COAL ASH FUSION TEMPERATURES - NEW CHARACTERIZATION TECHNIQUES, AND IMPLICATIONS FOR SLAGGING AND FOULING

The well-documented shortcomings of the standard technique for estimat ing the fusion temperature of coal ash are its subjective nature and p oor accuracy. Alternative measurements based on the shrinkage and elec trical conductivity of heating samples are therefore examined with lab oratory ash prepared at about 800 degrees C in crucibles, as well as c ombustion ash sampled from power stations. Sensitive shrinkage measure ments indicate temperatures of rapid change which correspond to the fo rmation of liquid phases that can be identified on ternary phase diagr ams. The existence and extent of formation of these phases, as quantif ied by the magnitude of ''peaks'' in the test, provide alternative ash fusion temperatures. The peaks from laboratory ashes and correspondin g combustion ashes derived from the same coals show clear differences which may be related to the evaporation of potassium during combustion and the reactions of the mineral residues to form combustion ash. A p reliminary evaluation of data from nine power stations indicates that shrinkage measurements can provide an alternative approach to characte rizing slagging. (C) 1998 Elsevier Science Ltd. All rights reserved.