Currently low reducing agent operation of blast furnace has been actively pursued in ironmaking due to the global warming. The precise and reliable control of blast furnace aiming at the low reducing operation is required to attain smoothly the stable operation. It is considered that the mathematical model on the ironmaking process can play an important role to ensure the stable blast furnace operation. A mathematical model is a powerful tool to improve conventional processes and to design new processes in ironmaking. These tendencies and requirements are common to every country. Thus, the development of advanced mathematical models of blast furnace like DEM (Discrete Element Method) has attracted a special attention in ironmaking field. Moreover, the combined model of DEM with the continuum model is under development for the purpose of the accurate understanding of inner state of blast furnace. In this paper, the recent activity and progress on the development of advanced mathematical model of blast furnace and future perspective for desirable model are described.

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The development and application of a 1-dimensional static blast furnace model, “Masmod”, written in a common spreadsheet environment, is described. The model includes blast furnace, hot stove, and burden models with recent additions of other operations including CO₂ stripping and top gas recycle. Although blast furnace modelling has become increasingly sophisticated, a relatively simple and flexible model is shown to be useful for evaluating burden options, equipment and operational strategies, and process development. Furthermore the Masmod model has been integrated with global steel plant optimization models and Process Integration models for more complex system analysis and optimization.

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Primary steelmaking is among the most energy intensive industrial processes in the world and being mainly coal-based it substantially contributes to the global fossil CO₂ emissions. It is therefore important to study potential ways of suppressing the use of fossil reductants and the rate of emissions in the process. This paper analyzes by simulation and optimization the concept of recycling CO₂-stripped top gas in the blast furnace under massive oxygen enrichment, and its impact on the production economy and emissions of the steel plant. The effect of CO₂ emissions and stripping/storage costs on the optimal states is presented. The system studied is demonstrated to exhibit complex transitions between the optimal states. The findings throw light on the importance of selecting a proper state of operation for achieving a cost-efficient production of steel with reduced environmental impact.

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The large scale database-based online modeling called LOM is the one of local modeling method. This method has been developed to apply the just-in-time modeling for the blast furnace by us. In this paper, we propose two new types of local models in LOM to improve the prediction performance. One is used weighted multiple regression model as a linear local model of LOM. The other is used on-line Bayesian learning model as a nonlinear local model of LOM. In order to compare the prediction performance of the two types of local models in LOM, we evaluate the prediction performance by using the real process data of the blast furnace.

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The present investigation intends to elucidate the transient behavior of burden descending, the influence of cohesive zone shape on the solid flow and the stress field through three-dimensional analysis by discrete element method (DEM) in blast furnace. Although many continuum models were developed to analyze the in-furnace phenomena such as solid flow, DEM enables to analyze the unsteady state solid flow, the stress distribution and slip of burden in the three dimensional state. In this study, it was clarified that the solid flow in blast furnace was composed of steady flow and transient flow which caused by burden charge and slip around raceway. Burden charge instantaneously causes high stress region and high velocity region to spread from upper part to lower part. High velocity region caused by slip around raceway spreads upwards and mitigates the stress field in the vicinity of raceway. The cohesive zone shape almost does not affect on the particle movement in the upper part of shaft and deadman shape. However, the distribution of high stress region and high slipping region is affected by the cohesive zone shape. Asymmetric high stress and slipping distribution are formed in the case of biased cohesive zone, and high cohesive zone enlarges the region of high stress. Weak slipping region in the upper part of shaft tends to be mitigated by the stress field in upper part. Belly receives the maximum stress from burden. The normal stress acting on the bottom is concentrated on the center of bottom by the buoyancy effect of pig iron in the hearth.

