Slag Formation Research Articles

Ferrochrome Production in a Submerged Electric Arc Furnace: Fundamental Analysis Based upon the FactSage‐Macro Program Approach

Around 80% of the FeCr produced worldwide is utilized in stainless steelmaking. Thus, the growth of the stainless‐steel industry is directly related to FeCr production. Although the FeCr production in submerged arc furnace (SAF) is fairly stabilized, new challenges have emerged in the furnace operation due to the depletion of lumpy ores, high SiO2 content, and lower Cr/Fe ratio in the low‐grade ores. In this regard, the addition of various fluxes such as quartz, magnesite, and bauxite are considered to improve the Cr recovery in SAF operation, particularly in the context of low‐grade ores. In this study, thermodynamic calculations are performed to discuss the effect of various additives (MgO in magnesite, Al2O3 as bauxite, and SiO2 in quartz form) on Cr recovery and slag formation temperature. In addition, a comprehensive thermodynamic‐based process model has been developed for FeCr operation that captures the most important thermochemical reactions. The modeling results are compared with the plant data, and suitable modifications in the slag compositions are made to maximize Cr recovery. Moreover, new plant trials are performed with modified slag composition, and its effect on Cr recovery is also discussed.

Blast Furnace Slag Formation Prediction Model Using Classical Thermodynamics

Blast furnace (BF) ironmaking is the most widely used technology for hot metal production. In steelmaking industry, 80% of the steel in the world is produced in the BF‐basic oxygen furnace route. It is well known that poor quality of the raw material i.e., high gangue content in the iron ore affects the BF process performance and the cohesive zone formation, which is the most critical zone in the BF operations. Increased gangue content in the iron ore causes variation in the slag formation and slag volume thus affecting the fuel rate and BF performance. Therefore, in this study, the slag formation is studied to understand the slag properties at different locations inside the BF. The model is based on classical thermodynamics and is implemented using ChemApp linked with FactSage databases. The model aids in understanding the slag formation in the BF for various burden chemistry, fuel, and flux inputs. The final hot metal and slag composition along with the exit gas volume and composition predicted from this model are compared with industrial BF plant data operating across different conditions.

Applicability analysis of burners arrangement for an improved entrained-flow fine slag gasifier

Fine slag with high carbon content is unsuitable for brick-making or road paving and is usually deposited in piles or landfills. The atmospheric entrained-flow gasification technology can make use of the unburned carbon in fine slag, thereby resolving the problem of wasted resources and environmental pollution caused by waste fine slag. The arrangement of burners has an impact on the flow field within the gasifier, which subsequently affects the gasification performance. It is important to find a suitable burner arrangement for different gasification raw materials. This study investigates the gas–solid flow characteristics in 10,000 Nm3/h fine slag entrained-flow gasifiers using a combination of two-phase experiments and numerical simulations. The flow fields were compared in detail for three different burner arrangements. The results indicate a clear central tangent circle under the co-biased burner arrangement, which leads to the highest particle concentration and swirl intensity near the membrane wall. This condition is most conducive to slag formation. No rotating flow field is generated in the gasifier under the opposed and counter-biased burner arrangements. The high-temperature region is located near the top of the chamber. Additionally, the residence time of fine slag is short. These factors make it unsuitable for powder gasification. The results will be helpful to the design and operation of entrained-flow powder-feedstock gasifiers with multiple burners.

COMPLEX MATHEMATICAL MODEL OF THE PROCESS OF LOADING A MULTICOMPONENT CHARGE INTO A BLAST FURNACE

The rational mode of loading the blast furnace is the most important condition for its highly efficient operation. The selection of rational values of the control parameters of the load mode is carried out on the basis of information obtained with the help of instrumental tools and mathematical models. Mathematical models of the process of blast furnace loading are necessary components of expert (intelligent) control systems for blast furnace melting. The presented complex mathematical model of the process of loading a multicomponent charge into a blast furnace differs from known developments taking into account the redistribution of components into the volume of loaded portions during movement along the path "charge feed - blast furnace", which provides the possibility of obtaining calculated characteristics of the distribution of each component of the charge and determining the composition of the formed mixtures of charge materials in any given zone of the furnace. The existence of such a model opens up new opportunities in the management of the blast furnace smelting process, as well as in conducting analytical studies of the conditions of slag formation and the distribution of properties of melts across the section of the blast furnace.

