刺猬紫檀材热泵干燥特性及工艺研究
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摘要
为了提高名贵木材刺猬紫檀的材干燥质量,以刺猬紫檀锯材为对象,采用热泵系统对锯材进行除湿干燥同时对其干燥特性进行分析,从而进一步优化干燥工艺。研究中重点分析了干燥过程中的干燥曲线、含水率、含水率偏差、干燥应力、干缩率等影响干燥质量的因素,并借助CT无损扫描技术建立了锯材含水率与CT值的数学模型,利用模型直观表征锯材分层含水率对干燥质量的影响。在此基础上进行干燥等级评定,进而优化刺猬紫檀材的干燥工艺。结果表明,刺猬紫檀材基本密度为0.84g·cm~(-3),弦向干缩系数为0.42%,径向干缩系数0.32%,体积干缩系数0.58%。刺猬紫檀干燥过程中锯材厚度上含水率偏差较大,应力梯度较大,采用较慢的干燥速率。通过建立CT值与分层含水率的线性回归方程y=0.149 8x+18.907 R~2=0.990 3,实现木材干燥过程中应力的变化与干燥质量的可控性,获得优化的干燥工艺:20mm厚、含水率42.2%的刺猬紫檀干燥528h后,其含水率达到10.24%,而且干燥质量达到GB/T6491-2012《锯材干燥质量》规定的一级要求。热泵干燥可有效减小干燥过程中的厚度含水率梯度及干燥残余应力,减少木材干燥产生皱缩、变形、表裂等缺陷。
In order to improve the drying quality of Pterocarpus erinaceus wood,the dehumidification drying and drying characteristics of the wood were analyzed with drying heat pump during the period of drying.Drying curve,moisture content and its deviation,drying stress and dying shrinkage rate were studied.Based on the CTscanning technology,the mathematical model between wood moisture content and CTvalue was established to study the influence of wood moisture content on drying quality.Based on drying stress,the drying grade was estimated.And drying process was optimized.The results showed that the basic density of the wood was 0.84 g·cm~(-3),the tangential coefficient of shrinkage was 0.42%,the radial coefficient of shrinkage was 0.32%,the volume coefficient of shrinkage was 0.58%.During the period of drying,the moisture content deviation of thickness was high and the stress gradient was large,indicating that we had to be reduced drying rate.From the linear regression equation of CTvalue and layer moisture content(y=0.149 8 x+18.907 R~2=0.990 3),controllability of stress change and drying quality could be realized during drying.When initial moisture content of the wood was 42.2%,the thickness was 22 mm,optimum dr-ying time was 528 h,the moisture content of is the wood was 10.24% after drying,from which the drying quality met the requirements of the first grade lumber of Chinese national standard(GB/T6491-1999 sawn timber drying quality regulation level requirements).Technology of drying heat pump could decrease moisture gradient of thickness and drying residual stress effectively during drying.At the same time,technology of drying heat pump could reduce the wood drying shrinkage,deformation,crack defects.
In order to improve the drying quality of Pterocarpus erinaceus wood,the dehumidification drying and drying characteristics of the wood were analyzed with drying heat pump during the period of drying.Drying curve,moisture content and its deviation,drying stress and dying shrinkage rate were studied.Based on the CTscanning technology,the mathematical model between wood moisture content and CTvalue was established to study the influence of wood moisture content on drying quality.Based on drying stress,the drying grade was estimated.And drying process was optimized.The results showed that the basic density of the wood was 0.84 g·cm~(-3),the tangential coefficient of shrinkage was 0.42%,the radial coefficient of shrinkage was 0.32%,the volume coefficient of shrinkage was 0.58%.During the period of drying,the moisture content deviation of thickness was high and the stress gradient was large,indicating that we had to be reduced drying rate.From the linear regression equation of CTvalue and layer moisture content(y=0.149 8 x+18.907 R~2=0.990 3),controllability of stress change and drying quality could be realized during drying.When initial moisture content of the wood was 42.2%,the thickness was 22 mm,optimum dr-ying time was 528 h,the moisture content of is the wood was 10.24% after drying,from which the drying quality met the requirements of the first grade lumber of Chinese national standard(GB/T6491-1999 sawn timber drying quality regulation level requirements).Technology of drying heat pump could decrease moisture gradient of thickness and drying residual stress effectively during drying.At the same time,technology of drying heat pump could reduce the wood drying shrinkage,deformation,crack defects.
