泥炭阴燃及阴燃气体生成规律的实验与机理研究

发布时间：2018-03-01 01:21

本文关键词： 泥炭地热解动力学阴燃火灾阴燃传播烟气分析数值模型　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：森林中含有丰富的天然燃料,其中腐烂的枯枝落叶、动物残骸,经过长时间的沉淀,会形成腐殖质或泥炭层。这些有机质在雷击或人为焚烧时易被点燃从而引发火灾。森林腐殖质或泥炭形成的地下阴燃火灾是森林中危害极为严重的地下火灾。泥炭地储存着大量的土壤碳,一旦发生阴燃,会释放出大量的温室气体和有害气体,对全球大气平衡以及人类健康造成严重威胁。随着全球气候的变暖,世界大面积的泥炭阴燃火灾频繁发生,泥炭阴燃研究已经受到越来越多的关注。目前有关泥炭阴燃过程气体生成规律的实验研究很少,主要建立在TG-FTIR,TG-MS,TG-GC等联用技术上的定性分析,主要关注点只在C02,CO,CH_4三种气体产物。理论研究方面,主要通过数值模型研究阴燃点燃的临界含水率和无机物含量、临界含水率和氧浓度之间的关系。目前还没有数值模型去揭示阴燃横向传播机理,特别是在有环境风作用下泥炭的多维横向传播结构需要深入研究。本文的具体安排如下:利用TG-FTIR-MS联用技术研究研究泥炭在惰性气氛下的热解行为,建立相应的热解动力学模型,假定泥炭热解为三个伪组分半纤维素、纤维素、木质素热解总和,利用基因遗传算法优化得到相应的动力学参数和每个组分热解的温度区间,利用FTIR和MS分析法辨别出热解主要的生成气体,找到各气体组分相应的生成温度区间,结合TG中固体组分热解的温度区间判断气体的生成来源。同样利用TG-FTIR联用技术研究泥炭在空气气氛下的燃烧行为,建立相应的动力学模型,假定泥炭燃烧分为水分蒸发、泥炭热解、泥炭氧化和炭氧化阶段,优化得到每步反应的温度区间,利用FTIR分析主要气体组分的温度生成区间,然后结合TG得到的固相热解氧化温度区间,从而得到气体组分的来源。利用惰性和空气下的TG/DTG数据,建立更优的五步反应动力学机制(包括水分蒸发、泥炭热解,泥炭氧化,a-char,β-char氧化),利用基因遗传算法逆向模拟得到相应的动力学参数,为后续章节阴燃数值模型提供参数输入。利用泥炭竖向阴燃实验台研究无机物含量和泥炭床初始高度对阴燃峰值温度,阴燃热解反应峰和氧化反应峰的传播速度,阴燃床形变的影响,同时通过COMSOL多物理场仿真软件建立一维阴燃数值模型,并通过移动网格技术模拟上表面的收缩特性扩展泥炭阴燃模型到二维,且利用COMSOL-Multiphysics中的移动网格技对上边界的移动位移进行计算,获取了泥炭阴燃的二维结构,研究无机物含量和边界热损失对阴燃二维结构,阴燃传播速度和阴燃时间的影响,同时利用相关实验去验证了提出的数值模型,模型预测的结果可以为我们提供对高无机物含量的泥炭阴燃火灾更深一步的认识。利用一小尺寸风洞研究横向环境风风速,环境氧浓度对浅层泥炭阴燃传播机理的影响。同时利用NOVAPLUS多功能烟气分析仪来测生成的CO_2,CO,CH_4,研究了氧气浓度对泥炭横向阴燃传播机理和生成气体的影响。然后建立相应的二维横向阴燃传播的数值模型,揭示了实验中高氧浓度下表面"glowing"灼热燃烧,即"overhang"消失的根本原因是表面层发生了二次炭氧化反应。通过实验和数值模拟相结合的方法可以使我们对泥炭横向阴燃传播机理有更进一步地认识。
[Abstract]:Contains natural fuel rich forest, including decaying litter, animal remains, after a long time of precipitation, formation of humus or peat layer. The organic matter in the lightning or artificially burned easily ignited causing the fire. The underground smoldering fire form forest humus or peat forest in the underground fire hazard is very serious the peat soil carbon storage. The event of smoldering, releases large amounts of greenhouse gases and harmful gas, the global atmospheric balance and human health caused a serious threat. As the global climate warming, peat smoldering fire large areas of the world occur frequently, peat smoldering research has attracted more and more attention at present. Experimental study on the formation of the peat smoldering process gas are mainly based on TG-FTIR, TG-MS, TG-GC combined qualitative analysis technology, the main concern Only in C02, CO, gas product three CH_4. The theoretical research, mainly through the study of smoldering numerical model ignited the critical moisture content and inorganic content, the relationship between the critical moisture content and oxygen concentration. There is no numerical model to reveal the mechanism of smoldering transverse propagation, especially when there is a need to study further the multidimensional transverse propagation the structure of cross wind conditions of peat. The paper is organized as follows: the pyrolysis behavior by peat research technique under inert atmosphere using TG-FTIR-MS combination, establish corresponding pyrolysis kinetic model, assuming three peat pyrolysis pseudo component of hemicellulose, cellulose, lignin pyrolysis combined, using genetic algorithm to optimize the