January 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
Ranby, B. G., and Grinberg, B., Compt. rend., 230, 1402-4
75
Sybel, H. v., Z. Ver. deut. Ing., Verfahrenstech., No. 3, 59-62 (1941).
(1950).
Razous, P., “ThBorie et Pratique du SBchage Industriel,” 5th ed., Paris, H.Dunod, 1949. Rigaut, P., and Ulmer, G., Fonderie, 38,1491-3 (1949). Robinson, R. R., J . Can. Ceram. SOC.,18,35-9 (1949). Roddy, W. T., Jacobs, J., and Jansing, J., J . Am. Leather Chemists’ ASSOC., 44,308-20 (1949).
Rudd, H. W., and Tysall, L. A., J . Oil Colour Chemists’ Assoc., 32, 546-63 (1949). Rudolph, W., Ind. Finishing, 26, No. 4, 30-2, 34, 37-8, 40 (1950). Rumpelt, H., Farbe u. Lack, 55,271-4 (1949). Schaeffer, A., Textil-Praxis, 5,3-6 (1950). Schneider. J., Kunstseide und Zellwolle, 28,264-78 (1950). Schneider, J., Melliand Textilber., 31,No. 4,2846 (1950). School, K.,TextiLPraxis, 5,32 (1950). Schultz, T.H.,Miers, J. C., Owens, H. S.,and Maclay, W. D., J . Phys. & Colloid Chem., 53,1320-30(1949). Seltzer. E.. and Settelmever. J. T.. “Advances in Food Research,” Vol. 11, “Spray Drying of Foods.” pp. 399-520, New York, Academic Press, 1949. Settelmeyer, J. T., Food Inds., 22,272,376, 378 (1950). Shikher, A. G..Shikher. M. G., and Petrova, N. Ya., Zhur. Priklad. Khirn., 22,947-51 (1949). Signer, R., and Roth, M.,Makromol. Chem., 3,281-5 (1949). Simril, V. L.,and Hershberger, A.,Modern Plastics, 27,No. 10, 97,98,100,102,150-2,154,156,158 (1950). Ibid., 27,NO.11, 95-6,98,100,102 (1950). Smith, D. A.,Chem. Eng. Progress, 45,703-7(1949). Smith, S. F., Paper-Makers (London), 119, 185-8, 190-2 (1950). Soap Sanit. Chemicals, 26, No. 9,61-2 (1950). Spooner, W. W., Ind. Heating Engr., 12,No. 52,50-2 (1950). Stringer, W. E.,Food Inds., 21,892-5 (1949).
Tamblyn, W. G., P u l p Paper Mag. Can., 50, No. 12, 101-7 (1949).
Tetrel, R., Rev. prod. chim., 53, No. 3-4, 26-7, 9,31, 33: No. 5-6,48-51(1950). Textile Age, 14,No.1, 104-6, 108-12 (1950). Thomas, F. W., J . SOC.Dyers Colourists, 65,478-83 (1949). Ueno, Seiichi, and Imade, Hiroshi, J . Nippon Oil Technol. SOC., 2,No.1, 1-4 (1948). Uihlein, Z. H., Chem.-Ztg., 74,No. 28,388-93(1950). Ullrich, E.,Tezti,?-Praxis, 5,130-3 (1950). Utley, H. F.,Pit & Quarry, 41,No. 5,1046 (1948). Vandoni, R., and Boivin, M., Mem. sewices chim. Qtal. (Paris), 33,239-46(1947). Van Kampen, G. R., Paper Trade J., 128,No. 14,26-7 (1949). Varley, J., Am. DyestuffReptr., 39,367-8 (May 29,1950). Walter, L.,Tertile-Mfr., 75,No. 894,282-4 (1949). Watts, A.J. C., Trans. Brit. Ceram. Soc., 49,No. 2,43-55,55-7 (1950). Weissberger, A., “Technique of Organic Chemistry,” Vol. 111, New York, Interscience Publishers, 1950. Whitewell, J. C., Bowen, C. F., and Toner, R. K., Textile Research J., 26,400-9 (1950). Whitwell, J. C., and Toner, R. K., Ibid., 19, No. 11, 755-8 (1949). Woodcock, R.W., Elec. World, 132,100 (Nov. 5,1949). Wride, W. J.,Iowa State Coll. J . Sci., 24,122-4 (1949). Yamamoto, Gi-ichi, Trans. Am. Oeophys. Union, 31, No. 3, 349-56 (1950). Zilske, Heinz, Seifen-~Ze-Fette-Wachse, 76, 89-93, 111-13 (1950). Zwolinski, B.J., Eyring, Henry, and Reese, C. E., J . Phys. & Colloid Chem., 53,1426-53 (1949). RECEIVED October 30, 1950.
