Limitations of the porous medium approximation in modelling of fixed bed combustion

Other conference contribution, 2005

Most models for combustion of solid fuels in fixed beds treat the bed as a porous medium and neglect gradients within the fuel particles. There is no information about the conditions for which the description of the bed as porous medium is valid. To investigate this, a one-dimensional porous bed model is used together with a two-dimensional particle model. The two models are connected to each other through the surface temperature of the particle which is given by bed simulations. The main parameter is particle size, but the influence of moisture content and inlet gas velocity is also investigated. The results show that only particles smaller than around 5mm at low gas velocities can be treated as a porous medium, without considering internal gradients.