Hydrogen Might Be the Best Hope for the Steel Industry
To meet climate goals, carbon emissions from steel must drop 50 percent by 2050.
Bridges and roadways, railroads and shipping, pipelines and powerplants, high-rise buildings and warehouses, vehicles, and wind turbines—iron and steel are the primary materials that have made possible the modern age. But they come at a price. Using traditional blast furnace technologies, 1.9 tons of carbon dioxide (CO2) is emitted for every ton of steel created from iron ore. Among industrial processes, iron and steel rank first for CO2 emissions and second for energy consumption. The iron and steel industry accounts for approximately 30 percent of global industrial CO2 emissions.
Image used courtesy of APEP/UCI
Reducing Iron Ore
Iron ore must have its oxygen removed (reduction) to be made into steel. This is typically accomplished through the use of fossil fuels like coal (or sometimes natural gas) in a process called Direct Reduced Ironmaking (DRI). Coal is used to generate heat and produce coke, whose carbon then combines with the oxygen in the iron ore resulting in metallic iron and a process gas high in carbon dioxide. According to the International Energy Agency (IEA), to meet global climate goals, the carbon emissions from the steel industry must drop by at least 50 percent by 2050 and be on a pathway to zero emissions by 2070.
There are a variety of different ways that have been proposed to reduce carbon emissions from steel-making, including carbon capture, use and storage (CCUS), bioenergy, and direct electrification. One of the most promising, however, is using hydrogen to reduce iron ore instead of carbon.
Hydrogen as a transportation fuel, either through combustion in a traditional piston engine or to make electricity in a fuel cell, is a topic that has received considerable recent attention, although the challenges of making it into a practical transportation fuel are many.
Using Hydrogen to Make Steel
There are two ways hydrogen is being studied for use in steelmaking. It can be blended with fossil fuel reductants like natural gas to reduce overall greenhouse gas emissions. The second method is to use pure hydrogen as a reducing agent for iron ore in a process called hydrogen direct reduction (H-DR), whose waste gas is water vapor.
Hydrogen has the potential to be made in a carbon-neutral manner using renewable electricity to split water into hydrogen and oxygen—this is called green hydrogen. Another low-carbon way to produce hydrogen is to extract it from biogas. At present, however, more than 90 percent of hydrogen is made in a carbon dioxide-intensive manner from fossil fuels. This is called grey hydrogen. When hydrogen is produced from fossil fuels in a facility that can capture and store the carbon dioxide released during its production, it is called blue hydrogen.
One of the projects underway to use green hydrogen in steelmaking is in Sweden. The HYBRIT initiative by SSAB, LKAB, and Vattenfall was started in 2016 and has built a pilot plant with support from the Swedish Energy Agency. The project has successfully produced hydrogen-direct reduced sponge iron from iron ore. The HYBRIT project uses a rock cavern storage facility to store green hydrogen from electrolysis using fossil-free electrical energy. The steel produced by the HYBRIT project is reported to have superior mechanical and aging properties compared to direct reduced iron made from fossil fuel processes. It is estimated that less than 0.1 tons of carbon dioxide will be emitted per ton of steel when green hydrogen is used to reduce the iron ore.
Rock cavern storage. Image used courtesy of HYBRIT
Electric Arc Furnaces
Another way to reduce the amount of carbon dioxide from steel making is by using electricity to power an electric arc furnace (EAF). This is the dominant way that steel is recycled from scrap steel stocks. EAF creates roughly 24 percent of global steel production, and depending upon electricity sources and iron type, the carbon emissions can be as low as 0.23 to 0.46 tons of CO2 per ton of steel. The location of an EAF can also be important as if it is far from the renewable energy source, high-voltage power transmission lines need to be run to service it.
The University of California Irvine’s Advanced Power and Energy Program (APEP) is examining the use of high-temperature Solid Oxide Electrolysis Cells (SOEC) that can produce hydrogen to reduce iron ore with only water as a waste product. High-temperature SOEC uses electrolysis to split hydrogen and oxygen from water but at high temperatures so that steam is converted rather than liquid water. The high temperature used to reduce the iron ore with the hydrogen is recovered and recycled to produce the steam used in the SOEC, reducing primary energy consumption by 30 percent and carbon dioxide emissions by 40 percent. The APEP uses a ceramic solid electrolyte (instead of the polymer electrolyte used in automotive-style fuel cells) and operates between 700 and 800 degrees Celsius.
With so much emphasis on the electrification of transportation and the growth of renewable energy sources like wind and solar, it is easy to forget that a world without greenhouse gas emissions will require significant changes in almost every aspect of modern technology. Steel will continue to be one of the most important building materials we have, but making it in a net zero manner will require new ideas, and hydrogen appears to be a viable answer.