中温对流条件下收缩性城市生活垃圾基元传热传质特性的研究
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摘要
干燥过程是城市生活垃圾焚烧前的必经阶段,干燥的好坏直接决定了焚烧的效率。由于城市生活垃圾是一种高含湿量的多孔介质物料,干燥过程中往往发生严重的收缩。因此,本文主要就热风干燥条件下收缩性垃圾基元内部热质传递规律开展研究。
通过在热风对流干燥实验台上进行垃圾基元的实验研究,得到温度、风速、垃圾基元种类及其几何因子对基元湿分迁移特性的影响规律以及基元干燥收缩特性的变化规律,结果表明收缩率与失重率之间呈现线性关系(R2>0.95),基元减少的体积近似地等于基元脱出的水分的体积。对正交实验结果进行了极差与方差分析,发现温度、风速及基元失重率对收缩率影响显著(a=0.05)；温度及基元厚度对干燥时间影响显著(a=0.05)。
基于Fick定律及能量守恒方程建立数学模型。通过MATLAB平台编写计算程序,采用隐式格式有限差分法计算得到基元内部湿分分布与温度分布,发现对流边界含湿量与温度呈现阶跃式的变化特征。通过模拟与实验对比得到平均有效湿分扩散系数为温度与含湿量的递增函数,范围为3.245×10-20.576×10-8m2/s。对基元干燥过程进行了动力学分析,整理出基元的Arrhenius方程,在本文研究条件下基元表观活化能为10-22kJ。
对干燥控制方程进行无量纲化重写与级数分析得到了垃圾基元内部热质传递规律。基元传热毕渥数Bi与传质毕渥数Bim级数为100-101之间,说明在干燥过程中,热质传递都是由内部控制的导热与湿分扩散过程,说明垃圾基元的内部传热传质特性受外界干燥条件(热风风速,热风相对湿度)的影响较小,而主要在于基元自身的热物理特性。在本文所研究的干燥条件下,垃圾基元表面传热系数为9.5-184.5W/(m2·K)；传质系数为：6.2×10-6-7.4×10-4m/s。
Drying process is the neccessary stage before the Municipal Solid Waste (MSW) incineration and its combustion efficiency is mainly determined by the quality of dry process. Serious contraction occurred in the consideration of MSW is a kind of porous materials which has the high moisture content. For this reason, this paper focus on the internal heat and mass transfer characteristic of shrinkable MSW matrixes during hot air convection drying.
The hot air convection drying experimental study of the MSW matrixes has been carried out and the influence rules of moisture migration characteristic by hot air tempertature, windspeed, matrixes kinds and geometric factor were obtained. Also, the shrinkage characteristic was obtained. Result shows the linear relationship between shrinkage factor and weight loss ratio (R2>0.95), the MSW matrixes volume reduced was approximately equal to the volume of water loss. Through the orthogonal experimental results of range and variance analysis, it shows that temperature, windspeed and weight loss ratio has significant effect on the shrinkage factor (α=0.05),the temperature and thickness has significant effect on drying time.
Based on the Fick law and energy conservation equation, the mathematical model has been built. Calculating programme has been designed base on the MATLAB, through the implicit finite difference method, the internal temperature and moisture distribution were obtained, moisture content and temperature on the convection boundary shows the step-like changes. Through the comparison between experimental value and calculating value found that average effective moisture diffusivity was an increasing function about moisture content and temperature, value range is 3.245×10-8～20.576×10-8m2/s. Throught the dynamic analysis, the Arrhenius equations were obtained. Under conditions in this study, the apparent activation energy range is 10～22kJ.
After dimensionless rewrite about the governing equation and series analysis, law of internal heat and mass transfer were obtained. Bi and Bim series were 100～101, it shows that heat and mass transfer were governed by the internal conduction and diffusion, external drying conditions (hot air velocity and relative humidityof dring air) has limit affect about internal heat and mass transfer process. Under conditions of this study, surface heat transfer coefficient of matrixes is 9.5～184.5W/(m2·K) and surface mass transfer coefficient of matrixes is 6.2×10-6～7.4×10-4m/s.
