Effect of Moisture, Hydrogen, and Water–Gas Shift Reaction on the Prereduction Behavior of Comilog and Nchwaning Manganese Ores

The ore–gas reactions in the prereduction zone in a ferromanganese furnace are largely decisive of the overall energy efficiency, carbon consumption, and climate gas emissions in ferromanganese production. An increased understanding of the prereduction zone is thus vital for optimization of the furnace operation. The ore–gas reactions are well known to be governed by kinetics rather than thermodynamics. The raw materials contain various amounts of both chemically bound and surface moisture when fed to the furnace, which may influence the reaction kinetics. This paper presents the investigation of the potential influence of moisture on the prereduction kinetics of two commercial manganese ores, i.e., Comilog and Nchwaning. TGA experiments were carried out by comparing dry and wet ore, as well as introducing H2(g) or H2O(g) to the CO–CO2 gas mixture.publishedVersio

Charcoal as an alternative reductant in ferroalloy production: A review

peer-reviewedThis paper provides a fundamental and critical review of biomass application as renewable reductant in integrated ferroalloy reduction process. The basis for the review is based on the current process and product quality requirement that bio-based reductants must fulfill. The characteristics of different feedstocks and suitable pre-treatment and post-treatment technologies for their upgrading are evaluated. The existing literature concerning biomass application in ferroalloy industries is reviewed to fill out the research gaps related to charcoal properties provided by current production technologies and the integration of renewable reductants in the existing industrial infrastructure. This review also provides insights and recommendations to the unresolved challenges related to the charcoal process economics. Several possibilities to integrate the production of bio-based reductants with bio-refineries to lower the cost and increase the total efficiency are given. A comparison of challenges related to energy efficient charcoal production and formation of emissions in classical kiln technologies are discussed to underline the potential of bio-based reductant usage in ferroalloy reduction process

SiC formation and SiO reactivity of methane at high temperatures

Methane (CH4) is a carbon source currently not in use in the production of silicon. Using a gaseous carbon source instead of conventional solid carbon sources presents an opportunity to rethink silicon production. Preliminary research into this topic has shown CH4 to have a very high SiO reactivity and it might even be a step on the way towards a closed silicon furnace. In this study SiC formation from SiO gas in CH4 containing atmospheres is investigated. A reference gas of pure Ar was compared to H2, CH4 and CO gases. SiC was produced by passing CH4 containing process gases through a layer of SiO producing pellets gas at 1650 °C and 1750 °C. A thermocouple, which measured the process gas temperature, was used to look for signs of thermal cracking of CH4. CH4 contents up to 8% was tested, the lack of a correlation between CH4 content and temperature showed that CH4 does not crack in the current setup despite the temperature being in the range 1650 °C–1750 °C. With a CH4 containing process gas, most of the SiC formed around the gas inlets and within the SiO producing raw material layer. The reaction between SiO and CH4 occurred instantaneously when the two gases met, and appeared to be favored over thermal cracking of CH4. At 1650 °C in H2 or CO containing process gases a thick layer of whiskers formed around the rim of the crucible. The whiskers were examined with STEM using EDS and EELS, which determined the whiskers to be made of SiC. These results suggest that relatively high CH4 pressures can be metastable at temperatures far away from the thermodynamic equilibrium. They also indicate CH4 to exhibit a very high SiO reactivity, which makes it a promising alternative for current carbon sources in the production of silicon.publishedVersio

Reaction Rate Analysis of Manganese Ore Prereduction in CO-CO2 Atmosphere

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Life cycle assessment of renewable reductants in the ferromanganese alloy production: a review

peer-reviewedThis study examined the literature on life cycle assessment on the ferromanganese alloy production route. The environmental impacts of raw material acquisition through the production of carbon reductants to the production of ferromanganese alloys were examined and compared. The transition from the current fossil fuel-based production to a more sustainable production route was reviewed. Besides the environmental impact, policy and socioeconomic impacts were considered due to evaluation course of differences in the production routes. Charcoal has the potential to substantially replace fossil fuel reductants in the upcoming decades. The environmental impact from current ferromanganese alloy production can be reduced by ≥20% by the charcoal produced in slow pyrolysis kilns, which can be further reduced by ≥50% for a sustainable production in high-efficient retorts. Certificated biomass can ensure a sustainable growth to avoid deforestation and acidification of the environment. Although greenhouse gas emissions from transport are low for the ferromanganese alloy production, they may increase due to the low bulk density of charcoal and the decentralized production of biomass. However, centralized charcoal retorts can provide additional by-products or biofuel and ensure better product quality for the industrial application. Further upgrading of charcoal can finally result in a CO2 neutral ferromanganese alloy production for the renewable power supply

Graphite crucible interaction with Fe–Si–B phase change material in pilot-scale experiments

