Mineral matter in coal and the thermal performance of large boilers

Abstract

The slagging gasifier is one of the best options for coal utilization to achieve carbon neutral due to high carbon conversion and low contaminative gas emission. The slagging gasifier requires proper ash fusibility to ensure smooth slag tapping, but the knowledge concerning fusion behaviors of coal ash with high sulfur and basic oxides level is unclear, which results in the limited utilization of coal which contains high level of sulfur and alkali in ash. Here, the fusion behaviors of coal ash with high sulfur and basic oxide level with/without additives are characterized by ash fusion temperature (AFT) analyzer and thermal mechanical analysis (TMA), and the underlying mechanism is revealed by combination of thermogravimetry (TG), X-ray diffractometer (XRD), and thermodynamic calculation. The results demonstrate that standard ashing procedure impacts the transformation of minerals of coal ash with high sulfur and basic oxide level. The influence of volatiles discharging during standard ash preparation on the shrinkage curve depends on the liquid phase sintering behavior. Besides, the performance of additives connects the ability of additives to volatiles retention. Specifically, accumulation of sulfates by additives leads to the AFTs of Neimeng coal ash increase with increasing additives in the range of 0 to 20%, while the retention of Na-containing minerals by kaolinite gives rise to the dropping AFTs of Wucaiwan coal ash. The study can support the utilization of coal which contains high level of sulfur and alkali in coal ash in the slagging gasifier.