【作者】 冯子洋；

【导师】 张金利；

【作者基本信息】 天津大学 ， 化工过程机械， 2013， 博士

【摘要】 费托蜡与铁基催化剂的有效分离是实现浆态床反应器在费托合成过程中经济、高效、可靠运行的一个重要挑战。高梯度磁分离作为一类可选择的分离技术因为其低廉的资金投入、平缓的操作压差、较高的选择性、高效的分离效率以及它对催化剂的可回收性等优点，近年来得到了广泛的关注。本文分析了高梯度磁分离的过程机理，针对分离器的内部构造形式进行了理论研究，在此基础上建立了磁分离过程的数学模型，对磁场强度分布及磁场力分布进行了模拟计算。研究结果表明磁场力作为分离过程的主导因素取决于分离器内的磁场分布情况，磁场力与磁场强度及磁场梯度均成正比关系。然而，分离器内的磁场分布与其内部的导磁构件排列方式及外加均匀磁场大小有着密不可分的联系。本文以流体力学软件Ansys Fluent13.0为操作平台，利用有限元分析手段，以柱状金属丝为基本构造单元对分离器内导磁构件中金属格栅的线间距、格栅间距、格栅排列角度及外加磁场强度等影响因素进行了模拟研究。结果发现过高的线间距及不恰当的排列方式会在磁分离器内形成渗流通道，渗流通道容易导致分离过程中获得较低的分离效率及不稳定操作。同时，外加磁场对整体分离过程起着决定性的作用，当金属格栅无法达到饱和磁化强度时，外加磁场降低会使内部磁场强度迅速降低，从而导致磁场力的迅速减弱。计算结果揭示了格栅常规90°排列方式中存在渗流通道这一缺陷，通过优化改进获得最为合理的分离条件为：外加磁场强度398089A/m，2mm线间距，2mm格栅间距以及45°的格栅排列角度。本文以费托合成中蜡及铁基催化剂分离这一典型工业过程为背景，依据上述理论分析结果，设计出一整套沉降加高梯度磁分离的工艺流程，磁分离器采用电磁线圈产生的纵向均匀磁场作为外加磁场，使用三种金属丝间隔的格栅叠加作为内构件进行分离实验。实验考察了格栅金属丝间隔、格栅轴向间距、格栅排列角度、外加磁场强度对分离效果的影响，实验结果验证了模拟的可靠性。利用模型分析与实验验证相结合的手段，在优化的排列方式条件下（线间距2mm；格栅间距2mm；排列角度45°；外加磁场强度398089A/m）通过磁分离后的蜡中铁含量减少至30ppm，分离效率超过99.95%，达到了工业生产的要求。更多还原

【Abstract】 Separating the iron-based catalyst/wax mixture from Fischer-Tropsch synthesis(FTS) products is one of the most important challenges in the development of FTSslurry bubble column reactor. High gradient magnetic separation (HGMS), with theadvantages of low cost, negligible pressure drop, high selectivity, excellent separationefficiency and ability to recycle the magnetic particles, is a promising technique forthe catalyst/wax separation.The mechanism of the high gradient magnetic separation (HGMS) process wasinvestigated in this dissertation. A three-dimensional mathematical model wasestablished to describe the magnetic field and magnetic force distribution withmulti-wires for HGMS of catalyst particles from FTS wax. The calculation resultsindicated that the magnetic force, as the dominant influence factor of the separationprocess, is determined by the distribution of the magnetic field. The magnetic force isproportional to the magnetic field strength and the magnetic field gradient. However,the distribution of magnetic field in the separator was significantly associated with thematrix arrangement patterns and the background uniform external magnetic fieldstrength.Based on the hydrodynamic software Ansys Fluent13.0, this dissertation studiedthe influence factors in the separation involving the wire interval, the matrix axialdistance, the arrangement angle as well as the back ground uniform magnetic fieldstrength in the column-wire-based unit by means of finite element analysis. It wasfound that both the excessive wire interval and the improper matrix arrangementpattern can lead to the formation of percolation channel in the separator. Thepercolation channel is a negative factor causing lower separative efficiency andinstability of the separation operations. Moreover, the magnetic force acting on aparticle is also proportional to the external magnetic field strength, which is a veryimportant influence factor when the magnetization of the matrix was not saturated.The simulation results shows that there are percolation channel with the arrangementangle of90°, and the optimal condition is the matrix with the wire interval of2mm,the axial distance of2mm, the arrangement angle of45°and the external magneticfield strength of398089A/m. A high gradient magnetic separation process was designed for the catalyst/waxmixture separation coming from a typical industrial process of F-T synthesis. Thehigh gradient magnetic separator adopted vertical uniform magnetic field generatedby electromagnetic, and the matrices with three kinds of wire intervals were used asinner parts. In order to validate the simulation results, experimental investigationswere also carried out to disclose the effects of four main factors involving the wireinterval, the axial distance between matrices, the arrangement angle between matricesand the external magnetic field strength on the separation efficiency in HGMS.Through the experimental optimization (the wire interval of2mm; the axialdistance of2mm; the arrangement angle of45°and the external magnetic fieldstrength of398089A/m), the magnetic iron content of the catalyst/wax mixture canbe reduced to less than30ppm, with the separation efficiency higher than99.95%which was in well accordance with the prediction of the established multi-wiremodels.更多还原