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Michael Zarl: Hydrogen Plasma Smelting Reduction - The Vision of Green Steel
from Materia 2/2024
How Hydrogen Plasma Smelting Reduction could aid on the way to a greener society
Europe is in the transition to a climate-neutral, competitive and circular or resource-efficient economy. Continent has set ambitious targets with the Green Deal. The iron and steel industry is a central part of the European economy. It has to face various challenges to achieve the climate targets associated with the transition towards CO2-neutral production by 2050.
Most steel made in Europe is produced via the blast furnace - basic oxygen furnace route (BF-BOF; ~60%) and the electric arc furnace route (~40%). Figure 1 illustrates possible steel production routes originating from iron ore in a condensed form. The production process of steel using the BF-BOF route consists of smelting and reducing the pretreated iron ore in the blast furnace, thereby generating hot metal which is subsequently converted into crude steel in an oxygen blast furnace. Even though these processes are optimized in terms of energy, they are nonetheless CO2-intensive. Other production routes starting from the ore are either the direct reduction (reduction in the solid-state) with subsequent smelting to crude steel in the electric arc furnace or smelting reduction, which produces a hot metal-like product. Particularly when considering the additional processing of the ore, the aforementioned routes consist of multiple stages. Hydrogen plasma smelting reduction (HPSR) enables direct conversion of iron ore into crude steel while providing a high CO2 reduction potential as compared to the integrated BF-BOF route. The primary feasibility has already been evaluated and validated on a laboratory scale. In the scope of the recently completed FFG project “SuSteel - Sustainable Steel” a test plant for the HPSR of iron oxides was erected at Voestalpine's Donawitz site (2020).
The plant consists of a refractory-lined lower vessel and a water-cooled double-walled upper vessel. The plasma gas as well as the feed materials are injected into the reactor from above by a movable plasma torch (hollow electrode with graphite bottom). A plasma flame (transferred arc) is formed between the electrode and the bottom anode, in which the material is reduced and melted within one step. The resulting crude steel is accumulated on the bottom of the lower vessel.
The off-gas of the process, which predominantly consists of water vapor and unconsumed hydrogen, is first fed into a scrubber (removal of dust components) and subsequently discharged via an off-gas duct. The process is operated discontinuously, with a maximum of 100 kg oxide ultrafine ore and a small amount of additives (e.g. lime) for one batch. The cycle takes approximately 1 hour, depending on the reduction rate. After completion of the trial, the produced crude steel solidifies in the lower vessel and is subsequently removed. There is presently no equivalent plant worldwide that enables the production of crude steel from iron ore in a single step with this production capacity. The current technology readiness level (TRL) of HPSR is 5, which clearly indicates that there are still long-lasting and challenging development stages ahead before a large-scale industrial implementation. Yet there is little time left to reach industrial readiness in order to counteract irreversible climate change and actively support global and European sustainability goals.
Scale-Up Project (SuS-F)
The planned measures are intended to set the course for further upscaling and integration into established steel production sites of this globally unique reduction technology for steel production from iron ores in one process step. This can significantly contribute to the decarbonization of steel production through the industrial use of green hydrogen as a reducing agent. In this way, sustainable development in Europe is to be ensured while at the same time safeguarding Austria as a business location. Furthermore, this project is intended to serve as an incentive for the progress and strengthening of developments in the hydrogen sector.
Figure 2 shows the planned layout of the facilities after the revamp in the SuS-F Project. The most important points addressed in the project are:
The process monitoring and automation which are critical for effective control, necessitating the implementation of optical emission spectroscopy (OES) and enhancements to existing gas mass spectrometry (MS). These technologies, already utilized in various applications, are pivotal for analyzing hydrogen plasma-based processes, necessitating adjustments to parameters based on sophisticated measurements. With new aggregates integrated into existing facilities, a unique concept is required to manage their interaction effectively.
Continuous feeding of pre-reduced ultrafine ore is essential for optimizing reduction kinetics. Investigating parameters such as hydrogen rate and feed material turbulence is crucial for minimizing material loss during operation. Handling pre-reduced ultrafine ores is complex due to the risk of reoxidation, necessitating a specialized conveying system design to prevent heat-induced damage.
Pre-reduction of ultrafine ores using process off-gas requires adjusting gas composition for optimal reduction and smelting coupling. Semi-continuous tapping is vital for maintaining process continuity, requiring the development of a hearth and tapping system.
Recycling and dehumidifying exhaust gas and dedusting are essential for complete off-gas recycling and economically optimizing specific hydrogen demand.
Aside from the shown project, a lot of other projects in the field of green steelmaking are focused on the development of the HPSR process. Figure 3 overviews the proposed and funded projects around the HPSR reactor development in Europe.
A lot of work is ahead of us to get the technology ready for industrial application in the years 2040-2050. The community is growing, and so is the rate of the development. Therefore, the whole international team included in the shown projects looks into a very exciting future with many things to learn. ▲
TEXT: MICHAEL ZARL, DIPL.ING. DR.MONT, SENIOR PROJECT MANAGER, K1-MET GMBH, AUSTRIA