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The cohesive zone, where the ore fed into the blast furnace softens and melts, is critical to the blast furnace performance and stability due to its influence on the gas and solid flow. Here we describe a project for the development of a process model to predict the cohesive zone properties and results of an important part of the work; the solid and gas flow models. The process model will be developed to describe a realistic solid burden flow and the formation of the cohesive zone, its shape, location, structure and permeability. This will be achieved using various simulation and computing tools: a combination of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD), the coupled DEM-CFD approach, together with models for the thermodynamics and reaction kinetics. The key benefits of the coupled approach lie in the coupling of the continuous phase and the discrete particles, and the possibility of introducing thermodynamics and reaction kinetics into the system in a more realistic manner. DEM and coupled DEM-CFD simulations in several geometries are presented for reduced scale blast furnace investigation on the influence of non-spherical particles and gas flow on the solid flow. A large influence of the geometry shape and boundary conditions on the solid flow was also found.

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The computational program for the particle and the air flows in an actual blast furnace using Distinct Element Method (DEM) for the coke and the iron ore particles of which number was about 16 million and the Finite Difference Method of which computational cell number was about 3 million for the numerical analysis of Navier–Stokes equations with the interaction terms between the air and the particles has been developed. The motions of coke and iron ore particles and the air flow in the blast furnace have been simulated using this program. The computational domain in the tangential direction was 1/4, which was 90 degree of the region of the horizontal plane and in which 10 tuyeres were arranged, of the actual blast furnace. The simulation results showed that the model softening melting cohesive zones, which were formed by the model that 50% volume of the ore particle melted and the diameter D_p reduced to 0.794 D_p by melting the particle surface at the 1200°C line and the residue of the ore particle melted down completely at the 1400°C line, largely affected the air and the coke particle flows and caused the non-homogeneous and unstable flows. The air was divided into two flows at the softening melting cohesive zones. The one was the flow with the slope angle nearly 45° from the horizontal toward the furnace wall in the central region and the other is vertically upward flow in the region near the furnace wall. The coke and ore particle velocities on the wide region of the furnace wall became very low. These nearly quiescent solid particle layers might cause the scaffold of the solid particle bed on the furnace wall. The results also showed that the interaction between tuyeres affected the shape and the stability of the raceway and influenced the particle and the air flows in the wide region on the raceway. Hereafter we will continue to calculate the air and the particle motions, and present the various unstable motions which would bring about an extraordinary event in the actual blast furnace.

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A blast furnace is modeled as a counter-current bed reactor filled with solid particles of coke and ore where the gas flows upward through the porous media while the bed material moves slowly in the counter-current direction of the gas flow. An axi-symmetric two-dimensional steady state model is proposed to simulate the gas and the solid flow, where thermo-chemical reactions and heat transfer process are considered. It is assumed that two phases of solid and gas exist in the furnace. The charged material is treated as porous media constructed by alternative coke and ore layers, which have different permeability. The internal gas flow of the furnace is governed principally by burden distribution. For understanding of the influence of the burden distribution on the internal situation, the entire layer structure is predicted from the measured top layer structure and the solid flow is assumed as the potential flow. Using this burden distribution, the flow, energy, and chemical species conservation equations are derived for each phase. In addition, the phase mass generation/consumption caused by reactions, heat transfer between gas and solid phases, and the reaction heat are reflected in source terms in the governing equations. For several different L_o/L_c (layer thickness ratio of ore and coke layer) cases, layer structures are constructed and numerical simulations are conducted. The finite volume method was used for the numerical simulations. Through this approach, the flow, composition and temperature distributions within the furnace are numerically predicted.

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Recently, discrete element method (DEM) had been applied for simulation of the blast furnace. For mitigating computation load and precise simulation of blast furnace, the determination of optimum physical parameters in DEM are very important. In the present study, influence of variation of hardness, rolling friction coefficient of particle and descending velocity on the solid flow and stress distribution in the blast furnace were investigated. Decreasing hardness of particle does not affect on shape of layers descending in the shaft, and causes acceleration of computation. However, stream line of particles and stress distribution vary with changing in hardness of particle. The softening of particle is not suitable for analysis of stream line and stress distribution of packed bed in the blast furnace. Stream lines of particle become smooth with an increase in the rolling friction coefficient. The value of the rolling friction coefficient should be controlled for representing shape of actual burden. It is confirmed that descending velocity of burden also affects on the stress distribution of the packed bed. Physical properties and calculation condition should be optimized depending on the purpose of analysis and phenomena in the blast furnace.

