2007 Volume 47 Issue 11 Pages 1590-1598
Quality of iron feed source plays a critical role on the efficiency and productivity of advanced ironmaking processes such as COREX. A bench-scale study was conducted to characterize the effect of gas composition on solid state reduction and swelling behaviour of pellets and lumpy state of iron ore for COREX application. Swelling and reduction behaviour of five commercials iron oxides were analysed in a horizontal tube furnace and a thermogravimetric analysis (TGA) reactor respectively by simulating the reducing gas composition and thermal profile of the reduction shaft of COREX process. The degree of reduction and swelling were related to the initial porosity of iron oxide samples. The study demonstrated the strong influence of the initial porosity of iron feed samples on both reduction and swelling characteristics such that high porosity pellets indicated faster reduction and less swelling when compared to low porosity pellets. However, cracks formed in the iron pellets during different stages of reduction could modify the degree of the influence of the initial porosity on the reduction rates due to modification of surface area growth. The compressive strength of samples was found to change non-linearly with progressive reduction such that the crushing strength of pellets declined continuously up to 30% reduction followed by rapid strength increase as the degree of reduction exceeds 50% which can be attributed to increasing sintering of metallic phases. The study implies that as far as physical properties are concerned, the initial porosity of iron feed samples can be used to optimize the reduction kinetics, the swelling tendency and the associated implications for the stability of COREX operations including fines generations in the reduction shaft.