摘要
发展生物质能源是缓解能源短缺和环境污染的有效途径，但生物质作为燃料利用尚存诸多缺陷，在规模化应用上十分局限。近年来发展起来的生物质烘焙技术是一项生物质燃料高值化预处理技术，其能够有效提高生物质材料的能源品质，降低物料的运输与储存成本。但目前国内对于该技术的研究还处于起步阶段，特别是对于木质生物质烘焙产物热转化过程的研究还有所欠缺。鉴于此，本文对我国典型木质生物质的烘焙特性及烘焙对其后续热解和燃烧过程中反应性的影响进行了深入地研究。
首先使用不同尺寸的荷木球状颗粒来作为实验样品，进行了不同加热温度和不同停留时间的烘焙实验。结果表明烘焙后样品的形貌特征会发生改变：烘焙后荷木颗粒的颜加深、体积收缩，质量上存在一定程度损失，且其质量变化幅度较体积更大，最终表现为密度的降低。在元素含量上，烘焙后荷木颗粒碳元素相对含量上升，氢、氧元素相对含量下降，因此样品的高位发热量也有所增加。并且由于烘焙过程中可燃气体组分的挥发，样品的能量得率有所下降。这些变化的程度都会随烘焙程度的增加而更为显著。综合各方面的影响因素来看，290℃1小时对于荷木颗粒是一个比较合适的烘焙条件。
然后以六种典型的木种作为研究对象，使用热重分析技术探究经不同烘焙条件预处理后各木质生物质样品的热解特性。结果表明烘焙前后各样品的热解过程符合双组分分阶段一级平行反应模型。并且烘焙对于不同木质生物质热解特性的影响基本一致：烘焙后各样品的热解过程均向高温处偏移，样品挥发分也释放得
更为集中和剧烈。但程度较深的烘焙会导致样品中的有机组分过度分解，从而使得样品挥发分析出的剧烈程度降低。并且由于生物质主要有机组分含量的相对变化，烘焙后不同阶段内样品的热解反应活化能和指前因子均有所上升。
最后，对烘焙前后的六种木质生物质样品的热解焦产率和焦反应性进行了实验分析。结果表明烘焙前后不同木质生物质样品的绝对焦产率变化幅度不相一致，其中榉木、桐木、松木和沙比利木的绝对焦产率与未烘焙样品相比变化幅度很小，而巴沙木和荷木的绝对焦产率则明显高于未烘焙样品。烘焙前后各样品热解焦在800℃的等温燃烧失重结果表明，烘焙对于不同木质生物质焦燃烧反应性的影响也不尽相同。对于松木和沙比利木来说烘焙会提升其焦的燃烧反应性，但对于桐木和荷木来说烘焙会使得其焦的燃烧反应性有所弱化，而烘焙对于巴沙木和榉木焦的燃烧反应性基本无影响。
关键词：生物质；烘焙；热解；焦产率；反应性
ABSTRACT
The development of biomass energy is an effective way to ease energy shortages and environmental pollution. But as a fuel, there are still a lot of defects in the application of biomass, which limits the applying scale of biomass. The biomass torrefaction developed in recent years is a pre-treating technology in which high value product can be obtained, which can effectively improve the energy qual
ity and reduce the transportation and storage cost of biomass materials. However, the domestic research about the technology is still at its early stage. And in particular the research about the thermal conversion process of woody torrefaction product is deficient. Therefore, the characteristics of typical woody biomass after torrefaction in China and the effect of torrefaction on the reactivity of its torrefaction product in the pyrolysis and combustion were studied in this paper.