EVAPOR AT1ON w. L. BADGER, ANN ARBOR,MICH. R. A. LINDSAY, THE DOW CHEMICAL CO., MIDLAND, MICH. AS
In the long-tube vertical evaporator i t is probably necessary to consider three zones within the tube instead of two as previously thought of: a nonboiling section, a boiling section with subsequent recondensation, and a true boiling section instead of the simpler assumption of nonboiling and boiling sections. This section of boiling and subsequent condensation was shown to have a heat transfer coefficient exceeding those predicted by any standard formula for liquid heating. In many investigations of heat transfer coefficients in evaporators, the so-called “nonboiling”section has revealedsuch coefficients. In some recent work on Dowtherm boilers, coefficientsin the liquid preheating section were found to be much higher than those expected. In view of McAdam’s work it i s certain that surface boiling was encountered. It had been thought previously that the known information on physical property was inaccurate, and the cause of the lack of correlation between the experiment and the calculated data. The authors in this paper report a heat flux in the neighborhood of 2,000,000 B.t.u. per square foot. As the liquid was subcooled below the boiling point the heat flux was higher. Increasing the velocity with other conditions remaining constant did not change the temperature difference a t which the boiling occurred, but did increase the maximum heat flux obtained.
has been true in the past several years, there is but little advance in the past year in the theory of evaporation or the design and operation of evaporators. There is evidence of increased interest in the range of film boiling, whereas in the past the major emphasis has been in the nucleate boiling range. This interest i s probably due to evaporation problems arising in jet engines and atomic energy work, where it is necessary to cool from a very high temperature level. The most prolific source of published information on evaporators continues to be the paper industry, and if one i s to judge by the amount of work reported, the problem of scale in sulfite waste evaporators is the most important stumbling block in the field of evaporation. The use of evaporation as a tool to secure ion-free water and to recover values from dilute solutions continues to decline in favor of ion exchange. Such work as presented b y Prescott (37) and others is evidence of this. Furthermore, the possibility exists that ion exchange may supplant in some instances both formation of the solution and its concentration. In theory it is possible with the proper exchange resins to take a dilute salt solution and convert it into a concentrated caustic solution. The food and pharmaceutical industries continue to apply evaporation technique learned in the heavy chemicals field. The illustration shows a unit for concentrating a heat-sensitive product in these fields. c
P
ROBABLY the most important recent contribution to the understanding of evaporation problems is that of McAdams et al. (966). This paper presents a very thorough investigation of the physical phenomenon of heating liquids, where the heat transfer area temperature exceeds the boiling point of the liquid under the pressure existing a t the surface. The investigation was performed with the use of high heat flux by means of a hot wire to liquid inside a vertical glass tube. It was noted and observed with high speed photography that vapor formed a t the surface subsequently was recondensed in the body of the Iiquid. It is obvious that in every natural circulation evaporator this situation must occur in some section of the heating area.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Xeuville (36)reportfi on a mathematical formula for multipleeffect evaporators based on the observed fact that with equal areas and no vapor removal from any of the effects the pressure difference between effects is always the same. The evaporation in each effect is shown to be proportional to the pressure difference. This formula is limited in scope, as heat effects introduced by feed conditions can make a considerable difference in the evaporation ratio between effects. Vedrilla (44) presents a simple formula and illustrates its application for chemical processes by calculating the heat losses and capacities of an evaporator and other chemical equipment. The coefficient encountered in film boiling from a horizontal tube is given by Bromley (?), who undertook the work to solve problems arising in the design of jet engines where the temperature difference exceeds the critical for