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

Abstract

To deeply explore the spontaneous combustion disaster of coal caused by air leakage and oxygen supply, low-temperature coal oxidation experiments under different oxygen concentrations (DOC) were carried out. Within the coal spontaneous combustion characteristic measurement system, a synchronous thermal analyzer (STA) and a Fourier transform infrared spectrometer (FTIR), the macro laws of gas and heat generation under DOC are analyzed, and the mechanism of the development of coal spontaneous combustion restricted by the lean-oxygen environment is also revealed. The results show that the change of oxygen concentration (OC) does not affect the critical temperature value and gas index change trend, but the lean-oxygen environment reduces the gas concentration and heat production rate very obviously. According to the temperature of the intersection, OC needs to be lowered to less than 5% when preventing spontaneous combustion of coal. The chain thermal reaction lags in the lean-oxygen environment, and the pyrolysis activity is significantly reduced. Meanwhile, the temperature points at T 6 and T 7 show significant differences. Furthermore, with increasing OC and temperature, the content of the aliphatic hydrocarbon presents an overall trend of first increasing, then decreasing, and continuously increasing after stage IV. It is concluded that • OH, aliphatic hydrocarbons, aromatic hydrocarbons, and carboxyl groups are the key groups for the coal spontaneous combustion evolution under DOC. To combine the spontaneous combustion reaction of coal in the DOC environment, the reaction path of the index gas in the macroscopic phenomenon and the reason for the concentration differences are revealed, the mechanism for exotherm varies caused by OC is clarified, and the microscopic inhibition affection on the chain reaction within the lean-oxygen environment is also explored. The results put forward the key groups evolution mechanism under the DOC for coal oxidation, which could provide the technical guidance for the fire prevention and control on coal mines.

Effect mechanism of nitrogen injection into fire-sealed-zone on residual-coal re-ignition under stress in goaf

“…As concluding the results, with the increase of uniaxial stress, it shows a trend of first decreasing and then increasing. According to our previous research (Liu et al 2021), compared with the heat release, nitrogen injection plays a key role in suppressing the spontaneous combustion of coal in the unsealed fire zone. However, judging from the heat release of coal re-ignition under different uniaxial stresses indicates that the heat generated during re-ignition of coal under uniaxial stress is quite different from the heat released by residual coal.…”

Effect of Water Evaporation on the Inhibition of Spontaneous Coal Combustion

“…According to the existing research results, CO and CO 2 were the two important gases generated in the whole process of coal oxidation and were believed to be directly related to the coal spontaneous combustion mechanism. 32 The larger the concentration of the two gases produced, the higher the spontaneous combustion tendency of the coal. The CO production rate trend was divided into two sections (Figure 1).…”

Study on the Change Law of Red-Green-Blue Values of Infrared Thermal Image in the Process of Anthracite Oxidation and Spontaneous Combustion

“…The heat production of coal is lower than the heat dissipation of the coal self-heating environment in the temperature range of 202.5-255.2 °C, but the difference gradually decreases as the temperature rises. Near 255.2 °C, the heat production and heat emission of coal are in balance, that is, the heat production of coal equals the heat dissipation of the coal self-heating environment; in the range of 255.2-314.6 °C, the heat production of coal exceeds the heat dissipation of the coal self-heating environment, and the gap gradually widens with temperature increase (Liu et al, 2021b). As a result, the temperature range corresponding to anthracite's self-heating period is 202.5-314.6 °C, and the critical characteristic temperature of the self-heating period is 255.2 °C.…”