Maximized energy recovery by catalytic co-pyrolysis of dewatered sewage sludge and polystyrene to contribute in bio-circular economy: Synergistic compositional analysis of bio-oil and syngas through artificial neural networking

Sewage sludge and polystyrene are considered very challenging for the waste management authorities in urban centers across the globe. In the current study, catalytic co-pyrolysis of the dewatered sludge (DS) and waste polystyrene (PS) was conducted. The co-pyrolysis of DS and PS; 60% polystyrene+40% dewatered sludge was concluded as optimum ratio with 11.21% higher energy production as compared with other compositions. The produced bio-oil were investigated having higher slags/wax and lower aromatics. Therefore, ZSM-5 (3% weight basis) catalyst was employed, and it had enriched the bio-oil quality, provided higher aromatic hydrocarbon yields with reduced wax and slag formation. To understand the thermodynamic behavior of all dewatered sewage sludge and polystyrene, detailed TGA analysis was carried out. The relative abundance of the aromatic hydrocarbons was identified by GC-MS and FTIR analysis. The synergist compositional analysis of the bio-oil and syngas was carried out by using artificial neural networking techniques. The aromatic components in bio-oil were found to have positive correlations when catalyst were employed. The proposed energy recovery model had capacity of generating 20,863 KWh/d of electrical energy, dealing 10 tons/d of biowaste: and leads the societies towards cleaner environment and positive contribution to bio-circular economy.

Changes in Microscale Liquid Formation in Lump and Sinter Mixed Burden Softening and Melting Tests with the Addition of Hydrogen

With the movement toward hydrogen-enriched blast furnace operation to lower greenhouse gas emissions, ferrous burden design must be reconsidered to optimize furnace permeability. Increasing the ratio of direct charge lump ore in the ferrous burden also presents an opportunity to lessen the emissions associated with the production of sinter and pellets. Under traditional blast furnace conditions, lump ore usage is improved by mixing it with the sinter in the burden to promote their favorable high-temperature interactions (both chemical and physical). As such, mechanistic changes to the interaction must be understood to optimize burden design, including for future operations with hydrogen addition. In this study, liquid formation in both the metallic and oxide components of ferrous burdens is microscopically investigated. Oxide liquid and solid phase stability at the interfaces of dissimilar burdens are visualized using a novel mapping technique, and metallic iron is etched to reveal microstructures indicative of carbon. Results indicate that the inclusion of hydrogen promotes the gas carburization of metallic iron in sinter, but not lump. It was concluded that mixed burden softening and melting performance with hydrogen addition were improved through the addition of lump in two ways: the highly metallic lump particles provide structural support for the collapsing sinter bed and also suppress the formation of early liquid slag from the sinter.Graphical

Microstructural evolution and high-temperature oxidation behavior of oxide dispersion strengthened Inconel 625 superalloy fabricated by directed energy deposition

In the present study, wire arc-directed energy deposition (DED) technology was developed to fabricate the Oxide dispersion strengthened (ODS) Ni-based superalloy employing an Inconel 625 flux-cored wire including nano-La2O3 oxides. The microstructural evolution, mechanical properties and high-temperature oxidation behavior were systematically investigated. The results indicate that the melting and decomposition of La2O3 are thought to take place within the melt pool, followed by rapidly combining with Ti to re-precipitate as La2Ti2O7 oxides during DED. These oxides can serve as a highly effective nucleation site according to edge-to-edge matching calculation, resulting in the columnar-to-equiaxed transition and the refinement of grains. However, it is found that plenty of La elements are absorbed by the molten flux in the filler wire, resulting in the formation of slag and the loss of La. Consequently, the strength increases slightly due to the combined effects of precipitation strengthening and grain boundary strengthening. Furthermore, The ODS Inconel 625 sample can achieve a higher oxidation resistance after high-temperature oxidation at 900 °C for 150 h. The fine microstructure promotes the rapid formation of dense Cr2O3 oxide scales. On the other hand, the precipitation of La-rich oxides retards the outward transport of cation such as Ni, Fe and Nb, leading to the formation of a protective δ-Ni3Nb layer beneath the Cr2O3 layer to prevent the oxidation of matrix.

