C E NT R I F UG AT I O N J. 0.MALONEY UNIVERSITY O F KANSAS, LAWRENCE, KAN. The art and science of centrifugation is advancing on all fronts. The theoretical treatment of centrifugal Separation and the design of mrchines is becoming more rophisticateb. The application of centrifuges to the coal, food, and pharmaceutical industria continues to increase. A single-unit machine capable of carrying out multistage solvent extraction followed by centrifugal separation of the phases appean to have many industrial possibilities.
suits were desired. Robatel (62)has confirmed these statements of Storrow et al. on the care necessary to obtain reproducible results. After developing a sound technique with a v a c m m tesbleaf filter he was abl’e to obtain reproducible results when centrifuging Lucite spheresof 150 to 2OOmesh size. The technique he employed differed from t h a t of Storrow in that the recycled filtrate was maintained at a fixed level in the bowl irrespective of the cake thickness. There are indications that the data from a vacuum leaf test can be used to predict the filtering rate in a perforatebasket centrifuge. Ambler ( 4 ) has presented a paper on the evaluation of centrifuge performance. H e redevelops the familiar centrifugal formulas for settling types of machines but divides his resulting equation into two parts. One part contains variables representing the properties of the liquid-solid system being separated; the other, termed the sigma function, contains variables representing the dimensions of the centrifuge, its speed, and the feed rate and holdup in the unit. H e shows how the sigma function can be used to predict the performance of the large supercentrifuge from the separation achieved in a laboratory supercentrifuge. H e states that the lack of knowledge of the relationship between the variables which control the behavior of the centrifugal filter frequently make long-term, large scale tests necessary. The operating details and general considerations in the selection of the proper Sharples units are described. He continues t o emphasize the necessity of experimental tests in the selection of equipment. The Bird Machine Co. (28)has installed extensive facilities in its recently completed research and development center for determining the performance of centrifuges on both large and small scale. It has also prepared a procedure for the evaluation of a solid-liquid mixture to determine what type of centrifuge would best achieve a separation. This procedure is one of the most extensive that the reviewer has seen. Smith (69),reporting on a study in which centrifuges were applied to vegetable oil refining, states that the quality of the effluent oil in every case followed the change predicted from theory. As a r e d t of several hundred tests a new unit of the tubular bowl type was designed, built, and successfully operated. Sokolov (71)has made a theoretical study of the separation of a liquid from a solid by a centrifugal filter. Some data are presented. The reviewer has not translated the article but hopes the information can be analyzed for the next review. Zychlin and Storrow (79)investigated the pressure drop-flow relationships when water flowed through capillaries of various diameters and lengths. They compared the flow obtained when the tube was stationary and when it was sufipended horizontally by one end and revolved. This study was prompted in part by a postulate that an increased resistance to flow might occur in beds of h e particles held in a centrifuge. The authors state that such a condition is unlikely. Preston et al. (67)have measured the amount of liquid retained on the surface and within the structure of fibrous materials when they are subject to a centrifugal field. The effect, on the residual amount of water, of the variables of centrifugal force, surface tension, contact angle, and filament denier, was found to be satisfactorily represented by a simple equation. Lyons (45) has assembled a number of results on the dewatering of coal using centrifuges. His compilation includes partial performance data
