•A particle scale model is developed to describe the spouting behavior of cohesive particles.•The effect of cohesive force on spouting behaviors is discussed.•The cohesive force between particles hinders the initiation of spouting.•When FCO = 10Fg, obvious agglomeration appears in a spouted bed.•The particle circulation fluxes decrease as the cohesive force increases.In the present work, a numerical model is developed by means of CFD-DEM to study the behavior of cohesive particles in a spouted bed. In the model, the magnitude of the cohesive force was assumed as a specified constant which can be related to the cohesive force for molten particles or the liquid bridge force for wet particles. The evolutions of the flow patterns during the spouting processes at different cohesive forces were obtained. Particle concentration, velocity and circulation fluxes were systematically compared between cohesive and non-cohesive particles. Numerical results reveal that introducing the cohesive force will hinder the initiation of spouting from the compacted state of the bed. Increasing the cohesive forces leads to agglomeration, and correspondingly, higher gas velocities are required to break through the upper bed surface. When the cohesive force FCO = 5Fg, where Fg is the particle weight, the spouted bed can be operated properly similar to the non-cohesive one. When the cohesive force is further increased to FCO = 10Fg, obvious agglomeration appears at the moment of onset of fluidization. Particle concentration in the fountain region decreases apparently at the stable spout state because the cohesive force hinders the particle transfer from annulus to spout. The average particle velocity in the annulus decreases by about 50% compared to the spouted bed of non-cohesive particles at the same spouting gas velocity Us. When the cohesive force FCO = 20Fg, de-fluidization happens in the spouted bed. Meanwhile, it is also found that the particle circulation fluxes under stable spouting condition decrease as the cohesive force increases at the same spouting gas velocity.Download high-res image (351KB)Download full-size image

•A full-scale 3D Eulerian-Eulerian model of bubbling gas absorbing tower is established.•Simultaneous deSO2 and deNOx characteristics in bubbling gas absorbing tower is investigated.•The best optimized method for simultaneous deSO2 and deNOx is proposed.•The method is verified by engineering tests.A full-scale three-dimensional Eulerian-Eulerian numerical model was established considering absorbing reactions in which the two-film theory model was adopted to describe the absorption process of SO2 and NOx. The established model was firstly verified by the industrial operation data of a 2 × 220 m2 sintering flue gas desulfurization tower. Then, using the model, numerical simulations of simultaneous desulfurization and denitration process were carried out based on three different methods including spraying-inside tower oxidation absorption of the composited NaClO2/NaClO/Ca(OH)2 slurry, oxidation absorption of the composited NaClO2/NaClO/Ca(OH)2 slurry and bubble absorption of Ca(OH)2 slurry. Numerical results revealed that the first method, spraying-inside tower oxidation absorption of the composited NaClO2/NaClO/Ca(OH)2 slurry had the best performance on denitration without influencing on the desulfurization efficiency. The result was then further verified by an industrial scale test on a 2 × 220 m2 sintering flue gas desulfurization tower.Download high-res image (237KB)Download full-size image

•An industrial spout-fluid bed is designed to mix biomass and carrier particles.•A 3D CFD-TFM model with three-phase flow is proposed to test the mixer performance.•Flow behaviors of biomass and heat-carrier particles in the mixer are described.•The effectiveness of the bed for mixing is demonstrated.•Effects of spouting gas flowrate and fluidizing gas flowrate are investigated.A new industrial-scale spout-fluid mixer (H = 3.4 m and I.D. = 0.8 m) was proposed for mixing 18.75 t/h of biomass (ρb = 400 kg/m3, db = 2 mm) and 281.25 t/h of heat-carrier (ρc = 2600 kg/m3, dc = 0.5 mm), and the corresponding three-dimensional computational fluid dynamics approach, facilitated with the Eulerian-Eulerian multiphase fluid model (CFD-TFM), was developed to simulate the three-phase mixing behaviors in the mixer. The performance of the mixer and effects of operating parameters were numerically investigated. It was found that the mixing effectiveness, Me, can reach over 80% under the proposed industrial operational conditions (for example, a spouting gas flowrate Qs = 0.067 kg/s and fluidizing gas flowrate Qf = 0.035 kg/s), and the flow pattern in this case is a “jet in the fluidized bed with bubbling”. Increasing Qs will increase the sizes of bubbles, as well as their generation frequency and rising velocity, which are conducive to the mixing of heat-carrier and biomass particles. However, a too large Qs will affect the falling solid flows in the distribution region and transition region of the mixer. Conversely, increasing Qf will aggravate the swaying and leaning of bubbles or jets towards the mixer walls, leading to a slight decrease of Me.Download high-res image (151KB)Download full-size image

A three-dimensional (3D) fast fluidized bed with the riser of 3.0 m in height and 0.1 m in inner diameter was established to experimentally study the cluster behaviors of Geldart B particles. Five kinds of quartz sand particles (dp = 0.100, 0.139, 0.177, 0.250 and 0.375 mm and ρp = 2480 kg·m− 3) were respectively investigated, with the total mass of the bed material kept as 10 kg. The superficial gas velocity in the riser ranges from 2.486 to 5.594 m·s− 1 and the solid mass flux alters from 30 to 70 kg·(m− 2·s)− 1. Cluster characteristics and evolutionary processes in the different positions of the riser were captured by the cluster visualization systems and analyzed by the self-developed binary image processing. The results found four typical cluster structures in the riser, i.e., the macro stripe-shaped cluster, saddle-shaped cluster, U-shaped cluster and the micro cluster. The increasing superficial gas velocity and particle sizes result in the increasing average cluster size and the decreasing cluster time fraction, while the solid mass flux in the riser have the reverse influences on the cluster size and time fraction. Additionally, clusters in the upper region of the riser often have the larger size and time fraction than that in the lower region. All these effects of operating conditions on clusters become less obvious when particle size is less than 0.100 mm.

•The physical model of plant canopy was applied for simulating wind field and contaminant dispersion in an industrial park.•The influence of weather conditions was taken into consideration.•The landform model of the industrial park was built up which is more accurate than idealized street canyon models.•The wind was blocked by the plant canopy and the flow direction was changed under unstable conditions.•Much of contaminant is stored inside plant canopy regions and the downstream regions was protected.Large Eddy Simulation (LES) combined with a dynamic Smagorinsky subgrid scale model was used to simulate the wind field and particulate pollutant dispersion considering the effects of plant canopies and weather conditions. The model of the plant canopy was adopted to present the effects of drag force and buoyancy force and validated by bench mark results from previous reference. Then, using the model, four study cases in the Nanjing Sample Industrial Park were simulated under different weather conditions to consider the momentum effect of plant canopy, energy effect of plant canopy and the effect of atmospheric instabilities, respectively. The numerical results were also compared with those of idealized street canyon models, and it was proven that the accurate landform model was more practical to be applied in the study. The wind field and pollutant distribution were analyzed in each case to investigate the influence of plant canopy. It was shown that the wind velocity was lower near the canopy regions, especially in unstable conditions due to the entrainment effect of the buoyancy force. Meanwhile, the streamline could be changed by the buoyancy force in an upward trend. The distribution of the turbulent kinetic energy indicated that the turbulent flow in the atmosphere was weakened through the plant canopy, especially in unstable conditions. Considering the effect of buoyancy force, the direction of pollutant dispersion in horizontal profiles was different to the neutral condition, which proved that plant canopy can protect the downstream regions in unstable atmospheric conditions.Download high-res image (252KB)Download full-size image

