Spouting Gas Velocity Research Articles

An XCT study on three-dimensional characteristics of a spout-fluid bed

Spout-fluid beds are widely used in the chemical and petrochemical industries for excellent mixing and heat and mass transfer properties. Understanding the behavior of jets in spout-fluid beds is crucial for optimizing these processes. In this paper, we present a novel experimental method for studying the three-dimensional characteristics of jets in spout-fluid beds using X-ray computed tomography. By employing a gas–solid flow parameter measurement system, we propose an accurate experimental fitting method for voxel voidage values, enabling the three-dimensional reconstruction of the time-averaged voidage in the entire flow field of a spout-fluid bed. These data are then used to develop an image processing algorithm for identifying and quantifying gas jets in the flow field, allowing for measures of jet length, volume, and diameter. We further investigate the effects of static bed height, spouting gas velocity, and fluidizing gas flowrate on the three-dimensional characteristics of jets.

Investigation of flow characteristics in a rectangular spouted fluidized bed using electrical capacitance volume tomography

The characterization of gas-solid flow behavior in rectangular spouted fluidized bed (RSFB) poses significant challenges due to the presence of complex gas-phase vortex flow within the bed. The flow characteristics of gas-solid two-phase flow in RSFB were investigated by using a self-developed 32-electrode electrical capacitance volume tomography (ECVT) system with an imaging speed of 105 frames per second when the spouting gas velocity Uf increased from 0.97 m/s to 1.78 m/s. Experimental results demonstrate that with increasing Uf, the flow transitions from weak bubbling/bubble fluidization to turbulent fluidization in the RSFB. The amplitude peak difference of particles in different planes of the fluidized bed gradually decreases, and the rising velocity of bubbles initially decreases and then increases. The gas-particle backmixing effect strengthens, while the entrainment effect during bubble rupture weakens. The research findings can provide valuable insights for understanding the flow behavior in RSFB and offer guidance for optimizing the process operation of fluidized bed reactors.

Super-quadric CFD-DEM study of spout deflection behaviour of non-spherical particles in a spout fluidized bed

Non-spherical particles are commonly encountered in chemical engineering processes including fluidization processes, yet their instability phenomena still lack understanding. In this study, the spout deflection – a typical instability phenomenon of non-spherical particles in a pseudo-two-dimensional (pseudo-2D) spout fluidized bed is first studied by a super-quadric computational fluid dynamics-discrete element method (super-quadric CFD-DEM) model. The intensity of spout deflection is quantified by the spout deflection angle concept. The effect of particle shape (i.e., sphere, cubic, ellipsoid, and cylinder) on the flow in terms of flow pattern, spout deflection, pressure drop, particle orientation, and normal contact force is systematically studied and compared by the time- and frequency-domain analysis. It shows that the spout channel becomes narrower for cubic, ellipsoid and cylinder particles where the particle aspect ratio increases. With the increase of spouting gas velocity, the median value of the spout deflection angle decreases and increases for cubic and ellipsoid particles, respectively. Furthermore, the pressure drops in the vertical and horizontal directions of the cubic, ellipsoid, and cylinder particles are different from each other. At last, In the bed of cubic particles, the ordered arrangements appear close to the wall region and random arrangements occur in the other regions. This work reveals the influences of non-spherical particles on spout deflection and offers insights into practical applications through optimal operation.

CFD-DEM study of spout deflection behavior of cohesive particles in a spout fluidized bed

