US2824807A - Spray drying process - Google Patents

Description

United States Patent O SPRAY DRYING PROCESS Richard Laster, Newtonville, Mass., Harvey S. Bower, Evansville, Ind., Menelaos Doumas, Hudson Heights, N. J., and Arno Huste, Forest Hills, N. Y., assignors to General Foods Corporation, White Plains, N. Y., a corporation of Delaware No Drawing. Application February 17, 1955 Serial No. 488,986

10 Claims. (Cl. 99-130) This invention relates to a method of spray drying solutions of gelatin, and particularly to an improved method of spray drying gelatin solutions of relatively high concentrations.

The conventional process of spray drying materials in solution or suspension comprises generally the step of spraying the solution or suspension to be dried into hot air. The spraying action causes the formation of droplets, the droplets pass through the hot air, and rapid evaporation of the water or other solvent from the solid material occurs. By the time the droplet has reached the end of the drying zone, the water or other solvent has been substantiallyremoved and a dry, particulate, free-flowing material is provided. This method of drying has been successfully employed for a large variety of .materials. Various food products, such as coffee extracts, sugar solutions, cereal extracts, starch compositions, milk, and the like, are now beingdried commercially. in this manner on a fairly large scale. Similarly, various soap products, dyes and the like are extensively processed in this manner.

In spray drying solutions of gelatin, however, a great deal of difliculty has been encountered, so that little if any spray drying of gelatin is carried out. The major difliculty in spray drying gelatin solutions is encountered inattempting the formation of droplets during the spray drying operation. Instead, filaments are usually formed. These'are caused by premature drying of liquid filaments formed near the spray nozzle before they can be broken up'linto droplets. To explain, a solution or suspension to be dried is usually atomizedv directly into a 'heated atmosphere so that drying begins as soon as the material leaves the nozzle. The atomization of the liquid from a nozzle normally proceeds in three distinct stages. The liquid leaves the nozzle as a sheet at a substantially high velocity. This'liquid sheet then forms thin filaments of liquid which at a third stage collapse to form droplets. As these droplets pass through the drying zone, the liquid is removed, leaving dry spherical particles.

Because of the favorable viscosity and surface tension of most atomized solutions or suspensions, discrete droplets formbefore any significant amount of surface hardening due to drying occurs. It has been found that with gelatin solutions, however, the time required for formation of discrete droplets after spraying is apparently unusually long with the result that, if ordinary spray drying methods are employed, the above-described premature drying of liquid filaments is encountered and the final product is a coherent, fiutfy web-like mass of gelatin rather than the desirable particulate free-flowing material. Formation of these filaments also results in a considerable loss of gelatin during drying because of plastering of the walls of the spray dryer and incomplete drying of the product.

Moreover, where pure solutions of gelatin have been spray dried in the.past, it has been generally necessary gelling ability per unit weight of gelatin, solutions having a concentration of more than 1% could not be satisfactorily spray dried because of aforementioned filament formation. Spray drying of these dilute gelatin solutions is not generally practical because of the costly processing conditions necessary to obtain the desired product. Where additives such as dextrose, sucrose, and the like, are contained in a solution along with the gelatin, a somewhat higher concentration of gelatin is permissible but the addition of such fillers may be unsuited to the desired end use of the gelatin'product and the increase in concentration of solutions that can be spray dried is not significant. Accordingly, the drying of gelatin solutions of such low concentration is considered uneconomical since it is desirable, as irithe case of spray drying any solution,'that a solution of relatively high concentration be-employed. For these reasons spray drying as a means of drying gelatin solutions has had limited application.

It is anobject of the present invention to provide a process whereby solutions of gelatin may be suitably spray dried.

Another object of this invention is to provide a process for spray drying relatively concentrated gelatin solutions which avoids the formation of the above-described undesirable filaments and the resultant coherent, fiulfy mass.

It has now been found that a solution of gelatin may be successfully spray dried by providing a cool air zone intermediate the point of atomization of the solution and the warmer drying zone and proximate said point of atomization. In this manner, evaporation of water from the solution is retarded until discrete droplets of solution are formed. As a result, the formation of stringy filaments of gelatin is completely avoided and a dry, particulate, free-fiowing gelatin product is obtained. It is believed that the retardation of evaporation of water more readily permits transition from the point of liquid sheet formation to the droplet phase, and substantially prevents drying of the solution while in the filament form.

