US2197804A

US2197804A - Process of drying lactose

Info

Publication number: US2197804A
Application number: US194167A
Authority: US
Inventors: Charles O Lavett
Original assignee: Buffalo Foundry & Machine Co
Current assignee: Buffalo Foundry & Machine Co
Priority date: 1938-03-05
Filing date: 1938-03-05
Publication date: 1940-04-23
Anticipated expiration: 1957-04-23

Description

April 1940- v c. o. LAVETT 2,197,804

PROCESS OF DRYING LACTOSE Filed March 5, 1938 2 Sheets-Sheet 1 may? Ewen? vapor-afar 15 52 .31 Dryer INVENTOR Czm (2m ATTO R N EY6 April 23, 1940. c, LAVETT v 2,197,804

PROCESS OF DRYING LACTOSE Filed March 5, 1958 2 Sheets-Sheet 2 ATTO R N EYS Patented Apr. 23, 1940 rnoonss 0F DRYING mo'rosn Charles 0. Lavett, Buflalo, N. Y., assignor to Buffalo Foundry & Machine 00., Buffalo, N. Y., a corporation of New York Application March 5, 1938, Serial No. 194,167

Claims.

This invention relates to the drying of solutions containing lactose and other solids in which not less than 55% of the solids is lactose, and more particularly to the drying of such solutions under such conditions of time and temperature that the lactose is crystallized in stable form, either principally in the form of the alpha hydrate or in the form of the beta anhydride. Such solutions may be very dilute and may contain proteins, mineral salts, and other constituents, an example of dilute solutions containing lactose. and other solids being whey which is the residue remaining after casein has been removed from skimmed milk in the manufacture of casein or cottage cheese, or remaining after fat and casein have been removed from whole milk in the manufacture of cheese.

This application is a continuation in part of my copending application Ser. No. 45,090, filed October 15, 1935.

One of the principal objects of the invention is to provide a low cost, high capacity and rapid process for drying solutions in which lactose comprises not less than 55% of the solids present and which can be carried out with relatively inexpensive and compact equipment and which produces a high grade, stable, non-caking, palatable, light colored, readily soluble and dry product.

Another object of the invention is to provide such a process in which the concentration and drying of the solution is effected as a continuous process and manual handlings of the material in process is eliminated.

Another aim is to provide such a process which can be carried out with the minimum consumption of steam as a heating medium and with minimum power, labor and drying time, especially as compared with tunnel drying methods now used.

Another object is to provide a process in which the concentration of the materials, prior to the crystallizing and drying step, is carried beyond the point which can be conveniently effected in a vacuum pan and to thereafter so cool the material that it is converted into a physical condition which permits of the removal of the residual moisture in a short space of time and ma continuous type of dryer.

Another object is to reduce, in providing a cooling step, the time necessary for cooling the material and to reduce the time necessary for the removal of most of the'residual moisture after this cooling step.

Certain facts concerning lactose have been published. Lactose in solution is in both alpha and beta forms, the relative proportions of which are more or less definitely fixed by a tendency toward equilibrium, e. g. published proportions vary from 61.3% beta to 38.7% alpha lactose at 77 F. to 57.1% beta to 42.9% alpha lactose at 212 F. Crystals formed from a solution at temperatures stated to be above 199.4 F. tend to be in beta form and those that form at lower temperatures tend to be in alpha form. When crystals 01' one form are formed equilibrium of the lactose remaining in solution tends to be re-established by conversion of one form to the other, e. g. when alpha crystals form, beta lactose still in solution is converted to alpha lactose in solution to replace the alpha lactose removed from the solution by crystallization. However, such conversion apparently requires time and the presence of water. Lactose that has crystallized from a solution, depending upon the temperature conditions under which it is crystallized and depending upon other conditions existing during the crystallization, such as the amount of water present, the length of time during which crystallization is proceeding, and the nature of other solids present, may be in the beta form in which the crystals do not require or carry any water of crystallization or in the alpha form in which the crystals are hydrated in that they carry a definite proportion of water of crystallization. Moreover, dry lactose may exist without being crystallized, and in such case the lactose tends to attract moisture.

