INDUSTRIAL AND ENGINEERING CHEMISTRY Kargin, V. A.. and ShtediFg, M. N., J . Phys. Chem. (U.S.S.R.), 20. 727-41 (1946).
Keller, J. D., Ind. heating, 14,.568-70, 572, 574, 676, 578, 580, 582, 584 (1947).
Kesler, C. C., Killinger, J. E., and Hjermstad, E. T.,
Paper Trade J . . 122. No. 13. 39-43 (1946). Khudyakov, G. N., Bull. acad. sci. U.R.S.S., Classe sci. tech.. 1946, 533-41. Koch, H., Schweiz. Arch. anqew. Wiss. u. Tech., 12, 176-84 (1946). Korchunov. S. S., Torfyanaya Prom., 23, No. 3, 24-7 (1946). Krishnappa, T., Subba Rao, K., and Sanjiva Rao, B., Ptoc. Zndian Acad. Sci., 25A, 162-73 (1947). Ibid., pp. 174-80. Zbid., pp. 181-5. Kronstad, H., Rock Products, 49, 94 (1946). Lehmann, A. H., I n d . Heating Engr., 9, No. 33, 35, 37 (1947). Lehmann. A. M.. Chem. Aae (London). 55, 594 (1946). Loasby, G., and Puls, H-. O., J . Textile Inst., 38, P30-40 (1947). Love, C. R., Chem. A g e (London),55,598-9 (1946). Lurie, M. Y., Izvest. VTZ, 15, No. 9/10, 51-5 (1946). Lyons, W. J., Ziifle, H. M., Nelson, M. L., and Mares, T., I n d i a Rubber World, 116,199-204, 207 (1947). McKnight, R. E., Agr. Eng., 27, 166, 168 (1946). Maisonneuve, J., Rev. aluminium, 23, 377-83 (1946). Marshall, J. R., Gas World, 126, No. 3268, Coking Sect., 40-3 (1947). Maxim, E., Food, 16, 113-16,2414 (1947). Mellon, E. F., Korn, A. H., and Hoover, S. R., J . Am. Chem. SOC.,69, 827-31 (1947). Miller, R. C., Agr. Eng., 27, 203-8 (1946). Mitton, It. G., J . Intern. Soc. Leather Trades Chem., 30, 330-4 (1946). Montfort. P. T.. Am. Ena.. 28. 95-7. 108 (1947). Montgom'ery, A. E., P u l p & Paper Mag. Can. (Convention No.), 48, 1 7 1 4 [F] (1947).
Moore, E. L., Atkins, C. D., Wiederhold, E., McDowell, L. G.. and Heid, J. L., Proc. Znst. Food Technol., 1945, 160-8.
Morse, R. S., IND. ENG.CHEM.,39, 1064-71 (1947). Nedey, G., Peintures, pigments, vernis, 22, 109-17, 153-60, 181-9, 219-25 (1946).
Noel, W. A., Gray, W. E., Hankins, 0. G . , and Hollingshead, R. S., Food Research, 10, 379-93 (1945). Nordberg, B., Rock Products, 50, No. 8 , 122-5 (1947). Perruche, L., Nature, L a , 1947, 184-6. Perry, R. L., Mrak, E. M., Phaff, H. J., Marsh, G. L., and Fisher, C. D., Calif. Agr. Expt. Sta., Bull. 698 (1946). Piraux, H., Mdtallurgie, 75, 15-16 (1943). Plank, R., Angew. Chem., B19, 36-8 (1947).
