RELEASE OF INORGANIC MATERIAL DURING COAL DEVOLATILIZATION

Experimental results presented in this paper indicate that coal devola tilization products convectively remove a fraction of the nonvolatile components of inorganic material atomically dispersed in the coal matr ix. Results from three facilities burning six different coals illustra te this mechanism of ash transformation and release from coal particle s. Titanium is chosen to illustrate this type of mass release from coa l particles on the basis of its low volatility and mode of occurrence in the coal. During moderate rates of devolatilization (10(4) K/s heat ing rate), no significant loss of titanium is noted. At more rapid rat es of heating/devolatilization (10(5) K/s) a consistent but minor (3%- 4%) loss of titanium is noted. During rapid devolatilization (5 x 10(5 ) K/s and higher), significant (10%-20%) amounts of titanium leave the coal. The loss of titanium monitored in coals ranging in rank from su bbituminous to high-volatile bituminous coals and under conditions typ ical of pulverized-coal combustion. The amount of titanium lost during devolatilization exhibits a complex rank dependence. These results im ply that other atomically dispersed material (alkali and alkaline eart h elements) may undergo similar mechanisms of transformation and relea se. Copyright (C) 1997 by The Combustion Institute.