Burning high-chlorine illinois basin coals in utility boilers

摘要

Numerous electric utilitieshave decades of experience burning high-chlorine (Cl) Illinois Basin steam coals in a large variety of boiler equipment with no reported Cl-related fireside problems. Nevertheless, it is difficult for Illinois producers to market these coals to non-traditional users because of concerns regarding Cl-induced corrosion. Coal chlorine (C1) was originally associated with fireside fouling and corrosion problems (Raask, 1985) in pulversized coal (p.c.)-fired utility boilers in the United Kingdon (UK), and more recently in municipal waste-to-energy plants world-wide. The work of Krause et al. (1977, 1979) on co-firing coal and municipal waste clarified the role of coal sulfur and ash constituents in eliminating corrosion from chloride in the waste. While UK utility experience burning UK coals produced correlations of high-temperature corrosion with coal Cl content, mroe recent studies by Latham et al. (1991) and up to ten years of favorable experience with low-NO_x burners discount entirely the role of chlorine in croosion of furnace walls in the UK. Us experience burning domestic coals identified coal alkali and sulfuras the principal contributors to external corrosion of boiler furnace wall and superheater/reheater (SH/RH) tubes. Current evidence shows that the primary cause of rapid furnace wall corrosion in modern powre plants is por combustion of the coal, not coal Cl content. Poor combustion produces local areas with high heat flux, high CO levels, excessive slag deposits, and an aggressive sulfidizing environment. The cause of accelerated SH/RH corrosion is molten alkali-iron sulfate attack of SH/RH tubes at the interface between the tube an dthe fouling deposit.