Experimental study on the characteristic mixing time of solids and its link with the lateral dispersion coefficient in bubbling fluidized beds

Sánchez-Prieto, J.; Hernández-Jiménez, F.; García-Gutiérrez, L.M.; Soria-Verdugo, Antonio

doi:10.1016/j.cej.2016.08.075

Cited by 35 publications

(16 citation statements)

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“…The lateral dispersion coefficient is influenced by many operating conditions such as bed size, gas velocity, and particle property. However, researchers also found that the lateral dispersion coefficient may change significantly with the experimental techniques applied [25][26][27][28]. In addition, former research on lateral mixing of solids in fluidized beds mainly fit the lateral mixing process by the Fickian-type diffusion equation to derive the lateral dispersion coefficient.…”

Section: Introductionmentioning

confidence: 99%

Experimental Quantification of the Lateral Mixing of Binary Solids in Bubbling Fluidized Beds

Huang

Liu

et al. 2021

Energies

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A novel experimental method for the lateral mixing of binary solids in bubbling fluidized beds was developed based on the capacitance probe technique. The evolutions of local mixing ratios in a fluidized bed which can be assumed as one mixing cell were analyzed in detail. The solids mixing within one mixing cell was resolved and the effect of convection and diffusion mechanism on lateral mixing was evaluated individually. The results show that at lower part of the fluidized bed, convection plays a more important role in the mixing process near the wall; meanwhile, diffusion is very important for the mixing around the center line. This is opposite with that at the higher part. A lateral micro dispersion coefficient was proposed to characterize the lateral mixing within the mixing cell and the value is generally between 0.005 and 0.025 m/s. A new mixing index was proposed to evaluate the lateral mixing quality of binary solids. It was found that at the lower part of the fluidized bed, the best mixing is acquired at the half radius, whereas mixing at the center line is the worst. At the higher part, solid mixing is better when increasing the distance from the wall. The influences of gas velocity and static bed on the lateral mixing were also discussed from a microscopic perspective.

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Section: Introductionmentioning

confidence: 99%

Experimental Quantification of the Lateral Mixing of Binary Solids in Bubbling Fluidized Beds

Huang

Liu

et al. 2021

Energies

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“…Several studies have investigated mixing using this approach (e.g. 31,15,6,4,32,33 ), but most of these employ 2D simulations and, therefore, overestimate mixing rates because resistance to the hydrodynamics from the front and back walls is not accounted for. 3,4 Therefore, in order to understand and quantify mixing in commercial systems, this study employs fine-grid 3D simulations of a large pilot-scale 50 cm fluidized bed so that the hydrodynamics are independent of wall effects.…”

Section: Introductionmentioning

confidence: 99%

Mixing dynamics in bubbling fluidized beds

2017

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Solids mixing affects thermal and concentration gradients in fluidized bed reactors and is, therefore, critical to their performance. Despite substantial effort over the past decades, understanding of solids mixing continues to be lacking because of technical limitations of diagnostics in large pilot and commercial‐scale reactors. This study is focused on investigating mixing dynamics and their dependence on operating conditions using computational fluid dynamics simulations. Toward this end, fine‐grid 3D simulations are conducted for the bubbling fluidization of three distinct Geldart B particles (1.15 mm LLDPE, 0.50 mm glass, and 0.29 mm alumina) at superficial gas velocities U/Umf = 2–4 in a pilot‐scale 50 cm diameter bed. The Two‐Fluid Model (TFM) is employed to describe the solids motion efficiently while bubbles are detected and tracked using MS3DATA. Detailed statistics of the flow‐field in and around bubbles are computed and used to describe bubble‐induced solids micromixing: solids upflow driven in the nose and wake regions while downflow along the bubble walls. Further, within these regions, the hydrodynamics are dependent only on particle and bubble characteristics, and relatively independent of the global operating conditions. Based on this finding, a predictive mechanistic, analytical model is developed which integrates bubble‐induced micromixing contributions over their size and spatial distributions to describe the gross solids circulation within the fluidized bed. Finally, it is shown that solids mixing is affected adversely in the presence of gas bypass, or throughflow, particularly in the fluidization of heavier particles. This is because of inefficient gas solids contacting as 30–50% of the superficial gas flow escapes with 2–3× shorter residence time through the bed. This is one of the first large‐scale studies where both the gas (bubble) and solids motion, and their interaction, are investigated in detail and the developed framework is useful for predicting solids mixing in large‐scale reactors as well as for analyzing mixing dynamics in complex reactive particulate systems. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4316–4328, 2017

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“…Besides, when analysing the evolution of the Lacey mixing index (Equation 1), it can be extracted that the results obtained using the white area recognition method (Equation 2 al. [62]. Overall, it can be observed that the inclusion of the friction term in the simulations improves the prediction of the numerical results when compared with the experimental findings.…”

Section: Theorymentioning

confidence: 51%

“…The initial state has the theoretical maximum white area and the final state is reached when no white area is detected in the images. Further details of the processing of the experimental images can be found in Sánchez-Prieto et al [62].…”

Section: Experimental Data Processingmentioning

confidence: 99%

“…The MFIX−TFM code was selected to carry out the numerical simulations [60,61] and the numerical results were compared with experiments obtained in a pseudo-2D fluidized bed. The experiments were performed by tracking particles of the same diameter and density but with different colours (black and white) [62]. The same methodology used in the experiments was employed in the TFM simulations.…”

Section: Introductionmentioning

confidence: 99%

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Lateral solids meso-mixing in pseudo-2D fluidized beds by means of TFM simulations

2018

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Experimental study on the characteristic mixing time of solids and its link with the lateral dispersion coefficient in bubbling fluidized beds

Abstract: Experimental study on the characteristic mixing time of solids and its link with the lateral dispersion coefficient in bubbling fluidized beds, Chemical Engineering

Cited by 35 publications

References 50 publications

Experimental Quantification of the Lateral Mixing of Binary Solids in Bubbling Fluidized Beds

Experimental Quantification of the Lateral Mixing of Binary Solids in Bubbling Fluidized Beds

Mixing dynamics in bubbling fluidized beds

Lateral solids meso-mixing in pseudo-2D fluidized beds by means of TFM simulations

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