Increase In Superficial Gas Velocity Research Articles

Column flotation hydrodynamics operating in the heterogeneous regime estimated by electrical resistance tomography and multi-phase CFD model

ABSTRACT This paper investigates the two-phase flow hydrodynamics of a column flotation operated from a homogeneous to a heterogeneous flow regimes using experimental and computational fluid dynamics (CFD) techniques. Experiments were conducted in a lab scale column flotation of 0.1 m internal diameter and 2.5 m length at various superficial gas velocities using a dual plane electrical resistance tomography (ERT). The mean gas holdup increased from 2 to 18% with the increase in superficial gas velocity from 0.6 to 7.2 cm/s. The gas holdup-based bubble swarm velocity method identified four distinct flow regimes, i.e. homogeneous bubbling regime, narrow discrete bubbling regime, a sustained helical flow regime and churn turbulent flow regime in the column. Further, transient simulations were conducted using a two-fluid model coupled with a population balance model to assess the flow behavior inside the column. Virtual mass, lift and drag forces were incorporated into the model to account for the interphase forces. Numerical simulations predicted mean gas holdup was matching with the experimental data at low gas velocities (<2.4 cm/s), and a marginal deviation was noted at higher gas velocities (>2.4 cm/s). The predicted radial gas holdup profiles were found to change from flatter to parabolic with the increase in gas velocities, i.e. similar to the experiments. The effect of particle size on the rate constant and recovery was estimated with Luttrell and Yoon’s performance model using the particle floatability input data and the two-phase experimental data. The developed CFD model can be useful to optimize the operating and design parameters for efficient operation of the column flotation process.

Effects of temperature on gas-solid bubbling fluidization with Geldart A particles characterized by electrical capacitance tomography and pressure drop measurements

The fluidization with Geldart A particles could be usually operated at high temperature which can significantly influence the fluidization behaviors. This paper describes the impacts of temperature on the fluidization of Geldart A particles using electrical capacitance tomography (ECT) and pressure drop measurements. Alumina particles, classified as Geldart A particles, are studied in a fluidized bed across a temperature range of 20 °C to 600 °C. As the superficial gas velocity increases, the minimum fluidization velocity and the minimum bubbling velocity are observed based on the change of solid fraction and pressure drop at high temperatures. As temperature increases, both the minimum fluidization velocity and minimum bubbling velocity decrease, and the solid fraction decreases. The trend agrees well with empirical correlations which consider the change of gas density and viscosity with temperature. Specifically, the increase in temperature leads to a higher gas viscosity, which enhances the hydrodynamic forces and significantly influences the fluidization behaviors. The broad agreement between ECT and pressure drop measurements suggests that ECT can be applied for the characterization of fluidization behaviors at high temperatures.

Dynamics of inclined simply supported piping system subjected to slug flow

In this paper, the linear and nonlinear dynamics of a simply supported inclined piping system conveying slug flow are investigated, by using a dimensionless approach. A method is proposed for constructing equivalent flow parameters in order to achieve a dimensionless model equation. The validity of this method has been verified through the literature data. The effects of superficial velocities and inclined angle on the stability of the system, as well as post-instability nonlinear dynamical behaviors, are investigated. The linear analysis results showed that the superficial gas velocity stabilized the system at lower values, but had a destabilizing effect at higher values. The main reason is the reduction in system mass resulting from the increase in superficial gas velocity. The superficial liquid velocity negatively impacted the system's stability, necessitating evaluation through the critical pipe length. The nonlinear analysis results showed that the inclined system, in the absence of modal coupling occurrence, may exhibit chaotic behavior due to its inherent nonlinearity. The system stability could be regained as the superficial gas velocity increased following self-weight instability under low superficial gas velocity conditions. This work is helpful for the design of operating parameters to ensure the safety of the piping system.

