Effects of varying oxygen content in suction gas during sintering of iron ore

The variation of the O2 content in the suction gas, in the range from 7 to 30 vol.%, during the iron ore sintering process, is investigated. Miniaturized laboratory-scale sintering experiments are carried out using an industry-like raw mixture to study the effects of O2 variation on the sintering process with particular emphasis on the off-gas composition, specific sintering parameters and the sinter strength as well as the chemical composition of the sinter. After the ignition at the bed surface, the gas hood is placed on the sintering column, allowing a synthetic gas mixture to be drawn through the sinter bed until the burn-through point is reached. For additional interpretation of the experimental results, the theoretical coke combustion rate as a function of the oxygen partial pressure was calculated and plotted against the experimentally measured peak temperature in the sinter bed of the respective sinter series. An increasing O2 content in the suction gas results in a faster flame front speed combined with a more gradual temperature rise of the heat wave and longer dwell time in the melt phase formation temperature range. Due to the more pronounced flame front, both sinter yield and strength increase, resulting in lower return rates. Below 12 vol.% O2, a sharp decrease in sinter yield and strength can be observed, probably due to the low extent of melt phase formation and the associated minor formation of silico ferrite of calcium and aluminum (SFCA). The carbon burnout as well as the calcination increases with increasing the O2 content in the suction gas, resulting in higher levels of CO2 in the off-gas, with more or less constant amounts of CO above 15 vol.% O2. The amounts of NO and SO2 show a similar trend with a continuous increase with increasing O2 supply, with the SO2 breakthrough starting earlier and being released over a shorter period. The chemical analysis of the sinter indicates the highest Fe(II) values in the range of 12–21 vol.% O2 in the suction gas.