Catalytic steam gasification of coal char with alkali carbonates: A study on their synergic effects with calcium hydroxide

The order of catalytic activity of three alkali carbonates (Li2CO3, Na2CO3, and K2CO3) towards the steam gasification of coal char varies depending on the presence and absence of the acidic mineral species and their enrichment in coal. In the gasification of an ash-rich coal char, Li2CO3 exhibits the severest catalytic deactivation among three alkali carbonates, whereas Na2CO3 is the most resistant to the deactivation. The impregnation of Ca(OH)2 to the ash-rich coal substantially increases the rate of char gasification for all three alkali carbonates as a consequence of the inhibited catalytic deactivation. In the gasification of an ash-free coal char, however, only the binary K2CO3/Ca(OH)2 catalyst shows a synergic effect on promoting the gasification rate, whereas the Li2CO3/Ca(OH)2 catalyst and the Na2CO3/Ca(OH)2 catalyst have a worse catalytic activity than their respective alkali carbonates alone. The mechanisms of the concerted effects between alkali carbonates and Ca(OH)2 on the gasification of the ash-rich char and the ash-free char are discussed.