US2570212A - Milk evaporation process - Google Patents

Description

5 Sheets-Sheet l Oct. 9, 1951 J. A. CROSS MILK EVAPORATION PROCESS Filed Sept. 9. 1946 3 Q 4 i a, 1 gm @2 w. F71. llrrll; v Ffziii i1. .l r1 ,J i i 2 K W 7 Oct. 9, 1951 Filed Sept. 9, 1946 J. A. CROSS MILK EVAPORATION PROCESS 3 Sheets-Sheet 2 Oct. 9, 1951 J. A. CROSS MILK EVAPORATION PROCESS 3 Sheets-Sheet 5 [HI E1712?!" Josqp/i lZ Cross e 3 1 2 2 24 flz-rllllflffir l d 4 I 3 a in n I Z z O an a Filed Sept. 9, 1946 Patented Oct. 9, 1951 ltIILK EVAPORATION PROCESS Joseph A. Cross, Westerville, Ohio, asslgnor to Mojonnler Bros. 00., Inc., Chicago, Ill., a corporation of Illinois Application September 9, 1946, Serial No. 695,642

4 Claims.

This invention relates to methods for evaporating milk at temperatures substantially below its atmospheric boiling point.

The invention in its preferred form employs a refrigerating cycle wherein a compressed refrigerant gas having a temperature higher than the milk, when under compression, is employed to supply the heat to be imparted to the milk undergoing evaporation, during which evaporation the refrigerant is largely liquefied as it gives up its latent heat, and following which the refrigerant gas it incompletely liquefied, is condensed and later cooled to a temperature below the temperature of the water vapor escaping from the evaporated milk. This water vapor is then condensed during heat exchange with the cooled liquid refrigerant, vaporizing the refrigerant, after which the refrigerant gas is recompressed and used again in the same cycle. The condensation of the water vapor induces a high vacuum upon the evaporating space in which the milk is being evaporated, thus facilitating evaporation of the milk at a low temperature.

The system is designed and constructed for continuous operation. While a small amount of steam may be employed for the ejection of non-condensible gases from the water vapor, no

other fuel is required by the system. Power is required for operating the refrigerant compressor and such pumps as the system requires, and only a relatively small amount-of water or other coolant is required for accomplishing a certain desired cooling of the refrigerant.

' One of the objects of the invention is to provide a method for accomplishing the foregoing objectives and which employs a refrigerating cycle.

Another object of the invention is to provide a method for evaporating milk in a continuous process intended normally to operate under uniform conditions but capable of adjustment and variation to alter the operating conditions.

Another object of the invention is to provide a method for evaporating milk under conditions which contribute to the preservation of the original qualities and ingredients of the milk, and to provide a condensed milk product which may be reconstituted to its original density with mini- I mum impairment of flavor.

Other objects and advantages of the invention will be specifically alluded to hereinafter, or will become apparent from a reading of the specification.

In the drawings:

Figure is a somewhat diagrammatic layout of an apparatus by means of which the invention may be practiced;

Figure 2 is an end view of the apparatus shown in Figure 1;

Figure 3 is a top plan view of the apparatus shown in Figure 1;

Figure 4 is an enlarged partial sectional view of the upper end of one of the evaporators;

Figure 5 is a vertical sectional view of the lower end of one of the evaporators;

Figure 6 is a sectional view on the line VI-VI of Figure 2; and

Figure '7 is an elevation of a condenser which may be used with the invention.

The apparatus includes principally an evaporator assembly into which hot compressed refrigerant gas is introduced to supply sensible and latent heat for evaporating the milk to be concentrated, and a condenser in which the low temperature water vapors from the evaporator assembly are collected and condensed during heat exchange with the liquid refrigerant returned from the evaporator assembly. This latter heat exchange vaporizes the refrigerant into a gas which is then re-compressed and re-used in the evaporator assembly.

While the practice of the invention is not restricted to the apparatus herein shown, I find the invention may be practiced very efiiciently with the use of the apparatus disclosed herein. In the evaporator assembly I employ a series of connected falling film type evaporator units, each unit including a vertical tubular evaporator having a shell II and a nest of tubes such as l2 which are retained in the upper and lower tube sheets l3 and l4.

' The compressor hot refrigerant gas is introduced into each evaporator through a pipe 15, and for circulation around the outsides of the tubes 12, being Withdrawn, principally as a condensate through a bottom outlet pipe 16. The inlet pipes 15 for the refrigerant gas are connected to a common supply pipe I'l.

