Effect of Biocarbon Addition on Metallurgical Properties of Mill Scale-Based Auger Pressing Briquettes

Abstract

This work focused on the usage of bio-based and secondary iron and steelmaking raw materials. Auger pressing briquettes, cold-bonded agglomerates made from by-products, mainly mill scale (80%), were successfully tested in industrial-scale blast furnace (BF) trials. The briquettes from industrial production were studied in two different laboratory-scale reduction experiments to compare them to laboratory-made briquettes. A blast furnace simulator (BFS) device was utilized in the simulations mimicking the temperature and gas profiles of an actual BF process. A reduction under load (RUL) device enabled the simulation of the physical load under reducing conditions. To determine how the high-temperature properties of the self-reducing briquettes depend on the amount of biocarbon, a bio-based reducing agent (2-10%) was added to the laboratory-scale briquettes that already contained 5.6% total carbon mainly originating from BF dust. For the recipes studied, a weight loss of about 30% under reducing conditions leads to the disintegration of a briquette under load. Based on the BFS experiments, adding biocarbon to the recipe was profitable in terms of a self-reducing effect up to 6% when the total carbon content was 11%. The RUL experiments showed that the structure of the briquette became extremely plastic with the addition of 4% biocarbon which covers 39% of the total carbon contained in the briquette. This was the upper limit for biocarbon addition due to telescoping and disintegration followed by the formation of fines. The industrial briquettes used in the BF corresponded well to the laboratory-made briquettes in terms of metallurgical properties.