Experimental and modeling of water evaporation and condensation during self-heating in biomass storage piles

The self-heating in biomass storage piles, driven by processes such as water evaporation, condensation, and biological and chemical reactions, poses a significant risk of spontaneous ignition and fire incidents. Accurate prediction of moisture content transitions in biomass is crucial for understanding the impact of moisture on self-heating tendencies and developing numerical models for biomass self-heating. We hypothesize that a comprehensive model integrating equilibrium and isotherm models can accurately predict the dynamic transition of biomass moisture. This study conducts extensive moisture migration experiments on six commonly used biomass types with different initial moisture contents. The experiments are conducted in a chamber held at constant temperatures (15 °C, 25 °C, 35 °C, 45 °C, and 55 °C) and constant relative humidities (60 % and 80 %) over a 7-day period, after which the final biomass moisture content is measured. The results unveil biomass moisture transition patterns and elucidate the impacts of initial biomass moisture contents and storage conditions. The proposed model, with constants determined using the least squares method combined with genetic algorithm, demonstrates high accuracy in predicting moisture dynamics. To affirm the model's reliability and precision, a second set of experiments examine moisture adsorption by six types of air-dried biomass exposed to various relative humidity and temperature conditions, in which the temporal evolution of biomass moisture contents is measured. The results from these validation experiments confirm the model's robustness and its ability to accurately track temporal moisture variations within biomass samples under diverse environmental conditions. Therefore, the proposed model can be employed for numerical analyses of biomass self-heating and spontaneous combustion processes, contributing to more accurate forecasts and safer biomass storage practices.