Molten Blast Furnace Slag Research Articles

Development and evaluation of a mathematical model of dry granulation of molten blast-furnace slag

Development and evaluation of a mathematical model of dry granulation of molten blast-furnace slag

Recycling of iron and steel slag for carbon reduction and low‐environment load application

AbstractThe high‐value utilization of blast furnace slag (BFS) and steel slag (SS) as a valuable resource in the field of carbon reduction represents a green revolution, and also is an indispensable path toward breaking through resource and environmental constraints and achieving high‐quality, sustainable development through solid waste utilization in the steel industry. Achieving resource recycling while harnessing the untapped latent energy of resources and exploring their carbon sequestration capabilities has become a crucial avenue for further valorization through waste utilization. BFS and SS discharged from iron‐making or steel‐making furnaces carry a significant amount of latent heat, especially the calcium oxide component in SS, which gives it a unique advantage in the field of comprehensive BFS and SS utilization and carbonation‐based SS utilization. This article discusses the current research status of low‐carbon‐waste‐heat utilization in the production of microcrystalline glass, cementitious materials, functional adsorbents, and other products through front‐end modification of molten BFS and SS. This report also provides an overview of carbon capture by utilizing BFS and SS, offering insights into the research directions for subsequent heat recovery, online quality adjustment, high‐value utilization, and carbon sequestration using BFS and SS in the steel industry.

Distributed activation energy model of pyrolysis kinetics of starch and lignin with blast furnace slag as heat carriers

Molten blast furnace slag (BFS) can be used as heat carrier for biomass pyrolysis, which has high industrial value. Lignin (LG) and starch (ST) were chosen as model compounds of lignocellulosic biomass, which were mixed with different proportions of BFS, respectively. Thermogravimetry-process mass spectrometry studied the characteristics of LG-BFS and ST-BFS pyrolysis. The activation energies were obtained by Kissinger-Akahira-Sunose (KAS) method and four kinds of Distributed Activation Energy Model (DAEM) methods. The results showed BFS has little effect on the temperature of LG and ST pyrolysis. The average activation energy of LG-BFS-30% and ST-BFS-50% calculated by KAS method was 167.74 and 155.57 kJ∙mol−1 respectively, which meant the addition of 30% and 50% BFS promoted the pyrolysis of LG and ST, respectively. The activation energy distribution (AED) obtained by the four kinds of DAEM methods could reflect the actual pyrolysis process more completely. The results showed that the Double Gaussian distribution (GAUSS-2)and the distribution-free method (DAEM-NM) were more closer to the pyrolysis process of LG-BFS and ST-BFS. Compared with the pure LG, the CO2 content in pyrolysis gas decreased by 9.61%, and the CO content increased by 22.14% in the LG-BFS-30% pyrolysis. Compared with ST-BFS and LG-BFS, LG-BFS-30% was more conducive to the generation of CO.

High‐Temperature Thermophysical Property Characterization of Molten Blast Furnace Slag: A Critical Reviews

Centrifugal granulation‐assisted thermal energy recovery (CGATER) remains the leading technology for the iron and steel industry to enable the low‐carbon treatment of high‐temperature blast furnace (BF) slag. Accurate knowledge of the thermophysical properties of BF slag is pivotal for the commercialization of the CGATER. However, it presents a formidable task to obtain these quantities due to the extremely high temperature of molten BF slag (≈1500 °C). To date, the thermophysical properties of BF slag have not been well characterized yet. Herein, five typical thermophysical properties including density, viscosity, surface tension, thermal conductivity, and emissivity are scrutinized with emphasis on the experimental measurements and empirical estimates. The working principles of these measurement methods are briefly overviewed and their merits and demerits are highlighted. It is noted that density, viscosity, and surface tension have been intensively studied; the quantities can be estimated with moderate uncertainty. However, the thermal conductivity and emissivity of BF slag are less tackled, mainly because of the scarcity of measurement tools at high temperatures. In the future, innovative measurement tools tailored for high‐temperature materials are essential, not only for enriching the thermophysical property database of BF slag but also for paving the way toward characterizing other complex high‐temperature melts.

