Top gas recycling blast furnace developments for ‘green’ and sustainable ironmaking

Abstract

The ultralow CO₂ steelmaking blast furnace process (ULCOS-BF) aims at minimising the CO₂ emissions of the BF by at least 50%. This process is based on the replacement of hot blast by oxygen, the recycling of hot decarbonated top gas into the lower shaft and normal hearth tuyeres, and the capture of CO₂ and its storage in a geological trap (full CO₂ capture and storage process). The paper highlights the main technologies of this process and the expected benefits for CO₂ mitigation. The ULCOS-BF has been demonstrated during three campaigns of 7 weeks each by coupling the LKAB experimental BF in Luleå to a pilot vacuum pressure swing absorption unit for CO₂ removal. The concept, preparation and results of the campaigns are described.     

Heat recovery from hot blast furnace slag granulates by pyrolysis of printed circuit boards

Abstract

Heat recovery from hot blast furnace (BF) slag is difficult to achieve but has great potential to recover energy and thereby reduce CO₂ emissions. The objective of this work is to utilise the heat of hot BF slag granulates to generate combustible gas from printed circuit boards. The results showed that this is a possible process and that, after cleaning, the combustible gas could be injected into the BF as a fuel and reducing agent. The new process has advantages over the traditional process in energy saving and pollution emissions.     

Operating experiences with Corex and blast furnace at JSW Steel Ltd

Abstract

JSW Steel Ltd is an integrated steel plant of 3·8 mtpa capacity, with two Corex and two blast furnace (BF) units for producing hot metal. It has started its integrated steel plant operation with Corex ironmaking technology and then synergised with the conventional BF ironmaking during plant expansion. Both these ironmaking furnaces are unique in nature, and have different operation philosophies. The performances of these units depend on the raw material charged, operational philosophies, maintenance, etc., and have their own advantages and disadvantages. This paper brings out the comparison between these ironmaking processes through the usage of raw material inputs, plant operation, maintenance, quality of hot metal and byproducts. This paper also highlights the benefits due to synergistic combination of Corex and BF in an integrated steel plant.     

Cost and Life Cycle Analysis for Deep CO2 Emissions Reduction for Steel Making: Direct Reduced Iron Technologies

Among heavy industrial sectors worldwide, the steel industry ranks first in carbon dioxide (CO₂) emissions. Technologies that produce direct reduced iron (DRI) enable the industry to reduce emissions or even approach net-zero CO₂ emissions for steel production. Herein, comprehensive cradle-to-gate (CTG) life cycle analysis (LCA) and techno-economic analysis (TEA) are used to evaluate the CO₂ emissions of three DRI technologies. Compared to the baseline of blast furnace and basic oxygen furnace (BF–BOF) technology for steel making, using natural gas (NG) to produce DRI has the potential to reduce CTG CO₂ emissions by 33%. When 83% or 100% renewable H₂ is used for DRI production, DRI technologies can potentially reduce CO₂ emissions by 57% and 67%, respectively, compared to baseline BF–BOF technology. However, the renewable H₂ application for DRI increases the levelized cost of steel (LCOS). When renewable natural gas (RNG) and clean electricity are used for steel production, the CTG CO₂ emissions of all the DRI technologies can potentially be reduced by more than 90% compared to the baseline BF–BOF technology, although the LCOS depends largely on the cost of RNG and clean electricity.     

Value-in-use of biocarbon fuel for direct injection in blast furnace ironmaking

Substitution of pulverised coal injection (PCI) by solid biocarbon fuel has the potential to achieve substantial reduction in GHG emissions associated with blast furnace ironmaking. A systematic evaluation was conducted on the performance of solid biocarbons produced from a single raw biomass source using different pyrolysis technologies. A techno-economic model was developed to evaluate the value-in-use (VIU) of the prepared solid biocarbon in blast furnace ironmaking. The VIU of solid biocarbon is strongly influent by its O/C (oxygen to carbon) mass ratio which is determined by the pyrolysis technology and conditions employed. It also dictates the cost of raw materials required to support the blast furnace ironmaking process and the potential GHG emissions achievable. In order to balance all factors that may affect the VIU of solid biocarbon, close collaboration between steelmakers and solid biocarbon producers is critical for producing suitable solid biocarbon fuel to replace PCI.     

