共查询到20条相似文献,搜索用时 15 毫秒
1.
Sofiane Benyahia 《American Institute of Chemical Engineers》2012,58(2):427-439
This study focuses on continuum model validation of the flow of air and small catalyst particles in a circulating fluidized bed. Comparison with available experimental data of pressure drop and solids circulation rate in the riser clearly demonstrates the need to modify the homogeneous drag model to accurately predict the formation of clusters of particles, which are typically observed in the fluidization of small particles. The need to correct the drag law is also demonstrated in simulations of polydisperse powder flows wherein three solids species are used to represent a typical catalyst size distribution. Finally, particle‐wall friction is found to have the most significant effect on the vertical gas pressure gradient while particle–particle friction has only a minor effect. Published 2011 American Institute of Chemical Engineers AIChE J, 58: 427–439, 2012 相似文献
2.
Jean‐François Parmentier Olivier Simonin Olivier Delsart 《American Institute of Chemical Engineers》2012,58(4):1084-1098
Due to computational time limitations, fully resolved simulations using the two‐fluid model of the flow inside industrial‐scale fluidized beds are unaffordable. The filtered approach is used to account for the effect of small unresolved scales on the large resolved scales computed with “coarse” realistic meshes. Using a fully resolved simulation, we highlight the need to account for a subgrid drift velocity to obtain the correct bed expansion when using coarse meshes. This velocity, defined as the difference between the filtered gas velocity seen by the particle phase and the resolved filtered gas velocity, modify the effective relative velocity appearing in the drag law. We close it as a correction of the resolved relative velocity depending on the filtered particle concentration and the filter size. A dynamic procedure is used to adjust a tuning parameter. Bed expansion obtained with a posteriori test on coarse‐grid simulations matches well to fully resolved simulations. © 2011 American Institute of Chemical Engineers AIChE J, 2012 相似文献
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4.
Jia‐Jun Wang Ying Han Xue‐Ping Gu Lian‐Fang Feng Guo‐Hua Hu 《American Institute of Chemical Engineers》2013,59(4):1066-1074
The effect of agitation on the fluidization performance of a gas–solid fluidized bed with a frame impeller is experimentally and numerically investigated. A 3‐D unsteady computational fluid dynamics method is used, combining a two‐fluid model and the kinetic theory of granular flow. The rotation of the impeller is implemented with a multiple reference frame method. The numerical model is validated using experimental data of the bed pressure drop and pressure fluctuation. Although the minimum fluidizing velocity and bed pressure drop are independent of the impeller agitation, a sufficiently high agitation speed yields higher fluidization performance with reduced bubble diameters and internal circulations of particles. The fluidized bed can be divided into three zones: inlet zone where the gas distribution plays a major role, agitated fluidization zone where the impeller agitation has a positive effect on fluidization, and free fluidization zone where the impeller agitation has no effect on fluidization. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1066–1074, 2013 相似文献
5.
K. Tuzla A.K. Sharma J.C. Chen T. Schiewe K.E. Wirth O. Molerus 《Powder Technology》1998,100(2-3):166-172
This paper presents new results from experiments performed in a 15 cm diameter down-flow fast-fluidized bed. Tests were conducted at room temperature and near atmospheric pressure, with 125 μm glass beads. Superficial gas velocities range from 0 to 6 m/s. A needle capacitance probe was used to obtain measurement of instantaneous solids concentration (εs) in a small sampling volume of approximately 0.1 cm3. With the downer operating at steady-state, the capacitance probe provided a time-trace of the local solid fraction, indicating that εs was generally less than 0.01. However the measurements indicated that the local concentration did have excursions to significantly higher concentrations for short durations. This behavior is indicative of clusters in the down-flow fast-fluidized bed. While clusters are known to be a dominant feature of upward fast fluidization in risers, their presence has been questioned for solid/gas down flows. Sample data are presented to indicate the density, duration, and time fraction of clusters observed in this downer fluidized bed. Preliminary comparisons are made to the limited data available for comparable operating conditions in a riser. 相似文献
6.