A
DDITIONAL information on the performance and application of centrifugal equipment continues to appear. f i r i n g thepast year two books havebeen issued which treat, in part, centrifuges. One (66) presents an elementary discussion and the other (23) gives an interesting historical description of the development of the centrifugal in the sugar industry. The reviewer encountered for the first time a pamphlet issued in 1938 by the British Standards Institution (16)on hydroextractors which describes materials for the construction of the basket, gives details of basket construction, and provides formulas for the determination of the thickness of the basket. A number of review articles have appeared. Gemmill (SI),in an extensive treatment, described the general features of centrifugal machines and showed where the various units are employed in the processing of foods. The use of the centrifuge in the claA fication of beer has been reviewed by Hurlimann (38)who also presented information on the effect of bowl speed, on the separation of bacteria from the beer, and on the brilliancy of the beer. The review by Ambler (3) described the use of Sharples units to the process indufitries and included several applications. He also pointed out the deficiency of the theory in predicting the performance of large scale units. A popular, well-illustrated article (69) presented information on centrifugal equipment which would serve as an excellent introduction to the subjcct for students studying this unit operation, The principles of centrifugal purification have been reviewed by Reed (60). Two more nomograms have appeared which can be used to calculate the centrifugal force developed in a rotating machine (94,39). A review of new German equipment has appeared (33). Grace (34) in a review on the selection of filtration equipment briefly outlined the field of application of the perforate-basket centrifuge. The ultracentrifuge has been the subject of a review by Gutfreund (36). FUNDAMENTAL STUDIES
Greater progress has been made during the past year in the theory of centrifugation and the application of theory to the performance of equipment than in any other comparable period. Although the reviewer cannot point to any specific article as a landmark of progress, there is a definite trend of advance from asorder toward order. S~OITOW and his coworkers (40) continue to study the fundamentals of batch filtration in a centrifugal. These investigators in both this study and in a previous one used the same technique. They deposited a cake of known thickness in the basket and then washed the cake with recycled filtrate. The rate of feed of the recycle fluid was fked and the rotational speed adjusted until a very thin layer of liquid was maintained on the surface of the cake. This rate of feed they termed the “critical wetting rate.” They have developed a photoelectric device which permits them to know when the surface of the cake is just covered with liquid. This instrument was used to measure the critical wetting rates for chalk. They concluded t h a t the previous history, especially the cake-forming technique and the exact test procedure, was important if reproducible re-
39
INDUSTRIAL AND ENGINEERING CHEMISTRY
40
Vol. 44, No. 1 APPLICATIONS
Table I. Name Luwesta extractor h i i d bowl continuous centrifugal (new washing arrangement) Solid bowl continuous centrifugal (higher speed operation) Screw-type concentrating feeder Centrifugal dryer
New Equipment Developments in Centrifugals Application
Manufacturer
Multistage extraction and centrif- Westphalia Separator A.G. ugal separation andNachine Lurgi Co. Washing of crystals Bird
Reference (20, $6, 97) (P8)
Usual applications
Bird Machine Co.
($8)
Increase concentration of solids to centrifugal Decrease moisture content of solids b y air-drying of cake discharge Controlled removal of a portion of cream from milk High speed centrifugation in vacuum High speed centrifugation
Baker Perkins, Tnc. Baker Perkins, Inc.
(46)
De Lava1 Separator Co.
(49)