Raw materials for Corex and their influence on furnace performance

Abstract

The scarcity of good quality coking coal for the blast furnace (BF) has made steel makers look for an alternative iron-making process that requires little or no coke. The Corex process has been developed as an alternative to BF iron-making, which uses non-coking coal and a small amount of coke as fuel, and pellet/lump ore as iron-bearing feed. JSW Steel operates two Corex units each of 0?8 Mtpa, commissioned in 1998 and 2001 respectively. Iron oxides and non-coking coals have to meet certain physical, chemical and high temperature properties for stable operation and to attain high performance levels. Experience of the Corex operation with various coals and iron oxides over the years has helped in understanding the influence and sensitivity of raw materials on its performance and develop new raw material specifications. Statistical analysis of plant data showed that the significant parameters affecting fuel rate and production are moisture, volatile matter, char strength after reaction of coal, reduction disintegration index (RDI; %, –6?3 mm) of pellets and slag rate. This helped achieve the most efficient operating parameters, surpass rated capacity and utilise steel plant waste. The present paper brings out the impact of various raw material properties, and the modified specifications of coal and iron oxides for Corex.     

Optimization of a Steel Plant with Multiple Blast Furnaces Under Biomass Injection

The allocation of resources between several blast furnaces in an integrated steelmaking plant is studied with the aim of finding the lowest specific operation cost for steel production. In order to reduce the use of fossil fuels, biomass was considered as an auxiliary reductant in the furnace after partial pyrolysis in an external unit, as a complement to heavy fuel oil. The optimization considers raw material, energy, and emission costs and a possible credit for sold power and heat. To decrease computational requirements and to guarantee that the global optimum is found, a piecewise linearized model of the blast furnace was used in combination with linear models of the sinter-, coke-, and power plants, hot stoves, and basic oxygen furnace. The optimization was carried out under different constraints on the availability of some raw materials as well as for different efficiencies of the hot stoves of the blast furnaces. The results indicate that a non-uniform distribution of the production between the furnaces can be advantageous, and some surprising findings concerning the optimal resource allocation under constrained operation are reported.     

Theoretical consideration of problems relating to high coal rate injection into blast furnaces

Abstract

Some key problems relating to high rate pulverised coal injection into the blast furnace are discussed, including furnace permeability in the lower furnace and raw materials quality, heat compensation and theoretical flame temperature, oxygen enrichment, material and gas distribution control and so on. A new method of calculation of theoretical flame temperatures is proposed, taking into account coal combustion efficiency in the raceway. Measures that should be taken for increasing coal injection rates are discussed.     

攀钢高炉锌平衡测定

对攀钢1、2号高炉的原燃料、生铁、炉渣、瓦斯泥、净煤气灰尘和出铁场烟尘进行了取样，根据试样化验的锌含量，结合高炉生产数据对攀钢1、2号高炉进行了锌平衡计算，分析了锌在高炉各收入项和支出项中的分布。结果表明：攀钢高炉的锌负荷很高，对高炉的正常生产造成严重危胁；入炉原料是攀钢高炉锌的主要来源，是造成攀钢高炉锌负荷高的主要原因：支出的锌主要通过炉顶随高炉煤气排出，绝大部分进入瓦斯泥。     

Effect of composition on the crystallisation behaviour of blast furnace slag using single hot thermocouple technique

When the content of glass in blast furnace slag is over 95%, it can be used as a raw material in the manufacture of cement. The critical cooling rate required for the formation of glassy slag is one of the important characteristics for molten BF slag. The crystallisation behaviour of molten BF slag has been studied by in situ observation with the single hot thermocouple technique. The isothermal and non-isothermal experiments were performed to construct time–temperature-transformation and continuous-cooling-transformation diagrams. The effect of MgO, Al₂O₃ and binary basicity (CaO/SiO₂) on the critical cooling rate of the CaO–SiO₂–MgO–Al₂O₃ slags were studied under conditions of CaO/SiO₂?=?1.1–1.4, 6–12?mass% MgO and 10–16?mass% Al₂O₃. The following finding are reported in the present paper: (i) Higher MgO content increased the critical cooling rate; higher Al₂O₃ content decreased the critical cooling rate; higher CaO/SiO₂ increased the critical cooling rate. (ii) The crystallisation temperature of molten BF slag lowers as the cooling rate increases, the slag have larger critical cooling rate, higher crystallisation temperature. The results could be used to design proper cooling path of molten BF slag for the formation of glassy.     