Vol. 40, No. 1
(129) Preston, J. M., and Chen, J. C., J . SOC.Dyers Colourists, 62, 361-4, 364-8 (1946). (130) Ramen, T., Svenslc Papperstidn., 49,418-22 (1946). (131) Ramser, J. H., and Lehmann, E. W., Agr. Eng., 27, 167-8 (1946). (132) Reithel, F. J., J . Chem. Education, 24, 286 (1947). (133) Sapp, J. E., and Gillespie, W. F., Paper Trade J., 124, 120 (Feb. 27, 1947). (134) Scheuppen, J., Paint, Oil, Chem. Rev., 109, 47 (Aug. 22, 1946). (135) Schutt, E. V. K., Gas, 23, No. 6, 37-9 (1947). (136) Shaaban, M. A., J . I m p . Coll. Chem. Eng. SOC.,1, 32-8 (1946). (137) Shedd, C. K., Agr. Eng., 27, 169-70 (1946). (138) Sherman, V. W., Elec. Commun., 21, 125-6 (194244). (139) Shreve, G. W., Pomeroy, H. H., and Mysels, K . J . , J . Phys. & Colloid Chem., 51,963-6 (1947). (140) Silman, H., Foundry Trade J., 75, 195-8, 217-21 (1945). (141) Skau, E. L., Textile Research J., 16,556-63 (1946). (142) Smith, S. E., J . Am. Chem. Soc., 69, 646-51 (1947). (143) Spanyer, J. W., Chem. Eng. Progress, 43, 523-6 (1947). (144) Spring, H. M., Paper Trade J., 124, No. 22, 104, 106, 108, 110 (1947). (145) Stamp, Lord, J. Gen. Microbial., 1, 251-65 (1947). (146) Steinbruegge, G. W., Agr. Eng., 27, 217-18 (1946). (147) Strakhov, V., Myasnuya i Molochn. Prom., 1946, No. 4, 4 1 4 . (148) Subba Rao, G. N., Subba Rao, K., and Sanjiva Rao, B., Proc. I n d i a n Acad. Scd., 25A, 221-8 (1947). (149) Subramanya, R. S., Subba Rao, K., and Sanjiva Rao, B , Ibid., 25A, 186-9 (1947). (150) Swenson, T. L., Electronics, 20, No. 2, 206 (1947). (151) Tschudin, K., Helv. Phys. Acta, 19, 91-102 (1946). (152) Van Arsdel, W. B., Chem. Eng. Progress, 43, 13-24 (1947). (153) Van Kleeck, L. W., Sewage Works J., 17, 1240-55 (1945). (154) Voronin, N. A,, Torfyunaya Prom., 24, No. 2,28-9 (1947). (155) Wagner, H. G., Tomkins, R. G., Brightwell, S. T. P., Allen, R. J. L., and Mapson, L. W., Food M f r . , 20, 289-93, 321-5 (1945). (156) Warburton, F. L., Proc. Phys. SOC.,58, No. 329, Pt. 5, 585-97 (Sept. 1, 1946). (157) Westfall, R. J., Miller, O.,and Westfall, I. S., Science, 105, 530 (1947). (158) White, A. S., Chem. Age (London), 55, 597-8 (1946). (159) Whitwell, J. C., and Toner, R. K., Teztile Research J . , 17, 99-108 (1947). (160) Williams, A. E., Znd. Chemist, 23, No. 265, 83-91 (1941). (161) Wulfinghoff, M. F., Southern Power and I d . , 65, No. 1, 52-5 (1947). (162) Yellott, J. I., and Singh, A. D., Power Plant Eng., 49, No. 12, 82-6 (1945). (163) Youker, M. A,, Chem. Eng. Progress, 43, 391-8 (1947). RECEIVED November 28, 1947.
EVAPORATION
c
ONSIDERABLE general information on evaporators and evaporation has been published recently. Fricke (16) discusses evaporators in a general way, presenting diagrams, layouts, and design information for one to several effects. The bent-tube evaporator designed so that temperature variations will cause flexure and subsequent scale removal is discussed, and operating instructions are given. Badger and Seavoy ( 3 ) havc published a booklet of considerable general interest. They show structural details on various standard types of evaporators. This presentation includes methods of calculation of heat transfer coefficients and indicates the effect of such variables as venting, liquor level, etc. Multiple-effect evaporation is discussed with emphasis on operation at minimum steam requirements and maximum economy. The use of extra or bleed-off steam is covered and an example of its use presented,
Worthen and Fox (46) have patented a design for an oilfired evaporator. Hedin (18)discloses a process for handling crystals and a n evaporator for control of crystal size. Hughes (19)discloses an evaporator with concentric liquor passages so designed that crystals settle through an upward flowing mother liquor stream thus classifying the crystals. Lindquist (26) shows an evaporator for the paper industry. Schumacher (39) discusses the production of chlorates and perchlorates. He indicates an evaporator for perchlorate mother liquor but does not discuss this machine. Little has been contributed to the general theory of evaporator operation. Rachko (36) presents experimental data on the boiling of water inside a vertical tube. The water enters the tube at a temperature below the boiling point and leaves as a steam-water mixture. The results of this Russian experiment
January 1948
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
me a t variance with American experience. Rachko reports no improvement in the coefficient if the velocity through the tube is increased by the admission of steam into the bottom of the tube. I t is reported further that the ratio of length to diameter of the tube has no influence on the coefficient. This says, in effect, that a standard vertical calandria will give the same coefficient as a long-tube, vertical machine. - It is stated that the material of construction is unimportant, whereas we have found that a carefully protected, highly polished ,surface can give extremely high coefficients. A second article (37) covers experiments designed to show the effect of diameter on the boiling coefficient in a vertical tube. I t is revealed that the coefficient is dependent on the heat flux only, varying as the 0.455 power below 70,000 calories