Hydrogen Plasma Smelting Reduction of Iron Ores (HPSR)

The HPSR process uses molecular, atomic, excited and ionised hydrogen species to reduce iron ores in a plasma reactor. HPSR enables direct conversion of iron ore into crude steel while providing a high CO2 emissions reduction potential when compared with the conventional integrated BF-BOF steelmaking production route. A pilot plant using this innovative technology is currently operated by K1-MET GmbH in Linz (Austria) . It is located at the site of Voestalpine Stahl Donawitz GmbH.

TECHNICAL DESCRIPTION
The hydrogen plasma smelting reduction reduces iron ores in a plasma reactor with hydrogen, thereby only producing water vapor as a reduction by-product. This innovative technique has been tested in the SUSTEEL project between Voestalpine, the K1-MET Competence Centre for Metallurgy and the University of Leoben. SUSTEEL was funded by the Austrian Research Promotion Agency and was carried out between 2019 – 2023. A follow-up Horizon Europe project (i.e. H2PlasmaRed) is now underway to further develop this technology up to TRL 7. The HPSR process uses molecular, atomic, excited and ionised hydrogen species to reduce iron ores in a plasma reactor.
The raw materials (iron ore) and the plasma gases are injected into the reactor through a hollow graphite cathode, which is located centrally above the bath. Argon is mixed to the hydrogen for stabilising the plasma before entering the cathode. The melt acts as anode for the transferred arc and provides a conductive path for the current to the crucible’s bottom electrode. Essentially, in the reaction zone, a plasma flame (transferred arc} is formed between the electrode and the bottom anode, in which the material is reduced and melted in one step. The resulting crude steel accumulates at the bottom of the lower vessel and is subsequently removed at the end of a trial. The process is operated discontinuously, and the cycle takes approximately one hour depending on the reduction rate.
The off-gases of the HPSR reactor are first fed into a scrubber (removal of dust components} and subsequently discharged via an off-gas duct. They contain mostly unreacted hydrogen, water-vapor, argon and small amounts of carbon monoxide and carbon dioxide. The last two compounds originate from the wear of the graphite cathode but their specific amount is rather low accounting only for a few kilograms per ton of produced metal. The unreacted hydrogen and inert argon can, for the most part, be recycled into the HPSR reactor again for improved efficiency.
The whole reactor vessel is sealed gas-tight and can be considered similar to a direct-current electric arc furnace. The reduction with atomic, excited and ionised hydrogen is much more favourable than with molecular hydrogen. Additionally, the reduction is faster at higher temperatures. This means that both factors provide thermodynamic and kinetic advantages for plasma processes compared to conventional alternatives, like hydrogen direct reduction in shafts or fluidised beds. In addition, the reduction of iron ores is nearly energy-neutral at around 1 600 °C, compared to being endothermic at lower temperatures. This makes the HPSR process only consume the energy required for melting and not for reducing the ores. Another benefit of the HPSR process is that it can be operated with any grade of iron ores. While hydrogen direct reduction techniques combined with electric arc furnaces are only feasible using high-grade iron ores, low-, medium- and high-grade ores as well as any mixtures thereof can be processed using the HPSR approach. Compared to conventional carbon-based smelters after a direct-reduction stage, the HPSR process is nearly carbon-neutral.
Potentially, in contrast to the conventional integrated steelmaking route, the HPSR process could avoid the need for coking, sintering or pelletising plants as well as the decarburisation step in the basic oxygen furnace leading to substantial cost savings in terms of equipment.

DEGREE OF MATURITY
Upon completion of the SUSTEEL project in 2023, the HPSR technology reached TRL 5.
At the end of the on-going H2PlasmaRed project foreseen in December 2027, it is expected that the technology will reach TRL 7. In this project, the scalability of the process will be tested by combining the pilot-HPSR reactor (hundred-kilogram-scale) together with a retrofitted pilot-scale DC electric arc furnace (5-ton scale) used as a hydrogen plasma reactor.
At this stage, the HPSR process shall feature continuous charging, a pre-heating and pre-reduction stage, a plasma smelting stage with the possibility to tap the produced metal and slag, off-gas cleaning as well as off-gas recycling with only a minimal bleed.

CROSS-MEDIA EFFECTS
The expected energy requirement is about 15GJ/t liquid steel. Like other H2-based reduction technologies, this technology is associated with increased electrical energy requirements compared to the conventional BF/BOF route.

BARRIERS TO IMPLEMENTATION
Given that H2-plasma technology requires both hydrogen and electricity, an economic barrier is clearly linked to high costs of both commodities. The possibility to retrofit existing EAF plants in order to potentially deploy further this plasma technology will need to be demonstrated to ensure wide implementation.

Basic information about the technique

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