How dust and sludge from flue gas purification become raw materials
With the advanced filters and techniques now available for flue gas treatment, the dust collection in modern steel plants is very effective. Increased production and more efficient filters mean that the amount of collected dust is tending to increase. This is most welcome from an environmental viewpoint.
Sludge from SSAB’s flue gas purification is dried out and sifted into fine grain material. Subsequently, briquettes of this material are produced which become a raw material for the blast furnace. Photo: Merox.
In the course of metallurgical high-temperature processes, dust is formed that accompanies the process gases and is separated in the fabric filters, venturi scrubbers or electro filters. The dust formed in connection with the re-pouring of molten iron or steel and also where the hot metal is exposed to air – and where oxidation and evaporation takes place – is also collected.
With the advanced filters and techniques now available in flue gas treatment systems, the dust collection is very efficient. Increased production and more efficient filters mean that the amount of collected dust increases which – from an environmental viewpoint – is welcome.
In flue gas treatment facilities, the dust is separated in a dry or wet state. Normally dry methods are used, but sometimes (owing to explosion risk) wet flue gas treatment methods are the only alternative. Wet dust forms a sludge that is then utilised after it has dried out.
Flue gas sludge becomes a blast furnace raw material
SSAB places sludge from the LD converter’s gas purification facility on a specially designated surface where it has to lie for two weeks and dry out; then it is sifted into a fine grain material. The material is subsequently turned into briquettes and recirculated as a raw material for the bast furnace.
Read more: Ferrous waste, a new lease on life (miljonytta.se)
External processing of metal-rich dust
Some of the dust is sent outside the plants for extraction of metals. Dust from the production of stainless steel is reporcessed for its chromium, nickel and iron content at Befesa Circular Alloys Sweden AB in Landskrona. Steel dust with a high zinc content is recycled at Boliden Mineral in Rönnskär. Subsequently, the metals obtained can be fed back into the steel production process.
