Disintegration of Cold-Bonded Agglomerates of Iron-Bearing Materials in Blast Furnaces and DRI Shaft Furnaces

The collected data on the influence of the parameters of the melting zone on the operation of a blast furnace (BF) give a new look on the formation of guidelines for the choice of the operating mode a bell-less top (BLT) charging system aimed at improving the efficiency of operation of the blast furnace and its lifetime. The management of the “no-feedback” bell-less top operation mode without application of the criteria of BF operation often results in the inefficient usage of its advantages, which sometimes leads to a decrease in the productivity of the BF. The operating control over the BLT charging system aimed at the improvement of the efficiency of BF should be realized with feedback with regard for the changes in the following operating criteria of the BF: optimization of the radial gas distribution in the BF top; minimization of the circumferential gas distribution in the BF top; optimization of the thermal state of the furnace; optimization of the shape and location of the melting zone in the boshes of the BF; monitoring and control of the temperature of materials and smelting products operating in contact with the furnace lining in the boshes, flare, and the bottom part of the furnace shaft. The strategic control over the BLT operation should be performed with realization of the target function, i.e., with an aim to increase the lifetime of the BF by using the following criteria of its operation: the minimization of the FeO content in the primary slag and the optimization of the temperature of materials and smelting products adjacent to the furnace lining in the boshes, in the flare, and in the bottom part of the furnace shaft.

Blast furnace (BF) ironmaking is the most important process that produces hot metal (HM) from iron-bearing materials continuously, rapidly, and efficiently. To date, the process is considered to have reached its limit in view of the achieved high process efficiency. In addition, the required high-quality materials are expensive and gradually getting depleted. Hot gas injection (HGI) into the shaft of the BF is an emerging technology recognized potential to solve the aforementioned problems. However, so far, limited information and studies are available, most of which are preliminary studies with regard to the feasibility and aerodynamics of the technology. This hindered the understanding and thus the effective use of this technology. This work presents a numerical study of the multiphase flow, heat, and mass transfer in a BF by a CFD-based process model. The effects of injection composition in terms of CO and CO2 contents in HGI are studied first. The calculated results reveal that HGI of 100% CO delivers the best BF performance. Then, the effects of key variables in relation to HGI of 100% CO, including position, rate, and temperature, are systematically studied. The in-furnace states and overall performance parameters have been analysed in detail. The results show that, through appropriate control of the injection variables, it is possible to achieve improved BF performance including low fuel rate and high productivity, which are considerably affected by the HGI parameters. The BF process model is also demonstrated to be a cost-effective tool in optimizing the key variables of HGI in BF for obtaining optimum process efficiency.

Based on computational fluid dynamics, chemical reaction kinetics, principles of transfer in metallurgy, and other principles, a multi-fluid model for a traditional blast furnace was established. The furnace conditions were simulated with this multi-fluid mathematical model, and the model was verified with the comparison of calculation and measurement. Then a multi-fluid model for an oxygen blast furnace in the gasifier-full oxygen blast furnace process was established based on this traditional blast furnace model. With the established multi-fluid model for an oxygen blast furnace, the basic characteristics of iron ore reduction process in the oxygen blast furnace were summarized, including the changing process of the iron ore reduction degree and the compositions of the burden, etc. The study found that compared to the traditional blast furnace, the magnetite reserve zone in the furnace shaft under oxygen blast furnace condition was significantly reduced, which is conducive to the efficient operation of blast furnace. In order to optimize the oxygen blast furnace design and operating parameters, the iron ore reduction process in the oxygen blast furnace was researched under different shaft tuyere positions, different recycling gas temperatures, and different allocation ratios of recycling gas between the hearth tuyere and the shaft tuyere. The results indicate that these three factors all have a substantial impact on the ore reduction process in the oxygen blast furnace. Moderate shaft tuyere position, high recycling gas temperature, and high recycling gas allocation ratio between hearth and shaft could significantly promote the reduction of iron ore, reduce the scope of the magnetite reserve zone, and improve the performance of oxygen blast furnace. Based on the above findings, the recommendations for improvement of the oxygen blast furnace design and operation were proposed.

