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| Mon, 2nd Dec 2019 13:47:00 |
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Can We Make Steel Without CO2 Emissions Using Renewable Hydrogen? |
Yes, in theory. Doing it in practice is a whole other story. This is another example of how the hydrogen economy is a fantasy.
Readers often complain that I am too negative about new technologies, and people keep saying that we can fix how we make things like concrete and steel, the making of which together produce 12 percent of the world's CO2. Perhaps I am too skeptical. After all, everyone is excited about the latest news about steel. Bloomberg titles its story 'How Hydrogen Could Solve Steel’s Climate Test and Hobble Coal; Renew Economy writes Another nail in coal’s coffin? German steel furnace runs on renewable hydrogen in world first.
They are talking about ThyssenKrupp Steel's recent world's first: "The Duisburg-based steel producer has launched a series of tests into the use of hydrogen in a working blast furnace. They are the first tests of their kind and are aimed at reducing significantly the CO2 emissions arising during steelmaking."
ThyssenKrupp explains:
In the classic blast furnace process around 300 kilograms of coke and 200 kilograms of pulverized coal are needed to produce a ton of pig iron. The coal is injected as an additional reducing agent into the bottom of the blast furnace shaft through 28 so-called tuyeres. At the start of the tests today hydrogen was injected through one of these tuyeres into blast furnace 9. The advantage is that whereas injecting coal produces CO2 emissions, using hydrogen generates water vapor. CO2 savings of up to 20 percent are therefore already possible at this point in the production process.
Here we have to do some basic chemistry. The blast furnace reduced the iron oxide content of the ore by blasting air and pulverized coal into the melted ore. The carbon monoxide from the burning coal reacts with the iron oxide, producing iron and carbon dioxide.
Fe2O3 + 3 CO becomes 2 Fe + 3 CO2
I am assuming that the hydrogen is reacting with the oxygen in the iron ore to produce water vapour instead of CO2. This is important. But the whole furnace and the air being blasted in is the bulk of the energy needed, and that is still running on coal. You would need a LOT of hydrogen to replace that.
Where does the hydrogen come from?
This is, in fact, the bigger problem. That Renew Economy title says German steel furnace runs on renewable hydrogen in world first. But it did not; it ran from standard Air Liquide hydrogen, which is made from steam reformation of natural gas (methane). This is how 95 percent of the world's hydrogen is made: you burn methane to make steam, 815 to 925 °C, which reacts with methane to make carbon monoxide and hydrogen.
CH4 + H20 becomes CO + 3H2
I tried to figure out how much energy it actually takes to turn methane into hydrogen, but according to Wikipedia, the process is only 65 to 75 percent efficient, so a lot is being wasted. So really, the hydrogen being used is nothing but laundered natural gas, a cleaned-up fossil fuel.
A hydrogen based economy only works if the hydrogen is "green" or made through electrolysis. Air Liquide has actually just announced plans to build a plant to produce 10,440 tons of hydrogen through electrolysis using 1300GWh of solar electricity by 2027.
This is where it all breaks down. ThyssenKrupp produces 12 million tons of steel per year. Making that currently burns through about 12 million tons of coal per year.
Hydrogen has about five times the energy content per ton as coal does, so all that hydrogen that Air Liquide is producing through solar power is comparable to 52,000 tons of coal. If one hundred percent of that year's supply of hydrogen was sent to ThyssenKrupp, they would burn through it in a day and a half.
The hydrogen fantasy
This is the fantasy of green hydrogen and carbon-free steel; yes, it can work, but we don't have time. We would need to transform the entire industry, and produce billions and billions of tons of hydrogen, and build all the infrastructure to make it.
It's why I always return to the same place. We have to substitute materials that we grow instead of those we dig out of the ground. We have to use less steel, half of which is going into construction and 16 percent of which is going into cars, which are 70 percent steel by weight. So build our buildings out of wood instead of steel; make cars smaller and lighter and get a bike.
ThyssenKrupp recently won a Best of the Best Red Dot design award for building a steel racing bike. I wonder if pushing this wouldn't have a bigger impact than pushing their new hydrogen process. Carbon-free steel isn't a fantasy, but it will take decades. Using less steel can happen a lot faster.
Read original full article
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