Experimental Falling Film Evaporator development
FOR PREPARATION OF JUICE AND PUREE CONCENTRATES AT LOW TEMPERATURE
L. H. WALKER
AND
D. C. PATTERSON
WESTERN REGIONAL RESEARCH LABORATORY, ALBANY, CALIF.
T
HE phenomenal success A n all-glass evaporator was designed and constructed for optimum pump speed and a t of frozen orange juice conthe study of behavior of juices and purees during cona n absolute pressure of 0.6 c e n t r a t e manufactured in centration and the effects of concentration on quality o f pound per square inch in the low-temperature concentraproduct. Data obtained have shown temperatures persystem was approximately 6 tors has created much interpounds per minute. missible for preservation of flavors and also have estabest in the application of this An example of the effect lished the rate of evaporation at various stages for apple process t o other juices and of degree of concentration juice and other materials. These data are useful in the purees. The equipment deupon the rate of evaporaselection of commercial equipment. scribed in this article was detion of water from a fruit signed to meet the need for juice (clarified, depectinized a n experimental unit which would provide products similar t o juice from Delicious apples) is shown in Figure 2. The rate of evaporation remained practically constant until the soluble those prepared in commercial units, keep batch sizes within solids content of the concentrate approached 40%, then dropped reasonable limits, permit variation of temperature and pressure sharply. over a wide range, and allow the operator t o observe behavior of the material under studv during concentration. The batch size varies with the degree of concentration desired and size of the concentrate receiver, F , used. The time required The unit (Figure 1) consists essentially of a vertical, jacketed t o concentrate a batch depends upon the degree of concentration evaporating tube (height, 150 em.; diameter, 7.5 em.), a vaporand the size of the charge, and ranges between 30 minutes and 2 liquid separator, a condenser, and a series of cold traps. Suitable equipment i s provided for obtaining and controlling vacuum, for hours. The temperature difference ( A t ) between jacket water adjusting flow of the falling film of liquid, for recirculating parand the falling film in the column is usually held as low as possible tially concentrated juice, and for removing distillate from the consistent with proper boiling characteristics in the column, in system. This unit is similar in design t o commercial units ( 9 , S), order t o avoid product changes due t o localized overheating. except t h a t cold traps have been added for essence recovery as suggested by Carpenter and Smith (1). The values for At are higher in this unit than those normally found in stainless steel commercial equipment, owing to lower rates of The unit has proved t o be exceedingly useful in the laboratory heat transmission through glass. preparation of various juice and puree concentrates a t the Western Regional Research Laboratory. Because practically all METHOD OF OPERATION the original material is retained in the system, the products (concentrate, distillate, and material caught in the traps) can be reFigure 1 presents a sketch of the assembled unit. Liquid to be combined for comparison with the original material in order t o deconcentrated is drawn by vacuum into t h e system from flask A termine the effects of concentration. The unit has been used t o into column head B , a here it passes through a variable annulus formed by ground joints, adjustable by raising or lowering male prepare concentrates a t various temperatures of evaporation in joint C. The liquid boils rapidly as it flows down in a film on the order t o determine the threshold temperature a t which an offinside of column D, absorbing heat through the glass wall from hot flavor becomes noticeable in the reconstituted product. The water circulating through the jacket. Concentrated liquid and effects of temperature of concentration upon other properties of water vapor pass into separator E, where liquid flows by gravity into receiver F M hile vapor passes upward and is rondensed in the product have also been noted. Details concerning application condenser G . Condensate is led through cooling coil R into reof the unit will be published in reports on the individual concenceiver N . Cncondensed gases pass through a series of three trates; the first of these (preparation of apple juice concentrate) cold traps immersed, respectively, in ice, dry ice-alcohol, and has been accepted for publication (4). liquid nitrogen. This combination will collect practically all essences volatilized during concentration. Additional feed is bled All-glass construction of the unit permits observations of wetinto the system from A a t the same rate as that a t which water 1s ting ability, maintenance of film, both type and degree of boiling being evaporated. Partially concentrated material is recirculated in the column, and changes in these characteristics during confrom F through pump H ( a stainless steel, rotary, positivecentration. Foaming in the separator and entrainment losses in displacement type) into the column head. Recirculation is continued until the desired degree of concentration has been reached. the condenser can be observed and controlled without difficulty. Receiver 1v is designed so that it can be removed, emptied, The unit has been operated over a range of absolute pressures evacuated. and reconnected into the system without interrupting from 0.23 t o 6.7 pounds per square inch (12 t o 347 mm.), or, in a run. terms of the boiling temperatures of water, from 57" t o 175" F. Hot water for the jacket is heated by steam passing through a coil immersed in tank I . Water temperature is maintained by a Initial evaporation rate was about 12 pounds of water per hour temperature-control unit which actuates a solenoid in the steam (5.4 liters) over the range of 0.23 t o 3.7 pounds per square inch line. A centrifugal pump, K , of 10 gallons per minute capacity, absolute when jacket temperatures were maintained 60' F. above is used to recirculate hot water continuously through the tank as evaporating temperatures. The rate of recirculation of water a t well as t o supply the jacket.
