January 1951
b
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Filling machines are now available for free-flowing and nonfree-flowing products in which rapid and dustless filling is obtained by applying a controlled vacuum to the containers being filled. Large machines operating on this principle fill as many as 300 containers per minute with high accuracy, but small machines are also made for filling limited production items (24). During 1950, i t seems that all types of materials handling devices were improved, even the wheelbarrow. William Gemienhardt, a member of the staff of the New York University College of Engineering, has designed a new wheelbarrow with an ingenious wheel suspension which permits a loaded wheelbarrow to ride over a 4-inch curb with relative ease (25). Purdue University and the American Materials Handling Society sponsored the Second Annual Materials Handling Conference at Lafayette, Ind., in February 1950. This conference i s only one of many evidences of the increased attention being given to materials handling. In spite of increased use of new and better materials handling equipment, great improvements can still be made in the actual handling of materials. Perlman (93) says that only 3 hours of the average freight car’s day are spent in over-the-road movement, while 21 hours are spent in terminal detention. He sags that by adding 4 minutes per day t o each car’s over-the-road movement, the nation’s car inventory could be increased by $100,000,000. This is only one of examples t h a t could be cited to show the great potential field for better handling methods and equipment. LITERATURE CITED
( I ) Arkell & Smiths, Canajoherie, N. Y . , personal communicationto
author. Atlantic Pump Corp., P.O. 6751, Philadelphia 32, Pa., unnumbered bulletin on Hermetik pump. 28, 3346 (1950). (3) CIiem. Eng. (4) CooperRessemer Corp,, Mt. Vernon, Ohio, bulletin on intensifier. (2)
111
(5) Distillation Products Industries, Division of Eastman Kodak Co., Rochester 3,N. Y., literature on KB-300 vacuum pump. (6) Engineering Societies Library, 29 West 39th St., New York 18, N. Y., “Bibliography on Pallets Used in Modern Materials Handling,” 1949. (7) Fab-Weld Corp., Pickwick and Richmond Sts., Philadelphia 34,Pa., unnumbered bulletin on Return-o-tainer. (8) Fairbanks, Morse & Co., 600 South Michigan Ave., Chicago 5, Ill., BUZZ. 5400 K-1. (9) General American Transportation Corp., 135 South LaSalle St., Chicago 90,Ill., literature and unnumbered bulletins on Trans-Flo car. Gilbert & Barker Mfg. Co., West Springfield, Mass., Bull. P-463. Goulds Pumps, Inc., Seneca Falls, N. Y., Bull. 636-1. Gramm Trailer Corp., Delphos, Ohio, bulletins on bottom hopper dump trailor and Air-Slide trailer. Hofman Laboratories, 216 Wright St., Newark 5, N. J., unnumbered bulletins on liquid helium container. Inpersoll-Rand Co., 11Broadway, New York 4, N. Y., Bull. 3150. Jeffrey Mfg. Co., 909 North Fourth St., Columbus 16, Ohio, unnumbered bulletin on mechanioal vibration conveyer. Mead Specialties Co., Inc., 4114 North Knox Ave., Chicago 41,Ill., literature on baby btdldoeer. Mech. Eng., 71, No. 10,848 (1949). Iba‘d., 72, No. 7, 583 (1950). Ibid., 72,No. 10, 821 (1950). Modern MuterTiuls Handling, 5, No. 9, 36 (1950). Ibid., No. 10, 16 (1950). Ibid., pp. 38, 39. Perlman, A. E., Mech. E n g . , 72, No. 8, 641 (1950). Pneumatic Scale Corp., Ltd., Quincy 71, Mass., unnumbered bulletin on Vacuflow fillers. Power Generution, 54, No. 6 (1950). Richardson Scale Co., Clifton, N. J., Bull. 3449. Roto-Flo Pump Corp., 2608 West Ruby Ave., Milwaukee 9, Wis., bulletins. Stephens Adamson Mfn. Co., Aurora, Ill., Bull. 849. Von Thaden, H., Mech; Eng., 72,No. 7, 549-51 (1950). Warren, R. F., Chem. Engr., 57, No. 1, 118-19 (1950). 42,79A (June 1950). Wright, R. E., IND.ENG.CHEM., RECEIVED October 16, 1950.
