Effects of coal blending on transformation of alkali and alkaline-earth metals and iron during oxy-fuel co-combustion of Zhundong coal and high-Si/Al coal

Abstract

Zhundong high-alkali coal has been studied a lot owing to its abundant reserve but serious ash-related issues. Oxy-fuel combustion profits the reduction of pollutant emissions and coal blending alleviates the ash-related problems practically. Nevertheless, little work if any has been carried out on oxy-fuel co-combustion of Zhundong coal, while the influences of blending on the migration of iron and alkali alkaline-earth metals have yet to be adequately understood. This study aims to illuminate the release and migration behaviors of alkali alkaline-earth metals, iron and aluminum in oxy-fuel co-combustion via a lab-scale experimental system. Experimental results showed that the yield, color, bulk, and composition of ash were greatly temperature-dependent and significantly affected by the blending ratio in oxy-fuel co-combustion. As the blending ratio was 50%, the transformation and release features of iron, sodium and calcium in the blend with combustion temperature were close to those of non-Zhundong coal. The blending of Lingxin coal into Zhundong coal could benefit the transformation from NH4Ac-soluble calcium to H2O-soluble form, and facilitate the transformation of HCl-soluble aluminum and iron to insoluble form. The occurrence modes of elements and the ash yield of individual coal both exerted profound impacts on the element release ratio and chemical forms within ash of the blends. The present research has potential to offer an improved knowledge on the functional mechanisms of alkali alkaline-earth metals, aluminum, and iron on ash-related issues during high-alkali coal oxy-fuel co-combustion.