Materials Processing Fundamentals 2023

A long-standing and effective way to recycle lead-acid battery materials is through processing of lead compounds into lead product within a reverberatory furnace. Exploration of process and design changes through unit modification can be costly, time-consuming, and potentially harmful to operational efficiency. Modeling of process behavior, including furnace heat transfer and material reduction/decomposition, can however be difficult. To this end, a method for reflecting the production capabilities of a lead reverberatory furnace under various operational conditions has been developed. Reactions of the lead compounds have been approximated within a steady-state computational fluid dynamics simulation by adding or removing heat from the domain depending on local thermal conditions. With this, process and design changes can be explored in the simulated environment before moving onto more-advanced stages of modeling or experimentation.

It is of great significance to study the variation of the multiphase flow during the entire service process of an impeller to improve the dispersion of the desulfurizer and the desulfurization efficiency during the KR desulfurization process. In the current study, the key dimensions of an actual KR impeller during the service process were quantitatively measured first. Then, a three-dimensional model coupled with the k-ε turbulence model, VOF multiphase flow model, DPM model, UDS model, and unreacted core desulfurization model was established to predict the multiphase flow and desulfurization during the KR mechanical stirring process with different wearing impellers. The results show that with the increase of the wear degree of the impeller, the stirring effect was gradually weakened, resulting in a gradual weakening of the desulfurization efficiency. The desulfurization end sulfur content was 58.2 ppm after the impeller employed 220 heats, which was more than 4 times higher than the 13.0 ppm with a new impeller.

In this work an OpenFOAM-based framework to simulate the evolution of microsilica, which is an important byproduct in the silicon/ferrosilicon industries, is proposed. The framework decouples the combustion reaction of CO and SiO from the microsilica generation based on the assumption that the combustion occurs in an oxygen rich environment - SiO\(_{2}\) generated by combustion is much larger than its depletion due to particle evolution. The combustion of the reactants in the furnace hood is performed using rhoReactingBuoyantFoam, and its results are used as input to a population balance solver that simulates the particle nucleation and growth (due to mass transfer onto the particle surface) as well as depletion of SiO\(_{2}\). The framework predicts particles of size around 30 nm at the outlet which is approximately in the smaller sizes of the particles observed in microsilica during experiments reported in literature.

In order to investigate the influence of oxygen content in sintering flue gas on the heat generated by coke combustion and sintering flue gas, the thermodynamic calculation was carried out with FactSage software. Combustion kinetics under different oxygen content was studied with thermogravimetric analyzer. Thermodynamic research results showed that under the condition of sintering with iron ore fines, the oxygen content in the combustion-supporting air was abundant. When the oxygen content was more than 7%, the solid fuel in the sintered layer could meet the combustion conditions and release all the heat. Kinetic experiment results showed that the combustion rate of coke breeze in 5 min with 13% oxygen content in flue gas was equivalent to combustion rate of coke breeze in 2.75 min 21% oxygen content in flue gas. The research is helpful for energy recovery of sintering process and reducing carbon emission of blast furnace ironmaking.

This paper covers the determination of time-spatial varying mold heat flux using mold temperatures measured by fast response thermocouples at a frequency up to 60 Hz. A two-dimensional transient inverse heat conduction problem (2DIHCP) is established, where 2DIHCP is developed based on the sequential function specification method implemented with the spatial regularization terms to reduce the fluctuations in the estimated heat flux in both time and spatial domain. Then, the inverse problem was validated using a designed numeric test-problem. Finally, the inverse problem is applied to calculating the heat flux across the mold hot surface for a continuous casting trial using the mold simulator.

