Effect of Kaolin Addition on Combustion Behavior of Zhundong Coal Pellet Using Flame Emission Spectroscopy

Kaolin, as an adsorbent, has been proven to be effective in inhibiting sodium release during high alkali coal combustion thereby alleviating severe slagging and fouling problems. Understanding the co-firing behavior of Zhundong coal with kaolin additives is essential for Zhundong coal utilization. In this study, the effect of kaolin additive on the combustion behavior of two Zhundong coals with different Na contents was investigated based on image analysis and flame emission spectroscopy (FES) method. Spectral and image results were able to distinguish the three stages of coal combustion. The addition of kaolin impacted all combustion stages for both types of coal. The results show the volatile combustion time of the blended coal sample was shortened, while the char burnout time was prolonged, which was attributed to the ash suppression effect. The two coals presented similar decrease trends with different blending ratios in terms of sodium concentration, pellet surface temperature, and thermal radiation. However, the changes were no longer evident after the blending ratio reached 8% and 12%. The replacement of combustible components in the coal by the kaolin altered the mineral fraction of the ash and thus affected the heat and mass transfer. Combining the online measurement results and the analysis of the ash fusion characteristics, the suggested addition of kaolin was 8% and 12% respectively.