It has also been found advantageous in some instances to. employ, in addition to the cool air zone described above, a degree of control over the temperature of the gelatin solution at the point of atomization. Undesirable filament formation can occur if the temperature of the gelatin solution being fed to the atomizer is excessively high. The maximum gelatin feed temperature varies inversely with the Bloom of the gelatin and the concentration of the gelatin contained in the solution. With relatively dilute solutions of relatively low Bloom gelatin feed solution temperatures as high as 195 F. may be employed without encountering filament formation. On the other hand, with relatively concentrated and high Bloom gelatin solutions feed solution temperatures as low as F. may need to be employed. Apparently the Bloom of the gelatin in solution is the most significant factor while the concentration of solids in solution is of somewhat lesser importance, although both factors enter into the determination of the maximum temperature allowable. It is generally preferred that higher feed solution temperatures be avoided because of possible deterioration of the gelatin through Bloom loss an'd'the like.

Generally, in pumping a gelatin solution under the high pressure required for atomization the temperature of they feed solution is usually cooled before pumping although. as discussed hereinbelow, suchcooling should not serve e itt is lutiq Patented reazs, 1958' V and highLBI bm geIatin solutions;tmemployrgiooling: Such coolingmay be 'accomplishedibyfcoolingthe pump r ,be employed isqgoverned':byIhecconsiderationsofiviscosity this. case;theIge latin solution would :beratomizedinto :the; f cooliair zones- Followinggthesformatiomofrdiscretefdropez lets thematerial wouldrpasssintol.thetzwarmercdryingzzonmi.

' asito dischargeithegcold u" below 100"'F. sincefthetztemperatnre rise occurring on pumping increases somewhat directly with. the .concentra-N tion and Bloom of the gelatin contained inthe solution, it may be necessary in spray drying relatively concentrated itself or providing cooling means: betwe'enrthe' pump' and j the atomizationrdevice;

The vminimumztempe'r atureiofi :Ee'edis'olution which m'ay and equipmerrclimitationsairc Thusgofor example, a 10% solutioniof. 1 80 .Bloom igelatinat agtemperaturebelow'l 9 F. has a higliwiscosity and is sextremely diflicult to -handle Presently; available EHOZZlfiSiAHdJ pnmpsixio mot-provide the degreezof atomization anda-fpressurezreqnired:tosatisfac ity; :Simflanidifficulties are encountered ataternperatures' below 100:3 F; with solutions ofiothe'niBloom -gelatins and 0f otherzgelatim concentrations andzaccordingly a feed solution terhperatureeabovee5109??"Fiiaprefrred;:

Thestcrnr rBloom' 5355 used Ehereinsand: .lin': the'happenrled i claims is ;definedias: thez-weightzini grams requireditoYim-Q press a t /iz-diarneterwplun'gers tmmzintoaa gelatin solutioni containing ,6 solidsagelledzaatzilpt C. ifon'rl Z hontsl: A 7 suitable gtests procedure "forijdtfill'l'litliflg :Bloo'mris :outli'ned 2' in Industrial and Engineering Chemistry, AnalyticalbEdilc The: desired: cooliainzonezmay be supplied by; any: numei: ber of; suitablef means: Forsrexample, a ax; conventional P QY ryersmayzbesmodifiedzby introduction2to co1d.:air1

surround-a thesatomizing': area ramiitorprovidetthe rret-arda tiongofevaporation necessary tOIfEiIIDW -fOIHIEIfiOHiLOEz'diSEi. cre tedroplctsa :As an alternative; a-spray-=dryer contains:- ing twt rdistinct zones may lbesconstructeds .ther'cool-r air.

zone being confined ftozthezarear immediately surrounding Li" the spraypatternifrom thernozzle'randtthe; remaindei'fof thex 1 dryer;area containinggthesusuali warmed drying zonesv In:

by gravity, air ifiow or any other suitable means'.':

