Carbon monoxide (CO) derived from COâ‚‚ is used in steelmaking as a reducing agent because it chemically strips oxygen from iron ore, converting iron oxides into metallic iron inside a blast furnace. This makes CO one of the most critical molecules in primary steel production. The sections below unpack exactly how this works, why recycled CO from COâ‚‚ is gaining traction, and what it means for the future of low-carbon steelmaking.
Why is carbon monoxide used as a reducing agent in blast furnaces?
Carbon monoxide is used as a reducing agent in blast furnaces because it reacts readily with iron oxides at high temperatures, donating its carbon atom to bind with the oxygen in the ore and releasing metallic iron as a result. This reduction reaction, where CO gains oxygen and iron ore loses it, is the chemical core of conventional primary steel production.
In a blast furnace, iron ore (primarily iron oxide, Fe₂O₃) is fed in alongside coke and limestone. Hot air is blasted through the bottom of the furnace, igniting the coke to produce CO₂, which then reacts with more coke to form carbon monoxide. That CO rises through the furnace and encounters the descending iron ore, reducing it to molten iron. The CO itself is oxidized back to CO₂ in the process.
What makes CO particularly effective as a reducing agent is its chemical affinity for oxygen at the temperatures found inside a blast furnace, typically between 900°C and 1,600°C. CO is thermodynamically favorable for iron oxide reduction across a wide temperature range, making it both efficient and controllable. Without a steady supply of CO, the reduction of iron ore simply cannot proceed at industrial scale.
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How is CO2 converted into carbon monoxide for steel production?
COâ‚‚ is converted into carbon monoxide for steel production by breaking the bond between one carbon atom and one of its two oxygen atoms. The most advanced method for doing this at industrial scale is plasma-based COâ‚‚ splitting, where renewable electricity energizes a plasma field that selectively activates and breaks COâ‚‚ molecules, producing CO without unwanted byproducts like carbon black.
Traditional routes for generating CO, such as steam methane reforming or partial oxidation of natural gas, rely on fossil feedstocks and produce significant greenhouse gas emissions. Plasma-based COâ‚‚ conversion technology offers a fundamentally different pathway: it starts with COâ‚‚-rich industrial off-gases, applies a plasma arc powered by renewable electricity, and outputs high-purity carbon monoxide that can feed directly back into steelmaking processes.
D-CRBN’s Plasma ARCâ„¢ platform takes this approach further by incorporating a downstream carbon bed, a gasification step that reduces electricity consumption to approximately 1,100 kWh per tonne of CO produced. This makes the process roughly five times more energy-efficient than competing conversion routes such as the reverse water-gas shift reaction. The reactor also operates at ambient pressure, requires no rare-earth materials, and can handle diluted COâ‚‚ streams containing up to 50% nitrogen, a practical advantage given that industrial off-gases are rarely pure.
The first industrial trial of this plasma-based COâ‚‚-to-CO conversion took place at a major European steel plant, where CO was supplied via pipeline to a carbon capture unit processing blast furnace off-gases. The pilot demonstrated safe operation at a major-hazard site, a record-low electricity consumption of 1.1 kWh per kilogram of CO produced, and confirmed that impurities naturally present in steelmaking gases do not compromise the conversion process. Learn more about electrified CO production and how it integrates into existing steel infrastructure.
What are the benefits of replacing coke-derived CO with CO from CO2?
Replacing coke-derived CO with carbon monoxide produced from recycled COâ‚‚ delivers three core benefits: it reduces coal consumption and associated direct emissions, it lowers a steel plant’s exposure to ETS carbon costs, and it creates supply chain independence from fossil feedstock markets. Unlike coke-based CO production, recycled CO from COâ‚‚ closes the carbon loop rather than opening a new one.
Emissions reduction and ETS cost savings
Every tonne of CO produced from recycled COâ‚‚ using renewable electricity avoids the emissions that would otherwise come from coke combustion. Conventional fossil-based CO production carries a lifecycle emission factor of around 2.1 tonnes of COâ‚‚-equivalent per tonne of CO produced globally. D-CRBN’s plasma process, when powered by renewable electricity and using biogenic COâ‚‚ as feedstock, achieves a figure of approximately 0.7 tonnes of COâ‚‚-equivalent per tonne of CO, making it carbon-negative overall. For steel producers operating under the EU Emissions Trading System, this directly translates into lower carbon compliance costs, which increasingly affect operational competitiveness.
Supply chain resilience and price stability
Coke and coking coal are globally traded commodities subject to significant price volatility and geopolitical supply risk. By producing CO on-site from captured COâ‚‚, a waste stream that the plant generates anyway, steel producers can reduce their dependence on imported fossil feedstocks. D-CRBN’s modular plasma systems are designed for on-site electrified feedstock production, meaning plants can generate the CO they need directly at the point of use, insulating themselves from external market disruptions. This is not a marginal improvement, it represents a structural change in how a plant sources one of its most critical process inputs.
