THE EFFECT OF POTASSIUM ON THE FUSIBILITY OF COAL ASHES WITH HIGH-SILICA AND ALUMINA LEVELS

The poor repeatability and reproducibility of fusibility temperatures of the ashes with high (SiO2 + Al2O3) levels are well known. A study w as, therefore, made of such ashes using thermo-mechanical analysis (TM A) to indicate the shrinkage of samples progressively heated at the sa me rate as the test for standard ash fusibility temperatures (AFT). Th e results confirm that the extent and rate of change of shrinkage of t he samples with low K2O levels (< 1 wt.%) is low in regions of the def ormation temperature (DT), resulting in poor accuracy of its determina tion. It was found that DT is mainly related to substantial melting of minerals containing K2O (i.e. illite) in these ashes. The scanning el ectron microscope (SEM) analysis of quenched ash samples and thermodyn amic calculations were used to illustrate the effect of K2O in terms o f the extent of slag generation necessary for shrinkage. The TMA test is shown to provide a more sensitive alternative procedure for charact erizing the ash fusibility. (C) 1998 Elsevier Science Ltd. All rights reserved.