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A new industrial-scale spout-fluid mixer (H = 3.4 m and I.D. = 0.8 m) was proposed for mixing 18.75 t/h of biomass ( ρ b = 400 kg/m 3 , d b = 2 mm) and 281.25 t/h of heat-carrier ( ρ c = 2600 kg/m 3 , d c = 0.5 mm), and the corresponding three-dimensional computational fluid dynamics approach, facilitated with the Eulerian-Eulerian multiphase fluid model (CFD-TFM), was developed to simulate the three-phase mixing behaviors in the mixer. The performance of the mixer and effects of operating parameters were numerically investigated. It was found that the mixing effectiveness, M e , can reach over 80% under the proposed industrial operational conditions (for example, a spouting gas flowrate Q s = 0.067 kg/s and fluidizing gas flowrate Q f = 0.035 kg/s), and the flow pattern in this case is a “jet in the fluidized bed with bubbling”. Increasing Q s will increase the sizes of bubbles, as well as their generation frequency and rising velocity, which are conducive to the mixing of heat-carrier and biomass particles. However, a too large Q s will affect the falling solid flows in the distribution region and transition region of the mixer. Conversely, increasing Q f will aggravate the swaying and leaning of bubbles or jets towards the mixer walls, leading to a slight decrease of M e . [ABSTRACT FROM AUTHOR]

Mixing efficiency is one of the most significant factors, affecting both performance and scale-up of a gas-solid reactor system. This paper presents an experimental investigation on the particle mixing in a multiple spouted bed. Image processing technique was used to extract the real-time information concerning the distribution of particle components (bed materials and tracer particles). A more accurate definition of the tracer concentration was developed to calculate the mixing index. According to the visual observation and image analysis, the mixing mechanism was revealed and the mixing rate was evaluated. Based on these results, the effects of operation parameters on the mixing rate were discussed in terms of the flow patterns. It is found that the detection of the pixel distribution of each component in RGB images is not affected by the interference of air void, thus maintaining good measurement accuracy. Convective transportation controls the particle mixing in the internal jet and spout, while shear dominants the particle mixing in the dense moving region. Global mixing takes place only when the path from one spout cell to the other is open. This path can be formed either by the bubbles or particle circulation flows. The mixing rate is linked to the bubble motion and particle circulation. Provided that there are interactions between the spout cells, any parameters promoting the bubble motion and circulation can increase the mixing rate. Finally, a mixing pattern diagram was constructed to establish the connection between the flow structure and mixing intensity. [ABSTRACT FROM AUTHOR]

Spoutcharacteristics, such as flow pattern, minimum spouting velocity,and maximum spoutable bed height, are investigated in a wet conical-cylindricalspouted bed. Water and glass beads (Geldart D type) are adopted asthe liquid and solid phases, respectively. The evolution of flow patternof a wet spouted bed is captured by a CCD camera. The experimentalresults indicate that the minimum spouting velocity decreases whenincreasing the liquid saturation. The increase of initial bed height,particle size, or spout nozzle size leads to increased minimum spoutingvelocities. A correlation is formulated based on the experiments resultsfor the prediction of minimum spouting velocities of wet spouted beds.Moreover, it is found that the maximum spoutable bed height Hmaxdecreases as particle size or spout nozzlediameter increases. However, Hmaxis almostconstant, approximately 1.5 times higher than that of its correspondingdry spouted bed, when increasing the liquid saturation. [ABSTRACT FROM AUTHOR]

Spouting behaviors of cylindroid and spherical particles in a spouted bed are experimentally investigated. The characteristics of flow pattern and pressure drop of the binary mixtures are figured out and three kinds of cylindroid particles with different sizes and shapes are involved in experiments to discuss effects of particle size and shape on the spouting behaviors in beds. The emphasis is laid on the influence of the volume fraction of cylindroid particles, Xc, on the spouting phenomena, including the total pressure drop, the minimum spouting velocity, and fountain height. Results show that, the shapes and sizes of cylindroid particles, mainly including equivolume diameter and aspect ratio, significantly affect the spouting behaviors. There is a maximum volume fraction, Xc,max, for each kind of cylinders to maintain the stable fountain at a certain gas velocity. With the same gas velocity, Xc,max is lower for the cylinders with higher aspect ratio. © 2014 American Institute of Chemical Engineers AIChE J, 61: 58-67, 2015 [ABSTRACT FROM AUTHOR]

