Drying characteristics of wood cylinders for conditions pertinent to fixed-bed countercurrent gasification

The convective drying of pine wood cylinders (40 mm diameter) in hot air has been investigated experimentally for conditions reproducing those encountered in the drying section of fixed-bed updraft gasifiers (nominal velocities of 0.4–1.2 m/s and maximum air temperatures of 435–600 K). Temperature profiles show a drying zone slowly propagating from the heat exposed surfaces towards the inside, whereas the global drying rate presents two maxima, corresponding to moisture evaporation along a thin superficial layer and sample heat-up, respectively. The drying times reproduce trends already known on dependence of the external heating conditions and the initial moisture content. From the quantitative point of view, a moisture content of 50% is observed to delay the particle heating times up to factors of 3–5. Acceptable quantitative agreement is obtained between these measurements and the predictions of a simplified model of moisture evaporation in wood, which can be used to treat single particle effects in the more complicated mathematical descriptions of gasifier behavior.