Dispersoid coarsening and slag formation during melt-based additive manufacturing of MA754

We have assessed the structural evolution and dispersoid coarsening behaviors of the oxide dispersion-strengthened superalloy MA754 during two different melt-based additive manufacturing techniques – metal laser powder bed fusion (PBF-LB/M) and directed energy deposition (DED). The mechanically alloyed MA754 powder posed challenges for both processes due to its irregular flaky morphology and large particle size. Successful consolidation with PBF-LB/M required increasing the layer height, decreasing the scanning speed, and increasing the laser power relative to typical Ni superalloy printing parameters. The resulting materials contained residual porosity and large Y-Al-oxide slag inclusions which formed in situ. The more prolonged thermal excursion during DED resulted in even larger, mm-scale slag inclusions, which spanned several build layers. In both PBF-LB/M and DED, these inclusions grew at the expense of nanoscale dispersoids, depleting the material of this strengthening phase. These observations motivate alternative approaches for preparing dispersion-strengthened powder feedstocks besides mechanical alloying and highlight the deleterious effects of Al microalloying on dispersoid stability and structure.

Char-based Fe-Ni-Ca material for capturing AAEM from biomass pyrolysis volatiles and recyclability in catalytic reforming of volatiles

Hydrogen production derived from biomass catalytic pyrolysis has received increasing attention, to solve the excessive consumption of renewable energy. However, considerable amounts of the issues (e.g., slag formation, corrosion, and scaling on the heat exchange surface) related to alkali and alkali earth metals (AAEM) have hindered its application. To address these challenges and improve the yield of H2, char-based Fe-Ni-Ca material is proposed to capture AAEM from biomass pyrolysis volatiles while increasing the H2. Char-based materials exhibit excellent AAEM capture ability, with K, Na, and Mg contents detected in spent materials being 3.4 times, 1.4 times, and 1.5 times higher than those in fresh, respectively. Besides, the spent Fe-Ni-Ca exhibits excellent stability after regeneration, with H2 production comparable to that of fresh material, and CO production exceeding that of fresh Fe-Ni-Ca. It was disclosed that the char support can adsorb AAEM in volatiles, and then chemical reactions will occur between metal elements (Fe, Ni, and Ca) in the material and AAEM in the volatiles, trapping AAEM in the material and catalytic reforming volatiles. This work provides a novel strategy to deal with AAEM in volatiles.

Modeling the process of slag formation in paste propulsion

The results of modeling the accumulation of slag residue in the combustion chamber of a propulsion system on pasty propellant obtained using a multiphase flow evolution model are presented. The influence of composition solutions on the process of slag formation is established; the significance of this process for the quality of such engines is shown. The nature of the influence of the parameters of the burning process for propellants of the type under consideration on the intensity of slag formation is determined. It is shown that the degree of involvement of metallic fuel in the agglomeration process has the greatest influence on slag formation. It has been established that the most effective "tool" for suppressing slag formation in the combustion chambers of paste propulsion is to change the regularities of the burning process, mainly associated with the formation of condensed products at the surface of the burning propellant.

