Calcium catalysed steam gasification of Yallourn brown coal

Steam gasification of calcium-loaded Yallourn coal has been carried out with a thermobalance. Calcium catalyst showed a high activity at ≈950K. Calcium hydroxide, carbonate, acetate, nitrate and chloride exhibited similar catalyst effectiveness. The gasification rate increased with increasing the calcium loading, and at a loading of 5 wt%, complete gasification was attained within 25 min at 973 K. Comparison of the uncatalysed and catalysed rates showed that calcium catalyst can lower the reaction temperature by 150K. The impregnation of calcium salt on devolatilized char in place of raw coal resulted in the formation of rather large catalyst particles, and their activity was low. High temperature X-ray diffraction analysis revealed that the interconversion between calcium carbonate and oxide takes place readily in the gasification temperature region. Calcium carbonate was the predominant species during the gasification at 923 K. Catalysis of calcium was discussed in terms of a carbonate-oxide cycle mechanism.