The campaign life of blast furnace （BF） hearths has become the limiting factor for safety and high efficiency production of modern BFs. However, the early warning mechanism of hearth security has not been clear. In ...The campaign life of blast furnace （BF） hearths has become the limiting factor for safety and high efficiency production of modern BFs. However, the early warning mechanism of hearth security has not been clear. In this article, based on heat transfer calculations, heat flux and erosion monitoring, the features of heat flux and erosion were analyzed and compared among different types of hearths. The primary detecting elements, mathematical models, evaluating standards, and warning methods were discussed. A novel early warning mechanism with the three-level quantificational standards was proposed for BF hearth security.展开更多
A long campaign life of blast furnaces is heavily linked to the existence of a protective layer in their hearths. In this work, we conducted dissection studies and investigated damage in blast furnace hearths to estim...A long campaign life of blast furnaces is heavily linked to the existence of a protective layer in their hearths. In this work, we conducted dissection studies and investigated damage in blast furnace hearths to estimate the formation mechanism of the protective layer. The results illustrate that a significant amount of graphite phase was trapped within the hearth protective layer. Furthermore, on the basis of the thermodynamic and kinetic calculations of the graphite precipitation process, a precipitation potential index related to the formation of the graphite-rich protective layer was proposed to characterize the formation ability of this layer. We determined that, under normal operating conditions, the precipitation of graphite phase ~om hot metal was thermodynamically possible. Among elements that exist in hot metal, C, Si, and P favor graphite precipitation, whereas Mn and Cr inhibit this process. Moreover, at the same hot-face temperature, an increase of carbon concentration in hot metal can shorten the precipitation time. Finally, the results suggest that measures such as reducing the hot-face tem- perature and increasing the degree of carbon saturation in hot metal are critically important to improve the precipitation potential index.展开更多
Al_(2)O_(3)-SiC castables,for the relining of BF hearths in mid-campaign repair,were sampled and investigated after two years’service.The chemical and mineralogical characteristics of the residual castables were anal...Al_(2)O_(3)-SiC castables,for the relining of BF hearths in mid-campaign repair,were sampled and investigated after two years’service.The chemical and mineralogical characteristics of the residual castables were analyzed by X-ray diffraction,scanning electron microscopy,and energy dispersive X-ray spectrometry to study the erosion mechanism.The results show that as gaseous K diffuses in the castables,leucite(KAlSi_(2)O_(8))and multiple cracks are formed.Molten iron and slag penetrate through the cracks to form anorthite([Ca,Na][Al,Si]_(4)O_(8))and iron,which will not form an embrittlement layer similar to carbon bricks.The entire repair of the hearth with Al_(2)O_(3)-SiC castables combined with the design of thin-wall lining hearth eliminates“elephant foot shaped”erosion,greatly prolonging the service life of the hearth lining.展开更多
Pursuing green,low-carbon ironmaking technology primarily aims to reduce fuel ratios,especially coke ratios.Simultaneously,the reduction in coke ratios causes the coke layer in the blast furnace(BF)to become thinner,d...Pursuing green,low-carbon ironmaking technology primarily aims to reduce fuel ratios,especially coke ratios.Simultaneously,the reduction in coke ratios causes the coke layer in the blast furnace(BF)to become thinner,deteriorating the gas and liquid permeability of the burden column.This exacerbates coke degradation,significantly impacting the smelting process and increasing the demand for high-quality coke.To investigate the existence state of coke in the hearth,a 2500 m3 BF in China was taken as the research object,and three sets of samples at different heights of the hearth were obtained during planned outage.The results indicate that coke undergoes a significant degradation upon reaching the hearth.The proportion of coke particles smaller than 50 mm ranges from 81.22%to 89.50%.The proportion of coke particles larger than 20 mm decreases as the distance from the centerline of the tuyere increases,while the proportion of particles smaller than 10 mm increases with this distance.Additionally,the closer the bottom of the furnace is,the smaller the coke particle size becomes.The composition of slag filling the coke pores is similar to that of the final slag in the blast furnace,and the graphitization of coke is comparable to that of the final slag.The graphitization of coke starts from the surface of coke and leads to the formation of coke fines,and the graphitization degree of−74μm coke fines is the highest.The temperature has an effect on the reaction rate of coke solution loss,and the higher the temperature is,the faster the reaction rate is.展开更多
For studying the carbon thermal reduction rules of titanium in hot metal and providing a theoretical basis for the blast furnace（BF） hearth protection, the distribution behavior of titanium between low-titanium slag...For studying the carbon thermal reduction rules of titanium in hot metal and providing a theoretical basis for the blast furnace（BF） hearth protection, the distribution behavior of titanium between low-titanium slag system of CaO-SiO2-MgO-Al2O3-TiO2 and hot metal was studied using analytical reagents in a temperature range from 1350 °C to 1600 °C. Through high temperature melting, rapid quenching, chemical analysis and thermodynamic model calculating, the results showed that the increase of reaction temperature, which improved the titanium distribution L（Ti） and lowered the system activity coefficient γsys, leads to the rise of equilibrium constant. Combined with Wagner and congregated electron phase models, the data obtained in distribution experiments were used to fit out the Gibbs free energy formula of titanium carbothermic reduction. Finally, the relations between the contents of Si and Ti in hot metal and the titanium load to reach the minimum w（Ti） for the formation of Ti C were given.展开更多
