Gas absorption with large heat effects in packed columns

The system of design equations recently proposed by Treybal for adiabatic packed absorbers has been tested experimentally for ammonia absorption. Examination of temperature profiles and solute recoveries measured in a 6 in. packed column indicated effective interfacial areas for non-isothermal absorption to be larger than those found by Shulman for isothermal absorption. A modification of Shulman's interfacial area relationship, giving good agreement between measured and predicted recoveries and temperature profiles, is proposed. A convenient algorithm for computer solution of the design equations is described.     

空分填料塔设计中的流体力学特性

空分精馏主要在-200℃左右的深冷条件下进行,填料塔内流体力学特性参数难以由试验直接获取,如何将常压常温状态(简称常态)下空气-水物系的流体力学测试结果转换适用于空分设计变得尤为关键。通过Bain-Hougen公式及SRP(Ⅱ)模型结合Sp iegel持液量计算推导出泛点及压降关联式以预测填料的流体力学特性。对空分中常用的750Y型金属孔板波纹填料进行常态下流体力学特性测试,结果表明:采用的方法可用于填料流体力学特性的预测。对空分状态下的泛点与压降结果预测表明,空分设计中采用常态下的流体力学数据进行设计偏于保守。     

Increasing the effective interfacial area in plastic packed absorption columns.

Effective interfacial areas for gas absorption were measured at various irrigation rates for Raschig rings made of a ceramic (industrial porcelain) and of various plastics. The plastics used were polyethylene and polypropylene having very low wettabilities with water. The surface of some of the plastic packings was covered with a hydrophilic layer. The absorption of pure oxygen by a sodium sulphite solution containing cobalt catalyst was used for the measurement of effective interfacial area. It has been found that the effective interfacial area of plastic packings was about 40 per cent of that of geometrically similar ceramic packings. The effective interfacial area of the plastic packings was increased about 2·5 times by application of the hydrophilic layer. Thus, the wetted surface areas of plastic packings with hydrophilic surface and of ceramic packings are practically the same.     

Adiabatic gas absorption in packed columns with large thermal effects

The performance of packed bed adiabatic gas absorbers has been analyzed using the enthalpy and material balance equations incorporating a new parameter, f_r, defined as the fraction of the heat of absorption that is accounted for in the gas stream. An experimental programme to evaluate f_r was carried out and the data correlated. It was found that f_r was dependent on the thermo-physical properties and the hydrodynamic conditions. It is postulated that the mechanism by which this heat transfer occurs is by turbulence at the interface and by entrainment.     

Liquid holdup determination in packed columns for sulfur dioxide absorption

Total, static and dynamic holdups have been measured for 0.012 m ceramic Raschig rings with air rates from 0 to 700 kg m⁻² h⁻¹ and sodium citrate solution rates from 2000 to 60 000 kg m⁻² h⁻¹ at 40°C using the draining method. Equations presented for estimating holdups are discussed.     

撞击流-旋转填料床萃取传质性能与微观混合效果的关系

为探寻撞击流-旋转填料床(IS-RPB)萃取效果与微观混合之间的关系,在相同操作条件下,分别对IS-RPB萃取传质性能与微观混合性能进行了实验研究。对于萃取传质性能研究过程中选用了水-苯酚-磷酸三丁酯(煤油)和煤油-苯甲酸-水2个萃取体系;对于微观混合效果的研究采用化学偶合法,以α-萘酚和对氨基苯磺酸重氮盐的串并联偶合反应为工作反应。结果表明:IS-RPB萃取传质性能与微观混合效果密切相关,在实验范围内,萃取传质性能随微观混合效果的增加而提高。通过因次分析方法,给出了描述IS-RPB设备参数、操作参数对萃取传质速率影响的关联表达式。     

Estimation of the efficiency of packed mass-transfer devices

The problems of assessing the effectiveness of packed mass-transfer devices in relation to distillation processes have been considered. The authors have shown that the existing dependences of determining the height equivalent to a theoretical plate cannot be used to calculate tray columns and columns with vortex packings, the contact surfaces of the phases and coefficients of mass transfer of which depend substantially on the water concentration (reflux ratio) and gas rate (vapor for distillation).     