per square meter per hour and as the 0.21 power a t values above 70,000. It is stated that the coefficientis independent of the Reynolds or the Prandtl number. The relation between the At and heat flux is shown to be different at the bottom and top of the tube. This work was done on an iron tube, the diameter varying from 1.8 to 25 centimeters. The free evaporation of water from a flat surface is presented by Boelter et al. (7). Equations and charts are given for predicting this rate as it applies to evaporative cooling and similar problems. Lee (66)describes the operation of an old secondhand horizontal tube evaporator at greatly increased rate. First operation caused considerable foam, and it was necessary to remove two rows of tubes from one end of the tube bank to permit good circulation. A complete investigation of carry-over in a horizontal tube evaporator is reported by O'Connell and Pettyjohn (33). These investigations were carried out with horizontal criss-cross unit containing 144 '/a inch X 16 gage X 26 '/z inch tubes. Three distinct types of carry-over were noted by the investigators: first, entrainment of small liquid droplets in the vapor; second, splash of liquid directly from the body to the condenser; and third, foaming. The entrainment per unit of evaporation decreased with increased heat flux density and increased boiling point. A relation is shown between the heat transfer coefficient and entrainment, explained by the fact that both were functions of the size and number of vapor bubbles formed. Splash is shown to be dependent on the heat flux. The data indicated less splash a t higher boiling points because of the lower vapor volume. The work indicated that a vapor space of one cubic foot for every cubic foot of vapor formed per second prevented splash. The splash. losses were several times the entrainment loss, and the authors indicate that more attention should be paid to this item in evaporator design. The writers indicate a greater foaming a t higher boiling points. This is somewhat contrary to the generally understood relation, but the statement is well supported. The relation given between entrainment and heat transfer coefficient is shown as a graph in which the logarithm of the entrainment is approximately a straight-line function of the logarithm of the over-all heat transfer coefficient. The authors believe that the horizontal tube evaporator is not satisfactory for foamingliquids; it is worth while to note the work of Lee (66)in this regard, The problem of handling wastes has caused considerable activity in evaporator work. This is particularly true in the paper industry, and as a result this industry is doing a considerable amount of work. A recent article (8) on the utilization of sulfite waste liquor for the production of yeast, vanillin, and tannin gives a good indication of the foreign work in this field. The general economics of such operations differ in this country from those in others, but the problems of scale, corrosion, foaming, and retention of useable valuables are the same. Lure (88) describes a Russian pulp mill a t Archangel where waste liquor is fermented to ethyl alcohol, a process not generally feasible here. The residue from this process contains 501, solids and is concentrated to about 50% for use as a bonding agent for foundry sand. The residue is first sprayed into boiler stack
23
gases a t 170" C. and then into flue gases at 700" to 900" C. Karlberg (88) describes the operation of a sulfite waste evaporator in Sweden. The fced contains 13 to 14% solids and is concentrated in a quadruple-effect evaporator. The heating units are so designed that steam and liquor sides of the tubes can be changed. This prevents scaling completely in the second and fourth effects. The first effect requires cleaning with nitric acid for complete cleaning, and the calcium sulfate in the third effect requires mechanical cleaning, 2000 pounds being removed from the vapor space annually. The discharge from this evaporator is 50% solids and is suitable for burning as a fuel. Edling (11) discusses the scale problem further and compares the reversal of steam and liquor side operation with other cleaning methods. Obviously the reversal procedure is not feasible where evaporator condensate is used for boiler feed. A report from Central Laboratory of the Cellulose Industry (Sweden) is given by Ulfsparre (46). A committee from this organization made a study of scale encountered in the evaporation of sulfite waste liquor. They present methods for its control both by process changes and special equipment design. It is suggested that stripping of sulfur dioxide from the feed liquor will greatly decrease the scale. The scale is carefully identified by Sillen (411, who made chemical and x-ray studies which indicated that it is principally calcium sulfate. He found very little calcium sulfite or silicate. The calcium sulfate appears in anhydrous, dihydrate, and hemihydrate form, depending on the temperature of formation. The scale difficulty is directly proportional to the amount of sulfate in the feed. It is claimed that the generally used analytical methods are not satisfactory, and a new method is presented. Various methods are