Open bath furnace (METIX technology)

The Open Bath Furnace (OBF) technology, developed jointly by METIX and the SMS group, is developed to melt DRI for the production of liquid iron, which can subsequently be processed into liquid steel via BOF steelmaking. The OBF process operates in conjunction with a direct reduction plant to produce pig iron that can be processed within existing brownfield BOF facilities. Unlike the EAF route, the OBF can efficiently process lower‑grade iron ores, with an iron content as low as 58%.

TECHNICAL DESCRIPTION
Key elements of the OBF technology are:
• Open bath furnace: The DRI is fed at an elevated temperature directly to the OBF, making use of the sensible energy to lower the specific energy consumption. The OBF provides precise control of high‑metallic‑content DRI feedstock and is compatible with both AC and DC power supplies. Furnace geometry (rectangular or circular) is selected according to the target annual throughput. Multiple OBFs are required for production capacity above 2.0 million tonnes per annum. At present, the maximum production capacity which may be reached is 2.5 million tonnes of steel using one direct reduction plant and two rectangular OBFs.
• Carburisation: Carburisation lances are used to produce pig iron and achieve the specific carbon levels required for downstream BOF processing. The OBF accommodates anthracite in place of coke and is compatible with bio‑reductants; fine anthracite fractions (<50 mm) are acceptable.
• Off-gas recovery: Hot DRI feed reduces overall energy demand, and off‑gas can be recycled to the direct reduction unit to improve thermal and carbon efficiency. The system is engineered for hydrogen‑ready operation in both pre‑reduction and furnace reduction stages.
• Slag production: Slag production is targeted at approximately 100–120 kg per tonne of metal and is processed to achieve cementitious properties suitable for use as a clinker substitute.
• Material efficiency: The OBF in combination with a direct reduction plant enables a reduced reductant usage <80 kg/ton pig iron t compared to a blast furnace (about 900 kg/ton pig iron).

DEGREE OF MATURITY
The OBF process has been comprehensively conceptualised and de-risked through first-principles mass and energy balances. Laboratory-scale testing was conducted on a 200-kW furnace, followed by successful upscaling to a 1.5 MW pilot furnace, designed and built in-house. The technology has currently reached TRL 7.
The first commercial OBF units are scheduled for commissioning by 2028, at which point this technology would reach TRL 9.

CROSS-MEDIA EFFECTS
The OBF process achieves substantial carbon reductions but is not fully carbon‑neutral due to the controlled use of carburisation. Carbon lances provide precise dosing and improve reductant efficiency, which mitigates net emissions; the system is also compatible with bio‑based reductants, providing a clear pathway for further decarbonisation.

The use of fluxes to optimise slag chemistry for cementitious applications introduces a modest carbon penalty, primarily driven by lime production and its energy demand. This adds approximately 0.2 kg CO₂eq per kg of slag, however it remains substantially lower than 0.8 kg CO₂eq per kg associated with conventional cement clinker production and therefore delivers a net environmental benefit.

Basic information about the technique

Participant Companies