Flow In Blast Furnace Research Articles

Automated Monitoring of Physical Processes of Formation of Burden Material Surface and Gas Flow in Blast Furnace

The paper is devoted to the issues of energy saving automatic control of radial burden distribution in the blast furnace throat. The main idea consists in control with prediction of the control resulting on the basis of automatic monitoring of burden surface texture. The paper develops the mathematic description of burden surface texture on the blast furnace throat by means of substantiation of minimum quantity of general indicators of the mixture being closely related to the main parameters of blast furnace processes. It is the first time that the optimum value of hoper depth in burden surface at 0.14 – 0.2 of throat diameter determined, the methods of its stabilization at the rate are substantiated, the new regularity of burden surface formation on the operating blast furnace throat is shown as consisting in the fact that the hoper depth on the surface is mainly changed responding the process of material charge rather than bulk material descent after the charge. It was also substantiated for the first time that radioisotopic methods for current control of burden distribution on the blast furnace throat provide timely formation of control actions for gas flow stabilization. The principle of self-tuning was theoretically substantiated for monitoring system of gamma profilometer responding to the monitoring conditions with respect to high penetration and random character of gamma rays. The principle enables significant improvement of accuracy, quick-response and radiological safety of gamma profilometer operation. The possibility of determination of burden surface texture on the throat of operating blast furnace and distribution of burden components according to infrared radiation of the surface without application of radiation hazardous monitoring means was proved for the first time.

INVESTIGATION OF CONTROL OPPORTUNITIES FOR THERMAL PERFORMANCE OF THE PERIPHERAL ZONE OF BLAST FURNACE

High content of FeO in primary slag prevents formation of stable skull thereby increasing the thermal load on the fridges and heat losses. Development of indirect reduction reactions that determine the FeO content in primary slag depends on heat transfer conditions. The purpose of this research was to develop methods of modeling of heat transfer in the peripheral zone of blast furnace. The model was developed using the laws of heat transfer and gas dynamics. It allows to estimate the infl uence of ore load, size distribution of iron materials on development of heat transfer processes and recovery work of the gas flow in blast furnace.

Influence of Cohesive Zone Thickness on Gas Flow in Blast Furnace Analyzed by DEM-CFD Model Considering Low Coke Operation

Reduction of the reducing agent aiming at the mitigation of carbon dioxide emissions decreases the gas permeability in blast furnace. Favorable control of burden distribution and optimization of packed bed might mitigate decreasing permeability. Especially, decreasing thickness of cohesive zone would be effective. In present study, the influence of the cohesive zone thickness on gas flow and pressure distribution was investigated using the DEM-CFD model to evaluate the effects of adoption of a thin-layered cohesive layer structure on gas flow and permeability changes in the cohesive zone during low coke ratio operation. Reducing the thickness of the cohesive zone can effectively increase permeability in the cohesive zone even in the thin coke slit of the low coke rate operation, and improvement in the permeability of the cohesive zone can be realized more effectively in combination with appropriate coke mixed charging.

Analysis on Non‐Uniform Gas Flow in Blast Furnace Based on DEM‐CFD Combined Model

AbstractBlast furnace technology is currently aiming at low reducing agent operation so as to decrease CO2 emissions. At the same time, the inner volume of blast furnaces has frequently been enlarged so as to increase production rate in some countries, including Japan. Operating conditions designed for low reducing agent in a large blast furnace tend to cause unfavorable phenomena such as slipping of the burden and gas channeling due to the decrease in coke rate. Mathematical models help to clarify the in‐furnace phenomena under these situations.From the above backgrounds, a new model has been developed that combines Discrete Element Method with Computational Fluid Dynamics (DEM‐CFD) to simulate precisely the gas flow and solid motion in a blast furnace. The present study aimed to develop a three‐dimensional mathematical model based on DEM‐CFD for simultaneous analysis of gas and solid flow in the whole blast furnace. The unbalanced gas flow in the case of clogging of the particular tuyere was analyzed to clarify the circumferential unevenness in the lower part of the blast furnace. Based on the combined DEM with CFD model, the non‐uniform gas flow in the lower part of the blast furnace was precisely evaluated.

