混合纳米颗粒添加粗颗粒流态化聚团破碎与团聚机制

Mixtures of nanoparticles, specially as nano-catalysts have been used in a lot of industrial fields. However, the feature of nanoparticles is also not employed effectively due to agglomeration. The issue at present is how to decrease or eliminate agglomerates in a fluidized bed. The larger agglomeraes can be broken up by adding coarse particles in the fluidized bed of nanoparticles. The advantage is that adding coarse particles in nanoparticles can be conducted at the existing equipments and keeping good feature of mass and haet transfer. However, the mechanism of agglomerate breakup and agglomeration is not clear so far in the fluidized bed of nanoparticles by adding coarse particles. This program focuses on the effect of adding coarse particles on the agglomeration and breakup of mixtures of nanoparticles in a gas-solid fluidized bed. The model for describing and predicting complicated systems can be developed and the interaction mechanism of interparticles, inter-agglomerates and inter-particles-agglomerates can be obtained based on the systemly research of agglomerating fluidization behavior of nanoparticles by adding coarse particles and effect of superficial gas velocity, type and amount of adding coarse particles on the fluidization behavior of mixtures of nanoparticles. The main contents include: 1) the interaction mechanism among the coarse particles and nanoparticles, among agglomerates and among particles and agglomerates in the fluidized bed of various mixtures of nanoparticles by adding coarse particles; 2) the mechanism of agglomerate breakup and agglomeration in a fluidized bed of mixtures of nanoparticles by adding coarse particles; 3) new equation of cohesive energy for the system of mixtures of nanoparticles by adding coarse particles in the model of core-shell proposed at this program.

混合纳米颗粒，特别是作为催化剂已应用于各个领域，但由于颗粒间力存在，极易团聚，其优良特性未得到有效利用。如何减少甚至消除大聚团使其以小聚团的形式流化，是目前急需解决的难题。在混合纳米颗粒中添加粗颗粒能破碎大聚团，具有不需要改变现有设备的优势，并能保持优良的传质和传热特性，但对混合纳米颗粒流化床中粗颗粒如何破碎大聚团的机制还不清楚，本项目拟通过对粗颗粒和纳米聚团的碰撞、聚集和破碎这种过程进行解析，构建能描述和预测这种复杂体系的数学模型。通过对添加粗颗粒后混合纳米颗粒的聚团流态化行为进行系统研究，解决其关键问题：1）混合纳米颗粒流态化复杂体系中颗粒与颗粒之间、聚团之间、颗粒与聚团之间的相互作用机制；2）添加粗颗粒对混合纳米颗粒在气-固流化床中形成的流态化聚团的破碎与团聚机制；3）核壳模型中新的混合纳米颗粒聚团的粘性力的表征方法。

混合纳米颗粒，特别是作为催化剂已应用于各个领域，但由于颗粒间力存在，极易团聚，其优良特性未得到有效利用。如何减少甚至消除大聚团使其以小聚团的形式流化，是目前急需解决的难题。在混合纳米颗粒中添加粗颗粒能破碎大聚团，具有不需要改变现有设备的优势，并能保持优良的传质和传热特性，但对混合纳米颗粒流化床中粗颗粒如何破碎大聚团的机制还不清楚，本项目拟通过对粗颗粒和纳米聚团的碰撞、聚集和破碎这种过程进行解析，构建能描述和预测这种复杂体系的数学模型。通过对添加粗颗粒后混合纳米颗粒的聚团流态化行为进行系统研究，解决其关键问题：1）混合纳米颗粒流态化复杂体系中颗粒与颗粒之间、聚团之间、颗粒与聚团之间的相互作用机制；2）添加粗颗粒对混合纳米颗粒在气-固流化床中形成的流态化聚团的破碎与团聚机制；3）核壳模型中新的混合纳米颗粒聚团的粘性力的表征方法。. 本项目通过对添加粗颗粒（Al2O3和 FCC）后混合纳米颗粒（SiO2/TiO2, SiO2/ZnO 和 TiO2/ZnO）的聚团流态化行为进行系统研究，采用高速摄像机在二维流化床中观察混合纳米颗粒添加三种不同粒径的FCC粗颗粒聚团碰撞与破碎过程，实验发现，纳米颗粒添加FCC粗颗粒后的流化性能改善是由于形成了新的核壳结构的聚团，核壳结构聚团的粘性、孔隙率和圆形度远远小于纯纳米颗粒聚团。分析了混合纳米颗粒聚团成分，结果表明，纳米颗粒均匀混合显著影响其流化性能。提出了核壳结构模型。纳米颗粒添加FCC粗颗粒后的流化性能改善主要是由于所形成的核壳结构聚团之间的粘性力显著降低所导致的。得到了纳米颗粒添加FCC粗颗粒后的流化性能改善的最优工艺条件，为工业应用提供理论和实际指导。