A CFD study on the start-up hydrodynamics of fluid catalytic cracking regenerator integrated with chemical looping combustion

ABSTRACT The integration of chemical looping combustion with fluid catalytic cracking (CLC-FCC) is an innovative concept that serves as a cost-effective method for CO2 capture in refineries. This approach has the potential to reduce refinery CO2 emissions by 25–35%, offering a promising solution. As in the conventional FCC unit, it is common for CLC-FCC regenerators to be exposed to an on-off process while they are being maintained and cleaned. The novelty of this research lies in its specific focus on a less-explored phase (start-up) of CLC-FCC regenerators, the application of advanced CFD modeling, and the comprehensive analysis of operational parameters that influence the system’s performance. To validate the CFD simulations of the different drag models for solid-gas granular, bed density profiles under steady-state conditions, collected from industrial processes, were used. For the flow period based on the start-up process of the drag models, the fluidization gas inlet geometry of the regenerator, flow regime (laminar and turbulent), and superficial gas velocity were comprehensively investigated to reveal their effects on hydrodynamic characteristics. The results show that Gidaspow and Syamlal-O’Brien drag models of the solid-gas multiphase granular flow exhibited a better fit with industrial data. The Syamlal-O’Brien and Gidaspow models closely align with industrial data under steady-state conditions, displaying similar bed densities in the dense phase region (230–310 kg/m3 for Syamlal-O’Brien and 235–300 kg/m3 for Gidaspow). During the initial stage (less than 0.2 seconds), both laminar and turbulent models yield comparable bed density profiles, approximately 510 kg/m3 in the dense phase. However, as the process progresses, the dense phase density decreases to about 250–350 kg/m3 at around 0.5 seconds, with laminar flow models showing a slightly better fit with industrial data. Notably, at 0.5 seconds of fluidization time, inlet geometries having better gas distribution achieve a highly diluted phase with bed densities of 10–20 kg/m3. Reaching a steady state, the bed density decreases from around 400 kg/m3 to 260–300 kg/m3, expanding into a higher section of the regenerator where it aligns well with industrial data. The increase in superficial gas velocity would result in the clarification of the difference and well mixing of the solid-gas multiphase flow.

CFD-DEM investigation of flow and heat transfer characteristics in a directly irradiated fluidized bed

The directly irradiated fluidized bed reactor has gained widespread attention due to its strong heat and mass transfer performance. However, there is still a lack of in-depth understanding of the gas–solid flow characteristics, heat transfer mechanisms, and flow pattern evolution in the fluidized bed. To address this, the computational fluid dynamics-discrete element method (CFD-DEM) was employed in this study to investigate the correlation between the flow pattern and the heat transfer path. The simulation results show that increasing the superficial gas velocity from the minimum fluidization velocity (umf) to 1.4umf induces a circulation pattern that significantly reduces the overheating phenomenon, resulting in a 40.52% decrease in the maximum particle temperature and a 74.59% decrease in the temperature standard deviation. The particle temperature increases in the top heat-collecting region, followed by thermal conduction and convection transferring the energy to low-temperature particles and fluid in the near-wall and bottom regions. As the superficial gas velocity increases, the proportion and frequency of particles entering the heat-collecting region increase, resulting in a more uniform temperature distribution within the bed. Taking into account factors such as heat transfer characteristics and fluidization energy consumption, a fluidization velocity of 1.6umf is recommended as the optimum operating condition for particles in this work, as it ensures a uniform temperature distribution within the bed and minimizes convective and radiative losses.

Bubble dynamics properties of B-particles in a quasi-2D gas-solid fluidized bed: Computational particle fluid dynamics numerical simulation and post-processed by digital image analysis technique

Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds. In this study, the bubble dynamics properties of four B-particles were investigated in a quasi-two-dimensional (quasi-2D) fluidized bed, including bubble equivalent diameter, bubble size distribution, average bubble density, bubble aspect ratio, bubble hold-up, bed expansion ratio, bubble radial position, and bubble velocity. The studies were performed by computational particle fluid dynamics (CPFD) numerical simulation and post-processed with digital image analysis (DIA) technique, at superficial gas velocities ranging from 2umf to 7umf. The simulated results shown that the CPFD simulation combining with DIA technique post-processing could be used as a reliable method for simulating bubble dynamics properties in quasi-2D gas-solid fluidized beds. However, it seemed not desirable for the simulation of bubble motion near the air distributor at higher superficial gas velocity from the simulated average bubble density distribution. The superficial gas velocity significantly affected the bubble equivalent diameter and evolution, while it had little influence on bubble size distribution and bubble aspect ratio distribution for the same particles. Both time-averaged bubble hold-up and bed expansion ratio increased with the increase of superficial gas velocity. Two core-annular flow structures could be found in the fluidized bed for all cases. The average bubble rising velocity increased with the increasing bubble equivalent diameter. For bubble lateral movement, the smaller bubbles might be more susceptible, and superficial gas velocity had a little influence on the absolute lateral velocity of bubbles. The simulated results presented a valuable and novel approach for studying bubble dynamics properties. The comprehensive understanding of bubble dynamics behaviors in quasi-2D gas-solid fluidized beds would provide support in the design, operation, and optimization of gas-solid fluidized bed reactors.