Numerical study of hot charge operation in ironmaking blast furnace

The cohesive zone in the blast furnace is largely affected by the softening and melting behaviors of ferrous burden. The Visual High Temperature Method (VHTM) has been employed, in present work, to explore the softening and melting behavior of sinter, two different types of lump ores, and one acid pellet. All iron bearing materials are observed to swell before they shrink. This observation is more dominant in case of dense structured lump ore B. The shrinking temperature intervals are different from one another. This contributes to the gas permeability of ore layer in the cohesive zone because “ore window” is formed. In addition to this, the softening and melting behavior of mixed burdens (consist of sinter and other acid materials) have also been studied. Results display that the softening and melting behavior of all materials are improved. This observation is more dominant for lump ore A. It is attributed to high temperature interactions between sinter and acid iron bearing materials. The high temperature interactivity is largely influenced by the chemical compositions, pore structure, and contact condition. Experimental results of two groups of integrated burdens verify the importance of high temperature interaction for improving the softening and melting characteristics of iron bearing materials.

The investigations on the production of coke iron and its appl icat ion for iron smelt ing were started during the Korean War. At first, by making use of the experience accumula ted during the investigation of the possibil i ty of the production of pig iron with the use of anthracite, and by ut i l iz ing the method of the manufacture of ore briquettes, we ~.~t0,5 carried out some e lementary experiments and thermody~aamic ~ ~ o O ~ 01ff ~ _ calculat ions which showed that i f the blast furnace is o ~ ~ ~ f i l led with briquettes made of a mixture of iron ore con~ = . centra te and coal then the iron oxide is rapidly reduced ~ . ~Yg~ ~ O t/ to a me ta l l i c state, provided that the strength of the bri~ ~ o O3 que~te is retained. Therefore, one can obtain pig iron from these briquettes in low shaft furnaces (during the war we were not in a position to build blast furnaces of a normal height but there was an urgent demand for pig iron). The workers and technica l pe r sonne lo f theKim Chak Iron and Steel Factory undertook to continue the invest igation of the production of pig iron in low shaft furnaces. In September~ 195!, we started to make briquettes from a mixture of Musan iron ore concentra te and various coals. These briquette~ were resistant to cold and high temperature and stood up well to the pressure in Iow shaft furnaces. They were ca l led "reducing i ron-ore briquettes." Under war eonditious, no exper imenta l apparatus Was ava i lab le for testing briquettes at a high tempera ture and, therefore, we carried out industrial tests direct iy in a small blast furnace during a tr ial smelt ing operation. To strengthen the briquette we subjected i t to thermal t rea t ment under pressure. The strongest briquettes were obta ined from a mixture of iron ore concentrate and coking coal. This is explained by the fact that, in the course of the thermal t reatment , the coal was converted into coke, and oxides of iron were reduced to m e t a l l i c iron. We ca l led such briquettes " i ron-conta in ing coke," and la te r on we gave it the name of coke iron. As a result of the laboratory preparat ion of coke iron the following facts were ascertained: 1. During the coking most o f the Musan iron ore concentrate is reduced to m e t a l l i c iron, the extent of the reduction being dependent on the conditions of coking. At the same t ime the grains of the reduced me ta l l i c iron adhere strongly to the neighboring grains of iron or carbon. Therefore, the mechan ica l strength of the coke iron produced depends on the content of iron ore concentra te in the charge prepared for coking. Up to a certain I imi t of the concentrate content the mechan ica l strength increases and then gradually decreases (F ig . ) . 2. When coke iron is used there is no need for high blast furnaces since the iron contained in the coke iron is a lready part ly reduced, 3. Cokei ron production makes i t possible to u t i l i ze pulvemlent iron ores.

