Gas-particle Flow Behavior Research Articles

Three-dimensional CFD simulation and experimental validation of particle segregation in CFB riser

PurposeThe purpose of this paper is to perform the computational fluid dynamics (CFD) simulation with experimental validation to investigate the particle segregation effect in abrupt and smooth shapes circulating fluidized bed (CFB) risers.Design/methodology/approachThe experimental investigations were carried out in lab-scale CFB systems and the CFD simulations were performed by using commercial software BARRACUDA. Special attention was paid to investigate the gas-particle flow behavior at the top of the riser with three different superficial velocities, namely, 4, 6 and 7.7 m/s. Here, a CFD-based noble simulation approach called multi-phase particle in cell (MP-PIC) was used to investigate the effect of traditional drag models (Wen-Yu, Ergun, Wen-Yu-Ergun and Richardson-Davidson-Harrison) on particle flow characteristics in CFB riser.FindingsFindings from the experimentations revealed that the increase in gas velocity leads to decrease the mixing index inside the riser. Moreover, the solid holdup found more in abrupt riser than smooth riser at the constant gas velocity. Despite the more experimental investigations, the findings with CFD simulations revealed that the MP-PIC approach, which was combined with different drag models could be more effective for the practical (industrial) design of CFB riser. Well agreement was found between the simulation and experimental outputs. The simulation work was compared with experimental data, which shows the good agreement (<4%).Originality/valueThe experimental and simulation study performed in this research study constitutes an easy-to-use with different drag coefficient. The proposed MP-PIC model is more effective for large particles fluidized bed, which can be helpful for further research on industrial gas-particle fluidized bed reactors. This study is expected to give throughout the analysis of CFB hydrodynamics with further exploration of overall fluidization.

Numerical simulations of gas-particle flow behavior created by low-level rotary-winged aircraft flight over particle bed

The aerodynamics of gas-particle suspensions is simulated as an Euler-Euler two-fluid model in a revolving rotor over a particle bed. The interactions of collisions between the blade and particles and particle-particle interactions are modeled using the kinetic theory of granular flow (KTGF). The gas turbulence induced by the rotation of the rotor is modeled using the kg-eg model. The flow field of a revolving rotor is simulated using the multiple reference frame (MRF) method. The distributions of velocities, volume fractions, and gas pressure are predicted while the aircraft hovers at different altitudes. The gas pressure decreases from the hub to the tip of the blade, and it is higher at the pressure side than that at the suction side of the rotor. The turbulent kinetic energy of the gas increases toward the blade tip. The volume fraction of particles decreases as the hovering altitude increases. The simulated pressure coefficient is compared with that in experimental measurements.

Numerical investigation of gas-particle hydrodynamics in a vortex chamber fluidized bed

Gas-particle hydrodynamic behaviour inside a vortex chamber fluidized bed is studied numerically with respect to different design and operating conditions. A three-dimensional computational fluid dynamics (CFD) model of a cylindrical vortex chamber is developed. Simulations are carried out with particles and without particles. In order to understand the gas-particle flow behavior velocity distribution, particle volume fraction distribution, radial pressure distribution and axial pressure distribution inside the vortex chamber are analyzed in detail. Particles of different diameters are used and its effect on the gas-particle flow behaviour is studied. Design parameters like the number of gas inlet slots and slot width are varied and their impact on the hydrodynamics of the vortex chamber is investigated. The numerical model is validated by comparing the numerical results with experimental results reported in literature.

Study on the flow behavior in spout-fluid bed with a draft tube of sub-millimeter grade silicon particles

An experimental study on gas-particle flow behavior in a spout-fluid bed with a draft tube was performed in a 182mm diameter cylindrical column with a flat distributor. Sub-millimeter grade silicon particles with wide particle size distribution were used as bed materials to investigate the effect of operating conditions and geometrical parameters on the flow behavior. The pressure drop and its standard deviation were recorded using a capacitive differential pressure transducer, which can be applied to evaluate the hydrodynamic properties. The effects of fluidizing gas and geometrical parameters of the bed on the hydrodynamic characteristics were analyzed. The results show that the minimum spout-fluidizing velocity increases with increasing the length of entrainment zone and the draft tube diameter, but it decreases with the increasing of fluidizing gas flow rate and static bed height. Furthermore, a correlation on the minimum spout-fluidizing velocity which has practical value is proposed based on the present experimental data, and the calculated data is in good agreement with the experimental results. In addition, seven flow regions can also be observed in different spouting and fluidizing gas velocity, and a new flow regime map for a spout-fluid bed is established with the consideration of the influence of flow regime on geometrical parameters. Such results mentioned above can provide important information on the flow behavior in the spout-fluid bed with a draft tube for process design.

CO2 Adsorption loop experiment with Eulerian–Lagrangian simulation

A full-loop circulating fluidized bed experimental carbon capture unit was constructed at the US DOE National Energy Technology Laboratory (NETL) to study gas-particle flow behavior and provide data against which math-based simulation tools could be compared. This paper compares cold-flow experimental results with math-based simulation results using the commercially-available Barracuda® software package. The simulation was three-dimensional, and the entire full-loop system was simulated. The gas-particle flow behavior predicted by the simulation matched well with video recordings of the experiment. Pressure drop predictions across several key fluidized bed vessels also showed good agreement between simulation and experiment.

Numerical Simulation of the Gas–Particle Flow Behavior in Oil Shale Semi-Coke Spouted Bed

Gas–particle flow behavior in a conical–cylindrical spouted bed was simulated using the Eulerian–Eulerian two-fluid model. The interaction between gas and particles was modeled by the Gidaspow drag model. The overall flow behavior within the spouted bed was predicted well by the above model. A stable spouted region, a fountain region, an annular region and typical flow characteristics of spouted bed were correctly predicted using the model. Distribution of particle concentration, particle velocity and pressure obtained can provide important information on the flow field within the spouted bed for process design and scale-up. Pressure distribution of simulation was compared with experimental results. The comparative results presented the good agreement.

