The influence of the drying medium on high temperature convective drying of single wood chips

Journal Article · Wed Oct 01 04:00:00 EDT 1997 · Drying Technology

DOI:https://doi.org/10.1080/07373939708917328· OSTI ID:533026

Johansson, A; Rasmuson, A ^[1]

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1. Chalmers Univ. of Technology, Gothenburg (Sweden). Dept. of Chemical Engineering Design

High temperature convective drying of single wood chips with air and superheated steam respectively is studied theoretically. The two-dimensional model presented describes the coupled transport of water, vapor, air and heat. Transport mechanisms included are the convection of gas and liquid, intergas as well as bound water diffusion. In the initial part of the drying process, moisture is transported to the surface mainly due to capillary forces in the transversal direction where evaporation occurs. As the surface becomes dry, the drying front moves towards the center of the particle and an overpressure is simultaneously built up which affects the drying process. The differences between drying in air and steam respectively can be assigned to the physical properties of the drying medium. The period of constant drying rate which does not exist (or is very short) in air drying becomes more significant with decreasing amounts of air in the drying medium and is clearly visible in pure superheated steam drying. The maximal drying rate is larger in air drying, and shorter drying times are obtained since the heat flux to the wood chip particle increases with increasing amounts of air in the drying medium. The period of falling drying rate can be divided into two parts: in the first, the drying rate is dependent upon the humidity of the drying medium whereas in the second, there is no such correlation.

• Sponsoring Organization: USDOE
• OSTI ID: 533026
• Report Number(s): CONF-9607189--
• Journal Information: Drying Technology, Journal Name: Drying Technology Journal Issue: 6-8 Vol. 15; ISSN DRTEDQ; ISSN 0737-3937
• Country of Publication: United States
• Language: English

Related Subjects

09 BIOMASS FUELS
AIR
CONVECTION
DRYING
MATHEMATICAL MODELS
PARAMETRIC ANALYSIS
STEAM
TWO-DIMENSIONAL CALCULATIONS
WOOD FUELS
WOOD WASTES