Alloy corrosion in a coal gasification system

The corrosion performance of alloys in coal gasification systems is of increasing industrial interest as more advanced coal-fired power generating systems are developed. It is necessary to consider the performance of candidate materials under likely exposure conditions to ensure that components have adequate lifetimes. Materials performance can influence the economic feasibility of these systems. This paper reports the high temperature corrosion performance of a range of materials exposed in British Coal's air-blown, spouted fluidised bed coal gasification pilot plant. The exposures were carried out in the hot gas path of this plant for periods of up to 660 hours, in three distinct temperature ranges between 330 and 920 "C (i.e. ranges representative of possible evaporator, superheater and ductwork conditions). By characterising the gasifier product gas using carefully selected elements and compounds, activity windows have been defined for sulphur and oxygen for this environment in the required temperature ranges. Standard metallurgical analyses were carried out on exposed alloys to determine their performance in the required temperature ranges. It was found that MA956 performed best in the higher temperature ranges, whilst alloys containing 22-28% chromium performed better in the lower temperature ranges.