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Contribution to the understanding of the role of inorganic elements in biomass steam gasification

Abstract : In the current energy context, there is a need to develop the use of renewable energy sources, such as biomass. A promising way to produce energy from biomass is through gasification. However, some biomass species can be problematic during the gasification process due to their high inorganic content that can strongly influence the reaction kinetics. To date, the inorganic effects are known but the underlying mechanisms are still poorly understood. In this context, the objective of the present work was to contribute to the understanding of the inorganic elements role during the biomass steam gasification. In particular, the phenomena involving K and Si during the biomass steam gasification, especially through the gas phase, and with particular attention on their influence on the reaction kinetics were investigated. Investigations were conducted at an experimental level, with thermogravimetric analyses and physicochemical characterizations of the chars and ashes. They were supported by calculations at thermodynamic equilibrium as well as by literature review. The results have proven that the biomass inorganic composition is the main parameter explaining the differences between the gasification kinetic behaviors of the biomass species. From this conclusion, the specific effects of K and Si—two major inorganic elements in biomass—were further investigated in details. A competition was highlighted between two reactions involving K, most likely in the form of KOH(g): i) the catalysis of the steam gasification—whose mechanism starts from the pyrolysis step—on the one hand, and ii) the heterogeneous reaction between KOH(g) and SiO2 to form non-catalytic species on the other hand. Additionally, it was showed that increasing the biomass SiO2 content, whatever its crystalline form, slows its gasification down in a non-linear way and until a saturation effect.
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Tilia Dahou. Contribution to the understanding of the role of inorganic elements in biomass steam gasification. Chemical and Process Engineering. Université Grenoble Alpes, 2019. English. ⟨NNT : 2019GREAI097⟩. ⟨tel-02519820v1⟩

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