Abstract:

To address the frequent spontaneous combustion accidents of photovoltaic silicon sludge, a multi-experimental approach was employed to reveal its dual-stage exothermic characteristics and critical spontaneous combustion size. An isothermal microcalorimeter was used to analyze the heat release sources of silicon sludge under a low-temperature environment of 30 ℃, and to investigate the effects of pH and particle size on heat release characteristics. Simultaneous thermal analysis was applied to investigate the thermal behavior of silicon sludge during the programmed temperature rise process of 40-1 300 ℃, and the flynn-wall-ozawa method was adopted to determine the activation energy of the oxidation stage, revealing the high-temperature reaction mechanism. Based on metal basket self-heating tests and Frank-Kamenetskii theory, the critical spontaneous combustion temperature and critical size of silicon sludge under different ambient temperatures and sample states were calculated. Targeted safety control suggestions for the safe storage and transportation of photovoltaic silicon sludge were proposed. The results show that in the low-temperature stage (30 ℃), the heat release of silicon sludge is dominated by silicon-water and silicon-alkali reactions. The alkaline environment and small particle size can increase the maximum heat release power to 837.5 μW, significantly enhancing the heat accumulation risk. In the high-temperature stage (>405 ℃), the silicon-oxygen oxidation reaction becomes the main heat release source, and the oxidation activation energy decreases from 177 kJ/mol to 141 kJ/mol, with the reaction transitions from interfacial chemical control to diffusion control. The critical spontaneous combustion size of dried silicon sludge, alkali-containing silicon sludge, and silicon sludge with small particle size is significantly reduced, and for every 10 ℃ increase in ambient temperature, the critical spontaneous combustion size decreases multiplicatively. The minimum critical stacking size is 2.2 m at 60 ℃.

Key words: silicon sludge spontaneous combustion, exothermic characteristics, critical spontaneous combustion temperature, pH value, exothermic power, activation energy