The continuous casting-rolling process is widely used due to the lower energy consumption and its compact process. However, the defect in continuous casting slab severely limits the development of the continuous casting-rolling technology. In this paper, based on big data mining technology, the quality prediction model for hot rolled coils and the corresponding optimization method for continuous casting parameters were proposed. Firstly, the GA (Genetic algorithm)-BP (Backpropagation) neural network prediction model with high accuracy was constructed according to the characteristics of actual production data. Then, the effect of continuous casting parameters on the probability of defects occurrence was investigated with the established model. The results show that the defects occurrence probability decreases firstly and then increases with the casting speed, as well as the temperature of molten steel, which are consistent with metallurgical theory. Meanwhile, the optimum casting speed and mold level are 1.3 m/min and 8200 mm, respectively. When the flow rate of argon blowing for stopper and nozzle are restricted to 8.5 and 8 L/min, the defects occurrence probability will be lower. Furthermore, the optimum critical values of temperature difference of mold cooling water and inlet temperature are 8 °C and 35 °C, respectively. This paper can provide the guidance for narrow range control of continuous casting parameters and contribute to the production of high-quality steel.

In the current study, a two-dimension solidification and heat transfer model was developed based on the slab continuous casting (CC) process in a domestic steel plant. The layout of jet nozzles of segment 2 and segment 3 in secondary cooling zones was adjusted to optimize the distribution of temperature along the width direction. The following main findings indicate that the temperature was more uniform. In segment 2 and segment 3, middle jet nozzles were replaced by those in side positions, and the distribution of water flow rate and temperature along the width direction was more uniform. In the outlet of segment 2, except for the slab corner, the fluctuation range of the temperature along the width direction decreased from 39.7 to 14.1 °C. In the outlet of segment 3, except for the slab corner, the fluctuation range of the temperature along the width direction decreased from 40.4 to 17.3 °C.

The production of steel casting can in some cases be complicated and difficult. To produce quality castings, it requires the casting to be clean and free from any defects. One of the main casting defects is hot tearing, also known as a crack or shortness. This phenomenon represents the formation of an irreversible failure (crack) in the steel semisolid casting. The second defect that commonly occurs in casting is porosity. Porosity is often used to describe any void or hole found in a casting. To control the porosity, you need to understand its sources and causes. Porosity can occur either by gas formation, solidification shrinkage, or non-metallic compound formation, all while the metal is liquid. This experimental work is focused on reducing the porosity defects in steel casting components at a production scale. The produced casting component was strongly affected by porosity defects.

The fluctuant solidification behavior of the solute-enriched liquid phase in the centerline of the continuous casting billets, which is closely related to the centerline segregation defect, will significantly affect the central quality uniformity along the casting direction. Meantime, the fluctuation phenomenon of the solidification end point during the continuous casting process is still unclear. In this work, the solid fraction in the centerline of the billets was analyzed based on a three-dimensional numerical model, and the fluctuation characteristics of the centerline solid fraction were revealed. At the same time, through the analysis of the actual solidification structure, the fluctuation of the centerline local cooling rate was also investigated, which was associated to that of the solid fraction. On this basis, according to the periodic fluctuation characteristics of centerline solid fraction and local cooling rate, the periodic fluctuation mechanism of the solidification end point of continuous casting was proposed.

Dispersed multiphase fluid flows, in which one phase is distributed as small inclusions in another, occur in a wide range of chemical and process industries. In pyrometallurgical smelting, these may manifest in the form of decoupling of gases from one of the molten phases. This can cause slag foaming, which occurs when gas bubbles are unable to escape from the viscous slag rapidly enough and a low-density foam layer builds up at the surface of the slag pool. Although uncontrolled slag foaming can cause hazardous equipment failures, controlled foaming has the potential to significantly reduce energy consumption of many smelting processes. Improvements in the understanding of slag foaming are therefore of value both from health and safety as well as economic and environmental aspects. This paper presents the evaluation and application of the dynamic multi-marker (DMM) method, a novel meso-scale computational fluid dynamics algorithm for efficient modelling of dispersed-phase systems, for slag foaming problems. Foaming behaviour and gas–liquid decoupling are studied using numerical simulations of test systems, and the results are compared to established empirical relationships.