Experimental investigation on the effect of superficial gas velocity on bubble dynamics properties of B particles in gas–solid fluidized bed reactor using digital image analysis technique

The bubble dynamics properties in gas–solid particle system play a crucial role in the design and optimization of gas–solid fluidized beds, and are significantly influenced by superficial gas velocity. In present study, the effect of superficial gas velocity on bubble dynamics properties in a classical B particle system were investigated at gas velocity ranging from (0.41 to 0.59) m·s−1 with umf = 0.067 m·s−1 in a quasi-two dimensional (quasi-2D) fluidized bed domain, including bubble equivalent diameter, bubble size distribution, bubble density, aspect ratio, bubble hold-up, bed expansion ratio, bubble rising and lateral velocity. Those were derived from the taken image by digital image analysis (DIA) technique. The results show that superficial gas velocity has a significant effect on the bubble equivalent diameter, while it has little effect on bubble size distribution (BSD), average bubble density distribution and bubble aspect ratio distribution for the same particle system. Both time-averaged bed expansion ratio and bubble hold-up increase with the increase of superficial gas velocity under the range of gas velocity in this work. Two uniform core-annular flows form in the bed for all cases. The bubble rising velocity coefficients of developed correlation range from 0.69 to 1.00. For bubble lateral movement, smaller bubbles may be more susceptible, and superficial gas velocity has a little influence on the absolute lateral velocity of bubbles. Overall understanding the effect of gas velocity on bubbles dynamics properties is good for the design and optimization of fluidized bed reactors, leading to the better process outcomes and performance.

Gas holdup, bubble size distribution, and mass transfer in an airlift reactor with ceramic membrane and perforated plate distributor

AbstractThe airlift reactor is one of the most commonly used gas–liquid two‐phase reactors in chemical and biological processes. The objective of this study is to generate different‐sized bubbles in an internal loop airlift reactor and characterize the behaviours of the bubbly flows. The bubble size, gas holdup, liquid circulation velocity, and the volumetric mass transfer coefficient of gas–liquid two‐phase co‐current flow in an internal loop airlift reactor equipped with a ceramic membrane module (CMM) and a perforated‐plate distributor (PPD) are measured. Experimental results show that CMM can generate small bubbles with Sauter mean diameter d32 less than 2.5 mm. As the liquid inlet velocity increases, the bubble size decreases and the gas holdup increases. In contrast, PPD can generate large bubbles with 4 mm &lt; d32 &lt; 10 mm. The bubble size and liquid circulation velocity increase as the superficial gas velocity increases. Multiscale bubbles with 0.5 mm &lt; d32 &lt; 10 mm can be generated by the CMM and PPD together. The volumetric mass transfer coefficient kLa of the multiscale bubbles is 0.033–0.062 s−1, while that of small bubbles is 0.011–0.057 s−1. Under the same flow rate of oxygen, the kLa of the multiscale bubbles increases by up to 160% in comparison to that of the small bubbles. Finally, empirical correlations for kLa are obtained.

Performance of bubble column for iodine removal in a lab scale setup of filtered containment venting system

Iodine is one of the most hazardous fission products that can get released into environment after a severe nuclear accident and can cause thyroid cancer. Removal of iodine is necessary to ensure safety of people and environment. Different experiments were performed in a lab scale setup of FCVS containing a bubble column. Purpose of this research was to understand the mechanism involved in wet scrubbing in order to improve the removal efficiency of iodine. Influence of many parameters such as gas flowrate, liquid level height, gas holdup, additives, bubble diameter etc. on retention of iodine was studied. Results showed major dependance of decontamination factor on gas flowrate and liquid level height. Bubble diameter was observed to be dependent on gas flowrate, viscosity of liquid and density of liquid and gas. Decrease in bubble diameter was observed with increase in superficial gas velocity which enhanced overall mass transfer and hence, removal efficiency was increased as well. Overall, greater than 99.9% removal efficiency was achieved.