通过在热风对流干燥实验台上进行垃圾基元的实验研究,得到温度、风速、垃圾基元种类及其几何因子对基元湿分迁移特性的影响规律以及基元干燥收缩特性的变化规律,结果表明收缩率与失重率之间呈现线性关系(R2>0.95),基元减少的体积近似地等于基元脱出的水分的体积。对正交实验结果进行了极差与方差分析,发现温度、风速及基元失重率对收缩率影响显著(a=0.05)；温度及基元厚度对干燥时间影响显著(a=0.05)。
基于Fick定律及能量守恒方程建立数学模型。通过MATLAB平台编写计算程序,采用隐式格式有限差分法计算得到基元内部湿分分布与温度分布,发现对流边界含湿量与温度呈现阶跃式的变化特征。通过模拟与实验对比得到平均有效湿分扩散系数为温度与含湿量的递增函数,范围为3.245×10-20.576×10-8m2/s。对基元干燥过程进行了动力学分析,整理出基元的Arrhenius方程,在本文研究条件下基元表观活化能为10-22kJ。
对干燥控制方程进行无量纲化重写与级数分析得到了垃圾基元内部热质传递规律。基元传热毕渥数Bi与传质毕渥数Bim级数为100-101之间,说明在干燥过程中,热质传递都是由内部控制的导热与湿分扩散过程,说明垃圾基元的内部传热传质特性受外界干燥条件(热风风速,热风相对湿度)的影响较小,而主要在于基元自身的热物理特性。在本文所研究的干燥条件下,垃圾基元表面传热系数为9.5-184.5W/(m2·K)；传质系数为：6.2×10-6-7.4×10-4m/s。
Drying process is the neccessary stage before the Municipal Solid Waste (MSW) incineration and its combustion efficiency is mainly determined by the quality of dry process. Serious contraction occurred in the consideration of MSW is a kind of porous materials which has the high moisture content. For this reason, this paper focus on the internal heat and mass transfer characteristic of shrinkable MSW matrixes during hot air convection drying.
The hot air convection drying experimental study of the MSW matrixes has been carried out and the influence rules of moisture migration characteristic by hot air tempertature, windspeed, matrixes kinds and geometric factor were obtained. Also, the shrinkage characteristic was obtained. Result shows the linear relationship between shrinkage factor and weight loss ratio (R2>0.95), the MSW matrixes volume reduced was approximately equal to the volume of water loss. Through the orthogonal experimental results of range and variance analysis, it shows that temperature, windspeed and weight loss ratio has significant effect on the shrinkage factor (α=0.05),the temperature and thickness has significant effect on drying time.
Based on the Fick law and energy conservation equation, the mathematical model has been built. Calculating programme has been designed base on the MATLAB, through the implicit finite difference method, the internal temperature and moisture distribution were obtained, moisture content and temperature on the convection boundary shows the step-like changes. Through the comparison between experimental value and calculating value found that average effective moisture diffusivity was an increasing function about moisture content and temperature, value range is 3.245×10-8～20.576×10-8m2/s. Throught the dynamic analysis, the Arrhenius equations were obtained. Under conditions in this study, the apparent activation energy range is 10～22kJ.
After dimensionless rewrite about the governing equation and series analysis, law of internal heat and mass transfer were obtained. Bi and Bim series were 100～101, it shows that heat and mass transfer were governed by the internal conduction and diffusion, external drying conditions (hot air velocity and relative humidityof dring air) has limit affect about internal heat and mass transfer process. Under conditions of this study, surface heat transfer coefficient of matrixes is 9.5～184.5W/(m2·K) and surface mass transfer coefficient of matrixes is 6.2×10-6～7.4×10-4m/s.
