生物反应器的CFD模拟及结构设计

利用计算流体力学（CFD）软件Fluent,以多重参考系法对发酵行业中的发酵罐搅拌流场进行整体数值模拟。基于标准的κ-ε紊流模型模拟了发酵罐内的流场分布,分析了垂直面和水平面上液相流的流场分布及规律,可为搅拌器的结构设计提供参考。     

基于FLUENT软件的管式搅拌反应器流场的数值模拟

运用商业计算流体力学(CFD)软件FLUENT对一种新型管式搅拌反应器进行流场模拟,用GAMBIT建立流场实体模型,采用标准k-ε湍流模型以及多重参考系法(MRF)处理搅拌桨区.结果表明,计算所选模型能较准确地预测搅拌反应器的速度场、压力场及湍流动能分布,考察流量为1 m3/h时不同搅拌转速对反应器内部混合的影响,此时对应的最佳搅拌转速为50 rpm左右.模拟结果将为实验研究提供适当的操作参数,对搅拌反应器的优化和放大具有一定参考价值.     

搅拌反应器中计算流体力学数值模拟的影响因素研究进展

回顾了搅拌反应器中计算流体力学（CFD）数值模拟方法的研究历程,包括搅拌桨叶边界条件法、内外迭代法、滑移网格法、多重参考系法、快速照相法等方法;结合各种模拟方法的特点,对机械搅拌反应器数值模拟过程中的挡板的存在、尾涡的消除、复杂桨叶类型的模拟、网格精度的影响、湍流模型的选择、离散格式的差异等几个因素的影响作了分析。提出了搅拌反应器的CFD数值模拟仍有待深入研究。     

搅拌反应器内计算流体力学模拟技术进展

综述了计算流体力学(CFD)技术应用在搅拌反应器的进展情况。重点对搅拌反应器内流动场模拟的各种处理方法,包括"黑箱"模型法、内外迭代法、多重参考系法和滑移网格法,进行了介绍与评价,指出了各种方法所具有的特点及存在的问题。阐述了搅拌反应器内CFD技术的发展方向,并就国内的研究现状进行了简单概述。     

甲醇反应器的CFD模拟与换热优化

混合气制备甲醇是目前较为常用的工业生产甲醇方法,利用CFD软件模拟甲醇的固定床反应器,在Fluent中输入主副反应的动力学,得到模拟结果并针对该强放热反应提出设备换热上的优化方案,在提高甲醇产量的同时,保证反应器内部有较高的正向反应速率。     

催化裂解法制备碳纳米管中试反应器优化研究

对催化裂解法(CVD)间歇制备多壁碳纳米管(CNTs)的中试流化床反应器的结构进行优化研究,以期简化结构、改变出料方式、实现半连续化操作。实验结果表明:床层内置加热器开启,CNTs产量下降15%,床层阻力增加67%;预热层高度为零,反应4h,产率最高为9.2g/g;催化剂量为100g,最佳匣钵高度是35cm;将间歇操作调整为半连续操作,生产周期将从24.0h降为8.5h。     

搅拌式反应器的模拟与优化设计

综述了计算流体力学（CFD）技术在搅拌式反应器中的研究进展。着重讨论了搅拌式反应器中流场的模拟方法,包括“黑箱”模型法、内外迭代法、多重参考系法和滑移网格法,并指出了CFD技术的发展方向。在该基础上,对反应器内流场的数学模型进行了介绍与评价。最后提出应用人工神经网络技术与遗传算法,优化生物反应的工艺操作条件,并结合CFD技术,实现生物反应器的结构优化,从而达到对生物反应系统整体优化的目的,以指导实验与工业生产。     

聚丙烯中试装置环管反应器的模拟

通过对中石油75kg/h聚丙烯中试装置环管反应器的分析和研究,建立了数学模型。通过对模型的求解,得到固含量、单体浓度、活性中心浓度、氢气浓度与环管反应器长度之间的关系,为中试装置环管反应器的操作优化提供了依据。     

自由基聚合反应器中多尺度流场的模拟进展

自由基聚合过程中,由于混合、传递及聚合反应的相互作用使得反应器内部存在复杂的多尺度流场,例如宏观尺度的速度、浓度、温度分布,介观尺度的液滴粒径分布,微观尺度的聚合反应速率、聚合物分子量和多分散性指数分布。这些复杂的多尺度流场分布使得聚合反应器的模型化研究成为难题。本文较为系统地介绍了自由基聚合反应器中存在的多尺度现象;简述了微观尺度聚合物性质流场分布的模型化与模拟研究方法;从悬浮聚合和乳液聚合两个方面介绍了介观尺度液滴粒径分布的模拟研究进展;从非理想混合的角度阐述了宏观尺度多相流流场分布的研究进展。最后,本文分析了多尺度模型的耦合求解方法。本综述也有本文作者对这个领域的初步观点,可为聚合反应器的设计、优化和放大提供参考。     

