Investigating char agglomeration in blast furnace coal injection

Blast furnace iron manufacturers aim to reduce expensive coke usage through the injection of coal. This paper investigates contrasting agglomeration behaviour with a view towards optimising blast furnace operations and limiting furnace permeability issues. A drop tube furnace (DTF) was used to investigate the performance of two coal particle size specifications that were representative of injection coal sizes: pulverised (100% < 300 mu m, 50% < 75 mu m), and granulated (100% < 1 mm, 50% < 250 mu m). A range of coals was subjected to DTF testing with issues arising from the injection of caking coals. Results show these coals exhibit signs of agglomeration, a potentially problematic effect concerning blast furnace permeability. Considering gasification reactivity upon leaving the blast furnace raceway, it was found that the agglomerated coal chars do not suffer from poor reactivity and are more reactive than the non-agglomerated chars. Pre-treatment through oxidation was found to be an effective means of eliminating agglomeration in the DTF as a result of the reduction in caking properties.