Fluidization Performance Research Articles

Fluidization behavior of stirred gas–solid fluidized beds: A combined X-ray and CFD–DEM–IBM study

Stirred gas–solid fluidized bed reactors are commercially employed in polyolefin manufacturing, but the complex gas–solid contacting dynamics pose challenges in design, scale-up, and operation. In this study, the influence of agitation on the fluidization performance of Geldart B particles was investigated experimentally by X-ray imaging and pressure drop measurements and numerically by Computational Fluid Dynamics (CFD) - Discrete Element Method (DEM) - Immersed Boundary Method (IBM). The experimentally obtained minimum fluidization curve and time-averaged pressure drop show good qualitative agreement with the simulation results. Visual observations underscore that an increase in the angular velocity of the agitator results in reduced bubble size and improved bed homogeneity, as further evidenced by reduced pressure fluctuations. Furthermore, the simulations reveal that while the impeller enhances solids agitation, a proper design study is imperative, considering that static immersed bodies, such as the stirrer shaft, can adversely impact solids motion.

Multi-scale simulation of particle density effects on hydrodynamics in dense gas-solid fluidized beds

Gas-solid fluidization has gained prominence in chemical engineering, particularly for processes involving high-density particles. However, a notable dearth of research on the fundamental fluidization of high-density particles exists, distinct from the well-studied low-density particles. This knowledge gap presents significant challenges in designing and operating fluidized beds for such processes. In this study, we employ the CPFD scheme to comprehensively investigate how particle density affects hydrodynamics. Simulation results consistently align with experiments for pressure drop and minimum fluidization velocity, underscoring the model reliability. Importantly, typical empirical correlations for predicting minimum fluidization velocity display substantial inaccuracies, particularly for high-density particles. Additionally, we identify marked disparities in fundamental fluidization behavior between high and low-density particles, with increasing density leading to deteriorating fluidization performance, characterized by larger bubbles, defluidized regions, gas streaming, and reduced bed expansion ratios. Investigating high-density particle gas-solid fluidization systems promises valuable theoretical insights, bridging the gap between theory and practice.

Machine Learning Aided Numerical and Experimental Investigation of Hydrodynamic Performance in the Circulating Fluidized Bed Boiler

Abstract This study attempts to illustrate the benefits of integrating the concepts of machine learning algorithms with the field of thermo-fluidic applications. The current work is aimed at identifying effective or significant hydrodynamic input parameters, which are capable of deriving full benefit of fluidization that could yield a better circulating fluidized bed (CFB) furnace design using the Apriori algorithm. For this, historical datasets from the literature are collected and pretreated based on the design under observation. Association analysis performed by this Apriori algorithm measures the comparative strength of parameters under consideration. Also, this algorithm is capable of identifying the right combinations of parameters that can produce maximum fluidization performance. The end results suggested by this Apriori algorithm are validated using the computational fluid dynamics package. For this, the transient behavior of a scaled-down (1:20) reactor model of a real-time industrial CFB boiler is simulated using ansys fluent 18.0. In specific, the effects of fluidizing velocities, inventory heights of the bed, and particle sizes recommended by the Apriori algorithm are investigated. Here, the effects are assessed in terms of volume fraction distribution and axial velocity profile distribution profiles. From the results of simulations, it was clearly found that 2 m/s inlet velocity produced good circulating fluidized bed patterns on a bed inventory height of 0.5 m for a mean particle size of 200 µm. The results obtained from the simulations are once again validated visually against snapshots obtained during real-time laboratory fluidization experimental runs. Among all the cases of comparisons, the best agreement is demonstrated by Apriori algorithm compared to the numerical and the experimentally obtained results. Also, it is found that the manual time taken to identify the right combinations of parameters is drastically reduced by this method compared to conventional optimization algorithm and trial error methods.

