Mechanism of sticking inhibition for fluidized bed hydrogen direct reduction using calcium ferrites modification
Hydrogen direct reduction via fluidized beds is one of the important directions for low-carbon development in the steel industry.The key premise to promote its large-scale application is to solve the problem of de fluidization caused by sticking during fluidized bed reduction.This work uses chemical reagents as raw materials to synthesize different types of calcium ferrites through high-temperature calcination,and modifies iron concentrate,investigates the hydrogen reduction behavior of the synthesized calcium ferrites,as well as its modified iron ore in a fluidized bed,reveals its inhibition mechanism on sticking,which lays a theoretical foundation for solving the sticking problem.The results of hydrogen reduction show that the reduction behaviors and reduction paths are quite different for differ-ent calcium ferrites.Both CF and CWF experience multi-step changes before being reduced to metallic iron,while C2F can be reduced to metallic iron in one-step,which are consistent with the thermodynamic analyses.Calcium fer-rites improve the stability of iron oxides during hydrogen reduction and C2F is the most difficult phase to be reduced.The surface morphology analysis results show that the reduced particles of Fe2O3 after roasting still maintain a dense structure,while the particles of calcium ferrites after hydrogen reduction show a porous structure.With the increase of CaO content,the surface morphology of CWF,CF,and C2F gradually evolves from a nearly cylindrical shape with a length of about 5 μm to small particles with a size of about 1 μm.The reduction product,nano structured iron particles,is found to be precipitated from the solid solution,which can effectively reduce the surface viscosity of the particles.The sur-face of iron ore concentrate modified by calcination with the addition of calcium oxide exhibits uniform distribution of cal-cium ferrites and good anti coherence performance.Therefore,the surface modification of iron ore with calcium ferrite through the addition of calcium oxide and calcination treatment can effectively suppress defluidization caused by sticking,thereby supporting the development and application of hydrogen direct reduction ironmaking via fluidized beds.
hydrogen direct reducitonfluidized bedcalcium ferritemodified iron oresticking inhibition
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