Liquid-solid Fluidized Bed Research Articles

Study on the flow characteristics of the pulsating intermittent liquid-solid fluidized bed with sinusoidal liquid velocity

The sinusoidal pulsation velocity was proposed in this work to further improve the relative velocity and mass transfer efficiency between the liquid and solids phases. The flow behavior of the particles and the relative velocity between the liquid and solids phases were simulated by Eulerian-Eulerian approach incorporating the kinetic theory of granular flow. The numerical results agreed well with the experimental data obtained by the laboratory experimental system. The average axial solids holdup in a whole time period of the sinusoidal liquid velocity was higher in the middle part and lower at the top and bottom of the fluidized bed. The average relative velocity between the liquid and solids phases of the whole bed changed in a sinusoidal form with the same time period of the liquid velocity. Based on the numerical results, the regressional empirical formula of the relative velocity between the liquid and solids phases was obtained.

Hydrodynamics of wet particles in liquid-solid fluidized beds using kinetic theory of rough spheres model

To actually describe the flow behaviors of particles in the liquid-solid fluidized bed, the effects of liquid film covered on the particles surface and the sphericity of particles need to be considered for quasi-spherical wet particles. Liquid-solid fluidization characteristics are predicted using a two-fluid model incorporating with the kinetic theory of rough spheres (KTRS) model. Simulation results show that the normal restitution coefficient for wet particles covered liquid film increases with an increase of the particles diameter. As for the sphericity of particles, a higher sphericity of particles gives rise to a lower granular temperature and higher solids pressure and viscosity. Also, the normal restitution coefficient of quasi-spherical particles is relatively small, compared with completely sphere. The simulation results obtained by the kinetic theory of rough spheres model for quasi-spherical wet particles are in satisfactory agreement with the experimental data from Lu et al.

Artificial neural network-based sensitivity analysis and experimental investigation of liquid–solid fluidization technique for low-grade coal upgradation

Liquid-solid fluidization technique is being applied where low-grade coal or minerals enrichment is mostly density-based. Static and dynamic behavior of particles in a fluid medium has been extensively investigated over the years because of its dynamic applications across various industries. In this work, bed characterization studies and experiments have been conducted to study coal washing ability of the liquid-solid fluidized bed separator. Results have been recorded in terms of ash rejection%, combustible recovery% and separation efficiency%. Minimum fluidization velocity and pressure drop values have been predicted using existing theoretical correlations and compared with the experimental values. A three-layered (4:5:3) feedforward back-propagation (FFBP) neural network model was developed using Levenberg-Marquardt algorithm, LOGSIG and MSE as training, transfer and performance functions respectively. Garson’s algorithm and connection weight approach have been employed for sensitivity analysis to interpret the neural network results physically. Coefficients of correlation, all R (including training, validation & testing datasets) obtained for outputs ash rejection (R = 0.9960), combustible recovery (R = 0.9952) and separation efficiency (R = 0.9944) suggest that predicted values are in agreement with the experimental values and the developed model is a good fit.

Effective drag coefficient correlation for coarse coal particle fluidization in transitional flow regime

Liquid–solid fluidized beds are widely used in industrial processes, such as polymerization, mineral processing, and water treatment. Among these processes, particle fluidization behaviors perform a significant function in determining heat and mass transfer performance. In this study, a large set of expansion experiments are performed to investigate the effects of the particle density, particle size, and liquid superficial velocity on bed expansion height and bed porosity. The drag coefficient is obtained based on experimental data. The relationship between drag coefficient and Reynolds number, Froude number and Stokes number is clarified, and an effective drag closure for coarse coal particle fluidization in the transitional flow regime is proposed. Then the developed drag coefficient correlation is incorporated into liquid–solid two-phase flow model to predict the bed expansion height. The output predictions agree well with the experimental data, ensuring the accuracy of the proposed drag closure.