•A dual circulating fluidized bed (DCFB) with symmetrical CFB units was established.•Five steady coupled flow patterns and their transitions in DCFB were studied.•Variation trends of riser solid holdup depend on supply chamber aeration condition.•Higher superficial gas velocity makes fluctuation along riser more homogeneous.•Solid holdup fluctuation characteristic in one unit is hardly affected by another.The particle flow characteristics in a dual circulating fluidized bed (DCFB) with symmetrical CFB units were experimentally studied. Each CFB unit consists of a riser (Hr = 3 m, Dr = 0.1 m), a downcomer (Hd = 1.73 m, Dd = 0.1 m), a cyclone separator and a loop seal. The solid material applied in the experiments was quartz sand (d = 140 μm, ρs = 2600 kg/m3) with a total solid inventory of 70 kg. Four steady flow patterns were formed in each CFB unit, including turbulent flow (TF), cluster flow (CF), annular flow (AF) and suspension flow (SF), which leads to five steady coupled flow patterns in DCFB, i.e. CF-TF, CF-CF, AF-CF, AF-AF and AF-SF. Axial solid holdups were examined at these plow patterns and their transitions. The fluctuation strength and particles flow stability were evaluated with standard deviation (σ) and coefficient of variation (CV) of time-series solid holdups, respectively. It was found that a growth in the superficial gas velocity of Unit B (Ug,B) would lead to a more uniform Unit B axial solid holdup. Meanwhile, the variation trends of Unit A solid holdup differed under different coupled flow pattern. With Ug,B increasing, σB along Unit B riser became more homogeneous while the change in σA was roughly linear with the variation of solid circulation rate. Meanwhile, σ and CV of Unit B solid holdups were found to have a similar variation trend under coupled flow patterns of CF-TF and CF-CF. As for coupled flow patterns of AF-CF, AF-AF and AF-SF, with increasing Ug,B, the CV of Unit B bottom region kept decreasing while constant growths were found in other regions.

•Mixing behaviors in a waste fluidized bed with 9 kinds of non-spherical particles were studied.•Dynamic stabilization of mixing could be achieved at fluidization number N > 1 (N = U / Umf) and mixing time t > 12 s.•The density has more remarkable influence on mixing than particle size and shape.•Well particles mixing was found when the density of NSP similar to that of FM.A transparent waste fluidized bed cold model (cross section of 0.2 m × 0.2 m and height of 2.0 m) was established. 9 kinds of non-spherical particles (NSP) were selected to represent municipal solid wastes, and silica sand was used as fluidization medium (FM). Binary-component (FM and single kind of NSP) and multi-components (FM and two/or more kinds of NSP) particulate systems were formed. Mixing behaviors in these systems were described by a self-defined mixing index M, and assisted with flow patterns. The effects of fluidization number N defined as the ratio between the gas superficial velocity to the minimum fluidization velocity, properties of NSP such as density, shape and size, and mixing time on the mixing behaviors were experimentally studied. It is found that a dynamic stabilization of mixing could be achieved when the fluidization number N > 1 and the mixing time t > 12 s. The density of NSP has a more significant influence on the mixing behavior than particle size and shape. In a multi-components particulate system, well mixing could be found when the density of NSP gets close to that of fluidization medium.

•Representation and contact detection of non-spherical particle are presented.•Force and motion models on non-spherical particles are reviewed.•CFD-DEM coupling methodologies are described.•Applications of DEM/CFD-DEM modelling are summarized.•Challenges and needs for future researches in this field are discussed.Particles encountered in nature and engineering practice are normally not spherical but of irregular shapes. Particle shape plays a key role in determining the behaviour of bulk solids, which poses a number of challenges in modelling and simulation of particulate systems. Discrete element method (DEM) has been recognized as a promising method to meet the challenges. This paper presents a review of the recent efforts in developing DEM approaches to model non-spherical particulate systems (NSPS) and strategies of coupling such a non-spherical DEM model with computational fluid dynamics (CFD) for particle-fluid flows. It mainly covers four important aspects: the techniques for representation of non-spherical particles and their contact detection, the models describing inter-particle collision dynamics and fluid-particle forces, CFD-DEM coupling methodologies including averaged volume method and immersed family methods and the applications of the developed theories to the modelling of different NSPS. The main findings are discussed and summarized as a part of the review. Finally, the needs for future development are highlighted.

•Fiber deposition experiments were carried out in a single-bifurcation airway model.•Deposition fractions and orientation under effects of impaction and sedimentation were recorded.•Deposition characteristics in lower airway were estimated by matching results for St and γ.•Orientations of deposited fibers were obtained by image processing method.•Gravitational effect on the deposition cannot be neglected for 0.0228 < γ < 0.247.Experiments carried out using a lung model with a single horizontal bifurcation under different steady inhalation conditions explored the orientation of depositing carbon fibers, and particle deposition fractions. The orientations of deposited fibers were obtained from micrographs. Specifically, the effects of the sedimentation parameter (γ), fiber length, and flow rate on orientations were analyzed. Our results indicate that gravitational effect on deposition cannot be neglected for 0.0228 < γ < 0.247. The absolute orientation angle of depositing fibers decreased linearly with increasing γ for values 0.0228 < γ < 0.15. Correspondence between Stokes numbers and γ suggests these characteristics can be used to estimate fiber deposition in the lower airways. Computer simulations with sphere-equivalent diameter models for the fibers explored deposition efficiency vs. Stokes number. Using the volume-equivalent diameter model, our experimental data for the horizontal bifurcation were replicated. Results for particle deposition using a lung model with a vertical bifurcation indicate that body position also affects deposition.

•3-D Eulerian models on solid circulation in CLC DCFB model have been developed.•Cross-sectional solid distribution and velocity field were numerically studied.•Coefficient of variation was used to evaluate circulation stability.•Effects of FR flow rate on circulation fluctuation strength and stability were studied.•Global and internal circulation stability was weakened by growth in LLS flow rate.A three-dimensional computational fluid dynamic (CFD) model has been developed for simulating full-loop solid circulation in a dual circulating fluidized bed (DCFB) chemical loop combustion (CLC) reactor model. The standard k-ε turbulence model and kinetic theory of granular theory based Eulerian multiphase model were used to describe the gas and solid motions, respectively. The simulations focused on the investigation of solid circulation in a CLC reactor model which consists of an air reactor (AR, height of 1.36 m, diameter of 0.05 m) and a fuel reactor (FR, height of 0.97 m, diameter of 0.054 m). Key gas–solid flow behaviors related to gas–solid circulation behaviors, e.g. the transient flow regime, solid velocity, solid distribution and circulation characteristics, were numerically investigated. It was found that a core–annulus flow structure appeared in FR. The influences of FR and LLS fluidization flow rate on global and internal circulation rate were studied separately. With FR fluidization flow rate increasing, the time-averaged axial solid volume fraction in the top region of FR first increased and then decreased. The influences of FR and LLS fluidization rate on circulation dynamic characteristics, including circulation fluctuation strength and circulation stability, were also numerically investigated in this work.

