Equipment and Desinn Anhydrous ammonia l o w temperature evaporation concentrates frozen juices, coffee extract, milk, and biochemicals by David E. Pierce NGINEERS
6
have long been interested
E in the fact that a pound of steam
coming from any evaporator contains almost enough heat to evaporate another pound of water, but that to transfer that heat its temperature level would have to be raised a few degrees and a corresponding rise in pressure would be needed if the desired evaporation was to take place in the same vessel or under the same boiling conditions. The theoretical energy requirement for such a rejuvenation has been known for many years to be a small fraction of the latent heat already in the vapor. However, the addition of this energy economically has been a difficult problem. Recompression of the vapor by means of high pressure steam jets or by mechanical means has been ac-
complished in a practical way in the not too distant past. The distillation of sea water is a good example of direct recompression stills. However, because of the great volume occupied by one pound of water vapor a t low temperatures, this method has not been economical except a t relatively high temperatures or for exceptional needs, such as prevailed under wartime conditions. For low temperature evaporation of heat-sensitive materials, especially, recompression of steam has seldom been economical. I n the past 10 years, however, the idea of recompression as a way to salvage B.t.u.’s has been given a new direction by the use of anhydrous amnionia instead of steam as the carrier of energy. Condensing water vapor from an evaporator by the boiling of anhy-
drous ammonia may seem quite normal, but compressing that ammonia vapor and then using it as a source of heat for again evaporating water will strike many as most unusual. Kowever, this method of using the heat pump principle has been in commercial use for the past 10 years. Many installations of evaporators of this sort have been made recently, and there are still new fields to be exploited. Joe Cross, the inventor and designer of the Lo-Temp evaporators manufactured by Mojonnier Bros. Co., classifies his process as “evaporation by indirect thermocompression.” Figure 1 shows low temperature evaporation equipment. The feed-e.g., orange juice-enters by a pump, goes to the top of the tube nest, and flows down the inside of the tubes, boiling
LEGEM
AMMOMA VAPOR
LlQUlO AMMONIA
w/ WATER VAPOR
CONDENSATE PUMP
Figure 1,
November 1955
PROOUCT PUMP (RECIRCULATIHG)
PROOUCT PUMP
(OISCHARGE)
PROOUCT PUMP
(IFEED)
Flow diagrammatic view of Mojonnier Lo-Temp evaporator
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Equipment and Design
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under vacuum a t about 75" F. The latent heat of vaporization is supplied by ammonia vapor condensing a t 108" F. Water vapor separates from the unvaporized juice in the separator and passes over to the condenser. Part of the concentrated product from the bottom of the separator is discharged to storage by a pump and part is recirculated along with fresh feed. Liquid ammonia, which has condensed around the evaporator tubes, flows down to the liquid receiver. From this tank, liquid ammonia flows through the line to an expansion valve which drops the pressure to 100 pounds per square inch. A small part of the ammonia flashes off, leaving the niajor part as liquid a t 64" F. The separation of ammonia vapor and liquid takes place in the liquid trap. From this trap the ammonia flows down and then rises through the condenser tubes. The condenser liquefies the water vapor at 75" F. by absorbing the latent heat in the ammonia which is boiling inside the tubes at 64" F. Noncondensable gas is removed from the condenser by an ejector or other type of vacuum pump. Ammonia vapor from the top of the condenser tubes passes through a trap for spray elimination and then by way of liquid trap into the suction pipe of the compressor. The latter compresses the vapor to 225 pounds per square inch and superheats it somewhat. The hot ammonia vapor is cooled to saturation temperature in the water-cooled desuperhester and then goes to the evaporator again for another cycle. Any ammonia condensed in the desuperheater flows down by gravity into the liquid receiver tank along with that condensed in the evaporator. Evidently, no steam at all is required in this process, although steam jets may be used for removal of noncondensable gases and maintenance of vacuum instead of motor-driven vacuum pumps. Some power is required for the cooling water pumped through the desuperheater but the major requirement is for the compression of the ammonia vapor. Inasmuch as the power required per pound of water evaporated depends on how muoh temperature difference is needed between the condensing ammonia and the boiling solution, i t is evident that
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 11
x
II
c
Purity is safeguarded. Under-
and over-chlorinated portions are separated from 2,4-D in this equipment. To maintain purity, fractionating column is solid nickel. Tanks are Nickel-Clad Steel. Both materials are also used i n other equipment for the same purpose.
-
1,
Man without a hoe
eeds.
Give the credit to 2,4-D, an amazing chemical discovery. It destroys only broad’1eaved weeds’ And gives food plants like corn, uheat, rice, oats and barley a new lease on life! Unlike older weed killers, 2,4-D is not a poison in the accepted sense. It.s practically harmless to humans or animals. But it disrupts the normal grouth cycle of broad-leaved weeds. i n three br four ueeks, they’re dead. What’s 2,4-O? Actually, 2,4& chlorophenoxyacetic acid. And there were tough problems to overcome at
hetter than one, and we may be able to help you find out how nickel - or one (sf the more than fifty Inco Kickel Alloys now available can solve your probem. Write The I n t e r n a i o n a l Nickel Company, Inc., 67 wall Street, New York 5, N. Y.
are specified for pipes and fittings, reactors. centrifuges. dry. ers, tanks and other equipment used in the making and handling of 2,4-D.