Table I1 gives either new applications or additional descriptions of earlier applications of centrifugals. N E W TECHNIQUES AND AUXILIARIES
The proper procedure for putting centrifugal screens inside a basket has been deUltracentrifuge Beams et a l . (19) scribed ( 2 ) . A double impulse Ultracentrifuge .... (61) wheel has been successfully developed for driving sugar centrifugals hydraulically ( l a ) . Wallace ( 7 5 ) reports on the Table II. Applications of Centrifugal Equipment use of semiautomatic centrifManufacturing Process Type Unit Materials Separated Reference ugals in a Hawaiian sugar facStarch Solid bowl Starch from water (1) tory. A centrifuge which loads Glass Perforate basket; solid bowl con- Sand from water (66) tinuous and unloads a t full speed has hap Solid bowl continuous Soap from lye (68,70) Penicillin Supercentrifuge Solids from penicillin solution (6) been described ( 1 0 ) . The conNapalm Dewatering of napalm (7) trol of a continuous centriVinyl chloride polymer Perforate-basket batch type Water from polymer (64) Synthetic fibers Perforate-basket batch type Acetic acid solution from cel(6) fuge separating salt from glyclulose acetate Well drilling .... Sand and chips from drilling (82) erol is the subject of an armuds ticle by Parker (63). Pickels Paper Bird solid bowl Lime mud from solution (11) Metallurgical .... Crystals from metal melts (69) (64)and Pickels and Scofield Brewing Solid bowl Suspended solids from stil(18, 1 9 ) lage ( 5 5 ) have developed several Brewing Disk bowl Clarification of beer (61) new devices for accurately Wine Westphalia Clarification of wine ($9) Paint ..... ... Clarification (66) controlling the speed of ultraGeneral applications .... (8) centrifuges. A procedure for Food (dairy fish meat, fruits and Variety Variety (91) vegetable:, citkus oil) the control of the speed of an air-driven centrifuge has been reported (47). The temperature of the material in an on nine Reineveld, five Carpenter, eight Centrifugal and Mechanultracentrifuge can be measured, it is claimed, to 0.1 ' C. (25). ical Industries, and seventeen Bird centrifugals. He compared The addition of water to miscella has been found to assist the capacities of these four types of machines. It is to be ingreatly in the removal of oil seed fbes from the solvent extraction ferred that only one size of each machine was studied. The feed (22). A device for observing microscopically the behavior writer was unable to determine from the article the speed, power of living cells during centrifugal clarification has been develconsumption, or equivalent centrifugal force of any of the maoped (9). Brokke ( 1 7 ) has described a density gradient prochines. The author appeared chiefly concerned with the breaking cedure for the separation of virus materials. A tube suitable up of the coal during the dewatering operation. While considerafor the use of heavy-liquid separations has been described (42). tions of the mechanical design of centrifuging equipment is usually not of major interest to chemical engineers, anyone inRECENT PATENTS terested i u the theory and design of self-balancing centrifuges should read Thearle's excellent series of articles ( 7 3 ) . A simpliThe recent patents which have come to the reviewer's attenfied procedure for calculating the stresses in rotating disks of nontion are as follows: uniform cross section has appeared (30). Beyerle et al. ( 1 4 ) have Centrifuge for red muds (16) completed a book giving a description of the apparatus and exCentrifuge for separating gas mixtures ($1) perimental results obtained when using gas centrifuges for the Continuous centrifugal machine (36) Centrifugal control system (37) separation of isotopes. Ch-nbined filter and centrifugal separation (44) Certain limitations on the separation achieved in an ultraClarification of liquid (48) centrifuge employing the separation-cell technique were pointed Centrifugal ore concentration (60) out ( 6 7 ) . Kendrick ( 4 1 ) has reviewed the formulas pertaining to Unloader arrangement for centrifugals (62) Centrifugal molten