计算流体力学在模拟生化反应器中的应用研究

计算流体力学是生化反应器模拟研究的重要手段，简述了流体力学理论研究概况及其在搅拌式生物反应器，气升式生物反应器中的应用，并指出了进一步研究的方向。     

300 kg/a规模流化床制碳纳米管中试研究

采用Ni-Mg-O复合氧化物催化剂进行了流化床甲烷催化裂解法制碳纳米管的中试实验,研究了主要操作变量对甲烷转化率、催化剂产碳率、产品团聚率及催化剂损失率的影响,得到了适宜的操作条件为：甲烷进气流速16~19 cm/s、催化剂粒径150~220 μm、催化剂加入量50~60 g、反应温度650~700 ℃、反应时间120~140 min。多批次重复性实验表明,在选定的操作条件下,甲烷转化率约为30 %,催化剂产碳率约为10 gCNTs/gCAT。对纯化后的产品进行SEM及TEM形貌表征显示,制得的碳纳米管管径均匀,中空结构明显,碳纳米管的外径为10~30 nm,内径为2~5 nm。     

Production of hydrogen and carbon nanotubes from methane decomposition in a two-stage fluidized bed reactor

Methane decomposition over a Ni/Cu/Al₂O₃ catalyst is studied in a two-stage fluidized bed reactor. Low temperature is adopted in the lower stage and high temperature in the upper stage. This allows the fluidized catalysts to decompose methane with high activity in the high temperature condition; then the carbon produced will diffuse effectively to form carbon nanotubes (CNTs) in both low and high temperature regions. Thus the catalytic cycle of carbon production and carbon diffusion in micro scale can be tailored by a macroscopic method, which permits the catalyst to have high activity and high thermal stability even at 1123 K for hydrogen production for long times. Such controlled temperature condition also provides an increased thermal driving force for the nucleation of CNTs and hence favors the graphitization of CNTs, characterized by high resolution transmission electron microscopy (HRTEM), Raman spectroscopy and XRD. Multistage operation with different temperatures in a fluidized bed reactor is an effective way to meet the both requirements of hydrogen production and preparation of CNTs with relatively perfect microstructures.     

Parametric study for the growth of carbon nanotubes by catalytic chemical vapor deposition in a fluidized bed reactor

Multiwalled carbon nanotubes have been produced from H₂-C₂H₄ mixtures on Fe-SiO₂ catalysts by a fluidized bed catalytic chemical vapor deposition process. Various parameters such as the catalyst preparation, the residence time, the run duration, the temperature, the H₂:C₂H₄ ratio, the amount of metal deposited on the support have been examined. The influence of these parameters on the deposited carbon yield is reported, together with observations of the produced material. This process allows an homogeneously distributed deposition of nanotubes (10-20 nm diameter), that remain anchored to the support.     

基于MP-PIC方法的冶金硅氢氯化流化床反应器模拟

冶金硅氢氯化流化床是目前多晶硅生产工艺中实现四氯化硅（silicon tetrachloride, STC）循环利用的关键反应器。基于MP-PIC方法建立了冶金硅氢氯化流化床反应器模型。模型中反应源项采用总包反应动力学进行计算。在网格以及计算颗粒包含的真实颗粒数量无关性检验的基础上,对反应器内三氯氢硅（trichlorosilane, TCS）初始浓度进行了无关性检验。模型验证结果表明,模拟结果与实验值符合良好。反应器特征分析结果表明：TCS产率受化学平衡与气固两相流动因素共同控制;反应器操作压力对TCS产率的影响较小;提高进口H₂/STC摩尔比,可以提高TCS产率但会降低H₂的转化率。     

基于MP-PIC方法的冶金硅氢氯化流化床反应器模拟

冶金硅氢氯化流化床是目前多晶硅生产工艺中实现四氯化硅（silicon tetrachloride, STC）循环利用的关键反应器。基于MP-PIC方法建立了冶金硅氢氯化流化床反应器模型。模型中反应源项采用总包反应动力学进行计算。在网格以及计算颗粒包含的真实颗粒数量无关性检验的基础上,对反应器内三氯氢硅（trichlorosilane, TCS）初始浓度进行了无关性检验。模型验证结果表明,模拟结果与实验值符合良好。反应器特征分析结果表明：TCS产率受化学平衡与气固两相流动因素共同控制;反应器操作压力对TCS产率的影响较小;提高进口H₂/STC摩尔比,可以提高TCS产率但会降低H₂的转化率。     

Polyelectrolyte-functionalized multiwalled carbon nanotubes: preparation, characterization and layer-by-layer self-assembly

