Steel with a shade of green
The history of steel is not completely clear and varies depending on the source. Frequently mentioned is the Middle Eastern tribe of the Chalybes that invented wrought iron as a precursor to steel around 1800 BC and used it to make weapons. Around 500 BC, the Chinese developed head-high blast furnaces in which they produced cast iron. In both methods, iron ore as the raw material was infused with carbon by mixing it with charcoal. The reducing agent extracts oxygen from the iron ore, thereby producing pig iron – the stage preceding steel, which Indian blacksmiths are assumed to have invented around 400 BC. In addition to adding charcoal, they mixed the iron ore with a few other suitable ingredients (glass shards and green leaves, among other things, according to literary references) and smelted it in crucibles. The resulting alloy called wootz with a carbon content of 1.5 percent is regarded as the first steel and became an export hit. In Damascus, Syrian blacksmiths refined the alloy from the east to create the famous Damascus steel swords. Equally feared were the melee weapons from Toledo, Spain, that were forged from Indian wootz. With them, the Romans conquered an empire.
Nearly 2,000 years passed until steel production took its next decisive step. In 18th century England, “ironmen” used baked coal instead of charcoal and heated their iron mix not in crucibles but in smelting furnaces. The steel quality of the resulting blocks was a quantum leap. Even so, there was still room for improvement. Especially the plants that heated iron to make steel in their red-hot furnaces became increasingly efficient. In the 19th century, steel became a mass product.
Currently, more than 2,500 standardized grades of steel are available worldwide, all of them produced predominantly from pig iron in blast furnaces by blowing in coal dust. For every ton of steel, nearly half a ton is needed as a reducing agent. That’s a fraction of what was required a few hundred years ago, but still too much because two tons of CO2 are emitted per ton of steel. Even the steel corporations have realized that this technology is not sustainable going forward and are thinking about departing from the archaic “blast furnace route” as it’s referred to in technical jargon. Their ambitious goal is to replace carbon by hydrogen to produce green steel. After all, climate protection makes exacting demands on the industry and in the end the quality of the product is the same. By 2050, CO2 emissions are to decrease by 80 percent compared to 1990, according to the Paris Agreement.
Innovations from the steel mill
By the same year, Thyssenkrupp, the steel company with a long history from Germany’s Ruhr region, plans to stop using coked coal and is working on respective concepts. So far, the tradition-steeped steel giant has been known primarily for its “Carbon2Chem” project in which carbon dioxide generated as a process gas is converted into basic chemical substances such as ammonia and methanol by means of water electrolysis to produce fertilizers or fuel from them. A steel mill consists of a coking plant, blast furnace and converter steel plant, plus auxiliary and processing facilities, and is a real energy hog. On the road toward a climate-neutral steel mill, the conversion of the process energy from fossil to renewable sources such as wind and solar power is just one of the smaller obstacles.
Especially the mammoth blast furnaces with their humongous coal consumption contribute to the bad carbon footprint of steel mills. This is precisely the area the steel company targets: In a new process, green hydrogen – i. e., hydrogen produced with renewable energy – is blown into the blast furnace, thereby replacing part of the PCI (pulverized coal injection) coal which results in steam instead of CO2. The advantage: There’s no need for new plant technology. Minor modifications of the existing infrastructure are sufficient. The hydrogen can only replace coke at this stage of the production process proportionally but, at least, CO2 emissions can be reduced by 20 percent in this way. Consequently, this approach is only an intermediate technology.
We are abolishing coal, not the steel millDr. Arnd Köfler,
Going forward, the company will be rolling out new technology – “Blast Furnaces 2.0” – that operate completely climate-neutral and are called direct reduction plants. Thyssen’s competitor Salzgitter, as well, is pursuing this approach that can be integrated easily into steel mills. In direct reduction plants, oxygen is extracted from iron ore by means of a reducing gas. This process takes place under overpressure and at 1,000 °C (1,830 °F). It no longer produces liquid pig iron but solid sponge iron as an intermediate product that’s smelted in an electric arc furnace together with steel scrap and refined into new steel. The technology doesn’t really break new ground and has been anything but climate-neutral due to the previous use of natural gas. This is where the “Salzgitter Low CO2 Steelmaking” project comes in. The plan is to successively replace the share of the fossil energy source by green hydrogen produced from green electricity and to thereby reduce CO2 emissions by up to 95 percent.
With a wind farm and an electrolysis plant, the steel giant is already independently producing green hydrogen for this purpose. In addition, the company is working on increasing the efficiency of producing green hydrogen and tested a high-temperature electrolyzer as part of a research project. At a temperature of around 150 °C (300 °F), this method uses steam generated by waste heat – as a by-product from steel production in a manner of speaking. However, no manufacturer has developed green steel production to industrial marketability yet. The conversion to low-carbon production has to be economically secured because a ton of green steel today costs about two thirds more than its conventional counterpart at the same level of quality. Even so, there’s demand for green steel already – for instance, in the context of carbon-free supply chains.
The automotive industry is one of the biggest customers of the steel industry worldwide. In Germany, for instance, it accounts for 26 percent. Together with its steel suppliers, Mercedes-Benz is pursuing the goal of a green steel supply chain and is planning to launch various vehicle models made of green steel starting in 2025. Today, a sedan from the premium brand consists of 50 percent steel on average, so this material accounts for about 30 percent of CO2 emissions in the manufacturing process. To underpin their plans, the Stuttgart-based manufacturer has joined other renowned investors in the H2 Green Steel startup. The young Swedish company is planning to establish a greenfield steel mill including hydrogen production at a giga scale, with a mammoth 800-megawatt electrolyzer as its core. Electric power is supposed to be supplied by surrounding hydropower stations and wind farms. The raw materials are supposed to consist of 60 percent scrap and 40 percent iron ore. The facility is planned to start producing five million metric tons (5.5 million short tons) of steel per year in 2030. BMW, as well, is investing in a startup that’s developing a method for carbon-free steel production.
Boston Metal is ringing in a new era in metallurgy using an electrolysis cell powered by renewable energy to produce liquid iron that will subsequently be processed into steel. Under a NASA tender around 15 years ago, its founder, Donald Sadoway, a chemist, had come up with a solution for extracting oxygen from the Moon’s surface. It produced molten metal as a by-product which inspired the researcher to adapt the approach to alternative steel production. In the coming years, the young company is going to establish demo plants for its technology in order to further develop it for industrial-scale use.
Schaeffler bearings in steel production
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