Fundamental evolution characteristics of alkali metal compounds in coal combustion

In combined cycle power generation systems for coal combustion and/or gasif ication, the vapor of alkali metal compounds may cause hot corrosion at the surface of blades of a gas turbine. The influence of coal type on fundamen tal evolution characteristics of alkali metal compounds, especially sodium compounds, in coal combustion is experimentally elucidated in this study by using a rapidly heated electrical batch combustor. Both classification of forms of sodium compounds and analysis of the cross-correlation coefficient s between the existing locations of sodium and other elements in the cross- section of a particle of raw coal by using an EDX (Energy Dispersive X-ray) system and an image correlation method are conducted in order to quantify the effect of coal type on the sodium evolution characteristics. As a result, the evolution characteristics of sodium are influenced by the coal type. Most of the sodium evolved is classified as mater-soluble sodium . Coal in which sodium chloride is contained as a major sodium compound evo lves sodium compounds more easily than other coals do. The distributions of sodium, silicon and aluminum in a coal particle contribute to the evolutio n characteristics of sodium. Coals with high cross-correlation coefficients between sodium and silicon/aluminum show low evolution fraction of sodium.