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Dense phase gas-solid flows in circulating fluidized beds.

机译：致密相气固在循环流化床中流动。

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Circulating fluidized beds (CFBs) are widely used in the chemical industry for fluid catalytic cracking and combustion applications. It is well known that under certain operating conditions, flow instabilities involving the entire CFB system can arise, leading to a breakdown in operation. However, the origin of such instabilities as well as the minimum physics needed in a mathematical model to capture these is not well understood. In this research such CFB loop instabilities have been experimentally and theoretically investigated.; The flow behavior of gas-Geldart type A particle mixtures in a pilot scale CFB under stable and unstable operating conditions has been examined. Stable dense phase flow is established at low aeration rates in the standpipe. At high aeration rates the flow becomes unstable, manifesting low frequency oscillations in the flow characteristics. Our results suggest that, under the conditions explored in the present study, this instability originates in the standpipe when the effect of frictional interactions becomes negligible. Any attempt to model this instability should consider the interaction between the various components of the CFB circuit, wall friction and the compressive yield stress of the particle assembly in the standpipe.; Careful measurements of pressure drop and bed height during fluidization-defluidization cycles in beds of different diameters have been used to quantitatively determine the compressive yield stress as a function of particle volume fraction for XL particles used in the CFB experiments. Analysis of the standpipe data reveals that the support provided by the standpipe wall can be estimated quantitatively from the standpipe holdup data and the estimated compressive yield stress.; A theoretical study of the flow of a gas-Geldart type A particle mixture in a uniformly aerated standpipe system has been presented. The theory is based on a one-dimensional treatment of the volume-averaged equations of motion. It is able to qualitatively capture many of the gas-particle flow features observed in our CFB experiments, such as the effect of aeration on the flow behavior and the operating conditions under which instabilities in the CFB can occur.; A frictional model for the rheology of a compressible granular material has been developed and numerical issues associated with its implementation in a CFD framework have been explored. The model is shown to capture the general features of dense phase flows in two test cases in a qualitatively correct manner.
机译：循环流化床（CFB）在化学工业中广泛用于流化催化裂化和燃烧应用。众所周知，在某些运行条件下，可能会出现涉及整个CFB系统的流量不稳定性，从而导致运行故障。但是，这种不稳定性的起因以及数学模型捕获这些不稳定性所需的最低限度的物理原理尚不十分清楚。在这项研究中，已经通过实验和理论研究了这种CFB回路不稳定性。在稳定和不稳定的操作条件下，研究了中试规模CFB中气体-Geldart A型颗粒混合物的流动行为。在竖管中以低曝气速率建立稳定的致密相流。在高通气率下，流量变得不稳定，流量特性表现出低频振荡。我们的结果表明，在本研究探索的条件下，当摩擦相互作用的影响可忽略不计时，这种不稳定性起源于立管。对这种不稳定性进行建模的任何尝试都应考虑CFB回路的各个组件之间的相互作用，壁摩擦以及竖管中粒子组件的压缩屈服应力。对于CFB实验中使用的XL颗粒，在流化床/去流体化循环期间在不同直径的床中仔细测量压降和床高度已被用来定量确定压缩屈服应力与颗粒体积分数的关系。对立管数据的分析表明，立管壁提供的支撑可以从立管滞留数据和估算的压缩屈服应力进行定量估算。提出了均匀充气立管系统中气体-Geldart A型颗粒混合物流动的理论研究。该理论基于对体积平均运动方程的一维处理。它能够定性地捕获我们CFB实验中观察到的许多气体颗粒流动特征，例如曝气对流动行为的影响以及CFB可能发生不稳定的运行条件。已经开发了用于可压缩颗粒材料的流变学的摩擦模型，并且已经探索了与它在CFD框架中的实现相关的数值问题。该模型显示出以定性正确的方式捕获了两个测试用例中密相流的一般特征。

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