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Magazine17 Min

Pathways towards green steel

Three cases for the decarbonization of the steel industry

The technologies for achieving climate-neutral steelmaking are available right now - ready to be implemented in existing and future plants. How, what, when, and where that can happen depends on several factors. Thankfully, there is an SMS group solution available for any scenario.

The green transformation of the steel industry is a marathon, not a sprint. By the middle of this decade, lighthouse projects like H2 Green Steel and thyssenkrupp Steel will prove that carbon-neutral steel production is possible. However, due to the long investment cycles for metallurgical plants, a large part of future CO2 savings must come from the conversion of existing mills. Here, there is no one-size-fits-all ‘best’ option. That’s why we have tailor-made solutions for any customer scenario that take into account local conditions such as iron ore quality, energy infrastructure, and existing equipment, as well as local policies, rules, and regulations.

All three major decarbonization routes have the potential to achieve climate neutrality by introducing innovative integrated process solutions in new (greenfield) or existing steel (brownfield) plants and by putting in place additional infrastructure for the use of fossil-free energy sources like hydrogen, biomass, or green electricity. Carbon capture can further be applied to go the last mile towards climate neutrality.

Brownfield case: Blue Blast Furnace Modernization

Today, the integrated, ‘primary’ Blast Furnace-Basic Oxygen Furnace (BF-BOF) route is the dominant configuration for iron and steel production. Despite its high CO2 emissions resulting from the use of large amounts of iron ore, mostly with low iron content, and limited amounts of scrap, blast furnace technology remains a crucial component of the iron and steel production process. Rapid greenhouse gas emissions reduction requires the gradual conversion of existing plants and infrastructure. That's why we have developed the ‘blue blast furnace’ technology as a bridging technology on the path to a greener future in steel production.

The defining feature of the blue blast furnace and the first main step towards EASyMelt is the generation of syngas and its injection through a new bustle pipe at the lower shaft portion of the blast furnace to achieve emission reductions of up to 28%. Synthesis gas – or syngas – consists primarily of carbon monoxide and hydrogen and performs as a reducing gas to enable a reduction of the iron burden in the shaft, thus replacing coke.

The gas may be produced via a variety of technologies. One is a new reforming process, the so-called dry reforming of coke oven gas in reformer stoves, during which blast furnace gas and coke oven gas are reformed at a high temperature. Since the process only uses exhaust gases from the steel plant and can replace coal, the potential to reduce CO2 is high. Apart from the reformer stoves, there are other available technologies to produce syngas, like the reforming of natural gas or coke oven gas and tar.

Pilot plant at ROGESA

Paul Wurth has successfully operated a pilot plant in Dillingen, Germany at ROGESA Roheisengesellschaft Saar mbH for testing the dry reforming process of coke oven gas with blast furnace gas. This is an important milestone in the development of dry reforming technology and the generation of syngas. The process involves producing syngas using a high-temperature catalyst-free reforming process. The first months of operation have proven the feasibility of the process, with excellent conversion ratios of up to 98%. The syngas produced by Paul Wurth's dry reforming process has the optimum composition and temperature for versatile use as reducing gas in the BF process, significantly surpassing the syngas quality produced by traditional catalytic reforming processes. The quality and high temperature of the reducing gas not only allow the utilization at the shaft level but also at the tuyere level.

Brownfield case: Upgrade with EASyMelt

Based on but going beyond the emission reduction potential of the blue blast furnace, SMS group is developing EASyMelt. This electric-assisted syngas smelter will function as an alternative to the direct reduction route and as a complementary block for filling the gap between iron ore availability and green steel demand.

The concept aggregates the latest technologies developed by Paul Wurth for substituting the traditional blast furnace in integrated steel plants and helping them achieve carbon neutrality. EASyMelt is an electrified direct reduction and melting process, using a minor quantity of coke to entirely replace the traditional hot blast with gases like coke oven gas, natural gas, hydrogen, and ammonia. Depending on the energy input, the technology can achieve emission savings of above 60% compared to the traditional BF-BOF route. Remaining direct emissions can be reduced by applying carbon capture or through the use of biomass or biogas as feedstock. Using existing plants as a basis, EASyMelt is less CAPEX-intensive than any other low-carbon ironmaking technology.

The process is flexible in its input, adds resilience against supply shortages and market volatility, and can be adapted to various scenarios. Most importantly, however, traditional sinter feed may still be used in EASyMelt, avoiding fierce competition for the limited supply of (high-grade) pellets pellets resulting with its energy flexibility to highly competitive operational costs. Just like the blue blast furnace, EASyMelt can be realized in a step-wise approach of implementing several technological elements that work together to net-zero ironmaking. The central elements are the shaft injection of reducing gas, plasma-based superheating of the tuyere injection, and finally, the capturing of remaining emissions for storage or utilization.

