Influence of the Grain Direction on the Low-Temperature Pyrolysis of Large Wood Particles

• Main Authors: H. Bennadji, E. Fisher
• Format: Article
• Language: English
• Published: AIDIC Servizi S.r.l. 2014-06-01
• Series: Chemical Engineering Transactions
• Online Access: https://www.cetjournal.it/index.php/cet/article/view/5705

Pyrolysis is the thermal decomposition of a solid fuel in an inert atmosphere. Biomass pyrolysis products are non-condensable gases, char, and tars. The amounts and compositions of the products depend on several operating parameters i.e. temperature, pressure, heating rate as well as the biomass properties. For large particles, the pyrolysis rate is affected by chemical kinetics, mass transfer and heat transfer. Owing to the anisotropy of the woody material, transport processes depend on the heating and flow direction relative to the wood grain, as well as on temperature, density, and moisture content. The present work investigates the effect of grain orientation on the wood pyrolysis. For this purpose, dried white pine wood cylinders of 1.9 cm diameter and 4 cm length were pyrolyzed using a flow of nitrogen heated to atemperature between 374 and 464 °C. The cylinders have two different grain orientations: parallel andperpendicular to the cylinder axis. The pyrolysis was performed in a turbulent nitrogen flow at atmospheric pressure for 30 min. Temperature profiles at three locations within the particle were measured using a sheathed K-type thermocouples with sheath diameter of 0.5 mm. The temporal evolution of several volatiles released during sample pyrolysis was measured using Fourier Transform Infrared (FTIR) and Non Dispersive Infrared (NDIR) analyzers. The data are compared in order to deduce the effects of sample grain orientation on the pyrolysis of woody biomass. It was noted that more gas and char were formed from the parallel gain orientation. This is due to the higher residence times of tars, such that there is a higher probability for their reacting to form secondary char and lighter gases prior to escaping from the particles.