Comparative analysis of particle density effects on initial fluidization in gas-solid fluidized beds

Gas-solids fluidization technology is commonly used in chemical engineering processes involving high-density particles, often encountering poor defluidization phenomena. However, there is limited research examining the applicability of flow characteristics and empirical correlations established for low-density, easily fluidizable particles in guiding the flow behavior of high-density particles. This knowledge gap poses significant challenges for designing and operating fluidized beds in relevant processes involving high-density particles. This study comprehensively evaluates the effect of particle density on hydrodynamics during the initial fluidization stage using experimental, empirical correlations and simulation methods. Results of preliminary experiments indicate that empirical correlations for predicting Umf may exhibit significant errors of high-density particles. However, the experiments face challenges in eliminating the influence of different particle size distribution. In contrast, the simulation results present a high consistency with the experiments after sensitivity analysis. Further simulation results illustrate that empirical correlations for Umf may only yield relatively accurate predictions within the narrow density range. As the particle density increases, the predicted errors tend to increase. During the initial fluidization stage, three distinct fluidization stages can be observed, as revealed by both experiments and simulations. These stages can be attributed to the practical particle size distribution. Furthermore, it is noted that as the particle density increases, the fluidization performance tends to deteriorate. This study endeavors to advance the understanding of the effect of particle density on hydrodynamics during the initial fluidization stage. Nonetheless, more studies are still needed to enhance and deepen the current knowledge of the fluidization of high-density particles.

CFD-DEM study of impacts of the porous distributor medium on fluidization characteristics of a 2D-fluidized bed

Gas–solid bubbling fluidized beds are widely used in chemical, energy, construction, and other industrial fields due to their excellent fluidization performance. 2D-fluidized beds with planar rectangular columns of finite thickness are widely used in fluidized bed studies, and it is essential for understanding the hydrodynamics of gas-particle systems. Moreover, the distributor (porous medium) at the bottom of the bed has a crucial influence on the fluidization performance of the 2D-fluidized bed. In this work, the fluidization mechanism and gas–solid dynamic characteristics of the fluidized bed under three porous media are studied by CFD–DEM coupled with the porous medium model, and the accuracy of numerical simulation is verified by a high-speed photography experiment. Results show that with the increase in the flow resistance of the porous medium, the average and standard deviation of the bubble diameter decrease, and the time and position of particles in the dead zone to participate in the core–annular flow advance. At a low fluidization velocity, the dead zone in the bed can be considerably reduced by increasing the flow resistance.

The novel SiO2-decorated highly robust waste-derived activated carbon with homogeneous fluidity for the CO2 capture process

Biomass-derived activated carbon (AC) is considered auspicious for alleviating various environmental pollutants. We reported the usage of a developed biomass-based AC as a potential adsorbent for CO2 uptake applications to overcome global warming. In this paper, AC was successfully synthesized from a highly-used fruit in the middle east, date seeds, and chemically activated by KOH to boost CO2 uptake activity. The fluidization behavior was tested and improved through a dry-mixing route with fluidizable nanopowder. To assess the impact of utilizing the chemical activator and easily-fluidizable compound, CO2 capture efficiency and fluidity of the raw and promoted adsorbent were evaluated and compared with commercial and other date-derived ACs. The original and modified ACs were characterized via SEM, EDS, BET, FTIR, and TG analysis; the KOH-promoted AC possessed a more fluffy-like configuration and a higher surface area of about 595.94 m2/g. Based on the TG analyses, 94% and 67% higher average CO2 capture capacity was recorded for KOH-promoted ACs compared to the original and commercial adsorbents. The KOH-promoted ACs and SiO2-covered counterparts fluidization's performance was assessed under 15 vol% CO2 balanced with N2 gas. Fluidization experiments proved the positive effect of employing hydrophobic silica nanoparticles (NPs) to develop the fluidity of the synthesized activated carbon. After mixing with 2.5 wt% SiO2 NPs, the SiO2-decorated modified ACs presented a 45% higher bed expansion ratio associated with a homogeneous and bubbleless fluidized regime.

Effects of injection angle and injector mode variation on the fluidization performance of a powder-fueled ramjet

Fluidization is a major problem in the supply system of a powder-fueled ramjet. The performance of fluidization mainly depends on the injection way of fluidizing gas. This paper has investigated the effects of variation of the injection angles and injector modes on the performance of fluidization, using the Euler-Lagrange approach for gas-particle flow. The injection angle varies among 30°, 45°, 60° and 90°, the injector mode includes single injector and dual injectors. We conclude that due to higher mixing quality and particle mass flow rate, the system performs better for both single-injector and dual-injector modes at an angle of 45°. Based on the analysis in the fluidization domain and external flow field, we observe that the dual-injector mode performs significantly better than the single-injector mode.