引文
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[8]陈东,谢继红.热泵干燥装置[M].北京:化学工业出版社,2007:63-68.
[9]张璧光,李延军.热泵干燥木材的技术现状与发展趋势[J].干燥技术与设备,2003(1):6-8.ZHAHG B G,LI Y J.Status and prospect of heat pump drying of wood[J]Drying Technology and Equipment,2003(1):6-8.(in Chinese)
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[11]张振涛,张璧光,顾炼百,等.两级压缩高温热泵木材干燥的研究[J].南京林业大学学报:自然科学版,2007(4):41-45.ZHANG Z T,ZHANG B G,GU L B,et al.Wood drying with two-stage compression high temperature heat-pump[J].Journal of Nanjing Forestry university:Natural Science Edition,2007(4):41-45.(in Chinese)
[12]张振涛.木材热泵干燥窑内的湿度模糊控制初探[J].华北电力大学学报,2004,31(6):88.
[13]张璧光.除湿干燥中临界除湿状态的分析[J].北京林业大学学报,2007,29(6):181-184.ZHANG B G.Critical dehumidified state during dehumidification drying[J].Journal of Beijing Forestry University,2007,29(6):181-184.(in Chinese)
[14]周永东,张璧光.湿空气旁通率对热泵除湿干燥机能耗影响的分析研究[J].林业科技通讯,1999(9):2-3.
[15]HANSSON L,ANTTI L.Modeling microwave heating and moisture redistribution in wood[J].Drying Technol,2008,26:552-559.
[16]徐兆军,丁涛,丁建文,等.基于断层扫描技术的木材含水率检测技术研究[J].木材加工机械,2009(4):7-9.XU Z J,DING T,DING J W,et al.Moisture content measuring of wood with commutated tomography[J].Wood Processing Machinery,2009(4):7-9.(in Chinese)
[17]李贤军,蔡智勇,傅峰.干燥过程中木材内部含水率检测的X射线扫描方法[J].林业科学,2010,46(2):122-127.LI X J,CAI Z Y,FU F.A new X-ray scanning method for measuring the internal moisture contentin wood drying[J].Scientia Silvae Sinicae,2010,46(2):122-127.(in Chinese)
[18]李贤军,乔建政,蔡智勇,等.微波干燥与常规干燥中木材内含水率动态分布[J].中南林业科技大学学报,2009,29(6):99-103.LI X J,QIAO J Z,CAI Z Y,et al.Dynamic distribution of wood moisture content during microwave drying and hot air drying[J].Journal of Central South University of Forestry&Technology,2009,29(6):99-103.(in Chinese)
[19]KEN WATANABE,YUKIE SAITO,STAVROS AVRAMIDIS,et al.Non-destructive measurement of moisture distribution in wood duringdrying using digital x-ray microscopy[J].Drying Technology,2008,26:590-595.
[20]李大纲.国内外木材干燥应力研究现状及发展趋势[J].建筑人造板,2001(2):15-19.