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On the basis of BF iron-making technical calculation, considering expert knowledge about mutual reactivity of the iron bearing materials at high temperature, the optimization model of blast furnace (BF for short) burden was built according to the linear programming theory and applied to the BF production. The results indicate that the model is reasonable, with the burden structure calculated according to the burden optimization model, the burden cost can be reduced, the metallurgical properties of burden can be improved, and the economic and technical indexes can be increased.

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Burden distribution control is one of main technologies to keep the good permeability and the high reaction efficiency in a blast furnace. However, in actual blast furnace operation, there are variations in burden distribution due to various factors, such as fluctuations in condition of the raw materials, fluctuations of the mechanical properties of charging devices, the changes of charging devices due to abrasion and so forth. Such variations could be a negative factor to conduct blast furnace operation in high productivity and low reducing agent rate. The advanced supporting system for burden distribution control at blast furnace top regards those variational factors as the characteristic parameters of burden distribution formation through analyzing on-line monitoring probe data to make effective supports for a proper burden distribution control. In this paper, the composition of the supporting system and the results of applying this system to actual blast furnace are described.

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The objective of this paper is to analyze the particle behavior in bell-type charging process of actual blast furnace by using Discrete Element Method (DEM). The circumferential balance of charged mass in the quad-hopper and the effect of the nut coke particle position in the quad-hopper on the traveling behavior and the segregation were discussed. The mass flow rate discharged from the rotating chute was fluctuated with the time, and the peak values gave when the directions of the chute movement became same as the one of the conveyor. It leads to the unbalance of charged particles in each part of the quad-hopper. The nut coke moved to the upward in the sintered ore particle layer during traveling to large bell from the quad-hopper due to the particle segregation, when they were segregated at the bottom of hopper. However their relative positions moved downward when they were segregated at the top, because the time for starting discharging of nut coke became faster. The installation of the damper at the way to the small bell from the hopper affects on the circumferential balance of mass of nut coke. Most of nut coke particles were charged at near the wall of blast furnace, and the small peak of the distribution of its specific charged mass was seen around 3.0 m in the radial distance from the center, it caused by the particle segregation during flowing on the particle layer. The relative radial distribution of the nut coke particles wasn't affected by their positions in the large bell and the total mass. Thus, keeping the circumferential balance of nut coke mass in the large bell is very important. The position of nut coke particle didn't affect on the segregation of sintered ore. The radial distributions of relative charged mass for all conditions were quite similar.

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Real time data warehousing, process visualization and data based modeling are the basis of any diagnosis carried out in iron making area of Tata Steel. Large volume of data generated during the making of coke, sinter and iron are being archived along with quality and performance data in a central data repository. These data is being constantly used by analyst to diagnose process disturbances and also to optimize various process and consumption parameters. To squeeze out greater level of information from the data, various process models are constantly being developed. These models are of various types. Few are based on simple mass balance where as others are empirical or statistical diagnostic model based on on-line measurements. Some are visualization models where large numbers of data are organized and given a form which can be better visualized by the analyst. Some of such models developed for in-depth analysis of blast furnace like ‘cohesive zone model,’ ‘hearth liquid level monitoring’ etc. are described in this paper. Mainly the brief development process and applications in process analysis of each models have been described here.

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Cold model experiments were conducted to investigate the dripping behavior of molten iron in the coke packed bed filled with molten slag. The dripping behavior or dripping rate of pseudo-iron droplets in packed beds filled with immiscible liquid was described well by three comparatively simple mathematical models.

