Study on the Mechanism and Reaction Kinetics of Biomass Spontaneous Combustion

Biomass, widely adopted as a coal‑alternative fuel, has high volatility, increasing spontaneous‑combustion risks in storage and transportation. Conventional thermal‑analysis approaches for ignition temperature determination are largely empirical and inadequate for accurate fire risk prediction. Using a simultaneous thermal analyzer, this work investigates the self-ignition mechanisms, burnout behaviors, and reaction kinetics of rice husk (RH), corn straw (CS) and Hongshaquan bituminous coal (HSQ) via the DSC inflection point method, TG-DTG-2 method, and general surface activation function model (GSAFM). Results reveal volatile‑matter‑dominated homogeneous ignition for biomass, contrasting with char‑governed heterogeneous ignition for coal. At β = 1/60 K/min, RH, CS and HSQ have self‑ignition temperatures Tis of 253.65°C, 251.97°C, and 283.40°C and corresponding spontaneous‑ignition heats of 4.85 × 103 kJ/kg, 4.80 × 103 kJ/kg, and 13.50 × 103 kJ/kg, confirming the higher spontaneous-combustion propensity of biomass. Their char‑ignition temperatures Tig are 370.99°C, 414.64°C and 410.61°C. Although CS has a lower Tis than RH, its Tig is approximately 40°C higher because its higher volatile-matter content prolongs volatile-combustion and delays char ignition to a higher temperature under non-isothermal heating. The TG-DTG tangent method underestimates burnout temperature, while the DSC inflection point method produces abnormal trends at high heating rates. TG-DTG-2, based on the second DTG peak, provides a more reasonable burnout temperature. GSAFM predicts reaction rates more accurately than the Flynn-Wall-Ozawa (FWO). The variable activation energy from GSAFM features double peaks at Tis and Tig, where the system needs to overcome high energy barriers to trigger volatile spontaneous ignition and char ignition, respectively, consistent with the ignition mechanism identified by the DSC inflection point method. This study provides theoretical foundations and key parameters for biomass spontaneous‑combustion risk management.