Hot Metal Pretreatment Research Articles

Complete Hot-recycling Technique of Dephosphorization Slag for Hot Metal Pretreatment with Convertor

Complete Hot-recycling Technique of Dephosphorization Slag for Hot Metal Pretreatment with Convertor

A novel soft sensing modelling approach for sulphur content estimation in hot metal pretreatment process

In the hot metal pretreatment desulphurisation process, the sulphur content needs to be controlled precisely. A novel soft sensing modelling method is proposed to address the problem that sulphur content cannot be directly measured online. Firstly, the main desulphurisation behaviour is represented with the proposed simplified mechanism model for boosting computational efficiency. Moreover, the complex influence of the changing operation condition on the parameters of the simplified mechanism model is described with neural networks to compose a hybrid structured hz. Then, for training this hybrid model, a conjoint learning scheme is designed to ensure stability and reliablity. The experimental results show that the proposed hybrid model obtains higher prediction accuracy and better robustness compared with the pure mechanism modelling technique and the existing benchmark data-driven modelling methods. In addition, the proposed method is able to provide real-time prediction ability, which is substantial to the optimisation control of the hot metal pretreatment process.

Development of Solid Waste-Based Composite Calcium Ferrite Flux and Its Application in Hot Metal Pre-Dephosphorization.

To enhance the slagging efficiency of the lime-based slag system during the pre-treatment stage of hot metal, a composite calcium ferrite flux based on aluminum industry solid waste was developed in this study. The melting characteristics of the flux and its application in the pre-treatment of hot metal were investigated. The results indicated that the main phases of the composite calcium ferrite were CaFe2O4, Ca2Fe2O5, and Ca2(Fe,Al)2O4. It exhibited high oxidation, high alkalinity, and a low melting point, thereby achieving excellent melting performance. Simulations of various dephosphorization fluxes in the pre-treatment of high-phosphorus hot metal, ordinary hot metal, and kilogram-scale dephosphorization experiment processes were conducted. Under the same experimental conditions, the composite calcium ferrite flux was able to achieve a dephosphorization rate of over 90% and a final phosphorus content of less than 0.02 wt% under high carbon content ([%C] = 3.2 wt%). In the application of hot metal pre-dephosphorization, this flux was able to achieve efficient melting and rapid slagging of lime at a lower temperature, and its slagging time was 50% faster than that of calcium ferrite flux. In addition, this flux enhanced the utilization efficiency of lime during the steelmaking process, effectively prevented the agglomeration of slag, and achieved efficient slag-metal separation. These characteristics were significantly better than the application effect of calcium ferrite flux. This flux has significant implications for the industrial application of deep dephosphorization in the pre-treatment stage of hot metal or the early stage of converter steelmaking.

A study on the preparation and characterization of pigment quality from mill scale steel wastes.

Every day, significant quantities of solid wastes are generated in steel companies which causes environment pollution. These waste materials differ from one steel plant to other depending upon the steelmaking processes adopted and pollution control equipment installed. The most common type of solid wastes originated in steel plant are hot metal pretreatment slag, dust, GCP sludge, mill scale, scrap, etc. At present, various efforts and experiments are being carried out in order to make use of 100% solid wastes products in order to reducing cost of disposal, saving raw materials and conserving energy. Then, the purpose of our paper is the access to reuse potential of the steel abundant mill scale for sustainable industrial applications. This material is a very valuable industrial waste due to its richness in iron (about 72% Fe), chemical stability, and variable usage in multiple fields which implies that it can bring social and environmental benefits. This work aims to recover Mill scale and reuse it to synthesize three iron oxide pigments; hematite (α-Fe2O3, red color), magnetite (Fe3O4, black color), and maghemite (γ-Fe2O3, brown color). To achieve this objective, Mill scale needs to be refined and granted to react with sulfuric acid to obtain ferrous sulfate FeSO4.xH2O which is used to produce hematite by calcination between 600 and 900°C, then, magnetite by reduction of hematite using a reducing agent at 400°C and maghemite from a thermal treatment of magnetite at 200°C. It was shown within the experiments that the mill scale contains between 75% and 86.66% of Fe and a uniform distribution of particles size with a low span. That gave red particles size (0.18-0.193µm) and specific surface area SSA: 6.12m2/g, black particles sizes (0.2-0.3µm) and SSA 4.92m2/g, brown particles size (0.18-0.189µm) and SSA 6.32m2/g. The results revealed that the mill scale was successfully converted into pigments with good qualities. So, it is recommended to work from the beginning at synthesis hematite by copperas red process and then magnetite and maghemite in order to control shape of magnetite and maghemite (spheroidal) to get the best results economically and environmentally.

