Torrefaction of sawdust in a fixed bed reactor

Abstract

Torrefaction of sawdust was performed in a fixed bed reactor under nitrogen flowrate of 150 ml/min from room temperature to torrefaction temperature of 200-300 °C at holding time of 20, 40 and 60 minutes. It was observed that the mass yield of torrefied sawdust decreased upon increasing torrefaction temperature. This was due to the contribution of lignocellulosic removal during devolatilization stage as carbon dioxide (CO2), carbon monoxide (CO) via decarboxylation and decarbonylation reactions respectively. The proximate analysis predicted carbon (C), hydrogen (H) and oxygen (O) as well as predicted heating values were performed on raw and torrefied sawdust. It was determined that from proximate analysis, the moisture content and volatile matter decreased upon increasing torrefaction temperature. The predicted elemental analysis showed that the C content increased but H and O content decreased upon increasing torrefaction temperature. The predicted high heating value of torrefied sawdust also increased with increasing torrefaction temperature. The removal of volatile gaseous products contributed to these phenomena. Obviously torrefaction process had improved the moisture content and heating value of sawdust. The kinetics parameters for torrefaction of sawdust was evaluated by Coats-Redfern Method. The values of activation energy (Ea) for torrefaction of sawdust were in the range of 41.77 – 48.21 kJ/mol for holding time of 20, 40 and 60 minutes. The values of pre-exponential factor (ln A) were in the range of 4.66–6.08 respectively. The existence of functional group on the surface of raw and torrefied sawdust were determined by Fourier Transform Infrared (FTIR) spectroscopy. Several functional groups such as O-H, C-H were C=O were identified.