【作者】 崔志刚；

【导师】 姜秀民；

【作者基本信息】 上海交通大学 ， 热能工程， 2010， 博士

【摘要】 在世界范围内能源需求不断增长的今天,油页岩是一种非常重要的替代能源,其本身及所含页岩油都具有潜在的利用价值,寻求储量巨大的油页岩有效开发与经济利用的途径,进行热转化规律及工程应用研究,对于缓解能源供需矛盾,推动社会的发展,具有重大的现实意义。作为一种燃料油页岩的挥发分含量高,固定碳含量低,其热解、燃烧特性与常规煤种有很大差别,燃烧以挥发分为主,如桦甸油页岩挥发分的放热量为固定碳的2.57倍,有必要对油页岩这种燃料的特殊性开展深入研究。另外,对油页岩炼油废弃物,也即油页岩半焦的资源化利用,也是油页岩利用的重要研究内容。油页岩及其半焦应用于流化床燃烧实践中,氧化亚氮排放浓度高于一般煤粉炉,N₂O是一种破坏臭氧层的温室气体,是排在二氧化碳、甲烷之后的第三大温室气体。随着当前环保要求的日益提高,如何有效控制N₂O的排放是流化床燃烧急需解决的重要问题。本文基于以上对油页岩有效开发利用的实际问题分析,根据油页岩热转化的进程,研究了油页岩热解、燃烧反应机理,为深入剖析油页岩在流化床燃烧中N₂O的生成机理,通过油页岩及其半焦在基础流化床实验台及半工业流化床实验装置中的燃烧过程监测,得到终产物排放特性,所得连续燃烧下的运行参数用于进一步模拟N₂O的生成,分析模拟结果以得到生成N₂O的关键组分和反应步骤。油页岩热解过程的研究中,分析了油页岩的结构组成,进一步研究了油页岩热解条件下转化为不凝气、页岩油和页岩焦的过程,并对油页岩中含有的官能团如何转化进行了分析。通过改进的热天平实验台,采用气相色谱方法测量油页岩热解反应时不凝气的浓度。元素总量平衡模型,首先基于C、H、O、N、S各元素总量平衡方程,再通过建立页岩油族组成模型,得出油页岩热解产物中十种主要的气相组分含量,并与色谱实验结果进行对比,二者吻合较好。油页岩燃烧反应过程的研究中,建立了不凝气中可燃成分进行燃烧时的基元反应机理,建立含氮物HCN和NH₃的基元反应机理,对含氮中间产物分类并分析其转化路径,并得到了燃烧过程中各组分的转化路径图。在此基础上利用含氮前驱物HCN和NH₃的基元反应机理,重点研究了柱塞流反应器中HCN:NH₃在五种不同比例下的N₂O排放特性,结果反映出在HCN:NH₃比例高时,N₂O生成浓度明显增高,HCN有趋向于生成N₂O的特征。油页岩流化床实验台中的燃烧特性研究中,利用小型流化床进行了油页岩及其半焦的燃烧特性实验,小型实验台研究结果为设计半工业化流化床提供了指导作用。在小型流化床实验台上,进行了颗粒直径、钙硫比、床料高度、床温、过量空气系数、二次风率和循环倍率这七个运行参数对N₂O排放的影响规律,并采用油页岩掺混半焦比例分别为10%、20%、30%、50%、75%及100%的燃料,进行燃烧特性试验,得到了各因素对流化床污染物排放的影响规律,并采用灰色关联方法对七个因素对N₂O排放浓度的关联度进行排序,发现床温和过量空气系数的影响相对显著。为验证小型流化床实验结果,并为工业化流化床锅炉实践运行提供基础数据,设计并搭建了大型流化床实验装置,采用XDC800控制系统,对油页岩与油页岩半焦掺混比例分别为25%、50%、75%和100%的混合燃料进行了燃烧实验,对运行过程中给风量、压力以及炉膛高度方向上温度分布的变化情况进行实时记录,采用氧化锆氧量分析仪以及GASMET便携式红外分析仪对燃烧过程中的气体排放浓度进行了在线监测,综合以上数据得到了大型流化床中油页岩及其半焦的污染物排放特性。在无辅助热源的条件下,油页岩及其掺混不同比例下的520℃干馏制得的半焦,所得各燃料自身燃烧生成的热量都能够使流化床温逐渐升高到某一平衡温度,反映出燃料的燃烧特性良好。结合油页岩元素总量模型和燃烧反应机理模型,建立油页岩流化床燃烧分区模型,并结合热态流化床实验中各工况相对应的运行参数,计算值和实验值吻合较好,所得结果显示,N₂O在密相区的生成份额远高于稀相区。对流化床密相区和稀相区N₂O的生成规律进行分别研究,对N₂O的主要生成反应在密相区和稀相区的重要性进行了对比。对N₂O生成的机理结果进行详细分析,得到了N₂O生成的主要路径图,以及影响N₂O生成的关键组分和反应式,NH是影响N₂O生成的关键组分,N₂O最主要的生成反应NH+NO=N₂O+H。这些结果为将来采取相应措施控制N₂O排放提供理论依据。最后对复杂的基元反应机理进行简化,得出具有较高准确性的简化机理,更有助于发现并分析影响N₂O生成的关键步骤。更多还原