CFD Modeling and Simulation of the Hydrodynamics Characteristics of Coarse Coal Particles in a 3D Liquid-Solid Fluidized Bed

In this study, a Eulerian-Eulerian liquid-solid two-phase flow model combined with kinetic theory of granular flow was established to study the hydrodynamic characteristics and fluidization behaviors of coarse coal particles in a 3D liquid-solid fluidized bed. First, grid independence analysis was conducted to select the appropriate grid model parameters. Then, the developed computational fluid dynamics (CFD) model was validated by comparing the experimental data and simulation results in terms of the expansion degree of low-density fine particles and high-density coarse particles at different superficial liquid velocities. The simulation results agreed well with the experimental data, thus validating the proposed CFD mathematical model. The effects of particle size and particle density on the homogeneous or heterogeneous fluidization behaviors were investigated. The simulation results indicate that low-density fine particles are easily fluidized, exhibiting a certain range of homogeneous expansion behaviors. For the large and heavy particles, inhomogeneity may occur throughout the bed, including water voids and velocity fluctuations.

Statistics of velocity fluctuations in a homogeneous liquid fluidized bed

A liquid-solid fluidized bed is investigated by means of optical techniques involving index matching. Statistics of velocity fluctuations of both phases are determined. A physical model distinguishing between interstitial and wake regions is introduced. It reproduces the velocity fluctuation distributions up to the third-order-moment, explaining the reversal of the skewness when increasing the solid concentration.

Motion and clustering of bonded particles in narrow solid–liquid fluidized beds

This paper presents an experimental and numerical investigation of solid–liquid fluidized beds consisting of bonded spheres in very narrow tubes, i.e., when the ratio between the tube and grain diameters is small. In narrow beds, high confinement effects have proved to induce crystallization, jamming, and different patterns, which can be intensified or modified if some grains are bonded together. In order to investigate that, we produced duos and trios of bonded aluminum spheres with a diameter of 4.8 mm and formed beds consisting either of 150–300 duos or 100–200 trios in a 25.4 mm-ID pipe, which were submitted to water velocities above those necessary for fluidization. For the experiments, we filmed the bed with high-speed and conventional cameras and processed the images, obtaining measurements at both the bed and grain scales. For the numerical part, we computed the bed evolution for the same conditions with a computational fluid dynamics–discrete element method code. Our results show distinct motions for individual duos and trios and different structures within the bed. We also found that jamming may occur suddenly for trios, where even the microscopic motion (fluctuation at the grain scale) stops, calling into question the fluidization conditions for those cases.

Estimation of dispersion coefficient in a solid-liquid fluidised bed system

Particle dispersion behaviour in a solid liquid fluidised system leads to interesting outcomes such as mixing and segregation which are often quantified by an empirical dispersion coefficient. The present study aims at providing a better estimation of particle dispersion behaviour from a fundamental definition analogous to diffusion coefficient. By tracking a tracer particle using high speed image analysis, fluctuating velocity components (Vi/) were determined in a solid-liquid fluidised bed comprising glass particles (dS = 8 mm, ρS = 2230 kg m−3) and water as a fluidising medium. Both inter-particle and particle-wall collisions were determined from the time varying jerk data. The particle mean-free path (λ) was then estimated as a distance between two successive peaks in the jerk profile. Finally, dispersion efficient D was computed based on the product of λ and V. Estimated dispersion coefficients were compared with the available correlations and reasonable agreement was obtained.

Numerical Studies on Teeter Bed Separator for Particle Separation

Teeter Bed Separators (TBS) are liquid–solid fluidized beds that are widely used in separation of coarse particles in coal mining industry. The coal particles settle in the self-generating medium bed resulting in separation according to density. Due to the existence of self-generating medium beds, it is difficult to study the sedimentation of particles in TBS through experiments and detection methods. In the present research, a model was built to investigate the bed expansion characteristics with water velocity based on the Euler–Euler approach, and to investigate the settling of foreign particles through bed based on the Euler–Lagrange approach in TBS. Results show that the separation of in TBS should be carried out at low water velocity under the condition of stable fluidized bed. Large particles have a high slip velocity, and they are easily flowing through the bed into the light product leading to a mismatch. The importance of self-generating bed on separation of particle with narrow size ranges are clarified. The model provides a way for investigating the separation of particles in a liquid–solid fluidized bed and provides suggestions for the selection of operation conditions in TBS application.

