Abstract
In blast furnaces it is desirable for the burden to hold a lumpy packed structure at as high a temperature as possible. The computational thermodynamic software FactSage (version 7.2, Thermfact/CRCT, Montreal, Canada and GTT-Technologies, Aachen, Germany) was used here to study the softening behavior of blast furnace pellets. The effects of the main slag-forming components (SiO2, MgO, CaO and Al2O3) on liquid formation were estimated by altering the chemical composition of a commercial acid pellet. The phase equilibria for five-component FeO-SiO2-CaO-MgO-Al2O3 systems with constant contents for three slag-forming components were computed case by case and the results were used to estimate the formation of liquid phases. The main findings of this work suggested several practical means for the postponement of liquid formation at higher temperatures: (1) reducing the SiO2 content; (2) increasing the MgO content; (3) reducing the Al2O3 content; and (4) choosing suitable CaO contents for the pellets. Additionally, the olivine phase (mainly the fayalitic type) and its dissolution into the slag determined the amount of the first-formed slag, which formed quickly after the onset of softening. This had an important effect on the acid pellets, in which the amount of the first-formed slag varied between 10 and 40 wt.%, depending on the pellets’ SiO2 content.
Highlights
Blast furnaces are still the dominant process for making iron in the world
A future megatrend will be the reduction of CO2 emissions in steelmaking, which might speed up the shift from traditional blast furnace (BF)-based ironmaking to new, breakthrough technology-based, fossil-free steelmaking [2]
We suggest that computational thermodynamic software, such as FactSage, can be utilized to study the effects of pellet chemistry on its softening behavior, some limitations were found in the thermodynamic computations because of the need to define the system to a certain degree of simplicity
Summary
Blast furnaces are still the dominant process for making iron in the world. Pig iron is first produced in a blast furnace (BF) from iron ores and further refined into crude steel in a basic oxygen furnace. The world’s total crude steel production was 1878 million tonnes in 2020, of which 73.2% was produced via the blast furnace–oxygen steelmaking route. An alternative route is electric arc steelmaking, in which electric energy is used to melt scrap, direct reduced iron (DRI) or hot briquetted or compacted iron (HBI/HCI). Electric furnace steelmaking constitutes 26.3% of the world’s crude steel production. The rest, which corresponds to 0.5%, was produced via old-fashioned open-hearth furnaces or other technologies [1]. A future megatrend will be the reduction of CO2 emissions in steelmaking, which might speed up the shift from traditional BF-based ironmaking to new, breakthrough technology-based, fossil-free steelmaking [2]
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