【作者】 段佳；

【导师】 罗永浩；

【作者基本信息】 上海交通大学 ， 热能工程， 2008， 博士

【摘要】 生物质气化是一种主要的生物质能利用方式,但是在气化过程中产生的焦油给生物质气化技术应用带来了一些问题。由于焦油凝结、形成烟雾、聚合成更复杂的结构,造成生物质气化气输送管道的堵塞,损害内燃机和燃气轮机,因而焦油成为限制生物质气化技术应用的瓶颈。虽然学者们对脱除焦油做了大量研究工作,但是目前还缺少高效、经济的脱除焦油的成熟技术,从而限制了生物质气化技术商业化应用。由于焦油氧化可以转化为C1-2烃类物质,这些烃类物质具有还原NO的能力,所以本文提出采用含焦油的生物质气化再燃还原燃煤锅炉NO这一技术路线,不需要脱除焦油,以便使焦油得到资源化综合利用,并对生物质气化焦油还原NO、含焦油的生物质气化再燃开展基础研究,所得到的研究成果对含焦油的生物质气化再燃技术工程应用有指导作用。由于焦油组分很多,所以本文选取典型的焦油模型化合物开展研究。本文采用热重-质谱联用仪,对生物质热解、气化焦油组分进行了分析。分析结果表明,苯、甲苯、苯乙烯和苯酚均有明显的累积离子流峰面积,是生物质焦油的主要组分,涵盖了初级、二级和三级焦油产物,所以选取苯、甲苯、苯乙烯和苯酚作为典型的生物质焦油的模型化合物。为了揭示焦油还原NO的内在机理,本文对一种典型焦油模型化合物还原NO的化学反应动力学机理模型进行了研究。基于焦油氧化裂解生成化学结构简单的烃类与非烃类分子、自由基,然后通过这些中间产物还原NO的反应机理,以甲苯作为代表性的焦油模型化合物,开展了甲苯还原NO的化学反应动力学机理模型的研究。提出了简单烃类和非烃类混合物还原NO的简单烃类与非烃类混合物还原NO的NRMF机理模型和甲苯还原NO的NRT机理模型,其中NRT机理模型是在NRMF机理模型的基础上加入甲苯氧化裂解反应步骤后得到的。通过实验对NRMF和NRT机理模型的验证,以及机理分析,得出以下结论:在焦油还原NO的过程中,焦油趋向于生成含C≡C键的HCCO和C2H自由基中间产物,这两种自由基还原NO的反应活性比CHi(i=1, 2, 3)自由基高,对还原NO的作用比CHi自由基更重要。本文对所选取的苯、甲苯、苯乙烯和苯酚等典型焦油模型化合物还原NO开展了实验研究,分析各焦油组分还原NO的特性。得出以下结论:表征燃料与氧量浓度比率的当量比φ和温度是决定NO还原效率的主要因素。具有取代基的甲苯、苯乙烯、苯酚还原NO的效率比苯高,而且含烃基取代基的甲苯、苯乙烯还原NO的效率甚至可以超过乙炔。工程实际在利用焦油还原NO时,可以使生物质气化多生成含烃基取代基的焦油。这四种典型的焦油模型化合物同时还原NO时,随着氧量减少,在900-1100℃时NO还原效率单调增加,在1300、1400℃时NO还原效率单调降低,在1200℃时,为过渡阶段。由于焦油是混合在生物质气化气中的,因此本文开展了含焦油的生物质气化再燃特性的实验研究,得出以下结论:在含焦油后,生物质气化气还原NO的效率明显地比不含焦油时有所提高;当量比φ和温度是影响含焦油的生物质气化再燃的重要因素,工程实际中应控制再燃区有适当的氧气浓度,控制焦油聚合、甚至生成碳黑,以便实现含焦油的生物质气化再燃还原NO能力的最大化。更多还原

【Abstract】 Gasification is a main conversion technology of biomass energy, but tar produced in gasification process cause some problems to the technology. Tar is undesirable due to condensation, formation of tar aerosols and polymerization to form more complex structures, which cause blockage in transporting pipe and damage to engines and turbines. Then, tar is still the bottleneck of the technology. Though many researchers have been working on tar removal, the efficient and cheap removal of tar is still immature and the main technical barrier for the successful commercialization of biomass gasification technology. Some research indicate that oxidation of tar produces light C1-2 hydrocarbons that can reduce NO, which means that tar can reduce NO. So, a technical routine of biomass gasification gas reburning with tar, or biogas reburning without tar removal, is put forth to deal with the comprehensive utilization of tar in the present work. The work is to investigate some basic issues of NO reduction by biomass gasification tar and by biogas with tar. The research results have the guiding role for the engineering application of the technology of biomass gasification gas reburning with tar.Tar compositions are so complex that some typical tar model compounds are selected to study. TG-MS apparatus is used to analyze the tar compositions produced in pyrolysis and gasification of several typical biomasses. The TG-MS analyses indicate that the cumulated ion intensity area of benzene, toluene, styrene and phenol is large. The four compounds are main compositions of tar, and they cover from the primary tar to the tertiary tar. Then, those four hydrocarbons are selected as the typical tar model compounds for the further research.The chemical kinetic modeling of NO reduction by a typical tar model compound is studied, in order to discover the mechanism of NO reduction by tar. Base on the mechanism of NO reduction by hydrocarbon and non-hydrocarbon intermediates produced in the tar oxidative decomposition, the chemical kinetic modeling of NO reduction by toluene is studied. The chemical kinetic model of NO reduction by a mixture of light hydrocarbon and non-hydrocarbon fuels (NRMF) is developed at first. Then, the chemical kinetic model of NO reduction by toluene (NRT) is developed, after some reactions of toluene oxidative decomposition are added into the NRMF model. The validity of the NRMF model and the NRT model is proved, experimentally. The reaction pathway of NO reduction is analyzed. The study indicates that tar tends to yield HCCO and C2H radicals. The reaction activity of the two radicals is higher than CHi (i=1, 2, 3) radicals, so that the two radicals are more important in NO reduction.Experimental study of NO reduction by the four typical tar model compounds, benzene, toluene, styrene and phenol, is carried out to analysis the experimental characteristics of them. The results of the experiments indicate that the bulk equivalence ratio,φ, and temperature are the main factors in NO reduction; the NO reduction ability of tar model compound with substituent is higher than benzene; toluene and styrene, which have hydrocarbon substituent, can reduce more amount of NO than acetylene under suitable conditions. Then more tar with hydrocarbon substituent is expected than benzene in the engineering application of biomass gasification gas reburning with tar. The experiment of the four typical model tar compounds simultaneous reburning indicates that the NO reduction efficiency increases at 900-1100℃, and increases at 1300-1400℃, as the content of oxygen decreases. It is a transition stage as 1200℃.Tar is mixed in biogas from gasifier, and NO reduction by biogas with tar is investigated, experimentally. The experimental results show that tar can improve the NO reduction by biogas with tar with comparison to by biogas without tar. The bulk equivalence ratio,φ, and temperature are the main factors in biogas reburning with tar. Then, remaining proper oxygen concentration and controlling tar polymerization even to yield soot is needed to maximize the ability of NO reduction by biogas reburning with tar.更多还原