Study on the high-temperature corrosion mechanism of boiler steel 15CrMoG in ammonia-coal co-firing environment

In recent years, ammonia has been used primarily as a carbon-free, hydrogen-rich fuel for internal combustion engines, gas turbines, and various industrial applications. Ammonia-coal co-firing has garnered significant attention due to its potential to reduce CO2 2 emissions from coal-fired power stations. However, as a strong reducing agent, NH3 3 can potentially induce high-temperature corrosion in the water-wall of the boilers, a phenomenon that has not yet received attention. In this study, we conducted high-temperature corrosion experiments on 15CrMoG at various ammonia concentrations by simulating the gas-phase environment of the water-wall in subcritical and supercritical boilers, under conditions of ammonia-coal co-firing. The corrosion kinetic curves showed that the corrosion resistance of 15CrMoG progressively decreased as the ammonia concentration increased from 0 % to 40 %, resulting in an increase in corrosion weight gain per unit area from 6.68 mg/cm2 2 to 13.32 mg/cm2. 2 . Characterization through SEM-EDS and XRD analyses revealed a continuous increase in the depth of the corrosion layer from 46.92 mu m to 57.63 mu m in the presence of ammonia. Furthermore, the XRD results indicated a significant reduction in the diffraction peaks of Fe2O3, 2 O 3 , identifying the main components of the corrosion film as Fe2O3, 2 O 3 , Fe, Fe4N, 4 N, and (Cr, Fe)2O3. 2 O 3 . Thermodynamic calculation software was used to determine the high-temperature corrosion mechanism of NH3 3 in an ammonia-coal co-firing environment. Prolonged exposure to high concentrations of NH3 3 led to the destruction of the dense Fe2O3 2 O 3 oxide layer on the alloy's surface. This corrosion process transitioned from Fe2O3 2 O 3 to Fe3O4, 3 O 4 , then to FeO, and ultimately to Fe. Generally, the primary cause of high-temperature corrosion in the water-wall was the intensified destruction of the dense oxide film, driven by a rise in ammonia concentration.