nucleate boiling. The film is described as continuous with ripples of varying thickness along the length of the tube. Variation in film thickness also occurs with time a t k e d point on the area. This results in a coefficient that is higher than would be predicted if the film were of uniform thickness. The result can be compared to a finned tube, in that the phase boundary between the vapor and the liquid is extended, The metal surface is important, but much less so than in nucleate boiling. It is shown that liquid-vapor surface tension is an important factor in the size of the critical heat flux, as is the total pressure on the system. Bromley presents a formula for stable film boiling along with experimental data. Fatica and Kata (16) report on dropwise condensation and a formula for predicting it. This matter is of considerable interest in the design of forced-circulation and long-tube vertical evaporators where it is often possible to obtain boiling coefficients exceeding the steam-film coefficient. A discussion of the effect of surface roughness indicates that the commercially available surfaces are generally so rough as to forbid the possibility of anything but film condensation, because of the many peaks presented and their relation to the contact angle b e h e e n the surface and liquid condensate. Maisel and Sherwood ($7, 68) present data on the evaporation of various liquids into turbulent gas streams. They cover evaporation from planes, cylinders, spheres, and disks. TTlater evaporation was investigated irom ail surfaces into air Water into carbon diovide and helium, benzene into air, and carbon tetrachloride into air were investigated from cylinders. The effect of velocity, shape, liquid properties, and pas properties is presented and the correlation of mass and heat transfer is shown. Boiling coefficients from iinned tubes are reported by Zieman and Katz (48). The tubes investigated had an area ratio of 2.4 to 1 and the heat flux per lineal unit is shown to be 1 4 to 2 0 times as great as with a smooth tube Data are shown for hexane and isobutane. The nork revealed that the problem of condensate removal from the inside of the tube was of extreme importance. When the %foot tube was tilted to a total of 2 inches the over-all coefficient increased by 8%. Partial condensation of the steam was used to investigate the sweeping effect of steam velocity on condensate removal. Inlet steam velocities up to 40 feet per second gave over-all coefficients of 500, a t 240 feet per second the coefficient was 750, and at 300 and above it was 900. .4 short tube of 0.65 foot, compared to 3 feet, gave a coefficient of 1000 a t a nominal inlet steam velocity Witzig, Penney, and Cyphers ( 4 6 )present data on the evaporation of Freon-12 from inside of a copper tube, 0.305 inch in inside diameter. The effect of flow rate, oil contamination] and temperature difference was investigated. The results show that temperature difference has a big effect, while evaporation temperature, flow rate, and oil contamination are of decreasing importance. The problem of evaporating organic liquids is considered by Klein (22), who presents a formula for estimating the latent heat, relating it to the critical state. Data are presented for many liquids and the formula is shown to give results which compare well with experimental data. Berman ( 4 ) shows the
Vol. 43, No. 1
effect of noncondensable gases OD steam film coefficients. This problem is particularly important in multiple-effect evaporators, where the steam source is often under a vacuum and complete air exclusion is impossible. It is shown that the decrease in coefficient is considerably greater than the percentage of nonrondensable present. McAdams (66) lectures on the present-day level of our knowledge of heat transfer, including evaporation. He shows that as a liquid is heated for evaporation it is first heated by natural convection and the coefficient is proportional t o the temperature difference to the five-fourths pon-er. Secondly heat is transferred by nucleate boiling where vapor bubbles are formed on the heating surface and are displaced with liquid In this range the heat flow varies as the temperature difference to the nth pon-er, where n ranges from 3 to 4. Next, i t is transferred where part of the surface is continuously covered by vapor. Fourth is transfer to vapor, where the surface is completely covered by vapor and heat is transferred by conduction and radiation through the vapor film to the liquid. Lastly, it is transferred where the area is a t a high enough temperature so that radiation