Alkali metal migration and slagging characteristic during Zhundong high-alkali coal gasification

The Tianchi Mulei high-alkali coal gasification in a circulating fluidized bed (CFB) was conducted to study the operating characteristic and the migration of alkali metals, and the phenomenon of bed particles agglomeration was examined by some analytical technologies. The results show that the water-soluble and ammonium-acetate-soluble Na is released into gas while the insoluble Na is mainly remained in semi-char, indicating that the transformation of alkali is different for different modes of occurrence. At higher gasification temperature, both of Na existed in slag and gas become more, while the Na in fly ash declines. The condensation rate of Na in gas phase is higher than that of K with the decreasing of down stream temperature. It seems that the degree of agglomeration increases with the increase of temperature, resulting in bed temperature fluctuation. The eutectic with strong viscosity, formed by a direct reaction between alkali and mineral component of ash or SiO₂ of bed material, is considered as the key factor leading to the agglomeration of particles.