Combustion characteristics of low-rank coal chars in O₂/CO₂, O₂/N₂ and O₂/Ar by TGA

The combustion reactivity of two chars prepared from two low-rank coals in Northwest China were studied using a thermogravimetric analyzer (TGA). The effects of different atmospheres (O₂/CO₂, O₂/N₂ and O₂/Ar) and different oxygen concentrations on the combustion characteristics were investigated. The results indicate that both atmosphere and oxygen concentration show effectiveness on combustion of char. Compared with N₂ and Ar, CO₂ could significantly promote the reaction. When combustion atmosphere changes from O₂/CO₂ to O₂/Ar, the burnout temperature increases by 63.7 and 68.8℃ for the two chars respectively. Meanwhile, when the combustion atmosphere changes from O₂/CO₂ to O₂/N₂, that is 135.9 and 129.6℃, respectively. An increase in concentration of oxygen can also improve the combustion performance of chars in the test. At the same time, kinetic analysis of the combustion profiles of the chars reveals that both the apparent activation energy E and the pre-exponential factor A increased with increasing oxygen concentration and the compensation effect exists between activation energy E and pre-exponential factor A of chars' combustion.