Dynamically structured fluidization: Oscillating the gas flow and other opportunities to intensify gas-solid fluidized bed operation

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

“…which has a value r = 1 for exact periodic repetition of structure and r = 0 for no periodic repetition of structure. In Equation (11), N is the number of CFD cells in the region of interest, i is the cell index, ε g,i and ε 0 g,i are the gas void fraction averaged over the depth direction at cell i in the current time and in the time after two vibration or gas flow pulsation periods, respectively, and ε g and ε 0 g are the average of ε g,i and ε 0 g,i over the region of interest, respectively. While calculating the correlation coefficient in free bubbling simulation cases with a constant superficial gas velocity and a constant gravity, the same time interval of 0.4 s was used to be consistent with cases with vibration.…”

“…As mentioned earlier, pulsed gas flow at some specific conditions can also create structured bubbling pattern in fluidized beds. 9,11 Herein, CFD-DEM simulations with pulsed gas flow and with both single-layer and two-layer configurations were performed. For the single-layer configuration, equivalent simulations as in Figure 2 with a 6 mm thick virtual distributor were studied.…”

“…16 (III) Methods which change body forces include the use of magnetic fields, 17 electric fields, 18 and centrifugal fields. 19 Among all of the methods used, Coppens and co-workers 9,11 found that using pulsed gas flow and at some specific conditions, the bubbles in the bed can be structured dynamically into a triangular pattern. Notably, the pattern repeats itself every two periods of the gas pulsation.…”

“…However, when the system height is increased, the bubbling structure degrades significantly, due to the occurrence of bubble coalesce higher in the bed. 11,20 Typically, the very ordered bubbling structure can only maintain for a particle height of ~10 cm, well below the height of most industrial fluidized beds. Therefore, it is necessary to come up with a design to maintain the ordered bubbling structure to a higher particle height.…”

“…In the past few decades, various ways have been proposed to alter the overall bubble dynamics in fluidized beds to improve particular processes. A recent intensive review 11 classified different ways into three categories according to how they apply an additional source of energy to the bed: (I) Methods which change particle‐particle or particle‐wall contact force include the use of vibration 12 and the addition of flow conditioners 13 . (II) Methods which change gas‐solids inter‐phase force include the use of pulsed flow, 14 fractal gas injectors, 15 and internals 16 .…”