径向流吸附器流体流动特性及其结构参数优化

径向流吸附器通常存在流体沿轴向床层分布不均匀,从而导致吸附剂利用率下降和空分系统运行安全性问题。通过对表征Z型径向流吸附器流动特性的微分控制方程中包含的结构参数进行量纲1化,系统地研究了各结构参数对吸附器内流体分布的影响。同时针对实验室已有的一台Z型径向流吸附器,采用理论求解和实验数据对照的方法验证了模型的可靠性。结果表明,减小吸附床层轴向高度和吸附剂颗粒直径能显著提高Z型径向流吸附器内流体分布的均匀性;当空气的运动黏度和其他结构参数不变时,吸附器的空气处理量在一定范围内变化对吸附床层内流体的均匀性影响不大。     

径向流吸附器流体流动特性及其结构参数优化

径向流吸附器通常存在流体沿轴向床层分布不均匀,从而导致吸附剂利用率下降和空分系统运行安全性问题。通过对表征Z型径向流吸附器流动特性的微分控制方程中包含的结构参数进行量纲1化,系统地研究了各结构参数对吸附器内流体分布的影响。同时针对实验室已有的一台Z型径向流吸附器,采用理论求解和实验数据对照的方法验证了模型的可靠性。结果表明,减小吸附床层轴向高度和吸附剂颗粒直径能显著提高Z型径向流吸附器内流体分布的均匀性;当空气的运动黏度和其他结构参数不变时,吸附器的空气处理量在一定范围内变化对吸附床层内流体的均匀性影响不大。     

真空变压吸附制氧径向流吸附器的流动特性模拟

真空变压吸附制氧是一个复杂的动态过程,深入了解真空变压吸附制氧过程中吸附器内的流动特性是吸附器设计与完善的基础.基于Fluent中的多孔介质模型,通过用户自定义函数功能,建立了真空变压吸附制氧用径向流吸附器的二维轴对称模型,研究了真空变压吸附首次和第二次循环中径向流吸附器的流动特性,对比分析了吸附剂颗粒直径、流道截面积...     

多床层径向反应器中床层的流场行为

在直径3m、高5m的大型多床层径向反应器冷模装置上,通过测定流体在流道和各分床层内的静压分布,考察了各分床层的流体流动行为和特征.结果表明,当流道静压差的均方根偏差小于1%时,各分床层静压差的均方根偏差小于5%,流体在各分床层的径向流速沿轴向分布均匀,流速最大偏差小于5%;当流道静压差沿轴向的差别大于10%时,则其沿轴向分布显著不均匀,且靠近流道静压变化梯度大的分床层的径向流速均匀性最差,床层上下端流速偏差达70%.Π型流动形式是动量交换型径向反应器的最佳选择,适宜的两流道静压差设计可实现径向流速沿床层轴向完全均匀分布。     

径向流固定床反应器的流动特性研究及结构参数的合理选择

径向流固定床反应器的操作状态和反应效果在很大程度上取决于反应器内穿越催化剂床层径向气流沿反应器轴向分布的均匀程度，亦即床层内催化剂负荷的均布程度。本文对此类反应器内的流动特性进行了研究，对立了描述反应器内流动规律的基本运动方程。研究结果表明，径向气流的轴向分布情况与反应器的流动结构型式、反应器内分流流道与合流流道截面积的比值、催化剂床层的阻力系数以及反应器的高径比等参数有关。并提出了如何合理选择反     

离心型径向固定床分气流道内局部动量交换系数

针对离心型径向固定床气体流道内变质量流动特点，在一套冷模实验装置上，分别采取Π型和Z型操作模式，测量并分析了两气流道内压力分布，发现分气流道内的压力沿气体轴向流动方向呈增加趋势，集气流道与之相反。根据颗粒床层压降分布不均匀度和采用Ergun方程求得的径向气速轴向分布，发现离心Π型均略优于离心Z型。通过对气流道内微元控制体进行流量和动量衡算，由颗粒床层径向气速轴向分布可依次得到分气和集气流道内气速、局部动量交换系数计算方程。相较于集气流道，分气流道内动量交换系数对压力测量误差的敏感度较小。分气流道中，整体动量系数几乎不随操作模式、气体流量和轴向位置发生变化；而局部动量交换系数仅是流速比u/u0的函数，随流速比增大先降低后保持稳定。根据实验结果，回归得到的分气流道局部动量交换系数计算方程的误差在11%以内，有望为气流道内局部压力计算和结构优化设计提供参考。     