Simultaneous Three-dimensional Analysis of Gas–Solid Flow in Blast Furnace by Combining Discrete Element Method and Computational Fluid Dynamics

Low reducing agent operation of the blast furnace is an essential method for mitigating CO2 emissions in ironmaking. Because the coke rate is reduced in low reducing agent operation, gas permeability tends to deteriorate. Recently, blast furnaces with inner volume larger than 5000 m3 have become usual not only in Japan, but also in other Asian nations. Under these conditions, detailed information on in-furnace phenomena is required to attain stable operation.In the present study, a combination model using the discrete element method and computational fluid dynamics (DEM-CFD) was introduced to understand the fully three-dimensional in-furnace phenomena in the whole blast furnace. Due to the limitations of computational resources, the number of DEM particles must be reduced when applying DEM to the whole blast furnace. On the other hand, small cells must be used in the continuum model in order to calculate the gas flow in detail. Thus, mutual conversion between the location of particles in DEM and the property of the cells in the continuum model is needed. In this study, a method of converting information on the locations of cluster-approximated particles treated in DEM to continuum cells was proposed. Furthermore, optimization in which cells could be obtained without conversion parameters was performed to avoid losing local information obtained by DEM calculations. Simulations of solid movement and gas flow were successfully carried out with this coupled DEM-CFD model. As a result, it became possible to understand the three-dimensional stress field among particles under gas flow, transient gas flow and pressure distribution caused by charging of the burden materials, as well as solid motion.

Effect of Interface Resistance on Gas Flow in Blast Furnace

Any improvement in Blast Furnace productivity under a given set of operating conditions is fundamentally related to better flow distribution of gas through layered burden structure in Blast Furnace. Flow distribution and hence pressure drop of gas in granular zone of blast furnace is dependent on number and thickness of alternating layers of coke and metallic burden. A significant part of this total pressure drop in granular zone can be attributed to interfacial resistance between two successive layers. Whereas, pressure drop in porous layers of materials can be described by well known Ergun's equation in terms of all physical parameters, interface resistance needs specific treatment. Systematic study to investigate the effect of interfacial resistance on gas flow between two successive layers of different material has been attempted in this work. Laboratory scale experiments in scale down model of blast furnace were conducted to establish and quantify interface resistance for different layer configurations.

Gas–solid flow in an ironmaking blast furnace — I: Physical modelling

The paper presents an experimental study of gas–solid flow in an ironmaking blast furnace under various conditions to address a few important issues: two-dimensional (2D) slot model vs full three-dimensional (3D) model, normal vs abnormal operations, and spherical vs non-spherical particles. The quantitative comparisons made between the 2D slot and the full 3D models under comparable conditions reveal that whilst the key solid flow features are similar in both models, the relative sizes of the different flow zones in a model furnace differ considerably. The effects of operational parameters on the flow behaviour are examined in both 2D and 3D models, including gas and solid flow rates, material properties such as particle roughness and shape, and abnormal conditions such as asymmetric charging and scabs. It reveals that the stagnant zone is significantly affected by gas and solid flow rates in the 2D slot model, but not in the 3D model. Particles with angular shapes and a high internal angle of friction produce steep profiles of the stagnant zone. The solid flow behaviour with layers of different materials and a homogeneous mix of materials are similar. Studies in asymmetric flow experiments reveal that the flow behaviour on one side is largely independent of the flow on the other side in the 2D slot model. The presence of scabs causes retardation of the flow on the wall, and the layer orientation changing from horizontal to vertical. The results are useful not only in developing further understanding of solid flow in a BF but also in verifying different mathematical models, particularly the discrete particle simulation which has been increasingly used in the literature. The paper presents an experimental study of gas–solid flow in an ironmaking blast furnace (BF) under various conditions to address a few important issues: a two-dimensional slot model vs a full three-dimensional model, normal vs abnormal operations, and spherical vs non-spherical particles. The results are useful not only in developing further understanding of solid flow in a BF but also in verifying different mathematical models. ► An experimental study is carried out on the gas–solid flow in a blast furnace (BF). ► The effects of model type, operational and material conditions are investigated. ► The findings are useful to understanding and modelling of solid flow in a BF.

Transient Behavior of Burden Descending and Influence of Cohesive Zone Shape on Solid Flow and Stress Distribution in Blast Furnace by Discrete Element Method

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.

Large Scale Simulation of Coke and Iron Ore Particle Motions and Air Flow in Actual Blast Furnace

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 Dp reduced to 0.794 Dp 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.