ANN-Based Model to Predict the Viscosity of Molten Blast Furnace Slag at High Temperatures of > 1600 K

ANN-Based Model to Predict the Viscosity of Molten Blast Furnace Slag at High Temperatures of > 1600 K

Influence of B2O3 on the thermophysical properties of molten blast furnace slag

The thermophysical characteristics of blast furnace molten slags have crucial implications for their smelting process and the subsequent utilization of resources. To efficiently recover molten slag waste heat resources, the thermodynamic properties and viscous flow characteristics of molten blast furnace slag systems with various B2O3 contents were investigated. The stability of the slag at high temperatures was evaluated by calculating its heat capacity and critical heat release. The structural evolution of the melt under varying B2O3 contents was comprehensively studied using Raman spectroscopy and Nuclear Magnetic Resonance. From the perspective of viscous flow characteristics, the impact of B2O3 resulted in a reduction in viscosity of the slag, while the electrical conductivity of the slag increased. Concerning the thermodynamic properties, the break temperature decreased from 1377 °C to 1280 °C with an increase in B2O3 content in the range of 0 to 6 wt.%, while heat capacity and critical heat release of the slag both increased. The introduction of B2O3 facilitated smoother the blast furnace smelting conditions while enhancing the superiority of the granulated product and the efficiency of heat recovery. Adding B2O3 to the molten slag disrupted part of chain structure (Si-O-Si) to create a more flowable cyclic borosilicate structure (Si-O-B).

CFD Numerical Simulation on the Mode of Ligament Disintegration during Centrifugal Granulation of Molten Slag by Using a Spinning Cup

In order to study the behavior of molten blast furnace slag ligament breakup into droplets by centrifugal granulation with a spinning cup, three-dimensional transient CFD model simulations were performed in the present work to study the process of the slag deformation into ligaments upon leaving the spinning cup, which eventually disintegrate into droplets. The formation of molten slag ligaments at the edge of the spinning cup and their disintegration into droplets were numerically revealed so that the behavior and mechanism of the slag ligament breakup into droplets could be investigated. This work specifically examined the influence of cup spinning speed on the diameter and length of the molten slag ligaments around the cup periphery and the diameter of the droplets produced. The simulation results show that, for the same slag flowrate, with the increase in cup spinning speed, the slag film thickness at the cup edge decreases, the number of molten slag ligaments increases, and the diameter of the ligaments decreases, thus reducing the diameter of slag droplets. Moreover, as the number of molten slag ligaments increases as a result of the increased cup spinning speed, the flowrate of a single ligament decreases, so that the ligament disintegrates in a shorter radial distance, that is, the length of the ligament is shortened. In addition, this work also investigated the behavior and mechanism of a single molten slag ligament breakup into droplets. It was found that the process of molten slag ligament breakup into droplets under the action of centrifugal force and surface tension can also be approximately explained by the theory of the Rayleigh disintegration mechanism.

CFD Modeling and Cold Physical Model Simulation on Single Molten Slag Ligament Disintegration into Droplets

Aiming at the mode of liquid ligament disintegration into droplets in the process of the centrifugal granulation of molten blast furnace slag using a spinning cup, in order to gain an in-depth understanding of the behavior and mechanism of droplet formation by liquid ligament disintegration and to obtain appropriate conditions to control the size of the produced slag granules, a three-dimensional CFD model describing water–air two-phase flow with a free surface was established in this work for simulating the process of a single water ligament breakup into droplets under the action of gravity, surface tension and inertial forces, so as to compare with the process of a molten slag ligament disintegration into droplets due to centrifugal force exerted by the spinning cup. By studying the disintegration behavior and mechanism of a single water ligament, the similar phenomenon of a molten slag ligament disintegration is examined. The numerical simulation results on the breakup of a single water ligament show that the length of the ligament before its disintegration and the diameter of the droplets formed both increase with the increase of the velocity of the ligament initially exiting a capillary nozzle. In addition, an experimental set-up was established in the laboratory to conduct cold physical model simulation experiments on single water or liquid paraffin ligament disintegration. The experimental results are compared with the numerical simulation results so that the reliability of the CFD model is verified. The results of the present study show that, in the centrifugal granulation process of blast furnace slag using a spinning cup operated in the ligament disintegration mode, the breakup of a single molten slag ligament is very similar to that of a single water or liquid paraffin ligament, and both approximately follow the Rayleigh Disintegration Mechanism, which provides a theoretical basis for analyzing the breakup process of the ligaments of different liquids as references for guiding the operation of centrifugal granulation of molten slag.

