The traditional method of steel production is based on blast furnace - BOF route: iron ore is reduced and molten in a blast furnace using coke before refining in BOF converter. The coke burns and produces energy and the iron ore is reduced due to its reactions with carbon and carbon monoxide. This produces a large amount of carbon dioxide. For example, the SSAB steel mill in Raahe causes 7 percent of Finland's CO2 emissions.
Fighting climate change has created a need for steel industry involving less carbon consumed. One of the ways to achieve this goal is hydrogen reduction, in which hydrogen is used instead of carbon in the reduction process. Increased recycling of steel is another way. Hydrogen reduction functions in a solid state, producing water as a by-product. Recycled steel is already in a metallic state and does not need to be reduced.
As these production routes do not require carbon, an electric arc furnace is used instead of a blast furnace. Steel scrap or solid-state reduced, so-called sponge iron, is smelted in a furnace using an arc produced by electric current. The proportion of electric arc furnaces in steel production is expected to increase in the future. For example, in China these are currently used to produce only ten percent of the steel, but the amount of recycled steel, and consequently the need for electric arc furnaces, is increasing constantly there. In Finland, slightly less than half of the country's steel production is based on recycled steel.
Electric arc furnaces, recycled steel, and hydrogen reduction also play a key role in a plan by SSAB to offer fossil-free steel from the beginning of 2026.
New measuring method analyses light in electric arc
The electric arc furnace process related research has been a focus area at the University of Oulu's Centre for Advanced Steel Research (CASR) already for about a decade. Development challenges of the electric arc furnace are also being tackled in the Oulu-based “ecosystem” of the university and companies in the steel business, as well as in the national Platform economy in refining metal (AMET) project, which bring together both academic entities as well as SMEs and large corporations.
One of the most important solutions is a new kind of measuring technique which makes it possible to monitor what happens in an electric arc furnace during smelting in real time. It is especially important to know when the steel scrap in the furnace has melted: steel scrap comprises bulk goods that vary considerably in density and chemical composition, which means that the smelting time fluctuates.
“And when the scrap has melted, the waste of energy accelerates”, explains Matti Aula, head of research at the Oulu-based company Luxmet. “Information on the melting tells us when the furnace needs to be charged again. This helps avoid wasting heat, while accelerating the process.”
The key to the knowledge is the method developed by Luxmet, a spin-off company that emerged from steel research at the University of Oulu, in which optic fibres are placed on the cover of the electric arc furnace. They collect light from the electric arc, which is analysed in real time using artificial intelligence.
At present, the optical online emission spectroscopy method mainly indicates melting, but the goal is to analyse the composition and purity of the molten steel. These also vary considerably with recycled steel, and the differences only grow as increasing amounts of poor-quality steel are recycled.
Until now, taking samples has been the only way to ascertain the composition, and this requires stopping the process. “Now we have noted that we can get the necessary data from online measurements, but the technical details still need to be perfected”, Aula says. He believes that the online measurement of composition will reach the market in five years. A simpler online system is already available.
“It is also capable of diagnosing where the light comes from - the slag, the flames, or the arc.” This makes it possible to know more accurately how efficiently energy is used, for example.”
Modelling improves competitiveness of electric arc furnaces
The analysis of the light from electric arcs is linked to a broader theme – the modelling of the electric arc furnace process, which is a speciality of the University of Oulu's Centre for Advanced Steel Research.
“We study how the process can be modelled in such a way that we can get a real-time forecast of the final outcome”, says Ville-Valtteri Visuri, deputy director of the Process Metallurgy research unit. “This is not just about getting a real-time picture of what is happening in the furnace, but rather a wider forecast of where the electric arc furnace process is going. Optical emission spectroscopy can be utilised as one of the sources of information for the model.”
Analysis of the light is the only measurement that is done directly in connection with the electric arc furnace process. Other sources of information include measurements taken before and after the process, such as analyses of steel and slag compositions, cooling water, and flue gas analysis.
In addition to measurement data, mathematical methods are also needed. “The model comprises mathematical descriptions of phenomena that occur inside the furnace”, says Timo Fabritius, Professor of Process Metallurgy. “These include the combustion of metallic elements that are oxidised, the production of heat, and heat losses.”
For example, the model predicts when melting begins, and for energy consumption per ton of steel produced, after which corrective measures can be taken. “It also enables the use of different practices that are suitable for different situations, like running the furnace at lowered power input when more time is available to complete the smelting, or if time is short, it can be turned up to maximum output”, Fabritius says.
With the help of modelling, improved efficiency in the electric arc process can advance steel production with decreased CO2 emissions. “One reason for blast-furnace type production is its competitiveness”, Ville-Valtteri Visuri says. “The more competitive the electric arc process is, the greater the share of recycled steel in the production.”
