Spouted Bed Research Articles

A Hybrid Lumped Parameter/Neural Network Model for Spouted Bed Drying of Pastes with Inert Particles

The current study analyzed the suitability of a hybrid CST/neural network model to describe the highly coupled heat and mass transfer during paste drying in a spouted bed. In the present approach, the main information was the moisture content predictions in the powder. The model was based on global energy and water mass balances in the liquid and the gaseous phases. In this model, the inter-phase coupling term r, which reflects both water evaporation and particle coating, was described by an artificial neural network. Artificial neural networks are efficient computing models which are extensively used whenever theoretical models fail to properly represent a given phenomena and reliable data basis of the main variables involved is available. Simulations were done in MatLab. The drying experiments for model verification were carried out in a conical semi-pilot scale spouted bed, from which measurements of gas and solid phase moisture were done. The good agreement between calculated and measured powder moisture content suggested that the well-mixed hypothesis could be applied for paste drying in a spouted bed. The robustness of the model with respect to changes in feed flow rates and other operating conditions showed the merits of using a trained neural network.

Statistical Evaluation of the Protein Enrichment of Rice Bran Using Spouted Bed

This study evaluated the viability of the spouted bed technique in the enrichment process of degreased rice bran, in the pellets form, with bovine blood. The protein enrichment of the pellets was carried out in a cone-cylindrical spouted bed, in order to obtain a final product with protein content of around (pet food type). The effects of pellet load, flow rate of blood solution, and inlet air temperature were analyzed. The responses were protein content and mass yield of product. The best condition was found with pellet load of 1.6 kg, flow rate of blood solution of 1.6 L h−1, and inlet air temperature of 110°C. In this condition, mass yield values of 90.2 ± 0.1% and protein content of were found. Increased protein solubility and digestibility in the product in relation to the pellet in natura were observed.

Using DPM on the Way to Tailored Prismatic Spouted Beds

AbstractSpouted beds are used for miscellaneous applications such as drying, granulation, coating of solids and for chemical reactions. The discrete particle model (DPM) is a powerful tool supporting developers to create tailor‐made spouted beds for specific process requirements. The limitation of DPM for large‐scale simulations, resulting from high computational effort, can be avoided by simulation of rectangular apparatuses of appropriate thickness, since the fluid and particle dynamics are independent in this direction and scale‐up can simply be achieved by extending of the apparatus thickness. In this contribution DPM was used to investigate the influence of the gas flow rate, the particle friction coefficient and the geometry basis angle on the particle dynamics in the spouted bed.

Drying of Tropical Fruit Pulps: Spouted Bed Process Optimization as a Function of Pulp Composition

Results of drying of tropical fruit pulps in spouted beds (SBs) are presented, focusing on the effects of fruit pulp composition on the SB fluid dynamics and process performance and the development of new products formulated from mixtures of pulps with varied composition. It was verified that high starch and lipid contents favored stable fluid dynamics and high powder production efficiency, while high reducing sugar concentrations resulted in bad dynamic regime and very low powder production. Powder production efficiency was statistically correlated with the pulp composition. Also, drying of mixtures of fruit pulps with addition of starch and lipids was investigated. Results of fluid dynamics, drying performance, and sensory tests of yogurts enriched with the powders revealed promising potential of the SB for obtaining high-quality fruit powders.

Effect of Temperature on Fine Particle Drying in a Draft‐Tube Conical Spouted Bed

AbstractThe performance of a draft‐tube conical spouted bed for drying fine particles under batch operating conditions has been assessed at several temperatures using nonporous and open‐sided draft tubes, and the results have been compared with those obtained when operating without a draft tube. In order to ascertain the influence of temperature on drying, experimental runs have been carried out in the 25–300 °C temperature range. The open‐sided draft tube provides the best performance due to the excellent gas‐solid contact attained with this device, which enables shorter drying times. A maximum air temperature of 200 °C is recommended for energy optimization. An open‐sided tube protruding above the stagnant bed by at least 2/3 of the latter's height produces much lower and denser fountains than a tube flush with the upper surface of the bed.