In the practice of this invention the lactose and other constituents present in the final product are in such form that while, like most products of this kind, the final product may take on and give off moisture under changing conditions. of humidity, it does not take on moisture to such extent as to cause the product to cake or become sticky, and the lactose is not discolored or has not sufiered such discoloration as undesirably to impair the color of the product, dried whey made in accordance with this invention being stable, noncaking, readily soluble, palatable and of a light color. .In carrying out the process'of the present invention, the product can be produced to contain a preponderance of either alpha or.beta lactose. It is believed that the presence of the lactose in crystalline form and the high proportion of the lactose in either alpha hydrate or beta form are largely responsible for the non-caking character of the dry product.

In the practice of this invention, the several features thereof, which may be used in conjunction or separately, are directed to causing the dried product to possess the above stated characteristics.

Features of this invention are the continuous production of a concentrated whey of such concentration that it will solidify upon cooling and the continuous cooling of such a product with or without simultaneous seeding with lactose crystals and with or without simultaneous crystallization of the lactose. A further feature of the invention is the conversion of the concentrated whey into such form that it can be dried without any necessity for an extensive holding period to permit crystallization of the lactose and for simultaneous drying and crystallization of a considerable part of the lactose. A further feature of the invention consists in conducting the cooling operation in such a manner that crystallization of the lactose can take place in the form of the beta anhydride or in the form of the alpha hydrate, and that in such cooling operation a small amount of water is evaporated preparatory to final drying. Further features of this invention are that, where seeding is employed, the concentrated material is worked after lactose seeding crystals are brought in contact therewith; that the supply of lactose seeding crystals is effected automatically and that some of the cooled material containing such crystals is used as a source of lactose seeding crystals. 7

To facilitate the embodiment of these features in the practice of this invention, further features of the preferred form of my invention, which may be used conjointly or separately, are that the material, while at a concentration that promotes the formation of lactose crystals is fed to a revolving surface, seeded or unseeded with lactose crystals, which preferably is in the form of a pair of internally cooled rolls rotating in close relation on parallel axes; that the material is fed to a point on said rolls near and moving toward the bite or point of closest approach of those rolls and is spread or worked into a thin layer as it is passed through the bite; that the seeded material divides into two continuous thinner layers respectively adhering to the rolls after the material passes through the bite; that the formation of crystals, an effect which involves a time element, continues simultaneously with the cooling of the material and that when the material is removed from the rolls it is in a physical condition to permit of rapid removal of the residual moisture contained therein.

Actual use of this invention indicates that to obtain best results it is desirable to concentrate the solution as far as possible in order to have the smallest possible volume to cool and to'produce the largest possible amount of lactose crystals when the concentrated solution is cooled and also because it is more economical to remove water in an evaporator than in a dryer. Actual use of this invention indicates that hot lactose containing solutions having not substantially less than 75% of solids can be readily solidified and crystallized by cooling and placed in favorable condition for rapid removal of the residual moisture. To obtain solutions having a concentration of solids not substantially less than 75% it is necessary to effect a concentration of such lactose containing solutions as are ordinarily available, e. g. whey which contains in the neighborhood of 6% solids, all percentages hereinstated being on the basis of weight.

Preconcentration of dilute lactose containing solutions can be effected in vacuum evaporators up to a concentration of about 70% solids but only by concentrating in batches in a single effect vacuum pan and with the possibility of the concentrated solution setting in the vacuum pan to a solid mass and with the dimculties that the heating surfaces become badly coated and evaporation is slow because of this coating and the high viscosity of the fluid, thereby requiring large heating surfaces and close supervision of the operation. Furthermore, if a lactose solution at 70% concentration is allowed to cool and crystallize, a soft, mushy product-is obtained which becomes very hard and dense when dry and for this reason dries quite slowly. n the other hand, a solution containing 30-50% of solids can be obtained readily in any one of various ways, and a. continuous supply can be obtained from a multiple effect evaporator.

It is a feature of this invention, which contributes to the possibility of its being a continuous process and which cooperates advantageously with the crystallizing, solidifying and drying operations, above described, that there is an intermediate concentration between the preconcentration, as in a multiple eflect evaporator, and the cooling and crystallizing operation. Since lactose has a limited solubility and whey contains proteins which increase the viscosity of the whey at higher concentration, it is especially advantageous in the drying of whey to limit the initial concentration of the whey under vacuum to a point at which the concentrate is free flbwing and easy to handle and does not deposit lactose crystals, as long as kept warm.

