Thursday, December 31, 2020

Green Steel: DRI, HBI and Finex

I had assumed that the CO2 emissions for making steel with blast furnaces was because of the burning of the coke to provide the needed high temperatures to melt the rocks (iron ore and limestone). And the making of the coke itself also produces a lot of emissions. But I've learned that another source of CO2 in the blast furnace is the reduction of the iron ore. "Reduction" means ripping the oxygen atoms out of the iron ore to leave pure iron. The reduction is done by the carbon atoms in the coke combining with the oxygen atoms in the iron ore to create CO2 and CO. If you grab the oxygen atoms with hydrogen instead of carbon, you create H2O instead of CO2. Of course, H2O is simply water vapor, which is not a greenhouse gas. Powering a blast furnace with hydrogen instead of coke is called direct reduced iron (DRI). An intermediate step towards green steel is using natural gas instead of coke. Since natural gas is mostly methane, CH4, this reduces two of the iron's oxygen atoms with hydrogen instead of carbon. So the CO2 emissions are a third of that emitted when using coke.

This Mitsubishi article below indicates that the cost of hydrogen needs to be an order of magnitude (a factor of 10) cheaper than it is now to be competitive with using coke as the reduction agent. But they expect society will be beefing up the world's hydrogen infrastructure and that those cost reductions will be realized.

safe_image for Mitsubishi Heavy to build biggest zero-carbon steel plant [paycount]
Mitsubishi Heavy Industries will build the new hydrogen steel pilot plant at a complex of Austrian steelmaker Voestalpine.   © Reuters
"Iron ore reduction accounts for much of the CO2 emissions in steelmaking. Japanese steelmakers including Nippon Steel are developing hydrogen-consuming reduction processes based on the conventional blast furnace design. Mitsubishi Heavy's plant adopts a process called direct reduced iron, or DRI. New blast furnaces require trillions of yen (1 trillion yen equals $9.6 billion) in investment. Although DRI equipment produces less steel, the investment is estimated at less than half of blast furnaces. For DRI to attain the same level of cost-competitiveness as blast furnaces, low-cost hydrogen will be key. Market costs for hydrogen now stand at around 100 yen per normal cu. meter, estimates the Ministry of Economy, Trade and Industry. The government aims to get the hydrogen costs down to 30 yen per normal cu. meter by 2030, mainly via mass production. But for DRI to be feasible in the steel industry, 'the level needs to go below 10 yen,' said an executive at a large steelmaker....Mitsubishi Heavy will capture the steel industry's demand for hydrogen to offset the softer growth prospects for thermal power plant equipment."
Jim Hewett Jr.: Interesting. That mill is no stranger to new technology. VoestAlpine is used to being a pioneer in the steel industry. That is where the very first B.O.F. was developed.
Richard Allison: The whole idea is to inject coke oven gas and hydrogen into tuyeres of blast furnaces to reduce CO2 by 50% by 2030. Blast furnaces will still use a little bit of coke and blast furnaces will never be zero percent carbon so HBI and DRI will be using green hydrogen, not gray hydrogen to be produced and melted down in EAFs and replacing blast furnaces. Blast furnaces will start closing down soon but ones still operating by 2030 will have to have 30% cut in CO2 and all of them by 2050. Some steel companies are accelerating this plan to happen sooner. That is one reason AM sold the US operations. This is a win for steel companies because they will be supplying steel to build hydrogen infrastructure and make steel with much fewer steelworkers.

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[At 2:40 it indicates that the process generates carbon monoxide and hydrogen instead of CO2. Both of those gases are combustible. Although the burning of the CO will create CO2.]



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