CFD–DEM investigation into the scaling up of spout‐fluid beds via two interconnected chambers

Abstract

The hydrodynamics and chamber interaction in a three-dimensional spout-fluid bed with two interconnected chambers are investigated via computational fluid dynamics coupled with discrete element method (CFD-DEM), because multiple interconnected chambers are key to scaling up spout-fluid beds. The overall solid motion, spouting evolution, and spoutannulus interface is studied, followed by time-averaged hydrodynamics, particle-scale information, spout-annulus interaction, and inter-chamber interaction. The results show that inter-chamber interactions lead to unique characteristics distinct from that for a single-chamber system, including (1) asymmetry of the hydrodynamics within each chamber, (2) alternative spouting behavior in the two chambers, (3) smaller pressure drop in terms of magnitude and fluctuations, (4) two peaks in the solid residence time (SRT) frequency histogram of the annulus, (5) average SRT in the spout is twice that in a single-chamber, and (6) larger solid dispersion in all three directions. The results provide meaningful understanding for the scale-up of spout-fluid beds.In view of its excellent performance and widespread application, numerous experimental efforts have unsurprisingly focused on various aspects of this apparatus, spanning the hydrodynamics, 11,12 solid circulation, 13,14 particle velocity profile, 15 pressure drop 16 and fluctuation, 17 flow reigme, 18-20 maximum bed height, 21 particle mixing, 22 minimum spouting velocity, 23 effect of draft plates, 24-26 thermal behavior, 27 and so on. In tandem with experimental investigations, the numerical simulation of the dense two-phase flow has progressed too. As is well-acknowledged, two approaches, namely, the twofluid model (TFM) and computational fluid dynamics combined with discrete element method (CFD-DEM), are available to model the dense gas-solid flow. 28,29 The critical difference between these two approaches lies in the resolution of the solid motion: the solid phase is treated as a continuum and tracked individually in the Lagrangian framework in TFM and CFD-DEM, respectively. Zhong et al. 30 numerically explored the gas/solid flow in the three-dimensional (3-D) spout-fluid bed using TFM, wherein the kinetic theory of granular flow provided the closures. The results demonstrated that the simulation results are strongly affected by the restitution

Improving the operational stability of the multi‐chamber spout‐fluid bed via the insertion of a submerged partition plate

“…Clearly, in contrast to the system without partition plate (Figure a), for the bed with partition plates of h p = 200 mm (Figure c), the eight patches of high Fgx values are symmetrical about the center of the spout inlet (i.e., x / X = 0.25 and 0.75), which indicates stable spouting behavior as inter‐chamber interaction is minimized. With respect to Fgz, the clear difference between Figures b and 3d lie in the enhanced spout stability in the latter.…”

“…Figure presents the contour plots of time‐averaged gas flux in two directions (namely, x and z ) in the central x–z plane of y / Y = 0.5 in the absence of partition plate and presence of partition plates with h p = 200 mm. Clearly, in contrast to the system without partition plate (Figure a), for the bed with partition plates of h p = 200 mm (Figure c), the eight patches of high Fgx values are symmetrical about the center of the spout inlet (i.e., x / X = 0.25 and 0.75), which indicates stable spouting behavior as inter‐chamber interaction is minimized. With respect to Fgz, the clear difference between Figures b and 3d lie in the enhanced spout stability in the latter.…”

“…Figure shows the vector plot of time‐averaged solid velocity in the spout‐fluid bed at two y/Y positions and for the systems with and without partition plates. Compared with Figures a and b, Figures c,d show that inserting a plate with h p = 200 mm gives rise to three noteworthy differences in the solid distribution: (1) parallel spouting channels of the solid phase in the central region of each chamber; (2) diminished downward solid velocity (Us) in the central annulus region, mainly due to the dominance of inter‐particle collision and also the comparatively larger upward gas flux (Fgz) observed in Figure b; and (3) two parallel, non‐interacting fountains in the fountain region. Thus, the efficacy of the partition plate with h p = 200 mm in improving spouting stability in such multiple‐chamber spout‐fluid beds is apparent.…”

“…Van Buijtenen et al conducted experimental and numerical investigation on the hydrodynamics of a multiple‐chamber spout fluidized bed, and found that the presence of multiple spouts significantly affects the flow behavior, which indicated that the understanding to date on the single‐chamber system cannot be applied directly to multiple‐chamber systems. Recently, Yang et al carried out CFD‐DEM simulations of the three‐dimensional, two‐chamber spout‐fluid bed to study the hydrodynamics and inter‐chamber interaction. The results indicated that significant interaction exists between the chambers, such that the spout and fountain of each chamber are inclined toward each other, leading to prominent inter‐chamber gas and solid interactions in the fountain region of the bed.…”

“…In view of this, an approach to improve the spouting robustness and stability in terms of minimizing inter‐chamber interactions in the spout‐fluid bed with multiple chambers is necessary. Armed with the knowledge that the spout and fountain regions of each chamber tend to sway toward the corresponding regions in the other chamber in a two‐chamber spout‐fluid bed, the investigation of the feasibility of a vertically submerged partition plate to minimize interactions between the chambers is warranted to enable scale‐up.…”