COREX用焦在铁水中的渗碳特性

 钢铁工业是支撑国民经济发展的基础产业,同时也属于资源和能源密集型行业,随着国家严格的环保政策的逐渐实施,其面临的资源和环保要求日益增加。传统高炉炼铁生产工艺由于存在能耗高、污染物排放多的弊端,发展受到了限制,因此非高炉炼铁工艺的研究和应用日益受到钢铁行业的重视。系统研究了COREX熔融还原非高炉炼铁工艺使用的顶装焦、捣固焦和气煤焦在铁水中渗碳特性,并分析了3种不同样品在铁水中的渗碳动力学行为。研究结果表明,高温铁水与碳原子接触时发生渗碳反应的吉布斯自由能远小于Fe₃C生成反应的吉布斯自由能,焦炭与高温铁水接触被消耗的过程以渗碳反应为主。顶装焦、捣固焦和气煤焦3种焦炭样品与高温液态铁水接触后迅速发生渗碳反应,铁水中碳含量快速增加,但铁水中碳含量增加的幅度随着铁水中碳含量的升高而快速降低,在渗碳反应时间超过120 min后铁水中的碳含量基本保持恒定。3种焦炭在铁水中的渗碳速率由高到低分别为气煤焦、顶装焦和捣固焦,铁水温度对渗碳过程具有明显的影响,随着温度的升高,渗碳速率和最终铁水中的碳含量增加。动力学分析表明,捣固焦在铁水中的渗碳活化能最高,顶装焦次之,气煤焦最小。     

The Evolution of Structural Order as a Measure of Thermal History of Coke in the Blast Furnace

Investigations were carried out on cokes heat treated in the laboratory and on cokes extracted from the experimental blast furnace (EBF) raceway and hearth. X-ray diffraction (XRD) measurements were performed to investigate changes in structural order (L _c), chemical transformations in coke ash along with comparative thermodynamic equilibrium studies and the influence of melt. Three data processing approaches were used to compute L _c values as a function of temperature and time and linear correlations were established between L _c and heat treatment temperatures during laboratory investigations. These were used to estimate temperatures experienced by coke in various regions of EBF and estimated raceway temperatures were seen to follow the profile of combustion peak. The MgAl₂O₄ spinel was observed in coke submerged in slag during laboratory studies and in cokes found further into the raceway. Coke in contact with hot metal showed XRD peaks corresponding to presence of Fe₃Si. The intensity of SiO₂ peak in coke ash was seen to decrease with increasing temperature and disappeared at around 1770 K (1500 °C) due to the formation of SiC. This study has shown that the evolution of structural order and chemical transformations in coke could be used to estimate its thermal history in blast furnaces.     

Application and analysis of slag holdup model in BF deadman

The operation of blast furnace is considerably influenced by slag performance, particularly in BF hearth. Slag holdup in deadman has negative effects on hearth, such as sharp peripheral flow of hot metal and carbon brick erosion. Therefore, it is urgent to monitor the slag holdup. In this paper, a slag holdup model was proposed to give a transient snapshot of the internal state of BF. Based on the analysis of practical example of Jingtang (Hebei, China) No. 1 blast furnace, three typical models and the slag holdup model were compared. Furthermore, the effects of slag basicity(CaO/SiO₂), MgO/Al₂O₃ ratio, temperature of hot metal, diameter of coke, shape factor of coke and voidage of deadman on slag holdup were investigated. The results show that current slag holdup model can timely predict the general trend of the permeability of the deadman and internal state of hearth. In addition, the influence extent of the six factors which affect the slag holdup is in the following order (from large to small effect): the voidage of deadman, shape factor of coke, diameter of coke, basicity(CaO/SiO₂), MgO/Al₂O₃ ratio, temperature of hot metal. The weighting ratio of these factors is 1:0.92:0.69:0.69:0.38:0.23.     

