A CFD study of biomass pyrolysis in a downer reactor equipped with a novel gas–solid separator — I: Hydrodynamic performance

• The hydrodynamics in a downer for fast biomass pyrolysis is investigated using CFD.
• The reactor with a novel separator allows better control of the gas residence time.
• The separation efficiency is sensitive to the separation length and the cone angle.
• Gas disengagement height is proposed to aid in estimating the gas residence time.

This study presents the first part of a CFD study on the performance of a downer reactor for biomass pyrolysis. The reactor was equipped with a novel gas–solid separation method, developed by the co-authors from the ICFAR (Canada). The separator, which was designed to allow for fast separation of clean pyrolysis gas, consisted of a cone deflector and a gas exit pipe installed inside the downer reactor. A multi-fluid model (Eulerian–Eulerian) with constitutive relations adopted from the kinetic theory of granular flow was used to simulate the multiphase flow. The effects of the various parameters including operation conditions, separator geometry and particle properties on the overall hydrodynamics and separation efficiency were investigated. The model prediction of the separator efficiency was compared with experimental measurements. The results revealed distinct hydrodynamic features around the cone separator, allowing for up to 100% separation efficiency. The developed model provided a platform for the second part of the study, where the biomass pyrolysis is simulated and the product quality as a function of operating conditions is analyzed.