A three-dimensional numerical model coupled the fluid-flow simulation and the reaction kinetics was established to study the evolution of the sulfur content in the molten steel. The VOF, k-ε, and DPM models were employed to simulate the fluid flow of three phases in the ladle furnace, including the steel, the slag, and the air. Reactions between the steel and the slag were considered in the simulation using a series of user defined functions. The steel-slag reactions had a significant effect on the sulfur content in the molten steel, resulting the continuous decrease of the sulfur content. The [S] content reduced from 0.077 wt% into 0.01 wt% in 50 min. The distribution of [S] in the molten steel was uneven, with the lowest near the steel-slag interface and the highest in the middle zone between the argon blowing point and the ladle wall.

Based on the minimum Gibbs free energy method, a modified thermodynamic model was established to predict the composition of inclusions during the calcium treatment process. Three types of phase were contained in the steel-inclusion system, including the molten steel phase, the liquid inclusions phase, and the solid inclusions phase. The Wanger model was applied to calculated activities of elements in the molten steel. Reported interaction parameters were evaluated and used to improve the accuracy of thermodynamic calculation results. The coexistence theory was applied to calculate activities of Al₂O₃ and CaO in liquid inclusions. According to the thermodynamic calculations, the effect of T.Ca content in the molten steel on the transformation of inclusions was discussed. Combining the established thermodynamic model and a calcium yield prediction model, a software for precise control of calcium treatment process was also developed.

The start-up and operation of DC furnaces for ferrochrome and titania slag but also ferronickel and ferrocobalt have proven again and again to be more challenging than anticipated. A combination of few furnaces in operation, a limitation on shared operational experience, quick response times between operational decisions and consequences, and a limited fundamental understanding of process mechanisms is a part of the causes for the results. Understanding the process chemistry, energy balance, and interactions between them is fundamental to investigating the mechanisms taking place in a DC furnace. As part of a PhD investigation of process mechanisms and behaviour of DC ferrochrome furnaces, this paper will describe the potential operational consequences of ignoring something as basic as the formation enthalpy of reductants. Only one of many pitfalls, reductant is used as an example to demonstrate that fundamental understanding of process chemistry is required for designing, operating, and studying DC furnaces. Only with at least an understanding of process chemistry it can be possible to connect operational experiences to process mechanisms. The paper will conclude with a brief discussion of the presented results, and how these relate to the PhD study.

Electric arcs are necessary for high Si yield in submerged arc furnaces (SAFs) for Si/FeSi production, and a certain fraction of heat dissipation in the arc enables optimal operating conditions. Direct measurement of the arc characteristics is impossible due to hostile conditions inside the SAF, so controlling the heat dissipation is both a science and an art. The arcs exhibit non-linear electrical characteristics and behave in a complex manner. Hence, implementing a data acquisition (DAQ) system to collect current and voltage waveforms typically on the electrodes or transformer connections combined with appropriate signal processing offers an estimate of the actual arc parameters, enabling improved understanding of the arcing in the furnace, and improving furnace operation. In this paper, a DAQ system gathering data from a FeSi SAF will be discussed, and the data is processed and used to determine various furnace conditions including arc and charge current as well as harmonics.

The high grade iron ore has depleted necessitating the need to investigate the use of low grade ores that may include arsenic-containing iron ores. Arsenic (As) is volatile increasing the possibility of its removal from the ore by roasting or sintering. As volatilization from iron ore is limited by many chemical interactions with other metallic elements and oxides within the ore. The possibility of the volatilization of As from a hematite ore was investigated using the thermogravimetric-differential scanning calorimetry (TG-DSC) and the vertical tube furnace by raising the temperature at a rate of 10 K/min in the temperature range of 298 to 1623 K. Predictions of the most stable As compound formed in the sintering temperature range were done first using basic thermodynamics, then X-ray diffraction (XRD) measurements were done on the cooled and crushed samples to identify the change in phases after heating to temperatures above 1273 K. Electron probe microanalysis (EPMA) verified the possibility of the existence of some of the phases identified by XRD. Results showed that the percentage weight loss of the pellet and As loss from the pellet increased with temperature. Metallic element distribution above 1273 K showed that As was highly concentrated in the same area as Ca, Si, and Al in agreement with the XRD results and the thermodynamic predictions that showed that 3CaO·2As₂O₅(s) and the AlAsO₄(s) as the most stable As-containing phases even after heating to temperatures of about 1623 K.

