Hydrodynamics of Gas-solids Downflow Fluidized Bed (downer) Reactor PDF Download

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Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: J.R. Grace
Publisher: Springer Science & Business Media
ISBN: 9400900953
Category : Science
Languages : en
Pages : 599

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Since the late 1970s there has been an explosion of industrial and academic interest in circulating fluidized beds. In part, the attention has arisen due to the environmental advantages associated with CFB (circulating . fluidized bed) combustion systems, the incorporation of riser reactors employing cir culating fluidized bed technology in petroleum refineries for fluid catalytic cracking and, to a lesser extent, the successes of CFB technology for calcina tion reactions and Fischer-Tropsch synthesis. In part, it was also the case that too much attention had been devoted to bubbling fluidized beds and it was time to move on to more complex and more advantageous regime,S of operation. Since 1980 a number of CFB processes have been commercialized. There have been five successful International Circulating Fluidized Bed Confer ences beginning in 1985, the most recent taking place in Beijing in May 1996. In addition, we have witnessed a host of other papers on CFB funda mentals and applications in journals and other archival publications. There have also been several review papers and books on specific CFB topics. However, there has been no comprehensive book reviewing the field and attempting to provide an overview of both fundamentals and applications. The purpose of this book is to fill this vacuum.

Author: John G. Yates
Publisher: Springer
ISBN: 3319395939
Category : Science
Languages : en
Pages : 214

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The fluidized-bed reactor is the centerpiece of industrial fluidization processes. This book focuses on the design and operation of fluidized beds in many different industrial processes, emphasizing the rationale for choosing fluidized beds for each particular process. The book starts with a brief history of fluidization from its inception in the 1940’s. The authors present both the fluid dynamics of gas-solid fluidized beds and the extensive experimental studies of operating systems and they set them in the context of operating processes that use fluid-bed reactors. Chemical engineering students and postdocs as well as practicing engineers will find great interest in this book.

Author: Onno Cornelis Snip
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 240

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Author: Aijie Yan
Publisher: Library and Archives Canada = Bibliothèque et Archives Canada
ISBN: 9780612968851
Category :
Languages : en
Pages : 550

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The scale-up effect on the hydrodynamics of gas-solids circulating fluidized bed riser reactors of different riser diameters was systematically studied in two 10 m high, 76 mm and 203 mm internal diameter risers by measuring the pressure drops, solids holdup, particle velocity, and solids flux with pressure transducers, a reflective-type fiber optic concentration-probe, a five-fiber optic velocity probe and a non-isokinetic sampling probe. A large number of measurements from the two risers with special design features of solids inlet valve make it possible to obtain information over a wide range of riser operating conditions. The similarities and differences in the flow behaviours of the two risers are clearly observed. Solids concentration increases with the increase of riser diameter, while the cross-sectional average particle velocity decreases somewhat for the larger riser. Meanwhile, a larger riser has steeper radial profiles for solids concentration, particle velocity and solids flux at each axial level. Asymmetry of the radial profiles of solids concentration and particle velocity at both entrance and exit regions are also observed. Such asymmetry is much stronger with higher flux. For both risers, the flow development in the riser centre is nearly instantaneous at the riser bottom under all operating conditions and there is no significant difference for the two risers in the center region throughout the riser. On the other hand, in the wall region, the flow development slows down for both risers, and such a slow down is much more significant for the larger riser. In the wall region, the solids holdup of the 8 inch riser is higher than that of the 3 inch riser, but the particle velocity is lower. The downflow solids flux at the wall of the larger riser is higher. The solids inventory and riser diameter appears to have little influence on the shape of the axial profile, but the average solids holdup is higher with higher solids inventory. The maximum of operable solids fluxes increases with the increase of solids inventory and decreases with the increase of riser diameter. Increasing solids flux also slows down the flow development, but increasing superficial gas velocity makes the flow development faster. Based upon the theoretical analyses and the systematic experimental data obtained in this study, a series of correlations is proposed to predict the radial profiles of particle velocity and solids holdup for the CFB riser reactors. In all locations measured, there was a clear dependence between the local particle velocity and solids concentration of both risers. Gas distribution and particle aggregation are considered the key factors that affect the local hydrodynamics in the twin-riser system. The information obtained from this study could be beneficial, especially for FCC industrial design and operation.