径向流反应器流场分布的数值模拟分析

径向流反应器是一种高效节能反应器。为了深入研究四种不同流动类型的径向流反应器的流场分布特征,在验证模拟可行性的基础上,引入多孔介质模型,运用FLUENT软件对不同类型的径向流反应器内的流场进行数值模拟。在边界条件设置一定时,模拟分析四种类型径向流反应器内分流流道与集流流道间的压降沿轴向的变化程度,结果说明:离心流动的流体分布均匀度优于向心流动,П型离心的径向流反应器内部流场分布最均匀,其次是Z型离心流动、П型向心流动、Z型向心流动。     

空气预纯化的技术研究进展

空气预纯化在空分设备流程中起着保障整套设备安全运行的重要作用。本文综述了近年来国内、外空气预纯化技术的研究和应用情况。指出目前目前存在的问题是:工艺流程大多通过增加均压、多塔循环等工艺步骤来提高空气预纯化效果,但系统尺寸较大、流程较复杂;吸附剂大多采用单一吸附剂、几种混合吸附剂或复合吸附剂来纯化气体,但纯化效果不理想且成本较高;吸附器大多采用立式轴向流、卧式垂直流、立式径向流等结构,通过改进气流分布器、改善分子筛布局及装填方式等提高吸附效率,但受到场地、能耗等因素限制。未来的研究重点应放在工艺流程的改进及开发新型模块式流程系统、原有吸附剂的改性及寻找新型吸附剂材料、原有吸附器结构的改进及开发新型吸附器结构等方面。     

丁烯氧化脱氢径向床反应器流体力学特性研究

流体沿催化剂床层轴向高度均匀分布是丁烯氧化脱氢径向床反应器保持较高性能的必要条件。应用计算流体力学(CFD)软件对径向床反应器内的流场进行三维数值模拟计算,分别考察影响π型反应器和z型反应器内流场均布的关键因素。结果表明:高径比越小,π型反应器内流体分布越均匀,综合压降方面的考虑,高径比选10为最佳;内外流道截面积比对π型反应器的性能影响显著,当取值在1/3—1/2区间时,流场均布情况较好。提出了一种z型反应器内导流锥的设计方法,适当尺寸的导流锥引入明显改善了z型反应器内的流体均布程度。     

大型干法脱硫径向反应器流场数值模拟分析

利用CFD计算机模拟技术,对大型高炉煤气径向脱硫反应器进行流场模拟,分析┡形套装三通特殊结构的进气口对外分布器流道入口的气体分布和压降的影响;分析径向反应器的催化剂层气体分布均匀情况,优化反应器的设计参数。     

A Mathematical Model for Designing Optimal Shape for the Cone Used in Z-flow Type Radial Flow Adsorbers

Nonuniform flow distribution along the radial direction usually exists in a Z-flow type radial flow adsorber, which will decrease the utilization of adsorbent and the switching time and may result in operating safety problems in cryogenic air separation. In order to improve the uniformity of the flow distribution along the radial direction in the adsorber, a differential equation is derived through pressure drop analysis in the Z-flow type radial adsorber with a cone in the middle of the central pipe. The differential equation determines the ideal cross-sectional radii of the cone along the axis. The result shows that the cross-sectional radius of the cone should gradually decrease from 0.3 m to zero along the axis to ensure that the process air is distributed uniformly in the Z-flow type radial flow adsorber and the shape of the cone is a little convex. The flow distribution without the cone in the central pipe is compared under different bed porosities. It is demonstrated that the proposed differential equation can provide theoretical support for designing Z-flow type radial flow adsorbers.     

