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

•High temperature (1226 °C) combustion experiment of oxidatively torrefied (OT) wood.•Linear relationship between char burnout time and char particle mass (R2 = 0.989).•Char yield increases with higher torrefaction temperature and O2 concentration.•Linear regressions of fast/slow pyrolysis char yield by torrefaction mass yield (R2 ≥ 0.83).•Varying OT O2 concentration (0–8 vol%) has a negligible effect on char reactivity.