Prediction and Mitigation of H₂S-Induced High-Temperature Corrosion in a 660 MW Boiler Water-Wall

The high-temperature corrosion (HTC) caused by H₂S poses a critical threat to the water-wall of unity boilers. To address this challenge, the present work develops a predictive corrosion depth model that integrates two critical determinants: the local concentration of H₂S and the temperature of the water-wall metal. The proposed methodology is applied to evaluate HTC risks under three distinct thermal loads: boiler maximum continuous rating (BMCR), 75% turbine heat acceptance (THA) and 50% THA. Furthermore, the protective effect of near-wall air (NWA) ratio injection using recirculated flue gas (RFG) was numerically investigated, to quantify their influence on both HTC mitigation and in-furnace combustion characteristics. Key findings indicate that at BMCR load, elevated sidewall temperatures combined with H₂S enrichment produce a peak corrosion depth of 33.7 μm. At 50% THA, the peak H₂S concentration drops sharply to 150 ppm, and the corresponding corrosion depth falls to only 7 μm. Consequently, it is recommended that NWA protection measures be implemented whenever the boiler load exceeds 50% THA. Even at a 7% NWA ratio, the impact on the furnace temperature field remains negligible. Meanwhile, it significantly reduces the corroded area and halves the peak corrosion depth, confirming that RFG-based NWA offers a flexible and effective engineering solution for mitigating HTC in coal-fired utility boilers.