The iron and steel industry is positioned at a significant turning point. As global demand for green steel grows, researchers and engineers are exploring new technologies to eliminate carbon emissions in the iron ore reduction process. One of the most promising options is Hydrogen Plasma Smelting Reduction (HPSR). This high-temperature process uses atomic hydrogen plasma to reduce iron oxides without carbon, producing only water vapour as a byproduct. Recent advances in pulsed arc reactors and gas-stabilised hydrogen plasmas are reviving this idea. Experimental setups have reached important milestones in both plasma control and ore reduction kinetics.

Reduction Phenomenon:

At the core of the HPSR system is a magnetically driven arc passing through a mixture of hydrogen and argon. This creates a high-energy plasma filled with atomic hydrogen, the most reactive form of hydrogen. Fine iron oxide particles are injected into this plasma zone, where they undergo rapid thermal and chemical reduction:

Fe₂O₃ + H → 2FeO + H₂O

FeO + 2H → Fe + H₂O

Unlike traditional carbon-based methods, this technique avoids CO₂ emissions altogether.

Early trials show that atomic hydrogen remains active for up to 4 milliseconds after the arc stops, allowing enough time for effective reduction. Even oxides like TiO₂ have been partially reduced in these conditions, showcasing the high reactivity and potential scalability of the system.

Reactor Design Requirements

The Hydrogen Plasma Smelting Reduction (HPSR) system utilises a pulsed DC arc with energy inputs of up to 5 kW, controlled via Silicon-Controlled Rectifier (SCR) technology for precise power modulation. The arc maintains stable lengths exceeding 20 mm and operates with lifetimes sufficient to achieve complete reduction of iron oxides such as FeO and Fe₂O₃. Atomic hydrogen generation is confirmed through Hα spectral emissions, which indicate the persistence of reactive hydrogen species even after the arc discharge ends. Iron ore fines are introduced into the plasma zone using a powder feed system that delivers material at a consistent rate of approximately 3 grams per minute. These integrated advancements position HPSR as a compelling approach to decarbonising ironmaking, offering both high thermal efficiency and precise process control.

Influence on CO₂ emissions:

The steel sector contributes nearly 8% of global CO₂ emissions. Hydrogen-based direct reduction (DRI) is gaining traction, but plasma-based hydrogen systems provide an even more effective route to eliminate reliance on fossil fuels by avoiding solid reductants or natural gas. Additionally, HPSR is especially suited for high-grade ore fines. This allows for easier integration with renewable electricity sources and flexible batch-scale operation, making it ideal for future decentralised steel production models.

Current Status:

Current research efforts focus on scaling arc systems to handle higher feed rates and longer residence times. These factors are crucial for increasing output in industrial applications. Improving arc stability under changing feedstock and gas flow conditions is another priority; consistent plasma behaviour is vital for effective reduction. Researchers also work to optimise the generation of atomic hydrogen. Their goal is to boost their reactivity and persistence within the reactor environment. At the same time, real-time diagnostic tools are being added to monitor plasma characteristics and track the progress of ore reduction processes. These advancements are setting the stage for pilot-scale projects, with support from collaboration among metallurgists, plasma physicists, and energy engineers.

“Hydrogen Plasma Smelting is moving beyond theory. It is becoming a practical solution for clean, flexible, and efficient ironmaking. As reactor technology and materials handling improve, HPSR may soon play a key role in carbon-free steel production.”