Super-heated Steam Pretreatment Process Of Fast-growing Poplar And Its Influence On Drying Quality

In this paper, fast-growing Poplar was taken as experimental material. Through changing of the rule of temperature field, moisture content and pretreatment quality in the process of super-heated steam pretreatment, the pretreatment process of the optimum super-heated steam of the fast growing poplar wood was obtained. And the experiment material after the optimal pretreatment process conventional drying, compare and analysis the treated wood and untreated wood of drying characteristics, and the cost differences of drying process, in order to providing a reference of super-heated steam pretreatment factory application. The conclusions are as follows:(1)The poplar of thickness of 2cm、4cm-6cm, during the process of super-heated steam pretreatment, the variation trends of temperature field inside the wood is basically the same, simulate the relation formula of different pretreatment conditions with different thickness of poplar through data regression. The theoretical relation formula can be used to predict the change of temperature field in the process of super-heated steam pretreatment.(2)After the super-heated steam pretreatment, the change of moisture content in poplar under different treatment conditions was obtained. Through the regression analysis of the variation of moisture content in poplar under different treatment conditions, the relation formula between the reduction of moisture content in poplar and the pretreatment condition of super-heated steam pretreatment was obtained. The theoretical relation formula can be used to predict the change of moisture content of poplar under different pretreatment conditions.(3)When the super-heated steam pretreatment temperature is 180℃, the surface of poplar widespread occur significant cracking and shrinkage; when the temperature is 150℃, long processing time (1.5h/cm) will cause slight shrinkage and cracking on the surface of poplar; when the temperature is 120℃, the surface of poplar do not occur obvious defects. Synthesize the moisture variation and the quality of wood surface, obtain the optimal condition of super-heated steam pretreatment of poplar is 150℃,1.0h/cm.(4)Though super-heated steam pretreated 7cm poplar’s conventional drying time is 432 hours, untreated wood is 960 hours, the drying rate of the two cases were 0.099%/h and 0.065%/h. The drying rate increases 55%.(5)The gradient of moisture content after the super-heated steam pretreatment is 8%, the gradient of moisture content of untreated wood is 11%; drying force index of untreated wood is 0.0375, the treated wood is 0.0221, reducing the drying force index up to 41%; the average swelling radio of wood air dry volume of super-heated steam pretreatment wood is 5.267%, lower 1.2% than the untreated wood, swelling ratio of wood water absorption volume of super-heated steam pretreatment wood is 14.453%, lower 3.7% than untreated wood. Super-heated steam pretreatment can release wood drying stress and improve dimensional stability of poplar.