Application of aging effect model in numerical simulation for predicting spontaneous combustion of coal stockpiles.

The conventional Arrhenius equation that estimates the heat generation of coal in numerical simulation has been widely applied. However, the aging effect markedly influences the exothermic behavior of coal at low temperature and cannot be achieved using the conventional Arrhenius equation. In this paper, an improved wire-mesh basket test was performed to measure the temperature and concentrations of CO and CO2 emitted from coal piles. The aging effect model based on the theory of equivalent oxidation exposure time successfully matched the experimental results. Then, a two-dimensional (2D) multifield coupling model of coal stockpiles was developed considering the aging effect to investigate the developments on values and moving paths of temperature and O2 concentration. Effects of decay-power factor, which determines the diminishing coal oxidation, and other main variables on spontaneous combustion of coal stockpiles were systematically investigated. The results indicated a unique critical value of 1.25 × 10–6 s−1 for decay-power factor. Increasing decay-power factor enlarged the safe storage time and hardly affected the moving paths of the hotspot. There are two critical values for particle size (0.7 mm, 9 mm) and porosity (0.18, 0.58), and one critical value for wind velocity (8.5 m s−1) and stockpile width (9 m). Porosity and stockpile width have significant effects on the self-ignition of coal stockpiles when their values are lower than the base ones (0.33 and 15 m). The model considering aging effect is expected to reliably predict the spontaneous combustion of coal stockpile and become the tool for inspecting the reasonability of the relative preventing measures. [ABSTRACT FROM AUTHOR]