CORROSION IN COAL-GASIFICATION ATMOSPHERES

Corrosion of metallic materials by coal gasification atmospheres has b een the subject of extensive study for over 20 years. While many alloy s were found to be resistant to attack by high moisture content gases representative of fluidized bed gasifiers at temperatures up to 900-de grees-C, good resistance could not be sustained for more than a few th ousand hours as a result of changes in the structure and composition o f oxide scales. A shift to use of entrained slagging gasifiers by the electric power industry during the past 12 years has largely eliminate d the need for metallic materials to operate above 600-degrees-C. Howe ver, the moisture content of the gas has been reduced greatly and near ly all materials form non-protective sulfide/oxide scales and can have high rates of surface recession, even at low temperatures. The challe nge for the 90's is to develop a basic understanding of factors contro lling the rate of surface recession in such atmospheres and to develop new alloys that will have adequate resistance to attack. Research sho uld be directed to the effect of alloy and gas composition on corrosio n mechanisms and kinetics in low moisture gas representative of entrai ned slagging gasification at high temperature reacting with metal surf aces at temperatures of 300-600-degrees-C.