Two kinds of polyelectrolyte: polyacrylic acid (PAA) and poly(sodium 4-styrenesulfonate) (PSS), were grafted onto the convex surfaces of multiwalled carbon nanotubes (MWNTs) by surface-initiating ATRP (atom transfer radical polymerization) from the initiating sites previously anchored onto the convex surfaces of MWNTs. The grafted polyelectrolyte can be efficiently quantified by the feed ratio of monomer to MWNT-based macroinitiator, and the maximum amount of grafted polymer is higher than 55 wt%. The polyelectrolyte-coated MWNTs resembled core-shell structures justified by the TEM images of the samples obtained, which provided direct evidence for the covalent modification of MWNT. FTIR, ¹H NMR and TGA were used to determine the chemical structure of the resulting products. Comparison of UV-Vis spectra demonstrated that the products were water-soluble, and that PSS was more effective for improving the water solubility of carbon nanotubes. Using the polyelectrolyte- and carboxylic acid-functionalized MWNTs as templates, and poly(2-(N,N-dimethylaminoethyl) methacrylate (PDMAEMA)/hyperbranched polysulfone amine (HPSA) and PSS as polycation and polyanion, respectively, layer-by-layer (LbL) electrostatic self-assembly was conducted in order to explore the application of the functionalized nanotubes. It was found that the functionalized MWNTs have a high efficiency for loading polyelectrolytes by the LbL approach (the adsorbed polymer quantity is higher than 10 wt% in one assembling step). TEM observations showed that the assembled polymer shell on the MWNT surfaces was very even and flat.     

Parameter setting on growth of carbon nanotubes over transition metal/alumina catalysts in a fluidized bed reactor

This work investigates the synthesis of multilayered carbon nanotubes (CNTs) using the catalytic decomposition of acetylene at 700-850 °C over Fe- and Ni-supported Al₂O₃ catalysts in a fluidized bed reactor. Thermogravimetric analysis showed that the CNTs grown in a fluidized bed reactor have better thermal stability and higher production yield, compared to that in a fixed bed reactor. The CNT production yield increased with the growth temperature, and Fe-catalyst exhibited greater activity than Ni-catalyst in the formation of CNTs. According to Arrhenius plots, the apparent activation energies for the growth of CNTs were estimated to be 25.6 kJ/mol for Fe-catalyst and 65.6 kJ/mol for Ni-catalyst. The as-grown CNT products were characterized by high-resolution transmission electron spectroscopy, N₂ physisorption, Raman spectroscopy, and X-ray diffraction. After purification, the CNT products were of the multilayered type, which were composed of perfect graphene layers. The results of this study demonstrate that the fluidized bed technology favors the large-scale production of CNTs with uniformity and at low cost.     

Effect of operating parameters inside circulating fluidized bed reactor riser with ring baffles using CFD simulation and experimental design analysis

The effect of the operating parameters on the system hydrodynamics and mixing inside two circulating fluidized bed reactor (CFBR) risers with different ring baffle configurations were investigated using computational fluid dynamics simulations and a 2⁴ factorial experimental design analysis. The operating parameters varied were the gas inlet velocity, and the mass flux, diameter and density of the solid particles, while the response variables were the standard deviation of the solid volume fraction (SVF) in the radial direction (SDSVF-RD) and the average SVF (ASVF). The results from the two CFBR risers with different ring baffle configurations showed a similar trend. The operating parameters that significantly affected the ASVF in both modified CFBR risers were the inlet gas velocity and solid particle mass flux, while those that significantly affected the SDSVF-RD were the inlet gas velocity and the inlet gas velocity–solid particle diameter–solid particle density interaction. For these systems, the lowest and highest ASVF was approximately 0.07 and 0.20, respectively, while the lowest and highest SDSVF-RD was 0.01 and 0.04, respectively. The low variability of the solid particle distribution and the high solid particle concentration will be suitable for chemical reactions. All the obtained results could be explained in terms of the system hydrodynamics. Finally, regression models to predict the mean solid particle concentration and variability of solid particle distribution in the system were obtained.     

A computational fluid dynamics design of a carbon dioxide sorption circulating fluidized bed

A kinetic theory based hydrodynamic model with experimentally determined sorption rates for reaction of CO₂ with K₂CO₃ solid sorbent is used to design a compact circulating fluidized bed sorption‐regeneration system for CO₂ removal from flue gases. Because of high solids fluxes, the sorber does not require internal or external cooling. The output is verified by computing the granular temperatures, particle viscosities, dispersion, and mass transfer coefficients. These properties agree with reported measurement values except the radial dispersion coefficients, which are much higher due to the larger bed diameter. With the solid sorbent prepared according to published information, the CO₂ removal percentage at the riser top is 69.16%. To improve the CO₂ removal, an effort is needed to develop a better sorbent or to simply lower the inlet gas velocity to operate in a denser mode, leading to a larger system. Also, the effect of temperature rise on the removal efficiency is investigated. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

CFD在自吸反应器气液流动和传质特性研究中的应用

针对配置气体分布器的六叶轮自吸反应器建立了欧拉气液两相流三维瞬态模型,耦合Higbie气液传质模型,采用CFX软件对其气液混合过程的流场、气含率、吸气速率及溶氧传递过程进行数值模拟,获得了反应器的流动特性、气液分散性能、吸气特性及气液传质特性.分析了反应器内水平及竖直位置上的流型特征及溶氧传递性能,结合实验数据及经验关联式对比分析了对气含率及吸气速率的预测作用.结果表明,六叶轮转子及其配置的气体分布器可以获得较均匀的气液混合,气含率及吸气速率的预测与实验值偏差分别为5.2% 和17.6%,模拟发现在反应器底部近壁处溶氧及混合效果不佳.