Corrosion of iron-base alloys by coal char at 871/sup 0/ and 982/sup 0/C

Abstract

The high pressures and temperatures required for the processing of coal lead to accelerated corrosion of gasifier components by oxygen and sulfur present in the gas phase. Coal char, the solid byproduct of coal processing, contains sufficient inorganic sulfur to result in internal attack of the alloys composing the gasifier components. The role of coal char in coal processing and of thermodynamics in gas phase corrosion are discussed. Experiments were performed to determine whether CaSO/sub 4/ or FeS are responsible for the internal attack on Fe--Cr--Al and Fe--Cr--Ni alloys observed under conditions of both high oxygen partial pressure and 982/sup 0/C and low oxygen partial pressure and 982/sup 0/C. Exposure at 871/sup 0/C resulted in virtually no attack from coal char and FeS and very slight attack from CaSO/sub 4/. The morphologies and rates of attack indicate that at very low oxygen partial pressures (about 10/sup -19/ atmosphere) the presence of CaSO/sub 4/ can result in internal sulfidation whereas at higher oxygen partial pressures (about 10/sup -15/ atmosphere), the presence of FeS can result in internal sulfidation. Comparison of these results with those actually observed from coal char at 982/sup 0/C indicate that FeS is primarily responsible for attack bymore » coal char but that CaSO/sub 4/ can also result in such attack although the overall mechanism and rate of attack may be different.« less