Steam Pretreatment Characteristics Of Small-diameter Eucalyptus Wood And Building Of Drying Model

Under the current situation,the efficient use of small-diameter wood is an effective means to alleviate and solve the current shortage of forest resources in China.However,small-diameter wood has high growth stress and is prone to cracks and other defects,which makes its comprehensive utilization rate low.Studies have shown that steaming pretreatment technology is an important means to improve the quality of wood drying.Therefore,this paper takes the small-diameter Eucalyptus half-section wood as the research object,explores the initial moisture content of the small-diameter Eucalyptus half-section wood,and the steaming pretreatment temperature on steaming The pretreatment effect,the drying quality of the conventional drying process,and the influence of the drying rate,and to determine an optimized steam pretreatment of small-diameter Eucalyptus timber-conventional drying process.The main evaluation indicators are the visible defects generated during steam conditioning and after steam pretreatment,and during the conventional drying process,combined with the temperature field analysis,microstructure analysis,chemical composition and chemical composition of the test material during steam pretreatment.Content analysis,as well as analysis methods such as function model analysis at various stages,were further explored,and the main conclusions were as follows:(1)The process of adjusting the diameter of the Eucalyptus half-cut timber from the average initial moisture content of 110.7%to the moisture content of about 30%took about 1300h,and the final moisture content was adjusted to 55%with better drying quality;The model of the relationship between the convective mass transfer coefficient and the time in the process of water content modulation is shown,and the model fitting effect is better.k=2.4851252×10-8-0.00024987519/?0.5+0.24163405ln?/?+1089.34/?+505.30113/?1.5-22620.847ln?/?2+178511.26/?2(2)Analyzed the temperature field changes of the test materials under different pretreatment conditions,obtained the S-type function model of the temperature field change of the small-diameter Eucalyptus half-section wood during steaming pretreatment,and regressed the small-diameter Eucalyptus half-section The material preheating time model fits the heating model at different positions of the test material,and the model fitting effect is better.S-shaped function model:T=A1+A2-A1/1+10(A3-t)p,t?350min Warm-up time model:T=1216.67144-81.62157r+2.2314r2-0.02564r3+1.0722×10-4r4 Heating model:T=(a+ct+es+gt2+is2+kts)/(1+bt+ds+ft2+hs2+j ts)(3)Steaming pretreatment at 100? and 120? can rupture the pore membrane;when the steaming pretreatment temperature is 100?,the test material with an initial moisture content of 55%and 40%has a benzene-alcohol solution extraction The extract content decreased by 50.57%and 44.85%,and the hot water extract content decreased by 30.48%and 27.57%year-on-year.(4)Using the determined drying criteria of the small-diameter Eucalyptus half-section timber,the optimized "water content modulation-steaming pretreatment-conventional drying" process parameters were MC=55%,T=100?;The three-dimensional model of"rate-time-steaming pretreatment temperature" and the S-shaped function model of the drying rate change of half-section material have a good fitting effect.3D model:MC55=-68.762849+143.779531n(t)-34.692883(ln(t))2+2.5434001(ln(t))3-0.01357072(ln(t))4-2.508168×10-5(ln(t))5-1.2643103T+0.0059979661T2 S-shaped function model:V=A+(B-A)/(1+10(t+C)/D)(5)Under the conditions of this experiment,when the steaming pretreatment temperature is 80?,100?and 120?,the average drying rate of the small-diameter Eucalyptus semi-timber with an initial moisture content of 55%is dried to a final moisture content of about 9%It is 0.10%/h,0.12%/h and 0.11%/h.