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微型流化床煤半焦水蒸汽气化反应特性与动力学研究
Alternative TitleCoal char steam gasification characteristics and kinetics in micro fluidized bed
季颖
Subtype工程硕士
Thesis Advisor许光文
2014-05
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword水蒸汽气化   煤半焦   急冷   微型流化床反应分析仪   反应动力学
Abstract气化技术是煤炭转化的重要途径,是实现煤清洁高效利用的关键技术。半焦气化反应是煤气化过程中重要的限速步骤,研究煤焦水蒸汽气化反应动力学是气化技术设计、放大、优化的基础,对实现煤的高效利用和过程模拟具有重要的指导意义。 文献报道的煤焦-水蒸汽气化反应及相关活性的研究大多采用自然冷却半焦(热解后在惰性气氛下自然冷却至室温的半焦),不能完全反映实际工艺过程的半焦气化行为包括动力学。而文献报道的半焦-水蒸汽等温气化反应动力学研究主要利用热重分析仪(TGA),靠气体切换的方式进行测量,切换过程造成的气氛变化必定会对测试结果的准确性产生严重影响。同时,热重只考察半焦反应物的整体质量变化的动力学特性,难以揭示某个产物形成的反应特征行为及其反应途径(体系)对应的动力学参数。本文利用中国科学院过程工程研究所开发的微型流化床反应分析仪(MFBRA)研究了煤半焦等温气化反应动力学。实验对半焦气化实验的操作条件进行了系统研究和优化。在最小化气体扩散影响的条件下,利用MFBRA测试了半焦-水蒸汽气化反应特性,并与TGA求取的动力学数据进行了对比,证明了MFBRA在半焦气化、尤其是在复杂气氛下对等温微分反应的适用性,也为流化床、气流床气化炉的设计和放大提供重要的基础数据。 本论文的主要研究内容和结果如下: (1) 制备在液氮中急速冷却和在氩气中自然冷却的两种半焦,采用扫描电镜(SEM)、液氮吸附仪、红外光谱分析仪(FTIR)、X射线衍射仪(XRD)等方法系统比较了两种半焦的结构,并利用MFBRA研究包括动力学在内的水蒸汽气化反应特性。研究发现:急速冷却半焦(Char-Q)具有更大的比表面积和更小的平均孔径,而自然冷却半焦(Char-S)的石墨化程度更高。在MFBRA中进行的气化反应结果揭示了Char-Q具有更快的反应速率,且比较通过等转化率法算出的活化能发现:Char-S水蒸汽气化反应的活化能更大。利用MFBRA不仅求得了半焦水蒸汽气化的总体C转化的反应活化能(总体动力学),而且获得了生成各气体组分的反应(实际上为多个反应构成的体系)的活化能,实现了半焦水蒸汽气化反应分析。因此,选择Char-Q作为分析试样更能反映真实热态半焦的气化行为,而MFBRA为深入研究涉及水蒸汽参与的微分反应特性提供了有效的仪器与方法。 (2) 基于煤样热解后采用液氮急速冷却的制焦方法,系统地考察并比较了四种不同煤化程度的煤焦(葫芦素烟煤、特变戈壁次烟煤、东明褐煤和锡林浩特褐煤)结构,利用MFBRA研究半焦-水蒸汽气化动力学。比表面积的分析结果显示四种半焦的比表面积大小顺序依次为:锡林浩特褐煤煤焦、东明褐煤煤焦、特变戈壁次烟煤煤焦、葫芦素烟煤煤焦;XRD和FTIR测试结果表明:随着煤变质程度的提高,煤内部碳基质有序度增加,碳微晶尺寸增大,煤焦表面的活性位数减少,所以煤焦的反应性下降。MFBRA中研究半焦水蒸汽气化反应活性及动力学结果表明:无论是主要生成气的反应活化能或是碳消耗的反应活化能,东明和锡林浩特两种褐煤焦的反应活化能值均低于葫芦素烟煤煤焦、特变戈壁次烟煤煤焦的活化能。相对于低挥发分的东明褐煤,高挥发分的锡林浩特褐煤焦的气化反应活化能值明显较低。因此,煤化程度越高,其与水蒸汽反应的活性越小;而在同类型煤阶(褐煤或者烟煤)中,挥发分含量高的煤样其气化反应性更好。这些结果与针对不同煤阶的25个煤样在微型流化床反应分析仪中测试水蒸汽气化反应的活化能数据所得到的结果相符。 关键词:水蒸汽气化;煤半焦;急冷;微型流化床反应分析仪;反应动力学。
Other AbstractGasification is an efficient technology for converting coal and other fuels cleanly and environmentally friendly, which can be divided into initial rapid pyrolysis of raw coal and subsequently gasification of the resulting char. Being the rate-limiting step, char gasification dominates the whole gasification process, and thus a precise understanding of the kinetics is very important and essential for the design, simulation, optimization and scale-up of a gasifier. Numerous studies have been reported in the literature about char gasification with steam. However, the char sample used in most studies was cold char made by naturally cooling the char of coal pyrolysis to room temperature in inert gas, which would strongly affect the gasification reactivity of char. The study on steam gasification of char is performed usually in the thermogravimetric analyzer (TGA) by gas switching method. The gas switching procedure is very long so that the measured reaction characteristics and estimated kinetic parameters would much deviate from their true cases or values. Meanwhile, TGA gives only the overall reaction kinetics but difficult to estimate the kinetic parameter for individual product formation. Considering these limitations of TGA, the so-called micro-fluidized bed reaction analyzer (MFBRA) has been developed by the Institute of Process Engineering (IPE), Chinese Academy of Sciences (CAS) to test the gas-solid reactions, measure their kinetics and analyze the involved mechanisms. This study is devoted to investigating the isothermal gasification