Laser modification of heating surfaces: A new approach to reduce boiler slagging

Slagging and fouling of boilers are typical technological problems in the combustion of solid fuels (especially coal and biomass). This study proposes a novel approach based on laser texturing of the near-surface layer of steel used to make heating surfaces of coal-fired boilers. This approach is aimed at improving the resistance of metal surfaces to slagging. The formation of slag deposits on the surfaces of AISI 310 S steel modified by laser radiation has been experimentally studied. The formation of slag melt was analyzed on the surface of modified and polished steel plates during heating to 1400 °C. High-temperature heating and interaction with slag led to a change in the chemical composition of the steel. A significant increase in the chromium content (up to 47%) of the steel surface and the transformation of its texture with the formation of grains up to 2.5 µm in size were established. Laser surface treatment significantly increased the resistance of the steel to such changes and also reduced the grain size to 1.5 µm. As a result of laser modification of surfaces, the temperature of slag formation shifts to higher values (higher by 60–75 °C compared to the unmodified polished surface). The anisotropic texture (cauliflower type) contributed to a decrease in the size of the slag spreading front, and also had by self-cleaning properties from the mineral melt. The latter allows to increase the reliability and energy efficiency of boiler equipment.

Study on the continuum formation pathway and formation mechanism of slag phase in cohesive zone

Several methods are conducted to reveal the formation mechanism of slag phase in cohesive zone. The notable diffusion capacity of CaO to 2FeO·SiO2 and FeO to 2CaO·SiO2 determines different pathway of initial slag formation in pellet and sinter, respectively. The less destructive effect of Al2O3 on the original system makes FeO-CaO-Al2O3-SiO2 the dominant slag system in cohesive zone. Poor diffusion of MgO into 2FeO·SiO2 and 2CaO·SiO2 systems results in a low MgO content in cohesive zone slag. The formation process of interfacial slag is further subdivided into formation interaction and component interaction according to the formation pathway.

Formation Mechanism of High‐MnO‐Content SiO2/SiO2–MnO–(CaO–Al2O3) Dual‐Phase Inclusions in Si–Mn‐Killed Steel

This study investigates the deformation characteristics of SiO2–MnO–(CaO–Al2O3)‐type inclusions in silicon manganese deoxidized steel from continuous casting to rolling. The results reveal that the inclusions contain 60–80% SiO2, 10–35% MnO, and a combined CaO and Al2O3 content of <20%. SiO2 precipitates inside the inclusions during the continuous casting and rolling processes, which results in the formation of pure SiO2/SiO2–MnO–(CaO–Al2O3) dual‐phase inclusions in the remaining components owing to the increase in the MnO content to 15–40%. According to the experimental results of melting rate measurement and thermodynamic calculation using FactSage8.1, the SiO2–MnO–(CaO–Al2O3) phase has a high proportion of liquid components at 1100–1360 °C and exhibits good deformation properties during the breaking down and rolling processes. When the total content of CaO, Al2O3, and MgO in the SiO2–CaO–Al2O3–MgO–MnO inclusions reaches 30–50%, SiO2 precipitation is inhibited during the continuous casting to rolling process. Through the addition of metal manganese and carbon powder during the pre‐deoxidation process, followed by alloying with ferrosilicon and metal manganese, and then the addition of acidic synthetic slag for slag formation, the proportion of SiO2/SiO2–MnO–(CaO–Al2O3) dual‐phase inclusions in the casting billet is increased from 12% to >60%.

In-situ visualization of high temperature slag corrosion process for alumina-magnesia refractory

The stringent service environment of refractory, which is composed of complex photo-thermal radiation, limits the evaluation of its corrosion process and corrosion mechanism. The visualization of interaction between refractory and slag at the temperature range of 1350∼1600 °C was realized based on the development of high-temperature resistant speckles combined with digital image correlation technology. The corrosion processes of alumina-magnesia refractories can be divided into three stages: slag penetration, refractory dissolution, and formation of new precipitates. The relationship between corrosion and corrosion processes induced strain was established: the stress caused by slag penetration and refractory dissolution was about 1.29 times that of the formation of new precipitates, such as CA6. With the quantification and identification of slag penetration and corrosion area using the full-field chemo-mechanical strain distribution on the refractory surface, a new method for precise research and real-time evaluation of corrosion behavior of refractory under extreme environment is established.

