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By thermogravimetry (TG) experiments, evolution behaviors and properties of thermal oxidation processes at low temperature (< 230.0 °C) of a bituminous coal with five moisture contents were investigated. A novel Acceleration Temperature Point Method (ATPM), defined as the transition point from low-temperature oxidation to rapid self-sustained heating-up period, was proposed to determine the role of moisture content in accelerating such process. Results show that segments of water evaporation and gas desorption dominate in stage 1 (65.0–150.0 °C), while segments of generation of coal-oxygen complex and structure oxidation dominate in stage 2 (150.0–275.0 °C). In the moisture range of 9.16–12.06%, the promoted effect of physical desorption capacity becomes weak with increasing moisture content. This is owing to five aspects: the equilibrium of vapor pressure and wetting capability of physically bound water, the change of mass and heat transfer between gas phase (water vapor)-condensed phase (bulk coal particle), the diffusing effect of gaseous water, the heat from dissolving and swelling of gaseous water into bulk coal pores, and the heat of pyrolysis derived from coal particles. Taking Acceleration Temperature Point (ATP) as a barometer to evaluate the spontaneous combustion susceptibility, the critical moisture content of Gengcun bituminous coal is 9.16%. [ABSTRACT FROM AUTHOR]

air-fuel equivalence ratio and timescales of kinetic reaction and oxygen transport were used to analyze the combustion of underground coal fires at different temperature stages. At high temperature stage, due to the fast rate of kinetic reaction, oxygen concentration transported from galleries or cracks was lower than that required by theoretical kinetic reaction. Thus the oxygen consumption rate of coal combustion was controlled by oxygen transport rate and the coal fires were incomplete combustion because of lean oxygen concentration. According to the Single-Particle Reaction- Diffusion model proposed by Krishnaswamy, a formula to estimate oxygen consumption rate of underground coal fires with lean oxygen concentration and incomplete combustion at high temperature was developed. A numerical case study was conducted to analyze and examine the proposed formula. The investigated results show that the proposed formula can effectively estimate oxygen consumption rale controlled by oxygen transport at high temperature. [ABSTRACT FROM AUTHOR]

To analyze the oxidation kinetics reason that self-ignition tendency of coal with different metamorphic degree are different, based on the basic assumptions of coal adiabatic self-heating process, a oxidation kinetics analysis on the reaction characteristics of the process was made combined with the Arrhenius equation, then this paper studied four feature parameters: adiabatic process apparent activation energy (Ec), the critical temperature ( Tc) and the average heating rates each stages of the adiabatic process, (Rhm,Rjs), finally, the relationship between each characteristic parameter and coal metamorphic level was made by numerical fitting. It is show that the oxidation kinetics characteristics are characterized by the four parameters (Ec, Tc, Rhm and Rjs) in the difficulty degree of coal self-ignition reaction (Ec),the difficulty degree of control ( Tc) and the heating speed (Rhm and Rjs) ;with the increase of coal metamorphic grade, Ec has a logarithmic relation with it, Tc has a linear relation, however, Rhm and Rjs have a negative exponent relation. The difference of self-ignition tendency of coal with different metamorphic degree is studied on oxidation kinetics, and it is of great significance to self-ignition control. [ABSTRACT FROM AUTHOR]