Experimental Studies of Gas‐Liquid‐Powder Flow in Moving Particles

An experimental study has been carried out of gas‐liquid‐powder flow in moving particles in one‐ and two‐dimensional packed beds, simulating the complex four‐fluid flow conditions in an ironmaking blast furnace which involves the upward flow of gas and unburnt coal/char and the downward flow of coke and molten iron and slag. It is shown that the contacts between packed particles are important for powder entrapment, and the presence of a liquid phase can significantly increase the powder hold‐up and gas pressure drop. Only when the packed particles have significant downward velocity can the flow of powder and liquid be maintained without flooding. Depending on the flowing conditions, both steady and unsteady flows can be observed, giving the so‐called operational and non‐operational regimes. For the gas‐glass powder‐water system considered, the effects of solid, liquid, powder and gas flow rates on the two regimes have been quantified. The non‐operational regime stems from the flooding caused by high gas and liquid flowrates and/or hanging caused by high powder and low gas flow rates. The operational regime expands with solid flow rate, and contracts with an increase in gas, liquid and/or powder flow rates. Implications of the findings to blast furnace operations are also discussed.     

Numerical Study of Gas‐Solid Flow in the Raceway of a Blast Furnace

This paper presents a numerical study of gas‐solid flow in a blast furnace raceway using a 2D slot cold model. Numerical experiments are conducted by combining the discrete element method for the solid phase with computational fluid dynamics for the gas phase. The motion of particles caused by lateral gas blasting under conditions similar to that in the blast furnace process is examined at a particle scale. Combustion and associated solids movement around the raceway are simulated by extraction of particles from the bottom of the bed. The effect of bed height or solid pressure is considered by imposing a downward force on the top layers of particles in the bed. It is shown that depending on the gas velocity, the bed can transit from a fixed bed to a fluidized bed or vice versa. Two zones can be identified in such a bed: a stagnant zone in which the particles remain at their initial positions, and a moving zone in which particles can move in various flow patterns. In particular, if the gas velocity is in a certain range, the moving zone is formed just in front of the gas inlet, giving the so‐called raceway in which the particles can circulate. The effects of gas velocity, solid pressure and solid extraction are quantified. The fundamentals governing the gas‐solid flow and the formation mechanisms of a raceway are discussed in terms of particle‐particle and particle‐fluid interaction forces.     

Numerical Evaluation of Blast Furnace Performance under Top Gas Recycling and Lower Temperature Operation

The new process of top gas recycling by hot reducing gas (HRG) injection has been developed in this study in order to overcome the disadvantageous problems under the lower temperature operation, to enhance the utilization of top gas carbon and to reduce carbon dioxide emission of blast furnaces. Numerical evaluation of blast furnace top gas recirculation together with lower‐temperature operation was performed by means of a multi‐fluid blast furnace model. The simulation results show that, (1) under the lower temperature operation, the shaft injection, or simultaneous shaft and tuyere injection of hot reducing gas is effective to increase the heat supply and to enrich the reduction atmosphere in the shaft zone, to improve the reduction of iron burdens, and enhance the efficiency of the shaft zone. (2) If top gas is recirculated by HRG on the basis of lower temperature operation, a highly efficient low‐carbon blast furnace is obtained. The productivity of the furnace shows a remarkable increase and the total reducing agent rate shows a considerable decrease. Furthermore, the top gas carbon utilization is enhanced and the carbon dioxide emission rate is lowered. (3) Generally, shaft efficiency, carbon emission and heat efficiency under simultaneous tuyere and shaft injection are comparatively better than in the other two methods of single injection.     

Choking Phenomena of Gas‐Powder Flows at Sonic Velocity

Choking phenomena of gas‐powder flows in a horizontal constant cross‐section duct are experimentally studied using three kinds of powders: Al₂O₃, hollow Al₂O₃ (H‐alumina) and Al, with different physical properties such as densities, specific heat capacities and thermal conductivities. The relationship between the mass flowrate and inlet stagnant pressures is analysed and the apparent sonic velocity (ASV) of gas‐powder flows is defined. The influences of physical properties of powders on the ASV are obtained by the comparison between the experimental results of different powders. Two characteristic parameters, the effective specific heat capacity (ESHC) of solid phase and the effective isentropic exponent (EIE) of the mixture, are defined to describe the choking phenomena. The ESHC is not only measured through experiment but also calculated by numerical method. The calculated results are well consistent with the measured ones. As a preliminary application test for choking phenomena ‐ in order to uniform the pulverized coal injection (PCI) into a blast furnace ‐, a model PCI system with two branch pipes was set up and tests were carried out to verify the choking effect. The test results show that, during choking, the PC flow rates in the branch pipes can be well equalized no matter how much the downstream conditions differ from each other.     

