Flash Ironmaking Hits Combustion Wall Amid Steel’s Decarbonization Shift

Last Updated on: 25th June 2025, 06:03 pm

My recent update of my global steel projection through 2100, driven by China’s declining demand for cement and infrastructure construction, has refocused my attention on pathways for steel decarbonization. The dynamics of steel consumption and emissions are closely linked to building and infrastructure development, sectors traditionally responsible for about half of global steel demand. With China’s massive construction boom winding down, it appears the peak for steel demand has already been reached, altering the economics and urgency of different decarbonization strategies.

One approach, flash ironmaking, had surfaced as a compelling idea due to headlines, which upon closer inspection proved likely to be hallucinatory nonsense, about a Chinese announcement of cutting process time from minutes to seconds. That was on top of its potential to significantly cut emissions and energy intensity compared to conventional blast furnaces. Upon closer examination, flash ironmaking reveals intrinsic challenges tied directly to its need for combustion.

Flash ironmaking traces its origins to research led by Professor Hong Yong Sohn and his team at the University of Utah beginning in the early 2000s. The concept emerged as a response to the entrenched inefficiencies of blast furnaces, aiming to eliminate cokemaking, sintering, and pelletizing by directly reducing fine iron ore particles.

Mea culpa: I had read something that attributed its development to being an offshoot of a flash copper smelting process developed in China by the same Chinese researcher and asserted that in previous articles. Instead, it’s a Finnish copper process from the 1940s that a Korean-American born in Korea then educated in Canada and California built upon for flash ironmaking. Indeed, the only source I can find for a recent Chinese innovation is a thermal lance piece in “Interesting Engineering,” which I consider to be a clickbait site for engineering p*rn, being neither interesting nor engineering but merely a site where people who like looking at engineering’s butt read anything. My bad for not digging deeper earlier, but I’m making up for it now and admitting my due diligence failure, so please forgive me my most recent lapse. 

Early bench-scale systems demonstrated the feasibility of this rapid reduction using entrained-flow reactors with natural gas or hydrogen. As research progressed, pilot-scale designs were developed to explore continuous operation, gas-solid mixing, and reactor scaling. By the 2010s, flash ironmaking had matured into an alternative technology under active development, drawing support from the U.S. Department of Energy and attracting global academic interest.

At first glance, flash ironmaking technology holds substantial promise. It bypasses the traditional blast furnace route by directly reducing finely ground iron ore particles in a short reaction time, typically measured in minutes. These fast reaction speeds dramatically reduce the scale and complexity of plants. Proponents highlight that it could eliminate the need for coke production and pelletizing of iron ore, two energy-intensive and polluting steps in traditional ironmaking.

Laboratory and pilot-scale demonstrations have indicated impressive energy savings of up to 60% and carbon dioxide emissions reductions exceeding 50% compared to conventional blast furnaces. On paper, flash ironmaking could simplify steel manufacturing and significantly mitigate its environmental impacts. But 50% reductions still leave 50% of the emissions.

Unfortunately, the critical caveat in flash ironmaking is its unavoidable reliance on combustion. The process demands extremely high temperatures and rapid heating to enable the necessary ultra-fast reactions. This heat is typically provided by combusting gases like natural gas, biomethane, or hydrogen with pure oxygen. While flash ironmaking greatly outperforms blast furnaces in emissions intensity, its requirement for combustion introduces significant complications for deep decarbonization. Natural gas combustion inevitably releases substantial carbon dioxide, even if total emissions are lower than traditional methods. This reliance puts a clear ceiling on how sustainable flash ironmaking can become unless paired with zero-carbon fuels.

Biomethane is severely constrained by availability and economics. Biomethane production today is limited by resource constraints, agricultural land competition, and the costs associated with upgrading biogas. It’s an essential industrial feedstock for syngas, necessary for methanol, acetic acid, formaldehyde and more, and that’s an essential use case. Beyond that, it’s an obvious candidate for dunkelflaute storage as we have literally everything required from strategic methane reserves to methane burning turbines and reciprocating engines, with no Houdini hydrogen required.

We currently have a massive methane emissions problem, from both the fossil fuel industry and the human biomass pathways including food, agriculture, animal husbandry and forestry. We’re going to have to first eliminate all the emissions in that space that we can, then capture as much of what we can’t mitigate as possible. That’s going to be enough for syngas and seasonal storage, but not for burning it for daily industrial processes, electricity generation or heat. It will be reserved for high merit use cases, and that includes direct iron reduction as a feedstock, but not as a combustible.

We can make more biomethane just the way we do today, by putting biomass in a sealed container without oxygen and letting it rot. The microbes that break down biomass produce methane instead of carbon dioxide. Scaling biomethane production to industrial levels necessary to support large-scale flash ironmaking would be exceptionally challenging. Further, current distributed methane biodigesters leak like a sieve, with 40% emissions in one study of distributed ones in Europe. I’m very bearish on significant creation of additional potent greenhouse gases, and don’t consider making more methane intentionally a particularly wise idea.