Investigation on two-phase flow-induced vibrations of a piping structure with an elbow

The dynamic behaviors of a horizontal piping structure with an elbow due to the two-phase flow excitation are experimentally investigated. The effects of flow patterns and superficial velocities on the pressure pulsations and vibration responses are evaluated in detail. A strong partition coupling algorithm is used to calculate the flow-induced vibration (FIV) responses of the pipe, and the theoretical values agree well with the experimental results. It is found that the lateral and axial vibration responses of the bend pipe are related to the momentum flux of the two-phase flow, and the vibration amplitudes of the pipe increase with an increase in the liquid mass flux. The vertical vibration responses are strongly affected by the flow pattern, and the maximum response occurs in the transition region from the slug flow to the bubbly flow. Moreover, the standard deviation (STD) amplitudes of the pipe vibration in three directions increase with an increase in the gas flux for both the slug and bubbly flows. The blockage of liquid slugs at the elbow section is found to strengthen the vibration amplitude of the bend pipe, and the water-blocking phenomenon disappears as the superficial gas velocity increases.

Image Processing and Measurement of the Bubble Properties in a Bubbling Fluidized Bed Reactor

The efficiency of a fluidized bed reactor depends on the bed fluid dynamic behavior, which is significantly influenced by the bubble properties. This work investigates the bubble properties of a bubbling fluidized bed reactor using computational particle fluid dynamic (CPFD) simulations and electrical capacitance tomography (ECT) measurements. The two-dimensional images (along the reactor horizontal and vertical planes) of the fluidized bed are obtained from the CPFD simulations at different operating conditions. The CPFD model was developed in a commercial CPFD software Barracuda Virtual Reactor 20.0.1. The bubble behavior and bed fluidization behavior are characterized form the bubble properties: average bubble diameter, bubble rise velocity, and bubble frequency. The bubble properties were determined by processing the extracted images with script developed in MATLAB. The CPFD simulation results are compared with experimental data (obtained from the ECT sensors) and correlations in the literature. The results from the CPFD model and experimental measurement depicted that the average bubble diameter increased with an increase in superficial gas velocities up to 4.2 Umf and decreased with a further increase in gas velocities due to the onset of large bubbles (potential slugging regime). The bubble rise velocity increased as it moved from the lower region to the bed surface. The Fourier transform of the transient solid volume fraction illustrated that multiple bubbles pass the plane with varying amplitude and frequency in the range of 1–6 Hz. Further, the bubble frequency increased with an increase in superficial gas velocity up to 2.5Umf and decreased with a further increase in gas velocity. The CPFD model and method employed in this work can be useful for studying the influence of bubble properties on conversion efficiency of a gasification reactor operating at high temperatures.

Migration and diffusion of unsteady-state flow of volatile organic compounds on activated carbon adsorption beds under reverse ventilation

Despite increasing attention to the influence of unsteady-state volatile organic compounds (VOCs) on the adsorption of activated carbon, studies in this regard are rare. Therefore, in this study, an investigation into the migration and diffusion of unsteady-state VOCs on activated carbon adsorption beds under reverse ventilation was conducted. Here, reverse clean air was introduced when the activated carbon bed reached the penetration point. The influence of reverse ventilation temperature, reverse superficial gas velocity, activated carbon filling height, and different ventilation modes on the adsorption of unsteady toluene by activated carbon were studied. Our experimental results show that when the reverse ventilation temperature increased from 20 °C to 60 °C, the quasi-first-order desorption rate constant increased from 0.00356 min−1 to 0.00807 min−1, an increase in the reverse superficial gas velocity led to a higher rate constant, and at greater reverse superficial gas velocities, the stripping capacity increased. It was observed that the maximum stripping capacity was achieved at a reverse superficial gas velocity of 0.3 m/s. For different activated carbon filling heights, following reverse ventilation, the stripping capacity of a 5 cm and 30 cm activated carbon bed accounted for 41.43% and 65.85% of the original adsorption capacity, respectively. The study concludes that concentration of toluene first increased and then decreased with time under forward ventilation, whereas the concentration gradually decreased under reverse ventilation.