[21]田仲富,黎粤华,郭秀荣.木材干燥原理及影响其干燥速度的因素分析[J].安徽农业科学,2013,41(33):1290-1294.TIAN Z F,LI Y H,GUO X R.Wood drying principle and factors for influencing drying speed[J].Journal of Anhui Agricultural Science,2013,41(33):1290-1294.(in Chinese)
[22]周永东,傅峰,李贤君,等.微波处理对桉木应力及微观构造的影响[J].北京林业大学学报,2009,31(2):146-150.ZHOU Y D,FU F,LI X J,et al.Effects of microwave treatment on residue growth stress and microstructure of Eucalyptus urophylla[J].Journal of Beijing Forestry University,2009,31(2):146-150.(in Chinese)
[23]杨亮庆,刘一星,蔡英春.PEG400预处理枫桦圆盘干燥特性研究[J].西北林学院学报,2013,28(4):153-157.YANG L Q,LIU Y X,CAI Y C.Drying characteristics of betula costata disk pretreated with PEG400[J].Journal of Northwest Forestry University,2013,28(4):153-157.(in Chinese)
[24]韦鹏练,廖克波,符韵林,等.山白兰木材干燥特性研究[J].西北林学院学报,2012,27(1):229-231,245.WEI P L,LIAO K B,FU Y L,et al.A study of drying characteristics of Paramichelia baillonii[J].Journal of Northwest Forestry University,2012,27(1):229-231,245.(in Chinese)
[25]孟兆新,李尚,肖定,等.木材干燥窑内部流场改进与风速均匀性研究[J].西北林学院学报,2016,31(3):247-251.MENG Z X,LI S,XIAO D,et al.Improvement of internal flow field of wood drying kiln and its wind speed distribution uniformity[J].Journal of Northwest Forestry University,2016,31(3):247-251.(in Chinese)
[2]张振涛.两级压缩高温热泵干燥木材的研究[D].南京:南京林业大学,2008:1-122.
[3]顾炼百.我国实用木材干燥技术的进展及思考[J].林产工业,2006,20(2):19-22.GU L B.Review and remarks on applied wood drying technology in China[J].China Forest Products Industry,2006,20(2):19-22.(in Chinese)
[4]谭辉,张璧光,伊松林.改善干燥质量与木材加工其他环节对低碳经济的贡献[J].干燥技术与设备,2011,9(1):9-32.
[5]YI S L,ZHOU Y D,LIU Y R,et al.Experimental equilibrium moisture content of wood under vacuum[J].Wood and Fiber Science,2008,40(3):321-324.
[6]张璧光,高建民,伊松林,等.我国木材干燥节能减排技术研究现状[J].华北电力大学学报:自然科学版,2009(3):38-42.ZHANG B G,GAO J M,YI S L,et al.The present research situation of solar-heat pump and heat pipe technology on lumber drying in China[J].Journal of North China Electric Power University:Natural Science Edition,2009(3):38-42.(in Chinese)
[7]谢大斌.高温除湿-常规蒸汽联合干燥木材的优化[D].北京:北京林业大学,2006.
[8]陈东,谢继红.热泵干燥装置[M].北京:化学工业出版社,2007:63-68.
[9]张璧光,李延军.热泵干燥木材的技术现状与发展趋势[J].干燥技术与设备,2003(1):6-8.ZHAHG B G,LI Y J.Status and prospect of heat pump drying of wood[J]Drying Technology and Equipment,2003(1):6-8.(in Chinese)
[10]张绪坤,胡文伟,张进疆,等.国内外热泵干燥的现状与展望[J].江西科学,2009(4):629-633.ZHANG X K,HU W W,ZHANG J J,et al.Recent developments and future trends of heat pump drying at home and abroad[J].Jiangxi Science,2009(4):629-633.(in Chinese)
[11]张振涛,张璧光,顾炼百,等.两级压缩高温热泵木材干燥的研究[J].南京林业大学学报:自然科学版,2007(4):41-45.ZHANG Z T,ZHANG B G,GU L B,et al.Wood drying with two-stage compression high temperature heat-pump[J].Journal of Nanjing Forestry university:Natural Science Edition,2007(4):41-45.(in Chinese)
[12]张振涛.木材热泵干燥窑内的湿度模糊控制初探[J].华北电力大学学报,2004,31(6):88.
