Discrete element study of particle circulation in a 3-D spouted bed

A spouted bed is simulated by a discrete element method in a full 3-D cylindrical coordinate system. The vessel is a flat-bottomed cylinder 0.5 m in height and 0.15 m in diameter. In the simulation 300,000 mono-sized spherical glass beads are used. The numerical scheme is based on a second order finite difference method in space and a second order Adams-Bashforth method for time advancement. Gas-particle interaction is modelled to obey the Ergun equation for void fraction less than 0.8, and the Wen-Yu model, for void fraction greater than 0.8. In the present study, particle motion and circulation are investigated. Predicted streamlines of time-averaged particle flow are almost vertical in the upper part of the bed, gradually bending to the spout core in the lower region. Particle velocities along the streamlines are uniform in the upper part of the annulus, becoming non-linear with respect to the distance from the dead zone in the lower part of the annulus. The predicted total passages of particles across the spout-annulus boundary are in good agreement with measurements reported in the literature. Particles are found to feed from annulus to spout along the entire length of the spout. The net mass flux (from annulus to spout) is found to be constant in the upper part of the bed, increasing gradually with the depth in the lower part.