temperature range the kinetic parameters of each group and the corresponding points of pyrolysis, using FTIR and MS analysis to identify the main pyrolysis gas generated, for generating temperature of each gas component corresponding Interval judgment by the generation source gas temperature interval of solid component of pyrolysis TG. The combustion behavior also use TG-FTIR technology of peat in air atmosphere, establish the corresponding dynamics model, assuming that the peat is divided into water evaporation and burning of peat peat pyrolysis, oxidation and carbon oxidation stage, optimal temperature range of each reaction is obtained the FTIR analysis of the use of temperature interval to generate the main gas components, and then combined with the solid phase oxidation temperature interval TG, so as to get the source of gas components. The number of TG/DTG inert and air condition according to the five step reaction mechanism, establish better (including water evaporation, peat peat pyrolysis, oxidation, a-char -char, beta oxidation), using genetic algorithm for inverse simulation to obtain the corresponding kinetic parameters, provide input parameters for the following chapters. The numerical model of the use of peat smoldering vertical smoldering. The test bench of inorganic content and peat bed height on the initial peak temperature of smoldering, smoldering pyrolysis and oxidation peak peak velocity, bed deformation and smoldering effect, by COMSOL multiphysics simulation software to establish the numerical model of one-dimensional smoldering, and extended to two-dimensional model peat smoldering by moving grid method on the contraction characteristics of the surface the use of mobile technology and grid COMSOL-Multiphysics in displacement on the upper boundary of the calculation, obtain a two-dimensional structure of peat smoldering, inorganic content and boundary heat loss on the smoldering two dimensional structure, influence of smoldering propagation velocity and combustion time, and use related experiments to verify the proposed numerical model, prediction model the results can provide the high mineral content of peat smoldering fire a deeper knowledge for us. With a small size of horizontal wind tunnel The ambient wind speed, influence of environmental oxygen concentration on shallow peat smoldering propagation mechanism. At the same time using the NOVAPLUS multi function flue gas analyzer to measure the generated CO_2, CO, CH_4, studied the influence of oxygen concentration on the peat smoldering propagation mechanism and horizontal gas production. The numerical model is then established the corresponding two-dimensional transverse smoldering propagation, reveals high oxygen concentration in the experiment under the surface "glowing" hot burning, "the main reason for the overhang" disappear is the surface layer occurred two times of carbon oxidation method. By combining experiments and numerical modeling can help us further understanding of the mechanism of lateral peat smoldering propagation.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.21

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