Catalytic effects of Na and Ca from inexpensive materials on in-situ steam gasification of char from rapid pyrolysis of low rank coal in a drop-tube reactor

Cost of catalysts is a crucial factor in realizing coal catalytic gasification process. In this study, inexpensive raw materials, soda ash (Na2CO3) and slaked lime (Ca(OH)(2)), were selected as catalyst precursors, and Na-, Ca- and Ca/Na-loaded coals were prepared by an ion-exchange procedure using a sub-bituminous coal (Adaro coal, Indonesia). These coal samples were rapidly pyrolyzed and in-situ gasified in an atmospheric drop-tube reactor (DTR) at 850-1000 degrees C under a steam partial pressure of 0.05 MPa. The Na and Ca catalysts showed remarkable activity for gasification, and the Ca/Na-loaded coal exhibited the highest reactivity among the coal samples prepared. The char yield of the Ca/Na-loaded coal at 1000 degrees C was as low as 17.6 mol-C per 100 mol-C of coal, and more than 70% (on carbon basis) of its primary char was gasified within 3 s. At 900 degrees C, the coal with Ca-loading of 3.2 wt.% showed catalytic activity higher than the coal with Ca-loading of 0.52 wt.%. At 950 and 1000 degrees C, however, the coal with the lower Ca-loading showed higher activity. The XRD analysis suggested that the Ca catalyst with the lower loading was more resistant to coarsening along with the progress of char gasification. (C) 2013 Elsevier B.V. All rights reserved.