Investigation of the heat generation and spontaneous ignition of disaster waste generated after the 2011 Great East Japan Earthquake

Review on Self-Heating of Biomass Materials: Understanding and Description

“…During self-heating and its development into spontaneous ignition, heat may be generated through various physical, biological, and chemical processes occurring in parallel or in sequence at different temperature ranges. ,,− The major processes and consequent temperature evolution are schematically shown in Figure .…”

“…However, moisture adsorption or condensation due to sudden change in the ambient humidity or addition of liquid water, for example, rainfall, can contribute heat at relatively higher temperatures, causing a temperature spike in the pile , and even triggering the spontaneous ignition of a pile under subcritical conditions. , On the other hand, water vaporization is strongly endothermic. The elevated temperature driving the evaporation and subsequent transport of water vapor outward through diffusion and convection cause heat loss from the pile, which restrains the temperature increase or cools the pile. , Such an effect is more important at relatively higher temperatures. ,, …”

“…The microbiological processes under both aerobic and anaerobic conditions are exothermic. Microbial activity can contribute heat to the self-heating in the temperature range of 0–75 °C if microorganisms are present in a significant quantity, but it is of the greatest importance at temperatures between 20 and 60 °C − limited by the tolerance of the microorganisms to the temperature and heat. The strong thermal power of microbial activity determines microbial heating potentially dominating self-heating in this temperature range .…”

“…Chemical processes involved in self-heating are various chemical reactions, including the oxidation, pyrolysis and hydrolysis of organic constituents and oxidative reactions of inorganic matter. The proposed reactions include but are not limited to direct oxidation at temperatures as low as 30–50 °C oxidation and decomposition of fatty acids at 50–80 °C , water-mediated oxidation (hydrolysis) with a maximum effect near 60 °C , pyrolysis at temperatures as low as 80 °C , direct oxidation of hemicelluloses, cellulose, and lignin at over 100 °C ,, adsorption of gases including oxygen on biomass at low temperatures − and on charred biomass at higher temperatures chemical oxidation of inorganic matter in wastes up to 70–90 °C − …”

“…Some oxidative reactions such as oxidation of fatty acids and wet oxidation can contribute heat at temperatures similar to those for microbial heating and physical processes; the oxidation of inorganic matter, for example, Fe–S–O compounds in sewage sludge, can raise the temperature up to 90 °C. Nevertheless, it is generally recognized that chemical processes require elevated temperatures and therefore prevail at temperatures above 70–90 °C (Figure ) and dominate in driving the self-heating toward spontaneous combustion. ,,, However, without the strong heating of microbial activity or other processes to raise the temperature critical for strong chemical oxidation, it is unlikely for the self-heating to develop into spontaneous ignition. , Additionally, at temperatures around 100 °C, the endothermicity of water vaporization may retard the self-heating process approaching self-ignition. ,,,, …”