👩💻A new report on female students in tech came out in Finland on Monday. The results were shocking but, unfortunately, not surprising to me. I have studied engineering and work in tech and can relate to the findings.
To put things into perspective, check this out: We mined 3.2 billion tons of metals in 2019. 3 billion tons (94%) of those mined metals were iron ore, which we use to make steel. Try to find that tiny pile of lithium on the chart.
🪨What is steel?
Steel is an alloy, a combination of iron and carbon.
A small amount of carbon improves the strength and fracture resistance. Typically, steel contains less than 0.25% carbon of the total weight.
Every time we produce one ton of steel, we emit, on average, 1.85 tons of CO2 into the atmosphere.
To understand why steelmaking produces so much emissions and how we could decarbonize it, we must first understand the steelmaking process.
➡️Metallic inputs in steel production
1. Iron ore
Iron is the primary “ingredient” in steelmaking. Iron occurs naturally in iron ores on Earth’s crust. Typical iron ores are hematite and magnetite. Iron is chemically bonded with oxygen and sometimes with other elements in iron ore.
Metallic iron can be extracted from iron ore for steel production. If iron ore is the main input, we refer to these operations as primary production.
When steel scrap is used as the metal feedstock in steel making, we refer to this as secondary production.
⚒️Commercial routes of steelmaking
There are currently three main ways of making steel:
Blast Furnace - Basic Oxygen Furnace (BF-BOF)
Scrap - Electric Arc Furnace (Scrap-EAF)
Direct Reduced Iron - Electric Arc Furnace (DRI - EAF)
I initially struggled to grasp the different steelmaking routes. Thus, I created this illustration that you can refer back to when you continue reading.⬇️
1. Blast Furnace - Basic Oxygen Furnace (BF-BOF)
70% of the steel is produced via the BF-BOF route, making it the most common process for producing steel today.
First, 1)iron ore, 2)limestone, and 3)coal are pre-treated and fed into a furnace with as high temperature as 2000°C / 3600°F.
The pre-treated coal, coke, helps to extract metallic iron from iron ore. The coke is ignited, and it turns into CO2(😖) and carbon monoxide (CO). The carbon monoxide then reacts with iron ore and forms metallic iron and carbon dioxide. Carbon monoxide is also referred to as the reducing agent, because it reduces the iron ore (=steals oxygen from the iron ore).
Limestone is used to get rid of silicate materials found in iron ore. When limestone is heated, it turns into lime (calcium oxide) and CO2(😖). The lime reacts then with silicate materials and forms molten slag on top of the molten iron.
Next, the molten iron is put into another hot furnace called the Basic Oxygen Furnace. Oxygen is blown into molten iron, where oxygen reacts with impurities such as carbon, silicon, phosphorus, and manganese.
2. Scrap - Electric Arc Furnace (Scrap - EAF)
25% of steel is produced via the scrap - EAF route.
First, steel scrap is fed into an EAF. In an EAF, a powerful electric current is passed through the furnace via electrodes, generating an electric arc. The resulting heat melts the steel scrap.
Then, lime, carbon, and oxygen are added. They combine with the impurities of the steel scrap and form slag. The resulting slag is then easy to separate from steel.
If you are interested in learning more about the BF-BOF and Scrap - EAF pathways, I recommend checking out the video below.
3. Direct Reduced Iron - Electric Arc Furnace (DRI - EAF)
5% of the global crude steel is produced via the DRI-EAF route.
DRI is sponge iron that is produced from iron ore via a direct reduction process. The iron ore is not melted, so the direct reduction requires a lower temperature (1000°C / 1800°F) than a blast furnace (BF) (2000°C / 3600°F).
In direction reduction, the iron ore is exposed to a gas mixture of carbon monoxide and hydrogen, which turns iron ore into sponge iron. The gas mixture acts as the reducing agent, as coke does in a blast furnace. The gas mixture is usually derived from fossil fuels, like natural gas or coal.
The resulting sponge iron is then further processed into steel in an EAF.
In Part 2 of this deep dive series, we’ll dive into the decarbonization strategies for steelmaking. And yes, you guessed it right. These decarbonization strategies involve some awesome technologies!