Computational Fluid Dynamics-Assisted Process Intensification Study for Biomass Fast Pyrolysis in a Gas-Solid Vortex Reactor

The process intensification possibilities of a gas-solid vortex reactor have been studied for biomass fast pyrolysis using a combination of experiments (particle image velocimetry) and non-reactive and reactive three-dimensional computational fluid dynamics simulations. High centrifugal forces (greater than 30g) are obtainable, which allows for much higher slip velocities (>5 m s^-1) and more intense heat and mass transfer between phases, which could result in higher selectivities of, for example, bio-oil production. Additionally, the dense yet fluid nature of the bed allows for a relatively small pressure drop across the bed (∼10⁴ Pa). For the reactive simulations, bio-oil yields of up to 70 wt % are achieved, which is higher than reported in conventional fluidized beds across the literature. Convective heat transfer coefficients between gas and solid in the range of 600-700 W m^-2 K^-1 are observed, significantly higher than those obtained in competitive reactor technologies. This is partly explained by reducing undesirable gas-char contact times as a result of preferred segregation of unwanted char particles toward the exhaust. Experimentally, systematic char entrainment under simultaneous biomass-char operation suggested possible process intensification and a so-called "self-cleaning" tendency of vortex reactors.