It is a further feature of this invention that the intermediate concentrating step which raises the concentration from that readily and desirably eifected by a multiple eflect evaporator to that required for efiecting solidifying on the cooling rolls, may be accomplished on a pairof revolving heated surfaces, preferably a pair of internally heated rolls rotating in contact or close relation on parallel axes, the surfaces of the rolls moving upwardly at the bite. Such a double drum type of concentrating means is preferred because time for effecting the desired concentration should be short; the concentration is effected at high temperature and in layers and rapidly, and without formation of lactose crystals; the viscous concentrated material from these concentrating can be regulated by adjusting steam pressure therein, the speed of rotation thereof and the level of the liquid therebetween.

An important feature of the invention is that by efiecting such intermediate concentration the light color of whey is preserved by reason of the rapidity of the concentration. The concentrate is cleanly removed from the surface of the intermediate concentrating means. An advantageous feature of the intermediate or concentrating drums is that their surfaces move upwardly at the bite permitting better control of the concentrating step and permitting transfer of the con centrate to the lower drums by gravity without any mechanical device, and permitting all of the solution which adheres to the upper drums to remain in undisturbed condition until removed therefrom and carried bygravity to the cooling drums, and permitting a layer of greater thick- 75 adhering to the drums, which layer would then be divided into two thin layers adhering respectively to the two drums. The withdrawal of such thin layers from the trough or valley between the drums in that case would result in an undesirable concentration of the material therein, and control of the operation of the drums would .be more difficult as well as the transfer of the concentrate to the cooling drums. Inasmuch as the surfaces of the concentrating rolls move upwardly at the bite the thickness of the layer on the rolls is the full thickness of the layer that will be carried out of the trough by adherence to the surfaces of the rolls. That thickness will depend upon the properties of the material that is being withdrawn from the trough between the rolls as layers upon the surfaces of the rolls and upon the conditions under which the drums are operated. The relation of rate of feed to the trough to the rate of withdrawal therefrom is important to maintain the proper level in the trough and the desired layer thickness. The layer should not be so thin that it is likely to be burned or scorched on the rolls and it should not be so thick that the body of the material inthe layer is too great for proper concentration before the material is passed on to the lower rolls.

Up to the time that the material is deposited on the cooling rolls no crystallization takes place therein and, consequently, no crystallization has taken-place in the material leaving the upper rolls. If any crystallization has occurred in the material being fed to the upper rolls, as by reason of allowing the material to cool before being fed to the upper rolls, such crystals are dissolved when the material is heated in the trough between the upper rolls. The absence of crystallization of the material prior to the deposit of the material on the cooling rolls has been shown by analysis of samples of viscous material leaving the upper drums. Such samples show that beta and alpha lactose are present therein approximately in the proportion of 6040, which is the approximate proportion existing in the original lactose solution. The material leaving the upper drums is a viscous material and free from the grittiness that would indicate the presence of crystals therein. Seeding tests made with solutions of pure lactose showed the absence of either alpha or beta lactosecrystals prior to the deposit of the material on the cooling drums.

As above mentioned, the process is particularly adapted to and effective in the drying of whey, an operation which involves special difficulties due to the dilute character of the raw material, the presence of protein, salts'and acids due to fermentation of the milk or to the addition of acid for the precipitation of casein. Raw whey contains only 6% of solids, of which 60-75% is lactose and 40-25% is proteins, salts and free acids, the respective percentages and natures of which vary considerably with the source of milk and the procedure by which the whey is produced as a by-product. In efforts to dry whey by a continuous operation the features of the procedure whereby continuous operation is sought have caused difllculties to arise which are overcome by this invention. As above pointed out, the high viscosity of concentrated, whey has causeddifllculties in producing and handling whey solutions of high concentration and those difficulties are overcome by procedure in accordance with this invention. Accordingly, in the practice of this invention whey to bedried is preferably heated by passage through a heater, as set forth in my co-pending application, Ser. No. 179,403, filed December 13, 1937, that will sufficiently coagulate the proteins. Such treatment is' preferably applied to the whey prior to the initial concentration thereof. The coagulation of proteins in the whey serves to give more uniform concentration and he at transmission through the layer of whey, prevents local 'overheating and discoloration in the layer on the concentrating rolls and gives a more uniform coating thereon.

