Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to show that isolated sawdust particles, similar to 1.5 mu m in size, are enriched in sulfur (up to 6.8 wt%). Differential scanning calorimetry data of sawdust and pine shells were used to analyze the distribution and variation of the pre-exponential factor, and the kinetic parameters of the combustion process in air were studied using the iso-conversional Friedman method. It is known that while the combustion process of biomass fuel can be divided into two main stages (smoking and flame burning), the burning of elemental sulfur occurs mainly during the smoking stage. The smoking and flame burning stages can be accurately distinguished by analyzing the variation and the first-derivative curve of the natural logarithm of the pre-exponential factor. By terminating the combustion at the transition stage between smoking and flame burning, the desulfurization of biomass can be completed, and the best total desulfurization efficiency could reach approximately 80%.