Use of biochar poses its own challenges
Decreased CO2 emissions is also the aim of research on the use of biomass-based carbon. In an electric arc furnace carbon is needed as an alloying element; whereas excess carbon needs to be removed from steel reduced in a blast furnace, it needs to be added to hydrogen-reduced steel. Second, carbon monoxide and carbon dioxide increase the amount of so-called foamy slag, which prevents the radiation from electric arcs onto the walls of the furnace, thereby improving its energy efficiency. In addition, the foamy slag process creates fine materials, such as dusts, which are utilised by feeding them back into the process. The challenges of biochar usage are linked with these three aspects.
“We are studying how biochar dissolves into steel, how it can be used to generate foamy slag, and how different kinds of dusts should be recycled to control the slag chemical composition, and to make it froth well and in a stable manner”, Fabritius says.
Using coal and coke dust to achieve foamy slag is relatively easy and they dissolve well into steel. Things are different with biochar, Matti Aula observes. “It is very reactive and the effervescence can collapse quickly.”
To keep the slag foaming under control it is important to follow it in real time, and in this as well, the Luxmet optical online emission spectroscope is of great significance. This spring the company plans to test its first timing system for slag foaming.
“The topic has not been studied before in the pursuit of carbon neutral metal production, and nobody is doing anything like this anywhere in the world”, Fabritius says.
The steel company SSAB is also seeking to minimise CO2 emissions, and plans to make its steel production fossil free. At the Raahe steel mill, electric arc furnaces will replace the first blast furnace in 2030 and the second in 2040.
Initially, the electric arc furnace will be used mostly for melting steel scrap, says Jarmo Lilja, Process Development Manager at the Raahe steel mill. The manufacture of hydrogen-reduced sponge iron is set to begin at a demonstration plant in 2026 and the location of the production facilities is still unknown.
“If something like that were to come to Raahe, our electricity consumption would grow considerably”, Lilja says. In addition to the furnaces, additional electricity is needed for the production of hydrogen through electrolysis.
“Then our energy needs would be 12 terawatt hours a year. About 20 percent of this would be produced using biogas, because we need to shift to renewable energy even in the heating of the slabs.”
The comment is a reminder that recycled steel and hydrogen reduction alone are not enough to make steel production a low-carbon effort. In addition to the electricity needed for them, the surrounding processes, such as refining the raw steel and the rolling of the steel slabs, must also be carbon neutral.
The use and accessibility of fossil-free energy sources are being examined in the SSAB's Energy4HYBRIT project in which the Raahe mill is a pilot plant. In addition to energy companies, the University of Oulu, and VTT Technical Research Centre of Finland are both involved, studying and modelling all of the energy and material flows in the mill.
Players in the steel field ecosystem complement each other
In addition to low CO2 emissions, flexibility is an argument on behalf of electric arc furnaces. “The process is extremely flexible compared with blast furnace production, which cannot be turned off at will in accordance with the market situation”, Ville-Valtteri Visuri says. “It also makes it possible to produce steel profitably even on a small volumes.”
The Oulu-based ecosystem in the field, as well as the AMET project, funded by Business Finland add their own input into the development work of the electric arc furnace. SMEs are developing ways to identify scrap baskets using bluetooth technology, the monitoring of how full the scrap basket is, and how it is tipped over, and measuring the wear on the electrodes. The last mentioned is the responsibility of Sapotech Oy, whose chairman of the board, Juha Roininen, is pleased with how well the ecosystem works together.
“The situation in Finland is good, because the different players in the steel field know each other and there is little competition against each other. Everyone can participate in their own specialised fields. Large metallurgical companies offer a platform for compiling new methods, and SMEs get international references from these global players. Digital technology creates completely new aspects for competition; in the past, technological players tended to be inflexible large companies, but digital solutions require such expertise that great opportunities will be available for SMEs that are flexible and focused on the matter. State funding through Business Finland is also important.”
The main research activities are focused on the study of pyrometallurgical and other high-temperature processes, and teaching that is based on it, with an emphasis on skills and knowledge in methods required in research and development work. Process metallurgy is one of the key areas of the University of Oulu's Centre for Advanced Steel Research (CASR).
Luxmet develops guidance systems based on light for more precise monitoring of metallurgical processes. The company was founded in 2014 on the basis of multidisciplinary electric arc research conducted by the process metallurgical research group.
Sapotech designs and supplies clients in the steel and metal industry with real-time monitoring and measurement systems. Core expertise of the company include the monitoring and imaging of high-temperature processes. Sapotech's roots are in the Process and Environmental Technology Section. The company was founded in 2012.
Main picture: Measurement techniques have been developed at the University of Oulu that can help monitor function of an electric arc furnace. With the help of spectural analysis it is possible to improve cost-efficiency and quality of the process.
Text: Jarno Mällinen
Last updated: 19.8.2020