an
II/Ec]Unit Operations Review
Gas Absorption by Max Leva, Consulting Chemical Engineer, Pittsburgh, Pa. Chin-Yung Wen, West Virginia University, Morgantown, W . Vu. Emphasis is on the most recent advances in gas-liquid correlations as they can be used in gas absorption processes
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As the contributions during the past year have again been considerEXPECTED,
able from sources that report in English and other western tongues. The contributions from Slavic and, in particular, Russian sources have, however, also been considerable. Since the cost of translations is ridiculously high and the brief summaries that appear in the usual abstracting media are often too sketchy to be used as a basis for a review, it was decided to omit these important references. Regrettably, it is realized and admitted that thereby this review effort assumes more than a tinge of incompleteness. This will, however, immediately be remedied in future reviews as soon as the source material can be made readily available a t a price that a can be afforded for this task-through universal translation service or through some other means. As a note of reference, the current issues of Chemical Engineering Science give a listing of selected titles of Soviet papers of interest to chemical engineers. The title of this review has been altered. The specific reports dealing with humidification are so few in number that the old title was hardly justified. Of course, any studies dealing with humidification, specifically or in general, are included. This review covers the literature through Dec. 31, 1960.
Flow Through Equipment 9.
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A discussion of single phase flow through beds of various tower packings was given by Crowther and others (8). A generalized correlation for pressure drop, by a type of equation suggested earlier by Ergun, was proposed. Another specific study of single phase pressure drop, in which the effect of the hole size in the Raschig ring was investigated, was reported by Fan (18). Data were provided for cylinders and two sizes of related rings. Pressure drop in an irrigated 6-inchdiameter column packed with Raschig rings was investigated by Whitt (45). With small rings of about 0.5-inch nom-
inal size, the gas seemed to pass mainly through the interpacking spaces, whereas with larger rings the flow distribution improved. As far as the liquid component was concerned, this appeared to be equally distributed in small ring beds. However, with large rings the inside ring volume is favored by the liquid flow. A study of the effect of fluid properties on packed bed pressure drop was reported by Cecchetti ( 3 ) ,whereas Sonntag (38) investigated the effect of voidage on the flow resistance through beds of spheres, cylinders, and Raschig rings. I t is interesting that with rings the inside void space seemed only effective to an extent of about 20%. Nonuniformities in the flow pattern of gas through rings were also reported by DeMaria and White (70). T o detect this they resorted to a tracer technique, using helium. The nonuniformity became more severe as the flooding zone of the packing was approached. The nature of liquid hold-up was investigated by Turner and Hewitt (42). They reduced the situation to the most simple case of two neighboring, touching spheres. Liquid hold-up and flow distribution through packings were also studied by Hwa and Beckmann (26), who used a radiological method. A correlation study of pressure drop, loading, and flooding data was undertaken by Eduljee (74). For a considerable segment of the available data, he suggested a correlation which was conceived by combining the loading point correlation of Otake and Kimura with the generalized isobaric pressure drop, loading, and flooding presentation previously given by Leva. Because of the paucity of concurrent flow data that appear in the literature, the concurrent flow data of Dodds and others (72) are indeed appreciated. They worked with an 18-inch-diameter column charged with Raschig rings and Berl and Intalox saddles and reported pressure drops and liquid hold-up. With all the gas-liquid flow studies reported, there was also a liquid-liquid study. Thus Venkataraman and Laddha
(44) worked with a 2-inch-diameter column and a number of liquid-liquid systems. Limiting flow velocities and hold-up were observed for some ring packings, Berl saddles, Lessing rings, and spheres. A nomograph for evaluating vapor velocities through bubble cap columns, equipment not closely related to the above type of units but certainly of more than general interest, was given by Davis ( 9 ) .
Absorption Equipment Tests Pressure drop, flooding data, as well as capacity coefficients for the systems air-water and air-methanol, were reported by Ellis and others (77). The Spraypak sections studied were 15 and 27 inches long and 2.75 and 7 feet high. For the two systems considered, a generalized data presentation by way of the square root of the Schmidt numbers was not wholly satisfactory. Design and operating data for HCI recovery, using a packed column as well as a cascade falling film-type absorber, were reported by Bingeman and Reynolds ( 7 ) . Falling liquid curtains were considered by Bromley and others ( 2 )for absorbing C O Zand NHI by water. The observed mass transfer coefficients seemed of the same order of magnitude that would be expected from packed columns, operating under similar loading conditions. As expected, this contacting system is capable of permitting operation under very high liquid mass velocities. An interesting extension of the wetted wall column into the realm of an evaporative crystallizer was suggested by a study reported by Chandler ( 4 ) . T h e use of graphite blocks for recovery of HCI was described by Hilliard (25).