Performance characterization and misplacement studies of liquid–solid fluidized bed density separator for coal beneficiation using Taguchi-ANOVA method

Coal preparation plants commonly use density-based separators to remove high-density inorganic matter (rock) from low-density carbonaceous matter (coal). Liquid–solid fluidized bed separators (FBS), segregates particles with different size, shape, and density. Particles with different terminal velocities report to various heights of the fluidization column. This property has been used to beneficiate the low-grade coal particles. As the material systems in mineral processing vary broadly in physical characteristics, misplacement of particles to an undesired destination is a prevalent occurrence. The present work aims at understanding the influence of input variables on the separation performance and particle misplacement in FBS. Quantitative and qualitative analyses of the performance characteristics and misplacement have been studied using Taguchi statistical design and ANOVA. Misplacement and normalized misplacement indexes were calculated to quantify the extent of misplacement during segregation. The optimized mean separation efficiency was obtained at optimized combination of mean particle size of 400 µm, bed height of 20 cm, superficial velocity of 2.83 cm/s, and overflow tap height of 12 cm, whereas the optimized mean normalized misplacement index was obtained at mean particle size of 400 µm, bed height of 20 cm, superficial velocity of 2.12 cm/s, and overflow tap height of 12 cm.

Study and Experimental Setup of Liquid-Solid Fluidization in Rangsit University

This article explains the basics of fluidization theory and how to construct of liquid-solid fluidization apparatus for the laboratory of the chemical engineering department at Rangsit University. The minimum fluidization velocity of solid particles (calculate from the Ergun equation) is essential for the effective operation and design of fluidized beds. All Chemical engineers need to learn about this technique to apply to the mixing processes, drying process, leaching, and washing processes. In this paper, the apparatus of a fluidized bed constructed with three different diameters of the column; that was 2.7, 5.4, and 10 cm, respectively. The three different diameters of round glass bead were a solid phase; that was 2, 3, and 4 mm, respectively. The parameter in the fluidized bed was the minimum fluidization velocity (Umf). This paper describes the experimental investigation of the liquid-solid fluidized bed. The pressure drops across the fluidized bed measured at a different liquid flow rate. The data analyzed by the graphical method. It found that the minimum fluidization velocity increases with increasing particle size, the height of the bed, and decreasing particle sphericity.

Improvement of voidage prediction in liquid-solid fluidized beds by inclusion of the Froude number in effective drag relations

A novel effective drag relation for liquid-solid fluidisation is proposed, suitable for application in full-scale installations. This is achieved by presenting new insights related to the influence of the temporal-spatial heterogeneity on the effective hydrodynamic drag for large fluidised systems. While heterogeneous flow behaviour can be predicted increasingly accurately in CFD simulations that explicitly model the heterogeneous solids distribution, for the operation of many large-scale applications it is infeasible to perform such computationally intensive simulations. Therefore, there is a clear need for full-scale drag relations that effectively take into account the heterogeneous behaviour and irregular spatial particle distributions. Our new drag relation is based on a large set of experiments, which shows that the degree of overall expansion is not only dependent on the ratio of laminar-turbulent flow, but also on the amount of homogenous versus heterogeneous flow, which is not included in current full-scale drag relations. To include the effect of heterogeneity, the standard drag relation, based on the Reynolds number, is extended with a specific type of Froude number. Because fully turbulent flow regimes are rare in applications of liquid-solid fluidisation, our focus is not on the turbulent flow regime but instead on laminar and transitional flow regimes. In these regimes, three types of models are investigated. The first type is based on a theoretical similarity with terminal settling, the second is based on the semi-empirical Carman-Kozeny model, and the third is based on empirical equations using symbolic regression techniques. For all three types of models, coefficients are calibrated on experimental data with monodisperse and almost spherical glass beads. The models are validated with a series of calcium carbonate grains applied in drinking water treatment processes as well as data obtained from the literature. Using these models, we show that the voidage prediction average relative error decreases from approximately 5% (according to the best literature equations which use Reynolds number only) to 1–2% (using both Reynolds and Froude number). This implies that our new models are more suitable for operational control in full-scale fluidised bed applications, such as pellet softening in drinking water treatment processes.

