GOALI: Segregation and Elutriation of a Binary Mixture

国家科学基金会-化学和运输系统颗粒和多相工艺计划(1415)提案编号：0650893主要研究人员：Hrenya，Christine附属：科罗拉多大学博尔德分校Proposal标题：GALI：二元混合物的分离和淋洗气固两相流动无处不在，尽管还没有被很好地理解。对固体加工厂的研究表明，80%的工厂遇到了固体处理问题，如管道堵塞，这些操作的性能通常只有设计的40%-50%。此外，即使是“可靠的”催化裂化装置的经验关联式也往往是不充分的。拟议的目标努力旨在促进与一种现象相关的基本知识，这种现象通常是通过经验处理的，即淘洗。淋洗是指在鼓泡的气态流态化床中携带细粉。尽管在过去的二十年里，文献中已经提出了50多个淋洗关联式，但实验和经验预测之间的不一致通常超过100%，在某些情况下，相差可能超过百分之一。对鼓泡床(稠密)和干舷(稀薄)区域的研究将并行进行。两个悬而未决的问题将推动这项工作：(I)什么物理机制(S)导致观察到的鼓泡床区的分离(解混)和鼓泡模式，以及(Ii)什么物理机制导致在干舷区观察到的与直觉相反的行为，在该区域中，已知向床层添加细粉会增加相对粗颗粒(即，终端速度大于床层运行的表面速度的颗粒)的淋滤率？假设粒子之间的相互作用在这两个区域都起到了关键作用。类似地，对在干舷观察到的违反直觉的行为，一个看似合理的解释是，预计细颗粒与向上移动的粗颗粒的下半部分优先碰撞(因为细颗粒由于其质量减少而以更高的速度移动)。粗颗粒底部的这种额外的碰撞力预计会导致它们的淋溶增加。这些假设将通过基于新的混合物动力学理论的双流体气固模型进行检验，该模型不涉及以前理论中的任何假设(近弹性、能量等分、麦克斯韦速度分布)。模型验证将使用本地和特定物种(物种速度和浓度)的测量进行。将开发一种新的探头，既能测量物种的速度和浓度，又能适应工业环境。由此得到的数据将是对两种非粘性材料的分离和淋洗的首次详细测量，并将首次表征非均匀颗粒对起泡行为的影响。此外，模型数据比较将是基于基本面(没有可调参数)来预测淋洗的首次尝试。广泛影响这项工作是由每个合作伙伴的互补利益推动的：科罗拉多大学(多分散和分离)、千禧大学(淋洗建模)和PSRI(流态化仪器和淋洗)。这个跨学科的团队在粒子技术方面拥有50多年的经验。产学互动将通过参与该项目的博士生的行业实习、博士生的共同建议以及定期会议和电话会议来促进。结果将通过标准方法(会议报告、同行评估出版物、网站等)与公众分享。通过将新模型整合到MFIX(www.mfix.org)中，MFIX是一个开源、免费的CFD代码，所有PI都有丰富的经验。拟议的工作还将涉及培训粒子技术领域的学生研究人员，这已被确定为国家需要。PI在让本科生参与研究和促进多样化劳动力方面有着良好的记录。

National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)Proposal Number: 0650893Principal Investigators: Hrenya, ChristineAffiliation: University of Colorado at BoulderProposal Title: GOALI: Segregation and Elutriation of a Binary MixtureGas solid flows are ubiquitous, though not well understood. A study of solids processing plants indicates that 80% of the plants experienced solids handling problems such as pipe blockage and that the performance of such operations was typically only 40-50% 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%, and in some cases may differ by a factor of more than a hundred.Intellectual MeritTo better predict the elutriation phenomenon, a combined modeling and experimental effort is proposed. Research on the bubbling bed (dense) and freeboard (dilute) regions will be pursued in parallel. Two outstanding questions will drive this effort: (i) what physical mechanism(s) lead to the observed segregation (de-mixing) and bubbling patterns in the bubbling bed region, and (ii) what physical mechanisms lead to the counter-intuitive behavior observed in the freeboard region in which the addition of fines to the 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)? It is hypothesized that particle particle interactions play a key role in both regions. Similarly, a plausible explanation for the counter-intuitive behavior observed in the freeboard is the expected preferential collision of fine particles with the bottom half of upwardly moving coarse particles (since the fines travel at a higher velocity due to their reduced mass). This additional collisional force on the bottom of the coarse particles is expected to lead to their increased elutriation. The hypotheses will be tested by means of a two-fluid gas-solid model based on a new kinetic theory for mixtures that does not involve any of the assumptions of previous theories (nearly elastic, equipartiton of energy, Maxwellian velocity distribution). Model validation will be carried out with measurements that are both local and species-specific (species velocities and concentrations). A new probe will be developed that is both capable of measuring species velocities and concentrations and is adaptable to an industrial setting. The resulting data will represent the first detailed measurements of segregation and elutriation of two non-cohesive materials, and will be the first to characterize the impact of non-uniform particles on bubbling behavior. Furthermore, the model data comparison will be the first attempt to predict elutriation based on fundamentals (no adjustable parameters).Broader ImpactsThis work is motivated by complementary interests of each partner: the University of Colorado (polydispersity and segregation), Millennium (elutriation modeling), and PSRI (fluidization instrumentation and elutriation). This interdisciplinary team has over 50 years of experience in particle technology. Industry-university interaction will be promoted via industrial internships of PhD students involved in the project, co-advising of PhD students, and regular meetings and telecons. The results will be shared with the public using standard methods (conference presentations, peer-evaluated publications, website, etc.) and via the incorporation of the new model into MFIX (www.mfix.org), an open-source, no-cost CFD code which all of the PI's have extensive experience with. The proposed work will also involve the training student researchers in the area of particle technology, which has been identified as a national need. The PI has a strong record in involving undergraduates in research and promoting a diverse workforce.