Cold Briquetting of DRI Fines for Use in Steel Making Process

DRI fines, generated during its manufacture and handling, generate high content of fines in the size fraction less than 2 mm. It has iron content above 80%. It is difficult to directly use such iron-rich material in the primary steel making process, without agglomeration. At JSW Steel Vijayanagar, around 50 to 70 tons per day of DRI fines with < 2 mm size fraction get generated. The fines are used in base sinter mix or it may be agglomerated suitably to use it as a coolant in the primary steel making process. Since the fines are extremely reactive, they are susceptible to oxidation if it is not agglomerated as soon as it is generated. The present study brings out the development of an agglomeration process for the DRI fines to a dense metallized briquette, for use as a coolant in basic oxygen furnace. Initially, the conditions for briquetting such as use of binder, hardener, lime, dust, moisture, briquetting and curing conditions were established in a 10 kg batch size. This was followed by industrial-scale processing, at 500 kg batch size. The physical and chemical characteristics of the fines and briquettes were assessed at different stages. The cold compressive strength of the cured briquette was found to be a function of moisture content. The handling parameters in the production condition, for long-term pile-up of briquettes against oxidation, were brought out. The successful use of the briquettes in basic oxygen process was demonstrated.     

Processing of Agglomerated Red Filter Dust in the Converter Operation from Metallurgical Point of View

Red filter dust (RFD) from steel works contains up to 50 mass% iron, which therefore can serve as raw material for steel production. It should be possible to recycle a fraction of the RFD in the converter process of a steel works wherein also scrap for recycling is used. The aim was the investigation of the reduction behavior of the iron oxide in the RFD. This was accomplished by contact of the dust with pig iron containing up to 3.9 mass% carbon and also by addition of bio‐char to the dust, creating self‐reducing briquettes. The experimental results were compared to the theoretical achievable iron oxide reduction. The reaction time of selected briquettes was calculated by a kinetic approach. Additional the behavior of lead and zinc in the dust was investigated. The mass balance of the converter process indicated the influence of the dust recycling especially regarding the zinc mass flow.     

Strength and high temperature behaviour of carbon composite pellets containing BOF fine dust

Abstract

Steel plants produce significant amounts of dust and sludge during iron and steel production. These wastes contain valuable elements, such as Fe, Cr, Ni, C, K and Na and should be handled properly to prevent them from polluting the environment. In order to utilise the BOF fine dust, the effects of the dust on cold bonded pelletising, solid state reduction and reduction melting behaviours of composite pellets made from iron ore and anthracite with added BOF fine dust were investigated at laboratory scale. The BOF dust was found to improve the cold compressive strength of the wet green carbon composite pellet, and increased with increasing dust content. Almost four times the amount of dust was needed to get the same effect on the strength of the pellet when it was used to replace bentonite. The carbothermic reduction of the composite pellet proceeded effectively at temperatures above 1200°C. The BOF dust had a positive effect on the reduction rate of the pellet, and the rate increased with increased dust content. The reduction of iron oxide was topochemical and conformed to a shrinking core kinetic model. The dust was found to improve the iron and slag melting separation rate of reduced pellets at 1400°C when its content was less than 23·11 wt-%. The liquidus temperature of the slag would decrease with the content of BOF dust increasing from zero to ～30 wt-% and then increase if the content continued to become more in the experiment. Utilising the BOF dust as the binder and flux to adjust the composition of the slag system can potentially reduce the slag ratio and production cost compared with using bentonite and limestone. This work can help to find a new process for the effective utilisation of BOF dust in a more appropriate and environmentally friendly way.     

Decomposition,Reduction and Dissolution Mechanism of Calcium Sulfate in Iron Oxide Dust Pellet

Iron oxide dust generated during oxygen blowing in the BOF process contains a high content of iron. This iron oxide dust can be used as a material of iron source in the BOF slag reduction process or as de‐siliconisation flux or dephosphorization flux of hot metal pretreatment. One of the most practical uses of iron oxide dust is recycling as a form of pellets in the BOF considering easy application and the amount that can be recycled. In the process of making iron dust pellets cement is used as a binder that contains a lot of calcium sulfate. This calcium sulfate is reduced and dissolved in the molten metal during refining in the BOF. If the oxygen content in slag and molten steel is high enough, the reduced sulfate cannot be dissolved into molten metal and it can be removed as SO_x gas. The behaviour of calcium sulfate has been studied using of 50kg high frequency induction furnace and industrial‐scale plant tests were carried out at a 300ton BOF. The results show that for low carbon steels the evaporation of decomposed sulfate increases with increasing oxygen content in the slag while for high carbon steels the decomposed sulfate is reduced into the molten metal.     

