Spouted Bed Research Articles

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.

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

Evaluation of different mathematical models in the CFD-DEM simulation of conical spouted bed fluid dynamics

The input parameters, empirical, and semi-empirical models significantly influence the responses obtained by CFD-DEM simulations. In this work, the effects of three turbulence models, three conditions of the particle rotation, and five drag models, on the fluid dynamic behavior of a conical spout bed applied to the drying of sorghum grains were evaluated. Experimental data on the solids pressure drop, height, and shape of the fountain were used to validate the simulations. Results showed the importance of including the particle rotation in the model to approximate the results simulated with the experimental behavior. Compared with experimental data, considering the particle rotation by the Dennis et al. model, the deviation was 2% for the fountain height and 9.18% for the pressure drop. Whereas, for the model without the particle rotation, the deviations were 106.33 and 42.31% for the fountain height and pressure drop, respectively. For the analyzed case, the standard k-? turbulence model showed a greater agreement with the experimental data. For the drag models evaluated, the best fit with the experimental data was obtained by the Koch-Hill drag model, followed by the Gidaspow model, with deviations less than 10%.

The impact of swirling on the dynamics of a spouted bed

This work is devoted to a numerical study of inflow swirl on the flow field in a spouted bed. The Eulerian-Eulerian multiphase model was used to simulate the hydrodynamics of a gas-solid flow in a 2D axisymmetric spouted bed under an unsteady laminar regime. The results of the simulations are validated with the experimental data obtained by He et al. (Can. J. Chem. Eng. Vol. 72, pp. 229–234 and pp. 561–568, 1994). The comparison of the results shows that the numerically obtained profiles of the time-averaged axial solid velocity agree well with the experimentally measured values. The results of the simulations revealed that the slightly increase in the swirling ratio of the inlet flow leads to an enhanced spouting process, while a strong swirling ratio has an adverse effect on the mixing between gas and solid particles. Thus, the use of the inflow swirl enables control of dynamics of spouted beds.

Numerical study on solar spouted bed reactor for conversion of biomass into hydrogen-rich gas by steam gasification

A solar-powered biomass steam gasification system was developed, in which heat transfer model, flow model and chemical model were constructed to predict the distributions of temperature, pressure, mole fraction of syngas, and solar incident flux. Several key parameters of gasifier were designed to ensure the fluidization stability. Based on the model validation, gasifier performance simulations in the design working conditions were obtained. The effects of the key variable parameters, including the rim angle of the dish collector, steam-to-biomass mass flow ratio, biomass feeding rate and the solar irradiance in the different operation working conditions on the composition of syngas, lower heating value, and efficiencies were investigated. The results reveal that the coupled system implements the best gasification performance in the design conditions which the rim angle, steam-to-biomass mass flow ratio, and biomass feeding rate are set at 60°, 0.4, and 2.5 g/min, while the LHV, carbon conversion, and gasification energy efficiencies are 11.51 MJ/m3, 78.17%, and 93.01%, respectively. The overall energy efficiency considering solar energy is 30.79%.

Experimental Study on the Solids Residence Time Distribution in Multiple Square-Based Spouted Beds

The present work aims at investigating the residence time distribution (RTD) of a multiple spouted bed reactor, which will be applied for the pyrolysis and gasification of residual biomass. The unit is composed of square-based spouted beds, placed in series and at descending heights, and communicating with each other through an opening in the lateral wall. The gas is fed evenly in parallel. The experimental analysis is based on tracer experiments in cold-flow units, assessing the influence of the number of units and the bed height. The tests proved the good mixing properties of the spouted beds, which create a stable fluidization regime and do not feature dead zones. Each spouted bed can generally be well assimilated to an ideal continuous stirred tank reactor (CSTR). The RTD of the device seems adequate for the application, and also seems to be well tuneable through the selection of the bed height and number of units. Given the good similarity with ideal reactor networks, these represent a valid tool to estimate the final behavior in terms of RTD.

