Scrap Melting Research Articles

Optimization of Water Leaching of Chlorides from Aluminum Salt Slag

Aluminum recycling generates large amounts of hazardous wastes, known as salt slags, consisting mainly of oxides, metallic aluminum, and salt fluxes. Water leaching is a common technique used for salt removal, being a decisive operation due to water usage and the need to achieve sufficient salt recovery. In this study, water leaching tests under varied operational conditions (water type, slag particle size, solid content, and leaching time) were carried out in salt slag samples obtained from a Brazilian aluminum scrap melting company. Leaching efficiency was assessed by the % chlorine leached. The optimal leaching condition, defined as the one that resulted in the highest chloride removal from the slag together with appropriate operational conditions (larger viable slag size, lower leaching time, etc.), was identified for a slag size below 2.8 mm, 30 wt% of solids in pulp, and a leaching time of 90 min. The results showed that it was possible to recover more than 92% of the salts initially contained in the raw slag, resulting in a leached material with less than 2.5% salts. The recovered salt characteristics showed potential for recycling and could be re-mixed to the salt flux used for aluminum melting. The possibility of achieving higher efficiencies and lower water consumption during leaching was also discussed, as was a preliminary flowsheet for salt slag treatment.

Numerical investigation of scrap melting in high-carbon hot metal

Abstract Scrap melting in the steelmaking process has recently attracted considerable attention. This study developed a mathematical model to investigate the effects of sizes, initial temperatures and carbon contents of scrap, and bath flow on its melting behaviors. The results showed that the volume of the solidified shell on the melting interface could be decreased or eliminated by increasing the initial temperature of the scrap. The initial carbon content also significantly influenced the melting behavior. The completion melting time decreased from 253 to 80 s when the carbon content increased from 0.10% to 0.30%. Importantly, the natural convection or driven flow formed in the bath significantly influenced the melting behaviors. Moreover, the dominating factors changed as the melting proceeded. Therefore this study provides more insights into the melting behavior of the scrap during the steelmaking process at different operating conditions.

Effect of coherent jet burner on scrap melting in electric arc furnace

Modern electric arc furnace (EAF) steelmaking relies on the coherent jet burner to melt scrap at the cold spots inside the furnace, but the relevant computational fluid dynamics (CFD) modeling of this process has not been reported and systematically studied. The present work established an innovative comprehensive CFD model including a scrap melting model and a coherent jet model based on the detailed physical principles, which couples the solid–liquid-gas three-phase system with coherent jet and scrap melting/re-solidification for the investigations of key evaluation factors including burner efficiency, scrap heating rate, and scrap melting cavity. An experiment was designed and implemented specifically in an industrial-scale EAF for validating the proposed model. The model was employed to explore the impacts of burner power, scrap porosity, scrap preheat temperature, and scrap blockage on burner energy utilization. An understanding and guidance of coherent jet burner operations were provided based on the studies for more effective scrap melting.

Simulation of Scrap Melting Process in an AC Electric Arc Furnace: CFD Model Development and Experimental Validation

The electric arc furnace (EAF) is a critical steelmaking facility that melts the scrap by the heat produced from electric arc and burners. Simulation and optimization of EAF scrap melting are of great interest to the steel industry, which helps to improve product quality and production efficiency. However, the relevant computational fluid dynamics (CFD) modeling of this process has not been reported so far. The present study established a three-dimensional (3D) integrated CFD model to simulate the scrap melting process in the alternating current (AC) EAF. The scrap melting model was developed to simulate the dynamic scrap melting and collapse based on the dual-cell approach and the stack approach. The electric arc model and the coherent jet model were introduced and integrated with the scrap melting model to estimate the electrical and chemical energy inputs need for melting. The CFD-compatible Monte Carlo method and electrode regulation strategy were developed respectively to predict the arc radiative heat dissipation and track the instant electrode movement. The experiments for the scrap melting by both electric arc and coherent jet burner were designed and implemented in the industry-scale NLMK 150-ton EAF for the model validation. The proposed model was applied to simulate the scrap melting process under the NLMK EAF typical run, and the scrap melting behavior, the electric arc performance, and the burner performance were evaluated and discussed based on the simulation results.

