Mathematical Modeling of the Kinetics of Carbothermic Reduction of Iron Oxides in Ore-Coal Composite Pellets

Abstract

The kinetics of the carbothermic reduction of iron oxides in a composite pellet made of taconite concentrate and high-volatility coal has been studied by means of mathematical modeling that simultaneously takes into account the transfer rates of both the mass and the heat, and the rates of chemical reactions. The computational results, which have been validated with experimental data in the literature, confirm that the overall rate of the carbothermic reduction, which is strongly endothermic, is limited by heat-transfer steps. From a kinetics viewpoint, the optimum composition of the composite pellet is approximately in accordance with the stoichiometry, when CO is assumed to be the sole oxide of carbon in the gas. To raise the temperature of the pellet from its ambient value to furnace temperature, the heat required is greater than that needed for sustaining all chemical reactions, including the Boudouard reaction. The gaseous product consists mainly of CO and H 2 , except in the very initial stage. The overall observable reaction rate, in terms of the volumetric rate of the generation of gases, peaks at approximately 30 seconds of reaction time.

Characterization and Reduction Behavior of Mill Scale

“…19). The activa- These values are also close to the low limit of the range of activation energy reported in the literature 15,20,24) for wustite reduction by CO.…”

“…[20][21][22][23][24][25][26][27][28] These studies, with different iron oxides and carbon bearing materials, have shown that the self reduction mechanism and kinetics are more complicated because beside the reaction of reduction it includes sensibly endothermic carbon gasification reaction which very often is found to control the overall rate of self reduction. Moreover, other phenomena could influence 28) (like a devolatilization of the reducing agent) or even control 24) (like a heat transfer) the rate of self reduction. © 2011 ISIJ When compared with other iron oxides containing materials, such as the iron ores, sinters, pellets, the gaseous reduction of a mill scale was rarely investigated in detail.…”

Carbon Gasification in Self-reducing Mixtures

“…[16][17][18][19][20] Pure heat transfer control has also been postulated and modelled. 21) These findings are based on different experimental approaches such as the continuous weight loss of composite sample, the reactor output gas analysis and the temperature profiles inside the composite piece. The influence of the constituent particles nature and size of iron oxide, carbonaceous materials and some additives on the kinetics of overall reaction and the magnitude of its apparent activation energy are often used to identify a rate controlling step.…”

“…[28][29][30] The mechanism and kinetics of self-reduction has already been modelled to better understand the rate phenomena and to optimize the iron oxide/carbon composite technology by better selection of constituents and their processing conditions. 10,[18][19][20][21]24) These models take into consideration not only the kinetics of gasification and reduction reactions but also the mass and heat transfer phenomena and balances. They need precise measures of the involved reactions rate constants and some structural parameters (porosity, specific surface, etc.)…”

Carbothermal Reduction of Boron-bearing Iron Concentrate and Melting Separation of the Reduced Pellet

“…The activation energies (Ea) of different chemical reactions during iron oxide reduction are given in Table 3. 18) According to the value of apparent activation energy in the present reduction process, the reduction process may be mixed control by the Boudouard reaction and the chemical reaction of FeO reduction by CO at the mean time. Fig.…”