Influence of Ashing Temperature on Predicting Slagging Characteristics of Xinjiang High-Sodium Low-Rank Coal and Strategy of Using Mineral Additives as Potential Slagging Preventatives.

ABSTRACT

It is crucial to accurately evaluate the slagging characteristics of coal before industrial application. However, when evaluating the Xinjiang high-sodium low-rank coal (XJc) according to the properties of the ash prepared at 815 °C, the ashing temperature of the coal sample specified by Chinese standards, forecasting failures are frequent. To figure out the internal reason, the influence of ashing temperature on predicting slagging characteristics of XJc was investigated via an ashing test and thermodynamic equilibrium calculation. Experimental results show that when XJc is ashed at 815 °C, the ash yield apparently reduces compared to the case when ashed at 500 °C since numerous volatile components are released. The release of these components contributes to an obvious inhibition in the formation of the liquid phase in the residual ash, especially at temperatures below 1200 °C. Hence, reducing the ashing temperature is conducive to the acquirement of more real ash compositions of XJc and thereby to the accurate prediction of the slagging behaviors. By a comparison with reported experimental results, it is found that the liquid ratio-temperature curve calculated from the ash compositions of the ash prepared at 500 °C basically reflects the actual slagging tendency of XJc. According to the evolution of minerals with temperature, two slagging mechanisms, self-fusion of sodium-bearing salts and low-temperature eutectics, are confirmed. In addition, effects of antislagging measures of adding refractory oxides greatly differ among coal types due to the diversity in ash compositions.