Research On Oxidation Kinetics Testing Method For The Propensity Of Coal To Spontaneous Combustion

Spontaneous combustion of coal is one of the major disasters in our country's coal industry. Spontaneous combustion will not only waste a lot of coal resources, resulting in huge economic losses, but also evoked gas and coal dust explosion, which bring great disasters to the coal mines . Therefore, the spontaneous combustion of coal and its related work ,which should depend on the identification of the propensity of coal to spontaneous combustion, has always been paid great attention by the mine management departments at all levels;. But our country's fundamentals for the identification of the propensity to spontaneous combustion is relatively weak, and the existing oxygen adsorption method for testing the propensity of coal to spontaneous combustion, can only reflect physical oxygen adsorption characteristics on coal surface, rather than the inherent kinetic characteristics, so this method and its results have been widely questioned. In the thesis, Oxidation Kinetics testing method for the propensity of coal to spontaneous combustion and its classification indicators were studiedIn this paper, self-developed adiabatic oxidation experimental system was used to simulate the adiabatic oxidation process of different coals, with the obtained adiabatic oxidation temperature rise curves, and temperature rise rate of different coals, kinetic parameters at different temperatures, and the critical temperature were calculated and analyzed. According to the research ,it was demonstrated that the development of coal spontaneous combustion is a non-linear and kinetic process, which can be divided into several obvious stages, including the low-temperatures slow heat accumulation, the critical point and accelerated oxidation stage ; the reaction kinetics of coal in different stages differ greatly, that is, some types of coal in the slow oxidation stage are more reactive, with relative high temperature rise rate, while in higher temperature, the temperature doesn't rise very fast ,other types of coal are less sensitive in low-temperature oxidation stage, in this case, the temperature rises slowly firstly, but much rapidly later, Therefore, just using the characteristics of only one stage to evaluate the whole coal oxidation process is not comprehensive. In view of this, the new ideas and ways of Oxidation Kinetics testing method for the propensity of coal to spontaneous combustion, with the whole kinetic process from low-temperature oxidation to self-ignition as study objects, thermal theory and free radicals chain reaction theory as fundamentals, comprehensive testing technique with multiple variables as means, were firstly proposed in this paper. Based on the thermal theory and free radicals chain reaction theory, by using DSC-TG thermal analysis technology, electron spin resonance techniques (ESR), the change rules of heat release rate and the concentration of free radicals were studied at different stages, and then the testing results and adiabatic heating rate of were analyzed comprehensively . It was showed that, the reaction mechanisms in different stages of the coal oxidation are different. The low-temperature oxidation stage is a gradual heat accumulation process, which mainly has thermal characteristics of spontaneous combustion ,and two parallel reaction sequences are supposed to occur during this stage, that is ,the direct burnoff and sorption sequences, in which the unstable intermediate carbon-oxygen complex and gaseous products(CO2, CO, H2O) are generated, the different thermal responses between the heat of adsorption and reaction in the parallel sequences result in the temperature rise changes ; while the accelerated oxidation stage is mainly a process influenced simultaneously by heat accumulation and free radicals chain reaction, temperature rises due to the combination influence of both aspects, and because the thermal effects and change rate of the concentration of free radicals are not the same, the temperature rise characteristics are also different.According to different reaction mechanisms at different stages, the concentration of oxygen in the outlet of sample vessel at 70℃,and the crossing-point temperature at temperature-programmed conditions, which can reflect the characteristics of the low-temperature oxidation and accelerated oxidation stages respectively, were selected as the fundamental parameters of Oxidation Kinetics testing method. On this basis, the comprehensive Oxidation Kinetics determination index I for the propensity of coal to spontaneous combustion was proposed, which can reflect the whole process of spontaneous combustion. By using this self-developed adiabatic oxidation experimental system, more than 200 samples in 24 major domestic coal mines were tested, based on comparative analysis presented to the index, a new standard for classification of the propensity of coal to spontaneous combustion was proposed. In November 2007, the standard was approved by the experts in National Technical Committee of Standardization for Production Safety at Coal Mines, as the State Production Safety Industry Standard.