January 1952
INDUSTRIAL A N D ENGINEERING CHEMISTRY CATALYST-GAS MIXING
Aekins, Hinds, and Kunreuther ( I ) give data on the mixing of gases in fluidized beds as found in catalytic cracking units. A description is given of the technique of sampling and analyzing the gases in the fluidized beds. It was found that gaa mixing waa rapid but that the ratio of length t o diameter of fluidized beds had a marked effect on the mixing and uniformity of gas compositions. Under conditions where “bubblestJof gaa rise through the bed, mixing is poor. With fluidization of the type desired for etability of operation, mixing is rapid and satisfactory. MISCELLANEOUS
Two short notes appeared in Chemical Enginesring (6,11) on suggestions for the use of differential gears for speed reducere for mixers. These a p similar t o those appearing in several standard textbooks on process equipment. LITERATURE CITED
(1) Askins, J. W., Hinds, G. P., Jr., and Kunreuther, F., Chem. Eng. P ~ o g ~ e e47.401 s, (1951).
91
Bulloak. H. L.. IW., 47,397 (1951). Chem. Eng., 58, 190 (August 1951). Cumminga, 6. H., and West, A. S., I n . ENG.CHEM.,42, 2303 (1960).
Flatheim, O., Chem. Eng.. 58,132 (April 1951). Foretall, W., Jr., and Shapiro, A. R.,J. Applied Mechanics, 17, 399 (1950).
Hixeon, A. W., and Knox, K. L., IND. ENG.CEEIM.,43, 2144 (1951).
MaoDonald, R. W., and Piret, E. L., Chem. Eng. Progreae, 47, 363 (1951).
Mack, D. E., Chem. Eng., 58, 109 (Maroh 1951). Mason, D. R., and Piret, E. L., Im.ENG. CEEM., 43, 1210 (1951).
Miller, R. L., C h m . Eng., 58.139 (August 1951). Perry,E., and Mae, F. E., Chem. Eng. Proprsss, 47,354 (1951). Robinson, D.B.,and Katz, D. L., Ibid., 47,317 (1951). Rushton, J. H., I b M , 47,485 (1951). Rushton, J. H., IND. ENQ.CHEW.,43,111‘(1951). Sell, H. S., and McCutoheon, R. J., Ibid., 43, 1234 (1951). Taylor, J. F., Grimmett. H. L., and Comings, E. W., C h m . Eng. Progrsss, 47, 175 (1951). RECSIVED October 23. 1951.
SIZE REDMCTIOW LINCOLN T. WORK 420 LEXINGTON AVE., NEW YORK 17, N. Y.
several new asp& occur in current work on size reduction. ACS symposia on aerosols and nucleonicscontribute to this field. Continuation of calorimetry studies and a new theory of comminution by Bond serve to clarify theory. There is much activity in fluid energy devicest Linde uses liquid nitrogen to embrittle solids in hammer mill grindinst and several papers r e s k ter operating characteristia and applications of the Domlons.
T
RERE has been substantial development dnce the laat report (70) which advance8 the technology of Size reduotion and the cloaely related field of dispersion, classification, collection, and particle d m measurement. Some of the more striking developments are briefly summarized before the more detailed discussion.
