Spout-fluid Bed Research Articles

Optimization of bitter orange (Citrus aurantium L.) essential oil microencapsulation through spout fluidized bed drying

Optimization of bitter orange (Citrus aurantium L.) essential oil microencapsulation through spout fluidized bed drying

Jet injection and spout formation in a fluidized bed

A single jet was studied in a rectangular fluidized bed by analyzing the pressure fluctuations data to characterize the jet hydrodynamics. The bed contained with glass beads of different mean sizes (450, 650, and 920 µm) as well as pharmaceutical pellets (920 µm). The analysis of the pressure fluctuation data was performed using the power spectral density function (PSDF) and discrete wavelet transforms technique. This study investigated how the flow regime changed from a jet in a fluidized bed to a spouted regime as the gas injection velocity was increased. Increasing the mean particle size led to an increase in the minimum spouting velocity. The minimum spouting velocity for 450, 650, and 920 μm glass bead particles and for 920 μm pharmaceutical pellets were determined to be 32.47 m s-1, 38.66 m s-1, 44.78 m s-1, and 44.47 m s-1, respectively. The study also examined how the dominant frequency of the various particles and the energy percentage of scales changed with increasing injection velocities. The ratio of energy percentages of meso-scale changes as the injection velocity increases and these changes were used to estimate the minimum spouting velocity. Wavelet sub-signals analysis revealed that the Daubechies 2 (DB2) wavelet was the most effective at capturing the characteristics of the jet. Based on the Shannon entropy of the approximate coefficients, the wavelet analysis showed that 11 levels of decomposition were required. By combining the wavelet analysis and PSDF, a more detailed analysis of the meso-scale was achieved. This study provided valuable insights into the behavior of jets and spouts in fluidized beds, which can greatly contribute to the optimization of a jet in fluidized beds and spout-fluidized beds by enhancing our understanding of jet behavior in such environments.

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.

Extraction and Microencapsulation of Phytochemical Compounds from Mango Peel (Mangifera indica L.) var. “Kent” and Assessment of Bioaccessibility through In Vitro Digestion

The peel from mango (Mangifera indica L.) var. “Kent” is a good source of bioactive compounds (BC). BC are sensitive to oxygen, temperature, humidity, light, and gastrointestinal digestion, which change their biological function and health benefits. This study was aimed at the extraction of the bioactive compounds present in the peel from mango var. “Kent” and their microencapsulation using spray drying (SD) and spout-fluid bed drying (SFB). The bioaccessibility of BC was also evaluated. Two consecutive extractions of 90 min at 30 °C and 80% v/v ethanol were used. The microcapsules produced via SD and SFB presented high retention and encapsulation percentages of the bioactive compounds; nevertheless, SFB showed better protection during in vitro gastrointestinal digestion. The non-encapsulated extract showed a decrease (p ≤ 0.05) of BC at the end of in vitro gastrointestinal digestion. The results show that these microcapsules might be used in the food industry as an ingredient to produce functional foods and, thereby, to obtain the health benefits that the bioactive compounds provide.

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 investigation of particle breakage in spout-fluidized beds

In a fluidized bed, particles undergo mechanical stress resulting from collisions with other particles, the bed walls, or internal equipment. Particle breakage exerts a significant impact on the hydrodynamics and overall performance of the fluidized bed by modifying the particle size distribution. This study explores this phenomenon through the application of an enhanced computational fluid dynamics-discrete element method (CFD-DEM) coupled with a particle breakage model in three distinct flow regimes: spouted bed, jet-in-fluidized bed, and spouting-with-aeration bed. The simulations revealed various aspects related to particle breakage, encompassing the spatial and temporal distribution of particle sizes, the location of breakages, breakage rates, solid particle fraction, and the height of the bed. The findings establish a pronounced correlation between the breakage rate and the velocity of the jet, with the spouting-with-aeration bed displaying the highest level of particle breakage. Furthermore, it is noteworthy that nearly 98% of the breakages occur within the distributor zone.