The flow patterns and transitions in a gas–liquid–solid three phase spouted bed were investigated. Experiments were carried out in a cylindrical and a semi-cylindrical spouted bed with conical base. Glass beads and water were used as the solid phase and liquid phase, respectively. The changes in pressure drop and photographs were used to determine the flow patterns. Five distinct flow patterns were identified and described, i.e. fix bed (FB), grain spouting (GS), cluster spouting with slugging (CS-S), solid fixed with gas–liquid bubbling (SF-GLB), and slurry agitated bed (SA). Flow pattern maps of a three phase spouted bed ( d = 2.6 mm, H 0 / D t = 1.86) under different liquid saturations were plotted. It was found that the flow pattern transition with the spouting gas velocity increasing at different liquid saturations ( S ) could be divided into three stages, i.e. transition from FB to GS when S < 0.2, transition from FB to CS-S when 0.2 < S < 0.5, and transition from SF-GLB to SA when S > 0.5. Increase in liquid saturation ( S ) always leads to increasing of the amplitude of pressure fluctuations. Besides, in stage I (GS), the minimum spouting velocity increases initially and then decreases apparently with increasing S . The range of stage I region becomes wider with lower initial bed height and particle diameter. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) computational fluid dynamics (CFD) model, coupling with two-fluid model (TFM) approach is adopted to investigate the interactions of spout jets and to evaluate the effects of baffles in a multiple-spouted bed. For two typical flow patterns, that is single spouting and double-spouting, characteristics of flow patterns, solid velocity and voidage are investigated with varying spouting gas flow rates. Influence of baffles set in the bottom of the bed is also studied in three typical flow patterns. Results show that for double-spouting, the central spouting push off the lateral spouts, and the push force is increasingly obvious with increasing central spouting gas flow rate; for single spouting, when the lateral spouting gas flow rates increase, the central spout is destroyed and the gas-solid flow becomes unstable. Baffles in different flow patterns (single spouting, double-spouting and triple-spouting) exert different effects on the solid movements. [ABSTRACT FROM AUTHOR]

Experiments on the spouting of non-spherical particles in a conical-cylindrical spouted bed, with an inside diameter of 200 mm and a conical base of 60°, were carried out. The minimum spouting status of six kinds of non-spherical particles, the equi-volume sphere diameter ranges from 1.9 to 6.2 mm and the sphericity ranges from 0.73 to 0.95, were tested and compared with two spherical particles. It was found that the changes of minimum spouting velocity with initial bed height and spout gas inlet diameter were similar to the spouting of spherical particles in conventional spouted beds, while decrease in particle sphericity would lead to an increase in the minimum spouting velocity. The tested minimum spouting velocities were well represented by the Mathur−Gishler equation of Ums, however a more satisfied prediction could be achieved for non-spherical particles when replacing dp in Mathur−Gishler equation with a modified term φ−0.5 dv. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) Eulerian-Eulerian multiphase model (two-fluid model, TFM) was developed to predict the minimum spouting velocity ( ums) of spouted beds, with the aid of UBC experiments in a 152-mm conical-cylindrical vessel. The gas motion was simulated by the k- ϵ two-equation turbulent model, while the particle phase motion was estimated from the kinetic theory of granular flow. The inlet minimum spouting velocity, ums, was numerically predicted by visual observations and analysis of simulated distributions of the solid volume fraction and particle vector field for decreasing gas flow. The effects of particle diameter, static bed height and fluid inlet diameter on ums were checked, in order to confirm the validity of the present developed method. In addition, numerical predictions are compared with the predicted values from several empirical correlations reported in the open literature. Best congruence is with the popular Mathur-Gishler equation. [ABSTRACT FROM AUTHOR]

Numerical simulations based on a three-dimensional (3D) Eulerian-Eulerian multiphase model (two-fluid model, TFM) were carried out to study the minimum spouting velocities of scaled up spouted beds. The spouted bed with a diameter of 0.152 m from the experiments of He et al. was scaled up by factors from 2 to 8, resulting in diameters from 0.304 to 1.216 m. The effects of the static bed height, particle diameter, particle density and fluid inlet diameter on the minimum spouting velocity in different size beds were numerically investigated. A new empirical correlation is proposed for predicting the minimum spouting velocity in both small and large beds. [ABSTRACT FROM AUTHOR]

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

Abstract: A back-propagation neural network (BP-neural network) model was developed to predict the minimum spouting velocity (U ms) in spouted beds. Five dimensionless variables involving seven key geometric and operating parameters of spouted beds, i.e. column diameter, spout nozzle diameter, base angle, static bed height, particle diameter, particle density and gas density, were constructed as model inputs. An adaptive genetic algorithm was used to determine the nuclear parameters in a BP-neural network. 164 experimental data from the published literature were divided into two equal groups, for training and validating the neural network model, respectively. Comparisons of predictions by the BP-neural network and existing empirical equations with experimental data showed that U ms values predicted by the BP-neural network were in good agreement with experimental values, with a mean relative error of 12.9%, somewhat better than calculations by existing empirical equations. This indicates that an artificial neural network is a useful and promising way to predict U ms as an alternative to empirical equations, especially when the relationship of geometric and operating parameters to U ms is complex and difficult to describe. [Copyright &y& Elsevier]

