GOALI: Toward a Fundamental Understanding of Elutriation in Fluidized Beds

目标：对流化床淘析有一个基本的了解

• 批准号: 0318999
• 负责人: Christine Hrenya
• 金额: $ 35万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-04-01 至 2007-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0318999&HistoricalAwards=false
• 关键词: GOALI; Toward; Fundamental; Understanding; Elutriation

AbstractCTS-0318999C. Hrenya, University of Colorado, BoulderGas-solid flows are ubiquitous, though not well understood. A study of solids processing plants indicates that 80 percent of the plants experienced solids handling problems such as pipe blockage and that the performance of such operations was typically only 40-50 percent of design. Furthermore, even reliable empirical correlations for fluid catalytic cracking units are often inadequate. The proposed GOALI effort is targeted at advancing the fundamental knowledge associated with a phenomenon that is typically handled empirically, namely elutriation. Elutriation refers to the carryover of fines in a bubbling, gas-fluidized bed. Although more than 50 elutriation correlations have been proposed in the literature over the last two decades, the disagreement between experiments and empirical prediction is typically over 100 percent and in some cases may differ by a factor of more than a hundred. Furthermore, even the qualitative nature of elutriation may be anti-intuitive. For example, the addition of fines to a fluidized bed is known to increase the elutriation rate of relatively coarse particles (i.e., particles which have a terminal velocity that is greater than the superficial velocity at which the bed operates). In order to better predict the elutriation phenomenon, a combined modeling and experimental effort is being proposed. Attention will be focused on a binary system composed of two species that differ in both size and density. The impetus for this choice is twofold: (i) this system is of specific interest to Millennium Chemicals (one of the two industrial partners on this proposal), and (ii) the binary system represents the simplest form of a polydisperse system. The modeling effort will be based on a kinetic-theory analogy. Preliminary work has indicated that an equipartition of energy between unlike particles, which is a common assumption of existing kinetic-theory models, does not exist. Preliminary calculations have also indicated that non-equipartition gives rise to additional components of the driving force for size/density segregation; the existence of such driving forces has not been previously documented. Because the segregation (or de-mixing) of unlike particles in both the bed and freeboard section will impact system hydrodynamics (and thus elutriation), an investigation on the impact of the non-equipartition effects is needed. Thus, the first part of the proposed study will involve the derivation of a kinetic theory for binary systems in which non-equipartition (and non-Maxwellian) effects are included. The resulting continnum heory will then be incorporated into two CFD (computational fluid dynamics) codes: a standard Eulerian-Eulerian framework (both phases are treated as a continuum) and a new multi-phase particle-in-cell (MP-PIC) formulation developed by Arena-Flow (an industrial partner on this proposal). A unique feature of the latter formulation is the combined Eulerian and Lagrangian approach to the particle phase, which allows for a computationally efficient description of systems with multiple particle types. Unlike previous studies, the experimental portion of the proposed work will involve elutriation measurements on beds composed of two Group B species which differ in size and density. Both overall and local measurements of fluxes for each species will be obtained. Application of the models to the experimental system will represent the first elutriation predictions without empricism (i.e., no adjustable parameters). The resulting comparisons between model predictions and experimental data will indicate the impact of non-equipartition effects on bed hydrodynamics, and the viability of the Eulerian-Eulerian and MP-PIC frameworks in predicting elutriation, which is of immense interest to both industrial partners. This work is motivated by the combined and complementary interests of each partner: the University of Colorado (polydisperse particulate systems), Millennium Chemicals (elutriation), and Arena-Flow (MP-PIC method). The proposed effort is designed to ensure continual interaction and exchange between the partners, with annual meetings and extended visits to both industrial sites by both the PI and PhD students. Broader impacts of the work include the following: (i) a more fundamental understanding of polydisperse systems, which is needed before current treatments can be extended beyond two particle sizes, (ii) training of graduate students in the area of particle technology, which has been identified as a national need, and (iii) sharing of learned information with both the technical community and the student community (via incorporation into coursework and outreach).

Abstractcts-0318999c。科罗拉多大学的Hrenya，Bouldergas-Solid流无处不在，尽管不太了解。 对固体加工厂的研究表明，80％的植物经历了固体处理问题，例如管道阻塞，并且此类操作的性能通常仅占设计的40-50％。 此外，即使是流体催化裂纹单元的可靠经验相关性，通常也是不足的。 拟议的目标努力旨在促进与通常在经验上处理的现象相关的基本知识，即流行。 洗脱是指在冒泡的，燃气的床中罚款的结转。 尽管在过去的二十年中，文献中已经提出了超过50个理性的相关性，但实验和经验预测之间的分歧通常超过100％，在某些情况下可能会差异超过一百多个。 此外，即使是质化的定性性质也可能是反直觉的。 例如，已知在流化床中加入罚款会增加相对粗糙的颗粒的放松率（即具有末端速度的颗粒大于床的表面速度的末端速度）。 为了更好地预测洗脱现象，正在提出合并的建模和实验努力。 注意将集中在由大小和密度不同的两个物种组成的二元系统上。 这种选择的动力是双重的：（i）该系统对千年化学物质（该提案中的两个工业伙伴之一）具有特定的兴趣，并且（ii）二进制系统代表了polydisperse系统的最简单形式。 建模工作将基于动力学理论类比。 初步工作表明，与粒子之间的能量平选（这是现有动力学理论模型的常见假设）不存在。 初步计算还表明，非设备会导致尺寸/密度分离的驱动力的其他组成部分。此类驱动力的存在以前尚未被记录。 由于床和干型截面中的颗粒的分离（或解混合）将影响系统流体动力学（从而消除），因此需要对非企业效应的影响进行研究。 因此，拟议的研究的第一部分将涉及针对非设备（和非马克斯维利亚）效应的二元系统的动力学理论的推导。 然后，由此产生的连续性主体将被合并到两个CFD（计算流体动力学）代码中：标准的Eulerian-Eulerian框架（两个阶段均被视为连续体）和一个由Arena-Flow（由该提案的工业伙伴）开发的新的多相粒子（MP-PIC）配方。 后一种公式的一个独特特征是颗粒相的欧拉和拉格朗日组合方法，它允许对具有多种粒子类型的系统的计算有效描述。 与以前的研究不同，所提出的工作的实验部分将涉及由大小和密度不同的两个B组物种组成的床上的放松测量。 将获得每个物种通量的总体和局部测量。 模型在实验系统中的应用将代表没有Empricism（即没有可调节参数）的第一个流行预测。 由此产生的模型预测与实验数据之间的比较将表明非设备对床水动力学的影响以及Eulerian-eulerian和MP-PIC框架对预测洗脱体的生存能力，这对两个工业伴侣都具有巨大的兴趣。 这项工作是由每个合作伙伴的联合和互补利益的动机：科罗拉多大学（多分散颗粒系统），千年化学物质（Elutriation）和Arena-Flow（MP-PIC方法）。 拟议的努力旨在确保合作伙伴之间的持续互动和交流，并通过PI和PHD学生进行年度会议以及对两个工业网站的延长访问。 这项工作的更广泛的影响包括：（i）对多分散系统的更基本的理解，在当前治疗可以扩展到超过两种粒径之前，（ii）在粒子技术领域对研究生进行培训，这已被确定为国家需求，（III）与技术社区和学生社区（通过将学习信息）共享（III）（通过将课程和宣传纳入课程）。