Carbon structure of coke at high temperatures and its influence on coke fines in blast furnace dust

A thermal annealing study of three industrial cokes was carried out in a horizontal tube furnace at a range of temperatures up to 1600 °C under N₂. Evolution of the carbon structure of cokes was established by determining the stack height (L₀₀₂) of aromatic carbon layers on the basis of the 002 carbon peak in their X-ray diffraction (XRD) spectra by using the classical Scherrer’s approach. The heat-treatment temperature is shown to have a strong impact on the growth of crystalline order of coke carbon by demonstrating a linear correlation between the carbon crystallite height (L₀₀₂) and the annealing temperature. The intensity of the thermal effects on the growth of the crystalline order of coke carbon is influenced by the coke ash chemistry, particularly with the iron content of the coke. The carbon structure of blast furnace (BF) dust samples was also analyzed by using XRD and scanning electron microscopy (SEM). Under a similar range of heat-treatment temperatures, growth of the carbon crystallite (L₀₀₂) of coke, in both the laboratory and the industrial BF, was found to be of the same order of magnitude. The correlation between the carbon structure (L₀₀₂) of coke and the annealing temperature is used to ascertain the temperature of the origin of coke fines in a BF. The carbon structure of coke is shown to have a significant influence on the coke behavior in a BF such that highly ordered coke displayed lower reactivity as well as higher proportion of coke fines in the dust. The carbon structure of coke fines in BF dust has been shown as an indicator of the crystallite dimension (L₀₀₂) of the coke in a BF, and has a potential to assess coke performance, particularly of the coke fine generations from different thermal regimes of a BF and also their subsequent consumption.     

高炉焦炭在铁水中溶解行为研究现状及展望

在当前及未来大型高炉高冶炼强度的条件下,加快焦炭在铁水中的溶解速率、提高高炉炉缸铁水的碳饱和度是削弱碳不饱和铁水对炉缸炉衬侵蚀、保证炉缸正常工作及延长高炉寿命的重要措施,同时可以为下游的炼钢工序提供部分热量来源。首先对国内外焦炭在铁水中溶解的试验和模拟研究方法进行了概括,然后对焦炭自身结构性能、焦炭中矿物质、铁水的物理性质等影响焦炭溶解速率的因素进行了详细分析。结果表明,碳结构的有序度和铁水温度的升高有利于焦炭的溶解,而焦炭中矿物质及铁水中硫、磷等元素的存在会抑制铁水的进一步渗碳。研究结果为高炉操作者理解焦炭在铁水中的溶解行为提供借鉴,指导钢铁工业的节能减排。     

Effect of titanium additives on carbon anode reactivity

In order to ascertain the impact of titanium additives on carbon anode reactivity, different titanium content of carbon anodes were prepared with the single factor experimental method, and test its reactivity in CO₂ and air atmosphere respectively. The micro structure of carbon anodes and pitch cokes were tested by XRD. The pyrolysis process of pitch was tested with the TG-DTG method. The results show that the residual rate and chalking rate of carbon anode can also be significantly improved by increasing titanium content. Titanium additives can refine the crystallite size of carbon anode, promote the asphalt carbonization. The titanium additives can increase the apparent activation energy and pitch coke yield of the pyrolysis process, when the titanium content is 1.5%, E _a is 56.405 KJ/ mol, reaction order is 6.4, and the rate of pitch coke yield is 50.5%.     

COREX炉内块煤裂化成焦的热态强度

通过对COREX所用2种块煤在不同条件下所成半焦的显微结构、热态强度进行观察,分析了影响块煤成焦质量的内在因素。比较2种块煤所成半焦的组成结构及性能差异后,发现兴隆庄煤成焦结构要优于大同煤,但兴隆庄原煤组织反应性较高,故在前期其煤成焦强度低于大同煤,直至成焦结构较多时,才高于大同煤。通过对COREX风口焦及实验室自制半焦的微观形貌和性能进行对比,确定了风口焦的来源,风口前兴隆庄煤形成焦炭的表面呈现出较浅的孔洞,其热态强度明显高于大同煤形成的焦炭。     

Use of Waste Bakelite as a Raw Material Resource for Recarburization in Steelmaking Processes

Bakelite is a thermoset plastic commonly found in electronic and automobile components. CaCO₃ is generally found in the polymer as a filler material. Since it cannot be remelted, the disposal of this material has become an environmental issue. The present study investigates a new route to utilize waste bakelite as a source of carbon in EAF steelmaking process. This paper reports the carbon dissolution behaviour of bakelite/coke blends into liquid steel at 1550 °C. The carbon pick up in the liquid steel after reaction with varying blends of bakelite/coke for 30 minutes ranged between 0.13 wt% to 0.17 wt%; these were generally higher than that observed from coke alone (0.1 wt%). The dissolution rate (K) was also found to improve and the observed trend was BK2 (0.045 × 10^?3 s^?1) > BK3 (0.023 × 10^?3 s^?1) > BK1 (0.005 × 10^?3 s^?1) > coke (0.003 × 10^?3 s^?1). The reaction products formed at the interface after 30 minutes of contact between liquid steel and bakelite/coke blends were observed to be a CaS‐Al₂O₃ complex. The presence of CaS in the interfacial layer due to the CaO in the ash, lowered melting temperature of the layer, thereby allowing for increased removal of the ash layer and greater carbon pick‐up. The CaO is formed from the decomposition of CaCO_3, and its presence was found to have a positive effect on modifying the properties of the coke, and thereby enhancing the carbon dissolution behaviour.     

