Spout-fluid Bed Research Articles

Modeling and Optimization for Gas Distribution Patterns on Biomass Gasification Performance of a Bubbling Spout Fluidized Bed

Gas distribution patterns exert a great impact on the gas–solid flow, heat and mass transfer, and reaction characteristics and thus affect significantly the thermal conversion efficiency inside the...

Spout Fluidized Bed Assisted Preparation of Poly(tannic acid)-Coated Urea Fertilizer.

Slow-release fertilizers (SRFs) have been widely used to reduce environment pollution derived from excessive nutrients. Coated fertilizers have been designed and prepared using various materials. However, development of new green coating materials and simple process is still a huge challenge. In this study, tannic acid (TA), a natural polyphenol, was used to prepare poly(tannic acid) (PTA)-coated fertilizers with urea prills as the core, and the technology of the coating process in a spout fluidized bed was developed. PTA coating could be formed rapidly by the fast oxidation of TA by an oxidation solution containing CuSO4 and H2O2. The coated urea release behavior was systematically studied in water and soil. In both water and soil, the release rate of nitrogen from coated urea is much slower than that from raw urea. Raw urea was completely dissolved within 30 min, while 27% of urea was released from coated urea. The pot experiments indicated that coated urea has a positive effect on the plant growth as well. Our results provide an effective method to prepare environment-friendly SRFs, indicating a promising application in sustainable agriculture.

Numerical investigation of gas–solid flow behavior in a novel integral multi-jet spout-fluidized bed

A novel integral multi-jet spout-fluidized bed (IMJSFB) is designed so as to reduce the dead zone at the bottom of the annulus and omit auxiliary equipment for bypass fluidizing air. The gas–solid flow behavior in the IMJSFB was numerically simulated using an Eulerian–Eulerian two-fluid model. A number of slits (4) were formed on the cone side of the cylindrical spouted bed to form an auxiliary multi-jet structure, which can create spoiler effects on the boundary of the pyramidal. The distributions of particle velocity and concentration in the IMJSFB were obtained by numerical simulation. The CFD results show that, compared with the conventional spouted beds, the IMJSFB structure can effectively enhance the particle’s velocity in the annulus of the spouted bed (especially in destroying flow dead zone at the annulus). The enhanced particle motion significantly decreases the volume fraction of the boundary layer on the cone. The particle concentration and velocity distribution along the radial direction become more uniform, and the decrease in value of the coefficient of variation (CV) of the particles’ velocity is 22.9% in IMJSFB. The turbulent kinetic energy of the gas phase can be significantly enhanced and the strengthening effect on the turbulent kinetic energy of the gas remains good with the increase of the bed height.

Particle-Scale Study of the Effect of Operating Conditions on Spout Deflection Behavior in a Flat-Bottomed Spout-Fluidized Bed

Spout deflection is a common instability phenomenon in spout fluidized beds The hydrodynamics of spout deflection under several key operating variables, including static bed height (H0), background velocity (Ubg) and reactor column width (W), is investigated by means of Computational Fluid Dynamic-Discrete Element Method (CFD-DEM) coupling approach. The results show that non-alternating spout deflection can be easily observed when the H0 is larger than 236 mm or the W is less than 0.14 m in this study. For alternating spout deflection, firstly, there is an upper limit for its amplitude because of self-locking phenomenon in the bottom corner. Large W promotes the regularity while the effect of H0 on regularity is neglectable. Thirdly, the main frequency of the alternating spout deflection reduces with increasing H0 and increasing Ubg, and finally stabilizes at 1.7 Hz. This study sheds light on the design, optimization and operation of spout fluidized beds.

Simulation of coal pressurized pyrolysis process in an industrial-scale spout-fluid bed reactor

A three-dimensional Eulerian-Lagrangian model, facilitated with multiphase particle-in-cell (MP-PIC) method, was developed to simulate gas-solid flow and pyrolysis characteristics of coal (with the capacity of 500 thousand tons per year) in an industrial-scale spout-fluid bed reactor (H = 16.6 m and D = 3.1 m), aiming at providing guidance for industrial application of pressurized grade conversion of coal. The performance of the reactor and the effects of operating parameters such as coal feeding rate, semi-coke to coal ratio, and particle sizes were numerically investigated. It was found that the flow pattern in this case is a “jet in the fluidized bed with bubbling”. The raise of pressure has a positive impact on the spouting structure and the flow uniformly. The increase of the semi-coke to coal ratio is beneficial to the coal pyrolysis, but the improvement of the pyrolysis is limited and the number of particles in the reactor will be sharply increased. With the increase of particle sizes, the flow pattern in the pyrolysis reactor tends to be stable while the mixing effectiveness is getting worse. It is suggested that the particle size of the material should range within 0–6 mm.

