Numerical Analysis of Blast Furnace Performance Under Charging Iron-Bearing Burdens With High Reducibility

The reducibility of iron-bearing burdens was emphasized for improving the operation efficiency of blast furnace. The blast furnace operation of charging the burdens with high reducibility has been numerically evaluated using a multi-fluid blast furnace model. The effects of reaction rate constants and diffusion coefficients were investigated separately or simultaneously for clarifying the variations of furnace state. According to the model simulation results, in the upper zone, the indirect reduction of the burdens proceeds at a faster rate and the shaft efficiency is enhanced with the improvement under the conditions of interface reaction and intra-particle diffusion. In the lower zone, direct reduction in molten slag is restrained. As a consequence, CO utilization of top gas is enhanced and the ratio of direct reduction is decreased. It is possible to achieve higher energy efficiency of the blast furnace, and this is represented by the improvement in productivity and the decrease in consumption of reducing agent. The use of high-reducibility burdens contributes to a better performance of blast furnace. More efforts are necessary to develop and apply high-reducibility sinter and carbon composite agglomerates for practical application at a blast furnace.     

Numerical Analysis of Blast Furnace Performance Under Charging IronBearing Burdens With High Reducibility

The reducibility of ironbearing burdens was emphasized for improving the operation efficiency of blast furnace. The blast furnace operation of charging the burdens with high reducibility has been numerically evaluated using a multifluid blast furnace model. The effects of reaction rate constants and diffusion coefficients were investigated separately or simultaneously for clarifying the variations of furnace state. According to the model simulation results, in the upper zone, the indirect reduction of the burdens proceeds at a faster rate and the shaft efficiency is enhanced with the improvement under the conditions of interface reaction and intraparticle diffusion. In the lower zone, direct reduction in molten slag is restrained. As a consequence, CO utilization of top gas is enhanced and the ratio of direct reduction is decreased. It is possible to achieve higher energy efficiency of the blast furnace, and this is represented by the improvement in productivity and the decrease in consumption of reducing agent. The use of highreducibility burdens contributes to a better performance of blast furnace. More efforts are necessary to develop and apply highreducibility sinter and carbon composite agglomerates for practical application at a blast furnace.     

Numerical Simulation of Innovative Operation of Blast Furnace Based on MultiFluid Model

A multifluid blast furnace model was simply introduced and was used to simulate several innovative ironmaking operations. The simulation results show that injecting hydrogen bearing materials, especially injecting natural gas and plastics, the hydrogen reduction is enhanced, and the furnace performance is improved simultaneously. Total heat input shows obvious decrease due to the decrease of heat consumption in direct reduction, solution loss and silicon transfer reactions. If carbon composite agglomerates are charged into the furnace, the temperature of thermal reserve zone will obviously decrease, and the reduction of ironbearing burden materials will be retarded. However, the efficiency of blast furnace is improved just due to the decrease in heat requirements for solution loss, sinter reduction, and silicon transfer reactions, and less heat loss through top gas and furnace wall. Finally, the model is used to investigate the performance of blast furnace under the condition of top gas recycling together with plastics injection, cold oxygen blasting and carbon composite agglomerate charging. The lower furnace temperature, extremely accelerated reduction rate, drastically decreased CO2 emission and remarkably enhanced heat efficiency were obtained by using the innovative operations, and the blast furnace operation with superhigh efficiency can be realized.     

Analysis of Effect of Gas Temperature on Cooling Stave of Blast Furnace

In order to study the effect of gas temperature variation on cooling stave,temperature,stress and displacement distributions of cooling stave were analyzed respectively when gas temperature inside blast furnace increases from 1000 to 1600℃.The results show that the temperature field on cold side is under control of cooling pipes and hardly changes when gas temperature increases.The temperature gradient and change rate with time near hot sides are greater than those in other regions and the later can reach 100℃/s.The stress intensity near middle area of hot surface is up to 400MPa and that's why there are lots of cracks at this place.The edge of stave is bent to cold side and middle regions between fixed bolts and pin moves to hot side.The displacement around fixed pin is smaller but larger on the edge and the maximum is located on hot side of top surface.The maximum displacement in z direction is about 4mm and 3mm in y direction.If the expansion coefficient of packing layer is 1/4,the thickness of packing layer between the cooling staves is 32mm and 24mm between sides up and down.     

