Time-dependent Behavior of the Particle Size Distribution in Fluidized Bed Systems with Recirculation of Solids PDF Download

Author: Cornelis Klett
Publisher:
ISBN: 9783899270020
Category :
Languages : de
Pages : 109

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Author:
Publisher:
ISBN: 9780791846988
Category : Science
Languages : en
Pages : 968

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Author: Pajongwit Pongsivapai
Publisher:
ISBN:
Category : Fluidization
Languages : en
Pages : 214

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In a conventional well-mixed fluidized bed the solids are almost completely mixed and the residence time for individual particles may vary between zero and infinity. For materials especially sensitive to the processing time, a wide distribution of residence time is extremely undesirable. A multi-compartment fluidized bed was proposed to minimize this problem. The two-compartment fluidized bed system was designed and experimentally investigated with positive results. Residence time distributions were measured with glass bead particles of 379 p.m mean diameter size. Tracer particles were colored glass beads which had exactly the same properties as the particles used for bed material. Two theoretical models were proposed to predict the flow behavior of solids through the two-compartment fluidized bed vessel. The results show the solids flow pattern can be described by the axial dispersion plug flow model and the tanks-in-series model. The parameters of both models can be determined by minimizing the sum of the squared differences between experimental data and model predictions curves. The influence of fluidization velocity, diameter of the orifice connecting the two adjacent compartments, and the height of the overflow exit orifice were investigated. The two-compartment fluidized bed can improve the residence time distribution of solids from a single fluidized bed. The residence time distribution of solids was also improved with decreasing fluidizing gas velocity. Orifice diameter and height of the overflow exit orifice did not influence significantly on particles flow in the two-compartment fluidized bed system. However, a solids mass flow through the partition orifice is predicted reasonably well, within moderate range of variance, by equation developed by de Jong (1965) [12].

Author: K. S. Sutherland
Publisher:
ISBN:
Category : Bulk solids flow
Languages : en
Pages : 58

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The development of a continuous method for determining changes in particle size and particle size distribution in fluid-bed systems has been studied experimentally. Differential pressure measurements were employed to study the effects of solid particle size on the behavior of gas-fluidized beds. The relevant bed properties are briefly described and a review given of previous work on the study of fluidized-bed quality. It is shown that, within certain limitations, measurements of bed quality can be used to indicate changes in particle size. Gas-bubble velocities, while increasing in proportion to the square root of bubble diameter, are also shown to be dependent on particle size, increasing as the particle size decreases.

Author: H. M. Katz
Publisher:
ISBN:
Category : Fluidization
Languages : en
Pages : 44

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A technique for the study of distribution of particle sizes in fluidized beds consisting of two particle sizes has been devised, and data have been obtained for a number of such systems. It has been shown that both static electricity in the bed and surface absorption of moisture affect the particle size distribution. Experimental data indicate that the effects of these variables can be eliminated by use of a conducting column of conducting particles and the use of dry air for fluidization. In addition, a qualitative relationship between minimum fluidizing velocity for mixed particle sizes and pressure drop across the bed has been demonstrated.

Author: Tom Wytrwat
Publisher: Cuvillier Verlag
ISBN: 3736965710
Category : Technology & Engineering
Languages : en
Pages : 200

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An in-depth experimental study of the fluid dynamics of turbulent fluidized beds with particles of Geldart’s Group B was carried out. For this purpose, fluidization behavior was investigated in different fluidized bed plants having diameters in the range of 0.05 m to 1 m. Pressure fluctuation analysis has been used as an identification tool for the turbulent fluidized bed regime. Different fluidization conditions have been investigated by variation of the fluidized bed properties, the bed material properties, and the gas properties. Based on the measured data, a correlation predicting the transition velocity from bubbling to turbulent fluidization is introduced. To investigate the local flow structure, capacitance probe measurements have been carried out. Using this measurement technique, local solids concentrations and properties of rising bubbles have been determined and analyzed. Finally, an empiric fluid dynamic model was developed using the local measurement data. It is mainly based on capacitance probe measurements and shows high accuracy in comparison to pressure data.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 81

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The overall objectives of this project are to develop experimental techniques for measuring the forces of fluidized particles, and to predict the solid-gas performance in fluidized beds by using data analysis system, and by elucidating the intrinsic mechanism of erosion and attrition phenomena in fluidized beds. The reduction of erosion and attrition rates is one of the critical engineering problems for the design and operation of fluidized bed combustors. Specifically, the objectives are to: (1) develop the experimental techniques to measure the forces of solid particles prevailing in fluidized beds: (2) measure and characterize the forces of solid particles in various types of fluidized beds with various configurations (conventional and spouted fluidized beds) and with different scales (10, 20, and 30cm) under various fluidization conditions (particle size, bed aspect ratio and gas velocity); (3) find and verify the mechanism of erosion rates of in-bed tubes and attrition rates of fluidized particles by forces of solid particles in fluidized beds. We developed three different kinds of measurement methods, i.e., fracture sensitive sensor, piezoelectric sensor and gas pressure fluctuation method. By using these methods the exact forces of solid particles, including the transient corporate in fluidized beds, were systematically measured. Simultaneously, the erosion rates of in-bed tubes and attrition rates of fluidized particles were measured. 69 figs., 9 tabs.

Author:
Publisher:
ISBN:
Category : Fossil fuels
Languages : en
Pages : 1126

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Author:
Publisher:
ISBN:
Category : Power resources
Languages : en
Pages : 900

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Author: Amin Jaberi
Publisher:
ISBN:
Category :
Languages : en
Pages : 142

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In this work the hydrodynamic behavior of an inverse liquid-solid circulating fluidized bed (ILSCFB) system was studied. In addition, the hydrodynamic characteristic of the inverse liquid-solid fluidization under the conventional fluidization regime was also studied. The system consists of a downer with an inner column diameter of 7.6 cm and a height of 5.4 meters, an upcomer (riser) with an inner column diameter of 20 cm, a separator, and feeding and returning pipes which connect the downer and the upcomer. Based on the axial hydrodynamic behavior of the ILSCFB, it was found that the axial solids holdup in the downer is uniform. Similar to the heavy-particle LSCFB, the circulating fluidization regime in the downer was separated into the two zones including the initial circulating fluidization zone and the fully developed circulating fluidized zone as a function of the total liquid velocity in the downer. The effects of the solids inventory and the counter current flow in the upcomer on the hydrodynamics of the downer were also studied. Afterwards, the radial distribution of particles was studied in the downer of the ILSCFB. Interestingly, the radial structure of the two-phase flow was completely different from the case of the heavy-particle LSCFB. It was found that the solids holdup was greater in the center than near the wall of the downer. Finally, the conventional (non-circulating) inverse liquid-solid fluidization was studied in a column with a large diameter for the first time. The minimum fluidization velocity was obtained experimentally and compared with the Richardson and Zaki model. It was concluded that the Richardson and Zaki model can predict the bed expansion in the case of the inverse liquid-solid fluidization when the terminal velocity was calculated by the model of free rising light particles.