described and compared for the removal of sulfate from the feed liquor, Nyman (31) furthers our knowledge of this scale problem with a review covering eighteen articles on the subject. The scale discussed is that encountered in concentrating sulfite waste to a point where it can be used as fuel (50% solids). It is noted that organic material can be used to increase &he vetastability of calcium sulfate, and it may be possible to so prevent deposition of the scale. The use of surface active agents is disaouraged, and the use of reverse steam and liquor flow is discussed. Further discussion of the operation of a sulfite waste liquor evaporator is presented by Ramen (%), who describes a quadruple-effect unit in which the fourth effect gave difficulty with scale. Increasing the velocity of liquor flow decrertsed the rate of scale formation. Sectional heaters are described that can be cleaned one part at a time without stopping normal operation. An evaporator for black lye from a sulfate cellulose process is described by Nyquist (38). The unit uses hot gases from a soda furnace containing carbon dioxide, sulfur dioxide, sodium sulfate, and sodium carbonate to neutralize alkaline values and concentrate the solids. Lignin is precipitated and recovered in the process. Bergstrom and Trobeck (6)disclose a process for concentrating black liquor. A multiple-effect evaporator is used to carry the concentration to SO%, then direct fire at low temperatures in presence of gas to 70-80%, and finally superheated steam to 90-95%. The liquor is oxidized by air and other gases to save the hydrogen sulfide values. They note that this can also be accomplished by treating the feed with sulfur dioxide. Katz (63) discusses the corrosion encountered in the third effect of a sulfite waste evaporator. Small funnel-shaped holes were observed passing completely through the tube with the larger end on the inside (liquor side) of the tubes. The tubes were scaled with calcium sulfate, and the other effects which were free of scale were free from corrosion. I t was discovered that parasitic elcctric currents were causing the difficulty. Coated and uncoated test strips were hung in the unit; the coated strip had an electromotive force of 196 millivolts with respect to the uncoated. When t,he velocity of circulation was
24
INDUSTRIAL A N D ENGINEERING CHEMISTRY
increased, the scale problem was eliminated and the corrosion difficulty disappeared. McIntosh (99) investigated the use of corrosion-resistant alIoys in kraft mill equipment including evaporators, and reached the conclusion that the time and maintenance savings more than offset the increased initial cost. A sextuple-effect, seven-body kraft black liquor evaporator is described by Seavoy (40). A complete heat balance is presented, and the significance of the temperature drops in the various effects is discussed. The progress in waste liquor evaporator design and operation is presented by Bergstrom and Lientz (6); the improvements have centered around a better understanding of the long-tube, vertical evaporator through operating experience and laboratory work. The importance of tube proportions Tor maximum performance is understood. Feed distribution, the ratio of length to diameter, and other factors have been investigated. Longer tubes are now in use, and multiple-pass heaters have been used in the first effect. The sum of these is such that as much a.s 5.5 pounds of evaporation per pound of steam has been realized in seven-effect evaporators. Foam loss has been reduced and catch-all design has been approved to reduce pressure drop; this permits more effects with a given steam pressure, or with lower steam pressure required. The use of clad 302 and 304 stainless steel has reduced the cost of avoiding corrosion difficulties, and chromium-plated tubes have reduced scale problems. Instrumentation has been developed to the point where product control is better, and i t is now possible for a single operator to handle two to four sets of evaporators. The sugar industry has continued to show considerable interest in improving evaporation operations. Delgado (10) presents a complete survey of the generation and use of steam in the sugar industry. The Swedish Sugar Corporation (44)reports on research work, indicating several possible improvements in the control of sugar boiling and vacuum pan design. Loumiet (97) describes a device for adding steam to the bottom of tubes in sugar evaporator. The mheme permits evaporation from a thin film moving at a high velocity, and an increase of 30% in the capacity of.the evaporator is reported. Further work on this device is reported by Gonzhlez Maiz (17). He states that the proper use of steam injection will increase the capacity as much as 50%. This method greatly decreases the scaling and entrainment normally encountered. Mujica ($0)gives a complete description of the use of inhibited hydrochloric acid for cleaning sugar evaporators. A method for the suppression of foam and decreasing the scale in sugar evaporators is disclosed by Larsen (34). This covers a fatty acid composition, consisting of 30 to 40% of a fatty acid mixture free from glycerol and 60 to 70% of an unsaturated hydrocarbon from