An ensemble model to predict the minimum spouting velocity for two types of spouted beds

Spouted beds are extensively used in different industries. The minimum spouting velocity is a critical hydrodynamic parameter needed for the design and scale-up of these systems. This study deals with an ensemble method involving Multi-Layer Perceptron (MLP) network, the Adaptive Neuro-fuzzy Inference System (ANFIS), the Gaussian Process Regression (GPR), and a Regression Tree (RT) model for predicting minimum spouting velocity for coarse particles in conical spouted beds equipped with nonporous draft tubes (CSBDTs) and conical-cylindrical spouted beds. Some dimensionless variables related to the physical properties of the conical bed and particles’ material were constructed and used as model inputs. The proposed method was validated against the measured data. The results revealed that the ensemble method was capable of predicting the minimum spouting velocity with an average absolute relative error (AARE) of 10.52% and 10.35% for the testing data points in the case of CSBDTs and conventional spouted beds, respectively. It was also shown that the proposed ensemble method provided the best results in comparison with the other methods. Therefore, the ensemble method is a useful and powerful technique for predicting the minimum spouting velocity in spouted beds with and without the draft tube.

Particle segregation in spouted bed pyrolysis reactor: Sand-coconut shell and sand-cocoa shell mixtures

The singularity of air-particle flow characteristics and segregation phenomenon are still the main obstacles for application of conical spouted bed (CSB) for fast pyrolysis. This paper aims to investigate statistically the operating parameters (minimum spouting velocity and bed pressure drop) and biomass segregation (biomass mixing index) in a CSB composed of biomass (coconut and cocoa shells) and sand mixtures. Models for the pressure drop and inlet air velocity at the minimum spouting condition and for the axial mixing index were obtained. The bed voidage does not change significantly with the increase of biomass mass fraction (coconut and cocoa shells), therefore, larger amounts of biomass can be used without greatly increasing or decreasing the inlet air velocity to stabilize the spouted regime. From the analysis of bed stability and particle segregation, significant insights were obtained for future application of the CSB for the pyrolysis of biomasses. It is recommended the use of mixtures with 40 wt% of coconut shells and 75 wt% of cocoa shells in initial pyrolysis tests in CSB reactor. The cocoa shells particles are more suitable to pyrolysis because of their higher flowability.

On the performance of a spouted bed type device for feeding spent coffee grounds to a circulating fluidized bed reactor

Using solid biomass wastes as feedstocks for industrial generation of renewable energy is appealing to meet company's energy demands with environmental awareness; however, maintain continuous feeding of wastes to reactors remains a challenge in processing. In this study, the performance of a non-mechanical spouted bed (SB) feeder was evaluated for handling dry and moist spent coffee ground (SCG) powders to a circulating fluidized bed reactor. A comprehensive experimental study was carried out to investigate the effects of operating variables and air inlet nozzle configuration on the solids circulation rates and pressure profiles. Using a convergent nozzle at the air inlet improved feeding stability compared to a conventional orifice air inlet. The circulation rates could be varied from 3.0<WS<11.0g/s by adjusting the air flowrate and the entrainment length. Although SB performance was affected by the powder's flowability, the feeder operation was rather stable, with fluctuations less than 20% in WS. Moreover, WS could be accurately predicted from pressures measured at the feeder and riser. The SB showed enhanced flexibility in handling SCGs with different properties compared to a non-mechanical L-valve. It suggests that SBs might be an appealing alternative to feed waste biomass powders into reactors in a continuous mode.

Fabrication of Highly Filled Composites with an Innovative Miniaturized Spouted Bed

In nature bio-composites such as nacre show remarkable mechanical properties due to their complex hierarchical structure and high-volume fraction of its hard component. These composites are highly interesting for structural applications in different branches of industries for mechanical engineering and process technology. The aim of this work was to provide a scalable method for the production of highly filled composites by mimicking the structure of bio-composites. Therefore, composites from iron oxide (Fe2O3) and SBC-polymer (styrene-butadiene block copolymer) were fabricated by using a miniaturized spouted bed with an innovative fluidization gap design. Small iron oxide particles (25–45 μm) were fluidized in the spouted bed and coated with a polymer solution via a bottom spray nozzle. Afterwards the coated granules were hot-pressed and the mechanical properties of the obtained composites were tested. By this method composites with a bending strength of up to 6 MPa were fabricated. Although the mechanical properties of these artificial composites are still lower than those of the natural role models, it was shown that the spouted bed is a suitable technique for the fabrication of highly filled composites. For further optimization of the mechanical properties more complex and tailor-made starting materials will be used in following studies.

