The production of metallic raw products is one of the most important industrial sectors. Germany, for example, is one of the world’s leading countries in the production of steel, aluminium, lead, copper and tin. According to the authors Schulten and Echterhof (Industrielle Anwendungen von Biomassekarbonisaten. Metallurgie, in Quicker/Weber 2016, Biokohle), it is possible to substitute fossil coal or coke with biochar in almost all areas of metallurgy. The processes for metal extraction require large quantities of energy raw materials and carbon carriers to reduce metallic ores, i.e. to separate oxygen from metal. The metallurgical industry is one of the largest consumers of fossil coal in the world and thus also one of the largest sources of CO2 emissions. In addition: Both ore and coking coal prices have risen by 200% in some cases in recent years. In conjunction with CO2 certificate trading, these cost increases mean that operators of metallurgical processes are increasingly considering the use of alternative input materials such as biomass carbonates. However, the requirements placed on the carbonates vary greatly depending on the process.
Biochar in sintering plant & blast furnaces
According to Schulten and Echterhof, the biomass carbonates must have a high content of fixed carbon with low volatile components for use during the sintering process (thermal process step as pretreatment for the iron ore). If this is the case, up to 100% of the fossil fuels can be replaced by biochar in this process. No technical limitations were found in experimental studies, in some cases even an increase in productivity was observed.
The situation is similar with the use of biomass carbonates for iron production in blast furnaces. A certain amount of coke can be saved by injecting PCI (pulverized coal injection) as fuel. This biochar has carbon contents of more than 80 mass percent and volatile components of at least 25 mass percent. Several studies have shown that injection rates of 150–200 kg/Mg of pig iron can be achieved. Due to their larger specific surface area, some of the biomass carbonates tested have even better properties than the hard coal used conventionally.
Biochar in the electric steel process
According to the authors, the share of electric steel production in crude steel production in Europe is increasing all the time. Steel scrap (98% in Germany), sponge iron or pig iron and various surcharges are used. These come into an electric arc furnace and are melted down there with the help of energy sources such as coal. In addition to the steel melt, a slag is formed which is intended to absorb impurities from the scrap. In industrial practice, the use of fossil coal causes about 40–70% of the direct CO2 emissions of the electro-blasting process. According to Schulten and Echterhof, coal is used in electric arc furnaces for several reasons: It is used for basic carburisation, contributes to the formation of foam slag and realises a chemical energy input during oxidation. Tests have shown that biomass carbonates from palm kernels are a viable alternative to fossil metallurgical coke for the slag foaming process. A research project funded by the European Research Fund for Coal & Steel also found a larger increase in the volume of slag in the use of biomass carbonates compared to fossil coal. Further studies in which fossil batch coal was replaced by biochar also showed the general suitability of biomass carbonates and that these have no negative influence on the process.
Biochar in the production of non-ferrous metals
Not only in the field of iron metallurgy, but also in the production of non-ferrous metals coal products are required as reducing agents or energy sources. For example, in melting processes in the copper and aluminium industry, lead and zinc production. According to the authors, the use of alternative carbon carriers as reducing agents is also possible here.