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535
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1951
I
SPECIAL RUBBER TUBE AT-. BOTH ENDS
I
I K
r
I
I !
i
IJ" REFRIGERANT TANK.
I
!
I
COLD WATER LIN
i I
I
I
4
Figure 1. Diagram of Evaporator P. Borosilicate glass. R.T. Rubber tubing. S.S. Stainless steel
100
r
-
-Po -z
I
1
-I--
1
I -4
Y
W
60
CK
z 0 + 4 0 ~ a
Ea
i l
Figure 2. Effect of Degree of Concentration upon Rate of Water Removed during Concentration of Apple Juice
Ice water, brine, or other refrigerating mediums may be used as coolants in the condenser. Ice water can be used for runs at pressures higher than 1 inch of mercury in a system similar to tank J complete with a circulating pump, K. However, at lower pressures, the condenser becomes overloaded and a considerable amount of water vapor passes over into the first cold trap. Condenser temperatures below 32' F. are required for runs a t pressures less than 1inch. The vacuum source consists of a n oil-type two-stage vacuum pump having a rated capacity of 54 liters of air per minute a t 0.1micron pressure. The manometer, M , consists of a simple mercury-filled U-tube. The Cartesian manostat, L, maintains pressure within the system at the desired figure without the necessity of bleeding in air. Air should not be bled into the system for the purpose of controlling the amount of foam in the separator, as volatile flavoring constituents tend to be swept into the vacuum pump and such air tends to collect as liquid air in the liquid-nitrogen trap. Adequate control can be obtained through regulation of the amount of heat supplied to the jacket.
Property Total solids, ' Brix Specific gravity Viscosity, 68" F., cp. Viscosity, 120' F., cp.
Single-Strength Juice
&Fold Concentrate
13.7 1.0506 1.106 0.664
47.5 1.2102 1,488 0.865
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Operation of the unit without recirculation is not recommended, because 2 to 3 liters of material must be passed through the system before it begins t o operate properly. NOTES ON CONSTRUCTION
Standard-taper spherical (ball and socket) joints have been used t o facilitate assembly of equipment and t o eliminate the necessity of making rigid metal-to-glass seals. The open-tapered joint at the column head is connected t o an adjustable shaft in order that fluid flow may be controlled either through an annulus, over a weir, or both. Clearances between walls and coil of the condenser are made as small as practicable, in order t o obtain maximum efficiency of operation. The unit can be constructed of stainless steel; however, provision should be made for internal inspection and cleaning, as entrained material has been found occasionally in the condenser system. The internal diameter of the coil in condenser R is designed t o be large in relation t o the
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Vol. 43, No. 2
volume of condensate flowing through it, in order to avoid air locks. The seal at the top of the column head, B, is a commercial type normally used in boat propeller-shaft assemblies, and is pressed into a 0.25-inch stainless steel plate. The jacket on column D is held in place by rubber tubing, over which light copper bands are clamped. With the type of manostat used, diffusion of oil vapor from the vacuum pump back into the traps is not a problem. LITERATURE CITED
(1) Carpenter, D. C., and Smith, E. C., IND.ENG.CHEM.,26,449-454 (1934). (2) Cross, J. A., and Gemmill, A. V., Food Inds., 20, 1421-3 (1948). (3) KelIey, E.J., Zbid., 21,1386-90 (1949).
