MEASUREMENT OF INTERFACIAL AREA AND MASS TRANSFER COEFFICIENTS BY CHEMICAL METHOD OF C02 ABSORPTION INTO AQUEOUS SOLUTIONS OF NaOH IN A MODEL COLUMN WITH EXPANDED METAL SHEET PACKING

The theory of gas absorption accompanied by fast pseudo-fast order reaction which considered dependences of diffusivity, kinetic constant and Henry's law constant on absolute temperature and ionic strength was used to obtain values of effective interfacial areas and mass transfer coefficients in gas and liquid phase.

Experimental measurement of carbon dioxide absorption from mixture with air was performed in a pilot-plant column with expanded metal sheet packing irrigated with sodium hydroxide solution.

Resulting liquid and gas-side mass transfer coefficients are compared with values obtained from physical Absorption measurement of carbon dioxide into water and with measurement of gas-side mass transfer coefficient for sulphur dioxide in the same column.

The differences between determined values are discussed.     

Mass Transfer In Trickle‐Bed Reactors With Structured Packing

An experimental investigation was carried out to examine the fluid dynamic and mass transfer behavior of structured packing, with the liquid and gas phase flowing co‐currently downwards in the column. Liquid to packing mass transfer coefficients for three positions within the pack were measured by an electrochemical method, varying both the liquid and gas loads as well as the physical properties of the liquid phase. Due to the high void fraction of structured packing, much higher liquid flow rates can be used than in traditional particle trickle‐beds. It was found that in the range studied, the gas superficial velocity has no effect on the mass transfer rate and thus, a general mass transfer correlation in terms of liquid Reynolds number only, was developed. Wetted areas and the radial distribution of liquid through the packing element were determined by a colorimetric method. Within the range of liquid flow rates investigated, complete wetting is not achieved, even with the low viscosity solutions. The measured ratios of hydraulic to geometric area, agree reasonably well with values predicted by existing relationships.     

Gas holdup and mass transfer in solid suspended bubble columns in presence of structured packings

Electrochemical gas absorption or biotechnical purification processes using structured packing as electrode or as biological support, respectively, may operate in bubble columns in presence of suspended solids. In both systems the knowledge of mass transfer rates from the liquid to the packing is important for the design of equipment. In the present investigation, the fluid dynamic behavior of a simple bubble column and a bubble column containing small size particles, both in presence of structured packing, was studied. Furthermore, mass transfer coefficients between the liquid and the structured packing were obtained by the electrochemical method. The influence of physical properties of the liquid phase, gas flow rate, kind and concentration of the suspended particles on both gas holdup and mass transfer was investigated. Correlations of the experimental data of mass transfer using dimensionless groups were derived and compared to previous correlations. Similarity with a heat transfer expression already used in two-phase systems was found.     

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.     

Gas/liquid mass transfer processes in a carbon dioxide/alkane system

A gas/liquid mass transfer process has been studied using carbon dioxide/alkane systems in a stirred vessel. Four linear alkanes (n‐heptane, n‐octane, n‐decane and n‐dodecane) have been used as the liquid phase in the present paper, and they have been employed to study the influence of the carbon length upon the mass transfer velocity. The mass transfer along the liquid phase has been studied using the mass transfer coefficient of the liquid phase, k_L. Pure carbon dioxide has been employed as the phase in all cases for this reason. The effects of the power supplied to the liquid phase and the gas flow rate upon the absorption process have also been analysed. Finally, the equations that allow calculation of the mass transfer coefficients have been applied for these systems, with acceptable results. Copyright © 2005 Society of Chemical Industry     

Interpretation of mass transfer measurements in bubble columns considering dispersion of both phases

Mass transfer measurements in two bubble columns with an inner diameter of 100 resp. 140 mm with the systems air/water/carbon dioxide and nitrogen/n-propanol/carbon dioxide have been evaluated with the axial dispersion model. The dispersion coefficients of both phases have been determined in separate investigations. As the results revealed a strong influence of the liquid viscosity, additional dispersion coefficient measurements have been carried out with the system air/glycol. It could be shown that the liquid phase dispersion coefficient decreases with increasing viscosity while the gas phase dispersion coefficient increases with increasing liquid viscosity. Both coefficients are strongly dependent on the gas throughput and the column diameter. Using these coefficients, the mass transfer coefficients have been calculated by fitting the calculated concentration profile to the measured values and by splitting the volumetric mass transfer coefficient with the experimental value of the interfacial are a. The results agree best with a correlation of Calderbank and Moo-Young.     

