Experimental study on the influence of CO2 injection on coal spontaneous combustion characteristics and molecular functional groups

Abstract

The study aims to investigate changes in the spontaneous combustion characteristics of coal and its microscopic reaction mechanisms in a CO₂ atmosphere. Programmed heating experiments and thermogravimetric analysis were conducted to examine index gas and combustion parameters in both air and CO₂ atmospheres. Molecular functional group changes were analyzed via in situ infrared experiments, and their correlation with index gases was assessed using the grey correlation method. The results revealed that CO₂ injection during the initial heating stage increased the production of CO, CH₄, and C₂H₄. However, beyond 160 °C, CO₂ effectively reduced the oxidation activity of functional groups and significantly inhibited the production of indicator gas. The characteristic temperature range of coal samples exhibited a 'lag' phenomenon under the influence of CO₂, resulting in a prolonged combustion stage with reduced mass loss and heat discharge. Following CO₂ injection, the -OH concentration significantly decreased, while C=O gradually increased. Additionally, the concentrations of -COOH, aliphatic hydrocarbons, and aromatic hydrocarbons initially increased with rising temperature and then declined. The contribution of these groups to gas generation followed the sequence of oxygen-containing functional groups > aliphatic hydrocarbons > -OH > aromatic hydrocarbons.