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可燃固体废弃物热转化动力学及其基元表征体系研究
张金芝
学位类型博士 ; 学位论文 ; 博士 ; 学位论文
导师张金芝
2016-05
学位授予单位中国科学院大学
学位授予地点北京
学位专业化学工程
关键词可燃固体废弃物 热解 气化 基元 分布式活化能模型
摘要可燃固体废弃物热解气化处理技术由于在无氧或贫氧条件下进行,可以有效抑制二噁英的产生,是替代焚烧法最有前景的技术之一。可燃固体废弃物热解气化特性与反应动力学等基础科学研究对工业规模反应器的设计以及工艺参数的优化具有重要指导意义。本论文将复杂的可燃固体废弃物分为木材、食物残余、纸张、塑料橡胶和织物五大类,选取了纤维素、半纤维素、木质素、果胶、杨木屑、淀粉、蛋白质、土豆、白菜、米饭、桔皮、打印纸、报纸、生活用纸、棉、涤纶、羊毛绒、PE、PVC和橡胶共20种组分作为研究对象,利用热重分析仪和热重质谱联用仪全面系统地对可燃固体废弃物各组分的热解特性、水蒸气气化特性和热解气化动力学进行了研究,并在各组分失重曲线的基础上,试着建立了一种基元表征体系,采用数量有限的基元预测复杂可燃固体废弃物的热化学反应行为。主要研究内容包括以下几个方面:(1)在环境气氛为氮气,升温速率为5 K min-1的条件下对20种组分的热解特性进行了详细研究。结果表明,对于纸张类和食物残余类来说,每一类别中各物质的热解行为非常相似:在纸张类中,打印纸、报纸和生活用纸三种物质的失重区间均较窄,失重区间为540~650 K;在食物残余类中,淀粉主要失重区间为500~733 K,土豆和米饭的失重特性与淀粉非常相似。然而,对于木材、塑料橡胶和织物来说,每一类别中各物质的热解行为却具有明显差异:在木材类中,纤维素、半纤维素和木质素三种组分的热解行为差异较大,半纤维素最先开始分解,纤维素次之,木质素最难分解;在织物类中,羊毛绒的失重区间为540~740 K,棉的失重区间为500~640 K,羊毛绒比棉更难分解;在塑料橡胶类中,PE呈一段式失重,PVC呈两段式失重,橡胶呈现三段式失重。(2)获得了20种组分在水蒸气气氛下的失重曲线。首先,将各组分在水蒸气气氛下的失重曲线与惰性气氛下的失重曲线进行了对比,结果表明,木质素、半纤维素、杨木屑、白菜、打印纸、果胶、玉米蛋白、棉和羊毛绒在水蒸气气氛下的热失重过程可分为热解和气化两个阶段。与惰性气氛下的失重曲线相比,在温度低于850 K时,水蒸气的存在对各组分的失重过程几乎没有影响;但是,当温度高于850 K时,水蒸气促进了半焦或固定碳的气化反应,产生了一个新的失重阶段。其次,利用热重质谱联用仪对热失重过程所产生的CH4、CO2、CO和H2四种轻质气体进行了分析,结果表明,在热解阶段,这些轻质气体的逸出曲线与失重变化率曲线(Differential Thermal Gravity, DTG)的走势基本一致,说明热解过程中产生了CH4、CO2、CO和H2;在气化阶段,CO2和H2的逸出曲线与DTG曲线走势一致,进一步验证了在热解阶段产生的半焦和固定碳与水蒸气发生了反应。(3)基于多峰拟合法,建立了一种可用于描述可燃固体废弃物的热解气化行为的新型多高斯分布式活化能模型。结果表明,多高斯分布活化能模型对20种组分的拟合曲线与试验曲线吻合良好。利用模式搜索法获得了20种组分的热转化动力学参数:热解阶段和气化阶段的活化能分布范围分别为150~270和280~330 kJ mol-1,气化阶段的活化能明显高于热解阶段;采用主曲线法获得了各组分热解和气化阶段的动力学机理函数。(4)基于可燃固体废弃物的热失重行为,初步建立了一种基元表征体系,确定了纤维素、半纤维素、木质素、淀粉、果胶、蛋白质、涤纶、橡胶、PE和PVC共10种物质作为基元。在基元线性表征的基础上,重点考察了双基元的交互作用规律,建立了用双基元混合反应特性重构多组分混合反应特性的方法,采用9种实际典型可燃固体废弃物验证了基元表征方法的可靠性。根据基元表征方法获得的热化学反应动力学参数与多高斯分布活化能模型求取的动力学参数吻合良好。
其他摘要Pyrolysis/gasification technology of combustible solid waste (CSW) is conducted in the condition of non-oxygen or lean-oxygen, which will reduce the production of dioxins. Therefore, it is regarded as one of the most promising alternatives to incineration. Pyrolysis/gasification characteristics and kinetics of CSW have great instructive significances to the design and the optimization of operating parameters for industrial reactors. In this paper, CSW was divided into five categories: wood, food residue, paper, plastics-rubber and textile. Twenty components including cellulose, hemicellulose, lignin, pectin, poplar, starch, protein, potato, cabbage, rice, orange peel, printing paper, newspaper, household paper, cotton, polyester, wool flock, PE, PVC and rubber were selected as experimental samples. The thermogravimetric analyzer (TGA) and thermogravimetric-mass spectrometry (TG-MS) were applied to comprehensively and systematically study the pyrolytic characteristics, steam gasification characteristics and thermal kinetics of all components. A pseudocomponent characterization system was established, by which the thermochemical reaction behaviors of the complex CSW can be described just using a limited number of pseudocomponents. The main research contents are as follows: (1) The pyrolytic characteristics of all components were studied in detail under N2 atmosphere at the heating rate of 5 K min-1. Results showed that materials in paper or food residue categories have similar pyrolytic behaviors: in the paper category, printing paper, newspaper and household paper all had narrow weight loss temperatures range (540~650 K); in the food residue category, the main weight loss temperature of starch was 500~733 K, and both potato and rice had similar weight loss behaviors. However, materials in wood, plastic-rubber, and textile categories all showed different pyrolytic behaviors: in wood