Afconventional spray dryerimay lac-modified according:-

eneasov 7 a I a r anddescribes a truncated cone 9"'inh'eiglit and 25" iii 7 base. diameter, The. iuppersextremity sofrthenshieldwisratr torilyzspraydryithese solutionsrofeextremely high viscos through the zonerbetween thetinnereand outer shield :Thi's arrangement preventsentrance ofi *any warnr 'dry ngairtto the cool air zone surrounding th nozzleancfhordSflo calized heating;of. rtheratornizedisolution. Alsoggthepair of concentric cones pnovideseamoreiunitorm distribution of cool air around thespray patternoflatomized, solution leaving the spray zl t v t V In the operation of the dryer a warm air mass at a 'temperaturerin; the orde'F Of-SSO F5,=' is'-' uniformly introminutej(standardtconditionsl atzthe top of tl1'e'=dryerand-f is directed downwardly past the outer conical fs'hie 'At theisarnezitime coollainrat a temperature of aboutflo rFi is introducedibyz'suitable means thr'oughtheiduct' and into' the :area surroundiri'grthesprasfi pattern at a rate- 0f Zabout 1000-.cubic, ftrpersminuter (standard tonditions); Under theseaconditionss cool ainriszintmducecl'fit a velocity sulfi 1 cient to preventrentrance of: warml air f-rom the warm zone 0' into the area;immediatelyrsurroundingi the spray pattern 3 i into the body of the dryer, the cold air being directedio spraye'nozzleitforms'sa sheet whiclrirapi'dlyirbreaks'zdown;

to the present inventiomby providingtor'the:introduction v of:a-streamofcold3airzat the:nnzzle;area.: In manycases it will zbeapreferred torlfollow this proceduresrather-rthanc incur the expensezofzconstnuetingmnew dryerzz Insmodie fyingg thez conventional-z'dryerg axcold lair;duct;is:preferably;, inserted: into-the:v dryeriat a ipoint; adjacentzthemozzle sol"? I over thetzoneof.atomization..; Preferably the cold air- ;is;,directedi;coaxially withziand-int;

theldirection' of:atornizati0n.:-, At the endvof therductimr- V V mediatelyzadjacent theznozzle:azconicaltshield is..preferably constructed coaxial with: the duct and: the; spray pats tern which causes cold :ainrintroduced;iintontherdryer.;to.-

spread within.- the dryer:rand coivercsubstantially theasarne area-as;thespray'pattern from the "nozzles: Thesolution is then atomized into the area: 'of-.coo'l .air surroundingihe nozzle and: allowed to form drepletsfwhichFthereafteppass. 6O

into-theswarmer drying-iairof thevspmy dryer; V .7 As a specific example of -the present invention; gelatin. solutionsarespray driedin-a conventionalrdryer:having.; the followingcharacteristics. The spraydryencompu ises a cylindricalatower lo ft..in diameter and.-30ft.vin-.height.

The dryenis ofthe co-curre ntatype whereim warmed dry-r 5 in'jg air isintroduced at the'top ftthedryerandis removed at the bottom of the dryer. 7 The dryer has asprayfdryin'g nozzle, .ST -21 described fully in Industrial; Spray= Nozzle' 's ipublished by Spraying. "Systems/slncorporated l953 Catalog Noh24.atpagesZSrZZ, v -V V 7 .theslower portiom ofi thisvrangeg arez;employed, an-,exn} tremely long-iperiod ofn-contacti'between solution-and dryw 0 Thisl nozzle,.located= in .the centersofiihe dryergapproxie matelyQ ZiS ft. fromz-itshtop, is adaptedhtosdirect.theratongw r ized solution downwardly; in a rconical spray: patterns, A:

12"diameter:cold airzduct terminatessinga 'ccgnicahshield A1T:'10% "solution ofrl 8(hzBloomzgelatim et "F31 drawn from,tthegholdingztankianmpassed:througha triplex pump. to: buildaupaa zpressnrezsofr 15(10 lbs;=' per :sq. in.-

(gauge): The; solutionisitherrfediilndersthistpressure td themozzlewand; inopassirrg through ct heppum p wil-l increasein-temperaturez t'o. 13533:Fe Asz-thecsolution 16aVeS'=thB-* into-I filaments.:,and; then; individuakrdnopletsc .Completes droplet: formation Lisa-assured :byrzreason rnfs'thecrel'ativelys slow rate of evaporation taking placenimthezcooliain-zone' intermediate; the: pointiof ratomizationiandtthea exterior of the conical -shield. ;s A-ftersfonmatidnzzof '=the':. individual: droplets, they pass: downwardlyiwith the :d'riying airtandi-n aretcornpletely dried:into,sphericaltparticlesbefore reach-n I ing the bottomrofitheitspray tower-.1:- The total-rdrying'pe-s I'iQdeiIl: thee-spray; towefrkjn: IhQiDITdEILOf .1 0';20;seconds r't unders;.-th'e conditionsndescribethrhereina fIhezrresnlting 1:,

product-obtained=;is:tasparticulateafreeeflowingematerial1:

having ;a.-density ofia'pproximatelya6'lbsapencubic foot and: a particle size: rangeizof substantially 50511-50 microns and Q is freeofianyistringwfilamentsswhiehihayeheretofioresehamzrj acter-ized-suchzspray driedmaterials.

