【作者】 刘永卓；

【导师】 郭庆杰；

【作者基本信息】 青岛科技大学 ， 化学工艺， 2010， 硕士

【摘要】 近年来全球变暖引发的频繁极端天气使人们更加关注减少二氧化碳等温室气体的排放问题,二氧化碳的捕集和封存技术因此也成为了各国研究的热点。其中化学链燃烧过程被认为是一种极具发展前景的二氧化碳捕集技术。化学链燃烧技术无需消耗额外能量即可实现CO2内分离,并且还可以控制燃料型、热力型NOx的生成和实现能量的梯级利用。化学链燃烧技术成为解决能源与环境问题的创新性突破口,而载氧体的研究又是化学链燃烧技术能够实施的先决条件。本文围绕化学链燃烧技术对钙基载氧体进行了一系列的研究。首先利用双外推法分别对硫酸钙在惰性和还原性氛围下的热反应动力学进行了研究。在不假定机理函数的前提下,采用精确的动力学方程温度积分形式计算得到30种常用机理函数所对应的动力学参数。将升温速率和转化率双外推为零,得到了无任何副反应干扰、体系处于原始状态时的动力学参数E和lnA。硫酸钙的初期分解过程和与还原性气体反应过程均受成核核增长机制控制,其机理函数分别为G(α)=[-ln(1-α)]2、G(α)=[-ln(1-α)]1/3和G(α)=[-ln(1-α)]1/2。实验考察了温度和还原性气体分压对载氧体与还原性气体反应的影响。反应产物会随温度的不同而有所改变。温度升高,反应产物中的副产物CaO增多,对于硫酸钙循环不利,但是温度过低,又会降低反应速率。所以控制较低的温度和升温速率能改善提高载氧体的再生性能。在一定范围内,还原性气体的分压越大,越有利于主反应正向进行。当还原性气体的分压达到一定值后,反应产物几乎全部为CaS。此时产物组分不再随分压增大而改变,反应速率也不再随还原性气体分压增大而增大。在硫酸钙载氧体的反应动力学研究基础上,根据硫酸钙的结构特点和反应特性,分别采用了两种方法对硫酸钙载氧体进行了物理化学性质上的改性。首先利用不同粒径的碳酸钙对硫酸钙载氧体进行改性,实验研究表明碳酸钙改性使载氧体在反应性和再生性上都得到了很大改善,并且在一定程度上抑制了副反应发生。利用纳米碳酸钙对硫酸钙载氧体改性使硫酸钙的循环再生性能得到提高。当用纳米碳酸钙对酸处理过的硫酸钙载氧体进行改性时,硫酸钙载氧体在八个氧化还原循环后减少量较小。考虑到固体燃料化学链燃烧速率较慢,分别利用微量的三种金属氧化物(氧化铁、氧化铜和氧化镍)逐滴浸渍到硫酸钙中对硫酸钙载氧体进行改性。金属氧化物对反应起到催化作用,改性后的硫酸钙载氧体与固体燃料的反应速率得到提高。利用SEM和XRD分别对其表面形貌和反应前后物质形态进行了表征,金属氧化物改变了载氧体的基本孔结构和表面性能,在一定程度上也抑制了SO2的产生。本论文还设计了一套带有多角度射流管的高温流化床化学链燃料燃烧反应器。并考察了载氧体的流化特性和温度对最小流化速度的影响。通过实验和经验式推导均得到,载氧体颗粒最小流化速度随温度升高而减小。还考察了同粒径异密度的载氧体和煤颗粒双组份体系最小流化速度。其最小流化速度处在两组份各自单独流化时最小流化速度之间。载氧体颗粒的质量比越大时,与研究者经验关联式的误差越小。大密度的载氧体颗粒占比例越大时,流化效果会变得较差。更多还原

【Abstract】 More attention is paid to reduce emissions of greenhouse gases such as carbon dioxide due to the frequent extreme weather caused by global warming in recent years. Concequently, carbon dioxide capture and storage technology has become a research hotspot. Chemical looping combustion (CLC) technology, characterized by CO2 inherent separation without extra energy consuming, low NOx emission and high efficient, is considered as a promising technology of carbon dioxide capture. Chemical looping combustion technology gives a new way to solve the problems of energy and the environment, while the oxygen carriers are the prerequisites to explore the process of chemical looping combustion. A series of investigations on the oxygen carriers for chemical looping combustion were carried out in this paper.Firstly, the mechanism of calcium sulfate pyrolysis and its reaction with reducibility gas (H2, CO) using double extrapolation was studied in this paper. Thirty kinds of common mechanism functions of and their corresponding kinetic parameters were presented using the precise temperature integral form. The most probable mechanism is evaluated to be nucleation and nuclei growth model, and their probable mechanism functions were G(α)=[-ln(1-α)]2, G(α)=[-ln(1-α)]1/3 and G(α)=[-ln(1-α)]1/2 respectively.The effects of temperature and partial pressure of reducing gas on the reaction between oxygen carrier and reducing gas were also investigated. The reactant components varied with the reaction temperature. The fractions of by-products CaO are increased with increasing temperature. However, the above reaction rate would be very low at low temperature; oxygen carrier particles show a good regeneration at a relatively low temperature and heating rate. To some extent, the higher reducing gas partial pressure was, the greater main reaction rate favored reactions. Reaction products were almost the calcium sulfide when the partial pressure of reducing gas reached a certain value, and then the reaction products and the reaction rate would not change with the partial pressure of reducing gas increasing.Based on the study on calcium sulfate oxygen carrier and its structure characteristics and reaction feature, the chemical and physical properties of calcium sulfate oxygen carrier were modified by different particle sizes of calcium carbonate. The experiment results showed that the reactivity and regeneration of calcium sulfate oxygen carriers modified by calcium carbonate were improved with less side reaction. The regeneration of the calcium sulfate oxygen carrier modified by the nano-calcium carbonate was better then unmodified oxygen carriers. When the acid treated calcium sulfate was modified by the calcium carbonate, the loss of calcium sulfate was very low after eight redox cycles.Considering the reaction rate of the solid fuels for chemical-looping combustion slower, calcium sulfate oxygen carrier was modified by three trace metallic oxides (ferric oxide, copper oxide and nickel oxide) using the wet impregnation method. The reaction rate of the modified calcium sulfate was improved. The reduced calcium sulfate was characterized by scanning electron microscopy (SEM) and XRD respectively on its surface morphology and physical form. It has been found that the main cause on higher reactive of oxygen carrier modified by metal oxides was attributed to its basic pore structure and surface properties, and also the catalyticaction of the metallic oxide.The fuel reactor, a high temperature fluidized bed with multiple angles jetting pipes, was designed in this paper. And the cold and heat flow characteristics of the oxygen carriers and solid fuel particles were researched in the reactor. The effect of temperature on the minimum fluidization velocity of particles was examined. Through experiment and empirical equation, the law that the minimum fluidization velocity of oxygen carrier particles increased with temperature decreasing was obtained. Also the minimum fluidization velocity of the oxygen carrier particles and coal particle binary system with the same particle size and different density was studied in this paper. The error between experiment value and calculate value become smaller with the mass ratio of coal particles and oxygen carriers increasing, due to the relatively larger difference of the density between two particles.更多还原