Numerical simulation on the melting kinetics of steel scrap in iron-carbon bath

Steel scrap melting kinetics is a key factor that affects the scrap ratio and temperature trajectory of Basic Oxygen Furnace steelmaking process and the productivity and energy utilization of Electric Arc Furnace steelmaking process. In this paper, the interface between steel scrap and melt is analyzed and a novel theoretical model of steel scrap melting in iron-carbon bath is established. Moreover, the effects of bath temperature, bath carbon content, preheating temperature and characteristic length of steel scrap on the melting rate of steel scrap, mass transfer coefficient of carbon, heat transfer coefficient and interface carbon concentration were investigated. The results show that the ultimate steady melting rate increases from −2.04 × 10 −4 to −3.32 × 10 −3 m/s with the increases of bath temperature from 1793 K to 1873 K, the ultimate steady heat and mass transfer coefficient first increase and subsequently decrease, are in the range of 1.04 × 10 5 to 2.86 × 10 5 W/m 2 /K and 0 to 2.89 × 10 −4 m/s, respectively. As the bath carbon content increase from 1.0 wt% to 4.0 wt%, the ultimate steady melting rate increases from −8.85 × 10 −5 to −3.23 × 10 −4 m/s, the ultimate steady heat transfer coefficient first increases and subsequently decreases, is in the range of 7.59 × 10 4 to 1.01 × 10 5 W/m 2 /K. Furthermore, the ultimate steady mass transfer coefficient and the ultimate steady interface carbon content gradually decreases from 1.40 × 10 −4 to 5.21 × 10 −5 m/s and from 0.73 to 0.69 wt%, respectively. With the increase of preheating temperature and characteristic length of steel scrap, the ultimate steady melting rate, heat transfer coefficient between steel scrap and melt, mass transfer coefficient and interface carbon concentration remain almost constant, about −8.85 × 10 −5 m/s, 8.40 × 10 4 W/m 2 /K, 1.40 × 10 −4 m/s and 0.70 wt%, respectively.

Green LD (BOF) Steelmaking—Reduced CO2 Emissions via Increased Scrap Rate

The basic oxygen furnace (BOF) is the dominating primary steelmaking process. It is an autothermal process where hot metal and scrap are used as charging materials. The decarbonization and transformation of integrated BOF steelmaking will be the most important challenge in the coming years. Steel scrap is a charge material without new CO2 emissions, whose availability is expected to grow significantly and will play a key role in this decarbonization process. Several solutions have been developed by Primetals Technologies to provide additional energy for processing higher scrap rates in integrated BOF steelmaking. Such solutions include simple upgrade packages installed on existing converters such as process models for heat optimization, post-combustion, and scrap preheating lances. For higher scrap rates from 30% to 50%, a combination blowing converter and JET converter is required to provide sufficient mixing during scrap melting and the highest heat transfer from the increased post-combustion. Hybrid EAF–BOF operation and limitations regarding scrap quality also need to be considered for the transformation of steelmaking. Scrap sorting and processing can be a solution to reduce residual levels in crude steel for high scrap rates. Based on reference plant data, the CO2 reduction potential of the presented solution versus the effort and complexity of implementation is compared.

A wavelet feature-based neural network approach to estimate electrical arc characteristics

Electric Arc Furnaces (EAFs) account for almost half of the North American steel production. Arc furnaces draw high and dynamic electrical power to melt scrap metal loads and as the result, they are highly non-linear and time-varying in nature. Because of the power system problems associated with EAFs, there is an ongoing need to accurately model EAFs to properly assess the impact of these types of nonlinear loads. This paper proposes a wavelet feature-based neural network approach for modeling the dynamic voltage-current (v-i) characteristic of the EAF. This method uses the data from the operational electric arc furnaces to describe the underlying processes, and unlike conventional mathematical techniques does not rely on presumed model structures, or simplified assumptions. The simulation results obtained by using the proposed method are compared with the actual measured data, and it is shown that the proposed method accurately models the EAF dynamic v-i behavior.

