The key causes and characteristics of spontaneous combustion of coal seams affected by igneous intrusion

Abstract

In order to find out the key causes of changes in spontaneous combustion characteristics of igneous intrusive coal seams, this paper took the Daxing Coal Mine in Tiefa Coalfield as example for analysis, which was widely invaded by igneous and had serious coal spontaneous combustion disasters.Metamorphic coal and unaffected primary coal were collected from the study area.Specifically, this paper studied the patterns of heat production and temperature rise, gas production rules, and microscopic structure parameters of coal samples by synchronous thermal analyzer and coal spontaneous combustion characteristic measuring device.The experimental results show that the igneous intrusion caused the mutation in the spontaneous combustion characteristics of the coal.Compared with the primary coal, there was significantly higher oxidation heat release of the metamorphic coal at the low temperature stage.Also, the crossing point temperature of metamorphic coal was reduced by 13.2 ℃, and it entered the stage of oxidation and weight gain earlier than the primary coal.When the environment temperature exceeded 90 ℃, the oxidation heat generation and reaction rate of metamorphic coal increased rapidly, which showed higher oxygen consumption rate and faster generation rate of oxidative gas products such as CO and CO2.This demonstrated higher oxidation activity of metamorphic coal than that of primary coal.The analytic results of physicochemical microstructure showed that the high temperature and pressure of igneous intrusion changed the pore structure of coal, which reduced the pore volume and specific surface area of micropores/mesopores in metamorphic coal, and the pore volume of macropores was three times higher than that of primary coal.The average pore size and porosity increased significantly, which was conducive to the transport, migration and adsorption reaction of oxygen molecules in the coal structure.At the same time, igneous intrusion reduced the oxygen-containing functional groups of metamorphic coal, and the content of aliphatic hydrocarbons with higher activity increased from 27.98 % to 29.07 %, which enhanced the oxidative activity of metamorphic coal.Moreover, igneous intrusion caused problems such as increased air leakage, long oxidation time of left coal, and wide oxidation zone during the mining, eventually leading to severe coal spontaneous combustion disasters.

Keywords

• igneous intrusion
• spontaneous combustion of coal
• generated heat
• key causes
• physicochemical structure