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 - 0318999 c。科罗拉多大学的Hrenya， boulder - gas -solid流动无处不在，尽管还没有被很好地理解。对固体加工厂的一项研究表明，80%的工厂遇到了固体处理问题，如管道堵塞，而这种操作的性能通常只有设计的40- 50%。此外，流体催化裂化装置的可靠经验相关性往往是不够的。拟议的GOALI努力旨在推进与通常经验性处理的现象（即洗脱）相关的基础知识。洗脱是指在鼓泡的气体流化床中细颗粒的结转。虽然在过去的二十年中，文献中提出了50多种洗脱相关性，但实验和经验预测之间的分歧通常超过100%，在某些情况下可能相差超过100倍。此外，即使是洗脱的定性性质也可能是反直觉的。例如，已知在流化床中添加细颗粒可增加相对粗颗粒（即终端速度大于床运行时的表面速度的颗粒）的洗脱速率。为了更好地预测淋溶现象，提出了一种模拟与实验相结合的方法。我们将把注意力集中在由大小和密度不同的两个物种组成的二元系统上。这一选择的动机是双重的：(i)该系统对千年化学公司（本提案的两个工业合作伙伴之一）特别感兴趣，（ii）二元系统代表了多分散系统的最简单形式。建模工作将基于动力学理论类比。初步工作表明，不同粒子之间的能量均分是不存在的，而这是现有动力学理论模型的共同假设。初步计算还表明，非均分会产生尺寸/密度偏析驱动力的额外成分；这种驱动力的存在以前没有文献记载。由于床层和干舷段不同颗粒的分离（或分离）将影响系统流体动力学（从而影响洗脱），因此需要对非均分效应的影响进行研究。因此，提出的研究的第一部分将涉及二元系统动力学理论的推导，其中包括非均分（和非麦克斯韦）效应。由此产生的连续体理论将被整合到两个CFD（计算流体动力学）代码中：一个是标准的欧拉-欧拉框架（两相都被视为连续体），另一个是Arena-Flow（该提案的工业合作伙伴）开发的新的多相细胞内颗粒（MP-PIC）公式。后一种公式的独特之处在于结合了欧拉和拉格朗日方法来描述粒子相，它允许对具有多种粒子类型的系统进行有效的计算描述。与以前的研究不同，拟议工作的实验部分将包括在两种大小和密度不同的B族物种组成的床上进行洗脱测量。将获得每一物种通量的总体和局部测量值。将模型应用于实验系统将代表第一个没有经验主义（即没有可调参数）的洗脱预测。模型预测和实验数据之间的比较结果将表明非均分效应对床层流体动力学的影响，以及欧拉-欧拉和MP-PIC框架在预测淋滤方面的可行性，这对两个工业合作伙伴都非常感兴趣。这项工作的动机是每个合作伙伴的综合和互补利益：科罗拉多大学（多分散颗粒系统），千年化学公司（洗脱）和Arena-Flow （MP-PIC方法）。提议的努力旨在确保合作伙伴之间的持续互动和交流，每年举行会议，并由PI和博士生对两个工业基地进行长期访问。这项工作的更广泛影响包括：(i)对多分散系统有更基本的了解，这是在目前的处理方法可以扩展到两种粒径以上之前需要的；（ii）在粒子技术领域培训研究生，这已被确定为国家需要；（iii）与技术界和学生界分享所学信息（通过纳入课程作业和外展）。