气固环流床取热器内传热强化机理研究

The harmful events, such as the limited heat transfer capacity and heat tube damage, occur frequently in current industrial external catalyst cooler, due to the non-uniform particles flow and temperature distribution, respectively. To solve these problems, the idea of annular fluidized bed technology is introduced to develop a new type of catalyst cooler. In this annular catalyst cooler, the wall-to-bed heat transfer intensification caused by the internal circulation of particles is closely determined by the interaction among different fluidization regions. This application focuses on the effect of internal circulation on the particles renewal on heat transfer surface and the mechanism controlling the heat transfer intensification in different fluidization regions. Based on the previous study about the heat transfer intensification, a specially designed electrical heat tube is employed to measure the heat transfer coefficient between bed and tube surface. The surface hydrodynamics of particles are explored by installing an optical fiber probe at the tube surface. The intensification mechanism of heat transfer is revealed by comparing both the annular catalyst cooler and the base catalyst cooler. A comprehensive model for describing the heat transfer intensification in annular catalyst cooler is explored based on the packet renewal theory. According to the gas-particles hydrodynamics in the different flow regions, the effect of radial position of heat tube on heat transfer intensification is revealed in detailed. The quantitative calculation methods of the internal circulation capacity and the internal circulation height is established for better understand the synergic relationship between them. These results should provide some necessary information of theoretical guidance and fundamental data for the industrial scale-up and optimization of the new FCC annular catalyst cooler.

针对工业外取热器普遍存在因流化不均而造成的取热负荷受限及温度不均而导致的爆管等技术瓶颈，将环流技术引入取热器中，通过增设颗粒内循环以强化传热过程可有效解决这一技术瓶颈。影响环流床取热器内传热强化的关键因素是各区域间的相互作用。本课题拟围绕着颗粒有序内循环运动对表面更新速度的影响机制及各区域间传热强化的耦合调控规律，在前期研究工作的基础上，采用自行设计的多段传热系数测量方法和壁面流动特性分析方法，研究环流床取热器区域传热强化机理，并在颗粒团更新理论的指导下，建立新型环流床取热器的传热强化机理模型；基于取热器不同流化区颗粒分布规律和流动特性的研究，重点揭示加热管径向位置对传热强化的作用机制；建立颗粒内循环强度和内循环高度的定量计算方法，分析颗粒内循环高度与传热强化高度之间的协同关系，重点考察颗粒内循环强度对传热强化高度的调控规律，为新型环流床取热器的工程化应用和优化设计提供理论指导和基础数据。

针对工业外取热器普遍存在因流化不均而造成的取热负荷受限及温度不均而导致的爆管等技术瓶颈，将环流技术引入取热器中，通过增设颗粒内循环以强化传热过程能有效解决这一技术瓶颈。研究发现影响环流床取热器内传热强化的关键因素是各区域间的相互作用以及颗粒流动与传热间的协同关系。本项目采用冷模实验、理论分析和数值模拟，考察了颗粒有序内循环运动对表面更新速率的影响机制及各区域间传热强化的耦合调控规律。采用自主设计的多段传热系数测量方法，考察了自由床和环流床取热器内不同区域的传热过程，发现环流床取热器的下部区域为关键传热强化区，结合颗粒团更新理论中的关键流动参数，发现了换热管不同周向位置的传热强化控制因素，即换热管表面靠近床中心一侧为颗粒团平均停留时间，靠近床壁一侧为颗粒团分率。根据传热与流动之间的协同关系，建立了颗粒团更新传热强化模型。.通过考察两种取热器内不同流化区的颗粒分布规律和流动特性，发现在传热强化高度上部区域，两种取热器的颗粒浓度和速度分布在加热杆不同周向位置的流动特性均相似；而在传热高度范围内，自由床取热器内颗粒流动特性与上部区域一致，环流床内不同周向位置存在明显的流动差异。当换热管处于非中心位置时，靠近床中心一侧的颗粒以低浓度向上运动为主，靠近床壁一侧的颗粒以高浓度向下运动为主。换热管越靠近环流床取热器内两分布器的临界位置，其内循环流动越稳定。.通过分析不同操作条件下各流化区内颗粒速度和密度的轴径向分布规律，建立了颗粒内循环强度和内循环高度的定量计算方法。传热强化高度与颗粒内循环高度成正比，与颗粒内循环强度成反比。颗粒内循环高度随表观气速的增大而增大，受内外环气速比影响较小。表观气速越小，内外环气速比越大，颗粒内循环强度越大。进一步，分别提出了颗粒入口区、传热强化高度影响区和未影响区的优化设计方法。上述研究可为新型流化床取热器的工程化应用和优化设计提供理论指导和基础数据。