Spout characteristics, such as flow pattern, minimum spouting velocity, and maximum spoutable bed height, are investigated in a wet conical-cylindrical spouted bed. Water and glass beads (Geldart D type) are adopted as the liquid and solid phases, respectively. The evolution of flow pattern of a wet spouted bed is captured by a CCD camera. The experimental results indicate that the minimum spouting velocity decreases when increasing the liquid saturation. The increase of initial bed height, particle size, or spout nozzle size leads to increased minimum spouting velocities. A correlation is formulated based on the experiments results for the prediction of minimum spouting velocities of wet spouted beds. Moreover, it is found that the maximum spoutable bed height Hmax decreases as particle size or spout nozzle diameter increases. However, Hmax is almost constant, approximately 1.5 times higher than that of its corresponding dry spouted bed, when increasing the liquid saturation.

•A 3-D LES-DPM of gas-particle flow on opposed round jets has been developed.•Effects of particle size, mass flux ratio and initial gas velocity were discussed.•The vortex structure evolutions were increased when decreasing dp and increasing U0.•When St > 1, particles could penetrate through the opposed plane.•On opposed round jets, rm at “radial jets” was almost independent with U0.A three-dimensional simulation was performed on the turbulent gas–solid flow in a cylindrical channel with opposed round jets. Large eddy simulation (LES) coupled with discrete phase model (DPM) was employed for carrier gas and laden particles respectively, to investigate the turbulent gas–solid behaviors. Simulations were focused on the effects of particle sizes (dp = 5 μm, 14 μm and 40 μm), Stokes numbers (St = 0.125, 1 and 8), mass flux ratios (Zm = 0.00128, 0.035 and 0.66) and initial gas velocities (U0 = 15 m/s, 25 m/s and 35 m/s) on the vortex structure evolution, particle motion, time-averaged velocity profiles and turbulence intensity. It was found that the evolutions of vortex structure, including the destruction of large scale coherent structures to tiny vortices and the lateral spreading of vortices at the impingement zone, were augmented when using smaller particles and higher initial gas velocities. In addition, particles followed more closely and were easier to reach quasi-equilibrium state with the decrease of Stokes number (St < 1), whereas more particles penetrated the impingement plane when increasing the Stokes number (St > 1). And, with the increase of mass flux ratio, the momentum transfer was augmented as well as the turbulence intensity. Moreover, the position (rm) with maximum radial velocity was almost independent of the initial gas velocity on far-spaced opposed round jets.With the same particle numbers conveyed to the computation zone, the vortex structure evolution under the influences of different particle sizes was described as the following:(1)the destruction of large scale coherent structure to numerous tiny vortices and the lateral diffusion of vortices were increased with the decreasing particle sizes;(2)for larger particles, the rigidity of carrier jet was increased, and the lateral spreading of vortices was suppressed due to more inertia;(3)the vortex structure evolution was increasing when increasing the carrier gas velocity.

A calcium–magnesium–aluminum (Ca–Mg–Al) mixed oxide sorbent was synthesized for the removal of HCl at medium–high temperatures. The operating conditions were specified in terms of the temperature of the gas (300–700 °C), the initial HCl concentration (500–1000 ppm), and the mass flow rate (0.5–1.3 L/min). X-ray powder diffraction (XRD) was applied to investigate the characteristics of Ca–Mg–Al mixed oxides. The results show that, because of the better properties of Ca–Mg–Al mixed oxides than traditional sorbents, which is related to the special structure in as-prepared, the reaction between HCl and Ca–Mg–Al mixed oxides is accelerated. The adsorption capacity of Ca–Mg–Al mixed oxides is the highest when compared to MgO, NaHCO3, and CaO. The removal efficiency of Ca–Mg–Al mixed oxides is more than 95% and even up to 99% under all of the operating conditions.

In this paper, a three-dimensional numerical model has been developed to study the gaseous pollutant emissions during the circulating fluidized-bed (CFB) combustion of combustible solid waste. On the basis of the Eulerian–Eulerian approach, the gas phase is modeled with a k–ε turbulent model and the particle phase is modeled with a kinetic theory of granular flow. The hydrodynamics, heat and mass transfer, and chemical reactions are simultaneously taken into account. Reactions during combustion consist of waste devolatilization, volatile combustion, char combustion, SO2 formation and recapture by calcium oxide, NO and N2O formation, and diminution by heterogeneous and homogeneous reactions. The model has been applied to the CFB riser with a height of 1.8 m and a diameter of 0.125 m at atmosphere. The influences of an excess air ratio on the emissions of SO2, NO, and N2O are studied. The model predicts a growth in the SO2 emission when excess air increases. The emissions of NO and N2O also gradually increase with the increasing excess air ratio. Meanwhile, the CO and CH4 concentrations show a decreasing tendency. The distribution of the bed voidage, flow pattern development, profiles of gas compositions, and related reaction rates inside the riser are also discussed.

•Flow behaviors in a pressurized spouted bed were numerically studied by CFD-TFM.•The increasing pressure causes a decrease in the local minimum spouting velocity.•The fountain is quicker to be established and more stable at higher pressures.•Distributions of particle velocities and concentrations were investigated.•The spout diameters tend to increase with increasing pressure.Numerical simulations of gas-solid flow behaviors were carried out in a pressurized conical-cylindrical spouted bed with absolute pressure elevated to 1.0 MPa. The three-dimensionally coupled computational fluid dynamic (CFD) technology and Eulerian two-fluid model (TFM) were adopted to model the complex gas-solid flow. The results show that the local minimum spouting velocity (ums) decreases with increasing pressure, while the corresponding gas mass flow rate presents an increasing trend. Simulations conducted with local inlet gas velocity of 1.2ums for varying pressure conditions indicate that an increase in the pressure causes an increase in the fountain height, and the fountain is quicker to be established in simulation time and more stable at higher pressures. The particle velocities have the similar varying tendency along the central axis under different pressures, but in the decelerating region, the deceleration rate of lower pressures is bigger than that of higher pressures. The radial profiles of the particle velocities and concentrations show that the particle velocities decrease with increasing pressure in the lower bed levels, but increase in the upper ones. Conversely, the particle concentrations increase with increasing pressure in the lower bed levels, but they decrease in the middle and upper bed levels. In addition, the defined spout diameter appears to increase with the pressure increasing.

•Gas–liquid–solid three phase spouted bed were established.•Five distinct flow patterns were identified and described.•The pressure fluctuation amplitude value is higher for higher saturation level.•Flow pattern maps under different operating conditions were plotted.•The grain spouting region is wider for lower bed height and particle diameter.The flow patterns and transitions in a gas–liquid–solid three phase spouted bed were investigated. Experiments were carried out in a cylindrical and a semi-cylindrical spouted bed with conical base. Glass beads and water were used as the solid phase and liquid phase, respectively. The changes in pressure drop and photographs were used to determine the flow patterns. Five distinct flow patterns were identified and described, i.e. fix bed (FB), grain spouting (GS), cluster spouting with slugging (CS-S), solid fixed with gas–liquid bubbling (SF-GLB), and slurry agitated bed (SA). Flow pattern maps of a three phase spouted bed (d = 2.6 mm, H0/Dt = 1.86) under different liquid saturations were plotted. It was found that the flow pattern transition with the spouting gas velocity increasing at different liquid saturations (S) could be divided into three stages, i.e. transition from FB to GS when S < 0.2, transition from FB to CS-S when 0.2 < S < 0.5, and transition from SF-GLB to SA when S > 0.5. Increase in liquid saturation (S) always leads to increasing of the amplitude of pressure fluctuations. Besides, in stage I (GS), the minimum spouting velocity increases initially and then decreases apparently with increasing S. The range of stage I region becomes wider with lower initial bed height and particle diameter.Typical flow pattern map at various spouting gas flow rates under different liquid saturations conditions (d = 2.6 mm, H0/Dt = 1.86).

