Electrification of the heat treatment process for iron ore pelletization at LKAB

Typ
Examensarbete för masterexamen
Master Thesis
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Publicerad
2019
Författare
Thureborn, Emil
Lindén, Erik
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Sammanfattning
LKABisaSwedishstate-ownedminingcompanythatextractsandrefinesironoreforthe global steel industry. Their main product is iron ore pellets which accounts for around 83 % of LKAB’s iron ore products. The straight-grate process is used for heat treatment of the pellets and is the most energy-intensive part of the refining process. The heat is supplied by fossil fuel burners with considerable emissions of greenhouse gases and pollutants such as nitrogen oxides, which should be reduced to comply with emission targets set by LKAB as well as the Swedish government. This project investigates electrical heating alternatives in the form of plasma torches and microwaves to replace the fossil fuel burners, providing potential for a CO2-neutral productionprocess. Theworkfocusonhowprocessconditionsareaffectedwhenswitchingto anelectricheatsource. Processperformanceisevaluatedthroughproductquality, energy efficiency, emissions of CO2 and NOx. Furthermore, new potential process optimization measures as a result of the implementation of electric heating are discussed. A previously established process model of the straight-grate process was used to establish a reference case and several new cases where modifications were made to simulate the implementation of electric heating. NOx emissions from plasma torches were studied by reaction modelling in Chemkin and results were evaluated against data from previous practical experiments. Results showed that electric heating through microwaves may supply energy at low temperature to the drying process, which would allow for a more compact drying zone and replacement of up to 1 MW of fossil fuels. However, the total power demand of the process increased by 15 - 20 %. To supply heat at the high temperature required in the firing zones, plasma torches have the potential to replace the entire fossil fuel demand and achieve a CO2 neutral process. The implementation of plasma torches only had a slight effect on pellet quality and energy efficiency. Simulations regarding NOx emissions from plasma torches when mixing hot plasma gases with air shows that the formation of NOx may be higher than from a fossil fuel burner. The most important factor for determining the NOx emissions is the gas residence time at high temperatures. Reburning using small amounts of natural gas was the most efficient NOx reduction strategy with NOx reduction of up to 65 %. Future work should be directed towards financial analyses of the implementation of electric heating and experimental tests to prepare for practical implementation.
Beskrivning
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Energi, Hållbar utveckling, Energiteknik, Energy, Sustainable Development, Energy Engineering
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Skala
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