【作者】 何亮；

【导师】 李瑞； 刘六军；

【作者基本信息】 北京林业大学 ， 木材科学与技术， 2013， 硕士

【摘要】 快速热解液化是将固态的农林剩余物转化为液态的生物油一种热化学转化手段,生物油可以作为燃料提供能量,也可以作为原料提供高附加值化学成分,具有巨大的发展潜力。快速热解是一个物理和化学反应相耦合的复杂过程,虽然目前建立了很多热解模型,如一维、二维、三维、湿材、缩核模型等,但模型还有许多地方需要完善,如模型方程中反应热源项的表达内容、模型适用情况等。本文结合实验室制备的搅拌式快速热解反应器,采用动力学热分析方法和偏微分数值求解有限元软件,研究了一维、二维、三维数学模型的适用情况；平板、圆柱体两种几何模型对颗粒温度分布的影响；第一类和第三类两种边界条件对颗粒温度分布影响；采用热解过程4个阶段动力学方程表示不同温度阶段的反应热源项对颗粒温度分布的影响；热解气体在x、y轴方向扩散对颗粒温度分布的影响；5种不同尺寸对热解过程中颗粒温度分布的影响。本文主要获得了如下成果：(1)落叶松树皮和实木的热失重曲线有明显的区别；颗粒尺寸对热解主要阶段起始温度有影响；在一定范围内,失重率随含水率增大而增大。(2)采用积分法和微分法及40种动力学机理函数,对4种不同尺寸和含水率的落叶松树皮进行了动力学分析,并分别求解获得了其热解过程中4个阶段的动力学参数和方程,含水率为15%,大小为0.8mm的树皮颗粒适合热解。(3)粉碎后的落叶松树皮颗粒主要呈现片状和针状外形,在建立热解过程中几何模型时,平板和圆柱体几何模型比较符合实际情况。通过对两种几何模型的模拟计算,表明圆柱体几何模型热解时间比平板几何模型要减少约1倍；圆柱体几何模型受气体扩散影响较大,需要考虑各向异性和扩散压力。(4)建立的平板三维传热模型如下,并可以对其进行简化得到一维和二维模型。建立的圆柱体二维模型方程为：(5)树皮颗粒尺寸小于1mm时,可以采用一维或二维模型模拟其热解过程的温度分布；颗粒尺寸小于0.8mm时,不适合采用三维模型模拟温度分布；三维模型模拟大颗粒温度分布时,应尽量考虑物性参数的各向异性及热解气体的扩散阻碍等情况。(6)对于尺寸小于0.8mm的树皮颗粒,采用第一类和第三类边界条件对模拟获得的温度分布没有显著影响。(7)热解气体扩散方向对颗粒温度分布有显著的影响,沿着扩散方向,温度呈现由高到低趋势。(8)采用动力学方程参与表达反应热(∑i=14(H*dα/dt)i)比Arrhenius常数K参与表达反应热(∑i=14(H*K)i)更加准确。更多还原

【Abstract】 Fast pyrolysis is a thermochemical conversion method that transform agricultural and forestry residues into bio-oil, the bio-oil can supply enegy as fuel and the high added value chemical compositions also can be utilized by extraction. As it’s a complex process coupled with the physical and chemical reactions, authorities in general use pyrolysis model to study the pyrolysis process. Some heat transfer models for pyrolysis has established at here and abroad, however, the models need to be improved, such as the expression of the reaction heat and use what kind of model in different conditions. In view of the above problems, we do researches in some aspects, including different dimensions, shapes, boundary conditions, pyrolysis gas diffusion, particle size and reaction heat expression. We has obtained four step kinetic equations of larch bark pyrolysis process and use the equations as the reaction heat expression.Then, we use the partial differential software do numerical solution for the heat transfer model equation of larch bark. Through the results of temperature distribution, we analysis the effects of dimension, gas diffusion, expression of reaction heat and particle size to pyrolysis process. The main results in this paper are as followed:(1) The thermo-gravimetric curves of larch and larch bark have obvious differences; particle size can effect the starting temperature of pyrolysis steps; the weightlessness rate increases with the moisture content increases in a certain range.(2)We study the kinetics of different moisture and particle size larch bark by integral and differential methods and forty mechanism functions, obtain the four pyrolysis steps kinetic parameters and equations,0.8mm larch bark with15%moisture content is suitable for pyrolysis.(3)The larch bark particles after crushed mainly presenting flake and acicular; plate and cylinder geometrical model are more suitable for pyrolysis heat transfer model; pyrolysis time of cylinder geometrical model is half to plate model; however, we need consider gas diffusion pressure and anisortropy for the effect of diffusion to cylinder model.(4) The three dimension heat transfer model equation for larch bark is: Cylinder two dimension heat transfer model equation is:(5)When the particle size (?)1mm, we can use both one and two dimension model simulate the temperature distribution of larch bark particle; three dimension is not suitable for the simulate the temperature distribution of the particle size which less-than0.8mm; we need to consider the anisortropy and gas diffusion when we use three dimension model for large particle.(6)For the particle with0.8mm, the first and three boundary conditions have significant influence of the temperature distribution.(7)The direction of gas diffusion is important to the temperature distribution, temperature has a decrease trend along the gas diffusion direction.(8) The expression of heat reaction by kinetic equation (∑i=14=1(H*α/dt)i) is more accuate than the expression of Arrhenius rectant (∑i=14k(H*K)i)更多还原