The combination of higher merit alternative use cases and manufactured biomethane supply chain issues makes me think it’s not going to be a great alternative to natural gas for flash ironmaking.

Green hydrogen, produced via electrolysis using renewable electricity, could theoretically offer a fully decarbonized combustion alternative. In practice, however, green hydrogen currently remains expensive and difficult to deploy at the necessary scale. While optimistic projections have frequently floated the possibility of hydrogen costs dropping below $2 per kilogram, real-world experience and current industry expectations place sustainable green hydrogen production closer to $5-$8 per kilogram, particularly in the short to medium term. At these higher price points, flash ironmaking powered by green hydrogen rapidly loses its economic appeal. The steel industry is famously cost-sensitive, operating on tight margins with little tolerance for significant increases in raw material or energy costs.

And then there’s hydrogen’s Mr. Hyde, its indirect greenhouse gas status and escape artistry. While hydrogen’s Dr. Jekyll — nothing but electricity and water out of fuel cells — gets the press, its dark side is that it leaks 1%+ at every touch point in supply chains of 5-9 touch points and has a GWP20 of 37. Flash ironmaking wouldn’t be exempt from this.

Further complicating the matter, hydrogen combustion is notoriously tricky to manage at industrial scales. Hydrogen’s low volumetric energy density, wide flammability range, and propensity to cause embrittlement and leaks demand sophisticated, expensive engineering solutions. Flash ironmaking systems combusting hydrogen would face substantially higher capital and operational complexities compared to natural gas or conventional systems. Given the operational sensitivity and technical constraints of steel plants, this added complexity presents a major barrier to rapid and widespread deployment of hydrogen-based flash ironmaking.

Flash ironmaking’s dependence on pure oxygen for combustion introduces a set of logistical and economic challenges that are often overlooked in optimistic assessments of the technology. Producing high-purity oxygen is energy-intensive and expensive, typically requiring cryogenic air separation units or advanced membrane systems. These systems carry a high capital cost and draw significant electrical loads, which reduce the overall efficiency gains promised by flash reactors. In regions without existing oxygen infrastructure, either large-scale on-site generation or frequent cryogenic deliveries would be necessary, both of which come with substantial cost and complexity. For greenfield plants in remote locations or developing markets, this adds a layer of logistical burden that could make flash ironmaking less attractive than other emerging pathways.

Even where oxygen is available, integrating high-volume combustion into industrial workflows carries serious safety and design implications. Pure oxygen is a powerful oxidizer that heightens the risk of fire and explosion, especially in a high-temperature environment involving powdered metal and flammable gases like hydrogen or methane. The infrastructure upgrades required to manage those risks — specialized piping, emergency systems, and operator training — are not trivial. And unless the electricity powering oxygen production comes from fully renewable sources, the emissions footprint of flash ironmaking can grow substantially, undercutting its value as a climate solution. In the end, the oxygen requirement, while technically manageable, chips away at the economic and environmental case for flash ironmaking, and places it in an increasingly narrow band of realistic deployment opportunities.

The recent projection shift in global steel demand due to China’s reduced infrastructure expansion offers some breathing room for the steel industry’s transition. Declining or plateauing demand could ease pressures and enable gradual phasing out of blast furnace technology while facilitating greater reliance on recycling via electric arc furnaces. Electric arc furnace-based steelmaking is fundamentally simpler to decarbonize since it can directly utilize renewable electricity. For virgin steel production, direct reduction methods using biomethane with process heat from electricity or purely electric technologies such as molten oxide electrolysis, will likely prove more practical, despite their own technical and economic hurdles.

Hydrogen reduction of iron is running into similar challenges to flash ironmaking, specifically that green hydrogen’s real cost makes the process completely uncompetitive, hence the number of green hydrogen steel failures in recent months. I’ll be digging into those drawbacks as well as deep dives into biomethane and electrical process heat iron and molten oxide electrolysis, but at present I’m leaning to electric arc furnaces, biomethane DRI with electric process heat and molten oxide electrolysis to be the long term winning combination. If that’s true, my hydrogen demand projection, already massively heterodox to clearly inflated projections, deflates further, as the only major growth area was hydrogen direct reduction of iron, with biofuels hydrotreating a mere 4 million tons a year. I’ll wait until I’ve done more on the technoeconomics to pull that trigger, however.

In light of this, flash ironmaking’s reliance on combustion feels disappointingly misaligned with the long-term goals of truly low-carbon steel production. While the process could provide interim improvements over blast furnaces, the structural limitations around fuel availability and emissions management dampen optimism for flash ironmaking becoming a dominant, sustainable solution. The steel industry faces a challenging road ahead to reach carbon neutrality, and technologies that fundamentally avoid combustion appear far more promising and strategically aligned with long-term sustainability objectives. Flash ironmaking, despite its theoretical attractiveness, remains constrained by combustion, placing it as a partial solution rather than a transformative one in steel’s critical journey toward deep decarbonization.