[Objective] With the introduction of the "dual carbon" goals, biomass fuels have gained widespread attention due to their abundant supply and zero -carbon-emission characteristics, leading to the rapid development of direct biomass combustion and co -firing technologies in pulverized coal boilers. Unlike the sulfuric acid corrosion in traditional coal -fired boilers, the low -temperature heating surface corrosion of biomass boilers is mainly caused by deliquescent chlorides. It is primarily driven by deliquescent NH 4Cl and CaCl 2, which can absorb moisture from unsaturated vapor, thereby raising the corrosion temperature. Meanwhile, Cl - ions further promote corrosion, increasing the difficulty of material selection for low -temperature heating surfaces in biomass boilers. 

[Methods] In this study, NH 4Cl and CaCl 2 were used as representative deliquescent salts. Corrosion experiments under simulated flue gas conditions were conducted on three commonly used low -temperature heating surface materials—20G, ND steel, and Corten steel. The corrosion rate, micromorphology, and corrosion products were analyzed using the weight loss method combined with SEM, EDS, and XRD. To match th e temperature of the low -temperature heating surfaces in boilers, the experimental temperature ranged from 60 °C to 120 °C. 

[Results]The following conclusions were obtained: at different temperatures, the corrosion resistances of 20G, ND steel and Corten steel showed only minor differences. When loaded with deliquescent salts, the corrosion rate increased as the temperature decreased. Apart from that, for the loaded NH 4Cl, the corrosion 2 rebounded slightly above 100 °C due to the release of HCl from parti al decomposition. At all experimental temperatures, the corrosion rate of NH 4Cl was significantly higher than that of CaCl 2, and the difference between the two increased as the temperature decreased. 

[Conclusion] The deliquescence ability of salts does not fully correspond to their corrosiveness; instead, corrosiveness correlates strongly with the pH of the solution, and salts with lower pH values exhibit stronger corrosion ability. For example, the critical relative humidity of NH 4Cl is much higher than th at of CaCl2, yet the corrosion rate of NH 4Cl was consistently higher than that of CaCl 2 at all experimental temperatures, and the lower the temperature, the larger the difference in their corrosion rates. When the salt with strong deliquescence ability is mixed with the salt with weak deliquescence ability, the deliquescence ability will not be strengthened, but the corrosion ability of the mixture may be stronger than that of either individual salt. For example, NH4Cl was mixed with CaCl2 at 100 ℃. CaCl2 has a stronger deliquescence ability. This enhanced the corrosion ability of NH4Cl.