Structured bubbling in layered gas‐fluidized beds subject to vibration: A CFD‐DEM study

Abstract

Bubble dynamics in gas fluidized beds are mathematically chaotic and difficult to predict. Various ways have been proposed in the past to alter the overall bubble dynamics to improve particular processes. In particular, it has been shown that pulsed gas flow and vibration can be used to transform the chaotic motion of gas bubbles into a dynamically structured pattern. The structured bubbling pattern does not change with the system width, opening opportunities to address key issues in scaling up gas-solids bubbling fluidized beds. However, the pattern can only maintain for a limited particle height, well below the height of most industrial fluidized beds. Herein, we proposed to use a layered configuration with multiple stages of gas distributors to maintain the ordered bubbling structure to a higher particle height. Computational fluid dynamics-discrete element method (CFD-DEM) simulations performed here demonstrate the effectiveness and key parameters for maintaining structure in the proposed design, providing potential for industrial use.

Heat transfer within dynamically structured bubbling fluidized beds subject to vibration: A two‐fluid modeling study

“…In particular, Table 3 compares the positive and negative aspects of the structured bubbling fluidized bed and freely bubbling fluidized bed. Previous works have demonstrated that the structured bubbling pattern has the advantages of (i) creating highly reproducible and highly predictable bubble structures, 14,23 (ii) achieving controlled motion of particles, 14,26 and (iii) scaling up easily with maintaining the pattern naturally while the system width is increased 14,23 and maintaining the pattern to an overall higher height using a layered configuration 24 . This work further shows that the structured bubbling pattern (i) can achieve the best mixing and thus the most uniform solids temperature distribution and (ii) can compartmentalize heat transport.…”

“…23 Due to the interaction of bubbles higher in the bed, the bubbling structure degrades significantly in a system with an overall high height. However, a recent Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulation study 24 demonstrated that at the same vibration and gas flow conditions, the use of a layered configuration with multiple stages of gas distributors can maintain the ordered bubbling structure to a higher particle height. This layered arrangement requires a sufficiently large distributor pressure drop and a sufficiently large distance between neighboring layers to ensure uniform and vertical gas flow through all distributors.…”

Formation of Ordered Bubbles in Pulsed Fluidized Beds─A CGDPM Study

“…In addition, changing the system scales without affecting the well-aligned bubbles creates opportunities to address the key issue of the reactor scale-up . However, due to the significant interphase dissipation, the ordered bubbles become more susceptible to bed structures and operating conditions; therefore, it is imperative to examine the relationship between the configuration of ordered bubbles and the fluidized bed structures or operation conditions so as to suggest appropriate design.…”

Structured bubbling in vibrated gas-fluidized beds of binary granular particles: experiments and simulations

“…26 The dynamics of these bubbles are typically mathematically chaotic; 19 however, oscillating gas flow 19,20 or combined constant gas flow and vibration 8 can structure bubbles to form and rise in a triangular array pattern. Structured bubbling has been demonstrated to form the same bubble patterns when scaled vertically 27 and horizontally 8 as well as create predictable particle convection patterns, 28 thus addressing issues with scale-up and optimization of fluidized bed processes. 19 So far, structured bubbling has only been demonstrated in monodisperse particles.…”