Fluidization of micronic particles in a conical fluidized bed: Experimental and numerical study of static bed height effect

Abstract

in Wiley Online Library (wileyonlinelibrary.com).The numerical simulations and experimental data of bed hydrodynamics in a conical fluidized bed unit are compared. Experimental studies have been carried out in a bed containing TiO 2 particles belonging to A/C boundary of Geldart's classification with a wide particle-size distribution. Thus, pressure measurements and an optical fiber technique allowed determining the effect of static bed height on the fluidization characteristics of micronic particles. Numerical simulations have then been performed to evaluate the sensitivity of gas-solids drag models. The Eulerian multiphase model has been used with different drag models and three boundary conditions (BC) consisting of noslip, partial-slip, and free-slip. The numerical predictions using the Gidaspow drag model and partial-slip BC agreed reasonably well with the experimental bed pressure drop measurements. The simulation results obtained for bed expansion ratio show that the Gidaspow model with the free-slip BC best fit with the experimental data. V V C 2011 American Institute of Chemical Engineers AIChE J, 58: 730-744, 2012 Keywords: fluidization, hydrodynamics, CFD simulation, conical fluidized bed, drag models, boundary conditions Introduction Fluidization in conical vessels is a useful technique with a variety of applications in drying, [1][2][3][4] food processing, 5,6 pharmaceutical industry, [7][8][9][10] gasification and pyrolysis reactors, [11][12][13][14] and catalytic polymerization reactors. 15,16 A conical fluidized bed is a hybrid gas-solid contacting system, and therefore shares the characteristics of both fluidized and spouted beds. The naming of these types of beds in the literatures is often informed by their geometrical shape and the ratio of bed inlet diameter to particle size. 3,17 This bed provides means for the good mixing and circulation for small solid particles with a wide size distribution. Therefore, knowledge on the hydrodynamics of gas and particle flow in conical fluidized bed is essential for their design at both labscale and in industrial applications.Extensive research has been conduced on the fluidization behavior of classical powders in the 30 to 1000 lm size range 18 and, consequently, their behavior is relatively well understood. [19][20][21][22]23 studied the effect of fine particles beds with a wide size distribution on local voidage in a bench-scale conical fluidized bed. Their main conclusion is that fines form a monolayer around the relatively coarser particles and act as a lubricant, thus lowering the apparent bed viscosity. A lower apparent viscosity corresponded to smooth fluidization with fine bubbles. Geldart 19 argued that the effect observed could be explained by the reduction in mean particle diameter due to the addition of fines. Geldart's Correspondence concerning this article should be addressed to A. Bahramian at bahramian@profs.hut.ac.ir. 730AIChE Journal March 2012 Vol. 58, No. 3 measurements for Geldart A powder revealed a definite influence of size dis...

CFD–DEM modeling of gas fluidization of fine ellipsoidal particles

“…Particularly, there is an interval of nonbubbling expansion for fine particles between the minimum fluidization velocity U mf and the minimum bubbling velocity U mb . Many experimental and numerical studies have been conducted focusing on these flow regimes. Fluidization parameters such as pressure drop, minimum fluidization, and bubbling velocities, and bed expansion ratio, are usually used to characterize these flow regimes.…”

Effect of slip boundary conditions on the simulation of microparticle velocity fields in a conical fluidized bed

“…In a previous article, 44 we found that the optimum values for the restitution coefficient, e ss , are those corresponding to particle-particle friction and maximum particle packing values of 0.9 and 0.67, respectively.…”

“…They reported that the choice of free-or no-slip BC affects the behavior predicted for FCC catalyst particles near the riser wall. Recently, Bahramian et al 43 and Bahramian and Olazar 44,45 used an Eulerian-Eulerian two-phase model with different drag models and various wall BCs.The model was used to analyze the dynamic pressure and bed expansion ratio of conical fluidized beds. Their study shows that the Gidaspow drag model with a partial-slip BC agrees reasonably well with the experimental data for dynamic pressure, and the same drag model with a free-slip BC can better predict the bed expansion ratio.…”

CFD‐DEM simulation of the spout–annulus interaction in a 3D spouted bed with a conical base

“…In the TFM, the fluid and solid phases are treated as continuums and governed by the Navier–Stokes equations with sub‐models to describe the inter‐phase interaction . On the other hand, the DEM approach, that can resolve the solid motion at the particle level, has been vastly adopted to study the gas–solid flow behaviours in the two‐phase dense flow . Takeuchi et al evaluated the particle circulation behaviour in a spouted bed with the DEM method.…”

“…[13][14][15] On the other hand, the DEM approach, that can resolve the solid motion at the particle level, has been vastly adopted to study the gas-solid flow behaviours in the two-phase dense flow. [16][17][18][19][20][21][22][23] Takeuchi et al [24] evaluated the particle circulation behaviour in a spouted bed with the DEM method. They reported that the predicted streamline of the time-averaged particle flow shows a vertical behaviour in the upper part of the bed and bends to the spout core in the lower region of the system.…”