Lipak Kumar Sahoo

The fluidized bed magnetizing roasting of low‐grade iron ore fines is employed as a beneficiation technique in iron‐making and steel‐making industries. In the present work, the unreacted shrinking core reaction kinetic model is coupled with the two‐fluid and kinetic theory of granular flow gas–solid flow model to simulate magnetizing roasting of hematite to magnetite in iron ore fines using a fluidized bed reactor. The model is validated with published experimental findings. Thereafter, the influence of different process parameters such as gas temperature, composition, velocity, and particle size on the reduction fraction and rate along with mass fraction and emission is studied. The reduction rate increases with gas temperature and mass fraction while it decreases with particle size. The emission increases with gas temperature, particle size, and mass fraction. However, the influence of gas velocity on these parameters is not significant. The reduction rate and time vary from 0.0010 to 0.0067 s⁻¹ and 65 to 553 s, respectively, at a reduction fraction of 0.5. The mass fraction and emission range from 0.80 to 0.92 and from 0.63 to 4.14 g kg⁻¹ ore, respectively.

Gas–solid fluidized beds are widely employed in metallurgical industries to produce direct reduced iron. For such practical applications, tapered fluidized beds are most suitable for handling particles with wide size distribution due to the axial velocity gradient. Herein, the slug behavior in binary tapered fluidized beds has been studied using a high‐speed camera and digital image analysis method. The influence of taper angle, air velocity, and fine fraction on local parameters such as slug size, rise velocity, and aspect ratio, and bulk parameters such as slug number and its area fraction, and bed expansion ratio has been investigated. The local parameters increase with taper angle, air velocity, and fine fraction. The slug area fraction and the bed expansion ratio increase with air velocity and fine fraction. The bed expansion ratio increases while the slug area fraction decreases with taper angle. The slug number fraction, slug area fraction, and bed expansion ratio range from 0.027–0.241, 0.20–0.63, and 1.11–1.42, as taper angle, air velocity, and binary composition vary from 0°–15°, 0.20–0.35 m s⁻¹, and 0.25–0.75, respectively. An empirical correlation is proposed for bed expansion ratio prediction. Based on the present investigation, the optimum taper angle is 5°–10°.

Gas–solid fluidized bed reactors are extensively utilized in direct reduced iron production. In practice, these reactors will have a wide particle size distribution, which is better handled by tapered fluidized beds due to their vertical velocity gradient. Herein, a simplified bubble size relation is proposed to remove implicit interdependency between the bubble size and its drag coefficient in the bubble‐based energy minimization multiscale (EMMS) heterogeneous drag model. Further, the proposed drag model is coupled with the two‐fluid kinetic theory of granular flow model to investigate hydrodynamics. The heterogeneous flow structure predicted by the model is similar to experiments. Further, the bulk parameters such as bed expansion ratio and bubble fraction obtained from the simulations using a simplified EMMS drag model are compared and are found to be in good agreement with the experimental findings, with mean relative deviations of 3.95% and 14.64%, respectively. The time‐averaged bubble fraction and bed expansion ratio are found to increase with air velocity and decrease with taper angle, whereas a reverse trend is observed for the mean particulate fluidized area fraction. Based on the current study, the taper angle between 5° and 10° is found to be most suitable.