引文
[1]陈勇,马晓茜,李海滨等.固体废弃物能源利用[M].华南理工大学出版社.2002：1-5
[2]李华.垃圾焚烧发电产业的扶持政策述评[J].重庆科技学院学报(社会科学版).2009,12：98-99
[3]陈天生.生活垃圾焚烧行业：发展现状与趋势[J].浙江经济.2009,16：58-59
[4]袁克,萧惠平,李晓东.中国城市生活垃圾焚烧处理现状及发展分程[J].能源工程.2008,05：43-46
[5]汪玉林.垃圾发电技术及工程实例[M].北京：化学工业出版社.2003
[6]刘锋,郭娟.循环流化床锅炉脱硫技术分析[J].中州煤炭.2008,155：54-55
[7]毛群英.城市垃圾填埋的技术及发展动向[J].山西建筑.2008,34(2)：43-46
[8]唐远华,宋英俊.政府支持垃圾焚烧发电的公共利益分析[J].中国环保产业,2010,3：16-19
[9]吕玉坤,彭鑫.垃圾焚烧发电技术主要问题及其对策.发电设备,2010,2：138-141
[10]卢苇,马一太.垃圾焚烧的发展趋势分析[J].太阳能学报,2002,6(23)：800
[11]张于峰.城市生活垃圾的处理方法及效益评价[J].自然科学进展,2004,8(14)：863
[12]李建新,王永川,张美琴,等.国内城市生活垃圾特新及其处理技术研究[J].热力发电,2006,1：11-14
[13]刘广青,侯吉聪,王凤宇,等.美国城市生活垃圾处理模式分析及思考[J].中国科技信息,2006,12
[14]徐忠升.垃圾焚烧发电余热炉过热器管损坏的原因[J].水泥,2007,7：52
[15]许鑫星.热风对流条件下典型城市生活垃圾基元湿分迁移过程动力学特性研究.[D].北京交通大学,2009
[16]魏琪,林建海.含湿多孔介质内部热质传递规律的国内外研究概况[J].四川工业学院学报,1995,14(2)：121-124
[17]丁小明.多孔介质干燥的孔道网络模拟及实验[D].中国农业大学,2003
[18]施明恒,虞维平,王补宣.多孔介质传热传质研究的现状和展望[J].东南大学学报,1994,24：1-7
[19]潘永康.干燥过程特性和干燥技术的研究策略[J].化学工程,1997,25(3)：37-41
[20]别舒.焚烧炉条件下典型城市生活垃圾基元干燥过程的数值模拟[D].北京交通大学,2008
[21]Andre LSC Sarmento,Frederic Couture,Stephane Laurent,etal. A New Modeling of Heat and Mass Transfport duing drying of Deformable Media. Proceedings of the 13th International Drying Symposium,2002.
[22]马先英,赵世明.不同干燥方式对胡萝卜干燥特性的影响[J].大连轻工业学院学报, 2006,25(2)：155-156
[23]赵耀华,鹤田隆治.高含水多孔介质体的干燥机构研究[J].中国工程热物理学会2002年学术会议,2002：421-424
[24]田晓亮,王兆俊.对流干燥领域中几个值得研究和探讨的问题[J].青岛大学学报,1997,12(4)：76-79
[25]郊娆,顾芳珍.干燥过程模型化[J].化学工业与工程,1996,13(1):5-9
[26]解国珍,李德英,王瑞祥.干燥物料动态特性的活化能方法研究[J].2002.103-113
[27]D.S.Sogi,U.S.Shivhare,S.K.Garg,et al.Water Sorption Isotherm and Drying Characteristics of Tomato Seeds.Biosystems Engineering,2003,84(3):297-301
[28]Najmur Rahman,Subodh Kumar.Evaluation of convective heat transfer coefficient during drying of shrinking bodies.Energy Conversion and Management,2006,47:2591-2601
[29]M.M.Hussain,I.Dincer.Two-dimensional heat and moisture transfer analysis of a cylindrical moist object subjected to drying:A finite-difference approach.International Journal of Heat and Mass Transfer,2003,46:4033-4039
[30]Gligor H.Kanevce,Ljubica P.Kanevce,Vangelce B.Mitrevski,etal.Inversus Approaches to Drying of Thin Bodies With Significant Shrinkage Effects.Jorrnal of Heat Transfer, 2007,129:379-386
[31]Z.B.Maroulis,M.K.Krokida,M.S.Rahman.A structural generic model to predict the effective thermal conductivity of fruits and vegetables during drying.Journal of Food Engineering,2002,52:47-52
[32]Pascual E.Viollaz,Clara O.Rovedo.A drying model for three-dimensional shrinking bodies. Journal of Food Engineering,2002,52:149-153