Characteristics of Solid Flow and Stress Distribution Including Asymmetric Phenomena in Blast Furnace Analyzed by Discrete Element Method

Since the solid flow in blast furnace is composed of each particle motion, the discontinuous phenomena of burden descending can be occasionally observed. Understanding of the solid flow is important for blast furnace operation. Discrete Element Method (DEM) can offer the behavior for each particle of burden in the furnace. Three dimensional analysis of solid motion containing the ununiform region became possible with using DEM.In the present study, a blast furnace of 2000 m3 inner volume with 16 tuyeres was taken as the object for the simulation. Firstly, the stream line of solid, velocity variation and stress field in blast furnace were simultaneously analyzed by using the characteristic of DEM on each particle movement. Especially, the transient behavior on velocity and stress distribution during charging and slipping were calculated. The fundamental characteristics of burden descending became clear. Secondly, this study has focused on the asymmetric phenomena in the blast furnace on the basis of the above results. In this calculation, number of active tuyere was intentionally varied. The stress network showed the remarkable change in this case. Moreover, it was found that many local slips between particles were distributed in the bosh and they concentrated on the region nearby the active raceway due to the weakened stress. The stress network is closely related the particle velocity distribution. The consumption rate of coke in the tuyere significantly affected on the circumferential uniformity. Totally, the discontinuous burden descending and the characteristic of particle movement were essentially understood.

Discrete particle simulation of gas–solid flow in a blast furnace

Gas–solid flow plays a dominant role in the multiphase flow in an ironmaking blast furnace (BF), and has been modelled by different approaches. In the continuum-based approach, the prediction of the solid flow pattern remains difficult due to the existence of the stagnant zone in the BF lower central part. This difficulty has recently been shown to be overcome by discrete particle simulation (DPS). In this work, the DPS is extended to couple with computational fluid dynamics (CFD) to investigate the gas–solid flow within a BF. The results demonstrate that the DPS–CFD approach can generate the stagnant zone without global assumptions or arbitrary treatments. It confirms that increasing gas flow rate can increase the size of the stagnant zone, and in particular changes the solid flow pattern in the furnace shaft. More importantly, microscopic information about BF gas–solid flow, such as flow and force structures that are extremely difficult to obtain in continuum-approach or experiments, can be analyzed to develop better understanding of the effect of gas phase, and the underlying gas–solid flow mechanisms.

Modeling of Solid Particle Flow in Blast Furnace Considering Actual Operation by Large-scale Discrete Element Method

The objective of this paper is to analyze the solid particle flow in a blast furnace having bell-type charging system by using large-scale Discrete Element Method (DEM). About 500000 particles were calculated in this work. The particle discharging behavior of laboratory-scale blast furnace was compared to confirm the material properties used in the simulation work, and the simulated trajectories of tracer particle correlated with those of experimental very well. The melting behavior of iron ore and combustion of coke in the actual blast furnace were modeled by shrinking particles. The simplified bell-type charging system in this simulation mimicked the actual blast furnace, the collapse of coke layer at the top was observed, and the time change of stock level was quite similar. The particle pulsating flow was observed at the upper area of blast furnace, and the descending velocity near side wall was much larger than that of center in this calculation. The melting position of ore was mapped and the most of iron ore were melting above the raceway. This area should be cohesive zone. This modeling is the first step of the analysis of blast furnace by using Discrete Element Method. Although only contact force was considered and simplified melting zone or raceway were introduced, this large-scale simulation has a high potential to analyze the solid flow in the blast furnace, and the abnormal phenomena or serious problem in blast furnace operation will be analyzed in the future by considering gas flow or heat transfer.

Gas-powder flow in blast furnace with different shapes of cohesive zone

With high PCI rate operations, a large quantity of unburned coal/char fines will flow together with the gas into the blast furnace. Under some operating conditions, the holdup of fines results in deterioration of furnace permeability and lower production efficiency. Therefore, it is important to understand the behaviour of powder (unburnt coal/char) inside the blast furnace when operating with different cohesive zone (CZ) shapes. This work is mainly concerned with the effect of cohesive zone shape on the powder flow and accumulation in a blast furnace. A model is presented which is capable of simulating a clear and stable accumulation region in the lower central region of the furnace. The results indicate that powder is likely to accumulate at the lower part of W-shaped CZs and the upper part of V- and inverse V-shaped CZs. For the same CZ shape, a thick cohesive layer can result in a large pressure drop while the resistance of narrow cohesive layers to gas-powder flow is found to be relatively small. Implications of the findings to blast furnace operation are also discussed.

