Superficial Gas Velocity (superficial + gas_velocity)

Distribution by Scientific Domains


Selected Abstracts


Mixing Time in a Short Bubble Column

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2003
M Ravinath
Abstract Mixing time measurements have been carried out in a 0.2m I.D. short bubble column (Hc/D , 5) with different spargers and for different clear liquid height to diameter (HC/D) ratios. Superficial gas velocity has been varied in the range of 0.01m/s to 0.1m/s. Effect of bulk fluid viscosity on the mixing time has also been studied. The circulation cell model, with two fitted parameters viz. number of circulation cells, S and the inter-cell exchange velocity, Ve, has been used to predict and explain the variation in mixing time and the flow pattern in the short bubble column for different types of spargers. On a effectué des mesures de temps de mélange dans une colonne à bulles courte de 0,2 m de diamètre intérieur (Hc/D , 5) munie de différents aérateurs et pour différents rapports entre la hauteur de liquide clair et le diamètre (HC/D). On a fait varier la vitesse de gaz superficielle dans la gamme de 0,01-0,1 m/s. L'effet de la viscosité en masse du fluide sur le temps de mélange est également étudié. On a utilisé le modèle de zones de circulation, comprenant deux paramètres calés, à savoir le nombre de zones de circulation, S, et la vitesse d'échange entre les zones, Ve, pour prédire et expliquer la variation du temps de mélange et le profil d'écoulement dans la colonne à bulles courte pour différents types d'aérateurs. [source]


Nonintrusive characterization of fluidized bed hydrodynamics using vibration signature analysis

AICHE JOURNAL, Issue 3 2010
M. Abbasi
Abstract There are many techniques to characterize the hydrodynamics of fluidized beds, but new techniques are still needed for more reliable measurement. Bed vibrations were measured by an accelerometer in a gas,solid fluidized bed to characterize the hydrodynamics of the fluidized bed in a nonintrusive manner. Measurements were carried out at different superficial gas velocities and particle sizes. Pressure fluctuations were measured simultaneously. Vibration signals were processed using statistical analysis. For the sake of the evaluation, the vibration technique was used to calculate minimum fluidization velocity. It was shown that minimum fluidization velocity can be determined from the variation of standard deviation, skewness, and kurtosis of vibration signals against superficial gas velocity of the bed. Kurtosis was proved to be a new method of analyzing vibration signals. Results indicate that analyzing the vibration signals can be an effective nonintrusive technique to characterize the hydrodynamics of fluidized beds. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]


Preparation of LiMn2O4 powders via spray pyrolysis and fluidized bed hybrid system

AICHE JOURNAL, Issue 7 2006
Izumi Taniguchi
Abstract A novel technique has been developed to directly produce fine ceramic powders from liquid solution using a spray pyrolysis and fluidized bed hybrid system. Using this technique, the preparation of lithium manganese oxides LiMn2O4, which are the most promising cathode materials for lithium-ion batteries, has been carried out for various superficial gas velocities U0 = 0.30-0.91 m/s, static bed heights Ls = 50-150 mm, and medium particle sizes dpm,g = 294-498 ,m. The resulting powders had spherical nanostructured particles that comprised primary particles with a few tens of nanometer in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Moreover, the as-prepared powders showed better crystallinity and smaller specific surface area than those by conventional spray pyrolysis. The effects of process parameters on powder properties, such as specific surface area and crystallinity, were investigated for a wide range of superficial gas velocities and static bed heights. An as-prepared sample was used as cathode active materials for lithium-ion batteries and the cell performance has been investigated. Test experiments in the electrochemical cell Li/1M LiClO4 in PC/LiMn2O4 demonstrated that the sample prepared by the present technique was superior to that by the conventional spray pyrolysis and solid-state reaction method. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]


Fluid dynamics in coal liquefaction reactors using neutron absorption tracer technique

AICHE JOURNAL, Issue 8 2000
Naohide Sakai
Hydrodynamic properties in the coal liquefaction reactors at the Kashima pilot plant, which was constructed based on the NEDOL process, were investigated using the neutron absorption tracer technique. The reactor system is composed of three vessels, each with 1.0 m ID and 11.8 m in height. The gas velocity in the reactors under coal liquefaction conditions was estimated using a reaction simulator that contained reaction rates and vapor,liquid equilibrium. The axial dispersion coefficients in the first and third reactors at superficial gas velocities of 0.06,0.07 m/s were much smaller than those reported for air,water systems under ambient conditions. This suggests that the pilot-plant reactors operated fundamentally in the homogeneous bubble flow regime. [source]


