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Draft Tube (draft + tube)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

Solids Circulation Flux and Gas Bypassing in a Pressurized Spout-fluid Bed with a Draft Tube

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2002
Rui Xiao
Abstract An experimental study on solids circulation flux and gas bypassing of a spout-fluid bed with a draft tube at elevated pressures up to 600 kPa was performed in a 200 mm diameter cylindrical steel column with a 608 conical distributor. Glass beads with mean diameter 2.067 mm were used as bed materials to investigate the effect of operating conditions and geometric configuration on the solids circulation flux and the gas distribution between the annulus and the draft tube. A novel technique has been developed to measure the solids fluxes under pressure, and gas (CO2) traces have been employed to investigate gas bypassing characteristics. The solids circulation flux is greatly enhanced when operating pressure and auxiliary gas flowrate are increased, and it is also strongly influenced by geometric configuration. Two experimental relations are proposed for predicting solids circulation flux enhancement factors. Une étude expérimentale sur le flux de circulation des solides et la dérivation du gaz d'un lit jaillissant muni d'un tube d'aspiration à des pressions élevées jusqu'à 600 kPa, a été réalisée dans une colonne d'acier cylindrique de 200 mm de diamètre avec un distributeur conique à 608. Des billes de verre d'un diamètre moyen de 2,067 mm ont été utilisées comme matériaux de lit pour étudier l'effet des conditions opératoires et de la configuration géométrique sur le flux de circulation des solides et la distribution du gaz entre l'espace annulaire et le tube d'aspiration. Une nouvelle technique a été élaborée pour mesurer les flux de solides sous pression et les caractéristiques de la dérivation du gaz ont été étudiées à l'aide de gaz traceurs (CO2). Le flux de circulation des solides est grandement amélioré lorsque la pression de fonctionnement et le débit de gaz auxiliaire sont augmentés, et il est également fortement influencé par la configuration géométrique. Deux relations expérimentales sont proposées pour la prédiction des facteurs d'amélioration du flux de circulation des solides. [source]

Modeling Growth Rate Dispersion in Industrial Crystallizers

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2003
G.M. Westhoff
Abstract The phenomenon of healing appears to be a plausible explanation for the growth rate dispersion observed in many industrial crystallizers. In this paper a growth model is postulated, which describes the healing of plastically deformed attrition fragments. The rate of healing is assumed to be inversely proportional to the initial strain and to the rate of change of either the length, the area, or the volume of the crystal. The validity of the proposed model is verified by the simulation of growth of the smallest crystals (L0) in time in a growth experiment for specific combinations of the model parameters. In addition, the applicability of the proposed model is evaluated through simulations of steady state experimental data obtained in a 75-liter Draft Tube (DT) crystallizer. It is concluded that the proposed model is able to fit reasonably well the experimental crystal size distribution. The model predicts the existence of a ,dead time' during which attrition fragments with large initial strain do not grow and which may last several residence times. [source]

Hydrodynamic considerations on optimal design of a three-phase airlift bioreactor with high solids loading

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2003
Jaroslav Klein
Abstract The hydrodynamic study of a three-phase airlift (TPAL) bioreactor with an enlarged gas,liquid dual separator was carried out. Different lengths and diameters of the draft tube were tested to show how the design of the separator zone affects the hydrodynamic performance of the TPAL reactor. Ca-alginate beads with entrapped yeast biomass at different loadings (0, 7, 14 and 21% v/v) were used in order to mimic the solid phase of conventional high cell density systems, such as those with cells immobilized on carriers or flocculating cells. Important information on multiphase flow and distribution of gas and solid phases in the internal-loop airlift reactor (ALR) with high solids loading was obtained, which can be used for suggesting optimal hydrodynamic conditions in a TPAL bioreactor with high solids loading. It is finally suggested that the ALR with a dual separator and a downcomer to riser cross-sectional area ratio (AD/AR) ranging from 1.2 to 2.0 can be successfully applied to batch/continuous high cell density systems, where the uniform distribution of solid phase, its efficient separation of particles from the liquid phase, and an improved residence time of air bubbles inside the reactor are desirable. Copyright © 2003 Society of Chemical Industry [source]