【Abstract】 With the growing demand for energy and the gradual decrease in conventional energy resources, oil shale would be a very important alternative energy resource, which could demonstrate potential value for utilization as well as shale oil that it contains. How to efficiently exploit and utilize oil shale rich and widespread throughout the world, and to carry out thermal conversion and engineering application, will be of great practical significance for balancing energy supply and demand, and promoting social development. Oil shale has high volatile content and low fixed carbon content, which determines that its pyrolysis and combustion characteristics are so different from conventional coal that volatile is the major content of oil shale combustion, for example, the releasing heat of volatile is 2.57 times that of fixed carbon for Huadian oil shale. The special characteristics of oil shale make it necessary to carry out thorough research. In addition, it is also an important research content that realizing the resource utilization of oil refining residue - shale char. As a utilization method, fluidized bed combustion of oil shale would produce higher nitrous oxide （N₂O） emission concentration than the general pulverized coal. N₂O is an ozone-layer depleting greenhouse gas, and is ranked third largest of greenhouse gases following the carbon dioxide, methane. With the increasing requirements of environmental protection, how to control the emissions of N₂O effectively in fluidized bed combustion is an urgent issues needing to resolve.For the purpose of utilizing domestic oil shale resources cleanly and efficient, and on the basis of analyzing the above practical problem, the paper carried out the concrete research through the path of thermal conversion process of oil shale, which included pyrolysis and combustion reaction mechanism of oil shale. In order to model N₂O formation mechanism, the combustion experiment of oil shale and its shale char in small-scale and semi-industrial fluidized bed were carride out, and it was monitored and recorded that the pollutant emission of oil shale fluidized bed combustion according to the operation characteristics. Based on all these theoretical model and experimental results, the N₂O formation in fluidized bed was modeled in order to find the key component and reaction affecting N₂O formation.During the research of oil shale pyrolysis, the structural composition of oil shale was analyzed, and in the further study, the process that oil shale converts to non-condensible gas, shale oil and shale char at pyrolysis conditions, and how the functional groups in oil shale evolve were investigated. By the improving thermogravimetric test units, gas chromatography methods was used to measure the concentration of non-condensible gas in oil shale pyrolysis reaction. Based on total balance equation of each element C, H, O, N, S in ultimate analysis, gross equilibrium model was built up by assuming group-composition distribution of shale oil. The contents of ten major gas outputs in pyrolysis were calculated, and the results were validated by experimental data.During the detailed process research of oil shale combustion, the detailed combustion mechanism of combustible component in non-condensible gas was established, and the fine elementary reaction mechanism of nitrogen-containing materials HCN and NH₃ was built too in a hierarchical manner. The nitrogen-containing intermediates were classified and the conversion path of them was analyzed, and then the conversion map in the combustion process was deduced. Using the above model about nitrogen-containing precursors HCN and NH₃ fine reaction mechanism, the N₂O emission characteristics of the plug flow reactor were studied at five different HCN: NH₃ ratios. The results shows that HCN: NH₃ ratio is higher, N₂O formation concentration is significantly higher, and HCN tends to produce N₂O.During the experimental research of fluidized bed combustion characteristics, the small-scale fluidized bed experimental rig were used to carry out the combustion experiment of oil shale and shale char, which can provide some guidance for designing large-scale fluidized bed. In the small-scale fluidized bed, the experiments were proceeded which consisted of the effect of seven operating factors on N₂O emission, such as particle size, Ca/S ratio, bed material height, bed temperature, secondary air ratio, secondary air rate circulation ratio, and adopted samples of five mixture ratio including 10%, 20%, 30%, 50%, 75% and 100% of shale char content to apply tests about combustion characteristics. The grey relational analysis was used to treat the experiments data of seven operating factors and made order for them using obtained grey relational degree. The calculation results indicate that bed temperature and excess air have marked influence on N₂O emission.Based on the small-scale fluidized bed experimental results, the large-scale fluidized bed experimental device adopting XDC800 control system were designed and built which could provide the foundation for industrial fluidized bed boiler, the continuous combustion experiments were done for five mixture ratio including 25%, 50%, 75% and 100%, recording the operation course relating to air flow, pressure and temperature distribution in furnace height in real-time, and using zirconia oxygen analyzer and GASMET portable infrared analyzer to on-line monitor flue gas emissions in the process of combustion. Combined with all these data, pollutant emission characteristics of oil shale and shale char were analyzed under the large-scale fluidized bed. In absence of auxiliary heat source, bed temperature would be gradually increased to a certain balance temperature by formation heat of the fuel samples including oil shale and different mixture ratio with shale char obtained at pyrolysis conditions of 520℃, which reflected good characteristics of fluidized bed combustion.Combined with element gross equilibrium models and combustion reaction detailed mechanism model of oil shale, the zone model of fluidized bed combustion was established, and then was used to calculate simulation cases under the conditions corresponding to the same operating parameters of the experiment cases. The calculation results were in good agreement with thermal experimental data. The results showed N₂O formation in the dense phase region is far higher than that in the dilute phase region. N₂O formation in the dense phase region and dilute phase region of fluidized bed was discussed separately, and importance factor of N₂O major formation reaction was studied in the dense phase and dilute phase region. After detailed analysis of N₂O formation mechanism from the calculation results, the main N₂O formation map was obtained as well as the key component and reaction affecting N₂O formation. NH is the key component, and NH+NO=N₂O+H is the key reaction of N₂O formation. These results will provide a theoretical basis for taking effective measures to control N₂O emissions in the future. Finally, the detailed elementary reaction mechanism was simplified to obtain the simplified mechanism with high accuracy, which would help to identify and analyze a critical step affecting N₂O formation.更多还原