Slag Fluidity Research Articles

Physical properties of cement composite with monoethanolamine

This study analyzed the fluidity, air content, flexural strength, compressive strength and carbon dioxide adsorption performance of cement, furnace slag and fly ash-based cement composite using appropriate substitution values of MEA derived from preliminary experiments. Fluidity and air content were found to increase as the fly ash substitution rate increases. It is believed that the increases are due to the fly ash ball bearing effect in combination with the creation of micropores by MEA. The compressive strength was found to decrease with lower furnace slag substitution ratios. This is believed to have resulted because the Pozzolanic reaction of the fly ash plays a more dominant role in determining the compressive strength than does the latent hydraulic activity of furnace slag as the furnace slag substitution rate is decreased. It is determined that the compressive strength was reduced because the Pozzolanic reaction reduces the density of the texture and pore structure of the interfacial transition zone. Carbon dioxide values increase as the furnace slag substitution rate was increased.

Effect of B2O3 on the viscosity, structure and crystalline phase of CaO–MgO–Al2O3–SiO2–MnO-based high alumina slags

The effects of B2O3 on viscosities, structures and phase transitions of CaO–MgO–Al2O3–SiO2–MnO-(0-8.0 wt%)B2O3 slags were investigated in this work. From the viscosity experimental results, the slag viscosities declined and the Eη decreased from 205.19 to 175.95 kJ/mol with the addition of B2O3 in slags from 0 to 8.0 wt%. From the structure analysis by using FTIR and XPS, B2O3 entered into the silicate network to increase the slag polymerization degree, while the formation of simple two-dimensional BO3 trihedral units could significantly decline the symmetry and stability of the structure. The effects of decreasing the network stability and forming low-melting eutectics were more dominated than the effects of increasing the structure polymerization degree, which could reduce the slag viscosity. Furthermore, adding B2O3 could decrease the slag initial precipitation temperature and change the primary crystal phase of the slag from melilite to spinel. The comprehensive effects of reducing the slag structure stability and decreasing the influence of solid phase on viscosity eventually resulted in the improvement of the slag fluidity.

Study of Tuyere Combustion Flame Temperature in Vanadium and Titanium Blast Furnaces by Machine Vision and Colorimetric Thermometry

The steel industry is an important foundation of the national economy and the livelihood of the people, producing a large amount of carbon dioxide gas, accounting for about 70% of the carbon dioxide gas generated in the steel industry, which occurs during the ironmaking process. Therefore, the key technology to reduce the pollution and improve competitiveness is to increase the stability of blast furnace production and the quality of hot metal. Since the operation requirements for temperature control in the vanadium-titanium blast furnace are dramatically different compared to the traditional ones due to the low fluidity of vanadium-titanium slag, maintaining the required hot metal temperature within a narrow range with smaller fluctuations is essential. In addition, the adjustment parameters of the lower part have a significant influence on the tuyere combustion flame temperature during the daily operation of blast furnaces. At present, there is no relevant research on the online detection and analysis of vanadium-titanium blast furnace tuyere combustion flame temperature. In this study, the temperature of four tuyeres in a 500 m3 vanadium and titanium blast furnace at Jianlong Steel was detected by an online detection system. The tuyere combustion flame temperature was then calculated using colorimetric temperature measuring methodology at various times and at four distinct locations. After that, the calibration analyses, imaging parameter and the temperature tendencies in different directions of the blast furnace were investigated. This study not only offers new methods for understanding the regularity of operation and increasing the degree of visualization in vanadium and titanium smelting blast furnaces but also provides technical support for intelligent and low-carbon operation in blast furnaces.