Effect of the Solid Inlet Design on the Continuous Drying of Fine and Ultrafine Sand in a Fountain Confined Conical Spouted Bed

The effect the solid inlet design has on the continuous drying of sand in a conical spouted bed has been studied. Five designs have been tried, four feeding the solid from the top and the fifth one...

Obtenção de batata-doce em pó em leito de jorro e influência da temperatura de secagem nas propriedades físico-químicas

O presente estudo teve como objetivo obter a farinha da batata-doce através do processo de secagem por atomização, em leito de jorro e avaliar o efeito das temperaturas utilizadas nas suas propriedades físico-químicas. A batata-doce foi submetida ao processo de secagem em leito de jorro nas temperaturas de 50, 60 e 70 °C, vazão do ar no bico atomizador de 3,0 m3/min e vazão de alimentação da bomba de 2,7 ml/min. A batata-doce in natura e as farinhas obtidas foram caracterizadas quanto aos seguintes parâmetros físico-químicos: umidade, sólidos totais, atividade de água (aw), cinzas, lipídeos, carboidratos, pH, acidez total tilulável (ATT), sólidos solúveis totais (SST) e ratio (SST/ATT cinzas quando se teve aumento da temperatura de secagem. A secagem possibilitou redução no teor de umidade, atividade de água da batata-doce in natura garantindo uma maior vida de prateleira do produto. Houve). O batata-doce in natura apresentou alto teor de umidade de 69,48% e aumento nos teores de diferenças estatísticas significativas entre as temperaturas utilizadas com relação aos parâmetros físico-químicos. No entanto, a temperatura de 80 °C possibilitou o maior valor de sólidos solúveis totais, ratio (SST/ATT) e carboidratos totais evidenciando o potencial tecnológico do produto em pó.

Eulerian-Eulerian Numerical Study of the Flue Gas Desulfurization Process in a Semidry Spouted Bed Reactor.

The Eulerian–Eulerian two-fluid model (TFM) in conjunction with kinetic theory of granular flows (KTGF) was used for analyzing water vaporization and the semidry flue gas desulfurization process in a two-dimensional powder–particle spouted bed (PPSB). In an environment with high-temperature gas, desulfurization slurry is wrapped on the surface of moving particles and evaporated, along with the application of the user defined function (UDF) method to accomplish water heat and mass transfer by considering evaporation in the simulation process. The simulation results revealed that the best mass- and heat-transfer effect of each phase can be found in the outer annulus and the near spout region, both of which are also the main areas where water vaporization occurs. The rate of desulfurization products decreases with the increase in inlet gas temperature as the water vaporization rate increases. The volume fraction of desulfurization reaction products decreases with the increase in inlet flue gas temperature. Compared with other working conditions, the highest desulfurization efficiency reaches 84% when the inlet flue gas temperature is 480 K. The change of the desulfurization product rate with the radial distance is the same under different superficial gas velocities, with the peak desulfurization efficiency appearing in the annulus. The optimal operating parameter for the desulfurization process is available in PPSB, and the desulfurization efficiency and gas handling capacity reach the best result when the superficial gas velocity equals 1.2 Ums.

Novel Porous Draft Tube To Manipulate Fluid Throughput from Spout to Annulus in a Spouted Bed

A porous draft tube (DT) with suitable converging and diverging angles having varying porosity is newly introduced in a spouted bed (SB) for manipulating the fluid exchange rate from the spout to t...

Particle-scale characteristics of the three distinct regions in the multi-chamber slot-rectangular spouted bed

The particle-scale characteristics of the solid phase in the three distinct regions of the dual-column slot-rectangular spouted bed are studied, along with the effects of operating parameters and scaling up, via the computational fluid dynamics coupled with discrete element method (CFD-DEM). Results demonstrate that: (i) the spout-annulus interface expands from the bottom initially and then shrinks to a neck; (ii) the majority of the particles are in the annulus and the solid residence time (SRT) patterns are distinctly different in the three regions; (iii) the collision force is much larger than the fluid force, with the greatest magnitudes in the spout region and bed surface; (iv) significantly different solid dispersion patterns are observed among three directions; and (v) scaling up the capacity of the multi-chamber spouting system by horizontally aligning more chambers negligibly alters the flow pattern or the particle-scale information (e.g., SRT) during steady spouting.

