Spouting Velocity Research Articles

Spouting behavior of binary mixtures of spherocylindrical and spherical particles in a spouted bed

Gas-solid spouted bed systems involving biomass utilization have received much attention in recent years. In actual biomass industrial processes, some fine inert particles are usually added to assist the fluidization of biomass particles. However, the flow mechanisms of binary particle systems containing biomass particles in spouted beds are still poorly understood so far. In this study, spherocylindrical particles representing biomass particles and spherical particles representing inert particles were used as the objects of study. The macroscopic and microscopic flow characteristics were explored based on CFD-DEM modeling when the volume fractions of spherocylindrical particles in the binary particle mixtures were 25 %, 50 %, 75 % and 100 %, respectively. The results showed that the minimum spouting velocities (Ums) were in the range of 150–173 m/s, but did not show a correlation with the different particle systems. During fluidization in binary particle systems, separation of spherocylindrical and spherical particles occurs. There is no significant correlation between the particle systems with different volume fractions of spherocylindrical particles and particle orientation. As the volume fraction of spherocylindrical particles increases, the average bed height of the particles decreases and the translational kinetic energy of the particles decreases/rotational kinetic energy increases. Furthermore, the wall effect influences the spherocylindrical particle orientation and volume fraction, driving the spherocylindrical particles near the wall surface toward the vertical direction.

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.

Minimum spouting velocity of fine particles in fountain confined conical spouted beds using machine learning and least square fitting approaches

AbstractThe present study concerns the development of new models to estimate the minimum spouting velocity (Ums) in various configurations of fountain‐confined conical spouted beds (FC‐CSBs) with fine particles. Existing literature correlations were found to be inaccurate for FC‐CSBs. Therefore, smart modelling techniques were employed to design more accurate predictive tools. The radial basis function (RBF) approach provided the best predictions for systems without draft tubes as well as those with open‐sided draft tubes. Additionally, the Gaussian process regression (GPR) approach yielded the best predictions for systems with nonporous draft tubes. The mean absolute percentage error (MAPE) values for the testing phase were 5.80%, 5.67%, and 5.59%, respectively. These models consider how bed shape and particle properties affect Ums. The sensitivity analysis was conducted to determine the factors with more importance in controlling Ums. Finally, simpler correlations were derived for Ums prediction in different FC‐CSB configurations, with accuracy around 12% error.

Functional variation of minimum spouting velocity with static bed height in conical spouted beds

Static height (H0) is a key parameter in spouted bed as it is dictated by the amount of solids. Knowledge of minimum spouting velocity (ums) is a pre-requisite for optimal spouting condition for the loaded bed. Although a linear variation of ums with H0 has been reported, this is not strictly true. Runs were performed using particles having a wide range of densities (2500–16000 kg/m3) and sizes (570–2440 μm). ums was measured for a wide range of H0 values from those in the conical zone to those having a double height in the upper cylindrical one. Expressing ums ∝ H0α, with α being the exponent of the bed height, this exponent has a high dependency (∼0.5–2.0) on the particle features, and therefore on the bed regime. This will help to rightfully choose the value of α for a given set of particles processed in conical spouted beds with different H0.

Sensitive dependency of minimum spouting velocity on angle of repose of solid particles and cone angle in conical spouted beds

Minimum spouting velocity (ums) varies with the geometry of a Spouted Bed (SB) contactor and the gas-solid properties. The angle of repose (θr), being an important bulk property of the solid granules, is found to play a critical role causing the variation of ums with a change in contactor angle (γc). A systematic experimental study was conducted considering three different types of solid particles having significantly different θr (25°, 36° & 45°) and three different γc (28°, 45° & 60°) for three different gas inlet diameters, to evaluate Ums and bed pressure drop (ΔPb). The variation of Ums is correlated with (tan γc/2) and it is found to have three distinct zones for different θr for which exponent over (tan γc/2), Ɛ, is highly affected making a significant change in ums.

Applying conventional and intelligent approaches to model the minimum spouting velocity of vegetable biomasses in conical spouted beds

Applying conventional and intelligent approaches to model the minimum spouting velocity of vegetable biomasses in conical spouted beds

Effect of temperature on the minimum spouting velocity of heavy particles in conical spouted bed used for nuclear fuel coating

The minimum spouting velocity (Ums) of heavy particles in conical spouted bed at high temperatures are critical importance for nuclear fuel coating, which are different from that at room temperature. However, current researches on the Ums were concentrated on the Cold Mockup spouted bed. There were few studies about the Ums of heavy particles in conical spouted bed at high temperatures. In this study, the effect of temperature (373–1273 K) on the Ums is systematically investigated. A new Ums correlation with temperature, cone angle, static bed height, particle diameter and particle density is obtained:Ums=3.30×108∙dp1.63∙ρp0.57∙tanγ21.18∙H0Dc1.45∙T-1.44. The equation extends the application of the Ums at high temperatures and can be applied to determine the Ums value well under different temperature. Besides, the influence mechanism of temperature, cone angle, static bed height, particle diameter and particle density on the Ums has been discussed. This correlation is recommended for the determination of the Ums well at high temperatures and thus provides significant reference for producing coated fuel particles of high quality.

