(112b) CFD-DEM Simulation of Fluidization in a 3D Spouted Bed and Flow Regime Prediction Using MFIX-DEM

The spout-fluidized bed offers several advantages in chemical looping combustion operation using solid fuels based on the multiphase behavior. The difference in size and weight between the large, spoutable oxygen carrier particles and the smaller coal and ash particles allows the oxygen carrier to be easily segregated for recirculation; the increased solids mixing due to dynamic flow pattern in the spout-fluidization regime prevents agglomeration. A 3D spouted bed simulation is set up in MFiX-DEM based on a previous flow regime mapping experiment using 4-mm-diameter glass beads. The minimum fluidization condition is determined based on the change in the relationship of the pressure drop with velocity as the bed transitions from a packed bed configuration to a fluidized one. The operating conditions in the CFD-DEM simulation are subsequently normalized by the minimum fluidization velocity.

At each operating condition, the flow is classified into the internal spout, spouting with aeration, spout-fluidization, jet in fluidized bed, or slugging bed regime based on the multiphase flow pattern. The flow regimes predicted by the MFiX-DEM simulation show excellent agreement with the experimental flow regime map at all operating conditions. Spectral analysis of the pressure fluctuations in the bed quantitatively corroborates the visual observations of the flow pattern based on the particle trajectories. The qualitative trends in the shape, frequency, and power of the dominant peak in the frequency spectra follow the expectations from theory and experiment. The results of this work confirm that the MFiX-DEM model can effectively predict the flow regime in a spouted bed with high accuracy.

A reduced value of the spring stiffness coefficient, required for the particle collision calculations, is used in this work as it would take months to complete the simulations with the exact value. A parametric study is conducted on the spring stiffness to rule out errors in the results due to the reduced value. It was found that the value used as a starting point in the simulation was sufficient to produce accurate results and increasing the value does not affect the flow regime prediction even in the worst-case scenario.