PERFORMANCE OF A WETTED-WALL SHEET BUNDLE COLUMN

The performance of a wetted-wall sheet bundle column with vertically aligned sheets placed inside as liquid film supports was investigated as an alternative to a wetted-wall fiber bundle column used for gas and liquid contacting. It avoids or simplifies some of the design problems associated with using fibers and still retains the advantages possessed by the fibers such as low pressure drop and high mass transfer coefficient. A comparison with the conventional Raschig ring packings and stainless steel tube bundles show that the fibers and sheets which were made of light weight material has definite advantages in reducing the weight and cost of the packing material in the column substantially     

Simultaneous heat and mass transfer in binary distillation—II: Experimental

A theoretical study of simultaneous heat and mass transfer in binary distillation has shown that heat and mass transfer coefficients can be appropriately evaluated if liquid phase temperatures and compositions are measured as functions of height in a column. In this study, the experiments were carried out in a wetted-wall column using a methanol-water binary system at one atmosphere.Special probes were designed to determine the state of the liquid phase. Temperatures were measured with microthermocouples and liquid samples were analyzed with a high precision refractometer. The liquid phase was found to be saturated which indicated, in accordance with the conclusions from a theoretical study, that all the resistance to mass transfer was in the vapor phase. Local transfer coefficients were calculated using the composition data as a function of column height. The results were correlated by an equation showing close agreement with the Chilton-Colburn equation. $\text{k}{}_{\mathrm{y}}\text{a}{}_{\mathrm{m}}\text{V}\text{= 0.039}\text{Sc}{}_{\mathrm{y}}$^{?$\text{2}\text{3}$}Re_y^?0.20 cm^?1.It is concluded that mass transfer in the vapor phase is the controlling resistance in distillation and that there is no additional evaporation within the liquid phase caused by heat transferred from the vapor phase as proposed by some previous investigators.     

Simultaneous Absorption of Hydrogen Sulfide and Carbon Dioxide into di-isopropanolamine Solution

The simultaneous absorption of hydrogen sulfide and carbon dioxide into di-isopropanolamine (DIPA) solution was investigated in a 183 cm long, 2.72 cm OD wetted-wall column at atmospheric pressure. The influence of liquid flow rate, gas flow rate, temperature and liquid concentration on the absorption rate, overall gas-phase mass transfer coefficient and selectivity factor were studied at a constant gas feed ratio. The results show that the absorption rate of CO₂ increases rapidly with increasing liquid flow rate (the Reynolds number of the turbulent liquid film ranges from 2600 to 4350) but increases moderately with increasing gas flow rate (G = 18-91 L/min), indicating that it is liquid-phase mass transfer controlled. In contrast, the absorption rate of H₂S increases very slowly with increasing liquid flow rate but increases rapidly with increasing gas flow rate, indicating that it is gas-phase mass transfer controlled. The absorption rate of CO₂ also increases with increasing temperature (26-80°C) but H₂S absorption rate decreases with increasing temperature. When the concentration of DIPA solution increases from 0.2 to 2.6 mol/L, the absorption rate of both CO₂ and H₂S increases but with a larger rate of increase for CO₂ For selective H₂S removal, it is preferable to operate at low liquid and high gas flow rates, low temperatures and low DIPA concentrations.     

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.     

GAS ABSORPTION INTO WAVY AND TURBULENT FALLING LIQUID FILMS IN A WETTED-WALL COLUMN

Experiments are conducted for gas absorption in a long wetted-wall column. Liquid-side mass transfer coefficients are measured for absorption of CO₂ and O₂ into falling water films on the outside of a stainless steel pipe 2.72 cm OD and 183 cm absorption length. The liquid film Reynolds number ranges from 129 to 10500 which encompasses the wavy-laminar, wavy-transition and turbulent flow regimes. The experimental data are correlated by a dimensionless equation of the form kt = (k_tD) (v²/g) ^1/3 = a-Re^p-Sc^1/2. The correlation is well supported by a viscosity-damped turbulence model at the gas-liquid interface which tends to confirm that viscosity is probably the major mechanism causing eddy damping and not surface tension as proposed by Levich and Davies. The form of the above correlation also represents previous experimental work at different temperatures and for different gases quite well.     

Surfactant effects on gas absorption in a coke-oven gas treatment process

The effect of organic impurities in industrial stripped coal water (SCW) on the absorption of CO₂ was measured experimentally. Removal of these impurities via activated carbon showed a marked improvement in interphase mass transfer of a vertical wetted-wall column absorber. However, this benefit was not found in a stirred-cell absorber, in which a different flow pattern from that in wetted-wall column absorber is expected. An ad hoc systematic study on the effects of three deliberately added surfactants on gas absorption by pure water in three different absorbers with different flow patterns was thereafter conducted. The experimental results reveal that absorption deterioration also prevails only in a vertical, wetted-wall column absorber and the reduction in liquid phase mass transfer by the addition of surfactant can be satisfactorily correlated with surface pressure of solutions. This indicates that the effect of the industrial impurities in SCW on gas absorption may successfully be simulated under the same flow pattern by a surfactant solution with the same surface pressure. A possible modification of the existing coke-oven gas (COG) treatment process for the benefit of absorption enhancement was finally proposed.     