a naphthenic, asphaltum, or paraffin base crude. I t is stated that about one gallon of this mixture is required per ton of sugar produced. Several special types of evaporators are discussed in recent literature. Ames ( 1 ) reports on a special laboratory evaporator designed to handle gelatin solutions and other materials that are heat sensitive. Distilled water evaporators for merchant ships are discussed by Ireland ( 2 1 ) . Particular emphasis is placed on the economic features of low pressure evaporating plants. Impagliazzo (20)compares low pressure steam-heated water evaporators with vapor compression units. H e reports that vapor compression units are feasible only where steam facilities are not available. This coinpalison is further discussed by Flamant (13). He covers the use of multiple-effect evaporators and thermo and turbo compression units for purified water. Three very complete articles covering the concentration of sulfuric acid have appeared recently. Chambers and Peterson (9) describe the D u Pont falling film evaporator. This unit is designed for a moderate production capacity, requires a minimum of corrosion-resistant equipment and maintenance, and involves no fumes. The unit uses high silicon iron tubes 8 inches inside diameter X 12 feet long individually steam-
Vol. 40, No. 1
jacketed. I n effect the unit consists of two separate heating chests with a common vapor head, feed distributor, and product collecting tank. The steam jacket is divided into two sections; the upper section is heated with 130 to 250 pounds steam, the lower with 250 pounds steam. Normally the feed concentration is 72% and the product 92% sulfuric acid. The writers report a maximum temperature difference for the best heat transfer coefficient and show this on a chart as a function of the feed concentration of the acid. The heat transfer coefficient was found to be in the order of 80 P.c.u./(sq. ft.)(' C.)(hr.) in both the falling film evaporator and the preheater. Berger and Gloster (4)discuss the Chemic0 drum-type concentrator. The writers report that this unit has proved the most suitable available for the concentration of chamber acid (77%) to 60" Be. (93.2%) and that there are some 250 units in this or similar service. The unit uses hot gas from the gas- or oil-fired furnace for concentrating in two steps, acid and gas flow being countercurrent. The biggest problem encountered in this unit is the removal of mist from the exit gases. I t is noted that if nitric acid is present, lead is not satisfactory for the electric mist precipitators, and carbon was found to be the most suitable material. The writers cover the entire operation completely and discuss motor failures, pipe troubles, and many other difficulties. The Simonson-Mantius process for concentrating sulfuric acid is presented by Burke and Mantius (8). The writers describe five different types of vacuum evaporators that have been developed for the concentration of different amounts and strengths of feed and product acid. The type most generally used for the concentration of any strength acid to 95% uses bayonet-type heating tubes in a cylindrical vertical shell. This unit is a steel shell, lined with lead, protected by one or more layers of acidproof brick laid in acid-resistant cement. It uses a vacuum booster and jet type condenser, operates at a 25 to 29 inch vacuum, and is generally heated with 200 to 300 pounds steam but sometimes with Dowtherm. The acid losses in this unit are small, being as low as 2% when concentrating to 95% acid. Several special materials and methods of design and operation have been presented recently, Ernst (19) describes a treatment to prevent evaporator scale in fish water by adding phosphorus acid or its compounds in sufficient quantity so that the pH remains acid all during the concentration. Ulmer (48) shows mechanical and chemical methods for overcoming corrosion of plant equipment due to caustic, magnesium chloride, etc., in steam and water. The purification of evaporator bleed-off steam is discussed by Powell (3.4, and acid cleaning methods have been claimed (35). Foley (14) describes the behavior of dust particles and separators. This work is of interest for the evaluation of catch-all designs. Williamson (45) discloses a float-operated feed regulator for maintaining constant level in any evaporator. The use of graphite in heat exchange equipment is discussed by Ford (16). He gives figures on a rayon spin bath evaporator using graphite tubes and antimonial lead tube sheets. The tubes are held in by special gaskets described by Badger and Seavoy ( 3 ) . The unit is fed with 770 gallons per minute of feed containing 8.5% sulfuric acid and 2170 sodium sulfate, and evaporates 20,800 pounds of water per hour. The machine operates a t 3.5 inches of mercury absolute with 15-pounds steam pressure a t a temperature difference of about 110' F. The liquor head is rubber-lined steel. LITERATURE CITED (1) Ames, W. M., Chemistry & I n d u s t r y , 1946, 194. ( 2 ) Anonymous, Papeterie, 68,194 (1946). (3) Badger, W,; L., and Seavoy, G. E., "Heat Transfer and Crystallization, Smcnson Evaporator Co. (1945). (4) Berger, J. H.,and Gloster, A, J., Trans. Am. Znst. Chem. Engru.