Investigation on a vertical radial flow adsorber designed by a novel parallel connection method

Due to the increasing global demand for industrial gas,the development of large-scale cryogenic air separation systems has attracted considerable attention in recent years.Increasing the height of the adsorption bed in a vertical radial flow adsorber used in cryogenic air separation systems may efficiently increase the treatment capacity of the air in the adsorber.However,uniformity of the flow distribution of the air inside the adsorber would be deteriorated using the height-increasing method.In order to reduce the non-uniformity of the flow distribution caused by the excessive height of adsorption bed in a vertical radial flow adsorber,a novel parallel connection method is proposed in the present work.The experimental apparatus is designed and constructed;the Computational Fluid Dynamics (CFD) technique is used to develop a CFD-based model,which is used to analyze the flow distribution,the static pressure drop and the radial velocity in the newly designed adsorber.In addition,the geometric parameters of annular flow channels and the adsorption bed thickness of the upper unit in the parallelconnected vertical radial flow adsorber are optimized,so that the upper and lower adsorption units could be penetrated by air simultaneously.Comparisons are made between the height-increasing method and the parallel connection method with the same adsorber height.It is shown that using the parallel connection method could reduce the difference between the maximum and minimum radial static pressure drop by 86.2％ and improve the uniformity by 80％ compared with those of using the height-increasing method.The optimal thickness ratio of the upper and lower adsorption units is obtained as 0.966,in which case the upper and lower adsorption units could be penetrated by air simultaneously,so that the adsorbents in adsorption space could be used more efficiently.     

Cyclic adsorption separation processes: analysis strategy and optimization procedure

An innovative analysis strategy and an optimization procedure have been developed with the purpose of design, evaluation and optimization of small- and large-scale units of cyclic adsorption processes using the classical Skarstrom's cycle: pressure swing adsorption (PSA) and vacuum swing adsorption (VSA).The system of partial differential equations of the dynamic simulator model was solved using a recent numerical technique developed within our group, based on an adaptive multiresolution approach, thus ensuring stability and accuracy. The simulator provides models for the multiple phenomena involved in fixed-bed adsorption: pressure drop, mass transfer resistance and energy balance.An extended parametric analysis is presented for the particular case of oxygen production from air by PSA and VSA: influence of the normalized purge flow rate, the high and low pressure values, dimensionless pressurization time, dimensionless production time, pressure drop and temperature in the bed.     

Liquid distribution and redistribution in packed columns-I Theoretical

When liquid is uniformly distributed at the top of a packed column it is found that there is a preferential flow to the wall, and early theoretical work has suggested that the observed radial velocity is proportional to the radial gradient of axial velocity. A set of consistent boundary conditions has not been found. In this paper the experimental observation of preferential liquid flow is interpreted as a difference in permeability between the wall and bulk region of packing, and the existence of a potential for liquid redistribution is inferred from an examination of experimental work on two-phase flow in porous media, and of the internal consistency of the early relation between radial velocity and the radial gradient of axial velocity. The existence of a potential for liquid redistribution, and a difference in permeability between the wall and bulk regions are shown to lead to a differential equation describing liquid distribution in the packing, defined by consistent and well-posed boundary conditions that are determined from the physical analysis.The solution to the partial differential equation describing redistribution from an initial axisymmetric distribution is given.     

π型向心径向流吸附器变质量流动特性研究

对径向流吸附器内变压吸附(PSA)制氧的变质量流动规律进行研究,有助于准确掌握吸附过程及床层内的变量因素对制氧性能的影响。对π型向心径向流吸附器建立气固耦合的两相吸附模型,并对其PSA制氧过程进行了数值模拟研究,得到了床层内氧气浓度分布、温度分布以及产品气浓度的变化规律。结果表明：首次循环结束时床层内氧气最高摩尔分数可达66.02%,回收率29.2%。非稳定循环期间,氧气摩尔分数从66.02%升高至 97.5%,回收率从29.2%提高至38.5%。循环达到稳定后,床层内氧气摩尔分数最高可达98.6%,回收率38.9%左右,且达到稳定状态后床层内气固两相温差减小,逐渐达到热平衡。获得了吸附器内部气体与吸附剂两相间的传质、传热过程,为π型向心径向流吸附器用于PSA制氧提供技术支持。     

