The Role of Inorganic Matter in Biomass Self-Ignition

Solid biomass, such as wood pellets, can replace coal for heat and power generation in existing com-bined heat and power plants. This requires storing and processing such materials in large quantities, where they have shown a tendency to self-heat, and possibly spontaneously ignite. From a plant operator’s point of view, it is highly relevant to model and predict such behavior, ideally based on available fuel data. Inorganic matter present in biomass has been known to promote thermal conversion, both under oxidative and inert atmospheres. In this study, biomasses with different inorganic content and composition (pine, beech, wheat straw, sunflower husks) are screened in lab-scale fixed-bed heating experiments, and reaction rates for these materials are determined by thermogravimetric anal-ysis. No clear connection between ash-forming elements naturally present in the biomass materials on one side, and reaction onset behavior or reaction rates at 150–230 °C on the other was found. However, adding KCl to pine wood increased reaction rates compared to the raw sample. The results presented here suggest that catalytic effects play a role, but across different materials, the low-temperature behavior is (likely) dominated the composition in terms of cellulose, hemicellulose, lignin, and extractives. Further research is necessary to confirm these findings.
Keywords: solid biofuel, reactivity, combustion, ashes, lignocellulose, low temperature