Spouted Bed Research Articles

Three‐Dimensional Computational Fluid Dynamics Modeling of a Prismatic Spouted Bed

AbstractModern simulation tools like discrete particle models or continuum models have been established as precious methods to gain insight into the complex processes in fluidized and spouted beds. Valuable information on parameters influencing the hydrodynamics can be obtained directly from computer simulations. Numerous researchers applied two‐dimensional discrete and continuum models to simulate fluidized and spouted beds. However, only few publications deal with three‐dimensional continuum simulations, and very often results of three‐dimensional experiments are compared with two‐dimensional results. In this work, a three‐dimensional simulation by application of a continuum model is presented in a prismatic spouted bed with slit‐shaped gas inlets. Comparisons with two‐dimensional simulations in the same geometry (Gryczka et al. 2009, Chem. Eng. Sci., in press) are also part of this publication. The influence of the third dimension on the hydrodynamic behavior (bubble formation, bubble size, etc.) will be discussed.

Grain Drying in a Paraboloid-Based Spouted Bed with and without Draft Tube

In this study, grain drying in a spherical-based spouted bed (SBSB), a cone-based spouted bed (CBSB), and a paraboloid-based spouted bed (PBSB) with and without draft tube was investigated. Spouted-bed bases with the same volume in different shapes—spherical, cone, and paraboloid—were used for the drying experiments to investigate the effect of the spouted-bed base shape on drying. The drying experiments were carried out with perforated and solid draft tubes. The effects of the distance between the gas inlet nozzle and the bottom of the draft tube (entrainment zone height) and the draft tube diameter as geometric parameters on drying were also investigated. It was seen that the geometrical shape of the contactor base influenced the drying time. The highest drying rate was achieved for drying in a paraboloid-based spouted bed. The results also showed that using a draft tube caused a significant increase in drying time. Because the perforated draft tube allows a higher gas flow rate through the annulus, it decreases the drying time when compared with the solid draft tube. Drying time decreased slightly with the decreasing height of the entrainment zone but draft tube diameter did not have a considerable effect on drying.

Flow Patterns and Transitions of a Novel Annular Spouted Bed with Multiple Air Nozzles

Experimental study on the flow patterns and transitions in a novel annular spouted bed with multiple air nozzles was carried out. Three distinct stable flow patterns, i.e. internal jet, jet-spouting, and fully developed spouting were identified. Two transitional flow patterns and flow instabilities, single internal jet, single jet-spouting, and bubbling or slugging were found. Schematic diagrams and typical flow pattern images obtained by a digital charge-coupled display (CCD) camera were presented for classifying these flow patterns. Experimental results show that the internal jet or jet-spouting is easier to occur for forward nozzles than for angle nozzles with the increasing of spouting gas velocity. Due to the interaction of spouting gases from different nozzles, the turbulent exchange or mixing of particles among the nozzles in the fully developed spouting state can be observed distinctly. The total bed pressure drop varied with the spouting gas velocity increases, as a result of the transition of flow pattern. Typical flow pattern map at various static bed heights and spouting gas velocity were plotted for describing the transitions between flow patterns.

Fountain Geometry of Beds Consisting of Plastic Wastes in Shallow Spouted Beds

The fountain is especially important in the design of spouted beds for the treatment of plastic wastes. The height and structure of the fountain in shallow spouted beds have been determined by means of an optical fiber as well as by an image treatment system. The effect of the operating variables on the fountain geometry (height and amplitude) has been analyzed by carrying out the operation with different values of the geometric factors of the contactor (base angle and gas inlet diameter) and of the operating conditions (stagnant bed height, particle diameter, particle density, particle shape, and air velocity). The materials studied are different plastic wastes (polyethylene, polypropylene, and polystyrene, both extruded and expanded). In the fountain, the core or solid ascending zone and the periphery or solid descending zone have been delimited. The experimental results prove the validity for plastic materials of the equation proven previously for prediction of the height of the fountain in cylindrical...