Hydrodynamic characteristics of gas,solid fluidization at high temperature

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010
Shabnam Sanaei
Abstract Effect of temperature on the hydrodynamics of bubbling gas,solid fluidized beds was investigated in this work. Experiments were carried out at different temperatures ranged of 25,600°C and different superficial gas velocities in the range of 0.17,0.78,m/s with sand particles. The time-position trajectory of particles was obtained by the radioactive particle tracking technique at elevated temperature. These data were used for determination of some hydrodynamic parameters (mean velocity of upward and downward-moving particles, jump frequency, cycle frequency, and axial/radial diffusivities) which are representative to solids mixing through the bed. It was shown that solids mixing and diffusivity of particles increases by increasing temperature up to around 300°C. However, these parameters decrease by further increasing the temperature to higher than 300°C. This could be attributed to the properties of bubble and emulsion phases. Results of this study indicated that the bubbles grow up to a maximum diameter by increasing the temperature up to 300°C, after which the bubbles become smaller. The results showed that due to the wall effect, there is no significant change in the mean velocity of downward-moving clusters. In order to explain these trends, surface tension of emulsion between the rising bubble and the emulsion phase was introduced and evaluated in the bubbling fluidized bed. The results showed that surface tension between bubble and emulsion is increased by increasing temperature up to 300°C, however, after that it acts in oppositely. L'effet de la température sur l'hydrodynamique de lits fluidisés de gaz-solide bouillonnants a fait l'objet de l'étude de cet ouvrage. Des expériences ont été faites à différentes températures se situant entre 25 et 600°C et différentes vélocités de gaz superficiels sur une plage de 0,17 à 0,78,m/s avec particules de sable. La trajectoire temps-position des particules a été obtenue à l'aide d'une technique de repérage par particules radioactives à haute température. Ces données ont été utilisées pour déterminer certains des paramètres hydrodynamiques (vélocité moyenne des particules ascendantes et descendantes, la fréquence de sauts bonds, la fréquence de cycles et les diffusivités axiales et radiales), lesquels sont représentatifs de solides se mélangeant dans le lit. Il a été démontré que le mélange de solides et la diffusivité des particules augmentent en haussant la température à environ 300°C. Cependant, ces paramètres diminuent en accroissant davantage la température au-delà de 300°C. Cela pourrait être attribué aux propriétés des phases de bouillonnement et d'émulsion. Les résultats de cette étude indiquent que les bulles croissent pour atteindre un diamètre maximum en augmentant la température jusqu'à 300°C. Au-delà de cette température, les bulles deviennent plus petites. Les résultats démontrent qu'en raison de l'effet de paroi, il n'y a pas de changement significatif à la vélocité moyenne des grappes descendantes. Afin d'expliquer ces tendances, la tension de surface de l'émulsion entre la bulle ascendante et la phase émulsion a été introduite et évaluée dans le lit fluidisé bouillonnant. Les résultats ont démontré que la tension de surface entre la bulle et l'émulsion augmente en haussant à température jusqu'à 300°C; cependant, après cette température, elle agit inversement. [source]


Investigation into the hydrodynamics of gas,solid fluidized beds using particle image velocimetry coupled with digital image analysis

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2008
Jan Albert Laverman
Abstract The hydrodynamics of a freely bubbling, pseudo 2-D fluidized bed has been investigated experimentally for different bed aspect ratios at different superficial gas velocities by using Particle Image Velocimetry (PIV) combined with Digital Image Analysis (DIA). Coupling of both non-invasive measuring techniques allows us to obtain information on both the bubble behaviour and emulsion phase circulation patterns simultaneously. In particular, the combination of DIA with PIV allows to correct for the influence of particle raining through the roof of the bubbles on the time-averaged emulsion phase velocity profiles. On a étudié de façon expérimentale l'hydrodynamique d'un lit fluidisé pseudo 2-D en bouillonnement libre, pour différents rapports de forme de lits à différentes vitesses de gaz superficielles par vélocimétrie à images de particules (PIV) combinée à l'analyse d'images numériques (DIA). Le couplage de deux techniques de mesure non invasives nous permet d'obtenir de l'information sur le comportement des bulles et les schémas de circulation de la phase d'émulsion, simultanément. En particulier, la combinaison de DIA et de PIV permet de corriger l'influence de la pluie de particules s'écoulant du toit de bulles sur les profils de vitesse de la phase d'émulsion moyennés dans le temps. [source]


Local Bubble Dynamics and Macroscopic Flow Structure in Bubble Columns with Different Scales

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2003
Wei Chen
Abstract Local bubble behaviours were investigated in three bubble columns with different diameters of 200, 400 and 800 mm. By means of a novel single-tip optical fibre probe employing laser Doppler technique, the local gas holdup, bubble frequency, bubble size and velocity were measured simultaneously at different locations of the columns. Measurements were performed in air-water system at superficial gas velocities up to 90 mm/s. The averaged profiles and instantaneous measurements were analyzed and compared for different columns. The presence of a coherent gross circulation structure spanning the entire column diameter in the larger column rather than a pair of symmetrical circulation cells observed in the smaller columns has been confirmed. Les comportements locaux des bulles ont été étudiés dans trois colonnes à bulles de diamètres différents, soient 200, 400 et 800 mm. Au moyen d'une nouvelle sonde à fibre optique à embout unique employant la technique laser Doppler, des mesures locales de la rétention de gaz, de la fréquence des bulles, de la taille des bulles et de la vitesse ont été effectuées simultanément à différents endroits dans les colonnes. Ces mesures ont été effectuées pour un système air-eau à des vitesses de gaz superficielles atteignant 90 mm/s. Les profils moyennés et les mesures instantanées ont été analysés puis comparés pour différentes colonnes. La présence d'une structure de circulation unique cohérente occupant tout le diamètre de la colonne dans la colonne la plus large plutôt qu'une paire de cellules de circulation symétriques observées dans les colonnes plus petites est confirmée. [source]


