Liquid‐side mass transfer coefficients in packed towers

Abstract

The physical absorption of gas by water in a tower packed with Raschig rings has been investigated. The liquid-side mass transfer coefficient which was separated by dividing the capacity coefficient by the wetted surface area is discussed from the standpoints of the two-film and penetration theories. A new and simpler dimensionless group is presented which correlates about 90% of the data reported, including the author's own, within an accuracy of f20%.The relation of the liquid-side mass transfer coefficient t o parked-tower performance and physical properties of the system is iniportant from the standpoint of packed-tower designs and interesting from the viewpoint of the mechanism of mass transfer. I n this paper physical gas absorption by water in a tower packed with Raschig rings is described, and kL is discussed. The relation of kL, which covers about 90% of the data reported, including the authors', within a 207, accuracy, was obtained. EXPERIMENTS AND RESULTSThe absorption of pure carbon dioxide by water was studied. T o ascertain the exponent of the Schmidt number, the absorption of pure hydrogen was also studied. Because the degree of purity of the gas was more than 99%, the gas-side resistance was regarded as negligible in comparison with the liquid-side resistance. The mass velocity of the liquid was ascertained by the measurement of the quantity of water flowing from the tower bottom per unit time. The termperatures at the top and bottom of the tower were almost the same and were maintained a t 25 f 1°C.T o measure the end effect samples were taken from the lower tower end and the funnel which was placed immediately below the support plate of the packing.For carbon dioxide a sample of 50 cc. was introduced into 0.2N barium hydroxide solution and then back titrated with 0.1N hydrogen chloride solution. The end effect for 6-, &, and 10-mm. Raschig rings was equivalent to a packing height of 3.6, 3.5, and 3.1 cm. respectively. Water Fig. 1 . Schematic diagram of the absorption system.For hydrogen a sample of 500 cc. was withdrawn by Swanson and Hulett's method (21) and analyzed by the explosion method.As stated above, the gas used was of more than 99% purity, and therefore the gas-side resistance could be assumed to be negligible. The liquid-side capacity coefficient can consequently be computed fromThe saturated concentration C, at 25°C. was taken from the International Critical Tables*.The results for carbon dioxide are shown in Figures 2, 3, and 4. I n these cases it is known by previous reports ( 1 1,16,24) that the gas velocity has no relation to the liquid-side capacity Coefficient under its loading point, and here it was about 50 -150 kg./(sq. m.)(hr.) [I1 -31 lb./ (sq. ft.)(hr.)].To test the dumped packing method the tower was repacked with 6-mm. Raschig ring, and the capacity coefficient was measured. The reproducibility was good (Figure 2).The capacity coefficient increases linearly with the increase of liquid velocity; that is,where for 6-, 8 , and 10-mm. Raschig rings c' and rn" were almost t...

Trickle‐bed reactor performance. Part I. Holdup and mass transfer effects

“…This form of correlation for kLa agreed well with our data as indicated by the straight lines obtained in Figure 7 where (lcLa/D) / ( p / p D ) % is plotted versus GJp. The solid curves in Figure 6 represent Equation (17) The dimensionless correlation of Onda et al (1959) for kLa for absorption columns packed specifically with Raschig rings does not agree with our data for trickle beds containing glass beads or granular particles. The effect of liquid rate on kLa predicted from this correlation is greater than observed experimentally, as shown by the dotted lines in Figure 6.…”

“…On the basis that the error in tliis estimation method is due to at not representing tlie eflective interfacial area, at in Equation (25) can be replaced with atG, The relation between a, and at lor 0.291-cm granular particles is not known. However, we can approximate this relation by employing the correlation cited by Onda et al (1959) for a, for columns paclced with Rascliig rings:…”

Predicting mass transfer in packed columns

“…(17) from the mass transfer resistance distribution on the liquid-side HTUL/HTUoL, cf. Eqs (18) and (19), and the overall concentration difference (x -x*). The latter can be determined from the operating and equilibrium lines, cf.…”

Diffusion‐driven desalination using waste heat in air streams

“…The specific diameter of the packing material is not well defined since the packing is structured. For the purpose of analysis, it is estimated to be d p ¼ 18 mm using the empirical correlation, d p ¼ 4:7=a [10]. This is in good agreement with an estimation of d p based on a cubic element of the structured packing.…”