In Steelmaking: Part 1, we learned about the role of steel in our and how we currently make it.
We also learned that steelmaking emits 2.6 Gt of direct CO2 emissions annually and accounts for 8% of the global final energy demand. Slashing the steel industry’s emissions- and energy intensity is crucial in tackling the climate crisis.
In this Part 2, we’ll look at three routes to producing low-emission steel. Get ready for some awesome science!
If you haven’t read Part 1 of this deep dive series yet, I highly recommend doing so before continuing reading.
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Decarbonizing steel’s primary production is tricky.
In the Blast Furnace-Blast Oxygen Furnace (BF-BOF) route, which makes 70% of our steel today, coal is an integral part of the process. Coal turns into carbon monoxide, which then acts as the chemical agent separating metallic iron and oxygen from the iron ore.
There are three ways to achieve limited CO2 reductions in primary production 1) BF-BOF process optimization, 2) Bioenergy, e.g. biocoke, and 3) Carbon Capture, Utilization, and Storage (CCUS). While these measures play a role in lowering the steel industry’s emissions in the short term, we cannot rely solely on them.
Luckily, there are three radical CO2 reduction technologies for steel’s primary production:
Hydrogen-based direct reduction
This kind of revolutionary stuff excites me, so let’s go through these technologies individually.
1. Hydrogen-based direct reduction
In hydrogen-based direct reduction, natural gas is replaced by hydrogen in the direct reduction process. Hydrogen acts as a chemical agent separating metallic iron and oxygen from iron ore.
The hydrogen plasma-based steelmaking process produces crude steel from iron ore in one single step.
In hydrogen-based direct reduction, the resulting sponge iron must still be processed in an EAF before it becomes crude steel. Using hydrogen plasma reduces these steps to one single step. The iron oxide gets reduced and melted at the same time.
Here’s an excellent explanation of the steelmaking process with hydrogen plasma.
The advantages of the hydrogen plasma process include lower capital cost and energy demand. Read more details about hydrogen plasma’s advantages in this research paper.
However, the hydrogen plasma process is still a novel technology and requires substantial development before it is scaled and its climate impact gets realized.
Electrolysis is an electrochemical process that can be applied to steelmaking in addition to making green hydrogen.
In electrolysis, the iron metal is extracted from the iron oxide by passing an electric current through electrodes. The process also needs an appropriate electrolyte.
Below is a video where Boston Metal explains how they make steel with the Molten Oxide Electrolysis process. Here’s an even better video explaining the extraction of metals from oxides via electrolysis. (Isn’t electrolysis cool!)
The disadvantage of the Molten Oxide Electrolysis process is that it requires a high temperature (1600°C / 2900 F). The iron oxide needs to be melted, as the name implies. Luckily, there’s a research project called Σiderwin developing low-temperature electrolysis for steelmaking. Here’s a great explanation of Σiderwin’s method.
Like hydrogen plasma-based steelmaking, electrolysis is a novel technology in steelmaking and requires substantial development before realizing its potential climate impact.
⚡2. Decarbonize secondary production: switch to renewable electricity
Decarbonizing the secondary production is much more straightforward than decarbonizing the primary production.
Secondary production uses an electric arc furnace (EAF) to melt the steel scrap and produce new steel. As the EAF’s name implies, it uses electricity as the energy source. The electricity can be easily switched to renewable energy.
♻️3. Increase the share of secondary production
Increasing the share of secondary production (=recycled steel) makes sense, even if all electricity could not immediately be supplied from renewable energy sources in secondary production,
Producing steel from scarp in an EAF (secondary production) is much less energy- and emissions-intensive than making steel from iron ore via the Blast Furnace-Blast Oxygen Furnace (BF-BOF) and Direct Reduction Iron - EAF (DRI-EAF) route (primary production).