Gas flow influences on bubbling and flow characteristics of fluidized bed with immersed tube under electrostatic effects

Industrial bubbling fluidized beds are used to fluidize particles. When particles are fluidized, electrostatic effects will cause the particles to form obvious agglomerates, thus reducing fluidization performance. For better fluidization performance, internal component immersed tubes are usually placed in fluidized bed to limit the bubble size and reduce particle agglomerates. Meanwhile, pulsed gas flow can increase particle disturbance, which is also an effective method to reduce particle agglomerates. In this paper, the CFD-DEM model under electrostatic effects is constructed to research the bubbling and flow characteristics in fluidized beds. Firstly, particle mixing qualities with and without the immersed tube are compared. Then, the effects of different superficial gas velocities are investigated with an immersed tube. Finally, different frequencies are applied to study the energy loss and flow characteristics around the immersed tube. The results show that the addition of the immersed tube can reduce bubble size to facilitate particle mixing. Due to the obstruction of the immersed tube, the bubbles are generated near the wall. As the superficial gas velocity increases, the larger bubbles are generated. Moreover, the electrostatic force applied to the particles varies periodically with the frequency of incoming pulsed gas flow, with fluctuations maximal at 2.5 Hz.

Investigation into the hydrodynamics of liquid-solid inclined micro-fluidized beds

The inclined micro-fluidized bed (MFB) can enhance heat and mass transfer rates compared to the vertically aligned counterparts, but the increased significance of surface forces and wall effects may cause poor fluidization performance. In this paper, the effects of column inclination and different particle-to-bed ratios (dP/dB) on the solid hydrodynamics are investigated in an inclined micro-fluidized bed. The results validated the suitability of using the Ergun equation to predict minimum fluidization velocities due to small deviations between 1.01 and 1.81 times the theoretical values, for a particle-to-bed ratio ranging from 0.025 to 0.165 at inclinations between 0° and 10°. Investigation into the effects on bed expansion behavior showed that the bed contracted with an increase in bed inclination. An unexpected observation during the bed expansion was the appearance of a secondary high voidage region and the appearance of strong circulation patterns with an increase in bed inclination. A detailed analysis of this phenomenon suggested the presence of a critical angle at 6° and 10° for the 85 µm particles, 4 × 4 mm bed cross-section and 165 µm particles, 1 × 1 mm bed cross-section, respectively. However, the liquid-solid back-mixing was observed due to the modified particle trajectories resulted in the disappearance of the high voidage region. This paper gives new insights into the micro-fluidization behavior in inclined beds thus contributing to the development of micro-fluidized beds and their future applications.

Evaluation of hydromechanical and functional properties of diversion-type microcapsule-suspension bioreactor for bioartificial liver.

To evaluate the performance of a diversion-type microcapsulesuspension fluidized bed bioreactor and a choanoid fluidized bed bioreactor as bioartificial liver support systems. We evaluated the performance between the modified fluidized bed bioreactor based on diversion-type microcapsule suspension (DMFBB) and choanoid fluidized bed bioreactor (CFBB). The fluidization performance, fluidized height, bed expansion, and the mechanical stability and strength of microcapsule were determined. The viability, synthetic, metabolism, and apoptosis of microcapsulated HepLi5 cells were evaluated. Finally, samples were collected for measurement of alanine aminotransferase, total bilirubin, direct bilirubin, and albumin concentrations. Uniform fluidization was established in both DMFBB and CFBB. The bed expansion, shear force, retention rate, swelling rate, and breakage rate of microcapsules differed significantly between two bioreactors over 3 days. The viability of microencapsulated HepLi5 cells and the activities of cytochrome P450 1A2 and 3A4 increased on each day in DMFBB compared to the control. The albumin and urea concentrations in the DMFBB displayed obvious improvements compared to the control. Caspase3/7 activities in the DMFBB decreased compared to those in the CFBB. At 24 h, the alanine aminotransferase concentration in the DMFBB declined significantly compared to the control. The total and direct bilirubin concentrations within plasma perfusion were decreased and albumin was increased in the DMFBB at 24 h than in the CFBB. The DMFBB shows a promising alternative bioreactor for use in bioartificial liver support systems for application of clinical practice.

