Fused Nano-composite Claddings For Ultra-Supercritical Coal Fired Boilers

In order to reduce CO2, SO2 and NOx emissions, ultra-supercritical boilers will operate at higher pressures and temperatures than traditional fossil-fired power plants. The majority of current high temperature materials that are commonly used for moderate temperature applications in oxidizing atmospheres do not posses the characteristics necessary in high-temperature hostile environments. Current coating materials and processes (weld overlay or coextrustion) are costly and slow, and are not suitable for upgrading or repair operations. This project will demonstrate an innovative nanocomposite spray and fuse process for coating ferritic and austenitic alloy substrates for use in ultrasupercritical coal fired boiler components. The coating will be resistant to high-temperature oxidation, carburization, sulfidation, corrosion, and abrasion/wear. Phase I will produce a series of nano-composite feedstocks in Ni-Cr and Fe-Al materials systems with tailored coefficient of thermal expansion (CTE), melt rheology, and reactivity. A novel containerless fusion process will be modeled analytically, and then 1-2mm thick coatings will be applied onto 304 and 800 alloy substrates, which will then be screened for steam oxidation, hot corrosion, coal ash corrosion, carburization, and erosion recession rates at 650-850oC in simlated ultrasupercritical boiler environments. Commercial Applications and other Benefits as described by the awardee: The development of low cost, high temperature structures would be an enabling factor in the acceptance of highly efficient ultrasupercritical boiler systems. The new low cost containerless spray and fuse process also could be used to repair and reftrofit current boilers to extend life. The new process would offer orders-of-magnitude lower cost than weld overlays or thermal spray techniques, while enabling much greater control over coating structures. This process also may be suitable for replacing chrome and weld processes throughout the mining, oilfield, and mineral processing industries.