Influence of inherent minerals on CO₂ gasification of a lignite with high ash content

Lignite samples with different ash contents and mineral composition were prepared by dry separation and acid washing. A drop tube reactor and thermogravimetric analyzer were used to study effect of inherent minerals on CO₂ gasification reaction of lignite at 1 000-1 200 ℃. The results show that the inherent minerals have positive effects on gasification, which are temperature sensitive. At lower gasification temperature (1 000 ℃) the inherent minerals can improve carbon conversion indirectly by obstructing the carbon structure order of nascent char. At higher temperatures (1 100-1 200 ℃)the inherent minerals can improve carbon conversion by catalyzing nascent char gasification directly. The alkaline index is not suitable for characterizing role of the inherent minerals of lignite in this case. Ca leads to the difference in catalytic activity of the inherent minerals where the most active form is carboxylate. Various catalytic mechanisms are the root cause of different catalytic activity of Ca in different chemical forms. Ca in the form of carboxylate can reduce the activation energy of coal/char gasification reaction, while CaO only promotes the apparent frequency factor.