•A novel Eulerian–Lagrangian approach was applied in the simulation of the hydrodynamic behavior of pressurized high-flux circulating fluidized beds.•The methodology is based on the multiphase particle-in-cell model.•The sensitivities of key model and modeling parameters on the predictions have been tested systematically.•A suitable drag model and a group of modeling parameters were determined and verified.A novel Eulerian–Lagrangian approach based on the multi-phase particle-in-cell (MP-PIC) methodology was applied in the simulation of the hydrodynamic behavior of pressurized high-flux circulating fluidized beds (DHFCFBs) in this work. The sensitivities of key model (i.e. the drag model) and modeling parameters (particle–particle restitution coefficient, normal particle–wall restitution coefficient, and tangential particle–wall restitution coefficient) on the predictions have been tested systematically. Experimental results of Richtberg et al. [Powder Technol. 2005, 155(2), 145–152] and Yin et al. [Chem. Eng. Technol.2012, 35(5), 904–910] were used as a numerical benchmark to assess the simulations quantitatively. The results show that the Gidaspow drag model displays better agreement with both the axial profiles of pressure drop and the radial distributions of particle volume fraction. Compared with the perfectly elastic particle collision (ep = 1.0), the non-ideal particle–particle interaction could get more reasonable prediction results. The particle–wall restitution coefficient has somewhat of an effect on the simulated gas–solid flow behaviors in the risers. However, no critical changes of simulated flow characteristic in the trends of pressure drop and solid volume fraction distribution have been found. Based on the comparison of simulation results with experiments, a suitable model (i.e., Gidaspow drag model) and a group of modeling parameters, namely a particle–particle restitution coefficient (ep = 0.9), a normal particle–wall restitution coefficient (ewn = 0.1) and a free-slip boundary condition (i.e. the tangential particle–wall restitution coefficient, ewτ = 1.0) for modeling the hydrodynamic behavior in the DHFCDB riser were determined and verified.A novel Eulerian–Lagrangian approach based on the multi-phase particle-in-cell (MP-PIC) methodology was applied in the simulation of the hydrodynamic behavior of pressurized high-flux circulating fluidized beds (DHFCFBs). The sensitivities of key model and modeling parameters on the predictions have been tested systematically. A group of suitable modeling parameters were determined and verified.

Numerical simulations based on the three-dimensional discrete element method (DEM) are carried out for studying the mixing behavior of monocomponent and binary particle systems in a spouted bed. The motion of individual particles is modeled by DEM, and the gas motion is modeled by the k − ε two equation turbulent model. The mixing quality is described by the Lacey mixing index, it is evaluated in terms of the mixing degree at the mixing equilibrium and the time required reaching the steady value. The state of mixing of uniform particles is studied by analyzing the effect of particle shape, density and spouting gas velocity. For binary systems, the effects of component shape and size are examined. The results show that spouting gas velocity and particle properties are important parameters influencing particle mixing quality in spouted bed. The mixing quality is found to be sensitive to particle shape, the spheres mix faster and more homogeneous than corns. In monocomponent corn system, the mixing quality increases with increasing of gas velocity and decrease with increasing particle density, and it is sensitive to particle shapes, the spheres mix faster and more homogeneous than corns. In binary corn–sphere system, particles with closer sizes and operated at higher gas velocity have better mixing quality. Besides, the mixing mechanism of corn-shaped particles is discussed based on the mixing process of monocomponent and binary systems. It is found that particles of different shapes, sizes and densities can have different trajectories in the fountain region, leads to a different radial landing position on the top of the annulus, and the subsequent path through the annulus region varies.Numerical simulations based on three-dimensional discrete element method (DEM) are carried out for studying the mixing behavior of monocomponent and binary particle systems in a spouted bed. The state of mixing of uniform particles is studied by analyzing the effect of particle shape, density and spouting gas velocity. For binary systems, the effects of component shape and size are examined.Highlights► Mixing behaviors of corn-shaped particles were studied in a spouted bed. ► The gas–solid flow is modeled by the combination of CFD–DEM. ► The mixing quality is sensitive to particle properties and gas velocity. ► The differences of component shape and size affect the distribution of particles. ► The mechanism of mixing process is discussed.

Co-fluidization characteristics of irregular particles with bed material have been investigated. Experiments were carried out in a solid waste fluidized bed with cross section of 0.2 m × 0.2 m and height of 2 m. Four particles differing in shapes, sizes and densities were used as simulative solid waste, and silica sand was employed as fluidization medium. The pressure drop, flow pattern and minimum fluidization velocity (Umf) under different operating conditions were investigated by recording pressure differential signals and fluidization images. A correlation of Umf was also developed. The results showed that during the fluidization of irregular particles with the bed material of silica sand, the pressure drop curve measured with increasing fluidization gas flow rate was visibly fluctuant and always underestimated the Umf value; while the pressure drop curve measured with decreasing fluidization gas flow rate was smooth and adequate to determine the value of Umf. The Umf was found to be increased with increasing volume proportion and effective particle density, while the initial static bed height has no significant effect on the minimum fluidization velocity. By comparing the Umf values predicted by the developed correlation with the present experimental data and those from literature, it was found that the correlation was quite satisfactory on predicting the Umf value for the fluidization of irregular particles with the bed material of silica sand. The correlation was also found to be applicable to the prediction of Umf values of a solid waste fluidized bed with a single kind or multi-kinds of irregular particles.Co-fluidization characteristics of irregular particles with bed material were investigated. Particles differing in shapes, sizes and densities were tested and silica sand was employed as fluidization medium. The pressure drop, flow pattern and minimum fluidization velocity (Umf) under different operating conditions were tested. Correlation of Umf was also developed.Highlights► Co-fluidization of irregular particles with bed material has been carried out. ► Four kinds of particles with different shapes, sizes and densities were used. ► Pressure drop, flow pattern and minimum fluidization velocity were obtained. ► A correlation of Umf for multi-component irregular particles was developed.

