Effect of H2O on pyrite transformation behavior during oxy-fuel combustion

•The decomposition process of pyrite in H2O-containing atmosphere is promoted.•Pyrite conversion and sulfur release are enhanced as H2O concentration increased.•Higher H2O concentration promotes the transformation of the product pyrrhotite into iron oxides.•The initial transformation process of pyrite in O2/H2O/CO2 atmosphere is improved.•A comprehensive pathway of pyrite transformation during oxy-fuel combustion is proposed.

H2O concentration in an oxy-fuel furnace is higher than that in a conventional air combustion furnace. Pyrite is a dominant factor that contributes to slagging in pulverized coal-fired furnace. This study investigated the effect of H2O on pyrite transformation in the presence or absence of O2 atmosphere. The TGA with a Netzsch STA449F3 thermobalance using a water vapor furnace was applied in the study. The results showed that the onset temperature To and the end temperature Te of pyrite decomposition decreased as H2O partial pressure increased in O2-free atmospheres. Higher H2O concentration promoted the product iron sulfide of lower sulfur content—pyrrhotite FeSx (here 1 < x < 2), and magnetite transformed into hematite in O2-free atmospheres. The thermal decomposition temperature of pyrite is lower in H2O than that in CO2 atmosphere. In H2O atmosphere, the reaction between pyrrhotite and H2O may form magnetite, H2S and SO2 during the thermal decomposition of the pyrite. As H2O concentration increased, pyrite conversion and the release of sulfur were increased in CO2 atmosphere. In O2-containing atmospheres, the presence of H2O improved the initial transformation of pyrite, and an increase in O2 concentration also achieved similar results. However, the overall effect of H2O concentration was weak in O2-containing atmospheres. A comprehensive pathway of pyrite transformation during oxy-fuel combustion was proposed.

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