Solid Particles In Fluidized Bed Research Articles

Data science integrated with computational fluid dynamics for particle collision modeling in fluidized bed

Fluidized beds are critical in numerous industrial applications, including chemical processing and energy production. Accurate modeling of solid particles and fluids within these beds is essential for process optimization and improved efficiency. In this study, we developed a machine learning model to predict the coefficient of restitution (COR) of solid particles in fluidized beds. Four variables—collision velocity, effective temperature, effective mass, and effective elastic modulus—were used in the model. Our dataset comprised 2446 data points from previous literature. We employed self-organizing map (SOM) and artificial neural network (ANN) approaches for data analysis. The initial ANN model, which did not incorporate data clustering, exhibited an impressive coefficient of determination (R-squared) of 0.989, indicating its high accuracy. To enhance the model further, we clustered the data into four groups using SOM and developed separate ANN models for each group. All four models achieved R-squared greater than 0.99, illustrating the effectiveness of data clustering. The resulting model can be integrated into simulation software, such as MFIX, to provide a more precise representation of fluidized bed behavior across various industrial settings. The findings emphasize the potential of machine learning models to enhance fluidized bed simulations, leading to increased efficiency and cost-effectiveness in industrial processes. Future studies should explore the inclusion of additional variables and extend the model's application to different industrial processes. Additionally, incorporating recommendations for optimizing fluidized bed behavior based on the model's predictions would provide valuable insights for process engineers.

Analyzing the interactions between fluid and solid particles

This study focuses on analyzing and modeling the interactions between fluid and solidparticles. A model based on the detection of contacts in granular medium is developedfrom a Discrete Elements approach (DEM) for solid phase, coupled with aComputational Fluid Dynamics (CFD) for fluid phase. The objective of this work is toinvestigate the interactions occurs between the fluid and solid particles in fluidized beds,and to better understand the various characteristic of these interactions which is the baseof work of unit operations in a set of industrial processes. A comparison betweendifferent models of fluid flow (laminar model, k- model, and k-ω SST model) in CFDcode is showed that; the k- model is most appropriate for calculation of fluid flow inindustrial applications. The interaction between the fluid and each particle is performedthrough a drag force. The effect of the local particle concentration on the drag force ismodeled by a porosity function. The simulations results are revealed that the value ofexponent of porosity shows substantial dependence on the size of the RepresentativeVolume Element (REV), tortuosity and the velocity of the fluid flow. Finally, thecomparison between numerical simulation results with experimental results, in terms offluidized bed height are showed that the bed expansion height of the fluidized bed isincreased with an increase of fluid velocity, and this presents already a very good fit,which eventually achieve an optimization of fluidization processes.

Effect of hydrodynamic and magnetic stabilization on fluidized-Bed adsorption

Direct fermentation broth processing using fluidized beds is extremely advantageous due to the low operating pressure drop of the device and the ability of the bed to process suspended-solids-containing solutions. Unfortunately, the solid particles in fluidized beds typically show a great deal of mixing compared to those in packed beds. This mixing may lead to early breakthrough and inefficient use of adsorptive capacity. Stabilization reduces the solids mixing and improves the performance and efficiency of a fluidized bed. A comparison of packed, fluidized, and stabilized beds reveals that, while normal fluidized beds do contain a significant amount of mixing, the breakthrough behavior of the bed is not drastically different than that of a packed bed. Magnetic stabilization of the bed usually leads to an increase in adsorption efficiency but is dependent on field strength and orientation. Permanently magnetized beds were also investigated and produced breakthrough efficiencies similar to those of packed beds.

Agglomeration Characteristics of Silica Sand-Rice Husk Ash Mixtures at Elevated Temperatures

Rice husk, a major by-product of the rice milling process, can be a significant energy resource in rice producing countries because of its high energy content. Fluidized bed gasifiers have been proposed for the recovery of energy from rice husk. The major advantage of fluidized bed gasifiers over fixed bed gasifiers is the high mass and heat transfer capability due to very high percentage of inert bed material such as silica sand. In addition, the vigorous mixing and agitation of solid particles in fluidized beds promote a uniform temperature distribution and a high conversion efficiency. However, attempts to utilize rice husk as a feed in fluidized bed gasifiers have been unsuccessful because of the high ash content of rice husk that may result in the agglomeration of inert bed materials at high temperatures. In this work, the effect of rice husk ash content (0.0, 5.0, 10.0, 15.0, 20.0, and 25.0%) on the agglomeration characteristics of silica sand was investigated at various temperatures (750, 850, 900, 950, and 1000°C) using a muffle furnace. A light microscope, an environmental scanning electron microscope, and an energy dispersive X-ray analyzer were used to characterize the structural changes and elemental makeup of the samples. There was no indication of agglomeration below 850°C, but at temperatures of 850–1000°C the silica sand loosely agglomerated in the presence of rice husk ash at all levels of ash content. The effect was more pronounced at 1000°C. The chemical interaction of the Si02 and the low melting temperature mineral oxides (K2O, Na20, and P205), present in notably low concentrations in rice husk ash, appeared to be the mechanism resulting in the formation of the loose agglomerates.