Solutions-Ufa gelatin;-. havingzzconcentration'szofzas high; as 5.7%. may;beasatisfactorily spray driedpin stheesnedifiedsi spray; dryer; andtunderntheaconditions;described above; Generally, it.. is? moreqrdifiicultvtogspnay; dry i solu'tionsmf high Bl'oom gel-atinz th-an fsolutionstofslow Bl'oom;gelatin-,.-1

of the same concentration; Thus; a.--12%-solution;of:28-5

Bloom-gelatin on a.30%asolutiom0E65,-;Bloom= gelatin:are

satisfactorily spray;dried under the..aforementioneddryingn conditions, g r r Variouszmodificationssmay";bemade in-t'theldryingxn 1 ditions. set.forthvabove withont departing fromtthe, spirit 7 oi thisinvention.=-L Warm aintemperature imthezdryixigg;

zone may rangea-fromtlior': topl 000?, F."- depending on the rate atawhich theisolution is torbeidried thei time -ofs contact .offainwitth; solution, andmomn e .-;tcmpera-tur andusize of theacoolnairrzoneg- 'Wherettemperatures ing airaandaa correspondingly longipolunmmf airsarer quil fld'cr 011 the; other; hand, where :extremelywhiglizdry e ing temperatures are employed, carrnmnstrbestakcrr ore avoid iexcessivenheating got. gthe;materialerbeinggdriedrn V In generalit is-preferred remplpyi dryingsairroftastcmpgre iduct zand dnwnsnl wardly througbnthe.topaoftihmm' hield aszwelhas V V The temperature of the cool air zone may range from F. or below'to about 200 F. Temperatures below 0 F. may be required in drying highly concentrated solutions of high Bloom gelatin at a relatively low feed solution temperature. Under present equipment limits however, use of low feed solution temperatures are not considered practical. For this reason and because of the unfavorable economics involved in using a cool air zone temperature below 0 R, such temperatures are generally not employed. Room temperature air in the order of 60-80 F. is generally preferred because of its ready availability.

Feed pressures for the gelatin solution will depend to some extent on the viscosity of the particular solution and upon the nozzle and equipment employed and may range up to 3000 lbs. per sq. inch (gage) or higher. Also, the proportion of cool air to warm air introduced into the dryer employed in the specific example above may be departed from, as long as adequate retardation of evaporation prior to complete droplet formation is achieved, and further providing that the cool air is introduced at a velocity sufficient to provide a cool air zone of the desired dimensions.

On the other hand, as above mentioned the temperature of the solution at the time of atomization has been found to be somewhat critical under certain circumstances. In the example given above the temperature of the feed solution at the time it leaves the nozzle must be maintained within the range of IOU-140 F. Solution temperatures below the range result in formation of insoluble materials and are extremely difficult to handle, the latter caused by the greatly increased viscosity of the solution. In this case spray drying of solutions at temperatures above 140 F. results in the formation of undesirable filaments. Further, it is realized that a change in the atomization, air temperature and air flow conditions described in the specific example will influence to some extent the maximum feed solution temperature which may be employed.

Gelatin dried according to the process of the invention is in the form of dry spherical free-flowing particles which dissolve when placed in cold water. The addition of sugar or other additives to the gelatin solution prior to drying further enhances cold water solubility. For example, a solution containing 6 parts by weight of dextrose to 1 part by weight of gelatin when spray dried according to this invention will provide a material which dissolves in water at 80 F. within 2 minutes. Furthermore, the addition of dispersing agents such as lecithin, sorbitol, fructose, polyoxyethylene sorbitan monostearate, and glycerol monostearate may be employed to improve the rate of solution, and various antifoaming agents such as sorbitan monolaurate may be employed to reduce the formation of foam during solution. Some of these materials such as lecithin, and polyoxyethylene sorbitan monostearate serve as both dispersing and antifoaming agents.