Numerical simulation on fluidization characteristics of tobacco particles in fluidized bed dryers

Three-dimensional simulations have been carried out to examine the gas–particle flow behavior of tobacco material in a fluidized bed dryer. The Euler–Euler model has been used to study the distribution of particles in the fluidized bed dryer. The simulation results indicate that tobacco particles usually concentrate in the near-wall region, and there exists a maximum particle concentration in the feed pipe. The predictions on the regions with high concentration of particles in the fluidized bed dryer agree well with the experimental findings. Moreover, this kind of dynamic particle aggregation might lead to particle clusters, and investigations of the particle motion and mixing behavior in the simulated systems indicate that there are particle clusters during fluidization. The diverse nature of clusters enriches the flow behaviors of particles and consequently leads to the macro-scale heterogeneity featuring fast fluidization: dilute at the top and dense at the bottom in the axial direction as well as the core–annulus structure in the radial direction. Therefore, the particle clusters is one of the key problems in drying processes, which must be known for understanding the material distribution inside the dryer, as well as for the system design of fluidized bed dryers. According to the results, some improvements on the fluidized bed dryer have been brought out and the relative numerical experiments have been performed. The numerical experiments show that the improvements can realize better uniformity and lead to a decrease in the particle concentration, which provides useful ways to solve the clustering problem.

Numerical Simulation of Hydrodynamics and Coke Combustions in FCC Regenerator

A gas-particle, two-phase flow-reaction model of fluid catalyst cracking (FCC) regenerators was established in this article according to the characteristics of FCC catalyst particle clusters and coke combustion reaction. Numerical simulations of the gas-particle flow behavior, heat transfer, and coke combustion process in the commercial regenerator were carried out to obtain detailed distributions of velocity, temperature, and species concentration. The fluidized processing can be well predicted, although there are still some differences between computational results and commercial data for the assumption of a mean diameter of an FCC catalyst. Obtained distributions of temperature and component concentration was also agreeable with commercial data.

CFD modeling of the gas–particle flow behavior in spouted beds

Gas–particle flow behavior in a cylindrical spouted bed and a three dimensional spout-fluid 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 hydrodynamic characteristics are compared with published experimental data. The overall flow patterns within the cylindrical spouted bed were predicted well by the model, i.e. a stable spout region, a fountain region and an annular downcomer region were correctly predicted by the model. The flow instabilities which develop in the spout-fluid bed are along with discussion of the mechanisms leading to instabilities. Bubble formation and motion of the bubbles inside the spout-fluid bed are also described. Such predictions can provide important information on the flow field within the spouted beds for process design and scale-up.

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.

LASER-BASED FLOW MEASUREMENTS OF DILUTE VERTICAL PNEUMATIC TRANSPORT

Dilute vertical pneumatic transport in a vertical lifter was studied using the sophisticated measurement techniques of laser Doppler anemometry (LDA) and phase Doppler anemometry (PDA). The vertical lifter consisted of a lower fluidized silo, an upper receiving tank, and a connecting vertical transport pipe made of clear glass. The experimental study was performed in order to get detailed information of the complex gas-particle flow behavior in a dilute vertical conveying system. Particle diameter, axial particle, and tangential particle velocities, as well as root mean square velocities, were measured simultaneously for different flow conditions. In addition, overall solid mass fluxes were obtained using weighing cells. Smooth and spherical zirconium oxide (ZrO2) solids were applied with two different particle size distributions. Measurements were performed using different flow rates of air. The air inlet condition was varied in order to study its effect on the flow behavior. The particle diameter measurements show that no axial or radial segregation by size occurs for this transport condition. The results show that the particle velocity is independent of the particle size as well. The axial velocity profiles at different heights are almost identical and flat, which indicates fully developed turbulent pipe flow. The turbulent velocity measurements show that turbulence is mainly caused by the velocity gradients, and not by particle-particle collisions in dilute flow. The solid mass flux measurements show the importance of optimum inlet condition and how this influences the mass flux.

Experimental studies on gas—Particle flows and coal combustion in new generation spouting—Cyclone combustor

Based on previous studies, an improved non-slagging spouting-cyclone combustor with two-stage combustion, organized in perpendicularly vortexing flows, is developed for clean coal combustion applied in small-size industrial furnaces and domestic furnaces. The isothermal model test and the combustion test give some encouraging results. In this study, further improvement of the geometrical configuration was made, a visualization method and a LDA system were used to study the gas-particle flow behavior, and the temperature and gas composition in combustion experiments were measured by using thermocouples and a COSA-6000-CD Portable Stack Analyzer. Stronger recirculation in the spouting zone and the strongly swirling effect in the cyclone zone were obtained in the improved combustor. The combustion temperature distribution is uniform. These results indicate that the improved geometrical configuration of the combustor is favorable to the stabilization of coal flame and the intensification of coal combustion, and it provides a basis for the practical application of this technique.

The erosion-corrosion of tubing steels in combustion boiler environments

A review of the behavior of materials exposed to elevated-temperature, combined erosion corrosion environments, such as occur in combustion boilers, is presented. The effects of such system variables as erodent particle composition and physical characteristics, gas-particle flow behavior, temperature and exposure duration on the behavior of various compositions of boiler steels as well as various types of protective coatings on them are discussed. The rates and mechanisms of material wastage determined from in-service tubes are compared to laboratory-test results and similarities and differences are discussed.