Influence of sodium-based materials on the slagging characteristics of Zhundong coal

Zhundong coal from the Zhundong coalfield in in Xinjiang, China, is charactered by high content of Na. Na-related slagging of Zhundong coal is unclear. The aim of this study is to determine the influence of Na-based materials on the slagging characteristics of the coal. The raw coal was prepared by first removing Na by chemical extraction and subsequently impregnating it with the Na-based materials, such as NaCl, Na2SO4 and NaAc. Laboratory slagging experiments in a muffle furnace were conducted using the mixtures of prepared Zhundong coal and quartz sand. It was found that the Na-based materials affected the slagging behavior of the coal in the order NaAc/Na2SO4 > NaCl. For the mixtures with the NaCl additive, fusion was most noticeable at 900 °C. However, for the mixtures soaked with Na2SO4 and NaAc, a monotonically increasing relationship was indicated between the degree of slagging and the temperature. Adding the Na-based materials to the coal resulted in increased Na content in the residual ash, especially in the instances with Na2SO4 and NaAc additives. The formation of silicates, which were ascribed to the reactions between the Na-based materials and the SiO2, was the primary cause of slagging. Various mineral elements, especially Fe, were captured by Na2O, derived from the decomposition of Na2SO4 or the combustion of NaAc, to exist in the form of a low-melting temperature eutectic. Additionally, the presence of Fe, Ca, K, and Mg in the ash aggravated slagging under the influence of Na2O.