Spouting Velocity Research Articles

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.

Smart models to predict the minimum spouting velocity of conical spouted beds with non-porous draft tube

The minimum spouting velocity, Ums, is a critical topic, and an exact prediction of this parameter certainly can be useful in design and scale-up of the conical spouted beds. In the present study, a number of intelligence methods was applied to predict Ums in conical spouted beds equipped with non-porous draft tube. Six dimensionless moduli comprising the essential operating and geometric parameters, namely, the gas density, the gas viscosity, the particle diameter, the particle density, the cone angle, the nozzle diameter, the static bed height, the length of the tube, the entrainment height, and the tube diameter were taken as models inputs. The total number of data samples is 1004 that includes 572 data points to train the smart models and 432 data points to test those models. The self-organizing map (SOM) was used to examine the effect of inputs correlation on the performance of the chosen smart models. Among the different models, a multi-layer perceptron (MLP) trained by Bayesian Regulation (BR) incorporating SOM i.e. (MLP-BR-SOM) predicted the best results with mean relative error of 9.71 and 12.45% for train and test data, respectively. In addition, sensitivity analysis (SA) of the proposed model was performed and it was shown the Ar, DT/D0, and H0/D0 have most influential parameters in prediction of Ums.

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.

Adjustment of the Minimum Spouting Velocity in a Conical Spouted Bed from Artificial Neural Networks

The minimum spouting velocity is one of the fundamental parameters in the application of the conical spouted bed pyrolysis, gasification and combustion, therefore it is necessary the adequate calculation and the use of a correlation with good adjustment, for this an artificial neural network has been applied, in order to improve the correlations of the literature. Six variables that involve different geometrical parameters and operation of the bed have been used. With the purpose to compare the results of the model with the experimental data and those predicted by the empirical equations, the quadratic error has been used. Although there is a complex relationship between the input variables and the output variables, and despite numerous of available data, the training and test steps of the network show a good adjustment with respect to the experimental values. This shows that an artificial neural network is an agile method to predict the minimum velocity of the bed at the pump, especially when the relationship between geometric parameters, operating parameters and minimum speed is complex and difficult to define.

Drying and extraction of astaxanthin from pink shrimp waste (Farfantepenaeus subtilis): the applicability of spouted beds

Abstract In this study, the spouted bed drying technique was used to obtain powder from shrimp wastes, with high quality for subsequent extraction of astaxanthin using vegetable oil, as alternative to organic solvents. Shrimp waste paste was dried in three inlet air temperatures (70, 80 and 90 °C), and air velocity used in the experiments was 100% over minimum spouting velocity. The minimum spouting, the velocities were 1.23, 1.33 and 1.39 m/s, for temperatures of 90, 100 and 110 °C respectively. The powder obtained in this work shows properties comparable to of the commercial products, indicating that the spouted bed is an alternative technique to obtain powdered products with quality good, at low cost and suitable for subsequent extraction of astaxanthin. The extractions of astaxanthin from shrimp waste were performed using palm olein at three different temperatures (50, 60, and 70 °C). At these conditions, maximum extraction of astaxanthin was 29.814µg/g of dried waste. The extraction kinetics were modeled using a simplified mass transfer kinetic model which showed a good agreement (0.9685<r2<0.9912), between the experimental and calculated data.

Spouting behaviour of binary mixtures in square-based spouted beds

From experiments, the influence of the physical characteristics of different binary mixtures of solids on the spouting regime of a pyramidal square-based spouted bed reactor is assessed. The applied methodology permits a more precise evaluation of the effects of the tested variables (diameter, density, sphericity) on the response variables (minimum air flows at which spouting begins and at which to maintain spouting conditions). The associated pressure drops along the bed of particles and the height of the formed fountain are analysed in each case. During the initial stages of fluidisation, binary mixtures containing different density ratios show dead zones. Segregation becomes more evident at large-size and high-density ratios. The lack of sphericity was found to be the main reason leading to blocking, channelling, and start-up problems when system failures occur. Nevertheless, the extent of segregation in all cases decreases with increasing the spouting velocity. In addition, a computational fluid dynamic model based on the discrete element method, previously validated for a single solid bed, is proposed as a tool to predict and evaluate potential segregation phenomena in binary mixtures. This model reproduced with high accuracy the encountered segregation phenomena. Its use may help define the technical limits inherent in the pyramidal spouted bed reactor.

