Stored sludge is recirculated to the blast furnace
A system study for SSAB in Luleå shows that stored blast furnace sludge can be recirculated to the process. Thereby, both raw material costs and the need for storage capacity can be reduced.
At SSAB’s steel mill virtually all generated dust and sludge is recirculated to the blast furnace process, for example, in the form of briquettes.
Utilisation of stored sludge
A residual material that could be better utilised is the sludge generated from the blast furnace off-gas (about 10,700 tonnes in 2016). The sludge contains zinc, which is undesirable in the process, and the sludge is therefore held in settling ponds.
Swerea has conducted a system study for SSAB in Luleå to determine how much sludge can be recirculated while still maintaining an acceptable zinc level in the process.
Less storage and decreased costs
The study has shown that recirculating the stored sludge is the most environmentally and economically viable alternative, since it results in a lower overall increase in the zinc content in the process as a whole. A greater amount of sludge can be recirculated than is produced. Thereby the total amount of stored sludge can be reduced and costs for building new storage are avoided. Since the sludge has a high iron and carbon content, recirculation also reduces the need for iron ore pellets and coke.
"This very successful, value-creating project has shown that stored blast furnace sludge, which was previously considered impossible to recycle without pretreatment, can actually be utilised. This results in savings in terms of blast furnace material costs, while investment in new storage facilities can be postponed for many years. Planning for utilisation of the sludge has already begun," says Anita Wedholm, process engineer at SSAB Merox.