A Mathematical Model of a Blast Furnace Injection Tuyere

One way to further utilise produced gases in an integrated metallurgical plant is to replace oil with gas as a reducing agent in a modern blast furnace. Accordingly, it is of great interest to study the injection of reducing gas into the blast furnace. Therefore, a three‐dimensional mathematical model has been developed which simulates the injection of the gas by lances into the tuyere. The model includes the coupled solution of the flow field and the chemical reaction of the gases in the tuyere. Two different types of fuel gas, coke oven gas (COG) and basic oxygen furnace gas (BOF) have been modelled using one injection lance. The modelling technique is presented and discussed as well as the implied results. Furthermore, process parameters such as different gas compositions etc. are investigated using the developed model. Not surprisingly, the main results show that the COG is combusted more completely than BOF gas, which leads to higher flame temperature of the blast putting demand forward to lower the heat load of the tuyere. However, the modelling of the raceway is as far not included in the model, hence the influence of the outlet boundary condition at the tuyere is not reflected in the presented results.     

高炉使用热压含碳球团操作的数学模拟研究

介绍了一种高炉炼铁新技术即高炉使用热压含碳球团技术,并利用多流体数学模型模拟该操作,对炉内现象和操作性能的变化进行了充分解析.数学模拟结果表明:热压含碳球团的使用将使得炉内温度水平降低,软熔带位置下降,但同时高炉产量增加,焦比显著降低.在一定范围内使用热压含碳球团,高炉热利用效率明显提高,操作性能将有效改善.     

Integration of the Blast Furnace Route and the FINEX®‐Process for Low CO2 Hot Metal Production

The blast furnace is the most important process for the production of hot metal. An integral part of this process route is the coking of coal and sintering of fine ore. The FINEX®‐process is a new technology for hot metal production which uses untreated fine ores and coal instead of sinter and coke. This paper deals with the investigation of integration concepts of the blast furnace and FINEX®. Low reduced iron (LRI) and/or reducing gas are/is produced in FINEX® and are/is considered as substitute/s of burden and fuel in the blast furnace, respectively. In the article the overall fuel demand and CO₂ emissions for the integration of the blast furnace and FINEX® are shown. For that reason two case studies for the integration are carried out and compared with the base case, that is, the two‐independent processes. The CO₂ emissions are calculated considering the fuel and electric power consumption of the different cases.     

Numerical Evaluation on Lower Temperature Operation of Blast Furnaces by Charging Carbon Composite Agglomerates

This paper places emphasis on evaluating ironmaking operation at lower temperature. Blast furnace operation with carbon composite agglomerates (CCB) charging and/or lower operation temperature has been numerically examined using a modified multi‐fluid blast furnace model under constant thermal conditions of the raceway. The numerical calculation shows that a lower in‐furnace temperature level is achieved under the operation with the CCB charging. With CCB charging, the location of the cohesive zone shifts downward and the temperature of the thermal reserve zone decreases. The decrease in heat requirements for solution loss, sinter reduction and silicon transfer reactions compensates the increase in heat demands for CCB reduction and direct reduction, and rather improves the efficiency of blast furnaces. Consequently, the productivity improves, the coke rate shows a notable decrease and the total reducing agent rate also tends to decline compared with conventional operation without CCB charging. Therefore, charging carbon composite agglomerates contributes to the enhancement of blast furnace performance. Furthermore, the model predicts that higher operation efficiency is achieved if the melting and/or tapping temperature could be dropped. The innovative technology of lower temperature ironmaking is expected to be applied in industrial blast furnaces after resolving the problems in engineering and economic evaluations.     

Modeling of Blast Furnace with Layered Cohesive Zone

An ironmaking blast furnace (BF) is a moving bed reactor involving counter-, co-, and cross-current flows of gas, powder, liquids, and solids, coupled with heat exchange and chemical reactions. The behavior of multiple phases directly affects the stability and productivity of the furnace. In the present study, a mathematical model is proposed to describe the behavior of fluid flow, heat and mass transfer, as well as chemical reactions in a BF, in which gas, solid, and liquid phases affect each other through interaction forces, and their flows are competing for the space available. Process variables that characterize the internal furnace state, such as reduction degree, reducing gas and burden concentrations, as well as gas and condensed phase temperatures, have been described quantitatively. In particular, different treatments of the cohesive zone (CZ), i.e., layered, isotropic, and anisotropic nonlayered, are discussed, and their influence on simulation results is compared. The results show that predicted fluid flow and thermochemical phenomena within and around the CZ and in the lower part of the BF are different for different treatments. The layered CZ treatment corresponds to the layered charging of burden and naturally can predict the CZ as a gas distributor and liquid generator.     

