Structural ordering in high temperature coal chars and the effect on reactivity

This study has been undertaken to determine the extent of structural orderi ng and thermal deactivation which can occur when coal chars are heated to h igh temperatures. The chars have been prepared using the captive-sample wir e-mesh reactor at temperatures up to 2200 degrees C at very short hold time s (500 ms), and the microstructures have been examined using high-resolutio n transmission electron microscopy (HRTEM). The char structures have been c ompared to those of natural graphites. Regions within the chars have been o bserved to show a similar degree of ordering to that present in the graphit es. The reactivities for oxidation of the high temperature chars and graphi tes have been determined by TGA methods and compared to the reactivity of c hars prepared at lower temperatures. The structural ordering and reactivity data indicates that thermal deactivation may account for the low reactivit y of a proportion of the char present in utility boiler fly ash. (C) 1999 E lsevier Science Ltd. All rights reserved.