Liquid-solid Fluidized Bed Research Articles

A universal drag model for liquid-solid fluidization: Experiment, data-driven modeling, CFD modeling and simulation

Various industrial applications are performed in liquid-solid fluidized beds where drag force plays a significant role in affecting the expansion characteristics of granular-bed, and then determines the mass/heat transfer performance. This study employs dimensionless learning data-driven modeling method, which is derived from the principle of dimensional invariance, to automatically discover the relationship between the drag coefficient and hydraulic dimensionless numbers from the liquid-solid fluidization data. It is found that the Fr number (=ul2/gds) also plays important role in improving the prediction accuracy of drag model except for Re number (=dsulρl/μl). The proposed data-driven modeling method has desired robustness, and the yielded drag model can be applicable to other liquid-solid systems, such as water-polystyrene spheres and water-coal particles, although it is derived from the fluidization of spherical glass beads in rising tap-water. The proposed drag model can also provide good CFD simulation results that agree very well with the experiment data with the relative error less than 5 %.

Deep recovery of clean coal from coking middlings: Pre-separation in liquid-solid fluidized bed and subsequent flotation

The coking middlings remaining after the production of coking coal contain a significant amount of clean coal, which has the high economic and environmental value if it can be effectively enriched. To improve resource utilization and avoid the negative environmental impacts of coking middlings, this study evaluated a new comprehensive separation process (i.e., pre-gravity separation in liquid-solid fluidized bed and subsequent flotation) to achieve high-yield recovery of clean coal from coking middlings. Preliminary enrichment by gravity separation achieved a combustible recovery rate, a clean-coal yield, and an ash content of 64.43 %, 49.62 %, and 15.89 %, respectively. This product was ground for 20 min to further dissociate clean coal and inorganic minerals and was further enriched by flotation separation. Under optimal flotation conditions (rotational speed, 2200 rpm; mass of collector, 2 kg/t; mass of frother, 200 g/t; and pulp concentration, 40 g/L), a clean-coal combustible recovery rate of 84.19 % was achieved. Overall, the comprehensive separation process achieved a clean-coal product with a high yield of 38.82 % and low ash content of 9.08 %, which is suitable for use as coking coal for steel plants. The tailings, with an ash content of 51.49 % and a yield of 61.18 %, are suitable as fuel for power plants. Therefore, the comprehensive separation process provides good economic benefits.

Study on the distribution of high ash slime in liquid-solid fluidized bed with different heights

ABSTRACT Liquid-solid fluidized bed (LSFB) sorting has been widely used in coarse coal slurry sorting in coal preparation plants in China. In this paper, the vertical distribution of high-ash fine sludge in the LSFB column was studied in depth, and the results showed that in the vertical direction of the column, the gradient of ash change of the + 0.25 mm particles was obviously larger than that of the −0.25 mm particles. For + 0.25 mm particles, the low-density fine coal particles accumulate in the middle and upper parts, while the high-density particles accumulate in the middle and lower parts, and the overflow −0.25 mm particles are basically uniformly distributed in each density class. In the overflow port and the upper part of the column, the ash content of −0.25 mm particle size is obviously higher than that of + 0.25 mm particle size, and the −0.125 mm high ash and fine sludge basically accumulate in the upper part of the LSFB, and eventually enter the overflow to seriously pollute the fine coal. This study is of great significance for the development and application of LSFB sorting machine and the optimization of coarse coal slurry sorting and recovery process.

Study on the anisotropic flow characteristics of wet particles in liquid-solid fluidized beds

In liquid-solid fluidized beds, the presence of a liquid film around the surface of particles influences their collision behavior, leading in turn to the restitution coefficient no longer a constant. The present study introduces a dynamic restitution coefficient for wet particles to describe its dynamic variation during the process of particles colliding. The liquid-solid two-phase flow is simulated with Eulerian-Eulerian two-fluid method incorporating the anisotropic kinetic theory of granular flow based on second-order moment (SOM) model, in view of the anisotropy of particle fluctuations. This study aims to probe into the influence of liquid film and anisotropy of particle fluctuation on the particle-particle interactions and collision mechanisms. The predicted particle velocity and solid volume fraction are verified by the Limtrakul's et al. experiments. The simulated results show that the particle velocity fluctuations exhibit significant anisotropy, and the SOM model is superior to the KTGF model in capturing inhomogeneity and anisotropy of the flow field. The existence of a liquid film enhances energy dissipation during particle collisions and diminishes the anisotropy of particle velocity fluctuations. Also, the enhancement of particle density leads to a thicker liquid film and higher restitution coefficient, while the second-order moments are weakened and the anisotropy is remarkable. Furthermore, the effect of liquid viscosity on the liquid film thickness and restitution coefficient is more significant, where the particle fluctuations are reduced and the anisotropy is intensified by enhancing the liquid viscosity. In brief, both the liquid film and the anisotropy have impact on liquid-solid two-phase flow, by comparison, the effect of anisotropy is greater than liquid film.