Value-added recycling of iron and titanium from bauxite residue (Red Mud) via a flux-free smelting separation process

With enriched iron and titanium elements, red mud produced by the lime-free Bayer process showing high recycling value. This work proposed a pre-reduction and flux-free smelting process to recycle Fe/Ti resources from this red mud. Considering the extraction of titanium from smelting slag, classical calcareous flux was abandoned to avoid the formation of refractory perovskite. Instead, the FeO generated by pre-reduction of red mud itself was creatively applied to regulate the subsequent smelting separation. The full melting temperature of slag can be reduced from > 1700℃ to 1450℃-1550℃, as the FeO content in slag reached 10-20 wt%. The transition from rutile to ferrouspseudobrookite contributed to this change. Since the pre-reduced sample was smelted at 1600℃ for 60 min, 93.60 wt% of the iron element in red mud can be recycled in the form of iron nugget with grade of 99.6 wt%. Titanium in red mud can be recycled as Ti-rich slag, with TiO2 content of 55.91 wt%, for titanium dioxide production. The FeO in slag also suppressed the side reactions (i.e., carbonization of titanium and iron, reduction of silicon) in smelting process, which improved slag fluidity and iron nugget purity. This technique also provides a new approach for the utilization of V-bearing titanomagnetite, ilmenite, and other similar resources.

A new experimental and numerical simulation method for measuring ash slag fluidity using VOF based on OpenFOAM

A numerical computational model of heated ash flow is proposed using the Volume of Fluid (VOF) method based on OpenFOAM. Established numerical model can accurately calculate the critical flow temperature (Tc) and critical flow velocity (Vc) of ash slag with the error of 1.5 % and 19 % from the experiment, respectively. Forty-five types of ash slag with widely varied properties in China were calculated based on the established model. Results show that high levels (>30 wt%) of Fe2O3 and CaO improve the flowability of the ash slag, and low levels of Al2O3 (10 wt%) also contribute to the flowability of the ash slag. Tc and Vc of the ash were distributed in the range of 1150 ∼ 1400 °C and 0.1 ∼ 1.0 mm/min, respectively. Tc and Vc change in opposite trends with the component content increases, indicating that a higher Tc corresponds to a lower Vc and fluidity reduction. Mathematical models for calculating the Tc and Vc of ash were obtained based on non-linear multiple regression and correlation coefficient, and prediction accuracy was within 10 % and 30 % for Tc and Vc, respectively. The proposed numerical simulation method and prediction model can provide an accurate reference for a wide range of ash fluidity. Also, it was demonstrated that elemental Na has a positive effect on ash flowability based on the model, which is important for measuring slag flowability in slag-tap furnaces.

High-Temperature Ash Melting and Fluidity Behavior upon the Cocombustion of Sewage Sludge and Coal.

Wastewater treatment produces a large amount of sludge, where the minimizing of the disposed sludge is essential for environmental protection. The co-combustion of sludge with coal is a preferable method for sewage sludge disposal from the economic and environmental perspective. The co-combustion of sludge has been widely used in the industry with the advantages of large processing capacity. The melting characteristics of ash are an important criterion for the selection of the co-combustion methods and furnace types. In this study, two types of sludge and four types of coal with different ash melting points were selected, where the ash melting behavior upon co-combustion is investigated by experimental and thermodynamical approaches. Especially, the slag fluidity upon co-combustion is explored via a modified inclined plane method. It has been found that the presence of SiO2 and CaO in sludge substantially enhances its fusion temperature owing to the high content of CaO, while SiO2 acts as a solvent, facilitating the co-melting of other oxides and raising the sludge fusion temperature. Fe2O3 exhibits a specific mass fraction within the range of 10-20%. Furthermore, the presence of CaO and SiO2 prohibits the flow ability of the slag at high temperatures, and Fe2O3 promotes the flow ability for sludge at high temperatures. With increasing base/acid ratio, the sludge flow velocity increases remarkably and peaks at 1.6. The interaction between Fe-Ca and Si-AI significantly affects the fluidity significantly. The findings are expected to optimize the condition of co-combustion and desirable furnace design for the incineration of sludge.

