Effect of key process parameters on properties and graphitization degree of iron coke

The development of raw materials suitable to be used in hydrogen-rich blast furnace is a key link to promoting industrialization of hydrogen-rich blast furnace smelting technology. Compared with ordinary coke, iron coke with high reactivity can reduce the temperature in the thermal reserve zone, promote the development of indirect reduction, and reduce CO₂ emissions of the blast furnace. In particular, iron coke used in hydrogen-rich blast furnace can accelerate metallic iron carburization and play a protective role in coke. Based on this, the preparation of iron coke was studied under laboratory conditions. The effects of key parameters, including the proportion of iron concentrate powder, carbonization temperature and time, on the properties and graphitization degree of iron coke were explored in order to provide theoretical support for the development of low-carbon attribute iron coke. The results indicate that the compressive strength of iron coke increases and then decreases with increasing the proportion of iron concentrate powder. Correspondingly, the iron coke reactivity(I_CRI) increases while the iron coke post-reaction strength(I_CSR) decreases. The compressive strength of iron coke are more than 3 000 N with iron concentrates in 7%-10%, while I_CSR are lower than 50% with iron concentrates beyond 7%. The compressive strength of iron coke rises when the carbonization temperature is increased in 900-1 100 ℃,and descends with continually increasing the temperature to 1 200 ℃. The I_CRI ascents and I_CSR declines with the increase of carbonization temperature in 900-1 200 ℃. The compressive strength is more than 3 000 N as the temperature exceeds 1 000 ℃. The compressive strength, I_CRI and I_CSR at 1 000 ℃ are 3 125 N, 33. 89% and 50. 13% respectively, 3 450 N,34. 15%,48. 89% at 1 100 ℃. The compressive strength first increases significantly and then decreases slightly with extending the carbonization time within 1. 0-2. 5 h, I_CRI first decreases and then increases slightly with the increase of carbonization time. Taking into account the compressive strength and high temperature metallurgical properties of iron coke comprehensively, the appropriate proportion of iron concentrate for preparing iron coke is 7%, the carbonization temperature is 1 000 ℃, and the carbonization time is 2. 0 h. The three factors above affect the disordered structure and graphitization degree of iron coke. When the proportion of iron concentrate powder increases from 0 to 15%, the graphitization degree decreases from 53. 05% to 43. 18% and the ratio of characteristic peak area increases from 3. 19 to 4. 04. The increase of both the carbonization temperature and time promotes the graphitization process of iron coke. The compressive strength and high-temperature metallurgical properties of iron coke are synergistically affected by many factors such as the microstructure of iron coke, porosity, metallic iron content and graphitization degree.