Occurrence and Transformation Characteristics of Recoverable Soluble Sodium in High Alkali, High Carbon Fly Ash during Zhundong Coal Gasification in a Circulating Fluidized Bed

In this reported study, the effects of bed temperature, air equivalence ratio (ER), heating surface wall temperature, and coal type on the occurrence and transformation of recoverable soluble Na in high alkali, high carbon fly ash during Zhundong (ZD) coal gasification were investigated in a 0.4 t/d circulating fluidized bed test system. The experimental results illustrated that the quantity of soluble Na in gasification fly ash of ZD coal was far greater than in the ZD coal. Na compounds in ZD coal gasification fly ash were present mainly as NaCl, with other compounds such as Na2SO4 and sodium aluminosilicates, including Na2SiO3 and NaAlSi3O8. The recoverable soluble Na accounted for 56-96.9% of the total Na in the ZD coal gasification fly ash. The proportion of soluble Na in ZD coal gasification fly ash was greatly affected by the gasification conditions. As the bed temperature was increased, the proportion of soluble Na decreased. As the ER was increased, the proportion of soluble Na increased, with the maximum proportion present at an ER of 0.50. Compared to the adiabatic condition, cooling of the heating surface increased the proportion of soluble Na. The soluble Na yield and the proportion of soluble Na were found to be high during gasification of Shaerhu (SEH) and Tianchi (TC) coals, which made them more suitable for recovery of soluble Na from their corresponding fly ashes: Shaerhu fly ash (SEHf) and Tianchi fly ash (TCf).