Hydrogen based ultra fine ore reduction combined with a continuous powered electric smelting furnace for liquid iron production (HYFOR / HY4SMELT)

This technique enables the replacement of the blast furnace ironmaking step with a new process combining an H2-based ultra fine ore reduction using a fluidised bed reactor cascade (designated as HYFOR®) in combination with an electrified smelting furnace for melting, carburisation and slag formation. It produces liquid iron and slags with similar compositions than that obtained with a conventional blast furnace. This is currently under development in Austria (Project Hy4Smelt - RFCS programme).

TECHNICAL DESCRIPTION
This innovative technique is currently under development through the project Hy4Smelt, funded under the Research Fund for Coal and Steel RFCS-2024-CSP-Big Tickets for Steel (Grant Agreement N. 101193416). It builds on the results of a previous research project which led to the development of the HYFOR pilot plant at the Voestalpine Donawitz site in Austria, involving K1-MET, Primetals Technologies, VoestAlpine and the University of Leoben as main partners.

The key steps involved in the Hy4Smelt approach are as follows:

Iron ore pre-processing (heating and oxidation): In this process step, the iron ore feed (composed of ultra fine iron ores which can be used directly without grinding or sinter feed which require preliminary grinding to a particle size typically < 150 µm and maximum 500 µm) is transferred to a cyclone cascade for calcination, oxidation, dehydration and preheating of the raw material at 900 °C. This is achieved using a fuel gas burner which provides hot gas in the temperature range of 1000 °C. During the development of the demonstration plant, natural gas will be initially used for the preheating step, but burners will be upgraded later to become CO2 neutral with use of green H2 as fuel in the future.

H2-based direct reduction (HYFOR fluidised bed reactors): After preheating, the iron ore feed is charged into the HYFOR fluidised bed reactors. In total, 2 successive reactors are used. In the reactors, the H2 gas fluidises the ore particles and, together with thermal energy, reduces the iron ore from Fe2O3 to Fe3O4, FeO and finally to metallic iron. The steam produced in the reduction reaction is separated from the process gas using a scrubber and the resulting water can either be discharged after treatment or collected as a resource for H2 production, in particular in arid areas. The degree of metallisation depends on the iron ore grade and type but is typically around 40 % after the first reactor stage, and up to 94.4 % after the second reactor stage. At the demonstration plant, green H2 is available and produced using a proton exchange membrane electrolyser (PEM) of 6 MW capacity (Production rate: 1 200 m3 / h H2) installed at the Voestalpine Stahl Linz site. This PEM electrolyser was built and commissioned as part of the Horizon 2020 funded project H2FUTURE during the period 2017-2021 (Grant Agreement N. 101193416) .
After reduction, the hot DRI (HDRI) is pneumatically fed to a bunker where the fluidised material is degassed. This gas stream leaving the fluidised beds is dry dedusted and sent through a pressure swing adsorption (PSA) unit to separate and recycle most of the H2 from the bleed gas. A heat exchanger ensures an efficient utilisation of the thermal energy of the gas. The dust collected is directly returned to the beginning of the HYFOR reactor to prevent material losses. The produced amount of HDRI production rate typically ranges from > 1.5 t/h up to 2.2 t/h. Below the HDRI bunker, the HDRI can be pressed to hot compacted iron (HCI) for storage or immediate use in the smelter. Preferably, the HDRI can be directly transported to the smelter saving the energy employed for compacting and reducing the required power for smelting by supplying hotter and high surface raw material which will contribute to an efficient process.

Smelter: The Hy4Smelt smelter is of circular design and uses graphite electrodes that will be positioned closer to the slag/hot metal resulting in shorter arcs. It enables the production of about 2.5 t/h hot metal in a continuous process. Two small bunkers are situated above the smelter. The first bunker is used to allow quick adjustments of the carbon content (using e.g. bio-carbon) and the second one provides an additional source of iron carriers (e.g. scrap).
The production targets for the smelter are as follows:

• Hot metal from C-free DRI/scrap for direct use in BOF or EAF with flexibility in C-content up to 4,5 %;
• Slag composition comparable with granulated BF slag usable for cement sector with FeO content < 1 %.


CROSS-MEDIA EFFECTS (Trade-offs)
After the technology has reached the market, increased H2 requirement of the steel industry poses an environmental and social risk in areas with low water availability, or which are prone to droughts. This can be mitigated by the recovery and the treatment of the water from the iron ore reduction in the HYFOR reactors either for direct recycling via electrolysis or other use. Additionally, the HYFOR off-gas system includes a dry dedusting step to minimise water treatment requirements and water losses via sludge.

BARRIERS TO IMPLEMENTATION
The only expected barrier for implementation of the Hy4Smelt technology is expected to be the availability of sufficient hydrogen at an acceptable price to compete with existing natural gas based direct reduction plants.

Basic information about the technique

Production data

Slag production: 1ton / hour Reduction fully based on green H2 (1.500 m3 / h) and heating fully electrified.

Associated main production process(es) and product(s): HYFOR/HY4SMELT demonstration plant

Production data: 3 ton / hour of hot metal

Participant Companies