Numerical gas-solid flow analysis of ring-baffled risers

Abstract In order to improve the gas-solid flow in a lab-scale circulating fluidized bed (CFB) riser, airfoil-shaped ring-type internals were used in a CFD-based design of experiments. The best geometrical properties and arrangement of the ring baffles in the riser were defined with a design of experiments. Four variables were studied: ring thickness, number of rings, spacing between rings and the insertion of a bottom ring. A catalyst-to-gas ratio of 0.181 kg/kg was used, with a gas velocity of 5.6 m/s. Numerical simulations were performed with the k-epsilon turbulence model and the Gidaspow drag model. KTGF was used to describe the solids properties. The solids distribution was evaluated through dispersion coefficient analysis. Four structures for the particle concentration were identified: U-shaped, A-shaped, O-shaped and I-shaped. The best result, with a 45% decrease in the solids dispersion coefficient in comparison with the case without rings, was found in the case with 10 mm ring thickness and four rings. Analysis of the best case showed that the rings promote winding flow, observed in the direction of gas and solid velocity vectors.