MIXING J. HENRY RUSHTON‘ ILLINOIS lNSTlTUTE OF T E C H N O L O G Y , C H I C A G O , ILL.
During the past year a large number of articles have appeared on agitation and mixing. There has been considerable activity along experimental lines, and important engineering performance data have been reported. Several articles give equipment performance data, both from the standpoint of power characteristics and process applications. Discussions have appeared which relate fundamental fluid mechanics theory to mixing. The most significant and valuable work available to date on mixing applied to fermentation (a gas-liquid-solid mixing operation) has been published. *
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H E previous annual review of developments in mixing AND was published in the January 1950 issue of INDUSTRIAL ENGINEERING CHEMISTRY (31) and it brought references u p to the date of October 1949. An annual survey of new equipment, as announced by equipment manufacturers, was published in Chemical Industries (8). A description of present theory and practice in mixing appears in “Technique of Organic Chemistry” (33). Special attention is directed to the proper use of mixers in organic chemical research. The new edition of “Chemical Engineers’ Handbook’’ (39) oontains a section on mixing. It includes most of the material of the previous editions t o which have been added very brief summaries of some of the recent literature. A list of applications for various types of mixers has been published by Lyons (18). 1 Also director of research, Mixing Equipment Co., Rbchester. N. Y.
Morello and Poffcnberger (24) published a n authoritative survey of commercial extraction equipment which includes performance characteristics of several in which mixers are used. A review of various methods reported in the literature for assessing the performance of mixers has been prepared by Black (4).
POWER CHARACTERISTICS OF MIXERS
Extensive data have been published by Rushton, Costich, and Everett (34) to establish basic mixing impeller characteristics. The fluid mechanical basis for power correlations is developed and shown to be an accurate basis for the correlation and interpretation of performance of the common types of mixing impellers, D a t a are correlated for impellers from 3 to 48 inches in diameter for tanks 8.5 to 96 inches in diameter, and for fluids with viscosities of from 1to 40,000 centipoises. From these data it is possible to predict power consumption for the majority of mixers in experimental and industrial use. The significance of power characeristics to proper use of impellers and tank fittings is pointed out. A technique is outlined whereby the operating characteristics of any impeller in any tank arrangement and fluid can be found by only a few experimental runs made a t significant conditions.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
O’Connell and Mack (27) published power characteristics data o n simple paddle mixers (2, 4,and 6 flat blades) in “fully baffled tanks.” The data can also be correlated conveniently by the method of Rushton, Costich, and Everett; these data make very useful additions to the constants and exponent values which are summarized in Tables IX and X of the Rushton et al. article (34). For those who prefer to use an alignment chart rather than a slide rule for calculating the Reynolds number for mixing, a small chart has been published by Schneider (36). N E W MIXERS
A description has been given for a pendulum- or shaker-type agitator which is useful as a high pressure autoclave (23) Poiver requirements are given. The article also gives a very brief review of power requirements to rotate Peveral types of impellers. A tabulation of some power requirements and their relation to effectiveness in several process applications is given by 1Iagnusson (19). A rotating drum-type mixer for handling high viscosity liquids is described briefly by Fesenko (13). Merz (22) describes two impellers and states that they may be used t o enhance solution processes. The radial blade turbine has holes drilled in the disk and blades; the propeller has stabilizer fins cast on the blades (like the stabilizer fins used in this country). Jackson (16) has designed a new blade shape for a propeller which is intended to chop and cut solids and aggregates in addition to creating the fluid motion required for mixing. THEORETICAL ASPECTS OF M I X I N G
An article by Fossett and Prosser (14) on the application of free jets to the mixing of fluids in bulk reports significant and important data on model tests and on large tank blending operations. Performance was determined for free jets of liquid used to mix liquid in large cylindrical tanks. The time required to achieve blending of gasoline in large storage tanks was measured in scale models and full size tanks, wherein the mixing was accomplished by one or more jets of liquid. The principles developed should be applicable to side-entering propeller mixers which are in wide u4e for such blending operations. The data give blending times for various light and heavy oils. Sufficient data are given to calculate power requirements for many conditions of operation. Several examples to illustrate the application of the data are worked out, and the theory developed enables prediction of performance in the largest tanks used (144 feet in diameter, 33 feet high). A short article by Bershader and Pai (3) describes a technique for measurement of flox and density distribution in the