Effect of oxidative torrefaction on high temperature combustion process of wood sphere

The present work studies the effects of oxidative torrefaction (OT) (200-290 degrees C, 0-8 vol% O-2) on the combustion process of wood sphere in a single particle combustor (SPC, 1226 degrees C, 3.0 vol% O-2, wet basis), together with such effects on the yield, reactivity and morphology of the high temperature produced char. Increased torrefaction O-2 concentration and temperature both result in higher char yield and prolonged combustion time, and the SPC char yield can be described by a linear regression equation (R-2 = 0.85) as a function of the decreased mass yield caused by the OT process. The correlation (R-2 = 0.83) between the low heating rate char yield (i.e., fixed carbon content) and the torrefaction mass yield is also validated against literature data, indicating that mass yield is a good indicator for both the OT and traditional inert torrefaction. The TGA analysis suggests that the char reactivity is significantly reduced by raised OT temperature up to 290 degrees C, while is only limited influenced by the increase in O-2 concentration (up to 8 vol% at OT temperature of 260 degrees C). The NMR analysis of the OT wood and the SEM observation of the OT char produce from SPC show some evidences that OT result in a more cross-linked aromatic structure, which may hinder the volatile release in the subsequent pyrolysis and thereby lead to less porous char surface and a denser and heavier char particle.

Automated summary

The study demonstrates that oxidative torrefaction (OT) affects the combustion process of wood spheres, increasing char yield and combustion time while forming a more cross-linked aromatic structure that hinders volatile release, resulting in denser and heavier char particles. The findings suggest that mass yield serves as a good indicator for both OT and traditional inert torrefaction processes.