Numerical Investigation of Particle Size on the Performance of Ironmaking Blast Furnace

Coke and ore sizes are important to the efficiency and stability of blast furnace (BF) operation in practice. However, their selection is usually determined by experience and there is no systematic study on the effects of ore and coke sizes on BF operation. This paper presents a numerical study on the multiphase flow and thermochemical behaviors inside the BF with different ore and coke sizes. This is done based on a recently developed 3D multifluid BF process model. The validation of this model is first confirmed by various applications. It is then used to study the effect of particle size on BF performance. The results show that as coke and ore sizes decrease, the thermochemical utilization efficiency is improved, which is reflected in low coke rate, low top gas temperature, high top gas utilization factor, and high productivity. However, there may be a minimum particle size for a given BF. Three indicators, namely gas pressure drop, liquid flooding in the dripping zone, and particle fluidization at the burden surface are used to determine this minimum particle size. Under the present conditions considered, the suggested minimum coke size should not be less than 20 mm and the suggested ore size should not be less than 12.5 mm. In addition, the effect of ore size on BF global performance indicators, e.g., fuel rate and productivity, is more significant than coke size. In terms of inner states, as ore size increases, the solid temperature drops in the BF shaft and the CZ position drops accordingly. On the contrary, as coke size increases, the solid temperature increases significantly in the BF shaft and the CZ position increases accordingly. Consistently, the increase of ore and coke sizes both increases the CZ thickness. Furthermore, the effect of locally charging large ore and coke particles is also studied. The results show that under the preset simulation conditions, locally charging large ore particles significantly reduces the gas pressure drop, but increases the fuel rate; however, locally charging large coke particles has limited influence on BF global performance indicators. The results provide some valuable guidance for coke and ore size selection in BF practice.