Experimental Flow Measurements of a Spouted Bed Using Pressure Transducer and X-Ray CT Scanner

Flow behaviour of an air-glass bead spouted bed (20 cm diameter, 1.31 m high) was investigated using wall pressure fluctuation measurements and X-ray Computed Tomography (CT) scanning. Spout shape, spout dimension, fountain shape and fountain height were visualized from CT images. Statistical and spectral analyses were applied to pressure fluctuation series measured along the column wall. Local and global gas-solids flow dynamics were compared. Gas velocity greatly affects hydrodynamics of the spout bed. A stable spouting regime was identified. This study enhances the understanding of gas-solid flow patterns and provides detail hydrodynamics for further modelling work.

Experimental Flow Measurements of a Spouted Bed Using Pressure Transducer and X-Ray CT Scanner

Flow behaviour of an air-glass bead spouted bed (20 cm diameter, 1.31 m high) was investigated using wall pressure fluctuation measurements and X-ray Computed Tomography (CT) scanning. Spout shape, spout dimension, fountain shape and fountain height were visualized from CT images. Statistical and spectral analyses were applied to pressure fluctuation series measured along the column wall. Local and global gas-solids flow dynamics were compared. Gas velocity greatly affects hydrodynamics of the spout bed. A stable spouting regime was identified. This study enhances the understanding of gas-solid flow patterns and provides detail hydrodynamics for further modelling work.

Stability of slot‐rectangular spouted beds: Effect of slot configuration

AbstractExperiments were carried out to determine the flow stability of slot‐rectangular spouted beds of 300 × 100 mm cross‐section with slots of different widths, lengths, and depths. The effects of slot expansion angle and diverging base were also investigated. Dependent variables included the minimum spouting velocity, bed pressure drop and standard deviation of pressure fluctuations. Based on the flow regimes and spout termination mechanisms, instability was found to be mainly due to the interaction of multiple spouts. Criteria were identified relating stable spouting to slot dimensions and particle size. Slots of limited cross‐sectional area can provide sustainable and symmetric spouting with little fluctuation, as long as the slot length‐to‐width ratio and depth are within certain limits, related to those for conventional spouted beds.

Particle–Gas Mass Transfer in a Spouted Bed with Adjustable Air Inlet

Spouted bed equipment has the potential of producing high-quality particulate materials with reduced energy consumption and environment impact. Particle-to-gas mass transfer was investigated in a spouted bed with a novel design of two rotating drums placed symmetrically in the apparatus to create air inlet openings of adjustable width, so that fluidization can be adapted to the requirements of each product and process. The mass transfer coefficients between particle surface and gas were derived from first-period drying experiments with porous, nonhygroscopic material by assuming perfect back-mixing or, alternatively, ideal plug flow of the gas. Respective Sherwood numbers were empirically correlated and found to be superior to the Sherwood numbers of conventional fluidized beds or conventional spouted beds.

Drying of Starch Suspension in Spouted Bed with Inert Particles: Physical and Thermal Analysis of Product

Drying in a spouted bed with inert particles promotes high heat and mass transfer rates due to the gas–solid contact, which in turn is successfully achieved by particles' cyclic movements. Because of its advantages and versatility, spouted bed drying of suspensions on inert particles is a potential alternative to flash and spray drying and has received attention in research and development in recent years. In this context, this article describes the drying process of cassava starch suspension (35% initial solids content) in a laboratory-scale cone-cylindrical spouted bed dryer with polypropylene particles. The setup consists of a cone-cylindrical spouted bed dryer (internal angle of 60°, 20-cm column diameter, and 5-cm inlet orifice diameter) with top feeding of suspension, which is sprayed by a double-fluid atomizer. The study focused on the fluid dynamics of polypropylene particles at inlet air temperatures of 60, 75, and 90°C and the effects of air temperature on dried starch properties, such as gelatinization temperature, pasting temperature, particle size distribution, crystalline profile, and final moisture content. The pressure drop fluid dynamic curves did not allow a proper analysis and assessment of minimum spout air flow when air was atomized in the bed. Therefore, the minimum spout air flow was determined by the visual observation of the fountain height in this case. Inlet air temperatures did not show a significant difference in the minimum spout air flow, but the bed presented dynamic instability with increasing inlet air temperature. The results showed that the spout fluid dynamic regime during drying was stable with air flow around 1.5 times the minimum spout air flow in the range of inlet air temperature studied. Drying air temperature influenced final moisture content of samples, which was lower than 13% for all conditions. However, physical properties of dried starch were not affected by process conditions.