-
uct purity. And they resist few metals do!
l&Q
INTERNAT IONAL NlCKEL 67 Wall
Street
New York 5, N. Y.
Nickel Alloys Perform Better Longer
Story behind the story. N i c k e l and M o n e l hold c o r r o s i o n down, give chlorinated organic high p u r i t y If you chlorinate organics, you may find t h e story behind t h i s Business Week advertisement (Sept. 24 issue) of particular interest.
Both corrosives a r e bad f o r equipment. Worse f o r product . . since even a little metallic pick-up adVerselY affects i t s color and purity.
When P i t t s b u r g h Coke & Chemical Company began t o make t h e nowfamous weed-killer, 2,4-D, a number of years ago, some formidable corrosion and contamination problems soon developed. D u r i n g t h e chlorination, small amounts of hydrochloric acid f o r m a n d some chlorine fails t o react.
Corrosion tests showed what to do
.
Or
Steel replaced other materials i n t h e still, steam coils, fractionating tower, condenser and storage vessels. Monel”, a n Inco nickel-copper alloy, is now used f o r t h e 2,4-D reactor, t h e dichlorophenol weighing tank,
..
t h e stripping column, t h e centrifuge and dryer. The result ? Practically troublef r e e operation. If you have a corrosion or contamination problem, ~ i ~ k ~ ~ ~ or other ~ nickel ~ 1alloys , may prove t h e answer. I ~ corrosion ~ ~ Engineering Section will be glad to help you look into it. J u s t write. * R e g i s t e r e d Trademark
THE INTERNATIONAL NICKEL COMPANY, INC. 67
A INCO ,
New York 5, N. Y.
Street
,
MOhEL”
“R”* MONEL “K”* MONEL
-.
“KR”* INCONEL*
MOKEL INCOXEL
-x”*. INCONEL “S”*
--
MOVEL
“W’* INCOLOY*NI-0-NEL NIMONIC*ALLOYS NICKEL* Low CARBON NICKEL DURANICKEL*
.
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November 1955
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Equipment and Design
KEEP PACE with
WHAT'S at the
OF COMMERCIAL MUSEUM and CO
Philadelphia So much is happening in the fast-changing chemical process industries that the latest developments often have a way of escaping us for lack of time. There's a way to catch up-and keep up-with the newest in equipment, materials, methods. T h a t way-and it's really the quickest and most effective way-is to personally inspect the more than 500 exhibits a t this year's great E X P O S I T I O N O F CHEMICAL INDUSTRIES. You can SEE and COMPARE the newest processing m e t h o d s . . . LOOK a t the year's biggest array of materials and equipment. . . TALK with technical representatives of the country's leading suppliers. Plan NOW to attend this great exposition,. . save time by writing today for advance registration and forms for hotel accommodations to M A N A G E M E N T .
I N T E R N A T I O N A L
E X P O S I T I O N
C O M P A N Y
480 Lexington Avenue, N e w York 17, N. Y. ~~~~
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12 A
the way to reduce power usage is to provide greater heat transfer surface so that the temperature difference can be reduced. By adding more evaporator surface, therefore, power cost is reduced but investment in square feet of tube surface increases. The designers of the Lo-Temp evaporator have established, as the present optimum condition for best economy of power and equipment cost, that the low pressure side of the ammonia system should be a t about 100 pounds per square inch and the high pressure side a t 225 pounds. With this compression ratio, the process requires 45 hp. per 1000 pounds of water evaporated. Many heat-sensitive materials are concentrated by the use of anhydrous ammonia low temperature evaporation. Using the established ammonia pressures, the highest temperature in the system is about 108" F. and the lowest, about 64" F. This range has been found very satisfactory for a variety of heat-sensitive materials that require concentration. Among them are frozen orange and lemon juice concentrates, concentrated coffee extract, milk concentrate for drying or for liquid use, insulin, biochemicals, and vanilla extract. I n this field of low temperature evaporation, the process has filled a real need. The relative cost of steam and of electricity is of great importance in determining whether this method or steam recompression is the more economical for any given installation. Assuming boiler fuel oil a t 5 cents per gallon and electric power at 1 cent per kilowatt hour, the cost of utilities per gallon of 42' Brix citrus juice has been calculated as 0.9 cent for the single effect and 0.7 cent for the double effect Lo-Temp evaporator, compared with 3.4 and 1.6 cents for single and double effect recompression evaporators. The over-all cost would, of course, have to include raw material, labor, depreciation, and other expenses. Differences in the cost of fuel or power as well as in the other items of cost might show greater economy for the steam units rather than for the ammonia system. However, in a great many cases the Lo-Temp evaporator has won the decision. Correspondence concerning this column will be forwarded if addressed t o the author, % Editor, INDUSTRIAL AND ENGINEERINGCHEMISTRY, 1155-16th St., N.W., Washington 6, D. C .
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