Making Green Steel with Hydrogen Released from Ammonia

Iron production is the single largest cause of global warming. Reducing iron ores with carbon generates about 8% of global carbon dioxide emissions to produce ≈1.85 billion tons of steel per year. This dramatic scenario is driving efforts to reinvent this sector through the use of renewable and carbon-free reductants and electricity. In a scientific paper published by our group in the Journal 'Advanced Science' (https://onlinelibrary.wiley.com/doi/1..., we discuss how to make sustainable steel by reducing solid iron oxides with green hydrogen released from ammonia. Ammonia is a 180 million ton per year traded chemical energy carrier with established transcontinental logistics and low liquefaction costs. It can be synthesized with green hydrogen and releases hydrogen again during the reduction reaction. This advantage links it to green iron production to replace fossil reducing agents. We have found that the reduction of iron oxide based on ammonia is carried out by an autocatalytic reaction, is kinetically as effective as direct reduction based on hydrogen, yields the same metallization, and can be industrially implemented with existing technologies. The iron/iron nitride mixture produced can then be melted in an electric arc furnace (or charged into a converter) to adjust the chemical composition to the targeted steel grades. Thus, a novel approach is presented to use intermittent renewable energy using green ammonia for a disruptive technology shift toward sustainable ironmaking. In summary, we show in this video that ammonia-based direct reduction is kinetically as effective for producing green iron as hydrogen-based direct reduction at 700 °C. The direct utilization of ammonia in the reduction process offers a process shortcut, alleviating the need for a preliminary ammonia cracking step into hydrogen and nitrogen. During the redox reaction, the gradually generated porous iron further catalyzes the decomposition of ammonia at elevated temperatures, to release hydrogen for the reduction of iron oxides. This autocatalytic reaction provides a path to further efficiency gains and cost reductions. The in situ nitriding from the process offers protection of the pure iron against environmental degradation that otherwise requires dedicated additional process steps that are energetically and logistically costly. Such a protective nitride phase can be completely dissolved and removed during a subsequent melting process. Thus, ammonia-based direct reduction provides a novel approach to deploying intermittent renewable energy for an unprecedented and disruptive technology transition toward sustainable metallurgical processes. With these benefits, it connects two of the currently most greenhouse gas intense industries (namely, steel and ammonia production industries) and opens a pathway to render them more environmentally benign and sustainable. At the same time, it can eliminate logistic and energetic disadvantages associated with the use of pure hydrogen, when it needs to be transported.