EAF Smelting Trials of Waste‐Carbon Briquettes at Avesta Works of Outokumpu Stainless AB for Recycling Oily Mill Scale Sludge from Stainless Steel Production

The EAF steel plant of Avesta Works, Outokumpu Stainless AB, has been used to perform smelting reduction trials of briquettes consisting of oily mill scale sludge, carbon and other wastes. A total of 7 briquette smelting trials were performed. The heats were processed smoothly smelting 3 t of briquettes or 3.4 mass‐% of metal charges. The quantities of FeSi powder and O₂ gas injected and electric energy supplied were increased to smelt briquettes of 6 t. No impacts were found on the analyses of the crude stainless steel tapped from the EAF during the trials. The results of the briquette smelting have been evaluated by referring to the data from the reference heats and results from earlier laboratory tests. The recovery of Cr, Ni and Fe elements from the briquettes was nearly complete and was found to occur mainly through carbon reduction. The slag masses were not increased in three trials as compared with the reference heats. There were moderate increases in the slag masses in four trial heats. The increases were, nevertheless, lower by 52‐69% than the slag masses generated by Sireduction of the briquette oxides. Afterwards, by referring results from the present trials, waste‐carbon briquettes amounting to 1‐3 t were smelted very smoothly in many of the EAF heats at Avesta Works to recycle the oily mill scale sludge and other wastes from stainless steel production.     

Life Cycle Assessment of Internal Recycling Options of Steel Slag in Chinese Iron and Steel Industry

 The internal recycling process of BOF slag which is one of the huge solid wastes from iron and steel industry was emphasized. Based on the four scenarios of different internal recycling strategies for BOF slag, life cycle assessment (LCA) as a valuable tool for industrial solid waste management was applied to analyze the contribution to reducing environmental impacts and resources burdens for each scenario. The global warming potential (GWP) results of the four scenarios show that the scenario which performs best in carbon reduction cuts off 14.2% of GWP impacts of the worst scenario. The results of this study show that the optimized internal recycling process of BOF slag can improve the environmental performance of crude steel. It is important to assess and choose an appropriate strategy to recycle BOF slag from LCA perspective to reduce the environmental impacts and resource burdens as much as possible.     

宝钢含锌尘泥的循环利用工艺简介

对宝钢的含锌尘泥(转炉二次粉尘、电炉粉尘和高炉瓦斯泥)的厂内循环利用进行了研究,通过将含锌尘泥分别应用于铁水三脱、转炉造渣和电炉造泡沫渣工艺对循环利用工艺进行了试验,具体如下:将转炉二次粉尘和电炉粉尘的混合物取代烧结矿粉作为铁水脱磷剂,通过改善流动性,达到了与烧结矿粉相当的脱磷效果,在三脱处理中粉尘中的锌和铅含量得到了明显的富集,为下一步回收处理打下了基础.将转炉二次粉尘和电炉粉尘的混合物通过添加一定量生白云石和锰矿加工成冷压块,在转炉吹炼前期加入,促进了石灰的溶解,改善了前期化渣,提高了脱磷率,LT压块和矿石的耗量减少.造渣剂加入没有引起钢水的增硫明显,粉尘造渣剂的加入对钢水和炉渣成分没有影响.将高炉瓦斯泥通过添加一定量生石灰和生白云石并加工成冷压块后,在电炉熔炼期加入,强化泡沫渣操作,减少金属损失和碳粉用量.瓦斯泥压块加入后对钢水、炉渣成分和电炉的粉尘不会产生明显影响.     

不锈钢除尘灰冷固结团块抗压强度的影响因素

采用冷固结成型法对不锈钢除尘灰进行造块,在微机控制电子式万能试验机上进行抗压强度测试。通过单因子实验,研究闷料时间、持压时间和球团失水各因素对团块强度的影响规律。并设计正交实验研究了石墨粉、水分、蔗糖和团压压力4个因素对球团强度影响的主次性。结果表明,闷料步骤对不锈钢除尘灰冷固结成型至关重要,球团失水对提高球团强度作用显著,持压时间对球团强度也有一定程度的影响;石墨粉等对团块抗压强度影响大小顺序为:水分蔗糖石墨粉团压压力。并且得到最优配比(质量分数):配加水分为13%、蔗糖为13%、石墨粉为11%,团压压力为30 MPa,此时球团可获得27 MPa以上的抗压强度。     

Development of fluxed micropellets for sintering utilising iron oxide waste fines