Optimization of the Internal Circulating Fluidized Bed Using Computational Fluid Dynamics Technology

The computational fluid dynamics (CFD) technology is analyzed and calculated utilizing the turbulence model and multiphase flow model to explore the performance of internal circulating fluidized beds (ICFB) based on CFD. The three-dimensional simulation method can study the hydrodynamic properties of the ICFB, and the performance of the fluidized bed is optimized. The fluidization performance of the ICFB is improved through the experimental study of the cross-shaped baffle. Then, through the cross-shaped baffle and funnel-shaped baffle placement, the fluidized bed reaches a coupled optimization. The results show that CFD simulation technology can effectively improve the mass transfer efficiency and performance of sewage treatment. The base gap cross-shaped baffle can improve the hydraulic conditions of the fluidized bed and reduce the system energy consumption. The cross-shaped baffle and funnel-shaped baffle can perfect the performance of the reactor and effectively strengthen the treatment in the intense aerobic process of industrial sewage.

Three-dimensional simulation of coal catalytic hydrogasification in a pressurized bubbling fluidized bed

Coal catalytic hydrogasification (CCHG) is an efficient approach to produce CH4 with high yield and high thermal efficiency. A numerical modelling of CCHG in a pressurized bubbling fluidized bed has been conducted to track the whole reaction process by using the multiphase particle-in-cell (MP-PIC) algorithm during the residence time of particles. The gas–solid flow dynamic properties, such as bubble size and bed expansion height, were validated against with empirical correlations. After incorporating the CCHG kinetics with MP-PIC, the simulated bed temperature, gaseous compositions, and CH4 formation behavior were verified with the experimental data. The trajectory and physiochemical properties of char particles (particle diameter, temperature, heat transfer coefficient and drag function) during the whole residence time were explored comprehensively. The results showed that a high temperature region appeared in the dense bed located 20–30 mm above the plate distributor initially, which led to the profound fluidization performance and reactivity of char particles with diameter range of 138–249 μm. With the CCHG proceeding, particle diameter decreased gradually, while the heat transfer coefficient and drag force were strengthened. A uniform bed temperature was generated afterwards resulted by the enhanced gas-particle heat transfer. Whereas, when the particle diameter decreased to less than 46 μm, char particles were blown out of the dense bed, resulting in the low reactivity and difficulty of separation for the practical application. The numerical results in this work shed light on further scaling up and design of pressurized fluidized bed for coal catalytic hydrogasification.

CFD-DEM investigation into flow characteristics in mixed pulsed fluidized bed under electrostatic effects

Static electricity has an important effect on gas–solid fluidized bed reactor fluidization performance. In the process of fluidization, electrostatic interaction between particles will obviously accelerate particle agglomerate formation, which consequently reduces the fluidization performance. Pulsed gas flow injection is an efficient method to enhance particle mixing, thereby weakening the occurrence of particle agglomerate. In this study, the two-dimensional hybrid pulsed fluidized bed is established. The flow characteristics are studied by using the coupled CFD-DEM numerical simulation model considering electrostatic effects. Influences of different pulsed frequencies and gas flow ratios on fluidized bed fluidization performance are investigated to obtain the optimal pulsed gas flow condition. Results show that in the presence of static electricity, the bubble generation position is lower, which is conducive to the particle flow. Pulsed gas flow can increase the particle velocity and improve the diffusion ability. The bubble generation time is different at different frequencies, and the frequency of 2.5 Hz has the most obvious effect on the flow characteristics. Different gas flow ratios have significant impacts on the particle movement amplitude. When the pulse gas flow accounts for a large ratio, the particle agglomerate tends to be larger. Therefore, in order to improve the fluidization effect, the ratio of pulsed gas flow to stable gas flow should be appropriately reduced to 0.5 or less.

Parameter affecting of slurry flow in perforated pipe on fluidization method to maintenance of channel

Slurry flow in pipes is one of the techniques in developing the method of fluidization, especially in the work of sand by passing for the maintenance of estuary channel, port channel, and others. The slurry flow in the pipe determines the fluidization performance, therefore many researchers have studied the slurry flow system in various approaches. This analysis focuses on the factors that influence the flow of slurry in the perforated pipe based on literature studies. The results of the study indicate that several factors are grouped into main parameters such as pipeline parameters, liquid parameters, solid particle parameters and system parameters. All parameters are concluded through the approach of dimensionless numbers such as Reynold Numbers, Froude numbers, concentration, ratio of settling particle to pipe diameter, ratio of hydraulic gradient to mean flow velocity. These parameters have an effect on head loss, friction, drag reduction which controls the flow of slurry in the pipe media. In addition, the constant pressure distribution is a factor that affects the discharge in the slurry flow in the perforated pipe.