The spout deflection problem limits the operating range and poses a threat to the normal production of fluidized beds especially when the cohesive particles are practised, yet these processes were not well understood at the particle scale in the past. In this work, the spout deflection behavior of cohesive particles in a pseudo-2D spout fluidized bed is studied by Computational Fluid Dynamics - Discrete Element Method featuring a cohesion sub-model. The model is validated against experimental measurements of two cases. Then three types of particles are studied including dry particles and two types of cohesive particles covered by water and honey, respectively, for comparison in terms of flow pattern, spout deflection, and bed pressure drop. The simulation results show that compared with the case of dry particles, the cases of cohesive particles have smaller spout deflection, 16.3% smaller for water-covered particles and 68.1% smaller for honey-covered particles in their base cases. Further, the effects of key parameters are studied. The median value of the spout deflection angle for dry and cohesive particles all increases with increasing spouting gas velocity. The median values of the spout deflection angle of cohesive particles are significantly affected by initial particle surface liquid content. At last, the gas pressure drops in the vertical direction caused by the particle resistance are almost the same between the cases of dry and cohesive particles; however, the gas diffusion in the horizontal direction is highly correlated with the initial particle surface liquid content, liquid types, and spouting gas velocity. This work unveils the impacts of cohesive particles on spout deflection and sheds light on the optimal operation for practical applications.

Insight into multi-level fluidization characteristics of a spout-fluid bed under different gas-solid actions: From monodisperse particles to bidisperse particles

In this study, the effects of gas flow and particle parameters on monodisperse and bidisperse particles were systematically modelled with CFD-DEM from multi-level characteristics: fluidity, periodicity and mixing. With increasing spouting gas velocity, the mixing rate increased and overall flow state changed from spout-fluid to the spout. By comparison, the increase of auxiliary gas velocity showed the opposite variation trend. For bidisperse particles, with increasing light and small particle ratios, the dominant particles of fluidization characteristics changed from coarse and heavy to light and small particles, whose variation regularities were similar to those of single particle size and density. Furthermore, the particle fluidity improved continuously and local particle concentration differences increased. Ultimately, the particle segregation mechanism was proposed by summarizing variation regularities of fluidization characteristics under different gas-solid actions. Besides, compared to particle density, the difference in particle size caused greater stratification, which would reduce the local mass transfer efficiency. • The spout-fluid bed is deeply analyzed from fluidity, periodicity and mixing. • The particle motion behaviors under different gas-solid actions are investigated. • The segregation mechanism between mono-and bidisperse particles is summarized. • The increase of light and small particles contributes to the fluidization quality.

Insight into hydrodynamics and heat transfer characteristics in a gas–solid spout fluidized bed from a multiple zone view

In this work, the hydrodynamics and heat transfer characteristics within a gas–solid spout fluidized bed were investigated from a multiple-zone view by employing the coupled computational fluid dynamic and discrete element method. Results show that both the axial and radial particle mixing rates are accelerated with the axial particle mixing rate much faster than the radial one when increasing the spouting gas velocity. Besides, the particle-scale and the multiple-zone heat transfer analyses show that the annulus zone makes the major contribution to inter-particle conduction with the particle–particle conduction and the particle–fluid-particle conduction heat fluxes taking up about 64 % and 73 %, followed by the fountain zone taking up about 28 % and 22 %, respectively. As for the particle–fluid convective heat transfer, the spouting and annulus zones make almost the comparative contributions being about 38 %, followed by the fountain zone being less than 24 %. Moreover, the full-bed time-averaged heat transfer analysis shows that the particle–fluid convective heat transfer plays a dominant role in the heat transfer process in the spout fluidized bed with the particle–particle conductive and the particle–fluid-particle conductive heat fluxes being about 0.1 % and 1 % of the particle–fluid convective heat flux. The results of this study can provide an efficient theoretical reference for the gas–solid flow-mixing-heat transfer processes optimization and intensification of spout fluidized beds.

Comparison of different drag models in CFD-DEM simulations of spouted beds

Spouted beds are commonly simulated through the Computational Fluid Dynamics – Discrete Element Method approach. The choice of the drag model is still a matter of debate, as they feature peculiar operative conditions. In this work, we simulated two spouted beds containing Geldart-D particles. We tested seven drag models: three are classic models, while four are developed through advanced computational techniques. The results indicate that the key variable is the ratio between the operative and the minimum spouting gas velocity (u/ums). At u = ums only the Gidaspow model can always predict fluidisation, but at low u/ums values the Beetstra model is the best compromise. For higher values, the Rong and Di Felice models behave better, while the others overestimate the particles' velocity. These results can be useful to identify the best performing model and show there is a need for more appropriate models for spouted beds.

