Properties of iron bearing materials under simulated blast furnace indirect reduction conditions - Part 3 Reducibility

A laboratory furnace was built to study the behaviour of materials in the shaft region of a blast furnace. In this paper the reducibility of two sinters, two lump ores, and a range of fluxed pellets was studied under a number of simulated blast furnace wall and centre conditions, i.e. vertical temperature and gas composition profiles. Reducibility values obtained were consistently much lower than equivalent values obtained by the popular JIS standard test. In addition, the ranking of the materials was different to that obtained using the standard test. For the standard test the reducibility of porous hematite lump ores was lower than the values obtained for sinters and significantly lower than the values obtained for fluxed pellets. However, under blast furnace simulated conditions the reducibility of lump ores was generally as good as, if not better than, values obtained for the fluxed pellets. The causes of this discrepancy are: (i) hematite reduces at lower temperatures comparison with the bonding phases present in the sinters and pellets, e.g. silicoferrite of calcium and aluminium (SFCA) and magnetite, and (ii) reduction occurs before the fine pores present in the ore coalesce and decrease the available intraparticle surface area, which occurs in the JIS test. In particular, the study also showed that, for lump ore, reducibility is a function of particle size, suggesting that lump ores charged into a blast furnace should be of smaller size than pellets or sinters. Finally, the study highlighted the important role of carbon dioxide, which is not included in standard test gas mixes, in suppressing reduction. IS/1326c. (C) 1998 The Institute of Materials.