J. J. Derksen 《American Institute of Chemical Engineers》2014,60(5):1880-1890
Direct, particle‐resolved simulations of solid–liquid fluidization with the aim of quantifying dispersion have been performed. In addition to simulating the multiphase flow dynamics (that is dealt with by a lattice‐Boltzmann method coupled to an event‐driven hard‐sphere algorithm), a transport equation of a passive scalar in the liquid phase has been solved by means of a finite‐volume approach. The spreading of the scalar—as a consequence of the motion of the fluidized, monosized spherical particles that agitate the liquid—is quantified through dispersion coefficients. Particle self‐diffusivities have also been determined. Solids volume fractions were in the range 0.2–0.5, whereas single‐sphere settling Reynolds numbers varied between approximately 3 and 20. The dispersion processes are highly anisotropic with lateral spreading much slower (by one order of magnitude) than vertical spreading. Scalar dispersion coefficients are of the same order of magnitude as particle self‐diffusivities. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1880–1890, 2014 相似文献
7.
Analysis of the effect of small amounts of liquid on gas–solid fluidization using CFD‐DEM simulations
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C. M. Boyce A. Ozel J. Kolehmainen S. Sundaresan 《American Institute of Chemical Engineers》2017,63(12):5290-5302
Gas–solid fluidization involving small amounts of liquid is simulated using a CFD‐DEM model. The model tracks the amount of liquid on each particle and wall element and incorporates finite rates of liquid transfer between particles and pendular liquid bridges which form between two particles as well as between a particle and a wall element. Viscous and capillary forces due to these bridges are modeled. Fluidization–defluidization curves show that minimum fluidization velocity and defluidized bed height increase with Bond number (Bo), the ratio of surface tension to gravitational forces, due to cohesion and inhomogeneous flow structures. Under fluidized conditions, hydrodynamics and liquid bridging behavior change dramatically with increasing Bo, and to a lesser extent with capillary number, the ratio of viscous to surface tension forces. Bed fluidity is kept relatively constant across wetting conditions when one maintains a constant ratio of superficial velocity to minimum fluidization velocity under wet conditions. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5290–5302, 2017 相似文献
8.
M. Abbasi R. Sotudeh‐Gharebagh N. Mostoufi R. Zarghami M. J. Mahjoob 《American Institute of Chemical Engineers》2010,56(3):597-603
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 相似文献
9.
Sutthichai Boonprasop Dimitri Gidaspow Benjapon Chalermsinsuwan Pornpote Piumsomboon 《American Institute of Chemical Engineers》2017,63(12):5267-5279
The most common technology for postcombustion of CO2 capture is the amine solvent scrubber. The energy consumption for capturing CO2 from flue gases using amine solvent technology is 15–30% of the power plant electricity production. Hence, there is a need to develop more efficient methods of removing CO2. A circulating fluidized bed using sodium or potassium carbonates is potentially such a process, as their high decomposition pressures allow regeneration at low temperatures using waste heat rather than steam from the power plant. But equilibrium data for the sorbents require the use of several cooled stages to achieve high CO2 conversions. Here, a method of computing such a number of stages for a given CO2 conversion was developed using multiphase computational fluid dynamics. It was found that it required six equilibrium stages to remove 96% of CO2 with the initial mole fraction of 0.15 in a sorption riser. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5267–5279, 2017 相似文献
10.
Alireza Abbasi Mohammad Ashraful Islam Paul E. Ege Hugo I. de Lasa 《American Institute of Chemical Engineers》2013,59(5):1635-1647
This study contributes with a computational fluid dynamic simulation based on the numerical solution of continuity and momentum balance equations in a three‐dimensional (3‐D) framework. The proposed down flow gas–solid suspension model includes a unit configuration and CD drag coefficients recommended for these units. Computational particle fluid dynamics (CPFD) calculations using suitable boundary conditions and a Barracuda (version: 14.5.2) software allow predicting local solid densification and asymmetric “wavy flows.” In addition, this model forecasts for the conditions of this study higher particle velocity than gas velocity, once the flow reaches 1 m from the gas injector. These findings are accompanied with observations about the intrinsic rotational character of the flow. CPFD numerical 3‐D calculations show that both gas and particle velocities involve the following: (a) an axial velocity component, (b) a radial velocity component (about 5% of axial velocity component), and (c) an angular velocity component. The calculated velocity components and the rotational flow pattern are established for a wide range of solid flux/gas flux ratios. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1635–1647, 2013 相似文献
11.
Fictitious particle method: A numerical model for flows including dense solids with large size difference
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Takuya Tsuji Kyohei Higashida Yoshitomo Okuyama Toshitsugu Tanaka 《American Institute of Chemical Engineers》2014,60(5):1606-1620
Large solids coexist with small solids in a number of dense gas‐solid flow applications such as fluidized beds and pneumatic conveyers. A new numerical model that is based on the discrete element method–computational fluid dynamics mesoscopic model and extended by introducing an idea appearing in volume penalization method is presented. In computational cells including large and small solids, the amount of momentum exchange between the fluid and the solids is estimated by assuming that a large solid consist of small, dense fictitious particles. We describe the proposed model in detail and show the optimal model parameters found through a number of parameter‐dependency studies. Validation study is performed for the motion of a large sphere in a bubbling fluidized bed and good agreements are confirmed for floating and sinking motions of the sphere between the present model and the experiment. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1606–1620, 2014 相似文献
12.