Local mass transfer and flow visualization around a cylinder in a liquid-solid fluidized bed

Adsorption method has been used for flow visualisation and determination of the local and average mass transfer coefficients around a horizontal cylinder in a liquid-solid fluidized bed. The obtained concentration fields on the adsorbent (silica-foils) represent a clear qualitative flow pattern around the cylinder. By comparison of the concentration fields around the cylinder in the single-phase flow and in the fluidized bed, a significant disturbance of the boundary layer by fluidized particles can be observed. Local mass transfer coefficients were shown to be dependent on the angular position around the cylinder with the maximum determined at the angle 140? (measured from the stagnant point 0?). Selected correlations were applied to predict the average mass transfer coefficients and the two best have shown deviations from the experimental data up to 5 %.

Density-induced segregation property of solid phase in a three-dimensional liquid-solid fluidized bed

This study employs the multiphase particle-in-cell method to explore fluid dynamics and solid segregation processes in a liquid-solid fluidized bed. The model reliability is established through rigorous experimental verification. Subsequently, this study scrutinizes the segregation behaviors of solid phase under various operational parameters. The findings indicate that turbulent viscosity predominantly localizes in regions where liquid and solid phases interact. Increasing the liquid inlet velocity amplifies both radial and axial mass fluxes of liquid and solid phases. Conversely, enlarging the diameter ratio between small and large solid particles, as well as adjusting the density of small solids, exerts negligible influence on radial and axial mass fluxes of liquid phase. As the liquid inlet velocity increases, a gradual reduction in solid concentration occurs, accompanied by an expansion in the solid movement zone. The diameter and density of solid particles exhibit little impact on the axial distribution of solid volume fraction. Notably, disparities in the particle Reynolds number become more apparent beyond an axial height of 0.05 m. Increasing the inlet velocity of liquid phase diminishes segregation intensity. Conversely, altering the solid diameter ratio and the density of smaller solid particles enhances solid segregation. However, solid segregation becomes constrained when the density of smaller solid particles exceeds 1700 kg/m3.

Superior role of LaB6 in enhancing O-scavenging efficiency during sintering Ti alloy from electrostatic self-assemble LaB6-coated Ti powder

LaB6 has been demonstrated as an effective O-scavenger for powder metallurgy (PM) Ti alloys to mitigate the detrimental effect of solid-solution O on the ductility. However, conventional mechanical mixing methods lead to the agglomeration and non-uniform distribution of LaB6, resulting in partial deactivation and reduced O-scavenging efficiency during sintering. Aiming at this issue, we propose an electrostatic self-assembly strategy that combined surface functional modification of LaB6 with solid-liquid fluidized bed powder coating treatment to synthesize a novel LaB6-coated Ti composite powder. Compared to traditional LaB6 additives in powder mixtures, the LaB6-coating particles exhibited excellent O-scavenging efficiency and higher utilization rate. Even at a low coating-content of 0.3 wt% LaB6, the tensile strength and elongation of the as-sintered Ti samples increased from 461 ± 26 to 579 ± 13 MPa and 5.6 ± 1.4% to 14.2 ± 0.3%, respectively. The achieved improvement rate (∼95%) in tensile elongation was significantly superior to the previously reported data of the rare-earth O-scavengers.

