Abstract
The paper proposes the use of microwave irradiation to lower the initial moisture content of wood chips. The study involved willow and fir chips fractionated by means of a sieve separator and unfractionated ash chips. The wood chips were exposed to a constant microwave power of 800 W for 30 s, 60 s, 120 s and 180 s. The chips were weighed before and after irradiation to measure loss of moisture. It was found that the decline in moisture content increased with wood chip size for a given irradiation time and microwave power. The initial moisture content of wood chips was not found to significantly affect loss of moisture as the drying rates of wood chips with higher and lower moisture content exposed to microwaves were not statistically different. The results showed that irradiation intensity increased with the time of exposure to microwaves and unit radiant energy per unit of evaporated moisture decreased with increasing wood chip size in the 3.15–31.50 mm range.
Highlights
Wood chips may be generated at the harvest site, at a nearby landing, or at the plant where they are to be utilized [1]
Sieve analysis—size distribution of wood chips Sieve separation revealed that the most abundant willow and fir fraction consisted of 8–16 mm wood chips, which accounted for more than 62.60 ± 1.96% and 48.96 ± 0.77% of the total material, respectively (Table 2)
The surface temperature of wood chips rose to 150 °C. These results show that wood chips should be irradiated in a continuous manner with a gradually decreasing microwave power to prevent local wood overheating which could potentially lead to ignition
Summary
Wood chips may be generated at the harvest site, at a nearby landing, or at the plant where they are to be utilized [1]. Their shape should approximate a parallelepiped and their size should be precisely defined with respect to their intended purpose. Wood chips used for these applications are sorted as the various fractions may differ in moisture content. Storing wood chips when raw material parameters and storage conditions are unfavorable may have negative effects on their quality. When storing large amounts of wood chips, it is very often necessary to reduce the water content from 60–90 to less than 40% if they will be transported, or to a level below 25%, in order to enable efficient burning or using wood chips as raw materials for production [4, 5]
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