Tissue composition and higher heating values differ among six bioenergy grasses

Perennial crops are considered as one of the most promising substitutions for fossil fuels for both ethanol production and direct combustion, but the quality and suitability of bioenergy feedstock is species dependent. The bioenergy feedstock value of different perennial crops is mainly determined by tissue composition and higher heating value (HHV). A common garden field experiment with four replications was conducted to investigate differences in cellulose, hemicellulose, lignin, ash, and 14 different tissue elemental concentrations as well as HHV from tissues of switchgrass (Panicum virgatum L.), Miscanthus (Miscanthus×giganteus), indiangrass (Sorghastrum nutans), eastern gamagrass (Tripsacum dactyloides), reed canary grass (Phalaris arundinacea), and giant reed (Arundo donax L.) grown in 2020 and 2021 in Midwest USA. Results showed that Miscanthus, switchgrass, and indiangrass exhibited higher holocellulose (cellulose + hemicellulose) concentrations compared with eastern gamagrass, reed canary grass as well as giant reed: 684–687 g kg-1 vs 597–646 g kg-1 (2-yr averages). Switchgrass and Miscanthus had higher lignin concentrations (97–108 g kg-1) than the other four species (66–84 g kg-1). Greater 2-yr averaged HHVs were observed in switchgrass (18.1 MJ kg-1) and Miscanthus (17.8 MJ kg-1) than for giant reed (17.3 MJ kg-1), eastern gamagrass (17.0 MJ kg-1), indiangrass (16.9 MJ kg-1), and reed canary grass (16.5 MJ kg-1), which was correlated with differences in ash concentration between switchgrass and Miscanthus (25–29 g kg-1) and the other four species (42–91 g kg-1). Switchgrass, Miscanthus, and indiangrass exhibited significantly lower nitrogen, sulfur, and potassium concentrations than the other grass species, which would lead to less NOx and SOx emission, and sintering or slag formation in the combustion chamber. Giant reed obtained the greatest potential ethanol and combustion yields on a single plant basis, followed by Miscanthus, switchgrass, indiangrass, eastern gamagrass, and reed canary grass; however, further studies are needed to evaluate biomass yields on an area basis.

Effect of operating conditions on release and transformation of sodium during CFB gasification of Zhundong coal

To provide some useful suggestions to the operation of circulating fluidized bed (CFB) gasifier, the effect of gasification temperature, residence time and agent on the release and transformation of sodium was studied by using a fixed bed reactor combined with Factsage software. The results indicated that gasification temperature was the significant factor to the release and transformation of sodium. For the promoting effect of sodium release, it was ascribed to the intense of sodium volatilization and competitive reaction between lime and meta-kaolin. Meanwhile, the high temperature promoted the formation of nepheline and slag. The threshold temperature of latter was near 950 °C. It was interesting to find that the release of sodium could be divided into two stages: coal pyrolysis and char gasification. In coal pyrolysis, part of organic and water-soluble sodium was released. The remainder either combined with char structure, or reacted with minerals. In char gasification, sodium, combined with char structure, was released along with char gasification. Due to the decrease of melting temperature and the formation of NaOH, steam showed a promoting effect on the sodium release. Oppositely, oxygen and nitrogen presented an inhibiting effect. The former was ascribed to the formation of Na2SO4, while the latter was caused by the chemical binding and physical wrapping effect of char.

Estimation of hot metal desulfurization by intermediate and final blast-furnace slag when using pellets of different basicity in blast-furnace charge

n the process of blast-furnace smelting, up to 90% of coke sulfur is captured by the iron ore charge, accumulating in hot metal in the amount that was absorbed from the gas phase. Desulphurization of cast iron occurs when it interacts first with the intermediate, and at the final stage, with the final blast-furnace slag. In this regard, it is of interest to evaluate the desulfurizing properties of the intermediate and final slag, which affect the sulfur content in hot metal. Melting mixtures of pellets of different basicity and sinter in a blast furnace leads to the formation of primary and intermediate slags of different chemical composition. When smelting hot metal in blast furnaces, mainly unfluxed pel-lets and fluxed sinter are used. In the course of the study, mixtures of sinter and pellets of different basicity were pre-pared, which ensured the production of final blast-furnace slag with a basicity of CaO/SiO2 = 1.15 units. The mixtures were reduced and melted in graphite crucibles with the smelting products filtered through a coke nozzle. The coeffi-cients of sulfur distribution between intermediate slag and hot metal obtained from iron ore charge with different basicity of sinter and pellets were determined. The lowest sulfur distribution coefficient between the intermediate slag and hot metal is observed when the basicity of the pellets is in the range of 0.5‒1.2 units. To increase the desulfurization capacity of the intermediate slag, it is advisable to use unfluxed and fluxed pellets with a basicity of 0.25 units in the blast-furnace charge and an sinter with a basicity of 1.78‒1.87 units. Studies of the kinetics of the interaction of hot metal and final blast-furnace slag have shown that the final slag provides a high degree of desulfurization of hot metal during their interaction for 1 hour or more