Analysis on the stamping coke dissolution of hot metal in the blast furnace hearth

By utilising the carburiser-cover methods, this article mainly focuses on the impacts of different carbon sources on hot metal carburising in the blast furnace hearth. The carburising rate, an indicator of the evaluation of coke including stamping coke and graphite, is compared at 1450–1550°C. Additionally, the apparent activation energy of carburisation of coke 1, coke 2 and graphite are 236.9, 178.8 and 46.0?kJ?mol^?1, respectively. The difference in activation energy for the three carbon sources in question is attributed to the mineral matters in coke, because it is capable of influencing the effective contact interface area between the liquid iron and carbon. As to the overall viscosity of the interface layer between the hot metal and carbon, it is mainly affected by the temperature and ash content and its composition. When the temperature increases from 1450 to 1550°C, the viscosity of the minerals on the interface layer will decrease correspondingly. The defined surface area of mineral reduces from 86.7 to 70.7% in coke 1 and from 82.5 to 69.3% in coke 2. Finally, to improve the carburising rate the basicity of the oxide contents in the coke should be increased by adding CaO or MgO.     

Numerical simulation on novel blast furnace operation of combining coke oven gas injection with hot burden charging

A novel blast furnace operation of coke oven gas (COG) injection simultaneously with hot burden charging has been proposed to solve the problem of insufficient heat in the BF shaft zone under the condition of COG injection and make full use of the abundant sensible heat of high temperature burden. In this paper, the novel process has been simulated with a multifluid blast furnace model. The results show that, in comparison with the operation of COG injection only, under the operation of COG injection together with hot burden charging, the temperature in the upper zone of the shaft increases while that in lower zone decreases. Furthermore, the reduction of iron bearing material is improved in the top zone, and the cohesive zone tends to descend and narrow. The coke ratio, fuel ratio and CO₂ emissions of the operation of charging hot pellet and coke with the temperature of 800°C are decreased by 4.0, 4.7 and 5.3% respectively, while the hot metal productivity is increased by 7.14%. Therefore, COG injection combined with hot burden charging operation not only increases temperature in the upper part of the blast furnace but also decreases energy consumption per tonne hot metal.     

Hot metal pretreatment by powder injection of lime‐based reagents

A mathematical model earlier proposed has been improved to predict the kinetics of multicomponent reactions in the hot metal pretreatment through the injection of reactive fluxes. It is assumed that there are two reaction zones along the flux injection operation: a transitory reaction between the rising particles and the bulk metal, and the permanent reaction between the metal and the top slag. A criterion to estimate the fraction of solids which will react with molten iron in a three‐phase jet (gas‐solid‐liquid) was considered; this fraction of solids carries out the transitory reaction. The model also takes into account the thermodynamic changes produced in the metal and slag due to the chemical reactions. Calculated results of the model are in good agreement with experimental results for the desulfurization of hot metal through the injection of CaO‐SiO₂‐CaF₂‐FeO‐Na₂O reagents at 1400 ‐ 1450 °C. Two kinds of hot metal were tested, one with a low carbon mass content of 3 % and the other with a high carbon mass content of 4.5 %.     

不同增碳剂对含钒铁水增碳的理论分析和试验

 用热力学方法计算并分析了铁水增碳过程中碳溶解反应自由能变化以及碳氧化反应自由能变化的关系,认为碳的氧化是阻碍铁液增碳的不利因素,增碳反应必须在氧气较少的气氛中进行。在此基础之上,进行增碳试验。首先利用过量石墨增碳,分别得到含钒铁水在1 450、1 500、1 550 ℃时的碳饱和溶解度,并拟合得到碳溶解度与温度的关系式,即[w(Cs)＝2.7×10－3T＋0.38。]然后将不同的增碳剂加入到由铁屑熔化而得到的含钒铁液中,并保温一定时间进行增碳试验。由试验结果可知,5种增碳剂的增碳效果优先顺序为：低氮增碳剂、石墨、无烟煤、碳粒、焦炭。由动力学计算可知,在本次试验条件下增碳反应速率常数的数量级为10－4 s－1。通过分析认为,提高温度可以促进增碳反应的进行,而增碳剂中的硫和灰分抑制增碳反应的进行。     