Inasmuch as whey from different sources varies in composition'it may be desirable to adjust the acidity thereof to facilitate drying and to obtain a light colored product and a higher capacity. In practice, however, it has been found that whey remaining after precipitation of casein by means of mineral acid is readily reduced to dry material in the practice ofthe invention when the titratable acidity thereof is approximately 0.4% (calculated as lactic acid) especially when the mineral acid is sulfuric acid. Whey produced in the manufacture of cheese or rennet casein is readily dried by the practice of the invention, especially if the acidity thereof is brought to approximately 0.4% (calculated as lactic acid) by a slight addition of sulfuric acid. Sour whey, such as produced in the manufacture of cottage cheese or lactic acid casein or such as results from the souring of whey otherwise produced is readily dried in the practice of the invention especially if it is at least partly neutralized by the addition of lime and then its acidity is brought up to approximately 0.4% (calculated as lactic acid) by the addition of sulfuric acid. In the case of sour whey, partial neutralization and addition of sodium bisulfite also has been found beneficial in combination with concentration on the upper drums to above 90%.

Further features of this invention and specific details of the operation thereof will appear in the following descriptionof illustrative examples of apparatus suitable for the practice thereof in connection with which an illustrative example of operation is given.

In the accompanying drawings:

Fig. l is a diagrammatic representation of a preferred form of apparatus suitable for use in carrying out my invention.

Fig. 2 is a'fragmentary diagrammatic representation of a modified form of apparatus for carrying out myinvention, the multiple effect evaporator used for preconcentrating the solution not being shown.

Fig. 3 is a diagrammatic representation of another form of apparatus suitable for carrying out my invention.

Fig. 4 is a diagrammatic representation of a steam heated drying drum and a cooling drum in contact therewith and which can be substituted for the four drums for the same purpose shown in Fig. 1.

In carrying out the invention with the apparatus shown in Fig. 1, the whey in the natural state,'but preferably preheated and also preferably treated to adjust its acidity, is first concentrated in a multiple effect vacuum evaporator, although it will be understood that any other apparatus can be used, the multiple effect evaporator shown being preferred to preserve the light color of thewhey and also for economy because it permits the maximum amount of water to be evaporated with a minimum amount of steam and because the flow of material is continuous. In this multiple effect evaporator the whey is concentrated to 30-50% solids. In the multiple effect evaporator shown the whey is admitted to the first effect I at 2 and the steam at 3. From the first eifect the concentrated material passes through a line 4 to the second effect 5. and the vapors pass through a line 6 to heat the material in the second effect. Similarly, the further concentrated material from the second effect passes through a line 1 and the vapors through a line 8 to the third effect 9. From the third effect the material is withdrawn by a pump l0 and discharged through a line H into an insulated storage tank |2, this tank being preferably so insulated to prevent the material from the multiple effect evaporator from cooling down as well as to prevent the formation of crystals. The vapors from the third effect pass out through an outlet I3 which is connected with a. barometric condenser and steam ejector (not shown) or the like so that evaporation in the several effects takes place at reduced pressure. Preferably a vacuum of 25 or 26 inches is maintained in the last effect 9. At a concentration of 30-50% solids the liquid is smooth and flows freely without any sign of crystal formation and is in condition for further concentration on a pair of concentrating drums. From the storage tank the preconcentrated whey is passed by a pump l4 through a. line l5 and is deposited in the space 20 between a pair of heated drums 2| and 22. The vapors generated by the heated drums 2| and 22 are drawn off through a. hood 23. These drums 2| and 22 have the usual end boards 24 for retaining a quantity of the whey in the space or valley 20 and it will be particularly noted that the drums 2| and 22 move upwardly at their point of closest approach. The quantity of whey in the space or valley 20 is purposely fed at such low concentration (30-50% solids) that it is maintained in a liquid-state in this space and free from any crystals. This body of whey boils and some of the water is evaporated from the body. The quantity of liquid in the space 20 is maintained at a proper level required to deposit the proper amount of material on the drum surface. The temperature of the material fed to the boiling liquid between these drums is almost instantly raised to its boiling point.

