Transformation and migration of alkali metal with different occurrences of Zhundong high-alkali coal during gasification

Circulating fluidized bed (CFB) gasification,three-step extraction and X-ray diffraction ( XRD) were con- ducted on Tianchi Mulei coal (TC) from Zhundong coal mine to study the migration and transformation of alkali met- als,referring to Na and K,in different occurrences. The results indicate that most of sodium in TC is water-soluble, which mainly exists in the form of NaCl,Na2 SO4 and K3 Na(SO4 )2 determined by XRD,and potassium mainly exists in insoluble form. Alkali metal in the ammonium-acetate-soluble and water-soluble form is released easily to gas during gasification. Though lots of NaCl in TC is found,there is little NaCl in slag and fly ash through the analysis of fly ashes phase,indicating that this component has volatilized. The content of insoluble Na mostly residing in slag in the form of aluminosilicate,increases after the process,and the water-soluble Na in fly ash is dominant. Higher gasification temper- ature leads more Na in the water-soluble and acid-soluble form to volatilize and more insoluble Na to generate. Water- soluble and acid-soluble Na in gas condenses to fly ash with the temperatures of back pass gas decrease,which may cause the contamination of tail heating surface.