Utilization of Waste of Enzymes Biomass as Biosorbent for the Removal of Dyes from Aqueous Solution in Batch and Fluidized Bed Column

The biosorption performance of both batch and liquid-solid fluidized bed operations of dead fungal biomass type (Agaricusbisporus ) for removal of methylene blue from aqueous solution was investigated. In batch system, the adsorption capacity and removal efficiency of dead fungal biomass were evaluated. In fluidized bed system, the experiments were conducted to study the effects of important parameters such as particle size (701-1400�m), initial dye concentration(10-100 mg/L), bed depth (5-15 cm) and solution flow rate (5-20 ml/min) on breakthrough curves. In batch method, the experimental data was modeled using several models (Langmuir,Freundlich, Temkin and Dubinin-Radushkviechmodels) to study equilibrium isotherms, the experimental data followed Langmuir model and the results showed that the maximum adsorption capacity obtained was (28.90, 24.15, 21.23 mg/g) at mean particle size (0.786, 0.935, 1.280 mm) respectively. In Fluidized-bed method, the results show that the total ion uptake and the overall capacity will be decreased with increasing flow rate and increased with increasing initial concentrations, bed depth and decreasing particle size.

Effects of flow behavior index and consistency coefficient on hydrodynamics of power-law fluids and particles in fluidized beds

Flow behaviors of particles and power-law fluids were numerically simulated by means of Euler-Euler model with kinetic theory of granular flow in liquid-solid fluidized beds, and effects of flow behavior index (n) and consistency coefficient (K) were studied. The simulation results were compared with the experimental measurements, and good agreements were achieved. The effective viscosity of the shear-thinning fluid decreases as it flows through the expanded bed due to the increase in fluid strain rate. Unlike the homogeneous distributions of particles in Newtonian liquid fluidized beds, four regions for particle flow were observed along the bed height when a non-Newtonian fluid acts as the fluidizing agent, which indicates the non-uniformity of particles distribution. With the decrease of n, the enhancement of shear-thinning characteristics of the fluidizing agent thickens the relative inlet region and enhances the non-uniformity of particles along the bed height. The increase of n accelerates the circulation of particles in the fluidized bed, which speeds up the renewal of the particulate materials throughout the reactor space. The increase in K increases the apparent viscosity of the fluidizing agent. The bed height increases and the average solid volume fraction decreases. However, the influence of K on the non-uniformity of particles in the bed is less significant than that of n.

Intermediate size fine coal beneficiation by Reflux ™ Classifier using statistical approach

The Reflux™ Classifier (RC) is the state-of-the-art liquid-solid fluidized bed gravity separator and its industrial acceptance and commercialization have been increasing in the coal preparation. Despite the significant advancement of this technology, optimization studies, which could be of paramount interest to the plant operator, were not found in the previously published literature. The objective of this research work is to develop a statistical model to predict the ash content and yield of the concentrate. Box-Behnken design of experiment was employed to analyze the gravity separation performance of the intermediate size coal fraction (0.25 × 2 mm). Three important operating parameters (bed setpoint, feed rate and fluidization water rate) were considered to study the separation efficiency of RC. To achieve minimum ash content with the maximum yield of concentrate, multi-response optimization was carried out using desirability approach to optimize the concentrate ash (%) and yield (%) simultaneously. The global optimum yield value of 50% concentrate was achieved with an ash content of 11.5%, at the bed density setpoint of 1100 kg/m3, feed rate of 5.9 l/min and water fluidized rate of 4.1 l/min. The influence of operating variables of the RC on ash content and yield of concentrate are presented and discussed in 3D surface plots. The developed statistical models for the ash content and yield of concentrate when tested were found to predict the yield with an average error of 5%. Partition curves showed that the separation density (ρ50) varied from 1.34 to 1.52 and the Ecart probable error (Ep) varied from 0.075 to 0.1 for the Reflux™ Classifier.

Mimicking layer inversion in solid-liquid fluidized beds in narrow tubes

This paper investigates experimentally and numerically the dynamics of solid particles during the layer inversion of binary solid-liquid fluidized beds in narrow tubes. Layer inversion can happen in solid classifiers and biological reactors, where different solid particles coexist and segregation by diameter and density occurs. The fluidized beds were formed in a 25.4 mm-ID pipe and consisted of alumina and aluminum beads with diameters of 6 and 4.8 mm, respectively. We placed initially the lighter particles on the bottom in order to force an inversion of layers, mimicking the layer inversion mechanism. In the experiments, we filmed the bed with a high-speed camera and tracked individual beads along images, while in numerical simulations we computed the bed evolution with a CFD-DEM (computational fluid dynamics - discrete element method) code. We found the distances traveled by individual particles during the inversion and the characteristic time for layer inversion.