Laboratory Assessment of the Technogenic Raw Materials Briquettes Effect on the Arc Furnace Electric Mode

The influence of partially reduced scale briquettes on the arc electrical characteristics in a laboratory single-phase arc furnace is considered. Briquettes were obtained from industrial scale by mixing it with coke production waste and flux-forming additives. Fluxes were selected with aim that their interaction provided the slag homogeneity. During the experiment, the conditions for entering a briquette into an electric arc furnace (EAF) were simulated. That includes imitation of simultaneous melting of briquettes and scrap and the formation of a slag cover (metal was melted, briquette was added, slag was introduced), and imitation adding briquettes to a liquid bath of metal with slag (metal was melted, slag was introduced, briquette was added). A slightly positive effect of the briquettes input on the arc burning conditions was noted, as well as a noticeable effect of slag foaming. It is assumed that a significant content of iron oxides in the briquette will also contribute to the lime accelerated assimilation in the slag, which may somewhat speed up the process of metal refining from phosphorus.

Experimental investigation of heat transfer characteristics of an inverse diffusion flame in a coaxial tube burner for with and without swirl

Heat transfer by flame jet impingement is widely used in many of the industrial and domestic applications like heating metal bars, scrap melting, shaping the glass, metal slab cutting, domestic cooking and others. Aim of the present experimental work is to study an effect of swirl on a local heat flux distribution of an inverse diffusion flame (IDF) jet impinging on a flat target surface in a coaxial tube burner. The twisted tape of twist ratio 3 (corresponding to the swirl number, S = 0.52) is used to create a swirl in the central air jet of the burner. The flame shapes and heat flux distributions are compared for the with and without swirling IDF under the different air jet Reynolds number (Rea) of 1000 to 2500, equivalence ratio (ϕ) of 0.4 to 1.3 and a burner-to-impingement plate distance (H) of 10 to 100mm. The distributions of heat fluxes are studied within a radius of 75 mm from the point of stagnation on an impingement plate. Results show that the swirling IDF helps in clean combustion of the fuel with much shorter flame height. Swirling in the flame jet enhances the peak heat flux for the higher air jet Reynolds number for slightly fuel rich conditions of ϕ = 1.1 at the optimal burner-to-target plate distance of 40 mm.

Experimental Investigation on Carbon Diffusion at the Solid–Liquid Interface During Scrap Melting in the Steelmaking Process

Experimental Investigation on Carbon Diffusion at the Solid–Liquid Interface During Scrap Melting in the Steelmaking Process

Numerical investigation of AC electric arc plasma heat dissipation in EAF

ABSTRACT The alternating current (AC) electric arc furnace (EAF) is a crucial steelmaking facility consuming electricity to melt the recycled scrap. The arc heat dissipation impacts the scrap melting rate. The present study established a mathematical model to simulate the AC electric arc and estimate its heat dissipation under different arc operations. The study was aimed to deduce the relationship between arc operating current, arc length and the share of different arc heat dissipation mechanisms for future application in the scrap melting model. Validations of arc modelling were conducted by comparing the results against experimental data and simulations in the literature. A statistical method based on data sampling was proposed to determine the AC arc state variables to approximate the arc heat dissipation. A scrap melting experiment was designed and implemented in NLMK EAF to validate the amount of share determined in the present study for different arc heat dissipation mechanisms.

Time- and component-resolved energy system model of an electric steel mill

Steel production is a highly energy- and emission-intensive process. Compared to the production via the integrated route, the melting of recycled steel scrap and directly reduced iron in an electric arc furnace operated on green power constitutes a way to reduce energy consumption and CO 2 -emissions. However, there is still potential to reduce energy consumption and CO 2 -emissions in electric arc furnace steel production by introducing new sub-processes, optimal operational design, and integration of renewable energy sources. For complex industrial processes, this potential can only be determined using models of the entire system. The batch operation, changing process parameters, and strongly fluctuating energy consumption require a holistic, temporally, and technologically resolved model. Within the scope of this paper, we describe an energy system model of an electric arc furnace steel mill. It allows assessing the optimal implementation of novel technologies and system integration of renewable energy sources using a reduced set of input parameters. The modular design facilitates the extension of the model, and the option of specifying several input parameters enables the model to be adopted for other electric steel mills.