An efficient flocculation flotation-hot filtration process was developed to recover elemental sulfur and sulfide minerals from a pressure acid leaching residue of zinc sulfide concentrate. The particle size distribution of the residue indicated that the portion of thin particle with the size of -37 um reached 67.65 and 36.27% of sulfur in the residue was distributed in this size fraction, necessitating the flocculation flotation for recovering the elemental sulfur and sulfide minerals. 94.59% of the sulfur was recovered with the flotation process of one-time blank rougher, two-time agent-added roughers, and two-time blank cleaners with Z-200 as the collector and polyacrylamide as the flocculant. After hot filtration for the flotation concentrate at 145 °C for 2 h, 85.32% of the elemental sulfur in the concentrate was recovered, and its product purity reached 98.64%. The filter cake of sulfide minerals can be returned to the leaching stage for zinc recovery.

Using an unsupervised convolutional neural network classifier, an automated workflow to generate the process map for printing Ti-6Al-4 V with laser powder bed fusion with minimal human supervision is proposed. Single scan vectors using a range of laser powers and scan speeds were printed on a bare Ti-6Al-4 V baseplate, which were then imaged using optical microscopy without further material preparation steps. After resizing and thresholding, the resulting dataset was used to train the neural network into automatically differentiating the tracks into categories. Post-analysis reveals that the model can differentiate between commonly observed track morphologies and map out the viable processing window automatically for the alloy.

In China, for the production of ferroalloys such as ferrosilicon and ferroaluminium, the mould casting is usually used, and the material of casting mould is usually cast iron. However, in the process of periodic heating and cooling, cracks appear at the edge of mould. This severely affects the service life, thus increasing the casting cost, which has become a bottleneck of the development of ferroalloy industry. In the casting process, the lower thermal conductivity of the cast iron causes greater alternating thermal stresses, which are the reason for damages of cast iron moulds. In this study, the copper which has excellent heat transfer properties was used as the mould material to develop a new type of ferroalloy mould. In order to study the service performance of copper mould, the casting process of ferroalloy in copper mould and the temperature field of copper mould under different water cooling intensities were simulated by using ANSYS Workbench 17.0 software. The results show that under water cooling conditions, the maximum temperature of the mould cannot reach 1083℃ in the casting process, so the molten ferroalloy would not destroy the copper mould, which has low melting point, proofing the feasibility of copper as the mould material. In addition, the water cooling intensity of the mould has great influence on the cooling rate of the mould. And the optimized water cooling intensity is important for proper operation of the copper moulds.

The length of the transition slab may be decreased by manipulating differences in temperatures or densities of new and old grade steels. The molten steel liquidus temperature and density are related to the composition. For most elements in steel, both the liquidus temperature and density of the molten steel decrease with an increase in their mass fraction. Therefore, the temperature and density of molten steel cannot simultaneously shorten the transition slab. This study compared the effect of temperature and density on the length of the transition slab using numerical simulation methods based on flow, heat transfer, and mass transfer. The model was verified using a physical simulation and an industrial experiment. Finally, the effects of temperature and density on the transition slab length were elucidated.

In this paper, the influence of structural parameters such as the area and shape of the side hole of the submerged nozzle on the flow behavior of steel and the distribution of liquid slag layer in the mold of large section stainless steel continuous casting slab at high casting speed is studied by combining physical model with mathematical simulation. The results show that with the increase of side hole area, the fluctuation of molten steel level in the mold decreases; the impact depth increases; the flow rate of molten steel decreases; the distribution of liquid slag layer is gradually uniform, and the number of slag entrainment decreases. Compared with the rectangular side hole shape, when the side hole shape is oval, the fluctuation of molten steel level in the mold is reduced; the distribution of liquid slag layer is more uniform, and the number of slag entrainment is reduced. The research results can provide a theoretical basis for designing a reasonable submerged nozzle.