Steel
Site visit: Megasa Siderurgia Nacional, Seixal, Portugal
Siderurgia Nacional (SN) Seixal is located 25 kilometers south of Lisbon. The facility, which exclusively produces recycled steel, is owned by the Spanish enterprise Megasa; it is one of the company’s two plants in Portugal. The plant operates 24 hours a day, 364 days a year, and employs 400 people. I was hosted by Francisco Ribeiro and Alexandra Broa, both engineers in SN Seixal’s Health, Safety, and Environment department. After donning the requisite safety gear, Francisco guided me around the facility.
Our tour started at the electric arc furnace, the sweltering hot core of the plant. The furnace makes liquid steel by melting scrap metals with additives. The dry materials are combined in a gigantic hanging basket before being poured into the furnace. The mixture is tweaked based on the type and quality of steel desired. Francisco compared it to making soup, the ingredients are adjusted as needed for different recipes. Once the mixture is poured into the furnace, graphite electrodes are lowered in and charged to create the electric arc that provides the intense heat needed for melting. The process is explosive and loud, expressing the magnitude of the energy and work at play.
From the furnace the molten steel is poured into molds for continuous casting into steel billets. A billet is an intermediate steel product that is subsequently made into final goods.
Once cooled, the billets are stretched into long coils that can be reheated and rolled into finished products such as rebar and wire mesh, or sold externally to be made into smaller items such as tableware.
The larger products, such as wire mesh (the type used in concrete casting), have dedicated production areas in the plant. Pedro, site manager in the wire mesh transformer facility, guided us through the process. The wire is cold rolled into ribbed rebar and then straightened and cut before being welded into the grid pattern. Cold rolling, as opposed to hot rolling, deforms the steel at a temperature below the recrystallization temperature, producing a higher yield strength and hardness. Building codes and construction techniques dictate the mesh’s physical and material properties, including the diameter of the coil and geometric pattern. These are all adjusted depending on the market demands. At the time of my visit, the plant was producing mesh for Spain and the United Kingdom, and thus being manufactured according to their construction codes. Pedro noted that only a small portion of the mesh is sold domestically for use in Portugal; the majority goes to Europe and Brazil.
Steel production is an energy intensive and environmentally burdensome process. For comparison, Francisco noted that the plant uses more electricity than all of Lisbon. However, the company is implementing measures to mitigate the impacts. They are exploring methods to reduce and reuse energy, like capturing the heat coming off of the newly formed billets. To reduce water demand, the process water is recycled in an onsite treatment plant. As such, it needs replacement only about once a year. On the periphery of the plant lay a mountain of slag, a waste byproduct of the steel smelting process. Much of this slag is sold for uses as a cement replacement in concrete. Nevertheless the enormous pile, visible from a distance, was a reminder of the intensity and magnitude of the production.
Our tour finished appropriately as the shift was changing, and I walked out with a group of wary workers leaving for the day.
Thank you to Megasa Siderurgia Nacional Seixal for allowing me to visit, and particularly to Francisco Ribeiro and Alexandra Broa for their time. The thoughts and information in this post are based on my tour of the facility and have not been externally verified unless otherwise noted.
All photos and video by Irmak Turan.