Intensification of Slurry Bubble Columns by Vibration Excitement

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Jürg Ellenberger
Abstract We show that application of low-frequency vibrations, in the 30 to 60 Hz range, to the liquid phase of an air , water , silica catalyst slurry bubble column causes significant enhancement of both gas holdup and volumetric mass transfer coefficient over a wide range of superficial gas velocities. The increase in the gas holdup is attributed mainly to a significant reduction in the rise velocity of the bubble swarm due to the generation of standing waves in the column. Furthermore, application of vibrations to the liquid phase serves to stabilize the homogenous bubbly flow regime and delay the onset of the churn-turbulent flow regime. On montre que l'application de vibrations de faibles fréquences (entre 30 et 60 Hz) à la phase liquide d'une colonne à bulles à suspensions de catalyseur air-eau-silice, permet une amélioration significative à la fois du coefficient de rétention de gaz et du coefficient du transfert de matière volumétrique pour une vaste gamme de vitesses de gaz superficielles. L'augmentation de la rétention de gaz est imputée principalement à une réduction importante de la vitesse de montée de l'essaim de bulles qui est due à la création de vagues stationnaires dans la colonne. En outre, l'application des vibrations à la phase liquide sert à stabiliser le régime d'écoulement à bulles homogène et retarde l'apparition du régime d'écoulement agité-pistonnant. [source]


Selectivity, Hydrodynamics and Solvent Effects in a Monolith Cocurrent Downflow Contactor (CDC) Reactor

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Mike Winterbottoma
Abstract The liquid phase hydrogenation of 2-butyne-1,4-diol (B) to cis-2-butene-1,4,-diol (C) was studied in a Monolith (CDC) Reactor. The effect of temperature, pressure, different solvents and gas and liquid feed rates on reaction rate and selectivity was determined. RTD measurements were made under different hydrodynamic conditions. The liquid flow was largely laminar with evidence of a stagnant wall film. Selectivity to C was observed to increase with hydrogen pressure and approaches 1 at high superficial gas velocities and conversion of B (>95%) as plug flow is approached. The flow regime was of influence on selectivity and kinetics, which was described by a dual site Langmuir-Hinshelwood mechanism. L'hydrogénation en phase liquide du butyne-2-diol-1,4 B en cis-butène-2-diol-1,4 C a été étudiée dans un réacteur à monolithe (CDC). On a déterminé l'effet de la température, de la pression, des différents solvants et des vitesses d'alimentation de gaz et de liquide sur la vitesse de réaction et la sélectivité. Des mesures de distribution de temps de séjour ont été effectuées pour différentes conditions hydrodynamiques. L'écoulement du liquide est largement laminaire avec un film de paroi stagnant évident. On a observé que la sélectivité pour C augmentait avec la pression de l'hydrogène et s'approchait de 1 à des vitesses de gaz superficielles élevées et à conversion de B élevée (>95%) quand l'écoulement piston devient piston. Le régime d'écoulement a une influence sur la sélectivité et la cinétique, et celle-ci est bien décrite par un mécanisme à site double de Langmuir-Hinshelwood. [source]


Holdup and Pressure Drop in Vertical and Near-Vertical Three-Phase Up-Flow: A Collection of Flow Regimes

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2002
P.L. Spedding
Three-phase oil, water and air data are reported for vertical and near vertical +86 5° upflow in a 0 026 m i d pipe In general, the liquid holdup for near vertical flow was greater than for the corresponding vertical upflow, the exception being at low liquid and superficial velocities under 0 6 m/s and high superficial gas velocities over 20 m/s Here the liquid holdup varied being sometimes below and other times above the corresponding vertical value These variations of liquid holdup were shown to depend on the fine structure of the flow patterns present The total pressure drop and its component parts showed significantly different patterns of behaviour depending on whether the superficial gas velocity was above or below the rise velocity of a Taylor bubble The total pressure drop generally was greater for near vertical flow compared to the vertical upflow case but reflected changes in the fine structure of the flow patterns A comprehensive collection of flow regimes is included in this paper [source]


Modelling of the fluid dynamic processes in a high-recirculation airlift reactor

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2001
David A. Sanders
Abstract This paper describes the creation of two models of the steady-state fluid dynamic processes occurring in a high-recirculation airlift reactor. The new models were created to provide information to assist in the design of a reactor, in particular considering the selection of parameters to adjust in order to achieve a steady state solution. The modelling of two-phase flow of air and water in small-scale airlift bioreactors is considered. This modelling was applied to the high-recirculation airlift reactor process. New computer simulations were created and tests performed to evaluate the new models. The results of this evaluation are presented. The evaluation showed that variation of the superficial gas velocity or the simultaneous variation of the downcomer and riser diameters could be used to produce a steady-state design solution. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Design and operation of unbaffled aerated agitated vessels with unsteadily forward,reverse rotating impellers handling viscous Newtonian liquids

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2003
Masanori Yoshida
Abstract Design and operation of unbaffled aerated agitated vessels with multiple unsteadily forward,reverse rotating impellers (AJITERs) for viscous Newtonian liquids were studied. The effects of operating conditions such as gas sparging rate, agitation rate and the number of impeller stages, geometrical conditions such as the diameters of vessel and impeller, and the physical properties of liquids on the drag and added moment of inertia coefficients, necessary to predict the average and maximum power consumptions of the impellers in AJITERs, were evaluated and the empirical relationships which estimate values of each of these coefficients are presented. The effects of operating conditions, geometrical conditions and liquid physical properties on the gas hold-up, ,gD, and volumetric oxygen transfer coefficient, kLaD, were evaluated in relation to the total power input which is the sum of the average power consumption of impellers, ie average agitation power input, and aeration power input. Empirical relationships, useful for design and operation of AJITERs, were obtained for each viscosity range, where the dependences of ,gD and kLaD on the specific total power input and superficial gas velocity differed, to predict ,gD and kLaD respectively as a function of the specific total power input, superficial gas velocity and liquid physical properties. © 2003 Society of Chemical Industry [source]


