The effect of mineral matter and pyrolysis conditions on the gasification of Greek lignite by carbon dioxide

Coal specimens with different mineral matter contents were produced from Creek lignite using various acid treatment conditions. Ash content and chemical composition of mineral matter depended on the type of acid used and the sequence of treatment stages. Gasification rates of coals were investigated by thermogravimetric analysis in a carbon dioxide atmosphere in the temperature range 700-900 degrees C. The combined effects of inorganic constituents and carbonization conditions such as heating rate and final temperature were determined. Gasification rates of chars with high ash content were higher than those of similarly prepared char with low ash content, due to the presence of catalytically active inorganic constituents. An almost proportional increase of gasification rate with Mg concentration was found, but such correlation was not evident for Ca, Na and K, possibly due to the chemical form of these elements in the organic structure. Slow carbonization led to the production of chars with higher reaction rates than those of chars prepared by rapid carbonization. The gasification rate increased with the concentration of CO2 in the reaction gases. The effects of heating rate and CO2 concentration on char gasification rate were more pronounced for samples from untreated lignite than for those from acid-washed lignite. Copyright (C) 1996 Elsevier Science Ltd.