Conical spouted bed combustor to obtain clean energy from avocado waste

The advantages of spouted bed technology for waste treatment are linked to the high excess of renewable biomass waste generated by the large worldwide consumption of avocado. Therefore, the applicability of avocado waste as fuel in a novel conical spouted bed combustor was investigated. The solid cyclic movement in this reactor innovatively promotes better mass and heat transfer, as well as better energy exploitation of the waste. Local heat transfer coefficients were experimentally determined in the beds of avocado waste in the combustor to assess their heat transfer and determine their value as biofuels. The combustion of the avocado beds in the spouted bed regime was performed at 300–600 °C in a conical reactor at the minimum spouting velocity. The exhaust gas evolution was monitored over time, and the emission ratios were calculated. The combustion efficiencies of avocado seeds, skin, and their binary mixtures, determined from flue gas concentrations, were compared, and the effects of temperature and bed composition on combustion efficiency were analyzed.

Experiment and CFD study on the hydrodynamics in novel internal-intensified spouted beds

To overcome the limitations of traditional spouted beds, two novel internal-intensified spouted beds were proposed: swirl-nozzle anticlockwise-axial-swirler (SNAAS) and swirl-nozzle clockwise-axial-swirler (SNCAS) spouted beds. The hydrodynamics of the novel internal-intensified, conventional, and swirl-nozzle spouted beds (SBs) were experimentally and numerically investigated. Adding internal-intensified structures could reduce the minimum spouting velocity and accelerate particle fluidization. The gas radial velocity in novel spouted beds with ξ = 3 is the largest, which is the optimal height ratio. Compared with conventional and swirl-nozzle SBs, adding novel internal-intensified structures can effectively promote the radial velocity of gas and particle, reduce the flow-dead zone in the bed, obtaining larger gas turbulent kinetic energy. The flow field uniformity of gas and particle within beds in descending order as SNCAS SB > SNAAS SB > swirl-nozzle SB > conventional SB. The enhancement factor I of flow field uniformity in novel internal-intensified SBs is 2 to 3 times that in the swirl-nozzle SB. Mesh of (a) Conventional SB, (b) Swirl-nozzle SB and (c) Swirl-nozzle axial-swirler SB. • Internal-intensified spouted beds were proposed by introducing axial swirler and swirl nozzle. • The minimum spouting velocity can be reduced by novel internal-intensified structures. • Internal-intensified improves gas-solid contact throughout the spouted bed. • The enhancement factor I in novel internal-intensified SBs is 2 to 3 times that in the swirl-nozzle SB.

Mass transfer in conical spouted beds equipped with internal devices

The gas–solid contact in spouted beds is characterized by a hydrodynamics leading to high heat and mass transfer rates. Several correlations have been proposed for estimating the minimum spouting velocity, and heat and mass transfer coefficients. However, those available for estimating the mass transfer coefficient are not suitable for conical spouted beds equipped with internal devices. Based on drying runs and a drying model already validated, mass transfer coefficients were estimated under different operating conditions and geometries of the internal devices. The features of the bed materials are those of greatest impact, followed by the air inlet temperature and velocity. Although the influence of the dimensions of the internals is less significant, they are also key parameters for the scaling-up of spouted beds. Therefore, a new correlation has been proposed, which accurately predicts the mass transfer coefficient in both plain spouted beds and those equipped with internal devices. • A validated model was used to estimate the mass transfer coefficient in spouted beds. • The geometry of the internal devices greatly influences the mass transfer coefficient. • A new correlation was proposed considering the geometry of draft tubes and confiner. • The correlation accurately predicts the mass transfer coefficient in spouted beds.