A variety of techniques, such as chemical analysis, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction, were applied to characterize the adhesion protective layer formed below the blast...A variety of techniques, such as chemical analysis, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction, were applied to characterize the adhesion protective layer formed below the blast furnace taphole level when a certain amount of titanium-bearing burden was used. Samples of the protective layer were extracted to identify the chemical composition, phase assemblage, andistribution. Furthermore, the formation mechanism of the protective layer was determined after clarifying the source of each componenFinally, a technical strategy was proposed for achieving a stable protective layer in the hearth. The results show that the protective layemainly exists in a bilayer form in the sidewall, namely, a titanium-bearing layer and a graphite layer. Both the layers contain the slag phaswhose major crystalline phase is magnesium melilite（Ca2Mg Si2O7） and the main source of the slag phase is coke ash. It is clearly determinethat solid particles such as graphite, Ti（C,N） and Mg Al2O4play an important role in the formation of the protective layer, and the key factofor promoting the formation of a stable protective layer is reasonable control of the evolution behavior of coke.展开更多
The high-temperature tube furnace was applied to simulate the rotary hearth furnace （RHF） for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonde...The high-temperature tube furnace was applied to simulate the rotary hearth furnace （RHF） for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonded briquettes made by mixing metallurgical wastes, such as dust from bag house filter, OG sludge, fine converter ash and dust from the third electric field precipitator of the sinter strand, in various proportions was investigated. More than 70% of metallization rate, more than 95% of zinc removal rate, 80% of lead removal, as well as more than 80M of K and Na removal rates were achieved for the briquettes kept at 1473-1603 K for 15 min during the direct reduction process respectively. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results suggested that the main phases of the soot were ZnO, KC1, NaC1 and 4ZnO · ZnC12 · 5H20. Furthermore, the content of Zn reached 64.2 %, which could be used as secondary resources for zinc making. It was concluded that KC1 and NaC1 in secondary dust resulted from the volatilization from the briquettes, whilst ZnO and PbO were produced by the oxidation of Zn or lead vapour from briquettes by direct reduction.展开更多
This paper summarizes melting methods of titanium and titanium alloy, such as vacuum arc melting(VAR) and electron beam cold hearth melting(EBCHM), and the related inclusions formed when using these melting methods. L...This paper summarizes melting methods of titanium and titanium alloy, such as vacuum arc melting(VAR) and electron beam cold hearth melting(EBCHM), and the related inclusions formed when using these melting methods. Low-density inclusions are resulted from contamination of air, and high-density inclusions are caused by refractory elements. The formation process of inclusions was analysed. The removal mechanism of different kinds of inclusions was specified. Low-density inclusions are removed mainly by resolving. This is a comprehensive process containing reaction diffusion. The resolving rate of high-density inclusions is so low that these inclusions are mainly removed by sedimentation. The experiments and physical models of inclusions are detailed. In various melting methods, vacuum arc melting is prominent. However, this method cannot remove inclusions effectively, which usually results in repeat melting. Electron beam cold hearth melting has the best ability of removing inclusions. These results can provide instructions to researchers of titanium and titanium alloys.展开更多
A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace （RHF）. In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account...A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace （RHF）. In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account. The behaviors of iron metallization and dezincification were analyzed by the numerical method, which was validated by experimental data of the direct reduction of pellets in a Si-Mo furnace. The simulation results show that if the production targets of iron metallization and dezincification are up to 80% and 90%, respectively, the furnace temperature for high-temperature sections must be set higher than 1300~ C. Moreover, an undersupply of secondary air by 20% will lead to a decline in iron metallization rate of discharged pellets by 10% and a decrease in dezincing rate by 13%. In addition, if the residence time of pellets in the furnace is over 20 min, its further extension will hardly lead to an obvious increase in production indexes under the same furnace temperature curve.展开更多
At the beginning of 1990s, Shougang blast furnaces （BFs） No. 2, No. 4, No. 3 and No. 1 were rebuilt se quently for new technological modernization in succession. The campaign life of BFs No. 1, No. 3 and No. 4 reach...At the beginning of 1990s, Shougang blast furnaces （BFs） No. 2, No. 4, No. 3 and No. 1 were rebuilt se quently for new technological modernization in succession. The campaign life of BFs No. 1, No. 3 and No. 4 reaches 16.4, 17.6 and 15.6 years, respectively, and the hot metal output of one campaign reaches 33.8, 35.48 and 26.37 Mt, respectively; the hot metal output of BF effective volume of one campaign reaches 13328, 13991 and 12560 t/m^3, respectively, which reaches the international advanced level of BF high efficiency and long campaign life. In BF desig-ning, several advanced BF long campaign technologies were adopted. BF proper inner profile was optimized, reasona- ble inner profile was adopted, and closed circulating soften water cooling technology was applied in 4 BFs. Double row cooling pipe high efficiency cooling stave was developed which could prolong the service life of bosh, belly and stack. Hot pressed carbon brick and ceramic cup hearth lining structure were applied and optimized. BF operation was improved continuously to ensure stable and smooth operation of BF. Hearth working condition control was strengthened, burden distribution control technology was applied to achieve reasonable distribution of gas flow, and heat load monitoring was strengthened to maintain BF reasonable working inner profile. Proper maintenance at the end of BF campaign was enhanced. Hearth and bottom service life was prolonged by adding titaniferous material and enhancing hearth cooling. Gunning of lining was carried out periodically for the area above tuyere zone.展开更多
