Axial Mixing of Large Solids in Fluidised Beds – Modelling and Experiments
Licentiate thesis, 2019
This work focuses on the axial mixing of large solids in fluidised beds with the aim to advance current knowledge on in-bed mixing with an emphasis on biomass particles. As the latter typically have a high content of moisture, volatile and ash and are larger and lighter than conventional fuels like e.g. coal or lignite, they are even more prone to segregate axially in the bed in a flotsam fashion. Yet, the effect of fuel density and size as well as the effect of fluidisation conditions on the axial mixing of fuel has not been fully understood.
To enhance the understanding of solids mixing, this work combines a one-dimensional semi-empirical model with experiments applying magnetic particle tracking (MPT) in a fluid-dynamically down-scaled fluidised bed. The model is used to identify governing mechanisms and the respective key parameters to be studied with dedicated experiments which, in their turn, contribute to the continuous upgrading of the model.
The key parameters in the axial mixing of larger solids in a fluidised bed are found to be: i) the apparent viscosity of the emulsion, for which MPT measurements confirmed its Newtonian character, and ii) the bubble flow, which experiments revealed to have a higher upwards velocity and fuel-to-bubble velocity ratio than shown in previous literature not accounting for hot conditions.
magnetic particle tracking
Chalmers, Space, Earth and Environment, Energy Technology, Energy Technology 1
Köhler, A. Modelling Axial Mixing of Fuel Particles in the Dense Region of a Fluidised Bed
Magnetic tracking of a fuel particle in a fluid-dynamically down-scaled fluidised bed
Fuel Processing Technology,; Vol. 162(2017)p. 147-156
Experimental characterization of axial fuel mixing in fluidized beds by magnetic particle tracking
Powder Technology,; Vol. 316(2017)p. 492-499
Enhanced performance in thermal conversion of biomass
Swedish Energy Agency, 2017-05-02 -- 2019-10-30.
Chemical Process Engineering
Chalmers University of Technology
Opponent: Henrik Ström, Chalmers University of Technology, Sweden