Thatchai Samruamphianskun Pornpote Piumsomboon Benjapon Chalermsinsuwan 《Chemical Engineering Research and Design》2012
In this study, the Eulerian computational fluid dynamics model with the kinetic theory of granular flow model was effectively used to compute the system turbulences and dispersion coefficients in a circulating fluidized bed (CFB) downer. In addition, the obtained model was used to simulate all the system velocities. 相似文献
13.
Experimental and computational study of the bed dynamics of semi‐cylindrical gas–solid fluidized bed
With computational fluid dynamics (CFD) it is possible to get a detailed view of the flow behaviour of the fluidized beds. A profound and fundamental understanding of bed dynamics such as bed pressure drop, bed expansion ratio, bed fluctuation ratio, and minimum fluidization velocity of homogeneous binary mixtures has been made in a semi‐cylindrical fluidized column for gas–solid systems, resulting in a predictive model for fluidized beds. In the present work attempt has been made to study the effect of different system parameters (viz., size and density of the bed materials and initial static bed height) on the bed dynamics. The correlations for the bed expansion and bed fluctuations have been developed on the basis of dimensional analysis using these system parameters. Computational study has also been carried out using a commercial CFD package Fluent (Fluent, Inc.). A multifluid Eulerian model incorporating the kinetic theory for solid particles was applied in order to simulate the gas–solid flow. CFD simulated bed pressure drop has been compared with the experimental bed pressure drops under different conditions for which the results show good agreements. 相似文献
14.
The granular pressure and granular temperature underpin various models of granular flows while they are playing an increasing role in modeling of other phenomena in granular systems such as heat transfer, segregation, erosion, attrition, and aggregation. The development and validation of these theories demand experimental determination of these two quantities. Diffusing wave spectroscopy (DWS) is now an accepted technique for measurement of granular temperature in dense granular systems. Using granular temperature data obtained from DWS with the kinetic theory of granular flow, we have derived the granular pressure data for a liquid‐fluidized bed. The determined variation of the mean bed granular pressure with mean bed solid volume fraction compares favorably with previously published experimental data and theoretical models of others. Where discrepancies do occur, they may be attributed to differences in particle inertia, suggesting further work on granular pressure models is required. Finally, we report the variation of the granular pressure with height above the distributor for several mean solids volume fractions. © 2011 American Institute of Chemical Engineers AIChE J, 2012 相似文献
15.
The erosion of the immersed tubes in a bubbling‐fluidized bed is studied numerically using an Eulerian–Lagrangian approach coupling with a particle‐scale erosion model. In this approach, the motion of gas and particles is simulated by the CFD–DEM method, and an erosion model SIEM (shear impact energy model) is proposed to predict the erosion of the tubes. The model is validated by the good agreement of the simulation results and previous experimental data. By analyzing the simulation results, some characteristics of the tube erosion in the fluidized bed are obtained, such as the distribution of the erosion rate around the tube, the variation of the erosion rate with the position of the tube, the effect of the friction coefficient of particles on the erosion, the relationship between the maximum and the average erosion rate, etc. The microscale behavior of particles around the tubes is also revealed and the linear relationship between the erosion and the shear impact energy is confirmed by the simulation results and experiment. The agreement between simulation and experiment proves that the microscale approach proposed in this article has high accuracy for predicting erosion of the tubes in the fluidized bed, and has potential to be applied to modeling the process in other chemical equipment facing solid particle erosion. © 2016 American Institute of Chemical Engineers AIChE J, 63: 418–437, 2017 相似文献
16.
Christopher J. Wareing Robert M. Woolley Michael Fairweather Samuel A. E. G. Falle 《American Institute of Chemical Engineers》2013,59(10):3928-3942
The development of a novel composite two‐phase method to predict the thermodynamic physical properties of carbon dioxide (CO2) above and below the triple point, applied herein in the context of Reynolds‐Averaged Navier–Stokes computational modeling has been detailed here. A number of approaches have been combined to make accurate predictions in all three phases (solid, liquid, and gas) and at all phase changes for application in the modeling of releases of CO2 at high pressure into the atmosphere. Predictions of a free release of CO2 into the atmosphere from a reservoir at a pressure of 10 MPa and a temperature of 283 K, typical of transport conditions in carbon capture and storage scenarios, is examined. A comparison of the results shows that the sonic CO2 jet that forms requires a three‐phase equation of state including the latent heat of fusion to realistically simulate its characteristics. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3928–3942, 2013 相似文献
17.
