Influence of Oxygen Enrichment on the Oxidation of a Magnetite Pellet Bed During Pot Furnace Induration

• Main Author: Eriksson, Anna
• Format: Others
• Language: English
• Published: Luleå tekniska universitet, Mineralteknik och metallurgi 2021
• Subjects: Oxygen enrichment; Magnetite pellet bed; Oxidation; Pot furnace; Induration; Fossil-free ironmaking; Metallurgy and Metallic Materials; Metallurgi och metalliska material
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-83529; http://nbn-resolving.de/urn:isbn:978-91-7790-821-0; http://nbn-resolving.de/urn:isbn:978-91-7790-822-7

This study was motivated by the excess oxygen that likely results from the current transition to hydrogen-based Swedish steel production. The potential usability of large amounts of oxygen in a process gas for iron ore pellet induration could improve the process efficiency in terms of fuel consumption and productivity. Iron ore pellets constitute the main raw material used in Scandinavian steel production. Knowledge of the effects of the process-gas oxygen level on induration is a prerequisite for establishing if, how, and to what extent oxygen enrichment can be exploited in an optimum manner to control temperature development and oxidation, while maintaining pellet quality. The objectives of this study are as follows: 1) to investigate the effects of the oxygen level in the inflow gas on pellet bed oxidation during induration, as well as the effects on the bed-scale temperature, oxidation degree, and cold compression strength (CCS) development; and 2) to identify the oxidation mechanisms corresponding to various oxygen levels and thermal histories. The current knowledge regarding the effects of high oxygen levels in the gas on oxidation is based on small-scale experiments; this study was conducted on a larger bed-scale and will thus contribute significantly to the knowledge pool of bed-scale effects resulting from different oxygen levels in the inflow process gas. An interrupted pot furnace experimental method was used, with the highest investigated oxygen level in the gas at 40% and an approximate bed-scale of 100 kg of pellets. The following conclusions were drawn from this study. First, efficient heating and a high degree of oxidation of an entire bed were rapidly achieved with the highest investigated oxygen level (40% O₂) compared to the results of the lower oxygen levels (6%, 13% and 30% O₂). The gas with 40% O₂ yielded improved pellet properties and a more uniform oxidation degree along the bed, compared to beds exposed to gas with lower O₂. Second, the temperature at the bottom of the bed increased more rapidly when exposed to a higher oxygen content in the gas compared to when only the gas temperature was increased. Third, the mechanical pellet properties (CCS and macrostructure) were improved in a bed exposed to gas with 40% O₂ compared to beds exposed to gas with lower oxygen levels. Finally, pellets from local conditions with comparable thermal histories oxidised according to similar mechanisms regardless of the oxygen level. Hence, it was demonstrated that the oxygen level influences the oxidation rate, whilst the temperature affects the oxidation mechanism. The overall trends in terms of the positive effect from the high oxygen content in the gas are promising, as they serve as a starting point for enabling faster production rates in the future.  === <p>E632 and a digital meeting in Zoom or Teams. Maximum 8 people will be allowed in E632 due to the covid-19 pandemic situation.</p> === HYBRIT research program 1