Research On The Mechanism Of Precipitated Iron Morphology Difference During FeO Reduction Process By CO And H₂

The typical non-blast furnace iron making method of iron extraction——fluidized iron making process.It uses iron ore powder directly and gets rid of the dependence on coke.This method attracts much attention because it has many advantages,for example,the mixing effect is sufficient between reducing gas and iron ore powder,and the reduction kinetics condition is also good.However,the sticking problem among iron ore powder is always the bottleneck of its industrial application during fluidized iron making process.A large number of experimental studies have shown that,the sticking of iron ore powder is closely related to the precipitated iron morphology during reduction process.The precipitation of iron occurs in the FeO?Fe stage during iron oxide reduction process under fluidized temperature,and the precipitated iron morphology changes significantly with different reducing gas,namely CO or H₂.The reaction behavior between reducing gas and FeO,and their interaction mechanism on gas-solid interface are researched based on the characteristics and bonding process of reactant molecules themselves.The root cause and control method of precipitated iron morphology difference are investigated,and it has important theoretical value and practical significance.First of all,the adsorption process of CO and H₂ molecules on Fe atom top site,and the chemical reaction process of CO and H₂ molecules on O atom top site in three typical crystal surfaces of FeO are simulated based on Density Functional Theory.Then,the diffusion process of precipitated iron on FeO surface during FeO reduction by CO and H₂ is studies based on the theory of Molecular Dynamics.On this basis,the reaction process of FeO reduction by CO and H₂ is studied based on Cellular Automata Theory,and the evolution process of precipitated iron formation and growth is regenerated dynamically during reduction process.The followings are main conclusions obtained through this research:?1?When CO molecule adsorbs Fe atom,the outer electrons of C nucleus are easy to enter the low energy level bonding orbital of Fe nucleus.C atomic hybridization type is transferred from sp-1 hybridization of CO molecule to the sp3 hybridization of Fe₃C molecule,it achieves a lower level of adsorption stability,and a bond of Fe-C is formed.At the same time,CO molecule produces a vertical upward induced dipole under Fe atomic electrostatic field as the guide of Fe atom to move upward,and the electrostatic force exerted by CO molecule acts as a driving force to facilitate the upward migration of Fe atom.When H₂ molecule adsorbs Fe atom,the outer electrons of H nucleus are easy to enter the high energy level antibonding orbital of Fe nucleus.The antibonding orbital electrons spin in the same direction and repel each other,which causes the two atoms are unable to form a bond,but only has physical electrostatic effect.Meanwhile,H₂ molecule produces a vertical downward induced dipole under Fe atomic electrostatic field as the guide of Fe atom to move downward,and the electrostatic force exerted by H₂ molecule acts as a driving force to facilitate the downward migration of Fe atom.The chemical reaction constant rate k of FeO reduction by CO and H₂ is affected by the partition functions of reactants and intermediate complexes,and the partition functions of this materials are closely influenced by the degeneracies of reactants and intermediate complexs.In the process of CO molecule reacting with O atom to form CO₂ molecule,the four degeneracies of second energy level of C atom have no change,so the reaction probability is only affected by the hybridization process.In the process of H₂ molecule reacting with O atom to form H₂O molecule,the central atom transfers from H atom to O atom.The one degeneracy of first energy level of H atom changes to be the four degeneracies of the second energy level of O atom,and O atom has a hybrid reaction when O atom transforms to be the central atom.So,the reaction probability is not only affected by degeneracy,but also affected by the hybridization process.?2?The diffusion coefficient D of precipitated iron on FeO surface is related to the pre-factor D₀,and the pre-factor D₀ depends on the vibration period of the Fe atom and its mean square moving distance.When the precipitated iron is covered with CO molecules,the adsorption of CO molecules strengthens the vibration of Fe atoms.As a result,the vibration period of Fe atoms is shortened,and the average square moving distance of Fe atoms increases,which eventually leads to the increase of Fe atom diffusion coefficient D.When the precipitated iron is covered with H₂ molecules,the adsorption of H₂ molecules weakens the vibration of Fe atoms.As a result,the vibration period of Fe atoms is lengthened,and the average square moving distance of Fe atoms decreases,which eventually leads to the decrease of Fe atom diffusion coefficient D.This different phenomenon is consistent with the research result based on the first principle of density functional theory.?3?The evolution process of precipitated iron formation and growth during FeO reduction by CO and H₂ is reproduced based on Cellular Automata Theory and combined with the results of Density Functional Theory and Molecular Dynamics Theory.The results show that,the precipitated iron grows into the whisker structure during FeO reduction by CO,but the precipitated iron grows into the porous or dense structure during FeO reduction by H₂.The different growth trends of precipitated iron are consistent with the macroscopic experimental results.