Flow and mass transfer in aerated viscous Newtonian liquids in an unbaffled agitated vessel having alternating forward,reverse rotating impellers

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2001
Masanori Yoshida
Abstract Flow and mass transfer characteristics in aerated viscous Newtonian liquids were studied for an unbaffled aerated agitated vessel with alternating rotating impellers (AAVAI), ie with multiple forward,reverse rotating impellers having four delta blades. The effects of operating conditions such as gas sparging rate, agitation rate and the number of impeller stages, and the liquid physical properties (viscosity) on the gas hold-up, ,gD, and volumetric oxygen transfer coefficient, kLaD were evaluated experimentally. The dependences of ,gD and kLaD on the specific total power input and superficial gas velocity differed, depending on the ranges of liquid viscosity. Empirical relationships are presented for each viscosity range to predict ,gD and kLaD as a function of the specific total power input, superficial gas velocity and viscosity of liquid. Based on a comparative investigation of the volumetric coefficient in terms of the specific total power input between the AAVAI and conventional aerated agitated vessels (CAAVs) having unidirectionally rotating impellers, the usefulness of AAVAI as a gas,liquid agitator treating viscous Newtonian liquids is also discussed. © 2001 Society of Chemical Industry [source]


Counter-current gas-liquid wavy film flow between the vertical plates analyzed using the Navier-Stokes equations

AICHE JOURNAL, Issue 8 2010
Yu. Ya.
Abstract The article is devoted to a theoretical analysis of counter-current gas-liquid wavy film flow between vertical plates. We consider two-dimensional nonlinear waves on the interface over a wide variation of parameters. The main interest is to analyse the wave structure at the parameter values corresponding to the onset of flooding observed in experiments. We use the Navier-Stokes equations in their full statement to describe the liquid phase hydrodynamics. For the gas phase equations, we use two models: (1) the Navier-Stokes system and (2) the simplified Benjamin-Miles approach where the liquid phase is a small disturbance for the laminar or turbulent gas flow. With the superficial gas velocity increasing and starting from some value of the velocity, the waves demonstrate a rapid decreasing of both the minimal film thickness and the phase wave velocity. We obtain a region of the gas velocity where we have two solutions at one set of the problem parameters and where the flooding takes place. Both the phase wave velocity and the minimal film thickness are positive numbers at such values of the velocity. We calculate the flooding point dependences on the liquid Reynolds number for two different liquids. The wave regime corresponding to the flooding point demonstrates negative u- velocities in the neighbourhood of the interface near the film thickness maximum. At smaller values of the superficial gas velocity, the negative u- velocities take place in the neighbourhood of the film thickness minimum. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]


Nonintrusive characterization of fluidized bed hydrodynamics using vibration signature analysis

AICHE JOURNAL, Issue 3 2010
M. Abbasi
Abstract There are many techniques to characterize the hydrodynamics of fluidized beds, but new techniques are still needed for more reliable measurement. Bed vibrations were measured by an accelerometer in a gas,solid fluidized bed to characterize the hydrodynamics of the fluidized bed in a nonintrusive manner. Measurements were carried out at different superficial gas velocities and particle sizes. Pressure fluctuations were measured simultaneously. Vibration signals were processed using statistical analysis. For the sake of the evaluation, the vibration technique was used to calculate minimum fluidization velocity. It was shown that minimum fluidization velocity can be determined from the variation of standard deviation, skewness, and kurtosis of vibration signals against superficial gas velocity of the bed. Kurtosis was proved to be a new method of analyzing vibration signals. Results indicate that analyzing the vibration signals can be an effective nonintrusive technique to characterize the hydrodynamics of fluidized beds. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]


Synthesis of multiwalled carbon nanotubes on Al2O3 supported Ni catalysts in a fluidized-bed

AICHE JOURNAL, Issue 1 2010
Jun Liu
Abstract Multiwalled carbon nanotubes (MWNTs) were synthesized on Al2O3 supported Ni catalysts from C2H2 and C2H4 feedstocks in a fluidized bed. The influence of the ratio of superficial gas velocity to the minimum fluidization velocity (U/Umf), feedstock type, the ratio of carbon in the total quantity of gas fed to the reactor, reaction temperature, the ratio of hydrogen to carbon in the feed gas, and nickel loading were all investigated. Significantly, the pressure drop across the fluidized-bed increased as the reaction time increased for all experiments, due to the deposition of MWNTs on the catalyst particles. This resulted in substantial changes to the depth and structure of the fluidized bed as the reaction proceeded, significantly altering the bed hydrodynamics. TEM images of the bed materials showed that MWNTs, metal catalysts, and alumina supports were predominant in the product mixture, with some coiled carbon nanotubes as a by-product. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Demarcation of a new circulating turbulent fluidization regime