Hydrodynamics of slot‐rectangular spouted beds: Effect of slot configuration on the local flow structure

AbstractThe local flow structure in a slot‐rectangular spouted bed column of 300 mm × 100 mm cross‐section was investigated with slots of equal area but different length‐to‐width ratios. Dead‐zones, spout shapes, and distributions of pressure, particle velocity, and voidage were explored. The local flow structure of the slot‐rectangular spouted bed became similar to conventional spouted beds as the height increased, with spouts from slots of different length‐to‐width ratios approaching similarity in the upper part of the bed. Static bed height was found to have little influence on the flow in the spout at a given level.

Методика экспериментального обоснования технологических параметров аппаратов с применением фонтанирующего слоя

Методика экспериментального обоснования технологических параметров аппаратов с применением фонтанирующего слоя

A Draft-Tube Conical Spouted Bed for Drying Fine Particles

A study has been conducted on the performance of a draft tube conical spouted bed for drying fine particles. Batch operation has been performed with nonporous, porous, and open-sided draft tubes in order to ascertain the optimum configuration of this internal device. The nonporous draft tube requires the lowest minimum spouting velocity. Nevertheless, the solid circulation rate and the drying efficiency of the open-sided draft tube are superior to any other spouted bed configuration. Moreover, it allows for reducing the height of the fountain and, consequently, the height of the drying equipment.

Numerical simulation of reactive transfers in spouted beds at high temperature: Application to coal gasification

Spouted beds are used in many physical and chemical processes that involve large particles (drying, combustion, film deposition, gasification, etc.). Understanding of bed hydrodynamics, coupled heat and mass transfer and chemical reaction phenomena is mandatory for designing, scaling up and optimizing spouted beds. In this work, a spouted bed reactor operating at high temperature has been modelled through one-dimensional model in which heat transfer has been carefully described at different levels of complexity. The process of coal gasification has been selected to demonstrate the models achievements and predictions have been compared to previous spouted bed reactor experimental results. Calculations have shown that a particular attention must be paid to describe heat transfer in spouted bed reactors operating at high temperature.

PHYCOCYANIN CONTENT OF SPIRULINA PLATENSIS DRIED IN SPOUTED BED AND THIN LAYER

ABSTRACT The aim of this work was to study the drying of Spirulina platensis, evaluating the final product characteristics about its phycocyanin content and its protein solubility in water. Two drying techniques were used: the spouted bed and the thin layer. For drying in a spouted bed, the cone‐cylindrical geometry was chosen, namely type conventional spouted bed (CSB) and jet‐spouted bed, with a paste concentration of 5%. The thin‐layer drying was performed at temperatures of 50 and 60C, with a load of material of 4 kg/m2 in the tray. The spouted bed dryer type CSB demonstrated good functionality, not presenting a collapse during the experiments. The solubility in aqueous mean was similar in all the drying techniques used, being the values found around 37%. The largest phycocyanin values were found in the thin‐layer temperature of 50C and in the spouted bed type CSB; however, the thin layer was excluded so as not to reach the commercial moisture content.PRACTICAL APPLICATIONSPhycocyanin is the major phycobiliprotein in Spirulina. Phycocyanin has significant antioxidant, anti‐inflammatory, hepatoprotective and radical scavenging properties. It is used as colorant in food and cosmetics. It was also shown to have therapeutic value (immunomodulating activity and anticancer activity). The drying operation is commonly used to prolong the shelf life of microbial biomasses. Preservation of cyanobacteria is a difficult process, since the cells are small and, moreover, the cultures are usually diluted. Drying of liquids and pastes in spouted beds with inert bodies has been presented as an alternative to spray drying in an attempt to obtain high‐quality powdered products at a low cost.

Minimum Spoutable Bed Height in a Screen-Bottomed Spouted Bed

It is well known that, in the case of traditional spouted bed without a draft-tube, there exists a maximum spoutable bed height, beyond which stable spouting is no longer possible, and also that there is no limitation on the bed height in the case of a spouted bed with a draft-tube. However, to date, there has been no report that a minimum spoutable bed height, or lower limit of the bed height, exists in any type of spouted bed. It was, however, found that there exists a minimum spoutabe bed height in a screen-bottomed spouted bed. The screen-bottomed spouted bed has a draft-tube, but it has no gas-inlet nozzle or orifice. The gas is fed uniformly over the cross-section of the vessel. When the bed height was less than the minimum spoutable one, the solid particles in the annulus were fluidized and then stable spouting could not be achieved.

