In this work, Chinese fir samples with a size of 400 mm (L) by 50 mm (W) 30 mm (H) weretaken as specimens, and drying rate and energy consumption were compared under the conditions, inwhich the absolute pressure was 0.02 , 0.04 , 0.06 and 0.10 MPa, respectively, and the temperature was80 oC. The results showed that, when the moisture content (MC) of the samples was above fibersaturation point (FSP), the vacuum drying rate was 0.96-1.24 times as high as the ambient pressuredrying rate. However, when it was below FSP, the vacuum drying rate was 1.26-1.32 times as high as theambient pressure drying rate. At the same time, when the MC was above FSP, the energy consumptionof vacuum drying was 81.1%-95.9% of that of ambient pressure drying; when the MC was below FSP,the energy consumption of vacuum drying was 62.40%-69.40% of that of ambient pressure drying.Therefore, the vacuum drying was superior to the ambient pressure drying in terms of drying rate andenergy consumption.
The effects of high temperature steam pretreatment on the change in wood moisture content （MC） and characteristics of vacuum drying were investigated in this study. Poplar and manchurian walnut woods were pretreated with high temperature steam at 100~C and 140~C, prior to vacuum drying. A comparison of the characteristics of vacuum drying between steam pretreated wood and untreated wood was carried out. The results show that during steam pretreatment, the MC of wood decreased within a few hours. The reduction of MC varied with the temperature; the higher the temperature, the faster the MC dropped. During the vacuum drying stage, the rates of drying ofpretreated samples were higher than those of untreated samples when MC was below the fiber saturation point. Furthermore, the total drying time of samples treated at a steam temperature of 140~C was lower than that of untreated samples. Therefore, a vacuum procedure after steam pretreatment can effectively shorten the drying time when drying wood.