turbulent jet of a fluid in supersonic flow. This article is of theoretical interest because the principles of jet flow are applicable to mixing and are aiding in a better understanding of the relation of fluid motion and mixing. A discussion of some applications of fluid mechanics theory to mixing was presented by Rushton (32) a t the 1949 Conference on Industrial Hydraulics. Data are presented which show the conditions necessary t o produce the same flow patterns and similar dynamic conditions in mixing tanks of two or more different sizes. The basic fluid dynamic theory is presented whereby scale-up to large size mixing equipment from pilot plant studies can be made. Serner (37) presented a discussion of an “effective radius of agitation” in viscous liquid mixing. Some arbitrary assumptions are made, after which data are calculated and presented in a chart purported to show the power input necessary to achieve a given flow turbulence at various effective radii for different viscosity fluids. There are no experimental data or fluid mechanics principles cited to justify the assumed flow patterns which are postulated. The author states that factors of safety must be applied in practical application of his ideas.
Val. 43, No. 1
Three recent articles (7, 9, 20) on the mixing of solid particles are of interest in leading to a better understanding of liquid as well as of solids mixing. Maitra and Coulson (9, 90) discuss experiments with solids designed to test theory which has previously been used in liquid mixing processes. They were particularly interested in detrrmining the degree of dispersion and the rate a t which the dispersion can be achieved in a mixing op-ration. Bv using solids they were able to start and stop a mixing operation a t will and thereby to make progressive sampling and analysis in a more accurate way than is convenient in fluid mixing. Their results check the fist-order rate equation. The results should be directly applicable to drum- or tumbler-type mixers. The authors also discuss some of the similarities and differences betaeen liquid mixing and the mixing of solid particles. Buslik ( 7 ) has investigated the deviation in size in random samples of granular solids of known size distribution. X relation was developed between the standard deviation and size distribution and was s h o r n to be applicable t o a study of the rate of mixing of solids of nonuniform size. Mixing is discussed from a statistical distribution viewpoint. The results are directly useful in specifying sampling techniques. The statistical theory and data are probably applicable to liquid mixing ratrs when liquid or solid aggregates are present in a continuous liquid phase. C O N T I N U O U S F L O W SYSTEMS
There has been need of a better understanding of mixing in vessels where fluid flow is continuous. 1Iason and Piret (21) have developed mathematical equations to account for the concentration changes which occur in continuously stirred tank reactor systems during transient periods of operation. Eldridge and Piret (12) developed equations for the effect of the mixer on reactions which occur in a series of continuous flow reaction vessels. Experimental data are given to show the validity of the theoretical equations. These articles provide a sound theoretical basis to account for the effect of changes in operating conditions and for the effect of starting and stopping the operation in a series of reactors. They showed in the experimental work that a first-order chemical reaction in a series of from one t o five reactors could be predicted as to degree of completion on the basis of the theoretical equations. Also, the rate constants were shown to be related t o power input. Power input was accounted for both by t h a t due to the rotating paddle impellers and by that due to the continuouslv flowing feed. The experimental work was done in baffled reactor vessels and under conditions which are reproducible in large scale equipment. Therefore, the results are useful for fundamental scale-up data. Johnson and Talbot (17) described an experiment using a series of nineteen mixers and settlers in series to study the distribution of oxalic and succinic acid between water and butyl alcohol. The work was done in small laboratory glassware. An equation for the operation was developed and corresponds to one of those given by Eldridge and Piret ( 1 2 ) . APPLICATIONS
OF MIXING T O SPECIFIC PROCESSES
Fermentation. Bartholomew and co-workers (1, 2 ) have presented a comprehensive study of application of turbine-type mixers to fermentation (penicillin and streptomycin). They describe a laboratory-pilot plant fermentor with a mixer, baffles, and air-inlet. Engineering data for scale-up to larger size can be obtained from such equipment. The important control variables have been studied. The authors ( I , $ ) state that other laboratory fermentors that have been described are unsatisfactory because they are radically different from conventional large scale fermentors] and thus the data obtained are not suitable for translation t o large scale. This is a n observation of utmost importance, and the authors are the f i s t t o have published results of experimental work in fermentation (gas-liquid mixing) using mixing
January 1951
