Numerical investigation of oxygen-enriched operations in blast furnace ironmaking

Abstract

Oxygen blast furnace (OBF) ironmaking promises to realize “zero carbon footprint” production via high oxygen enrichment in the blast. This paper presents a comprehensive study of the inner states and overall performance of the BF under such an operation. This is done by means of our recently developed multi-fluid process model, covering the oxygen content of the blast from 21% to 100%, with fixed hot metal temperature, bosh gas volume and blast temperature. The results show that with increasing oxygen enrichment, the fuel rate or coke rate increases initially to a minimum and then increases. This trend agrees with published experimental observations. On this basis, the flow and thermochemical behaviors are analyzed in detail. It shows that the cohesive zone becomes lower as the oxygen enrichment increases; meanwhile, the heat loss through reactions increases, but that through walls and top gas decreases. These opposite trends control the coke rate variation and explain the presence of the minimum coke rate. Some wide ore cohesive layers featured with long horizontal length appear at high oxygen enrichments, contributing to the high pressure drop in the lower part of the BF. Also, the dependence of OBF operations on blast temperature and top pressure is examined. It is shown that the increase in blast temperature or top pressure can both lead to a lower coke rate and higher productivity. The influence of blast temperature is less significant at higher oxygen enrichments. This is not the case for top pressure, whose effect on coke rate and productivity becomes more significant as the oxygen content increases. The analysis of reactions reveals that the coke reduction is caused by the increased indirect reduction rate and prolonged reaction time at a higher top pressure, but the enlarged indirect reduction zone for a hotter blast.