Some Factors Influencing the Design of Absorption Apparatus.

HE absorption of gases inliquids h a s i 11 t e r e s t e d T m a n y i n v e s t i g a t o r s .C o n s i d e r a b l e work has been done on the resistance to gas flow (27), the distribution of the liquid over the packed surface (S), the form of the packing material, and the mechanism of transfer ( 2 , 7 , 9, 10, 13, 15, 16, 21, 25, $4, 25, 27). S o study has been reported in the literature on the earliest type of absorption apparatus, the spray tower (12, 17). It has been the purpose of this investigation to obtain data on the absorptionOver-all transfer coefficients f o r the absorption of ammonici and sulfur dioxide into a water spray, and the absorption of benzene vapor from air into art, oil spray, were determined for a n inner "wall-free" section of a spray type absorption tower.The effects of variable jluid jlows at three tower heights were investigated. Empirical equations indicating the correlation of these variables are developed and the results compared, when possible, with previous accepted data. The use of these equations for practical spray tower design is pointed out with special consideration of their limitations.of typical gases in Ypray towers and to discover, if possible, a correlation for the more important variables. PHYBIC.4L COKCEPTS O F hfATERIAL TRAKSFERThe following mathematical equation for expressing the mechanism of material transfer from a gas to a liquid has been developed by Lewis (24) :where P = gas concn. C = liquid concn. S = interfacial surface dW/de = weight of material transferred per unit of time Subscripts g, i, L refer, respectively, to conditions at the outside of the gas film, a t the interface, and at the inside of the liquid film.Equation 1 in the integrated form is:where W / e = weight of material absorbed, lb./min. a = interfacial area, sq. ft./cu. ft. of tower vol. (an indeterminate quantity and usually expressed with K g as Koa) Koa = material absorbed, 1b.l min./cu. ft. of tower vol. /mm. of partial pressure driving force V = vol. of the tower, cu. ft. ( AP)av. = logarithmic mean partial pressure ( d r i v i n g force) difference in the s o l u t e gas a n d t h e l i q u i d between the top and bottom of the tower The evaluation of these over-all coefficients under various conditions has been determined hy a number of investigators. Seedless to state, the data are far from complete even with the most common gases. Hasl a m , H e r s h e y , and Keen (9) give data for the absorption of sulfur dioxide in a wetted wall tower. These authors have analyzed the data and found that the over-all gas film resistance, 1/K, is proportional to 1/G0.8, where G is the mass velocity of the gas. The correlated data of several workers (24) in this field indicate that for a packed column the over-all t r a n s f e r resistance is p r o p o r t i o n a l to I where L / A represents pounds of effluent per ~V ' W G O .~ square foot per minute.Kowalke and others ( I S ) , working on the absorption of ammonia in various types of towers, took the over-all coefficient and set it equal...

“…ure 10 indicates the effect of gas and liquid flow on the over-all coefficient at several tower heights.…”

Section: Absorption Of Benzene Vapor By Straw Oilmentioning

confidence: 99%

“…flow (27), the distribution of the liquid over the packed surface (8), the form of the packing material, and the mechanism of transfer (2,7,9,10,18,15,16,21,28,24,25,27). No study has been reported in the literature on the earliest type of absorption apparatus, the spray tower (12,17).…”

mentioning

confidence: 99%

Absorption of Gases in Spray Towers

Hixson¹,

Scott²

1935

“…Haslam, Ryan, and Weber (8) found values of Ksa between 0.45 and 0.68 for the absorption of sulfur dioxide by water in a small spray tower 8 inches in diameter and 30 inches high. Their data show the importance of both liquid and gas film resistances for the absorption of sulfur dioxide.…”

Section: Previous Workmentioning

confidence: 99%

Absorption of Gases by Liquid Droplets Design of Simple Spray Scrubbers

Johnstone¹,

Williams²

1939

“…• -pa, and dps = -dp a. Hence Equation 2a becomes dpB _ WA p B kw (3) For any section of an apparatus operating continuously, Wa is constant and, as shown by Lewis and Chang (6), Equation 3 may be integrated from x = 0 to x = x, and from ps = psi to ps = ps;, giving for point conditions: wherein kw is the diffusion coefficient expressed in weight units, (grams) (cm. )/(hour) (sq.…”

Section: Basic Laws Of Diffusion Of Gases Through Gasesmentioning

confidence: 99%

Studies in Absorption

Hanks¹,

McAdams²

1929

The laws expressing the rate of diffusion of one gas through another have been adapted to the absorption of a soluble gas from an insoluble gas by a liquid.Equations have been developed to express the influence of the major variables normally encountered on the rate of absorption of gases by liquids, in a given type of apparatus where gas-film diffusion controls the absorption rate.Data are presented on the steady absorption of ammonia by water, where the concentration of ammonia in the gas was varied between 6 and 65 mol per cent.It is shown that the absorption equations generally used are inadequate to explain these data. The equations here developed appear to be satisfactory. It is shown that the film coefficient ordinarily employed may vary with the partial pressure of the inert gas in the gas film, and a method of allowing for this change is given.Data are shown on the effect of absorbing ammonia by water in a wetted-wall tower from three different carrier gases, having a sixfold range in specific diffusion coefficients.Hydrogen, air, and butane have been studied. and it is found that the gas-film coefficients, for a given mass velocity, are greatest through hydrogen, lower through air, and the least of all through butane. The data are explained quantitatively by changes in the diffusion coefficients of the gas mixtures, and by differences in film thickness occasioned by different mass velocities and viscosities of the gases.