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pilot plant” or standard converter had a capacity of 30 liters. The position of impeller, angle of blades, and position of baffle do not correspond to prevalent large scale commercial practice, or t o conditions normally considered best for mixing or best for scale-up data. Results for fermentation were satisfactory and the effect of air flow and impeller speed were evaluated. It is doubtful whether the results can be translated to large scale operation. The production of circulin was studied (26) in small scale and in 100-gallon fermentors. The fermentors are described, turbine agitators were used, but no relations are reported for variations in impeller speed or for variations in air flow. Riboflavin produced by fermentation was described (29) for pilot plant operations on two sizes. Aeration and agitation (two speeds) were studied along with other bio-variables. One fermentor was equipped with a side entering propeller Microbiological Pilot Plant Fermentors agitator. Air wm introduced through porous stones and a pipe-cross sparger. The other fermentors were equipped with techniques found to be most effective in large size fermentors. top entering propeller agitators. The agitation used is not norThe science of mixing will gain markedly when small scale experimally considered to be good for gas-liquid contacting, No mentation is carried out under mixing conditions which are power data are reported and no holdup data are given, so that known to be optimum in larger scale equipment (33); Bartholomew et al. give ample justification t o this point of view. a comparison cannot be made with fermentors of conventional types like those used by Bartholomew et al. A theory is presented (g) for oxygen absorption by suspended mycelia in aerated nutrient broth, which is complete and in acPetty, in a short article on fermentation (88),states that the horsepower input by a mixer for fermentation varies from 0.3 t o cord with modern chemical engineering principles. Experiments 2.0 hp. per 100 gallons. Unfortunately no mention is made of were performed to isolate various steps in the process, and the resize of equipment or other engineering variables. sults clarify the concept of the mechanism of deep tank fermentation. Data are given for rates of the several controlling steps in the process. The effect of agitation was measured in terms of EXTRACTION AND OTHER PROCESSES power, impeller size, and speed. The data are applicable for There are many types of continuous liquid-liquid extraction scale-up purposes, and show the optimum conditions for the imequipment, and mixing impellers are an integral part of some of portant fermentation variables. them (24). One type which has been developed recently by In addition to the articles just mentioned, there were six others Scheibel has been used for the extraction of acetic acid from dealing with fermentation in which mixers of various types were methyl isobutyl ketone-water pair, and the reverse (36). The used. None of them give data suitable for engineering purposes performance data for a 12-inch diameter column are given. The as is the case for the work of Bartholomew et al. However, they are of interest for various reasons and are mentioned here briefly. vertical column consists of alternate packed and open sections; flat paddle-type impellers are rotated in the middle of each of the Hixson and Gaden (16) experimented with oxygen transfer in three unpacked sections. The object of the arrangement is to submerged fermentation, They measured rates of transfer in a disperse one liquid in a secondary immiscible liquid by means of fermentor of small diameter and without baffles. It is doubtful the mixing impeller, and then to coalesce the drops as they pass that the data can be projected to large scale because dynamic simithrough the packed section. Thus the unit simulates the ordilarity cannot be achieved in a larger tank without baffles or their nary mixer-settler technique for liquid-liquid extraction. Contact equivalent. The data are in substantial agreement with the thestage efficiencies have been measured for various throughput rates ory developed by the authors and by Bartholomew et al. and for various impeller speeds. It was found that there is an opBrown and Peterson reported on penicillin fermentation in a Waldhof fermentor (6) and in a turbine-type fermentor of uncontimum impeller speed for highest stage efficiency. High flows of liquids could be handled and some runs were achieved a t efventional design (6). The Waldhof fermentor is the type used ficiencies of over 90%. Runs were also reported for other liquid in some German fermentation work, No power or other data suitable for large scale design are given. Comparison was made pairs. These are the f i s t data reported in terms of engineering with this unconventional fermentor (6) and it was concluded that variables for this type of mixer-settler-contactor . the yields were slightly higher than in the standard fermentor, Hydrogenation and hydrogenolysis operations were discussed “but the difference may not be significant.” The so-called “semiby O’Boyle (26), and he gives a description and drawings for sev-
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era1 large scale hydrogenators using mixing impellers to distribute gas, mix the liquid, and transfer heat. Dwyer and co-workers ( 1 0 , 1 1 ) report results of their studies on the desorption of unreacted isoprene from synthetic rubber latex. They show the effect of mixing variables on the desorption r a k . A propeller was used, deeply submerged in a small cylindrical vessel. The data are indicative of the effect of mixing in large scale reactors.
