Experimental investigation and evaluation of influence of oxygen concentration on characteristic parameters of coal spontaneous combustion

Abstract

Understanding the oxidation characteristics of coal spontaneous combustion and the variation of characteristic parameters is of great importance to further clarify the intrinsic mechanism of coal spontaneous combustion and to ensure safe production in coal mines. In this paper, the oxidation process of coal samples was tested at four oxygen concentrations of 21%, 15%, 10% and 5% using a programmed temperature rise experiment. Important parameters of coal spontaneous combustion, such as oxygen consumption rate, gas production rate and exothermic intensity, were calculated for the coal oxidation process. The relationship between coal temperature and oxygen concentration and the spontaneous combustion characteristics of the coal was analyzed and discussed in detail. The results show that oxygen concentration is positively correlated with the concentration of gas production. The oxygen consumption rate, CO generation rate, CO2 generation rate and exothermic intensity of the coal samples varied exponentially with temperature, due to the fact that the higher the temperature, the more intense the chemical reaction between coal and oxygen. The oxygen consumption rate and the exothermic intensity of the coal samples at different oxygen concentrations show a linear increasing relationship, which has been justified by previous investigations. A simple mathematical expression relating the oxygen consumption rate to the heat release intensity was developed and the associated proportionality factor was defined as the exothermic factor A, which was employed as an indicator for the initial determination of the intensity of the oxidation reaction of spontaneous coal combustion for different oxygen concentrations and coal types. The greater the oxygen concentration the greater the A, which can be expressed as a linear equation. For both coal samples selected for this paper, increasing the oxygen concentration increases the degree of oxidation reaction. However, Sample YQ is more sensitive to oxygen concentration than Sample CC, and the exothermic factor A at low oxygen concentrations (5-10%) is much lower than at high oxygen concentrations (15%-21%), so special attention should be paid to the prevention of coal spontaneous combustion at high oxygen concentrations by nitrogen and carbon dioxide injection during coal mining. Sample CC has a higher A at both low and high oxygen concentrations, and has a higher risk of spontaneous combustion in both oxygen environments. Comparatively, Sample CC has a higher risk of spontaneous combustion at low oxygen concentrations than Sample YQ. The research results are expected to provide some support for understanding the oxidation process of coal spontaneous combustion and preventing fire hazards in the coal mining industry.