One of the bottlenecks of the blast furnace （BF） campaign is the life length of hearth bottom. The basic reason for the erosion of hearth bottom is its direct contact with hot metal. According to the theory of heat ...One of the bottlenecks of the blast furnace （BF） campaign is the life length of hearth bottom. The basic reason for the erosion of hearth bottom is its direct contact with hot metal. According to the theory of heat transfer, models of BF hearth bottom are built based on the actual examples using software and VC language, and the calculated results are in good agreement with the data of BF dissection after blowing out. The temperature distribution and the capability of the resistance to erosion for different structures of hearth bottom are analyzed, especially the two prevalent kinds of hearth bottom arrangements called ＂the method of heat transfer＂ for all-carbon brick bottom and ＂the method of heat isolation＂ for ceramic synthetic hearth bottom. Features of the two kinds of hearth bottoms are analyzed. Also the different ways of protecting the hearth bottom are clarified, according to some actual examples. After that, the same essence of prolonging life, and the fact that the existence of a ＂protective skull＂ with low thermal conductivity between the hot metal and brick layers is of utmost importance are shown.展开更多
In a continuous annealing furnace, the hearth rollers are affected by heat, which in turn affects the stable operation of the steel strips. In order to ensure the stable operation of the steel strips the ability of th...In a continuous annealing furnace, the hearth rollers are affected by heat, which in turn affects the stable operation of the steel strips. In order to ensure the stable operation of the steel strips the ability of the rollers to correct themselves and to prevent the steel strips from buckling, effective measures are required to control the surface crown of the rollers inside the furnace. Starting from production, this study analyzes the way in which the crown of the hearth rollers inside the continuous annealing furnace changes. The study suggests control measures to prevent buckling and and misalignment. The study definitely provides guidance to the stable operation of steel strips in continuous annealed furnaces.展开更多
Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was con...Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was constructed to study the reduction kinetics of iron oxides and ZnO in the dust composite pellets. It was validated by comparing the calculated values with experimental results. The effects of furnace temperature, pellet radius, and pellet porosity on the reduction were investigated by the model. It is shown that furnace temperature has obvious influence on both of the reduction of iron oxides and ZnO, but the influence of pellet radius and porosity is much smaller. Model calculations suggest that both of the reduction of iron oxides and ZnO are under mixed control with interface reactions and Boudouard reaction in the early stage, but only with interface reactions in the later stage.展开更多
Thermal spray coatings have been widely used on hearth rolls in a continuous annealing line to improve steel sheet quality and prolong the roll service life. One of the common defects formed on a working hearth roll i...Thermal spray coatings have been widely used on hearth rolls in a continuous annealing line to improve steel sheet quality and prolong the roll service life. One of the common defects formed on a working hearth roll is the oxide pickup. The most common cause of the pickup formation is that the active Mn oxide reacts with coating. The potentials of two different coatings, CoCrAlYTa-Al2O3 (No. 1) and CoCrYNi-Y2O3 (No. 2), to duplicate pickups by reacting with Fe and Mn oxides were studied. There are three stages during pickup producing and growing. No. 2 coating effectively reduced the corrosion of Mn oxide. The characterization and modification of the surface oxide formed can be changed with different dew points. The results indicate that the dew point from — 53 to — 10 ℃ can change the depth of Mn oxide, such that an alteration can prevent the first stage and second stage and is good for preventing the pickup growing.展开更多
The liquid flow in blast furnace hearth can result in the erosion of hearth. To prolong the campaign life of blast furnace, the effects of coke bed structure, coke porosity and deepness of taphole on liquid flow in he...The liquid flow in blast furnace hearth can result in the erosion of hearth. To prolong the campaign life of blast furnace, the effects of coke bed structure, coke porosity and deepness of taphole on liquid flow in hearth were studied by re model under different conditions. The results show that with the decrease of coke porosity, the peripheral flow is enhanced. Moreover, the existence of narrow coke free zone and the deepness reduction of taphole can increase the flowability on the bottom of hearth.展开更多
Cooling water provides the best protection for refractory in the blast furnace hearth. Stable and suitable water quality and abundant cooling water are the basis for long service life of the hearth. Some phenomena abo...Cooling water provides the best protection for refractory in the blast furnace hearth. Stable and suitable water quality and abundant cooling water are the basis for long service life of the hearth. Some phenomena about cooling system in the commercial blast furnaces were described, and reasonable explanations of these phenomena were analyzed. The results show that increasing the amount of cooling water and reducing the inlet temperature of cooling water can increase the cooling effect significantly in the case of water scaling. Heat flux in the blast furnace hearth is the average heat flux of cooling stave, and the erosion of carbon brick is uneven. There is no direct connection between the actual erosion condition and the heat flux in the hearth. The change trend of thermocouple temperature and heat flux in the hearth can reflect whether the gaps exist among the bricks or not, providing an effective guidance for industrial production and the evaluation of safety state in the hearth. And, the film boiling will not occur in the normal cooling system in the blast furnace hearth.展开更多