Given the shortage and high price of coking coal, efforts are underway to reduce their consumption in their primary uses, including blast-furnace production and the smelting of copper and nickel ore in shaft furnaces. A promising approach is the replacement of some or all of the coke by less expensive coal [1] or by dust‐coal mixture injected in the blast furnace [2]. The lean, poorly clinkering coal and anthracite used to replace coke in blast furnaces has a considerable content of volatile components (low-molecular thermaldestruction products), which enter the water and sludge of the blast-furnace gas-purification system as petroleum products. Therefore, it is important to study the influence of coal on the petroleum-product content in the water and sludge within this system. The liberation of primary thermal-destruction products is investigated for anthracite with around 4 wt % volatiles, using a STA 449C Jupiter thermoanalyzer equipped with a QMC 230 mass spectrometer. The thermoanalyzer determines small changes in mass and thermal effects with high accuracy (weighing accuracy 10 ‐8 g; error in measuring thermal effects 1 mV). This permits experiments with single layers of coal particles, eliminating secondary reactions of its thermal-destruction products. Samples are prepared from natural anthracite in powder form. Particles of size class 0.5‐2 mm (first series of experiments) or <0.5 mm (second series) form a single layer; in the third series, (0.5‐2)-mm particles form several layers. The experiments are conducted in a current of argon. The results are shown in Figs. 1 and 2 in the form of curves of the mass (TG) and the rate of mass change (DTG) and differential scanning-calorimetry (DSC) plots with standard leucosapphire samples, along with mass-spectrometric data. According to experimental data, the evaporation of free water ends at 200‐220 ° C, and the formation of low-molecular thermal-destruction products of coal begins at 250 ° C. The liberation rate of volatiles from a single layer of (0.5‐2)-mm particles, like the evaporation rate of water (Fig. 1), is considerably higher than for the other series of experiments. In the particle layer, more favorable conditions for the reaction of intermediate products released from a single particle with other particles or thermal-destruction products are created. When the coal is ground to powder, the structure of the macromolecules is destroyed, and the resulting fragments of different molecular mass and chemical activity react at once with each other and with the partially disintegrated coal grain. This necessarily affects the decomposition rate. These aspects of the thermal destruction of anthracite particles must be taken into account in selecting the fraction of coal-dust fuel for injection in steel-smelting furnaces. According to mass-spectrometric data (Fig. 2), the basic components of the gas phase in the thermal destruction of anthracite are CH 4 , CO 2 , H 2 , and H 2 O. No carbon monoxide is observed, in contrast to [3]. The content of C n H m and N 2 is no more than 1 vol %, according to [3]; this is probably why it is not detected mass-spectrometrically. The composition of the gas phases varies considerably as a function of the temperature. Intense methane liberation occurs in the range 440‐500 ° C, while the CO 2 content gradually declines. At 580 ° C, hydrogen begins to predominate in the gas. Above 580 ° C, the hydrogen content increases, and the methane content declines; this is associated with displacement of the equilibrium in the reaction CH 4 = C + 2H 2 toward the products.

A problem of estimating the velocity of subsidence of a column of charge materials using non-contact methods was considered. This is important because the level of furnace charge materials and the velocity of their subsidence are main indicators of melting intensity determining the furnace productivity. The design of a blast furnace and its blast path were described and existing methods and means of controlling the velocity of charge materials in the blast furnace were analyzed. A mathematical model was presented for estimating the velocity of subsidence of charge materials in a blast furnace based on the magnitude and fluctuations of gas pressure along the furnace shaft height. The model is based on the fact that the furnace gases rise up in the furnace shaft through elementary channels in the column of charge materials consisting of a combination of capacitances and resistances. Volume of capacities and values of resistance of elementary channels are constantly changing. This changes hydraulic resistance to gas movement in the blast furnace. The system of differential equations describes the dependence of the amplitude of pressure fluctuations on the amplitude of change in coefficients of resistance and frequency of pressure fluctuations on the frequency of change in coefficients of resistance. The experimental data on velocity of the column of charge materials and fluctuations in the pressure differential in the furnace were processed and their significant relationship was shown to confirm the previous theoretical study results. To assess the model adequacy, the simulation method was used. The results of the simulation model work were confirmed by experimental data. The developed mathematical model can be introduced into production. This will make it more economical and safer through better and more predictable control and improved flexibility in operation under different production conditions.