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Numerical simulation of blast furnace phenomena has significantly contributed to the better understanding of iron making process. Recent interest on minimizing fuel consumption and reducing environmental problems have also benefitted from the development of comprehensive simulation models based on physical principles. One of the under-developing fields, however, is related with the internal phenomena in the lower part of the blast furnace under the cohesive zone, where the liquid phase of metal and slag flows downward over the bed of solid coke particles. Hot flow of sluggish liquid phase is further complicated by the chemical reactions including the transfer of silica into the silicon in the hot metal. Silica enters the furnace as a constituent of coke ash and ferrous gangue, and exits as either molten silica in slag or dissolved Si in the hot metal. Silica reduction is an endothermic reaction, which would alter the heat transfer in the lower furnace, thus affecting the hot metal temperature.
Effective flow in the dripping zone is important for stable operation of the blast furnace with high productivity of iron. Study of the liquid flow behavior and secondary reactions in a packed bed allows to investigate the effect of various operational changes in the dripping zone. In this research, a systematic numerical approach for the liquid flow is presented where the flow behavior is solved along with heat transfer associated with physic-chemical reactions among representative components.

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A two-dimensional mathematical model is developed to describe iron oxides reduction in the shaft furnace of COREX^® smelting reduction process. Combined with mass, momentum and heat transfers between gas and solid phases in steady state, the model calculates and demonstrates the basic characteristics of the shaft furnace, such as velocity, pressure, temperature fields of relevant phases and species' mass fraction distributions. The reduction from magnetite to wustite occupies most part of the furnace, and the reduction degree of burden located near wall is comparatively higher than that close to centre. The model also considers the influence of down pipe gas, driven by the pressure drop between the shaft furnace and melter gasifier, on the reduction behaviors inside furnace. Compared with the base case, the down pipe gas featuring higher temperature prefers to flow toward the symmetry axis, where both gas temperature and solid metallization are promoted remarkably.

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A three-dimensional mathematical model that can simulate the transient heat and mass transfer phenomena in a hot stove has been developed. This mathematical model can treat the turbulent mixing of fuel and air, combustion of fuel, buoyancy convection, heat radiation, and the heat exchange between the gas and heat storage bricks. Comparison of the calculated results with actual measured data was done in order to verify the availability and accuracy of the mathematical model, and computational results gave good agreement with measured data. Brick alignment and operating conditions for a new hot stove can be designed by using this mathematical model.

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In order to prolong the service life of coke ovens, the tolerable limit of localized force on damaged oven walls is investigated by discrete element method simulation. A simulation model comprising three flues and five or fifteen layers of bricks was constructed and the effect of various wall damages on the tolerable limit of localized force was examined. It was found that the following liner brick damages cause an extreme decrease in the tolerable limit: 1) loss of tongue and groove constraint, 2) wear which reaches tongue and groove (ca. over 35 mm), 3) cracks over 2.5 mm wide, and 4) loss of horizontal constraint. These findings provide useful guidelines for effectively repairing old coke ovens to prolong oven life.

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Knowledge of heat wave is a key to control the iron ore sintering process. To enhance the knowledge, numerical integration of differential equations for gas and solid is prevailing; this report, otherwise, used an analytical method and introduced several solutions by the assumption that the heat wave descended in steady state and that gas and solid temperatures coincided. The solutions correlated characters of heat wave with operational factors in a simple and explicit manner like:
1) Heat behind speed (U_B) was a function of gas velocity (u_g) as U_B=(c_gu_g)/(c_sρ_s);
2) Solid maximum temperature (T_P) comprised an adiabatic temperature increase due to coke combustion (θc) and a heat convection due to downdraft necessary for solid temperature to heat up to coke ignition (θig) as T_P=θc+θig;
3) Heat front speed (U_F) correlated with U_B (=ν) and the terms for coke combustion heat generation (θc) and ignition temperature (θig) as U_F=ν·(1+θc/θig).

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