The effect of the particle size on the mixing and segregation in a spout-fluid bed has been investigated (Zhang, Y.; Zhong, W. Q.; Jin, B. S.; Xiao, R. Mixing and segregation behavior in a spout-fluid bed: effect of particle size. Ind. Eng. Chem. Res.2012, 51, 14247–14257). This paper presents the effect of the particle density on the mixing and segregation behavior in a spout fluid. Four kinds of solid particles having the same size of 2.8 mm and different densities of 900, 1230, 1640, and 2540 kg/m3 were used. Three kinds of binary mixtures were obtained, indicated as PB–SP, PB–MB, and PB–GB. For each mixture, three different mass ratios were prepared so that the mixing and segregation processes were examined. Thus, nine binary mixtures were made by mixing the bed material and tracer in different mass ratios. The initial bed stayed in the state of well-mixed and complete segregation, respectively. A wide range of flow regimes were covered by changing the ratio of spouting-to-fluidizing gas flow. The mixing and segregation were analyzed in terms of the concentration profile, mixing index, and flow regimes. The results show that, in the flow regime of IJ, local segregation occurs in the initial well-mixed case, whereas bed inversion takes place in the initially complete segregation bed. In the case of JFB, the entire bed is divided into three sections due to segregation: a pure layer of light particle, one jet region occupied nearly by a heavy particle, and one annulus remaining at the initial distribution at rest. In the flow regime of F, the segregation pattern is dependent on the mass ratio and density difference between the light and heavy particles. On the mixing/segregation pattern map, even though the bed is operated at the same flow regime, the mixing degree varies with the gas velocity. Also, a monotonic increase in the spouting or fluidizing gas velocity is not necessary to promote mixing. There lies one major difference on the mixing/segregation pattern map; that is, the location of the transition region for a binary mixture with different densities (DD mixture) is different from one for a binary mixture with different sizes (DS mixture).

The mixing and segregation behavior of a binary mixture have been investigated experimentally in a spout-fluid bed. Three types of binary mixtures were used by mixing glass beads with equal density and dissimilar size. The spouting and fluidizing gas flow rate were adjusted to cover a range of flow regimes, typically including internal jet (IJ), jet in fluidized bed with bubbling (JFB), spouting (S) and spout-fluid (SF). The mixing and segregation behavior were analyzed in terms of flow regimes, concentration profile, and mixing index. The results show that in IJ, the particle circulation is combined with the local segregation where smaller particles migrate to the interface between the jet and stagnant region, even into the latter. In S, the distribution of particle depends greatly on the fountain structure. In JFB, the axial segregation takes place where the smaller particles prevail in the upper part of the bed. Segregation becomes more pronounced with increasing the particle size difference. In addition, a mixing/segregation pattern map is constructed. Three regions including mixing region, segregation region, and intermediate region, are identified by the criterion of mixing index.

This paper presents the mixing behaviors of binary particle mixtures with equal diameter and different density within a spouted bed by three-dimensional coupled computational fluid dynamics (CFD) and discrete element method (DEM).The particle motion is modeled by the DEM, and the gas motion is modeled by the k − ε two equation turbulent model. The numerical computation is based on a cylindrical spouted bed which the inside diameter, height and conical base are 200 mm, 700 mm, and 60°, respectively. Binary particle mixtures are composed of spherical particles with equal diameter of 4 mm and the heavy-over-light density ratio ranges from 1 to 4. The mixing process, evaluation of mixing quality, particle circulation and distribution of particle concentration along both radial and axial directions are obtained on the basis of simulations. The mixing process is illustrated by the development of solid flow patterns with time. The results show that the process of particle mixing mainly contains three stages: macro-mixing stage, micro-mixing stage and stable mixing stage. The mixing quality is described by Lacy mixing index, and is evaluated by two parameters: mixing degree at the mixing equilibrium phase and the time required reaching the steady value. The effect of sample size act on the mixing degree is also investigated and an optimum size is found. The results show that the mixing quality increases with increasing of gas velocity and decreases with increasing particle density differences of the binary mixture. By comparing the typical trajectories for two tracer particles with different densities, the mixing mechanism is further analyzed. Besides, the mixing rate in radial and axial directions is characterized by the time required for the concentration of the mixtures constituent to maintain a basic equilibrium. It is found that the mixing process along the axial direction is slower than that of the radial direction, and in both directions, mixture with smaller component density difference shows a higher mixing rate and better mixing uniformity.Mixing process in the spouted bed (ρl = 1416 kg/m3, ρh = 2832 kg/m3, us = 1.2 ums). Mixing behaviors of binary particle mixtures with equal diameter and different density within a spouted bed are investigated by CFD–DEM. The research focuses on examining the effect of spouting gas velocity and component density differences on the mixing quality and the mixing rate in radial and axial directions.Highlights► Mixing behaviors of binary mixtures were studied by CFD–DEM in a spouted bed. ► Particle mixing process mainly contains three stages. ► The effect of gas velocity and density ratio on the mixing quality is investigated. ► Mixing along the axial direction is slower than that in the radial direction.

Including the effects of particle–particle collision and particle rotation as well as the volume of particle occupied in the fluid, the Computational Fluid Dynamics (CFD)–Discrete Element Method (DEM) approach could properly predict the behavior of gas–solid flow with strong coupling and the motion of non-spherical particle, thus show good potential in simulations of alveolar region and fibrous particle transport and deposition. CFD–DEM has been developed to investigate the particle transport and deposition characteristics in human airway. An idealized pulmonary airway model of generations 3 to 5 has been established using the same geometric parameters as previous experiment conducted by Kim and Fisher (C. S. Kim and D. M. Fisher. 1999). The predicted deposition efficiencies are in good agreement with experimental data. Thus, CFD–DEM could properly simulate the particle behaviors in pulmonary airway. Based on the simulations, particle motions are studied by analyzing the particle positions at different time intervals. The results show that the initial position of particle would notably affect its trajectory. The near wall particles distribute evenly in the daughter tubes when they cross the airway. The most centered particles at inlet travel through the model via the inner side tubes of generation 5. The trajectories of other particles would shift from the inside tubes to the lateral ones of last generation as the distance between particle initial position and tube center increases.Graphical abstractComputational Fluid Dynamics (CFD)-Discrete Element Method (DEM) has been developed to investigate the particle transport and deposition characteristics in human airway. The predicted deposition efficiencies are in well agreement with experimental data, which indicates that CFD-DEM could properly simulate the particle behaviors in pulmonary airway. Qualitative and quantitative investigations of the particle motions have also been carried out.Highlights► CFD–DEM has been developed to investigate particle characteristics in airway. ► The particle transport in pulmonary 3–5 generation airway has been investigated. ► CFD–DEM could properly simulate the particle behaviors in pulmonary airway. ► The characteristics of particle motions have been obtained based on simulation.

A comprehensive three-dimensional numerical model was developed to study the gas/solid flow behaviors in a pulmonary airway affected by chronic obstructive pulmonary disease (COPD), a high morbidity lung disease and the patients of which suffer from respiratory difficulty caused by narrowed airway. The gas phase was modeled with laminar computational fluid dynamics (CFD) model and the particle phase was modeled with discrete phase model (DPM). Computational gas–solid flow behaviors in a three-generation airway were validated with experiment. After that gas/solid flow characteristics in an obstructed four-generation model were investigated by simulations. The air flow patterns and flow rates changing along the time series of transient inhalation and particle deposition patterns and efficiencies of the obstructed tube and adjacent generations under real inhalation condition were compared with the steady inlet results. It is found that air flow rates of the obstruction and its downstream generations reduce due to the stagnation and recirculation zones development with unsteady inhalation. Deposition area could enlarge and become more scattered than steady inlet. Secondary flow may contribute to the particle deposition in the inflamed airway for real inhalation. The deposition efficiency outcomes of the constricted tube indicate that transient inhalation condition may be more appropriate for COPD or similar obstructed airway simulation than steady inlet condition.A numerical model was developed to study the gas/solid flow behaviors in a pulmonary airway affected by chronic obstructive pulmonary disease (COPD). It was found that stagnation and recirculation zones caused by obstructed tube could significantly change the air flow, particle deposition pattern and efficiency under the unsteady inhalation comparing to steady inlet condition.Highlights► Gas/solid flow behavior was simulated in a COPD affected four generation airway. ► Air flow field and particle deposition of cyclic inlet are different from steady one. ► COPD patient may suffer more from oxygen deficiency than steady inlet simulation. ► The deposition pattern of unsteady inhalation is more dispersed. ► The simulated deposition efficiency with unsteady inlet may be more appropriate.