Fluctuations in inertial dense homogeneous suspensions

A theoretical model of liquid and particle random fluctuations is proposed for gravity-driven flows of inertial homogeneous suspensions. It is based on a paradigm assuming that fluctuations of both liquid velocity and particle slip velocity are driven by fluctuations of the phase indicator function. It is shown that this model accurately predicts the energy of the fluctuations of both the fluid and particle phases measured in a homogeneous solid-liquid fluidized bed over a wide range of particle volume fractions, from 10% to 45%

A value-added insight of reusing microplastic waste: Carrier particle in fluidized bed bioreactor for simultaneous carbon and nitrogen removal from septic wastewater

Turning microplastic litter into reusable products is a resource-saving and eco-friendly strategy of disposing of plastic pollution. This work realized a value-added insight of reusing microplastic waste by processing the recycled microplastic items with clay waste into composite particle (CP). Furthermore, the systematic evaluation of CP particle was carried out in a Liquid-solid fluidized bed bioreactor (LSFBBR-CP) treating septic sewage with low COD to nitrogen ratio (C/N ≤3). The commercial inorganic particle, bioceramsite (BC), was tested in the LSFBBR-BC for comparison. During the 257-day stepwise operation, two LSFBBRs constantly achieved effluent of TCOD <45 mg L−1 and low observed sludge yield (Yobs ≤0.067 g VSS g-1 COD). Comparatively, the lower fluidization velocity for the CP particles (ul, 0.67-1.20 cm s-1) not only contributed to high biomass attachment (17.2 mg VSS g-1 CP particles) but also favored nitrifiers (Nitrosomonas, Nitrosospira, Nitrobacter and Nitrospira) enrichment. Additionally, the LSFBBR-CP outperformed the LSFBBR-BC in energy conservation by consuming 41.1–47.4% less energy for fluidization, due to the lower ul. Contrary to BC particles’ attrition regarding to particle size decrease and surface chemicals loss, the CP particles exhibited superiority in physio-chemical stability. Those comparative advantages confirmed that the CP could be a promising alternative for BC as a carrier particle in LSFBBR, suggesting that turning microplastic litter into reusable carrier particle for FBBRs is feasible.

A model for the prediction of thermal resistance of calcium sulfate crystallization fouling in a liquid–solid fluidized bed heat exchanger with cylindrical particles

Calcium sulfate fouling was determined experimentally in a heat exchanger during liquid–solid fluidized bed with cylindrical particles and forced convective (without particles) heat transfer. Then a model to predict the fouling resistance during the solid–liquid fluidized bed heating system was proposed. According to the proposed model and experimental data, a correlation is presented for the prediction of fouling resistances of calcium sulfate during liquid–solid fluidized bed heating at any time. Finally, the prediction of the presented correlation for performed fouling is compared with measured data. Results show that the absolute average percent relative error between experimental data and those obtained by the proposed model vary between 0.6 and 22.8.

Axial acoustic field along a solid-liquid fluidized bed under power ultrasound

This work investigates the ultrasound propagation within a liquid-solid fluidized bed. The acoustic mapping of the reactor is achieved by means of a hydrophone. A spectral analysis is carried out on the measured signals to quantify the cavitation activity. The effects of several parameters on the spectral power distribution is appraised – including emitted ultrasound power, liquid superficial velocity and solid hold-up. Results show that increasing US power promotes a higher energy transfer from the driving frequency toward the broad-band noise – which is the signature of transient cavitation – and yields a stronger acoustic shielding. The presence of a flow opposite to the acoustic streaming may affect the sonoreactor behavior by sweeping the cavitation bubbles away from the ultrasonic horn. Finally the presence of millimeter sized particles significantly increases wave attenuation, presumably due to viscous losses on the one hand, and through the contribution of their surface defects to bubble nucleation on the other hand. Moreover, the influence of the solid hold-up appears to depend upon the particle material (glass or polyamide).