MOISTURE EQUILIBRIUM OF WOOD AND BARK CHIPS IN SUPERHEATED STEAM

Citation
H. Bjork et A. Rasmuson, MOISTURE EQUILIBRIUM OF WOOD AND BARK CHIPS IN SUPERHEATED STEAM, Fuel, 74(12), 1995, pp. 1887-1890
Citations number
11
Categorie Soggetti
Energy & Fuels","Engineering, Chemical
Journal title
FuelACNP
ISSN journal
00162361
Volume
74
Issue
12
Year of publication
1995
Pages
1887 - 1890
Database
ISI
SICI code
0016-2361(1995)74:12<1887:MEOWAB>2.0.ZU;2-X
Abstract
This study relating to the steam drying of biofuels suggests that the activities of water in air (defined as relative humidity) and of water in superheated steam (defined as the ratio of the saturated pressure and the saturated pressure at the superheated temperature) are identic al. The dependence of the activity in superheated steam on the equilib rium moisture content was studied in various experiments for different wood materials at constant temperatures of 140 and 160 degrees C. The equilibrium moisture content was found to depend on the following fac tors: the activity of the superheated steam, the temperature and the m aterials used, the first of these being the most important. The experi mentally determined sorption isotherms were compared with different so rption theories. The Dent model gave a good correlation with the exper imental data. The sorbed water can be divided into primary water with high binding energy and secondary water with low binding energy. If bi ofuels are to be dried with superheated steam, an equilibrium moisture fraction of similar to 0.05 seems to be relevant. It will probably be possible to reach this with activities in the range 0.2-0.4 for all r eal materials.