Corrosion in coal gasification atmospheres

Corrosion of metallic materials by coal gasification atmospheres has been the subject of extensive study for over 20 years. While many alloys were found to be resistant to attack by high moisture content gases representative of fluidized bed gasifiers at temperatures up to 900 OC, good resistance could not be sustained for more than a few thousand hours as a result of changes in the structure and composition of oxide scales. A shift to use of entrained slagging gasifiers by the electric power industry during the past 12 years has largely eliminated the need for metallic materials to operate above 600 OC. However, the moisture content of the gas has been reduced greatly and nearly all materials form non-protective sulfideloxide scales and can have high rates of surface recession, even at low temperatures. The challenge for the 90's is to develop a basic understanding of factors controlling the rate of surface recession in such atmospheres and to develop new alloys that will have adequate resistance to attack. Research should be directed to the effect of alloy and gas composition on corrosion mechanisms and kinetics in low moisture gas representative of entrained slagging gasification at high temperature reacting with metal surfaces at temperatures of 300-600 C.