Nowadays the use of charcoal in metallurgy is intimately linked to small blast furnaces in Brazil. Due to the challenge for CO2 mitigation, interest for charcoal use as a renewable energy source is rising. In the scope of European efforts to mitigate carbon dioxide emissions in the steel industry in the post-Kyoto period, the use of charcoal in cokemaking and ironmaking has been investigated. This paper presents results of an experimental study on charcoal behaviour under the blast furnace simulating conditions performed at the Department of Ferrous Metallurgy, RWTH Aachen University and at the National Centre for Metallurgical Investigations, Madrid. Conditions in the raceway and in the furnace shaft were simulated using thermo-analytical, laboratory and pilot facilities. Charcoal samples were produced in two furnaces for pyrolysis from different wood types at various carbonisation conditions. Furthermore technological and ecological assessment of blast furnace process when injecting different types of charcoal was performed using a mathematical model. All the experiments and calculations were also performed with reference mineral coals for injection. Conversion efficiency of all the tested charcoals is better or comparable with coals. Change in coke rate, furnace productivity and further operation parameters when replacing pulverised coal with charcoal depends on charcoal ash content and composition.

Numerical analysis on blast furnace performance with novel feed material by multi-dimensional simulator based on multi-fluid theory

The softening–melting properties of iron-bearing materials play a crucial role in the reduction process in the lumpy zone in the blast furnace (BF) and affect the height, thickness, and shape of the cohesive zone, as well as gas permeability in the BF. A novel softening–melting method was developed based on actual BF production practices, which consistently matches the reduction index and metallization degree observed in actual BF operations compared to the conventional methods. Under the novel softening–melting testing method, the characteristic temperatures (T40 and TS) increase by about 5 °C and 49 °C, respectively, compared to the conventional method. Additionally, the permeability index (S) of the sinter in the novel method is about 707 kPa·°C lower compared to the conventional method. Clearly, the novel method results in higher softening–melting characteristic temperatures for iron-bearing materials compared to the traditional method, more closely matching actual BF conditions. This approach can provide valuable insights for improving gas permeability and enhancing the reduction process of iron-bearing materials in the BF.

The work presents generalized experience in the development and implementation at PJSC Severstal of technological measures to extend the campaign of blast furnace No. 5. The authors carried out an analysis, identified and described the problem areas, generalized the principles for ensuring the safety of the shaft lining, boshes and metal receiver of the blast furnace. The results of a study of the working space of blast furnace No. 5 in 2006 are also presented. The identified technological factors ensure an increase in duration of the unit campaign. Technolo­gical measures are given for: washing the blast furnace hearth, reducing chemical erosion of the carbon blocks of the hearth and flange, forming a protective skull in the blast furnace shaft, special methods for loading solid coke substitutes, and organizing an effective structure of the charge column in the blast furnace. It is necessary to use digital models integrated into the blast furnace expert system for operational control of blast furnace technology. The results of the current blast furnace campaign were compared with previous ones. It was proven that the systematic use of all elements of the developed technology makes it possible to achieve high economic indicators while exceeding the standard duration of the campaign by 1.75 times. Experience in technology development made it possible to increase the furnace campaign duration to 17.46 years, achieve a reduction in specific coke consumption by 15.9 %, and increase the specific consumption of natural gas for cast iron smelting by 46.4 %; reduce the specific carbon consumption for cast iron smelting by 6.3 %.