毛细管中泰勒流液侧传质特性及其强化机理的CFD模拟

采用计算流体力学（CFD）的方法,研究了圆管中泰勒流的液侧传质特性,分析了泰勒气泡上局部传质特性,并研究了气泡上升速度、液膜长度和液栓长度对液膜处和气泡半球帽处平均传质系数的影响。结果表明,泰勒气泡表面局部传质系数存在3个峰值,液膜处的平均传质系数随气泡上升速度增大显著增大,随液膜长度增大而减小,而半球帽处的平均传质系数随气泡速度和液膜长度的增大变化较小,即膜接触时间增加时,液膜处的传质系数降低,而半球帽处传质系数变化较小。另外,引入场协同原则对单元胞内速度场和浓度场进行分析,解释了局部传质特性及强化机理。最后,给出了分别预测短和长膜接触时间下泰勒流液侧体积传质系数的关联式,该式在较宽的管径尺度范围（0.25～3 mm）内的预测误差在±20%以内。     

A study of local liquid/solid mass transfer in packed beds under trickling and induced pulsing flow

Induced pulsing flow (by cyclic liquid feeding) in packed beds, operated in the trickling flow regime, is studied as a method of overall improvement of catalytic reactor operation. In this paper results are reported of experiments aimed at determining local and global liquid/solid mass transfer rates, mainly for the so-called fast mode of ON-OFF periodic liquid feeding, with frequencies of order 0.1 Hz. Such mass transfer data for the fast mode of induced pulsing are not available in the literature. Uniform 6 mm glass spheres and alumina cylindrical extrudates, of 1.5 mm diameter and a narrow distribution of lengths, are employed in the tests. For completeness, results are also reported for single-phase (liquid) and trickling flow through the same packed beds. A well-known electrochemical technique is employed to measure instantaneous local mass transfer coefficients by means of quite a few probes distributed throughout the bed. The hydrodynamic characteristics under the above conditions, reported in companion papers, are helpful in interpreting the new mass transfer data.There is a wide spread of the time-averaged local mass transfer rates, in all cases tested, apparently due to packing and flow non-uniformities. This spread is much smaller in the case of packed uniform spheres. In general, the benefits of cyclic liquid feeding are more evident in the packed bed of spheres than in that of cylindrical extrudates; for instance, with increasing mean liquid rate, induced pulsing tends to reduce the spread of local mass transfer coefficients, which suggests that more uniform fluids distribution is promoted. The imposed liquid pulses are reflected in the observed periodic variation of local mass transfer coefficients; the latter appear to decay along the bed in the same manner as the liquid pulses. Other trends of local mass transfer rates are identified and discussed in relation to measured variation of liquid holdup, under the same conditions. For packed spheres, the measured global mass transfer rates are in fair agreement with literature correlations obtained for the trickling flow regime, unlike the case of packed extrudates where significant deviation is observed.     

Absorption in packed towers with concurrent downward high-velocity flows—II: Mass transfer

Measurements were made of mass transfer coefficients with gas and liquid phase controlling resistance using a concurrent flow packed column with a wide range of operating conditions and four types of packing. Mass transfer coefficients were much larger than those obtainable in countercurrent towers. The results were correlated with dissipated energy values. The correlations obtained can be used to determine absorption efficiency. Experimental results show that the use of a high velocity concurrent flow column is particularly suitable when mass transfer is controlled by the liquid phase resistance with chemical reaction in the liquid.     

塑料花环填料的流体力学及传质性能研究

本实验用空气-水-氨体系,在内径为φ600 mm的塔中,对塑料花环填料进行了流体力学及传质特性的测试。结果表明花环填料通量大、压降低、在高液体负荷下具有极好的传质性能,而且耐腐蚀、不易堵塞。实验测定的塔填料因子和传质系数有设计参考意义。     

DYNAMICS OF FRACTIONATORS WITH STRUCTURED PACKING

A generalized dynamic mode! of a distributed staged (packed) fractionator is developed in this work. In particular we consider the dynamics of fractionators which employ structured packings as a means of achieving mass and heat transfer in multi-component systems.