Influence of a sound field on the flow pattern of hollow microbeads in a spout-fluidized bed with a draft tube

In this study, instead of ultrafine powder agglomerates, hollow microbeads with an average particle size of 150 μm were employed as raw materials in a half-cylindrical acoustic spout-fluidized bed with a draft tube, using a high-speed atmosphere jet as the spouting gas. Analyses of pressure drop–velocity curves and pressure fluctuations, as well as observations of the experimental phenomena, allowed determination of the flow patterns of the spout and annulus, as well as transition velocities. The influence of a sound field on the flow patterns was then investigated. The results showed that the sound field effectively inhibits gas channeling and bypass and promotes the breakup of bubbles and dispersion of particles. Under the influence of the sound field, the critical transition velocities of the flow pattern and the minimum fluidization velocity in the annulus decreased, whereas the operating flexibility of the spout-fluidized bed with a draft tube increased.

Particle-scale study of spout deflection in a flat-bottomed spout fluidized bed

Spout deflection is a common instability phenomenon in spout fluidized beds. However, spout deflection was not well characterized and quantified in the past. In this work, spout deflection in a flat-bottomed spout fluidized bed is investigated at the particle scale by means of Computer Fluid Dynamic-Discrete Element Method (CFD-DEM) coupling approach. Two types of spout deflections – alternating and non-alternating spout deflections are captured by the CFD-DEM simulations and qualitatively analyzed in terms of voidage distributions and particle momentum profiles. The spout deflection angle is defined and used to characterize the intensity of spout deflection quantitatively. Then, the effects of spouting velocity on alternating spout deflection are investigated quantitatively using the spout deflection angle. The simulation results indicate that spouting velocity has a limited effect on the amplitude and frequency of alternating spout deflection. The relation between solid flow pattern and spout behaviour are also investigated with the help of spout deflection angle. The results indicate that spout deflection angle is highly relevant to particle distribution non-uniformity at the upper region of the bed. The study offers a cost-effective tool to characterize and quantify spout deflection in a spout fluidized bed.

Analysis of pneumatic nozzle operation with the stochastic Euler-Lagrange model

The aim of this study was to develop a CFD model for initial qualitative analysis of the operation of the pneumatic nozzle used for dry coating. The calibration consisted in comparing the droplets velocity yielded by the model with our own experimental data. The impact of the sheet and ligament constants as well as of the application of secondary coalescence and breakup models on dispersed phase velocity were taken into consideration. It turned out that the secondary phenomena had the largest impact on the dispersed phase velocity. Only after they had been taken into consideration was the agreement between the computation results and empirical data satisfactory.Afterwards, the best set-up of the model was used for describing the plasticizer atomization in a draft tube of a spout-fluid bed apparatus. It was concluded that this process should be carried out with the atomizing gas at a pressure of 2 ∙ 105 Pa.

The analysis of the influence of the normal restitution coefficient model on calculated particles velocities by means of Eulerian-Lagrangian approach

The main aim of the research presented in the paper was to determine the sensitivity of the model describing the flow of the dispersed phase in the spout-fluid bed apparatus operating in a fast circulating dilute spout-fluid bed regime to the way of calculating the normal restitution coefficient during collisions of particles with the wall. On the basis of relevant literature, four models were selected that could be applied to microcrystalline cellulose particles used in the described device: Thornton's, two variants of Jackson-Green, and LWT (Li-Wu-Thornton). The results of the dispersed phase velocity in the draft tube and annular zone of the device obtained from the computer simulations were compared with the experimental data. The LWT model, which accurately reproduces the particle velocity in the draft tube zone, provided the best match with the measured data.

Impact of friction coefficient on particles circulation velocity calculated by euler-lagrange model in spouted bed apparatus for dry coating

This paper is a continuation of research concerning gas-solid flow modelling using the Euler-Lagrange approach in a spout-fluid bed apparatus. The major challenge in this case was to determine the friction coefficient for particles hitting against the walls of the apparatus. On the basis of the properties of similar materials the value of this quantity was estimated at 0.2. Therefore, it proved useful to check the model’s sensitivity to the value of this parameter. The study investigated the effect of friction coefficient on calculated values of particles velocity in the draft tube and the annular zone of the device for various volumes of the circulating bed. In the course of calculations, a relatively small influence of friction coefficient on particles velocity was observed in the tested zones of the apparatus. The changes were most visible for large volumes of the bed, which was connected with an increase in the number of collisions of particles with the walls.

