Control of ash deposition on the surface of heat transfer tube

Ash deposition, called fouling, is one of major problems occurring in boiler that incinerates waste products as fuel. Ash deposition layer on heat transfer tube in a boiler causes not only heat transfer inhibition but also corrosion of the surface of heat transfer tube. Compared with pulverized coal combustion boiler, a concern of fouling becomes larger under waste incineration conditions due to their high contents of chlorine compounds. In this study, using ash samples derived from waste incineration processes, ash deposition experiments were carried out in vertical ash deposition furnace with a thermal spraying burner. Ash samples deposited on the tube surface were analyzed for elemental compositions and their distributions, using CCSEM equipped with EDX. A thermal spraying technique was applied to improve the surface properties of heat transfer tubes in boiler for reduction of ash deposition. Ni alloy as a thermal spraying material showed a positive effect to reduce ash deposition even under waste incineration conditions. In addition, to clarify the mechanism of ash deposition, thermal equilibrium analysis was also carried out.