Minimum spouting velocity of binary mixture with non-spherical particles

The minimum spouting velocity, Ums, defined for stable external spouting, is found also crucial to ensure good mixing when multi-component particles are involved in spouted beds. In this study, experiments were performed in a cylindrical-conical spouted bed to study the influences of diverse factors on the Ums of a binary system with the cylindrical particles and the spherical bed material. The results showed that the changes in Ums with the particle properties (particle shape, size, and density) and operating conditions were closely related to the blending ratio of the mixture. When the volume fraction of the non-spherical particles was relatively small (less than 40% to 50%), Ums mainly depended on the properties of the bed material. It was considered acceptable to estimate Ums by assuming that the system only consisted of the spherical bed material. Otherwise, the cylindrical particle shape has a significant influence on the flow dynamics and Ums. For such spouting systems, an equivalent diameter of the bed material was proposed to reflect the shape effects of non-spherical particles, whereby Ums would be independent of the blending ratio. Consequently, a novel empirical correlation is proposed to quantitatively predict the Ums of binary mixtures.

Numerical Studies on Particle Dynamics in a Spouted Bed

A coupled computational fluid dynamics (CFD)-discrete element method (DEM) technique has been adopted to examine the dynamic behavior of particles in a rectangular spouted bed. Eulerian method has been used to solve the Navier–Stokes equation for the gas phase (for the CFD) and Lagrangian method (for the DEM) for the particle phase, where the k–ϵ two-equation turbulence model has been used to capture the effect of gas-phase turbulence. In the present work, we sought to predict the minimum spouting velocity (Ums) numerically for a fixed bed height and particular particle properties. The effects of the inelastic collision and the friction on translational and rotational dynamics of the particles in spout, annulus, and fountain zones have been brought out with the intensive parametric study. The results reported here would be a way forward for a better understanding of the spouted bed processing where translational and rotational dynamics of particles play a key role.

Experimental study on the temperature distribution in fluidised beds

Heat management problems often prevail in reactors when highly exothermic chemical reactions occur. In these situations, fluidised bed reactors are often preferred due to their excellent heat transfer capabilities. However, the design, scale-up and operation of these reactors is still challenging due to the complex hydrodynamics. To gain a better understanding on the heat transport in these reactors, the degree of temperature non-uniformity for several fluidisation regimes in a pseudo-2D fluidised bed was quantified using Infra-Red Thermography. The Probability Density Functions were obtained from the whole-field temperature data, which were quantified using the standard deviation, i.e. the width of the distribution, and skewness, i.e. the dominant temperatures in the distribution. Based on the heat loss data and bubble frequencies, the standard deviation and skewness are good indicators for the solids mixing behaviour for the studied fluidisation regimes. In addition, the effect of spout velocity on the thermal characteristics was studied.

Draft tube design based on a borescopic technique in conical spouted beds

Draft tubes have emerged as promising internal devices to overcome the scale up limitations of the spouted bed. Although only a few parameters define draft tubes, the design of these devices is complex and remains a challenging task, as knowledge concerning the gas–solid flow pattern in the spouted bed is required for a proper implementation. Therefore, this study aims to propose a new criterion for the design of draft tubes (nonporous and open-sided) based on the average spout diameter measured by a borescopic technique in conical spouted beds without draft tube. Based on the radial and axial particle velocity profiles, hydrodynamic analysis, and cycle time distributions, the new configurations are compared with those without tube and with conventional draft tubes. The new open-sided tube provides maximum particle velocities of 480.90 ± 14.60 mm/s in the spout and 90.10 ± 4.40 mm/s in the annulus. These values are lower and higher than the particle velocities obtained without draft tube in the spout and annulus regions, respectively, which means it modifies particle residence time in these regions. The new open-sided tube provides a more efficient gas–solid contact than any conventional one, with spouting behaviour being very similar to the configuration without tube (differences in the minimum spouting velocity being in the 2–6% range), which is a key aspect for scale up purposes.

Unresolved CFD-DEM simulation of spherical and ellipsoidal particles in conical and prismatic spouted beds

Various drag models were implemented in a superquadric CFD-DEM code and validated for the simulation of spherical and ellipsoidal particles in spouted beds. The most suitable drag models were identified by comparing the predicted local particle velocity with those measured by particle tracking velocimetry (PTV). The model by Beetstra et al. is the one that best reproduces the experimental results for the spouting of spherical particles, whereas the one by Sanjeevi et al. is the most suitable for ellipsoidal irregular ones. Their capability for the prediction of key operating parameters was demonstrated in both conical and prismatic spouted beds, as they correctly predict the minimum spouting velocity (ums) and fountain height in different configurations (without draft tube and different draft tubes) for particles of different size and shape. The CFD-DEM model predicts the preferential orientation of ellipsoidal particles at each location in the bed and the influence of internal devices on this parameter, which is of the utmost importance in the design of reliable coating apparatuses in the pharmaceutical industry.