高炉风口小套前端磨损机理研究

为了减少风口小套前端碰撞磨损的发生,利用离散单元模型和计算流体力学的耦合模型对焦炭在风口前的运动行为进行了研究,并根据得到的焦炭速度矢量场分析了风口小套前端物理磨损的机理。结果表明:风口小套前端处于靠近高炉壁面的区域时,焦炭颗粒运行速度较小,磨损不会很严重,但小套长度较短,会导致炉体中心气流不盛;处于远离高炉壁面的区域时,焦炭运行速度快、粒度较大、数量较多,磨损严重;处于离高炉壁面最远的区域时,焦炭运行速度快,但速度方向与小套前端相切,且焦炭粒径小,因此磨损很小。     

氧气高炉回旋区内煤粉燃烧行为的三维数值模拟研究

炉顶煤气循环氧气高炉是一种全新的炼铁新工艺,它可以有效提高煤比、减少CO₂的排放.但是其复杂的燃烧条件将使煤粉在回旋区内的燃烧及高炉下部的行为发生很大变化.为了了解氧气高炉炼铁新工艺条件下喷吹煤粉的复杂现象,建立了一个氧气高炉条件下的氧煤枪-直吹管-风口-回旋区-焦炭床的三维数学模型,研究了氧气高炉下部的温度场、浓度场及煤粉的流动和燃烧特性.模拟结果表明,氧气高炉条件下的回旋区温度显著升高、高温区面积扩大,CO₂含量提高,焦炭床内CO含量显著增加.此外,与传统高炉相比,氧气高炉回旋区表面的煤粉燃尽率增加了10.24%.      

Mathematical Modeling of the Energy Consumption and Carbon Emission for the Oxygen Blast Furnace with Top Gas Recycling

The ironmaking process is the most significant source of CO₂ emission in the iron and steel industry, which generates large quantities of greenhouse gases. Recently, oxygen blast and top gas recycling have been applied to the blast furnace to improve the energy efficiency and reduce the pollution from the ironmaking process. However, as a new ironmaking technology, the oxygen blast furnace with top gas recycling (TGR‐OBF) is still under development. This paper focuses on the investigation of the energy consumption and carbon emission for the TGR‐OBF process by modeling the stack, the bosh, the combustion zone, and the gas recycling system. Effects of the key parameters in the TGR‐OBF process on the carbon consumption of reactions and the energy consumption of the system are investigated by orthogonal experiments. Our results indicate that the TGR‐OBF process has the advantages of reducing energy consumption and CO₂ emission. The low temperature and high reducing environment in the new furnace is favorable to lower the coke gasification and increase the reaction rate of iron oxide. The recycling of the top gas can significantly reduce CO₂ emission, and the main advantage comes when the stripped CO₂ is stored.     

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.     

高炉富氧喷吹还原性气体工艺分析

为降低高炉炼铁中固体碳耗、高效利用冶金高温副产煤气,提出高炉富氧喷吹还原性气体工艺流程,建立基于物料平衡与热平衡的高炉数学模型,并修正了理论燃烧温度计算公式。应用该模型分别对传统高炉、炉缸富氧喷吹还原性气体以及炉身喷吹循环煤气的炼铁流程进行技术参数分析。结果表明,炉缸富氧喷吹还原性气体以及炉身喷吹循环煤气的炼铁流程中,当氧气浓度达到50%、炉缸还原性气体喷吹量为267 m3/t时,焦比为291 kg/t,煤比为150 kg/t,直接还原度为0.195,相比传统高炉,燃料比降低109 kg/t,综合能耗降低4.8%。还原性气体温度每升高100 ℃,可多喷吹5.8 m3左右的还原性气体,降低焦比约5.5 kg/t;还原性气体喷吹量对理论燃烧温度影响较大,炉缸每喷吹1 m3/t、1 000 ℃的还原性气体,理论燃烧温度可降低约1.9 ℃。     

高炉喷吹还原气操作的数学模拟研究

副产煤气的高效利用对钢铁产业的节能降耗和环境保护意义重大。为此,提出了一个新的高炉风口喷吹高炉、转炉和焦炉煤气技术,并利用多流体高炉模型对其进行了详细模拟研究,预测了炉内现象和操作性能的变化。在维持回旋区温度、炉腹煤气量及渣面处铁水温度一致的条件下,模拟结果表明与现行常规操作相比,风口喷吹煤气后炉身温度下降,但整个炉内H₂/CO浓度显著提高,炉身烧结矿间接还原加速,产量明显增加,热利用效率明显改善。其中喷吹焦炉煤气效果最为显著,高炉CO₂产生量大幅度降低。随工艺氧制备等技术的进步,高炉喷吹副产煤气技术具有广阔的应用前景。     