lead purifier (68) the separation of materials by centrifugal force. Centrifugal sludge separation (72) Discharger for centrifugal separators (74) Improvements in centrifugal separators (76) N E W EQUIPMENT Friction brake control for centrifugal machines 77) Loading gates on charging spouts for centrifugals [78) One of the most interesting new developments to the writer is the Luwesta countercurrent, solvent extractor (20, 26, 97) which comprises three contactors and separators in one unit. The LITERATURE CITED separation is achieved by centrifugal forces. This German machine has been employed in the solvent extraction of acetic ~ . ~ . u ~ ~~~ ~ " ~* ~&; ;2 ~ ~ 2 ~ ~ ~ ~ . ( 1 9 5 1 ' . acid from cellulose acetate manufacture and in the solvent ex(3) Ambler, c. M., Chem. Eng. Progress, 46, 549-53 (1950). (4) Ambler, C. M.,preprint of W h i t e Sulfur Springs meeting, 97traction of penicillin with butyl acetate. Table I lists the new 117, Am. Inst. Chem. Engrs. (March 11-14, 1951). applications which have, come to the reviewer's attention during ~ ~ ~ ' ~ ~ No' ~ 4p ~174-7 * (1951)* l f ~ - & ~ l the last year. The maintenance costs for continuous horiaontaf machines, suspended basket centrifuges, and underdriven centrif(7) Anon., chent. week,69, NO. 12, 26-7 (1951). (8)Ibid., No. 16,29-30 ugals can be estimated (43). Standardizing clarifier
iki i&::,
{:;
(48)
January 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
(0) Anon., J. Inst. Brewing, 62, 64 (1951). (10) Anon., Product Eng., 21, No. 8 , 104-5 (1950). (11) Anon., Pulp & Paper Mag. Can., 52, 111 (1951). (12) Anon., Sugar, 45, No. 5,38-40 (1950). (13) Beams, J. W., et al., Rev. Sci. Instrumenls, 22, 77-80 (1951). (14) Beyerle, K.,el al., “Uber Gaszentrifugen Anreicherung der
Xenon, Krypton und Selen-Isotopes,” Weinheim, Verlag Chemie, 1950. (15) Boivinet, J. H.,U. S. Patent 2,557,629(June 19, 1951). (16) British Standards Institution, “Specifications for Hydroextractors,” London, 1938. (17) Brokke, M. K., J . Am. Chem. SOC.,73, 1847-8 (1951). (18) Carson, C. T., Eng. Contract Record, 34, No. 1. 106, 108, 110, 112-15 (1951). (19) Carson, C. T., Water & Sewage Works, 98,312-17 (1951). (20) Christie, J. J., Chem. Eng., 57, No. 10,161-2 (1950). (21) Cohen, K., and Urey, H. C., U. S. Patent 2,536,423(Jan. 2, 1951). (22) Crockin, J. M., Chem. Eng., 57, No. 11, 160-2 (1950). (23) Deerr, N.,“The History of Sugar,” Vol. 11, pp. 573-8, London, Chapman and Hall, 1950. (24) Dole, V. P.,and Cotdas, G. C., Science, 113, 552-3 (1951). (25) Ecker, P. G., et al., Rev. Sci. Instruments, 20, 799-801 (1949). (26) Eisenlohr, H., Chem.-Ing.-Tech., 23, 12-14 (1951). (27) Eisenlohr, H., Industrial Chemist, 27, 271-3 (1951). (28) Ferney, F. X., private communication, Bird Machine Co. (Sept. 14, 1951). (29) Fessler, J., Wines and Vines, 32, No. 9,29 (1951). (30) Gawain, T. H., Product Eng., 22, No. 7, 152-6 (1961). (31) Gemmill, A. V., Food Inds., 22, 2070-81 (1950). (32) Gibbon, A., World Oil,132, No. 3, 99 (1951). (33) Goethel, H., Chena.-Ing.-Tech., 22, 520-1 (1950). (34)Grace, H. P.,Chem. Eng. Progress, 47,602-7 (1951). (35) Gutfreund, H.,Research, 3, 442-7 (1950). (36) Hertrich. J.. U. S. Patent 2.462.098 (Feb. 22. 1949). ’ (37j Ibid., 2,466,988(April 12, 1949j. (38)Hurlimann, H., J. I n s t . Brewing, 57, No. 1, 21-7 (1951). (39) Hyam. J. F.,Power, 93, No. 11, 136 (1949). (40) Inglesent, H., and Storrow, J. A., Industrial Chemist, 27, 76-81 (1951). (41) Kendrick, A., “The Application of Centrifugal Force,” Boston, International Equipment Co.,1951. (42) Landergren, S., Geol. Foren, i Stockholm Fohr., 73, 315 (1951). (43) Leonard, J., Chem. Eng., 58, No. 9,149-53 (1951). (44) Lindgren, H. O.,Swedish Patent 127,806 (April 4, 1950). (45) Lyons, 0.R., Trans. Am. Inst. Mining Met. Engrs., Tech-Pub. No. 3044F [Mining Eng.,3, 417-25 (19511.1
41