Surface-to-bed heat transfer for high-density particles in conical spouted and spout–fluid beds

Bed-to-surface heat transfer experiments from a vertically submerged cylindrical surface were conducted in laboratory-scale (Dc=25cm) conical spouted and spout–fluid beds at two different conical angles (31° and 66°) in the high particle density range (2500kg/m3≤ρp≤6000kg/m3). The effects of the bed design parameters (conical angle and inlet diameter of spouting gas entrance) and operating conditions (static bed height, particle size, density, and spouting and fluidization gas flow rates) on the heat transfer characteristics were investigated in detail. The heat transfer coefficients were shown to be dependent on the density and size of the particles. The minimum stable spouting velocities of the denser and larger particles were higher, which led to higher operational spouting velocities and thereby resulted in higher heat transfer coefficients. The positive effect of increasing the particle diameter on heat transfer was more pronounced in the spout and at the spout–annulus interface, whereas this effect was diminished in the annulus region. The heat transfer coefficient increased with increasing spouting gas velocity up to 1.0Ums–1.1Ums, beyond which no significant change was observed regardless of the particle type. The heat transfer coefficient in the annulus decreased with increasing conical angle because of reduced particle circulation. The spout–fluid operation increased the heat transfer coefficient by a maximum of 10% at the expense of a significant increase of the total gas flow rate. This result was attributed to the inability of the fluidizing gas to penetrate the annulus. An empirical correlation for the average heat transfer coefficient in the annulus was also proposed based on the data obtained in this work.

Parameters Affecting Efficient Solid Circulation Rate in Draft Tube Spouted Bed

Solid circulation rate in a draft tube spouted bed is an important parameter for its industrial use. It can be manipulated adjusting the dimensions of the draft tube and entrainment height above the gas inlet nozzle and is studied here for a wide range of spouting gas velocities. A maximum entrainment height is identified and seen to show strong correspondence with the ratio between the projected volumes of annulus and spout zones below the draft tube. Overall energy loss at the spout-annulus interface has been reported for the first time as a function of particle size. Solid circulation rate is seen to be highly affected by flow resistance due to the passage of solid flow between conical apparatus wall and the draft tube and solid pressure in the annulus and can be well varied by changing the spouting gas velocity and fixing at a critical value.

Fluidization Characteristics of TiO2 Ultrafine Particles in an Acoustic Spout-fluid Bed with a Draft Tube

Abstract An experimental study was performed to investigate the effects of spouting gas velocity, fluidizing gas velocity, sound wave frequency and sound wave pressure level on fluidization behaviors of ultrafine particles in an acoustic spout-fluid bed with a draft tube. A half-cylinder with a diameter of 120 mm and height of 1200 mm was used as the fluidization column, TiO2 ultrafine particles with an average diameter of 290 nm were employed as the bed materials while the high-speed atmosphere jet was utilized as the spouting gas. Results showed that high-speed jet as spouting gas could effectively disrupt the agglomerates of TiO2 ultrafine particles and reduce the agglomerate size significantly. The introduced fluidized gas in annulus was conducive to eliminate dead-zone in the bottom of bed. Sound wave could break bubbles, restrain channeling making the axial fluidization state in annular region to be more uniform and homogeneous, thus significantly improved the fluidization quality of agglomerates in the annulus, reduced the minimum spouting velocity of particles, and promoted the stable circulation of inner particles in spout-fluid bed with a draft tube.

