| In recent years,blast furnace are gradually being made larger and longer-lived to reduce energy consumption and improve quality of pig iron,while accompany in smelting intensity places higher demands on refractory materials for blast furnace.The taphole is the weakest area of blast furnace due to its harsh working environment,including long-term temperature fluctuations and serious corrosion by slag and molten iron.Therefore,the refractory material,taphole clay(THC),used in the taphole area is a key factor in operation of blast furnace.At present,there are problems with the plasticity control of THC,which is empirical and extensive,and corrosion resistance of THC is not satisfactory,resulting in short tapping time,difficult to keep the iron flow rate stable,and frequent reaming phenomenon,resulting in the destruction of the carbon bricks in the taphole area directly eroded by slag/molton iron,which leads to frequent blast furnace shutdowns and even shortened service life.Therefore,in this thesis,by optimising the structure and composition of THC,a systematic plasticity change law of THC was established based on Benbow-Bridgwater model and the fitting of experimental data.And the physical and chemical evolutions of THC during the corrosion process of high-temperature slag/molten iron were investigated by FactSage thermodynamics calculation and Comsol Multiphysics simulation software.The corrosion resistance of THC is further improved by increasing its critical strength at high temperature and forming separation layer with high-melting point by employing B2O3 and TiO2 as additives.In addition,the industrial solid waste was introduced into THC not only promotes sintering using the liquid phase,but also improves the performance of the THC,which is explored for the use of industrial solid waste in THC.Draw the following conclusion:(1)Based on Benbow-Bridgwater model,with the modulus of distribution n and the binder addition increase,the THC plasticity index decreases and tend to converge.The intermediate parameter distance between particles λ was introduced,which was related to the Benbow-Bridgwater model,a plasticity index equation obtained with practical significance,and the correlation coefficient R2 between the equation and the actual plasticity index was over 0.90.When the distance between particles λ is greater than 5.5 μm,the THC has better plasticity index,and the influence of the modulus of distribution n and binder addition on the plasticity index are little.Considering the mechanical properties of taphole clay,the best composition of THC with the modulus of distribution n=0.24 and binder addition=14 wt%.(2)Based on the study of erosion kinetics,the corrosion rate and penetration rate of high temperature slag on THC could be calculated,which are 0.132 mm/h and 0.253 mm/h,respectively.According to the FactS age thermodynamic calculation and static corrosion resistance experiment,it can be seen that the main corrosion phase of THC under high temperature slag corrosion is anorthite,accompanied by a samll amount of gehlenite and monticellite.Through Cosmol Multiphysics and dynamic corrosion resistance experiment,the erosion process could be divided into three parts.Firstly,THC reacted with slag and formed an corrosion layer due to chemical corrosion,reducing its the critical strength.The physical erosion that accompanies the slag/iron circulation caused rapid destruction of the contact surface before further chemical corrosion.The new interface exposed by chemical corrosion and physical erosion accelerates the corrosion process and the cycle was rapeatly with evental destruction of the THC.(3)B2O3 was introduced into THC to promote the process of sintering and particle interlinking and growth by using the "indirect liquid phase sintering" mechanism,and the in-situ formation of boron-containing mullite with larger length-to-diameter ratio forms a interlocking structure,which both increased the critical strength of THC.By introducing TiO2 into THC,it could reduce the viscosity of liquid phase and accelerate the sintering process,at the same time,TiO2 could react with ferro-silicon nitride and coke to generate Ti(C,N)phase,dispersing in the slag make the slag viscosity rise,and improve the corrosion resistance of THC.(4)The sintering mechanism of calcium alumino-titanate(CAT)was studied:CAT aggregate could react to form the liquid phase wrapping on the surface,making the surrounding particles to enhance particle-matrix bonding strength under the capillary force.CAT powder could react and generate liquid phase quickly,the expansion accompanying by reaction caused the formation of cracks in the matrix,leading to the decrease of mechanical properties.Therefore,introducing CAT as aggregate into THC obtain better thermo-mechanical properties.By introducing CAT,ferro-chromium slag(FCS)and ferro-vanadium slag(FVS)respectively as aggregate into taphole clay,the dynamic corrosion resistance experiment results show that the corrosion resistance of taphole clay by begin to:CAT>BA=FCS>FVS.The application of improved taphole clay in 1680 m3 and 2800 m3 blast furnace has obtained great results,the frequency of abnormal phenomenon during tapping process has been obviously decreased,and the tapping time has been increased. |
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