Technologies for emission-reduced steel production already exist. Plant manufacturers can already incorporate them into a large number of existing and future plants. However, how, what, when and where this can happen depends on several technological factors. We explain what these are here using several practical examples.
The green transformation of the steel industry is more of a marathon than a sprint. By the middle of the decade, the first lighthouse projects should show that carbon-neutral steel production is possible. But due to the long investment cycles for metallurgical plants, a large part of the future CO2 savings will have to come from retrofitting existing smelters. There is no patent recipe for the 'best' option here.
That is why companies like the Düsseldorf-based SMS group offer individual solutions for different customer scenarios. The aim is to take local conditions into account. These include the quality of the iron ore, the energy infrastructure, the existing plants as well as local guidelines and regulations.
All three major decarbonisation routes can reduce emissions by integrating process solutions into new ("greenfield") or existing ("brownfield") steel plants. In addition, an infrastructure for the use of fossil-free energy sources such as hydrogen, biomass or green electricity must be established. Furthermore, additional carbon capture, utilisation and storage technologies can serve to remove the last emissions from circulation.
The integrated primary blast furnace (BF-BOF) is still the predominant technology for the production of iron and steel. Despite the high CO2 emissions resulting from the use of large quantities of iron ore with mostly low iron content and limited quantities of scrap, conventional blast furnace technology remains a crucial part of the iron and steel production process.
Only by gradually converting such plants can their greenhouse gas emissions be reduced. The SMS group shows how this can work with the bridge technology of a "blue blast furnace". Its central feature is the generation of synthesis gas and its feed through a so-called bustle pipe in the lower shaft area of the blast furnace. According to SMS, this can result in an emission reduction of up to 28 %. Synthesis or syngas consists mainly of carbon monoxide and hydrogen and serves as a reducing gas to reduce the iron load in the shaft.
Syngas can be produced in various ways. One process has only recently been developed: the "dry reforming" of coke oven gas in reformer furnaces. In this process, blast furnace gas and coke oven gas are reformed at high temperature. Since only the waste gases from the steelworks are used here, replacing the coke-coal, there is great potential for CO2 reduction. Another way to produce syngas is to reform natural gas or coke oven gas and tar.
Engineering company and SMS subsidiary Paul Wurth has tested a pilot plant at ROGESA Roheisengesellschaft Saar mbH in Dillingen using this 'dry' reforming process. The first months of operation are considered proof of the feasibility of the process. The synthesis gas produced by dry reforming has the optimal composition and temperature for versatile use as a reduction gas in the BF process. The synthesis gas quality even exceeds that of conventional catalytic reforming processes.
The SMS group wants to increase the emission reduction potential of the 'Blue Blast Furnace: through the EASyMelt process. This electrically assisted syngas smelter is intended to close the gap between the availability of iron ore and the demand for green steel as an alternative to direct reduction.
The electrified direct reduction and metallisation process uses a small amount of coke to replace the highly heated steam completely with gases such as coke oven gas, natural gas, hydrogen or ammonia. Depending on the energy input, emission savings of more than 60 % are to be achieved in this way compared to the conventional BF-BOF process. The remaining emissions can also be reduced here by using CCS (carbon capture and storage) or by using biomass or biogas as feedstock. Based on existing plants, EASyMeltcould also beless CAPEX-intensive thanothertechnologiesforemission-reduced iron production.
The process promises greater resilience to supply shortages and can be adapted to different scenarios. Most importantly, EASyMelt can continue to use conventional sintered material, avoiding fierce competition for the limited supply of (high-quality) pellets. Just like the Blue Blast Furnace, EASyMelt is to be realised in a step-by-step approach in which several technological elements interact. The central elements are shaft injection of reduction gas, plasma-assisted superheating of the nozzle injection and, finally, capture of the remaining emissions for storage or use.
The MIDREX direct reduction plants in Paul Wurth's portfolio offer three main technologies to bridge the transition from 100% natural gas to 100% hydrogen:
MIDREX NG allows up to 30% of natural gas to be replaced by hydrogen without the need to modify the plants.
MIDREX Flex should be able to work with any mixture of natural gas and hydrogen (up to 100% hydrogen) after a few modifications.
MIDREX H2 can be used as a feed gas for up to 100% hydrogen in a MIDREX shaft furnace
Greenfield example: Direct reduction into an electric arc
If green hydrogen is available in sufficient quantities at competitive prices, the combination of direct reduction and electric steelmaking is the best solution according to many experts.
However, in order tooperate a direct reduction plant competitively, sufficient quantities of natural gas or green electricity are required. For this reason, natural gas-based direct reduction plants have been built in the Middle East, North Africa, North America and Russia, for example. The pre-reduced iron ore pellets are reduced in a MIDREX shaft and then fed as hot DRI into an electric arc furnace. In the electric arc furnace, the material is melted and liquid steel is produced. No intermediate step is required and - depending on the MIDREX technology used - only a minor carburisation to reduce the nitrogen content of the steel.
By switching from natural gas to green hydrogen, this method has the greatest potential for CO2 reduction. The carbon content of low to zero carbon DRI from hydrogen reduction can be modified in the lower cone of the shaft furnace, also called the cooling zone. Scrap can also be fed into the EAF, capped only by potential scrap contamination and the quality requirements of the downstream processing stages. This route is particularly interesting for greenfield projects at newly constructed steelworks sites.
An example of the application of this technology is the H2 Green Steel project in Boden, northern Sweden. Here, the feasibility of producing high-quality DRI using 100 % hydrogen is to be demonstrated. As the world's first near carbon neutral steel plant, H2 Green Steel has the potential to contribute to the path towards a more sustainable steel industry
Learn more about the possibilities of emission-reduced steel production and visit wire and Tube in Düsseldorf from 15-19 April 2024! Here you can experience the SMS group, Paul Wurth and H2 Green Steel, among others, live and learn more about the current status of their decarbonisation projects.