Exploiting the Molten Slag to Decarbonize Iron and Steel Industry: Feasibility Analysis of Centrifugal Granulation‐Assisted Thermal Energy Recovery System beyond Pilot Scale

Waste heat recovery from molten blast furnace slag at ≈1500 °C represents new opportunities for slag valorization. This is now gaining the spotlight but still remains a grand challenge in the iron and steel industry (ISI). To address this issue, centrifugal granulation‐assisted thermal energy recovery (CGATER) is proposed and is regarded as the leading slag treatment technology. The CGATER provides a viable alternative to exploiting the waste heat in molten slag. Yet, large‐scale implementation of CGATER is little explored beyond laboratory‐scale tests. The fate of CGATER toward future commercialization is rarely considered and analyzed, either qualitatively or quantitatively. This work intends to provide, for the first time, a paradigm of a commercial‐scale CGATER prototype, which allows for slag treatment with a rated throughput of 36 t‐slag h−1. The feasibility of commercial‐scale CGATER with a comprehensive scrutinization of its energy, resource, and environment flows is analyzed. The CGATER prototype demonstrates attractive attributes of 1) being nearly water free and 2) suppressing sulfur‐related emissions, although with higher energy consumption than the water quenching method. This work provides not only an inclusive figure of CGATER design but also sheds light on the feasibility of CGATER commercialization to decarbonize ISI.

Centrifugal-Granulation-Assisted thermal energy recovery towards low-carbon blast furnace slag treatment: State of the art and future challenges

• Global status of blast furnace slag including production and end uses was detailed. • Working principle of CGATER and hierarchical structure of its R & D were overviewed. • Advances in CGATER practices were included and analyzed at laboratory and pilot scale. • Future challenges and possible solutions were pointed out. The iron and steel industry (ISI) is pursuing technology breakthroughs to accelerate the transition towards carbon neutrality. Deep cut of CO 2 emission involves with not only technological revolution of producing iron and steel, but also exploiting energy in byproducts and off-process wastes. Molten blast furnace slag (BFS), one of the largest high-temperature byproducts, remains the last untapped waste heat source in ISI. Of ever-increasing interest is the centrifugal-granulation-assisted thermal energy recovery (CGATER) from high-temperature BFS. This technique features waste energy harvest and vitreous slag utilization. Such striking merit opens up new possibilities of enabling more sustainable and greener iron and steel production, and makes CGATER one of the most promising technologies in the portfolio of ISI CO 2 mitigation. Despite the rapid development of CGATER in last decade, most previous efforts were dedicated to understanding the CGATER physics and its closely allied matters. To date, large-scale implementation of CGATER has been little explored beyond the laboratory or pilot scale. It is imperative to provide a critical, timely review on the status of CGATER and most importantly, the challenges in its further deployment at industrial scale. This article first provides an inclusive figure of global BFS production and its versatile role in civil engineering. The working principle and research status of CGATER are detailed to highlight its strength and weakness. Future challenges towards the CGATER industrialization have been scrutinized. Other new-emerging technologies or concepts are also included.

Improved Multidomain Convolutional Neural Network for Intelligent Tracking of Marangoni Effect Process Sequence Images

Sequence image target tracking has two requirements of accuracy and speed. Aiming at the problem of slow speed of convolutional neural network (CNN) target tracking algorithm, an improved algorithm for sequence image target tracking is designed by using a fusion of Faster multidomain CNN (MDNet) and optical flow method. The target algorithm designed in this article is improved on the basis of MDNet. The optical flow method is used to obtain the primary selection box first, which can effectively deal with the challenges brought by scale change and in-plane rotation, and has good tracking speed and performance. The objective algorithm of this article is used to explore the Marangoni effect in the melting process of solid iron tailings in molten blast furnace slag. Because the main component of iron tailings is Silica, and the melting point of Silica is the highest, so taking Silica as the research object, an intelligent analysis of Marangoni effect in high-temperature melting process of Silica particles is realized. The results show that the target algorithm achieves the real-time standard (FPS > 24), the average distance precision (DP) is 97.3%, the average success rate (SR) is 98.02%, the average center location error (CLE) is 6.2684 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m, and the average overlap precision (OP) coverage is 63.86%. The target algorithm has certain advantages in the following five evaluation indexes: DP, SR, CLE, OP, and frames per second.