AICHE JOURNAL, Issue 3 2009
Xiaobo Qi
Abstract Transient flow behaviors in a novel circulating-turbulent fluidized bed (C-TFB) were investigated by a multifunctional optical fiber probe, that is capable of simultaneously measuring instantaneous local solids-volume concentration, velocity and flux in gas-solid two-phase suspensions. Microflow behavior distinctions between the gas-solid suspensions in a turbulent fluidized bed (TFB), conventional circulating fluidized bed (CFB), the bottom region of high-density circulating fluidized bed (HDCFB), and the newly designed C-TFB were also intensively studied. The experimental results show that particle-particle interactions (collisions) dominate the motion of particles in the C-TFB and TFB, totally different from the interaction mechanism between the gas and solid phases in the conventional CFB and the HDCFB, where the movements of particles are mainly controlled by the gas-particle interactions (drag forces). In addition, turbulence intensity and frequency in the C-TFB are significantly greater than those in the TFB at the same superficial gas velocity. As a result, the circulating-turbulent fluidization is identified as a new flow regime, independent of turbulent fluidization, fast fluidization and dense suspension upflow. The gas-solid flow in the C-TFB has its inherent hydrodynamic characteristics, different from those in TFB, CFB and HDCFB reactors. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Hydrogenation of 2-ethylanthraquinone under Taylor flow in single square channel monolith reactors

AICHE JOURNAL, Issue 3 2009
Dingsheng Liu
Abstract The hydrogenation of 2-ethylanthraquinone (EAQ) to 2-ethylanthrahydroquinone (EAHQ) was carried out under Taylor flow in single square channel monolith reactors. The two opening ends of opaque reaction channel were connected with two circular transparent quartz-glass capillaries, where Taylor flow hydrodynamics parameters were measured and further used to obtain practical flow state of reactants in square reaction channels. A carefully designed gas-liquid inlet mixer was used to supply steady gas bubbles and liquid slugs with desired length. The effects of various operating parameters, involving superficial gas velocity, superficial liquid velocity, gas bubble length, liquid slug length, two-phase velocity and temperature, on EAQ conversion were systematically researched. Based on EAQ conversion, experimental overall volumetric mass transfer coefficients were calculated, and also studied as functions of various parameters as mentioned earlier. The film model, penetration model, and existing semi-empirical formula were used to predict gas-solid, gas-liquid, and liquid-solid volumetric mass transfer coefficients in Taylor flow, respectively. The predicted overall volumetric mass transfer coefficients agreed well with the experimental ones. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Fischer-Tropsch synthesis product grade optimization in a fluidized bed reactor

AICHE JOURNAL, Issue 8 2006
Fabiano A. N. Fernandes
Abstract Fischer-Tropsch synthesis is an important chemical process for the production of liquid fuels and olefins. In recent years, the abundant availability of natural gas and the increasing demand of olefins, gasoline, diesel and waxes have led to a high interest in further developing this process. A mathematical model of a fluidized-bed reactor used for syngas polymerization was developed and the carbon monoxide polymerization was studied from a modeling point of view. Simulation results show that several parameters affect syngas conversion and carbon product distribution, such as operating pressure, superficial gas velocity, bed porosity, and syngas composition. Optimization of liquid hydrocarbon products was done and the best operating conditions for their production were found for an iron catalyst that produces hydrocarbon chains according to a dual mechanism theory. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]


Axial liquid mixing in high-pressure bubble columns

AICHE JOURNAL, Issue 8 2003
G. Q. Yang
Axial dispersion coefficients of the liquid phase in bubble columns at high pressure are investigated using the thermal dispersion technique. Water and hydrocarbon liquids are used as the liquid phase. The system pressure varies up to 10.3 MPa and the superficial gas velocity varies up to 0.4 cm/s, which covers both the homogeneous bubbling and churn-turbulent flow regimes. Experimental results show that flow regime, system pressure, liquid properties, liquid-phase motion, and column size are the main factors affecting liquid mixing. The axial dispersion coefficient of the liquid phase increases with an increase in gas velocity and decreases with increasing pressure. The effects of gas velocity and pressure on liquid mixing can be explained based on the combined mechanism of global liquid internal circulation and local turbulent fluctuations. The axial liquid dispersion coefficient also increases with increasing liquid velocity due to enhanced liquid-phase turbulence. The scale-up effect on liquid mixing reduces as the pressure increases. [source]


Early warning of agglomeration in fluidized beds by attractor comparison

AICHE JOURNAL, Issue 11 2000
J. Ruud van Ommen
An enhanced monitoring method, based on pressure fluctuation measurements, for observing nonstationarities in fluidized-bed hydrodynamics is presented. Experiments show that it can detect small changes in the particle-size distribution. Such a monitoring method is useful to give an early warning of the onset of agglomeration in a fluidized bed. In contrast to earlier methods, this method is insensitive to small changes in superficial gas velocity and can handle multiple signals, making it relevant to industrial application. By carefully choosing the measurement position, the method becomes also insensitive to small bed mass variations. It uses the attractor reconstructed from a measured pressure signal, which is a "fingerprint" of the hydrodynamics of the fluidized bed for a certain set of conditions. Using this method statistically the reconstructed attractor of a reference time series of pressure fluctuations (representing the desired fluidization behavior) is compared with that of successive time series measured during the bed operation. [source]


