Back­ground

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.

Orig­i­nal article (German): Indus­trielle Anwen­dun­gen von Bio­massekar­bon­isat­en. Met­al­lurgie
Author: Marc Schul­ten, Thomas Echter­hof
Pub­lished in: Peter Quicker, Kathrin Weber (Hrsg): Biokohle. Her­stel­lung, Eigen­schaften und Ver­wen­dung von Bio­massekar­bon­isat­en. Springer Verlag 2016, p. 254–277