The operational conditions, including temperature and gas composition, vary along the radial position in a blast furnace. Nevertheless, very few studies can be found in the literature that discuss how the reduction behavior of the ferrous burden varies along the radial position. In this study, the effect of the radial charging position on the reducibility of acid iron ore pellets was investigated using a laboratory-scale, high-temperature furnace in CO-CO2-N2 and CO-CO2-H2-H2O-N2 atmospheres up to 1100 °C. The experimental conditions were accumulated based on earlier measurements from a multi-point vertical probing campaign that was performed for a center-working European blast furnace. The main finding of this study is that the pellet reduction proceeded faster under simulated blast furnace conditions resembling those in the center area, compared to the wall area, because of a higher share of CO and H2 in the gas. Therefore, the pellet charging position affects its reduction path in a blast furnace. Additionally, it was shown that the presence of H2 and H2O in the reducing gas enhanced the progress of reduction reactions significantly and enhanced the formation of cracks slightly, both of which are desirable in blast furnace operation. The reducibility data attained in this study are important in understanding how temperature and gas composition is connected to the reduction degree under realistic process conditions.

The briquetting technique holds significant potential to replace traditional iron burden materials due to its lower greenhouse gas emissions. In addition to briquettes’ thermomechanical and metallurgical properties, the blast furnace performance is also considerably affected by the ferrous burden permeability concerning the gas rising through the shaft zone of this reactor. Therefore, this study focused on bed permeability and pressure drop characteristics of iron ore briquettes compared to blast furnaces’ traditional iron ore burdens. Using laboratory experiments and computational fluid dynamics simulations, the research evaluates how different iron burden materials affect gas flow in the blast furnace shaft. The materials tested include sinter, pellets, lump ore, and two types of briquettes (B1 and B2), assessed in both single and mixed beds. The experimental and simulation techniques were in good agreement, and the results indicate that single beds of lump ore, sinter, and briquette B2 exhibit higher permeability, while beds composed exclusively of pellets or B1 briquettes showed lower void fractions, resulting in greater resistance to gas flow and the highest pressure drop. In single beds of B1 briquettes, the pressure drop was approximately 20% higher than that of sinter, while B2 briquettes demonstrated similar permeability and pressure drop to sinter under blast furnace conditions. Mixtures containing pellets also showed increased pressure drops, especially when the pellet mass fraction exceeded 25%, with pressure drops rising by up to 45% compared to sinter beds. Comparisons at varying substitution ratios further indicated that binary beds composed with B1 or B2 performed similarly up to a 50% substitution ratio; however, at a 75% substitution, B2 beds achieved a 10% lower pressure drop than B1 overall, making B2 a potential substitute for sinter to reduce CO 2 emissions. These findings underscore the critical role of material geometry and size distribution in optimising blast furnace efficiency.

Hydrogen metallurgy is a technology that applies hydrogen instead of carbon as a reduction agent to reduce CO2 emission, and the use of hydrogen is beneficial to promoting the sustainable development of the steel industry. Hydrogen metallurgy has numerous applications, such as H2 reduction ironmaking in Japan, ULCORED and hydrogen-based steelmaking in Europe; hydrogen flash ironmaking technology in the US; HYBRIT in the Nordics; Midrex H2™ by Midrex Technologies, Inc. (United States); H2FUTURE by Voestalpine (Austria); and SAL-COS by Salzgitter AG (Germany). Hydrogen-rich blast furnaces (BFs) with COG injection are common in China. Running BFs have been industrially tested by AnSteel, XuSteel, and BenSteel. In a currently under construction pilot plant of a coal gasification-gas-based shaft furnace with an annual output of 10000 t direct reduction iron (DRI), a reducing gas composed of 57vol% H2 and 38vol% CO is prepared via the Ende method. The life cycle of the coal gasification—gas-based shaft furnace—electric furnace short process (30wt% DRI + 70wt% scrap) is assessed with 1 t of molten steel as a functional unit. This plant has a total energy consumption per ton of steel of 263.67 kg standard coal and a CO2 emission per ton of steel of 829.89 kg, which are superior to those of a traditional BF converter process. Considering domestic materials and fuels, hydrogen production and storage, and hydrogen reduction characteristics, we believe that a hydrogen-rich shaft furnace will be suitable in China. Hydrogen production and storage with an economic and large-scale industrialization will promote the further development of a full hydrogen shaft furnace.