1. Symposia: The ACS Division of Industrial and Engineering Chemistry devoted its December 1960symposium t o the subject of aerosols. This was divided into four parto; generation, plLrticle size analysis, transfer and collection, and filters. Several papers in the b t three groups have been printed and are within the scope of this review. The December 1951 symposium a t Northwestern University ia on the somewhat related field of nualeonics. 2. Principles of Size Reduction: Current studies in calorimetry add to the knowledge of grinding energy, while the analysis of particle size data allows better interpretation of the nature of particle breakdown. F. d. Bond ( 6 , 6 ) has interpreted the Kick and Rittinger theories and has advanced a third theory for comminution. The economic use of power in ball mill grinding continues t o lead in plant studies reported in the literature. 3. Fine Grinding: Several new devicee using fluid enezgy or high speed mechanical action for producing mt&l essentially below 5 or 10microns are under development. 4. Classification: Dorrclone wet cyclonic clasdcation has established a place in tine classificationand in thickening. Fluidizing equipment is also being employed for size fractionation at coamer cute. 5. Cold Grinding: Cooling with liquid nitrogen in hammer mille to embrittle the material being ground has become an mtive
subject, through developments of the Linde division of Union Carbide. PARTICLE SIZE
The preparation of materials in a tine state of subdivision and their dispersion in air were treated extensively in the ACS Symposium. As background in evaluating particle size, Cadle and Magill ( 8 ) have prepared artificial smog utilizing a generator which they developed. It is of the aspirating type, drawing in air and the powder at an e d l y controllable rate. Lane (49) has presented an interesting photographic study of the action of air streitms in shattering drop, and he has analyzed the mechanism of atomization. Bourne and Fosdick ( 7 ) have investigated the collection of mists and dusts for particle size measurement utilizing electrostatic precipitation on the hemacytometer. Fahnoe, Lindroos, and Abelson ($6)have recognized the difficulties in collecting fine aerosols and have shown techniques for agglomeration of these materials for more simple recovery. They have employed steam and ethylene glycol vapor t o promote condensation and have also studied sonic agglomeration. For microscopic observation they have wed the cyclone jet iqpinger. Sawyer and Walton (60)have reported on the conifuge, a size separating sample device for airborne particles. Mugele and Eva- (60) have analyzed the droplet size distribution in sprays and have presented a study of their “upper l i t equation.” They have compared it with other distributions claiming that i t fits the available spray data more accurately than do the others. Kottler (8?, 40) har presented a series of papers dealing with the distribution of particle Size and the “goodness of fit” of such data. A comparison of methods for the fit of bimodal particle size distribution curves waa made by Dallavalle (89). This subject is important not only for the aerosols which he conaidered, but because of the bimodal characteristias in grinding as well as the multimodal qualitme of ground mixtures.
92
INDUSTRIAL AND ENGINEERING CHEMISTRY
In sieve analyses, the National Bureau of Standards (18) has developed a simple procedure for determining the effective size of opening. This method employs calibrated glass spheres of graduated )&e and should be applicable in the cement, paint, sugar, abrasive, and other industries. I n the finer sizes Haultsin (SO)discusses the sizing of fine particles with air and describes a new Infrasizer. Sedimentation methods for particle size are exemplified by a numb& of contributions in both gravity w d centrifugal range. Leith (43)describes a sedimentation cylinder for particle size analysis. Kamack (36)shows a centrifugal pipet sedimentation device and method for application in the range 0.1 to 2.0 microns. The theory for this method was worked out, and equations were derived for calculating particle size distribution from the experimental data. Thi8 method jointly with gravity
COURTEBY PATTERSON FOUNDRY & MACHINE M.
