The effect of wood particle properties and operation conditions on conversion rates and bed temperatures were investigated experimentally in fixed-bed reactors. Conversion rates were strongly dependent on initial moisture and size of the solid particles as well as on air feed. Experimental setups were modeled numerically with the assumption of the fixed bed representing a porous medium composed of spherical particles that undergo drying and pyrolysis with simultaneous burnout and gasification of the volatile and solid (char) pyrolysis products. The model described experimental results with good accuracy. Further investigations with different fuels and fuel mixtures were performed, and thus a comprehensive database is available to understand and predict the behavior of large industrial facilities, for example, biomass- and solid-recovered fuel incinerators with grate furnaces.