Evaluation of Mass Transfer Coefficient during Scrap Melting

Mass transfer is a critical scrap melting step. Herein, mass transfer coefficients (k) during scrap melting were calculated using laboratory-scale experiments. Correlation analysis and the entropy weight method were used to determine the effect of variables on k. The evaluation model under natural and forced convection was established. It was consistent with the experimental results. Under forced convection, at 1573 and 1673 K, when the rotation speed was increased from 141 to 423 r/min, k increased from 7.50 × 10−5 to 1.54 × 10−4 m/s and from 8.42 × 10−5 to 1.72 × 10−4 m/s, respectively. Furthermore, as the bath temperature was increased from 1573 to 1723 K, the k value of a stationary specimen increased from 3.14 × 10−5 to 5.31 × 10−5 m/s, respectively. Correlation analysis and the entropy weight method indicated that the effects of variables on k decreased as follows: molten pool stirring rate > bath temperature > scrap type. Moreover, the explicit functional relationships between k and the factors affecting k under natural and forced convection conditions were established, and the results were consistent with the experimental data. Our results can be used to determine the quantitative relationships between k and the factors affecting k.

MODELING THE MELTING OF SCRAP METAL OF DIFFERENT DENSITY IN A BOF SMELTING

The results of mathematical modeling process of melting scrap metal in the bath of an oxygen converter are presented. The influence relative amount of scrap metal in the charge of oxygen-converter smelting and its density on dynamics bath temperature during melting, slag oxidation and liquid metal yield was studied. It is shown that due to change in the shape of scrap metal during its melting, the classical approach to determining the reactive surface area of ​​the latter needs to be clarified.Mathematical descriptions of scrap metal melting in converter smelting by linear dependence and using fourth degree polynomials, which take into account the influence of initial and current carbon concentration in the bath, are offered. The influence of density and fraction of scrap metal, which is a part of metal charge, on duration of its melting in bath of oxygen converter, content iron oxides in slag, temperature mode process and yield liquid metal is investigated. It is shown that increasing mass of scrap metal in the metal charge to 40%, in the absence of its preheating, significantly changes the appearance both the oxidation curves of carbon and the dynamics of the bath temperature in the initial period melting.The latter may be due to the preservation active surface area of ​​scrap metal as its mass changes. Additional heat consumption for melting an increased amount preheated («cold») scrap metal leads to a decrease in the temperature of the liquid bath, which confirms the feasibility using the technology melting with preheating an increased amount of scrap.It is shown that from the point of view ensuring the rational course of converter smelting it is expedient to use equal shares heavy and lightweight scrap metal, regardless of the share latter in the metal charge. In the case using, under the considered conditions, «cold» scrap metal, the maximization yield of liquid metal is provided at the amount scrap up to 22% of the total mass metal charge.

Lance Design for Scrap Melting Aggregates

Metallurgical aggregates, which are used for metal waste melting, are equipped with lances for blowing gaseous media. These gaseous media allow especially scrap melting and intense homogenization of the resulting melt. In connection with this, the blowing systems are developed both for blowing of gaseous media itself on the bath surface or into the melt and for blowing of the gas mixture with powdered substances. When designing the blowing systems and the individual lance tips and nozzles, it is necessary to respect certain criteria, the derivation of which is based on long-term experience and acquired knowledge in this field. The submitted paper summarizes the design recommendations, including the determination of the selected design characteristics of the nozzles for blowing gaseous media on the bath surface in the metallurgical aggregate. These design characteristics help designers and engineers to design systems that meet the high demands on quality, efficiency and operational reliability.