Continuous Mill
sedimentation permits an extension of the particle size distribution measuremeht for fine materials. The ultracentrifuge in sedimentation was discussed by Wales (66) and Gray (98). Cbhan and Watson (19)have utilized the electron microscope as well as adsorption methods for evaluating the shape factor and other fundamental qualities of carbon black. The General Electric Co. has announced a new photoelectric instrument for automatically measuring and recording the quantity of suspended particles in a liquid. This recording turbidimeter is compact in design and is offered for the control of turbidity in water supplies (16). Yudowitch (73)has studied the particle size of latex in relation to x-ray diffraction peaks. Ergun (86)has developed a gas flow method for particle density employing gas flow rate and bulk density measurements. The method .is self-checking, and his alternative equations are largely independent of each other. Kraus and Thiem (41) dotermine the surface area of powders using a simpified air flow method. The surfaces of paint pigments and other fine powders are a routine measurement under the procedure of Carman and Malherbe (11). Strohl and Schwellenbach (66) have reported on the determination of particle density in crushed ore solids. Gregor, Held, and Bellin (80) have investigated methods for determining the external volume of ion exchange resin powders. Comparing suction, blotting, and centrifuge methods, they find centrifuge best with a precision of &0.2%. Swelling and shrinkage complicate thie problem. There has been considerable work on gas adsorption. The relatively small surfaces of pulverized materials compared t o pigments, precipitates, and adaorbents has necessitated modification
Vol. 44, No. 1
of the original method. %cent work haa made this method a p plicable. Bloecher ( 4 ) finds nitrogen is not applicable for ma& r i d coarser than No. 150 to 200 sieves; ethane needs sensitive technique, but krypton cooled with liquid nitrogen is fast, safe, and accurate. Loebenstein and Dietz (46) determine surface area by adsorption of nitrogen from its mixture with helium. I n a study of shape factor in carbon black, Cohan and Watson (IS) have compared nitrogen and iodine adsorption methoda, with an expected poor correlation. MILLS AND MILLING
The 1950 review for the mining industry ($3)indicates some of the trends that have been extended this year. The use of larger ball mills with slower speed of operation, some aspects of structural design, auxiliary equipment, and automatic controls have received attention. Allis-Chalmers ( 4 8 ) announced a “superior” gyratory crusher, flexible in installation and adjustment and having increased crushing ability. Patterson Foundry and Machine has announced a heavy-duty continuous ball mill (17).Structural elements such as choosing a drive for a grinding mill (S7),stud welded structures (80),and welded crushers ( $ 1 ) have received attention. A few examples on operating practices are also noted, as limestone crushing plant designed for flexibility (64), rock crushing with Diesels ( g 4 ) , crushing, hoisting, and conveying a t the Kerr Addison Mine (IO), lower costs a t Pend Oreille (S@, progress a t Tennessee Copper (83) with low speed mills a t high dilution, controlled impact action in a new breaker (6S), and a symposium on production problems (66). Applications as conditioners in sulfide flotation (46)and even a challenge to flotation (6.9)are noted. The National Bureau of Standards (33)announced a new vibratory mill for fine grinding. It grinds cotton to a fine state of subdivision and has been tested on pigments, ceramic materials, metal powders, and resins. Steel balls in a jar are involved in over 100,000 collisions per second. Allis-Chalmers (33)is doing laboratmy and test work on this type of mill. Announcement of impact pulverization of cold embrittled solids by Linde Air Products Co. (16,47,67) may a1a need. The author recalls his experience of over twenty years ago, when he ground fresh coconut in a vented ball mill with dry ipe. This produced a material which was pasty a t room temperature but free of fibers. Economy in grinding resilient powders and the ability to attain Gneness of food products in one pass are indicated. The cycle for the liquid nitrogen used as coolant requires efiective heat exchange such as the system furnishes. Considerable development has taken place in fine grinding devices of both the fluid energy and the mechanical types. Some of this haa b e gun to reach the trade through potential customer tests, while other developments are nearing that stage. Bechtel and Croft (3) have discussed the fluid energy pulverizer in its relation to steam generation. Studies in basic principles have largely been focused on the energy of grinding, but a few other papers along these lines have a p peared. The effect of grinding on particles was studied by Bradshaw (8). Roberts (66)applies the probability theory to wet ball milling. Yancey, Geer, and Price (78)seek to resolve the problem of abrasiveness of coal, which is not entirely associated with grindability. They employ a set of wearing blades revolving for a fixed number of revolutions in a charge of coal and use the loss in weight of the blades as a measure of abrasiveness. With abrasive coals, results areconsistent within 3% and run up to ISYO for low abrasive coals. Ehergy studies have been applied to 9.5 X 10 foot grate-type ball mills grinding cement raw materials. In this, Schellinger and Lalkaka (88) found surface energy efficiencies of 10.2, 19.7, and 19.9%. Schellinger (61) has also reported on a calorimetrir method for studying grinding in a tumbling medium. He has developed and calibrated a laboratory calorimeter. Making IW-IS on