Mechanistic understanding of strengthening in a novel MXene/AlSi10Mg matrix composite processed by laser powder bed fusion

The fabrication of high-performance two-dimensional nanosheets strengthened Al matrix composites (AMCs) is challenging due to the agglomeration issue of traditional nanosheets (graphene) and their high reactivity with Al powder. To address these concerns, Ti3C2 MXene nanosheets with superior chemical stability were employed as a substitute for graphene in this study. Furthermore, a novel MXene/AlSi10Mg composite powder for the laser powder bed fusion (LPBF) was synthesized using a powder coating strategy. The approach involves three steps, including intercalation treatment of MXene flakes, uniform dispersion of the delaminated MXene nanosheets in aqueous solution, followed by the powder coating treatment using a solid-liquid fluidized bed. Differing from conventional methods for making powder mixtures, such as mechanical blending and ball milling, our powder coating approach achieved uniform distribution and high purity of MXene on the surface of AlSi10Mg powder, while maintaining the original sphericity and flowability of powder. The MXene-coating exhibited exceptional stability under intense conditions of high-energy laser exposure and high-temperature Al melt, enabling the successful retention of MXene nanosheets after LPBF processing. Experimental results show that the retained MXene effectively strengthened the Al matrix through load transfer from Al matrix, pinning effect on the movement of grain boundaries, and inhibiting effect on the deformation and fracture of eutectic Si. Consequently, compared to the bare AlSi10Mg sample processed by LPBF, a small addition of MXene (0.25 wt%) yielded a significant improvement in tensile strength (over 60%), while maintaining an acceptable ductility.

Re-concentration of coking middling particles in a liquid-solid fluidized bed: Fluidization characteristics and density segregation

The re-enrichment of coking middling particles is an important way to realize the efficient utilization of coal resources. In this study, by combining numerical simulation and experimental method, the density segregation process and mechanism of coking middling particles in a liquid-solid fluidized bed are studied. The results show that the density segregation process of coking middling particles is mainly divided into the falling outer ring at the sidewall and the rising inner ring. Herein, the ash distribution variance of coking middling particles also shows a changing trend of first increasing and then decreasing with the values increase of operating parameter. Further, after the separation process in the fluidized bed, the cleaned coal product with a yield of 42.77 and an ash content of 8.69% is enriched from 1 to 3 mm coking middling coal (ash content of 28.2%), indicating that coking middling particles are separated efficiently in the liquid-solid fluidized bed.

Crystallization and refluidization in very-narrow fluidized beds

Fluidization of solid particles by an ascending fluid is frequent in industry because of the high rates of mass and heat transfers achieved. However, in some cases, blockages occur and hinder the correct functioning of the fluidized bed. In this paper, we investigate the crystallization (defluidization) and refluidization that take place in very-narrow solid–liquid fluidized beds under steady flow conditions. For that, we carried out experiments where either monodisperse or bidisperse beds were immersed in water flows whose velocities were above those necessary for fluidization, and the ratio between the tube and grain diameters was smaller than 6. For monodisperse beds consisting of regular spheres, we observed that crystallization and refluidization alternate successively along time, which we quantify in terms of macroscopic structures and agitation of individual grains. We found the characteristic times for crystallization and propose a new macroscopic parameter quantifying the degree of bed agitation. The bidisperse beds consisted of less regular spheres placed on the bottom of a layer of regular spheres (the latter was identical to the monodisperse beds tested). We measured the changes that macroscopic structures and agitation of grains undergo and show that the higher agitation in the bottom-layer hinders crystallization of the top layer. Our results bring new insights into the dynamics of very-narrow beds, in addition to proposing a way of mitigating defluidization.

Elutriation characteristics of binary particle mixture in pseudoplastic liquid: Empirical correlation and GA-ANN modelling

The elutriation of the binary mixture from irregularly shaped particles with different diameters in non-Newtonian liquids of different densities has been investigated in an SLFB (Solid Liquid Fluidized Bed). The influence of various parameters like particle size of the binary mixture, column diameter, bed weight and rheological properties of the non-Newtonian liquid on minimum elutriation velocity (Ume) have been carried out experimentally. It has been found that Ume increases as column diameter and particle size increase while decreasing when SCMC concentration increases. An empirical correlation was developed to predict the minimum elutriation velocity associated with suitable statistical parameters. GA-ANN (Genetic Algorithm and Artificial Neural Network) modelling was successfully employed.