Analysis of the energy performance of a modified mechanically spouted bed applied in the drying of alumina and skimmed milk

Several spouted bed configurations have been proposed in order to overcome the limitations and disadvantages of the conventional spouted bed (CSB). This paper evaluates the performance of a modified mechanically spouted bed (MMSB) fitted with a helical screw, which was applied in the drying processes of alumina and skimmed milk. In this equipment, the cyclic movement of the solid phase was promoted by the screw and the air was supplied perpendicularly, following the CSB design. The main objective of this study was to analyze the energy performance of the MMSB. The results showed that the MMSB provided a drying process under stable conditions at air velocities lower than the minimum spout velocity, due to inclusion of the helical screw, leading to greater energy efficiency and lower energy consumption.

Determination of flow patterns by a novel image analysis technique in a rectangular spouted bed

The focus of this paper is to present a systematic and integrative image analysis technique for assessing the solids behavior in fluidized systems, particularly spouted beds. In doing so, an experimental study has been carried out to investigate the hydrodynamic characteristics of the gas-solid flow in a rectangular spouted bed (30.2 mm × 101.6 mm) under three initial bed heights (0.0762 m, 0.102 m, and 0.127 m) for two different nozzle sizes (0.0096 m and 0.0127 m). To demonstrate this technique, six different flow patterns are identified through frame-by-frame examination of the images with one of these being asymmetrical spouting. The formation of a “curved gas path” and a “stagnant region” might cause the asymmetrical spouting. Additionally, an algorithm based on image analysis to determine the bed height is developed. The bed expansion ratio profiles show that the bed expansion ratio is a constant value of 1.4 at the onset of the external spouting, regardless of the initial bed heights and the nozzle sizes for the current configuration and operating conditions. The external spouting velocity and the internal spouting velocity can be determined from the bed expansion ratio curve and the bed pressure drop curve respectively. These two velocities are helpful in discriminating the different flow regimes. It is found that the external spouting velocity is more significantly influenced by the nozzle size compared to the internal spouting velocity. For the current bed material, Nylon particles, which are in the classification of Geldart D group, the external spouting velocity is two times the internal spouting velocity.

An experimental investigation on the drying of thorium oxalate in a batch spouted bed dryer

In the present work, drying of thorium oxalate slurry has been investigated using a batch spouted bed dryer containing inert spherical glass particles. The results show that the fine and discretized dried particles could be produced in this type of dryer. Moreover, the effect of temperature and velocity of inlet air on the drying kinetics of thorium oxalate has been studied. Drying experiments have been conducted at three different temperature (90, 100 and 110 °C), and three different air inlet velocities (1, 1.2 and 1.5 times the minimum spouting velocity). Five widely applied models with velocity and temperature dependent constant were chosen to predict the drying kinetic. Three criteria of statistical analysis including the root mean square error (ERMS), reduced Chi-squared (χ2), and the coefficient of determination (R2) have been used to analyze the quality of fitted models. All examined models were satisfactory but the predication capability of Logarithmic model was the best for describing the drying kinetics of thorium oxalate.

Experimental Study of Transient Hydrodynamics in a Spouted Bed of Polydisperse Particles

In industrial processes such as chemical looping combustion, single-component spouted beds of monodisperse particles are very rarely used but the spouted beds of polydisperse particles have been widely used. The flow characteristics of polydisperse particles are much more complex than the single particle fraction in a fluidized bed. To investigate the gas–solid two-phase flow characteristics of the particles with different diameters in a spouted bed, the segregation and mixing characteristics, bubble morphology, minimum spouting velocity, and pressure fluctuations of the particles with different sizes under different superficial gas velocities are studied experimentally. The results show that higher the initial bed height and larger the volume fraction of the bigger particles, higher is the minimum spouting velocity. Moreover, the magnitude of the minimum spouting velocity increases exponentially with increase in the volume fraction of the bigger particles. At low superficial gas velocity, there is a clear trend of segregation between the particles of different diameters. At moderate superficial gas velocity, the mixing trend among particles of different diameters is enhanced, and the pressure fluctuations in the bed present some degree of regularity. At high superficial gas velocity, the particles of different diameters tend to separate again, the pressure fluctuations become intense, and the particle flow turns into a turbulent state. Furthermore, when the bed becomes stable, the particles of different diameters distribute within the bed with regular stratification.

