What is an optimal route for green steelmaking?

The European Union aims to become climate-neutral by 2050, posing challenges and opportunities for the steel industry as it transitions to green steel amidst hurdles like raw material and energy availability, environmental impacts, and strict requirements. Traditional steelmaking, which relies on fossil fuels, competes with emerging technologies utilising renewable resources, with biofuels and carbon capture offering interim solutions. However, a shift towards electrical and potentially nuclear energy is vital for sustainability.

The optimal production route for green steelmaking looks different depending on the geographic location. Since the whole market is fundamentally changing, one must consider other aspects than just the route that is technically optimal.

Decarbonising steel requires new production methods

The dialogue around the production of green steel has emerged as a focal point in recent years within the steel industry. Technology suppliers have already started to refine their existing product portfolios, including for example Direct Reduction Processes (DRP), EAF, and Open Slag Bath Furnace (OSBF) technologies, to align with the prerequisites of green steel production. Concurrent advancements in large-scale hydrogen production technologies have also played a crucial role in facilitating this shift. As an example, in Figure 2, a more detailed process flow for a gas-based DRP (100 % hydrogen) + EAF route for green steel production is illustrated.

Differences in green steel production between countries

The definition of green steel varies among producers, influenced by their production facilities and technologies. This shift towards green steel increases the focus on utilities' roles in facilitating these changes, especially as the technology for reducing emissions—like gas-based direct reduction—depends heavily on the geographical location of the steel plants. In Europe, advancements in green steel rely on hydrogen produced through electrolysis, while in the United States, natural gas reforming is used to produce the necessary reducing gas. Currently, it appears that Europe's investment in hydrogen technology is the only path to achieving zero emissions, as the United States' reliance on natural gas falls short due to its inevitable carbon dioxide production. Given hydrogen's high cost, the question remains whether Europe can economically support this transition and what the implications are if it fails to do so. Should Europe not adapt, the steel industry may be compelled to relocate to the US, Asia, and other countries where costs are more manageable.

Table 1 presents a comparison of total emissions from green steel production before secondary metallurgy, considering different geographical locations and various production routes. The traditional Blast Furnace – Basic Oxygen Furnace (BF-BOF) method is the industry baseline, compared with gas-based Direct Reduction Process-Electric Arc Furnace (DRP-EAF) routes using hydrogen in Sweden and Germany or natural gas in the USA, and a coal-based method in India. The calculation of total emissions accounts for all steps in the production process, assuming the use of renewable electric energy. This highlights the complexity of achieving green steel production.

Comparison of EAF and OSBF

EAF and OSBF are currently the main production routes for green steel. These technologies, having been in existence for many years, are highly refined. Concurrently, there are other emerging technologies in the field; however, they currently lack the necessary capacity and technological maturity to be considered viable alternatives.

Iron ore is the primary raw material used in steelmaking, predominantly consisting of the iron oxides hematite (Fe2O3) and magnetite (Fe3O4), with hematite being the most common. In its pure state, hematite has an iron content of 70%, while magnetite contains 72% iron. Iron concentrations in high-grade ores typically range from 50% to 68%, whereas lower-grade ores have iron contents between 30% and 50%. The other components in iron ore are typically acidic or acidic-like gangues such as silica and alumina​. It's important to note that each iron ore deposit is unique in terms of geology and mineralogy.

Considering two different qualities of raw material and the two different production routes, specific energy, and raw material consumptions between them are compared below. According to techno-economic analysis in studies conducted by AFRY, 200 kg slag / t steel has been identified as a threshold between the OSBF route and the EAF route when using ~87 % DRI in charge mix. Slag output over the threshold favors OSBF and lower values favor EAF. However, the desired product portfolio and potentially higher scrap share (high quality scrap being readily available) influence the final decision making. The used parameters for EAF and OSBF are presented in Table 3.

The impact of different types of DRI on selected specific consumptions and outputs of EAF and OSBF are presented in Table 4. The specific electrical consumption in EAFs varies depending on the burner configuration and usage.

The performed analysis supports the view that if the calculated slag output is less than 200 kg/ t steel, the EAF route is preferred. With lower-quality DRI in the EAF slag output exceeds the identified threshold, subsequently increasing energy consumption and overall OPEX. Therefore, for lower-quality DRI, selection of the OSBF process route is preferred purely from a techno-economic sense. However, to produce less demanding steel grades, a higher scrap share in the charge mix would make the EAF route feasible even with a lower-quality DRI.

An optimal route for green steelmaking

Building on the analysis presented earlier, it becomes clear that the optimal approach to green steel production is influenced by a large set of variables. By affixing several of these variables from the beginning it is possible to make an early decision on the appropriate production technology and find balance between technical and practical considerations. Major pitfalls for a potential green steel plant are the potential choice between modifying and connecting into an existing plant or building a new one, underestimation of national/local utility infrastructure, availability of raw materials, and long-term supply security of higher-quality raw materials.

Crafting custom solutions for green steel production

The pursuit of green steel production does not lend itself to a one-size-fits-all solution. The optimal route depends on the local conditions, availability of energy, raw materials and skilled labor, the environmental and social impacts and the market demand and competition. AFRY’s expert role lies in crafting tailor-made solutions that are fit for purpose. Identifying each client's unique parameters, their specific raw material base, the availability of utilities and commodities like electricity, hydrogen, and natural gas as well as the developing product portfolio. More efficient energy usage and utilisation of by-products and waste such as slags, skulls, used refractories and dust are in focus. Moreover, ensuring seamless integration with existing operations, downstream processes, and other infrastructure components is critical. This approach allows for the development of a techno-economically optimised process chain tailored to each unique situation.

This article was written by Suvi Rannantie, Aleksi Laukka, Petri Palovaara, Jussi Niemelä, Matti Sakaranaho, Virpi Leinonen and Janne Tikka.