Demonstration Test of New Corrosion-resistant Boiler Tube Materials in High Efficiency Waste Incineration Plant

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Abstract
In order to develop a 9.8 MPa/500°C highly efficient waste incineration boiler with 30% electric efficiency, application of highly corrosionresistant materials for superheater and corrosion-resistant coatings for waterwall are indispensable. Corrosion life of six conventional and six newly developed superheater tube materials and two waterwall coatings were evaluated for two years in the NEDO waste incineration pilot plant. As the results of the test, an excellent durability of more than six years for Ni-Cr-Mo alloy seamless and composite tubes of tertiary superheater, for Ni-Cr-Fe alloy tubes and cermet spray coating of secondary superheater and for alloy625 weld overlay and NiCrSiB alloy HVOF coatings of waterwall were clarified. Also the corrosion rate equation capable of corrosion life estimation was suggested by multiple regression analysis. Particularly, an addition of Mo to Ni base alloy was effective to prevent corrosion in severe corrosive conditions. Furthermore, the effect of corrosion factors that important to design the plant, i.e. soot blower effect, gas/metal temperature, time dependence of corrosion thickness loss etc. were clarified quantitatively.