Gas Classification of Particles Using a Packed Bed

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 4 2008
Wei Yang
Abstract Gas classification of particles using a packed bed is, for the first time, proposed and tested for two materials, i.e., glass ballotini and microcrystalline cellulose (MCC). A 2,m long column with 9.5,mm diameter is packed with 2,mm spherical particles. The particles to be classified are injected into the inlet of the packed bed by a carrier gas. Measurements of the breakthrough curves of the particles are carried out at the outlet of the packed bed. The results show that the particle elution order is particle size dependent with large particles elutriated faster than small ones. Taking the particle size into account, the retention time of irregular MCC particles is much longer than that of spherical glass beads and the difference is attributed to the particle shape and cohesiveness. Based on the findings, binary mixtures of both, glass and MCC beads are injected into the packed bed for the classification experiments. The results show different dependence on the superficial gas velocity of the particle classification efficiency. The particle classification efficiency of glass particles increases with decreasing superficial gas velocity, whereas that of MCC particles increases with increasing superficial gas velocity. [source]


Clustering behaviour in gas,liquid,solid circulating fluidized beds with low solid holdups of resin particles

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010
Jianhua Liu
Abstract The flow in a gas,liquid,solid circulating fluidized bed is self-organised and manifests itself with clustering of particles and bubbles. The clustering behaviour in the fluidized bed at low solid holdups of resin particles was experimentally investigated with a high-speed image measurement and treatment technique of complementary metal oxide semiconductor to enhance the fundamental understanding on such a flow. Several new physical quantities were suggested to characterise such ordered flow structures. The main findings are as follows. The clusters of solid particles largely exist as doublets and triplets, the mixed groups of particles and bubbles mostly exist as one bubble carrying two to four particles. Increasing superficial liquid velocity, particle diameter or density weakens the aggregation degrees of both particle and mixed clusters in the riser and downer, except that the increase of superficial liquid velocity enhances the mixed clustering behaviour in the riser. The climbing of the auxiliary liquid velocity or liquid phase viscosity intensifies the aggregation behaviour, except that the increase of liquid phase viscosity reduces the mixed clustering degree in the riser. The influences of superficial gas velocity and surface tension of liquid phase on the clustering behaviour seem to be a little complex and the trends are not simply increasing or decreasing. The life cycle of solid particle clusters in the GLS riser is not sensitive to the operation conditions, being around 0.07,s. The mixed clusters' life cycle is more sensitive to the conditions and physical properties of phases, changing from 0.02 to 0.07,s. L'écoulement dans un lit fluidisé de circulation gaz-liquide-solide s'organise souvent de lui même et se manifeste avec l'agrégation des particules et des bulles. Le comportement de l'agrégation dans le lit fluidisé à faible retenue de particules de résine solide a été étudié expérimentalement en utilisant une technique d'imagerie ultra-rapide de mesure et de traitement à base de semi-conducteur complémentaire à l'oxyde de métal afin d'approfondir la compréhension fondamentale d'un tel écoulement. Plusieurs nouvelles quantités physiques ont été suggérées pour caractériser une telle structure d'écoulement auto-organisé. Les principaux résultats sont comme suit. Les agrégations de particules solides existent principalement en tant que doublets et triplets, les groupes mixtes de particules et de bulles existent pour la plupart sous la forme d'une bulle comportant deux à quatre particules. Une augmentation de la vitesse superficielle du liquide, du diamètre des particules ou de la densité affaiblit à la fois les degrés d'agrégation des particules et des agrégats mixtes dans la colonne montante et dans la colonne descendante, sauf que l'augmentation de la vitesse superficielle du liquide intensifie le comportement d'agrégation mixte dans la colonne montante. L'accroissement de la vitesse auxiliaire du liquide ou de la viscosité de la phase liquide intensifie le comportement d'agrégation, sauf que l'augmentation de la viscosité de la phase liquide réduit le degré d'agrégation mixte dans la colonne montante. Les influences de la vitesse superficielle du gaz et de la tension de surface de la phase liquide sur le comportement de l'agrégation semblent être quelque peu complexes et les tendances ne sont pas simplement croissantes ou décroissantes. Le cycle de vie des agrégats de particules solides dans la colonne gaz-liquide-solide montante n'est pas sensible aux facteurs, tournant autour de 0.07,s. Le cycle de vie des agrégats mixtes est plus sensible aux conditions de fonctionnement et aux caractéristiques physiques des phases, évoluant de 0.02 à 0.07,s. [source]


Simulations of Bubble Column Reactors Using a Volume of Fluid Approach: Effect of Air Distributor

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2007
M. Abid Akhtar
Abstract Two- and three-dimensional numerical simulations have been performed on a laboratory scale bubble column reactor using a volume-of-fluid approach. The effect of hole-size and superficial gas velocity on the bubble size distribution and their trajectories has been investigated on a 20 cm diameter and 1 m high cylindrical reactor. All simulations were performed in a transient manner using a FLUENT solver. Surface tension between two phases has been modelled as a body force with a constant value. Turbulence was modelled using the k-, turbulence approach. A comparison between simulation predictions and the reported experimental studies has shown a good agreement. On a effectué des simulations numériques bi et tridimensionnelles dans un réacteur à colonne à bulles à l'échelle de laboratoire à l'aide d'une approche volume-de-fluide. L'effet de la taille du trou et de la vitesse de gaz superficielle sur la distribution de tailles des bulles et leurs trajectoires a été étudié dans un réacteur cylindrique de 20 cm de diamètre et de 1 m de hauteur. Toutes les simulations ont été réalisées selon un mode transitoire à l'aide du logiciel FLUENT. La tension de surface entre deux phases a été modélisée comme une force volumique avec une valeur constante. La turbulence a été modélisée par la méthode de turbulence k-,. Une comparaison entre les prédictions des simulations et les études expérimentales mentionnées montre un bon accord. [source]