[13]张璧光.除湿干燥中临界除湿状态的分析[J].北京林业大学学报,2007,29(6):181-184.ZHANG B G.Critical dehumidified state during dehumidification drying[J].Journal of Beijing Forestry University,2007,29(6):181-184.(in Chinese)
[14]周永东,张璧光.湿空气旁通率对热泵除湿干燥机能耗影响的分析研究[J].林业科技通讯,1999(9):2-3.
[15]HANSSON L,ANTTI L.Modeling microwave heating and moisture redistribution in wood[J].Drying Technol,2008,26:552-559.
[16]徐兆军,丁涛,丁建文,等.基于断层扫描技术的木材含水率检测技术研究[J].木材加工机械,2009(4):7-9.XU Z J,DING T,DING J W,et al.Moisture content measuring of wood with commutated tomography[J].Wood Processing Machinery,2009(4):7-9.(in Chinese)
[17]李贤军,蔡智勇,傅峰.干燥过程中木材内部含水率检测的X射线扫描方法[J].林业科学,2010,46(2):122-127.LI X J,CAI Z Y,FU F.A new X-ray scanning method for measuring the internal moisture contentin wood drying[J].Scientia Silvae Sinicae,2010,46(2):122-127.(in Chinese)
[18]李贤军,乔建政,蔡智勇,等.微波干燥与常规干燥中木材内含水率动态分布[J].中南林业科技大学学报,2009,29(6):99-103.LI X J,QIAO J Z,CAI Z Y,et al.Dynamic distribution of wood moisture content during microwave drying and hot air drying[J].Journal of Central South University of Forestry&Technology,2009,29(6):99-103.(in Chinese)
[19]KEN WATANABE,YUKIE SAITO,STAVROS AVRAMIDIS,et al.Non-destructive measurement of moisture distribution in wood duringdrying using digital x-ray microscopy[J].Drying Technology,2008,26:590-595.
[20]李大纲.国内外木材干燥应力研究现状及发展趋势[J].建筑人造板,2001(2):15-19.
[21]田仲富,黎粤华,郭秀荣.木材干燥原理及影响其干燥速度的因素分析[J].安徽农业科学,2013,41(33):1290-1294.TIAN Z F,LI Y H,GUO X R.Wood drying principle and factors for influencing drying speed[J].Journal of Anhui Agricultural Science,2013,41(33):1290-1294.(in Chinese)
[22]周永东,傅峰,李贤君,等.微波处理对桉木应力及微观构造的影响[J].北京林业大学学报,2009,31(2):146-150.ZHOU Y D,FU F,LI X J,et al.Effects of microwave treatment on residue growth stress and microstructure of Eucalyptus urophylla[J].Journal of Beijing Forestry University,2009,31(2):146-150.(in Chinese)
[23]杨亮庆,刘一星,蔡英春.PEG400预处理枫桦圆盘干燥特性研究[J].西北林学院学报,2013,28(4):153-157.YANG L Q,LIU Y X,CAI Y C.Drying characteristics of betula costata disk pretreated with PEG400[J].Journal of Northwest Forestry University,2013,28(4):153-157.(in Chinese)
[24]韦鹏练,廖克波,符韵林,等.山白兰木材干燥特性研究[J].西北林学院学报,2012,27(1):229-231,245.WEI P L,LIAO K B,FU Y L,et al.A study of drying characteristics of Paramichelia baillonii[J].Journal of Northwest Forestry University,2012,27(1):229-231,245.(in Chinese)
[25]孟兆新,李尚,肖定,等.木材干燥窑内部流场改进与风速均匀性研究[J].西北林学院学报,2016,31(3):247-251.MENG Z X,LI S,XIAO D,et al.Improvement of internal flow field of wood drying kiln and its wind speed distribution uniformity[J].Journal of Northwest Forestry University,2016,31(3):247-251.(in Chinese)