Modeling of Strip Temperature in Rapid Cooling Section of Vertical Continuous Annealing Furnace

 The strip temperature is affected by many factors in rapid cooling section (RCS) of the vertical continuous annealing furnace (VCAF). They can be divided into four types: the physical properties of cooling gas, the geometry characteristics of configuration of cooling equipment, the heat transfer between the strip and the cooling gas, and the conductivity of the strip. It aims to model the strip temperature in the cooling section based on the fundamental heat transfer theory and the four aspects factors. The model for transient Nusselt number is obtained by considering Reynolds number, Prandtl number and geometry characteristics of RCS. Then cooling model of the strip transient temperature is built by Nusselt number, heat transfer coefficient and heat conductivity of the strip. The results are compared with the data from production line. The comparisons indicate that the model can well predict cooling temperature of the strip. It is hoped that the proposed model can be used for design and control of the vertical continuous annealing furnace.     

Dome Combustion Hot Blast Stove for Huge Blast Furnace

 In Shougang Jingtang 5500 m3 huge blast furnace (BF) design, dome combustion hot blast stove (DCHBS) technology is developed. DCHBS process is optimized and integrated, and reasonable hot blast stove (HBS) technical parameters are determined. Mathematic model is established and adopted by computational fluid dynamics (CFD). The transmission theory is studied for hot blast stove combustion and gas flow, and distribution results of HBS velocity field, CO density field and temperature field are achieved. Physical test model and hot trail unit are established, and the numeral calculation result is verified through test and investigation. 3-D simulation design is adopted. HBS process flow and process layout are optimized and designed. Combustion air two-stage high temperature preheating technology is designed and developed. Two sets of small size DCHBSs are adopted to preheat the combustion air to 520-600 ℃. With the precondition of BF gas combustion, the hot blast stove dome temperature can exceed 1420 ℃. According to DCHBS technical features, reasonable refractory structure is designed. Effective technical measures are adopted to prevent hot blast stove shell intercrystalline stress corrosion. Hot blast stove hot pipe and lining system are optimized and designed. After blowing in, the blast temperature keeps increasing, and the monthly average blast temperature reaches 1300 ℃ when burning single BF gas.     

Mathematical Model Development of Raceway Parameters and Their Effects on Corex Process

  Corex is an alternative ironmaking process and raceway is one of the important areas to maintain the stability of the furnace. The raceway parameters are well established for blast furnace operation. But for Corex process, it has not yet been established and optimized. Thus, a mathematical model was developed to determine various raceway parameters such as RAFT (raceway adiabatic flame temperature), tuyere gas velocity and kinetic energy. The model provides an idea about the raceway geometry, zone temperature and kinetic energy accumulated in tuyere gas. Besides, all the raceway parameters have been analyzed to find out their effects on the Corex process. It is found that RAFT influences the gasification reaction kinetics and higher RAFT generates more CO in reduction gas, which improves the metallisation degree of the DRI in shaft. It is also found that increased gas velocity and kinetic energy generate more fines and demand more coke to maintain char bed permeability. High coke rate increases the production cost and lowers the production of hot metal.     

Influence of Profile of Blast Furnace on Motion and Stress of Burden by 3D-DEM

 The objective of the present investigation is to analyze the influence of profile of blast furnace on the burden motion and stress field through 3D-DEM (three-dimensional discrete element method). It is clarified that the decrease of shaft angle speeds up the velocity of burden descending and decreases normal stress between particles or particle and wall. This change is good for the smooth operation of blast furnace. However, ore and coke would be mixed for the too small shaft angle (75°), which would influence the permeability in blast furnace. Thus, the appropriate shaft angle is around 80°. Decrease of bosh angle prevents the burden descending motion and increases normal stress between particles and bosh wall. Meanwhile, maximum normal stress acting on the wall moves from belly wall to bosh wall in the case of 68° bosh angle, which accelerates abrasion of refractory in bosh by friction force between particles and wall. Although burden descends smoothly in the case of 88° bosh angle, room is not enough for the ascending heated gas flow. Thus, the appropriate bosh angle is about 78°.     