The mathematical model is described by a large set of partial and ordinary differential equations coupled with non-linear algebraic constraints (PODAEs). These equations arise from the mass and energy balances on a distributed column-section together with the fluid dynamic relations. A computational algorithm is developed which employs a polynomial approximation leading to a large differential-algebraic equation (DAE) system. This is solved using standard implicit DAE algorithms.

In this work, the liquid holdup and transfer coefficients (both mass and heat) are computed from established correlations and detailed thermodynamic relations. This differs from most of the previous work reported, which used very simple correlations based on a single variable such as liquid or vapour rate. The results show that the more rigorous computation of transfer coefficients is essential to the veracity of the model.

The model has been applied to the case of an industrial depropanizer which uses a Mellapak 250Y structured packing. The generalized model can be used to study the control and optimization of such fractionators, which are becoming more prolific in the petroleum and related industries.     

Mass transfer studies on split-packing and single-block packing rotating packed beds

In this work, SO₂ absorption in aqueous NaOH (gas side mass transfer resistance controlled system) and O₂ desorption from the water (liquid side mass transfer resistance controlled system) are experimentally evaluated for enhancement in the controlling side volumetric mass transfer coefficient using the novel split-packing and conventional single-block rotating packed bed (RPB) designs. In the split-packing RPB design, mass transfer characteristics for co-rotation and counter-rotation of adjacent rings are studied. For the SO₂ absorption system, results show a significant reduction in the controlling mass transfer resistance for split-packing over single-block packing for large RPBs. However, the mass transfer coefficients for co- and counter-rotation are comparable. For the O₂ desorption system, at low rotation rates, the split-packing design gives higher mass transfer rates compared to the single-block packing. This difference disappears as the rotation rate is increased. Possible reasons for the experimental observations are speculated. The results suggest the split packing design to be more suitable for gas side mass transfer resistance controlled systems.     

MEASUREMENT OF INTERFACIAL AREA AND MASS TRANSFER COEFFICIENTS BY CHEMICAL METHOD OF C02 ABSORPTION INTO AQUEOUS SOLUTIONS OF NaOH IN A MODEL COLUMN WITH EXPANDED METAL SHEET PACKING

The theory of gas absorption accompanied by fast pseudo-fast order reaction which considered dependences of diffusivity, kinetic constant and Henry's law constant on absolute temperature and ionic strength was used to obtain values of effective interfacial areas and mass transfer coefficients in gas and liquid phase.

Experimental measurement of carbon dioxide absorption from mixture with air was performed in a pilot-plant column with expanded metal sheet packing irrigated with sodium hydroxide solution.

Resulting liquid and gas-side mass transfer coefficients are compared with values obtained from physical Absorption measurement of carbon dioxide into water and with measurement of gas-side mass transfer coefficient for sulphur dioxide in the same column.

The differences between determined values are discussed.     

Hydrodynamics and mass transfer of gas–liquid flow in micropacked bed reactors with metal foam packing

Hydrodynamics and mass transfer of gas–liquid flow such as pressure drop, liquid holdup, and gas–liquid mass-transfer coefficient in micropacked bed reactors (μPBRs) with metal foam packing are investigated with an automated platform. Parametric studies are conducted varying gas and liquid superficial velocities, pore diameters of foam packing, and liquid physical properties. Experimental results show that μPBRs with foam packing have comparative mass transfer rate and 10 times lower pressure drop compared to the microparticles. The values of mass-transfer coefficient for three types of foam packing in μPBRs are 1–2 orders of magnitude larger than those in large-scale trickle bed reactors with foam packing. Furthermore, empirical correlations of pressure drop, liquid holdup, and gas–liquid mass-transfer coefficient in μPBRs with foam packing are proposed and the predicted values are found to be in good agreement with the experimental values.     

