Influence of several conditions on abnormal swelling of hematite pellets during reduction with H2–CO gas mixtures

Abstract

Swelling behaviour during reduction of hematite pellets made of reagents in H2–H2O–CO–CO2 gas mixtures was examined in elevated temperatures. The influence of adding lime, H2/(H2+CO) gas ratio, sulphur activity in gas, oxidant gas content H2O and CO2 in inlet gas, total gas flow rate and temperature on swelling were examined in order to comprehensively investigate the swelling further. When gas mixtures have low sulphur activities incapable of sulphurising iron (aS in the range of 10−2 to about 1, maximum swelling around aS=0·5 at 900°C), a marked abnormal swelling during reduction of hematite pellets was observed accompanied with a large number of fine fibrous irons. When the reduction proceeds with moderate metallisation rates under conditions such as controlled gas supply or gas mixtures having oxidants, abnormal swelling was observed. It was reconfirmed that these abnormal swellings necessitated the existence of gaseous sulphur in the gas mixtures. The addition of CaO in pellets enhanced fairly abnormal swelling and lessened metallisation rates slightly when the reduction proceeded under the existence of gaseous sulphur with moderate metallisation rates. The above-mentioned conclusions were analogous to those in our previous research. The degree of abnormal swelling increased gradually with increasing hydrogenous composition of H2–H2O in H2–H2O–CO–CO2 gas mixtures, because pellets were reduced with moderate metallisation rates under controlled gas supply.