Effects of Chlorine in Ash on the Corrosion Performance of Ni-Based Alloys in a Simulated Oxy-Fuel Environment

Alloy materials can be severely degraded by corrosive gases and coal ash in service of coal power plants at high temperature. To better understand alloy corrosion in coal power plants, it is necessary to study the effect of each constituent from coal combustion on alloy corrosion. Chlorine-containing compounds in coal are corrosion-accelerating agents. The concentration of chlorine increases a lot in the gas environment of oxy-fuel combustion due to the absence of airborne nitrogen gas acting as a diluent. The role of chlorine in ash corrosion is investigated in simulated oxy-fuel environments. Long time tests over 3000 h were performed on various alloys at 750 degrees C. The degradation depth, weight change, and microstructural characteristics of oxide scales on Ni-based alloys are reported after exposure at 750 degrees C in an oxy-fuel combustion environment for over 3000 h. Synchrotron nanobeam X-ray analysis was performed to evaluate the phase and chemical composition of the oxide layers on the alloy surface. Nanobeam X-ray and SEM analyses indicate that chlorine can modify the diffusion mechanism near the alloy surface and, thereby, increase the corrosion rate.