Simulation on scrap melting behavior and carbon diffusion under natural convection

A 3D model applying temperature- and carbon concentration- dependent material properties was developed to describe the scrap melting behavior and carbon diffusion under natural convection. Simulated results agreed reasonably well with experimental ones. Scrap melting was subdivided into four stages: formation of a solidified layer, rapid melting of the solidified layer, carburization, and carburization + normal melting. The carburization stage could not be ignored at low temperature because the carburization time for the sample investigated was 214 s at 1573 K compared to 12 s at 1723 K. The thickness of the boundary layer with significant concentration difference at 1573 K increased from 130 µm at 5 s to 140 µm at 60 s. The maximum velocity caused by natural convection decreased from 0.029 m·s−1 at 5 s to 0.009 m·s−1 at 634 s because the differences in temperature and density between the molten metal and scrap decreased with time.

Process Improvements for Direct Reduced Iron Melting in the Electric Arc Furnace with Emphasis on Slag Operation

Steelmaking based on direct reduced iron (DRI, and its compacted derivative hot briquetted iron, HBI) is an anticipated important global alternative to current steel production based on FeOx reduction in blast furnaces due to its lower specific CO2 emission. The majority of DRI is melted and refined in the electric arc furnace with different process conditions compared to the melting of steel scrap due to its raw material composition being rather different. We provide data and analysis of slag composition of DRI charges vs. steel scrap charges for 16 industrial electric arc furnaces (EAFs). Suggestions for optimized slag operation and resulting process improvements of DRI melting in the EAF are given. A dynamic mass and energy model of the DRI melting in the EAF is introduced to illustrate the implications of the adapted slag operation on the EAF process with DRI charges.

Evaluation and Modeling of Scrap Utilization in the Steelmaking Process

The study of scrap melting provides data for increasing the scrap utilization rate. Here, an evaluation model is established to analyze the effect of each factor on scrap melting using statistical methods for the first time. Subsequently, the quantitative relationship between the influencing factors and melting parameters is obtained. Back propagation (BP) neural networks and multiple regression are used for predictions. For scrap melting controlled by carbon mass transfer when the bath temperature range is 1573–1723 K, the relative contribution of each parameter was mixing power > bath temperature > specific surface area > carbon content. The predicted values of the BP neural network are more accurate than those of multiple regression. The relative errors of average melting rate, average mass melting speed, and mass transfer coefficient of training sets are 14.02%, 13.95%, and 7.19%, respectively, which decrease by 22.71%, 47.22%, and 69.46%, respectively, compared with those of the regression equations after outliers are removed.

Cold Model Study on Melting of Ice Made by KCl Solution in Gas-Water Two-Phase Plume Area

With the increasing of scrap usage in steelmaking processes, the melting of scrap becomes a very important phenomenon that limits the productivity and tap-to-tap time. Ice-water systems have been widely used to study the melting of scrap and alloys. In this study, the melting rate of saturated KCl solution ice spheres in gas-water two-phase plume zone are studied as a function of height of location, gas flowrate, and melt temperature. The results show that the shape of the ice sphere gradually changes firstly from spherical to elliptical, and finally becomes an irregular state. 1) The decreasing of the distance between the ice sphere and the bottom plugs, 2) the increasing of the gas flowrate, 3) the slightly increasing of bath temperature will all benefits the melting rate of ice spheres.

Environmental impacts of brass melting: an Indian case study

Brass metal handicrafts are the traditional cultural heritage of Indian society. Its artisans are still using age-old technologies and coal for the melting of brass scrap. The present case study compares the environmental aspects associated with 1.0 t brass scrap melting using coal and light fuel oil. The effects of coal and light fuel oil on different climate impact categories are analyzed for production as well as for the use phase. In the production phase, the coal has a lower global warming potential (7.05 kg CO2-Equiv.), acidification potential (0.04 kg SO2-Equiv.), abiotic depletion potential-elements (2.87 E-7 kg Sb-Equiv.), and human toxicity potential (0.613 kg DCB-Equiv.) compared to light fuel oil. However, during the use phase, i.e., thermal energy production for melting (1.0 t brass scrap), the light fuel oil has a lower global warming potential (76.15 kg CO2-Equiv.), acidification potential (0.24 kg SO2-Equiv), eutrophication potential (0.045 kg phosphate-Equiv.), and minimum human toxicity potential (1.82 kg DCB-Equiv.). It appears evident that the overall phases need to be considered in order to make a well-balanced decision for sustainable development.