Hydrodynamic behavior of silicon particles with a wide size distribution in a draft tube spout-fluid bed

An experimental study on the hydrodynamic behavior of silicon particles with a wide size distribution in a draft tube spout-fluid bed was performed in a 182 diameter cylindrical column with a flat gas distributor. Effects of spouting and fluidizing gas velocity, static bed height, entrainment zone height and draft tube diameter on the maximum spouting pressure drop, minimum stable spouting velocity and solids circulation rate were investigated. The results show that the maximum spouting pressure drop increases with static bed height, entrainment zone height, draft tube diameter and fluidizing gas velocity. The minimum spouting velocity increases with entrainment zone height, while it decreases with static bed height, draft tube diameter and fluidizing gas velocity. Two correlations on the maximum pressure drop and minimum spouting velocity are proposed respectively based on the experimental data, which are in good agreement with the present experiments. In addition, the solids circulation rate increases with static bed height, draft tube diameter, fluidizing and spouting gas velocity. It also increases with entrainment zone height at a lower fluidizing gas velocity, however it decreases with entrainment zone height at a higher fluidizing gas velocity.

Statistical and frequency analysis of pressure fluctuation in an annular spouted bed of coarse particles

The pressure fluctuation characteristics of an annular spouted bed filled with coarse particles were studied by statistical and frequency analysis. The effects of spouting gas velocity, static bed height, and measuring point height on pressure fluctuation standard deviation and major frequency were systematically examined. The peak frequencies and the behavior of bubbles in the gas-solid spouted bed were observed. Experimental results show the unique features of the novel spouted bed filled with coarse particles: the pressure fluctuation standard deviation increases with the increasing of spouting gas velocity and static bed height; however, it decreases with the increasing of measuring point height. For Ug<Ums, two distinct peaks with one around 0.5Hz and the other around 5.5Hz are shown; while for Ug>Ums, three peaks with the highest one at around 4Hz can be observed in the spectra, and the major frequency decreases apparently with the increasing of spouting gas velocity, and also decreases with the increasing of static bed height or measuring point height. The peaks in the power spectral density (PSD) of pressure fluctuation are in good agreement with the observed behavior of bubbles in the annular spouted bed. The results would be helpful for the identification of flow pattern in the annular spouted bed of coarse particles.

CFD-DEM study on cohesive particles in a spouted bed

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.

Influence of operating parameters and flow regime on solid dispersion behavior in a gas–solid spout-fluid bed

The dispersion behavior of the solid phase in a three-dimensional spout-fluid bed was numerically investigated via the approach of coupled computational fluid dynamics and discrete element method (CFD–DEM), in which the fluid and solid phases were solved using the Eulerian and Lagrangian framework, respectively. Detailed trends of both the local and overall dispersion behaviors of the solid phase in the system were quantitatively studied, and the impact of various operating parameters (namely, spouting gas velocity (Usp), background velocity (Ubg), particle diameter (dp), the bed depth (L) and bed height) and flow regime on lateral and vertical solid dispersion was investigated. The results show that varying Usp, Ubg and dp affects the local solid dispersion in the spout and fountain regions more than the annulus. To enhance the overall solid dispersion, either Usp or Ubg or L can be increased, or dp and bed height can be decreased. Meanwhile, the total gas flow rate plays the dominated role for overall dispersion of solid phase. Finally, solid dispersion is the most effective in the Jet-in-fluidization regime, followed by the Spouting-with-aeration then the Intermediate/spout-fluidization regimes.

Investigation of fluidization behavior of high density particle in spouted bed using CFD–DEM coupling method

CFD–DEM coupling simulation method is used to study the fluidization behavior of particle with different densities in the spouted bed. The simulation results show that the particle spouting behavior is incoherent and periodic in the stable spouting state. The cycle periods of the whole bed and single particle are obtained from particle trajectory and compared with experimental results. The relationships between the minimum spouting gas velocity, the steady pressure drop and the particle density are obtained. It can be found that the gas velocity range of stable spouting state expands when the particle density increases. The dual, single and multiple dominant frequencies are found in the stable spouting process of high density particle. Through detailed analysis on the mechanism of spouting dominant frequency, the flow pattern map with different superficial gas velocities and particle densities is given and can be divided into five regions: fixed bed with internal spouting, transitional stable spouting state with dual dominant frequency, main stable spouting state with single dominant frequency, transitional stable spouting state with multiple dominant frequency, and unstable spouting state. The stable spouting gas velocity is influenced by the particle density, while the dominant frequency of the particle spouting process will keep invariant even if the particle density increases, as long as Ug/Ums is not changed. The influence of particle density on the particle residence time distribution in the spout region, which can be used to characterize the gas solid contact efficiency, is also discussed based on simulation results.