(40) Mack, K. A., private communication, Baker Perkins, Inc. (Sept. 13,1951). (47) Majumdar, S. D., and Sarkar, G. N., Rev. Sci. I m l r u m a t s , 19, 5414 (1948). (48) Merrlees Watson Co., Ltd., British Patent 635.591 (April 12, 1950). (49) Meystre, F. J., private communication, De Lava1 Separator Co. (Sept. 24,1951). (50) Morton, W.N. T., U. S. Patent 2,554,480(May 22, 1951). (51).Munder, H., Brauwell, 40, 845-8 (1950). (52)Olcott, C. A., U. S. Patent 2,517,409(Aug. 1, 1950). (53)Parker, J. A., Chem. Eng., 57,No. 12,109 (1950). (54)Pickels, E. G., Machine Design, 22, No. 9, 102-7 (1950). (55)Pickels, E. G.,and Scofield, P. F., Elec. Mfg., 45,66-9,164,166 (1950). (56)Plummer, J. A., Oficial Digest Federation Paint & Varnish Production Clubs,No. 314, 158-64 (1951). (57)Preston, J. M.,et al., J . Textile Inst., 42, 79-90 (1951). (58)Rao, T.V.,Soap (India), 1, No. 10, 12-14 (1948). (59)Ratcliff, J. O.,Popular Mechanics. 93, No. 1, 144-9 (1950). (60) Reed, K.D., Diesel Power, 29,No. 2,60-2 (1951). (61) Reerink, H.,Chem. Weekblad, 47, 40-1 (1951). (62)Robatel, M.,University of Kansas, thesis, 1951. (63)Roth, W. Z.,Erzbergbare U.Metallhutten W . , 3, 328-34 (1950). (64) Ruebensaal, C. F.,Chem. Eng., 57, No. 12, 102-5 (1950). (65) Rumford, F.. “Chemical Engineering Operations,” pp. 254-65, London, Constable and Co., 1951. (66) Seddon, Eric, J. Inst. Fuel. 24, 165-7 (1951). (67) Singer, 8. J., and Siegel, A., Science, 112, 107-9 (1950). (68) Sittner, G. H., U. S. Patent 2,550,502(April 24, 1951). (69)Smith, F.H., private communication, Sharples Corp. (Sept. 13, 1951). (70)Smith, J. C., Chem. Inds., 63, 786-90 (1948). (71) Sokolov, V. I., Zhur. Tekh. Fiz., 18, 105-14 (1948). (72)Svensjo, N. E., U. S. Patent 2,532,792(Dec. 5, 1950). (73) Thearle. E.L.,Machine Design, 22,No. 9,119-24,No. 10,103-6 (1950). (74) Thou, J. E., U.S. Patent 2,485,465(Oct. 18,1949). (75)Wallace, A. F.,Rept. Hawaiian Sugar Technol., 9th Ann. Meeting, pp. 89-92 (1950). (70)Western States Machine Co., British Patent 626,444 (Aug. 28. 1947). (77)Ibid., 630,810(Oct. 21,1949). (78)Ibid., 637,818 (March 15, 1950). (79) Zychlin, H., and Storrow, J. A,, J. SOC.Chem. I d . (London),69, 379-84 (1950). RECEIVED November 17, 1951.
CRY STA 1LlZATlO N C. S. GROVE, JR. SYRACUSE UNIVERSITY, SYRACUSE, N. Y .
J. B. GRAY, E N G I N E E R I N G
DEPARTMENT,
E. 1. DU P O N T D E N E M O U R S & CO., INC., W I L M I N G T O N , DEL.
Recent publications on crystallization include many papers on the techniques of crystallizing specific substances. Modern processes for the production of sugar and sodium chloride have been described in detail. Methods of making large single crystals have continued to receive attention. Liboratory techniques were described in a book edited by Weissberger. A cornprehensive review of the literature on all aspects of crystal growth was published in a book by Buckley.
C
RYSTALLIZATION has continued to receive the attention of chemists, engineers, and others who are interested in the development and operation of industrial crystallizing processes, or who are interested in the fundamental nature of these processes. I n this review are summarized the papers which were published in the past year on the theory of crystallization, on the variables affecting the rate and habit of crystal formation, and on industrial processes and equipment. Svanoe (69) and Kearney (46)state that in the past year basic principles have been extended t o the field of industrial crystalliza-
tion in five general ways: (1) con tinuous evaporator crystallizer units for producing organic chemicals; (2) when two chemicals are crystallized a t the same time as single crystals, equipment has been developed t o separate these in the crystallizer; (3) Krystal equipment has been extended in the heavy chemical field; (4)crystallizers have been applied increasingly in the field of synthetic fertilizers in producing materials with free-flowing qualities; and ( 5 ) nonscaling equipment has been designed for so-called “scaling liquors” containing gypsum by crystallizing out such constituents. The authors report that extensive work is being carried out in the field of nucleation, crystal growth, and hydraulic classification, but the major part of it has not progressed far enough t o be available for publication.
