【作者】 杨瑛；

【导师】 张衍林；

【作者基本信息】 华中农业大学 ， 农业生物环境与能源工程， 2014， 博士

【摘要】 农作物秸秆从生产、收集、加工、运输到能源利用转化,秸秆废弃物都会对生态环境产生直接或间接的影响。针对该问题,将农业废弃物棉花秸秆转化为绿色能源---生物炭,进行分散式热解炭化技术有效利用棉秆资源,不仅能变废为宝,还能减少对环境的污染。通过综述分析国内外在废弃生物质原料热解炭化方面开展的研究,提出将农业废弃物棉花秸秆采用分散式热解炭化的模式,从炭化方式、炭化装置和影响固体产物得率的因素方面进行试验研究,达到生物质秸秆资源的就地处理、经济利用的目的。本论文以农作物秸秆棉花秸秆为对象,通过直接热解炭化为技术路线,利用分散式热解炭化炉,以固体产物生物质炭为目标产物,深入地研究直接热解炭化的影响因素和目标产物的性质,为生物质资源的有效利用提供理论支撑。得到以下研究工作：(1)研究棉秆的机械物理特性测试、元素分析和热重动力学分析。基于原料的成分和热失重的关系出发,分析棉秆直接热解固体产物得率的影响因素,并提出直接热解棉秆合适的的参数范围：最低温度大于300℃、最高温度小于600℃升温速率小于30min/℃。(2)分别在不同热解装置中对棉秆进行热解炭化试验研究,工艺参数选择不同热解温度、不同保温时间和不同升温速率,获得热解前后的原料质量变化及热解参数与热解产物的关系,经分析得出：未经粉碎的棉秆在热解温度400℃进行热解炭化后,生成的秸秆炭的比例最高。在棉秆热解过程中,随着反应温度的增加,热解固体产物质量不断减小。通过正交试验得到了直接热解最优组合的热解工艺参数为：热解温度400℃,升温速率5℃/min,保温时间2h。其得炭率可达49.98%。在单因素试验的基础上,采用Box-Benhnken试验设计和响应面分析法建立二次回归数学模型,得到优化工艺参数,研究表明分散式炭化原料与燃烧原料质量比2：1,得炭率达50%。(3)利用ANSYS软件研究生物质热解炉内部温度场的分布,分别对热解炉炭化室、燃烧室和添加传热片后炭化室内温度的变化进行模拟。热解炉内由于气体的流动,温度分布是不均匀的、且温度差异较大。为了满足热解所需温度,必须要有足够的保温时间使炉内温度达到设置温度,才能让炭化原料充分炭化；为了保证原料的完全炭化,在热解炉的设计中要尽量增大烟囱与炭化原料的接触面积；通过对炭化室在500℃温度场变化情况的分析,发现接近炭化室外壁和外侧的温度偏低,在改进方面可以通过添加保温层来解决。炭化炉的底部温度偏低,可以通过添加传热片的方法,利用传热片良好的传热效果将热量传递到底部和侧面,尽量达到温度场的均匀分布；将添加传热片先后炭化室内温度场进行比较,可以看出添加传热片的效果很明显,温度死角明显减少,提高了底部温度和外侧温度。(4)分析了不同热解条件下的固体产物性质。随着热解条件的改变,固体产物质量分布比例和产物中各元素的比例都发生了变化。采用SEM、元素分析仪、红外光谱仪等分析仪器对直接热解炭化的固体产物理化结构、固定炭含量等进行分析。随着热解温度的升高,固体产物中各元素含量都发生了变化。在500℃时,棉秆炭中的固定炭含量最高。对棉秆热解后的固体产物理化特性进行研究得到,棉秆炭发热量接近30MJ/Kg,含水率小于6%,灰分小于9%,挥发分小于30%,固定炭含量32%,堆积密度421Kg/m3,堆积角58.16。,摩擦系数0.45-0.60,流动性指数69.1。棉秆炭不易于成型、不易流动和发热量较高。(5)分散式热解炭化炉应用预测分析。从原料适应性、能源转化效率、分散热解炭化与集中建厂炭化、秸秆压缩利用的生产成本和经济效益方面,预测炭化炉的可应用性。通过试验发现,炭化炉不仅适用于棉秆,还可以普遍适用于大部分农作物秸秆和农林废弃物。预测分析以10000t/a炭化棉秆为例,比较炭化成本,表明分散就地炭化与集中建厂炭化、秸秆压缩利用,分散炭化成本较低,利润较好。生物质热解炭化过程是一个非常复杂的过程,不仅与生物质原料的种类、外界环境等有很大的影响,还与热解工艺参数和实际热解设备条件有关。本文对生物质资源中的棉花秸秆展开热解研究,通过试验和仿真分析,研究利用生物质资源高效的热解工艺和优化。更多还原