CFD-DEM simulation of heat transfer in spout-fluid beds

It is necessary to study the flow regimes of spout-fluid beds before considering their application in the industry. A three-dimensional computational fluid dynamic coupled with the discrete element method (CFD-DEM) was employed to study the heat transfer of the jet-in-fluidized bed flow, spouting-with-aeration flow, and intermediate/spout-fluidization flow regimes of the spout-fluid bed. To determine the efficiency of heat transfer in these flow regimes, extensive CFD-DEM simulations were conducted along with a heat transfer model. The heat transfer in these flow regimes was investigated using particle temperature distributions, mean convective heat flux, and average particle temperature. Compared to the other flow regimes, the jet-in-fluidized bed flow regime demonstrated a higher degree of heat transfer due to the presence of bubbles in the annulus. Moreover, it was observed that the spouting-with-aeration flow regime exhibits a better convective heat transfer compared to the intermediate/spout-fluidization. The stable and continuous spout channel of the spouting-with-aeration flow regime helps convective heat transfer more than the interrupting spout channel of the intermediate/spout-fluidization.

Investigation of wetting and drying process in a spout-fluid bed using acoustic sensor and electrical capacitance tomography

To investigate complex gas-solids flow characteristics of a spout-fluid bed with bafflers in wetting and drying process, a non-intrusive measurement technique combining pressure, acoustic transmitters and an electrical capacitance tomography (ECT) sensor is proposed in this paper. The proposed approach can collect acoustic and pressure signals and realize visualization in three flow regions separated by two bafflers synchronously. By ECT images and power spectrum and wavelet analysis of the pressure drop signals, two typical flow state transitions in the wetting and drying process can be identified. The result analysis based on acoustic transmitter indicates that the particle–wall collision frequency band is narrow and the particle–particle collision frequency band is wide. A key recurrence quantization parameter of acoustic signal, Laminarity, increases with the decrease of particle flowability. The parameter of Laminarity combined with the capacitance signal related to the particle moisture content can effectively reflect the wetting rate and provide an accurate monitoring of de-fluidization process in the bed.

Comparative CFD-DEM study of flow regimes in spout-fluid beds

Spout-fluid beds are unique systems that require thorough study prior to their industrial application. In this study, the hydrodynamics of spout-fluid beds were investigated using 3D computational fluid dynamics coupled with discrete element method (CFD-DEM). Three flow regimes, including jet-in-fluidized bed, spouting-with-aeration, and intermediate/spout-fluidization were studied, and the particle mixing was quantified in these regimes using the Lacey mixing index. The results showed that both axial and lateral mixing rates are better in jet-in-fluidized bed and the spouting-with-aeration flow regimes, with the axial mixing being superior to the lateral in all flow regimes. Examining the diffusivity coefficient revealed that mixing in the jet-in-fluidized bed flow regime is better due to the formation and eruption of bubbles in the annulus. Additionally, the granular temperature was analyzed in all flow regimes, and higher particle velocity fluctuations were observed in the spouting-with-aeration and the jet-in-fluidized bed flow regimes due to the higher spout gas velocity and formation of bubbles in the annulus. This study provides valuable insights into the hydrodynamics of spout-fluid beds in different flow regimes, which can aid in the design and optimization of spout-fluid bed reactors for various industrial applications.

Numerical and experimental study on the particle erosion and gas–particle hydrodynamics in an integral multi-jet swirling spout-fluidized bed

In this paper, using the computational fluid dynamics based on Euler Lagrange and the commercial software Barracuda VR, the gas–particle hydrodynamics and the erosion of particles on the inner wall and internal components of the spouted bed in the integrated multi-jet swirling spout-fluidized bed (IMSSFB) are studied. Erosion experiments have obtained the characterization of particle erosion on internal components and verified the relevant numerical models. The results show that: the particle distribution within the IMSSFB is uneven due to the cyclonic effect of the axial swirl vane (ASV), resulting in particle erosion for the ASV being concentrated on one side; when the gas reaches the top, too high an erosion gas velocity leads to gas backflow. As the filling height increases, there is a tendency for the erosion position of the particles on the ASV to expand upwards. However, the effect of increasing gas velocity on the erosion position is insignificant.

