Charcoal as an alternative reductant in ferroalloy production: A review

This 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

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

This 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

Modeling the influence of potassium content and heating rate on biomass pyrolysis

This study presents a combined kinetic and particle model that describes the effect of potassium and heating rate during the fast pyrolysis of woody and herbaceous biomass. The model calculates the mass loss rate, over a wide range of operating conditions relevant to suspension firing. The shrinking particle model considers internal and external heat transfer limitations and incorporates catalytic effects of potassium on the product yields. Modeling parameters were tuned with experimentally determined char yields at high heating rates (>200 K s−1) using a wire mesh reactor, a single particle burner, and a drop tube reactor. The experimental data demonstrated that heating rate and potassium content have significant effects on the char yield. The importance of shrinkage on the devolatilization time becomes greater with increasing particle size, but showed little influence on the char yield

Characterization and reactivity of charcoal from high temperature pyrolysis (800-1600°C)

This study presents the effect of wood origin and heat treatment temperature on the CO2 reactivity, nanostructure and carbon chemistry of chars prepared at 800, 1200, and 1600° C in slow pyrolysis reactors. The structure of charcoal was characterized by transmission electron microscopy, Raman spectroscopy, mercury intrusion porosimetry and N2 adsorption. The CO2 reactivity of char was investigated by thermogravimetric analysis. Results showed that spruce and oak chars have similar reactivity at all heat treatment temperatures. The oak char prepared at 1600 C contained long and at graphene layers and interplanar distance that is similar to graphite and thus, was more ordered than the spruce char. The TEM analysis showed that charcoal had structural characteristics of non-graphitizing carbon. Thus, increasing heat treatment temperature increases the graphitization of char structure, leading to the reactivity that is nearly similar to that of low reactive metallurgical coke

Hydrothermal carbonization of olive wastes to produce renewable, binder-free pellets for use as metallurgical reducing agents

Torrefaction or hydrothermal carbonization processes were compared for conversion of olive pulp into metallurgical reducing agent. The dependence of yield, CO2 reactivity, and mechanical properties to reaction time and heat treatment temperature was investigated. Hydrochar yield increased with increasing residence time and the maximum solid yield was observed for a residence time of 15 h. On the other hand, CO2 reactivity slightly decreased with increasing heat treatment temperature at a residence time of 2 h. Notably, the CO2 reactivity of hydrochar was less than that of olive pulp char produced by torrefaction, approximating that of carbon-based reducing agents derived from non-renewable resources. An additional heat treatment improved hydrochar pellet durability to greater than 95%, whereas stable torrefied char pellets could not be produced under any set of conditions. Hydrothermal carbonization is superior to torrefaction for production of renewable reducing agents with reactivity and mechanical properties comparable to those afforded by reducing agents from non-renewable sources

Characterization of renewable reductants and charcoal-based pellets for the use in ferroalloy industries

This study investigates the effect of high-temperature pyrolysis and post-treatment processes on spruce and oak charcoal yields and CO2 reactivity in a slow pyrolysis reactor. Post-treatment processes such as co-pyrolysis of biomass and recirculated tar mixture with that to the distillation of the charcoal-tar blend gave similar increase in charcoal yields. From a technological standpoint, co-pyrolysis of charcoal and tar mixture decreased the CO2 reactivity of the charcoal approaching that of fossil-based coke. This emphasize the importance of tar addition and high temperature treatment on charcoal properties. Moreover, the findings of this work show the potential use of the tar organic fractions as a binder that can be used for the charcoal pellet preparation. The results are promising as they show that the charcoal-based pellets have comparable properties of pellets from herbaceous biomass leading to the cost reduction in charcoal transportation and storage

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.</p

Supercritical extraction and microwave activation of wood wastes for enhanced syngas production and generation of fullerene-like soot particles

This work demonstrated that supercritical carbon dioxide extraction is effective as a pre-treatment technology to generate soot particles with the fullerene-like structure and increase syngas yield from extracted residues during coupled microwave activation with gasification. Supercritical carbon dioxide extraction removes over half of the fatty and resin acids from needles and branches, whereas the extraction of needles generates greater yields of value-added compounds. The high yields of extractives indicate the effective conversion of waste wood for the sustainable production of value-added chemicals. The wood extraction did not influence the solid residue yields during pyrolysis/gasification emphasizing the significant potential of integrating the extraction process into the holistic biorefinery. Interestingly, supercritical carbon dioxide extraction had a significant effect on the structure and quality of soot particles formed. The differences in the extractives composition led to the formation of needle soot particles with a porous and less ordered nanostructure, whereas the soot branches obtained a ring graphitic structure. The greater yields of steroids and terpenes during the extraction of needles compared to the branches pretreatment indicated the influence of the extractives type on the soot nanostructur

The effect of wood composition and supercritical CO2 extraction on charcoal production in ferroalloy industries

This work demonstrates that the integration of supercritical carbon dioxide extraction with slow pyrolysis is an effective method for the production of value-added chemicals and charcoal that is an attractive alternative to coke for industry. Integration of technologies is key for the development of holistic biorefineries that exploit all parts of the biomass feedstock and generate little or ideally no waste. In fact, the use of waste or low valued wood fractions is attractive due to their plentiful abundance and lack of exploitation. Supercritical carbon dioxide has been demonstrated to be effective at the removal of over half of extractives from low quality wood and forestry wastes, which can account for up to 11 wt %, of the dried biomass in waste needles. High extractive yields by supercritical carbon dioxide extraction illustrates the potential of utilizing low quality wood as an alternative feedstock for the sustainable production of value-added chemicals. High yields of steroids and derivatives, terpenes and other plant metabolites were obtained in the extracts of needles, branches and bark. Importantly, supercritical carbon dioxide extraction had little impact neither on the physical properties of original wood nor on the yield of solid charcoal. This indicates that extraction by supercritical carbon dioxide can be used as a method for adding further value to the process by removal of bio-based chemicals, whilst still maintaining the yield of the solid fuel product. Moreover, the heat treatment temperature and supercritical carbon dioxide extraction had a significant impact on the tar yields during pyrolysis, leading to an increase in naphthalene, polycyclic aromatic hydrocarbons, aromatic and phenolic fractions with greater temperature. These results are promising as they show that the charcoal obtained from this renewable feedstock could be used as an alternative to fossil-based coke in applications including ferroalloy industries

Effect of operating conditions and feedstock composition on the properties of manganese oxide or quartz charcoal pellets for the use in ferroalloy industries

This study investigates the effect of heat treatment temperature on the properties of charcoal composite pellets used for the reduction of ferroalloys. The heavy fraction of biooil was used as a binder for the charcoal ore pellet preparation. The effect of heat treatment temperature on the pellet shrinkage was related to the degree of reduction which varied with feedstock and ore composition. The results showed that the size and shape of the charcoal pellets were not affected by the biooil devolatilization. Manganese charcoal pellets showed higher electrical resistance during pyrolysis, whereas the structure, composition and electrical resistance of silica composite pellets remained unaffected by heat treatment temperatures < 1650 °C. However, the secondary heat treatment decreased the CO2 gasification reactivity and electrical resistivity of charcoal composite pellets. In addition, the findings of this work demonstrate the potential for using biooil as a binder for the charcoal composite pellets used in ferroalloy industries. The composite pellets are suitable to pre-reduce the manganese ore in the low temperature zones of an industrial furnace, and the charcoal pellets can be used as an alternative bed material. However, the high CO2 reactivity may create challenges during the direct replacement of metallurgical coke with the bio-reductants