Effective interfacial area and liquid and gas side mass transfer coefficients in a packed column

The theory of gas absorption accompanied by fast pseudo-mth order reaction was used to obtain values of effective interfacial area in a packed column, irrigated with aqueous solutions and provided with 1 in. ceramic Raschig rings, 1 in. P.V.C. Raschig rings, 1 in. ceramic Intalox saddles, 1 in. polypropylene Intalox saddles, 1 in. stainless steel Pall rings and 1 in. polypropylene Pall rings. The values of liquid side mass transfer coefficient were obtained by physical absorption of carbon dioxide in water. In addition, the values of gas side mass transfer coefficient for a range of gas and liquid flow rates were obtained.     

Performance of Spray,Sieve Tray,and Packed Contactors for High Pressure Extraction

Abstract

The performance of various contactors in high pressure extraction service was studied. The mass transfer efficiency of a spray column and columns filled with sieve trays, 1.27 cm ceramic Raschig rings, and no. 15 metal Intalox saddles were obtained from a “windowed” high pressure extraction column with an internal diameter of 9.88 cm and a column height of 168 cm. The extraction column has an internal diameter of 9.88 cm and a contacting height of 168 cm. Glass windows in the extractor allowed visual observation and photography. Supercritical and liquid carbon dioxide were used to extract isopropanol from water at pressures of 81 to 150 atmospheres and 297 to 318 [ddot]K. The sieve tray extractor yielded the highest mass transfer efficiency followed closely by Raschig rings and metal Intalox saddles. The spray column was by far the least efficient. The mass transfer efficiency was observed to be independent of the operating conditions studied in this work. Sauter mean drop diameters and dispersed phase (free) hold-up were also obtained in this work. These data will provide a reliable high pressure mass transfer and hydraulic database for future correlation and design efforts.     

Mass transfer in packed liquid—liquid extraction columns

The mass transfer characteristics of 3·5, 7·3, 10·16 and 15·6 cm i.d. packed liquid—liquid extraction columns were studied with a variety of packings such as, $\text{3}\text{8}$, $\text{1}\text{2}$ and 1 in. ceramic Raschig rings, $\text{5}\text{8}$ in. stainless steel Raschig rings, $\text{1}\text{2}$ and 1 in. ceramic Intalox saddles, $\text{5}\text{8}$ and 1 in. stainless steel Pall rings, and 1 in. polypropylene Intalox saddles and Pall rings. Some data were also obtained for the co-current mode of operation (up-flow) for packed columns, and without packings. In addition the mass transfer charactersitics of a packed extraction column with film flow were studied.The theory of extraction accompanied by a fast pseudo-first order reaction was employed to measure the values of effective interfacial area. The values of overall (continuous and/or dispersed phase) mass transfer coefficient were measured by the Colburn—Welsh technique. A fairly wide range of physical properties of the two phases was covered.The values of overall (continuous phase) mass transfer coefficient and effective interfacial area for new packings such as Pall rings and Intalox saddles, under otherwise similar conditions, are only about 10 and 35 per cent higher, respectively, than those provided by the conventional packings of the same nominal size. However, the flooding velocities for the newer packings are as much as 80 per cent higher than those for the conventional packings of the same nominal size.     

Enzyme mass transfer coefficient in aqueous two phase system using a packed extraction column

Fractional dispersed phase hold-up and dispersed side mass transfer coefficients for amyloglucosidase were measured in a 56 mm i.d. packed extraction column using a sodium sulphate-polyethylene glycol 4000 system. Raschig rings (3 to 13.3 mm), Berl saddles (12 mm), Pall rings (12.6 mm), glass spheres (5.2 mm) and structured wire gauze were used as packings. The effect of packing size was investigated in the case of ceramic Raschig rings. The effect of phase composition of the aqueous phase system also was studied. Correlations have been developed for fractional dispersed phase hold-up and volumetric mass transfer coefficient with packing voidage, dry surface area of packings, superficial dispersed phase velocity and the liquid phase physical properties.     

Ergebnisse einer Untersuchung der Gasverteilung über dem Querschnitt einer Füllkörperkolonne

The gas distribution has been investigated over a cross-section of a 472 mm diameter column assembled with two types of inlet devices with and without equalizing packing layer, respectively. The minimum height of Raschig rings, Pall rings, Intalox saddles and four types of horizontal expanded sheet packing, at which a uniform velocity profile can be obtained, was found. It is shown that when applying these packings no increase occurs in the velocity of the nearwall layer.     

Identification of Flow Regimes in a Concurrent Gas Liquid Upflow through Packed Beds

The flow regimes bubble flow, pulse flow, and spray flow were identified by visual observation in a packed column. Three gas‐liquid systems (air/water, air/56 % glycerol, and air/monoethanolamine) and four column packings (Raschig rings, Intalox saddles, and two sizes of spheres) were investigated to cover wide ranges of physical properties of gas liquid systems and characteristics of column packings affecting the flow regime transition. Criteria for the flow regime transition were developed in terms of system and operating variables.     

