Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Recycling of oily sludges and mill scale from steelworks

The study focused on the search for a conditioning technique for oily mill sludges with a view to bulk recycling in the iron and steel process. With respect to recycling at the steel mill (briquetting without deoiling), the lignosulfonate bonded briquettes allowed very satisfactory industrial handling but the increase in sulphur content in liquid steel constituted a major hindrance and other recycling routes were explored. New binders were tested and the use of thermoplastic wastes allowed briquettes to be produced with exceptional mechanical properties. Questions concerning the associated atmospheric pollution need further study. Recycling at the blast furnace (briquetting and deoiling) was tested. At the laboratory scale, the crushing strength remained satisfactory at least up to 700 C, sulphur remaining in the briquette up to 900 C and the hydrocarbon content reduced to 0.1 % with 30 min curing at 400 C. Pre-industrial trials gave positive feasibility results. The desulphurization cost of pig iron, caused by the use of lignosulfonates, has been estimated. A laboratory characterization of the main gaseous effluents generated by the process has been carried out. A pilot plant was built to produce briquettes for the mechanical tests required for a charging into the blast furnace. These tests consequently gave negative results. An explanation for these bad results could be a weathering of the binder in the temperature zone required for a full deoiling. With respect to recycling at the sinter plant (after a bulk deoiling), the possibility has been confirmed of using the plant to deoil the sludges in bulk, with a view to their recycling as iron ore at the sinter plant. To counteract hindrance caused by the very fine grain size of the crude deoiled sludge it has been shown that micropelletization was feasible in order to increase the recycling rate. This process is proving efficient, versatile, simple and inexpensive and the possibility of adapting such a deoiling process to the recycling of residues is being studied.

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