Characterization of bubble behaviors in a dense phase pulsed gas–solid fluidized bed for dry coal processing

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

“…In comparison with a constant flow, the gas retention time increased up to 51% when the air oscillated at the natural frequency of the bed. Following on from these early works, an increasing number of researchers have explored the effects of pulsation on performance, showing that it mitigates channelling in a broad range of fine powders [131] and reduces bubble size [132] as well as rising velocity [133]. For example, when pulsating Geldart A/B alumina particles in 15 cm deep cylindrical beds, Bizhaem and Tabrizi [134] observed a 25% reduction in the bubble size when increasing frequency from 1 to 4 Hz.…”

“…The rising velocity is predicted with reasonable accuracy using standard models. Li et al [133] showed that bubble size and velocity are generally smaller for Geldart A than for Geldart B particles; they used the Shen et al [139] and Davidson models [140] to predict the bubble velocity within 20% deviation from the experimental data.…”

Experimental study of convective heat transfer coefficient for pulsed fluidized bed using microcapsule phase change material

“…Fluidization offers uniform distribution, high particle mixing, stable mixture, and high heat and mass transfer rate. 1 Generally, fluidization means moving particles relative to each other, walls, and fixed surfaces while overcoming drag, gravity, and cohesive forces between particles. 2,3 The gas carrier's flow rate in a fluidized bed should be high enough to overcome particles' weight for fluidization.…”

“…One of the complex gas–solid flows is particle fluidization. Fluidization offers uniform distribution, high particle mixing, stable mixture, and high heat and mass transfer rate 1 . Generally, fluidization means moving particles relative to each other, walls, and fixed surfaces while overcoming drag, gravity, and cohesive forces between particles 2,3 .…”

Gas–Solid Distribution Theory in a Pulsed Fluidized Bed Based on the Intermediate Phase

“…However, this theory overlooks the fact that not all the gas that exceeds the minimum fluidization velocity can form bubbles and that some gas will continue to enter the emulsion phase, resulting in a reduction in the total volume of the bubble phase. On this basis, some revisions to this theory have been proposed; − however, due to the influence of pulsation on bubbles and particles, even the modified two-phase theoretical model does not provide an accurate reflection of the gas–solid distribution in the pulsed fluidized bed. , In particular, when bubbles rise, the pressure at the tail end of the bubble is lower than that elsewhere, causing the entrained particles to form a wake and rise up with the bubble. The generation of a wake affects the efficiencies of the particle mixing, mass and heat transfer, chemical reaction, and drying processes. , A specific example where this effect is quite unfavorable is in the process of fluidized bed coal preparation, wherein the gangue left after separation is entrained in the wake and then rises to the bed surface, mixing with the clean coal products.…”