January 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
93
-100 +200 quartz, he found the thermal efficiency to be a function of mineral quality, pulp density, and the like. A range of 10 to 19% thermal efficiency was obtained, and peak efficiencies in wet and dry gunding were similar. Efficiency dropped with dilution. The results were comparable with earlier work on the subject and similar to his own data on commercial mills. Bond and Wang (6)have derived a n empirical equation for the total energy input in crushing and grinding. It is based on the deformation of the particle to attain rupture, with most of the energy reappearing as heat. Bond (6) has gone further and announced the “third theory of comminution.” In this he differs with both Kick and Rittinger. The former calls for energy varying as Da while the latter is a DS function. I n Bond’s concept, both of these relations apply in part. Kick holds for t h e initial compression to start fracture; but, since the particle form is not cubic, local fracture gives an energy flow more like Rittinger. is an average, which is also the theoretical relation for spheres. Using extensive data, he has correlated results developed from this concept to derive a work index. There may well be further interesting development of this theory, and it may explain some of the differences in grinding by impact, by slow loading, and by attrition. CLASSIFICATION
In the art of sieving, the introduction of the electrically heated screen by Tyler (3.9)permits tbe feeding of moist materials without blinding the screen. The Symons centrifugal screen is another current development which makes separation more positive. Classification by settling under gravity or centrifugal force has had several contributions this year. Yancey and Geer ( 7 1 ) give data on the efficiency and sharpness of separation in evaluating coal washery performance. It is a critical study of a type which may be used for other applicationfi. The problem af blowing fines out of a fluidizing system is being employed constructively to effect size separation while fluidizing. As illustration, Leva (4) contributed a paper on the elutriation of fines from fluidized systems, pointing out that the rate is similar to that of a firsborder reaction. The cyclone separator for liquid-solid systems is finding its place in a variety of applications-size separation, concentration, and collection. Weems ( 6 7 ) shows metallurgical applications of the Dorrclone. Dahlstrom @ I ) , Kennedy and Criner (.96), and Phillips and Blair (61) tell about its use with clay, silt, and coal. Data on the performance of Cottrell precipitators was given by Sproull and Nakada (64). Emphasis was placed on moisture and temperature. The performance of wet cell washers for various aerosols was given by First, Moschella, Silverman, and Berly (87); Schauer (60)shows recoveries larger than 0.3 micron using standard steam exhausters and condensing steam nozzles. Still not achieved except for the cases cited and the work on superfine filters is marked improvement in air classification at fine sires and in collection equipment for dusts in air and in industrial products in gases or liquids. APPLICATIONS
To supplement examples in the previous seqtions, a few other selected applications show how size reduction and control are being attacked in industrial operationa. Kopelman and Gregg (38)report on partiale agglomeration in tungsten metal powders. Ivey (34)gives particle size analyses of fluid cracking catalysts. In ceramics, Sane and Cook (68) note the effect of grinding and firing treatment on the crystalline and glass content and the physical properties of whiteware bodies. Winslowand Matreyek (&?)discuss particle size in suspension polymerization arid point out how the nature of the system, the molecular weight, and concentration control the size of spheroids. Rubber technology affords a number of studies of carbon black
COURTESY ALLIS-CHALMERS MFO. 0 0
Hydrocone Type
R Crusher with Wobble Plate Feeder
and colloidal noncarbon materials. In the latter case, Schmidt (6.9)has evaluated inorganic colloids and finds that small particle size is of prime importance in reinforcenlent, while chemical nature is secondary. Wolf, Hall, and Bachmann (69)report on color reactions betweea silica pigments and certain accelerators and antioxidants. In carbon, Cines (18) shows the effect of surface oxidation of furnace black on rubber properties. Cohan and Watson (19)sbow distribution, surface area, and shape for blacks. I n paint technology, Baker and Vozrella ( 2 ) have studied the relation between particle size distributions in pigment dispersions and fineness gage data as well as paint film characteristics. has presented a review of some mixing and grindMountsier ing equipment. Hoback (3g) has presented some practical aspects of pigment dispersion. This paper is copiously illustrated and shows the effects of pigment type, vehicle, and milling on dispersion. Baker and Vozzella ( 1 ) discuss the roll mill, pebble mill, and kneader as pigment dispersion equipment. Carr ( 1 3 ) shows how ease of gritlding, lower absorption, and lower viscosity for a given concentration of pigment may be obtained by controlled use of wetting agents. Chadwick ( 1 4 ) discusses factors affecting rheological properties of paints and lacquers, noting types of rheological behavior, solvent qualities, temperature, and particle shape as significant factors. These are but a few examples of applications where size measurement, reduction, and creation find industrial application.