Investigation of flow behaviors in a fluidized bed reactor with binary mixture of Geldart-A and B particles

Flow dynamics in bubbling and turbulent fluidized beds containing both Geldart-A and B particles were investigated in this research. The numerical model was validated against experimental data, with a 6.16% average deviation. Results show that binary mixture segregation is enhanced as superficial gas velocity decreases. A larger flotsam packing ratio promotes homogeneous flotsam distribution; Second, bed density decreases with increasing bed height or superficial gas velocity. As the flotsam packing ratio decreases from 81.10 to 10.70%, bed density reaches the maximum at 41.50%, indicating the most severe volume contraction; Third, when the flotsam packing ratio decreases, the local mixing index's variances between upper and lower sections in dense phase first increases, then decreases, with stronger radial fluctuation detected; Fourth, as superficial gas velocity or flotsam packing ratio increases, the full mixing height ratio improves; Finally, multivariate correlations for dense phase bed expansion are established, yielding a 3.94% average error. • A modified EMMS drag model was adopted to examine flow features in a bidisperse fluidized bed. • The quantified impacts of superficial gas velocity and packing state on flow are obtained. • Multivariate correlations for dense phase bed expansion were fitted with high accuracy.

Hydrodynamic characteristics of a pilot-scale gas-driven inverse liquid-solid fluidized bed with a central draft tube

A new pilot-scale gas-driven inverse liquid-solid fluidized bed with a central draft tube (GDFB-II) was studied. With gas bubbles rising through the draft tube and enabling an upflow liquid, the associated liquid downflow fluidizes light particles downwards in the main column, forming a GDFB. Hydrodynamic characteristics of the GDFB-II were carefully studied using particles of different diameters and densities. Three flow regimes including packed bed, fluidized bed, and circulating bed regimes were identified and these regimes were demarcated by the initial fluidization gas velocity (Ug,if) and the minimum circulating gas velocity (Ug,mc). Ug,if and Ug,mc increase with the increase of particle diameter or the decrease of particle density. The effects of the draft tube diameter and the gas injection tube diameter on Ug,if and Ug,mc were also investigated. As the superficial gas velocity increases, the particle bed height increases first and then plateaus, while the average solids holdup decreases rapidly first and then remains constant.

Effect of Liquid Properties on Frictional Pressure Drop in a Gas-Liquid Two-Phase Microchannel

The flow characteristics in a ring-shaped microchannel with an inner diameter of 1 mm were studied in two-phase flow systems with air-water, air-glycerol aqueous solution and air-ethanol aqueous solution using the differential pressure method. The effects of liquid properties (surface tension and viscosity) and gas/liquid superficial velocity on frictional pressure drop were discussed. The experimental results show that the frictional pressure gradient increases with the increase of superficial gas velocity, superficial liquid velocity and liquid viscosity, and increases with the decrease of liquid surface tension, which has a good agreement with the literature values. The friction pressure drop data are compared with the classical models and correlations in literature, and a reliable correlation is proposed for prediction of two-phase friction coefficient in microchannels.

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.

Numerical simulation and experimental verification for the sorting behaviors of mixed biomass particles in a novel Z-shaped fluidized bed

Inclined gas–solid fluidized bed has excellent particle separation and purification performance. Hence, Z-shaped fluidized bed as a novel fluidization system is designed in this work. The effect of superficial gas velocity on the sorting behaviors of mixed biomass particles is investigated by using the computational fluid dynamics and discrete element method, and a high-speed fluidization image experiment platform is established. The density and elastic modulus of biomass particles are experimentally measured, and the shapes are characterized by sphericity. Detailed information (i.e., distribution behavior and flow velocity of particle and fluid, particle residence time, and particle force) are obtained and analyzed. Results show that particles and fluid phases are not uniformly distributed, and a core-annulus structure is observed. The mixed particles movement process is divided into rising, settling, resuspension, and separation. The predictions on the solid distribution and sorting behaviors in the fluidized bed agree well with the experimental findings. Given the different densities and sizes, clean products flow upward and impurities flow downwards when the inlet air velocity is 1.5 m/s. As the superficial gas velocity increases, the transport efficiency of mixed particles improves, but the separation degree decreases. Clean products and impurities are effectively separated under the optimal gas velocity of 1.5–2.5 m/s. Particles in the channel center have a good following performance, moving in a zigzag pattern with the fluid, but they tend to slide along the inclined wall. The dynamic forces of the mixed particles are influenced by the channel section area. These findings provide valuable insight into the development and optimization of particle purification appliances in multiphase reactors.

