炼油减压精馏塔汽提工艺传质过程模拟与分析

为了揭示减压塔汽提工艺的传质过程特性,进而改进汽提操作,采用改进的减压精馏过程模拟方法和传质计算方法,分析了炼油常减压装置的汽提工艺的传质特点。在深化对于汽提工艺的理解基础上论证了采用填料汽提塔(段)的必要性以及设计、分析的基本方法。计算分析结果表明侧线汽提塔内填料分离性能保持恒定,汽提塔的分离效率与减压塔对应分离段接近,所以在设计和操作中应给予汽提塔(段)充分重视。减压塔底汽提段的工艺和水力学特点与侧线汽提塔相同。塔底汽提蒸汽质量流率应小于减压塔进料质量流率1%,否则将导致减压塔整体分离效率降低。     

Towards the Development of Advanced Packing Design for Distillation in Rotating Packed Beds

The growing demand for flexible and compact separation technologies has promoted the application of high‐gravity technology, like rotating packed beds (RPBs). Mass transfer characterization and packing design play an important role in the development of this technology. This article provides a systematic approach towards the evaluation of packing and the development of advanced packing design for distillation in RPBs. For the latter, an additive manufacturing approach is used to develop a new Zickzack packing for RPBs. The new packing provides better mass transfer at reduced pressure drop compared to available conventional packings, while being competitive in terms of mass transfer with the industrially applied rotating zigzag bed at significantly reduced pressure drop.     

Well-developed mass transfer in axial flows through randomly packed fiber bundles with constant wall flux

An analysis of the effects of fiber packing on mass transfer coefficients for axial fluid flow through fiber bundles with uniform wall flux in the well-developed limit is presented. The finite element method is used to solve the governing momentum and conservation of mass equations. The effective mass transfer coefficient depends strongly on fiber packing. Randomly packed fiber bundles have much lower mass transfer coefficients than regularly packed fiber bundles. Mass transfer rates are controlled by the lowest fiber packing regions through which most of the flow occurs.     

规整填料塔多元蒸馏过程混合型模型的模拟

填料塔精馏过程的模拟设计大多采用平衡级模型,但由于单一板效率值的难以确定,很多场合模拟很不成功;而新提出的非平衡级模型认为塔内传质传热均处于非平衡状态,由于方程数和经验性参数多,模型求解非常困难。文章针对规整填料的特点,建立了规整填料塔蒸馏过程的一种混合型模型,模型的主要特征是认为气液二相传质处于不平衡状态,而传热处于平衡状态。模型建立在实际填料基础上,既舍去传统的平衡级模型不确定性,又省略了非平衡级模型中复杂的经验性传热系数和液相传质系数的计算。模型计算值和实验值符合较好,也证实混合型模型既反映实际,又使模型求解变得相对容易。     

Mass transfer characteristics in a rotating packed bed with split packing

The rotating packed bed (RPB) with split packing is a novel gas–liquid contactor, which intensifies the mass transfer processes controlled by gas-side resistance. To assess its efficacy, the mass transfer characteristics with adjacent rings in counter-rotation and co-rotation modes in a split packing RPB were studied experimentally. The physical absorption system NH3–H2O was used for characterizing the gas volumetric mass transfer coeffi-cient (kyae) and the effective interfacial area (ae) was determined by chemical absorption in the CO2–NaOH sys-tem. The variation in kyae and ae with the operating conditions is also investigated. The experimental results indicated that kyae and ae for counter-rotation of the adjacent packing rings in the split packing RPB were higher than those for co-rotation, and both counter-rotation and co-rotation of the split packing RPB were superior over conventional RPBs under the similar operating conditions.     

PREDICTION OF MASS TRANSFER COEFFICIENTS IN REGULAR PACKED COLUMNS

Developments in the area of packed columns, particularly structured packed columns, are ongoing, specifically in the area of liquid-liquid extractions. Accurate predictions of mass transfer coefficients lead to more accurate design of columns. In the present study, mass transfer coefficients were measured experimentally for packed columns of different heights to study the effect of packing height and specific area. Two experimental pilot regular packed extraction columns were examined using toluene/acetic acid/water and n-butyl acetate/acetic acid/water systems. Based on the results, a novel model for prediction of effective diffusivity has been proposed that is a function of column height and specific area. The mass transfer coefficients obtained by this prediction were compared with other models. The results of this new model are in good agreement with the experimental data. Therefore, this new model can be used to design better regular packed columns.     

Investigation on catalytic distillation for ethyl acetate production with different catalytic packing structures

The catalytic packing is the core component of the catalytic distillation, and how the catalyst exists in the packing has significant influence on the process. To investigate the effect of catalyst packings on the catalytic distillation process, the classical ethyl acetate reactive distillation system was utilized, and a supported catalytic packing(SCP) was prepared in comparison with the conventional tea-bag catalytic packing(TBP). Laboratory scale experiments showed that the ethyl acetate conv...     

