Experimental and CFD study of the hidrodynamics of air-urea bubbling fluidized beds

ZAMBÓN, MARIANA; MORA BASAURE, CLAUDIA; VELIZ MORAGA, SUSSY; BUCALÁ, VERÓNICA; MAZZA, GERMÁN

Lille

Congreso; Congrès de la Société Française de Génie des Procédés; 2011

SFGP

particle size. The study involves experimental measurements in a urea pilot scale fluidized bed and CFD simulations conducted in the frame of the ANSYS 12.1 CFD software. This contribution is the first stage to make possible the CFD simulation of the entire urea melt granulation fluidized bed. The experiments were carried out in a conical pilot-scale unit. To this end, a bubbling air-urea fluidized bed filled with urea granules of a mean diameter of 2.6 mm (Geldart D group) was used. The superficial air velocities ranged between 0 and 3 m/s. A multifluid Eulerian approach for granular flow, with the fluid and solid phases treated as interpenetrating continuum phases, was selected for the fluidized bed simulation. The 2D computational domain was discretized in rectangular cells and the corresponding mesh validation was done in order to guarantee mesh independence results. The CFD model uses empirical drag laws to calculate the momentum exchange between the fluid and the solid phases. Several drag laws are available and their influence on hydrodynamic parameters was explored in this work. The drag models used were: Symlal_O´Brien, Gidaspow, Wen-Yu, Symlal_O´Brien (with customized parameters), Richardson-Zaki, Representative- Unit-Cell (RUC) and Hill-Koch-Ladd. The fluid dynamic parameter investigated were the pressure drop, the minimum fluidization velocity and the bed expansion. The numerical results show that the code ANSYS-Fluent is capable of predicting the gas-solid behavior of a urea bubbling fluidized bed at the explored operating conditions. Concerning the drag law model, this study shows that O’Brien´s law is the most appropriate approach to be used for the simulations dealt with here.