A strategy for tailored design of efficient and low‐pressure drop packed column chromatography

Packed chromatographic column, with higher efficiency and lower pressure drop is designed by using inert core adsorbents as stationary phase. The analytical solutions for moments and height equivalent to a theoretical plate (HETP) are given under the conditions of linear adsorption kinetics by taking into account of the axial dispersion, film mass‐transfer resistance, intraparticle diffusion resistance, and the sorption rate for chromatographic column packed with inert core adsorbents. By minimizing HETP, a nonlinear algebraic equation was derived to predict the optimized value of the inert core radius. For a given adsorbent with the optimized inert core radius, a strategy was presented to tailor the design of new packed chromatographic column with higher efficiency and lower pressure drop. As an example for supercritical carbon dioxide chromatography, reduced equations in terms of dimensionless inert core radius were derived by “order of magnitude” analysis. The quantitative analysis shows that the major benefit of the inert core adsorbent is a shorter diffusion path compared to conventional fully porous particles. The shorter diffusion path reduces dispersion of solutes and minimizes peak broadening leading to lower pressure drop while maintaining high‐separation efficiency. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

两段炉内的压降以及速度分布

化学热回收两段组合式气化炉有效地提高了高温合成气的显热回收。为进一步了解该新型两段炉内气体的流动规律,在自行搭建的冷模实验装置上,考察了该组合式两段炉内的二段床层压降以及速度分布情况。研究表明,采用Montiller经验公式能够准确预测二段固定床的床层压降,当气体达到二段床层表面时,将产生一个冲击区。拟合得到单喷嘴顶喷的轴向速度衰减公式以及四喷嘴撞击后的向下径向射流速度衰减公式。轴向速度的径向分布中,中心气速最大并且衰减最快,采用四喷嘴对喷的形式达到管流区所需的轴向距离较单喷嘴顶喷小1.8D。     

流化床管式分布器内流场模拟和布气性能分析

以催化裂化装置（FCCU）再生器的管式气体分布器为研究对象,对流化床管式气体分布器的布气性能进行了分析。首先,对气体分布器分支管内的流场进行数值模拟,计算结果表明沿分支管内气体流动方向,压力逐渐增大,截面流量逐渐减少,沿程喷嘴流量逐渐增大;同时分支管上游入口还存在着明显的偏流现象,从而导致了上游喷嘴的出口流量小于设计流量,下游喷嘴的出口流量高于设计流量,造成流化床内非均匀布气。然后,依据分支管的变质量流动特点,将一般变质量流动的动量方程用于分析分支管内的流动过程,表明分支管的流动过程属于“动量交换控制模型”,具有始端静压低末端静压高的特点,固有压力分布不均匀的特征。这种不均匀的压力分布导致了喷嘴布气不均匀和磨损等系列问题。最后,结合流化床内的压力特点,综合分析气体分布器的分支管压降和喷嘴压降,明确了喷嘴出口流量与分支管压力分布的关系,喷嘴临界压降与设计压降的关系,结论表明分支管的结构改进可以优化和改善分布器的布气性能。     

径向流动反应器流体力学特性研究

本文提出了表征径向流动反应器内流体流动规律的数学模型.该模型为一特殊的二阶微分方程的边值问题.对于Ⅱ型流动:Au′u″+Bu′u+Cu~2=0对于Z型流动:Au′u″+Bu′u+Cu′+Eu~2+F(1-u)~2=0边界条件为y=0,u=1;y=1,u=0式中模型参数A、B、C、E、F决定于径向反应器分布流道结构尺寸、穿孔阻力系数和径向床层特性等因素.为简化Ⅱ型径向反应器边值问题的求解过程,本文推荐一种解析求解方法.该模型应用于径向氨氧化炉操作工况和径向氨合成塔设计工况的模拟,揭示了径向流动反应器内的流体力学特性.