On the packing properties of fixed beds for thermal fuel conversion

Packed beds of fuel wood in the form of chips or pellets are commonly found in thermal conversion processes such as combustion or gasification. This thesis is concerned with the characterization of spatial voidage distribution inside fuel wood chip beds, which is of great importance for flow and reactor modelling. On the basis of a random deposition approach, a packing model was developed in order to transfer geometrical bed structures into CFD software for subsequent flow simulations. In addition, an experimental investigation of voidage distribution by bed solidification, sectioning, and subsequent image analysis of the cuts was carried out for packings of different commercially available wood chips and pellets, in order to derive a mathematical expression correlating radial voidage distribution. The findings of both the experimental results and the simulations are used to interpret fixed-bed wood combustion results from a laboratory-scale combustion tube and a commercial small-scale underfeed stoker.