During operation, hydrogen-rich gas boilers often face high-temperature corrosion issues on their heating surfaces caused by hydrogen combustion. The core mechanism lies in the direct reaction between the reducing atmosphere (such as H₂S and CO) generated by hydrogen combustion and the metal surface, with the strongest corrosiveness occurring in the 300℃ to 500℃ temperature range. This corrosion not only accelerates the thinning of the metal tube walls but can also lead to safety accidents such as tube rupture, seriously affecting the boiler's safety and economy. Therefore, a comprehensive approach is needed, encompassing material selection, combustion control, structural design, and surface protection, to construct a multi-layered anti-corrosion system.
Material selection is the foundation of corrosion prevention. The heating surface tubes must possess excellent high-temperature strength, oxidation resistance, and corrosion resistance. For heating surfaces operating below 500℃, low-carbon steel or low-alloy steel, such as 20G and 12CrMo, can be used due to their good processability and low cost. When the temperature rises above 550℃, alloy steel, such as 12Cr1MoV and SA-213TP347H austenitic stainless steel, must be used. These materials form a dense oxide film by adding elements such as chromium and molybdenum, which can effectively block corrosive media. For ultra-supercritical units, high-temperature nickel-chromium alloy steel is the preferred material for high-temperature heating surfaces due to its higher heat resistance.
Combustion control is crucial for corrosion prevention. Hydrogen combustion easily produces a localized reducing atmosphere, leading to an increase in H₂S concentration and thus exacerbating corrosion. Therefore, it is necessary to optimize burner design, adjust the air distribution ratio, and enhance airflow mixing within the furnace to ensure complete and uniform combustion. For example, staged combustion technology can be used to mix fuel and air in stages, reducing the flame center temperature, decreasing the generation of thermal nitrogen oxides, and suppressing the formation of a reducing atmosphere. In addition, adding side or wall-mounted airflow to form an oxide protective layer near the water-cooled wall can further mitigate high-temperature corrosion.
Structural design has a significant impact on corrosion resistance. Properly arranging the position of heated surfaces, ensuring that areas with high working fluid temperatures are avoided from the impact of high-temperature flue gas, can reduce tube wall temperatures and slow down the corrosion rate. For example, placing high-temperature superheaters and reheaters in areas with lower flue gas temperatures, or adopting a co-current arrangement, can match the inlet flue gas temperature with the tube wall temperature, preventing localized overheating. Simultaneously, using throttling coils to reduce inter-tube deviation and control wall temperature fluctuations ensures that the entire heated surface remains within a safe temperature range.
Surface protection is a direct means of improving corrosion resistance. Thermal spraying technology, by spraying corrosion-resistant materials (such as nickel-based alloys, ceramic coatings, etc.) onto the metal surface, forms a dense insulating layer that effectively prevents contact between corrosive media and the substrate. For example, a power plant used supersonic spraying technology to apply a CT45 nickel-based alloy coating to a boiler burning high-sulfur coal. After operation, no tube ruptures due to corrosion occurred, proving that this technology can significantly extend the service life of the heating surfaces. Furthermore, surface repair welding or replacement with composite steel pipes on water-cooled wall tubes can also improve the surface condition of the metal and enhance corrosion resistance.
Operation and maintenance are essential supplements to the corrosion prevention system. Regularly checking the ash condition of the heating surfaces and promptly cleaning deposits can prevent sulfur, chlorine, and other elements in the ash from reacting with the metal at high temperatures to form corrosive compounds. Simultaneously, strengthening water quality management and controlling the impurity content in steam can avoid the combined effects of steam-water side corrosion and fire-side corrosion. In addition, real-time tracking of parameters such as tube wall temperature and flue gas composition through online monitoring systems can detect potential corrosion problems early, providing a basis for preventative maintenance.
High-temperature corrosion prevention of hydrogen-rich gas boiler heating surfaces needs to be implemented throughout the entire life cycle, including design, manufacturing, operation, and maintenance. Through comprehensive measures such as material upgrades, combustion optimization, structural improvements, and surface protection, a multi-layered anti-corrosion barrier can be constructed, effectively extending the service life of the heating surface and ensuring the safe and efficient operation of the boiler. In the future, with the development of new heat-resistant materials and intelligent monitoring technologies, the corrosion resistance of hydrogen-rich gas boilers will be further enhanced, providing strong support for the large-scale application of clean energy.