Estimation of liquid film mass transfer coefficients for randomly packed absorption columns

Empirical and theoretical correlations, published since 1940 are reported which predict liquid film mass transfer coefficients in packed columns. Brief comments on the usefulness of the equations are given together with the range of operating variables, where available. Dimensional constants in the empirical correlations have been recalculated for the cases where the original values were not in SI units.     

旋转填料床中2种填料压降和传质特性的对比

分别以空气-水和磷酸钠溶液吸收模拟烟气中SO2为实验体系,对装填有θ环和波纹丝网填料的逆流旋转填料床压降和传质特性进行了对比研究,结果表明:在实验操作范围内,逆流旋转填料床的湿床压降随气量、超重力因子的增大而增大,受液量的影响很小;2种填料的湿床压降相差不大,且均低于750 Pa。2种填料的Kya均随喷淋密度、空床气速和超重力因子的增加而增大,当U=6 m3/(m2·h),u=0.73 m/s,β=85及更高的操作范围时,θ环填料的Kya比波纹丝填料高25%以上,说明θ环填料的传质性能明显优于波纹丝填料;最后得到装填θ环和波纹丝填料的旋转床湿床压降和体积传质系数的经验关联式。文中的研究结果对旋转填料床的设计和选型有重要意义。     

On flooding in packed columns

A mechanism for flooding in packed columns, based on interactions between holdup and pressure gradient is proposed and is shown to be consistent with experimental observations. The differences in the flooding mechanism between wetted wall columns and packed columns are considered also.     

Recent developments in packed columns

Highlights of a recently concluded four year experimental program on random packings are presented. They include (a) a revised definition of loading to achieve better reproducibility; (b) discussion of the erratic behavior near the “flood” point which helps explain the scatter in the published “flood” data; (c) new data showing that with proper distribution, efficiency is stable over a broad range; and (d) controlled maldistribution studies leading to guidelines for distributor design, fabrication and installation. The need to precisely define commonly used terms is emphasized.     

Absorption in packed bubble columns

The mass transfer characteristics of packed bubble columns were studied by employing various packings of different sizes and shapes in 10–38·5 cm i.d. columns. The theory of absorption accompanied by pseudo-mth order reaction was used to obtain the values of effective interfacial area. The values of liquid side mass transfer coefficient were obtained by using the theory of absorption accompanied by slow chemical reaction. The superficial gas velocity was varied from 5 to 25 cm/sec. The packed bubble columns showed a considerable improvement in the performance over empty bubble columns. A criterion for the scale-up of these columns has been suggested.     

Simulations of chemical absorption in pilot-scale and industrial-scale packed columns by computational mass transfer

A complex computational mass transfer model (CMT) is proposed for modeling the chemical absorption process with heat effect in packed columns. The feature of the proposed model is able to predict the concentration and temperature as well as the velocity distributions at once along the column without assuming the turbulent Schmidt number, or using the experimentally measured turbulent mass transfer diffusivity. The present model consists of the differential mass transfer equation with its auxiliary closing equations and the accompanied formulations of computational fluid dynamics (CFD) and computational heat transfer (CHT). In the mathematical expression for the accompanied CFD and CHT, the conventional methods of k-ε and are used for closing the momentum and heat transfer equations. While for the mass transfer equation, the recently developed concentration variance and its dissipation rate ε_c equations (Liu, 2003) are adopted for its closure. To test the validity of the present model, simulations were made for a pilot-scale randomly packed chemical absorption column of 0.1 m ID and 7 m high, packed with 1/2^″ ceramic Berl saddles for CO₂ removal from gas mixture by aqueous monoethanolamine (MEA) solutions (Tontiwachwuthikul et al., 1992 ) and an industrial-scale randomly packed chemical absorption column of 1.9 m ID and 26.6 m high, packed with 2^″ stainless steel Pall rings for CO₂ removal from natural gas by aqueous MEA solutions (Pintola et al., 1993). The simulated results were compared with the published experimental data and satisfactory agreement was found between them in both concentration and temperature distributions. Furthermore, the result of computation also reveals that the turbulent mass transfer diffusivity D_tvaries along axial and radial directions. Thus the common viewpoint of assuming constant D_t throughout the whole column is questionable, even for the small size packed column. Finally, the analogy between mass transfer and heat transfer in chemical absorption is demonstrated by the similarity of their diffusivity profiles.     

