Forced convective drying of willow chips

The forced convective drying process of willow chips was described with a deep bed drying model. The model was validated experimentally for bed moisture content, air temperature and relative humidity, and adequately described ambient air drying of a 1 m deep willow chip bed. At the top layers of the chip bed, the model overestimated the drying rate due to vapour condensation which was not incorporated into the model. However, the drying model was an appropriate tool to gain insight into the forced convective drying process of willow chips. The drying costs of willow chips using farm facilities for storage and drying of potatoes were assessed, based on average monthly weather data. March to September was the most suitable period for drying due to favourable ambient weather conditions. In this period, energy costs for drying from a moisture content of 1–0.18 kg (water) kg−1 (DM), which corresponds to 50% (wet base) to 15%, ranged from 12 to 25 EURO t−1 (DM), or from 28 to 59 EURO t−1 (DM) when investment costs were partly accommodated.