Cracked: A mystery that could allow hydrogen to massively greenify steelmaking Premium

If iron oxide is heated with hydrogen instead of coke, to remove oxygen, the sector’s carbon emissions could nosedive. Scientists have finally found a way to replace coke with hydrogen by cracking a longstanding metallurgical mystery.

Hydrogen is a crucial part of the world’s plans to greenify its manufacturing and automobile industries as a fuel whose production and use needn’t emit carbon. But in the steelmaking industry, hydrogen can also be used instead of carbon in an important chemical reaction that contributes to 5-7% of the global greenhouse-gas emissions and 11% of carbon dioxide emissions. That is, if scientists can surmount an old roadblock.

In particular, if the results of a new study are borne out, this barrier may finally be giving way. Researchers in Germany have reported that they may have figured out why using hydrogen as a reactant in a reaction with iron oxide proceeds more slowly than expected, a fact that currently renders the element infeasible as a substitute for carbon.

The researchers’ paper was published in Physical Review Letters on April 19. Xuyang Zhou, deputy group-leader at the Max Planck Institute for Iron Research, Düsseldorf, and one of the paper’s authors, told The Hindu in an email that research like this is “essential” to “reduce energy consumption” in steelmaking.

India is the world’s second-largest steelmaker, having produced 118.2 million tonnes in 2021. Making one tonne of steel releases 1.8 tonnes of carbon dioxide, making the sector’s decarbonisation plans an integral part of the country’s ability to achieve its climate commitments.

Strong steel consists of a tiny amount – less than 1% – of carbon. To achieve this mix, iron oxide is heated with coke (a form of coal with high carbon content) at 1,700 C inside a blast furnace. The carbon reacts with oxygen to form carbon dioxide, leaving iron with around 4% carbon behind. This iron is remelted and oxygen is blown through it, producing more carbon dioxide and reducing the amount of carbon in the iron to a desirable level.

“The blast furnace ironmaking process is the predominant primary metal production process, with the carbon emissions accounting for approximately 90% of the total value of the entire steelmaking route,” a paper published in December 2021 said. “Therefore, it is under severe pressure to reduce carbon emissions.”

In the first step, when oxygen leaves the iron oxide, scientists know that it leaves behind minuscule pores in the iron.