Recent trends in the application and life evaluation of corrosion-resistant thermal spray coatings in waste incineration boiler

摘要

In order to increase in the electric power generating efficiency and reduce in the total cost of a waste-to-energy plant, it is important to develop and apply suitable corrosion-resistant materials and coatings. In modern highly efficient waste-to-energy boilers, having a severe corrosive environment, the use of Ni base alloy spray and weld overlay coatings in superheaters and waterwalls is becoming common. Especially, the application of thermal spray coatings such as NiCrSiB alloy UVOF for waterwall protection gradually increased in Japan, and enlarge to more than SC plants. Also, in the Japanese 773K/9.8MPa highly efficient plant, NiCrSiB alloy HVOF and alloy 625 weld overlay on the waterwall have been clarified to have a long durability of six years or more. Deterioration such as, spalling and swelling of spray coating layer occur due to the corrosion of bonding interface by the corrosive gas penetration. To obtain a highly durable coating, it is important to select both suitable materials and processes forming a dense coating layer. The concept of spray coating system applied for high efficiency waste-to-energy boilers was suggested.