43,225 (1947). (5) Bergstrom, H.0. V., and Trobeok, C., U. S. Patent 2,406,581 (Aug. 27,1946).
January 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
(6) Bergstrom, It. E., and Lientz, J. It., Paper Trade J . , 125,No.1, 42 (1947). (7) Boelter, L. M. K., Gordon, H. S., and Griffen, J. R., IND. ENG. CHBM.,38,596 (1946). (8) Burke, J. P., and Mantius, E., Chem. Eng. Progress, 43, 237 (1947). (9) Chambers, F.S., and Peterson, R. F., Ibid., 43,219 (1947). (10) Delgado, 5. V.,Intern. Sugar J., 48,236 (1946). (11) Edling, G.,Pulp & Paper Ind., 19,No. 12,58 (1946). (12) Ernst, R.C.,U.S. Patent 2,403,174(July 2, 1946). (13) Flamant, A. C., Chalezir et ind., 28,8 (1947). (14) Foley, R.B., Trans. Am. Soc. Mech. Engrs., 69, 101 (1947). (15) Ford, C.E., Chem. Eng., 54,No.2, 132 (1947). (16) Fricke, G. A., Combustion, 17,No. 10,39 (1946). (17) GonsAlez Maiz, J. C., Intern. Sugar J . , 48,150 (1946). (18) Hedin, C. B.,Swedish Patent 113,423(Mar. 13,1945). (19) Hughes, J. S., U. S. Patent 2,384,747(Sept. 11, 1945). (20) Impapliazzo, A. M., Mech. Eng., 69,387 (1947). (21) Ireland, M. L., Trans. SOC.Naval Architects and Marine Engrs., 53.38 (1945). (22) Karlberg,‘ R.,Svensk Papperstidn., 49,412 (1946). (23) Kats, W., Chem. A p p . , 28,87(1941). (24) Larsen, R. H.,U. S. Patent 2,412,276(Dec. 10,1946). (25) Lee, C. A.,Chem. Eng., 53,No. 8 , 128 (1946).
25
(26) Lindquist, B. O.,Swedish Patent 113,680(Apr. 3 , 1945). (27) Loumiet, J., Intern. Sugar J., 48, 150 (1940). (28) Lur6, M.Yu., Izvestiya V T I , 15,No.3, 4 (1946). (29) McIntosh, W., Puper Trade J . , 123,No. 15,180 (1946). (30) Mujica, A. C., Cuba, 19,241 (1945). (31) Nyman, C., Svensk Papperstidn., 49,73(1946). (32) Nyquist, B. S., Swedish Patent 105,515(Sept. 15, 1942). (33) O’Connell, H. E., and Pettyjohn, E. S., Trans. Am. Inst. Chem. Engrs., 42, 795 (1946). (34) Powell, J. A., U. S. Patent 2,398,396(Apr. 16,1946). (35) Powell, 5. T.,Trans. Am. SOC.Mech. Engrs., 68,905 (1946). (36) Rachko, V. A.,J . Tech. Phys. (U.S.S.R.), 16,993 (1946). (37) Ibid., 16,713 (1946). (38) RamBn, T.,Svensk Papperstidn., 49,418 (1946). (39) Schumacher, J. C., Chem. Eng. Progress, 43, 177 (1947). (40) Seavoy, G. E.,Paper Ind. umd Paper World, 27, 1795 (1946). (41) Sillen, L. G., Svensk Papperstidn., 49,387 (1946). (42) Ulfsparre, S., Ibid., 49,383 (1946). (43) Ulmer, R.C., Power Plant Engr., 51, No. 1, 108 (1947). (44) Wiklund, O.,Socker Handl., 2 , 245 (1946). (45) Williamson, W. R.,U. S. Patent 2,392,893(Jan. 15, 1946). (46) Worthen, E.P., and Fox, B., Ibid., 2,384,226(Sept. 4,1945). RECEIVED November 28, 1947.