As indicated in Figure 4, the upper ends of the tubes [2 are fixed in the upper tube sheet l3. It is intended that the space above the upper tube sheet will be kept flooded with milk and in order to regulate the flow of milk into these tubes and downwardly, I insert in each tube I2 a removable tube I8 which is supported centrally in the top of the tube by a bracket in the form of a spider 19 having three or more legs which rest upon the top of the tube sheet, the legs being se- 3 cured by welding or in any other suitable manner to the tubes I8 to support them in an upright position.

It will be noted that the lower end of each tube I8 is flared outwardly as shown at to retard the flow of the milk past that area and to cause it to positively come into contact with the inner walls of the tubes l2. The supply of milk which is caused to flow downwardly through these tubes is brought to the top of each evaporator by means of a pipe 2 I. It is apparent that the layer of milk above the tube sheet may be varied in depth, the greater the depth, the greater the rate of flow past the flared lower end of the regulating tubes [8. For maximum and most eificient operation the tubes l2 should be kept covered with a milk film to their lower ends. Since these tubes iii are readily removable along with their supporting spiders, cleaning of the upper end of the evaporator and with vertical tubes is facilitated.

As indicated in Figures 2 and 3. the lower ends of the tubes I2 open directly into a curved hood '22 which will serve to conduct the vapors and the unvaporized milk from the lower ends of the tubes. The milk will fiow into a sump 23 while the vapor will be drawn into a cylindrical chamber 24 and evacuated therefrom through a central aperture 25 and an outlet pipe 26 into the condensing unit.

The evaporator unit shown in Figures'l and 3 consists of three vertical tubular evaporators of substantially identical construction, all supplied with the hot refrigerant gas by the common supply pipe I! and interconnected at their lower ends through the communicating drums 24, shown in section in Figure 6..

The sumps 23 are interconnected as shown by the pipes 28 and 29, to permit flow of milk from the first sump to the next one to the right thereof, and from the second to the third sump, after which the concentrated milk is withdrawn through an outlet pipe 30 by a pump 3|, from the system.

Connected with the bottoms of the sumps are the pipes 32. each of which leads to a pump 33 for recirculating milk back again to the top of the same evaporator from which it is withdrawn, that is through the pipes 2 I.. It is intended that,

in the use of these falling film evaporators, rapid recirculation pumps will be provided which will keep a constant supply of milk above the top tube sheet in each evaporator and return to the top of each evaporator whatever milk passes downwardly through the tubes without having become evaporated. In the meantime any vapor escaping from the milk within the tubes is drawn downwardly and passes into the drums 24 with a whirling motion which serves to throw entrained particles, if any, centrifugallv against the outer walls of the drums, to thus free the vapor of droplets before it is evacuated through the central opening 25 and the vapor outlet pipe 26. It will be noted that the central openings 25 are formed by means of the inturned end flanges of the individual drums 24, these flanges being readily riveted or welded together, but having the large central openings indicated.

Each chamber 24 preferably will have an arcuate baiile 24 secured to the margin of opening 25 which will assist in imparting centrifugal motion about a horizontal axis to the vapors and prevent their more direct flow through ports 25.

The fresh dilute milk is supplied to the system of evaporators from a de-aerator (to be described later) through a pipe 34 connected to the downfiow pipe 32 in the first evaporator. Each evaporator unit therefore performs a substantial portion of the total evaporationjob, and because of the action of the outflow pump 3|, there will be a continuous flow of milk from the first evaporator successively through the others to the last. The first evaporator, because it contains the most dilute milk, will evaporate the largest numbers of pounds of water per hour. Evaporation from the succeeding evaporators will be at a lower rate per hour and in the final evaporator the evaporation will continue at the lowest rate of evaporation until the desired density has been attained. A sight glass 23' on each sump, as in Figure 5, will facilitate maintaining adequate levels in the units, j"

The water vapor evacuated from the evaporators through the pipe 26 is conducted to a large tubular condenser 35, the vapor surrounding the tubes while evaporation of the liquid refrigerant within the tubes will cause condensation of the water vapor. The water vapor condensate will be withdrawn by a pipe 36 into a tank 31 and pumped therefrom by a condensate pump 38. The sight glass 31' will enable the operator to make certain that the pump is always primed.

As there may be some uncondensable gases such as air in the water vapor, these gases will be withdrawn from the evaporator 35 through a pipe 39 by an ejector 40, of any suitable design.

