Cyclone reburning retrofit-corrosion evaluation

Reduction of oxides of nitrogen (NO{sub x}) from cyclone-equipped boilers is best accomplished by the application of reburning technology. Reburning process involves injection of a supplementary fuel above the cyclone to create a reducing zone for NO{sub x} removal. Overfire air is introduced above this zone to achieve complete combustion. Since the reburning zone must operate substoichiometrically, tube corrosion due to H{sub 2}S formation within the modified combustion zones can be a potential concern when the reburning fuel is a high-sulfur coal. H{sub 2}S is a corrosive gas and its concentration is an indicator of the tendency for fireside corrosion in fuel-rich combustion systems. This research program was undertaken to assess corrosion resistance of three commercially available alloys (carbon steel, SA210-A1; low-alloy steel, SA213-T22; and stainless steel, SA213-TP304) as well as coated steel alloy (SA213-T2). The surface chromium contents of the alloys ranged from 0 to 30%. Four air-cooled corrosion probes, each containing segments of the selected alloys were constructed. The probes were exposed for up to 1200 hours and at a metal temperature of 850{degrees}F to combustion gases generated by firing a high-sulfur Illinois {number sign}6 coal at conditions simulating coal reburning.