Existence state and structures of extracted coke and accompanied samples from tuyere zone of a large-scale blast furnace

An in-depth understanding about the existence state and structure of materials in the high-temperature zone of a blast furnace is critical to optimize both the ironmaking blast furnace and many other metallurgical processes based on carbothermic reduction. In the present study, coke as well as other accompanied samples (slag, metal and fines) were extracted from an industrial large-scale blast furnace (BF) tuyere zone and were comprehensively characterized to evaluate their existence state and structure. It was found that the weight percentage of slag and metal in the total extracted samples increases first and then keeps at a relative stable level, while the average coke particle size decreases firstly and then keeps at a relatively small size when the position is closer to the blast furnace center. This indicates that smelting and separation of slag and iron as well as the main coke degradation process occur mainly in the center part of BF, and the state in the region (deadman) is relatively stable with similar permeability. Tuyere cokes with various sizes are all extensively reacted with highly developed pores. Due to the improvement of coke pore size, blast furnace melts (bosh slag or molten coke/coal ash) can migrate into the coke matrix through those connected open pores. Coke carrying slag in its inner pores may enter the iron bath of the BF hearth, which might affect coke dissolution into hot metal and degrade the refractory of the hearth bottom. Alkalis content increase significantly when the distance to the tuyere entrance increases, indicating the alkali vapors are mainly recycled and enriched in the center part of blast furnace. The graphitization of coke in the high temperature zone start from the coke surface and the graphitization process may lead to the formation of coke fines.