The hearth of “heat transfer method” and the ceramic cup synthetic hearth bottom of “heart isolation method” are two most popular designs for blast furnace (BF). Although there are successful real examples, some d...The hearth of “heat transfer method” and the ceramic cup synthetic hearth bottom of “heart isolation method” are two most popular designs for blast furnace (BF). Although there are successful real examples, some disadvantages, for instance large heat loss and high cost, still exist for these designs. According to the theory of heat transfer, based on the calculation of temperature distribution of the hearth bottom, it is elucidated that all brick layers at the hearth bottom may not be considered as the only reason why different structures exhibited different temperature distributions although total heat resistance is the same, and then based on the effect of hot metal and cold water on different temperature distribution ranges, the concepts of “heat resistance” and “cooling enhancement” are put forth. Based on this, the disadvantages and the factors affecting temperature distribution, of the two types of hearth bottoms were illustrated. On the basis of these analyses, a novel structure for BF hearth bottom designing that can easily form “self-protecting” slag layer stably, called “the method of gradient brick layout that has an optimum combination of cooling enhancement and heat resistance” was proposed; it can not only prolong the hearth bottom longevity but also reduce the cost and heat loss. Also, the optimum arrangement of thermal couples in hearth bottom was suggested based on the previous studies on erosion prediction carried out by the author.展开更多
One of the methods forming the shell is to appropriately design the coolingstaves and hearth without overheating during the campaign life of the furnace. The three-dimensionalsteady mathematical models for calculating...One of the methods forming the shell is to appropriately design the coolingstaves and hearth without overheating during the campaign life of the furnace. The three-dimensionalsteady mathematical models for calculating the temperature distribution in the coolers andtwo-dimensional unsteady mathematical models with phase-change latent heat for calculating thetemperature distribution of the hearth bottom were established. The calculation results show thatthe formation of the slag-metal protection shell can be achieved by optimizing the design parametersof the coolers. Increasing the heat conductivity of the carbon brick can move the isothermal lineof 1150 deg C upward outside the hearth bottom.展开更多
The treatment of iron-bearing dusts and sludges by the rotary hearth furnace process has the advantage of sufficient utilization of valuable metals and a high impurity removal rate,but the lower strength of the metall...The treatment of iron-bearing dusts and sludges by the rotary hearth furnace process has the advantage of sufficient utilization of valuable metals and a high impurity removal rate,but the lower strength of the metallized product needs to be addressed.The effects of quaternary basicity R4(w(CaO+MgO)/w(SiO_(2)+Al_(2)O_(3)))on the reduction behavior and physical and chemical properties of metallized pellets,including phase composition,compressive strength,microstructure and soft melting area,were investigated with FactSage thermodynamic software and experiments.The strength of metallized pellets depended on the gangue composition,such as CaO,MgO,Al_(2)O_(3) and SiO_(2),due to the altered chemical composition,physical phase composition,microscopic morphology and stability of the slag phase.The reduction of carbon-bearing pellets was significantly promoted by suitable basicity.The lower basicity(R_(4)<1.4)facilitated the formation of low melting point iron-containing compounds from SiO_(2) and Al_(2)O_(3) with FeO,resulting in increased liquid phase generation,but lower metallization rate,due to the hindered precipitation and growth of iron grains.Interestingly,the higher basicity(R_(4)>1.8)also increased the amount of liquid phase and improved the strength of the pellets,due to the granular iron crystals bonded into sheets.Notably,the main component of the liquid phase in high-basicity conditions was calcium ferrite.Although the additional amount of liquid phase was beneficial to the strength of the metallized pellets,calcium disilicate was formed at R_(4)=1.6,resulting in a reduction in the compressive strength of the pellets to 1521.9 N/pellet.展开更多
The rotary hearth furnace iron nugget process has advantages of short reaction time, high-quality reduced product and wide adaptability of raw materials and meets the trend in ecofriendly development of iron and steel...The rotary hearth furnace iron nugget process has advantages of short reaction time, high-quality reduced product and wide adaptability of raw materials and meets the trend in ecofriendly development of iron and steel industry. Although the rotary hearth furnace iron nugget process cannot replace blast furnace process, which is affected by production scale, thermal efficiency and technical maturity, it is still a feasible technology for iron production. In order to realize the efficient utilization of high Al2O3 iron ore resources, preparation of iron nuggets with high Al2O3 iron ore was studied. Using iron concentrate as raw material, the effects of slag basicity, Al2O3 and MgO on melting separation of iron ore–coal composite pellets, such as the melting separation temperature, the melting separation time, the morphology of melting separated product, and the recovery rate of iron nugget, were studied. The results showed that relatively low or high liquidus temperature of slag had a negative effect on reduction and melting separation of iron ore–coal composite pellets. The increase in fluidity index of slag resulted in a decline in the melting separation temperature and time of iron ore–coal composite pellets. Optimum basicity to produce iron nuggets using iron ore–coal composite pellets was 0.8–1.0, 0.4 and 0.8 for iron concentrate containing 2, 4 and 6–10 wt.% Al2O3, respectively. Corresponding liquidus temperature and fluidity index of slag were 1300–1475 C and above 4.5, respectively. Under this condition, the lowest melting separation temperature and the shortest melting separation time of iron ore–coal composite pellets were 1375 C and 7 min, respectively. The recovery rate of metallic iron in the form of iron nugget could reach about 94%.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 61271303)the Fundamental Research Funds for the Central Universities of China (No. FRF-TP-12-029A)
文摘The campaign life of blast furnace （BF） hearths has become the limiting factor for safety and high efficiency production of modern BFs. However, the early warning mechanism of hearth security has not been clear. In this article, based on heat transfer calculations, heat flux and erosion monitoring, the features of heat flux and erosion were analyzed and compared among different types of hearths. The primary detecting elements, mathematical models, evaluating standards, and warning methods were discussed. A novel early warning mechanism with the three-level quantificational standards was proposed for BF hearth security.
