密相输运床气固流动相似性研究

发布时间：2018-09-10 09:48

【摘要】：粉煤加压密相输运床气化技术是我国发展IGCC和多联产的重要技术选择。密相输运床反应器内的气固两相流动行为非常复杂,提升管内的气固流动属于密相悬浮上升流,立管内的气固流动则属于非流态化的移动床流动。由于不同流型的流动特征明显不同,已有相似性研究多针对于鼓泡流态化和快速流态化,需对密相输运床的气固流动相似性进行研究,分析适用的相似准则,通过实验和模型研究对其有效性进行验证,以为装置的设计和放大提供参考。本文在冷态和热态实验的基础上,对密相输运床提升管、立管开展相似性研究及系统压力平衡建模,主要结果如下：1.针对密相输运床提升管和立管所处的不同流型,采用因次分析的方法,从流动基本方程出发,分别得到了适用于密相悬浮上升流和负压差下行移动床的气固流动相似准则。同时得到了返料阀部分的气固流动相似准则。其中,Ar数是影响气固两相相间作用力的重要物性参数,在进行实验时应首先选择Ar数相同或相近的物性条件,再根据提升管和立管的不同流动相似准则设计相应的操作条件。2.根据分析得到的密相悬浮上升流气固流动相似准则,选取适合的固体颗粒及气体进行了流动实验。在较宽的操作范围内,对提升管中Geldart B类石英砂颗粒的流动行为进行了研究。在高固体循环流率条件下,充分发展段的表观固体浓度可超过0.07,满足密相悬浮上升流的条件。由于气体沿轴向存在明显的膨胀加速,固体浓度仍然呈下浓上稀的非均匀分布,但不出现快速流态化条件下的典型S形分布。当前文分析得到的相似准则数相同或相近时,固体浓度和固体速度呈现相似的分布形式,表明应用有关相似准则可以实现密相输运床提升管内的气固流动相似。将实验数据与理论分析结合,得到用于计算密相悬浮上升流参数分布的流动模型。基于作用力分解的方法建立了提升管气固流动模型,模型计算得到的提升管压降与实验结果吻合较好。3.基于非流态化气固两相流的经验关系式,结合密相输运床立管流动特点,得到了负压差下行移动床的气固流动模型。由模型计算得到的立管轴向压力分布和空隙率分布情况与理论分析一致。由于实验物料的物性参数和实验装置充气位置的布置形式与理想状态存在差异,进行实验时实际通入的松动风流量比计算值偏大。根据本文研究获得的相似准则,计算了不同物料在不同操作条件下的立管空隙率和压力梯度分布情况,结果表明各计算工况下的立管移动床的气固流动表现出相似性。4.将提升管和立管模型结合,对系统压力平衡进行分析。建立了适合于密相输运床的系统压力平衡模型,能够较准确地对提升管内固体浓度分布进行描述。通过进一步对于系统结构的分析表明,增大立管和提升管直径比及颗粒密度均有利于增大立管压降,从而获得更大的返料驱动力。
[Abstract]:The pressurized dense phase transport bed gasification technology of pulverized coal is an important technical choice for developing IGCC and multiple cogeneration in China. The gas-solid two-phase flow behavior in a dense transport bed reactor is very complex. The gas-solid flow in the riser belongs to the dense phase suspended upwelling flow, while the gas-solid flow in the vertical pipe belongs to the non-fluidized moving bed flow. Because the flow characteristics of different flow patterns are obviously different, the similarity studies have been mainly focused on bubbling fluidization and rapid fluidization. It is necessary to study the similarity of gas-solid flow in dense phase transport bed and analyze the applicable similarity criteria. The validity of the device is verified by experiments and model studies, which provides a reference for the design and amplification of the device. In this paper, on the basis of cold and hot state experiments, the similarity study and pressure balance modeling of riser and riser in dense phase transport bed are carried out. The main results are as follows: 1. According to the different flow patterns of the lifting tube and the riser in the dense phase transport bed, the similarity criteria of gas-solid flow for the dense phase suspended upwelling bed and the negative pressure differential downward moving bed are obtained by using the dimensionality analysis method and starting from the basic flow equation. At the same time, the similarity criterion of gas-solid flow in the return valve is obtained. The ar number is an important physical parameter which affects the interaction force between gas and solid phases. In the experiment, the same or similar physical property conditions with the same Ar number should be selected, and the corresponding operating conditions should be designed according to the different flow similarity criteria of the riser and riser. According to the similarity criterion of gas-solid flow in dense phase suspended upward flow, the flow experiments were carried out by selecting suitable solid particles and gases. The flow behavior of Geldart B quartz sand particles in the riser was studied in a wide operating range. Under the condition of high solid circulation rate, the apparent solid concentration of the fully developed phase can exceed 0.07, which satisfies the condition of dense phase suspension upwelling. Due to the obvious expansion and acceleration of the gas along the axial direction, the concentration of the solid is still distributed inhomogeneously with lower concentration, but there is no typical S-shaped distribution under the condition of rapid fluidization. At present, when the number of similarity criteria is the same or similar, the distribution of solid concentration and velocity is similar, which indicates that the similarity criterion can be used to realize the similarity of gas-solid flow in the riser of dense phase transport bed. By combining the experimental data with theoretical analysis, a flow model for calculating the parameter distribution of dense phase levitation upwelling is obtained. The gas-solid flow model of the riser is established based on the method of force decomposition. The calculated pressure drop of the riser is in good agreement with the experimental results. Based on the empirical expression of non-fluidized gas-solid two-phase flow and combined with the characteristics of vertical pipe flow in dense phase transport bed, a gas-solid flow model for moving bed with negative pressure difference is obtained. The axial pressure distribution and voidage distribution obtained from the model are consistent with the theoretical analysis. Due to the difference between the physical property parameters of the experimental material and the arrangement of the inflatable position of the experimental device and the ideal state, the calculated value of the actual flow rate of the loosening air in the experiment is larger than the calculated value. According to the similarity criterion obtained in this paper, the void rate and pressure gradient distribution of riser under different operating conditions are calculated. The results show that the gas-solid flow of riser moving bed under different working conditions shows a similarity of .4. The pressure balance of the system is analyzed by combining the riser model with the riser model. A pressure balance model suitable for dense phase transport bed is established, which can accurately describe the distribution of solid concentration in the riser. Through further analysis of the system structure, it is shown that increasing the diameter ratio of riser and particle density can increase the pressure drop of riser and obtain a greater return driving force.
【学位授予单位】：中国科学院研究生院(工程热物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ051.1

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