010Jun Liu Abstract Multiwalled carbon nanotubes (MWNTs) were synthesized on Al2O3 supported Ni catalysts from C2H2 and C2H4 feedstocks in a fluidized bed. The influence of the ratio of superficial gas velocity to the minimum fluidization velocity (U/Umf), feedstock type, the ratio of carbon in the total quantity of gas fed to the reactor, reaction temperature, the ratio of hydrogen to carbon in the feed gas, and nickel loading were all investigated. Significantly, the pressure drop across the fluidized-bed increased as the reaction time increased for all experiments, due to the deposition of MWNTs on the catalyst particles. This resulted in substantial changes to the depth and structure of the fluidized bed as the reaction proceeded, significantly altering the bed hydrodynamics. TEM images of the bed materials showed that MWNTs, metal catalysts, and alumina supports were predominant in the product mixture, with some coiled carbon nanotubes as a by-product. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Particle-scale simulation of the flow and heat transfer behaviors in fluidized bed with immersed tubeAICHE JOURNAL, Issue 12 2009Yongzhi Zhao Abstract A kind of new modified computational fluid dynamics-discrete element method (CFD-DEM) method was founded by combining CFD based on unstructured mesh and DEM. The turbulent dense gas,solid two phase flow and the heat transfer in the equipment with complex geometry can be simulated by the programs based on the new method when the k-, turbulence model and the multiway coupling heat transfer model among particles, walls and gas were employed. The new CFD-DEM coupling method that combining k-, turbulence model and heat transfer model, was employed to simulate the flow and the heat transfer behaviors in the fluidized bed with an immersed tube. The microscale mechanism of heat transfer in the fluidized bed was explored by the simulation results and the critical factors that influence the heat transfer between the tube and the bed were discussed. The profiles of average solids fraction and heat transfer coefficient between gas-tube and particle-tube around the tube were obtained and the influences of fluidization parameters such as gas velocity and particle diameter on the transfer coefficient were explored by simulations. The computational results agree well with the experiment, which shows that the new CFD-DEM method is feasible and accurate for the simulation of complex gas,solid flow with heat transfer. And this will improve the farther simulation study of the gas,solid two phase flow with chemical reactions in the fluidized bed. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Laser diagnostic investigation of the bubble eruption patterns in the freeboard of fluidized beds: Simultaneous acetone PLIF and stereoscopic PIV measurementsAICHE JOURNAL, Issue 6 2009C. R. Müller Abstract For the first time PIV has been applied simultaneously with acetone-PLIF in the freeboard of a fluidized bed. Here, the eruption profile of single bubbles and a continuous stream of bubbles were studied. As stereoscopic PIV was applied the out-of-plane component of the velocity was also measured. The out-of-plane component is not negligible. The observed bubble eruption patterns were in general agreement with the bubble model of Levy and Lockwood,24 Yorquez-Ramirez and Duursma5 and Solimene et al.1 No qualitative difference between the eruption of a single bubble and a stream of bubbles was observed. Based on the calculated vorticity of the gas in the freeboard, it was found that the bubble induced turbulence decays fairly rapidly. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Extension of PIV for measuring granular temperature field in dense fluidized bedsAICHE JOURNAL, Issue 1 2007W. Dijkhuizen Abstract In this work a particle image velocimetry (PIV) technique has been extended to enable the simultaneous measurement of the instantaneous velocity and granular temperature fields. The PIV algorithm has been specifically optimized for dense granular systems and has been thoroughly tested with artificially generated images. The new PIV technique has been successfully applied to a fluidized bed at incipient fluidization conditions in which a single bubble is injected by a jet and to a freely bubbling fluidized bed. The instantaneous spatial distribution of the solids-phase velocity and granular temperature that can be measured with this new technique can be used to validate CFD models for dense granular systems, such as multifluid continuum models using the KTGF (kinetic theory of granular flow) to describe the internal momentum transport in the particulate phase. © 2006 American Institute of Chemical Engineers AIChE J, 2007 [source] Early warning of agglomeration in fluidized beds by attractor comparisonAICHE JOURNAL, Issue 11 2000J. Ruud van Ommen An enhanced monitoring method, based on pressure fluctuation measurements, for observing nonstationarities in fluidized-bed hydrodynamics is presented. Experiments show that it can detect small changes in the particle-size distribution. Such a monitoring method is useful to give an early warning of the onset of agglomeration in a fluidized bed. In contrast to earlier methods, this method is insensitive to small changes in superficial gas velocity