A corrugation geometry based model for efficiency of structured distillation packing

Although the structured packing is a well established gas–liquid contacting device, the understanding of its function is insufficient and often leads to poor exploitation of the available phase separating potential. This is a consequence of a rather superficial approach to modelling the packing performance through the years resulting in a lack of information on the nature and extent of interaction between counter-currently flowing gas and liquid phases and the micro and macro geometry of a rather ordered structure with a pronounced flow discontinuity at the transition among packing elements. This paper addresses the relation between the fluid-dynamics imposed by packing geometry and the mass transfer efficiency, and introduces a performance prediction method which does not require packing specific constants to describe mass transfer coefficients of phases.     

Mass transfer in structured corrugated packing

The performance of structured corrugated packing has been simulated by establishing mechanistic models for liquid distribution, liquid flow on the packing surface and mass transfer. The models were used to investigate the effect of packing height, liquid load, initial maldistribution as well as differing initial distribution and solid-liquid contact angle on the packed column performance. Wetted surface area is the primary value of interest and the simulated results compare very well with those predicted by Onda (1968). The results clearly demonstrate that the wetted surface area is a strong function of the solid-liquid contact angle. Other predicted values such as mass transfer coefficients and overall height of a transfer unit show reasonable agreement with published data.     

Performance of combined mesh packing and sieve tray in distillation

The hydraulic and mass transfer performance of a combined knitted mesh packing and sieve tray has been measured for the distillation of methanol-water mixtures. It was found that by adding a shallow bed of packing, the Murphree tray efficiency increased by 40–50% over a wide range of concentrations and flow rates. This increase in tray efficiency can be attributed to a much smaller and more uniform bubble formation on the packed tray. Hydraulic measurements have shown that the packed trays have lower weeping and entrainment, as well as slightly higher froth heights and pressure drops.     

三元恒沸精馏生产无水乙醇工艺研究及共轭环的应用

用CHEMCAD软件对乙醇、苯和水三元恒沸体系生产无水乙醇的工艺进行了模拟。根据模拟研究结果设计并建成了年产1 800 t无水乙醇的生产装置。主塔和回收塔中均采用共轭环塔填料。生产实践表明,共轭环塔填料具有传质效率高、单位填料层压降低和操作弹性大的特点;通过对生产工艺的优化,得到无水乙醇产品的苯质量浓度小于0.2 mg/mL,水质量浓度小于0.5 mg/mL。研究结果对设计无水乙醇生产装置有很好的参考价值。     

填充密度对中空纤维膜接触器精馏过程壳程传质的影响

探讨了填充密度对新型聚丙烯中空纤维膜接触器精馏过程中壳程传质的影响。中空纤维膜接触器在填充密度为4.7%、9.5%、19%时均可在远离常规填料液泛线以上的气速范围操作。低填充密度下,壳程的Sherwood数理论值大于实验值,但填充密度较高时,实验值大于理论值。高Reynolds数有利于壳程传质,低填充密度时的Sherwood数高于高填充密度时。随着F因子逐步增大,壳程气相传质阻力随之变小,且膜接触器的填充密度越高,气相传质阻力越大。3种不同填充密度膜接触器的气相总传质系数随着接触器填充密度的增大而迅速减小,由391.84×10^-5 m·s^-1降低为83.28×10^-5 m·s^-1。     

Quantifizierung der Trenneffizienz einer strukturierten Packung mittels numerischer Simulation

The numerical simulation of the distillation and absorption/desorption process is made possible by coupling a transient two‐phase simulation in a structured packing with a model for the simulation of the species transfer. The two‐phase flow is modeled by the volume of fluid (VoF) method. The simulation of the locally resolved species transfer is conducted using the generalised continuous species transfer (GCST) model. The simulation data are evaluated for the separation efficiency of the tested packing by calculating the HETP value.     

Vapour- and liquid-side volumetric mass transfer coefficients measured in distillation column. Comparison with data calculated from absorption correlations

