Influence Mechanism Of Zinc On The Solution Loss Reaction Of Coke

Coke fulfills four major roles in the blast furnace:?i?as a source of reducing gas for the reduction of iron ore and for the regeneration of CO from CO₂;?ii?a source of energy/heat;?iii?supporting the weight of the burden and providing a matrix of permeable material especially in the lower regions of the furnace;and?iiii?a source of carbon for carburizing hot metal,which is regarded as one of the most important raw materials for blast furnace ironmaking.However,both the strength and the size of coke are decreased due to the mechanical damage,thermal stress,solution loss reaction and slag-iron corrosion in blast furnace.Solution loss reaction is the main reason for coke quality degradation in blast furnace,moreover the recycling zinc have been confirmed to catalyze the coke gasification.Yet,there is limited information available about the mechanism of zinc on degradation of coke thermal performance.This study focuses on how zinc affect the reaction behavior using the acetate adsorption.The influence of zinc on the kinetic model and parameters of coke gasification reaction was investigated by the main curve fitting method.The evolution characteristics of microcrystalline structure,pore structure,micro morphology and optical texture of coke were analyzed by X-Ray diffraction?XRD?,BET,scanning electron microscopy?SEM?and optical microscopy in present research.The main content and conclusions are follows:?1?Study on coke reactivity showed zinc adsorbed on coke has catalytic effect on the gasification reaction of coke,but the difference of catalytic effect at different temperatures is larger.Furthermore,CRI and CSR values of coke are deteriorated with the increase of zinc content in coke,and reached a limitation when the content of zinc exceeds 1.17 wt%,indicating that the catalytic effect of zinc on coke gasification may reach the limitation.?2?The nonisothermal method was adopted to study the coke gasification kinetics under the influence of zinc using TGA.The results showed that the carbon conversion and conversion rate curve shifted to a lower temperature zone with the increasing zinc content.Ten kinetic models were adopted and calculated to determine the most probable mechanism function of coke gasification.It was found that the experimental data were best described by the shrinking core model for Zn-enrich coke gasification.Further,the accuracy of this model was verified through the iso-conversitional method.The values of activation energy and pre-exponential factor were calculated with the best probable kinetic equation,and the activation energy of coke was found to decrease obviously with the increasing zinc content.In addition,the compensation effect was confirmed to exist between activation energy and pre-exponential factor in catalysis of zinc on coke gasification.?3?In the catalytic process of the gasification reaction,microcrystalline layers of anisotropic texture with high degree of orientation are destroyed first,and then carbon atoms are dissociated to form CO one by one in the decomposition of ketone groups,resulting in the acceleration of the reaction.The catalysis directly leads to the production and expansion of micropores,resulting in increase of the pores diameter and the SBET.Thus,the permeation of zinc vapor and CO₂ gas is accelerated,meanwhile,the interfacial reaction areas of gasification reaction are increased,resulting that the reaction is further intensified.In addition,the serious damage of the coke structure and formation of honeycomb cavern are resulted from coalescence and transfixion of macroscopic pores caused by zinc catalysis,which greatly decreases the strength of coke.?4?The catalytic mechanism of zinc on solution loss of coke can be explained based on Electron Cyclic Donor-Acceptor Catalyzing Theory?ECDAT?.Further,the applicability of the ECDAT on catalytic effect of zinc on coke gasification was proved through calculation using Materials Studio software.On one hand,the catalysis of zinc is attributed to the electron transfer,accelerating the decomposition of the ketone group.On the other hand,the energy required for the decomposition of ketone group was decreased under the influence of zinc,resulting in increasing the coke reactivity.