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|Title: ||Fuel dispersion and bubble flow distribution in fluidized beds|
|Authors: ||Olsson, Johanna|
|Department: ||University of Borås. School of Engineering|
|Issue Date: ||2011|
|Series/Report no.: ||Skrifter från Högskolan i Borås;27|
|Publisher: ||Chalmers University of Technology ; University of Borås|
|Media type: ||text|
|Publication type: ||licentiate thesis|
|Keywords: ||fluidised bed|
digital image analysis
|Subject Category: ||Subject categories::Engineering and Technology::Chemical Engineering::Chemical Process Engineering|
|Research Group: ||IH Energi och material|
|Strategic Research Area: ||Resource Recovery|
|Abstract: ||Fluidized bed technology is used for thermal conversion of solid fuels (combustion and
gasification) and is especially suitable for conversion of low-rank fuels such as biomass and waste. The performance of fluidized bed units depends on the fuel mixing and fuel-gas
contact. Thus, it is important to understand these two phenomena in order to develop
models for reliable design and scale up of fluidized bed units. This work investigates, under conditions representative for industrial fluidized bed units, the lateral fuel mixing (in a unit with a cross section of 1.44 m2 both at hot and cold conditions) and the bubble flow distribution (in a 1.2 m-wide 2-dimensional unit).
The work confirms previous findings on the formation of preferred bubble paths and shows
that these bubble paths are enhanced by lowering the fluidization velocity, increasing the dense bed height and reducing the pressure drop across the gas distributor.
From the fuel mixing experiments, an estimation of the lateral effective dispersion coefficient to values in the order of 10-3 m2/s is obtained under both hot and cold conditions.
The experiments under cold conditions give additional qualitative information on the fuel mixing patterns such as flotsam/jetsam tendencies. The camera probe developed for fuel tracking under hot conditions enables to study the fuel dispersion under real operation at relevant industrial scales.
Based on the characteristics of the bubble path flow, a model for the horizontal fuel
dispersion on a macroscopic scale is formulated and shown to be able to give a good description of the experimental data. As opposed to the commonly applied diffusion-type modeling of the lateral solids dispersion, the proposed model facilitates integration with models of the bubble flow. Thus, the present modeling work is a first step to provide a modeling of the fuel dispersion, which uses as inputs only the main operational parameters of the fluidized bed.|
|Appears in Collections:||Licentiatavhandlingar / Licentiate theses (IH)|
Skrifter från Högskolan i Borås
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