Volumetric mass transfer coefficients in liquid and vapour phases in distillation column were measured by the method consisting of a fitting of the concentration profile of liquid phase along the column obtained by the integration of a differential model to the experimental one. The mathematical model of distillation process includes mass and energy balances and the heat and mass transfer equations. The film model flux expressions with the convective transport contributions have been considered in the transfer equations. Vapour and liquid phases are supposed to be at their saturated temperatures along the column. Effect of changes of phase flows and physical properties of phases on the mass transfer coefficients along the column and non-ideal thermodynamic behaviour of the liquid phase have been taken into account. The concentration profiles of liquid phase are measured in the binary distillation of the ethanol-water and methanol-ethanol systems at total reflux on metal Pall Rings and Intalox saddles 25 mm in the column with diameter of 150 mm. The distillation mass transfer coefficients obtained by the fitting procedure are compared with those calculated from absorption data using Onda's, Billet's and Linek's correlations. The distillation heat transfer coefficients calculated from the model assuming saturated temperatures in both phases are compared with those calculated from the Chilton-Colburn and penetration model analogy between mass and heat transfer. The results have confirmed an agreement neither between distillation and from absorption correlations calculated mass transfer coefficients nor between analogy and from enthalpy balance calculated heat transfer coefficients. Also the concentration profiles obtained by the integration of the differential model of the distillation column using the coefficients from absorption correlation have differed from the experimental profiles considerably.     

Distillation studies in rotating packed bed with split packing

Rotating packed bed (RPB) with split packing has been developed recently to overcome the limitation of negligible tangential slip velocity between vapor and packing obtained with single rotating packing element of conventional RPB design. This work evaluates the performance of this contactor for separation of binary mixture methanol–ethanol by distillation. Experiments were carried out at total reflux condition. The height equivalent of a theoretical plate (HETP) of 2.9 cm was obtained at F-factor = 0.6 (m/s) (kg/m³)^0.5 and rotor speed of 1100 rpm. Comparison with distillation studies reported for this system in the literature indicated that the mass transfer performance of this rotor design was superior to that of conventional RPB. Analysis of the experimental data also suggested that the rotor speed influenced the overall volumetric mass transfer coefficient to a greater degree in this design.     

Experimental validation of a flexible modeling approach for distillation columns with packings

The two main concepts for the modeling of distillation columns are the equilibrium‐stage (EQ) and the nonequilibrium‐stage (NEQ). A model is presented which combines decisive features of both conventional concepts. Based on the idea of a reduced nonequilibrium‐stage (RNEQ), this model can be used for the simulation of distillation columns with packings. In contrast to the conventional NEQ approach, this model neglects the influence of liquid side mass‐transfer coefficients, which ultimately allows to come up with only one empirical equation describing the overall mass transfer. Thus, a considerable reduction in model complexity is reached, which allows for an efficient consideration of new experimental distillation results. Fitted to experimental data, the model is able to predict, how different pressures and chemical systems might affect the separation efficiency. By comparing calculation results with experimentally determined separation efficiencies for three different packing types, these valuable RNEQ qualities are illustrated. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3833–3847, 2014     

Hydrodynamic‐Analogy‐Based Modeling Approach for Distillative Separation of Organic Systems with Elevated Viscosity

A modeling approach based on hydrodynamic analogies is applied to predict the influence of elevated viscosity on the separation efficiency of distillation processes in structured packed columns. An advantage of this approach compared to traditional models based on the film theory is that separation columns can be described without empirical mass transfer coefficient correlations. The separation efficiency was evaluated for two systems with distinct viscosities at different gas and liquid loads and various operating pressures. Simulated concentration profiles and height of a theoretical plate (HETP) values were compared with the data obtained from own experiments. The developed model is capable of correctly predicting the differences in the HETP values of the two evaluated systems.     

规整填料精馏塔的设计计算

通过大量的文献调研，比较了规整填料精馏塔和板式塔的优缺点，对规整填料精馏塔内压降、传质及液泛时压降的计算公式进行了比较，总结出设计计算规整填料精馏塔的步骤与方法，为规整填料精馏塔的应用提供了基础。     

Analysis of packed distillation columns with a rate-based model

Multicomponent packed column distillation is simulated using a rate-based model and the simulation results are compared with the experimental results obtained from a 0.2 m diameter pilot-scale packed column. The simulation algorithm used is previously proposed by the authors, which based on an equation-tearing method for (6c+7) equations of one packing segment and the whole column is solved by an iterative segmentwise calculation with the overall normalized θ method for acceleration. The performance of two packings is examined by simulating the pilot-scale column experiments using the published correlations for estimating liquid and vapor phase mass transfer coefficients and an effective interfacial area.     

催化蒸馏合成乙二醇乙醚的过程模拟

修正了非平衡级速率模型,使之能适用于催化蒸馏过程的模拟.此催化蒸馏塔的精馏段和提馏段为一般的填料塔结构,而反应段为CR＆L公司提出的特定结构的催化剂填充层.采用专门测定此特殊结构的催化剂填充层的气膜和液膜传质系数关联式来计算反应段中的传质速率,用Onda的关联式计算精馏段和提馏段填充层中的传质速率.结合在NKC-01分子筛催化剂上环氧乙烷与乙醇反应的动力学方程式,采用Newton-Raphson技术完成了催化蒸馏合成乙二醇乙醚过程的模拟,结果是令人满意的.