Effect of combining multi-jet component with axial swirl blade on evaporation in a spouted bed

To improve the fluidization behavior and the heat and mass transfer process in a spouted bed, a multi-jet–axial-swirl-blade spouted bed (MJ-ASB SB) was developed. The water evaporation process of the MJ-ASB SB was simulated and compared with those of the conventional spouted bed (CSB) and an integral multi-jet spout-fluidized bed (IMJSFB). The simulation results showed that the MJ-ASB SB combined the staged spouting action of multi-jet with the swirling action of the axial swirl blade, which promoted particle turbulence in the annulus region and ensured effective particle mixing. The swirl number of the MJ-ASB SB ranged from 0.0816 to 2.7239 with enhanced vortex intensity, thus promoting momentum and heat transfer of gas and particles in the spouted bed. The MJ-ASB SB had a higher slip velocity than the other two bed types, which indicates that the combined internal structure could improve the fluidization state of the bed and intensify the movement and mixing of phases in the spouted bed. The three-phase temperature, water evaporation rate, and gas humidity of the MJ-ASB SB were higher than those of the CSB and IMJSFB, and water evaporation occurred in an enlarged region in the MJ-ASB SB. The mass transfer intensification factors I of the MJ-ASB SB (2.62) and IMJSFB (1.92) were 91% and 161% higher than that of the CSB (1), respectively, indicating that the combined internal structure of the MJ-ASB SB significantly contributed to the water evaporation process.

Effect of the novel combined internal devices on gas−solid flow behavior in spouted beds

To reduce the flow dead zone in spouted beds (SBs), a novel multi-jet–axial swirl blade spouted bed (MJ-ASB SB) is proposed. Experimental verification and simulation analyses of the MJ-ASB SB, a conventional SB (CSB), and an integral multi-jet spout-fluidized bed (IMJSFB) were carried out. The simulation results showed that the combined structure resulted in more powerful turbulence, better radial mixing of particles in the spouting and annulus regions, and improved the flow−field uniformity. The intensification factor of the MJ-ASB SB was more than 20%, which was better than that of the IMJSFB, and the enhancement factors of the gas and particle velocities were four and five times those of the IMJSFB, respectively. Optimal structural parameters were obtained by analyzing the different structural parameters of the novel internal devices, and it was found that particle fluidization in the MJ-ASB SB was best when the height ratio ξ was 3, the width ratio was 1.3 and the rotation was clockwise.

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.

Numerical study of multi-jet structure impact on flue gas desulfurization process in 3D spouted beds

Multiple jets were added in the cone area of spouted beds to form an integral multi-jet spouted-fluidized bed (IMJSFB) to improve the flue gas desulfurization efficiency. The flue gas desulfurization process in the conventional spouted bed (CSB) and IMJSFB was simulated, and the accuracy of the adjusted mesoscale drag model and desulfurization prediction model was verified experimentally. The simulation results show that the spouting gas of CSB would skew after adding the slurry, while the spouting morphology of IMJSFB was less affected by slurry adding. The multi-jet structure can significantly enhance the flow field uniformity and interphase heat and mass transfer in spouted beds, especially in the cone area. The outlet gas moisture content in IMJSFB was 41 % higher than that of CSB. The desulfurization efficiency of CSB and IMJSFB was 77.75 % and 87.97 %, respectively, and the desulfurization efficiency was increased by 10.22 % by using the multi-jet structure.

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.

On-line monitoring of flow process in a spout-fluid bed by combining electrical tomography and high-speed CCD camera

To investigate spouted flow characteristics in a rectangular spout-fluid bed with bafflers, a non-intrusive measurement approach, which combines electrical capacitance tomography (ECT), pressure measurements and high-speed CCD imaging technology, is proposed. The ECT sensor has 12 electrodes on the external wall and 12 electrodes inside, forming three imaging regions with 8 electrodes in each region. The flow hydrodynamic characteristics in the spouted bed e.g., pressure fluctuation, particle packing fraction and fountain form, are investigated. The frequency domain of pressure and particle packing fraction signals as well as ECT images indicate that the flow regime in the jet region transits from slugging to spouting in fountain formation process, and when the fluidization velocity in one side increases, the flow regime in the same region transits into slugging bed. The spouting pressure drop is affected by the fluidization condition in the side region, and the high characteristic frequency of pressure signal decreases when the side region condition changes from blockage to fluidization. The fountain height increases linearly with the superficial gas velocity. When the gas velocity is high, the fountain tends to be offset by the influence of the lateral airflow which is caused by the imbalance of the air pressure on two side regions.