A new piece of the puzzle: slag and ore analysis to reconstruct the prehispanic smelting technology at the Atacama Desert, Chile

The Incas appropriated many local metallurgical technologies throughout the Andes, each of which had its unique peculiarities and was based on local ancestral knowledge. The widespread use of tin-bronze during the Inca expansion, the development of mining and smelting sites, as well as ethno-historical records evidence the Incas’ interest in copper smelting, a key activity in the Andes since ca. 1400 BC. However, little is known about the technical parameters achieved by ancient metallurgists and the changes that occurred during the Inca expansion. In this paper, we address these changes through a case study of Copiapó valley, focusing on the Viña del Cerro site, one of the most famous Inca smelting centres of the southern Andes. Although this place was architectonically restructured by the Incas, its operations began long before the imperial expansion and used wind-powered furnaces. We analysed 19 slag and 11 copper ore samples using OM, SEM–EDS, WD-XRF, and XRD analyses. Results identified heterogeneous and viscous slags, rich in SiO2 (43 wt%) and poor in FeO (13 wt%). Copper retention was high (up to 60 wt%). Microstructural analyses indicate that slags were formed under unstable oxidising conditions, reaching temperatures that ranged between 1000 to 1100 °C. The copper produced was very pure. High-grade copper ores containing up to 69 wt% CuO were reduced at the site, combining carbonates (malachite, azurite), halides (buttgenbachite, clinoatacamite), and some sulphates (brochantite). We propose that even under the relatively unfavourable conditions for slag formation, the smelting conditions generated at Viña del Cerro were competent enough to extract metal, but not necessarily enough to form liquid slag. These conditions were facilitated by the local metallurgists’ thorough knowledge of the wind flow and their ability to select the right ore. This new information contributes to understanding the efficiency of metallurgical technology and the knowledge, skills, and adaptability of the ancient metallurgists from Copiapó valley, a group that was integrated into the economic networks of the Inca Empire.

Slag Formation during Additive Manufacturing of Dispersion-strengthened Superalloys.

Slag Formation during Additive Manufacturing of Dispersion-strengthened Superalloys.

Hydrothermal treatment (HTT) improves the combustion properties of regional biomass waste to face the increasing sustainable energy demand in Africa

The increasing worldwide energy demand in parallel to the increasing climate change effects require the utilization of sustainable energy sources. Biomass residues are a feasible energy source, but their chemical composition often compromises their utilization due to slag formation or high emissions. It is investigated in this study whether hydrothermal treatment (HTT) can improve the combustion properties of biomass residues from Ghana. Six biomass residues (Prekese pods, ground nut husks, coconut husks, cassava peels, shea cake, deoiled shea cake) treated at three temperatures (150 °C, 170 °C, 185 °C) were analyzed for combustion properties and emission precursors according to European Standards. The results were evaluated considering consistencies of combustion related properties and especially of ash element reduction behavior. There was a clear trend to increasing mass loss and increasing heating value with increasing treatment temperature that was reflected in the carbon, hydrogen and oxygen amounts, while the ash content and its composition varied. Consistencies in the ash element behavior were highlighted and discussed in order to identify chemical key parameters that led to or inhibited specific ash element reductions. HTT was identified as a feasible biomass upgrade method with advantages over water leaching at room temperature and high temperature hydrothermal carbonization in case of the availability of off-heat from e.g. biomass electricity production.