Testing of candidate materials for their resistance to alkali-vapor adsorption in PFBC and gasification environments. Final report

Laboratory-scale studies were performed to identify metallic material(s) having no, or limited, affinity for alkali vapors in an environment of either the off-gas from pressurized fluidized-bed combustion (PFBC) or the fuel gas from coal gasification. Such materials would be potential candidates for use as components in advanced coal-utilization systems. The following materials were tested for adsorption of NaCl vapor at 870--875 C and atmospheric pressure in a simulated PFBC off-gas (oxidizing) doped with 80 ppmW NaCl vapor: iron-based Type 304 stainless steel (304 SS), nickel-based Hastelloy C-276 and Hastelloy X alloys, cobalt-based Haynes No. 188 alloy, noble-metal-coated 304 SS, aluminized 304 SS, and ZrO{sub 2}-coated 304 SS. The Haynes No. 188 alloy and the aluminized 304 SS were also tested for their NaCl-vapor adsorption in a simulated gasification fuel gas (reducing) under the same test conditions as in the PFBC off-gas test. After 100 h of testing, the specimens were analyzed with a SEM equipped with an energy dispersive X-ray analyzer, and by an AES. The aluminized 304 SS had the least tendency to adsorb NaCl vapor, as well as an excellent resistance to corrosion as a result of the formation of a protective layer of Al{sub 2}O{sub 3} on its surface. In the reducing environment, however, the aluminized 304 SS was badly corroded by H{sub 2}S attack. The Haynes No. 188 showed virtually no NaCl-vapor adsorption and only limited H{sub 2}S attack. The authors recommend further long-term parametric studies to quantitate alkali-vapor adsorption as a function of operating variables for (1) the aluminized 304 SS in the PFBC off-gas environment and (2) the Haynes No. 188 in the gasification fuel gas environment.