Estimation of Minimum Spouting Velocity in a Rectangular Spouted Bed

A study was conducted to explore the effects of static bed height, nozzle diameter, cone angle, and particle properties on the minimum spouting velocity in a 4 in × 1 in rectangular spouted bed. Tests were conducted with various solids materials (including 871 μm HPDE pellets, 3.2 mm nylon beads, 707 μm glass beads, and 1.5 mm alumina spheres), two gas inlet nozzle diameters, and two cone angles. Experimentally obtained minimum spouting velocities were compared to existing published correlations developed for cylindrical spouted beds. In each case, it was determined that the existing correlations did not adequately predict the minimum spouting velocity for a rectangular spouted bed. A new correlation is proposed.

Study of Pressure Drop in the 2D Spouted Bed with Conical Base of Binary Particle Mixtures: Effects of Particle Size and Density

In this study, the pressure drop for the binary mixtures of particles differing in size and density in a pseudo-2D spouted bed was experimentally studied. A binary mixture of solid particles including sand, Gypsum, and polyurethane was used in the experimental setup. Effects of static bed height, cone angle, particles diameter, and a particles weight fraction on the bed pressure drop were evaluated. The relationship between the peak pressure drops of the binary mixtures to the minimum spouting velocity was discussed. The trend of variation of pressure drop versus superficial gas velocities for binary particle mixtures in the spouted beds was found to be similar with that for the single sized particle system. The particles that sink to the bed bottom are called jetsam, whereas those gathered at the upper section of the bed are called flotsam. At the same air velocity for jetsam and flotsam rich systems, the maximum pressure drop in the jetsam rich system was larger than the flotsam one. The measured values of minimum spouting velocity were compared with some empirical correlations for single sized particles in spouted beds.

A new correlation for minimum spouting velocity for conical spouted beds operating with high density particles

Hydrodynamics of conical spouted beds operating with high density particles was studied by means of measuring the minimum spouting velocity and analysis of pressure signals in time and frequency domains. Three different types of particles, zirconia (dp = 1 mm; ρp = 6050 kg/m3), zirconia toughened alumina (ρp = 3700 kg/m3; dp = 1, 2 and 2.4 mm) and glass beads (ρp = 2460 kg/m3, dp = 1 and 2 mm) were used in the experiments. Experiments were performed in three small scale (γ = 30°, 45° and 60°) and two large scale (γ = 31° and 66°) beds at different gas inlet diameters and static bed heights. It was found by the analysis of pressure signals that the pressure drop in the stable spouting bed increases with increasing bed size, static bed height, gas inlet diameter and density of particles, and decreasing particle size and cone angle. The minimum spouting velocity increases with increasing particle size, cone angle, static bed height and density of particles, and decreasing bed size and gas inlet diameter. Power spectral density of the pressure signals also revealed significant influence of the above mentioned parameters on the hydrodynamics of conical spouted beds. Based on the results of the experiments, a new correlation is proposed for prediction of the minimum spouting velocity in conical spouted beds operating within the density range of 2460–6050 kg/m3 particles. The average relative error and correlation coefficient of the proposed correlation was found to be 10.55% and 0.95, respectively, which shows the potential of the proposed correlation for prediction of the minimum spouting velocity in conical spouted beds with high density particles.

Hydrodynamics, numerical study and application of spouted bed

Abstract This article reviews the major research and development on spouted beds (SBs). Due to its unique structural and flow characteristics, the SB is a very successful system in most applications. Two-phase and sometimes three-phase interactions generate a large number of variables to be noted in each process. Up-to-date information on the fundamentals and applications of SBs has been briefly presented, based on the published works. Thousands of interesting studies on hydrodynamic characteristics, numerical simulations, and new applications of SBs are reported. In the first step, the present work presents a review of hydrodynamic characteristics (circulation of solids in SB, measurement techniques for particle tracking and empirical hydrodynamics, pressure drop, maximum spoutable height, minimum spouting velocity, and diameter of the spout). In the second step, main mathematical models and computational fluid dynamics (CFD) simulation of the SB to predict and analyze different processes are described. Some main mathematical modeling and the recent advances of two fluid methods and discrete element method approaches in CFD simulation of SBs are summarized. In the last step, some new applications of the SB are presented. As the result of this review, we can observe the importance of further development of hydrodynamics structure, working on modeling and related correlations and improve the applications of SBs.

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.

