【作者】 吴昌宁；

【导师】 金涌； 程易；

【作者基本信息】 清华大学 ， 化学工程与技术， 2007， 博士

【摘要】 面对低碳烯烃不断增长的市场需求以及车用燃料日益提高的环保标准,传统的提升管催化裂化过程难以适应多产低碳烯烃兼顾清洁汽油生产的炼化一体化需求。在清华大学反应工程研究组长期的下行床和提升管研究基础上,本文提出多区反应控制的新型下行床-提升管组合反应器设计思想:利用下行床平推流的特性进行短停留时间、高苛刻度操作达到多产低碳烯烃目的;提升管采取低温、长停留时间操作以促进氢转移反应降低汽油产品的烯烃含量。构建了大型冷模装置,证明了上述概念设计的可操作性。系统的颗粒循环量可达400 kg/m2/s以上,下行床完全发展段可实现固含率达5%的高密度操作。建立了全床压力平衡模型,分析了系统内不同组件导致的压降随设计和操作条件的变化,以及在整个压力平衡中的贡献,与实验数据可较好地吻合。进一步建立了耦合反应-扩散方程、流体力学方程、传热方程、集总动力学的二维反应器工程模型,成功预测了提升管、下行床和不同方式的组合反应器的催化裂化行为,结果表明:相比于提升管,下行床可以更好地控制反应深度以增大中间产物的选择性,在高剂油比时更为显著。将二者优势相结合,可实现催化裂化过程多产低碳烯烃兼顾降低汽油烯烃含量的炼化一体化要求。为深化气固反应流机理研究,建立了CFD-DEM跨尺度反应流模型,考虑基于颗粒尺度的流动、传热、催化剂行为以及基于连续介质尺度的气相反应行为,成功地瞬态模拟了提升管和下行床用于催化裂化过程所不同的反应器特性,在广泛的剂油比下比较了提升管和下行床反应器的催化裂化反应行为,证明了下行床平推流流型对催化裂化过程的重要性。模拟结果与文献报道吻合较好。为实现复杂多相流的无干扰流场测试技术,从理论角度出发,提出并建立了一维轴对称X射线CT技术和快速X射线CT技术的新方法,通过实验不同层次地验证了技术的可行性和先进性,为X射线CT技术用于多相流实验研究乃至工业应用提供了新的解决方案。更多还原

【Abstract】 With the growing demand on the production of ethylene and propylene as well as the environmental concerns on the cleaner fuels for automobile, conventional fluid catalytic cracking (FCC) riser reactors can hardly facilitate the multifunctional purpose for the integration of refinery and petrochemical processes. A multi-zone reactor design, i.e., a coupled downer-to-riser reactor (DTRR), was proposed in this work to carry out the main primary and secondary reactions in two different reaction zones with different hydrodynamics and process conditions. The feed oil first enters into a downer reactor, undergoing a high severity operation but a short contact time between phases, for production of light olefins. After a certain conversion, the reacting flow transfers into a riser for the further cracking reactions of the heavy components adsorbed on the catalysts. Here a lower temperature and a longer residence time are favorable, especially to promote hydrogen shift reactions which reduce the olefins content in the product of gasoline.A pilot-scale experimental setup (cold model) was built to demonstrate the feasibility of running gas-solid flows smoothly in the DTRR system. High solids flux conditions, i.e., above 400 kg/m2/s, were achieved in the experimental apparatus, where the solids volume fraction in the fully developed region of the downer reaches up to 5%. Hydrodynamics in such a reactor coupling system was studied using a compressive model that considered the pressure balances around all the sub-units in the prototype. The continuity closure condition was used to determine the material balance of the solid particles flowing in the circulating fluidized bed system. The model predictions had good agreement with the experimental data in rather wide operating conditions.A two-dimensional convection-diffusion-reaction model incorporated with hydrodynamics and a 14-lump kinetic model was established to predict the conversion and yields of different products in a single riser, a single downer and different coupling schemes of the reactor columns. The results showed that downer reactor has better control on the desired intermediate products (e.g., gasoline) than riser reactor due to the plug-flow performance, especially under the conditions of higher catalyst to oil ratios. The DDTR design combines the advantages of both riser and downer, in which more yields of gasoline and light olefins can be achieved. Furthermore, it was predicted that the coupled reactor design has more potential to obtain cleaner gasoline with less olefin content.For a better description of the gas-solid reacting flows, a computational fluid dynamics (CFD) model for gas-phase flow combined with a discrete element method (DEM) for particle movement, i.e., CFD-DEM, was extended to incorporate the heat transfer behaviors between particles and between gas and particles. This is a so-called cross-scale modeling of gas-solid reacting flows due to the particle movement, heat transfer and catalysis at the particle-scale together with gas-phase reactions at the grid-scale. This Eulerian-Lagrangian model has clearer physical meanings by considering the particle behavior in a discrete manner than a Eulerian-Eulerian (two-fluid) model by assuming the particle phase as a continuous medium. The transient simulations for riser/downer based FCC process showed that downer reactor benefits from the plug-flow performance in comparison with riser for the FCC process. The predicted reactor performances had good agreement either qualitatively or quantitatively with the corresponding hot-model data available in the literature.In order to measure the multiphase flow behavior in a non-intrusive way, two types of X-ray computed tomography techniques were proposed in theoretical schemes: one is for one-dimensional measurement of concentration field with axisymmetric character, another is a novel method for fast measurement of dynamic concentration variations. The proposed new methodologies were demonstrated by both different experiments and numerical simulations. For the reduced request on the X-ray hardware, the two approaches are expected to serve the experimental studies in lab-scale even in some industry applications.更多还原