F ILTRATION OF KANSAS, LAWRENCE, KANS.
F
ILTRATION work of which published accounts have appeared during the past year reflects a return to a rate of development and application characteristic of peacetime industry, notwithstanding the occmional reports of war-born activities which continue to be divulged. The effects of the war are still noticeable, however; the fact that the majority of the researches, inventions, and industrial applications described originated on this continent may be attributed in large part to an economy, productivity, and academic continuity relatively less disturbed by the war here than in other parts of the world. It is encouraging that this year has brought an increase in scientific and technical publications from Europe and Eurasia, an increase which we trust will continue. The scope of this review, like that of last year’s, is the field of conventional filtration, excluding sedimentary liquid-solid separations (sedimentation, elutriation, centrifugation) and gas clarification. A few articles unintentionalIy omitted from the last review are included. Completeness of coverage is not claimed; in general, the items reported are those believed to be of broadest interest or those contributing quantitative information. Theory. The importrtncc of porosity in determining the permeability of a filter cake has again been declared. Following the suggestion of Ruth’s earliest papers, Belkin (10) presented a form of the filtration equation involving cake porosity. His equation includes a term which characterizes compressibility and another term which is a function of the specific cake resistance, but it does not attempt tto define the effect of solid particle size. Reevcs (61) pointed out that, since filtration rate is inversely proportional to filtrate viscosity, a viscous liquid may be diluted advantageously with a low viscosity solvent before filtration. When the high viscosity inatcrial is the desired product, however, continued dilution ultimatcly bccomes uneconomical. Reeves dcrived the theoretical optimum degree of dilution by using an empirical relation between the viscosities of the two liquids involved and the composition of the mixture. He showed that his theoretical optimum rtgrccd well with values determined experi-
mentally. This method is applicable only when dilution of the filtrate is permissible. Viscose filtration and the accompanying problem of filter medium plugging have been approached theoretically by Bergek and Ouchterlony (IS). These investigators ascribed the plugging of the filter medium in part to the deterioration of xanthate aggregates because of the shearing stress encountered, and they related plugging quantitatively to the structure and concentration of the dispersed cellulosic particles. The most recent attack of filtration theory is that of Brownell and Kate (18). Only the first of three installments of their paper had been published a t the time this review was prepared, however; a report of their work will be deferred, therefore, until the entire series of articles has appeared. Equipment. The attention of the chemical process and related industries continues to focus on rotary vacuum filters. Semiworks machines of this type have been described in both British (9) and American (36) use, the lat,ter by Hignett in connection with a pilot plant for the extraction of aluminum from clay. Hignett presented operating data for two %foot drum filters but failed to state cake thickness and final moisture content. RRck (60) summarized the performance of a B-foot-diameter by 4-foot-face drum filter which dewaters finely ground fluorspar from an initial concentration of 60-65y0 solids to a final moisture content of S-lO%. Klein, McCall, and Liente (49) related a method of washing paper pulp countercurrently in five stages by means of three rotary vacuum filters, two of which had two sets of washing sprays and dual filtrate receiving lines. These investigators studied the effects of washing rate, quantity of wash, and pulp type. They reported handlingcapacity figures. Talmud and Khazin (67) discussed various types of equipment, including vacuum filters, suitable for filtering alumina suspensions. Peterson and Peterson (67) modified the double-drum filter to invent a truly continuous precoat filter. The precoat is picked up from tanks at the bottom of the drums (as in ordinary vacuum filtration), while the slurry is applied at the top of the drums from a slurry pool contained in the pinch between the cylinders.