Kinetic Simulation of Hot Metal Pretreatment: Desulfurization Using Powder Injection

Kinetic Simulation of Hot Metal Pretreatment: Desulfurization Using Powder Injection

Self-digestion of Cr-Bearing Vanadium Slag Processing Residue via Hot Metal Pre-treatment in Steelmaking Process

Self-digestion of Cr-Bearing Vanadium Slag Processing Residue via Hot Metal Pre-treatment in Steelmaking Process

Effects of Impeller Rotational Speed and Immersion Depth on Flow Pattern, Mixing and Interface Characteristics for Kanbara Reactors Using VOF-SMM Simulations

The Kanbara Reactor (KR) is a primary desulfurization technology in the hot metal pretreatment refining process that is widely employed in the modern steelmaking industry. The operating parameters of KR impeller immersion depth (IID) and rotation speed (IRS) have a crucial impact on the process performance and the desulfurization effect. Still, their influences have not been fully understood. This study systematically investigated the effects of IID and IRS on the flow pattern, mixing behavior, vortex core depth, and free surface characteristics for KR processes based on a 3D Volume of Fluid (VOF) model coupled with the sliding mesh method (SMM). The model was validated via scale-down water model experiments and then applied to the KR process, and simulations found that IID and IRS have different impacts on the flow pattern. Specifically, the discharge flow location moves downward with IID increasing, but the discharge strength and mean velocity hardly changes. Comparatively, the rise of IRS significantly increases the mean velocity, but few changes occur to the discharge flow position. Increasing IRS improves bath hydrodynamics, strengthens recirculation, and efficiently shortens mixing time, but IID has a neglectable effect on these features. The minimum mixing time is 55 s at a maximum IRS of 260 rpm. Moreover, the vortex core depth and free surface velocity visibly increase with the increase of IRS. Comparatively, IID has a limited effect on the flow and mixing behavior but directly impacts the distribution of recirculation regions at the axial direction and the velocity gradient on the free surface at the radial direction. Furthermore, the correlation equations of these critical parameters as a function of the operating parameters were obtained. The results from this study may provide references for operating optimizations and industrial practices of KRs.

Development and Prospects of Refining Techniques in Steelmaking Process

The development of refining techniques in the steelmaking process over the last 60 years and the prospects for the future were reviewed. In Japan, hot metal pretreatment started in the 1960s with the aim of reducing refining costs and improving quality, and its purposes have now transitioned to meeting new requirements for reduced treatment time, reuse of steelmaking slag and use of diverse iron sources. In converter refining, in addition to high speed decarburization, visualization of phenomena and sensing modeling techniques are becoming more important for combined use with data science techniques. In ladle metallurgy (secondary refining), techniques to realize high speed treatment and heating of the molten steel are key issues. The necessity of process revolution to contribute to a sustainable social environment is also discussed briefly.

A new method of red mud recycling in the process of hot metal pretreatment

To realize a large-scale consumption of red mud in the steelmaking industry, a new recycling method was investigated through the pre-reduction roasting experiment and the slag-metal interaction experiment simulating the hot metal pretreatment process in the steelmaking industry. In virtue of the sensible heating of the hot metal and the reducibility of [C] and [Si], the iron could be separated and recovered from the pre-reduced red mud pellets into the hot metal directly with a recovery rate exceeding 75%. With the composition adjustment of the residual oxides in the pre-reduced red mud (PRRD) using CaO and Al2O3 or aluminium dross (AD), a slag having a low melting point (below 1300 °C) and a high sulfide capacity (lgCS = −2.3) was formed, and more than 94% of [S] in the hot metal could be removed into this slag through the slag-metal interaction. The desulfurization efficiency of the flux (PRRD-CaO–Al2O3; PRRD-CaO–AD) is approximate to the traditional desulfurizing flux (CaO–CaF2). The advantages of this method are summarized as the low energy cost and the slag valorization.