原燃料条件对高炉理论燃烧温度的影响

为了探索低品质原燃料条件下保持高炉顺行的合理热制度,推导出红钢3号高炉新的理论燃烧温度经验公式。对新旧经验公式进行对比分析,得出原燃料条件改变时风温、富氧率、煤比、鼓风湿度对高炉理论燃烧温度的影响。结果表明：原燃料条件不同,保持高炉顺行需要的理论燃烧温度不同;当原燃料条件变差时,保持高炉顺行的理论燃烧温度降低。     

Recycling of steel plant mill scale via iron ore pelletisation process

Abstract

Mill scale is an iron oxide waste generated during steelmaking, casting and rolling. Total generation of mill scale at JSWSL is around 150 t/day and contains 60–70%FeO and 30–35%Fe₂O₃. To recover the iron, the mill scale must be smelted in a blast furnace or other reduction furnace; however, it is usually too fine to use without previous agglomeration such as via pellet or sinter mix. JSWSL operates a 4·2 Mtpa pellet plant to produce pellets for Corex and BF ironmaking units. The aim of this study is to determine the effect of mill scale on pellet properties. Detailed laboratory basket trials were conducted using up to 40% of mill scale in the pellet mix. The addition of mill scale up to 10% is considered to provide the optimum balance of chemical, physical and metallurgical properties of the pellet.     

高炉中铅元素的循环富集及其抑制措施

通过对高炉入炉原料和支出物料铅元素平衡计算,采用扫描电镜和能谱分析仪对高炉风口部位滴出的金属液进行系统的取样分析研究,分析了高炉生产中铅的行为规律。针对铅元素的循环富集给高炉冶炼带来的不利影响,提出了减少入炉原料的铅含量、提高高炉排铅率、在高炉内设置排铅孔的抑制措施。     

Mixed burden softening and melting phenomena in blast furnace operation Part 1 – X-ray observation of ferrous burden

Abstract

The cohesive zone in the blast furnace (BF) is largely affected by the high temperature properties of the ferrous burden. Lowering and minimising the width of this zone will increase the productivity and performance of the BF. Recently part of the BF ferrous burden has been replaced by direct reduced iron (DRI) and hot briquetted iron (HBI). The objective of the present work is to expand the current understanding of softening and melting (SM) mechanism of ferrous raw materials including DRI, HBI, pellets, lump ore and mixed burdens. A small scale 'deformation under load' experiment was designed to examine the interaction of ferrous burdens. The SM tests were conducted with ferrous burdens in different combinations and parameters such as bed contraction, pressure loss, reduction degree, etc. were measured. In addition, the process was visualised using X-ray fluoroscopy. There were microstructural differences between the ferrous materials which governed the initial compaction of bed. The softening of the single burdens of DRI and HBI occurs owing to softening of iron phase. In mixed burdens composed of DRI and pellets/lump ore, initial deformation is not affected by the presence of DRI; however the melting of the bed is dependent on the melting of DRI indicating its dominance over other burden components at later stages of deformation. The change in reduction degree between SM temperatures was found to be small.     

Zinc accumulation during recycling of iron oxide wastes in the blast furnace

Abstract

Byproducts/wastes of iron- and steelmaking processes and steel scrap are the main sources of iron units recycled in the steel plants. Direct recycling of the iron oxide wastes (dusts and sludge) in the blast furnace (BF) is however hampered by its chemistry (>0·1%Zn in the charge). Vaporisation, condensation, oxidation and circulation of zinc may collectively lead to the accumulation in the furnace. Very fine particles are deposited on other particles that have high surface areas which diminish BF refractory life and impair the quality of high quality pig iron produced. For effective continuous recycling of iron units, it is necessary to identify their sources, determine their composition and evolve device and appropriate technology for the treatment of zinc bearing units. The present paper analyses the process of zinc accumulation in the BF and derives an algebraic model to determine the extent of the accumulation. On the basis of analysis of zinc base formation, its recirculation in the furnace and other related productive units, a homograph (alignment chart) of zinc accumulation is designed. The paper also outlines the feasible processes of zinc removal from the close-looped system (sinter plant–BF–sinter plant).     

