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Purification of solar grade silicon in wide surface reactors

Abstract : Solar grade silicon, needed to supply the ever-growing photovoltaic market, has to be purified from metallurgical silicon. The classical chemical route for purification has a high energy cost and environmental drawbacks. The alternative metallurgical route has to decrease its production cost to meet with the low market price. In this work, we study a technology breakthrough compared to existing processes to remove boron, such as the plasma process previously studied in the SIMaP laboratory.The first chapter of this thesis presents the context of silicon production for solar cells, with focus on the chemical route and the metallurgical route for silicon purification, and explains the goal of this work. The second chapter discuss a state of the art of the processes to remove boron by gas blowing. Different setups of different teams are presented, and the literature survey is specially focused on the role of each gas species, the kinetics of the boron removal and the purification limit due to the formation of a silica layer.Chapter three presents a theoretical model developed during this PhD to describe the boron removal by gas blowing, in continuous reactors with counter-current gas and liquid flows. The model takes into account a chemical equilibrium at the interface, mass transfer to the bulk fluids and the limit on the oxidant fraction due to the formation of a silica layer. It was run at laboratory scale and then used to extrapolate at industrial scale.The experimental part of the thesis is presented in chapters four and five, where the design, realisation and tests of a laboratory scale experiment are detailed. Thermal tuning was performed and new phenomena were reported, involving capillarity and condensation of gaseous species. Boron removal results are shown for situations where the continuous flow of silicon was suppressed. As shown in our last chapter, further experimental developments would be fruitful at laboratory scale, together with studies at industrial scale using our theoretical model.
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https://tel.archives-ouvertes.fr/tel-02982220
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Submitted on : Wednesday, October 28, 2020 - 2:53:31 PM
Last modification on : Tuesday, November 24, 2020 - 4:00:09 PM

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  • HAL Id : tel-02982220, version 1

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Hamza Abouchi. Purification of solar grade silicon in wide surface reactors. Materials. Université Grenoble Alpes [2020-..], 2020. English. ⟨NNT : 2020GRALI035⟩. ⟨tel-02982220⟩

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