Abstract
Lowering the carbon consumption and fossil CO2 emissions is a priority in blast furnace (BF) ironmaking. Renewable biomass is one option that can play an important role in future low-carbon ironmaking particularly in the countries rich in biomass resources. In this study, full-scale trials to investigate the impact of briquettes containing torrefied sawdust on the BF efficiency and process stability have been conducted. Briquettes containing 1.8% of torrefied pelletized sawdust (TPS), 86.2% of steel mill residues, and 12% cement with sufficient mechanical strength have been produced on industrial scale. The bio-briquettes were charged at two different rates: 37% ( ~ 39 kg/tHM) and 55% ( ~ 64 kg/tHM) bio-briquettes to the SSAB BF No. 4 in Oxelösund. The gas utilization was higher during bio-briquette-charging periods without change in pressure drop up to 55% bio-briquettes, indicating sustained shaft permeability. BF dust generation or properties did not change significantly. Measurements of the top gas composition using mass spectrometry did not indicate release of hydrocarbon from TPS in connection to the charging of bio-briquettes. Evaluation of process data has been carried out using a heat and mass balance model. The evaluation of operational data in the model indicated lowering of thermal reserve zone temperature by 45 °C and reduction in carbon consumption by ~ 10 kg/tHM when charging 55% bio-briquettes compared to the reference case. The total CO2 emission was reduced by about 33–40 kg/tHM when using 55% bio-briquettes.
Highlights
The steel industry contributes, according to World Steel Association, to the global CO2 emissions by 7–9% [1], mainly caused by the use of coal and coke as reductants in the blast furnace (BF)
The middle fractions 8–63 mm were not generated in FR0, while it was high in bio-briquettes with 5% torrefied pelletized sawdust (TPS) and 10% cement (R5, R6, and R13)
Results show that the Fe and CaO contents were lower while C, SiO2, and Al2O3 contents were higher during the 37%Bio period compared to 55%Bio period in both BF flue dust and isokinetic samples indicating less coke leaving the BF during 55%Bio period
Summary
The steel industry contributes, according to World Steel Association, to the global CO2 emissions by 7–9% [1], mainly caused by the use of coal and coke as reductants in the blast furnace (BF). All evaluated concepts with specified assumptions, as the ULCOS top gas recycling BF, high injection of H 2 combined with Carbon Capture and Storage, use of bio-based reductants, charging of charcoal or carbon composite agglomerates including those involving biomass products were shown to significantly reduce the C O2 emission from the BF. Estimation results from the MASMOD model using operational parameter settings-based on experience showed that the use of bio-coal (pretreated biomass) by injection or top-charging had the largest effect on the fossil CO2 emission when taking the whole process system into account [3]
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