Gas-solid Reaction Mechanism Of Coke And Iron Oxide In Blast Furnace

With the advent of a low-carbon economy,the conventional blast furnace iron-making process with high pollutant emissions and high energy consumption faces unprecedented challenges.To reduce carbon emissions,steel companies are gradu-ally moving from carbon metallurgy to hydrogen metallurgy globally.Therefore,it is crucial to conduct research on gas-solid reactions in blast furnaces.Presently,most studies on gas-solid reactions in blast furnaces focus on using various methods such as dissection during overhaul and tuyere sampling to obtain iron oxides and coke from blast furnaces and then analyze the rules governing the evolution of their physical and chemical properties.Additionally,laboratory simulations are con-ducted to study the effects of different atmospheres and minerals on gas-solid reac-tions of coke and iron oxides.This study focuses on the macroscopic description and rate analysis of the gas-solid reaction process.There is a lack of in-depth re-search on the fundamental theory of the gas-solid reaction process,especially on the most intrinsic behaviors of coke and iron oxides in the gas-solid reaction process at atomic and electronic levels.Therefore,this study takes an approach that com-bines experiments with density functional theory(DFT)simulations to reveal the influence of the pore structure of coke on gasification at the electronic level,to clarify the mechanism of CO2 adsorption on the surface of coke,and to determine the influence of minerals on the gas-solid reaction between coke and iron oxides.Four types of coke with different pore structures were produced by controlling the moisture content of coal,and the influence of different pore structures on the rate of reaction of gasification was studied.The SEM-EDS results showed that the coke obtained from completely dry coal had a relatively small pore size and thin pore walls.The porosity and percentage of large pores in coke increased with the increasing moisture of the incoming coal.The thermogravimetric analysis result showed that the 4 types of coke had different reactivity,with the coke obtained from completely dry coal having the highest reactivity.The four types of coke in powder form had similar rate of reaction curves for gasification,and the volumetric reaction model fitted well with the gasification experimental data.The four types of coal had activation energies of 191.9 kJ/mol,203.1 kJ/mol,190.1 kJ/mol,and 190.8 kJ/mol.The deterioration of pores during gasification results in more active sites in the car-bon layer of coke,such that CO2 is trapped easily,thereby increasing coke reactivity.The pore structure is a key factor affecting gasification.DFT was used to reveal the CO2 adsorption process in the gasification of coke carbon layers with different defects at the electronic scale.The results show that there are 3 modes of CO2 adsorption in all coke carbon layers:physisorption,chem-isorption,and repulsion.The deformation energy and interaction energy of CO2 chemisorption are much larger than those of physisorption,whereas the charge transfer of CO2 physisorption is much less than that of chemisorption.The original coke carbon layer exhibits weak CO2 adsorption with a long adsorption distance(3.39 A),whereas carbon atoms with dangling bonds have a much stronger phy-sisorption capacity.The single-vacancy unsaturated carbon atoms in the coke mi-crocrystalline carbon layer are more reactive than the triple-vacancy unsaturated carbon atoms.This facilitates the chemisorption of CO2 gas.The gasification experiment was conducted by mixing iron of different con-tents with coke,and DFT calculations was conducted to model the reaction process of iron-catalyzed gasification.The experimental results showed that gasification started at temperature Ti and ended at temperature Tf,where Tf decreased gradually with the increase in iron content.The kinetic analysis results showed that the ran-dom pore model fits well with the experimental data of gasification.The activation energies of the 4 types of coke(218.1 kJ/mol,212.3 kJ/mol,204.2 kJ/mol,and 197.1 kJ/mol)decreased with the increase in iron content.The DFT simulation results show that the C-O bonds of CO2 molecules are stretched when CO2 is adsorbed on the Fe surface.Additionally,strong hybridization occurs between the atomic orbit-als of C and O in CO2 molecules and the 3d,4s,and 4p atomic orbitals of Fe.Thus,the Fe surface has the ability to activate CO2 molecules and catalyze the gasification process.DFT calculations were used to model the surface interaction between MgO/CaO and FeO clusters to reveal the effect of MgO/CaO on the reduction pro-cess of FeO clusters.The results showed that the adsorption energy of FeO clusters on the surface of MgO(100)and CaO(100)were-2.07 eV and-2.32 eV,respec-tively.As the adsorption energy on the CaO surface is higher,FeO clusters are ad-sorbed more easily on the CaO surface with a more stable adsorption structure.Comparing the reduction process of FeO by CO and H2 shows that when an H2 molecule is adsorbed by FeO,it dissociates to form 2 O-H bonds,generating an intermediate molecule of H2O.Additionally,in the early stage of the reaction,CO gas has an advantage in the interfacial reaction as it has larger adsorption energy,whereas the low dissociation energy of H2 gas is conducive to product dissociation.DFT calculations were used to establish the adsorption model of Na/K vapor onto Fe2O3 crystal surfaces and to reveal the effect of Na/K vapor on the Fe2O3 reduction process.The results showed that the adsorption energies of K and Na on Fe2O3 surface are the same at 0.34 eV.The adsorption energy of CO molecule on Fe2O3 surface is-2.42 eV.The adsorption energy of CO on Na-Fe2O3 surface and K-Fe2O3 surface is-2.57 eV and-2.61 eV,respectively.There is a relatively large interaction between CO and K-Fe2O3,which promotes the interface chemical re-action.The dissociation of CO2 intermediate products from the Fe2O3,Na-Fe2O3,and K-Fe2O3 reaction interfaces overcomes the energy barriers of 0.27 eV,0.36 eV and 0.41 eV to form CO2 gas.In this process,the intermediate products on the Fe2O3 surface are easier to dissociate from the surface.The adsorption energies of H2 and O atoms on the three surfaces are-0.23 eV,-0.21 eV and-0.17 eV,respectively.H2 has a very weak adsorption effect on the three surfaces,so the reduction of H2 is controlled by the interface chemical reaction.