Theoretical And Experimental Evaluation On A New Technique For Preventing Spontaneous Ignition Of Stockpiled Coal

This dissertation deals with the spontaneous combustion and ignition behavior of stockpiled coal. A new technique was proposed to prevent the ignition of stockpiled coal according to the mechanism of low-temperature coal oxidation, by which air is isolated from coal with a layer of coal-based combustible mixture covered in order to suppress the low temperature oxidation in coal piles and then prevent the spontaneous ignition.Numerical and experimental studies were conducted on the influence of the diffusion of oxygen at the boundary of the coal stockpiles on spontaneous ignition, with a one-dimensional mathematical model and an experimental model of stockpiled coal. The results of numerical simulation show that when the coal stockpile is isolated from air the concentration of oxygen decreases faster and the temperature increases slower compared to that in the coal stockpile without cover. Similarly, experimental results show that the temperature in the coal stockpile with cover increases slower than that in the coal stockpile without cover. These results not only demonstrate that the spontaneous ignition of coal stockpile is controlled by air diffusion but also indicate that air can be effectively isolated with the mixture formulated by the authors.The results of numerical simulation show that Arrhenius parameters of oxidation of coal were very important to the spontaneous combustibility and ignition behavior of stockpiled coal. In terms of stockpiling practices for particular coals, valuable predictive information is obtainable from calculated heat-release rates, and this requires values for the Arrhenius parameters E (activation energy, J/mol) and k0 (pre-exponential factor, s-1). It is found that the Arrhenius parameters were reliant on the selected data range when using traditional ways to deal with of TGA experiment with partial TGA data, so a new algorithm based on the least squares was put forward in this study with which full range of TGA data was used to improve the numerical accuracy and stability. It is shown that the results obtained with the algorithm agree well with experimental data.This dissertation also studied the relative thermal physical properties of the coal-based combustible mixture. Results show that its low void feature makes it possible to isolate stockpiled coal from air and its effective thermal conductivity is at the similar magnitude to that of the stockpiled coal so that there is no extra thermal resistance results from the cover mixture.