Evaluation Indicator for the Spontaneous Combustion of Biomass Fuel Pellets and Its Self-Ignition Control

Abstract

ABSTRACT To investigate the spontaneous combustion characteristics of biomass fuel particles, spontaneous combustion processes of 10 biomass samples were simulated by programmed-heating and continuous oxidation experiments. Analysis results indicated that during the very initial stage of spontaneous combustion (<90 °C), each biomass fuel particles merely yielded CO at 0–20 ppm, while the subsequent exponential growth of gas emissions tended to exhibit a significant variation on spontaneous liability. Due to the diversity of biomass material sources, its spontaneous combustion tendency is not only determined by internal properties, but also influenced by external factors such as particle size, ventilation rate, moisture, etc. There are many factors affecting the spontaneous combustion tendency, which cannot be analyzed accurately and quantitatively. Therefore, it is necessary to propose a stable indicator based on thermal analysis to objectively evaluate the tendency of biomass spontaneous combustion. A scientific index was proposed to precisely assess the spontaneous combustion tendency of biomass materials. Specifically, the activation energy (E) at the O2 gain stage was adopted as the priority criterion: If E < 70 kJ/mol, the biomass was defined to be highly flammable; if 70 ≤ E ≤ 80 kJ/mol, the biomass was considered to be prone to self-ignition; and if E > 80 kJ/mol, the biomass was regard as non-spontaneous combustion. Besides, data from cross-point temperature tests fundamentally support the reliability of mentioned evaluation methodology. In fire-extinguishment experiments, a conventional approach, such as suffocate by self-extinguishing, only reduced the temperature to 99.9–238.7°C. The comparison of extinguishing materials such as gaseous N2/liquid nitrogen, CO2, and C3HF7 revealed that extinguishing fire with C3HF7 exhibited a dramatic advantage at burning temperature > 500°C. However, fire extinguishing with CO2 was more suitable for the spontaneous combustion ignition of biomass at temperature ≤ 300°C.