At first, Schima spherical particles taken as experimental samples, the torrefaction experiments with different conditions of different heating temperatures, different dwell times and different particle sizes were carried out. The results showed that the morphological characteristics of the samples after torrefaction would change. The color of the wood particles after torrefaction was deeper, and the volume and quality of samples became smaller. The variation range of particle mass was larger than their volume, so the density of samples increasesed after torrefaction.In terms of elemental content, the relative content of carbon increasesed after torrefaction, however the relative content of oxygen and hydrogen decreasesed, so the higher heating value of the samples also increasesed. But the energy yield of the samples decreasesed due to the volatilization of combustible gas components during the torrefaction process. These changes would be more significant with the deeper degree of torrefaction. All factors being taken into conderation, the torrefaction condition of heating temperature 290 ℃and dwell time 1 hour were appropriate for Schima woody particles.
Then, the pyrolysis characteristics of the woody biomass samples from six typical wood species in China after pretreatment in different torrefaction conditions were investigated by thermogravimetric analysis. The results showed that the pyrolysis process of each sample before and after torrefaction followed the first order bi-component separate-stage model. And the effect of torrefaction on the pyrolysis characteristics of different woody biomass was
similar. The pyrolysis process of each sample after torrefaction was shifted to higher temperature, and the volatile releasing interval of each sample was more centralised and violent. But the deeper torrefaction would lead to excessive decomposition of the organic components in the sample, resulting in reduced volatility of the sample. Besides, the activation energies and the pre-exponential factors of the samples after torrefation in different raction stages all increased due to the relative change of the main organic components.
Finally, the pyrolytic char yield and char reactivity of the six woody biomass samples before and after torrefaction were analyzed in detail. The results showed that the change range of absolute char yield from before and after torrefaction was inconsisitent. The absolute char yeild of beech, phoenix pine and sapele didn’t change a lot after torrefaction while the absolute char yeild of balsa and Schima would be enhanced after torrefaction.The results of isothermal combustion experiment at 800 ℃showe生物能源
d that the effects of torrefaction on the char combustion reactivity of different woody biomass were different. For pine and sapele, the combustion reactivity of the char would be enhanced after torrefaction, but the char combustion reactivity of phoenix and Schima would be weakened after torrefaction, while the char combustion reactivity of balsa and beech didn’t change after torrefaction.
Key words: Biomass; Torrefaction; Pyrolysis; Char yield; Reactivity
目录
摘要 (Ⅰ)
ABSTRACT (Ⅱ)
第一章绪论 (1)
1.1研究背景及意义 (1)
1.1.1能源现状及气候形式 (1)
1.1.2可再生能源发展现状 (2)
1.1.3生物质能源发展现状 (3)
1.2生物质烘焙技术 (5)
1.2.1生物质烘焙技术概述 (5)
1.2.2生物质烘焙技术研究现状 (6)
1.3课题的提出及主要研究内容 (9)
第二章生物质烘焙实验研究 (12)
2.1生物质原料 (12)
2.2实验方法及设备 (13)
2.3荷木烘焙产物特性分析 (14)
2.3.1形貌特征分析 (14)
2.3.2质量及密度分析 (15)
2.3.3元素含量分析 (17)
2.3.4发热量分析 (19)
2.3.5能量得率分析 (20)
2.4荷木烘焙过程分析 (21)
2.5本章小节 (23)
第三章烘焙生物质热解特性研究 (24)
3.1实验部分 (24)
3.1.1实验原料 (24)
3.1.2实验方法 (25)
3.1.3实验仪器及操作步骤 (25)
3.2数据处理及分析 (27)
3.2.1热解过程分析 (27)
3.2.2热解特性参数 (31)
3.3烘焙生物质热解动力学研究 (34)
3.3.1动力学分析基本理论 (34)
3.3.2动力学分析 (37)
3.4本章小节 (41)
第四章烘焙生物质焦产率及焦反应性研究 (42)
4.1实验部分 (42)
4.2数据处理及分析 (43)
4.2.1焦产率 (43)
4.2.2焦反应性 (45)
4.3本章小节 (50)
总结与展望 (51)
1.全文总结 (51)
2.进一步的工作展望 (52)
参考文献 (53)
攻读博士/硕士学位期间取得的研究成果 (58)
致谢 (59)
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