Development of Effective Voidage Correlations in Pilot-Scale Liquid–Solid Fluidized Bed Based on Data-Driven Modeling

Liquid–solid fluidized beds can meet many different demands from chemical, environmental, and pharmaceutical processes, and it is very crucial to accurately predict their voidages, which, however, are usually underestimated by the classical Richardson–Zaki equation. In this study, a data-driven modeling method was applied to develop the voidage correlation based on the experimental data from pilot-scale liquid–solid fluidized bed where the fluidization experiments of spherical glass beads were performed at different particle sizes, particle densities, liquid superficial velocities, and operating temperatures. By selecting different parametric spaces, various high-accuracy voidage correlations based on different dimensionless numbers (i.e., Re, Ret, Ar, Fr, St) were discovered and all of the values of R2 were approximately 0.99. In comparison, the combination of Re and Ar numbers could better characterize the voidage and the mean square error was as low as 2.29 × 10–4. The proposed correlation also performed very well in predicting the voidage of the fluidization of irregular calcite pellets in a pilot-scale fluidized bed and the voidage of the fluidization of coarse coal particles in a laboratory-scale fluidized bed, thus indicating its universality.

Insights into the influence of particle density and column inclination in polydisperse liquid–solid fluidized beds

In this work, the impact of particle density difference on the expansion behavior of combined size and density varying binary mixtures in an inclined fluidized bed is examined using a transient multi-fluid Eulerian technique coupled with the Kinetic Theory of Granular Flow (KTGF) model. Additionally, the effects of particle density differences in binary mixtures with varied geometrical parameters, such as angle of inclination, width of the channel, and number of plates in the inclined section are also studied and elaborated. The results delineate that change in the angle of an inclined liquid–solid fluidized bed, the width of the channels, and the number of channels considerably influence the flow behavior of the complex polydisperse mixtures.

Simulation study on the flow behavior of wet particles in the power-law liquid-solid fluidized bed

Simulation study on the flow behavior of wet particles in the power-law liquid-solid fluidized bed

Numerical Investigations of Hydrodynamics in a Liquid-Solid Fluidized Bed

The liquid-solid fluidization bed is an effective method for removing hard ions from water. However, it is widely believed that the flow in the liquid-solid fluidization bed is homogeneous, which limits the transfer rates of heat, mass, momentum, and mixing. In this study, the results of the computational fluid dynamics (CFD) method showed significant heterogeneous particle–fluid patterns in the liquid-solid fluidization bed. On the other hand, simulations of the hydrodynamics behavior in the liquid-solid fluidized bed were first performed using different solid particle sizes, then particle classification, velocity distribution, and the vortical structures in the liquid-solid fluidized bed were assessed. In addition, a new model was proposed in this study to predict the flow behavior of the fluid-particle system used. The obtained results demonstrated the presence of the heterogeneous flow regime in the liquid-solid fluidized bed. The developed model for the onset of heterogeneous fluidization behavior revealed reasonable prediction results. Therefore, this model can be applied in future related studies on the hydrodynamics of the liquid-solid fluidized bed.

Study on the flow characteristics of the pulsating intermittent liquid–solid fluidized bed with step liquid velocity by CFD approach

AbstractA new type of liquid–solid fluidized bed (LSFB), the pulsating intermittent LSFB (PI‐LSFB), which uses pulsating liquid flow, was analyzed through numerical and experimental study. A good agreement between numerical simulation results and laboratory experimental measurement data was achieved. The mass transfer efficiency between the liquid and solids phases was enhanced since the relative velocity was significantly improved. The flow characteristics of the PI‐LSFB were analyzed through the Eulerian–Eulerian approach, incorporating the kinetic theory of granular flow. The solids holdup in the middle part of the PI‐LSFB increases first and then decreases as the step liquid velocity increases. The relative velocity increases first and then decreases as the pulsation period or the liquid velocity increases. The PI‐LSFB performs similar flow regimes under step and sinusoidal liquid velocities. The proposed PI‐LSFB may provide a reference in biological wastewater treatment applications.

