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.     

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.     

新型网架规整填料的传质性能

对一种新型网架规整填料用于萃取时的传质效率进行了实验研究。在Φ50mm的填料萃取塔中,选用煤油–苯甲酸–水和30%TBP(煤油)–乙酸–水两种不同界面张力的物系,测定了该填料和Φ10mm的鲍尔环填料在不同操作条件下的表观传质单元高度。扣去影响因素,网架填料的表观传质单元高度至少会比鲍尔环填料低25%,而网架填料的堆积密度仅为鲍尔环的38%。同时对影响传质的因素进行了分析,并针对该填料的特点,提出了优化设计原则。     

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.     

A dimensionless model for predicting the mass‐transfer area of structured packing

The mass‐transfer area of nine structured packings was measured in a 0.427 m ID column via absorption of CO₂ from air into 0.1 kmol/m³ NaOH. The mass‐transfer area was most strongly related to the specific area (125–500 m²/m³), and liquid load (2.5–75 m³/m²·h). Surface tension (30–72 mN/m) had a weaker but significant effect. Gas velocity (0.6–2.3 m/s), liquid viscosity (1–15 mPa·s), and flow channel configuration had essentially no impact on the mass‐transfer area. Surface texture (embossing) increased the effective area by 10% at most. The ratio of mass‐transfer area to specific area (a_e/a_p) was correlated within the limits of ±13% for the entire experimental database ${{a_{\rm{e}} } \over {a_{\rm{p}} }}= 1.34 \left[ {\left( {{{\rho _{\rm{L}} } \over \sigma }} \right)g^{1/3} \left( {{Q \over {L_{\rm{p}} }}} \right)^{4/3}} \right]^{\,0.116}$ . © 2010 American Institute of Chemical Engineers AIChE J, 2010     

高比表面积金属丝网波纹填料的实验研究

在50 mm的微机化多功能精馏实验装置中,以乙醇-正丙醇为体系对4种高比表面积(分别为900,1100,1700,2500 m2/m3)的金属丝网波纹填料的流体力学和传质性能进行了研究。结果表明,2500Y型填料的阻力很高而传质效率较低。其他3种填料的传质效率随比表面积增大而提高,但900Y和1100Y型填料的综合性能较好。     

Mass transfer and hydrodynamic characteristics of new carbon carbon packing: Application to CO2 post-combustion capture

A novel structured packing, the 4D packing, has been characterized in terms of hydrodynamics, effective area and gas side mass transfer coefficient. The increase of the 4D opening fraction allows to reduce pressure drop and to get a better capacity than Mellapak 500Y and 750Y, for which the geometric areas are similar. The 50% open 4D packing, 4D-50%, leads to effective areas which are higher than Mellapak 500Y ones, and doubled compared with MellapakPlus 252Y ones. Effective areas for the 4D do not decrease when the opening fraction increases from 30 to 50%, this indicates that a non-negligible amount of droplets is generated at 50%. Gas side mass transfer coefficient had been measured with an original experimental method: water evaporation. Corresponding results seem to be in agreement with the literature, and with the fact that a large amount of droplets is generated. Correlations are proposed for both effective area and gas side mass transfer coefficient for the 4D-50%.The 4D-50% packing could be very interesting for post-combustion CO₂ capture since it generates low pressure drop and a very high interfacial area. This will be further confirmed by an economic study for which the absorber plant will be designed with a rate based model.     

Performance characteristics of a new spherical metal mesh packing

Various tests and analysis on hydrodynamics and mass transfer properties show that, the newly invented spherical metal mesh packing (SMMP) has excellent properties from three aspects: (i) high void space (∼99%) and lower material cost; (ii) high mass transfer efficiency; (iii) easy installation, good liquid distribution, and prevention of wall flow. Moreover, SMMP is a type of isotropic spherical unit with numerous hollow holes, which realizes the regularization of random packing. The results indicate the potential of developing high-efficiency and energy-saving SMMP-based equipment.     