Fluidization of fungal pellets in a 3D-printed micro-fluidized bed

Micro-fluidized bed (MFB) can be used as a fast screening tool for preliminary testing of engineering designs, but the applications of MFB for bioprocessing research such as microorganism cultivation is still deficient. This paper reports the unique fluidization performance of fungal pellets in a 3D-printed micro-fluidized bed, thus giving insights to the hydrodynamic study of pellets and broadening the potential of MFB in the bioprocessing and bioproduction fields. The results indicated that the static bed voidage were substantially larger (around 0.6) than the conventionally used value of 0.4. The observed decrease in packed bed voidage with increasing pellet mass was attributed to the increased compaction of pellets. A novel extended bed regime was observed prior to partially and fully fluidized bed regimes for liquid-solid fluidization. Due to the wall effect and surface forces, higher values of the minimum fluidization velocity and Richardson-Zaki empirical constants (n and K) were determined. In liquid-solid-gas fluidization system, fluidization regimes including packed-bed regime, fluidization regime and elutriation regimes were mapped. The effects on gas flow and pellet weight on fluidization performance were also investigated. It was noticed that pellets were fully fluidized at low biomass weight (i.e. 0.5 g) but the increase of pellet mass led to partially fluidization where the packed bed height increased with increasing pellet mass but decreased with increasing gas flowrate. Pellet fluidization velocity including axial velocity and radial velocity were measured by PIVlab analysis. The results indicated that pellet axial velocity was mainly affected by vertical gas flow while radial velocity was dominated by vortexes and surface forces.

Numerical study of hydrodynamic characteristics in a moving bed biofilm reactor

The moving bed biofilm reactor (MBBR) has certain advantages, such as high wastewater treatment efficiency, low maintenance and operating costs, and simple operation. It has emerged as a valuable option for small decentralized facilities. The filling ratio, aeration mode and aeration intensity are the main factors that affect the performance of MBBRs in wastewater treatment. However, the information that concerns the used criteria that pertain to the process design for the MBBR is not adequate. In this study, a three dimensional computational fluid dynamics (CFD) model was constructed and the maximum error was only 1.98%, which was much smaller than the traditional 2D-CFD model. The filling ratio, aeration mode and aeration intensity of MBBR were optimized by CFD model from the point of view of fluid mechanics. The results show that the fluidization performance of the filling is the best under the one-side aeration mode with 30% filling ratio. The cost-performance ratio of the reactor with 30% filling ratio was 1.53, 25% and 35% filling ratio were only 1.17 and 1.14 respectively. Increasing the aeration intensity could improve the fluidization performance. However, the effect of high aeration intensity on the fluidization performance of the carrier was limited and the energy consumption increased greatly. The results revealed that when the aeration intensity increased from 0.07 min−1 to 0.13 min−1, the proportion of the carrier area increased by 16.56%. The proportion of the carrier area with an aeration rate of 0.20 min−1 was only 4.23%, which is higher than 0.13 min−1. The main factors that control the fluidization of the carrier were the range of the flow zone and the flow velocity of the liquid. Increasing the range of the flow zone could facilitate the flow of the carriers. The critical value of the flow velocity of the liquid in the flow zone was 0.04 m/s. These results could guide the optimization design of the filling ratio and the aeration conditions and provide a theoretical basis for the application of MBBR.

Experimental and numerical investigations on the hydrodynamics of gas-solid fluidized bed with an inclined agitator

The effect of inclined agitation on the fluidization quality of a gas-solid fluidized bed is experimentally and numerically investigated. The pressure characteristics are characterized by the standard deviation of pressure drop and power spectra. The particle velocity, solid volume fraction and granular temperature distributions are investigated by numerical modeling. It is found that inclined agitation enhances the gross circulation of solid particles and enlarges the affect region of the agitator, improving the gas-solid fluidization quality. The increase in the agitation speed leads to higher frequency of collisions and more activity of particles, resulting in decreases of bubble sizes and a more homogeneous solid volume fraction distribution. Wide-blade agitator can also improve the fluidization performance.

