Replacing Fossil Carbon in the Production of Ferroalloys with a Focus on Bio-Based Carbon: A Review

Metallurgical Properties of Biocarbon in Ferroalloy Production-A Review

The significant volume of CO2 emissions contributes to global warming, which has drawn substantial attention. Metallurgical processes contribute to around 30% of these emissions, with ferroalloy smelting alone equivalent to the collective mean CO2 emissions from 11.8 million people. Biocarbon emerges as a promising substitute for fossil reductants, and its research and industrial application have the potential to significantly curtail emissions on a relatively short time scale. As a result, extensive research has been conducted on biobased carbon materials and their practical utilization in metal production processes. In this review, an overview of the methodologies employed to assess the CO2 reactivity, electrical conductivity, reactivity toward slag and SiO, and mechanical strength is illustrated. The impact of characterizations on its behavior within furnaces is concluded. Furthermore, the ongoing efforts to substitute traditional fuels with these environmentally friendly materials in the sintering process are introduced. The metallurgical properties of biocarbon are closely related to its chemical composition and physical characteristics, such as porosity, surface area, and internal structure. It has higher CO2 reactivity, lower electrical conductivity, higher SiO reactivity, and lower mechanical strength than conventional coke. Some of the drawbacks can be addressed through techniques such as densification, pyrolysis, carbonization, and agglomeration, effectively mitigating these limitations. Additionally, the current application situation on sintering has demonstrated that the substitution of specific coke amounts with biobased reductants in the ore agglomeration process can save energy. The incorporation of biocarbon in metallurgy is a feasible and potential way to reduce CO2 emissions, and this work deserves a valuable and significant endeavor.

Enabling CO2 neutral metallurgy for ferrochromium production using bio-based reducing agents

The metallurgical industry is a major source of anthropogenic greenhouse gas emissions. This study explores the replacement of fossil-reducing agents with potentially CO2-neutral bio-based reducing agents. Since reducing agents remove oxygen bonded with metal oxides present in the ore, they are a necessity for the production of metallic elements. The investigated metal is chromium, a major part of stainless steel, and therefore a highly relevant element for the transition from a fossil-based energy system to a renewable one. The state-of-the-art smelting reduction and pre-reduction process followed by subsequent smelting using various reducing agents are investigated in this article. The obtained products, metallurgical efficiencies, energy consumption and off-gas generation were compared. While the products produced with bio-based reducing agents are comparable with the reference trials using metallurgical coke regarding the major components in the metal, the concentration of detrimental phosphorus is significantly higher using bio-based reducing agents. The metallurgical efficiency of the process is comparable to the usage of bio-based reducing agents and coke. However, the energy consumption and the generation of off-gas is higher, when coke is replaced by bio-based reducing agents.

Life Cycle Based Climate Emissions of Charcoal Conditioning Routes for the Use in the Ferro-Alloy Production

Renewable reductants are intended to significantly reduce CO2 emissions from ferro-alloy production, e.g., by up to 80% in 2050 in Norway. However, charcoals provide inferior properties compared to fossil fuel-based reductants, which can hamper large replacement ratios. Therefore, conditioning routes from coal beneficiation was investigated to improve the inferior properties of charcoal, such as mechanical strength, volatile matter, CO2 reactivity and mineral matter content. To evaluate the global warming potential of renewable reductants, the CO2 emissions of upgraded charcoal were estimated by using a simplified life cycle assessment, focusing on the additional emissions by the energy demand, required chemicals and mass loss for each process stage. The combination of ash removal, briquetting and high-temperature treatment can provide a renewable coke with superior properties compared to charcoal, but concomitantly decrease the available biomass potential by up to 40%, increasing the CO2-based global warming potential of industrial produced charcoal to ≈500 kg CO2-eq. t−1 FC. Based on our assumptions, CO2 emissions from fossil fuel-based reductants can be reduced by up to 85%. A key to minimizing energy or material losses is to combine the pyrolysis and post-treatment processes of renewable reductants to upgrade industrial charcoal on-site at the metallurgical plant. Briquetting showed the largest additional global warming potential from the investigated process routes, whereas the high temperature treatment requires a renewable energy source to be sustainable.

Metallurgical Coke Production with Biomass Additives: Study of Biocoke Properties for Blast Furnace and Submerged Arc Furnace Purposes

Biocoke has the potential to reduce the fossil-based materials in metallurgical processes, along with mitigating anthropogenic CO₂- and greenhouse gas (GHG) emissions. Reducing those emissions is possible by using bio-based carbon, which is CO₂-neutral, as a partial replacement of fossil carbon. In this paper, the effect of adding 5, 10, 15, 30, and 45 wt.% biomass pellets on the reactivity, the physicomechanical, and electrical properties of biocoke was established to assess the possibility of using it as a fuel and reducing agent for a blast furnace (BF) or as a carbon source in a submerged arc furnace (SAF). Biocoke was obtained under laboratory conditions at final coking temperatures of 950 or 1100 °C. Research results indicate that for BF purposes, 5 wt.% biomass additives are the maximum as the reactivity increases and the strength after reaction with CO₂ decreases. On the other hand, biocoke’s physicomechanical and electrical properties, obtained at a carbonization temperature of 950 °C, can be considered a promising option for the SAF.