Influence of magnesia on sintering characteristics of iron ore

Abstract

The MgO in blast furnace slag provides an optimum condition in terms of both good flowability and desulphurisation. The mode of its addition to the blast furnace changed from, initially, as raw flux in the form of dolomite, to via sinter, with the argument that raw flux demands energy for its decomposition inside the blast furnace. Thus, the decomposition reaction was diverted from the blast furnace to the sintering bed, and the energy source for decomposition was changed from costly blast furnace coke to a relatively cheap coke breeze. Now olivine/dunite/serpentine is being used as a source of MgO, where energy for decomposition is not required; this also provides a source of SiO₂, which eliminates need for the addition of quartzite. The effect of MgO on blast furnace slag is fairly well established, but its effect on sintering and sinter quality is unclear. Operating results of the sinter plants show that, with an increase of MgO, the sintering rate, the fuel rate, and sinter strength and reducibility deteriorate; however, high temperature properties such as the reduction degradation index and the softening-melting characteristics of the sinter improve. The present work attempts to establish this influence on the sintermaking process and sinter quality with the help of operating plant data.     

Developments in Alternative Ironmaking

Alternative ironmaking processes compete with the blast furnace process route. The blast furnace, the most important hot metal producer, has improved over the years and continues to do so. Consequently replacing the blast furnace is a formidable task. The success rate of alternative processes has been low, i.e. limited to niche applications. Why do we continue to work in this field? Because the drivers to develop alternative processes are very strong. For example, the expected coke shortage has been the driver for coal based developments in Europe in the period 1980–1990. Some of the recent developments evolved from the work done in that period. In later years, around the year 2000, the Climate Change issue became the driver for development. And the high price level of iron ore of the last decade can spur a new wave of ironmaking developments. The HIsarna alternative ironmaking process is an example of a development that combines several of the drivers mentioned above. The process has the potential to considerably reduce the CO₂ emissions per ton. But it can also use more economically priced raw materials such as non coking coals and iron ores outside the quality range for blast furnace ironmaking. Therefore the process can offer economic benefits as well as environmental benefits.     

Production of ammonia from top gas

Conclusions Computer apodeling and economic analysis have shown that “oxygen” blast-furnace smelting (oxygen content of the blast 55–60% oxygen is both parcticable and highly cost-effective with a natural-gas consumption that makes it possible to obtain top gas suitable for producing ammonia. Here, the cost of the pig iron is reduced by more than 30%, while the wholesale price of the top gas increases in proportion to its calorific value. The use of top gas in place of natural gas for ammonia production also significantly reduces ammonia production costs when the wholesale price of the top gas is 5.5–7 times less than the price of natural gas. Cooperation between blast-furnace shops and nitrogen-fertilizer producers to make use of top gas as the raw material for ammonia production will also lead to a substantial reduction in atmospheric emissions of CO₂. Moscow State Institute of Steel and Alloys (MISiS) and the Open Joint-Stock Company Cherepovetskii Azot. Translated from Metallurg, No. 12, pp. 27–29, December, 1999.     

高Al_2O_3含量渣系高炉冶炼工艺探讨

针对当前高炉炼铁原料中A l2O3含量不断提高,导致炉渣中A l2O3含量也不断提高的新情况,从分析炉渣的物理化学特性入手,剖析了高A l2O3含量高炉给操作带来的危害,并分析了在高A l2O3含量条件下改变炉渣碱度、成分对高炉冶炼的影响,探讨了高A l2O3含量条件下高炉的冶炼工艺。分析表明,炉渣中A l2O3含量高时,不能通过提高碱度的方法改善炉渣的脱硫能力;适宜地提高炉渣中M gO的含量,将有助于降低炉渣粘度和提高炉渣脱硫能力,渣中适宜的M gO含量应为8%~11%;提出了合理添加M gO的新型工艺。     

中国高炉实现低碳低成本炼铁问题探讨

针对当前国家制定的低碳方针及炼铁成本偏高、钢铁企业追求低成本炼铁的目标,采用Rist操作线法及C-rd两种方法分析了高炉炼铁过程中的碳消耗。对高炉炼铁成本进行系统分析得出:两种方法计算出的高炉炼铁碳消耗结果基本相同,误差范围在1%~2%;在ηCO55%~58%热消耗接近9 GJ/t的情况下,单位生铁的碳消耗是高炉炼铁的低碳目标,目前中国高炉的燃料比要比低碳炼铁的燃料比高出80 kg/t以上;原燃料价格低并不等于生铁成本低,应根据焦炭、煤粉、熔剂、矿石及烧结矿的综合成本来科学计算评估炼铁生产成本。由于当前产能过剩,高炉工作者应从追求产能转变为保证炉况顺行、稳定炉腹煤气量、实现低碳低成本炼铁。