kinetics of coal char with H2O using MFBRA. This gives the gasification behavior of char with H2O and its kinetic parameters under the conditions with the minimized inhibition from heat and mass transfer, and the data are compared with that from TGA. It aims at verifying the applicability of MFBRA for steam-involved gas-solid reactions and revealing the characteristics of steam gasification of char made by different cooling ways. (1) Two types of char were made through rapid quenching in liquid nitrogen (Char-Q) and natural cooling in argon (Char-S), respectively. Comparison was made for the chars in terms of structure, surface properties and gasification characteristics shown in MFBRA. The Char-Q had the higher surface area but smaller average size of pores, while the Char-S from slow cooling showed the higher degree of graphitization. Gasification tests in MFBRA demonstrated that the Char-Q has obviously higher reaction rate, and the activation energy determined according to the iso-conversion method was higher for the Char-S. Particularly, MFBRA enabled the determination of activation energy not only for the overall C conversion but also for the formation reactions (possibly a reaction system) of every individual gas components, thus allowing a comprehensive understanding of the reaction nature. Consequently, in order to obtain the gasification characteristics close to the intrinsic nature of hot char the quench Char-Q should be used, while MFBRA provides a more effective instrument for measuring the differential reaction characteristics involving steam agent. (2) The coal chars were made by rapid quenching for four kinds of coal with different coalification degrees (HLS bituminous coal, TBGB sub-bituminous coal, DM lignite and XLHT lignite), and comparison was made for their structures and steam gasification kinetics measured in MFBRA. From automatic volumetric sorption analysis by N2 at 77 K, it was seen that the specific areas of such chars followed the order of XLHT coal char > DM coal char > TBGB coal char > HLS coal char. The results of XRD and FTIR analyses show that increasing the coal rank elevated the order degree of carbon crystallite matrix, and the active sites on the surface of carbon decreased to indicate the lower gasification reactivity. This was further verified by the results of char gasification with steam in MFBRA. For the same rank of coal, the steam gasification reactivity is correlated with the volatile content of the coal. The higher the coal volatile content was, the better the reactivity of its char tended to be. This work also measured the activation energy of steam gasification for 25 different coal samples with different coal ranks or coalification degrees. The obtained data complied well with the preceding clarification about char steam gasification based on such 4 coal char samples investigated in detail. Overall, the work shows well the good applicability of MFBRA for measuring the isothermal gas-solid reaction characteristics involving steam agent. Keywords: steam gasification, coal, quenching char, MFBRA, reaction kinetics.
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15576
Collection研究所(批量导入)
Recommended Citation
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季颖. 微型流化床煤半焦水蒸汽气化反应特性与动力学研究[D]. 中国科学院研究生院,2014.
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