Free radical reaction characteristics of coal low-temperature oxidation and its inhibition method

Abstract

Study on the mechanism of coal spontaneous combustion is significant for controlling fire disasters due to coal spontaneous combustion. The free radical reactions can explain the chemical process of coal at low-temperature oxidation. Electron spin resonance (ESR) spectroscopy was used to measure the change rules of the different sorts and different granularity of coal directly; ESR spectroscopy chart of free radicals following the changes of temperatures was compared by the coal samples applying air and blowing nitrogen, original coal samples, dry coal samples, and demineralized coal samples. The fragmentation process was the key factor of producing and initiating free radical reactions. Oxygen, moisture, and mineral accelerated the free radical reactions. Combination of the free radical reaction mechanism, the mechanical fragmentation leaded to the elevated CO concentration, fracturing of coal pillar was more prone to spontaneous combustion, and spontaneous combustion in goaf accounted for a large proportion of the fire in the mine were explained. The method of added diphenylamine can inhibit the self-oxidation of coal effectively, the action mechanism of diphenylamine was analyzed by free radical chain reaction, and this research can offer new method for the development of new flame retardant.

Thermal Properties and Key Groups Evolution of Low-Temperature Oxidation for Bituminous Coal under Lean-Oxygen Environment

“…The heat released by the reaction is used to break new bonds, producing more active groups. 35 Active aliphatic hydrocarbons can still generate a small amount of peroxides (−C–O–O) in a lean-oxygen environment and generate heat at the same time. And because H 2 O is mainly derived from the hydroxyl groups of aliphatic hydrocarbons combined with a large amount of hydrogen, during the development of coal spontaneous combustion, most of the oxygen-containing functional groups are consumed to generate carbon radicals (R).…”

Effect of coalbed methane airflow with optimum action concentration on coal oxidation under low temperatures

“…These free radicals have high chemical reactivities and can easily interact with O 2 in air to release heat. The accumulation of heat leads to a continuous increase in the coal temperature, finally triggering coal spontaneous combustion 14,30–32 . Therefore, the oxidation reactivity can be reflected by free radicals in the coal.…”

“…The spontaneous combustion duration of coal is shortened, and the combustion area is expanded, which seriously threatens safety production in mines 11–13 . Li put forward the free radical reaction theory, considering that free radicals triggered coal spontaneous combustion 14 . Xi et al confirmed that coal oxidation could be inhibited by interrupting free radical chain reaction 15 .…”

Study on the Effect of Extraneous Moisture on the Spontaneous Combustion of Coal and Its Mechanism of Action

“…For internal moisture, physical-state moisture exists on the coal particle surface, and there is a moisture layer on the surface, which reduces the porous structure and specific surface area and affects the oxygen diffusion; hence, the low-temperature oxidation of coal is inhibited [4,14]. On the other hand, chemical-bound moisture can participate in the formation and decomposition of a carbon-oxygen complex during the spontaneous combustion of coal [15][16][17][18]. Beamish et al [19] investigated the effects of moisture content on the R 70 self-heating rate contents and found there was a critical level of moisture content at approximately 40-50% of the moisture-holding capacity of the coal, above which the heat produced by oxidation was dissipated by moisture evaporation and coal self-heating was significantly delayed.…”