AN UNEXPECTED TREND IN THE COMBUSTION BEHAVIOR OF HVBB COALS AS SHOWNBY THE STUDY OF THEIR CHARS

This study is an attempt to find useful relationships between the petr ographic characteristics of coals and their efficiencies during pulver ized fuel combustion through the study of their pyrolysis chars, Speci fically, the effects of coal rank have been investigated using a serie s of vitrinite-rich coals ranging from subbituminous to low volatile b ituminous coal. The behavior of these coals during combustion at 500 a nd 1100 degrees C and the petrographic characteristics of their pyroly sis chars (1000 degrees C) were investigated. In a foregoing paper (Bo rrego et al.(10)), unexpectedly poor combustion performances were foun d for some hvBb coals, which were attributed to rank rather than macer al effect. A general pattern of variation of coal burnout with rank wa s found in this study, providing additional data in which those unexpe cted results could be fitted. The observed trend was explained in term s of the changes undergone by coal both during coalification and pyrol ysis, which make the number and accessibility of active sites vary in opposite directions, thus leading to a nonuniform variation of coal co mbustion efficiency with rank.