Hydrodynamics and mass transfer characteristics of co-current downflow packed tube columns

Hydrodynamics and effective interfacial area in a 25 mm i.d. packed tube column were studied over a wide range of operating conditions for demister pad packings (DPP). Flow maps have been prepared. Values of effective interfacial area as high as 1880 m^?1 in the spray flow regime were obtained. Data on pressure drop and effective interfacial area have been correlated for different flow regimes. Values of liquid side volumetric mass transfer coefficient, k_L a , were measured by absorption and desorption of oxygen in different packed tube columns containing Pall rings (standard and low height to dia. ratio), multifilament wire gauge packings (MFWGP) and DPP. kL a was found to vary from 0.017 to 0.34 s^?1 for DPP. Values of wall side solid-liquid mass transfer coefficient, k_SL, were obtained in a 25 mm i.d. copper tube column packed with MFWGP by the dissolution of copper in acidic dichromate solutions. Values of wall side heat transfer coefficient could be obtained by analogy.     

Gas distribution in large-diameter packed columns

The aim of the present work was to determine the extent of gas maldistribution in large-diameter columns containing corrugated-sheet structured packings. A large-diameter column simulator has been designed for this purpose (cross section, 3 m × 0.5 m; packed bed height, 4.4 m) with 15 independent inlets for gas, allowing the introduction of diverse initial distribution profiles. The gas velocity profiles leaving the top of the packed bed are discussed in terms of lateral spreading and observed effects of gas load, liquid load and the height of the packed bed.     

Predicting mass transfer in packed columns

Countercurrent-flow columns are widely used in production processes in the chemical industry and their application in ecological engineering is of increasing importance. A theoretical model is presented here that allows mass transfer to be described in terms of packing geometry and physical properties which influence the gas-liquid or vapour-liquid systems in absorption, desorption and rectification columns. The relationships derived from the model can be applied to all countercurrent-flow columns, regardless of whether the packing has been dumped at random or arranged in a geometric pattern.     

不同填料错流旋转填料床气液传质特性研究

为了探索不同填料错流旋转填料床的传质性能,以Na2CO3水溶液吸收空气中硫化氢为实验体系,对装有不锈钢丝网、塑料波纹孔板和θ环填料的错流旋转填料床的气液传质性能进行研究。实验确定的适宜操作条件为:超重力因子7.8,气体流量2 m3/h,液气比20 L/m3,碳酸钠质量浓度12 g/L;在此条件下,3种填料的脱硫率均可达到90%以上。在相同操作条件下,不锈钢丝网填料的脱硫率及气相总体积传质系数大于塑料孔板填料大于θ环填料;错流旋转填料床中,规整填料的气液传质效果优于乱堆填料。文中的研究结果为错流旋转填料床填料的选取及在脱硫方面的应用提供了依据。     

Modelling of pressure drop in packed columns

The correct choice of packing is of decisive importance for optimum process efficiency in the operation of two-phase countercurrent columns. An important criterion for this choice is the pressure drop in the gas flow. Theoretical relationships are derived for calculating the pressure drop in beds with dry and trickle packings. It has been demonstrated by comprehensive experiments that these relationships allow the pressure drop to be determined more accurately than by previous methods. The experiments were performed at the Department of Thermal Separation Processes of Bochum University on 54 different packed beds, using 24 different systems.