Mass transfer performance of structured packings in a CO2 absorption tower

This paper studies the mass transfer performance of structured packings in the absorption of CO2 from air with aqueous NaOH solution. The Eight structured packings tested are sheet metal ones with corrugations of different geometry parameters. Effective mass transfer area and overall gas phase mass transfer coefficient have been measured in an absorption column of 200 mm diameter under the conditions of gas F-factor in 0.38–1.52 Pa0.5 and aqueous NaOH solution concentration of 0.10–0.15 kmol·m?3. The effects of gas/liquid phase flow rates and packing geometry parameters are also investigated. The results show that the effective mass transfer area changes not only with packing geometry parameters and liquid load, but also with gas F-factor. A new effective mass transfer area correlation on the gas F-factor and the liquid load was proposed, which is found to fit experiment data very well.     

新型组合式规整填料在液液萃取中的传质性能

采用质量分数30%磷酸三丁酯-煤油-醋酸-水物系,对一种新型萃取用组合式规整填料的传质性能进行了测定,考察了连续相流速和分散相流速对其传质效率的影响。实验结果表明:在相同的二相流速下,组合式规整填料的表观传质单元高度比16 mm鲍尔环平均低约54%。固定连续相流速,随着分散相流速的增加,填料的表观传质单元高度降低,传质效率提高;固定分散相流速,随着连续相流速的增加,填料的表观传质单元高度增大,传质效率降低。     

规整填料传质性能计算的研究进展

综述了规整填料传质性能的计算方法和模型,并对这些模型的理论基础和适用条件进行了分析和比较。归纳了近年来对于传统规整填料传质模型的修正和扩展,并对影响传质性能的有效比表面积的经验关联式进行了讨论,指出了规整填料传质性能研究方面进一步的探索方向和应改进的若干问题。     

Hydrodynamic and mass transfer efficiency of ceramic foam packing applied to distillation

In addition to a high void volume and specific area, solid foams possess other properties (low density, good thermal, mechanical, electrical, and acoustical behaviour) that make them attractive for applications such as heat exchangers and reformers. Applications using foams as catalysts or structured catalyst supports have demonstrated higher performance than classical catalysts. Several studies have explored the hydrodynamic behaviour of foams in monophasic and countercurrent systems and have reported very low pressure drops. This paper describes the application of ceramic foam to distillation. The β-SiC foam contains 5 pores per inch (PPI) with a 91% void volume and a surface area of 640 m²/m³. Performance parameters including pressure drop for the dry and wet packing, flooding behaviour, and dynamic liquid hold-up were measured in a column of 150 mm internal diameter. The mass transfer efficiency in terms of the height equivalent to theoretical plate (HETP) was determined by total reflux experiments using a mixture of n-heptane and cyclohexane at atmospheric pressure. The experimental results were used to develop a set of correlations describing pressure drop and liquid hold-up in terms of a dimensionless number. The hydrodynamic performance and mass transfer efficiency were compared with classical packing materials used in distillation.     

Liquid-solid mass transfer in a rotating packed bed reactor with structured foam packing

A rotating packed bed (RPB) reactor has substantially potential for the process intensification of heterogeneous catalytic reactions. However, the scarce knowledge of the liquid–solid mass transfer in the RPB reactor is a barrier for its design and scale-up. In this work, the liquid–solid mass transfer in a RPB reactor installed with structured foam packing was experimentally studied using copper dissolution by potassium dichromate. Effects of rotational speed, liquid and gas volumetric flow rate on the liquid–solid mass transfer coefficient (k_LS) have been investigated. The correlation for predicting k_LS was proposed, and the deviation between the experimental and predicted values was within ± 12%. The liquid–solid volumetric mass transfer coefficient (k_LSa_LS) ranged from 0.04–0.14 1⁻¹, which was approximately 5 times larger than that in the packed bed reactor. This work lays the foundation for modeling of the RPB reactor packed with structured foam packing for heterogeneous catalytic reaction.     