Effectiveness of mass transfer in a packed distillation column in relation to surface tension gradients

In packed columns large differences occur in the wetting of the particles and especially in the refreshing of the liquid on the wetted particles due to gradients in surface tension of the liquid/gas interface. Mass transfer rates may differ with a factor 2. In a column packed with Berl saddles distillation experiments were performed with a mixture n-heptane/cyclohexane. Ceramic Berl saddles of 4, 6 and 10 mm were used as well as aluminum Berl saddles of 4 mm. In some of the experiments the saddles were coated with PTFE (teflon). The driving force for mass transfer was varied over a wide range. Both negative and positive driving forces were realized. The influence of the surface tension driven refreshment of the interface is most pronounced for small particles; for larger liquid flow rates, that may be applied in beds with larger particles, the effect is obscured by the inertia of the downcoming liquid.     

Active surface of the elements of irregular heat and mass transfer packings

The mechanisms of active surface formation in irregular heat and mass transfer packings were analyzed. The packings under study included Raschig, Pall, and GIAP-N3 rings and Intallox saddles. The efficiencies of GIAP-N3 packings of different sizes under different gas and liquid loads were compared. The packing designs were compared in terms of the useful factor of packing.     

QH-2型扁环填料的流体力学和传质性能研究

在内径60 0填料塔中 ,用空气 富氧水系统对3 8和5 0QH 2型扁环填料的流体力学和传质性能进行了研究 ,得出计算其压降、液泛气速和传质单元高度的关联式。并与3 8鲍尔环、5 0鲍尔环和3 8环矩鞍填料进行了比较 ,结果表明 ,QH 2型扁环具有优良的流体力学和传质特性。     

散装填料塔设计及核算软件开发

在查阅了大量国内外文献资料的基础上,研究了填料塔的流体力学计算模型以及其他一些参数的计算模型。并利用Microsoft Visual Basic6．0开发了一套可适用于拉西环、鲍尔环、阶梯环、弧鞍、矩鞍、金属环矩鞍等散装填料塔设计及核算软件。本文主要通过金属阶梯环介绍了散装填料塔设计及核算软件的具体开发过程,并以具体实例作为软件的考核评估。     

Predictions of moisture removal efficiencies for packed-bed dehumidification systems

Liquid desiccant-based dehumidification systems have been widely used to remove water vapour from air in a packed column using different liquid desiccants. The liquid desiccants are usually grouped into two categories: aqueous solutions of inorganic salts and aqueous solutions of organic compounds. In order to design such a desiccant—dehumidification system, correlations of the column performance parameters are necessary. A correlation of column efficiency for different packings and desiccant solutions was developed in this study using lithium chloride (LiCl) as the inorganic salt and triethylene glycol (TEG) as the organic compound. This correlation involves the air and liquid flow rates, air and liquid inlet temperatures, column and packing dimensions, and the equilibrium properties of the desiccant solutions. The correlation was tested for polypropylene Flexi rings, ceramic Berl saddles, glass Raschig rings and polypropylene Pall rings. The average value of the errors between predicted values and experimental data was about 7%.     

新一代的乱堆填料——梅花扁环

The hydrodynamics and mass transfer of Plum Flower Mini Ring(PFMR),Pall Ring and Intalox Saddle were studied in a 600mm diameter column with air-oxygen-water system over a wide range of liquid loasds.It was shown from the experiments that PFMR had much lower resistance,larger throughput and higher mass transfer efficiency than Pall Ring and Intalox Saddle.It was clear from the comparison that existing equations could not predict the performance of packings very well at high liquied loads.Therefore,new semi-empirical equations of pressure drop,flooding gas velocity and height of transfer unit(HTU)were proposed based on the experimental data.     

PRESSURE DROPS IN PACKED BUBBLE COLUMNS

Pressure drops were measured for air-water system in a cocurrent, upflow bubble column containing each of four types of packing: Raschig rings, Intalox saddle, open-end screen cylinder and solid cylinder. The ranges of variables studied vary from 0 to0.09m/s for gas flow rate, 0 to 0.094 m/s for liquid flow rate and 0.475 to 0.976 for bed porosity. The experimental data well support a single-parameter model developed on the basis of the separated flow concept of Murdock (1962) and Lin (1982).     

