Effect of coal ash on the performance of alloys in simulated oxy-fuel environments

Oxy-fuel combustion can increase efficiency and reduce pollution from coal power plants. To study material performance in an oxy-fuel environment, both Fe- and Ni-based alloys were exposed to simulated oxy-fuel environments at 750 degrees C for long terms up to 6300 h. The effects of ash and gas compositions (SO2, CO2, H2O and O-2) on the performance of alloys were studied. Results from these tests are used to address the role of CO2, steam, and ash in the long-term corrosion performance of alloys. Detailed results are presented on weight change, scale thickness, internal penetration, microstructural characteristics of corrosion products, and cracking of scales for the alloys. Oxide scales were studied by synchrotron nano-beam X-ray diffraction. An incubation period and a propagation period were observed for ash corrosion. Before incubation time, alloys gain weight. After incubation time, localized corrosion damages the protective scales, alloys lose weight and corrosion rates dramatically increase. Since the incubation time can be over 4000 h, long-term test results are more helpful in evaluating the alloy performance in an oxy-fuel combustion environment with ash than the results from a short-term test. The mechanism of ash corrosion is also discussed. (C) 2013 Elsevier Ltd. All rights reserved.