DEM simulation of gas-solid flow behaviors in spout-fluid bed

To gain insight into the hydrodynamics of spout-fluid beds, an experimental and numerical study was carried out. Particle image velocimetry was successfully developed and applied to determine particle velocity profiles, whereas voidage profiles were determined by digital image analysis. A 3D hard-sphere discrete particle model was used to simulate the flow in a spout-fluid bed. The simulations and experiments showed a similar influence of the background fluidization velocity on the spout behaviour.

Validation of a Discrete Particle Model in a 2D Spout-Fluid Bed Using Non-Intrusive Optical Measuring Techniques

Spout fluidized beds: Recent advances in experimental and numerical studies

The particle mixing mechanism affects the rate of the process and the achievable homogeneity. This paper presents a numerical study of the particle motion and mixing in flat-bottom spout-fluid bed. In the numerical model, the particle motion is modeled by discrete element method (DEM) and the gas motion is modeled by κ–ɛ two-equation turbulent model. Validation with experiments is first carried out by comparing solid flow pattern and bed pressure drop at various gas velocities. Then, particle velocities, obtained from DEM simulations, are presented to reveal the mixing mechanisms. On the basic, the dependence of mixing index on the time and the effect of gas velocity on mixing and dead zone (stagnant solid) are discussed, respectively. The results indicate that the spouting gas is the driving force for the formation of particle circulation roll, resulting in the mixing. The convective mixing caused by the motion of circulation roll, shear mixing induced by the relative move of circulation rolls and diffusive mixing generated by random walk of particle among circulation rolls are three different mixing mechanisms in spout-fluid bed. The increase of spouting gas velocity promotes the convective and shear mixing. While increasing the fluidizing gas velocity improves significantly the convective mixing and but weakens the shear mixing. Both of them yield a reduction in the dead zone.

DEM simulation of particle mixing in flat-bottom spout-fluid bed

Hydrodynamic characteristics of spout-fluid bed: Pressure drop and minimum spouting/spout-fluidizing velocity

Detailed hydodynamic measurements have been obtained for fully cylindrical spout-fluid beds of 1.3 mm, 1.8 mm and 2.5 mm glass beads in a fully cylindrical column of diameter 152 mm using three different types of optical fibre probes. The reallocation of up to 43% of the air to auxiliary air introduced through the conical base caused some decrease in spout voidages, but remarkably little change in spout diameter compared with spouted beds where there was no auxiliary air addition. Auxiliary air led also to some decrease in particle velocities in the spout and to a modest decrease in the net solids circulation rate.

Denis L Pianarosa

Papers

Voidage and particle velocity profiles in a spout-fluid bed