Fluidization of forest biomass-sand mixtures: experimental evaluation of minimum fluidization velocity and CFD modeling

Abstract

An experimental fluid-dynamic study of sand-forest biomass mixture fluidization was conducted. Different proportions of biomass/sand were tested. Sawdust from the Abra Ancha sawmill, located in the town of Aluminé, Argentina, was adopted as the forest biomass material. In parallel, computational fluid dynamics (CFD) simulations of the fluidization process of these mixtures were performed to obtain exhaustive knowledge of their fluid-dynamic behavior. As a result, sand incorporation, even at low concentrations, reduces the cohesion and bonding forces between biomass particles and decreases the segregation and preferential channel formation in sawdust, thus improving fluidization. Satisfactory qualitative results were obtained in relation to the agitation state, bed expansion, and formation of bubbles in the different fluidized mixtures analyzed. The occurrence of two different fluidization regimes was confirmed in both the biomass and biomass-sand mixtures. This phenomenon allows the definition of the incipient ((Formula presented.)) and complete ((Formula presented.)) fluidization velocities. The potential of ANSYS-Fluent software as a simulation tool of sand-sawdust mixture fluidization was verified, and a suitable simulation methodology for predicting the minimum fluidization velocity was developed. This study constitutes the first and most indispensable stage to achieve complete simulation, including chemical reactions, of a sawdust fluidized bed gasification reactor.