基金supported the National Science Foundation for Young Scientists of China (No. 51304014)the Open Foundation of the State Key Laboratory of Advanced Metallurgy (No. 41603007)
文摘A long campaign life of blast furnaces is heavily linked to the existence of a protective layer in their hearths. In this work, we conducted dissection studies and investigated damage in blast furnace hearths to estimate the formation mechanism of the protective layer. The results illustrate that a significant amount of graphite phase was trapped within the hearth protective layer. Furthermore, on the basis of the thermodynamic and kinetic calculations of the graphite precipitation process, a precipitation potential index related to the formation of the graphite-rich protective layer was proposed to characterize the formation ability of this layer. We determined that, under normal operating conditions, the precipitation of graphite phase ~om hot metal was thermodynamically possible. Among elements that exist in hot metal, C, Si, and P favor graphite precipitation, whereas Mn and Cr inhibit this process. Moreover, at the same hot-face temperature, an increase of carbon concentration in hot metal can shorten the precipitation time. Finally, the results suggest that measures such as reducing the hot-face tem- perature and increasing the degree of carbon saturation in hot metal are critically important to improve the precipitation potential index.
文摘Al_(2)O_(3)-SiC castables,for the relining of BF hearths in mid-campaign repair,were sampled and investigated after two years’service.The chemical and mineralogical characteristics of the residual castables were analyzed by X-ray diffraction,scanning electron microscopy,and energy dispersive X-ray spectrometry to study the erosion mechanism.The results show that as gaseous K diffuses in the castables,leucite(KAlSi_(2)O_(8))and multiple cracks are formed.Molten iron and slag penetrate through the cracks to form anorthite([Ca,Na][Al,Si]_(4)O_(8))and iron,which will not form an embrittlement layer similar to carbon bricks.The entire repair of the hearth with Al_(2)O_(3)-SiC castables combined with the design of thin-wall lining hearth eliminates“elephant foot shaped”erosion,greatly prolonging the service life of the hearth lining.
基金supported by the National Natural Science Foundation of China(Grant No.U1960205)China Baowu Low Carbon Metallurgy Innovation Foundation(Grant Nos.BWLCF202101 and BWLCF202104)China Minmetals Science and Technology Special Plan Foundation(Grant No.2020ZXA01).
文摘Pursuing green,low-carbon ironmaking technology primarily aims to reduce fuel ratios,especially coke ratios.Simultaneously,the reduction in coke ratios causes the coke layer in the blast furnace(BF)to become thinner,deteriorating the gas and liquid permeability of the burden column.This exacerbates coke degradation,significantly impacting the smelting process and increasing the demand for high-quality coke.To investigate the existence state of coke in the hearth,a 2500 m3 BF in China was taken as the research object,and three sets of samples at different heights of the hearth were obtained during planned outage.The results indicate that coke undergoes a significant degradation upon reaching the hearth.The proportion of coke particles smaller than 50 mm ranges from 81.22%to 89.50%.The proportion of coke particles larger than 20 mm decreases as the distance from the centerline of the tuyere increases,while the proportion of particles smaller than 10 mm increases with this distance.Additionally,the closer the bottom of the furnace is,the smaller the coke particle size becomes.The composition of slag filling the coke pores is similar to that of the final slag in the blast furnace,and the graphitization of coke is comparable to that of the final slag.The graphitization of coke starts from the surface of coke and leads to the formation of coke fines,and the graphitization degree of−74μm coke fines is the highest.The temperature has an effect on the reaction rate of coke solution loss,and the higher the temperature is,the faster the reaction rate is.
基金Project(2012CB720401)supported by the National Basic Research Program of ChinaProject(2011BAC01B02)supported by the National Key Technology R&D Program of China
文摘For studying the carbon thermal reduction rules of titanium in hot metal and providing a theoretical basis for the blast furnace（BF） hearth protection, the distribution behavior of titanium between low-titanium slag system of CaO-SiO2-MgO-Al2O3-TiO2 and hot metal was studied using analytical reagents in a temperature range from 1350 °C to 1600 °C. Through high temperature melting, rapid quenching, chemical analysis and thermodynamic model calculating, the results showed that the increase of reaction temperature, which improved the titanium distribution L（Ti） and lowered the system activity coefficient γsys, leads to the rise of equilibrium constant. Combined with Wagner and congregated electron phase models, the data obtained in distribution experiments were used to fit out the Gibbs free energy formula of titanium carbothermic reduction. Finally, the relations between the contents of Si and Ti in hot metal and the titanium load to reach the minimum w（Ti） for the formation of Ti C were given.