Liquid and gas flow patterns in random packings

Large-scale liquid and gas flow patterns were measured in a 0.5-m diameter column dumped with 25- and 50-mm plastic Pall rings and 38-mm ceramic Intalox saddles. Liquid gas velocity and profiles measured for these packings were shown as a function of the initial distribution of the liquid and gas, packed height and liquid and gas flow rates. There was an emphasis in the experiments to study the development of liquid wall flow as well as the interaction between countercurrent liquid and gas. In addition, the effect of maldistribution was studied by means of water cooling experiments. It was of a particular interest to see the extent to which liquid temperature profiles, or analogously concentration profiles, were affected by known velocity profiles.     

Absorption of carbon dioxide in ethylenediamine solutions ii. pilot plant study of absorption and regeneration

Carbon dioxide removal by aqueous ethylenediamine has been studied in 4-inch diameter absorption and stripping columns packed with 1/2-inch Intalox saddles Mass transfer coefficients for absorption were appreciably gas phase controlled and three to four times greater than those for caustic soda. Film theory predictions reproduced the absorption data to within 20% or better Equilibrium data were obtained by using the stripping column reboiler as an equilibrium stage. The enthalpy and rate of carbamate decomposition were inferred from these results, and transfer unit heights were determined for stripping The economics of this process are unfavourable because of the high steam demand and suggest that regeneration equilibria alone can be used for the rough evaluation of new chemical absorbents     

Multi-field synergy study of CO2 capture process by chemical absorption

Carbon dioxide capturing from the flue gas of power stations is an effective way to mitigate the global warming. In order to predict the performance from startup to stable operation in CO₂ absorption process, a multi-field synergy model was developed based on CO₂ capture process in a packed column by means of monoethanolamine (MEA). The model suggests that the integral diffusion–reaction coefficient plays an important role in the diffusion, fluid flow, heat transfer and chemical reaction processes. The influences of the fluid flow, heat transfer and chemical reaction can be justified using corresponding synergy numbers, quantifying multi-field interactive dynamic characteristics of the CO₂ capture process. The simulation shows a good agreement compared with data in the literature. The results show that the packing Reynolds number can be used as a criterion to choose the proper packing. The less the Reynolds number is, the more efficient the reaction absorption is. The average synergy number F_dc would be decreased by 20% with 6 K temperature drop and be descended by 7% with the 2.5% solvent weight percentage increment, which improved the efficiency of CO₂ capture by about 5% and 14%, and lowered the energy consumption by about 5%. The average synergy number F_dh would be decreased by about 8% with the 0.062 mol/molMEA lean solvent loading increment, which improved the efficiency by about 15% and lowered the energy consumption by 5%. After comparing with CMR-2, Raschig rings, Berl saddles and Pall rings, the 33% less average synergy number F_df of the CMR-2 packing with about 5% drop in energy consumption yields the highest efficiency of 71%, which is 10% higher than that of the Berl saddle packing. The results indicate that the proposed multi-field synergy model is an effective way to intensify the capture process as a guideline with the priority of precision and simplicity.     

Hydrodynamique et transfert gaz-liquide dans un réacteur verlifix rempli de différents garnissages

This study concerns several Verlifix three phase reactors formed by the association of a jet venturi upper on a column filled with different solid packings. The gas and liquid flows are downstream cocurrent. Four packings are studied: glass Raschig rings, Coming's monolithic ceramics, microporous alumina pellets and glass beads. For these packings and gas and liquid flow rates fixed, we measure the hydrodynamic characteristics (flow regime, liquid dynamic retention, pressure drop) of the fixed bed and gas-liquid mass transfer conductance of the whole reactor, then we specify the influence of the operative conditions and the type of packing.     

Studies in the vaporization of mercury in irrigated packed beds

Mass transfer coefficients have been measured for the vaporization of mercury flowing countercurrent to air in irrigated packed beds of spheres and Raschig rings. The measured coefficients increased with gas and liquid flow rates, and were correlated in terms of gas Reynolds number and liquid rate. The mass transfer data for liquid metal irrigation were lower than published data for wetting aqueous systems, due to the non-wetting nature of liquid metals. The lower mass transfer coefficients are believed to be attributed to a lower interfacial area for the non-wetting flow of liquid metals, although direct experimental proof was not obtained. The present results are in agreement with data for zinc absorption in molten lead in packed bed (Warner, 1959) when correlated in terms of the relative velocity and total liquid holdup. The results suggest that for liquid metal irrigated beds, the total hold-up is effective in gas phase transfer processes.     

Liquid/Solid Mass Transfer in Fixed Beds

The liquid/solid mass transfer behavior of a fixed bed of cylinders was studied using the diffusion‐controlled dissolution of copper in acidified potassium dichromate. Variables studied were solution velocity and cylinder diameter. For a steady flow, the data were correlated for the conditions 25 < Re < 600 and Sc = 990 by the equation Sh = 2.65 Sc^0.33 Re^0.5. A comparison between the present data and previously obtained data for a fixed bed of Raschig rings has revealed that cylinder packing produces higher rates of mass transfer than Raschig rings.