Speciation and Distribution of Sodium during Zhundong Coal Gasification in a Circulating Fluidized Bed

摘要

The speciation and transformation of sodium during Zhundong coal circulating fluidized bed gasification were investigated. Sodium speciation was investigated by chemical fractionation analysis using inductively coupled plasma atomic emission spectroscopy. X-ray powder diffraction was employed to analyze crystalline compounds in the ashes. H2O-soluble sodium is the predominant occurrence, accounting for 55-95% of total sodium. Insoluble potassium is the predominant occurrence, and the total content of potassium is relatively low, approximately one-tenth of sodium in Zhundong coals. The temperature and coal type are both important influencing factors on the volatilization of sodium during Zhundong coal gasification. Sodium in. Shenhua coal ashes evidently decreases with the increase of the temperature, whereas it increases in Shaerhu coal and Tianchi coal (TC) ashes. The occurrence of sodium in the fly ash is. different remarkably with that in the bottom ash. In the fly ash of gasification, sodium exists mainly as H2O- and NH4Ac-soluble and as HCl-soluble and insoluble chemical form in the bottom ash. Sodium aluminum silicate and sodium silicate were formed during the gasification process. The formation of sodium silicate leads:to slagging and defluidization during the gasification of TC.