A Modified Model for Calculating Theoretical Flame Temperature in Blast Furnace and Its Application

The theoretical flame temperature(TFT)before tuyere,always highly concerned by blast furnace(BF)operators,is one of the most important parameters for evaluating the thermal state of hearth.However,some influencing parameters,for example,the SiO2 reduction by carbon,were always neglected or inaccurate when calculating the TFT.According to the definition of TFT,the temperature of coke into raceway and the reduction rate of SiO2 in ash of coke and pulverized coal were obtained by analyzing the samples before tuyere in blast furnace.Taking full account of different factors,a modified model for calculating the TFT in blast furnace was established.The effects of the oxygen enrichment rate,the reduction rate of SiO2 in raceway,the ash content in coke and pulverized coal and the pulverized coal injection(PCI)rate on TFT were determined quantitatively.The modified model was applied to selecting the used coal for PCI in blast furnace.Considering the different SiO2 contents of mixed coal,the calculated TFT remained a stable level.This showed that the selected coal could be suitable for PCI in blast furnace.     

Cold Model Study of Coal Gas Component Concentration Distribution in Blast Furnace Raceway

 Primary distribution of coal gas in blast furnace raceway has an important effect on combustion of coke and pulverized coal injection, as well as whole ironmaking process. According to practical production parameters of No. 5 blast furnace in Chongqing iron &; steel Co. LTD, the theoretical calculation model recommended by Nomura is adopted to determine penetration depth, height and width of raceway. Three-dimensional cold model of blast furnace raceway is established. Coal gas component concentration distribution of vertical section and cross section in blast furnace raceway is simulated using natural gas.     

Shift From Coke to Coal Using Direct Reduction Method and Challenges

 Ironmaking involves the separation of iron ores. It not only represents the first step in steelmaking but also is the most capital intensive and energy intensive process in the production of steel. The main route for producing iron for steelmaking is to use the blast furnace, which uses metallurgical coke as the reductant. Concerns over the limited resources, the high cost of coking coals, and the environmental impacts of coking and sinter plants have driven steelmakers to develop alternative ironmaking processes that can use non coking coals to reduce iron ores directly. Since the efficiency and productivity of modern large capacity blast furnaces will be difficult to surpass, blast furnaces will continue to retain their predominant position as the foremost ironmaking process for some time to come. The alternative ironmaking processes are therefore expected to play an increasingly significant role in the iron and steel industry, especially in meeting the needs of small sized local and regional markets. It is likely that the importance of direct reduced iron (DRI) and hot metal as sources of virgin iron will continue to increase, especially in the developing countries where steelmaking is, and will be, primarily based on electric arc furnace (EAF) minimills. Consequently, the challenges that are faced by the new technology have to be embraced.     

Analysis of CO2 emission and mitigation methods in integrated iron and steel works

CO2 emission of the steel industry takes up a great proportion of the total emission of the world.It is necessary to reduce the CO2 intensity of steel products in order to save energy,protect the environment and keep a sustainable development in the steel industry.Based on the research of steel products’ life cycle inventory,those who conducted this research have focused on the analysis of CO2 emission factors and measures.Adopting the life cycle inventory model of a certain steelmaking site,together with the Tornado Chart,the researchers have identified significant factors,provided some explanation,and suggested some possible measures to reduce CO2 emission.The results have shown that the most important factors are the CO2 intensity of blast furnace gas (BFG), hot metal ratio of basic oxygen furnace (BOF) and the material utilization efficiency.Accordingly,some measures such as removing CO2 in BFG,decreasing the hot metal proportion in BOF,and improve material utilization efficiency in each process,may be taken to decrease CO2 emission.     

