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Bed Temperature (bed + temperature)

Distribution by Scientific Domains
Chemistry66%

Selected Abstracts

The Effect of Bed Temperature on Mass Transfer between the Bubble and Emulsion Phases in a Fluidized Bed

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2003
Wenyuan Wu
Abstract The rate of interphase mass transfer between the bubble and emulsion phases of a bubbling fluidized bed is of primary importance in all models for fluidized bed reactors. Many experimental studies have been reported, however, all these investigations have been carried out in fluidized beds operated at room temperature. In this work, the effect of the bed temperature on the interphase mass transfer is reported. Single bubbles containing argon , used as a tracer , were injected into an incipiently fluidized bed maintained at the required temperature. The change in argon concentration in the bubble was measured using a suction probe connected to a mass spectrometer. The effects of bed particle type and size, bubble size, and bed temperature on the mass transfer coefficient were examined experimentally. The interphase mass transfer coefficient was found to decrease with the increase in bed temperature and bubble size, and increase slightly with increase in particle size. Experimental data obtained in this study were compared with some frequently used correlations for estimation of the mass transfer coefficient. Le taux de transfert de matière interphasique entre les phases à bulles et à émulsion d'un lit fluidisé bullant est de première importance dans tous les modèles de réacteurs à lits fluidisés. Beaucoup d'études expérimentales ont été présentées; toutefois, toutes ces recherches ont été menées dans des lits fluidisés fonctionnant à la température ambiante. Dans ce travail, on décrit l'effet de la température du lit sur le taux de transfert de matière. Des bulles simples contenant de l'argon – utilisé comme traceur – ont été injectées dans un lit fluidisé naissant maintenu à la température requise. Le changement de concentration d'argon dans la bulle est mesuré à l'aide d'une sonde de succion reliée à un spectromètre de masse. Les effets du type et de la taille des particules de lit, de la taille des bulles et de la température de lit sur le coefficient de transfert de matière sont examinés de façon expérimentale. On a trouvé que le coefficient de transfert de matière interphasique diminuait avec l'augmentation de la température du lit et de la taille des bulles, et augmentait légèrement avec l'augmentation de la taille des particules. Les données expérimentales obtenues dans cette étude sont comparées avec quelques corrélations fréquemment utilisées pour l'estimation du coefficient de transfert de matière. [source]

Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bed

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2006
A. V. S. S. K. S. Gupta
Abstract In the present paper the effect of pressure on bed-to-wall heat transfer in the riser column of a pressurized circulating fluidized bed (PCFB) unit is estimated through a modified mechanistic model. Gas,solid flow structure and average cross-sectional solids concentration play a dominant role in better understanding of bed-to-wall heat transfer mechanism in the riser column of a PCFB. The effect of pressure on average solids concentration fraction ,c' in the riser column is analysed from the experimental investigations. The basic cluster renewal model of an atmospheric circulating fluidized bed has been modified to consider the effect of pressure on different model parameters such as cluster properties, gas layer thickness, cluster, particle, gas phase, radiation and bed-to-wall heat transfer coefficients, respectively. The cluster thermal conductivity increases with system pressure as well as with bed temperature due to higher cluster thermal properties. The increased operating pressure enhances the particle and dispersed phase heat transfer components. The bed-to-wall heat transfer coefficient increases with operating pressure, because of increased particle concentration. The predicted results from the model are compared with the experimentally measured values as well as with the published literature, and a good agreement has been observed. The bed-to-wall heat transfer coefficient variation along the riser height is also reported for different operating pressures. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Cohesive-driven particle circulation in the solids conveying zone of a single-screw extruder

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2008
Michael R. Thompson
Abstract Aspects of heat transfer within the solids conveying zone of a single-screw extruder were studied by using a specially constructed drum testing apparatus. Experiments were conducted with linear low-density polyethylene, polystyrene (PS), and polypropylene (PP) samples by examining their transient temperature profile while the heated drum was stationary or moving. In accordance with classic solids conveying theory, the granular beds of PP and PS remained as plugs while the drum rotated. In such cases, the dominant modes of heat transfer for these systems are conduction through the contact area of a particle and conduction through the interstitial gas. An exception to this behavior was found with PE, in which the bed temperature increased more rapidly while the drum rotated. Visual observations of the bed showed that the particles circulated in the presence of shear and that this complex flow pattern increased in velocity as the drum temperature approached the onset temperature for melting the PE material. With strong correlation between the rate of circulation and the temperature rise in the bed, the movement of particles was assumed to act in a convective heat transfer mode bringing about more uniform heating of the polymer. The circulation phenomenon was attributed to dominant adhesive forces at the particle,drum interface overcoming the cohesive strength of the bulk. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:74,88, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20121 [source]