Author: John R. Grace
Publisher: John Wiley & Sons
ISBN: 3527340645
Category : Technology & Engineering
Languages : en
Pages : 626

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A concise and clear treatment of the fundamentals of fluidization, with a view to its applications in the process and energy industries.

Author:
Publisher: 清华大学出版社有限公司
ISBN: 9787302125068
Category : Fluidized reactors
Languages : en
Pages : 452

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本书介绍了流态化科学与工程方面的研究进展,与多相反应工程和工艺相关的粉体、造粒、绿色化工和生态工业等前沿领域的新内容和新进展,以及能源与环境等涉及可持续发展的战略问题。

Author: Faraj Muftah Zaid
Publisher:
ISBN:
Category : Computational fluid dynamics
Languages : en
Pages : 448

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"This research studied the scale-up, flow regimes identification and hydrodynamics of fluidized beds using 6-inch and 18- inch diameter columns and different particles. One of the objectives was to advance the scale-up of gas-solid fluidized bed reactors by developing a new mechanistic methodology for hydrodynamic similarity based on matching the radial or diameter profile of gas phase holdup, since gas dynamics dictate the hydrodynamics of these reactors. This has been successfully achieved. However, the literature reported scale-up methodology based on matching selected dimensionless groups was examined and it was found that it was not easy to match the dimensionless groups and hence, there was some deviation in the hydrodynamics of the studied two different fluidized beds. A new technique based on gamma ray densitometry (GRD) was successfully developed and utilized to on-line monitor the implementation of scale-up, to identify the flow regime, and to measure the radial or diameter profiles of gas and solids holdups. CFD has been demonstrated as a valuable tool to enable the implementation of the newly developed scale-up methodology based on finding the conditions that provide similar or closer radial profile or cross sectional distribution of the gas holdup. As gas velocity increases, solids holdup in the center region of the column decreases in the fully developed region of both 6 inch and 18 inch diameter columns. Solids holdup increased with the increase in the particles size and density. Upflowing particles velocity increased with the gas velocity and became steeper at high superficial gas velocity at all axial heights where the center line velocity became higher than that in the wall region. Smaller particles size and lower density gave larger upflowing particles velocity. Minimum fluidization velocity and transition velocity from bubbly to chum turbulent flow regimes were found to be lower in 18 inch diameter column compared to those obtained in 6 inch diameter column. Also the absolute fluctuation of upflowing particles velocity multiplied by solids holdups as one of the terms for solids mass flux estimation was found to be larger in 18-inch diameter column than that in 6-inch diameter column using same particles size and density"--Abstract, leaf iii.

Author: Michael John Bly
Publisher:
ISBN:
Category : Bioreactors
Languages : en
Pages : 300

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Author: Abdelsalam Efhaima
Publisher:
ISBN:
Category : Computational fluid dynamics
Languages : en
Pages : 262

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"This research focuses on validating our newly developed mechanistic scale-up methodology for hydrodynamics similarity of gas-solid fluidized bed reactors (FBRs) by implementing our advanced non-invasive measurement techniques which are gamma ray computed tomography (CT) and radioactive particle tracking (RPT) that measure local hydrodynamic parameters. Experiments were carried out in two fluidized beds of 14 cm and 44 cm in diameter using air as the gas phase and particles of different materials. Since in these reactors the gas dynamic dictates the bed hydrodynamics, the new mechanistic scale-up methodology is based on maintaining similar or closer time averaged radial profiles of gas holdups at a height within the bed in two different gas-solid fluidized beds in order to achieve local and global similarity of dimensionless hydrodynamic parameters. The findings validate the achievement of hydrodynamics similarity in local solids and gas holdups distribution obtained by CT technique and in three dimension local solids velocities, solids shear stresses, normal stresses, turbulent kinetic energy, and turbulent eddy diffusivities measured by RPT technique. Also in this work we found based on local hydrodynamic parameters obtained by using CT and RPT that the scale-up method of matching a set of dimensionless groups is invalid for hydrodynamics similarity and the proposed dimensionless groups are insufficient to capture the key phenomena in these reactors. In addition, we studied the effect of bed height and particles type, size, and density on gas holdup, particle velocity, and turbulent parameters measured by these advanced techniques"--Abstract, page iv.