Steel making today and tomorrow@Model.TitleHeaderType>
There are major differences between the steel making process of today and the HYBRIT-process of tomorrow.
In the current blast furnace based process, coal is the main source of energy. The use of coke ovens produces metallurgical coke and coke oven gas. The coke is used in the blast furnace process, and the coke oven gas is used as the major fuel in the whole steel mill.
Iron ore in the form of fines is normally processed in sintering plants into sinter, and in some cases in pelletizing plants to iron ore pellets. Iron ore sinter and pellets are then charged together with coke from the top of the blast furnaces. Pulverised coal, oxygen and hot blast air are injected through tuyeres in the lower part of the blast furnace.
Molten iron (called hot metal) and slag are tapped regularly from the bottom of the furnace. The top gas from the blast furnace contains mainly nitrogen from blast air, and carbon dioxide and monoxide. The blast furnace gas is used as fuel in the steel mill after being scrubbed. SSAB’s blast furnaces use 100% pellets mainly supplied by LKAB. The hot metal from the blast furnace is then refined by using oxygen in converters to crude steel, which in turn goes through alloying and refining operations before being cast into slabs, ready for rolling and further heat treatment before shipping to customers. Because of the high-quality iron ore pellets and continuous improvement of operational parameters, SSAB’s blast furnace based facilities are among the most efficient in the world in terms of CO2 emissions.
Hydrogen-based metallurgical process
In the HYBRIT- concept, specially developed iron ore pellets are reduced by hydrogen gas in a so-called direct reduction process. Reduction occurs in a solid state at a lower temperature than in the blast furnace process and produces an intermediate product, sponge iron or direct reduced iron (DRI), with water vapour emitted from the top of the furnace. Water vapour can be condensed and scrubbed before reuse in the plant. Hydrogen gas is produced by electrolyzing water using renewable electricity (e.g. from hydro or wind power plants), with oxygen gas as a by-product. Hydrogen storage of sufficient capacity is used to balance between the DRI- process and the electricity grid allowing a significant amount of intermittent power generation by e.g. wind or solar power plants to be connected/to be connected to it. The sponge iron can be used as hot DRI and melted immediately in an electric arc furnace (EAF) together with recycled scrap. The DRI can also be processed into hot briquetted iron (HBI), which can be stored and shipped to another site. The crude steel from the EAF goes through a similar process as in the blast furnace based route, i.e. alloying and refining before being cast into slabs, ready for rolling and further heat treatment before shipping to customers.
HYBRIT faces two major challenges
•To develop an effective process to use 100% hydrogen on an industrial scale.
•To produce hydrogen in an energy-efficient way so that it is economically justifiable/commercially viable.