Under the pressure maintained on the refrigerant gas during this operation, most of this gas will become condensed to a liquid state, the latent heat of liquefaction of the refrigerant being transferred to the boiling milk. The refrigerant whether partially or wholly condensed will be withdrawn from each tube chest through a pipe it into a common header 4|, thence through a water cooled condenser 42, pipe 42' and a liquid refrigerant cooler 43. Cooling water for the cooler and condenser are supplied by a pump 44 to the cooler 43 and through the interconnecting pipe 45 to the condenser 42, and is discharged through an outlet pipe 48.

The liquid refrigerant then flows through pipe 41 to a receiver 48. If desired the admission of the liquid refrigerant into the receiver 48 may "he controlled by a float valve 49, although it may be controlled by some other valve which will serve to maintain pressure on the high pressure side of the system.

Liquid refrigerant from the receiver 48 is conducted through a pipe 50 to the bottom of the tubular evaporator 35, which is preferably of a common tubular chest construction, and allowed to flow upwardly through the vertical tubes therein which are sufilciently indicated by a partial sectional view.

In the operation of this system for condensing milk, it is contemplated that ammonia, if used as the refrigerant, will be compressed to aboit 205 lbs. gauge pressure with a superheat which may attain 180 F, The sensible heat in the gas will be utilized but most of the evaporation is performed by the latent heat of liquefaction of the gas. The refrigerant will condense at about 102 F. and emerge from the evaporator at about 102 F. Even though the cooling water available may be as high as F., it will be entirely practi-' cal to cool the refrigerant from 102 F. down to about F. in the condenser and cooler.

The degree of cooling of the refrigerant and the total heat removed therefrom at thispoint is a for regulation in order to maintain uniform operatin pressures and temperatures in the system. This control and an alternative control for the same general purpose will be described hereinafter.

Before bringing the liquid refrigerant into heat exchange relation with the water vapors which are to be condensed, it is desirable to chill the refrigerant below the temperature of the vapor. In the process contemplated the milk will be evaporated at about 60 F., and in order to attain an adequate temperature differential in the condenser 35 between the water vapor and the liquid refrigerant the latter preferably may be cooled to about 50 F., by flashing off some of the liquid into the suction side of the line. By maintaining the compressor suction pressure at about 75 pounds gauge pressure the refrigerant will vaporize in the condenser at about 50 F.

Vaporized refrigerant will then be withdrawn from the space in the condenser above the upper end of the tubes through a pipe 5! into the receiver l8 and thence through a pipe 52 into a compressor 53 of any suitable construction from which it is then delivered to the pipe I 1 for recirculation again through the evaporators.

Thus, briefly, the latent heat of vaporization of the refrigerant is supplied by the water vapor, thus condensing the latter, while the sensible heat and latent heat of liquefaction of the refrigerant is transferred to the milk in the evaporator to boil the water therefrom. Through the use of a suitable ejector and a condensate pump and an evacuator pump for the concentrated milk the high vacuum produced principally by the condensation of the water vapor, can be maintained such concentration and removal from the evaporator system be immediately frozen or at least kept at very low temperature until it can be reconstituted again by the addition of pure water into a milk solution of normal density.

Where pasteurization of the milk is practiced it may first-be pasteurized before being introduced into the evaporator system. In any case, it may be desirable tdde-aerate the milk before it is introduced into the system and I make provision therefor, as shown in Fig. 1. The milk may be introduced through pipe 54 into a de-aerator tank 55, and allowed to flow downwardly in a thin film over a spiral channel 55, and then fall into the bottom of tank 55 from which it will be withdrawn by the pipe 34 and variable output pump 34 for regulating the supply of milk to the evaporators and introduced into the downflqw pipe 32 of the first evaporator. A vacuum pump 51 of any suitable construction will evacuate the air from the film of milk flowing over channel 56. Thus foaming of the milk in the evaporators will be prevented and counterpressures due to excess air in the water vapor space in condenser 35 will be avoided.

It will be assumed that the usual accessories such as valves, pressure gauges, and thermometers will be supplied throughout the apparatus so that uniformity of desirable operating conditions may be observed and regulated.

It is contemplated that the evaporation methods and apparatus herein described will be operated on a continuous basis, and to be used successfully the operation should proceed without substantial variation in the temperatures and pressures maintained in various parts of the system. Heat exchange with variable temperatures in the surrounding atmosphere will tend to alter the operating temperatures and pressures.

The amount of refrigerant which must be evaporated per hour in the water vapor conden ser, under constant load conditions, is such that this same quantity of refrigerant will contain more total heat when it passes through the milk evaporators than is required for production of the predetermined water vapor load. This excess heat will be due largely to the heat of compression of the refrigerant. Unless this excess heat is constantly eliminated from the system the high side gas pressure will continuously rise and disrupt the operation of the system.

