Prediction of correlation between ash fusion temperature of ASTM and Thermo-Mechanical Analysis

Abstract

Ash problems, such as slagging and fouling, are important because of their negative effect of reducing the heat transfer on the furnace wall and tube in pulverized coal boilers and decreasing the boiler safety. However, slagging has positive effect on gasifier. Slagging is protecting furnace wall and reducing heat loss in gasifier. Slagging and fouling are related to ash deposition, which is determined by the coal-ash fusion temperature, chemical composition of coal ash, and boiler operating conditions et al. The coal-ash fusion temperature is a particularly important factor in slagging and fouling. To measure the ash fusion temperature, the ASTM D1857 test is used, not only by thermal power plants and steelmaking companies in South Korea but all over the world. In this study, the fluid temperature (FT) of ASTM D1857 was predicted by Thermo-Mechanical Analysis (TMA). Three bituminous coals (Glencore, Trafigura, Moolarben) and four sub-bituminous coals (KPU, Berau, Jembayan, PRB) were selected for the TMA tests, wherein T25, T50, T75, and T90 were measured. These four temperatures corresponded to shrinkage levels of 25%, 50%, 75%, and 90%, respectively. The T90 of the bituminous coals and T50 of the sub-bituminous coals were similar to the initial deformation temperature (IDT) of ASTM. The T90 of the bituminous coals was greater than 1300°C, and the T90 of the sub-bituminous coals was ∼1250°C. Two FT-prediction equations—for bituminous coal and sub-bituminous coal—were established according to the T25, T50, T75, and T90 relationships of each coal. The FT-prediction equations indicated an average gap of 71°C in the sub-bituminous coals. For the sub-bituminous coals, the average difference was quite low: ∼23°C. The FT-prediction equations matched the FT of ASTM and are useful for determining the ash fusion temperature in a short time.