基金financially supported by the Natural Science Foundation of China(No.51304014)the Natural Science Foundation of China and Baosteel(No.51134008)the National Basic Research Program of China(No.2012CB720401)
文摘A variety of techniques, such as chemical analysis, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction, were applied to characterize the adhesion protective layer formed below the blast furnace taphole level when a certain amount of titanium-bearing burden was used. Samples of the protective layer were extracted to identify the chemical composition, phase assemblage, andistribution. Furthermore, the formation mechanism of the protective layer was determined after clarifying the source of each componenFinally, a technical strategy was proposed for achieving a stable protective layer in the hearth. The results show that the protective layemainly exists in a bilayer form in the sidewall, namely, a titanium-bearing layer and a graphite layer. Both the layers contain the slag phaswhose major crystalline phase is magnesium melilite（Ca2Mg Si2O7） and the main source of the slag phase is coke ash. It is clearly determinethat solid particles such as graphite, Ti（C,N） and Mg Al2O4play an important role in the formation of the protective layer, and the key factofor promoting the formation of a stable protective layer is reasonable control of the evolution behavior of coke.
基金Item Sponsored by China Postdoctoral Science Foundation(2012M510320)Demonstration Project about Recycling Economy in2007of National Development and Reform Commission of China([2007]3194)
文摘The high-temperature tube furnace was applied to simulate the rotary hearth furnace （RHF） for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonded briquettes made by mixing metallurgical wastes, such as dust from bag house filter, OG sludge, fine converter ash and dust from the third electric field precipitator of the sinter strand, in various proportions was investigated. More than 70% of metallization rate, more than 95% of zinc removal rate, 80% of lead removal, as well as more than 80M of K and Na removal rates were achieved for the briquettes kept at 1473-1603 K for 15 min during the direct reduction process respectively. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results suggested that the main phases of the soot were ZnO, KC1, NaC1 and 4ZnO · ZnC12 · 5H20. Furthermore, the content of Zn reached 64.2 %, which could be used as secondary resources for zinc making. It was concluded that KC1 and NaC1 in secondary dust resulted from the volatilization from the briquettes, whilst ZnO and PbO were produced by the oxidation of Zn or lead vapour from briquettes by direct reduction.
基金financially supported by the National Key Research and Development Program of China(2016YFB0301200)
文摘This paper summarizes melting methods of titanium and titanium alloy, such as vacuum arc melting(VAR) and electron beam cold hearth melting(EBCHM), and the related inclusions formed when using these melting methods. Low-density inclusions are resulted from contamination of air, and high-density inclusions are caused by refractory elements. The formation process of inclusions was analysed. The removal mechanism of different kinds of inclusions was specified. Low-density inclusions are removed mainly by resolving. This is a comprehensive process containing reaction diffusion. The resolving rate of high-density inclusions is so low that these inclusions are mainly removed by sedimentation. The experiments and physical models of inclusions are detailed. In various melting methods, vacuum arc melting is prominent. However, this method cannot remove inclusions effectively, which usually results in repeat melting. Electron beam cold hearth melting has the best ability of removing inclusions. These results can provide instructions to researchers of titanium and titanium alloys.
基金financially supported by the National Key Basic Research and Development Program of China(No. 2012CB720405)
文摘A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace （RHF）. In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account. The behaviors of iron metallization and dezincification were analyzed by the numerical method, which was validated by experimental data of the direct reduction of pellets in a Si-Mo furnace. The simulation results show that if the production targets of iron metallization and dezincification are up to 80% and 90%, respectively, the furnace temperature for high-temperature sections must be set higher than 1300~ C. Moreover, an undersupply of secondary air by 20% will lead to a decline in iron metallization rate of discharged pellets by 10% and a decrease in dezincing rate by 13%. In addition, if the residence time of pellets in the furnace is over 20 min, its further extension will hardly lead to an obvious increase in production indexes under the same furnace temperature curve.
文摘At the beginning of 1990s, Shougang blast furnaces （BFs） No. 2, No. 4, No. 3 and No. 1 were rebuilt se quently for new technological modernization in succession. The campaign life of BFs No. 1, No. 3 and No. 4 reaches 16.4, 17.6 and 15.6 years, respectively, and the hot metal output of one campaign reaches 33.8, 35.48 and 26.37 Mt, respectively; the hot metal output of BF effective volume of one campaign reaches 13328, 13991 and 12560 t/m^3, respectively, which reaches the international advanced level of BF high efficiency and long campaign life. In BF desig-ning, several advanced BF long campaign technologies were adopted. BF proper inner profile was optimized, reasona- ble inner profile was adopted, and closed circulating soften water cooling technology was applied in 4 BFs. Double row cooling pipe high efficiency cooling stave was developed which could prolong the service life of bosh, belly and stack. Hot pressed carbon brick and ceramic cup hearth lining structure were applied and optimized. BF operation was improved continuously to ensure stable and smooth operation of BF. Hearth working condition control was strengthened, burden distribution control technology was applied to achieve reasonable distribution of gas flow, and heat load monitoring was strengthened to maintain BF reasonable working inner profile. Proper maintenance at the end of BF campaign was enhanced. Hearth and bottom service life was prolonged by adding titaniferous material and enhancing hearth cooling. Gunning of lining was carried out periodically for the area above tuyere zone.
