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 fr om Creek lignite using various acid treatment conditions. Ash content and chemical composition of mineral matter depended on the type of aci d used and the sequence of treatment stages. Gasification rates of coa ls were investigated by thermogravimetric analysis in a carbon dioxide atmosphere in the temperature range 700-900 degrees C. The combined e ffects 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 pr epared char with low ash content, due to the presence of catalytically active inorganic constituents. An almost proportional increase of gas ification rate with Mg concentration was found, but such correlation w as 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 pr epared by rapid carbonization. The gasification rate increased with th e concentration of CO2 in the reaction gases. The effects of heating r ate and CO2 concentration on char gasification rate were more pronounc ed for samples from untreated lignite than for those from acid-washed lignite. Copyright (C) 1996 Elsevier Science Ltd.