| 1. |
- Köhler, Anna, 1989, et al.
(författare)
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Modeling the motion of fuel particles in a fluidized bed
- 2021
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 305
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Tidskriftsartikel (refereegranskat)abstract
- A semiempirical model for the mixing of fuel particles in a fluidized bed is presented and validated against experimental data from the literature regarding lateral fuel mixing. The model of fuel particle mixing categorizes the fluidized bed into three mixing zones: a rising bubble wake solid zone, an emulsion zone with sinking bulk solids, and a splash zone located above the dense bed. In the emulsion zone, the axial motion of the fuel particle is described by a force balance, applying a viscoplastic stress model, i.e., with a dominant yield stress and only a minor contribution of the shear stress, using an empirical expression from the literature. In the lateral direction, the model is divided into so-called ‘recirculation cells’, which are crucial for the lateral mixing. Comparisons of the modeled and measured lateral dispersion coefficients of different fuel types measured in three different large-scale fluidized bed units under both hot and cold conditions (covering a broad range of coefficients: 10−4–10−1 m2/s) reveal satisfactory agreement. The validated model was used to investigate how the lateral mixing of fuel particles depends on the excess gas velocity, the bed height, and the lateral distribution of bubbles over the bed cross-section (which is typically uneven in industrial FB furnaces), as well as the size and density of the fuel particles.
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| 2. |
- Lundberg, Louise, 1987, et al.
(författare)
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The role of fuel mixing on char conversion in a fluidized bed
- 2016
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Ingår i: Fluidization XV.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Operational conditions, such as the fluidization velocity and the solids cross-flow, affect the degree of char conversion in a fluidized bed by influencing the different mechanisms related to the fuel mixing. Char conversion is influenced by fuel mixing in both the lateral direction (affecting the fuel residence time) and the axial direction (affecting the char gasification rate). In the present work, this effect is investigated through a combination of dedicated experiments in a cold unit, in which the effect of the excess velocity on the char segregation is quantified, and validated mathematical modelling. The case of indirect gasification of wood pellets in the Chalmers 2–4-MW indirect gasifier is used to exemplify the findings. The experimental investigation shows that char segregation strongly decreases as the excess velocity is increased over a certain threshold. The larger the char particle, the higher is the threshold fluidization velocity above which the char particle becomes immersed in the dense bed. The model shows that the degree of char conversion in the gasification chamber of an indirect gasifier decreases strongly as the fluidization velocity is increased, due to the decrease in the fuel residence time caused by enhanced lateral mixing. Neglecting the effect of fuel axial mixing on the gasification rate results in modelled char conversion degrees up to 1.3 times higher than when axial mixing is accounted for. This impact of fuel axial mixing increases with the solids cross-flow. While both axial and lateral mixing affect the degree of char conversion in the indirect gasification chamber studied, the effect of fuel lateral mixing is much stronger than that of fuel axial mixing, for the conditions investigated in the present work.
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| 3. |
- Lundberg, Louise, 1987, et al.
(författare)
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The role of fuel mixing on char conversion in a fluidized bed
- 2017
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 316, s. 677-686
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Tidskriftsartikel (refereegranskat)abstract
- Operational conditions, such as the fluidization velocity and the solids cross-flow, affect the degree of char conversion in a fluidized bed by influencing the different mechanisms related to the fuel mixing. Char conversion is influenced by fuel mixing in both the lateral direction (affecting the fuel residence time) and the axial direction (affecting the char gasification rate). In the present work, this effect is investigated through a combination of dedicated experiments in a cold unit, in which the effect of the excess velocity on the char segregation is quantified, and validated mathematical modelling. The case of indirect gasification of wood pellets in the Chalmers 2–4-MW indirect gasifier is used to exemplify the findings. The experimental investigation shows that char segregation strongly decreases as the excess velocity is increased over a certain threshold. The larger the char particle, the higher is the threshold fluidization velocity above which the char particle becomes immersed in the dense bed. The model shows that the degree of char conversion in the gasification chamber of an indirect gasifier decreases strongly as the fluidization velocity is increased, due to the decrease in the fuel residence time caused by enhanced lateral mixing. Neglecting the effect of fuel axial mixing on the gasification rate results in modelled char conversion degrees up to 1.3 times higher than when axial mixing is accounted for. This impact of fuel axial mixing increases with the solids cross-flow. While both axial and lateral mixing affect the degree of char conversion in the indirect gasification chamber studied, the effect of fuel lateral mixing is much stronger than that of fuel axial mixing, for the conditions investigated in the present work.
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