A Review of Experiences With AL-6XN® and Zeron® 100 Alloys in Air Pollution Control Systems

Coal fired power plants are faced with increasingly strict air quality control laws and EPA rules. New multi-pollutant legislation is controlling a wider range of emissions, especially sulfur compounds. A significant number of flue gas desulfurization (FGD) units worldwide employ wet scrubbing to reduce sulfur dioxide emissions by more than 90 percent. Wet scrubbing has also been found to be effective at removing mercury in many cases. Due to the inherent contaminants generated by the combustion of coal, wet FGD’s require the use of corrosion resistant materials in their construction. A variety of metallic corrosion resistant alloys are currently used in these pollution control systems. This paper will review the use of AL-6XN and Zeron 100 alloys in various FGD applications around the world. Examples of AL-6XN and Zeron 100 in actual service in FGD units will be presented. AL-6XN and Zeron 100 are alloys that have been chosen for these systems when conditions are too severe for either 316L stainless steel or 2205 duplex stainless steel. Experimental data will be reviewed that supports the use of these alloys in the high chloride containing environments encountered by the many components of the pollution control systems. AL-6XN and Zeron 100 alloys have proven to be cost effective materials of construction that fill the gap between the lower alloyed stainless steels such as 317L, 904L, and 2205, and the high molybdenum and nickel based alloys such as C-276. As AL-6XN and Zeron 100 alloys are established materials of construction, they are readily available in product forms necessary to complete an FGD system.