A spontaneous increase in coal temperature with a possible transition into fires represents a direct hazard to coal storage and transportation. This paper evaluates the self-heating characteristics of a sub-bituminous coal under adiabatic oxidation conditions. This paper assesses the effect of relative humidity of the gas supply on the self-heating rates of coal. It is shown that an increase in the gas supply relative humidity has a marked affect on the self-heating rates of the coal. In this work the sub-bituminous coal sample undergo oxidation most rapidly when the relative humidity of the gas supply is about 70%. The effect of relative humidity decreases as oxygen concentration in the gas supply increases. A practical consequence of this finding is that improved fire safety measures should be considered during sub-bituminous coal related operations in hot and humid regions.
In this study, modeling of the crossing point temperature (CPT) phenomenon in the lowtemperature oxidation of coal was carried out using COMSOL Multiphysics®. Lowtemperature oxidation can lead to spontaneous combustion of coal stockpiles. The CPT phenomenon was modeled with the kinetics data obtained from a prior laboratory experimental study. The coupling of the heat-transfer phenomenon through conduction and convection determined the thermal evolution model. In this case, coal received the initial heat of the oven temperature increases. As the coal temperature rose, the heat generated from oxidation was released into the environment via conduction and convection. Meanwhile, oxidation products and oxygen were transferred by convection and diffusion. The effects of moisture and the humidity were not considered. The outcomes of modeling were validated through comparison with the results of experimental tests, and the modeling result agreed well with the experiment tests, with temperature deviations of about 0.9%. The effects of airflow rate, oxygen concentration, porosity, and the initial temperature on low-temperature coal oxidation were also examined.
Low-temperature oxidation of two Indonesian low rank coals was characterized by Thermogravimetric analysis (TGA). The effect of particle size on the spontaneous combustion of coal was examined. Coals were classified to-599+299, -299+249, -249-150, -150+76 and-76 μm size groups and through non-isothermal method scanned from 24 to 600°C at heating rate 5°C/min with air flow rate 50 mL/min. DTA thermogram shows that the transition temperatures decrease by decreasing the particle size. Furthermore, the weight loss increases by decreasing particle size. It is indicated that the propensity of coal to spontaneous combustion increase with decreasing particle size. The moisture loss activation energy and oxidation activation energy were calculated by an integral method using the Coats-Redfern formula. The results show that the propensity for spontaneous combustion of two coal samples (judged by the activation energy) increases by decreasing particle size.
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