At the concentration effected by the preconcentration of the whey and its boiling in the space 20, the drums 2| and 22, rotating upwardly at their point of closest approach, pick up a heavy thick layer of the boiling solution, these layers being very much thicker than those which would be obtained if the drums were rotated in the opposite direction. The. thick layers on the surfaces of the drums 2| and 22 are quickly reduced to any desired moisture content governed by the density of the solution fed, the level of the liquid between-the drums, the steam pressure and the speed of the drums. In the present process the layer is preferably concentrated to 8-25% of moisture and the drums are preferably rotated at such speed that the thick layers are retained on the drums for from 15 to 100 seconds. The steam pressure in thedrums is preferably maintained at from 30 to 60 pounds gage and the temperature of the layer during the concentrating time is raised to 218-240" F. The thick layers on the drums 2| and 22 are removed by v the doctor knives 25 in the form of a very viscous material which drops at a temperature close to its boiling point inpatches or strips onto a lower set of

drums

30, 3|. l

The lower drums 30 and 3| provide the means for rapidly cooling the concentrated whey, these drums being cooled in any suitable manner as by passing cooling water through these drums. The viscous material removed from the upper drums spreads out somewhat and forms patches on the cooling drums 30, 3|, these patches remaining soft as they are being carried to the bite of the drums. The cooling drums 30 and 3| rotate in the direction reverse of the drums 2| and 22, i, e. the

drums

30 and 3| travel downwardly at their bite so that the deposited patches are united and pressed between the drums, emerging on the underside of each drum and adhering to each drum as a heavy layer. The layers on the two drums are rapidly cooled by the water passing through the drums. By cooling these layers the whey is solidified and readily removed from the cooling drums by knives 32 located on opposite sides of the drums and which deposit the cooled whey in sheet or granular form in screw conveyers 33 or the like.

It is generally preferable to incompletely remove the layers of cooled concentrated whey from the cooling drums 30, 3| so as to leave a thin layer of material on the cooling surfaces, this thin layer containing crystals of lactose which serve as seed crystals for the crystallizatiion of fresh material applied to the cooling rums.

By concentrating the material to 75-92% solids on the upper drums 2| and 22, a cooled product is obtained from the cooling drums 30, 3| which can be passed directly into a dryer and does not require any extensive holding period for crystallization of the lactose. The consistency of the cooled product removed from the cooling drums by the knives 32 is such that it gives up most rotating shell of the rotary dryer by means of a fan 38. By quickly cooling the hot concentrated whey it is converted into a condition in which the time required for drying is greatly reduced as compared to the time needed for drying a product which has been allowed to cool as a solid mass.

The cooling drums 30 and 3| are preferably maintained at such temperature that the hot concentrated material removed from the upper drums 2| and 22 is quickly-cooled below 199.4" F., thereby to initiate crystallization of the lactose in the form of the alpha hydrate. By using cooling drums for this purpose the cooling of the hot concentrated whey containing 8-25% moisture is greatly expedited while at the same time a small amount of water is evaporated and a product of the desired temperature and physical characteristics can be obtained in less than one revolution of the cooling drums, the amount of moisture present in the concentrated product from the upper drums and in the cooled product from the cooling drums being more than sufllcient to allow the lactose to crystallize in the form of alpha hydrate. By incompletely removing the material from the cooling drums a residual coat- 8 ing containing crystals of alpha lactose hydrate may be allowed to remain to act as seed crystals for the fresh material applied to the drum surface and thereby expedite the formation of alpha lactose crystals.

10 Depending upon the speed of the cooling drums, the temperature of the cooling water and the clearance between the drums, which governs the thickness of the layer 0'. material on the drums, a product can be obtained which, when removed ll from the drums. can be varied from a coarse powder or flake which can be conveyed by a screw conveyer, to a condition in which it is still relatively soft but will not pack or cake unless pressed. In such condition the percentage of lactose inthe alpha form varies from about 70% to the equilibrium percentage of about 40%, indicating the degree of crystallization that has taken place. Lower speed, lower temperature and a thinner layer on the cooling drums are favorable to a higher degree of crystallization. It has been found desirable to use a watertemperature of about 100-125" F. in order not to form a hard layer of cold material on the cooling drums and to prevent undue wear of the knives which remove the cooled material.