controls the rate of heat transfer. It is pointed out that one of the conventional problems yet to be completely investigated is the pressure drop and heat transfer rate in natural-circulation evaporators. One of the stumbling blocks in this investigation is the fact that it is impossible to separate completely the various methods of transfer that occur in this type of evaporator. Even in a simple unit like a natural evaporator heat transfer occurs by natural convection, boiling with subsequent condensation, and eventually by nucleate boiling. Instruments and controls for paper-industry evaporators are discussed by Murphy (81) I t is shown that by the proper operation of the evaporators a considerable increase in the recovery of chemical values can be realized. Malikov (29) shows a control method for a sugar plant where all of the process is synchronized with the evaporator operation. A complete discussion of instruments and their use, including control of salt concentration in evaporators, is presented by Broadhurst et al. (6). Among the several papers covering the handling of sulfite waste liquors is one by Samuelson (39) who presents data on the precipitation of calcium sulfate and the type of hydrate formed. The minimum solubility occurs a t a p H of 3.5, as shown by graphs and tables. The amount of calrium sulfate precipitated increases with higher temperatures, and seeding with fine crystals increases the rate of precipitation. The amount of total solids present has little effect on the amount or rate of precipitation. Laboratory work was checked on a plant unit showing less scale with neutral liquor than was experienced with acid liquor. Examination of the crystals by x-ray revealed that anhydrite material is precipitated a t 130" C. and above, and the hemihydrate from 100" to 130' C. Nyman (33) discusses the treatment of sulfite waste liquor by adjusting the pH to 6 to 6.5 with sodium carbonate. This is reported to form a suspension of calcium sulfite which is coprecipitated with calcium sulfate and results in a scale that can be easily removed with acid. Butler (9) reviews 51 references on the evaporation and burning of calcium-base sulfite liquors. Grewin and Lindberg (18)disclose a method of scale removal by alternating the steam and liquor flow every 30 hours. The steam is mixed with sulfur dioxide from the liquor and the condensate removes the scale. The evaporation of su!fite liquor has always been a serious problem because of the presence of large amounts of calcium sulfate. Several companies in Sweden are now evaporating sulfite liquors with one or the other of two relatively new processes. The RosenbIad (24,38) system uses a plate-type heating element in which the even-numbered passages are used for liquor and the odd-numbered passages for the heating steam. After a certain number of hours, by an ingenious arrangement of valves, the flow is switched so that the liquor goes through the odd-numbered passages, and the steam goes through the even-numbered passages.
January 1951
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INDUSTRIAL AND ENGINEERING CHEMISTRY
The condensate dissolves off the calcium sulfate scale. This system has been installed in four mills. The Ramen system, which has not been described in the literature, is based on the fact that the solubility of calcium sulfate in sulfite liquors is very much higher at room temperatures than in pure water. The system uses an evaporator with a considerable number of effects. The liquor is concentrated first in the lowest temperature effects, where the solubility is greater and the liquor does not reach saturation at these temperatures. The liquor is then heated by the direct injection of first effect vapors to such a temperature that a considerable amount of calcium sulfate i s thrown down. This liquor is then evaporated in intermediate effects, still below the saturation of calcium sulfate. It is then heated again by the direct injection of high pressure steam, to such a temperature that most of the calcium sulfate remaining is thrown down, and then evaporated in the first effects of the multiple. By such a cycle, the evaporator bodies proper are always operating below the saturation point of calcium sulfate; the reheating where calcium sulfate is precipitated i s done in apparatus in which scale does not form because the heat does not pass through a heating surface; and the calcium sulfate is thus thrown out as insoluble anhydrite, whose rate of solution is so slow that it does not redissolve appreciably during the time the liquor is in the evaporator. This system is