What is the difference between carbon capture and storage (CCS) and carbon capture and utilization (CCU) in steelmaking?
The key difference between CCS and CCU in steelmaking is what happens to the captured COâ‚‚. Carbon capture and storage (CCS) permanently sequesters COâ‚‚ underground or in geological formations, treating it as waste to be isolated. Carbon capture and utilization (CCU) converts captured COâ‚‚ into a useful product, such as carbon monoxide for use as a reducing agent, keeping carbon in active industrial circulation rather than removing it from the economy entirely.
For steel producers, this distinction has significant practical implications. CCS requires substantial infrastructure for COâ‚‚ transport and injection, carries long-term liability for stored carbon, and generates no commercial return on the captured gas. CCU, by contrast, transforms a liability into a feedstock. When a steel plant captures blast furnace off-gases and converts the COâ‚‚ content back into CO using plasma technology, that CO re-enters the blast furnace as a reducing agent, replacing coke-derived CO and generating value from what would otherwise be an emission.
D-CRBN’s approach is explicitly CCU-focused. The company’s Plasma ARCâ„¢ platform converts COâ‚‚-rich off-gases directly into carbon monoxide without requiring geological storage or producing residual waste streams. This circular model is more economically attractive for industrial operators because it generates a saleable or internally usable product, and it avoids the ongoing costs and regulatory complexity associated with permanent carbon storage.
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Which steel production processes can use CO from recycled CO2?
Carbon monoxide from recycled COâ‚‚ can be used in blast furnace-based steelmaking as a direct substitute for coke-derived CO in the iron ore reduction process. It is also applicable in direct reduction of iron (DRI) processes, where CO acts as the reducing gas that converts iron ore pellets to metallic iron without requiring a full blast furnace setup.
In the conventional blast furnace route, CO from COâ‚‚ recycling integrates at the point where reducing gases enter the furnace shaft. Because the chemistry of iron ore reduction does not distinguish between CO derived from coke combustion and CO produced via plasma conversion of COâ‚‚, the substitution is technically straightforward, provided the CO meets purity and flow rate specifications. D-CRBN’s pilot at a major European steel plant confirmed that CO produced from blast furnace off-gases can be recycled back into the same process, creating a closed carbon loop within the plant boundary.
Direct reduction plants, which use a shaft furnace fed with a mixture of CO and hydrogen to reduce iron ore pellets at lower temperatures than a blast furnace, are another strong candidate. These facilities already handle CO-rich gas streams and are designed for precise gas composition control, making them well-suited to accept CO sourced from COâ‚‚ conversion. As the steel sector moves toward lower-emission production routes, DRI plants that can source their reducing gas from recycled carbon rather than natural gas reforming represent an important transition pathway. Explore D-CRBN’s CO feedstock solutions for both blast furnace and direct reduction applications.
How much CO2 can steelmakers avoid by using recycled carbon monoxide?
The COâ‚‚ avoidance potential depends on the scale of CO substitution and the carbon intensity of the electricity used, but the lifecycle numbers are substantial. Using plasma-converted CO from COâ‚‚ instead of coke-derived CO can shift a plant’s CO production footprint from roughly 2.1 tonnes of COâ‚‚-equivalent per tonne of CO (the global fossil-based average) to approximately 0.7 tonnes of COâ‚‚-equivalent, a reduction of around 1.4 tonnes of COâ‚‚-equivalent per tonne of CO produced.
At industrial scale, this adds up quickly. A steel plant consuming tens of thousands of tonnes of CO annually as a reducing agent could avoid hundreds of thousands of tonnes of COâ‚‚-equivalent emissions by switching to electrified, recycled CO. These avoided emissions directly reduce the plant’s ETS compliance burden, which at current and projected European carbon prices represents a meaningful financial benefit, not just an environmental one.
The process also becomes more carbon-negative over time as electricity grids decarbonize. D-CRBN’s lifecycle analysis indicates the process remains carbon-negative as long as the grid it draws from emits below 0.4 tonnes of COâ‚‚ per MWh, a threshold already met by several low-carbon national grids in Europe and one that will become easier to meet as renewable capacity expands. By 2035, D-CRBN’s stated target is a cumulative 5.5 million tonnes of CO production, corresponding to an estimated 3.8 million tonnes of COâ‚‚ actively removed from the atmosphere across its customer base.
For steel producers evaluating their decarbonization roadmap, the COâ‚‚ avoidance case for recycled carbon monoxide is no longer theoretical. It has been validated at industrial pilot scale, and the economics are competitive with fossil-derived alternatives, particularly when ETS costs and fossil feedstock price volatility are factored in. To explore how electrified CO production could fit your plant’s specific configuration, speak with D-CRBN’s team or review the syngas production options for broader feedstock flexibility.