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).

摘要CTS-0318999 C。Hrenya，科罗拉多大学，博尔德气固流动是无处不在的，虽然没有得到很好的理解。 一项对固体处理厂的研究表明，80%的工厂遇到了管道堵塞等固体处理问题，这些操作的性能通常只有设计的40%-50%。 此外，对于流化催化裂化装置，即使可靠的经验关联式也常常是不够的。 拟议的GOALI努力旨在推进与通常凭经验处理的现象（即淘析）相关的基本知识。 淘析是指在鼓泡气体流化床中携带细粒。 虽然在过去的二十年里，文献中已经提出了50多个淘析相关性，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，甚至淘析的定性性质也可能是反直觉的。 例如，已知向流化床中添加细粒可提高相对粗颗粒（即，具有大于床操作时的表观速度的终端速度的颗粒）。 为了更好地预测淘析现象，提出了建模和实验相结合的努力。 注意力将集中在一个二元系统组成的两个物种，不同的大小和密度。 作出这一选择的动力有两方面： (i)该体系是Millennium Chemicals（该提案的两个工业合作伙伴之一）特别感兴趣的，和（ii）二元体系代表多分散体系的最简单形式。 建模工作将基于动力学理论类比。 初步的工作表明，现有的动力学理论模型中普遍假设的不同粒子之间的能量均分是不存在的。 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分量;这种驱动力的存在以前没有记录。 由于不同颗粒在床层和稀相区的分离（或分层）将影响系统流体动力学（从而影响淘析），因此需要对非均分效应的影响进行调查。 因此，拟议的研究的第一部分将涉及非均分（和非麦克斯韦）效应的二元系统的动力学理论的推导。 由此产生的continunum理论将被纳入两个CFD（计算流体动力学）代码：一个标准的欧拉-欧拉框架（两相被视为连续体）和一个新的多相粒子在细胞（MP-PIC）制定开发的Arena流（该提案的工业合作伙伴）。 后者的配方的一个独特的功能是结合欧拉和拉格朗日的方法来粒子相，这使得计算效率的描述系统与多种粒子类型。 与以往的研究不同，拟议的工作的实验部分将涉及由两个B组物种的大小和密度不同的床淘析测量。 将获得每一物种的总通量和局部通量测量值。 将模型应用于实验系统将代表第一次没有经验主义的淘析预测（即，无可调参数）。 模型预测和实验数据之间的比较将表明非均分效应对床流体力学的影响，以及欧拉欧拉和MP-PIC框架在预测淘析中的可行性，这对两个工业合作伙伴都具有极大的兴趣。 这项工作是由每个合作伙伴的综合和互补利益的动机：科罗拉多大学（多分散颗粒系统），千年化学品（淘析），和阿里纳流（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，年度会议和PI和博士生对两个工业基地的长期访问。 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，这是目前的治疗方法能够扩展到两种粒径以上之前所需要的，（ii）在颗粒技术领域培训研究生，这已被确定为国家的需要，以及（iii）与技术社区和学生社区分享所学到的信息（通过纳入课程和推广）。