Simultaneous heat and mass transfer in binary distillation—I: Theory

Binary distillation in continuous contact equipment is modeled as a simultaneous heat and mass transfer process. In order to account for the interactions between heat and mass transfer between the two phases, the equations developed from enthalpy and material balances are analyzed simultaneously and it is revealed that the individual phase mass transfer coefficients can be evaluated rigorously by measuring liquid phase compositions and temperatures in distillation experiments. Using the theoretical relations, it is proved that the liquid phase in a distillation column will be saturated if and only if there is negligible resistance to mass transfer in the liquid film. For the case of comparable resistances in both phases, the possible amount of superheat in the liquid phase would be considerable and thus convenient to determine experimentally. The liquid phase temperatures are shown to be important in experimental analysis (i.e. in determining the individual phase transfer coefficients) but not in design applications. For the latter case, the model equations reduce to the conventional mass transfer relations which are not as sensitive to temperatures.     

Gas absorption into a turbulent liquid

Mass transfer coefficients were measured for the liquid phase for gas absorption into a turbulent liquid flowing down a long wetted-wall column. Helium, hydrogen, oxygen and carbon dioxide were absorbed into distilled water over a Reynolds number range of 1300–8300. The results indicate that the liquid phase mass transfer coefficient is proportional to the molecular diffusion coefficient raised to the 0·54 power. The results are interpreted in terms of an eddy diffusivity model and indicate that the eddy diffusivity increases as the square of the distance from the interface.     

GAS ABSORPTION INTO WAVY AND TURBULENT FALLING LIQUID FILMS IN A WETTED-WALL COLUMN

Experiments are conducted for gas absorption in a long wetted-wall column. Liquid-side mass transfer coefficients are measured for absorption of CO₂ and O₂ into falling water films on the outside of a stainless steel pipe 2.72 cm OD and 183 cm absorption length. The liquid film Reynolds number ranges from 129 to 10500 which encompasses the wavy-laminar, wavy-transition and turbulent flow regimes. The experimental data are correlated by a dimensionless equation of the form kt = (k_tD) (v²/g) ^1/3 = a-Re^p-Sc^1/2. The correlation is well supported by a viscosity-damped turbulence model at the gas-liquid interface which tends to confirm that viscosity is probably the major mechanism causing eddy damping and not surface tension as proposed by Levich and Davies. The form of the above correlation also represents previous experimental work at different temperatures and for different gases quite well.     

喷雾冲击条件下液膜流动与传热模型

针对现有喷雾冷却计算模型的不足,以质量、动量、能量守恒方程为基础,建立喷雾冷却非沸腾区的液膜流动与传热方程,并采用数量级分析的方法对方程简化,最后运用数值方法对模型进行求解。给定液滴速度及液体温度,由模型计算液膜厚度、平均热通量与液体流出温度,与实验测试结果对照。结果显示,液膜厚度的计算结果与实验结果相差6%以内;平均热通量和液体离开待冷却表面的最终温度计算结果与实验结果相差10%以内,且超过60%的计算结果偏差小于5%。计算结果与实验结果的高度匹配证明该模型可较好地反映喷雾冷却过程的流动与换热。由模型可以获取不同位置处液膜厚度与温度,从而加深对喷雾冷却传热机理的理解。     

甲基二乙醇胺水溶液在改进的湿壁塔上吸收二氧化碳的动力学模型

To get more accurate kinetic data of the absorption of CO2 into aqueous solution of N-methyldiethanolamine, a wetted wall column was modified to more uniformly distribute the liquid on the column surface and gas in the absorbing chamber and change the length of the column. The average liquid film thickness and the liquid-phase mass transfer coefficient were measured, and a correlation for the Sherwood number, Reynolds number and Schmidt number was obtained for the modified wetted wall column. The equilibrium concentrations in chemical reactions were calculated with a minor absolute error for calculating the rate constant more accurately. A mathematical model for the CO2 absorption was established based on the diffusional mass transfer accompanied with parallel reversible reactions, and the partial differential equation was solved by Laplace transform. An analytical expression for the concentration of carbon dioxide as a function of time and penetration depth in liquid film and the average interphase mass transfer rate was obtained. This model was also used to calculate the rate constant for a second-order reaction, which was in good agreement with reported data.     

改良型湿壁塔液膜传质特性与端末效应的研究

本文采用疋田晴夫等提出的改良型湿壁塔作为建立研究传质的基础实验装置.测定了液膜厚度沿壁的分布,实验结果表明膜厚的实验值与理论值吻合较好;又选用CO_2-H_2O系统对塔的液膜传质特性进行了研究,并提出了液膜传质系数的无因次准数关联式;实验结果与渗透理论计算值比较,获得了良好的一致性.研究还表明通过简单地操作控制即能消除由端末效应引起的偏差.因此改良型湿壁塔是进行气液传质研究的良好装置.     

