Study on industrial radio-frequency/vacuum drying of Manilkara bidentata wood
LIU Honghai;ZHANG Xin;YANG Lin;LI Xingchang;WU Zhihui;College of Furnishing and Industrial Design,Nanjing Forestry University;Zhong Shan Tai Xing Furniture Co .,Ltd.;
Radio-frequency/vacuum( RF/V) technology can dry wood with high drying rate and high quality because the radio-frequency can heat wood fast and the vacuum condition can lower water boiling point,accelerating water transfer rate. It has significant advantages for the drying of large dimension or high valued wood. Many studies of RF/V drying have been conducted to apply this technology to the drying industry. However,most of them conducted by using the lab-scale dryers,not the industrial scale. To solve the industrial production problems on drying technology and schedule development,this study investigated the drying related parameter calculation methods and selection rules. In addition,the hardwood lumber( Manilkara bidentata) RF/V drying tests were carried out according to the calculated parameters for comparison. The wood quality such as final moisture content( MC) distributions,cracks,power cost,energy conversion efficiency,drying rate and efficiency of dehydration after drying was explored. The results indicated that the unit input power( Pu) should be determined firstly according to the wood dry characteristics and size,then determined by other factors,such as,input current( IP),input voltage( EI) and oscillation efficiency( R). The quantity of dehydration by 1% MC was important for MC monitoring during the drying process. There were no cracks on ends,surface and inner of lumber,and the MC was even for all size of materials and the wood quality after R/FV drying can meet the grade 2 of the GB/T 6491-2012 standard. The power cost in the heating stage took 11.2% of the total energy consumption,and the energy cost of the RF heating counted 71.7% of the whole process. Since the energy conversion efficiency in heating stage and drying stage were 44.5% and 27.7%,respectively,the energy conversion efficiency should be considered in the parameter calculation. The total average drying rate was 1.2% each day,and decreased as the MC decreased. The efficiency of dehydration was affected by lumber temperature and the MC. When the MC was between 20.9% and 10. 0%,it was of positively related with the lumber temperature. The efficiency of dehydration had quadratic relations with the MC and it reached the peak at an MC of about 14.5%.The parameter calculation method and selection rules as well as the results of this study can provide industrial RF/V drying productions with useful technical information.
【Fund】： 国家自然科学基金(31570558 31500479);; 苏北科技专项(SZ-SQ2017014);; 江苏省“青蓝工程”资助项目;; 南京林业大学大学生实践创新训练计划项目(201610298125H 201610298123H)
【CateGory Index】： S781.71
【CateGory Index】： S781.71