The steel and metals industry has been developing new solutions for years to reduce its greenhouse gas emissions from fossil fuels. This is because the steel and metal industry is responsible for 5-7 percent1Rita Khanna, Kejiang Li, Ziming Wang, Minmin Sun, Jianliang Zhang, Partha Sarathi Mukherjee, 11 – Biochars in iron and steel industries, Editor(s): Mejdi Jeguirim, Lionel Limousy, Char and Carbon Materials Derived from Biomass, Elsevier, 2019, Pages 429-446, https://doi.org/10.1016/B978-0-12-814893-8.00011-0 of global greenhouse gas emissions. Biochar can also be used effectively in this industry as a substitute for fossil raw materials, thus helping to improve the environmental footprint.
However, this application is not suitable for carbon preserving and no carbon removal credits can be issued. Thus, for this application the term biocarbon should be used instead of biochar.
Advantages of biocarbon in the metal industry
- Very high heating value2Ye, L., Peng, Z., Wang, L. et al. Use of Biochar for Sustainable Ferrous Metallurgy. JOM 71, 3931–3940 (2019). https://doi.org/10.1007/s11837-019-03766-4 and good energy conversion
- Replacement of fossil reducing agents and fuels
- Significantly improved carbon footprint of the steel
Degree of Development
The use of biocarbon in the European iron, steel and metal production is not yet established, although it is currently becoming more widespread in the Scandinavian countries. The high price compared with fossil raw materials, as well as transport and supply problems, have so far hindered widespread use.
Biocarbon is used both on a development and pilot scale and on an industrial and commercial level in steel production and metallurgy. For example, biocarbon is used in the sintering of iron ore. When coke breeze is replaced with biocarbon (up to a maximum of 60% proportionally), promising ecological and economic advantages arise, in addition to only very minor losses in sintering material quality. The use of biocarbon in sintering requires that the biocarbon is adapted in its microstructure and chemical reactivity.3YE, Lei, et al. Use of biochar for sustainable ferrous metallurgy. Jom, 2019, 71. Jg., Nr. 11, S. 3931-3940.
Crucial properties of biocarbon for the production of metallurgical coke are mainly flowability, expansion/contraction of the biocarbon-charcoal mixture, particle size, CO2 reactivity of the biocarbon, and the strength of the produced biogenic coke.4Rita Khanna, Kejiang Li, Ziming Wang, Minmin Sun, Jianliang Zhang, Partha Sarathi Mukherjee, 11 – Biochars in iron and steel industries, Editor(s): Mejdi Jeguirim, Lionel Limousy, Char and Carbon Materials Derived from Biomass, Elsevier, 2019, Pages 429-446, https://doi.org/10.1016/B978-0-12-814893-8.00011-0
Another application of biocarbon in steel production is in composite pellets, which are used in the production of sponge iron for direct reduction processes. Biocarbon partially or completely substitutes hard coal in the composite pellets, and the energy conversion is technically feasible, thus the process has environmental advantages. Biocarbon is also used as a fuel substitute for coke and pulverized fossil coal in the blast furnace process without technical barriers. Nevertheless, the quantity added and the process must be strictly controlled because mass and heat transfer as well as temperature profile and gas distribution are changed. If biocarbon is to be used in the electric arc furnace process, it can only be used with prior conditioning. Biocarbon must be compacted to reduce its reactivity due to the high specific surface area so that it can be used in the electric arc process as a fuel, slag former and steel carburizer.
In some metallurgical applications, there are still certain technical barriers to biocarbon. Biocarbon used in the coking process must be precisely selected in terms of particle size, ash content and porosity, and the addition must be strictly controlled so that the quality of the resulting coke is consistent.5YE, Lei, et al. Use of biochar for sustainable ferrous metallurgy. Jom, 2019, 71. Jg., Nr. 11, S. 3931-3940.
Application
The optimum biocarbon for the application is one with high carbon content, low ash and water content, and biomass-based coke made from compacted biocarbon with additives. This is usually available in the form of pellets.
Suitable source materials are, for example, residual wood of pine and spruce, as well as waste wood from the construction industry and dismantling of buildings. For targeted use, the biocarbon must be carefully selected, because each biocarbon is different due to the feedstock and the way of production.
Approval & Certification
Within the certification system of the European Biochar Consortium (EBC), the EBC-BasicMaterial or EBC-ConsumerMaterial standard is recommended for biochar used in the steel and metal industry.
Intra-industry standards do not yet exist. However, interest in green steel is increasing and so is the activity to standardize application-specific biocarbon parameters. The physical properties of the biocarbon are based on the fossil coal used to date.
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