Solid Velocity in Shallow Spouted Beds Consisting of Solids of Varying Density

The vertical component of solid velocity has been measured in shallow spouted beds by means of an optical fibre, for different geometric factors of the contactor (angle and inlet diameter) and under different experimental conditions (height of the stagnant bed, particle diameter and air velocity). The study has been carried out with glass beads and materials of lower density (high- and low-density polyethylene, polypropylene and extruded and expanded polystyrene) in the spout zone of shallow spouted beds. The calculation of velocity along the axis has been carried out by solving a force balance rising along the spout and the core of the fountain.

Mixing Characteristics of a Novel Annular Spouted Bed with Several Angled Air Nozzles

A novel spouted bed, namely, an annular spouted bed with several angled angled air nozzles, has been proposed for dryness, catalytic pyrolysis, and gasification of biomass. It consists of two concentric upright cylinders with eight annularly located angled air nozzles between inner and outer cylinders. A rotating cone is adopted as an accessorial feeder. Experiments have been performed to study mixing characteristics of the annular spouted bed. The test materials studied are soybean and black bean. The effect of feeding mode and air velocity as well as static bed height on particle mixing of the spouted bed under various operating conditions was investigated. In addition, the lateral particle motion was studied experimentally and theoretically.

Simulation of the Hydrodynamics and Drying in a Spouted Bed Dryer

Gas–particle flow behavior in a spouted bed of spherical particles was simulated using the Eulerian–Eulerian two-fluid modeling approach, incorporating a kinetic–frictional constitutive model for dense assemblies of the particulate solid. The interaction between gas and particles was modeled using the Gidaspow drag model and the predicted hydrodynamics is compared with published experimental data. To investigate drying characteristics of particulate solids in axisymmetric spouted beds, a heat and mass transfer model was developed and incorporated into the commercial computational fluid dynamics (CFD) code FLUENT 6.2. The kinetics of drying was described using the classical and diffusional models for surface drying and internal moisture drying, respectively. The overall flow patterns within the spouted bed were predicted well by the model; i.e., a stable spout region, a fountain region, and an annular downcomer region were obtained. Calculated particle velocities and concentrations in the axisymmetric spouted bed were in reasonable agreement with the experimental data of He et al. (Can. J. Chem. Eng. 1994a, 72:229; 1994b, 72:561). Such predictions can provide important information on the flow field, temperature, and species distributions inside the spouted bed for process design and scale-up.

Hydrodynamic Characteristics of a Novel Annular Spouted Bed with Multiple Air Nozzles

A novel spouted bed, namely, an annular spouted bed with multiple air nozzles, has been proposed for dryness, pyrolysis, and gasification of coal particulates. It consists of two homocentric upright cylinders with some annularly located spouting air nozzles between inner and outer cylinders. Experiments have been performed to study hydrodynamic characteristics of this device. The test materials studied are ash particle, soy bean, and black bean. Three distinct spouting stages have been examined and outlined with the hold-ups increase. In the fully developed spouting stage, three flow behaviors of particles have been observed and delimited. The effects of nozzle mode and spouting velocity on the maximum spouting height of the dense-phase region, spoutable static bed height, and spouting pressure drop in the bed have been investigated experimentally.

Low temperature drying of pomace in spout and spout-fluid beds

The solid residue that originates from virgin olive oil production has a consistency that falls between a paste and a particulate solid, consists of two phases: the crushed olive kernel and the fruit pulp. The kernel particles can be used as high quality solid fuel, while oil can be extracted from the pulp residue. Two technological problems should be tackled to optimize the extraction process: drying the solid residue at low temperature and separating the two phases. The pomace was dried batchwise in a 0.17 m diameter spouted bed and continuously in a 0.29 m diameter draft tube spout-fluid bed with independent control of the air flow rate to the spout and to the annulus. Experimental drying tests were carried out. The drying kinetics were measured during each test in the 0.17 m diameter bed. The solids circulation rate was measured in the larger unit, under a wide range of air flow rates to both the spout and the annulus. An operation regime map has been obtained from a characterization of the quality of the fluidization under a wide range of hydrodynamical conditions. The drying efficiency of both apparatuses was studied.