Monitoring Method for Blast Furnace Wall With Copper Staves

 A monitoring method that has been designed for the first time for blast furnace wall with copper staves manufactured in China was introduced. Combining the method of “inverse problem” and the concept “non inverse problem”, the monitoring program for blast furnace wall with copper staves has been realized, which can be used to calculate online the accretion thickness and temperature of hot surface of copper staves after obtaining the values of thermocouples of copper staves. The accretion state obtained in the actual investigation has proved that the result of the program is correct. The monitoring program shows that the accretion would easily fluctuate when the accretion layer is extremely thick or thin, thereby the stable and smooth operation of the blast furnace is hindered. By maintaining appropriate accretion thickness, both long campaigns and high productivity of the blast furnace can be achieved; furthermore, it can also optimize the operation of blast furnace and maximize its production. Approximately 30-50 mm in thickness of accretion layer is maintained on the wall of Shougang blast furnace 2, which can meet the requirement for obtaining both long campaign and high productivity.     

Failure Mechanism and Material Requirements for Coal Lance in Blast Furnace

 Abstract： Pulverized coal injection (PCI) is a key technology in modern ironmaking by blast furnace (BF) and the life of injection lance has a great influence on PCI operation and on normal running of blast furnace. It is found that the main reasons for the failure of the lances are their outer surface oxidation and the inner surface erosion through monitoring some lances used in BF. The outer surface oxidation of the lances made of lCr18Ni9Ti is inevitable under high hot blast temperature condition through thermodynamics analysis. A mathematical model for calculating the temperature of common monocular coal lance had been developed according to the principles of mass and energy balance. Increasing temperature and flow velocity of the hot blast would cause a rise in the lance temperature. The influence of hot blast temperature is more obvious. The lance temperature would decline when compressed air flux increases. Conveying technology of dense phase pulverized coal is beneficial to extending lance′s life because decreasing solid-gas ratio would intensify erosion and burning loss. The anti-oxidation temperature of lance materials needs to be over 1000 ℃ for BF intensified smelting. In order to increase the resistance to oxidation of the coal lance′s outer surface, oxidation-resistant steel or Al coating stainless steel is the appropriate material for BF use. Employing the metal surface treatment technology to enhance the hardness of the coal lance′s internal surface could prolong the service life of coal lance.     

Study on the Corrosion Resistance of Multiphase TRIP Steels

Multiphase TRIP (Transformation Induced Plasticity) steels are known to combine higher strength with higher ductility.In this paper,the corrosion resistance of this steel has been has been investigated by accelerated corrosion tests,such as wet/dry cyclic corrosion and the weight loss in laboratory.The morphologies of their rust layers were observed by using scanning electron microscopy,and the corrosion performance of these steels was discussed by analyzing the protective mechanism.The results show that the corrosion rate of steel A is significantly greater than that of steels B and C in wet/dry cyclic corrosion and weight loss tests.The corrosion performance of conventional C-Mn-Si TRIP steel is deteriorated in both NaHSO 3 and 3.5 wt.% NaCl aqueous solutions.And superior corrosion performance is exhibited for TRIP steel with low alloying contents due to its high thermodynamic stability.The enhancement of corrosion performance of TRIP steel is attributed to the additions of alloying elements,such as Al,Cu,Cr,Mo,Ni,etc.The alloying elements increase the compactness of rust layers,so electrochemical characteristic of TRIP steel is improved.     

“Redistribution” Effect of Lumpy Zone for Gas Flow in BF

 The gas flow from tuyere to raceway zone by blasting involves three distributional zones, such as dripping, cohesive, and lumpy zone. The gas flow distribution in lumpy zone directly affects the gas utilization ration and smooth operation in the blast furnace. However, the furnace closeness brings about great difficulty in the study of high temperature gas flow. The charging and blasting system affecting the gas flow and whether the top gas flow distribution could reflect its inner condition as well as the furnace state, such as hanging or scaffolding, which have become the main problems for the research on gas flow. Recently, several researches overseas studied gas flow distribution using the numerical simulation method; however, such a research was rare amongst the natives. In this study, the flow model of gas in cohesive and lumpy zone was established using the numerical simulation software and the gas flow distributions with uniform distribution of burden permeability, scaffolding of wall, and nonuniform charge level were analyzed. As a result, the effects of cohesive zone and lower parts on the gas flow are very limited and the charge level largely affects the distribution of top gas flow. Therefore, it was found that the distribution of top gas flow could hardly reflect the inner gas flow. The process is called “redistribution” effect, which means that the gas flow after passing through the raceway, dripping, and cohesive zone is distributed when it flows into the lumpy zone.     