A metallurgical approach for separation and recovery of Cu, Cr, and Ni from electroplating sludge

Electroplating sludge is extensively produced in chemical precipitation–based treatment of electroplating wastewater. It poses a huge threat to environmental safety if not properly disposed, ascribed to its high contents of heavy metals. An innovative metallurgical approach was proposed a to recycle Cu, Cr, and Ni from it. Ammonia leaching was firstly performed to selectively leach Cu from Cr, in which the Cu oxide and sulfide were leached into the leachate while the Cr oxide and Ni carbide (NiCx) retained in the residue. (NH4)2SO4 increased the Cu leaching rate via increasing the dissolved oxygen amount in the ammonia leachate and converting CuS to Cu2+. Under the optimal conditions, the leaching efficiency of Cu achieved 96.5 % while that of Cr was only 0.1 %. In the followed aluminothermic reduction, C in the leaching residue could be effectively removed via a thermal oxidation, which in turn decreased the formation of a C-containing compound of high melting point and benefited the Cr and Ni recovery. Cr and Ni from the residue were reduced and recovered in a Cr-Ni alloy, and the reductant of Al first changed to a refractory Al2O3 and then transformed to a low melting point 12CaO·7Al2O3 with the additive of CaO. This transformation increased the molten slag fluidity and promoted the separation of Cr-Ni alloy from slag. Moreover, the excessive Al increased the Cr and Ni yields and concentrated all of them to be together. Partial Al was used as reductant, and the other Al transferred into Cr-Ni alloy to decrease its melting point. Cr and Ni contents in the smelting slag could be decreased to 0.11 wt% and 0.12 wt% respectively, showing an efficient recovery. This work provided a high efficiency method to recover Cu, Cr, and Ni from waste electroplating sludge.

Review and Perspectives of Ash Slag Fluidity during Co-gasification of Industrial Solid Waste and Coal: Characteristics, Chemistry, Controlling Mechanisms, and Regulation

Review and Perspectives of Ash Slag Fluidity during Co-gasification of Industrial Solid Waste and Coal: Characteristics, Chemistry, Controlling Mechanisms, and Regulation

Boroksit ve üleksit cevherlerinin ferromangan üretiminde kullanımı

This study investigated the possibilities of using low-grade manganese ores in ferromanganese production by smelting process. Fluorspar, ulexite, and boroxide (as flux) were added to manganese ores. Fluxes consisting of activated carbon, charge basicity, and charging materials were used in the smelting experiments. Reference samples without flux were also used for comparison. Charge materials were placed in capped graphite crucibles and smelted at 1650 °C for 2 hours. The metal/slag phases were separated from each other and their chemical analyses were made. At the end of the experiments, it was determined that boron ores instead of fluorspar reduced the manganese leakage in the slag to 1% and increased the manganese in the metal phase to 99%. As a result, it was determined that the fluidity of slag increased more than fluorspar and the smelting time decreased, and it is possible to use boron ores in ferromanganese production.

Physicochemical properties of cinder and alkaline modification in tuyere birdnest region of blast furnace

An important factor in increasing gas utilization and lowering carbon emissions is the removal of cinder from the tuyere birdnest region of the blast furnace. Based on a 2200 m3 blast furnace in China, the physicochemical characteristics of cinder are investigated in this paper. Alkaline flux’s chemical modification and flux injection content are examined to alter the fluidity of cinder slag. Firstly, the basicity and aluminum content of cinder slag are 0.80 and 40.33%, respectively. The melting characteristic of cinder slag is high and the liquid phase fluidity is poor. Secondly, as the content of CaO, MgO, and FeO grow while the viscosity keeps declining, the melting temperature of the cinder first decreases and then rises, rises, and decreases. Compared to Mg2+, Ca2+ and Fe2+ have higher diffusion rates and a stronger interaction modification impact. The potential of flux modification is CaO + FeO > CaO + MgO > CaO > FeO > MgO. Finally, the optimum chemical modification occurs when the basicity of cinder slag is 1.05 and the FeO content is 0.40%. During regular blast furnace operation, 1.62 kg/tHM of limestone and 5.92 kg/tHM of basic oxygen furnace (BOF) slag are injected into the tuyere.

Simulation and experimental study on the effect of iron on the structure and flow properties of coal ash slag

Slag fluidity is an important parameter affecting the stable operation of the gasifier. Above liquid temperature, slag fluidity is closely related to its structure. In the present study, the effect of iron on the three-dimensional connection state between [SiO4]4- and [AlO4]5- tetrahedrons in the SiO2-Al2O3-FeO-CaO slag system at 1773 K was deeply discussed by applying molecular dynamics (MD) simulation and ring statistics methods, and the slag network structure was divided into three rings with different functions according to the three-dimensional connection state. It was found that Fe2+ operated as a network modifier ion and substituted Si4+ and Al3+ in the slag and combined with O2–, thereby continuously depolymerizing higher-order rings into lower-order rings. This phenomenon simplified slag structure, reduced internal friction force, and improved fluidity. Finally, the ring distribution coefficient (Rdc) was defined and it was found that there was a linear relationship between Rdc and viscosity.