Reduction of Pellets‐Nut Coke Mixture under Simulating Blast Furnace Conditions

In recent years an intensive work has been carried out to decrease the coke losses of the blast furnace through mixing small‐sized coke called “nut coke” in the iron ore burden layers. In order to clarify the influence of nut coke on the pellets reducibility, industrial iron ore pellets were reduced with and without nut coke participation under different temperatures and atmospheres. Isothermal and non‐isothermal reduction tests under simulating blast furnace conditions were performed using an experimental laboratory rig. Furthermore, reflected light microscopy, scanning electron microscopy and X‐ray technique were applied to characterize the microstructure and different phases developed in the origin and reduced pellets. Pellets reduced isothermally without nut coke participation exhibited reduction retardation (RR) at elevated temperature (≥1373 K) whereas the presence of nut coke had a positive effect of preventing such phenomena. The non‐isothermal reduction of pellets showed that, as the amount of nut coke in pellets bed increased, the reducibility of pellets increased, too. The rate controlling mechanism of pellets and pellets‐nut coke mixtures was predicted from the correlation between apparent activation energy calculations and microstructure examination.     

高炉内渣铁焦界面润湿行为研究现状及展望

 高炉作为目前世界上最大的移动床式冶金反应器,保持高炉内良好的透气透液性是保证高炉稳定顺行的关键。高炉内部被软熔带分割开来,分为上部固体散料区和下部固液共存区,下部的固液共存区是决定高炉透气透液性和煤气流分布的重要区域,因此若想明晰高炉影响透气透液性的关键,必须对高炉下部固液共存区的反应进行全面研究。高炉高温区焦炭床与渣铁的相互作用行为是决定铁-焦-渣交互作用及高炉透气透液性的重要因素,调控好液态渣铁与焦炭床的润湿性变化,可以有效改善高炉内部的透气透液性,最终会影响高炉生产效率和稳定性。因此,明晰高炉内渣铁焦的界面润湿行为显得尤为重要。首先对界面润湿现象进行了概述;然后详细从铁水成分以及焦炭性质对铁-焦界面润湿行为的影响进行了总结;其次详细分析了炉渣温度、炉渣成分以及焦炭自身性质对渣-焦界面润湿行为的影响。结果表明,目前高炉内渣铁焦界面润湿行为的研究已经从实验室试验以及基础模拟方面进行了研究,研究结果可为高炉操作者理解高炉内渣铁焦界面润湿行为提供初步理论指导,但仍需在可反映高炉内实际复杂情况的润湿行为变化方面进行深入研究。     

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.     

Calculation and Analysis of Liquid Holdup in Lower Blast Furnace by Model Experiments

A hydromechanics experiment on the countercurrent flow of gas and liquid simulating the flow conditions in the lower blast furnace was carried out. A cold model of a packed bed with various packing materials and liquids was used to study the holdup of liquid. Correlations for static holdup, dynamic holdup, and total holdup were obtained. A good agreement was found between the calculated and experimental data. A mathematical model simulating the flow fields was applied to study the effect of liquid holdup in blast furnace. The results of the model calculation show that static holdup is the determinant of the total holdup of molten materials when the blast furnace works in stable condition. The slag phase generally reaches flooding holdup ahead of the hot metal. The radial distribution of gas flow is almost not influenced by the holdup of molten materials, but it has a greater influence on the pressure drop. The size of coke has far greater influence on static holdup than liquid properties does. The study is useful for acquiring a deeper understanding of the complex phenomena in the blast furnace and for determining appropriate operational actions under different production conditions.     

Industrial Practice of BiPCI Process of Pulverized Coal Injection for Blast Furnace Ironmaking at SSAB

BiPCI technology of pulverized coal injection for blast furnace ironmaking was applied to No.2 Blast Furnace of SSAB Oxelösund in Sweden, and notable effectiveness of this BiPCI practice at SSAB has been achieved. The results show that if the tuyere injection rate of pulverized coal is kept nearly unchanged, (1) BiPCI can increase the overall coal rate and decrease the coke rate. When the second injection rate of pulverized coal attains 5 kg/tHM, the coke rate could be reduced by 5 kg/tHM; (2) BiPCI can increase the burden permeability, decrease the pressure drop of the furnace, and produce proper gas flow distribution, which is favourable to keep smooth running of the blast furnace and decrease the total reducing agent rate (RAR). During the test, the RAR showed a decrease by 2.8 kg/tHM (corrected RAR by 1.45 kg/tHM); (3) The pulverized coal through the second injection can be effectively used to protect the coke from fast degradation and improve the coke strength in the blast furnace, which is favourable to lower the high requirement on the coke quality under high coal rate operation.