To make steel, raw materials are turned into liquid iron, either in a blast furnace or using the direct reduced iron process ![[Pasted image 20231125231850.png]] ## Blast Furnace Before iron ore can be used, oxygen must be removed from it. Known as ‘reducing’, this can be done either in the blast furnace, where hot air is injected into a continuous feed of coke, sinter and lime, or by the direct reduced iron (DRI) process. The result from both is liquid iron, which is then transported to the basic oxygen furnace. The blast furnace process also produces two important by-products: carbon dioxide (CO2), and slag (a mixture of minerals). Blast furnace **slag is used to make cement**, saving significant CO2 emissions compared to the primary cement-making process. Carbon monoxide is used to fuel electricity generation. Top gas from the blast furnace is recovered for use within the plant, mainly as a fuel for stoves that heat air before it is injected into the blast furnace. The remaining blast furnace gas is sent to a power plant to produce electricity. ## DRI Furnace Instead of sinter, the DRI process uses pelletised iron ore. But just like sinter, it still has to have the oxygen removed. This process is known as ‘reducing’. Instead of coke, the energy source used in the DRI furnace is natural gas. Again, the result is liquid iron. From the DRI furnace, the iron moves to the electric arc furnace on conveyors. ## Scrap Steel Steel that has been previously manufactured and used, and which has then come to the end of its life in that form, can be infinitely recycled. As such, it is another important raw material in steelmaking. There are about 20 different grades of scrap that can make different types of new steel. Scrap is usually melted down in an electric arc furnace (EAF), but can also be added to the mix in a basic oxygen furnace (BOF) to control heat in that part of the steelmaking process. There’s not enough scrap to satisfy the growing demand for steel and not all scrap is of a high enough quality to make new steel. Our modelling suggests that primary steel (mined from iron ore) will be needed for another 50-60 years in developed countries and for over a century in the developing world. After that, we could make the majority of new steel from recycled scrap, however certain high-quality steels will still rely on primary steel from iron ore. ## Electric arc furnace These furnaces are typically charged with scrap steel. They use high-power electric arcs to melt the scrap. They also convert direct reduced iron into liquid steel, reaching the same quality that can be achieved in an integrated steel plant. The electric arc furnace creates valuable slag as a by-product, just as the blast furnace does. Just as in the basic oxygen furnace, the melt is then further treated to adjust its chemical composition. ## Basic oxygen furnace Oxygen is blown into the molten iron, reducing its carbon content from 4% to <0.5%. Scrap is added to control the temperature. Steel is then tapped from the furnace vessel into a steel ladle ready for casting, and slag is removed. Waste gases containing carbon monoxide are captured and used for power generation. Depending on the required steel grade, the melt is further treated to adjust its chemical composition. Treatment has to be individual and very precise. BOF gas contains even more **carbon monoxide** than blast furnace gas. This makes it very valuable for the production of **ethanol** and other chemicals. ## Blast Furnaces vs DRI Furnaces > Blast furnaces can operate at higher capacity and produce more valuable by-products. DRI production is more flexible and has significantly lower CO2 emissions due to the usage of natural gas. It also has the potential to use hydrogen instead of natural gas, which means it could have CO2 emissions close to zero if the hydrogen was produced with renewable energy.