新型垂直板规整填料流体力学及传质性能

采用氧解吸实验,在直径190 mm的有机玻璃塔内,液相喷淋密度10～38 m³·m^-2·h^-1,F因子0.2～3.2 m·s^-1·（kg·m^-3）^0.5的实验条件下测定了一种新型垂直板规整填料的流体力学及传质性能。实验结果表明：垂直板填料的操作压降及传质性能均显著优于商业波纹填料。通过与几种经改进的250型波纹填料相比发现,两者泛点F因子整体上相当;在较高液体喷淋密度下,垂直板填料传质性能及压降均高于改进250型波纹填料;在低喷淋密度下,垂直板填料可实现压降低于改进250型波纹填料,而两者传质性能相当。此外,对填料结构改进对其性能的影响进行了单因素考察。     

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.     

鼓泡塔中非牛顿流体体系的传质研究

本文在直径0.10 m、高1.05 m的鼓泡塔中,以羧甲基纤维素钠作为模拟介质,采用单孔喷嘴布气、孔径d_o=0.01 m,测定了该类反应器的比相界面积和容积传质系数,提出了比相界面积和传质系数的关联式。     

Performance characteristics of a packing with boundary layer turbulizers. III. Liquid film controlled mass transfer

Liquid film controlled mass transfer in a novel design of a honeycomb packing (Turbo-Pack) with turbulizers in the region of the boundary layer has been studied. For comparison, packings without turbulizers have also been investigated. Dimensionless equations for evaluation of mass transfer are proposed and their constants have been analyzed statistically. It is shown that the presence of turbulizers leads to an increase of the mass-transfer coefficient by up to 55% and to a decrease of up to 4.5-times in the packing pressure drop per mass transfer unit. A comparison over the most effective packings known from the literature shows that, as far as its low pressure drop per mass transfer unit is concerned, the novel packing is superior to all other packings.     

Region-dependent mass transfer behavior in a forced circulation airlift loop reactor

The contribution of local regions to global mass transfer holds the key to optimization and scale-up of a reactor. Extensive study has been conducted to investigate gas-liquid mass transfer occurring in the internal airlift loop reactor, but mostly restricted to global mass transfer performance. A cold model forced circulation internal airlift loop reactor was employed and divided into six regions in which dissolved oxygen concentration in slurry and mass transfer interfacial area were measured respectively. Different models were utilized to calculate volumetric mass transfer coefficient. Contributions of individual region to global mass transfer performance were calculated and compared. It was found that mass transfer coefficient and mass transfer interfacial area of individual region increases with increasing superficial gas velocity and slurry feed flowrate. The feed affected region has the greatest mass transfer coefficient and volumetric mass transfer coefficient, contributing more than 30% to global mass transfer in most operating condition. Mass transfer interfacial area is close in the gas distributor region, feed affected region and the gas-slurry separator region. In the present work, circulating bubbles are rare and contribute negligibly to the global mass transfer. Global volumetric mass transfer coefficient is close to that of the gas-slurry separator region, ranging from 0.02 to 0.1 1/s. Comparison of k_La is made between this work and literatures, suggesting a great improvement of mass transfer due to external liquid circulation.     

滴流床小颗粒催化剂滴流区和脉动流区传质的研究

本文研究了滴流床小颗粒催化剂在滴流区和脉动流区的气相容积传质系数k_Gα,气液接触有效界面积“α”和脉动流形成时分散气泡的平均直径d_b。实验表明:不同流区的传质与流型和流动介质的能量损失有关。强化传质会增加流动介质的能量消耗及减小催化剂粒度。     

Influence of Chitosan and Chitosan Derivatives on Hydrodynamics and Mass Transfer in a Bubble Contactor

The behavior of chitosan and two kinds of chitosan derivatives in carbon dioxide absorption in a bubble column contactor is analyzed. The effects of absorption type (physical or chemical), polymer type, concentration, and liquid‐phase physical properties on hydrodynamics (bubble size, gas holdup, and specific interfacial area) and mass transfer (absorption rate and mass transfer coefficient) are evaluated.