Numerical investigation of the time-related properties of solid phase in a 3-D spout-fluid bed

Numerical simulation of the two-phase flow in a 3-D spout-fluid bed is carried out to investigate the time-related properties of solid phase based on the In-house code by CFD–DEM coupling approach. The mixing time, distribution properties of the cycle time, global residence time and local residence time of solid phase are explored. Moreover, the influences of spouting gas velocity, background velocity, particle diameter and bed thickness on these properties are discussed. The results illustrate that the mixing time is lowered with the increase of spouting velocity or the decrease of background velocity. Cycle time shows a log-normal distribution behavior and grows with the increase of the particle diameter but decreases with the increase of spouting velocity or background velocity. Moreover, nearly 60% of the total particle time elapses in the annulus and 34% of that in the fountain while only 6% of that is paid in the spout. The solid residence time (SRT) in the spout or annulus diminishes with increasing spouting velocity or background velocity and also the decrease of particle diameter. However, the SRT in the fountain region shows the opposite response behavior. The scale-up of the bed thickness enlarges the cycle time and SRTs in three regions of the bed. Besides, small local SRT appears in the spout while large value exists in the annulus especially the corners of the bed bottom. The geometrical configuration of the bottom leads to the opposite distribution of local SRT near walls in the annulus and fountain. Moreover, the local SRTs in different regions of the system show distinct distribution properties.

Effects of Operating Parameters on Hydrodynamic Behavior of Spout-fluid Beds without and with a Draft Tube

The spout-fluid bed (SFB) is one of many modifications to conventional spouted bed, which is achieved by introducing an auxiliary gas flow into the annular region of a spouted bed through a distributor. Therefore, the SFB has better gas-solid contact and mixing, and reduces the risks of particle agglomeration and dead zone. In addition, the gas-solid contact and the solids circulation rate can be controlled more easily and flexibly by installing a draft tube in the bed (DSFB). In this study, the effects of operating parameters on flow characteristics of the SFB and the DSFB were investigated and they were compared, using the same semi-cylindrical column and the same particles. As the results, the flow regime maps were recognized based on pressure fluctuation data and the DSFB had wide range of operating conditions for stable spouting, comparing with the SFB. The minimum spouting gas velocity for stable spouting state (spouting with aeration) decreased with increasing the auxiliary gas velocity. Also, longitudinal and radial distributions of particle velocity in the spout and the annulus were obtained in detail for the stable spouting state by means of the particle image velocimetry (PIV). Particle velocities in the spout and the annulus were increased with increasing the auxiliary gas velocity. Moreover, the distributions of particle velocities in the DSFB showed that particles in the draft tube were accelerated remarkably and particles in the annulus descended uniformly with small velocity, comparing with the SFB.

Flow pattern and transition in gas–liquid–solid three phase spouted bed

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=2.6mm, 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.

Distribution of particle velocity in a conical cylindrical spouted bed

AbstractInvestigations of particle velocities in a 200‐mm diameter conical cylindrical spouted bed were carried out. A direct measurement approach, coupled optical‐fibre endoscope with high‐speed photography, was used to determine the local velocity of glass bead and corn at various spouting velocities. The results showed that the radial particle velocity profiles when spouting of corns are similar to glass beads. The changes of particle velocities with increasing spouting gas velocity were more remarkable in the spout and fountain regions than in the annulus. The velocity of the glass beads is higher than the corns in the spout region, while they appear a reverse trend in the fountain region and annulus region at the same spouting velocity.

Numerical simulation on the mixing behavior of corn-shaped particles in a spouted bed

Abstract 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 − e 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.