Exothermic characteristics of coal during low-temperature oxidation based on grey correlation method

This study investigated the exothermic characteristics of coal during its low-temperature oxidation and determined the main factors affecting the exothermic intensity of the oxidation process. Four coal samples with different degrees of coalification were prepared to study the variation in the exothermic heat of oxidation at temperatures ranging from 25 to 70 °C through constant-temperature coal oxidation experiments. A grey correlation analysis was conducted including the volatile matter, moisture, sulphur content, ash, oxygen concentration, temperature, and exothermic intensity associated with the oxidation of coal. The results showed that the oxygen consumption rate, CO release rate, and CO2 release rate of the coal increased exponentially with the increase in the temperature; under the same oxygen concentration and temperature, the above factors were found to be directly proportional to the volatile content of the coal and negatively correlated with the degree of coalification. At constant temperature, the oxidation heat release intensity of the coal was directly proportional to the oxygen concentration; under a constant oxygen concentration, the oxidation heat release intensity of the coal increased exponentially with the increase in the temperature. The relationship between the oxidation heat release intensity of coal, volatile matter, moisture, sulphur content, ash, oxygen concentration, temperature, and oxygen concentration in the temperature range of 25–70 °C was deduced using the grey correlation analysis method. The grey correlations between the volatile matter, moisture, sulphur content, ash, oxygen concentration, and temperature were 0.8349, 0.6206, 0.6555, 0.7645, 0.7477, and 0.5649, respectively. The differences in the intensity of the oxidative exothermic effect of coals with different degrees of coalification were mainly influenced by the volatile content, and the intensity of the oxidative exothermic effect of the same coal was mainly influenced by the oxygen concentration.