Effect of hydrogen sulfide on the combustion reactivity of ilmenite ore with coal volatiles under steam reforming

Sulfur contamination in coal is an important issue that needs to be handled carefully in the coal chemical-looping combustion process. Sulfur impurities can damage oxygen carriers and decrease their reactivity, in addition to causing environmental and CO2 capture and storage problems. In this study, the effect of H2S on the combustion reactivity of ilmenite with coal volatiles under a steam reforming environment was investigated in a two-stage fixed bed reactor. Actual volatiles from the slow pyrolysis of coal were used as fuel to react with ilmenite in a steam-H2S atmosphere. Ilmenite's combustion reactivity with carbon volatiles was greatly improved in the presence of H2S, and more CO2 was obtained than without using H2S. However, the combustion reactivity improvement of ilmenite decreased with a higher concentration of H2S due to the formation of sulfur deposits (e.g., Fe1-xS) on the reduced iron particles. Furthermore, eight-cycle redox tests of ilmenite with H-2 and air were performed with various concentrations of H2S. Although the presence of H2S greatly enhanced the initial reaction rate of ilmenite with H-2, the higher amount of H2S decreased the combustion reactivity of ilmenite due to sulfidation.