Abstract
Suspension reduction kinetics of hematite ore particles at 1710 K to 1785 K was described by the Johnson-Mehl-Avrami-Kolmogorov model with Avrami exponent of 1.405. The apparent activation energy is 105.5 kJ mol−1 with the rate determining step of nucleation and growth. The reduction degree of the hematite at the endpoint is a linear function of temperature and the logarithmic oxygen potential of the reacting gas. A peak function of reaction rate constant with particle size has been verified in this work, and the maximum value of the reaction rate is located at around 85 µm particle size. The influence of heat transfer on the reaction process has been evaluated. The results suggest that the heating-up process for large particles, 244 µm particles, for instance, cannot be ignored. It can retard the reaction rate compared to small particles. Normally, the reaction rate constant decreases linearly with the increase of ln[p(O2)] of the reacting gas mixture. However, 95 vol pct CO2 in the reacting gas can accelerate the reaction rate of thermal decomposition of hematite due to the emissivity of CO2 gas. It results in a higher reaction rate of 110 µm particles in 95 vol pct CO2-containing gas than that in other less CO2-containing gases.
Highlights
HISARNA is an emerging and promising alternative ironmaking process, developed to reduce CO2 emissions
The reaction rate constant was suggested to be an inverse relationship with particle size when the particle diameter is larger than 85 lm, for the particular iron ore tested in this study
The effect of particle size on the reaction rate constant has been discussed in detail in our previous work,[11] which reported that the reduction rate of the particles with particle size of 85 lm reached the highest, while quadratic equations were adopted for the description of the effect of particle size on the reduction process at
Summary
HISARNA is an emerging and promising alternative ironmaking process, developed to reduce CO2 emissions. In order to develop alternative ironmaking processes, experimental work has been done to explore the reduction kinetics of iron ore particles in suspension reduction in recent 10 years.[1,2,3,4,5,6,7,8,9] Especially, the reduction of fine hematite particles has been studied at the temperature range from 1550 K to 1750 K in CO2 reaching atmospheres to support the development of the HIsarna process.[10] It still needs more experimental work on the high-temperature suspension reduction kinetics, of which the temperature is higher than 1710 K At such temperature, the reduction products become half molten or fully melted.[9] The effects of reaction temperature, gas composition, and particle size on the reaction kinetics need to be explored. The effect of gas composition, particle size, and temperature on the kinetics are discussed in detail
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