Accordingly for controlling the system to make it operate uniformly I provide two methods of control, and will employ whichever heat elimination method suits local plant conditions.

For example, if the water available for cooling is warmer than the water vapor I may elect to eliminate excess heat by means of such cooling water flowing through the condenser 42 and liquid cooler 43. In this instance I install a pressure regulated valve 70, of any well known design, such as a diaphragm controlled valve, in the water intake pipe ll leading to pump 4-4. A pipe 12, containing a fluid suitable for transmission of the regulating pressure, will connect this valve to the housing 13 which contains a diaphragm whose upper side is subject to pressure variations in the high pressure refrigerant gas line H. Thus the rate of water flow, and hence heat discharge, will be controlled by the pressure of the compressed gas.

In the event that water available for cooling at the plant is colder than the water vapor temperature I may use the other method for eliminating excess heat from the system. In this latter instance I may install the condenser shown in Figure '7, connecting it to condenser 35 in place of the ejector 49 shown in Figure 1. The pipe M will be connected to the upper end of the water vapor space, in place of pipe 39 and will admit water vapor into the condensing chamber 15. A housing 16 containing a diaphragm will be connected to the compressed gas line I1 and its diaphragm, subject to the pressure in the gas line, will transmit pressure variations through pipe Tl to a diaphragm controlled valve 18 positioned in the water supply line 19 which delivers water to the condenser 15. Water spilling over the weir 83 and falling down over the splash plates 8! will condense the water vapor and be discharged through a barometric leg 812. A high pressure steam jet 83 will eject non-condensable gases through ejector 84.

Pressure in the compressed gas line will determine and regulate the amount of water vapor amount of refrigerant evaporated, compressed arid delivered into the pipe [1 is thus regulated to produce enough compressed gas at the predetermined desired, pressure to accomplish a uniform amount of evaporation per hour. The water vapor and refrigerant temperatures and pressures may thus be kept uniform. This control method, of course, contemplates that pre-cooling of the refrigerant liquid before entry into condenser 35 will be accomplished, as heretofore explained by the flashing off to the suction side of the compressor of enough refrigerant to effect the desired pre-coolihg.

In view of the improved means for distributing and storing frozen food products, it is apparent that frozen concentrated milk produced in accordance with this invention can be stored and wrapped merely in paper containers occupying much less space than milk stored in the customary glass or paper containers. Furthermore, it is apparent that when the milk is concentrated and frozen promptly, either following pasteurization or without pasteurization, bacterial growth may be completely or substantially terminated.

When the milk has previously been pasteurized this method of concentrating milk to a small volume followed by subsequent reconstituting to its normal volume by the addition of water, eliminates the peculiar flavor which is characteristic of pasteurized milk. This in itself is a substantial advantage and attraction for the many persons who object to the pasteurized flavor of milk.

' Substantial improvement in the preservation of the normal and original vitamins of the milk is believed to be obtainable through the use of this invention in conditioning milk for storage at low temperatures. Of course, after the milk has been concentrated in accordance with this invention, it may be stored at room temperatures in the concentrated form and if any treatment to condition it for such storage is necessary it may easily be practiced.

Reference may be made to methods and apparatus for evaporation which are disclosed and claimed in my copending applications, Serial No. 631,922 filed November 30, 1945, Serial No. 695,641 filed September 9, 1946, and Serial No. 554,015 filed September 14, 1944, now Patent No. 2,554,138. I

It should be understood that while a preferred method of practicing the invention is disclosed herein, the invention is not limited to the precise details described, but is susceptible of some variation and modification within the scope of the appended claims.

I claim as my invention:

1. A continuous process for evaporating milk while maintaining the milk during evaporation far below pasteurizing temperatures comprising continously supplying fresh milkto the first of a series of successively connected evaporators, recirculating said milk through the flrst evaporator by causing it to fall therethrough in thin films and to be repeatedly elevated by pumping to fall again therethrough in thin films, progressively conducting the progressively concentrated milk to the succeeding evaporators and recirculating it in each evaporator in the aforesaid recirculation manner, and withdrawing the milk at a desired concentration from the last of said evaporators, subjecting the milk in each evaporator to heat exchange with a compressed refrigerant gas supplied thereto at a common pressure from a common source at its liquefaction pressure corresponding to a'temperature far below the pasteurization temperature of the milk and high enough to transmit latent heat to the milk, coolilg the refrigerant, which has been liquefied in said evaporators, to a temperature below the water .vapor temperature in said evaporators, introducing the cooled liquid refrigerant and the water vapor, discharging the condensed water vapor compressing the refrigerant gas and reusing it again in said evaporators, and under control of the pressure of the compressed gas regulatably continuously discharging from the system a portion of the heat extracted from the refrigerant during said cooling that would otherwise be returned in the refrigerant to the evaporators, for maintaining substantially uniform temperatures and pressures in the refrigerant throughout the entire cycle on a constant compressor output and constant milk flow.