Study on the flow behavior of irregular plastic particles in a spout-fluid bed with a draft tube

ABSTRACTThis work presents an experimental investigation on the hydrodynamic performance of a draft tube spout-fluid bed with irregular particles. Nonmetal particles from waste printed circuit boards (NPCBs) were used as a spouting solid, and polypropylene (PP) particles were selected as an assistant to fluidization particles. The flow pattern, minimum spouting velocity (Ums), and minimum spout-fluidization velocity (Umsf) were investigated under different operating conditions. The irregular cohesive particles from NPCBs showed poor flowability and channeling, which restrained stable spouting in the spout-fluid bed. The quality of fluidization and spouting improved when greater than 40 wt.% PP particles were added into the NPCB/PP mixtures. The mechanism was that the PP particles accelerated the movement of NPCB particles. Meanwhile, lower density differences between NPCB and PP particles decreased the segregation of the mixtures. The minimum spouting velocity decreased with an increase in fluidization gas velocity and the ratio of NPCB particle in the NPCB/PP mixtures. Two flow patterns, unstable spouting and unstable spouting fluidization, were observed over a large range of gas velocity. The ranges of gas velocity in these two flow patterns enlarged with the increase in mass fraction of NPCB particles within the NPCB/PP mixtures.

Minimum spouting velocity of flat-base spouted fluid bed

Experiments were performed on spout characteristics of a cylindrical spout-fluidized bed (I.D.=10cm) with different static heights and two materials (Al2O3 and high density polyethylene). Results of minimum spouting velocity obtained in this study were compared with reported correlations for both spouted and spout-fluidized beds. Considerable discrepancies were found between the values obtained using different model equations as well as with respect to experimental results. Based on the Mathur–Gishler correlation, a new correlation is proposed for calculating the minimum spouting velocity that introduces the ratio U/Umf. It was found that the minimum spouting velocity decreases with increasing fluidizing gas velocity (U/Umf). The pressure drop at the point of minimum spouting velocity is also correlated using this dimensionless group and is presented in this work. This investigation demonstrates that the use of correlations reported in the literature that focus primarily on conical bottom spouted beds are not applicable to flat-bottom spouted and spout-fluidized beds.

Influences of the fluidizing and spouting pulsation on particle motion in spout-fluid beds

Effects of variable airflow on particle motion in spout-fluid beds are studied. Computational fluid dynamics using Navier–Stokes equations for the gas phase coupled with the discrete element method using Newton’s laws for the solid phase have been employed. Results indicate that increasing the fluidizing velocity diminishes dead zones and increases both the total height of the bed and the traversed distance by particles in the steady spout-fluid bed. In pulsed airflows, two configurations are investigated, namely, the spouted pulsed-fluidized bed with pulsed flow of the fluidizing velocity, and the pulsed-spouted fluidized bed with pulsed flow of the spouting velocity. The positive effect of pulsation on particle motion is shown and the effects of parameters, such as amplitude and frequency, on the dynamics of the bed are investigated in each configuration. An increase of up to 19% in traversed distance is found for the range studied, which suggests flow pulsation as a promising technique for increasing particle mixing in spout-fluid beds.

DEM simulation of wet granular-fluid flows in spouted beds: Numerical studies and experimental verifications

Discrete Element Model (DEM), embedded into computational fluid dynamics (CFD), is developed to simulate the behaviors of wet granular-fluid flows in a thin spouted bed possessing two-dimensional characteristics. A cohesive contact model in presence of pendular liquid (polydimethylsiloxane oil) bridges between particles is improved on the basis of lubricated sliding friction and restitution coefficient of the wet grains. Special algorithm and array structure are designed to search the neighbors of wet grains. Then, the comparison of frequency, granular patterns, connecting networks, particle velocity profiles and spout geometry between the DEM simulations and our previous experiments are performed. The DEM simulation results indicate that the minimum spouting velocity (Ums) is almost the same for both wet and dry system, which agrees well with the prediction by a simplified formula. The voidages and gas velocities along the spout axis of wet granular system are found to be larger than those of dry one. It well explains the larger vertical particle velocities of wet grains over those of dry ones. Finally, the granular temperature distributions are discussed. High granular temperature occurs not only along the spout, but also at the fountain-annulus corner. Comparing granular temperature at different bed levels, we found that granular temperature of wet case is larger than that of dry one in most regions of spout and fountain, but it is nearly the same in annulus.