CAUSES OF SWELLING (SIZE CHANGES) OF PELLETS AND BRIQUETTES DURING OXIDATION OR REDUCTION PROCESSES
DOI:
https://doi.org/10.32339/0135-5910-2026-3-18-30Keywords:
pellets, briquettes, swelling, firing, oxidation, reduction, iron oxidesAbstract
The article discusses the causes of changes in the size of iron ore pellets and briquettes during oxidation or reduction processes (this phenomenon is also called swelling). Swelling can affect both the gas permeability of the charge and the efficiency of metallurgical units. The process of volume change can lead to the destruction of the lumpy charge, as well as affect the entire technological process. The paper analyzes the main mechanisms underlying the processes of changing the volume of materials. These include: the formation of iron filamentous crystals (“whiskers”) during the reduction of iron from wustite; the destruction of the metal crust formed during the reduction by the pressure of the gas phase at the interface; as well as the occurrence of internal stresses caused by differences in the crystal structure and specific volumes of iron oxides (hematite, magnetite and wustite) at various stages of phase transformations. Special attention is paid to the key factors determining the intensity and nature of swelling. The influence of pre-firing conditions (temperature, time), parameters of the reducing gas (chemical composition, temperature, flow rate), the presence and nature of impurities and the initial porosity of the material were systematized. Understanding these conditions is important for developing a strategy for managing the reduction process and creating high-quality, swelling-resistant iron-containing charge materials. Based on the analysis of experimental data obtained by various research groups, it has been shown that the introduction of certain additives and optimization of process parameters make it possible to effectively control and suppress undesirable expansion of raw materials during oxidation or reduction processes. Data analysis demonstrates that the development and intensity of swelling are determined by the complex interrelated influence of the mineralogical composition of raw materials and technological parameters.
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