Drying of Pharmaceuticals: The Applicability of Spouted Beds

ABSTRACT This study evaluates the performance of conventional spouted beds (CSB) with inert bodies in the drying of pharmaceutical pastes, based on the dry product quality. The powder obtained by drying annatto extracts shows properties comparable to one of the commercial products, indicating that the spouting is competitive with other industrial and lab-scale processes. The contents of bixin and caffeine in annatto and guarana dry powders demonstrated a strong dependence on the inlet air temperature. Also, the properties of indomethacin-containing microcapsules dried in CSB and spray dryers revealed that spouting is a promising technique to obtain pharmaceutical forms with unique drug release qualities.

Spout Geometry in Shallow Spouted Beds with Solids of Different Density and Different Sphericity

Spout diameter has been measured in shallow spouted beds by means of an optical fiber probe, for different geometric factors of the contactor (base angle and gas inlet diameter) and under different experimental conditions (stagnant bed height, gas velocity, particle density, particle size, and particle shape). The study has been performed with glass beads and low-density solids (high and low-density polyethylene, polypropylene, and extruded and expanded polystyrene). A correlation that is valid to predict the average spout diameter in cylindrical spouted beds for beds composed of solids of different density, size, and shape has been developed that is in agreement with the experimental data. This equation is interesting for the proposal of real models for gas-solid flow.

Hydrodynamic Characteristics of a Powder‐Particle Spouted Bed with Powder Entrained in Spouting Gas

AbstractSpouting of 3.7 mm polyvinyl chloride particles in a cone‐based cylindrical column is subjected to entrainment of FCC powder in the spouting air. It is found that the powder entrainment reduces the minimum spouting velocity, increases the bed pressure drop and reduces the maximum spoutable bed height. At any given bed height and value of U/Ums, there is a critical value of powder loading ratio above which spouting gives way to slugging.

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20–25% wb) from 40 to 110 W/m3 K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.

High Temperature Spouted Bed Paddy Drying with Varied Downcomer Air Flows and Moisture Contents: Effects on Drying Kinetics, Critical Moisture Content, and Milling Quality

This research is an experimental study on paddy drying conducted in a two-dimensional spouted bed batch dryer to investigate the effects of downcomer airflow, drying temperature, and initial moisture content on drying kinetics, milling quality, and thermal energy consumption. The system of spouted bed drying and a comparison of spouted bed drying in the present study, and fluidized bed drying in the related literature, are also discussed. Downcomer air flows of 0, 20, and 30% ([defined as mass flow rate of downcomer air/total mass flow rate of air] × 100%), inlet air temperatures of 110, 130, and 150°C, and initial moisture contents of 18–35% d.b. were used. It was found that moisture transfer did not only occur in the spout region but also took place in the downcomer region. The moisture content and temperature of the paddy dropped as grain moved downward in the downcomer, which resulted from the presence of an evaporative cooling phenomenon. The characterization of drying curves regardless of any drying condition could be described by nearly linear relationships between moisture content and time. Although high downcomer air flow and drying temperature could enhance effective moisture reduction, they caused an adverse decrease in critical moisture content and HRY (head rice yield). Critical moisture content and HRY could also increase with an increase in initial moisture content. The difference in moisture content between the initial and critical moisture contents varied between 4.5 and 8.0%d.b., depending upon drying conditions. No significant effect on color was evident. From the point of view of HRY, the correct management of a two-stage spouted bed drying system could be a suitable and attractive alternative for rice mills. Finally, a comparison between the spouted bed drying and fluidized bed drying showed that the spouted bed had advantages over the fluidized bed in terms of product quality. The specific drying rates (kg water evaporated h−1 m−3) of both techniques were comparable. With respect to energy consumption, spouted bed drying was not as efficient as fluidized bed drying for intermediate initial moisture content, but a contrary result was obtained for low initial moisture content.