Brownfield case: Direct reduction into Open Bath Furnace

Another leading candidate in the race to decarbonize existing sites is the combination of the well-proven MIDREX® direct reduction process using a shaft furnace and an open bath electric furnace (OBF) for substituting existing blast furnaces. The first example of this case will installed at thyssenkrupp Steel.

The technology combines two key processes: the direct reduction of iron ore in a shaft furnace and the conversion of the resulting sponge iron into high-quality steel. Initially, it is possible to run the direct reduction plant (DRP) on a natural-gas basis, gradually introducing hydrogen at higher rates.

The OBF is similar in design to a conventional Submerged Arc Furnace (SAF) operated in a so-called ‘brushed arc’ mode. SMS group has several hundreds of references for these kinds of furnaces.

The DRP-OBF route is both suitable for brownfield and greenfield projects. In existing steelworks, this combination replaces the BF and its associated sintering-, stove- and coke facilities. The ideal combination of a DRP and associated OBFs is to have both installed alongside one another from the start. This enables hot charging DRI to the OBF, making use of sensible energy to lower the specific energy consumption.

The combination of direct reduction based on natural gas together with an OBF already reduces CO2 emissions by about 50% compared with the conventional BF-BOF route. These emission savings are achieved thanks to the higher hydrogen content in natural gas. In a second step, the natural gas can gradually be replaced with hydrogen as a reducing gas, which allows for further CO2 reduction of up to around 65%.

One of the main benefits of this technology is that it reduces the need for coking coal, a key ingredient in traditional steelmaking processes. The direct reduction with OBF and BOF converter technology is highly flexible and adaptable. Today’s direct reduction shafts require pellets or high-grade lump ore. The OBF would then ideally be charged with the hot DRI, significantly reducing electrical energy consumption. Alternatively, the OBF also accepts any pre-reduced iron ore feed, including hot briquetted iron (HBI), cold DRI pellets, or even DRI fines. Thanks to its reducing nature, the OBF is not sensitive to low ore quality, addressing the Electric Arc Furnace’s inefficient processing of low-grade iron ores and making hydrogen-based green steel from low-grade ore more feasible in the future. In addition to the hot DRI fed to the OBF, up to 10% of the OBF material feed can be comprised of agglomerated waste or free-flowing scrap. This allows steel plants to consume wastes from their existing facilities by utilizing an inexpensive agglomeration process to prepare these for addition to the furnace. The OBF can also generate a slag similar to BF slag that can be granulated and valorized in the cement industry.

Iron making with MIDREX® technology

Based on a construction license agreement, Paul Wurth supplies MIDREX® direct reduction ironmaking plants as part of its portfolio. MIDREX offers three main technologies bridging the transition from 100% natural gas to 100% hydrogen:

  • MIDREX NG™ allows up to 30% of natural gas to be replaced with hydrogen without equipment modifications.
  • MIDREX Flex provides the flexibility to operate on any mixture of natural gas and hydrogen (up to 100% hydrogen) with some minor modifications
  • MIDREX H2 is designed to use up to 100% hydrogen in a MIDREX Shaft Furnace as feed gas.
The DRI plant of Algerian Qatari Steel (AQS) was supplied by MIDREX and Paul Wurth as consortium partner.

Greenfield case: Direct reduction into an Electric Arc Furnace

In a greenfield project and with green hydrogen available at competitive prices in sufficient quantities, the combination of direct reduction and electric steelmaking is the best solution.

To operate any direct reduction technology while remaining competitive, sufficient natural gas or green electricity are a necessity. This is the reason why gas-based direct reduction plants have been built in locations like the Middle East, North Africa, North America, and Russia. The pre-reduced high-grade grade iron ore pellets are reduced in a MIDREX® shaft and then fed into an electric arc furnace as hot DRI. The EAF then melts the material and produces liquid steel. No intermediate step is required, and – depending on the MIDREX® technology in use – only minor carburization is needed to reduce the nitrogen in the steel.

Switching from natural gas use to renewable hydrogen, this route comes closest to carbon neutrality. The carbon content of low to zero carbon DRI resulting from H2 reduction may be modified in the lower cone, also called the cooling zone, of the shaft furnace. Scrap can be added to the EAF with only the potential scrap contamination and quality requirements of downstream processing stages setting an upper limit. This route is particularly interesting for greenfield projects – hence on newly constructed steelmaking sites.

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