Volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasitication of Victorian brown coal. Part VI. Further investigation into the effects of volatile-char interactions

The purpose of this study is to further investigate the effects of volatile-char interactions on the volatilisation and dispersion of alkali and alkaline metallic species and changes in char structure during pyrolysis. Ion-exchanged (H-form, Na-form and Ca-form) Loy Yang brown coal samples were pyrolysed in a novel two-stage fluidised-bed/fixed-bed reactor over a wide temperature range of 500-930 degreesC. Our results indicate that soot formation and destruction on char (pore) surface during volatile-char interactions could be catalysed by Na and, to a lesser extent. Ca on char. Volatile-char interactions caused additional volatilisation of Na at temperatures higher than 700 degreesC although there are no effects on the volatilisation of Ca. The formation and simultaneous (catalytic) destruction of soot on char surface are closely linked to the volatilisation of Na from the char. Volatile-char interactions have also caused changes in char structure and/or changes in Na/Ca dispersion, as is reflected by the reduction in char reactivity. These results indicate that the volatile-char interactions are not limited on the char surface. It appears that H radicals must have penetrated into the char structure during volatile-char interactions. (C) 2004 Elsevier Ltd. All rights reserved.