An inertial number regulated stress model for gas-particle flows with particle friction and volume fraction gradient

In this study, a solid stress model that can be used in both dilute and dense regimes for simulation of gas-particle flows with comprehensive considerations of friction and the effect of local solid volume fraction gradient is proposed. In the dilute regime, solid stress is closed by a modified kinetic theory that accounts for the effect of particle friction and volume fraction gradient. In the dense regime, solid stress is closed by the inertial number model. The transition from dilute to dense regimes is realized by using a dimensionless parameter χ , which is a function of the inertial number I s . This new model is validated with experimental data and discrete particle simulation from spout-fluid bed and bubbling fluidized bed. When compared with the traditional kinetic-frictional stress model, this new model improves the transition from dilute to dense regimes and the particle velocity predictions in both beds. • A solid stress model is proposed in both dilute and dense regimes for gas-solid flow. • The model comprehensively considers the effect of friction and volume fraction gradient. • The expression of excluded volume is derived from the generalized van der Waals theory. • The model gives a better prediction of spout-fluid bed and bubbling fluidized bed.

Two-fluid simulation of spout-fluid bed with multiple chambers: Flow structure, hydrodynamic characteristics and heat transfer

Spout–fluid beds are widely applied in the process industry due to their advantages of efficient contact between particles and gas. In this paper, a TFM (two-fluid model) is set up to simulate the hydrodynamics and heat transfer of a 3D spout-fluid bed with single, double and triple chambers. Simulation results show that scale-up by aligning multiple chambers is complex in the regimes with low SF (spout-fluid ratio) due to chamber-chamber interaction. In the regimes with high SF , however, scale-up is simple because chamber-chamber interaction is hardly noticed. With increasing SF , gas and particle fluxes on inter-chamber interfaces prefer to occur in the annulus regions instead of in the fountain region. The kinetic heat flux of the solid phase has a similar preference. The molecular heat flux of the solid phase always prefers to pass through the inter-chamber interface in the annulus region. The preference however weakens with increasing SF .

Effect of novel intensification structure on drying of particulate materials in spouted beds

Through the hot air-drying experiment, the differences in drying rate, unit energy consumption, and bed pressure drop of the conventional spouted bed (CSB), the spouted bed with an integral swirling blade nozzle (ISBN), the spouted bed with spherical longitudinal vortex generators (LVGs), and the integral multi-jet spout-fluidized bed (IMJSFB) were studied. The Weibull distribution function was introduced to fit the drying data, and the differences in moisture diffusion coefficient, scale parameters, and drying activation energy of the four types of spouted beds were further discussed. The drying performance parameters of the four types of spouted beds were comprehensively evaluated. The results show that, compared with the CSB, LVGs and IMJSFB reduce the activation energy of the drying process, while the ISBN increases the activation energy of the drying process. The IMJSFB shows more excellent performance in terms of drying rate, scale parameters, unit energy consumption, and bed pressure drop, with the highest comprehensive score. Compared with CSB, ISBN and LVGs, the IMJSFB is more suitable for drying wet particles. For the IMJSFB, there exists an optimal value of particle diameter (d = 2 mm) for the drying process, which makes the particle drying rate reach maximum.

CFD–DEM simulation of wet granular-fluid flows and heat transfer in an integral multi-jet spout-fluidized bed

The hydrodynamic and heat transfer characteristics of dry and wet particles in quasi-two-dimensional integral multi-jet spout-fluidized bed (IMJSFB) and conventional spouted bed (CSB) were numerically studied using Computational Fluid Dynamics-Discrete Element Method (CFD-DEM), where the effect of wet content of particles is realized by introducing the liquid bridge force. In addition, the agglomeration, particle mixing, circulation, collision and heat transfer of IMJSFB and CSB under different moisture content were quantitatively studied. It is found that with the increase of gas velocity, the circulation capacity of particles in both spouted beds increases first and then decreases, and particle circulation characteristics of IMJSFB are obviously better than those of CSB. The appropriate moisture content of particles is beneficial to enhance the heat transfer effect, and compared with CSB, IMJSSFB has more obvious advantages in dealing with wet particles. This study has important significance for the mixing and heat transfer of class D wet particles, which is less studied in fluidization technology, and provides theoretical and technical reference for the actual design and operation of spouted bed.