(e)
LITERATURE CITED
Baker, C. P., and Vozzella, J. F., OfficialDigest Federation Paint & Varnish Production Clubs, 319,467-89 (August 1951). Baker, C . P.,and Vozzella, J. F., Paint, Oil,Chem. Rev., 113,
109-20 (1950).
Bechtel, L. D., and Croft, 0.M., Mech. Eng., 42,742-4 (1950). Bloecher, F. W., Jr., Mining Eng., 3,255-8 (1951). Bond, F. C., Am. Inat. Mining Met. Bngrs., Regional Meeting, Mexico City (October 1951).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
94
(6) Bond, F. C.. and Wane, J. T., Mining Eng.,187, 871-8 (ISM)). (7) Bourne, H. G., and Foedick, L. B., Anal. Chem., 22, 1583-5 (1950). ( 8 ) Bradshaw, B. C., J. C h .Phua., 19,1057-9 (1951). (9) Cadle, R. D., and Magill, P. L., IND. ENQ.CKIW., 43, 1331-5 (1951). (10) Can. Mining J., 72,119-20 (1951). (11) Carman, P. C., and Malherbe, P. L., J . Applied Chem., 1, 1058 (1951). (12) Carpenter, F. G., and Dietz, V. R., J . ReaeMch Natl. Bur. Sta?durds, 45, 328-46 (1950). (13) Carr, W., OficMl %eat Federation Paint & Varnish P d w t i o r , Clubs, 319,510-16 (August 1951). (14) Chadwick, E., Ibid.,321,636-51 (October 1951). (16) C h . Eng., 58, 106 (1951). (16) Chem.Eng. News,28, 2372 (1950). (17) Chem. Week, 69, 34 (Nov. 10, 1951). (18) Cines, M. R., Rubber Age, 69, 183-8 (195lj. (19) Cohan, L. H., and Watson, J. H. L., Ibid., 68,687-98 (1951). (20) h a a s e r , C. H., I r a Age, 167, 110-11 (1951). (21) Dahlstrom, D. A., Mining Eng., 190,163 (1951). (22) Dallavalle, J. M., and Om, C., IND.ENQ.(%EM., 43, 1377-9 (1951). (23) Design N e w , p. 40 (December 1950). (24) Dieael Power, 28, 40 (January 1951). (25) Ergun, S., Anal. Chm.,23,151-6 (1951). (26) Fahnoe, F., Lindroos, A. E., and Abelson. R. J.. IND. ENG. CHEM., 43, 1336-45 (1951). (27) First, M. W., Moschella, R., Silverman, L., and Berly. E., INU. ENQ.CHEM.,43, 1363-70 (1951). (28)Gray, G. W., 5ci. American, 1 8 4 , 6 5 1 (1951). (29) Gregor, H. E., Held, K. M., and Bellin. J., A w l . Chem., 23, 6202 (1951). (30) Haultain, H. E. T.,Capreseed Air M q . , 55,281 (1950). (31) Herbruck, C. G., Iron Age, 167,102-3 (1951). (32) Hoback, W. H., O m 1 Digest Federation Paint & Vamiah Production C l d s , 316, 255-91 (May 1951). (33) Holt, C;. J., Mining Eng., 190, 122-5 (1951). (34) Ivey, F. E., Jr., Petroleum Refiner, 30,99-103, 141-5 (1961). (35) Kamack, H. J., AnaZ. Chem., 23,844-50 (1951). (36) Kennedy, G. H.. and Criner, H. E., Mining Eng.. 3. 259-61 (1951). (37) Kloyers,E. J., Eng. Mining J . . 152,80-2 (1951). (38) Eopelman, B., and Gregg. C. C., J . Phys. & Colloid C h . .55, 557-83 (1951).