Estimation of the minimum spouting velocity and pressure drop in open-sided draft tube spouted beds using genetic programming

Explicit dimensionless models are proposed for estimating the minimum spouting velocity, operating pressure drop and peak pressure drop in open-sided draft tubes spouted bed using the genetic programming (GP). The models are developed based on 664 experimental data for minimum spouting velocity, 660 for peak pressure drop and 652 for operating pressure drop. The parameters of significant influence are considered as GP input variables, and reliable semi-empirical correlations have been obtained. The models predict the hydrodynamic parameters analyzed with average absolute relative errors of 12.90%, 15.99% and 10.92% for the minimum spouting velocity, peak pressure drop and operating pressure drop, respectively. A comparison of literature correlations with the present ones shows that the latter lead to considerably lower errors from the experimental data. The prediction capability of the new models was evaluated in a range of operating and geometric conditions and a close agreement with the experimental data was observed.

EXPERIMENTAL DETERMINATION OF A MINIMUM SPOUTING VELOCITY FOR CERAMIC-COATED BEARINGS IN CONICAL-CYLINDRICAL SPOUTED BEDS

EXPERIMENTAL DETERMINATION OF A MINIMUM SPOUTING VELOCITY FOR CERAMIC-COATED BEARINGS IN CONICAL-CYLINDRICAL SPOUTED BEDS

Experimental investigation of spout incoherence in a spouted bed

Spout incoherence is a typical instability phenomenon in spouted beds, in which the particles in the spout region move upward as groups, leading to poor spouting stability and efficiency. In this paper, the moving particle blockage in the spout region is measured to quantify the spout incoherence for the first time, by means of depicting the regularity, frequency and particle blockage length of the spout incoherence phenomenon. Specifically, the particle blockage is quantified using the particle concentration obtained by image processing method based on intensity differences between gas and solid phase in the spout centreline. The centreline of the spout channel is located by the particle velocity vector field. The method is validated by visual observation and frequency analysis. Then, the effects of static bed height and spouting velocity on the spout incoherence are investigated, respectively. The results show that the main features of spout incoherence, including frequency, regularity and particle blockage length, remain constant with varying spouting velocity in the investigated range. The results reveal that the static bed height has significant effects on the spout incoherence, and the increasing bed height reduces the frequency and particle blockage length of spout incoherence. This work quantifies the spout incoherence and unveil many interesting mysteries of the spout incoherence in spouted beds.

Pyrolysis of plastic wastes in a fountain confined conical spouted bed reactor: Determination of stable operating conditions

The performance of both fluidized and spouted bed reactors in the pyrolysis of waste plastics is conditioned by particle agglomeration phenomena, which worsens the quality of the gas–solid contact and eventually lead to defluidization. The objective of this work is to determine the optimum conditions for stable operation (without defluidization) in a bench scale plant fitted with a fountain confined conical spouted bed reactor and equipped with a nonporous draft tube, which operates in continuous mode. The insertion of these devices enhances the gas–solid contact, especially in the fountain region, and leads to a highly stable hydrodynamic regime, with these features being of especial relevance for the in situ catalytic pyrolysis of waste plastics. This paper deals with the effect different variables have on the minimum temperature for stable operation by avoiding defluidization. The variables analyzed are as follows: plastic type (HDPE, LDPE, PP, PS, PET and PMMA), plastic feed rate, mass of inert material in the bed, spouting velocity and use of catalyst. The results show that polymers whose chains decompose at low temperatures or have high degrees of branching require low operating temperatures. Besides, as the ratio of bed mass to plastic feed rate (Wbed/Qplastic) and/or spouting velocity were increased, the temperature required to avoid defluidization was also reduced. The use of a catalyst also reduced the temperature required for stable operation, as the activation energy of cracking reactions is greatly reduced, and so reaction rate is increased.

Fluid dynamic analysis and residence time distribution determination for rectangular based spouted beds

Fluid dynamic characterization for a set of three serial rectangular based spouted beds (RBSB) using sawdust or turnip seeds, were made. In batch experiences, the minimum spouting velocity (Ums) and the maximum pressure drop (ΔPmax) were determined based on the bed height and moisture content. With respect to the continuous solid feed experiences, initially the conditions that allowed the stationary operation for 1, 2 and 3 beds connected in series, were determined. Following, injecting colored particles and with an image analysis it was possible to determine the residence time distribution (RTD). When compared with expressions from literature, good agreement was found for Ums, whereas for ΔPmax an expression is proposed that includes the sphericity of the particles. The RTDs were adjusted with the tank in series model, finding that the effects of solids feed rate, air flow and moisture content are significant for each solid RTD.