Vol. 43, No. 1
Fesenko, N. G., Zavodskaya Lab., 15, 1396 (1949). Fossett, H., and Prosser, L. E., J . Inst. Mech. Eng., 160, No. 2 , 224, 240, 245 (1949).
Hixson, A. W., and Gaden, E. L., Jr., IND.ENQ.CHEW.,42, 1792 (1950).
Jackson, W.H., Chem. Eng., 57, 132 (1950). Johnson, J. D. A., and Talbot, A., 1 ~ a b t T e 164, . 1054 (1949) Lyons, E. J., Chem. Inds., 65, 517 (1949). Masmusson. Karl. Iua. 20. 90 (1949). Maytra, N. X., And Coulson,‘ J. M., J. I m p . Coll. Chem. Eng. SOC.,4, 135 (1948).
L A B O R A T O R Y STIRRERS
A number of types of small glass and metal impellers useful for laboratory experimentation are shown in “Technique of Organic Chemistry” (35). Potter and Kummerow (SO) described a mixer suitable for use with compressed air as the driving mechanism. Air is led from a hub out through arms and discharged as in a pin wheel to give rotary motion to a shaft attached to the hub. A small stirrer drive for use in a glass-enclosed system has been detailed by Tolbert, Dauben, and Rpid (38). The armature of a small induction motor is mounted in a glass cylinder attached to a ground joint flask fitting. LITERATURE CITED
Bartholomew, W. H., Karow, E. O., and Sfat, M. R., IND.ENG. CHEM.,42, 1827 (1950). Bartholomew, W. H., Karonr, E. O., Sfat, M. R., and Wilhelm. R. H., Ibid., 42, 1810 (1950). Bershader, D., and Psi, S.I., J . AppEied Phys., 21, 616 (1950). Black, C. R., J . I m p . CoZZ. Chem. Eng. Soc., 4, 111 (1948). Brown, W. E., and Peterson, W. H., IND.ENG.CHEX.,42, 1769 (1 w,n\.
\ _ _ _ _ , _
Ibid., p. 1823.
Buslik, David. A.S.T.M. Bull. 165. 66 (1950). Chem. Inds., 67, 275 (1950).
Coulson, J. M., and Maitra, N. X., Ind. Chemist, 26, 55 (1950). Dwyer, 0. E., and Baumann, J. B.,IND. ENG.CHEM.,42, 1230 (1950).
Dwyer, 0. E., and Burke, L. T., Ibid., 42, 1240 (1950). Eldridge, J. W., and Piret. E. L., Chenz. Eng. Progress, 46, 290 (1950).
Mason, D. R., and Piret, E. L., IND. ENG.CHEM.,42, 817 (1950). Merz, O., Chemie-Ing.-Tech., 21, 99 (1949). Mohle. Walter. Zbid.. 21. 335 (1949). Morello, Y. S., and Poffenberger, iY., IND. ENG.CHEM.,42, 1021 (1 950),
Nelson, R. A., DeBoer, C., and DeVries, W. € Ibid., I., 42, 1259 (1950).
