Abstract

During the underground coal gasification process, a large amount of heat will be released, causing the surrounding rock in the goaf to undergo a high-temperature baking process. Therefore, it is essential to study the pyrolysis characteristics and mechanism of rocks. In this paper, the red sandstone in Linyi city of China is taken as an example. According to the results of thermogravimetric analysis in argon and air, the thermokinetic parameters are calculated by non isothermal pyrolysis kinetic model, and the pyrolysis mechanism is analyzed. The results are as follows: in argon atmosphere, when the pyrolysis temperature is less than 500 °C, the DSC curve of sandstone has no obvious change; when the pyrolysis temperature is higher than 500 °C, the DSC curve reduce obviously, which is endothermic reaction; As the pyrolysis temperature increasing, the TG curve also decreases. In air atmosphere, the exothermic reaction occurs before 450 °C, and the endothermic reaction occurs after 450 °C; after 700 °C, the mineral absorbs oxygen and gains weight, and the TG curve increases obviously. During the pyrolysis of sandstone, a series of physicochemical reactions such as the escape of bound water and crystal water (200 °C), the escape of structural water and quartz phase transition (600 °C), the decomposition of cement (800 °C), and the melting of minerals (1100 °C). When sandstone is pyrolyzed in air, a large number of oxidation reactions will take place in the clay minerals, causing the sample mass, activation energy (E) and frequency factor (A) of sandstone being larger than that of sandstone pyrolyzed in argon. And the higher the heat treatment temperature, the greater the E and A.

Article highlights

1. 1.

   The sandstone is pyrolysis in argon atmosphere and the endothermic reaction occurs after 500 °C. In the air atmosphere, the exothermic reaction occurs before 450 °C and the endothermic reaction occurs after 450 °C.

2. 2.

   During the pyrolysis process of sandstone, the escape of structural water and quartz phase transition (600 °C) and the decomposition of cement (800 °C) need higher E.

3. 3.

   The occurrence of oxidation reaction and the increase of heat treatment temperature will make E and A increase.