MODELLING AND PRACTICAL OPERATION RESULTS OF A DRYER FOR WOOD CHIPS

ABSTRACT

A model of drying of fixed and moving bed in cross-flow is presented. A single particle model described as a multiple moving boundary problem applicable for an icy wood particle is proposed. The simultaneous drying and melting are described by shrinking cores and the effect of thermal storage is taken into account approximately. The results with both the single particle and the bed model compare favourably with reported laboratory measurements. The drying of a deep fixed bed is a two-stage process. A constant rate of drying period with saturated outlet air at constant temperature is followed by a decreasing rate of drying with increasing air outlet temperature and decreasing degree of saturation. The bed modelling is performed to support the development work of a boiler plant using a dryer. Practical operation of dryers within the boiler plants is discussed.

Keywords:

• Bed
• Boiler
• Drying
• Model
• Multiple moving boundary problem
• Particle

ACKNOWLEDGEMENTS

Funding from the National Technology Agency of Finland (TEKES), contract 487/401/99 and Nakkila Works are acknowledged. We thank Mr. Janne Paavilainen for help in computerizing and performing calculations.