Effects of Potassium on Spontaneous Combustion of Coconut Husk During Storage

Coconut husk is an agricultural byproduct with significant potential as a biomass resource in Thailand. However, the storage of coconut husk presents safety concerns due to the risk of spontaneous combustion. In this study, the influence of mineral composition on the thermal reactivity and ignition behavior of young (green) and mature (brown) coconut husks was investigated. The X-ray fluorescence (XRF) analysis showed that the young husk contained higher potassium and chloride concentrations, attributed to environmental leaching during storage and agricultural fertilizer inputs. The thermogravimetric analysis (TGA) under oxidative (air) and inert (nitrogen) conditions revealed that the young husk decomposed at a lower onset temperature and exhibited multi-stage degradation in air, while the mature husk degraded later but more intensely in the primary stage. Spontaneous ignition behavior was investigated by the Frank-Kamenetskii approach in a controlled oven setup, monitoring both oven and core temperatures. The ignition temperatures decreased with pile size, ranging from 185 to 160 °C for young husk and from 188 to 165 °C for mature husk. The activation energies were 74.86 kJ/mol for young husk and 81.76 kJ/mol for mature husk, indicating greater susceptibility of the young husk to self-heating. The findings demonstrated that higher potassium and chloride content accelerates oxidation and lowers ignition thresholds, increasing the fire hazard potential. The storage history and mineral depletion in the mature husk reduced reactivity but shifted the decomposition slower, and more stable oxidation. These results highlight the importance of mineral composition assessment and proper storage management to mitigate spontaneous combustion risks in biomass handling.