category, there existed large differences among the three components of cellulose, hemicellulose and lignin; hemicellulose was observed to be the first to loss weight, cellulose took the second place, and lignin was the last; in the textiles category, the main weight loss temperature range for wool flock was 540~740 K, but it was 500~640 K for cotton, indicating that it was harder for wool flock to lose weight than cotton; in plastic-rubber category, PE had only one weight loss stages, PVC had two weight loss stages, and rubber had three weight loss stages. (2) The thermogravimetric curves of all CSW components under steam atmosphere were obtained. Firstly, thermogravimetric curves under steam and N2 atmosphere were comparatively studied. It was found that the weight loss process of lignin, hemicellulose, poplar, cabbage, printing paper, pectin, zein, cotton and dacron were divided into pyrolysis and gasification stages. When the temperature was lower than 850 K, the existence of steam had almost no effect on thermogravimetric curves for all CSW components; however, when the temperature was higher than 850 K, the existence of steam promoted the gasification of char and fixed carbon, and one more weight loss stage was emerged. Secondly, TG-MS was applied to investigate the generated light molecular weight gases of CH4,CO2,CO,H2 during the weight loss process under steam atmosphere for all CSW components. Resutls showed that the trends of envolved curves for all gases were consistent with their DTG curves in the pyrolysis stage, indicating the four gases were produced from the pyrolysis process. The trends of envolved curves for CO2 and H2 were also consistent with their DTG curves in the gasification stage, which verified the ractions between char or fixed carbon and steam. (3) A novel multiple Gaussian DAEM reaction model was established based on multiple-peaks method, which can be used to describe the pyrolysis and gasification behaviors of CSW. Results showed that the calculated curves using the multiple Gaussian DAEM reaction model provided a good fit with experimental curves. The kinetic parameters of all CSW components were obtained using the pattern search method. The activation energy (E) of the pyrolysis stage was in the range of 150~270 kJ mol-1, which was lower than that in the gasification stage (280~330 kJ mol-1). The kinetic mechanism functions of all components in pyrolysis and gasification stages were obtained using the master plot method. (4) The pseudocomponent characterization system was established based on weight loss curves. Cellulose, hemicellulose, lignin, starch, pectin, protein, dacron, rubber, PE and PVC were all confirmed as pseudocomponents in this paper. On the basis of linear pseudocomponent characterization, the interactions between two pseudocomponents were detailed studied. And a method of reproducing reaction characteristics of multiple pseudocomponents using interactions between two pseudocomponents was established. The reliability of above-mentioned pseudocomponent characterization system had been validated using nine actual typical combustible solid wastes. The thermal reaction kinetic parameters were obtained using the pseudocomponent characterization method, whose values were consistent with those optimized from the multiple Gaussian DAEM reaction model.
作者部门热化学转化事业部
学科领域热化学转化
公开日期2016-06-30
学位类型博士 ; 学位论文 ; 博士 ; 学位论文
语种中文
文献类型学位论文
条目标识符http://ir.qibebt.ac.cn/handle/337004/9765
专题热化学转化团队
作者单位中国科学院青岛生物能源与过程研究所
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张金芝. 可燃固体废弃物热转化动力学及其基元表征体系研究[D]. 北京. 中国科学院大学,2016.
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