(39) (40) (41) (42) (43)
Vol. 44, No. 1
Kottler, F., J . FranklinZlnst., 250,339-56,419-41 (1950). Ibid., 251, 499-514, 617-41 (1951). Kraus, G., and Thiem, J. R., J. Applied Phvs., 21, 1065 (1950)
Lane, W.R.,IND.ENQ.C H E M . , ~ 1312-16 ~, (1951). Leith, C. J., Science, 113,412-13 (19511. (44) Leva, M., Chem. Eng. Progress, 47, 39-45 (1951). (45) Loebenstein, W. V., and Diets, V. R., J . Research Natl. B w Standards, 46,51-5 (1951). (46) McLachlan, C. G., Mining Eng., 3,347-50 (1951). (47) Miller, G., Food Eng., 23,313-7 (1951). (48) Mining Eng., 190,142 (1951). (49) Mountsier, S. R., Jr., Oj'icial Dzgest Federation Paint & Varnash Production Clubs, 315,233-6 (April 1951). (50) Mugele, R. A., and Evans, H. D., IND.ENG.CHEM., 43, 131724 (1951). (51) Phillips, V., and Blair, J. P., Mining Eng., 3, 699-702 (1951). (52) Ramsey, R. H., Eng. Mining J . , 152, 116-18 (1951). (53) Roada and Eng. Construction, 89, 70 (1951). (54) Ibid., pp. 70-3. (55) Roberts, E. J., Mining Eng., 187, 1267-72 (1950). (56) Rock Products, 54, 92-8 (1951). (57) Rubber Age, 68, 318 (1950). (58) Sane, S. C., and Cook, R. L., J . Am. Ceramic SOC.,34, 145-51 (1951). 159) Sawyer, K. F., and Walton, W. H., J . Sci. Instruments, 27, 272 0 (1050). (60) Schauer, P. J., IND. ENG.CHEM.,43, 1532-7 (1951). (61) Schellinger,A. K., Mining Eng., 3,518-22 (1951). (62) Schellinger,A. K., and Lalkaka, R. D., Ibid., 3, 523-4 (1951). (63) Schmidt, E., IND. ENG.CHEM.,43,679-83 (1951). (64)Sproull, W. T., and Nakada, Y., Ibid., 43,1350-7 (1951). (65) Strohl, J. J., and Schwellenbach, H. J., Mining Eng., 187, 1273-4 (1950). (66) Wales. M., J . Phvs. & CoZEoid Chem., 55,282-92 (1951). (67) Weoms, F. T., Mining Eng., 3,681-90 (1951). (68)Winslom. F. H., and Matreyek, W., IND.ENG.CHEM.,43, 110812 11951). (69) Wolf,'R. F:, Hall, G. E., Jr., and Bachmann, J. H., Rubber Age, 69,55-6 (1051). (70) Work,L. T., IND. ENQ.CHEM.,43, 1 1 6 1 6 (1951). (71) Yancey, H. F., and Geer, M. R., Mining E&, 3,507-17 (1951). (72) Yancey, H. F., Gem, M. R., and Price, J. D., Zbid., 262-8 (1951). (73) Yudowitch, K. L., J. Applied Phys., 22,214-16 (1951). REaHlXVgD
November 14, 1961.
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