Influence Mechanism of Acidic Mineral Components on the Reaction Behavior of Ion-Exchangeable Calcium during Coal Pyrolysis
Inherent minerals significantly influence the thermal conversion of coal, yet the interaction mechanisms among minerals affecting tar generation during pyrolysis remain unclear. This study investigates the effect of acidic mineral components on the behavior of ion-exchangeable Ca2+ during coal pyrolysis. Coal samples were prepared via HCl and HCl-HF acid washing followed by Ca2+ ion exchange. Pyrolysis was conducted in a fixed-bed reactor. Acid washing effectively reduced ash content but also decreased organic element contents (carbon, hydrogen). Loading ion-exchangeable calcium enhanced the thermal weight loss rate in the 500–550 °C range, shifting the peak temperature from 530 °C to 514 °C. At a final pyrolysis temperature of 600 °C with slow heating, kaolinite in acidic minerals underwent dehydroxylation to form metakaolin. The content of small aromatic rings (<6 rings) in char from Ca-loaded coal was lower than that from acid-washed coal without Ca. Coexistence of acidic minerals with ion-exchangeable Ca increased aliphatic hydrocarbon content in tar: YL-HCl-Ca reached 21.98% versus 13.60% for YL-De-Ca. Acidic mineral components inhibit the adverse effect of ion-exchangeable Ca2+ on tar lightening. These findings provide insights into mineral interactions during pyrolysis, aiding in optimizing coal conversion processes for improved tar quality.