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In this work, kinetic runs of self-reducing mixtures composed by pellet feed, BOF dust and biomass of elephant grass were performed using TGA-DSC method, for the temperatures, 900, 950, 1000, 1050 and 1100°C, and carbon percentages (15, 20 and 30% of carbon). The converted fraction versus time was calculated, and the different regions of the reactions progress were selected to analyze the reactions kinetics that occur in the mixture (devolatilization of biomass, Boudouard and sequence of reduction reactions). The kinetic behavior for the different steps showed good agreement with the first-order kinetic law. Using Arrhenius plot, was possible to estimate the apparent activation energy values obtained for the reaction mechanisms corresponding to Fe3O4→FeO and FeO→Fe. The kinetic constants for the 1100°C temperature and mixture containing 30% of carbon were the higher values: 0.0037 s-1 for the reaction Fe3O4 → FeO and 0.0258 s-1 for the mechanism FeO →Fe.

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A numerical model based on transport equations for momentum, energy and chemical species for the gas and solid phases is proposed to simulate the inner phenomena in the direct reduction of the shaft furnace process for producing directly reduced iron (DRI). The model is verified using industrial data for productivity, raw materials and final composition of the DRI product. The model is used to evaluate operational practices using new raw materials and the composition of the reducing gas in the process. Three cases were considered, which correspond to available raw materials commercialized by different suppliers. The effects on the gas and solid inner temperatures, pressure and phase composition distributions are quantified. The simulation results indicated that good agreement for overall parameters of the process could be achieved and afterwards, detailed features of the inner conditions of the process are predicted.