Preliminary hydrodynamic study on new multi-stage biomass gasifier

In this work, A new multi-stage biomass gasifier with three compartments is proposed. The aim of the design is to generate a low tar content product gas. Therefore, the system is composed of biomass pyrolysis zone, product pyrolysis gases combustion zone and gasification zone. Second and third zones are superposed and separated by a gas distributor. A computational fluid dynamics (CFD) study has been conducted using the software ANSYS Fluent to simulate the hydrodynamics behavior of flow inside the combustion and gasification zones. Based on a two-dimensional cold flow configuration, the Eulerian-multiphase model approach has been used. Sand is chosen as the bed materiel, belonging to Geldart B group, and fluidized by the air. The flow through the distributor is accurately modeled. The ultimate aim of this work is to study the effects of the gas distributor and some geometrical modifications in the gasifier on the pressure drop, the bed expansion ratio and the bed behavior. Results show that the pressure drop and the bed expansion are affected by the distributor's diameter and its holes diameter. Also, a combination of these changes could be used to optimize the fluidization and avoid slugging of the bed.