Study on liquid-solid fluidisation behaviour of coarse coal particles: Experiment and CFD simulation

To improve the recovery rate of clean coal, a liquid–solid fluidised bed is typically used to process coarse coal slime of 0.25–1.5 mm. In this paper, a combination of experimental measurements and computational fluid dynamics (CFD) simulations was used. The fluidisation behaviour of four groups of coarse coal particles with different sizes and densities in a fluidised bed with rectangular cross-section was investigated.The Euler–Euler method, shear stress transport k–ω turbulence model, kinetic theory of granular flow (KTGF) and modified Gidaspow drag model were used for CFD simulations. The experiment and CFD simulation results showed that when JL/Umf was greater than 1, the expansion ratio of the fluidised bed of coarse coal particles varied as a power function of the JL/Umf value. The bed expansion ratio model developed by Tripathy et al. in a fluidised bed with a circular cross-section was also applicable to a fluidised bed with a rectangular cross-section. The pressure drop data at different heights indicated that the measured values showed a linear pattern with the measured height. This indicated that when JL/Umf was greater than 1, the coarse coal particles showed a uniform fluidisation characteristic. After choosing appropriate initial conditions and models, the CFD simulation agreed well with the experimental data. The experimental data and simulation results can deepen the understanding of liquid–solid fluidised beds of coarse coal particles, which is beneficial to improve the fluidisation quality of the fluidised bed and further improve the separation effect.

Hydrodynamic characteristics of a rectangular gas-driven inverse liquid-solid fluidized bed

The hydrodynamic characteristics of a rectangular gas-driven inverse liquid-solid fluidized bed (GDFB) using particles of different diameters and densities were investigated in detail. Rising gas bubbles cause a liquid upflow in the riser portion, enabling a liquid downflow that causes an inverse fluidization in the downer portion. Four flow regimes (fixed bed regime, initial fluidization regime, complete fluidization regime, and circulating fluidization regime) and three transition gas velocities (initial fluidization gas velocity, minimum fluidization gas velocity, and circulating fluidization gas velocity) were identified via visual observation and by monitoring the variations in the pressure drop. The axial local bed voidage (ε) of the downer first decreases and then increases with the increase of the gas velocity. Both the liquid circulation velocity and the average particle velocity inside the downer increase with the increase of the gas velocity in the riser, but decrease with the particle loading. An empirical formula was proposed to successfully predict the Richardson-Zaki index “n”, and the predicted ε obtained from this formula has a ±5% relative error when compared with the experimental ε.

Two-Phase Liquid-Solid Hydrodynamics of Inclined Fluidized Beds

Although many fluidized systems are not vertically oriented, little research has been done on fluidization within inclined channels. The fluidization of the gravitational force and the tensile force may be substantially opposing in the vertical system. The theory of gravitational field fluidization, which is related to industrial fluidization processes like coal gasification, iron ore reduction, and catalytic cracking and calls for the use of standing tubes or angled risers, has to be developed in order to encompass various orientations. Without underlying theories, engineers must rely on vertical fluidization equations to build these sloping systems. A significant barrier to improving the design and optimization of new solid circulation systems is the tendency of fluidization. Based on historical developments and theoretical progress, the study presents an overview of recent advancements of liquid-solid fluidized beds in inclined columns. The fluidized bed is investigated as a whole by looking at the governing factors.

Investigation of the characteristics and mechanisms of the layer inversion in binary liquid–solid fluidized beds with coarse particles

This paper adopts an optimized Euler–Lagrange method proposed in our previous work to study the characteristics and formation mechanisms of layer inversion in binary liquid–solid fluidized beds (LSFBs) with coarse particles. The LSFBs are formed in a cylindrical pipe with a diameter of 50 mm and a length of 0.6 m and consist of two species of coarse particles with different sizes: 6 mm glass spheres (species 1) and 10 mm glass spheres (species 2) with the particle density of 2600 kg/m3. First, the characteristics of the layer inversion of LSFBs with coarse particles are qualitatively analyzed. The positions of species 1 and species 2 are converted during layer inversion. Second, the changes in the trajectory and volume fraction of two species of particles are quantitatively investigated. Finally, the formation mechanisms of layer inversion with coarse particles are analyzed. The results show that the relative magnitude of the fluid–solid interaction force and the gravity is the main reason for determining the layer inversion of binary coarse particles of different sizes. The collision force is to balance the net force of the particle–fluid interaction force and the net gravity, so that the fluidized bed is in relative equilibrium. In addition, through the analysis of the evolution of the network of contact forces, the constraint of the wall on coarse particles is discussed during the layer inversion.