Shrinkage modeling, drying kinetics and quality assessment of carrot cubes dried in a two stage spouted bed drying process

A relatively easy to apply mathematical model based on the second Fick’s law inserting a correction factor α to describe drying kinetics of unblanched carrot cubes in a two stage drying process considering shrinkage, using a semipilot spout bed dryer for the first stage and a lab scale spout fluidized bed dryer for the second stage was successfully developed. Drying of the carrot cubes was done at three drying temperatures 60, 70 and 80°C. It was possible to keep air velocity constant in each drying stage 1.65 m/s at the first stage and 0.68m/s and 1.35m/s in the annulus and spout respectively in the second stage. Effective moisture coefficients obtained 0.821 to 1.02 x 10-9 m2/s for the first drying stage and 0.262 to 0.481 x10-9 m2/s for the second drying stage were according to the published data for carrots in this kind of dryer considering shrinkage. The model fitted accurately the experimental drying with SEE of 0.122 to 0.210 when shrinkage was considered and α correction factor was inserted compared to SEE of 1.002 to 1.263 when shrinkage was neglected. Also residual analysis of models confirmed the adequacy of the model to predict drying kinetics. Quality parameters obtained β-Carotene retention (80±5.4%), peroxidase residual activity (30-35%), pectin methyl esterase residual activity (83-95%) and rehydration ratio (4.5-5.3 water absorbed/kg dried solids) resulted similar to the ones reported in the literature and except for β-Carotene retention they all showed dependence with drying temperature.

Paraboloid-Based Spouted Bed Drying of Paddy: Aerodynamics, Temperature Distribution, and Moisture Degradation

Aerodynamics, temperature variations in the annulus, and the moisture reduction of paddy in a paraboloid-based spouted bed (PBSB) dryer without draft tube and with solid and porous draft tubes were investigated. Draft tube caused a rapid decrease in the peak pressure drop and minimum spouting velocity when compared with PBSB without a draft tube. Pressure drops with draft tubes were 17 to 30% of the values for the PBSB without a draft tube. Temperature distribution along the bed height in the annular region during drying of paddy was also investigated. Heat-up in the spouted bed without draft tube was more rapid. The experiments were conducted for 70, 90, and 110 °C inlet air temperatures. The required length of drying time to dry the paddy with an initial moisture content of 0.35 db to a moisture content below 0.15 db could be reduced by 50–60% using a temperature of 110 °C instead of 70 °C. No constant rate period was observed. Drying took place in the falling rate period. Drying time decreased in the case of porous draft tube rather than the solid one. The highest drying rates were achieved by spouted bed without draft tube. Drying rates were in the range of 0.62–0.1, 0.51–0.06, and 0.37–0.06 (db.min−1) for the spouted bed without draft tube, with porous, and solid draft tubes, respectively.

Mathematical Model of Three Dimensional Spouted Bed Using Distinct Element Method

Spouted bed was simulated by a combining of Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) technique. In the simulation, DEM based on the Newton’s second law of motion was used to solve the particle motion and the fluid motion were obtained by CFD with the SIMPLE method and Upwind scheme. Programming was developed in Standard-C language and MATLABTM was used to visualize the results. The size of particles focused on this simulation is 2.5 mm in diameter (the density = 2,500 kg/m3, stiffness = 800 Nm -1). The time step used to maintain the stability of the simulation was 6.5 10-5 sec.In this simulation, three levels of the static bed height were studied: 45, 58, and 70 mm. The operating parameter effects (the static bed height on the pressure drop across the bed and the minimum spouting velocity) were investigated. The pressure drop across the bed and the minimum spouting velocity increased corresponding to the level increment. In the study of the pulsed and multi-pulsed frequency, it was found that the higher number of frequency introduced the higher heat transfer to the particles. Moreover, the effect of each type of flow on the average particles temperature was studied. The continuous flow gave the highest average particles temperature. Even though, the single pulsed flow and the multiple pulsed flows gave the lower heat transfer than continuous flow, the multiple flows produced a very good distribution in the heat transfer and also can reduce the dead zone problem of the spouted bed.

Distribution of Cycle Times in Sawdust Conical Spouted Bed Equipped with Fountain Confiner and Draft Tube

A study has been conducted on the joint influence of the fountain confiner and draft tube on the solid circulation in a conical spouted bed made up of sawdust. Knowledge of the performance of these...

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.