Three-Dimensional Numerical Simulation of Semi-Cylindrical and Cylindrical Spouted Bed Hydrodynamics

Understanding of detailed transport phenomena occurring in spouted beds is necessary and fundamental for increasing the range of industrial applications. Especially for drying processes, detailed information about hydrodynamics is important, because it is closely related to heat and mass transfer. The use of semi-cylindrical spouted beds is a classical technique that emerged as an alternative to obtaining experimental data on the fluid dynamics of full-column spouted beds. This technique has been questioned, because the geometry of the bed must be altered for the visualization of the hydrodynamics occurring inside it, which, nevertheless, is the only way to obtain visual information on solid dynamics behavior inside the column. Therefore, the objective of this study was to revisit the semi-cylindrical spouted bed technique using computational fluid dynamics to perform numerical simulations and verifying these results against experimental results obtained in cylindrical and semi-cylindrical beds. Both simulated and experimental results were compared for the fluid dynamics of each system. The simulated results indicated that the flat wall had a great influence on the solid velocity, which is in accordance with the experimental observations already presented in the literature. However, little influence of this wall on static pressure, porosity profiles, and spout channel shape was observed in the simulated results, indicating a high fluid dynamic similarity between cylindrical and semi-cylindrical systems.

Hydrodynamic characteristics of a pulsed spouted bed of food particulates

Pulsed spouted bed has been developed to offset some limitations posted by a conventional spouted bed and some other modified spouted beds that allow an intermittent operation, which has proved to offer many advantages over continuous spouting. However, detailed hydrodynamic behavior of a pulsed spouted bed is not yet available. The present study thus investigated the effects of various parameters, i.e., type of material, pulse frequency and static bed height, on the spouting behavior as well as other bed basic hydrodynamic characteristics viz. maximum spoutable bed height, maximum pressure drop (Δ P max), steady spouting pressure drop (Δ P s) and minimum spouting velocity ( U ms). Soybean, whole-shelled peanut and French bean were used as test materials to represent food particulates of different characteristics. Empirical correlations that can be used to predict the tested hydrodynamic behavior of the pulsed spouted bed were also developed.

Woody biomass and mill waste utilization opportunities in Alabama: Transportation cost minimization, optimum facility location, economic feasibility, and impact

AbstractFour biorefinery technologies were studied for feedstock allocation, optimum facility location, economic feasibility, and their economic impacts on Alabama. The studied technologies are: (1) circulated fluidized bed gasification of woody biomass for Fischer‐Tropsch (F‐T) fuels and power production; (2) simultaneous saccharification and fermentation (SSF) of paper sludge for ethanol production; (3) direct spouted bed (DSB) gasification with air and steam of woody biomass for power; and (4) direct combustion of woody biomass for power production. The optimum biorefinery locations for all four processes were southwestern Alabama. The average transportation distance for woody biomass was about 32 miles (51.5 km) to the biorefinery plants; however, longer transportation distances were required for paper sludge where the feedstock is provided by the pulp and paper plants in the region. The SSF process along with the DSB gasification process were the only economically feasible biorefinery technologies with an over 80 and 22.5% internal rate of return, respectively. Economic impacts of all the studied biorefinery technologies were comparable to each other. © 2010 American Institute of Chemical Engineers Environ Prog, 2010.

