Effect of H2–H2O on the Reduction of Olivine Pellets in CO–CO2 Gas

Large amounts of injectants are used in the blast furnace (BF) process to reduce coke consumption, but this changes the gas composition in the BF shaft where iron ore reduction takes place. H2 and H2O gases change markedly in the gas atmosphere at high injection levels, which makes it important to investigate their effects on the reduction of iron oxides in a CO–CO2 atmosphere. The gaseous H2 and H2O content in the BF shaft atmosphere is approximately 8%. In the present work olivine pellets were reduced in H2–H2O–CO–CO2 and CO–CO2 atmospheres with equal reducing potentials of H2 and CO by fixing the H2/H2O and CO/CO2 ratios. No significant differences in the reduction rates of iron oxides were found between the H2–H2O–CO–CO2 and CO–CO2 atmospheres at high temperatures but at lower temperatures H2–H2O–CO–CO2 had higher reduction rate. Activation energies determined for hematite to magnetite reduction for both gas mixtures indicated better initial stage and later stage reduction in the H2–H2O–CO–CO2 atmosphere. Field Emission Scanning Electron Microscope (FESEM) analysis was carried out on samples, and wüstite relics were found in the inner parts of pellets reduced to iron in the CO–CO2 gas but not in the samples reduced in the H2–H2O–CO–CO2 gas.