Development and Application of High Cr-High Si-Fe-Ni Alloys to High Efficiency Waste-To-Energy Boilers

Abstract

In order to improve the durability of high efficiency waste-to-energy boilers, it is essential to develop and apply high temperature corrosion-resistant materials having a long life time according to the intensity of the corrosion conditions. Two types of high Cr-high Si-Fe-Ni base and high Cr-high Si-Ni-Fe base alloy seamless tubes; MAC-N (26Cr-3.5Si-11Fe-Ni base) alloy and MAC-F (23Cr-3.8Si-38Ni-Fe base) alloy respectively which contain no expensive Mo and have better corrosion resistance than the existing alloys under severe corrosive environments of waste combustion gas, have developed. The optimum alloy composition range were defermined by confirming the effect of the alloying elements on the corrosion resistance in the laboratory corrosion tests. Furthermore, the seamless tubes were mounted on the actual superheater of the 500oC/9.8MPa high efficiency waste-to-energy boiler to examine the durability over a period of four years. As a result, it was confirmed that the MAC-N and MAC-F alloys have better corrosion resistance than the Alloy625 and 310HCbN. In addition, it has become clear that corrosion resistance of both alloys is displayed through the formation of SiO2 rich protective scale due to the combined addition of the principal elements, Si, Cr, Fe and Ni. Under conditions of high Cl content molten deposits and severe thermal cycle, the corrosion rate increases as the results of deterioration of protective oxidation scale.