(4) Walker, L.H., Nimmo, C. C., and Patterson, D. C., Food Technol., in press. RECEIVED May 29, 1950. ing Act of 1946.
Report of study made under Research & Market-
Vapor-Phase Hydrogenation of light and Heavy Oils M. L. WOLFSON, M. G. PELIPETZ, A. D. DAMICK, AND U.
E. L. CLARK
S. BUREAU OF MINES, BRUCETON, PA,
In order to provide equipment for hydrogenation of light and heavy oils over a fixed catalyst bed, a small plant suitable for operation at 500" C. and 10,000 pounds per square inch gage has been designed. The plant is described and results are presented of an operation designed to test the activity of a German hydrogenation catalyst in producing gasoline from light gas oil derived from coal. The results indicate that the catalyst of chromiummolybdenum-zinc on hydrogen fluoride-activated fuller's earth is suitable for the hydrogenation operation attempted. On a once-through basis at 500' C., a hydrogen pressure of 9,000 pounds per square inch, a space velocity
of 1 kg. of oil per liter of catalyst, the following results are obtained, based on weight per cent of feed: 46.670 gasoline, 4.2qo CI to Ca, and 2.8% hydrogen consumption. The nitrogen, oxygen, and sulfur content are greatly reduced. The gasoline has a high aromatic content and a motor method octane rating of 79.8. The results indicated the suitability of the plant for high pressure catalytic reactions. Good performance and ease of operation characterized the experimental work. The catalyst tested showed good activity in the production of aromatic gasoline from gas oil obtained by the hydrogenation of coal.
A
unit is only 20 cubic feet per hour, the compressor is only run intermittently and the compressed hydrogen after passing through the oil trap is stored in three accumulators which act as reservoirs. The oil trap and accumulators are of the type described by Clark et aE. (1) and illustrated in their Figure 5 and Figure 6, respectively. The oil feed is drawn from a vessel, which is weighed every half hour, into a piston pump which injects it a t system pressure into the hydrogen stream leaving the accumulators. The combined oil-hydrogen stream passes through a preheater consisting of a coil of 0.25 inch outside diameter by 0.125 inch inside diameter stainless steel tubing embedded in a block of aluminum, heated electrically by strip heaters. The stream then enters the bottom of the reactor, a stainless steel (Type 347) tube 2 inches outside diameter by 0.75 inch inside diameter by 4 feet long (excluding closure assemblies). The type of closure employed, illustrated in Figure 2, utilizes a stainless steel (Type 347) lens ring (Monel metal lens rings were tried originally, but they were attacked by the high sulfur content of the oil feed). The preheated stream of hydrogen and oil flows u p through the catalyst
MONG recent developments in the German synthetic liquid
fuels industry, considerable advantage was found in splitting aromatic oils in the gas-oil range (200" t o 325' C.) by highpressure hydrogenation (about 700 atmospheres of pressure). D a t a in captured German documents indicated promise for this process, which was incorporated into the design of the Bureau of Mines Demonstration Plant a t Louisiana, Mo., as a means of treating aromatic oils obtained from the hydrogenation of coal. To evaluate this process on a small scale and to test the activity of available German catalysts, a small hydrogenation unit suitable for operation a t 10,000 pounds per square inch gage and 500" C. was designed and operated a t the Bruceton laboratories. DESCRIPTIOX O F THE PLANT AND EQUIPMENT
A simplified flow diagram of the unit is illustrated in Figure 1. Commercial cylinder hydrogen is throttled into a 1000-cubic foot gas holder and drawn from there by a Norwalk five-stage compressor. I n order to utilize this available compressor which has a capacity of 600 cubic feet per hour, while the maximum flow in the