Furthermore, the process of this invention may be employed to advantage in the fixation of various water immiscible and water miscible materials in a gelatin matrix. Thus, various vitamins, vitamin oils, biological preparations, other food supplements and various flavoring materials may be emulsified or dissolved in the gelatin solution prior to spray drying to result in their being fixed or encapsulated in the gelatin particles. Citrus oils such as the oils of orange, lemon and lime and oils containing vitamins A and D may be satisfactorily fixed in gelatin by emulsifying said oil in a solution of gelatin and spray drying the emulsion according to the process outlined above. In this manner a dry particulate free-flowing material is obtained containing the material fixed Within the individual spray dried particle.

As a specific example of the manner in which Water immiscible oils such as the vitamins and citrus oils mentioned above may be fixed in gelatin employing the process of the present invention, an emulsion of 1 part by tastes;

weight of the oil to 16 parts by weight of a 25% solution,

erally, relatively concentrated solutions of relatively low' Bloom gelatin are employed in order to obtain the highest gelatin concentration while permitting sufliciently low gelatin viscosities for ease of handling. Similarly, watersoluble materials such as vitamins B 8;, C, B and the like, may also be fixed in a gelatin matrix by dissolving about 1 part by weight of the vitamin in about 10 parts by weight of a concentrated solution of low Bloom gelatin such as that mentioned immediately above and the solution spray dried as aforesaid.

Application of this fixation procedure to the various materials described above provides the advantages of improved storage stability and reduced loss of potency during handling and storage. Further, the free-flowing particulate form of the material contributes greatly to ease of handling and ease of incorporation of said material into various other food products.

While the process of this invention has been described with reference to specific examples of gelatin solutions, other concentrations of various gelatin types may be spray dried under a variety of processing conditions to produce the desired results characteristic of the present invention and will specifically provide for the formation of a particulate, free-flowing material which is substantially free of any stringy filaments. Accordingly, a broad interpretation of the accompanying claims is desired realizing that gelatin solutions of various Bloom types over a wide range of concentrations may be spray dried in accordance with the spirit of the present invention.

What is claimed is:

1. In a process of spray drying a gelatin solution, the improvement comprising the step of atomizing the solution into a cool air zone prior to introduction of the atomized solution into a drying zone.

2. In a process of spray drying a gelatin solution, the improvement comprising the step of atomizing the solution into a cool air zone having a temperature of 0-200 F. prior to introduction of the atomized solution into the drying zone.

3. In a process of spray drying a gelatin solution, the improvement comprising the step of atomizing the solution into a cool air zone having a temperature of 0-200 F. prior to introduction of the atomized solution into a drying zone having a temperature of 2501000 F.

4. A process for spray drying an aqueous gelatin solution which comprises atomizing the gelatin solution into a cool air zone within a drying chamber to retard solvent evaporation until discrete droplets of the solution are formed, passing said discrete droplets to a drying zone of elevated temperature, and drying said droplets.

5. A process according to claim 4 wherein the cool air zone has a temperature of 0200 F. and wherein the drying zone has a temperature of 2501000 F.

6. A process of fixing a water immiscible oil in gelatin comprising the steps of emulsifying said water immiscible oil in an aqueous gelatin solution, atomizing said emul sion into a cool air zone within a drying chamber to retard solvent evaporation until discrete droplets of the solution are formed, passing said discrete droplets to a drying zone of elevated temperature, and drying said droplets.

7. A process of fixing a water miscible material in gelatin comprising the steps of dissolving said water miscible material in an aqueous gelatin solution, atomizing said solution into a cool air zone within a drying chamber to retard solvent evaporation until discrete droplets of the solution are formed, passing said discrete droplets to a drying zone of elevated temperature, and drying said droplets.

8. A process of fixing in gelatin a vitamin preparation containing water miscible and water immiscible materials comprising the steps of dissolving and emulsifying U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,824,807 February 25, 1958 Richard Lester et all appears in the printed specification It is hereby certified that error correction and that the said Let cars of the above numbered patent requiring Patent should read as corrected below,

Column 3, line 23, for read i lines 26 and 27, for "Edition" read Editions column 4, line 66, for "Wi'bbh" read with Signed and sealed this 15th day of April 1958,

(SEAL) Attest:

KARL MINE ROBERT c. WATSON Atteeting Officer Comnissioner of Patents

Claims (1)

1. IN A PROCESS OF SPRAY DRYING A GELATIN SOLUTION, THE IMPROVEMENT COMPRISING THE STEP OF ATOMIZING THE SOLUTION INTO A COOL AIR ZONE PRIOR TO INTRODUCTION OF THE ATOMIZED SOLUTION INTO A DRYING ZONE.