Effect of acidity coefficient on crystallization behaviour of modified blast furnace slag

ABSTRACT Crystallization of molten blast furnace slag directly affects the fibre forming rate and stability of fibre. The single hot thermocouple technique was used to investigate the crystallization behaviour of modified blast furnace slag. The results revealed that, with increasing acidity coefficient of modified blast furnace slag during the isothermal process, the initial crystallization temperature of modified blast furnace slag gradually decreased, which were at 1390°C, 1330°C and 1180°C, respectively, and TTT curves changed from double C-type curve to single C-type curve. Through a continuous cooling process, the critical cooling rate decreased from 6°C s−1 to 0.5°C s−1 when the acidity coefficient of modified blast furnace slag increased from 1.05 to 1.40. Based on these findings, we conclude that, the crystal growth rate is controlled by diffusion driving force and undercooling driving force.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ И УПРАВЛЕНИЕ ДВИЖЕНИЕМ ОДИНОЧНОЙ КАПЛИ ДОМЕННОГО ШЛАКА В ПОТОКЕ ГАЗА ПРИ СУХОЙ ГРАНУЛЯЦИИ

Dry granulation plants of blast furnace slag allow obtaining granulated slag and use heat of liquid slag. When introducing dry granulation of slag, emissions of harmful sulfur compounds into the atmosphere are excluded. When designing the granulation chamber, it is necessary to evaluate the main size of the chamber - its diameter to avoid slag sticking to the walls of the chamber. The slag droplets must solidify before colliding with the wall. In this work, the authors developed a mathematical model for the movement of a single droplet of molten blast furnace slag during dry granulation, which allows controlling the cooling process of a single droplet of molten blast furnace slag in the granulation chamber.

Effect of Oily Sludge Treatment with Molten Blast Furnace Slag on the Mineral Phase Reconstruction of Water-Quenched Slag Properties.

Blast furnace slag, which is the main by-product of the ironmaking process discharged at 1450 °C, contains high-quality sensible heat, while oily sludge is the main solid waste produced in the process of gas exploration, storage, and transportation. The energy and resource utilization of blast furnace slag is complementary to the environmentally friendly treatment of oily sludge, which has provided a new idea for the multi-factor synergistic cycle and energy transformation of the two wastes. The pyrolysis of the oily sludge with the molten blast furnace slag was conducted in the current paper. Results showed that the oily sludge was rapidly pyrolyzed, and the heavy metal elements in the oily sludge were solidified. The solidification rate of the heavy metals exceeds 90%, except for vanadium. The reconstituted water-quenched blast furnace slag still has good activity, and it will not affect the further use of the slag after pyrolysis (BFS-P).

Effect of Unburned Pulverized Coal on the Melting Characteristics and Fluidity of Blast Furnace Slag

A substantial amount of attention has been paid to viscosity due to its substantial effect on the fluid dynamics of molten blast furnace slag and slag metal reaction kinetics during the pyrometallurgy process. To clarify the influence mechanism of unburned pulverized coal (UPC) on blast furnace (BF) slag viscosity, the effects of different contents of UPC on the BF slag viscosity, free-running temperature and viscous flow activation energy were investigated. The slag viscosity was measured by the rotating cylinder method, and the microstructure of the cooled slag was observed by SEM. As a result, the main reason for a change in the slag viscosity, free-running temperature and viscous flow activation energy was that the UPC entering the slag formed a large number of white particles that predominantly comprised deposited carbon and a high melting point solid solution. In addition, the disintegration or polymerization of the SixOyz- structure was also a contributing factor. When the content of the UPC was 0.6%, the free-running temperature and viscous flow activation energy of slag were 1623 K and 120.969 kJ/mol, respectively, which are lower than those of the slag without UPC. However, the free-running temperature and viscous flow activation energy increased to 1668 K and 286.625 kJ/mol, respectively, when the content of UPC increased to 4%, which are higher than those of slag without UPC.

Numerical investigation of breakup process of molten blast furnace slag through air quenching dry granulation technique

Molten slag is broken up by supersonic air into droplets through the air quenching dry slag granulation technique. The breakup process of blast furnace slag directly determines the droplet diameter and the waste heat recovery. In order to gain deep insight into the granulation mechanism and visualize the breakup process, three-dimensional unsteady numerical simulation based on the k-ω based shear stress transport turbulence model was conducted to simulate the transient breakup process of molten slag (k is the turbulent kinetic energy, and ω is the specific dissipation rate). The coupled level-set and volume-of-fluid method was utilized to capture the sharp air–liquid interface. The results show that a flat film is formed firstly under the effects of air impingement, recirculation zone and pressure gradients. Then, the axial wave and the spanwise wave appear simultaneously and the film is broken up into ligaments owing to the generation of vortex and hole structure at the intersection of axial trough and spanwise trough. Finally, the ligaments are broken up into droplets owing to Rayleigh–Taylor instability at the air–liquid interface. The droplets smaller than 3.00 mm account for 80%, with the average diameter of 1.95 mm.

