(653f) On the Euler-Lagrange Simulations of a Pilot Scale Circulating Fluidized Bed Riser: Experimental Unit CFD-Based Design, Flow Structures and Particle Forces Analysis

Circulating fluidized beds (CFBs) are commonly found in many industrial applications such as drying and coating of particles, polymerizations, combustion and gasification of coal and biomass, gasoil fluid catalytic cracking. Given the importance of physical understanding about CFBs, in this work simulations were carried out to explore and predict the upward gas-solid flow in pilot scale riser. Therefore, the Pilot Unit of Riser and Cyclones was designed based on Computational Fluid Dynamics (CFD) predictions, in order to subsequently allow carrying out validation experiments. The flow was simulated through an Eulerian-Lagrangian URANS, unsteady point-particle model, with inter-particles collisions and impact on rough walls, implemented on the in-house code UNSCYFL3D. Two turbulence models were used: the two-layer k-ε model and the k-ω SST model. Uncertainties due to spatial discretization were evaluated applying the Grid Convergence Index (GCI) method. The operating conditions refer to dilute gas-particle flows (Gs=4 – 12kg/m²s), since the study of typical riser phenomena under these conditions is one of the objectives. Simulations results have shown the formation of macro and mesoscale flow structures, caused by geometrical and fluid dynamics effects, respectively. Particle phase flow segregation occurs near the solids inlet and also recirculation at the top of the riser, due to the T shape outlet geometry. The well-known core-annulus structure was not predicted by the model, although high particles momentum transfer occurs in the transversal directions, at the bottom region of the riser. Saffman and Magnus forces were found to have a little influence over the particles flow, however great impact of the roughness wall model and on the turbophoresis effect (i.e. turbulence dispersion model) could be noted. The particle kinetic energy shows high velocity fluctuations near the wall mainly at the riser top section.

Keywords: Circulating Fluidized Bed. Euler-Lagrange Simulation. Turbophoresis.