Pharmaceutical applications of spouted beds: A review on solid dosage forms

Spouted beds (SBs) have a long history of successful applications for preparation of solid dosage forms of pharmaceuticals. The well-known versatility of SBs, provided by different design and operational factors, and their efficient mixing of solids allow for engineering of technological characteristics of pharmaceutical solid forms. Particle properties like morphology, size, porosity, flowability, and dissolution rate can be improved by managing geometric and operational conditions for spouting. Drying is probably the most disseminated operation for pharmaceutical processing in SBs, and many studies have investigated drying of medicinal plant extracts such as achiote (Bixa orellana sp.), guarana (Paullinia cupana sp.), passion flower (Passiflora alata D.), and rosemary (Rosmarinus officinalis L.) with excellent pharmacotechnical and stability results. Another important application is coating of tablets and gelatin capsules, and previous studies have shown that SBs and spout–fluid beds may be advantageous over traditional pan coating, especially for polymeric film coating. Recently, an alternative process for improving drug bioavailability has involved preparation of β-cyclodextrin inclusion complexes in SBs. The first study to propose SBs for this pharmaceutical application explored the advantage of obtaining solid forms of inclusion complexes in just one step, and obtained expressive increases in drug solubility. The technique has been applied in subsequent studies on inclusion complexes of the medication carvedilol and uxi (Endopleura uchi L.) extracts.

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.

Fluid dynamics performance of phase change material particles in a Wurster spout–fluid bed

Spout–fluid-bed coating of solid–lipid materials, including some Phase Change Materials (PCMs), is a rarely used approach because of the probability of a phase change during the process. However, if mastered, this process could enable the commercialization of high-load PCM particles to develop new materials. An understanding of the thermal and fluid dynamics profiles inside a reactor can be used to establish optimized coating conditions, to avoid premature PCM melting and to maximize the drying rate. This research studies, through computational simulation, the behavior of particles and the experimental thermal profile inside a Wurster spout–fluid bed. A simplified model approach of momentum was simulated using OpenFOAM and carnauba wax particles as a PCM material. The simulation showed that appropriate flow conditions inside the Wurster tube must vary between 200 and 300m3/h to ensure a better particle coating. The measured experimental thermal profile was uniform in the reactor and it was 5–10°C lower than the set temperature. Thus, a maximum airflow at 70°C that was used in the equipment is considered suitable for the further coating of PCM particles. The methodology proved useful for the preliminary identification of flow and temperature conditions in the spout–fluid process.

Particle electrification in an apparatus with a draft tube operating in a fast circulating dilute spout-fluid bed regime

The intensity of the electrostatic charge accumulated during the flow of Cellets® particles in a modified Wurster apparatus is investigated in terms of the bed mass, and the initial moisture and velocity of the spouting gas. Particle electrification is proportional to the increase in the velocity of the spouting gas, which is connected with a higher velocity of the cores and the strength of their impact on the walls of the device. The presence of moisture in the bed facilitates electrification, but does not affect circulation, since moisture simultaneously lowers the bed resistance and reduces the relaxation time of particles, leading to rapid discharging if brought into contact with the conducting elements of the apparatus. Therefore, with regard to classic dry-powder coating, the velocity of the spouting gas should be minimized to ensure good circulation, with the particle moisture held at the maximum level admissible for a given product. The investigations show that a unique construction of the apparatus, which brings about an intense natural electrification of the cores, makes it suitable for the electrostatic dry-coating process by means of a high-voltage feeder with the controlled charging of coating powder in the spray nozzle.

Characterization of flow properties of pharmaceutical pellets in draft tube conical spout-fluid beds

Experimental studies of the hydrodynamic performance of the draft tube conical spout-fluid bed (DCSF) were conducted using pharmaceutical pellets. The experiments were carried out in a DCSF consisted of two sections: (a) a conical section with the cross section of 120 mm×250mm and the height of 270mm, (b) a cylindrical section with the diameter of 250mm and the height of 600mm. The flow characteristics of solids were investigated with a high speed camera and a pezoresistive absolute pressure transducer simultaneously. These characteristics revealed different flow regimes in the DCSF: packed bed at low gas velocities, fluidized bed in draft tube at higher gas velocities until minimum spouting, and spouted bed. The stable spouting was identified by the presence of two dominant frequencies of the power spectrum density of pressure fluctuation signature: (i) the frequency band 6–9Hz and (ii) the frequency band 12–15Hz. The pressure drops across the draft tube as well as the annulus measured in order to better recognize the flow structure in the DCSF. It was observed that the pressure drop across the draft tube, the pressure drop across the annulus, and the minimum spouting velocity increase with the increase in the height of draft tube and distance of the entrainment zone, but with the decrease in the distributor hole pitch. Finally, this study provided novel insight into the hydrodynamic of DCSF, particularly minimum spouting and stable spouting in the DCSF which contains valuable information for process design and scale-up of spouted bed equipment.

