Comparative performance of packings for gas-liquid contacting columns

The performances of Raschig rings, Pall rings, Intalox saddles, and Berl saddles were compared in respect to pressure drop and mass transfer efficiency, in a 6-in. I. D. tower having a packed height of 4-ft., over a matrix of gas and liquid flowrates representing the irrigating and loading flow regimes. The mass transfer experiments were conducted employing a gas absorption system in which both phase films control the overall rate of mass transfer, an improvement in terms of industrial applicability over many previous studies. The Berl saddles were observed to yield the lowest pressure drops of the four. The Intalox saddles yielded the highest overall mass transfer coefficients, followed closely by the Berl saddles and Raschig rings.     

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.     

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.     

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.     

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.     

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.     

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%.     

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。     

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.     

填料塔气液传质参数研究（Ⅰ）──有效传质面积及容积传质系数

用化学吸收法测定了拉西环填料的有效传质表面积和容积传质系数，并进一步用物理法比较测定了容积传质系数。实验证明，用化学法测得的容积传质系数大于物理法测定值。并得出有效传质表面积及容积传质系数与喷淋密度的关系式。     

Dehumidification of Moist Air with Simultaneous Removal of Selected Indoor Pollutants by Triethylene Glycol Solutions in a Packed-Bed Absorber

Abstract

A packed bed absorber-stripper system was used to remove selected indoor pollutants during the dehumidification of air by triethylene glycol solutions. Triethylene glycol concentrations of 90% and 95% by weight in water were used. Both random and structured packings were employed to provide the contact surface between the liquid and gas phases. A six-inch I. D. absorption column was operated between 50% and 80% of flooding conditions. The heights of a transfer unit for mass transfer for randomly packed 5/8-inch polypropylene Flexi rings and 1/2-inch ceramic Intalox saddles varied from 0.12 m to 0.17 m when dehumidifying air only. However, the height of a transfer unit was in the range of 0.31 m to 0.40 m for the cross corrugated cellulose and PVC structured packings. Heat and mass transfer coefficients were also calculated from the experimental data and were correlated with various process variables. The values predicted by these correlations were within ±10% of the experimental data.

Pollutants used in the study included formaldehyde, toluene, 1,1,1-trichloroethane and carbon dioxide, and their concentrations in the air were controlled to 0.02 ± 0.005 ppm, 3 ± 0.02 ppm, 24 ± 0.1 ppm, and 1000 ± 5 ppm, respectively. Although nearly 100% of the toluene and 1,1,1-trichloroethane were removed by the 95% triethylene glycol solution, only 56% of the carbon dioxide and 30% of the formaldehyde could be removed from the air stream under similar conditions. As expected, the removal of these pollutants by the triethylene glycol solution was not affected by varying the relative humidity of the air.     

Mass transfer in packed columns: Co-current (downflow) operation: 1 in. And 1.5 in. Metal pall rings and ceramic intalox saddles: Multifilament gauze packings in 20 cm and 38 cm i.d. columns

The theory of gas absorption accompanied by fast pseudo-mth order reaction was used to obtain values of effective interfacial area, a, in 20 and 38 cm i.d. packed columns which were operated co-currently (downflow). Values of a were obtained for 1 in. and 1.5 in. metal Pall rings; 1 in. stainless steel Pall rings, having length (height) to diameter ratio of 1.0, 0.75, and 0.5; 1 in and 1.5 in. ceramic Italox saddles; and stainless steel multifilament wire gauze type packing over a wide range of gas and liquid superficial velocities. The gas superficial velocity was varied from 30 to 255 cm/sec in the 20 cm i.d. column and 14 to 73 cm/sec in the 38 cm i.d. column. The liquid superficial velocity was varied from 0.2 to 3 cm/sec in the 20 cm i.d. column and 0.2 to 1 cm/sec in the 38 cm i.d. column. Different flow regimes, namely, trickle flow (film flow), pulse flow and transition from pulse to disperse flow, were covered. The values of a were found to be in the range of 0.6 to 2 cm²/cm³ for the trickle flow (film flow) regime, and 2.4–5 cm²/cm³ for the pulse flow regime. In the case of multifilament wire gauze packing (MFWGP) remarkably high values of a up to 16 cm²/cm³ were obtained in the pulse to disperse flow regime.     