Benjapon Chalermsinsuwan Pornpote Piumsomboon Dimitri Gidaspow 《American Institute of Chemical Engineers》2010,56(11):2805-2824
A kinetic theory based hydrodynamic model with experimentally determined sorption rates for reaction of CO2 with K2CO3 solid sorbent is used to design a compact circulating fluidized bed sorption‐regeneration system for CO2 removal from flue gases. Because of high solids fluxes, the sorber does not require internal or external cooling. The output is verified by computing the granular temperatures, particle viscosities, dispersion, and mass transfer coefficients. These properties agree with reported measurement values except the radial dispersion coefficients, which are much higher due to the larger bed diameter. With the solid sorbent prepared according to published information, the CO2 removal percentage at the riser top is 69.16%. To improve the CO2 removal, an effort is needed to develop a better sorbent or to simply lower the inlet gas velocity to operate in a denser mode, leading to a larger system. Also, the effect of temperature rise on the removal efficiency is investigated. © 2010 American Institute of Chemical Engineers AIChE J, 2010 相似文献
18.
A method is described to estimate solid mass flow rate based on measurement of pressure drop in horizontal section of circulating fluid bed (CFB). A theoretical model was derived based on momentum balance equation and used to predict the solids flow rate. Several approaches for formulating such models are compared and contrasted. A correlation was developed that predicts the solids flow rate as a function of pressure drop measured in the horizontal section of piping leading from the top of the riser to the cyclone, often referred to as the cross-over. Model validation data was taken from literature data and from steady state, cold flow, CFB tests results of five granular materials with various sizes and densities in which the riser was operated in core-annular and dilute flow regimes. Experimental data were taken from a 0.20 m ID cross-over piping and compared to literature data generated in a 0.10 m ID cross-over pipe. The solids mass flow rate data were taken from statistically designed experiments over a wide range of Froude number , load ratio , Euler number , density ratio , Reynolds number , and Archimedes number . Several correlations were developed and tested to predict the solids mass flux based on measuring pressure drop in the horizontal section of CFB. It was found that load ratio is a linear function of the Euler number and that each of these expressions all worked quite well (R2 > 95%) for the data within the range of conditions from which the coefficients were estimated. 相似文献
19.
Maria N. Pantzali Jelena Z. Kovacevic Geraldine J. Heynderickx Guy B. Marin Vladimir N. Shtern 《American Institute of Chemical Engineers》2015,61(12):4114-4125
A unique normalized radial pressure profile characterizes the bed of a gas‐solid vortex reactor over a range of particle densities and sizes, solid capacities, and gas flow rates: 950–1240 kg/m3, 1–2 mm, 2 kg to maximum solids capacity, and 0.4–0.8 Nm3/s (corresponding to gas injection velocities of 55–110 m/s), respectively. The combined momentum conservation equations of both gas and solid phases predict this pressure profile when accounting for the corresponding measured particle velocities. The pressure profiles for a given type of particles and a given solids loading but for different gas injection velocities merge into a single curve when normalizing the pressures with the pressure value downstream of the bed. The normalized—with respect to the overall pressure drop—pressure profiles for different gas injection velocities in particle‐free flow merge in a unique profile. © 2015 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 61: 4114–4125, 2015 相似文献
20.
In order to simulate gas-solids flows with complex geometry, the boundary element method was incorporated into the implementation
of a combined model of computational fluid dynamics and discrete element method. The resulting method was employed to simulate
hydrodynamics in a fluidized bed with immersed tubes. The transient simulation results showed particle and bubble dynamics.
The bubble coalescence and break-up behavior when passing the immersed tubes was successfully predicted. The gassolid flow
pattern in the fluidized bed is changed greatly because of the immersed tubes. As particles and gas are come in contact with
the immersed tubes, the gas bubbles will be deformed. The collisions between particles and tubes will make the tubes surrounded
by air pockets most of the time and this is unfavorable for the heat transfer between particles and tubes.
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Translated from Chemical Engineering, 2007, 35(11): 21–24 [译自:化学工程] 相似文献