【Abstract】 Staw waste, produced in the process of production, gathering, processing, transportation and energy conversion of straw, has a direct or indirect impact on the ecological environment. Hence the study aims to convert cotton stalk into green energy--biochar by applying dispersed pyrolytic carbonization technology, which will utilize cotton stalk resource effectively and alleviate the environmental pollution. Having reviewed studies about pyrolytic carbonization of waste biomass materials at home and abroad, it applies a mode of dispersed pyrolysis carbonization in cotton stalks: experiments are conducted on carbonization mode, carbonizing device and carbonization process to achieve on-site treatment on biomass straw materials and realize economic benefits. The study is on cotton stalk. By conducting pyrolytic carbonization directly and utilizing dispersed pyrolytic carbonizing furnace, the paper, making solid biomass char as the target product, studied the factors of direct pyrolytic carbonization and the qualities of target product, providing theoretical support for effective utilization of biomass materials.The main findings are as follows.(1) Tests on mechanical properties of cotton stalks, elemental analysis and thermogravimetric analysis are conducted. Based on the relationship between the component of raw material and thermal weight loss, it analyzes the factors of the yield of direct pyrolytic solid product of cotton stalks and points out the parameters of direct pyrolysis of cotton stalk: the minimum temperature is higher than300℃, the maximum temperature is lower than600℃, and heating rate not suitable too high.(2) Study on the pyrolysis products of crushed cotton stalks pyrolysis experiments in the different equipment. The effects of three factors (pyrolysis temperature, pyrolysis heating rate and pyrolysis holding time) were investigated by using the mass of the products yield as the indexes. Through direct pyrolysis experiments on cotton stalks, the changes of raw material mass and the relationship between pyrolysis parameters and pyrolytic products are found. In the process of pyrolysis, the mass of pyrolytic solid product decreases as the reaction temperature increases; when the pyrolysis temperature is higher than400℃, fixed carbon(FC)content in solid product begins to decrease as reaction temperature increases. In order to determine the optimum technological parameter of pyrolysis, an orthogonal experiment is conducted. The maximum product yield of49.98%is obtained with5℃/min of heating rates,400℃of optimum pyrolysis temperature, and2h of holding time. Box-Benhnken design (BBD) and response surface methodology (RSM) are adopted to obtain the optimum parameters on the basis of results of single-factor experiments. The results indicate that the optimum parameters is ratio of raw material of carbonization chamber and combustion chamber2:1, maximum product yield of50%.(3) Temperature field on the biomass carbonization furnace is simulated and analyzed by the software, Ansys. Because of the gas flow in the pyrolysis furnace, temperature has not been evenly spread, and there is a large temperature difference. In order to meet the pyrolysis temperature, it must have had enough holding time, let the charring materials carbonize fully; it should increase the chimney and carbonized material contact area of pyrolysis furnace to increase the temperature of vents through stack draft; Through even arrangement of heat transfer around the coking furnace, use the heat transfer tablet to transfer heat to the bottom and sides, to achieve even distribution of temperature field.(4) With the development of the pyrolysis reaction, it changes the distribution proportion of solid products and elements. T he solid residues were analyzed by elemental analyzers, scanning electron microscopy (SEM), FTIR and thermogravimetric analyzer. When the temperature rises, the element in solid products gradually increase or decrease; fixed carbon(FC) content is maximum when the temperature is500℃. Study on the physicochemical properties of a solid product obtained after pyrolysis of cotton stalk found that calorific value of cotton stalk is30MJ/kg, moisture content10.125%, ash9%, volatile30%, fixed carbon content of32%, bulk density421kg/m3, Accumulated angle58.16°, friction coefficient0.45-0.60, flow property69.1. The results show Cotton carbon formed easily and is not so easy to flow with high calorific value.(5) This part is about prediction analysis about the application of dispersed pyrolytic carbonization furnace. To predict the applicability of carbonization furnace, it analyzes the raw material adaptability, energy conversion efficiency, dispersed pyrolytic carbonization and centralized plant carbonization, and the cost and benefits of straw compression. It is found that carbonization furnace could be applied not only to cotton stalk but also to most crop straw and agricultural and forestry waste. The enterprise production cost of plants with electricity as energy is higher than plants using oil and burning produced by pyrolysis carbonization furnace. By comparison with dispersed on-site carbonization, centralized plant carbonization and straw compression, it turns out that dispersed carbonization has low cost and high benefit.Biomass pyrolysis is a very complex process.Pyrolysis is not only relative to the raw material and environment., but also has intimate correlation to process parameters and pyrolysis equipmeng. Only part of the work of this paper, study of a raw material.It is verified by simulations and experimental.更多还原