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Research on Eucalyptus Veneer Drying and Its Energy Utilization

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Tutor: ZhouYongDong
School: Chinese Academy of Forestry
Course: Wood Science and Technology
Keywords: veneer drying,Eucalyptus Moisture,Content (MC),drying quality,heat utilization,e
CLC: TS653
Type: Master's thesis
Year:  2013
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Veneer drying is an important part of energy use in plywood manufacturing. In this thesis,six species of Eucalyptus (E. urophylla¡Ágrandis is the most widely used currently, and E.saligna, E. grandis, E.cloeziana,E. dunnii, and E. pellita are oriented cultivation for plywoodproduction) was used as raw material(veneer dimension:1270¡Á640mm), BG1333-jet rollerveneer dryer in plywood enterprise was used for veneer drying experiments. The veneer dryingquality, drying techniques, energy utilization of veneer dryer as well as optimized design ofveneer dryer in energy utilization were studied systematically. The main conclusions of thisstudy are as following:(1) The effects of species and thickness on veneer drying qualityEffects of species: the differences in final MC of veneer are reduced afterhigh-temperature (veneer dryer) drying. The final MC¡¯s uniformity of five Eucalyptus specieswith2.3mm-thickness-veneer is in the following sequence: E. cloeziana> E. pellita> E.urophylla¡Ágrandis> E. saligna> E. grandis; as for the drying defects, the increased length ofcrack and warp of2.3mm-thickness-veneer among six Eucalyptus species has no obviousregularity, and their increased number of cracks are almost consistent, within the range of6to9pieces for each veneer.Effects of thickness: The final MC¡¯s uniformity of three thickness of E. urophylla¡Ágrandis veneer after enquipment drying is in the following sequence:2.0mm>2.3mm>1.7mm;as for the drying defects, the increased number of crack in three thickness of E. urophylla¡Ágrandis veneer is different,1.7mm-thickness-veneer¡¯s increased number is the most, which is2.3times as that of the vneer with thickness of2.0mm and2.3mm, the increased length ofcrack and warp of three thickness of E. urophylla¡Ágrandis veneer is in the followingsequence:2.0mm>1.7mm>2.3mm. (2) The comparative analysis of the three kinds of veneer drying methodsEquipment drying (veneer dryer), air drying, and combined drying with air drying andveneer dryer drying were compared, there is not obvious influence from species(E. urophylla¡Ágrandis¡¢E. saligna) and veneer thickness(1.7mm¡¢2.0mm¡¢2.3mm) on veneer drying quality nomatter which drying method was used, But the laying style of air drying has a great effect onwarp of veneer, the warp in horizontal laying veneer is bigger than vertical laying style, there isno obvious influence on crack and hole number by air drying. The veneer warp occurred indrying is the smallest by using combined drying with horizontal air drying and veneer dryerdrying with up-up veneer laying.In veneer drying rate aspect: drying rate of horizontal laying veneer is faster than that ofvertical laying veneer. With horizontal laying veneer in air-drying, the drying rate sequenceamong different position inside veneer is central part <side parts; With vertical laying veneerin air-drying, the drying rate sequence among different position inside veneer is upside>central part>underside. Veneer thickness(1.7mm¡¢2.0mm¡¢2.3mm) has little influence ondrying rate of horizontal laying veneer in air-drying, but has obvious inluence on that ofvertical laying veneer in air-drying. During the summer, horizontal and vertical air dryingefficiency are7and312sheets veneer/(day m2); During the winter, horizontal and vertical airdrying efficiency are5and52sheets veneer/(day m2).Using combined drying with air drying and veneer dryer drying can save50%energy incomparison with using veneer dryer solely.(3) Energy utilization in veneer dryingHeat energy proportion of water evaporation is about60%of the total energy supply inveneer drying, The temperature of humid air discharged is high, which can be reused. it is apotential energy-saving point. The leaking Heat energy proportion is22.9%of the total energysupply, heat efficiency in veneer drying is61.9%, and its specific energy consumption is2.4¡Á103MJ/m~3; Equipment exergy efficiency¡¢equipment thermodynamic perfection¡¢inner exergyloss and veneer specific exergy consumption in veneer drying are55.2%¡¢73.7%¡¢26.3%¡¢2.3MJ/m~3correspondingly. (4) Optimization of Energy utilization in vene er dryingSystematically analyzing was conducted for the planning of heat-transfer oil supplyingpipeline laying out, which connected in series replace of the original parallel connection.This change(series connection with adding oil and without adding oil) has no influence onheat energy efficiency and specific energy consumption in veneer drying system; but total inputexergy¡¢inner exergy loss and veneer specific exergy were reduced:0.05¡Á10~3MJ/h and0.07¡Á103MJ/h¡¢0.38%and0.53%¡¢0.01¡Á10~3MJ/m~3and0.02¡Á10~3MJ/m~3. Equipment exergyefficiency and equipment thermodynamic perfection are increased:0.28%and0.40%¡¢0.38%and0.53%. So this is a better plan for energy utilization in veneer dryer¡¯s heat-transfer oilsupplying in comparison with the original one. But series connection without adding oil inheat-transfer oil pipeline is more reasonable and effective.1) Series connection with adding oil in heat transfering oil pipeline: total heat-transfer oilflow in the pipe decreased from131417kg/h to955756kg/h, outlet oil temperature decreasedfrom190¡æto179¡æ.2) Series connection without adding oil in heat-transfer oil pipeline: total oil flow in thepipe increased from131417kg/h to85536kg/h, outlet oil temperature decreased from190¡æto175¡æ.
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