Abstract

Ultrafine iron oxide wastes such as slime, blue dust and Linz–Donawitz (LD) converter sludge have very limited use in sintering of iron ore due to their excessive fineness (?50 μm). Pelletisation of these ultrafine materials for use in blast furnace involves high temperature curing, which is a highly energy intensive process. Briquetting of LD sludge requires costly binders and contains high moisture, which creates problem at high temperature of the downstream process. In order to alleviate these problems, the current study has developed a process for preparing micropellets of waste iron oxide fines (2–6 mm size) without using any binder. The strength of the micropellet has been increased by a novel CO₂ treatment process at room temperature. Developed micropellets exhibit very suitable drop strength (125 Nos), tumbler properties and cold compressive strength (～9 kg/pellet) to withstand cold handling. Low lime containing micropellets have the possibility of being used as a mixed material in usual sinter making, and high lime containing micropellets may be exploited for making super fluxed sinter that can be used as synthetic flux in the basic oxygen furnace process towards the formation of low melting oxidising slag at the early stage of blow.     

竖炉法冶炼含Cr和Ni的铁水试验研究

基于竖炉工艺,以不锈钢除尘灰、铁鳞、红土镍矿、铁精矿和铬矿为主要原料,采用小型试验竖炉进行高温冶炼模拟试验,探索竖炉工艺冶炼含Cr和Ni的铁水的可行性。研究结果表明：采用竖炉法处理不锈钢除尘灰,能实现除尘灰中Fe,Cr和Ni等有价元素的回收。Ni元素基本上全部进入铁水,其回收率高达99.80%,Cr的回收率也可达到95.82%。竖炉全红土矿冶炼含Cr和Ni的铁水是可行的,而且将红土镍矿球团和不锈钢除尘灰球团搭配入炉,不仅可充分回收Fe,Cr和Ni等元素,还可减少渣量、降低焦比。竖炉采用铬矿配加铁精矿球团和铁鳞球团冶炼含Cr铁水时,铁水中Cr质量分数可达到17.5%,最高可达20.48%,Cr回收率稍低,为87.15%,但有进一步提高的可能;随着铁水中Si含量的增加,Cr的回收率逐渐提高,磷的分配比逐渐减低;当铁水Si质量分数从1.38%提高到3.73%时,Cr的回收率和磷的分配比变化不大。     

提高转炉冶炼吨钢矿石用量生产实践

适当提高转炉冶炼吨钢矿石用量,可以降低钢铁料消耗,降低生产成本。但矿石的大量入炉改变了原有的热量和物料平衡,如果控制不当会给冶炼带来许多不利的影响。在提高转炉冶炼吨钢矿石用量生产实践中,可以通过对设备和工艺的优化,得到适合的操作模式,使转炉冶炼保持稳定。     

Analysis of the efficiency of alternative methods for recycling iron-bearing metallic wastes

This article compares the total amount of fuel used in making steel from dispersed iron-bearing metallurgical wastes by different alternative technologies. Recycling such wastes by briquetting them and then smelting the briquets in blast furnaces is shown to be clearly more advantageous from an economic and environmental standpoint. The availability of excess pig-iron production capacity at a metallurgical plant allows the plant to recycle the given type of wastes by the most cost-effective means while also reducing emissions of greenhouse gases. Similar results can be obtained by smelting the briquets in cupolas.     

转炉终点渣钢间锰平衡状况分析

为了推广锰矿直接还原技术在转炉内的使用,对转炉终点条件下锰矿的热分解、熔融还原和渣钢间平衡状态进行了分析。利用热力学分析方法讨论了国内外转炉锰矿直接合金化锰的平衡状态。结果表明,在转炉终点时刻,锰矿以MnO形式存在于渣中;锰在渣钢间的平衡主要以铁、锰竞争氧化的形式存在;理论计算锰分配比和实践生产数据有相同的趋势,且计算值大于实践生产数据;高温、高碱度、高w([C])、低w((TFe))可以降低锰分配比;渣量越小,锰收得率越高。此外,讨论了进一步提高转炉锰收得率的控制工艺。     

利用除尘灰生产海绵铁的试验研究

为了更好地实现循环经济,降本增效,合理利用太钢除尘灰资源,降低除尘灰中Zn、K、Na等元素对高炉的不利影响,采用隧道窑工艺,以转炉除灰尘、AOD除灰尘、铁鳞、高炉瓦斯灰等配料进行了试验研究。结果表明,采用该工艺处理除尘灰生产海绵铁是可行的,Fe金属化率达到80%以上,脱Zn及碱金属效果显著。     

Removal Mechanism of Zn,Pb and Alkalis from Metallurgical Dusts in Direct Reduction Process