Fe–26Si–9B alloy is a promising high temperature phase change material (HTPCM), due to its high heat of fusion, small volumetric change, abundance, and low cost. Additionally, graphite has been identified as a promising candidate for use as a container material for this alloy. In this study, the feasibility of using graphite for Fe–26Si–9B HTPCM is investigated in a pilot-scale. Specifically, 4–5 kg Fe–26Si–9B master alloys were melted in graphite crucibles using an induction furnace, which underwent 2–3 thermal cycles in the temperature range of 1,100–1,375°C. The results showed that SiC and B4C precipitates were formed in the alloys. However, these carbides were found to be present only on the surface of the solidified alloys and not in the main body. Still, the chemical composition of the Fe–26Si–9B alloy remained relatively stable during the thermal cycles. It was also seen that the graphite crucible withstood the temperature cycles without cracking. Therefore, the use of graphite as a container for Fe–26Si–9B phase change material is a promising approach.publishedVersio

The Effect of Pre-Oxidation on the Reducibility of Chromite Using Hydrogen: A Preliminary Study

The majority of ferrochrome (FeCr) is produced through the carbothermic reduction of chromite ore. In recent years, FeCr producers have been pressured to curve carbon emissions, necessitating the exploration of alternative smelting methods. The use of hydrogen as a chromite reductant only yields water as a by-product, preventing the formation of carbon monoxide (CO)-rich off-gas. It is however understood that only the Fe-oxide constituency of chromite can be metalized by hydrogen, whereas the chromium (Cr)-oxide constituency requires significantly higher temperatures to be metalized. Considering the alternation of chromite’s spinel structure when oxidized before traditional smelting procedures, the effects on its reducibility using hydrogen were investigated. Firstly, the effect of hydrogen availability was considered and shown to have a significant effect on Fe metallization. Subsequently, spinel alternation induced by pre-oxidation promoted the hydrogen-based reducibly of the Fe-oxide constituency, and up to 88.4% of the Fe-oxide constituency was metallized. The Cr-oxide constituency showed little to no reduction. The increase in Fe-oxide reducibility was ascribed to the formation of an exsolved Fe2O3-enriched sesquioxide phase, which was more susceptible to reduction when compared to Fe-oxides present in the chromite spinel. The extent of Fe metallization of the pre-oxidized chromite was comparable to that of unoxidized chromite under significantly milder reduction conditions.publishedVersio

Elimination of phosphorus vaporizing from molten silicon at finite reduced pressure

对有限负压下熔体硅中磷的挥发去除进行研究。采用电子级硅配制SI-P合金,并采用gd-MS来检测实验前后硅中的磷含量。理论计算结果表明:在有限负压下,硅中的磷以P和P2的气体形式从熔体硅中挥发。实验结果显示:在温度1873k、真空度0.6-0.8PA、熔炼3600S的条件下,熔体硅中的磷从0.046%(460PPMW)下降到0.001%(10PPMW)。实验结果与理论结果一致表明:当熔体硅中磷的含量大且炉腔内气压相对较高时,磷的去除与气压高度相关;而当炉腔气压很低时,磷的去除基本与气压无关。原因是在相对高磷含量的熔体硅中,磷主要以P2气体的形式挥发;在磷含量较低时,磷主要以单原子气体P的形式挥发。Elimination of phosphorus vaporizing from silicon was investigated.Si-P alloy made from electronic grade silicon was used.All the samples were analyzed by GD-MS.Theory calculation determines that phosphorus evaporates from molten silicon as gas species P and P2 at a finite reduced pressure.The experimental results show that phosphorus mass fraction can be decreased from 0.046% (460ppmw) to around 0.001% (10ppmw) under the condition of temperature 1 873 K, chamber pressure 0.6-0.8 Pa, holding time 1 h.Both experimental data and calculation results agree that at high phosphorus concentration, phosphorus removal is quite dependent on high chamber pressure while it becomes independent on low chamber pressure.The reason is that phosphorus evaporates from molten silicon as gas species P2 at a relatively high phosphorus concentration, while gas species P will be dominated in its vapour at low phosphorus content.Project(2007J0012)supportedbytheNaturalScienceFoundationofFujianProvince;China;Project(2007HZ0005-2)supportedbytheKeyTechnologicalProgramofFujianProvince;China;Project(BASIC-10341702)supportedbyNorwegianResearchCounci

The use of hydrogen as a potential reductant in the chromite smelting industry

The chromium (Cr) content of stainless steel originates from recycled scrap and/or ferrochrome (FeCr), which is mainly produced by the carbothermic reduction of chromite ore. Ever-increasing pressure on FeCr producers to curtail carbon emissions justifies migration from traditional FeCr production routes. The interaction between hydrogen and chromite only yields water, foregoing the generation of significant volumes of CO-rich off-gas during traditional smelting procedures. For this reason, the use of hydrogen as a chromite reductant is proposed. In addition to thermodynamic modelling, the influence of temperature, time, and particle size on the reduction of chromite by hydrogen was investigated. It was determined that, at the explored reduction parameters, the iron (Fe)-oxides presented in chromite could be metalized and subsequently removed by hot-acid leaching. The Cr-oxide constituency of chromite did not undergo appreciable metalization. However, the removal of Fe from the chromite spinel allowed the formation of eskolaite with the composition of (Cr1.4Al0.6)O3 in the form of an exsolved phase, which may adversely affect the reducibility of chromite. The study includes the limitations of incorporating hydrogen as a reductant into existing FeCr production infrastructure and proposes possible approaches and considerations.publishedVersio