Abstract <p>The mixed combustion experiments of biomass with varying particle sizes and pulverized coal (PC) were conducted using a thermogravimetric analyzer. The results indicated notable differences in the impact of biomass particle sizes on mixed combustion. Particularly, straw (X) exhibited better promotion than bamboo (Y), with X₁ and D showing the most favorable mixed combustion effects. On the other hand, Y relatively enhanced the combustion of Y₂ and Y₃. Analysis of the evolution of biomass functional group structure during the combustion process revealed that aliphatic hydrocarbons and C=C bands remained more stable at the initial stages of combustion, while aromatic hydrocarbons exhibited relative stability throughout the entire combustion process. During the decomposition of aromatic and aliphatic hydrocarbons, the fluctuations in the ratios of generated –CH₃ and –CH₃ of new radicals were minimal. However, there was a general trend of gradual reduction in the length of the aliphatic branch as the combustion time increased. Micro-characterization analysis demonstrated that during the degassing process of pulverized coal, pyrolysis reactions occurred, leading to the breakdown of oxygen-containing small molecules and aliphatic rings within aromatic structures present in the coal. The addition of biomass expedited the pyrolysis of pulverized coal and facilitated the graphitization process. Subsequent addition of bituminous coal resulted in an increase in stacking height, leading to a more orderly arrangement of carbon atoms.</p>