Discrete Particle Simulation of Solid Flow in a Model Blast Furnace

This paper reports a numerical study of solid flow in a model blast furnace under simplified conditions by means of discrete particle simulation (DPS). The applicability of the proposed DPS approach is validated from its good agreement with the experiment in terms of solid flow patterns. It is shown that the DPS is able to generate a stagnant zone without any need for any arbitrary treatment, and capture the main features of solid flow within the furnace at a microscopic level. The results confirm that the solid flow in a blast furnace can be divided into four different flow regions. However, the flow is strongly influenced by the front and rear walls in a 2D slot model furnace whereas the predicted stagnant zone decreases significantly with wall sliding friction. In a 3D model with periodic boundary conditions incorporated, a smaller stagnant zone is obtained. The effects of solid flow rate, particle properties such as sliding and rolling friction coefficients on the solid flow are also investigated. The results are analysed in terms of solid flow patterns, solid velocity field, porosity distribution and normal force structure. The implication to blast furnace operation is discussed.

A simplified mathematical model for gas?solid flow in a blast furnace

This paper presents a numerical study of the behaviour of solid flow in a two-dimensional blast furnace with or without gas flow. The mathematical model, as a simplified version of the more detailed model developed earlier, is similar to the so-called viscous flow model but the method to determine the stagnant zone profile is similar to that used in the kinematic model. The study shows that the simplified model is able to capture the key flow characteristics of solid flow in a blast furnace and describe reasonably the effects of gas and solid flowrates, and particle properties, although the predicted quasi-stagnant zone may be smaller. The advantage of the present approach is that it can be readily implemented in a full process model that needs to have a quick response to change for the purpose of control and optimisation.

Modelling of Gas-Powder Flow in a Blast Furnace

This paper presents a study of the gas-powder flow in a slot type packed bed in order to investigate the distribution of powder flow and accumulation in an ironmaking blast furnace. The effects of operational parameters such as gas flow rate, and cohesive zone shape are examined. It is shown that a distinct and stable accumulation region can be formed in the low gas-powder velocity zone in a bed with a lateral gas inlet. Also, the existence of a cohesive zone changes the powder accumulation pattern significantly. The inverse-V cohesive zone leads to low accumulation in the bed compared to other cohesive zone shapes. A mathematical model is developed to describe the gas-powder flow and powder accumulation. Its validity is verified by comparing the predicted and measured distributions of powder accumulation under various flow conditions.

Numerical simulation of solids flow in a blast furnace

This paper presents a numerical study of the behavior of solids flow in a 2D blast furnace (BF). The investigation considers the layer-charging of iron-bearing and coke and solids consumption due to, for example, coke combustion in the raceway and is based on a mathematical model recently developed for gas–solid two-phase flow. Input data includes the ore and coke profiles, productivity, and solids volume loss due to shrinkage, meltdown, reduction and combustion as determined from typical operating conditions. The results demonstrate that the mass loss strongly affects the solids flow pattern and deadman profile in a BF. In particular, increasing the solids consumption rate will increase the solid velocity and decrease the size of deadman.

Two dimensional analysis of burden flow in blast furnace based on plasticity theory.

Using a two-dimensional cold model, the dynamic behavior of particles in blast furnace was studied on a detailed analysis of the flow pattern. The field of the flow was characterized with the stagnant region formed in the central lower part of the apparatus and the flow channels consisting of two regions, i.e., slow moving and fast moving regions. On crossing the boundary between the slow and fast moving regions, the particles experienced a discontinuous, sudden change in the velocity as well as the direction of flow. An approximate method of predicting the flow pattern is described on the basis of plasticity theory. The velocity discontinuous boundary could be theoretically represented by the characteristic curve of the velocity. The boundary of the stagnant region corresponded to the characteristic curve of the stress, so-called slip line. Finally, the flow patern of burden material in a practical blast furnace was simulated, based on the calculas presented.

高炉内装入物の運動に関する理論解析と冷間模型実験

The characteristics of burden flow in blast furnace is discussed based on both theoretical analyses and observations in two types of cold model experiments with gas blowing. Sublimation of dry ice particles is utilized in the experiments to simulate coke combustion before tuyeres or the volume reduction of cohesive layers in blast furnace. Experimentally observed profile of deadman, which is formed just behind the raceway, is shown to be in good agreement with a slip line calculated for the passive stress state. Theoretical height of the deadman is increased by decreased angle of internal friction and increased angle of wall friction. The burden flow in the shaft is approximately described by a potential flow theory taking account of the volume change of burden. Below the lower end of the shaft, however, the viscous flow analysis gives more realistic flow field presumably due to the prevailing passive stress state.

Softening Property of Iron Ore Sinter and Its Inflence on Gas Flow in Blast Furnace

Softening Property of Iron Ore Sinter and Its Inflence on Gas Flow in Blast Furnace