Research On Direct Reduction Of Multilayer Carbon-containing Pellets Of V-Ti Iron Concentrate In Rotary Hearth Furnace

The rotary hearth furnace （RHF） technology has been widely used in all over theworld’s steel plant; however the energy utilization was very low from beginning to end.The initial reason was there is rarely any convective heat transfer between the high-energy flow gas and the burden. The energy needed by the burden reduction reactionwas mainly relying on the radiative transfer from top to bottom, with a quite slow ratewhich leads to thin raw material operation.Using the vanadium and titanium iron concentrate as the raw material, focusing onimproving the energy utilization in RHF, this thesis proposed several methods, such asthe software simulation、multilayer carbon-containing reduction and FeSi strengthen,to conduct definite research.Through Fluent simulation some conclusions can be got. For the cases simulated inthis study, when α equals to15°, the temperature field can meet the requirement of fast-temperature rising in the heating zone very well.With a heating rate of10℃/min, thethermoanalysis experiment was carried on inthe argon shield atmosphere from room temperature to1450℃.From TG-DTG-DSC curves, the strengthening mechanism of FeSi on V-Ti ironconcentrate can be summarized as follows:1)When T<1148K, FeSi rarely has anyinfluence on the reduction, the weight loss was mainly caused by the coal degasificationreaction;2)When1148K<T<1423K, the Boudouard reaction was promoted and the gas-solid reduction reaction mainly happened in this period, the FeSi strengthen effect onthe reduction is small;3)When1423K<T<1560K, the silicothermic reduction mainlyhappened: Si+4FeTiO₃=2Fe+2FeTi₂O₅+SiO₂and Si+2FeTi₂O₅=2Fe+4TiO₂+SiO₂.4)When1560K<T<1673K, the reduction of the sample with FeSi addition mainlyconsumed FeSi, thus the carbon residue is relatively higher and the carbothermicreduction meet a small peak; at the same time, the carbon residue in the sample withoutFeSi addition is very few and will be consumed slowly.The isometric diameter experiment of multilayer pellets reduction was carried inthe laboratorial RHF with an atmosphere of complete combustion. It can be generatedthat the reduction reaction would have a larger reaction rate if there is a highertemperature field and the reoxidation of the reduced pellet would be easier when theproportion of CO₂in the atmosphere is higher. The experiment results indicated that, the reduction reactions do not take placesimultaneous in the bed of multilayer pellets, where the top layer pellets was reducedand even then reoxidized while the bottom layer pellets was only reduced to someextent; the average metallization ratio of the pellets increased with the increasingtemperature and it exhibited an phenomena of firstly increased and then decreased withthe reduction time prolonged. In this progress there exists an optimal reduction time inorder to get the maximum metallization ratio which in this study is25min;In order to make the vision of synchronization reduction achived, the strengthenreduction of multilayer pellets experiment was carried out in the atmosphere of Ar. Theresults show that, the metallization of the pellets with FeSi addition was above82%at25min, FeSi has greatly positive impact on the synchronization reduction.