Effect of Bituminous Coals on Reduction of Ores and Carburization of Reduced Fe in FINEX Process

Abstract

One of the biggest issues facing the steel industry in the 21st century is carbon neutral. Global steelmakers and POSCO are developing technology with the goal of 2050 carbon neutrality. In particular, POSCO succeeded in developing FINEX technology that uses 100% pure oxygen, unlike blast furnaces using hot air, and completed commercialization in 2007, and operates two FINEX plants to produce 3.5 million tons of molten metal per year.

The FINEX process produces molten metal by charging bituminous coals and ore instead of pre-processed coke and sintered ore. Therefore, the performance of the operation varies depending on which coal is used in the FINEX process, because after the coal is charged into the FINEX process, heating, volatile matter decomposition, carbonization, and carburization during the hot-melt process are continuously performed.

The role of coal in the ironmaking industry can be classified into two categories. One serves as a reducing agent to reduce ore by generating a reducing gas, and the other is to act as a carburizing agent to form Fe-C by reacting with the reduced ore, Fe. This paper studied the characteristics of reduction and carburization with four types of coals called ‘FINEX Coal’, which are bituminous coals used in FINEX.

Two of the four types of coals easily discharged reducing gas at a relatively low temperature, and showed excellent characteristics as a highly reactive reducing agent with CO2 gas. In order to verify such reducibility, a direct reduction experiment was conducted by mixing ore and four coals respectively by heating with an inert gas, which also showed relatively excellent reduction characteristics.

Two experiments were conducted to quantitatively verify the effect as a carburizing agent for each type of coal. The initial Fe-C formation temperature for each type of coal was measured using Confocal Laser Scanning. Next, the experiment evaluated how much Fe3C phase was formed through X-ray analysis by carburizing coal on an iron plate with 99.99% purity. Through this, it was confirmed that one coal, which had low reactivity with CO2 gas, had a high carburization rate and formed Fe-C at a relatively low temperature.

In the future, research on various factors that can predict reducing and carburizing properties with various coals will be needed. Through these studies, it is expected that FINEX operations will maximize operational efficiency while appropriately controlling the strengthening of melting properties through improved reduction and carburization.