Three dimensionally coupled computational fluid dynamics (CFD) and discrete element method (DEM) were used to investigate the flow of corn-shaped particles in a cylindrical spouted bed with a conical base. The particle motion was modeled by the DEM, and the gas motion by the k-ɛ two-equation turbulent model. A two-way coupling numerical iterative scheme was used to incorporate the effects of gas–particle interactions in terms of momentum exchange. The corn-shaped particles were constructed by a multi-sphere method. Drag force, contact force, Saffman lift force, Magnus lift force, and gravitational force acting on each individual particle were considered in establishing the mathematical modeling. Calculations were carried out in a cylindrical spouted bed with an inside diameter of 200 mm, a height of 700 mm, and a conical base of 60°. Comparison of simulations with experiments showed the availability of the multi-sphere method in simulating spouting action with corn-shaped particles, but it depended strongly on the number and the arrangement of the spherical elements. Gas–solid flow patterns, pressure drop, particle velocity and particle concentration at various spouting gas velocity were discussed. The results showed that particle velocity reaches a maximum at the axis and then decreases gradually along the radial direction in the whole bed. Particle concentration increases along the radial direction in the spout region but decreases in the fountain region, while it is nearly constant in the annulus region. Increasing spouting gas velocity leads to larger pressure drop, remarkably increased speed of particle moving upward or downward, but decreased particle concentration.Graphical abstractComparison of experimental flow pattern with 3D simulation at us = 1.1ums.Highlights► Spouting of corn-shaped particles was simulated using a 3D CFD-DEM model with corn-shaped particles constructed by a multi-sphere method. ► The 4-spherical element construction showed smaller discrepancies between simulated and experimental results. ► Particle concentration increases in the spout region but decreases in the fountain region along the radial direction.

Studies on the drag of 28 kinds of cylinder-shaped particles with different sizes and materials were experimentally carried out in steady upward gas flow. The drags were determined by high-resolution digital image processing. Two charge-coupled devices with different frame rates were employed to record the particle movements during experimental investigations. The effects of particle properties (length, diameter, density, and sphericity) and operating conditions (gas velocity and particle Reynolds number) on drag coefficients of single falling cylinder have been systematically tested. The results showed that the drag coefficient first declines sharply and then gradually with increasing particle Reynolds number; finally, it can reach a constant level if the Reynolds number is large enough to exceed a certain value. It was found that the drag coefficient is significantly dependent on particle shape and size for a fixed particle Reynolds number. It increases with increasing particle length and density but decreases with increasing particle diameter and sphericity. In addition, the usability of correlations in publications for predicting the drag coefficient was evaluated by comparing our experimental data. A new correlation considering the effect of particle size, shape, orientation, and density was proposed for predicting the drag coefficient for cylinders, which was in satisfactory agreement with the present experiments and some published experimental results. The correlation is helpful for predicting the drag coefficient for cylinders in ranges of the particle Reynolds number Rep = 500–10 500, flatness ratio da/dv = 0.95–1.28, and sphericity φ = 0.70–0.87.

Three dimensionally coupled computational fluid dynamics (CFD) and discrete element method (DEM) were studied for modeling the turbulent gas–solid flow in a cylindrical spouted bed with a conical base. The particle motion was modeled by the DEM, and the gas motion was modeled by the k–ε two-equation turbulent model. Drag force, contact force, Saffman lift force, Magnus lift force, and gravitational force acting on an individual particle were considered in establishing the mathematical models. Calculations on the cylindrical spouted bed with an inside diameter of 152 mm, a height of 700 mm, and a conical base of 60° were carried out. Experimental results from the University of British Columbia [He, Y. L.; Qin, S. Z.; Lim, C. J.; Grace, J. R.Particle velocity profiles and solid flow patterns in spouted beds. Can. J. Chem. Eng. 1994, 72 (8), 561−568] were used as a numerical benchmark to quantitatively assess the simulations. Despite the somewhat larger simulated spout diameter found, the present simulated results were in well-agreement with the experiments. The average error of particle velocity was less than 15%. On the basis of the simulations, the development of spout with time and distributions of particle velocity, particle concentration, and spout diameters at various spouting gas velocities were obtained. Besides, detailed information on particle collision and drag forces adding on particles at different bed regions was discussed. The results showed that particle velocity gradually decreases along the radial direction, with speeds of particles moving upward decreasing with an increasing bed height, while in the annulus region, particles decelerate downward in the cylindrical section and then accelerate in the conical base. The particle concentration increases in the spout region, is kept nearly constant in the annulus region, but decreases in the fountain region along the radial axis. An increasing bed height leads to an increasing particle concentration in the spout region but a decreasing particle concentration in the annulus and fountain regions. Particle collision number, particle turbulent intensity, and the transient collision force and drag force are significantly larger in the spout region than in the annulus and fountain regions. Besides, an increasing spouting gas velocity leads to a remarkable increased speed of particles moving upward or downward, spout diameter, particle collision, drag force, and particle turbulent intensity but decreased particle concentrations.

Detailed knowledge of particle mixing dynamic is essential in successfully designing and reasonably operating spout-fluid reactor. Over the years, numerous methods for the investigation of particle mixing have been proposed. This paper presents a novel method for the investigation of particle mixing. The method was carried out in a well-designed microwave heater, in which the lab-scale spout-fluid vessel constructed with microwave-transparent Plexiglass was placed. Inside the bed, a number of polar tracer particles continuously heated by microwave energy were real-time tracked using a top-grade infrared camera. From this, the concentration field of the tracer particle could be obtained with high accuracy. This technique has been adopted to investigate the mixing dynamic of binary mixture differing in the density in a flat-bottom spout-fluid bed. The mixing quality was evaluated by the Shannon entropy mixing index. On this basis, the influence of important process parameters on the mixing progress in the initial mixing stage has been taken into account. The investigation results show that the mixing progress is improved when increasing the means gas velocity and the difference in density of bed particle. In addition, an empirical correlation as a function of gas velocity and particle density was developed for calculating the mixing degree. The errors between experimental data and the obtained ones from this correlation were within 28%.A novel method was developed to study particle mixing. The method was performed in a microwave heater, in which the spout-fluid vessel was placed. Inside the bed, a number of polar tracer particles continuously heated by microwave energy were real-time tracked using a top-grade infrared camera. From this, the concentration field of the tracer particle could be obtained.Research highlights►In the study, a novel method is developed, which is listed as follows. The spout-fluid vessel constructed with microwave-transparent Plexiglass is placed in a well-designed microwave heater. Inside the bed, a number of polar tracer particles, sharing the same characteristics with bed particles besides the density, are heated continuously by the microwave energy. Then, concentration field of the tracer particle is detected by means of a top-grade performance infrared camera. Based on it, the influence of important process parameters on the mixing progress in the initial mixing stage has been taken into account. ►The results show that the mixing progress is improved when increasing the means gas velocity and the difference in density of bed particle. In addition, an empirical correlation as a function of gas velocity and particle density was developed for calculating the mixing degree. The errors between experimental data and the obtained ones from this correlation are within 28%.