Synergistic effects and mechanism of the ternary flux system Fe2O3-CaO-MgO on the coal ash slag fluidity

Basic oxides are usually widespread in low-rank coals and cause many ash-related problems in gasification applications. In this paper, the synergistic effects of the ternary flux system of Fe2O3-CaO-MgO in lowering the ash fusion temperature and improving the viscosity-temperature characteristics were verified by testing the properties of samples with different Fe2O3/(CaO + MgO) ratios. The flow temperatures and temperatures of the critical viscosity decreased and then increased with the decrease of Fe2O3/(CaO + MgO) ratio and reached the lowest point when the iron oxide and alkaline earth metal oxide (CaO, MgO) contents were close to each other. From the perspective of mineral transformation, the formation of low melting point ferroan spinel and the eutectic between anorthite and ferroan spinel are the main mechanisms of synergism. No severe crystallization was observed in the iron-rich slags because Fe2+ could reduce the crystallization tendency. As CaO and MgO dominated the basic oxides, a CaO/MgO ratio of 4:6 effectively limited the crystallization and lower the temperature of critical viscosity (TCV). Thus, when regulating the coal ash fluidity, the content of iron oxide and the ratio between CaO and MgO should be consciously balanced to meet the requirements of the gasifier for slag removal.

Influence of Fly Ash on the Fluidity of Blast Furnace Slag for the Preparation of Slag Wool

Using fly ash as the modifier, blast furnace slag was modified to prepare slag wool, fulfilling the goal of using one type of waste to make use of another type of waste, and it is of great significance for the comprehensive utilization of industrial bulk solid wastes and resource recycling. In the process of forming fiber from blast furnace slag, fluidity is the key factor affecting the smooth formation of fiber from slag. To explore the changes in the fluidity of modified blast furnace slag, the temperature-dependent viscosity of modified blast furnace slag with different amounts of fly ash added was measured, and the effects of fly ash addition on the viscosity, fluidity, and activation energy of particle migration, and slag structure of modified blast furnace slag were investigated. The results indicated that with the increase in the amount of fly ash added, in the high-temperature region (>1324 °C), the viscosity of modified blast furnace slag increases gradually, the fluidity decreases gradually (i.e., the fluidity becomes worse), and the suitable fiber-forming temperature range gradually widens. When the fly ash addition increases from 5% to 25%, the trend of the activation energy of slag particle migration is as follows: increase, decrease, increase significantly, decrease. When the addition of fly ash is less than 20%, the SiO2 content and slag temperature jointly affect the breakage and reorganization of oxygen bridge bonding in the silicon-oxygen tetrahedron in the slag structure. When the addition of fly ash increases to 25%, the slag temperature dominates the breakage of oxygen bridge bonding in the silicon-oxygen tetrahedron in the slag structure. When using fly ash as the modifier to prepare slag wool, from the perspective of slag fluidity and process operability, the optimum addition amount of fly ash is 15%.

Exploring influence of MgO/CaO on crystallization characteristics to understand fluidity of synthetic coal slags

The crystallization has significant influence on fluidity of slag and slag discharge of entrained-flow-bed (EFB) gasifier. The crystallization characteristics and fluidity of five synthetic slags with different MgO/CaO ratios prepared on the basis of the range of oxide contents of Zhundong coal ash were investigated in this study. The results show that with the MgO/CaO ratio increase, the initial crystallization temperature increases, and the main temperature range of crystallization ratio growth moves to higher temperature range gradually which causes Tp25 (Tp25 is the temperature corresponding to the viscosity of 25 Pa·s) to increase. Mg-rich crystals are formed preferentially than Ca-rich crystals when adding the same amount of MgO and CaO during cooling. The effective slagging operating temperature range decrease from 217 °C for the slag with a 0:4 MgO/CaO ratio to 44 °C for the slag with a 4:0 MgO/CaO ratio with the MgO/CaO ratio increase. The slags with 2:2 and 1:3 MgO/CaO ratios show similar effective slagging operating temperature range, Tp25 and the temperature corresponding to the viscosity of 2 Pa·s. However, compared with the slag with a 1:3 MgO/CaO ratio, the crystallization ratio and rate of slag with a 2:2 MgO/CaO ratio are lower within lower temperature range (1300–1200 °C), causing its lower critical viscosity temperature and wider actual operating temperature range. Of the five slags, the widest effective slagging operating temperature range and the lowest Tp25 of the slag with a 0:4 MgO/CaO ratio due to its low crystallization ratio, and wider actual operating temperature range of the slag with a 2:2 MgO/CaO ratio make the two slags suitable for slag discharge of EFB gasifier.