and can handle multiple signals, making it relevant to industrial application. By carefully choosing the measurement position, the method becomes also insensitive to small bed mass variations. It uses the attractor reconstructed from a measured pressure signal, which is a "fingerprint" of the hydrodynamics of the fluidized bed for a certain set of conditions. Using this method statistically the reconstructed attractor of a reference time series of pressure fluctuations (representing the desired fluidization behavior) is compared with that of successive time series measured during the bed operation. [source] Thermal Blending Time Associated With a Charge of Hot Particles Added to a Fluidized Bed of Uniform TemperatureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2006W. A. Brown Abstract The process of heat transfer between particles in a fluidized bed is important for many industrial fluidized bed processes. The problem associated with studying this phenomenon is the confounding effect of particle mixing on heat transfer. The work described here was undertaken to describe the process in which heat is added to a fluid bed process by adding a hot charge of particles to a colder fluidized bed. The rate of heat transfer in this instance can have a significant impact on performance of the fluid bed process, depending upon its application. Both the method of analysis and the results of the work are applicable to other fluidized bed processes, particularly those associated with the thermal upgrading of heavy oil. The method of data analysis, based on binomial statistics, allowed useful data to be extracted from a complex system without the need for a large number of experiments. The analysis also allowed for some assessment of the relative importance of mixing and heat transfer, which has not been possible with other approaches. The results of the experiments were further explored using a bubbling bed model that incorporated both heat transfer and solids mixing. This allowed for the formation of a conceptual model, validated by the experimentation, that explains the relative functions of the two transfer processes in the dispersion of heat from a hot charge of particles to the bulk of a fluidized bed. Le procédé de transfert de chaleur entre les particules dans un lit fluidisé joue un rôle important dans de nombreux procédés industriels en lit fluidisé. Le problème associé à l'étude de ce phénomène est l'effet de confusion du mélange des particules sur le transfert de chaleur. Le travail décrit ici a été entrepris pour décrire le procédé dans lequel un lit fluidisé est chauffé en ajoutant une charge chaude de particules à lit fluidisé plus froid. Le taux de transfert de chaleur dans cet exemple peut avoir un impact significatif sur la performance du procédé en lit fluidisé, selon son application. Autant la méthode d'analyse que les résultats du travail sont applicables à d'autres procédés de lits fluidisés, en particulier ceux associés à la valorisation thermique de l'huile lourde. La méthode d'analyse des données, basée sur des statistiques binomiales, permet d'extraire des résultats utiles d'un système complexe sans avoir besoin de beaucoup d'expériences. L'analyse permet également de jauger l'importance relative du mélange et du transfert de chaleur, ce qui n'a pas été possible avec d'autres approches. Les résultats des expériences ont été analysés de manière plus approfondie au moyen d'un modèle à lit bouillonnant qui incorpore à la fois le transfert de chaleur et le mélange de solides. Ceci permet l'établissement d'un modèle conceptuel validé, qui explique les fonctions relatives des deux procédés de transfert dans la dispersion de la chaleur à partir d'une charge chaude de particules dans le coeur d'un lit fluidisé. [source] Prediction of Minimum Fluidization Velocity in Two and Three Phase Inverse Fluidized BedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Thiruvengadam Renganathan Abstract Generalized equations for predicting minimum fluidization velocities in two-phase L-S and three-phase G-L-S inverse fluidized bed are developed covering a wide range of variables using the experimental data obtained from the present work and that available in the literature. It is found that the classical Wen and Yu equation for predicting minimum fluidization velocity can satisfactorily be used for two-phase inverse fluidized bed. A model based on empiricism and another based on the gas perturbed liquid model, which reduce to limiting conditions such as liquid solid and three-phase batch liquid systems are proposed. Des équations généralisées pour la prédiction des vitesses de fluidisation minimales dans des lits fluidisés inverses biphasique liquide-solides et triphasique gaz-liquide-solides ont été établies pour une vaste gamme de variables à l'aide des données expérimentales issues du présent travail et de la littérature scientifique. On a trouvé que l'équation classique de Wen et Yu pour prédire la vitesse de fluidisation minimale peut être utilisée pour le lit fluidisé inverse biphasique. On propose un modèle empirique et un autre basé sur le modèle de liquide perturbé par le gaz, qui se réduisent aux conditions limitantes tels les systèmes liquides discontinus liquide-solides et triphasiques. [source] | ||||||||||