Experimental Study of Wood Chips Torrefaction in a Pilot-Scale Rotary Kiln

This work aims to study the beech chips torrefaction in a continuous pilot-scale rotary kiln. The effects of operating parameters temperature, residence time and solid hold-up on the temperature profile of the solid bed along the kiln and the process mass yield are evaluated. It has been verified that an increase of the temperature level or residence time leads to a decrease of the process mass yield. Furthermore, it has been evidenced that an increase of the solid hold-up tends to decrease the mass yield too. Studying the temperature profile along the kiln has enabled to locate the drying and torrefaction zones. Torrefaction only begins in the last third of the heating zone. It has also been observed that an important solid hold-up induces a slower heating of the biomass. On the other side, for high temperatures and/or solid hold-up, the biomass temperature exceeded the set-point temperature, which evidences the occurrence of exothermic reactions.