Entrainment Rate of Coarse Particles at Different Temperatures in Gas Fluidized Beds

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2007
Jeong-Hoo Choi
Abstract Based on available experimental data, an empirical relationship is developed for the entrainment rate of coarse particles at the exit of gas-fluidized beds, including the effects of fine particles in the bed, temperature, gas velocity, particle size and density, and column size. It predicts well the influence of fine particles on the entrainment rate of coarse particles, taking into account the momentum of the fine particles and the effect of superficial gas velocity. It also accounts well for the influence of temperature at different solid densities and gas velocities. À partir de données expérimentales disponibles, on a mis au point une relation empirique pour la vitesse d'entraînement des grosses particules à la sortie des lits fluidisés de gaz, incluant les effets des particules fines dans le lit, la température, la vitesse de gaz, la taille et la masse volumique des particules ainsi que la dimension de la colonne. Cette relation prédit bien l'influence des particules fines sur la vitesse d'entraînement des grosses particules, en tenant compte de la quantité de mouvement des particules fines et de l'effet de la vitesse de gaz superficielle. Elle prend bien en compte également l'influence de la température à différentes masses volumiques de solides et vitesses de gaz. [source]


A Study on Hydrodynamics and Heat Transfer in a Bubble Column Reactor with Yeast and Bacterial Cell Suspensions

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2005
Nigar Kantarci
Abstract Hydrodynamics and heat transfer experiments were carried out in a slurry bubble column with air-water-yeast cells and air-water-bacteria cells systems to investigate gas hold-up, bubble characteristics and heat transfer coefficients with cell concentrations of 0.1% w/w and 0.4% w/w and superficial gas velocity up to 0.20 m/s. The gas hold-ups and heat transfer coefficients were found to increase with increasing gas velocity and cell concentration. The heat transfer coefficients were higher at the centre of the column as compared to the near wall region. The development of empirical correlations to predict the heat transfer coefficient in two- and three-phase systems was carried out with ±15% confidence interval at most. On a réalisé des expériences d'hydrodynamique et de transfert de chaleur dans une colonne triphasique gaz-liquide-solide avec des systèmes de cellules air-eau-levure et de cellules air-eau-bactéries afin d'étudier la rétention de gaz, les caractéristiques des bulles et les coefficients de transfert de chaleur avec des concentrations de cellules de 0,1 % en poids et 0,4 % en poids et des vitesses de gaz superficielles jusqu'à 0,20 m/s. On a trouvé que les rétentions de gaz et les coefficients de transfert de chaleur augmentaient avec la vitesse de gaz et la concentration en cellules. Les coefficients de transfert de chaleur sont plus grands au centre de la colonne que dans la région proche de la paroi. Des corrélations empiriques pour prédire le coefficient de transfert de chaleur dans des systèmes bi et triphasiques ont été établies avec un écart de confiance inférieur ou égal à ± 15%. [source]


Determination of Minimum Spouting Velocities in Conical Spouted Beds

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2004
Zhiguo Wang
Abstract Minimum spouting velocities in conical spouted beds have been obtained from pressure drops versus the superficial gas velocity curves, based on both increasing and decreasing the superficial gas velocity. It has been shown that the minimum spouting velocity from decreasing the superficial gas velocity is lower than from increasing the superficial gas velocity in most cases. This phenomenon is similar to that in conventional spouted beds and different from the early works. The experimental results also showed that there isn't significant difference in the pressure drop and Ums under identical operating conditions between semi-circular and circular conical spouted beds, and the same Ums can be obtained from absolute pressure drops at any position above the gas inlet. The Ums is found to increase with increasing the cone angle and static bed height, as well as the gas inlet diameter to a less extent. Des vitesses de jaillissement minimales dans des lits jaillissants coniques ont été obtenues à partir des pertes de charge en fonction des courbes de vitesse de gaz superficielles pour des vitesses de gaz superficielles croissantes ou décroissantes. On montre que la vitesse de jaillissement minimale lorsqu'on diminue la vitesse de gaz superficielle est inférieure à celle que l'on obtient lorsqu'on augmente la vitesse de gaz superficielle dans la plupart des cas. Ce phénomène est semblable à celui observé dans les lits jaillissants classiques et est différent des observations antérieures. Les résultats expérimentaux montrent également qu'il n'y pas de grande différence dans la perte de charge et dans la valeur de Ums pour des conditions opératoires identiques entre des lits jaillissants coniques semi-circulaires et circulaires, et le même Ums peut être obtenu à partir des pertes de charge absolues à n'importe quelle position au-dessus de l'entrée du gaz. On a trouvé que Ums augmentait avec l'angle du cône et la hauteur de lit statique, ainsi qu'avec le diamètre de l'orifice d'entrée du gaz mais dans une moindre mesure. [source]