Effect of alumina bubble modification on properties of mullite castables

Mullite castables are widely used in the hot metal pretreatment processing equipment. In this work, the effects of modification of alumina bubbles with silica sol on the properties of mullite castables were studied. After the alumina bubbles were modified by silica sol, the bulk density of the samples was slightly increased, and the apparent porosity was decreased. The cold modulus of rupture values of experimental castables increased remarkably after drying at 110 °C and heating at 1400 °C for 3 h. The thermal expansion of the samples was obviously increased, while the thermal conductivity of the samples was decreased significantly. More columnar mullite crystals were formed at the alumina bubble/matrix interface after the alumina bubble modification and form a continuous inter-locking network structure, which was helpful to improve castables’ thermal shock resistance.

Effect of direct charging of hot recycled slag on hot metal pretreatment dephosphorization in a dephosphorization furnace

Industrial experiments were carried out to investigate the effect of the direct charging of hot recycled slag (DCHRS) on hot metal pretreatment dephosphorization in a dephosphorization furnace. The bulk compositions of semi-steel and slag show that a better dephosphorization effect could be achieved by applying the DCHRS process in the dephosphorization furnace. Compared with the bulk compositions in normal heats, the mean contents of phosphorus in the semi-steel and total Fe in the final slag were decreased by 0.006 and 1.93 wt.%, respectively, with an increase of approximately 6 °C in the semi-steel temperature. According to mineralogical observations, the dephosphorization slags in normal heats and test heats were similar in petrographic constituents, but the metal loss was markedly decreased in the DCHRS process. Thermodynamic calculations show that even though the dephosphorization slag in the DCHRS process had the same dephosphorization capacity as that in the normal refining process, the phosphorus distribution between slag and hot metal in the new process was slightly higher and closer to the reaction equilibrium. Meanwhile, proper operating conditions, including slag basicity, total Fe content in the final slag, bath temperature, slag formation and slag volume, were optimized to improve the dephosphorization efficiency under the condition of the DCHRS process. The consumption of lime, light-burnt dolomite and oxygen during blowing was significantly decreased by the DCHRS process.

Desiliconisation and Dephosphorisation Behaviours of Various Oxygen Sources in Hot Metal Pre-Treatment

In order to obtain a better understanding of the efficiencies of desiliconisation and dephosphorisation reactions during hot metal pretreatment in an open ladle, a number of simulation experiments were carried out with various oxygen sources. Three types of solid oxygen materials (sintered return ore, scale briquette and fine mill scale) were carefully investigated as hot metal pre-treatment agents, evaluating their desiliconisation and dephosphorisation efficiencies. The method applied for supplying gaseous oxygen was also assessed. The comparison between top blowing and injection methods indicated that injected oxygen gas is more advantageous for desiliconisation, while top-blown oxygen gas is favourable for dephosphorisation. The obtained information on the characteristics of gaseous oxygen can be used for the optimisation of blowing patterns, in order to improve the efficiency of the hot metal pre-treatment.

The impact of alumina bubble particle size on the microstructure and physical properties of mullite castables

Mullite castables are widely used in hot metal pretreatment processing equipment. In this work, the effects of alumina bubble particle size on the microstructure and physical properties of mullite castables were studied. Grey relational analysis is a useful method for analyzing patterns in multivariate cases. In this paper, the grey relational analysis was used to estimate the relationship between the properties of samples and the structure of alumina bubbles. Using grey analysis, the specific surface area of alumina bubbles was determined to have the greatest influence on the properties of apparent porosity, cold mechanical properties and thermal shock resistance. The hollow radius of alumina bubbles has the greatest relationship to bulk density, hot modulus of rupture, flow values and coefficient of thermal expansion of samples. Finally, the mullite castables with a high modulus of rupture and thermal shock resistance was obtained by adding alumina bubbles with a particle size between 0.5 and 1 mm. The high modulus of rupture was shown to be caused by the alumina bubble spherical shape, hollow structure and the appropriate bonding at the alumina bubble/matrix interface.