Comparison of mass transfer efficiency in horizontal rotating packed beds and rotating biological contactors

In this study, the mass transfer efficiencies of a novel horizontal rotating packed (h‐RPB) bed and the conventional disc‐type rotating biological contactor (RBC) were studied at four speeds and seven submergences. Pall rings of two different sizes (25, 38 mm), superintalox saddles and a wiremesh spiral bundle were used as packings in the h‐RPB. Volumetric gas–liquid mass transfer coefficients were determined by unsteady state absorption of atmospheric oxygen in de‐aerated water. Power consumption per unit liquid volume has been found for all geometries tested. The oxygen transfer efficiency values for the h‐RPB were found to be 2–5 kg kWh^?1 and for the disc RBC were found to be 1–2 kg kWh^?1. The performance of the h‐RPB was also compared with other gas–liquid contactors such as surface aerators. The study proves that the h‐RPB is a energy efficient alternative to conventional contactors. Copyright © 2005 Society of Chemical Industry     

Determination of mass transfer coefficients for packing materials used in biofilters and biotrickling filters for air pollution control—2: Development of mass transfer coefficients correlations

Correlations that allow determination of gas film mass transfer coefficients (k_Ga_t, k_Ga_w) and liquid film mass transfer coefficients (k_La_w) for packing materials used in biofilters and biotrickling filters for air pollution control are presented. Lava rock, polyurethane foam cubes (PUF), Pall rings, porous ceramic beads, porous ceramic Raschig rings, and various compost-woodchips mixtures were used as packing materials. The functionality of gas and liquid velocity on mass transfer coefficients (k_Ga_t,k_Ga_w,k_La_w) obtained experimentally (see Part 1 of this paper) was correlated using modified Onda-type equations. The correlation equations helped to better understand the sensitivity of gas and liquid velocities on mass transfer, and the effects of packing wetting. Each packing had a different functionality with gas and liquid velocity and different wetting property, hence different correlation equations were needed for the different packing materials. Most of the fitted data fell within ±20% of the experimental values.     

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.     

Counter-current absorption using wire gauze packings

The dynamic liquid hold-up, ?_LD, effective interfacial area, a, and the liquid side mass transfer coefficient k_La were determined for 0.1 m and 0.2 m multifilament wire gauze packings, 0.0125 m double walled wire gauze partition rings and 0.025 m wire gauze saddle packings in columns operated countercurrently. The theory of gas absorption accompanied by fast pseudo mth order reaction was used to determine the effective interfacial area. The values of liquid side mass transfer coefficient for the multifilament wire gauze packings were obtained by absorbing lean carbon dioxide in a buffer solution of sodium carbonate and sodium bicarbonate. K_La values for the other packings were obtained by absorbing pure carbon dioxide in tap water. The values of a and k_La for multifilament wire gauze packings were found to be two to four times higher as compared to the conventional ring or saddle packings. Further, the superficial liquid velocity was found to have marginal effect on a. The double walled wire gauze partition rings offered a values which were 1.5–2.0 times higher than that offered by 0.016 m s.s. Pall rings at low values of superficial liquid velocity (<3 × 10^{?3 m/s}.     

三种开孔环形填料传质性能的研究

本文介绍了在φ600mm的实验装置内,对Dg50mm聚丙烯鲍尔环（井）、聚丙烯鲍尔环（米）、聚丙烯阶梯环（Ⅰ）填料,用空气脱吸CO_2水溶液,测得的传质性能数据,并用此数据对液膜传质系数的不同关联方法进行了核算、对比。认为:恩田等所提出的计算液膜传质系数的关联式,在计算新型开孔环形填料时偏差较大,主要是由于他们所提出的形状系数a_td_p,未能反映这些新型填料的形状特征对其传质性能的影响。本文用形状修正系数ψ来代替a_td_p,这样恩田等的计算液膜传质系数的关联式,其应用范围被扩展到新型开孔环类型填料的范围。 采用新的形状修正系数ψ后,液膜传质系数的计算式改写为 k_L(ρ_L/μ_(Lg))~1/3=0.0095(L_G/a_ωμ_L)~2/3(μ_L/ρ_LD_L）~(-1/2)ψ~0.4对各种不同类型填料其形状修正系数值为 本式可适用于Dg50mm以下的上述各类填料的计算。     

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.     

填料塔气液传质参数研究（Ⅱ）──气膜传质系数

用拟一级快速化学反应吸收法测定了拉西环填料塔的气膜传质系数，并得出其无因次表达式。