Optimisation of steel plant recycling in Finland: dusts, scales and sludge

Abstract

The quantities of the dusts, scales and sludge arising in the steel plants of Rautaruukki Group (two in Finland, one in Sweden and one in Norway) and Imatra Steel (in Finland) have been determined. Not all materials can be recycled, a material may contain some harmful component(s) like Na, K, Zn, Pb, Cd, S, cyanide, oil or humus. It may also be too fine-grained and a small iron content may prevent utilisation or it may be too difficult to process the sludge. The total amount of the unutilised materials is 92140 t/a, that is about 32% of the fine-grained remains. The recycling capabilities of the sintering plant, the blast furnace (BF) and the basic oxygen furnace (BOF) have been evaluated. Usually, the fine-grained remains disturb the primary production processes. Additionally, most of the non-recycled remains contain harmful components and cannot be utilised in the sintering process or in the BF. In the BOF, it is possible to use the iron oxide remains, but the maximum amount would be only about 10000 t/a, so the recycling to the BOF can be only a partial solution. It is possible to recycle small amounts of appropriate dusts, scales and sludge to the sinter plant, to the BF or to the BOF, but this cannot be an overall solution of the waste problem. Big amounts of fine-grained remains must be treated separately. The costs of the separate process can be covered due to the savings caused by the more smooth-running primary processes. Moreover, it is possible to choose a separate unit process, the product of which can be fed back to the production chain in the optimal stage. The separate processing of the dusts, scales and sludge may also decrease the emissions and energy consumption of the steel plant.