生物质低温烘焙工艺基础及产物特性研究

QIBEBT-IR > 热化学转化研究组

	生物质低温烘焙工艺基础及产物特性研究
	胡晨
导师	吴晋沪
	2010-05
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位专业	热能工程
关键词	生物质烘焙热重红外联用分析差示扫描量热生物半焦
其他摘要	随着化石资源的日趋紧张和环境污染的加剧，世界各国已对来源广泛、有利于改善环境和可再生的生物资源的开发利用给予了极大的关注。热化学转化利用技术是生物质能源开发利用的主要途径之一，而生物质低温烘焙是以生物半焦为目标产品的慢速热解过程。其不仅可以将品质各异，低品位的原生生物质转化成品质统一，O/C 比较低，能量密度更高的生物半焦燃料，还可作为生物质气化及其他热化学转化技术的预处理技术。本文基于热重红外联用（TG-FTIR）技术和差示扫描量热（DSC）技术，对生物质烘焙过程的特性、热分解机理及影响机制进行了探讨，研究总结了生物质低温烘焙过程吸热量规律。并在此基础上，利用管式炉热解实验平台进行了生物质烘焙试验，对生物质低温烘焙工艺及产物特性进行了深入的研究。采用热重（TG）分析了温度、时间及升温速率对不同种类生物质烘焙特性的影响。研究表明，温度和烘焙时间是生物质烘焙过程的决定性影响因素。烘焙温度越高，时间越长最终的总失重越大，在烘焙温度范围内（220～300℃）生物质失重范围为 10.7%～50.7%；半纤维素的热稳定性最差，其热解起始温度为 200℃，而木质素的热稳定性更好。由于半纤维素与木质素热解特性的差异，也导致了不同种类生物质烘焙过程热失重特性的不同。草本生物质烘焙过程中热失重比例更大；升温速率也对生物质烘焙有一定的影响，选择适中的升温速率（如20℃/min）更利于烘焙过程及能量的利用。通过联用红外（FTIR），分析得出玉米秸秆烘焙过程析出产物主要为：H2O、CO、CO2和CH4以及一些可凝结有机物：甲醛、乙醛、蚁酸、乙酸和甲醇等；通过将生物质与其各种组分热分解过程及产物进行对比研究，分析了烘焙过程机理，探讨了各类气体的形成过程和形成机理。利用差示扫描量热（DSC）技术研究了生物质烘焙过程的热量需求规律。生物质烘焙过程所需热量主要集中在升温阶段，恒温烘焙阶段所需热量很少，当烘焙温度低于 260℃时所需热量为负值，说明生物质在低于此温度下烘焙时，热解反应是一个放热反应；探究发现可以通过将生物质Cp和Qp综合考虑，对DSC曲线处理和积分得出低温烘焙过程吸热量，并通过此方法获得了不同加热速率及温度下玉米秸秆烘焙所需热量。在以上烘焙特性，机理分析的基础上，通过管式炉生物质（玉米秸秆）烘焙试验，获得了各种烘焙条件下的生物半焦样品，分析了烘焙温度及时间对烘焙过程和生物半焦特性的影响。研究表明，生物半焦的低热值（LHV）随着烘焙温度和反应时间的增加而增加，而生物质质量和能量产率随之降低，但反应时间对其影响较小，因此较短的烘焙时间（20min）以及中等温度范围烘焙（<260℃）能获得较好的固体和能量产率，减少能量损失；通过烘焙可以有效降低生物质的O/C 比，并使物生半焦具有一定的疏水性。分析总结得出：260℃的烘焙温度、20℃/min 的升温速率以及 20min 的烘焙时间是较为合理的烘焙工艺参数。; In recent years increasing interest has been shown in sustainable biomass resources due to the global climate changes, environmental pollution and increasing lack of fossil energy resources. Thermochemical conversion is one of the energy recovery technologies which have the potential to convert the biomass into higher value fuels. Biomass torrefaction is a thermal pre-treatment that consists of a slow heating of biomass in a moderate temperature. It removes moisture and low weight organic volatile components, producing a brown to dark-brown solid product with an increased energy density, increased uniformity, lower O/C and greatly increased grindability. It also can be used as pretreatment technology of biomass gasification and other thermochemical conversion technology. In this work, we characterized the torrefaction behavior on the application of thermogravimetric analysis combined with the Fourier transform infrared spectrometer (TG-FTIR) and differential scanning calorimetry (DSC). The reaction mechanism of corn straw and caloric requirement of the process was determined. On this basis, we also carried out biomass torrefaction experiment on the tube furnace pyrolysis system. The technology base and product characteristics were studied in-depth.The weight loss of different biomass under different torrefaction conditions was studied by thermogravimetric (TG) analysis. It can be concluded that final temperature and residence time has a decisive influence on torrefaction. The higher temperature and the longer torrefaction time, the greater total weight loss. In the torrefaction temperature range the biomass weight loss range from 10.7% to 50.7%. Hemicellulose was the most reactive component. It started decomposing at 200℃ and the lignin was the most difficult one to decompose. The woody biomass (fir wood) and herbaceous biomass (corn straw) also have different reactivity. Herbaceous biomass looses considerably more weight than woody biomass. Heating rate is also one of the factors that could affect torrefaction of biomass. Select a moderate heating rate (eg 20℃/min) is more conducive to torrefaction process and energy use. By coupling a Fourier transform infrared spectrometer (FTIR) to the TGA we characterized the different compounds which were released in each stage during the process and deduced the reaction mechanism. The main products yield in the process of torrefaction were H2O, CO, CO2, CH4 and other condensable organics that included formaldehyde, acetaldehyde, acetic acid, formic acid, acetone and methanol.The law of caloric requirement of biomass torrefaction was studied using differential scanning calorimetry (DSC) technology. Most of the caloric demand of torrefaction is mainly focused on heating stage and constant temperature torrefaction stage required very little heat. When the temperature is lower than 260℃ the heat required is negative, indicating that the pyrolysis reaction is an exothermic reaction. A new method combining Cp and Qp，to achieve data of heat required by integrating the DSC curves directly was proposed. The values of the caloric requirement (torrefaction treatment at different temperatures for different times) were obtained.Based on the above analysis, biomass torrefaction experiment was also carried out on the tube furnace pyrolysis system. torrefied biomass samples under various torrefaction conditions was obtained. The effects of temperatures and time on characteristics of torrefied biomass were also investigated.The results show that Temperature with the temperature and reaction time increased, while the mass yields and energy yields decreases. But the reaction time had little effect then temperatures. Therefore, the moderate temperature range (<260℃) and shorter reaction time (20min) can obtain better mass yields and energy yields with minimal energy consumption. Additionally, torrefied biomass has a hydrophobic nature and more suitable O/C ratio. To sum up, temperature of 260℃, heating rate of 20℃/min and time of 20min are more reasonable torrefaction process parameters.
作者部门	热化学转化团队
学科领域	热化学转化
公开日期	2011-08-30
学位类型	硕士
语种	中文
文献类型	学位论文
条目标识符	http://ir.qibebt.ac.cn/handle/337004/336
专题	热化学转化研究组
推荐引用方式 GB/T 7714	胡晨. 生物质低温烘焙工艺基础及产物特性研究[D]. 北京. 中国科学院研究生院,2010.

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