Role of P2O5 in the viscous behavior and structure of yellow phosphorus slag

To clarify the role of P2O5 in the fluidity of yellow phosphorus slag during the centrifugal granulation process, the viscosity and structure of slag with various P2O5 contents were researched. It showed that increasing P2O5 content from 1.38wt% to 5.80wt% enhanced the slag viscosity and activation energy for viscous flow, which reduced the slag fluidity. P2O5 in slag existed as QP0 and QP1 units whose proportions were about 0.89 and 0.11, respectively, irrespective of the P2O5 contents. The introduced P2O5 promoted the polymerization of silicate structure because the metal cations coordinated by non-bridging oxygens in silicate structure became connected with the phosphate structure. P2O5 addition encouraged the conversion of [AlO4] units into [AlO5] units and reduced the polymerization degree of aluminate structure. The variations in the polymerization degree of silicate and aluminate structure played a competitive role in determining the slag viscosity, and the silicate structure was the dominant factor.

Performance of minerals and crystallization properties of synthetic slags with various CaO/MgO in slagging gasifiers

AbstractThe fluidity of coal ash slag at high temperatures is an important factor that determines its applicability and operating conditions in entrained flow gasification. In this study, six synthetic slags with different CaO/MgO rations were prepared to study their effect on slag fluidity. The results showed that the flow temperature of slags decreased first and then increased with the decrease of CaO/MgO ratio. When the slag had a high or low CaO/MgO ratio, or when the contents of CaO and MgO in the slag were similar, the homogeneous slag showed a lower viscosity. The crystallization tendency of Ca was stronger than that of Mg. During cooling, slags with high or low CaO/MgO ratio showed obvious crystallization tendency, and formation of crystals would lead to a sharp increase in slag viscosity, so that the temperature of critical viscosity of slags decreased first and then increased with the decrease of CaO/MgO ratio.

Unveiling the Effect of CaF2 on the Microstructure and Transport Properties of Phosphosilicate Systems.

As an effective flux, CaF2 is beneficial in improving the fluidity of slag in the steel-making process, which is crucial for dephosphorization. To reveal the existence form and functional mechanism of CaF2 in phosphosilicate systems, the microstructures and transport properties of CaO-SiO2-CaF2-P2O5 quaternary slag systems are investigated by molecular dynamics simulations (MD) combined with experiments. The results demonstrate that the Si-O coordination number does not vary significantly with the increasing CaF2 content, but the P-O coordination number dramatically decreases. CaF2 has a minor effect on the single [SiO4] but makes the structure of the silicate system simple. On the contrary, F- ions could reduce the stability of P-O bonds and promoted the transformation of [PO4] to [PO3F], which is beneficial for making the P element-enriched phosphate network structure more aggregated. However, the introduction of CaF2 does not alter the tetrahedral character of the original fundamental structural unit. In addition, the results of the investigation of the transport properties show that the self-diffusion coefficients of each ion are positively correlated with CaF2 content and arranged in the order of F- > Ca2+ > O2- ≈ P5+ > Si4+. Due to CaF2 reducing the degree of polymerization of the whole melts, the viscosity decreases from 0.39 to 0.13 Pa·s as the CaF2 content increases from 0% to 20%. Moreover, the viscosity of the melt shows an excellent linear dependence on the structural parameters.