[33]李友荣.多孔介质对流干燥过程的热力学理论[D].重庆大学,1999
[34]曲艳丽,李爱民,李润东.饼状污泥干燥特性的研究[J].燃烧科学与技术,2005,11(1)：96-99
[35]蔡亮,虞维平,施明恒.对流干燥过程中物料收缩效应的实验研究[J].应用科学学报,2001,19(1)：70-72
[36]徐娓,丁静,赵义,杨晓西.多孔物料干燥中物料体积的收缩特性[J].华南理工大学学报(自然科学版),2006,34(8)：61-65
[37]Alireza Yadollahinia,Acefeh Latifi,Reza Mahdavi.New method for determination of potato slice shrinkage during drying.computers and electronics in agriculture,2009,65:268-274
[38]L.Mayor A.M.Sereno.Modelling shrinkage during convective drying of food materials:a review Journal of Food Engineering,2004,61:373-386
[39]Lang,W,Sokhansanj,S.Bulk volume shrinkage during drying of wheat and canola.Journal of Food Process Engineering,1993,16:305-314.
[40]Zogzas, N. P., Maroulis, Z. B., Marinos-Kouris, etal, shrinkage and porosity of some vegetables during airdrying. Drying Technology,1994,12(7):1653-1666.
[41]Ratti, C. Shrinkage during drying of foodstuffs. Journal of Food Engineering, 1994,23(1):91-105.
[42]Mcminn, W. A. M., Magee, T. R. A. Physical character-istics of dehydrated potatoes-Part Ⅰ. Journal of Food Engineering,1997,33:37-48.
[43]Gabas, A. L., Menegalli, F. C.,Telis-Romero, J. Effect of chemical pretreatment on the physical properties of dehydratedgrapes. Drying Technology,1999,17(6):1215-1226.
[44]Choi, Y., Okos, M. R. Thermal conductivity of foods. In D. R.Heldman (Ed.), Encyclopedia of agricultural, food and biological engineering (pp.1004-1010). New York:Marcel Dekker, Inc. 2003
[45]M.A. Karim, M.N.A. Hawlader. Development of solar air collectors for drying applications. Energy Convers,2004,45:329-344
[46]Wang, N.,Brennan, J. G. The influence of moisture content and temperature on the specific heat of potato measured by differential scaning calorimetry. Journal of Food Engineering, 1993,19:303-310.
[47]Hwang, C. H.,Gunasekaran, S. Specific heat capacity measurement. In D. R. Heldman (Ed.), Encyclopedia of agricultural,food and biological engineering (pp.927-935). New York: Marcel Dekker, Inc.2003
[48]M.N.A. Hawlader, M.S. Uddin, J.C. Ho, A.B.W. Teng. Drying characteristics of tomatoes[J]. Food Eng,1991,14:259-268
[49]杨世铭,陶文铨.传热学[M].高等教育出版社,1998：146-150
[50]W.瓦格纳,A.克鲁泽.水和蒸汽的性质[M].科学出版社,2003：40-48
[51]陈梅倩.典型城市生活垃圾基元中温湿分迁移过程动力学特性研究[D].北京交通大学,2009
[52]刘伟,范爱武,黄晓明.多孔介质传热传质理论与应用[M].科学出版社,2006
[53]潘永康,王喜忠,刘相东.现代干燥技术.化学工业出版社,2006
[54]冈萨雷斯R.C.,伍兹R.E.,Eddins数字图像处理(MATLAB版)[M].电子工业出版社.2005
[55]S.Simal, M.C.Garau, A.Femenia, et al. A diffusional model with a moisture-dependent diffusion coefficient. Drying Technology.2006,24(5):551-559
