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| Fig. 1: Traditional Blast Furnace (Source: Wikimedia Commons) |
Steel is an essential material for building infrastructure due to its strength, durability, and versatility. Furthermore, it will only play a more prominent role in the next couple of decades as developing countries modernize and expand their cities. Globally, some estimates believe demand for steel will double by 2050. [1] This means that annual steel production could exceed 4 billion tons as current annual production levels nearly reach 2 billion tons. [1]
While steel has many performance benefits, steel's major drawback is its environmental impact. Because of the way steel is produced, the production of a ton of steel leads to 1.9 tons of CO2, which in sum accounts for 7% of global carbon dioxide emissions, more than any other industrial setting. [2] This is because steel production has not seen much innovation and over 70% of production occurs in century-old blast furnaces like the one that can be seen in Fig. 1. In this process, Coke, a carbon product that is formed by the high temperature thermal distillation of coal, is used to create a reducing atmosphere for the iron ore that is the base for the steel. [3] Coke is the primary source of CO2 emissions in this traditional process.
While most production is still done in the blast furnace, there are some possible solutions to emissions caused by steelmaking. The first simple solution is using more steel scrap and recycled steel in the production process. Because steel is a permanent resource, it is infinitely recycle-able and the U.S. is beginning to take advantage of this. In fact, over 70% of steel production in the U.S. made from scrap steel. [2] However, developing countries are lagging behind. For example, in China during the first half of 2021, 18 new steel projects using traditional blast furnaces were were announced. [2] So before introducing more complicated solutions globally, reusing scrap steel or direct reduced iron (DRI) in an electric arc furnace (EAF) is the best place to start.
When there is no scrap steel or DRI readily available, other technologies are needed to avoid the emissions associated with reducing iron ore. One such possibility is using hydrogen-based steel production. In this process known as direct reduction, pure hydrogen replaces coke as the reducing agent. [1] Instead of CO2 as a byproduct, using hydrogen as the reducer only produces water as a byproduct.
While hydrogen based steel production sounds quite idealistic, there are many challenges associated with this process. The primary challenge is that getting access to pure hydrogen is incredibly energy intensive. Today, the best way to do this is through electrolysis of water, where H2O is separated into its components by running a current through it. However, to create enough pure hydrogen through electrolysis to make a single ton of steel requires 2600 kWh's of electricity, which could power an average American home for three months. [1] Additionally, electrolysis is only green if the energy used in the process comes from renewable sources. Therefore, producing enough clean energy to achieve this process while accounting for growing steel production, would require significantly more clean energy than we currently have. For perspective, the amount of energy required that would be required to account for today's steel production levels is equivalent to that of 250,000-850,000 wind turbines. [1] This is far greater than roughly 350,000 turbines on the planet. [4]
While using hydrogen as the reducing agent to produce pure iron cuts steelmaking CO2 emissions by 90%, it is important to note the process will still have some CO2 emissions. [1] This is because to covert iron into steel, carbon is used as an alloy to increase strength and hardness. Furthermore, EAFs require electricity as well to heat and liquify this steel which depending on the source of electricity could generate emissions.
This is all to say that the best way to make steelmaking a more environmentally friendly process is to keep building renewable energy production facilities at unprecedented magnitudes. As with many other fossil fuel dependent industries, electrification will the be the path to cleaner solutions for steelmaking. However, carefully managing where clean energy is directed in the near term will be important, and right now hydrogen-based steelmaking is too energy intensive to justify a scaleable conversion from the traditional process.
© Samuel Beskind. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] M. Hutson, "The Promise of Carbon Neutral Steel," New Yorker, 18 Sep 21.
[2] A. MacDonald, "Steelmakers Grapple With How to Cut Carbon Emissions," Wall Street Journal, 21 Aug 21.
[3] "Available and Emerging Technologies for Reducing Greenhouse Gas Emissions from the Iron and Steel Industry," U.S. Environmental Protection Agency, September 2012.
[4] A. Frangoul, "There Are Over 341,000 Wind Turbines On the Planet: Here's How Much of a Difference They're Actually Making," CNBC, 8 Sep 17.