Heat Transfer in Gas Phase Olefin Polymerisation

MACROMOLECULAR SYMPOSIA, Issue 1 2009
Estevan Tioni
Abstract A fixed bed microreactor has been used to study heat transfer during the initial transient state of gas phase olefin polymerization on a supported catalyst. It has been shown that heat transfer during this stage of the polymerisation is critical, and under conditions found commercially problems can arise with hot spots and polymer melting. It is proven how the thermal properties of the gas mixture flowing on the catalytic bed exert great influence on heat dissipation reducing the sudden increase in temperature by as much as a factor of 5. Flow rate and especially the process gas composition are the key factors in controlling the bed temperature. [source]

The Effect of Bed Temperature on Mass Transfer between the Bubble and Emulsion Phases in a Fluidized Bed

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2003
Wenyuan Wu
Abstract The rate of interphase mass transfer between the bubble and emulsion phases of a bubbling fluidized bed is of primary importance in all models for fluidized bed reactors. Many experimental studies have been reported, however, all these investigations have been carried out in fluidized beds operated at room temperature. In this work, the effect of the bed temperature on the interphase mass transfer is reported. Single bubbles containing argon , used as a tracer , were injected into an incipiently fluidized bed maintained at the required temperature. The change in argon concentration in the bubble was measured using a suction probe connected to a mass spectrometer. The effects of bed particle type and size, bubble size, and bed temperature on the mass transfer coefficient were examined experimentally. The interphase mass transfer coefficient was found to decrease with the increase in bed temperature and bubble size, and increase slightly with increase in particle size. Experimental data obtained in this study were compared with some frequently used correlations for estimation of the mass transfer coefficient. Le taux de transfert de matière interphasique entre les phases à bulles et à émulsion d'un lit fluidisé bullant est de première importance dans tous les modèles de réacteurs à lits fluidisés. Beaucoup d'études expérimentales ont été présentées; toutefois, toutes ces recherches ont été menées dans des lits fluidisés fonctionnant à la température ambiante. Dans ce travail, on décrit l'effet de la température du lit sur le taux de transfert de matière. Des bulles simples contenant de l'argon – utilisé comme traceur – ont été injectées dans un lit fluidisé naissant maintenu à la température requise. Le changement de concentration d'argon dans la bulle est mesuré à l'aide d'une sonde de succion reliée à un spectromètre de masse. Les effets du type et de la taille des particules de lit, de la taille des bulles et de la température de lit sur le coefficient de transfert de matière sont examinés de façon expérimentale. On a trouvé que le coefficient de transfert de matière interphasique diminuait avec l'augmentation de la température du lit et de la taille des bulles, et augmentait légèrement avec l'augmentation de la taille des particules. Les données expérimentales obtenues dans cette étude sont comparées avec quelques corrélations fréquemment utilisées pour l'estimation du coefficient de transfert de matière. [source]

Investigation on SO2 emission from 410t/h circulating fluidized bed boiler burning petroleum coke and coal

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010
Lun-Bo Duan
Abstract Effects of operation parameters including bed temperature, Ca/S molar ratio, excess air coefficient, fly ash recirculation rate and limestone microstructure on SO2 emission were investigated on a 410t/h circulating fluidized bed (CFB) boiler burning petroleum coke and coal. Results show that for different fuels, SO2 emission is correspondingly related to the sulfur content in it under the same operation conditions. With increasing bed temperature, SO2 concentration in the flue gas reduces first and then increases. There is an optimal desulfurization temperature. For burning bituminous coal (BC) only or 70% BC + 30% petroleum coke (PC), the optimal desulfurization temperature is about 850 °C, while it is about 850,870 °C for burning 50% anthracite (AN) + 50% PC. SO2 emission decreases with the increase in Ca/S ratio, excess air coefficient and fly ash recirculation rate. Microstructure of limestone has distinct effects on their SO2 retention capacity, and bigger specific surface area and higher specific pore volume lead to stronger SO2 capture activities. The optimal temperature, Ca/S ratio and excess air coefficient for different fuels are recommended for industrial application. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]