Survey of heat transfer mechanisms in a slurry bubble column

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2001
Hanning Li
Abstract Heat transfer mechanisms in the bulk and distributor regions of a slurry bubble column are investigated based on the measurements of local heat transfer in a 0.28 m diameter Plexiglas column. The gas, liquid and solid phases used are oil-free compressed air, tap water and 35 ,m glass beads. The slurry concentration and superficial gas velocity are varied from 0 to 40 vol% and 0.05 to 0.30 m/s respectively. Measurements have been made with a fast response heat flux probe which provided local instantaneous heat transfer coefficients. The time-averaged heat transfer coefficients in the bulk region were on average about 50% higher than the distributor region of the column. The wall region heat transfer coefficients are well predicted by the correlation of Deckwer et al. (1980). Heat transfer mechanism in column centre can be adequately described by the consecutive film and surface renewal model. Les mécanismes de transfert de chaleur dans le coeur et dans la région du distributeur d'une colonne à bulles à suspensions sont étudiés en mesurant le transfert de chaleur local dans une colonne en plexiglass de 0.28 m. Les phases gazeuse, liquide et solide utilisées sont de l'air cornprimé déhuilé, de l'eau du robinet et des billes de verre de 35 ,m. On a fait varier la concentration des suspensions et la vitesse de gaz superficielle de 0 à 40% en volume et de 0.05 à 0.30 m/s, respectivement. Les mesures ont été faites à l'aide d'une sonde de flux de chaleur à réponse rapide qui fournit les coefficients de transfert de chaleur instantanés locaux. Les coefficients de transfert de chaleur moyennés dans le temps dans le coeur étaient, en rnoyenne, environ 50% supérieurs à ceux de la région du distributeur dans la colonne. Les coefficients de transfert de chaleur de la région de la paroi sont bien predits par la cordation de Deckwer et al. (1980). Le mécanisme de transfert de chaleur au centre de la colonne peut ,tre adéquatement décrit par le modéle de renouvellement de surface et de film consécutif. [source]


Lateral flux and velocity of FCC particles in a CFB riser

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2001
Stefan Malcus
Abstract The radial profiles of the lateral solids mass flux and the lateral solids velocity were determined for FCC particles in a 7 m tall circulating fluidtzed bed riser 0.14 m in diameter by applying a lateral flux probe and electrical capacitance tomography. The external solids mass flux was varied between 148 and 302 kg/(m2.s), while the superficial gas velocity was varied between 3.7 and 4.7 m/s. Under these conditions, a dense bottom region and an upper dilute region coexisted in the riser. Lateral fluxes in the dense bottom region reached 100 kg/(m2.s) at the wall, but fell to 14 kg/(m2.s) at the wall in the upper dilute region. At both axial locations, a net deposition of solids from the core to the annulus occurred, indicating that fully developed flow was never established under these conditions. The lateral fluxes in the bottom region were significantly larger than those found in previous studies. It was further concluded that considering the lateral solids flux to be only a function of solids concentration is an over-simplification. Les profils radiaux du flux massique de solides latéral et de la vitesse de solides iatérale ont été déterminés pour des particules de FCC dans une colonne à lit fluidisé circulant de 7 m de hauteur et de 0,14 m de diamètre, en appliquant une sonde de flux latérale et la tomographic par capacitance électrique. On a fait varier d'une part le flux massique de solides externe entre 148 et 302 kg/(m2.s) et d'autre part la vitesse de gaz superficielle entre 3,7 et 4,7 m/s. Dans ces conditions, une région inférieure dense et une région supérieure diluée coexistent dans la colonne. Les flux latéraux dans la région inférieure dense atteignent 100 kg/(m2.s) à la paroi, mais tombent à 14 kg/(m2.s) à la paroi dans la région supérieure diluée. Aux deux régions axiales, une déposition nette de solides se produit du coeur vers l'espace annulaire, indiquant que un écoulement pleinement développé n'a jamais été établi dans ces conditions. Les flux latéraux sont nettement plus important que ceux trouvés dans les études antérieures. II a en outre été conclu que le fait de considéer le flux de solides latéral uniquement comme étant fonction de la concentration de solides constituait une sur-simplification. [source]


Foam fractionation of ,-lactalbumin and ,-lactoglobulin from a whey solution

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009
A. P. Shea
Abstract Whey, a byproduct of cheese production, is often considered a waste stream. Separation and purification of whey proteins is a difficult and expensive task. Occasionally, it is transported out of the dairy plant for a per volume charge. One possible method to reduce the waste volume and disposal cost is to concentrate whey by foam fractionation and potentially produce a valuable coproduct, a concentrated whey protein solution. Foam fractionation is an adsorptive bubble separation method based on the hydrophobic/hydrophilic properties of proteins. In this study, foam fractionation was evaluated for the concentration of whey proteins, specifically ,-lactalbumin and ,-lactoglobulin, from a dilute whey protein solution. The effects of initial whey protein concentration (0.075 and 0.15 mg/ml), pH (3.8,5.5), superficial gas velocity (0.85 and 0.95 cm/s) and temperature (4 and 65 °C) on protein enrichment and recovery were examined. Higher enrichment was achieved with the lower initial protein concentration (0.075 mg/ml), and at pH values that were near the isoelectric points (pI) of ,-lactalbumin and ,-lactoglobulin (pH 3.8, 4.2, 4.5, and 5.2). Higher superficial gas velocity enhanced the amount of proteins recovered with a decrease in the enrichment. Cold temperature treatment and partial heat denaturation of whey proteins reduced enrichment and increased protein recovery simultaneously. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]