Mathematical modeling of the reduction process of iron ore particles in two stages of twin-fluidized beds connected in series

Abstract

A mathematical model is presented to describe the reduction process of iron ore particles in two stages of twin-fluidized beds (TFBs) connected in series: prereduction and final reduction stages. Main features of the model are the inclusion of particle degradation phenomenon to account for its effect on reduction of iron oxides and reduction kinetics for multiparticles having a wide size distribution. It was found that about 90 pct of overall particle degradation occurs in the prereduction stage mainly due to thermal stress and volume expansion. The reduction degree of particles larger than 1 mm decreased fast with increasing particle size in both the prereduction and final reduction stages. However, the particles sized between 0.2 and 1 mm showed mild increase in reduction degree, and steep increase for the fines smaller than 0.2 mm. The reduction degree was also gradually decreased with increasing the gas oxidation degree of feed gas in both the prereduction and final reduction stages. It was found that to obtain a desired reduction degree, it is of great importance to control the bed temperature in stage I rather than in stage II. The optimum range of residence time was 15 to 20 minutes in the prereduction stage and 30 to 35 minutes in the final reduction stage.

Kinetics and Mathematical Modeling of Hydrogen Reduction of NiO–WO₃ Precursors in Fluidized Bed Reactor

“…26) Hence, it is reasonable to assume that the mass transfer resistance of gases from the bulk to the particles surface is not significant. As very fine particles have been used in both TG as well as FB, diffusion through the porous reacted shell is also not expected to be significant.…”

“…27) On the other hand, the solid particles in the bed move in all random directions and hence can be considered to be in a perfectly stirred condition. 13,26,27) It is also well-known that the vigorous motion of the solid particles in a fluidized bed will ensure the temperature equalization along the bed. The isothermal character within the bed is one of the most characteristic properties of the fluidized bed reactor.…”

“…[9][10][11] The fluidized bed reactor have several advantages like nonagglomeration of the particles, excellent mass and heat transfer, temperature uniformity through the bed, excellent thermal efficiency and low investment costs. 12,13) On the laboratory scale, Srinivasan and Sheasby 14) have studied the hydrogen reduction of hematite to magnetite in a fluidized bed and they found that the reaction was controlled by the reaction at the gas-solid interface. Grace 15) has reviewed the work on modeling and simulation of fluidized bed reactors.…”

Simulation Study on Performance of Z-path Moving-fluidized Bed for Gaseous Reduction of Iron Ore Fines

“…And it has been observed in practice especially for fine iron oxide particles. [18][19][20][21] Hence, it is assumed that the mass transfer resistance of gases from the bulk to the surface can be neglected. Thurnhofer 18) conducted microscopical analyses of polished sections of reduced iron ore fines and observed that a high amount of pores were spread through the entire fine.…”

“…So pore diffusion is not limiting the reduction. Based on these assumptions and observations, Hahn,19,20) Thurnhofer,…”