基金Item Sponsored by National Natural Science Foundation of China (60472095)
文摘One of the bottlenecks of the blast furnace （BF） campaign is the life length of hearth bottom. The basic reason for the erosion of hearth bottom is its direct contact with hot metal. According to the theory of heat transfer, models of BF hearth bottom are built based on the actual examples using software and VC language, and the calculated results are in good agreement with the data of BF dissection after blowing out. The temperature distribution and the capability of the resistance to erosion for different structures of hearth bottom are analyzed, especially the two prevalent kinds of hearth bottom arrangements called ＂the method of heat transfer＂ for all-carbon brick bottom and ＂the method of heat isolation＂ for ceramic synthetic hearth bottom. Features of the two kinds of hearth bottoms are analyzed. Also the different ways of protecting the hearth bottom are clarified, according to some actual examples. After that, the same essence of prolonging life, and the fact that the existence of a ＂protective skull＂ with low thermal conductivity between the hot metal and brick layers is of utmost importance are shown.
文摘In a continuous annealing furnace, the hearth rollers are affected by heat, which in turn affects the stable operation of the steel strips. In order to ensure the stable operation of the steel strips the ability of the rollers to correct themselves and to prevent the steel strips from buckling, effective measures are required to control the surface crown of the rollers inside the furnace. Starting from production, this study analyzes the way in which the crown of the hearth rollers inside the continuous annealing furnace changes. The study suggests control measures to prevent buckling and and misalignment. The study definitely provides guidance to the stable operation of steel strips in continuous annealed furnaces.
基金financially supported by the National Basic Research Program of China (No. 2012CB720401)the National Key Technology Research and Development Program of China (No. 2011BAC01B02)
文摘Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was constructed to study the reduction kinetics of iron oxides and ZnO in the dust composite pellets. It was validated by comparing the calculated values with experimental results. The effects of furnace temperature, pellet radius, and pellet porosity on the reduction were investigated by the model. It is shown that furnace temperature has obvious influence on both of the reduction of iron oxides and ZnO, but the influence of pellet radius and porosity is much smaller. Model calculations suggest that both of the reduction of iron oxides and ZnO are under mixed control with interface reactions and Boudouard reaction in the early stage, but only with interface reactions in the later stage.
基金the financial support from National Natural Science Foundation of China(No.U1460101).
文摘Thermal spray coatings have been widely used on hearth rolls in a continuous annealing line to improve steel sheet quality and prolong the roll service life. One of the common defects formed on a working hearth roll is the oxide pickup. The most common cause of the pickup formation is that the active Mn oxide reacts with coating. The potentials of two different coatings, CoCrAlYTa-Al2O3 (No. 1) and CoCrYNi-Y2O3 (No. 2), to duplicate pickups by reacting with Fe and Mn oxides were studied. There are three stages during pickup producing and growing. No. 2 coating effectively reduced the corrosion of Mn oxide. The characterization and modification of the surface oxide formed can be changed with different dew points. The results indicate that the dew point from — 53 to — 10 ℃ can change the depth of Mn oxide, such that an alteration can prevent the first stage and second stage and is good for preventing the pickup growing.
文摘The liquid flow in blast furnace hearth can result in the erosion of hearth. To prolong the campaign life of blast furnace, the effects of coke bed structure, coke porosity and deepness of taphole on liquid flow in hearth were studied by re model under different conditions. The results show that with the decrease of coke porosity, the peripheral flow is enhanced. Moreover, the existence of narrow coke free zone and the deepness reduction of taphole can increase the flowability on the bottom of hearth.
基金This work National Science Foundation （51704019）. was financially supported by the for Young Scientists of China
文摘Cooling water provides the best protection for refractory in the blast furnace hearth. Stable and suitable water quality and abundant cooling water are the basis for long service life of the hearth. Some phenomena about cooling system in the commercial blast furnaces were described, and reasonable explanations of these phenomena were analyzed. The results show that increasing the amount of cooling water and reducing the inlet temperature of cooling water can increase the cooling effect significantly in the case of water scaling. Heat flux in the blast furnace hearth is the average heat flux of cooling stave, and the erosion of carbon brick is uneven. There is no direct connection between the actual erosion condition and the heat flux in the hearth. The change trend of thermocouple temperature and heat flux in the hearth can reflect whether the gaps exist among the bricks or not, providing an effective guidance for industrial production and the evaluation of safety state in the hearth. And, the film boiling will not occur in the normal cooling system in the blast furnace hearth.