2. A continuous process for evaporating milk while maintaining the milk at about 60 F. comprising flowing the milk during progressive concentration under vacuum through a heat exchange apparatus and maintaining the milk while it is subject to heating at substantially no hydraulic head in heat exchange relation with a condensible refrigerant gas on the opposite side of the heat exchange surfaces in said apparatus, compressing the refrigerant gas for use in said heat exchange apparatus to a liquefaction pressure corresponding to a temperature of about 102 F. and utilizing the latent heat of liquefaction of the refrigerant as the principal source of heat for evaporating the milk, continuously feeding fresh milk to said heat exchanger and continuously withdrawing therefrom milk of a desired concentration, cooling the refrigerant, which has been liquefied in said heat exchange apparatus, to about 50 F., continuously withdrawing from said heat exchangerthe water vapor and condensing said vapor and evaporating the cooled liquefied refrigerant in a condenser, recompressing the refrigerant gas and recycling it back through said heat exchange apparatus, maintaining a high vacuum upon the milk in said heat exchange apparatus by the condensation of the water vapor in the condenser, and maintaining substantially constant operating pressures and temperatures on the refrigerant throughout the system by continuously discharging from the system a portion of the heat extracted from the refrigerant during said cooling that would otherwise be retained and recycled by the refrigerant.

3. A continuous constant output process for evaporating milk while maintaining the milk far below its pasteurization temperature range comprising continuously compressing a refrigerant gas to its liquefaction pressure corresponding to a temperature within the range at which the milk evaporates in the process, continuously flowing the milk from its initial dilute stage to its concentrated stage and discharge from the sys tem over a series of heat exchange surfaces whereon films of the solution at successively higher concentrations on successive heat exchange surfaces are maintained at substantially no hydraulic head, evaporating water from the films on said surfaces'by absorption of the latent heat of liquefaction of the refrigerant gas introduced into the heat exchanger, cooling the refrigerant liquefied during the heat exchange with said milk to a temperature lower than the water vapor temperature, evaporating the cooled liquid refrigerant in a condenser by heat exchange with said water vapor and thereby condensing said water vapor, utilizing the condensation of said water vapor for maintaining a high vacuum on the milk undergoing evaporation, conat temperatures substantially below the pasteurization temperature of the milk comprising continuously feeding dilute milk into an evaporator system and therein partially: concentrating the milk in each of a plurality of successive stages of successively higher concentration by flowing the milk over successively communicating but otherwise segregated heat exchange surfaces until evaporation in the last stage reduces the milk to a desired density, continuously evacuating concentrated milk from the last stage, maintaining the milk under vacuum while on said surfaces at substantially the same degree oi. vacuum as the water vapor escaping therefrom, continuously compressing a refrigerant gas to a liquefaction pressure corresponding to a temperature lower than the pasteurization temperature of the milk but higher than the milk temperature undergoing evaporation, utilizing the latent heat of liquefaction oi the compressed gas for vaporizing water from the milk flowing over said heat exchange surfaces, cooling the refrigerant thus liquefied to a temperature below the temperature of the water vapor, establishing heat exchange between the cooled liquid refrigerant and the water vapor in a condenser separate from said evaporatorsystem to vaporize the refrigerant and condense the water vapor, continuously discharging the condensed water vapor and returning the vaporized refrigerant for recompression and reuse in the cycle, and maintaining substantially constant refrigerant pressures and temperatures on a constant compressor output by discharging from the process some of the heat that would otherwise be retained and recycled by the refrigerant, said discharge of heat being regulated by the compressed gas pressure.

The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 341,669 Lillie May 11, 1886 378,843 Lillie Feb. 28, 1888 780,612 Meyer Jan. 24, 1905 801,346 Tabret et al. Oct. 10, 1905 1,028,738 'Kestner June 4, 1912 1,119,011 Grosvenor Dec. 1, 1914 1,323,013 Christie Nov. 25, 1919 1,466,670 I Monti Sept. 4, 1923 2,374,232 Pteiifer et a1 Apr. 24, 1945 2,389,452 Patterson Nov. 20, 1945 FOREIGN PATENTS Number Country Date 8,269 Australia Aug. 3, 1933 321,378 Germany July 7, 1920 562,352 France Nov. 9, 1923

Images