Experimental studies on flow patterns and transitions were carried out in a visible multiple-spouted bed. The bed combines three spouted bed cells, each with a cross-section of 100 × 30 mm, and each cell has an independent spout nozzle of 10 mm in width. Polypropylene beads with a density of 900 kg/m3 and mean diameter of 2.8 mm were used as bed materials. Six distinct flow patterns, i.e., fixed bed (FB), internal jet (IJ), internal jet with bubble (IJB), single spouting (SS), multi-spouting (MS), and internal jet with slugging (IJS), were determined on the basis of criteria as well as schematic diagrams and typical flow pattern images obtained from a high-resolution digital charge coupled device (CCD) camera. Typical flow regime maps at three static bed heights were plotted to describe the transitions of flow patterns with central and auxiliary spouting gases. Besides, some important flow characteristics associated with flow patterns and transitions, i.e., minimum spouted velocity and pressure drop, were studied. The results showed that the kind of flow pattern was dependent upon the static bed height; in particular, the flow pattern of IJS was only found at a high static bed height. The central minimum spouting velocity increased with an increasing static bed height, decreased with a low auxiliary spouting gas flow rate, but increased with a high auxiliary spouting gas flow rate. The total pressure drop increased first and then decreased gradually with the auxiliary spouting gas at a certain central spouting gas flow rate, while it increased first and then remarkably decreased with the central spouting gas at a given auxiliary spouting gas flow rate.

Modeling of the hydrodynamic behaviors of high-flux circulating fluidized beds (HFCFBs) with Geldart group B particles has been performed using a Eulerian multiphase model with the kinetic theory of granular flow (KTGF). The essential models involved are the dispersed k−ε turbulence model, the Gidaspow shear viscosity model, and the Syamlal−O’Brien drag model, and the boundary condition is the Johnson and Jackson wall boundary condition. The sensitivities of key model parameters (i.e., particle−particle restitution coefficient (e), particle−wall restitution coefficient (ew), and specularity coefficient (φ)) on the predicted gas velocity, solids velocity, and solids volume fraction were tested. It was found that e has remarkable dependence on the particle diameter. Large-sized particles experience a more sensitive effect of e on predictions. The particle−wall restitution coefficient ew has somewhat of an effect on the simulated values of gas velocity, solids velocity, and solids volume fraction; however, no critical changes in the trends of their radial distributions have been found. The specularity coefficient φ has a slight effect on the gas velocity and solids velocity distributions but a pronounced effect on the solids volume fraction distribution. An increase in specularity coefficient results in a reduction in the solids volume fraction near the wall. Based on the comparisons of simulated results with experiments, a group of suitable model parameters for modeling the flow of Geldart group B particles in HFCFB risers by a Eulerian multiphase model with KTGF was determined and verified. Besides, some interesting simulated results that are difficult to measure experimentally were presented under the suggested model parameters.

A novel method of particle tracking combining microwave heating and infrared thermal imaging technology has been developed. The method is applied to study the particle circulation in a flat-bottom spout-fluid bed operated under ambient conditions. The spout-fluid vessel constructed with microwave-transparent Plexiglas is placed in a well-designed microwave heater. Inside the bed, a single polar tracer, sharing the same size but different densities with bed particles, is heated continuously by the microwave energy. Then its trajectory is detected by means of a top-grade infrared camera. Thus, two hydrodynamics parameters such as the cycle time distribution and residence time distribution are determined by processing the obtained thermal images. On the basis of this, the effects of tracer density and gas velocity on them are analyzed, respectively. The results show that there exist two kinds of cycles: short cycle and nonstandard cycle. The former is predominant in the case of heavy tracer, and the latter is more significant at lower gas velocities. Raising the spouting gas velocity lowers the mean cycle time and promotes high concentration of the residence time distribution in the vicinity of the wall. An increase in the fluidizing gas velocity leads to a lower mean cycle time and a more homogeneous residence time distribution in the annulus.

The concept of Shannon entropy increment analysis, that is, Shannon entropy increment (SEI) and Shannon entropy increment rate (SEIR) of pressure fluctuations, was developed to recognize the dynamic behavior of fluidizing of cylinder-shaped biomass fuels (2.6 mm in transection diameter and 6 mm in length). Experiments were carried out in a visible biomass fluidized bed with a cross-section of 0.1 m by 0.03 m and height of 0.5 m. The condition of high Shannon entropy was defined as a high level of uncertainty in the ability to predict the dynamic behavior of gas−solid flow. The SEI and SEIR were regarded as the change of uncertainty and the change speed of uncertainty with operating condition, respectively. The results showed that the flow patterns of gas/cylinder-shaped biomass transited in turn with under-fluidization, steady fluidization, and turbulent fluidization when the superficial gas velocities increased. Both SEI and SEIR were pronounced with these flow patterns and transitions. The lowest values of SEI and SEIR were found in the flow pattern of steady fluidization, whereas the highest values of both parameters were found in the flow pattern of turbulent fluidization.

Studies on the fluidization of biomass particles and binary mixtures of biomass particles with fluidization mediums were carried out. The biomass particles used were wood chip, mung beans, millet, corn stalk, and cotton stalk, and the fluidization mediums employed were silica sand, continental flood basalt (CFB) cinder, and aluminum oxide. Experiments were performed in a rectangular biomass fluidized bed (cross-sections of 0.4 × 0.4 m in a dense region and 0.5 × 0.5 m in a freeboard region, with a height of 4.4 m). The minimum fluidization velocity (UMF) of approximate sphere biomass particles (wood chip, mung beans, and millet) and long thin biomass particles (corn stalk and cotton stalk) in different transection diameters and ratios of length/diameter were tested. Furthermore, the UMF of binary mixtures of biomass particles with fluidization mediums of different particle densities and diameters was obtained. The results showed that the UMF of long thin biomass increases with an increasing transection diameter and aspect ratio of length/diameter, while long thin biomass with the aspect ratio over a certain value could not be fluidized; the UMF of binary mixtures increase with an increasing density and diameter of fluidization medium and an increasing mass fraction of biomass. On the basis of experimental data, new correlations were developed for predicting the values of UMF. Comparisons of the predicted UMF by the correlations with experimental data in both the present work and literature were carried out. It was found that the present proposed correlations reasonably well-predicted the UMF of biomass particles and binary mixtures of biomasses with fluidization mediums.