Abstract: Numerical simulations based on the three-dimensional discrete element method (DEM) are carried out for studying the mixing behavior of monocomponent and binary particle systems in a spouted bed. The motion of individual particles is modeled by DEM, and the gas motion is modeled by the k − ε two equation turbulent model. The mixing quality is described by the Lacey mixing index, it is evaluated in terms of the mixing degree at the mixing equilibrium and the time required reaching the steady value. The state of mixing of uniform particles is studied by analyzing the effect of particle shape, density and spouting gas velocity. For binary systems, the effects of component shape and size are examined. The results show that spouting gas velocity and particle properties are important parameters influencing particle mixing quality in spouted bed. The mixing quality is found to be sensitive to particle shape, the spheres mix faster and more homogeneous than corns. In monocomponent corn system, the mixing quality increases with increasing of gas velocity and decrease with increasing particle density, and it is sensitive to particle shapes, the spheres mix faster and more homogeneous than corns. In binary corn–sphere system, particles with closer sizes and operated at higher gas velocity have better mixing quality. Besides, the mixing mechanism of corn-shaped particles is discussed based on the mixing process of monocomponent and binary systems. It is found that particles of different shapes, sizes and densities can have different trajectories in the fountain region, leads to a different radial landing position on the top of the annulus, and the subsequent path through the annulus region varies. [Copyright &y& Elsevier]

The mixing and segregation behavior of a binary mixturehave been investigated experimentally in a spout-fluid bed. Threetypes of binary mixtures were used by mixing glass beads with equaldensity and dissimilar size. The spouting and fluidizing gas flowrate were adjusted to cover a range of flow regimes, typically includinginternal jet (IJ), jet in fluidized bed with bubbling (JFB), spouting(S) and spout-fluid (SF). The mixing and segregation behavior wereanalyzed in terms of flow regimes, concentration profile, and mixingindex. The results show that in IJ, the particle circulation is combinedwith the local segregation where smaller particles migrate to theinterface between the jet and stagnant region, even into the latter.In S, the distribution of particle depends greatly on the fountainstructure. In JFB, the axial segregation takes place where the smallerparticles prevail in the upper part of the bed. Segregation becomesmore pronounced with increasing the particle size difference. In addition,a mixing/segregation pattern map is constructed. Three regions includingmixing region, segregation region, and intermediate region, are identifiedby the criterion of mixing index. [ABSTRACT FROM AUTHOR]

Abstract: Detailed knowledge of particle mixing dynamic is essential in successfully designing and reasonably operating spout-fluid reactor. Over the years, numerous methods for the investigation of particle mixing have been proposed. This paper presents a novel method for the investigation of particle mixing. The method was carried out in a well-designed microwave heater, in which the lab-scale spout-fluid vessel constructed with microwave-transparent Plexiglass was placed. Inside the bed, a number of polar tracer particles continuously heated by microwave energy were real-time tracked using a top-grade infrared camera. From this, the concentration field of the tracer particle could be obtained with high accuracy. This technique has been adopted to investigate the mixing dynamic of binary mixture differing in the density in a flat-bottom spout-fluid bed. The mixing quality was evaluated by the Shannon entropy mixing index. On this basis, the influence of important process parameters on the mixing progress in the initial mixing stage has been taken into account. The investigation results show that the mixing progress is improved when increasing the means gas velocity and the difference in density of bed particle. In addition, an empirical correlation as a function of gas velocity and particle density was developed for calculating the mixing degree. The errors between experimental data and the obtained ones from this correlation were within 28%. [Copyright &y& Elsevier]

Abstract: Three-dimensional gas and particle turbulent motions in a rectangular spout-fluid bed were simulated. The particle motion was modeled by discrete element method and the gas motion was modeled by two-equation turbulent model. Shear induced Saffman lift force, rotation induced Magnus lift force as well as drag force, contract force and gravitational force acting on individual particles were considered when establishing the mathematics models. A two-way coupling numerical iterative scheme was used to incorporate the effects of gas-particle interactions in volume fraction, momentum and kinetic energy. The gas–solid flow patterns, forces acting on particles, the particles mean velocities, jet penetration depths, gas turbulent intensities and particle turbulent intensities were discussed. Selected stimulation results were compared to some published experimental and simulation results. [Copyright &y& Elsevier]