滴流床气液界面液相传质系数的研究

在气液并流向下的滴流床中,应用二氧化碳-空气-水系统和氢-空气-水系统进行了滴流床气、液界面液相容积传质系数k_La的研究.在内径为0.042m的床层中分别充填有直径d_p=0.0065、0.00475和0.00154m的玻璃球.气相流速为u_G=0.12-0.56m/s,液相流速u_L=0.003-0.04m/s.容积传质系数k_La与液相物性(Sc数)、填料直径和气液流动情况有关.根据传质情况,可以划分三个流区,它们与按流动情况划分的流区一致.用回归分析方法可以得到下述关联式:滴流区k_Lad_(p~2)/D_A=0.0904Re_(L~0.82)Re_(G~0.55)Sc~0.53(d_p/T)~(0.07)脉动流区 k_Lad_(p~2)/D_A=0.0211Re_(L~0.93)Re_(G~0.76)Sc~0.57(d_p/T)~(-0.12)     

用可视化方法实验研究规整填料的局部传质(英文)

A chromochemical reactive mass transfer technique has been employed to study local mass transfer characteristics of structured packing. This technology adopted by experiment is an Ammonia Adsorption Method (AAM) that yields the surface distribution of transferred mass by analyzing the color distribution on a filter paper with the results of the color chemical reaction. A digital image processing technology is applied for data visualiza-tion. The three-dimensional plot of the local mass transfer coefficients shows that there exist three peak values on different positions of a unit cell of structured packing. In order to improve mass transfer efficiency of the structured packing, one piece of baffle is added between packing sheets. As a result, the average mass transfer coefficient in-creases by (10-20)% and the pressure drop decreases by (15-55)%.     

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.     

Gas/liquid mass transfer in a slurry bubble column

Gas holdups and volumetric mass transfer coefficients (k_La) for oxygen were measured in suspensions of kieselguhr (7 μm), aluminium oxide (8 μm) and activated carbon (5 μm) in water or 0.8 molar sodium sulfate solution. By comparison to previously reported specific interfacial areas (a) determined by the sulfite oxidation technique, the liquid side mass transfer coefficients (k_L) can be evaluated. Most data are well correlated as a decreasing function of the effective viscosity. However, higher k_L values are determined at low concentrations of solids with a high density.     

Liquid film flow on structured wires: Fluid dynamics and gas‐side mass transfer

The liquid film flow on different structured wires and chains is observed experimentally to assess the suitability of a structured packing consisting of vertical wires. The results show that liquid beads as they appear on cylindrical wires are inhibited by certain chain geometries. This increases the flooding gas load up to F = 12 Pa^0.5. As the stabilized film shows no liquid bead motion, the liquid velocity at the interface is less which results in lower gas‐side mass‐transfer coefficients. An estimation of the packing characteristics for different chain geometries with an assumed wire packing density of 40,000 wires/m² is made. The interfacial area, mass‐transfer coefficients, and consequently the separation efficiency strongly depend on the liquid load. However, the proposed gas‐side separation efficiencies are slightly lower compared to common structured packings but the advantages are higher load limits, a better liquid distribution, and lower pressure drop. © 2012 American Institute of Chemical Engineers AIChE J, 59: 295–302, 2013     

A tool for mass transfer evaluation in packed-bed columns for chemical engineering students

This paper presents a Microsoft Excel tool to calculate liquid-gas mass transfer coefficients in packed towers to support numerical design activities in the courses of Unit Operations for Industrial Process and Sustainable Process Design for the Master’s degree in Chemical Engineering of the University of Naples Federico II (Italy).The Mass Transfer Solver Tool (MT Solver Tool) uses several available models to estimate, separately, the values of liquid and gas mass-transfer coefficients and the wet surface area for 144 random and structured packings of interest for absorption/stripping and distillation processes. In addition, a separate spreadsheet can be used in a user-defined mode, to evaluate the mass transfer coefficients with new packing types or to interpret experimental data when the geometrical and physical characteristics of the packing are known. Eventually, the tool is supplied with a data library, where packing geometry and model fitting parameters can be retrieved.The software is aimed to support students and educators in the Unit Operations for Industrial Process and Sustainable Process Design courses. In particular, this is meant to be an example on how the accuracy of design algorithms adopted in unit operation processes is affected by the use of the underpinning correlations for mass transfer rate or pressure drops. Besides, this is aimed to encourage comparison of different correlations when exact field data are not available. Besides, chemical engineers and researchers interested in packed columns design and modelling data may also benefit from the utilization of the software. The MT Solver Tool was introduced to students in a dedicated tutorial lesson after lecturers on packed column design algorithms for distillation, absorption and stripping. Most of the students of the course participated to a group training aimed to simulate the design of an absorption column supported by the MT Solver Tool providing feedback on its application.After the training, an anonymous survey was proposed to the students to monitor the approval rating of the proposed activity and the use of the MT Solver Tool software to support numerical calculations.