Preliminary Results for the Investigation of Hydrodynamic Scaling Relationships in Shallow Spouted Beds

This research is targeted at developing improved experimentally based scaling relationships for the hydrodynamics of shallow, gas-spouted beds of dense particles. The work is motivated by the need to more effectively scale up shallow spouted beds used in processes such as in the coating of nuclear fuel particles where precise control of solids and gas circulation is critically important. Experimental results reported here are for a 50 mm diameter spouted bed containing two different types of bed solids (alumina and zirconia) at different static bed depths and fluidized by air and helium. Measurements of multiple local average pressures, inlet gas pressure fluctuations, and spout height were used to characterize the bed hydrodynamics for each operating condition. Follow-on studies are planned that include additional variations in bed size, particle properties, and fluidizing gas. The ultimate objective is to identify the most important non-dimensional hydrodynamic scaling groups and possible spouted-bed design correlations based on these groups.

Fluid Dynamic Study of a Semicylindrical Spouted Bed: Evaluation of the Shear Stress Effects in the Flat Wall Region Using Computational Fluid Dynamics

Using a semicylindrical spouted bed to obtain experimental data of cylindrical vessels is an old technique and it has already been widely studied by experimental procedures. In the mathematical mod...

Fluid Dynamics Analysis of a Draft-Tube Continuous Spouted Bed with Particles Bottom Feed using CFD

In this work the fluid dynamics behavior of a draft tube continuous spouted bed with particle bottom feed was studied through experimental data of static pressure, fountain height, and fluid mass f...

Analysis of pressure fluctuations during water evaporation in spouted bed

AbstractThe aim of this work was to study the behaviour of conventional spouted beds during water evaporation and to analyze the pressure fluctuations at the maximum water evaporative capacity for different bed heights and air flow rates. The results showed that spout pressure drop could not indicate the proximity of maximum evaporative capacity; however this condition is denoted by a minimum in fountain height. The standard deviation and amplitude of the pressure fluctuations also showed a minimum point at the maximum water evaporation capacity. The frequency domain analysis of pressure fluctuations revealed that the dry bed has a dominant frequency varying from 6 to 8.2 Hz and that the peak of dominant frequency tends to disappear with the increase in water feed rate.

Heat Transfer in Sprayed Spouted Beds

AbstractAn experimental and theoretical study of the influence of various kind of beds, static bed height and ratio of mass flow of water to mass flow rate of gas on heat transfer coefficient was carried out. The results of the investigations were compared with literature correlations for predicting heat transfer in conical spouted beds. Moreover, a new correlation of dimensionless groups was developed for heat transfer during spraying spouted beds. Also, the model of Kmiec [Kmiec, “Bed Expansion and Heat and Mass Transfer in Fluidized Beds,” Sci. Pap. Inst. Chem. Eng. Heating Equip. Wroclaw Univ. Technol. 36, Monographs No. 19, Publishing House of Wroclaw University of Technology, Wroclaw, Poland, 1980a; Kmiec, Chem. Eng. J. 1980b;19,189–200] of particle circulation and heat transfer between spouting gas and particles was analyzed. The one‐dimensional mathematical models for solids flow in a spout and for heat transfer in a spouted bed analyzed here lead to differential equations which, solved numerically, give results in good agreement with experimental data.

Mass transfer during air humidification in spouted beds

AbstractThis article presents the results obtained from analysing the impacts of bed media, static bed height, and the water‐to‐air mass flow ratios on the mass transfer coefficient and Colburn factor. The experimental data were compared with the correlations for mass transfer and the analogy between heat and mass transfer in conical spouted beds described earlier in literature. Moreover, the aim of the article is to present some new correlations of dimensionless groups for description of mass transfer and analogy of heat and mass transfer in sprayed spouted beds, which were developed by the authors.

Preface to the Spouted Bed Special Issue in Honour of Dr. Norman Epstein's 85th Birthday

Preface to the Spouted Bed Special Issue in Honour of Dr. Norman Epstein's 85th Birthday