Some aspects on the reduction of olivine pellets in laboratory scale and in an experimental blast furnace

Abstract: The reduction behaviour of the olivine iron ore pellet MPBOwas studied in laboratory scale at KTH as well as in the LKABexperimental blast furnace. Initially, a newreduction-under-load, or so-called reduction/softening/melting,test equipment was developed. Experiments using differentreducing conditions, corresponding to different radialpositions of the blast furnace, were conducted. The experimentsincluded different temperature profiles, reducing atmospheresand mechanical loads applied on the sample bed to simulate thevarying conditions in the blast furnace process. The progressof reduction was investigated, as well as the processes ofsintering and contraction during reduction. A model of thecarburisation (pick-up of carbon by the reduced iron) andmelt-down process during rapid contraction was presented.Laboratory testing of MPBO pellets was compared with resultsfrom the LKAB experimental blast furnace. The reduction of ironore pellets in the experimental blast furnace was surveyed by adissection of the furnace after quenching. The high temperaturephenomena occurring when reducing the MPBO pellet, with limitedsoftening and a short temperature range of the melting process,resulting in a thin cohesive zone, were found to be the same inlaboratorytests and in the experimental blast furnace. Thereduction down through the burden of the experimental blastfurnace was similar, but not identical to the results of theRUL experiments. The differences were found to be due todifferent reducing conditions. Therefore, it was concluded thata simulation of the reduction occurring in the blast furnacecan be performed in laboratory scale, provided the experimentalconditions are correctly chosen.Finally, a modification to further improve the properties ofthe MPBO pellets was examined. With the aim to improve theblast furnace process, coating of blast furnace pellets wasinvestigated in laboratory scale, as well as in the LKABexperimental blast furnace. Olivine, dolomite and quartzitewere used as coating agents. In laboratory scale the stickingprevention action of the different coating materials wasverified, in established test methods as well as in new testmethods, modified for blast furnace conditions. Testing of thecoated pellets in the experimental blast furnace revealedseveral advantages; significantly reduced blast furnace fluedust generation, improved gas utilisation and a smoother blastfurnace operation with a potential for a lowered fuel rate.Keywords:Olivine, pellets, pellet testing,reduction/softening/melting, MPBO, blast furnace, reduction,quenching, dissection, coating, sticking, coated pellets.