Analysis of AllCarbon Brick Bottom and Ceramic Cup Synthetic Hearth Bottom

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.     

Effect of the Deformation Twin Density on the Corrosion Behavior in TWIP Steel

Based on its excellent tensile strength-ductility property combination,twinning-induced plasticity (TWIP) steel shows great potential in applications for structural components in automobile industry.The aim of this research is to investigate the corrosion resistance properties and corrosion mechanism under room temperature in TWIP steel.The influence of the deformation twin density on corrosion property was primarily considered by salt spray test.The specimens used in the investigation are as-annealed and as-deformed respectively.The microstructure and corrosion resistance property were characterized by scanning electron microscope (SEM),optical microscope (OM) and so on.There are some annealing twins distributed randomly in austenitic grains in the as-annealed specimen.After the specimen was subjected to tensile experiment,the density of the deformation twins increased sharply,which are different from the annealing twins in size and morphology.It was found that the corrosion potential of the as-annealed is lower than that of the as-deformed and the corrosion current density behaves contrarily.After immersed in 5% NaCl solution salt spray for 48h,the as-deformed showed a bit better than the as-annealed in corrosion resistance.With the time prolonged,the gap between the two specimens in corrosion resistance increased rapidly.The corrosion morphologies varied in color and shape.Further investigation,carried out by SEM and EDS,indicated that as-annealed and the as-deformed followed pitting corrosion and uniform corrosion mechanism respectively.The reason for the difference in corrosion mechanism is possibly the presence of the deformation twins.The deformation twins formed during the tensile test refine grains by way of segmentation.The twin boundaries largely belong to the coincidence site lattice (CSL),which is on lower energy state.It suggests that the twins not only play a role in strengthening,but also improve effectively the corrosion resistance in TWIP steel.     

Medium oxygen enriched blast furnace with top gas recycling strategy

Top gas recycling oxygen blast furnace(TGR-OBF)process is a promising ironmaking process.The biggest challenge of the TGR-OBF in operation is the dramatic decrease of top gas volume(per ton hot metal),which once led to hanging-up and shutdowns in practice of the Toulachermet.In order to avoid this weakness,the strategy of medium oxygen blast furnace was presented.The maneuverable zone of the TGR-OBF was determined by the top gas volume,which should not be far from the data of the traditional blast furnace.The deviation of ±12.5% was used,and then the maneuverable blast oxygen content is from 0.30 to 0.47 according to the calculation.The flame temperature and the top gas volume have no much difference compared to those of the traditional blast furnace.The minimum carbon consumption of 357 kg per ton hot metal in the maneuverable zone occurs at the oxygen content of 0.30(fuel saving of 14%).In the unsteady evolution,the N2 accumulation could approach nearly zero after the recycling reached 6 times.Thus far,some TGR-OBF industrial trials have been carried out in different countries,but the method of medium oxygen enriched TGR-OBF has not been implemented,because the accumulation of N2 was worried about.The presented strategy of medium oxygen enriched TGR-OBF is applicable and the strategy with good operational performance is strongly suggested as a forerunner of the full oxygen blast furnace.     

Evaluation of Scheme Design of Blast Furnace Based on Artificial Neural Network

Blast furnace scheme design is very important, since it directly affects the performance, cost and configuration of the blast furnace. An evaluation approach to furnace scheme design was brought forward based on artificial neural network. Ten independent parameters which determined a scheme design were proposed. The improved threelayer BP network algorithm was used to build the evaluation model in which the 10 independent parameters were taken as input evaluation indexes and the degree to which the scheme design satisfies the requirements of the blast furnace as output. It was trained by the existing samples of the scheme design and the experts＇ experience, and then tested by the other samples so as to develop the evaluation model. As an example, it is found that a good scheme design of blast furnace can be chosen by using the evaluation model proposed.