Profitable retrofit system could slash steelmaking emissions by 94%

Steel forms the structural backbone of modern life, but it accounts for about 8% of global carbon emissions and is the largest source of industrial greenhouse gases.

The path to a 100% clean future is clear enough. Ditch blast furnaces and charcoal coke reductants and replace them with electric arc furnaces and green hydrogen reductants that run on clean energy. Boom: Green Steel with water as the only by-product.

Here’s the problem: Humanity currently produces about 2 billion tonnes of steel annually in the world, but a very small percentage of that is clean, so blocks of green steel have actually been delivered to customers by 2021. It’s been big news this year. This is a huge industry with a vast amount of assets, facilities and machines already fully functional and built to last.

Switching to an electric arc furnace is no easy task. According to the world’s second largest steelmaker, it will cost him US$1.7 billion from 1.1 billion. This does not include charges related to stranded blast furnace assets. Because green hydrogen is not yet available on the scale needed, green steel costs 60% more to produce than dirty hydrogen.

Blast Furnace/Basic Oxygen Furnace (BF-BOF) steel will therefore be in use for decades to come. As such, this new retrofit system at the University of Birmingham could be one of the most important environmental technology advances of the year. , despite not being perfectly green.

This means that about 90% of the coke used in the blast furnace will be replaced by direct injection of carbon monoxide. Carbon monoxide comes from a system that separates carbon monoxide, carbon dioxide, hydrogen and nitrogen gases at high temperatures to recover and recycle the exhaust “top gas” of the furnace itself. These gases are sent to a twin reactor redox system that keeps the carbon in a closed loop.

Carbon dioxide is a double perovskite material (Ba₂calcium_0.66Nb_0.34FeO₆, or BCNF1 for brevity), which converts to carbon monoxide at about 800 °C (1,472 °F) at a rate of about 10.1% for each pass, extracting oxygen atoms from the carbon dioxide molecule and using them to fill the cubic structure. of BCNF1.

Meanwhile, nitrogen and a small amount of hydrogen from the top gas enter the second BCNF1 reactor for a thermochemical reduction process at 700 °C (1,292 °F), releasing pure oxygen from the BCNF1 structure. That oxygen is fed into a basic oxygen furnace that converts the hot metal from the blast furnace into molten steel, and excess oxygen can be sold. Exhaust gas from the deoxidizing furnace returns to the gas separator as it is.

Approximately every 24 hours, the BCNF1 structures in the reduction and oxidation chambers, respectively, begin to slow down by releasing or storing excess oxygen atoms. Steel mill operators simply switch the gas flow in and out of these two reactors to efficiently drive these reactions using perovskites in an infinite thermochemical redox cycle.

This system recycles both carbon and heat very effectively. However, by removing most of the coke and reusing the exhaust gases that are normally combusted, it takes away much of the energy normally used to run a steel plant. The system requires approximately 306 kWh of extra electrical energy per tonne of molten steel produced.

“If the electricity needed to power the electric heater and gas separator is sourced from renewable sources, this does not add to the TC-BF-BOF emissions,” said the Birmingham team study. teeth, journal of cleaner production“The cost of this electricity, and the electricity required to power the gas separator, is commensurate with the savings from replacing the coke in the system.”

In fact, the Birmingham team says retrofitting existing BF-BOF steel plants with this thermochemical redox system will significantly reduce the cost of steel production. Taking the British Steel (BS) facility at Scunthorpe as an example, the team found that BS has 10 of these switchable redox reactors about 15 m (49 ft) high and about 9.5 m (31 ft) in diameter. I estimate that it will be necessary. All of UK£359m (US$445m).

However, the company saved £187 million (US$232 million) a year on the coke budget, a figure that would impress Robert Downey Jr. in the late 1990s, and about £13 million (US$16 million) a year. will result in overselling of of pure oxygen. The report estimates that in just five years, BS will be around £640 million (US$740 million) better on its balance sheet. The BCNF1 material he needs to replace every 5 to 10 years, costing about £200 million (US$248 million).

If these figures are maintained, it is easy for steelmakers with BF-BOF facilities to think solely for economic reasons.

But the broader points are the planets. Emissions will also be completely cut by at least 90%, researchers say. He has only one other BF-BOF steelmaking facility in the UK, Tata’s in Port Talbot. That and his BF facility are now combined to emit about 11.4 million tonnes of carbon dioxide per year, which is about 3.1% of the UK’s total emissions. The system promises to bring that all together down to about 680,000 tonnes, which he calls a massive 94% reduction.

This means that with an upfront investment of about GBP 720 million (USD 893 million) and perovskite replacement costs of about GBP 400 million (USD 496 million) every 5 to 10 years, the UK will become the country’s total That means you have the potential to reduce your emissions by a whopping 2.9%. Years – Investments that pay large dividends within a few years.

And it’s only in the UK. About 70% of the world’s steel is now produced using his BF-BOF plants. The potential range of decarbonization opportunities here is enormous.

But there is always a but, but this is currently only a research paper, a first principles calculation on an idea. The team has yet to prototype such a facility, and there are some unknowns they’d like to explore before proceeding.

First, coke is used as a structural support in blast furnaces, and researchers say research is needed on how severely heat and mass flows would be affected if the coke was removed. . Second, the researchers say the focus should be on reducing the energy required to separate nitrogen and carbon monoxide. And third, many years of experiments are needed to understand the substitution rate of perovskite materials.

Still, given the huge emissions reduction potential here and the steelmakers’ impressive financial projections, I have to say that the team shouldn’t have trouble getting the funding to push this idea forward. No. It’s rare to find a decarbonization technology that seems to work for business owners as well as the planet.

“Current proposals to decarbonize the steel sector rely on phasing out existing plants and installing electric arc furnaces powered by renewable electricity,” said the researcher. Co-author Professor Yulong Ding said in a press release. The $1 billion he will spend on construction makes this switch economically unfeasible in the time left to comply with the Paris Agreement on Climate Change. Our proposed system can be retrofitted to existing plants, reducing the risk of asset stranding and immediately showing both CO2 savings and cost savings. “

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This research Journal of Cleaner Production.

Source: University of Birmingham