Modeling of solid particles in fluidized beds

A theory is proposed for the modeling of solid particles in fluidized beds based on ideas in the theory of interacting continua. The theory is capable of predicting the behavior of the mixture in the two extremes. That is, in one limit, as the concentration of solid particles becomes small, the theory reduces to the classical theory of incompressible viscous fluid. In the other limit, as the effect of the interstitial fluid becomes negligible, the theory reduces to the flow of incompressible granular materials. The mixture is considered to be made up of a linearly viscous fluid and granular materials. The stress tensor for the solid particles is derived using a modified version of Enskog's dense gas theory. The normal-stress effects that are observed experimentally in granular materials are predicted in this theory due to a solids fraction gradient. The dependence of the granular stress tensor on the solids fraction gradient arises by requiring that the correlating function that links the two-particle distribution function to the two single-particle distribution functions be the contact value for the radial distribution function of a non-homogeneous, hard sphere fluid. The interaction force is assumed to have contributions from density gradients, relative velocity (drag force), and relative acceleration (virtual mass force).

Average circulatory motion of particles in fluidized beds

Average circulatory motion of solid particles in fluidized bed affects the processes of heat and mass transfer in the bed. The primary circulatory motion is described by a solution of the averaged dynamic equations of multiphase flow as applied to a cylindrical bed in the absence of bubbles. Either of the cases of particles AWDC (ascending near the wall and descending at the center) and ACDW may arise, depending on the parameters of phase interactions. The direction of circulation is not necessarily affected by the depth of the bed but is influenced by the sign of (average terminal velocity of particles in the dense phase — average interstitial velocity): > O for ACDW, < O for A WDC, although the stability of the AWDC mode is affected by the bed height. Validity is supported by the results of an independent experimental study.

Testing of cold scaled bed modeling for fluidized-bed combustors

The purpose of this study was to determine whether cold scaled models with scaled particles give the correct hydrodynamic predictions for the gas and solids in an actual hot atmospheric pressure fluidized-bed combustor. Continuity equations and momentum balance equations of the gas and solid particles in fluidized beds were used in developing four dimensionless scaling groups which were utilized in sizing four different fluidized beds. Pressure fluctuations data collected from the different beds we are compared. Auto-correlation plots of the pressure fluctuations from one bed when compared with its scaled counterpart were observed to be of the proper scaled frequency. The fluctuations were of the same magnitude when scaled but the magnitudes were not statistically significant.

A new measuring system for flow patterns of solid particles in gas-solid fluidized bed.

A new system was developed to measure the flows of solid particles in fluidized beds. Porous particles, which were coated with a water-soluble fluorescent dye, emitted a strong visible light upon excitation by UV light. The illuminating UV light and the fluorescent visible light passed through clear silica fibers and plastic fibers, respectively. By using bifurcate optical probes and fluorescent tracer particles, pulse response curves at arbitrary locations were demonstratively measured. The output signals were processed by a microcomputer, and flow patterns of solid particles were visualized on CRT. The results show that the present system is useful in many situations of gas-solid contactors requiring observation of particle flows.

The processing of solid particles in fluidized beds

A general model is developed to determine the distribution function of solid particles in a fluidized bed reactor. Two consumption mass rates, the chemical reaction rate and the superficial abrasion rate, are considered, assuming that the reaction is described by the unreacted core model. Solid population balance relating the feed, overflow and elutriation to the physio-chemical changes of the particles in the bed are carried out, assuming that abraded solids are immediately elutriated. The results of Levenspiel et al. (8) and those of Chen and Saxena (9) are obtained as a particular case. The model has been developed for a noncatalytic solid-gas reaction, particularly for limestone or dolomite sulphuring and coal combustion, but it may also be applied to any catalytic reaction.

Residence time of polydisperse solid particles in fluidized bed

Residence time of polydisperse solid particles in fluidized bed

Jet pulverization of hard or solid particles in fluidized beds

Jet pulverization of hard or solid particles in fluidized beds

Leaching by Means of Fluidized Bed

The purpose of this study is to obtain data available for the design of a continuous fluidized-bed-type leaching equipment.Concerning the leaching of the extractable material from the sphere of a solid particle, theoretical analyses have been developed, taking into consideration the diffusion in the solid particle as well as in the film of the fluid.When the concentration of solution contained in a solid particle is uniform, or when the leaching interface can be assumed to exist in the solid particle, the following equations will be applicable, -Eqs. (4) and (10) for the distribution of the concentration of solute in solid phase, Eqs. (7) and (16) for the rate of solute leaving the surface of the solid particle due to diffusion, Eqs. (5) and (14) for the mass of extractable material remaining unextracted, Eqs. (6) and (15) for the nonleached fraction, and Eqs. (8) and (17) for the concentration of solute on the surface of the particle.Based on the diffusion in the film of fluid and in the solid phase, and on the assumption that solid particles are completely mixed in the bed, theoretical equations representing the longitudinal distribution of the concentration of solute in the leaching operation by a single-stage fluidized bed have been derived, -e. g., Eqs. (19)-(23) and Eq. (27).Experiments on the dissolution of solid particles in fluidized bed have been performed in order to compare the results with those of the theoretical curves obtained from Eq. (19).In Figs. 9 and 10 are illustrated graphical solutions for determining the number of stages necessary for a multistage-fluidized-bed-type extractor, when the diffusion in the film of the fluid is controlling.