Process Data Besides observing pressure drops and hold-up, Dodds and Stutzman ( 7 7 ) also obtained absorption data for concurrent flow. Again the tower was of 18-inch diameter and Raschig rings and Berl and Intalox saddles were used as VOL. 53,
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packings; C02-NaOH was the absorption system. The desorption of H2S from NaCl brines was studied by Piester (35) in an 8-inch-diameter column, packed with 1-inch carbon Raschig rings to a height of 14.5 feet. Thoughts about scale-up were also given. The recovery of selenium by absorbing SeOZ in a special set-up using a smallscale packed tower was described by Molyneux (33). Ethanolamine scrubbing of acid gases was discussed by Hall and Polderman (20) with a view to establishing proper operating procedures and studying corrosion problems. In an article which discusses primarily the Fischer-Tropsch process and problems relating to the technology of synthetic liquid fuels, Field and others ( 1 9 ) summarized briefly the related major gas purification processes.
Bubbling Flow, Films, and Liquid Jets
A special unit, consisting essentially of a n upright cylinder contained in another upright cylinder, was constructed by Timson and Dunn ( 4 0 ) . The absorbing medium was in the annulus, through which gas flow occurred as well. Since the inside cylinder could be rotated. the bubbles were thereby subjected to a shearing stress. The systems considered were oxygen or air and water containing various additives. An absorption mechanism study was made by Yoshida and others (46). Various techniques were used with the system of oxygen and NaS02, such as bubbling flow with and without mechanical agitation, as well as a trickling bead column and horizontal, mechanically agitated absorption surfaces. A somewhat similar study was also reported by Hyman and van den Bogaerde (27). They also used NaS02 as the absorbent with air, and contacting occurred in small-scale stirred vessels. T h e mechanics of bubble flow were studied by Siemes and Borchers (37). A column with porous bottom plate was used. Bubble size distribution was approximately symmetrical and was characterized by a peak diameter which could be readily presented by a standard deviation. The pore size in the plate had only little effect on bubble size. With increasing gas flow, bubble size increased, too, u p to a certain point. Though not dealing with absorption, a film flow study dealing with the dynamics of vertical falling film systems, made by Dukler (73), is of general interest. The kinetics of the absorption of phosgene into water jets and jets of aqueous solutions were studied by Manogue and Pigford (30). The results could be interpreted by an unsteady state absorption-plus-reaction theory. This was further supported by similar data pertain-
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ing to C O Zand SO2 absorption in water in the same equipment.
liquid and Gas Mass Transfer Coefficients on Packings Liquid-side mass transfer coefficients for the system C O Z and water were obtained by Onda and others (34). Berl saddles were used as packing. and, in accord with the suggestion of Lubin, the surface of the packing was calculated on the assumption that it is a hyperbolic parabaloid. The data xvere expressed by a correlation involving the usual experimental and floiv parameters. A study of COn absorption with water to which varying quantities of wetting agents were added was reported by Hikita (22). With the Raschig ring column used, the capacity data exhibited a minimum value for a certain wetting agent concentration. An interfacial absorption study for C O Z into various solvents contacted in packed Raschig ring and Berl saddle columns was described by Hikita and others (23). Experimenting with a single packing piece (Raschig ring, Berl saddle), Hikita and Ono (24) attempted to evaluate the mechanism of absorption by the film for systems of C O Zwith various solvents. New data for absorption of COz into K z C O ~KOH, , monoethanolamine, and mixtures of absorbents were offered by Ellis (75). Various ring- and coke-packed columns were considered, ranging in diameter from 5 to 244 cm. Despite this impressive size range of the equipment, it was nevertheless decided that data for scale-up were still insufficient. Air and carbon tetrachloride were contacted in a packed column by Shulman and Robinson (36). The data, being in satisfactory agreement with other similar material, could therefore be used to propose a generalized expression for the gas-phase mass transfer coefficient.