Kinetics and Mechanism of the Simultaneous Carbothermic Reduction of FeO and MnO from High-Carbon Ferromanganese Slag

The carbothermic reduction of 38.7 pct MnO-12.1 pct CaO-5.4 pct MgO-9.3 pct Al₂O₃-24.1 pct SiO₂-10.4 pct FeO slag in Ar at 1600 °C was studied using the sessile drop wettability technique. Pure graphite, coke, and charcoal were used as the carbon material substrates. The reduction rates were evaluated by sampling at different reduction times and by analyzing the chemical compositions of the reduced slag and the produced metal. The carbothermic FeO reduction from slag is initially fast followed by a much slower reduction rate. However, the rate of the MnO reduction is slow in the fast FeO reduction stage, and it starts to increase significantly during the slow FeO reduction stage. The kinetics of FeO and MnO reduction are affected by the type of carbonaceous materials. Moreover, the rate of the carbon dissolution/transfer into the produced metal phase and the amount of the transferred manganese to the metal phase depend on the type of carbon. Based on the experimental observations and the thermodynamic calculations, a mechanism for MnO reduction was proposed. According to this mechanism, MnO is mainly reduced through a metallothermic reduction by Fe and the rate of MnO reduction is controlled by the rate of the consumption of FeO from the slag, which takes place simultaneously. In contrast, the rate of FeO reduction in the fast initial reduction stage is controlled by the rate of the carbon dissolution/transfer into the metal phase. However, at the second slow FeO reduction stage, it is reduced mainly by the solid carbon.     

Interactions of Polymer/Coke Blends with Molten Steel at 1823 K: Interfacial Phenomena

With an aim to recycle waste polymers as a carbon resource in steelmaking, in‐depth investigations have been carried out on polymer/coke blends and molten steel at 1823 K. Three polymers, namely high density polyethylene (HDPE), polyethylene terephthalate (PET), and bakelite were blended with metallurgical coke and devolatilized at 1473 K using a drop tube furnace. High temperature interactions of various chars with molten steel were investigated at 1823 K using the sessile drop technique in argon atmosphere; the influence of polymers on the interfacial phenomena and carbon dissolution was determined. While the residual volatiles from HDPE did not affect the chemical composition of interfacial products, the coverage of the interfacial region was somewhat slower than metallurgical coke. Oxygen present in PET was found to oxidize liquid steel leading to the formation of FeO at the interface modifying both the chemical composition and the morphology of the interfacial region. CaCO₃, present as a filler impurity in bakelite was found to act as a fluxing agent and lowered the melting point of the ash layer at the metal/carbon interface. The addition of polymers improved the overall carbon dissolution into molten steel by a small extent as compared to metallurgical coke. This study has shown that a variety of waste polymers can be utilized to partially replace metallurgical coke in steelmaking.     

石油焦煅烧程度对铝用炭阳极显微结构及电解消耗的影响

以不同煅烧程度石油焦为骨料,煤沥青为黏结剂制备铝用低煅焦炭阳极.通过激光共聚焦扫描显微镜和图像分析方法对炭阳极孔隙结构进行分析表征,并考察阳极反应性和电解消耗性能.在煅后焦微晶尺寸1.7~2.7 nm范围内降低石油焦煅烧程度,炭阳极小孔隙逐渐沿骨料-黏结剂界面演变为裂纹状大孔隙,炭阳极孔隙率、形状因子及连通率均先减小后增大,视孔隙比表面积呈减小趋势.煅后焦微晶尺寸降低至1.9 nm较为适宜,对应的炭阳极空气和CO₂反应质量损失率最少为9.6%和3.0%,每吨铝阳极碳耗为355.4 kg.低煅焦炭阳极过量消耗机制从以黏结剂选择性消耗转变为骨料与黏结剂共同消耗,使碳渣量减少.     