CO2 capture and fluidity performance of CaO-based sorbents: Effect of Zr, Al and Ce additives in tri-, bi- and mono-metallic configurations

The Calcium-looping (CaL) technology is based on the reversible carbonation reaction of CaO with CO2 and has been developing rapidly as a potential low cost process for post-combustion CO2 capture. One of the main challenges of CaL process, is the identification of CaO-based sorbents that can maintain their activity in multiple cycles and have proper fluidization. The present study focusses on the influence of Zr, Al and Ce additives in mono-, bi- (Zr/Ce, Zr/Al and Al/Ce) and tri-metallic (Zr/Al/Ce) configurations on the performance of synthetic CaO-based sorbents. The developed sorbents presented a substantially improved performance over multiple cycles compared to limestone-derived CaO, due to the formation of stable, mixed Ca-inert phases. Incorporation of Al, Al/Ce and Zr/Al/Ce in CaO structure led to the development of sorbents with small crystallites and porous morphology, resulting in improved stability with less than 25 % deactivation after 50 cycles. The enhanced stability of the Zr/Al/Ce-promoted sorbent was attributed to the formation of CaZrO3 and Ca3Al2O6 mixed phases in the CaO matrix, providing a porous and stable structure. The fluidizability of the most promising sorbents was also investigated. SiO2 nanoparticles were mechanically mixed with the sorbents in different fractions to improve their fluidization performance. A minimum amount of 15 wt% SiO2 was required in order to achieve a completely smooth and homogeneous fluidization without gas channeling, bubbles or even fine agglomerates. The highest bed expansion, accompanied by a high Richardson-Zaki index n (5.9) and low Umf (2.2 cm/s) were obtained with a Ca/Zr/Al/Ce +15 wt% SiO2.

Intensification of the fluidization performances of polypropylene by using microwave absorbent

Fluidization is an effective method to better help the transfer and conversion of fuel particles. In this study, intensification of the fluidization performances of polypropylene was experimentally investigated by using microwave absorbent. The fluidization performances of polypropylene (PP) were initially presented and the effects of microwave absorbent (SiC) particle size, mass ratio of SiC to PP, and fluidization velocity on the co-fluidization performances were studied and presented. The results showed that the PP load significantly increased the initial bed height whereas slightly increased the critical fluidization velocity and bed expansion ratio. Adding microwave absorbent (SiC) can effectively improve the fluidization performance of PP particles. The smaller SiC particles (0.25−1 mm) had better fluidization performances than the larger ones (1–1.5 mm and 1.5−2 mm). The mass ratio of silicon carbide to polypropylene decreased the critical fluidization velocity. Fluidization velocity significantly affected the co-fluidization performance. For the co-fluidization of polypropylene and silicon carbide in the designed fluidized bed, the recommended fluidization parameters were: (a) the particle size of silicon carbide of 0.25–1 mm, (b) the mass ratio of silicon carbide to polypropylene of 3:2, and (c) the fluidization velocity of 0.66 m/s.

Effects of liquid content and surface tension on fluidization characteristics in a liquid-containing gas–solid fluidized bed: A CFD–DEM study

The fluidization process within gas–solid fluidized bed reactor can be intensified by adding liquid, as it can enhance mass and heat transfer between gas phase and solid phase. With the help of computational fluid dynamics(CFD) and discrete element methods(DEM), fluidization characteristics are investigated at different liquid contents(V^) and surface tension(Bog). To be specific, the bed expansion ratio, particle concentration and particle velocity profiles are compared and analyzed. Numerical simulations show that Bog should be less than 5 at V^ = 0.013. At this recommended range, liquid addition makes interparticle force increase and has little effect on fluidization performance. From transient particle agglomeration behavior, the Bog increase is more likely to enhance interparticle force, resulting in obvious particle agglomerations during fluidization process. The variation of stagnation zone height can be reflected from the abrupt increase of particle velocity in annulus region. It can be found that V^ increase reduces particle velocity at critical height but Bog increase is more likely to cause larger stagnation region. By analyzing the distribution of spout, annulus and fountain regions at different V^ and Bog, the annulus region expands with V^ increase below the initial bed height while the spout region expands with Bog increase.