Simplified comparison of the conventional direct reduced iron ore process (DRI) using natural gas versus a green hydrogen route which produces significantly less CO2 emissions.
The traditional iron ore reduction process in producing iron utilizes a chemical reaction between iron oxide and carbon monoxide generated from heating coke in a blast furnace. Coke is a processed carbon material made from coal which acts as both a fuel and reducing agent in the steel plant blast furnace operations, forming carbon monoxide when burned, and reacting with the iron oxide to produce molten pig iron and carbon dioxide. In 2017, every ton of steel produced resulted in an average of 1.83 tons of carbon dioxide emissions. That same year saw a global production of just over 1,864 million tons of steel. Steelmaking produces about 7% of the worldwide annual global green house gas (GHG) emissions of CO2.(1)
There are no new blast furnaces being installed due to current environmental pollution and emission considerations. The process of reducing iron oxide ore to iron metal is being replaced with an improved technology, the direct reduced iron ore (DRI) process. The process current process utilizes carbon monoxide (CO) or syngas, a mixture of CO and H2, produced from natural gas. Alternatively, companies have been looking at hydrogen (H2), which can also be used as the reducing gas. The sponge iron product from the DRI process can then be used in electric arc furnace (EAF)-based steelmaking.
On-site generation of green hydrogen using renewable energy sources can significantly reduce the CO2 footprint of the DRI iron in the steelmaking process. Hydrogen is being seriously considered as a clean alternative reducing gas in the conversion of iron ore to iron. Electrochemical systems such as proton electrolyte membrane (PEM), anion exchange membrane water electrolyzers (AEMWE), and alkaline water electrolyzer (AWE) systems are being considered as the competing electrochemical technologies in generating green hydrogen using renewable energy sources.
The two iron oxide reduction process chemistries using CO or H2 are listed below:
a. Utilizing carbon monoxide (CO) as the reducing gas:
Fe3O4 + CO → 3FeO + CO2 (1)
FeO + CO → Fe + CO2 (2)
This is the current commercial method that uses natural gas that has been reformed at high temperatures to generate CO and H2 to produce the reducing gas. The process consumes about 570 Nm3 of CO per metric ton of iron.
b. Utilizing green hydrogen (H2) as the reducing gas:
Fe3O4 + H2 → 3FeO + H2O (3)
FeO + H2 → Fe + H2O (4)
The process consumes about 540 Nm3 of H2 per metric ton of iron.
Green et. al discusses the energy and technical advantages of using hydrogen in the DRI process in a presentation paper at a U.S. DOE H2@ Scale workshop.(2)
Companies developing green hydrogen-based DRI processes include both U.S. and European based companies including ArcelorMittal, Hybrit, Thyssenkrupp Steel, Timken Steel, U.S. Steel, and Barry Metal Company among others.
Dioxide Materials is a leader in the development and scale-up of AEMWE technology in producing green hydrogen for industrial customers. The electrolyzer technology development utilizes a patented alkaline stable anion exchange membrane.
- Hydrogen as a Clean Alternative in the Iron and Steel Industry – Fuel Cell & Hydrogen Energy Association https://www.fchea.org/in-transition/2019/11/25/hydrogen-in-the-iron-and-steel-industry. Uploaded 7/10/2021.
- Ed Green, U.S. Department of Energy, H2@Scale Workshop, “The use of hydrogen in the iron and steel industry”, Aug. 1, 2018, Barry Metal Company. https://www.energy.gov/sites/prod/files/2018/08/f54/fcto-h2-scale-kickoff-2018-19-green.pdf.