TORREFACTION OF BIOMASS IN A CONTINUOUS ROTATING SCREW REACTOR

This work highlights the results that have been obtained from the continuous torrefaction of pine, in a lab-scale (2.5 kg/h feed) screw conveyor reactor. The temperatures observed in the reactor (as measured on the surface of the conveyor screw) are significantly lower than those measured at the wall of the reactor. Variation in the overall process yields and product qualities are related to variations in operating parameters. Reactor temperature and reactor residence times had the greatest effect on yields in the range of conditions investigated in this work. The overall solid product yield may be used directly to infer product qualities such as calorimetric value and proximate and elemental composition if sufficient data for a given feedstock is available. This makes a detailed knowledge of the thermal history of the biomass unnecessary in terms of quality estimation (if yields are known). Simple tests have been performed to determine the relative grindability of torrefied biomass and the composition of the gases produced during torrefaction are also presented.