Even if crystallization has merely started when the product is removed from the cooling drums 30, II it is unnecessary to hold the material in order to complete crystallization to a point where a stable product is formed. Whey containing 40 to 10% of the lactose in alpha form when removed from the cooling drums, contained as much as 82 to 91% after drying, thus indicating that the crystallization proceeds during the drying process.

Exetensive research and tests with the apparatus as illustrated in Fig. l in drying whey indicate the following as desirable operating conditions:

5 Pre-heating liquid whey:

The temperature may vary from a minimum of 190 F. to 212 F. Preferable range 200 to 210 F. Evaporator concentration in the multiple effect evaporator:

Density range of concentrated whey, 30 to 50% and preferably 35 to solids. Drum concentration:

Liquor feed, 30 to solids-preferably 3 35 to 45%. Concentrated to, '75 to 92% solids-preferably '15 to 85%. Steam pressure, 0 lbs. to lbs-preferably 15 to 40 lbs. Concentrating time on the hot surface, 15 to 100 seconds-preferably 20 o to 40 seconds.

Cooling:

' v Temperature of cooled whey, to 150 F.,

preferably to F. Time of cooling to below 199. F., preferably cl less than 60 seconds and from 199 F. down the temperature drop, may if desired, be prolonged over an indefinite period. I prefer to cool the whey' from 199 ,F. to within the preferable temperature range 70 of 100 to 125 F. in less than 60 seconds.

Final drying:

The temperature range of the heating medium, may vary from 80 to 190 F., however I prefer uslng a temperature of from as. no to r.

In the form of theapparatus for practicing the invention shown in Fig. 2 the lactose in the solution can be crystallized either in the form of the, alpha hydrate or in the form of the beta anhydride. In the apparatus shown in this figure, 5 cooling drums are not employed and an air cooler is substituted therefor. As with the form of the invention shown in Fig. 1, the whey is preferably first preconcentrated in a multiple effect evaporator to from .30-50% solids and m then further concentrated on the heated concentrating

drums

21, 22 to from 75-92% solids, the multiple efiect evaporator not being illustrated in Fig. 2. The viscous material removed as droppings from the heated drums 2|, 22 by 15 the doctor knives 25 is deposited upon the upper stretch of a belt 40 which carries the material into an air cooler 4|. Within the air cooler the material may be carried in a reverse direction by one or more return belts 42 in order to govern lo the length of time available for cooling. Coldair is shown as admitted to the air cooler M at 43 and drawn through the air cooler countercurrent to the flow of materials by a fan 44. The fan may be arranged to discharge into the heater :5 31 of the rotary dryer 36, this rotary dryer being of the same form as that illustrated in Fig. 1 and the cooled material from the cooler ll being discharged into the materials inlet of the rotary dryer 36. As the air drawn through the cooler 30 4| is used merely for cooling, the warm air withdrawn from this cooler by the fan M can be conducted to the inlet of the heater 31, as illustrated, and thence through the rotary dryer.

With the apparatus shown in'Fig. 2 it is also 85 possible to produce a product in which the preponderance of lactose is in the form of the beta anhydride. To accomplish this the cooling step is modified and the cooling ratio at the start made sufliciently slow to permit crystals of beta 40 lactose to form before the temperature of the whey drops below 199.4 F., the transition point of the lactose. In that case the initial crystals consist of beta lactose and further crystallization after the temperature drops below 199.4 F. tends 45 to continue to take place in the same form even after the temperature is below the transition point of the lactose and even if the temperature of the air used for, final drying is below this point. The initial formation of such beta lactose crys- 5o tals on the

belts

40 and 42 can be hastened by incompletely removing the material from the belts to act as seed crystals or by the introduction of whey previously dried by this method and containing such seed crystals. In order to make 55 the lactose crystallize in the form of the alpha hydrate the material is rapidly cooled tobelow 199.4" F. and the crystallization in this form hastened, if desired, by the introduction of whey previously dried by this method and containing, 60 crystals of alpha lactose hydrate. For the purpose of rapid initial cooling the product dropping from the drums 2|, 22 may be spread on the belt by mechanical means (not shown) and a .flow of cold air directed against the material 5 at the knives 25 and when it is spread on the belt.

