Experimental Study on Drying of Bark in Fixed Beds

Abstract

Bark has a heterogeneous particle size distribution and an irregular particle shape. For this reason, drying models usually give only rough estimations of the drying rate, and drying tests are needed to define the drying rate precisely. In this study, normal drying curves and a characteristic drying curve are experimentally determined for bark that has been dried in thick fixed beds. The study evaluates the shape of the characteristic drying curve as well as the accuracy of the characteristic drying curve method. In drying tests the influence of drying air temperature and bed height on drying time and the shape of the characteristic drying curve has been studied. Four different drying air temperatures (50, 70, 90, and 110°C) and three bed heights (50, 150, and 250 mm) have been used in the tests. Results indicate that a linear characteristic drying rate curve can be used in bark drying to extrapolate drying data from one set of drying conditions to another, when the bed height is high (in this study 150–250 mm) and the inlet air temperature is below 100°C. For thin beds (in this study 50 mm) the characteristic drying curve method cannot be used over such a wide range on drying temperatures as in the case of higher beds.

Keywords:

• Characteristic drying curve
• Constant drying rate
• Drying curve

Notes

*Air velocity means the air velocity per free sectional area of the drying chamber.

Relative error = |1−Time_CDC/ Time_DC| ∗ 100.