Blast furnace

Flue dust becomes blast furnace fuel

By recirculating flue dust as fuel in the blast furnace, both raw-material costs and environmental impact can be reduced. The method is now used at SSAB in Oxelösund.

The idea of using blast furnace dust and sludge as a fuel supplement in the blast furnace was conceived as early as the late 1990s. Flue dust is a residual product from iron production, containing fine-grained particles of coke, pellet fines and slag formers. Thanks to several years of joint development by Swerim, SSAB and LKAB, the method is now used in industrial scale by SSAB in Oxelösund.

Injection of flue dust

Flue dust is normally recirculated via blending with sinter feed. However, Sweden has no sintering plants, so the material is instead briquetted before recirculation to the blast furnace process. The method works well, but when flue dust is added to briquettes the cost increases, since flue dust impairs the mechanical strength of the briquettes, necessitating a greater addition of binder agent.

In light of this, injection of fine-grained material to the blast furnace is an interesting alternative. In that case, the flue dust is injected directly; however, this causes excessive wear and tear on equipment, which must be adapted.

Trials in experimental blast furnace

Successful co-injection trials using a blend of flue dust and pulverised coal have been conducted in LKAB 's experimental blast furnace, as well as with separate  lances  adjacent to the coal injection lance in SSAB's No. 4 Blast Furnace in Oxelösund. 

Lower use of coal and coke

Results show that transport of flue dust directly from the off-gas cleaning system to the injection plant is a satisfactory method. Coke breeze in the flue gas effectively replaces some of the coal and coke. In addition, environmental impact is reduced, since landfilling of the dust is avoided. 

The method is used in industrial scale at SSAB in Oxelösund and will also be used at SSAB in Luleå.