Mathematical Modeling and Exergy Analysis of Blast Furnace Operation With Natural Gas Injection

Blast furnace operation with natural gas (NG) injection is one of the effective measures to save energy, reduce CO₂ emission, and decrease environmental load for iron and steel industry. Numerical simulations on blast furnace operation with NG injection through tuyeres are performed in this paper by raceway mathematical model, multi‐fluid blast furnace model, and exergy analytical model. With increasing NG injection volume, the simulation results are shown as follows: (1) the theoretical flame temperature and bosh gas volume can be constant by decreasing blast volume and increasing oxygen enrichment. (2) The utilization rate of CO enhances while that of H₂ decreases. The proportion of H₂ in indirect reduction tends to be increased, which accelerates the reduction of burdens. The pressure drop shows that the permeability of blast furnace gets better. The blast furnace productivity is increased from 2.07 to 3.08 t · m^?3 · day^?1. The silicon content in hot metal is decreased from 0.26% to 0.05%. When BF operation with 125.4 kg · tHM^?1 NG injection, coke rate and carbon emission rate are decreased by 27.2% and 32.2%, respectively. (3) The thermodynamic perfection degree is increased from 88.40% to 90.50%, the exergy efficiency is decreased from 51.94% to 49.02% and the chemical exergy of top gas is increased from 4.69 to 6.22 GJ · tHM^?1. It is important to strengthen the recycling of top gas.     

The nitrogen reaction between carbon saturated Iron and Na2O-SiO2 Slag: Part 1. Thermodynamics

The nitrogen partition ratio between Na₂O-SiO₂ slags and carbon saturated iron was measured for slags containing from 0.4 to 0.55 mole fraction of Na₂O and the temperature range 1200° to 1350 °C. The nitrogen is dissolved in the slag as the cyanide ion (CN⁻) and the partition ratio is proportional to the oxygen pressure to the −1/4 power as predicted for CN⁻ dissolution. The oxygen pressure for carbon saturated iron silicon alloys is controlled by the Si (metal)-SiO₂ (slag) equilibrium. The nitrogen partition ratio and the cyanide capacity increase with Na₂O content and temperature. Calculations indicate that Na₂O-SiO₂ slags will absorb three times more nitrogen than CaO-Al₂O₃ slags at the same basicity and temperature. Based on thermodynamic calculations it is estimated that for a typical Na₂CO₃ hot metal treatment, half of the nitrogen in the metal could possibly be removed. F.Tsukihashi is on leave of absense from Department of Metallurgical Engineering and Materials Science, Faculty of Engineering, The University of Tokyo, Bunkyo, Tokyo 113, Japan     

Improving the energy efficiency of blast furnaces at PAO NLMK

Analysis of measures used to reduce energy expenditures shows that methods in which a single parameter is changed are ineffective. Coordinated adjustment of several parameters is required. Theoretical analysis reveals the combinations of parameters with the greatest effect. The influence of the granulometric composition of the sinter on the blast-furnace efficiency is considered in terms of the influence of the mean piece size on the reduction rate and the gas dynamics of the upper furnace region. When the reaction FeO + CO = Fe + CO₂ reaches equilibrium, the heat consumption in smelting is reduced by increasing the smelting rate. Analysis of specific approaches to reducing the heat consumption in blast furnaces for the example of PAO Novolipetskii Metallurgicheskii Kombinat (NLMK) indicates the basic measures that decrease heat consumption: optimization of the iron ore by reducing the proportion of the >45 mm fraction; increase in output of the blast furnaces to 75–90 t/day (per m² of hearth); operation with the highest permissible pressure (in terms of the charging-unit design); increase in hot strength of the coke to 60–62%; pulverized- coal injection at 140 kg/t of hot metal; and optimization of the ore distribution over the furnace radius. Between 2013 and 2016, those measures decreased coke consumption by more than 10 kg/t of hot metal. In addition, the total consumption of carbon fuel was reduced.     

焦炭添加剂对南钢焦炭质量的影响研究

通过对南钢冷态焦炭、凉焦台焦炭、热态焦炭喷洒焦炭添加剂溶液,测试其热态性能变化规律;在20 kg小焦炉上进行4种配煤方案的炼焦试验,研究焦炭添加剂对改善焦炭质量所起的作用.在此基础上,提出喷洒焦炭添加剂溶液的最佳生产工艺和技术参数,在焦化厂进行焦炭喷洒焦炭添加剂溶液试验,在炼铁厂3号高炉同步进行应用试验.试验表明:焦炭添加剂能改善焦炭的热态性能指标,高炉使用喷洒焦炭添加剂溶液后的焦炭,炉况顺行,增铁、节焦效果明显,经济效益显著.