' The evaporation of the whey may be effected in a vacuum pan 50 as illustrated in Fig. 3; The use of a vacuum pan generally involves a batch 7o process and would be applicable to small installa tions where the amount of whey to be dried would not warrant the expense and maintenance of continuous processing apparatus. The raw whey is admitted to the vacuum pan 50, as at 5i, and

can be concentrated therein up to about 70% solids. The concentrated whey can then be conducted to a screw conveyer 52 in which a suitperature in the vacuum pan is at all times considerably below 199.4 F. the dry product obtained by this modification of my method ordinarily will contain lactose in the form of th alpha hydrate.

Any suitable means can be provided for recycling a part of the dry product so as to raise the concentration of the material discharged from the vacuum pan 50 to a point where it can be handled by the cooling drums 30, 3| and provide seed crystals for hastening the crys-' tallization of the lactose. For example, the dried material from the rotary dryer can be transferred by a blower 55 to a collector 56 of the cyclone type, this collector having two valved discharges 51 and 58, one leading to the screw conveyer 52 and the other leading to a receptacle for receiving the dried product.

It is also possible to effect both the drum drying and the drum cooling of the material by a single pair of drums. Suitable apparatus for effecting this is shown in Fig. 4. In this form the whey after being concentrated to 30-50% solids in a multiple effect evaporator as shown in Fig. 1, or in any suitable manner, is pumped to a pan 60, this pan containing a bath of the preconcentrated whey. A steam heated drum BI is arranged to dip into this pan and this drum will pick up a layer of whey and will concentrate this whey further to any desired concentration. The cooling drum 62 can be cooled by means of water or in any suitable manner and contacts with the heated drum 6|, so as to remove the film of hot concentrated whey from this heated drum and cool this product and provide an opportunity for crystallization of the lactose, usually in the form of alpha hydrate. To assist in removing the layer from the surface of the drum 6|, the cooling drum 62 may be rotated at slightly higher speed than the heating drum 6|. After being so cooled the whey is removed by a doctor knife 63 and the further drying of the whey and crystallization of the lactose can be effected in a rotary dryer as illustrated in Figs. 1-3.

By heated at a temperature as used with reference to the drums in the following claims is meant the temperatures obtained by introducing steam into standard drying and concentrating drums at the temperature set forth, it being recognized that there is, in such drums, a very substantial difference between the steam temperature and the outside surface temperature, and it being also recognized that the drums could be heated by electricity or media other than steam.

From the foregoing it is apparent that the present invention provides a continuous, rapid and low cost process for reducing lactose solutions to a light colored, dry, stable and uniform product. While I have described specific apparatus for carrying out my process, other apparatus couldbe used and therefore the invention is not to be limited to the use of any particular apparatus or steps but is to be accorded the full range of equivalents comprehended by the accommnyins claims.

' thin layer to effect I claim as my invention:

1. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in concentrating the solution to produce a heavily concentrated solution containing not more than 92% solids, spreading said heavily concentrated solution in a thin layer,

seeding said thin layer with lactose seed crystals, cooling said thin layer to effect a crystallization of a part of said lactose and thereafter applying heat to said cooled material to dry the same.

2. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in concentrating the solution under vacuum to a solution having less than 50% solids, further concentrating said solution to produce a heavily concentrated solution containing not more than 92% solids, spreading said heavily concentrated solution in a thin layer, seeding said thin layer with lactose seed crystals, cooling said said lactose and thereafter applying heat to the cooled material to dry the same.

3. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in concentrating the solution to produce a solution of such heavy concentration as to prevent the free movement of seed crystals therethrough and containing not more than 92% solids, spreading said concentrated solution in a thin layer, seeding said thin layer with lactose crystals, cooling said layer to efiect a crystallization of a part of said lactose and thereafter applying heat to said cooled material to dry the same.

4. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in concentrating the solution to produce a solution of such heavy concentration as to prevent the free movement of seed crystals therethrough and containing not more than 92% a crystallization of a part of solids, spreading said concentrated solution in a thin layer on a surface seeded with crystalline lactose, cooling said layer to effect a crystallization of a part of said lactose, removing said layer from said surface and thereafter applying heat to the cooled material to dry the same.

5. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in concentrating the solution to produce a solution of such heavy concentration as ,to prevent the free movement of seed crystals therethrough and containing not more than 92% solids, spreading said concentrated solution in a thin layer on a surface seeded with crystalline lactose, cooling said layer to effect a crystallization of a part of said lactose, incompletelyremoving said layer from said surface to leave it in a seeded condition and thereafter applying heat to the cooled material to dry the same.

6. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in concentrating the solution under vacuum to a solution having less than 50% solids, further concentrating said solution to produce a solution of such heavy concentration as to prevent the free movement of seed crystals therethrough and containing not more than, 92% solids, spreading said solution in a layer, seeding said layer with a dry seeding material, cooling said layer for a suflicient length of time to effect a crystallization of a part of said lactose and thereafter applying heat to said cooled material to 'dry the same.

7. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in concentrating the solution under vacuum to a solution having between 30 and 50% solids, further concentrating said solution at a temperature above 199.4" F. to contain not more than 92% solids, spreading said solution in a layer, rapidly cooling said layer to a temperature below 199.4" E, further cooling said layer to effect the crystallization of a part of the lactose in the form of the alpha hydrate and thereafter applying heat to said cooled material to dry the same.

8. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in concentrating the solution under vacuum to a solution having between 30 and 50% solids, further concentrating said solution at a temperature above 199.4" F. to contain not more than 92% solids, spreading said solution on a surface, slowly cooling said material at temperatures above 199.4" F. to effect the initial crystallization of the lactose in the form. of the beta anhydride, continuing the cooling of said layer to effect a further crystallization of the lactose in the form of the beta anhydride and thereafter applying heat to said cooled material to dry the same.

9. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in preconcentrating the solution under vacuum to contain from 30-50% solids, applying said solution as a layer to a heated surface heated at a temperature not exceeding 307 F., retaining said layer on said surface for from 15 to 100 seconds to concentrate said solution to from -92% solids, spreading said concentrated material in a layer, cooling said layer to effect crystallization of apart of the lactose and thereafter applying heat to said cooled material to dry the same.

10. The process of drying whey which consists in preconcentrating the solution under vacuum to contain from 30-50% solids, applying said preconcentrated whey as a layer to a heated sur face heated at a temperature not exceeding 307 R, retaining said layer on said surface for from 15 to 100 seconds to concentrate said solution to from '75 to 92% solids, spreading said concentrated material in a layer, cooling said layer to effect crystallization of a part of the lactose and thereafter applying heat to said cooled material to dry the same.

11. The process of drying whey which consists in preconcentrating the whey under vacuum to contain from 35 to 45% solids, applying said solution as a layer to a heated surface heated by steam at 15 to 40 pounds steam pressure, retaining said layer on said surface for from 20 to 40 seconds to concentrate said solution to from 75.

to solids, spreading said concentrated material in a layer, cooling said layer to a temperature of from to F. to effect crystallization of apart of the lactose and thereafter applying heat at a temperature of from 110 to F.

12. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in preconcentrating the solution under vacuum to contain from 30-50% solids, applying said solution as a layer to a heated surface heated at a temperature not exceeding 307 F., retaining said layer on said surface for from 15 to 100 seconds to concentrate said solution to from 75-92% solids, spreading said concentrated material in a layer, cooling said layer to a temperature of from 80 to 150 F. to effect crystallization of a part of the lactose and thereafter apply-- ing heat to said cooled material to dry the same.

13. The process of drying a dilute solution containing solids a preponderance of which is lactose which consists in concentrating the solution to from 75 to 92% solids, spreading'said concentrated solution in a thin layer on a cooling surface, seeding said thin layer with lactose seed crystals, cooling said surface to effect a crystallization of a part of said lactose and thereafter applying heat to said cooled material to dry the same.

14. The process of drying a dilute solution containing solids, a preponderance of which is lactose which consists in concentrating the solution to contain from 75 to 92% solids, forming said concentrated material into thin layers, continuously moving said layers, seeding said layers with lactose seed crystals, passing cool air over said moving material to effect a crystallization of a part of said lactose and thereafter applying heat to said cooled material to dry the same.

15. The process of drying a dilute solution containing solids a preponderance of which is lactose, which consists in concentrating the solution to contain from 65 to 70% solids, adding dry lactose seed crystals to said concentrated solution, spreading said mixed material in a layer, cooling said layer to efiect a crystallization of a part of said lactose and thereafter applying heat to said cooled material to dry the same.

CHARLES O. LAVETT.