Dynamic behaviors and regime map of a molten blast furnace slag droplet impacting a solid surface

The dynamic morphologies of a molten blast furnace slag droplet impacting a quartz glass surface are studied visually for a wide range of dimensionless initial temperatures (1.604–1.951), Reynolds numbers (17.4–124.4), and Weber numbers (197–1191). Five morphological evolution modes are defined based on the final stage of the slag film as deposition, receding, prompt-splashing, retraction-deposition and retraction-splashing. An impact regime map is established with the Reynolds number and dimensionless initial temperatures as the coordinates and six boundaries dividing the different modes are identified in the regime map. The apparent temperature nephograms of the slag film are extracted by a home-developed optical calibration method. The dynamic spreading processes and temperature distributions of the different regimes are not simply determined by the initial impact parameters, the coupling effect of the flow of the high-viscosity liquid slag and the heat transfer at the interface will obstruct the consecutive morphological evolution. The regulation principle for the centrifugal granulation system is promoted based on the analysis on an energy barrier for the sufficient spreading of the droplet and the impact regime map.

Structure, viscosity, and crystallization of glass melt from molten blast furnace slag

AbstractMolten blast furnace slag (BF slag) was modified using liquid‐liquid mixing method for glass ceramics preparation, and the structure and viscosity of glass melt after modification were investigated. The BF slag proportion increased from 52.72 wt. % to 67.05 wt. %, and CaO/(SiO2 + Al2O3) also varied from 0.33 to 0.47. The structure of BF slag melt after modification was investigated using 29Si and 27Al MAS NMR spectra. With increasing CaO/(SiO2 + Al2O3), the amount of Q1 remarkably increased while that of Q2 decreased significantly. Specifically, when CaO/(SiO2 + Al2O3) was more than 0.38, Q3 disappeared in glass melt. The viscosity of glass melt with CaO/(SiO2 + Al2O3) of 0.47 exhibited a steep change at 1169°C, which was mainly caused by the sufficient crystallization of gehlenite confirmed by DTA cooling analysis, XRD, and FE‐SEM‐EDS analysis.

Structure, crystallization mechanism, and properties of glass ceramics from molten blast furnace slag with different B2O3/Al2O3

Glass ceramics with different B2O3/Al2O3 from molten blast furnace slag (BF slag) were prepared using traditional melting, annealing, and heat treatment method. According to DSC analysis, the parent glass samples were nucleated at 760 °C for 1 h, and then respectively crystallized at 900 °C, 920 °C, and 940 °C for 1 h. The structure of parent glass was characterized using XRD, Raman spectra, 27Al MAS NMR spectra. The results indicated that with an increasing B2O3/Al2O3, Q2 remained dominant in the glass network, Q0 disappeared and Q4 existed when B2O3/Al2O3 was 0.21. [BO3] and [BO4] were both characterized when B2O3/Al2O3 exceeded 0.09, but the further addition of B2O3 was prior to form [BO3] in glass network. The investigation of crystallization mechanism revealed that the crystallization activation energy Ec strikingly decreased from 403.8 kJ/mol to 277.8 kJ/mol with increasing B2O3, and surface crystallization was determined due to that the crystallization index n was below 3. The results of XRD and SEM-EDS analysis both confirmed the main crystalline in glass ceramics was gehlenite. The flexural strength of glass ceramics reached the minimum when B2O3/Al2O3 was 0.21. Glass ceramics nucleated at 760 °C for 1 h and crystallized at 940 °C for 1 h exhibited the highest flexural strength of 57.61 MPa.

Notice of Retraction: Perspective and Prediction of the Rule of High Temperature Melting of SiO₂ via Visual Analysis

This paper focuses on how to see through the melting behavior of solid iron tailings in molten blast furnace slag and take a new non-contact visual analytical method to predict its melting law. The optimized convolution neural network (CNN) is used to track the moving target in charge coupled device (CCD) camera system efficiently and accurately, and the melting behavior of SiO2 is described by coordinate translation transformation theory. Hierarchical agglomerative clustering (HAC) and delaunay triangulation were used to extract the characteristic parameters of the melting process of SiO2. The prediction model of the melting rate of SiO2 at high temperature was established by least square fitting (LSF) and dimensional analysis, and compared with the actual melting rate of SiO2 obtained by experiments. The results show that the melting characteristics of SiO2 at high temperature are in accordance with certain function rule. The performance of optimized CNN in terms of processing time and the accuracy are significantly improved, and the fusion rate prediction model of SiO2 is verified by 100% accuracy. It provides theoretical support and model basis for the improvement of slag cotton preparation technology.