The high-temperature tube furnace was applied to simulate the rotary hearth furnace （RHF） for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonded briquettes made by mixing metallurgical wastes, such as dust from bag house filter, OG sludge, fine converter ash and dust from the third electric field precipitator of the sinter strand, in various proportions was investigated. More than 70% of metallization rate, more than 95% of zinc removal rate, 80% of lead removal, as well as more than 80M of K and Na removal rates were achieved for the briquettes kept at 1473-1603 K for 15 min during the direct reduction process respectively. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results suggested that the main phases of the soot were ZnO, KC1, NaC1 and 4ZnO · ZnC12 · 5H20. Furthermore, the content of Zn reached 64.2 %, which could be used as secondary resources for zinc making. It was concluded that KC1 and NaC1 in secondary dust resulted from the volatilization from the briquettes, whilst ZnO and PbO were produced by the oxidation of Zn or lead vapour from briquettes by direct reduction.     

利用钢渣、炼铁除尘灰生产氧化锌

文章介绍了以钢铁生产中产生的固废冶金渣及收尘系统产生的尘灰为原料,通过回收其中的有用成份锌,实现了对固体废物的资源化和综合利用的方法和工艺,产生了良好的经济效益,减轻了环境污染。     

Direct chromium alloying by smelting reduction of mill scale and low grade chromite ore

Direct alloying is the process in which all of the elements needed for alloying can be reduced from their oxides in a furnace or a ladle. This process is one way of reducing the amounts of energy and materials, reducing the loss of alloying elements, and improving working condition. Mill scale produced in rolling mills is considered a rich iron source (> 67% Fe) with minimum impurities. In this paper, iron high-Cr alloy was produced by a direct alloying with chromium in carbo- thermal reduction using fine of low grade chromites ore and mill scale. The smelting experimental heats were carried out in a 5?kg pilot plant submerged electric arc furnace. The charging materials and reduction parameters were varied and the optimum conditions for obtaining alloy with the highest metallic yield and the highest iron and chromium recovery were determined. When using coke as the reducing agent in stoichiometric amounts, for a mixture of mill scale (55%) and chromite ore (45%), 89.1% of the iron and 72.5% of the chromium were recovered, producing iron high-Cr alloy containing 17.9%Cr, 3.73%C, 0.46%Mn and 1.47%Si. The maximum iron and chromium recoveries obtained were 99.3% and 72.5%, respectively when using excess carbon. The present study clarifies the possibility of using a mixture of chromite ore , mill scale and coke as the precursor for direct chromium alloying. This method offers an alternative process route with cheaper raw materials and fewer process steps (by avoiding the step of ferrochrome production) for producing high chromium iron or steel alloys.     

固体废弃物在莱钢烧结厂循环利用的技术探讨与实践

介绍了钢铁厂各类固体废弃物在莱钢烧结、球团工序的应用情况。在竖炉球团生产中配加炼钢干法除尘灰,每月应用3 000～4 000 t,球团矿指标基本不受影响;在烧结生产中配加炼钢污泥、焦化干熄焦除尘灰、氧化铁皮、钢渣等,替代了大量矿粉,降低了固体燃耗。采用不同的工艺方法,克服了固体废弃物应用过程中引起的生产波动,年创效益达2 000万元。     

Increasing the sustainability of steel production in the electric arc furnace by substituting fossil coal with biochar agglomerates

Biochar fines from a wood gasification plant and from pyrolysis of agricultural residues were investigated as substitutes for fossil coal used in the steel production in the electric arc furnace (EAF). During previous tests biochar fines with high specific surface showed problematic burn-off behaviour. Therefore the agglomeration behaviour of the biochar fines was investigated. Different binary and ternary mixtures of biochar with water and binders were tested in a hydraulic stamp press and evaluated with regard to green strength and fatigue strength of the briquettes after 3 days. One selected mixture was used to produce pillow briquettes in a double roll press. The abrasion behaviour of the produced briquettes was tested and compared to an anthracite reference coal (RC). Melting tests in a pilot EAF showed that the agglomerated biochar reacts similar to the RC. The briquetting leads to reduced reactivity and slower burn-off compared to the biochar fines.     

不锈钢生产过程中含镍废弃物的综合利用

在不锈钢生产工艺中,炼钢过程产生的除尘灰、热轧产生的氧化铁皮和污泥、冷轧酸洗过程生成的污泥等含镍废弃物,吨钢可达到100kg左右。从保护环境、节约资源角度出发,借鉴国外处理工艺,形成具有自己特色的高温还原综合利用工艺,生产出铬镍铁合金产品,作为不锈钢冶炼的一个重要的金属来源,降低了不锈钢冶炼成本。