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Materials for FGD Systems

AUTHOR: Zhangfa Wu
DATE: January 2000

Materials of construction for flue gas desulphurisation (FGD) systems in coal-fired plants are reviewed. The wet FGD process is the most commonly used in coal-fired power plants, accounting for over 80% of the total FGD capacity worldwide. However, the wet systems are exposed to the aggressive chemical and mechanical environments which require the use of appropriate materials of construction. The materials include non-metallic coatings/linings over carbon steel, nickel-containing alloys and fibreglass reinforced plastic (FRP). the non-metallic systems have been used extensively especially in early installations, providing the lowest initial material costs and corrosion protection to FGD systems.

However, some of the systems are not sufficiently resistant to the most corrosive areas in FGD systems, resulting in the failures of materials, and hence increased maintenance costs. In the last decade, nickel-containing alloys have been widely used in FGD systems, providing successful corrosion protection and lower maintenance but generally representing higher capital costs than non-metallic systems. The use of nickel-containing alloys is continuing to increase. FRP based on the epoxy vinyl ester resin has found successful applications in FGD systems, providing competitive costs and good performance. The material has mainly been used for non-structural components such as limestone slurry piping and demister assemblies, and it now also finding structural applications for scrubber body, outlet duct and stack liner. It is expected that FRP will be more widely accepted and increasingly used in FGD systems.