Evaluating the hot metal dephosphorization efficiency of different synthetic slags using phosphorus partition ratio, phosphate capacity and computational thermodynamics

Abstract Phosphate capability (CP) and phosphorus partition ratio (LP) are usually used to evaluate the thermodynamic efficiency of dephosphorization slags with different compositions in hot metal pretreatment. However, these parameters are only useful in equilibrium conditions, and they are not accurate when they are used to evaluate slag efficiency in industrial processes. The current study evaluated the hot metal dephosphorization efficiency of different synthetic slags in experimental tests at 1400oC. This evaluation was made by using CP and LP, and by the computational thermodynamic software FactSage 6.4. This software allows to calculate the amount of liquid and solid present in the slag, which directly affects kinetic reactions. Therefore, even the computational thermodynamic software calculations are from considering the equilibrium, which in these cases can be used to explain the kinetic behavior of the processes. The obtained results allow concluding that CP and LP are valid, but only when they are used for equilibrium calculations; and that they should not be used to measure slag efficiency in industrial processes. A parameter named Dephosphorization Factor (FDeP) was developed based on data determined by computational thermodynamics. It was developed to be related to the dephosphorization efficiency. The results obtained in the current study allow to conclude that the initial synthetic slags, which presented higher CaO activity value, higher liquid quantity and FeO activity, will be the most efficient ones. And allow to conclude too, that the higher the factor, the greater the slag dephosphorization efficiency.

Replacement of fluorspar in the desulfurization of hot metal

Abstract In the steel industry, lime is used as a desulfurizing agent and fluorspar as flux in the hot metal desulfurization process. However there are environmental concerns regarding the use of fluorspar, even when its harmful effects are not fully known. In order to reduce such risks and also to anticipate possible future restrictions, which could undermine the sustainability of steel production, it is proposed to replace the fluorspar for alternative materials in the composition of the desulfurizing lime based mixture. For this purpose new mixtures using aluminum dross, ilmenite, sodalite and ulexite were tested, comparing them with a reference mixture containing fluorspar. The impact of these mixtures on the refractories commonly used in hot metal pretreatment was also checked, since this is an important cost parameter for the steel industries. The laboratory tests showed ulexite as a feasible substitute since the lime (84.03%) - ulexite (10.97%) - graphite (5%) mixture presented the highest desulfurization ratio and low refractory wear (less than the standard fluorspar mixture). The sodalite mixture was the worst by comparison. The ilmenite and aluminum dross mixtures showed similar behavior when compared to the fluorspar mixture.

Investigation of the kinetic mechanism of the demanganization reaction between carbon-saturated liquid iron and CaF2–CaO–SiO2-based slags

The demanganization reaction kinetics of carbon-saturated liquid iron with an eight-component slag consisting of CaO–SiO2–MgO–FeO–MnO–Al2O3–TiO2–CaF2 was investigated at 1553, 1623, and 1673 K in this study. The rate-controlling step (RCS) for the demanganization reaction with regard to the hot metal pretreatment conditions was studied via kinetics analysis based on the fundamental equation of heterogeneous reaction kinetics. From the temperature dependence of the mass transfer coefficient of a transition-metal oxide (MnO), the apparent activation energy of the demanganization reaction was estimated to be 189.46 kJ·mol–1 in the current study, which indicated that the mass transfer of MnO in the molten slag controlled the overall rate of the demanganization reaction. The calculated apparent activation energy was slightly lower than the values reported in the literature for mass transfer in a slag phase. This difference was attributed to an increase in the “specific reaction interface” (SRI) value, either as a result of turbulence at the reaction interface or a decrease of the absolute amount of slag phase during sampling, and to the addition of calcium fluoride to the slag.

