Torrefaction of Biomass Residues in Pulsating Fluidized Beds for Pellet Production

Torrefaction is a mild pyrolysis, which maximizes solid yield, producing a high percentage of ‘biochar’ (70-80%wt) with improved grindability, prolonged durability, lower hydrophilicity and slower biological and thermal degradation compared to raw biomass. Torrefaction has been explored for pre-treatment of biomass residues to make torrefied pellets, which can be applied as a high quality feedstock in gasification for high quality syngas production and as a substitute for coal in thermal power plants and metallurgical processes. This presentaiton provides an overview of the advances made at UBC on developing a novel pulsating fluidized bed reactor for biomass torrefaction. The reactor is intended to address two major challenges in biomass torrefaction: stable fluidization of irregular biomass particles and narrow particle residence time distribution for uniform solids product. To achieve stable fluidization of sawdust particles with a narrow residence time distribution, a gas-pulsating horizontal fluidized bed reactor has been developed. The fluidization hydrodynamics, particle residence time distribution, biomass drying and torrefaction performance were performed systematically in both a cold model unit and a hot model unit. The suitable operating envelop of the reactor including fluidization velocity, pulsation frequency, reactor temperature and solids residence time were explored. The results demonstrated the superior performance of the novel reactor for torrefaction of biomass particles.