Comparative environmental assessment of coated ferritic steels suited to steam turbines of coal-fired supercritical and ultra-supercritical power plants

Abstract

Coated ferritic steels are the most common materials used for steam turbines construction in coal-fired power plants operating at supercritical and ultra-supercritical conditions of pressure and temperature because of their corrosion and oxidation resistance. However, the environmental implications associated to the steel-coating system have not been fully investigated to choose the best option in terms of sustainability.This work presents three types of ferritic steels as well as three coatings with its corresponding deposition technique, normally used in these environments. The designated materials are P91, P92 and VM12 ferritic steels, while the selected protective coatings are Ni50Cr applied by High-Velocity Oxi Fuel Spray (HVOF), CrN/NbN applied by High Power Impulse Magnetron Sputtering (HiPIMS) and slurry aluminide applied by painting and diffusion heat treatment. Taking these data as a starting point, comparative Life Cycle Assessments (LCA) and economic analysis are performed.This work aims to contribute to better understanding of environmental damages as well as the importance of considering the technical and environmental assessment in the steel-coating selection. The results obtained indicated that the P92 ferritic steel coated with slurry aluminide had the best performance. On the other hand, CrN/NbN coating showed the greater impacts in all the categories studied.