installed, with variations, in four mills in Sweden. Some mills use falling-film, long-tube evaporators with forced circulation, but a t present these installations are considered obsolete, because they require very frequent cleaning to remove calcium sulfate scale. A system similar to the Rosenblad is presented by Franklin and Goddard (17), using steam pressures from 200 t o 250 pounds per square inch gage. The vapor from the evaporators can be used to generate low-pressure steam for other plant uses. They suggest the use of three heaters alternately, with one being cleaned with acid condensate from the low-pressure steam generator a t all times. The unit described discharges a 60% solids products and the economics of the operation are presented. A similar high-temperature evaporator for sulfite waste liquors is presented by Aspegren ( 1 ) . Brauns (6) discusses a proposed sextupleeffect evaporator for high-temperature operation Superheated steam a t 240' C. is added t o the third effect to remove sulfate A diagram is shown along with heat and material balances for a unit to concentrate a feed containing 10.9 to 50% solids. An electrically heated evaporator for sulfite waste liquor is reported by Beath and Hill (3). In the ha1 pilot plant design the liquor flows through a perforated grounded electrode, past a high-voltage electrode, through a second grounded electrode, and past a valve into a vapor release space. Power input waR regulated by the steam bubble formation in the electrode chamber and the liquor concentration controlled by feed and withdrawal rates. I n the pilot plant voltage was varied from 700 to 1000 with the power a t 65 kw. Operat,ion of the unit a t 150 pounds per square inch gage caused 10% decomposition of the solids in the feed. This increased the heating value of the product, but made the solution viscous and difficult to handle. Collins ( 1 1 ) discusses the scale and slime problem in water evaporators. The discussion following the paper describes a brine evaporator holding 50,000 gallons. The brine contains calcium sulfate, which resulted in a scale 0.5 to 0.75 inch thick which was so hard that the turbine cut through the tubes rather than the scale. Chemcal treatment with 50% caustic was used. Neither lime nor sodium sulfate is soluble in 50% caustic. During treatment the unit was kept at 230' F. for 5 days with the liquor circulated continuously. At the end of 3 days the caustic concentration had dropped from 49.6 to 47.6% and the suspended lime and sodium sulfate gave a magma density of 15%. This slurry was removed and the unit recharged with fresh caustic solution. Intermediate inspection revealed no improvement in the appearance of the deposit. After 2 more days the caustic concentration had dropped t o 45.4%, it was evaporated to 48.270, and fresh 50 caustic was added. After another 1.75 days the concentration ad dropped to 46.9%.
T
COURTe8Y SWENSON EVAPORATOR 00.
Compound Triple-Effect Long-Tube Vertical Evaporator for Heat-Sensitive Food Products
The liquor sludge had overloaded the pump and it was necessary to shut down. The evaporator was about 90% clean and the liquor contained 14% solids. John (20)discusses mechanical tube cleaners and illustrates the better known types. The compression-type sea water evaporator and scale removal with sodium bisulfate and hydrochloric acid are discussed by Campobasso and Latham (IO). The unit is capable of handling 200 to 300 gallons per square foot before cleaning is required, and the use of chemical treatment will avoid the need for mechanical cleaning. It is reported that vacuum operation at 150" F. offers the possibility of avoiding scale entirely. Pichardo and Romero (36) report on the history of the addition of tetraphosphoglucosate for the control of scale in sugar evaporators A 6% solution in water is added a t the rate of 205 ml. per hour to evaporator feed and a like amount into the body of the fourth effect. This treatment decreased the steam consumption and reduced the down time from 2.29 to 0.9770. Hopper (19) also discusses the use of tetraphosphoglucosate in a commercial unit. He reports that at the end of 6 weeks' operation the unit's efficiency had dropped to 90 to 95%, whereas without treatment for a similar period t8heefficiency was only 75 to 80%. After the run with treated liquor there was very little scale except in the bottom of the third and fourth effects. Montgomery (30) uses Nalco number 918 a t the rate of 0.0031 to 0.025 pound per ton of juice to decrease scale formation. Such scale as is formed is easily removed. The treatment gives best results when used in the third effect as well as in the feed liquor. Petaold (36) presents graphs for the steam consumption of thermocompression evaporators. Vapor jet compressor data are used along with an enthalpy-entropy diagram to derive the information. Performance data for commercial equipment are shown to verify the theory presented. A review of the principles and use of the heat pump is presented by Peter (34),who covers recompression cycles for heat interchange and evaporation.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