Development of a Spouted Bed Reactor for Chemical Looping Combustion

We have investigated a novel gas/solid contacting configuration for chemical looping combustion (CLC) with potential operating benefits. CLC configurations are typically able to achieve high fuel conversion efficiencies at the expense of high operating costs and low system reliability. The spouted fluid bed (SB) was identified as an improved reactor configuration for CLC, since it typically exhibits high heat transfer rates and offers the ability to use lower gas flows for material movement compared to bubbling beds (BB). Multiphase Flow with Interphase eXchanges (MFIX) software was used to establish a spouted fluid bed reactor design. An experimental setup was built to supplement the model. The experimental setup was also modified for testing under high temperature, reacting conditions (1073–1273 K). The setup was operated in either a spouted fluid bed or a bubbling bed regime to compare the performance attributes of each. Results for the reactor configurations are presented for CLC using a mixture of carbon monoxide and hydrogen as fuel. Compared to the bubbling bed, the spouted fluid bed reactor achieved an equivalent or better fuel conversion at a lower pressure drop over the material bed. The spouted fluid bed design represents a viable configuration to improve gas/solid contacting for efficient fuel conversion, lower energy requirements for material movement and increase operational robustness for CLC. The research laid the groundwork for future research into a multi-phase reacting flow CLC system. The system will be developed from computational fluid dynamic modeling and pilot-scale testing to expedite the development of CLC technologies.

Numerical simulation and optimization of hydrodynamics in a novel integral multi-jet spout-fluidized bed

The hydrodynamics in a novel integral multi-jet spout-fluidized bed was simulated using both Eulerian-Eulerian approach and the kinetic theory of granular flows. The effect of side jet number and side jet width on gas-solid two phase flow in the integral multi-jet spout-fluidized bed (IMJSFB) was investigated. The CFD results show that when the number of side jet is greater than 1 (N = 2–5), a wave-like spout and stable spout structure is formed in the IMJSFB. Compared with simulation results in the single nozzle spouted bed, the profiles of particles' velocity and concentration along the radial direction in the IMJSFB become relatively flatter. The integral uniformity of particle velocity distribution in spouted bed can be enhanced by increasing δ/Di. The particle flow factor (η) decreases first and then increases with the increase of δ/Di, and η reaches its minimum value when δ/Di = 0.208. On the whole, there is a set of optimal design parameters of side jet (N = 4, δ/Di = 0.208), at which, the fluidization quality particle phase in spout-fluidized bed reaches the optimum state while the bypass fluidizing air supply auxiliary equipment is omitted. The fluidization quality of particles in annulus can be significantly enhanced in the IMJSFB while the bypass fluidizing air supply auxiliary equipment is omitted.

Experimental and modeling studies on mixing behavior of binary mixtures in a spout-fluid bed

ABSTRACTExperimental and modeling studies have been performed to determine mixing characteristics of binary mixtures in a spout-fluid bed. Spherical glass beads of diameters (3.075, 1.7, 1.2, and 0.75 mm) and air as fluidizing medium have been used in the study. Effect of various system parameters, namely, initial static bed height, gas velocity, diameter ratio, mixture composition, and sampling time on mixing of binary particles has been experimentally investigated. A dimensionless correlation has been developed for mixing index. Mixing behavior has been modeled using artificial neural networks (ANNs). Training of ANN was performed using the Levenberg–Marquardt (LM) backpropagation algorithm to predict the mixing index. The predictions of the ANN were found to be in good agreement with the experimental results and predictions from developed correlations.

Euler-Lagrange model of particles circulation in a spout-fluid bed apparatus for dry coating

The main objective of the study was to develop a model describing the flow of particles (cores) in an apparatus operating within the range of the fast circulating dilute spout-fluid bed. The greatest emphasis was placed on the selection of appropriate description of the particle-wall interactions (impact model or fixed values of restitution coefficients). Its influence on the dispersed phase velocity in the draft tube and annulus of the apparatus was investigated. Results obtained from computer simulations were compared with our own experimental data. The use of equations calculating normal and tangential restitution coefficient resulted in a noticeable improvement in the accuracy of results only in the area of the draft tube in relation to the fixed restitution coefficient approach. It was found that the flow hydrodynamics and apparatus geometry favour computing of low restitution coefficients in the annular zone.

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.