Structure and adaptability of FexO-SiO2-MgO-15 wt% CaO-0.026 wt% NiO slag with the Fe/SiO2 mass ratio of 1.2 in flash matte smelting

The high-magnesium gangue severely affects the melting performance and fluidity of slag in nickel matte smelting. To detect the adaptability when the CaO-modified slag for treating high-magnesia nickel sulfide concentrate in flash smelting, the synergistic effect of MgO and other oxides on the microstructure and physicochemical properties of slag were analyzed through molecular dynamics simulation associated with the experimental analysis. The results indicate that the MgO content increases from 5 wt% to 11 wt%, part of the Fe2+ ions in silicate are gradually replaced by Mg2+, and some of them are transformed into Fe3+ in the external atmosphere. Accordingly, the generated Fe3+ may destroy the bridge oxygen between Si4+-O2--Si4+ and more complex silicate ions will be dissociated into SiO44+. As a consequence, the Q0 proportion in the modified high-magnesia smelting slag improved from 24.33% to 29.69%, and the n(BO/T) decreased from 1.45 to 1.29. However, when MgO content is high enough, SiO44+ tetrahedron ions may attract Fe2+ and Mg2+ to form (Fe, Mg)2SiO4 with a more robust interaction network structure, resulting in an adverse effect on melting temperature and ions diffusion coefficient. The modified nickel slags with 5–11 wt% MgO represent hospitable melting temperature less than 1320 °C, viscosity lower than 0.091 Pa s, and surface tension between 0.4811 N/m to 0.4838 N/m. In brief, the CaO-modified slag turned out to be conducive for treating high-magnesium nickel sulfide concentrates in flash matte smelting, especially for those containing MgO less than 7 wt%.

Correlation study between microstructure and fluidity of molten slag during co-gasification of coal and indirect coal liquefaction residue: Molecular dynamics simulation

Co-gasification of indirect coal liquefaction residues (ICLR) and coal is an effective way to achieve harmless and sustainable treatment of hazardous wastes. The long-term and stable operation of a co-gasification largely depends on the flow behavior of coal-ash slag. Herein, classical molecular dynamics simulation (MD) and Raman spectroscopy were used to study the microstructure of slag and its relationship with viscosity during the co-gasification of ICLR and coal. The results showed that with the addition of ICLR, the viscosity of slag decreased continuously. This reduction in viscosity was attributed to the increase of FeO content in the system with the addition of ICLR. As a network modifier, FeO could easily provide O2− at high temperatures, thereby destroying bridge oxygen and converting more tricluster oxygen and bridge oxygen into non-bridge oxygen. This significantly reduced the structure complexity and polymerization degree of slag, thereby reducing its viscosity. Finally, the correlation between the microstructural and viscosity was further analyzed. It was found that there was a quadratic function relationship between Q4 proportion and viscosity, and the formula was μ = 0.025(Q4)2-Q4 + 12.03. The purpose of this work was to provide theoretical support for slag flow mechanisms during the gasifier slagging-tapping process and the resource treatment of hazardous wastes.

Evaluating the Effect of MgO/Al2O3 Ratio on Thermal Behaviors and Structures of Blast Furnace Slag with Low Carbon Consumption

In order to clarify the effect of the MgO/Al2O3 ratio on the fluidity of a low-alumina blast furnace slag system, the influence law of slag fluidity with different MgO/Al2O3 ratios was studied based on the composition of blast furnace slag through a viscosity experiment and themodynamic software. By studying the effect of the MgO/Al2O3 ratio on the activation energy of viscous flow of slag combined with FT-IR, the effect of the MgO/Al2O3 ratio on the thermal-stability of low-aluminum slag was interpreted from the microstructure level. Results indicated that the viscosity and the melting temperature of slag both showed a gradual downward trend due to the increase of the MgO/Al2O3 ratio. Besides, the temperature stability of the low aluminum slag became more stable due to the depolymerization of the complex structure of slag. Considering the actual operating conditions of blast furnace, the MgO/Al2O3 ratio of slag was suggested to be controlled to 0.60 and the basicity to be no higher than 1.20 under the conditions of this investigation. Industrial test results showed that the coke rate could be saved as 3.49 kg/t when the MgO/Al2O3 ratio decreased from 0.70 to 0.58.