文摘The hearth of “heat transfer method” and the ceramic cup synthetic hearth bottom of “heart isolation method” are two most popular designs for blast furnace (BF). Although there are successful real examples, some disadvantages, for instance large heat loss and high cost, still exist for these designs. According to the theory of heat transfer, based on the calculation of temperature distribution of the hearth bottom, it is elucidated that all brick layers at the hearth bottom may not be considered as the only reason why different structures exhibited different temperature distributions although total heat resistance is the same, and then based on the effect of hot metal and cold water on different temperature distribution ranges, the concepts of “heat resistance” and “cooling enhancement” are put forth. Based on this, the disadvantages and the factors affecting temperature distribution, of the two types of hearth bottoms were illustrated. On the basis of these analyses, a novel structure for BF hearth bottom designing that can easily form “self-protecting” slag layer stably, called “the method of gradient brick layout that has an optimum combination of cooling enhancement and heat resistance” was proposed; it can not only prolong the hearth bottom longevity but also reduce the cost and heat loss. Also, the optimum arrangement of thermal couples in hearth bottom was suggested based on the previous studies on erosion prediction carried out by the author.
基金The work was financially supported by"95"key project of China(No.1997-02-08).]
文摘One of the methods forming the shell is to appropriately design the coolingstaves and hearth without overheating during the campaign life of the furnace. The three-dimensionalsteady mathematical models for calculating the temperature distribution in the coolers andtwo-dimensional unsteady mathematical models with phase-change latent heat for calculating thetemperature distribution of the hearth bottom were established. The calculation results show thatthe formation of the slag-metal protection shell can be achieved by optimizing the design parametersof the coolers. Increasing the heat conductivity of the carbon brick can move the isothermal lineof 1150 deg C upward outside the hearth bottom.
基金support from the Outstanding Youth Fund of Anhui Province(Grant No.2208085J19)the National Key Research and Development Program of China(Grant No.2022YFC3901405).
文摘The treatment of iron-bearing dusts and sludges by the rotary hearth furnace process has the advantage of sufficient utilization of valuable metals and a high impurity removal rate,but the lower strength of the metallized product needs to be addressed.The effects of quaternary basicity R4(w(CaO+MgO)/w(SiO_(2)+Al_(2)O_(3)))on the reduction behavior and physical and chemical properties of metallized pellets,including phase composition,compressive strength,microstructure and soft melting area,were investigated with FactSage thermodynamic software and experiments.The strength of metallized pellets depended on the gangue composition,such as CaO,MgO,Al_(2)O_(3) and SiO_(2),due to the altered chemical composition,physical phase composition,microscopic morphology and stability of the slag phase.The reduction of carbon-bearing pellets was significantly promoted by suitable basicity.The lower basicity(R_(4)<1.4)facilitated the formation of low melting point iron-containing compounds from SiO_(2) and Al_(2)O_(3) with FeO,resulting in increased liquid phase generation,but lower metallization rate,due to the hindered precipitation and growth of iron grains.Interestingly,the higher basicity(R_(4)>1.8)also increased the amount of liquid phase and improved the strength of the pellets,due to the granular iron crystals bonded into sheets.Notably,the main component of the liquid phase in high-basicity conditions was calcium ferrite.Although the additional amount of liquid phase was beneficial to the strength of the metallized pellets,calcium disilicate was formed at R_(4)=1.6,resulting in a reduction in the compressive strength of the pellets to 1521.9 N/pellet.
基金The authors would like to express their gratitude for the financial support of Fundamental Research Funds for the Central Universities (FRF-TP-18-008A2)the National Natural Science Foundation of China (51804024)+1 种基金the China Postdoctoral Science Foundation (2016M600919)the State Key Laboratory of Advanced Metallurgy of University of Science and Technology Beijing (41618022).
文摘The rotary hearth furnace iron nugget process has advantages of short reaction time, high-quality reduced product and wide adaptability of raw materials and meets the trend in ecofriendly development of iron and steel industry. Although the rotary hearth furnace iron nugget process cannot replace blast furnace process, which is affected by production scale, thermal efficiency and technical maturity, it is still a feasible technology for iron production. In order to realize the efficient utilization of high Al2O3 iron ore resources, preparation of iron nuggets with high Al2O3 iron ore was studied. Using iron concentrate as raw material, the effects of slag basicity, Al2O3 and MgO on melting separation of iron ore–coal composite pellets, such as the melting separation temperature, the melting separation time, the morphology of melting separated product, and the recovery rate of iron nugget, were studied. The results showed that relatively low or high liquidus temperature of slag had a negative effect on reduction and melting separation of iron ore–coal composite pellets. The increase in fluidity index of slag resulted in a decline in the melting separation temperature and time of iron ore–coal composite pellets. Optimum basicity to produce iron nuggets using iron ore–coal composite pellets was 0.8–1.0, 0.4 and 0.8 for iron concentrate containing 2, 4 and 6–10 wt.% Al2O3, respectively. Corresponding liquidus temperature and fluidity index of slag were 1300–1475 C and above 4.5, respectively. Under this condition, the lowest melting separation temperature and the shortest melting separation time of iron ore–coal composite pellets were 1375 C and 7 min, respectively. The recovery rate of metallic iron in the form of iron nugget could reach about 94%.