[2]李华.垃圾焚烧发电产业的扶持政策述评[J].重庆科技学院学报(社会科学版).2009,12：98-99
[3]陈天生.生活垃圾焚烧行业：发展现状与趋势[J].浙江经济.2009,16：58-59
[4]袁克,萧惠平,李晓东.中国城市生活垃圾焚烧处理现状及发展分程[J].能源工程.2008,05：43-46
[5]汪玉林.垃圾发电技术及工程实例[M].北京：化学工业出版社.2003
[6]刘锋,郭娟.循环流化床锅炉脱硫技术分析[J].中州煤炭.2008,155：54-55
[7]毛群英.城市垃圾填埋的技术及发展动向[J].山西建筑.2008,34(2)：43-46
[8]唐远华,宋英俊.政府支持垃圾焚烧发电的公共利益分析[J].中国环保产业,2010,3：16-19
[9]吕玉坤,彭鑫.垃圾焚烧发电技术主要问题及其对策.发电设备,2010,2：138-141
[10]卢苇,马一太.垃圾焚烧的发展趋势分析[J].太阳能学报,2002,6(23)：800
[11]张于峰.城市生活垃圾的处理方法及效益评价[J].自然科学进展,2004,8(14)：863
[12]李建新,王永川,张美琴,等.国内城市生活垃圾特新及其处理技术研究[J].热力发电,2006,1：11-14
[13]刘广青,侯吉聪,王凤宇,等.美国城市生活垃圾处理模式分析及思考[J].中国科技信息,2006,12
[14]徐忠升.垃圾焚烧发电余热炉过热器管损坏的原因[J].水泥,2007,7：52
[15]许鑫星.热风对流条件下典型城市生活垃圾基元湿分迁移过程动力学特性研究.[D].北京交通大学,2009
[16]魏琪,林建海.含湿多孔介质内部热质传递规律的国内外研究概况[J].四川工业学院学报,1995,14(2)：121-124
[17]丁小明.多孔介质干燥的孔道网络模拟及实验[D].中国农业大学,2003
[18]施明恒,虞维平,王补宣.多孔介质传热传质研究的现状和展望[J].东南大学学报,1994,24：1-7
[19]潘永康.干燥过程特性和干燥技术的研究策略[J].化学工程,1997,25(3)：37-41
[20]别舒.焚烧炉条件下典型城市生活垃圾基元干燥过程的数值模拟[D].北京交通大学,2008
[21]Andre LSC Sarmento,Frederic Couture,Stephane Laurent,etal. A New Modeling of Heat and Mass Transfport duing drying of Deformable Media. Proceedings of the 13th International Drying Symposium,2002.
[22]马先英,赵世明.不同干燥方式对胡萝卜干燥特性的影响[J].大连轻工业学院学报, 2006,25(2)：155-156
[23]赵耀华,鹤田隆治.高含水多孔介质体的干燥机构研究[J].中国工程热物理学会2002年学术会议,2002：421-424
[24]田晓亮,王兆俊.对流干燥领域中几个值得研究和探讨的问题[J].青岛大学学报,1997,12(4)：76-79
[25]郊娆,顾芳珍.干燥过程模型化[J].化学工业与工程,1996,13(1):5-9
[26]解国珍,李德英,王瑞祥.干燥物料动态特性的活化能方法研究[J].2002.103-113
[27]D.S.Sogi,U.S.Shivhare,S.K.Garg,et al.Water Sorption Isotherm and Drying Characteristics of Tomato Seeds.Biosystems Engineering,2003,84(3):297-301
[28]Najmur Rahman,Subodh Kumar.Evaluation of convective heat transfer coefficient during drying of shrinking bodies.Energy Conversion and Management,2006,47:2591-2601
[29]M.M.Hussain,I.Dincer.Two-dimensional heat and moisture transfer analysis of a cylindrical moist object subjected to drying:A finite-difference approach.International Journal of Heat and Mass Transfer,2003,46:4033-4039
[30]Gligor H.Kanevce,Ljubica P.Kanevce,Vangelce B.Mitrevski,etal.Inversus Approaches to Drying of Thin Bodies With Significant Shrinkage Effects.Jorrnal of Heat Transfer, 2007,129:379-386
[31]Z.B.Maroulis,M.K.Krokida,M.S.Rahman.A structural generic model to predict the effective thermal conductivity of fruits and vegetables during drying.Journal of Food Engineering,2002,52:47-52
[32]Pascual E.Viollaz,Clara O.Rovedo.A drying model for three-dimensional shrinking bodies. Journal of Food Engineering,2002,52:149-153