Abstract: The jet penetration depth was proposed to be an important parameter to describe the jet action during the chemical process of spout–fluid bed coal gasification. A two-dimensional cold model of a spout–fluid bed coal gasifier with its cross section of and height of 2000mm was established to investigate the jet penetration depth. Four types of Geldart group D particles were used as bed materials. A multi-channel pressure sampling system and a high-resolution digital CCD camera were employed for experimental investigations. The effects of spouting gas velocity, spout nozzle diameter, static bed height, particle property and fluidizing gas flow rate on the jet penetration depth have been systematically studied by pressure signal analysis and image processing. Experimental results indicate that the jet penetration depth increases with increasing spouting gas velocity and spout nozzle diameter, while it decreases with increasing particle density, particle diameter, static bed height and fluidizing gas flow rate. Additional, a new correlation considered all of the above effects especially static bed height and fluidizing gas flow rate, was developed for predicting the jet penetration depth in spout–fluid beds. The correlation was compared with published experimental data or correlations, which was in well agreement with the present experimental results and some other references. [Copyright &y& Elsevier]

Abstract: This paper presents the mixing behaviors of binary particle mixtures with equal diameter and different density within a spouted bed by three-dimensional coupled computational fluid dynamics (CFD) and discrete element method (DEM).The particle motion is modeled by the DEM, and the gas motion is modeled by the k − ε two equation turbulent model. The numerical computation is based on a cylindrical spouted bed which the inside diameter, height and conical base are 200mm, 700mm, and 60°, respectively. Binary particle mixtures are composed of spherical particles with equal diameter of 4mm and the heavy-over-light density ratio ranges from 1 to 4. The mixing process, evaluation of mixing quality, particle circulation and distribution of particle concentration along both radial and axial directions are obtained on the basis of simulations. The mixing process is illustrated by the development of solid flow patterns with time. The results show that the process of particle mixing mainly contains three stages: macro-mixing stage, micro-mixing stage and stable mixing stage. The mixing quality is described by Lacy mixing index, and is evaluated by two parameters: mixing degree at the mixing equilibrium phase and the time required reaching the steady value. The effect of sample size act on the mixing degree is also investigated and an optimum size is found. The results show that the mixing quality increases with increasing of gas velocity and decreases with increasing particle density differences of the binary mixture. By comparing the typical trajectories for two tracer particles with different densities, the mixing mechanism is further analyzed. Besides, the mixing rate in radial and axial directions is characterized by the time required for the concentration of the mixtures constituent to maintain a basic equilibrium. It is found that the mixing process along the axial direction is slower than that of the radial direction, and in both directions, mixture with smaller component density difference shows a higher mixing rate and better mixing uniformity. [Copyright &y& Elsevier]

Abstract: An underfeed circulating spouted bed (UCSB) reactor was used as a desulfurization apparatus. In this study, an attempt was made to build a mathematical 3D model which couples the complicated flow and chemical reactions in the interest of system analysis and sulfur removal data analysis. A simplified reaction model was developed to describe the SO2 absorption process. Humidifying, evaporation, neutralization reaction have been considered in the model while the dissolution and ionization of calcium hydroxide are neglected. The effect of operating parameters including feed style, injecting velocity, jet water flow rate, humidifying style on sulfur removal efficiency were investigated. The results show that the calculation gives a good description of the experimental data under the range of operating conditions. It indicates that the model is successful in predicting the desulfurization efficiency of the UCSB system. [Copyright &y& Elsevier]

Abstract: The underfeed circulating spouted bed (UCSB) was designed as a new dry desulfurization reactor. In this article, pressure fluctuations along the axial direction were measured and time, frequency and Shannon entropy analysis of pressure signals were studied under different operation parameters. The results indicate: the pressure fluctuations express different characteristics at various axial locations. And the operation parameters have significant influence on the flow characteristic in the riser. Advancing the spouting velocity or the circulating ratio, the solid concentration in the riser increases and the amplitude of the pressure fluctuations rises. With higher injecting velocity or nozzle position, the gas–solid turbulence in the bottom bed gets more intense. It shows that the existence of injecting flow near the underfeed nozzle has a distinct effect on strengthening the particle mixing. The power spectrum density acquired from the signals can coincidently reflect the dynamic behavior of the gas–solid flow in the riser. Analysis of Shannon entropy also corresponds to the above summarization of flow characteristic very well. [Copyright &y& Elsevier]

Abstract: In this study, a detailed model was proposed to simulate the process characteristic of flue gas desulfurization with multi-level humidifying in the underfeed circulating spouted bed (UCSB). The model conducted a steady state one-dimensional model by means of infinitesimal analysis, incorporating with the models of droplet evaporation, shrinking core and sulfur absorption. The trends of moisture, temperature, and sulfur concentration along the axial direction are calculated. The predictions were also compared with the experimental results, and they are in very good agreement. The results indicate: The inlet temperature and jet water flow rate are found to be very important factors to the sulfur removal efficiency. Applying multi-level humidifying, the outlet temperature decreases. As a result, the droplet evaporation gets slower and the sulfur removal efficiency increases. Degressive distribution of jet water is also found beneficial to acquiring higher desulfurization efficiency. [Copyright &y& Elsevier]