Alloy selection for sulfidation-oxidation resistance in coal gasification environments

A series of iron-nickel-chromium and nickel-chromium alloys were studied for their combined sulfidation-oxidation resistance in simulated coal gasification environments. All alloys contained a minimum of 20 wt pct chromium, and titanium and aluminum in the range 0 to 4 wt pct. Corrosion resistance was evaluated at 1255 K (1800 °F) in both high BTU and low BTU coal gasification atmospheres with 1 vol pct H2S. Titanium at levels greater than 1 wt pct imparted significant sulfidation resistance due to an adherent, solid solution chromium-titanium oxide layer which prevented sulfur penetration. A luminum was less effective in preventing sulfidation since surface scales were not adherent. Of the commercial alloys tested, Nimonic 81, Pyromet 31, IN801, and IN825 exhibited the best overall corrosion resistance. However, further alloy development, tailored to produce solid solution chromiumtitanium oxide scales, may lead to alloys with greater sulfidation-oxidation resistance than those investigated here.