[33]李友荣.多孔介质对流干燥过程的热力学理论[D].重庆大学,1999
[34]曲艳丽,李爱民,李润东.饼状污泥干燥特性的研究[J].燃烧科学与技术,2005,11(1)：96-99
[35]蔡亮,虞维平,施明恒.对流干燥过程中物料收缩效应的实验研究[J].应用科学学报,2001,19(1)：70-72
[36]徐娓,丁静,赵义,杨晓西.多孔物料干燥中物料体积的收缩特性[J].华南理工大学学报(自然科学版),2006,34(8)：61-65
[37]Alireza Yadollahinia,Acefeh Latifi,Reza Mahdavi.New method for determination of potato slice shrinkage during drying.computers and electronics in agriculture,2009,65:268-274
[38]L.Mayor A.M.Sereno.Modelling shrinkage during convective drying of food materials:a review Journal of Food Engineering,2004,61:373-386
[39]Lang,W,Sokhansanj,S.Bulk volume shrinkage during drying of wheat and canola.Journal of Food Process Engineering,1993,16:305-314.
[40]Zogzas, N. P., Maroulis, Z. B., Marinos-Kouris, etal, shrinkage and porosity of some vegetables during airdrying. Drying Technology,1994,12(7):1653-1666.
[41]Ratti, C. Shrinkage during drying of foodstuffs. Journal of Food Engineering, 1994,23(1):91-105.
[42]Mcminn, W. A. M., Magee, T. R. A. Physical character-istics of dehydrated potatoes-Part Ⅰ. Journal of Food Engineering,1997,33:37-48.
[43]Gabas, A. L., Menegalli, F. C.,Telis-Romero, J. Effect of chemical pretreatment on the physical properties of dehydratedgrapes. Drying Technology,1999,17(6):1215-1226.
[44]Choi, Y., Okos, M. R. Thermal conductivity of foods. In D. R.Heldman (Ed.), Encyclopedia of agricultural, food and biological engineering (pp.1004-1010). New York:Marcel Dekker, Inc. 2003
[45]M.A. Karim, M.N.A. Hawlader. Development of solar air collectors for drying applications. Energy Convers,2004,45:329-344
[46]Wang, N.,Brennan, J. G. The influence of moisture content and temperature on the specific heat of potato measured by differential scaning calorimetry. Journal of Food Engineering, 1993,19:303-310.
[47]Hwang, C. H.,Gunasekaran, S. Specific heat capacity measurement. In D. R. Heldman (Ed.), Encyclopedia of agricultural,food and biological engineering (pp.927-935). New York: Marcel Dekker, Inc.2003
[48]M.N.A. Hawlader, M.S. Uddin, J.C. Ho, A.B.W. Teng. Drying characteristics of tomatoes[J]. Food Eng,1991,14:259-268
[49]杨世铭,陶文铨.传热学[M].高等教育出版社,1998：146-150
[50]W.瓦格纳,A.克鲁泽.水和蒸汽的性质[M].科学出版社,2003：40-48
[51]陈梅倩.典型城市生活垃圾基元中温湿分迁移过程动力学特性研究[D].北京交通大学,2009
[52]刘伟,范爱武,黄晓明.多孔介质传热传质理论与应用[M].科学出版社,2006
[53]潘永康,王喜忠,刘相东.现代干燥技术.化学工业出版社,2006
[54]冈萨雷斯R.C.,伍兹R.E.,Eddins数字图像处理(MATLAB版)[M].电子工业出版社.2005
[55]S.Simal, M.C.Garau, A.Femenia, et al. A diffusional model with a moisture-dependent diffusion coefficient. Drying Technology.2006,24(5):551-559