Flow behaviors of a large spout-fluid bed (I.D. 1.0 m) at high pressure and temperature were investigated by Eulerian simulation. The gas phase was modeled with k − ε turbulent model and the particle phase was modeled with kinetic theory of granular flow. The development of an internal jet, gas–solid flow patterns, particle concentrations, particle velocities and jet penetration depths at high pressure and temperature at different operating conditions were simulated. The results show that the bed operated at an initial bed height larger than the maximum spoutable bed height resembles the flow patterns of jetting fluidized beds. The radial profiles of particle velocities and concentrations at high temperature and pressure have the similar characteristic shapes to those at ambient pressure and temperature. The particle concentrations and velocities appear to depend on the bed heights when increasing pressure while keeping the gas velocities and temperature constant. The particle velocities in the lower region of the bed increase with increasing pressure, while they tend to decrease in the middle and upper regions of the bed. The particle concentrations have an opposite dependency with increasing pressure. They decrease in the lower region of the bed but increase in the middle and upper regions of the bed. Besides, the jet penetration depths are found to increase with increasing pressure.Flow behaviors of a large spout-fluid bed (I.D. 1.0 m) at high pressure and temperature were investigated by Eulerian simulation. The gas phase was modeled with k − ε turbulent model and the particle phase was modeled with kinetic theory of granular flow.

Differential pressure fluctuation time series were obtained at different locations in a two-dimensional spout-fluid bed with a cross section of 300 × 30 mm and height 2000 mm. Shannon entropy analysis of differential pressure fluctuations was developed to characterize the dynamic behavior. Effects of two important operating parameters (spouting gas velocity and fluidizing gas flow rate) on the Shannon entropy were examined. It was demonstrated that a spout-fluid bed at a high spouting gas velocity or fluidizing gas flow rate was a deterministic chaos system since the Shannon entropies at all bed locations increased sharply and asymmetric unstable flows occurred. Shannon entropies were found to be significantly different at various bed locations. Shannon entropies of different flow regimes were distinct, so they were used to identify the flow regimes. The results show that the Shannon entropy helps to grasp the complex characteristics of dynamic behavior in spout-fluid beds.

•Six flow regimes and three regime transition routes are classified and discussed.•Two unstable fluidization patterns are observed and their mechanisms are discussed.•ΔP-uf curve is used to indentify flow regime transition routes and stability.•Effect of particle properties and operating conditions are analyzed.•A contact force model for a cylindrical particle in a bed material cloud is derived.An experimental study of the flow regimes and transitions in a fluidized bed (cross-section of 200 mm × 200 mm and height of 2000 mm) containing a mixture of cylindrical particles and silica sand is carried out. Six different flow regimes are identified: fixed bed (F), bubbling fluidization (B), transition fluidization (T), partial fluidization (P), complete fluidization (C) and unable to fluidize (N). The flow regime characteristics are described using schematic diagrams and photographic images. Based on the flow regime classification, three types of flow regime transition routes are explained. The effect of various operating parameters on the flow regime transition is determined and the resulting flow regime map is presented. Two unstable fluidization patterns are observed and their fluidization mechanisms are discussed. It is shown that the change of the ΔP-uf profile, where ΔP is the bed pressure drop and uf is the superficial gas velocity, indicates when a flow regime transition occurs and the reproducibility of the ΔP-uf curve identifies fluidization stability. Furthermore, a contact force model for a cylindrical particle in a bed material cloud is developed considering particle orientation, based on which a theoretic model for cylindrical particle fluidization termination velocity (ub) was derived and validated.

Flow behaviors of four kinds of granular particles (i.e. sphere, ellipsoid, hexahedron and binary mixture of sphere and hexahedron) in rectangular hoppers were experimentally studied. The effects of granular shape and hopper structure on flow pattern, discharge fraction, mean particle residence time and tracer concentration distribution were tested based on the visual observation and particle tracer technique. The results show that particle shape affects significantly the flow pattern. The flow patterns of sphere, ellipsoid and binary mixture are all parabolic shape, and the flow pattern shows no significant difference with the change of wedge angle. The flowing zone becomes more sharp-angled with the increasing outlet size. The flow pattern of hexahedron is featured with straight lines. The discharge rates are in increasing order from hexahedron, sphere, binary mixture to ellipsoid. The discharge rate also increases with the wedge angle and outlet size. The mean particle residence time becomes shorter when the outlet size increases. The difference of mean particle residence time between the maximum and minimum values decreases as the wedge angle increases. The residence time of hexahedron is the shortest. The tracer concentration distribution of hexahedron at any height is more uniform than that of binary mixture. The tracer concentration of sphere in the middle is lower than that near the wall, and the contrary tendency is found for ellipsoid particles.

Experiments on simultaneous absorption of SO2 and NOX from sintering flue gas via a composite absorbent NaClO2/NaClO were carried out. The effects of various operating parameters such as NaClO2 concentration (ms), NaClO concentration (mp), molar ratio of NaClO2/NaClO (M), solution temperature (TR), initial solution pH, gas flow (Vg) and inlet concentration of SO2 (CS) and NO (CN) on the removal efficiencies of SO2 and NO were discussed. The optimal experimental conditions were determined to be initial solution pH = 6, TR = 55 °C and M = 1.3 under which the average efficiencies of desulfurization and denitrification could reach 99.7% and 90.8%, respectively. Moreover, according to the analysis of reaction products, it was found that adding NaClO to NaClO2 aqueous solution is favorable for the generation of ClO2 and Cl2 which have significant effect on desulfurization and denitrification. Finally, engineering experiments were performed and obtained good results demonstrating that this method is practicable and promising.In this study, experiments on simultaneous absorption of SO2 and NOX from sintering flue gas via a composite absorbent NaClO2/NaClO were carried out. The effects of various operating parameters such as NaClO2 concentration (ms), NaClO concentration (mp), molar ratio of NaClO2/NaClO (M), solution temperature (TR), initial solution pH, gas flow (Vg) and inlet concentration of SO2 (CS) and NO (CN) on the removal efficiencies of SO2 and NO were discussed. Moreover, reaction products were analyzed, the interaction mechanism of NaClO2/NaClO and the removal reaction mechanism were revealed with the main reaction equations summarized. Finally, engineering experiments were carried out to verify the practicability of the technology.Download high-res image (190KB)Download full-size image

•Statistical, Hurst, Hilbert–Huang transform and Shannon entropy analysis are used.•Flow regime transitions in a three-phase bubble column are detected.•EMD energy entropy is effective for flow regime identification.•Shannon entropy shows dynamic behavior characteristics of three-phase bubble columns.•The transition gas velocities show good agreement with the experimental results.Flow regime transitions in a gas–liquid–solid three-phase bubble column were investigated based on pressure time series. The statistical, Hurst, Hilbert–Huang transform and Shannon entropy analysis methods were applied to differential pressure fluctuation data measured in a two-dimensional (2-D) bubble column measuring 0.1 m in length and 0.01 m in width equipped with a sintered plate distributor (average diameter of holes was 50 μm). Air was used as the gas phase and tap water as the liquid phase. Glass beads measuring 150 μm in size with a particle density of 2500 kg/m3 constituted the solid phase. Based on sudden changes in both the EMD energy entropy from Hilbert–Huang transform and the Shannon entropy values, two flow regime transition gas velocities were successfully identified: the homogeneous regime shifted to the transition regime at a superficial gas velocity of 0.069 m/s; and the transition regime shifted to the heterogeneous regime at a superficial gas velocity of 0.156–0.178 m/s. The transition gas velocities showed good agreement with the experimental results. The EMD energy entropy and Shannon entropy analysis methods can reveal the complex hydrodynamics underlying gas–liquid–solid flow and are confirmed to be reliable and efficient as non-invasive methods for detecting flow regime transitions in three-phase bubble column systems.