Gas Holdup and Solid‐Liquid Mass Transfer in Newtonian and non‐Newtonian Fluids in Bubble Columns

Gas holdup and surface‐liquid mass transfer rate in a bubble column have been experimentally investigated. De‐mineralized water, 0.5 and 1.0% aqueous solutions of carboxy methyl cellulose (CMC), and 60% aqueous propylene glycol have been used as the test liquids. Effects of column diameter, liquid height to column diameter ratio, superficial gas velocity and liquid phase viscosity on gas holdup and mass transfer rate are studied. Generalized correlations for the average gas holdup and wall to liquid heat and mass transfer coefficients are proposed. These are valid for both Newtonian and pseudoplastic non‐Newtonian fluids.     

2,4-Xylidine Degradation with Ozonation: Mass Transfer and Reaction Kinetics

The kinetics of the degradation of 2,4-xylidine by ozonation as well as the ozone mass transfer in a wetted-wall column were investigated. A laboratory-scale ozone contactor was designed, and a steady-state wetted wall reactor model was developed. The model was based on countercurrent-connected and perfectly mixed mass transfer stages. It was possible to describe the evolution of the pollutant and ozone concentrations along the reactor length coordinate in various conditions. The model was used for the evaluation of the ozone mass transfer coefficient, reaction rate kinetics, and stoichiometric coefficient from experimental data. The ozone mass transfer coefficient for the wetted-wall column was estimated from the experiments in the absence of chemical reactions. When the estimated parameters were applied, the ozonation model of the wetted-wall column showed good agreement between the fitted and experimental data.     

Gas absorption in laminar falling films of pseudoplastic liquids

Gas absorption into laminar falling films of power-law liquids was studied theoretically and experimentally. The convective-diffusion equation was solved by the method of separation of variables and the analytical solution for the average Sherwood number was obtained as a function of the Graetz number and the power-law index of the liquid. Experiments were carried out on the absorption of pure carbon dioxide, hydrogen and helium into aqueous kaolin slurries by using a long wetted-wall column and the average absorption rates were measured as a function of the mass flow rate of the liquid. The experimental results were in good agreement with the theoretical predictions.     

An estimation of the film-penetration model parameters

It it shown in this paper that the process of evaporation of liquids into a turbulent gas flow in a wetted-wall column can be represented by the film-penetration model. The numerical values of the two parameters S and L of this model, estimated from mass transfer data, appear to be well defined functions of flow conditions. The surface renewal mechanism used in the considered mass transfer model was shown to be consistent with the momentum transfer concept.The results may be used to predict mass transfer processes with chemical reactions in similar flow systems, by applying the theoretical developments using the film-penetration theory [7–10].The same procedure may be used to estimate the film-penetration parameters in other flow systems, such as the flow of liquid films in a wetted-wall column, or other complicated system such as stirred tanks, bubble columns, packed columns etc.     

有机相的加入对气液体系流动及传质特性的影响

以难溶气体的吸收作为研究的基本过程，纯CO2为气体溶质，0.5MK2CO3／0.5MKHCO3为连续相，异戊醇、苯、正己烷分别作为有机相，探索有机相对气液传质的增强作用，实验探求从不同有机相以不同油分率、表观气速对三相传质系数、增强因子等的影响。     

Axial mixing and mass transfer in a vibrating perforated plate extraction column

The axial mixing and countercurrent mass transfer characteristics of a 5 cm diameter extraction column agitated by vibrating perforated Teflon plates have been investigated. The dispersed phase was an organic liquid (usually kerosene) and the continuous phase was water. Axial mixing was measured in both phases using pulse tracer techniques; in the continuous phase the axial mixing was estimated to have a significant effect on mass transfer, but axial mixing in the dispersed phase had a negligible effect. Mass transfer was measured for several different solutes; n-butyric acid, benzoic acid and phenol. The overall heights of a transfer unit (cont. phase) were in the order of 10-20 cm for the organic-acids but higher for transfer of phenol from very dilute solutions. The characteristics of the vibrating plate column have been compared with those of other types of extractor and suggestions are made for further development.     

PERFORMANCE OF A PACKED-BED REACTOR

We examined the conversion rates in a packed bed catalytic reactor with a two phase upward flow in a wide range of operating conditions. The oxidation of ethanol to acetic acid in the liquid phase on a Pd-Alumina catalyst was chosen as the test reaction.

Global reaction rates were measured by changing gas velocities, temperature, and feed concentrations of ethanol in the liquid phase. The observed rates were compared with those calculated using two models, assuming a total external wetting of the catalyst. In the first model, a “kinetic” conversion rate was calculated by neglecting any interphase mass transfer resistance. In the second model the interphase mass transfer resistance was considered and expressed by an overall coefficient evaluated from published correlations. The results show that there is an hydrodynamic influence, probably due to the mass transfer and/or to the partial effective wetting of the catalyst. Mass transfer, on the other hand, is better than that observed in other cases. A comparison with the performances of a downflow trickle-bed reactor operating at the same tested conditions showed a much smaller influence of mass transfer and hydrodynamics on the overall conversion rate for the upflow reactor.