Iron Ore Reduction Kinetics Model Considering Multicomponent Gas Diffusion

The iron ore gas-solid reduction reaction is one of the most important chemical reactions in the field of iron and steel metallurgy.Its macro-kinetic model has formed a relatively mature model system.These models mainly include single interface unreacted shrinking core model(USCM),multi-interface unreacted shrinking core model,and particle model,etc.The most widely used ones are single interface unreacted shrinking core model that only considers FexO?Fe,which is the most difficult step in reduction.The common processing method is to fit the experimental data with the equation of the model,and the relevant kinetic parameters can be obtained by regression.However,it is assumed that only equimolar counter diffusion of the reducible gas and the product gas is considered in the conventional model,even in the COCO2-N2 or H2-H2O-N2 three-component system,where actual diffusive rate has a certain deviation from the rate calculated by the model.The results of reduction experiments in CO-CO2-N2 and CO-CO2-He systems show that the introduction of inert components will affect the diffusion of the system.Therefore,this paper uses the Stefan-Maxwell equation describing multi-component gas diffusion to construct an iron ore reduction kinetics model(USCM with DABC).The calculation of the reaction rates for the two USCMs can be used to evaluate the error when only DAB is considered.The model can be verified by using the experimental data of the reduction under the H2-H2O-N2 system.Since the kinetic model constructed in this paper is more complicated,the model can be approximately simplified by quantitatively calculating the concentration change of N2 on the diffusion path.Finally,the reaction efficiency of the blast furnace heat preserve area is discussed.The main research results are as follows:(1)Under the CO-CO2-N2 system or the H2-H2O-N2 system,the error introduced by the USCM considering only DAB increases with the increase of volume fraction of N2 in the main gas stream,iron ore reduction degree and temperature.The reaction rate of the CO-CO2-N2 system calculated by USCM considering only DAB is lower than the theoretical value,but the error is less than 2%under various conditions,which can be ignored.The reaction rate of the H2-H2O-N2 calculated by USCM considering only DAB is higher than the theoretical value,and the error is generally greater than 5%.(2)In the H2-H2O-N2 system,the use of DAB in the conventional model will result in inaccuracies in the mathematical model,making the predicted value of the model higher than the experimental value.Therefore,the illusion that the macroscopic kinetic parameters appearing in the literature are related to concentration is also due to the inaccuracy of the model.(3)The simplified results of the model indicate that in the CO-CO2-N2 system,the USCM with DABC can be approximately replaced by the USCM with DAB.In the H2-H2O-N2 system,only when the volume fraction of N2 is less than 12%,the USCM with DABC can be approximately replaced by the USCM with DAB.(4)The efficiency of blast furnace can be improved matching highly reactive coke only when iron ore with high reducibility is used and indirect reduction is fully developed.