Iron Supply Capacity of Porous Concrete Using Steelmaking Slag Aggregate for Seaweed Beds or Fish Reef Blocks

The desertification of coastal regions is a worldwide problem. It is believed that one of the potential influences is a reduction in the concentration of dissolved iron in seawater. On the other hand, there is a high demand for the use of steelmaking slag generated from iron works. Steelmaking slag concrete, hereafter referred to as SSC, is made from the byproducts of steelmaking, such as steelmaking and ground granulated blast-furnace slags. It has been shown that although SSC releases iron, the dissolved iron is oxidized and precipitates promptly. In the present research, porous-type SSC (POSSC) using hot-metal pretreatment slag (HPS) as an aggregate was manufactured, with the purpose of increasing the amount of iron released from HPS. In addition, the influence of incorporating humus into the paste on the concentration of dissolved iron in artificial seawater and the compressive strength of POSSC was investigated. Two commercially available leaf mulches were used as the humus. The effects of the void ratio and the water-to-binder ratio of the paste were also examined. As a result, it was confirmed that the larger the measured void ratio of the POSSC, the higher the concentration of total iron released by the POSSC. It was also demonstrated that, although a humus fraction of 2% of the volume of the HPS caused an approximately 2 N/mm2 reduction in the compressive strength, the humus clearly stabilized the long-term presence of dissolved iron in the artificial seawater.

Effects of alumina bubble addition on the properties of mullite castables

Injecting lance is a key equipment for hot metal pretreatment. In this work, the lance castables with high mechanical properties and thermal shock resistance were obtained by adding alumina bubbles, due to its spherical shape and hollow structure. It is found that the addition of alumina bubble improves the flow values of castables. The bulk density values of samples with the addition of 4 wt% alumina bubbles (AB4) were the best of all the experimental castables. Alumina bubble addition is effective in heightening the thermal expansion, thermal conductivity of mullite castables and can resist the sharp decrease in thermal expansion above 1300 °C. The addition of alumina bubble can improve the mechanical strength of mullite castables. After heating at 1400 °C, a strong chemical bond forms between the bubbles and the binding phases. Due to the appropriate bonding at the alumina bubble/matrix interface, AB4 castable exhibits a relatively better thermal shock resistance.

Sulphur removal in ironmaking and oxygen steelmaking

Sulphur removal in the ironmaking and oxygen steelmaking process is reviewed. A sulphur balance is made for the steelmaking process of Tata Steel IJmuiden, the Netherlands. There are four stages where sulphur can be removed: in the blast furnace (BF), during hot metal (HM) pretreatment, in the converter and during the secondary metallurgy (SM) treatment. For sulphur removal a low oxygen activity and a basic slag are required. In the BF typically 90% of the sulphur is removed; still, the HM contains about 0.03% of sulphur. Different HM desulphurisation processes are used worldwide. With co-injection or the Kanbara reactor, sulphur concentrations below 0.001% are reached. Basic slag helps desulphurisation in the converter. However, sulphur increase is not uncommon in the converter due to high oxygen activity and sulphur input via scrap and additions. For low sulphur concentrations SM desulphurisation, with a decreased oxygen activity and a basic slag, is always required.

赤泥基铁水预处理脱硅脱磷剂的设计与开发

本文对拜耳法赤泥进行改质后制备出一种铁水预处理脱硅脱磷剂，在其熔化性能测定的基础上，进行了铁水预处理脱硅脱磷高温模拟实验研究。研究结果表明：在赤泥中适量加入CaO进行改质，可显著降低赤泥的熔点，提高其熔化速度。利用赤泥与CaO质量比为100:30的赤泥基脱硅脱磷剂进行铁水预处理，铁水脱硅率达到98.2%，脱磷率达到75.5%，脱硅脱磷效果显著。 A novel desilication and dephosphorization agent for hot metal pretreatment was designed and developed by the chemical modification of Bayer red mud. According to the determination results of melting properties for the red mud-based desilication and dephosphorization agent, the simulation experiment of the hot metal pretreatment was carried out at high temperature, and the results were shown as follows. The melting properties of the red mud-based desilication and dephosphorization agent could be improved remarkably by a proper addition of CaO. The red mud-based desilication and dephosphorization agent with the mass ratio of 100:30 for red mud and CaO was used in the simulation experiment process of the hot metal pretreatment. The desilication ratio and the dephosphorization ratio in the hot metal reached 98.2% and 75.5%, respectively.