Competition Mechanism Between Reducing And Slagging Reactions Of Wustite Under Unsteady State Inside Blast Furnace Cohesive Zone

The cohesive zone of blast furnace has a great influence on the smooth operation and fuel consumption,for it determines the gas flow distribution and utilization.It is of great importance to obtain the reasonable structure of the cohesive zone for blast furnace operation by studying its formation mechanism.The previous work is centered on the evaluation of the shape and permeability of the cohesive zone by measuring the physical indices of the softening and melting process of iron-bearing materials,such as temperature and pressure drop.However,the role of the chemical reactions during the process,especially the influences of the reducing and slagging reactions participated by wustite and the competition relation between each other are ignored in most of the previous research.Given that,this paper respectively studied the competition behavior of wustite reduction,competition behavior of slagging reactions and competition behavior between the reducing and slagging reactions participated by wustite in the cohesive zone of blast furnace.Then,a comparison is made between the individual and competition reactions of wustite at particular intervals and under different experimental conditions so as to find out the key parameters combining with the numerical calculation after a systematic study of the fundamental physical chemistry of the reactions.Then,a comparison is made between the individual and competition reactions of wustite at particular intervals and under different experimental.The main conclusions including:(1)The reduction rate of wustite by CO-H2 mixture gas is less than the sum of reduction rate of single gas.According to the settings of “Voltage” and “Resistance” in the circuit,six models based on the combined method,namely,C-S-S,C-S-P,C-P-S,and C-P-P,as well as two models based on the individual method,namely,I-P-S and I-S-P,were proposed.Compared with other models,the I-S-P model generated the closest predictions with the experimental measurements,and the maximum relative error for this model was <8.5% under the present experimental conditions.As a result,the nonlinear relationship on the reduction rate between the mixture gas and the individual component was described as below:(?)(2)Additions of CaO or Al2O3 decrease the starting softening temperature and no dripping behaviors are found in comparison with the base case results when only FeO is used.The addition of SiO2 or MgO rises the starting and ending softening temperature,at the same time,both the dripping temperature and the maximum pressure drop of the case with the addition of SiO2 are the lowest among all the cases in this work.According to the phase diagram and XRD analysis results,the initial phase with CaO addition in the primary-slags should be C2F(2CaO·Fe2O3)and that with SiO2,MgO,Al2O3 additions are fayalite(2FeO·SiO2,1189 ?),magnesioferrite(MgO·Fe O),hercynite(FeO·2Al2O3),respectively.(3)When adding CaO,SiO2,softening start and end temperature is affected by acid and alkali two oxide and showed a trend of neutralization,softening range is increase because influenced by end temperature increase.Adding SiO2,MgO,the softening temperature is decrease,but softening interval almost same to base case.Adding SiO2,Al2O3,the softening temperature is decrease more than the case of adding SiO2 and MgO,softening beginning temperature is 646 ?,softening end temperature is 828 ?.(4)The shrinkage rate of all samples at initial reaction stage is larger than latter reaction.Adding CaO is the greatest difference is about 9.7 times.Adding SiO2 is minimum difference only about 4.9 times.Pure wustitie,adding MgO and Al2O3 samples at about 6 times.When adding CaO,reduction rate of initial reaction stage is fater than wustite,and in contrast at later stage reaction.Adding SiO2 the regulation is contrary to adding CaO.Adding MgO,the shrinkage rate of whole process is larger than wustite.When adding Al2O3 shrinkage rate of the whole process is smaller than wustite.(5)The adding SiO2 or MgO binary slag is sensitive to atmosphere.When reducing atmosphere change from CO to H2,the softening of FeO-SiO2 banary slag is delaying,the softeing of FeO-MgO is advanced.The effect of reducer gas ro FeO-CaO binary slag is small.Further,the reducer gas has no effect to FeO-Al2O3 binary slag.(6)CaO will promote the softening of slag,and softening temperature is advance from 783? to 735? but when further increase content of CaO the promoting effect is decrease.When adding 10% SiO2 reduction reaction trend of FeO slag reaction is stronger than combination of FeO and SiO2,further after adding 20% SiO2,the regulationg is contray.When adding MgO alone,both adding 5% and 10% of the binary slag series will delay softening,and the higher the content of MgO content,softening delay phenomenon more obvious.It shows that MgO can promote the combination of FeO and MgO.When adding Al2O3,adding 5% will delay softening,on the contrary,adding 10% will promote softening.It state that adding Al2O3 will delay softening firstly,then the delay effect decrease.