In practice it is possible to obtain more than 4000 kg.-cal. equivalents for heating and more than 20,000 for evaporation per kilowatt-hour input. As a rule of thumb it is suggested that the heat pump becomes economical when the cost of 1 kw.-hr. of electric energy is not more than 0.5 lrg. of coal in the case of its use in heat exchange and not more than 1 kg. of good coal in the case of an evaporation process. Landorff (83) discusses the use of vapor thermocompression in sugar refineries. A Swiss patent (16) discloses a method of operating the boiling pans completely and the evaporators partly by thermocompression. A plant is described and the heat balance is shown. The use of thermocompression in the evaporation of sulfite waste liquor is presented by Elgee et al. ( 1 4 ) , who report that 4 hours' cleaning with acid condensate after 20 hours' operation keeps the unit in good condition and that no less scale is encountered if the feed is preheated, The use of foam inhibitors made the scale easier to remove. Thewritersreport their pilot plant required 22 kw.-hr. per 1000 pounds of evaporation. I n commercial operation they estimate 106 kw.-hr. will be required per ton of 50% solids recovered from a 10%feed. Smith (40)reports on a similar unit requiring 160 kw.-hr. per 1000 gallons of evaporation. He states that a commercial unit should not require more than 111 kw.-hr. per 1000 gallons of evaporation or 107 kw.-hr. per ton of 50% solids recovered from a 10% feed, The steam required for 1000 gallons of evaporation would amount to 1520 pounds per ton of 50% solids. The corrosion of lead linings in rayon spin-bath evaporators is discussed by Kleinert and Pospischill (89). This problem is ascribed to electrochemical effects caused by lack of homogeneity in the lining and by local concentration differences in the bath liquor being evaporated, as well as depolarization of hydrogen in the lead by contact with air (seam leaks). Corrosion is enhanced by recrystallization of the lead, forming cracks, and by sulfur attack at g a i n boundaries. Beamer and Fuqua (2) describe a method of lining sulfuric acid concentrators by coating with carbon. This is accomplished by filling the unit with dilute acid containing organic material and heating for several hours. The evaporation of hydrocyanic acid is disclosed by Cook and Rosenbloom (18). The unit operates under a vacuum with a hydrogen cyanide vapor removed by a liquid-operated eductor. The removal of sulfate from a mineral containing magnesium is disclosed by Burke, Smith, and Manning (8). The salt Is dissolved and evaporated until 2MgS0,.K2S04 is crystallized. When further evaporated until MgSOI.Ht0 can be removed, the product is suitable for use as cell feed. Szekely (41) reveals an apparatus for the evaporation of special pharmaceutical liquids. Zellner ( 4 7 ) describes a piece of laboratory equipment for both evaporation and distillation. A multipurpose unit suitable €orthe evaporation of foaming liquids is disclosed by Techochemie A.-G. (42). Vedrilla (46) presents data on the dimensioning of evaporators, and Ebert (IS) covers vacuum technique in laboratory evaporations. Trub reviews the types of evaporators and methods of evaporation used in Russian sugar factories.
(a)
LITERATURE CITED
(1) Aspegren, J. A., Swed. Patent 124,414 (March 22, 1949). (2) Beamer, C. M., and Fuqua, M. C., U. S. Patent 2,478,680 (Aug. 9, 1949). (3) Beath, L. R., and Hill, H. S., P u l p & Paper Mag. Can., 50, No. 8, 89-94 (1949). (4) Berman, L. D., Chem. Zentr., 1947, 11, 779-80. (5) Brauns, O., Svensk Papperstidn., 50, No. 11B, 61-2 (1947). (6) Broadhurst, J. W., Broderick, T. C., Foster, A. W., and Wheeldon, G. E., J . Inst. Elec. Engrs. (London),u, 94, 79-90 (1947). (7) Bromley, L. A,, C h m . Eng. Progress, 46, 221-7 (1950). (8) Burke, W. E., Smith, W. A., and Manning, P. D. V., U. 5. Patent 2,479,001 (Aug. 16, 1949). (9) Butler, 1%'. T., P u l p & PapeT Mag. Can., 50, No. 11, 108-21 (1949). (10) Campobasso, J. J., and Latham, A., Jr., Trans. Am. SOC.Mech. EngTs., 71, 837-8 (1949).
