Sulfation Propensity of Coal Ashes and Instability of Calcium and Magnesium Sulfates at High Temperatures

摘要

It is clearly recognized that the sulfation mechanism results from the transport of electrons from n-type conductivity oxides (rich in electrons) to physically adsorbed SO{sub}2 and O{sub}2 Oxides rich in electron holes such as oxides with p-type conductivity reduce sulfate stability. Both types of conductivities may be modified by impurities which may either promote or demote the sulfation propensities. The mechanism of sulfation and sulfate decomposition is analyzed on two oxides derived from coal ashes such as CaO and MgO. Monovalent impurities such as sodium and potassium decrease electron hole concentration in CaO and enhance limestone sulfation. Trivalent impurities such as iron and aluminum introduce cation vacancies that increase ionic mass transport in CaO.