Minimum spouting velocity in a spout-fluid bed with a draft tube

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009
Jian Xu
Abstract Minimum spouting velocity was measured in a 0.12 m cylindrical spout-fluid bed with a draft tube. The effects of fluidizing gas flow rate, entrainment height, and spout nozzle diameter on minimum spouting velocity were discussed. A correlation on minimum spouting velocity has been proposed based on the present experimental data. La vitesse de jaillissement minimale a été mesurée dans un lit fluide jaillissant cylindrique de 0,12 m muni d'un tube d'aspiration. Les effets du débit de gaz fluidisant, de la hauteur d'entraînement et du diamètre de l'orifice de jet sont examinés. Une corrélation sur la vitesse de jaillissement minimale est proposée à partir des présentes données expérimentales. [source]

Spouting Enhancement by Addition of Small Quantities of Liquid to Gas-Spouted Beds

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2006
Y. Nagahashi
Abstract The addition of liquid water to beds of polystyrene particles exceeding 3 mm in diameter enhanced spouting by causing a decrease in the minimum spouting velocity. While the degree of enhancement is quantitatively comparable to what we reported previously for fluidized beds of large light hydrophobic particles, the mechanism is quite different. Enhancement of spouting takes place because the liquid congregates at the spout-annulus interface, forming an effective nearly-impermeable draft tube which then increases the velocity of the gas up the spout. L'ajout d'eau liquide à des lits de particules de polystyrène de plus de 3 mm de diamètre améliore le jaillissement en causant une diminution de la vitesse de jaillissement minimale. Alors que le degré d'amélioration est du point de vue quantitatif comparable à ce que nous avons indiqué antérieurement pour des lits fluidisés à larges particules hydrophobes légères, le mécanisme est différent. L'amélioration du jaillissement se produit parce que le liquide s'agglomère à l'interface jet-espace annulaire, formant un tube d'aspiration quasi imperméable efficace, ce qui a pour effet d'accroître la vitesse du gaz en haut du jet. [source]

Solids Circulation Flux and Gas Bypassing in a Pressurized Spout-fluid Bed with a Draft Tube

The Effect of Adding Phosphate on the Size of Extremely Fine Needle-like Lepidocrocite Particles Prepared by Oxidizing an Aqueous Suspension of Ferrous Hydroxide

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2002
Naoki Mihara
Abstract Extremely fine particles of needle-like lepidocrocite (,-FeOOH) were synthesized by the oxidation of aqueous suspensions of ferrous hydroxide using a bubble column with draft tube at a constant temperature of 30°C, and the effects of the reaction conditions or the oxidation rate were investigated in order to determine the parameters that control the particle size. When the concentration of oxygen in the feed stream was varied under a constant gas velocity, the mean size based on the major axis of a needle-like particle decreased from 0.7 µm to 0.4 µm with increasing oxidation rate. By adding of NaH2PO4 to an aqueous Fe(OH)2 suspension, in concentrations up to 1.0 mol/m3 during the air oxidation, and up to 0.9 mol/m3 during the oxidation with 30% and 50% O2, the major axis could be reduced to ca. 0.3 µm with the minor axis and the oxidation rate remained almost unchanged. Des particules extra fines de lépidocrocite en forme d'aiguilles (,-FeOOH) ont été synthétisées par oxydation de suspensions aqueuses d'hydroxide ferreux à l'aide d'une colonne munie d'un tube d'aspiration à une température constante de 30°C et on a étudié les effets des conditions de réaction et de la vitesse d'oxydation afin de déterminer les paramètres qui contrôlent la taille de particule. Lorsqu'on fait varier la concentration d'oxygène dans le courant d'alimentation à une vitesse de gaz constante, la taille moyenne basée sur l'axe principal d'une particule en forme d'aiguille diminue de 0,7 µm à 0,4 µm avec l'augmentation de la vitesse d'oxydation. En ajoutant du NaH2PO4 à une suspension aqueuse de Fe(OH)2, à des concentrations atteignant 1,0 mol/m3 lors de l'oxydation de l'air et 0,9 mol/m3 lors de l'oxydation avec 30% et 50% de O2, l'axe principal pourrait être réduit à environ 0,3 µm, l'axe secondaire et la vitesse d'oxydation demeurant presque inchangés. [source]

The Influence of a Constructional Solution of the Crystallizer with a Jet Pump on Crystal Attrition

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2005
A. Matynia
Abstract The research results concerning attrition of sodium chloride crystals in two types of jet pump crystallizers are presented. It was demonstrated that in the crystallizer with a jet pump crystals undergo considerable smaller attrition compared to the one equipped with agitator and draft tube (circulation profile). The influence of the initial mean crystal size, crystal volumetric concentration in the suspension and the residence time of the suspension in the crystallizer on the degree of solid phase destruction was determined and quantified in the form of empirical equations. The DTM MSCPR construction demonstrates the least destruction capabilities. [source]