Alternative processing of sinter plant recycling materials

An important amount of iron oxides containing residues from the different iron and steelmaking processes are recycled via the sinter plants. The use of those sinter plant recycling materials is limited due to productivity drop, sinter quality as well as emissions. The production of cold bonded briquettes and their use as an additive raw material for the blast furnace can be an alternative way to relieve the sinter plants. Therefore the production of suitable briquettes for the utilisation as raw material in the blast furnace shall be investigated to develop an alternative route for the co processing of sinter plant recycling materials. In addition to that an assessment of the corresponding relief effects on the sinter process shall be made. For that reason this RFCS project focused on investigations to: a) development of an industrial process concept for alternative processing of recycling material which causes productivity and quality drop on a sinter plant b) assessment of possible emission reduction of sinter plants with reduced amounts of recycling materials in their sinter mix c) process development for production of self-reducing briquettes from sinter plant recycling material for the blast furnace with securing the high blast furnace productivity with briquette charging BFI and DK have characterised the most important components of the sinter mix which causes significant quality and productivity drop at DK sinter plant. Especially the carbonaceous materials like BF dust and sludge in combination with mill scale were identified as recycling materials which can be used to a very limited content for the production of the sinter. The recycling materials for the planned briquetting trials were chemically analysed, and the size distribution was determined. The BFI had done laboratory briquetting tests as well as strength investigations to determine suitable recipes for the technical scale trials. Mixtures based on BF sludge shows significant lower mechanical strength than mixtures based on BF dust. The use of coarse material like mill scale or iron ore leads to increased briquette strength. In the course of the laboratory examinations, sinter plant recycling material was processed into tablets of different compositions. A key characteristic of these tablets is their cold breaking strength. The cold breaking strength readings provide information on the tablet's mechanical behaviour. It was found that the highest strength levels are obtained with a cement concentration of 20% by weight and compositions based on blast-furnace dust instead of blast-furnace sludge. The low temperature disintegration and melting behaviour of laboratory-compacted tablets was tested. The selected tablet mixes were subjected to melting tests at a temperature of 1500°C and 1750°C. The investigations into the low-temperature disintegration behaviour of the tablets produced in the laboratory yielded no conspicuous results. All tablets essentially retained their shape stability. However, laboratory melting tests with selected mixes revealed some rather pronounced differences in the melting behaviour of the examined tablets depending on tablet constituents. In particular, high carbon contents led to poor melting results.