Vol. 43, No. 1
Collins, L. F., Ibid., 71, 871-4 (1949). Cook, L. H., and Rosenbloom, W. J., U. S. Patent 2,489,703 (Nov. 29, 1949). Ebert, H., Chem. Tech., 1, 19-23 (1949). Elgee, H., Craig, D., and Russell, J. K., Pulp h Paper Mag. Can., 51, No. 3, 178-89 (1950). Esoher Wyss Maschinenfabriken A,-G., Swiss Patent 262,257 (Sept. 16, 1949). Fatica, N., and Kata, D. Lo,Chem. Eng. Progress, 45, 661-74 (1949). Franklin, J. N., and Goddard, H. O., P u l p h Paper Mag. Can., 51, NO.3, 139-46 (1950). Grewin, F. mi., and Lindberg, S. G., U. S. Patent 2,490,750 (Dec. 6, 1949). Hopper, L. A., Repts. Hawaiian Sugar Technol., 8th Ann. RIeeting, 1949, 85-6. John, A., Trans. Am. SOC. Mech. Engrs., 71, 825-9 (1949). Klein, V. A., Chem. Eng. Progress, 45, 675-6 (1949). Kleinert, Th., and Pospischill, F., Mitt. Chem. Forsch.-Inst. I n d . Osterr., 2, 45-8 (1948). Landorff, B., Sucr. belge, 68, 312-14 (1949). Lockman, C. J., U. S. Patent 2,488,598 (Nov. 22, 1949). McAdams, W. H., Chenr. Eng. Progress, 46, 121-30 (1950). McAdams, W. H., Kennel, W. E., Minden, C. S., Carl, R., Picornell, P. &I., and Dew, J. E., IND. Exa. CEIEM.,41, 194553 (1949). Maisel, D. S., and Sherwood, T. K., Chem. E n y . Progress, 46, 131-8 (1950). Ibid., pp. 172-5. Malikov, A. D., L7.S.S.R. Patent 69,613 (h-ov. 30, 1947). Montgomery, J. W.,Repts. Hawaiian Sugar Technol., 8th Ann, Meeting, 1949, 83-4. Murphy, E. A., Paper Trade J., 129, No. 5, 23-26 (1949). Neuville, P., V I I Congr. Intern. Ind. AUT.Paris, 1, Pt. 2, 15-16 (1948). Nyman, C. H., U. S. Patent 2,484,046 (Oct. 11, 1949). Peter, R., Chimia (Switz.), 3, 114-18 (1949). Petzold, M., Chem. Ing. Tech., 22, 147-50 (1950). Pichardo, G. -V., and Romero, J. J. L., M e m . asoc. le'cnicos azucur. Cuba, 22, 187-92 (1948). Prescott, W. G., Brit. Patent 630,979 (1949). Rosenblad, C., P u l p h Paper Mag. Can., 51, No. 5 , 85-94 (1950). Samuelson, O., Saenslc Papperstidn, 52, 283-9 (1949). Smith, H. L., Jr., P u l p & Paper Mag. Can., 50, No. 9, 84-6 (1949). Szekely, G., U. S. Patent 2,472,992 (June 14, 1949). Teohochemie A.-G., Swiss Patent 249,100 (March 16, 1948) Trub, I. A., Sakhar Prom., 22, No. 11, 36-9 (1948). Vedrilla, St., Mitt. Chem. Forsch.-Inst.-Ind. Osterr., 3, 6 G 7 0 (1949). Ibid.. DD. 117-20. Wita'ig,*W.F.. Penney, G. TT., and Cyphers, J. 8 . ,Rejrig. Eng., 56, 153-7 (1948). Zellner, H., Osterr. Chem.-Ztg., 50, 97-100 (1949). Zieman, 11'. E., and Katz. D. L.. Petroleum Refiner. 26, h-0. 8. 78-82 (1947). RECBIVED Sovernber 16, 1950.
