Modelling axial mixing of char - application to the dense bottom bed in CFB boilers
Paper in proceedings, 2017
This work presents a semi-empirical two-phase model for the axial mixing of a spherical tracer particle, aiming to represent a char particle, with application to conditions relevant for the dense bottom bed flow in CFB boilers. The velocity fields of both the bubble and emulsion phases are modelled with validated expressions from literature, while the velocity of the tracer particle in the emulsion phase is obtained from the equation of motion. A correlation for the drag force created by the bed and acting on the tracer particle is found with the help of experimental data from fluid-dynamically down-scaled tests (Köhler et al, 2017). The model is used to predict trends in axial mixing with operational parameters (fluidization velocity, dense bed height) and tracer properties (size and density), which agree well with experimental findings in literature.