O’Boyle, C. J., Ibid., 42, 1705 (1950). O’Connell, F. P., and Mack, D. E., Chem. Eng. Progress, 46, 358 (1950),
Petty, R. D., Chem. Inds., 66, 184 (1950). Pfeifer, V. F., Tanner, F. W., Jr., Vojnovich, C., and Traufler, D. H., IND. ENG.CHEM.,42,1776 (1950). Potter, G. D., and Kummerow, F. A., Science, 110, 592 (1949). Rushton, J. H., IND. ENG.CHEM.,42, 74 (1950). Rushton, J. H., Proc. Natl. Conf. I n d . Hgdraulics, 111, 119 (1949).
Rushton, J. H., in “Technique of Organic Chemistry,” Weisberger, ed., 1-01. 111, chap. 3, New York, Interscience Publishers, 1950. Rushton, J. H., Costich, E. W., and Everett, H. J., Chem. Eng. Prowess. 46. 395. 467 11950). (35) Scheibel, E. G., and Karr, A. E., IND.ENG. CHEM.,42, 1048 (1950). (36) Schneidcr, Robert W., Chem. Eng., 56, S o . 5, 157 (1949). (37) Serner, H. E., Ibid., 57, 128 (1950). (38) Tolbert, B. M., Dauben, William G., and Reid, James C., Anal. Chem., 21, 1014 (1949). (39) Valetine, K. S., and TvIacLein, G., in section 17, “Chemical Engineers’ Handbook,” Perry, ed., New York, McGraw-Hill Book Co., 1950. RECEIVED October 24, 1950.
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LINCOLN T. WORK 420 L E X I N G T O N A V E . , N E W Y O R K 17, N. Y .
from a preprint; but the papers and discussion have just been published and reviewed (66). Fischer (38) devotes a 69-page chapter to particle size, covering size, its distribution, a detailed discussion of methods of measurement, tinting strength, overin jet grinding. Among developments in grinding media is the announcement of a cylindrical size particles, and data on many materials. The AMERICANCIIEMIball grinding medium of superior hardness and weight. CAL SOCIETY’S Christmas 1950 Symposium under the Division of IndusHE report last year ( 6 7 ) indicated that work in this field had trial and Engintering Chemistry is on the subject of aerosols, been intensified, and this past year has shown maturing and one session is devoted t o particle size measurement (63). Laboratory announcements have been made. Dalla Valle is results. Practically all t h e areas which have been discussed in recent years are marked by some progress in technical developing a micromeritics laboratory a t the Georgia Institute of Technology ( 1 9 ) . Allis-Chalmers Corp., Milwaukee ( d ) , publications, and some of the more striking of these are sumhas a basic industries research laboratory to give engineering marized here. information to guide in designing more efficient plants. It has a Books or symposia contribute markedly. The 1950 edition of complete pilot scale plant for crushing, grinding, and concentraPerry’s “Handbook of Chemical Engineering” (51) contains a section on size reduction (KO. 16) which is a complete revision tion tests. There is renewed activity in jet grinding. The R. T. Vanderby C. E. Berry. While plentiful in data, it gives new emphasis bilt plant for grinding large quantities of talc to fine sires is now to principles. A symposium was held in Britain in 1947 on operatingat Gouverneur, S Y. ( 1 % ) . methods and applications of particle size This was revieMed Last year’s report on crushing and grinding indicated intensified work in this field and the past year has shown maturing results. Practically all the areas discussed in recent years are marked b y progress in technical publications. Books and symposia contribute markedly. Dalla Valle is developing a micromeritics laboratory at the Georgia Institute of Technology, and Allis-Chalmers Corp. has a basic industries research laboratory with a complete pilot scale plant for crushing, grinding, and concentration tests, University of Minnesota workers and others are getting to the hard core of the fundamentals of grinding. There is renewed activity
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