Effect of oxy-firing on corrosion rates at 600°-800°C

Using oxygen, rather than air, in coal-fired boilers is a leading strategy to reduce NOx emissions and concentrate CO₂ for capture. However, with flue gas recirculation, higher levels of CO₂ and possibly H ₂O and SO₂ are expected and there is concern that higher corrosion rates may occur. Using synthetic coal ash, the behavior of a range of ferritic, austenitic and Ni-base alloys has been investigated from 600°-800°C to cover current to advanced ultrasupercritical boiler conditions. Both commercial and model alloys indicate that the worst-case oxy-firing condition is not significantly different than air-firing using the same synthetic ash. The oxide thickness measurements focused on the highest alloyed materials. For these materials, there was not a major increase in the amount of reaction product at 700°C. The results from the binary Fe-Cr alloys indicated that 30%Cr is protective over this temperature range.