Since the Industrial Revolution, atmospheric carbon dioxide levels have risen from 280 ppm to 413 ppm. Carbon dating shows this increase is linked to the burning of fossil fuels (coal, oil, and natural gas). While 1 degree Celsius may not seem like much, it is believed that any further increase would have serious consequences, such as the disappearance of sea ice, the retreat of glaciers, and a rise in sea level, currently measured at an average of 3.3 millimeters per year. To avoid the adverse effects of climate change, global warming needs to be kept below 2 degrees Celsius.
In terms of total global fossil and industrial emissions, the steel industry is a specialized single sector, accounting for 7% to 9% of greenhouse gas (GHG) emissions. It is a specialized industrial source of emissions, currently accounting for approximately 8% of global final energy demand. Therefore, it is a primary concern for governments worldwide. On the other hand, steel is essential to the modern economy, and therefore, global demand for steel is projected to grow to meet increasing social and economic welfare needs. It is also a key input in the clean energy transition. Electricity generation and consumption depend in part on the ferromagnetic properties of steel and its alloys. Steel is a critical input material for wind turbines, power transmission and distribution infrastructure, hydroelectric and nuclear power plants, and other key energy sector assets.
Green steelmaking involves the use of processes that reduce CO2 emissions. The EU, the US, Canada, the West, Japan, South Korea, Australia, and China are all developing green steelmaking processes. Five key directions are being explored for the development of green steelmaking technologies. These directions are: (1) technologies involving coal use, (2) technologies involving hydrogen use, (3) technologies involving electronics, (4) technologies involving biomass use, and (5) technologies involving carbon capture, use, and/or storage (CCUS). Figure 2 shows the pathway to breakthrough technologies for reducing CO2 emissions from ore-based steel production routes.
In the EU, breakthrough technologies are being developed under the ULCOS (Ultra-Low CO2 Steelmaking) program. Under this program, the following development work is underway: (i) a Top Gas Circulation Blast Furnace (TGR-BF) with Carbon Dioxide Capture, Use, and/or Storage (CCUS); (ii) the HIsarna process with CCUS involving smelting reduction; (iii) ULCORED with CCUS involving a novel direct reduction (DR) concept; and (iv) electrolysis. In addition, ULCOS is also investigating the use of carbon from sustainable biomass and hydrogen-based steelmaking.
In the United States, a public-private partnership is underway between the American Iron and Steel Institute (AISI) and the U.S. Department of Energy (DOE) and the Office of Industrial Technology. Two projects represent significant steps forward. These are (i) suspended hydrogen reduction of iron oxide concentrate and (ii) molten oxide electrolysis (MOE). In the near term, AISI members are developing a paired straight-hearth furnace, a coal-based DRI and molten metal process for long-term replacement of blast furnaces and coke ovens.
In Japan, development work is being carried out under the COURSE50 program, involving six steel and engineering organizations, the Japan Iron and Steel Federation, and the New Energy and Industrial Technology Development Organization. The research and development objectives of this program are: (1) to reduce carbon dioxide emissions during the reduction of iron ore in blast furnaces using alternative reducing agents (hydrogen); (2) to modify coke oven gas with the aim of increasing hydrogen content by utilizing waste heat; and (3) to reduce high-strength and highly reactive coke using hydrogen. Development work is also underway to capture carbon dioxide from blast furnace gas, including (i) chemical and physical absorption to capture, separate, and recover carbon dioxide, and (ii) utilizing waste heat from steel plants to reduce the energy requirements for capture, separation, and recovery.
In South Korea, development work is being carried out with the participation of POSCO, RIST, POSLAB, and POSTECH. Three promising routes for breakthrough carbon dioxide solutions have been identified. These are: (i) carbon refining of steel, including the FINEX carbon refining process and pre-reduction and heat recovery of hot sinter; (ii) carbon capture and storage (CCUS) in steelmaking by using ammonia to absorb carbon dioxide and by storing carbon dioxide in offshore gas fields; and (iii) hydrogen steelmaking by using hydrogen-rich syngas to reduce iron ore in the FINEX process and by using hydrogen-rich blast furnace processes.
Emerging technologies for reducing or avoiding carbon emissions in steelmaking can be divided into two distinct categories: (i) carbon capture, use, and/or storage (CCUS) and (ii) alternative reduction of iron ore. CCUS employs different methods to capture carbon dioxide emissions. It either stores them (e.g., in geological formations such as depleted subsea gas reservoirs) or treats emissions for continued use. CCUS alone cannot achieve carbon neutrality. However, if fossil fuels used in steelmaking are replaced with biomass, it can lead to a negative carbon dioxide balance.
The second category of potential technologies involves replacing coke or natural gas with alternative reducing agents for iron ore. These include hydrogen and direct current (DC). The advantage of these technologies is that, in theory, they can make steel production completely green. However, most of them may require more time and money to establish compared to CCUS.