Reviews and Miscelbneous Studies
A comprehensive account of correlations permitting estimation of liquidphase and gas-phase mass transfer coefficients for packed towers was given by Cornell and others ( 7 ) . Particularly informative are the summaries of literature studies. In a follow-up report, Cornell and others ( 6 ) presented new, large-scale mass transfer data, and some typical problems arising with packed to'iver design were presented. General difficulties and limitations attending the application of the twofilm theory to the procurement of data, and how to use them, were taken u p by Hardouin (27). Consideration of a typical gas drying operation, as given by
INDUSTRIAL AND ENGINEERING CHEMISTRY
the system air-HZSO1, illustrates the points raised. Various aspects of absorption were also discussed by Teller (39). For predicting flooding points and irrigated packed tower pressure drops, he proposed to use the generalized correlation developed earlier by Leva. Packing factors, having been reported in error, were corrected elsewhere (29). A graphical design method, where absorption with chemical reaction prevails, was worked out by King and Fielding (28). The method is actually an extemion of the McCabe-Thiele diagram, and the data considered pertain to absorption of nitrogen oxides in water. A thesis by Collins (5) dealt with the comparatively rare instance of gas absorption in concurrent flow. Sieve tray performance data under reduced pressure were reported by Ellis and others ( 1 6 ) , and tray efficiency as influenced by liquid dispersion was taken up by Miyauchi ( 3 2 ) . A brief note pertaining to a new type of sieve tray with liquid flow over the plate in radial direction was contained in a report by Melichar (37). The relationship between the duty and size of cooling towers was presented by Valentin ( 4 3 ) . A summary of cooling tower developments was given by Tow (47) ; comparing the various designs such as packed tvpe, splash type, and grid type, it was concluded that the latter was apparently most favorable.
Literature Cited (1) Bingeman, J. B., Reynolds, L. B., Chem. Eng. Progr. 5 6 , No. 12, 67 (1960). (2) Bromley, L., Read, S. M., Bupara, S.S., IND.ENG.CHEM.5 2 , 311 (1960).
(3) Cecchetti, R. L., Ph.D. Thesis, University of Maryland, 1959. (4) Chandler, J. L., Brit. Chem. Eng. 4, 83-7 (1959). (5) Cpllins. D. E., Ph.D. thesis, Purdue University, 1959. (6) Cornell, D., Knapp, W. G., others, Chem. Eng. Progr. 5 6 , No. 8, 48 (1960). (7) Cornell, D., Knapp, W. G., Fair, J. R . , Zbid., 5 6 , h-0. 7 , 68 (1960). (8) Crowther, R. H.? Taecker, R. G., Fan, L. T., Gknie chim. 84, No. 3, 73 (1960). (9) Davis, D. S., Brit. Chem. Eng. 5 , 810 (1960). (10) DeMaria, F., White, R. R., A.I.Ch.E. Journal 6. 473 (1960\. (11) Dodds, W.'S.,' Stutzman, L. F., Zbid., 6, 197 (1960). (12) Dodds, W. S., Stutzman, L. F., others, Itid., 6, 390 (1960). (13) Dukler, A. E.. Chem. Eng. Procr. 5 5 , N ~ i .n> -63-7' (1 059) \-'--/' Ediljee, H. E., Brit. Chem. Eng. 5 , ( Y 3 0 (1960). (15) Ellis. J. E.. Trans. Znst. Chem. Eners. (London) 38, 216 (1960). (16) Ellis: S. R . M., Barker, P. E., Contractor, R. N., Ibid., 38, 2 1 (1960). (17) Ellis, S. R. M., Barker, P. E., Hodgson, W. S., Zbid., 98, 267 (1960). (18) Fan, L. T., Can. J . Chem. Eng. 38, 138 (1960). \-. - - > . (19) Field, J. H., Benson, H. E.: Anderson I
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R. B., Chem. Eng. Progr. 56, No. 4, 44 (1960). (20) Hall, G. D., Polderman, L. D., Zbid., 56, No. 10, 52 (1960). (21) Hardouin, M. S., Ginie chim. 83, No. 2, 41 (1960). (22) Hikita, H., Chem. Eng. (Japan) 24, 9 (1960). (23) Hikita, H., Kataoka. T., Nakanishi, N.,Zbid., 24, 2 (1960). (24) Hikita, H., Ono, Y , Zbid., 23, 808 (1959). (25) Hilliard, A. J., Brit. Chem. Eng. 5 , 174-8 (1960). (26) Hwa, C. S.,Beckmann, R. B., A.Z.Ch.E. Journal 6 , 359 (1960). (27) Hyman, D., Bogaerde, J. M. van den, IND.ENC.CHEM.52, 751 (1960). (28) King R. W., Fielding, J. C., Trans.