Wax Deposition Law under a Gas-Liquid Bubbly Flow Pattern.

Under the high-pressure and low-temperature environment of the deep sea, wax deposition will occur in the wellbore. This study discusses the effect of gas–liquid two-phase bubbly flow on wax deposition. In this study, wax deposition experiments of a gas–liquid two-phase flow in vertical pipelines were carried out using waxy white oil and air as the experimental medium. The results show that under the bubble flow pattern, within a short period of time from the start of wax deposition, it rapidly accumulates to the peak, then rapidly cuts off part of it, and then presents a simple harmonic dynamic trend until the final stability. The average wax-deposit thickness decreases first and then increases with the increase of superficial gas velocity, and it increases first and then decreases with the increase of superficial liquid velocity. The average wax-deposit thickness decreases with the increase of oil temperature. The average wax-deposit thickness was substantially constant and then decreases with the increase of ambient temperature. The wax-deposit thickness increases with the increase of wax content in oil flow. This research is useful for people to further understand the changes in the wax deposition process.

Investigation of solid phase mixing in the multistage circulating fluidized bed

Solid mixing process plays a crucial role in evaluating the reaction performance of multiphase reactor. However, there still lacks the systematic research on solid mixing for the multistage circulating fluidized bed with enlarged sections. Solid mixing mechanism in a multistage riser is investigated numerically in this study. Some individual characteristics of solid mixing are found. It is shown by analyzing residence time distributions that solid mean residence time and the degree of solid dispersion increase with the increasing solid flux or the decreasing superficial gas velocity. Nevertheless, particle diffusion coefficient increases as solid flux decreases or superficial gas velocity increases. Moreover, the diffusion coefficient in enlarged sections decreases with the increasing height, which is contrary to the variations in traditional risers. Compared with the traditional riser, particle diffusion is weak, but overall solid mixing is enhanced in the multistage riser. Furthermore, two mixing patterns that gas-solid flow develops towards the plug-type flow in the center region of riser and the mixed-type flow in the enlarged section are identified. In addition, the dominant recirculation time of solids in the enlarged section is predicted as 1.5 s under examined cases.

Fluidization dynamics of wet Geldart D particles by pressure fluctuation analysis

The increase of liquid saturation badly affects the fluidization dynamics, even resulting in the failure of fluidization. Nevertheless, few researches focus on characterizing the flow pattern transition of wet particles. In this work, we discuss the effects of the liquid saturation, gas velocity and the particle size on the global fluidization dynamics of Geldart D particles by analyzing the pressure fluctuations in the fluidized bed. The results show that the bubble dynamics is intensified with the increasing liquid saturation and decreasing particle size. When the superficial gas velocity increases, the fluidization regimes change from expanding regime, to multi-bubbling regime and slugging. During the normal fluidization and slugging, the liquid bridge forces prevent the growth of large bubbles and promote the probability of bubble break-up. Thus, the average bubble size decreases and the number of bubbles increases, which lead to the intense bubble behavior. With the decreasing particle size, the effect of liquid bridge forces is enhanced, contributing to the intensified bubble dynamics, including fast rising, frequent coalescence and eruption of a large number of bubbles. Compared to dry particles, wet particles are easily to cause defluidization when the gas velocity is small. The PSD patterns have the sharp narrow peaks at frequency lower than 0.8 Hz. When the liquid saturation is increased to 30%, a gas channel forms in the bed, which resists the normal works of the fluidized bed. Basically, reducing the liquid saturation is a reasonable way to avoid defluidization.