Znst. Chem. Engrs. (London) 38, 71 (1960). (29) Leva, Max, Chem. Eng. 67, No. 21, 263 (1960). (30) Manogue, W. H., Pigford, R. L., A.Z.Ch.E. Journal 6, 494 (1960). (31) Melichar, B., Brit. Chem. Eng. 5, 723 (1960). (32) Miyauchi, Terukatsu, Chem. Eng. (Jafian) 24, 434 (1960). (33) Molyneux, J., Brit. Chem. Eng. 4, 40 (1959). (34) Onda, K., Okamoto, T., Honda, H., Chem. Eng. (Japan) 24, 490 (1960). (35) Piester, L. W., Chem. Eng. Progr. 56, 1, 64 (1960). (36 Shulman, H. L., Robinson, R. G., .I.Ch.E. Journal 6, 469 (1960). (37) .Siemes, W., Borchers, E., Chem. Eng. SGZ.12, 77-87 (1960).
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a I N T H E WORKS Coolant Purification and pH Control for Nuclear Reactors
T. F. Demmitt General Electric Co., Richland, Wash. High temperature, water-cooled nuclear reactors may require low pH recirculating water, to suit the materials of construction and the operating conditions. Ion exchange resins were used in tests to maintain coolant purity and minimize coolant borne activity. The results are of major interest in aluminum systems
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(38) Sonntag, G., Chem.-Zngr.-Tech. 32, 317 (1960). (39) Teller, A. J., Chem. Eng. 67, No. 14, 111-24 (1960). (40) Timson, W. J.. Dunn, C. G., IND. ENC.CHEM.52, 799 (1960). (41) Tow, D. J., Brit. Chem. Eng. 5 , 191-3, 256-9 (1960). (42) Turner, G. A , Hewitt, G. F., Trans. Znst. Chem. Engrs. (London) 37, 329-34 (1959). (43) Valentin, F. H. H., Brit. Chem. Eng. 5, 633 (1960). (44) Venkataraman, G., Laddha, G. S., A.Z.Ch.E. Journal 6, 355 (1960). (45) Whitt, F. R., Brit. Chsrn. Eng. 6, 179-82 (1960). (46) Yoshida, F., Ikeda, A., others, IND. ENG.CHEM.52, 435 (1960).
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Reducing Tungsten Oxides
L. G. Austin Pennsylvania State University, University Park, Pa. Previous experimental data on the kinetics of hydrogen reduction of tungsten oxides are re-examined. It is found thatthe over-all rate is controlled by the areas of the phase boundaries present. Rate constants and activation energies are given for each oxide
Stabilizing liquid-liquid Dispersions b y Agitation
Recovering Sodium Silicofluoride from Wet Process Phosphoric Acid Sydney Atkin and Enrico Pelitti Chemical Construction Corp., New York, N.
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A. P. Vila and John Hegedus American Cyanamid Co., Brewster, Fla.
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A continuous process has been developed for recovering fluoride from wet process acid, by precipitation with sodium carbonate. Over 75% of the fluoride is removed. Optimum conditions are outlined. In addition to by-product recovery, fume problems are reduced and effluent treating costs are lowered
J. M. Church and Reuel Shinnar Columbia University, New York, N. Y. Mixtures of molten wax in dilute aqueous solutions of protective colloids were used to determine the factors controlling stability of dispersions. A possible mechanism is suggested, and a method for predicting the approximate conditions required for stabilization is developed
Alkylation-An
I/EC Unit Processes Review
L. F. Albright and R. N. Shreve Purdue University, Purdue, Ind. Commercial production of aluminum alkyls, expected to find large-scale use as polymerization catalysts, pyrophoric fuels for ram jets, and intermediates, i s now a reality. Open discussions have revealed considerable divergence of opinion on the true effects of operating variables on alkylation reactions
Concentrution Control b y Electrochemical Methods
M. E. Findley Auburn University, Auburn, Ala. I f concentration can be determined by simple titration, the process can be controlled by pH or Redox potentials. The sample is approximately titrated with a solution containing a buffer, and the difference between actual and expected measurements actuates a controller. The control loop is simpler than direct titration equipment, and sampling dead time is reduced
Theory of Centrifugation Charles M. Ambler The Sharples Corporation, Philadelphia, Pa. The laws controlling particle movement are applied to centrifugation processes. Theory underlying the operation of gas centrifuges, ultracentrifuges, and centrifugal filters is explained, as well as the basis for more standard industrial equipment VOL. 53, NO. 5
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