US3414980A

US3414980A - Method of spray drying

Info

Publication number: US3414980A
Application number: US617533A
Authority: US
Inventors: Robert L Nezbed
Original assignee: Kraft Inc
Current assignee: Kraft Inc
Priority date: 1967-02-21
Filing date: 1967-02-21
Publication date: 1968-12-10
Anticipated expiration: 1985-12-10

Description

Dec. 10, 1968 R. 1.. NEZBED METHOD OF SPRAY DRYING Filed Feb. 21, 1967 INVENTOR P043527 4. /VZ5D United States Patent 3,414,980 METHGD 0F SPRAY DRYING Robert L. Nezbed, Highland Park, Ill., assignor to National Dairy Products Corporation, New York,

N.Y., a corporation of Delaware Filed Feb. 21, 1967, Ser. No. 617,533

5 Claims. (Cl. 349) ABSTRACT OF THE DISCLOSURE A method for preparing a dry composition wherein a portion of the desired ingredients of the dry composition is added to the chamber of a spray dryer in a substantially dry state while the remaining portion of the desired ingredients are dispersed in a liquid and are sprayed into the chamber. The sprayed liquid dispersion and substantially dry ingredients form an admixture which is dried to provide a homogeneous dry composition.

The present invention relates generally to the removal of liquid from liquid dispersions of solid materials. More specifically, it relates to a method and apparatus for the spray drying of liquid dispersions.

One method frequently utilized for largescale liquid removal operations is spray-drying. This method is particularly useful in removing liquid from dispersions of heat-sensitive substances, or when it is desirable to produce spherical particles of the solid material. In a conventional practice of this method, the liquid dispersion is conducted to a large chamber wherein it is atomized. Heated air is circulated through the chamber. The small size of the atomized droplets promotes extremely rapid evaporation and transfer of liquid therefrom to the air. There are thereby obtained dried substantially spherical particles which fall to the bottom of the chamber, from which they are removed.

Although spray drying permits the drying of some liquid dispersons which cannot be dried otherwise at all, some liquid dispersions are nevertheless very difiicult to spray dry. For example, dispersions containing sugar above a certain level are difiicult to pump and atomize. Furthermore, since sugar is highly hygroscopic, high levels of sugar tend to retard heat transfer between the atomized droplets and the circulating heated air. The decreased heat transfer rate may result in incomplete removal of liquid so that some droplets are still sticky when they encounter the wall of the spray chamber, resulting in clinging to the walls, and to each other. The resultant buildup of solids may soon require the operation to be shut down for cleanup.

It is an object of the present invention to provide an improved method and apparatus for spray drying materials that are otherwise difficult to spray dry. It is a fur ther object of the present invention to provide a method for spray drying which limits solids buildup on the walls of the spray chamber. It is a particular object of the present invention to provide an improved method for preparing a dry topping mix which may be used to provide a whipped topping.

These and other objects will become more readily apparent from the following disclosure and the accompanying drawing, comprising a flow sheet which also schematically illustrates apparatus suitable for the practice of the present invention.

Generally, and with particular reference to the drawing, there is provided a spray drying unit 11 comprising a spray chamber 13, hot air supply means 15, liquid dispersion supply means 17, a dry component supply means 19, product discharge means 21, and moist air discharge means 23. In accordance with the present invention, spray 3,414,980 Patented Dec. 10, 1968 drying of a liquid dispersion is improved by introduction of a dry component into the spray chamber 13 of the drying unit 11 to provide substantial economies in equipment investment and in operating costs. The spray drying unit 11 is particularly adapted for providing a dry topping mix which may be used to provide a whipped topping for desserts or like food products.

The spray chamber 13 comprises a generally cylindrical body portion 25, a circular cover 27 and a frusto-conical lower portion 29, all suitably joined to define the chamber 13. The particular configuration of the chamber 13 may be varied in accordance with conventional practice without departing from the scope of the present invention.

The drying unit 11 further includes a hot air supply means 15 through which air is drawn into chamber 13. The air supply means 15 includes a duct 16 which opens tangentially into the side of chamber 13 at the top of the cylindrical body portion 25. A heater 33 is provided to maintain the air drawn into chamber 13 at a selected temperature. The tangential introduction of the air into chamber 13 directs the flow of the hot air in a generally helical pattern around the inner wall. Other suitable means for providing a helical flow of hot air may also be used, such as a centrally located non-tangential hot air opening in combination with deflector baffles.

Drying unit 11 further includes cold air ducts 35 through which a regulated level of cold air may be introduced into the chamber 13 during the drying process.

The liquid dispersion distribution assembly 17 includes a liquid dispersion reservoir 37 and a pump 39 by means of which there is continuously made available a pressurized supply of the liquid dispersion to be processed. The liquid dispersion enters chamber 13 through a liquid dispersion feed conduit 41 which is in fluid communication with reservoir 37 and pump 39. A spraying mechanism 43 is secured to the end of conduit 41 in chamber 13. The spraying mechanism 43 may be of any conventional configuration, such as a spray nozzle or a centrifugal atomizer.

The moist air discharge assembly 23 provides means for removing dried particles which are entrained in the moist discharge air. The assembly 23 includes a moist air duct 45, and a cyclone separator 47 in fluid communication therewith. Moist air and entrained dry particles may thereby be conducted out of the chamber 13 and to the cyclone separator 47 wherein such dry particles are recovered from the air by centrifugal force. The cyclone separator includes a dry particle discharge port 49, through which dry particles may be recovered and utilized, a moist air discharge duct 53 connected to blower 31 through which moist exhaust air (depleted of dry particles) is discharged.

In accordance with the present invention, a dry component or components of the desired final dry product is introduced into chamber 13 so as to form an admixture with the components of the liquid dispersion, which are in droplet form. To provide optimum conditions for admixture of the dry component or components with the liquid dispersion droplets it is preferred to introduce the dry component into spray chamber 15 in a manner so as to provide a helical flow pattern.

To this end, a dry component distribution assembly 19 is provided. The assembly 19 comprises a hopper 55, a feeder 57, and a conduit 59. The feeder 57 includes means (not illustrated) to regulate the rate of flow of the dry component to provide the desired level of such component in the final product. The hopper 55 is connected with the conduit 59. The dry component distribution assembly 19 is adapted to controllably meter a desired level of a dry component from the hopper 55 by means of the feeder 57 and thence into the conduit 59.

The conduit 59 extends through the cylindrical wall 25 of the dryer 11 and into the chamber 13 in a manner so as to provide a helical flow pattern. The location of conduit 59 is not critical and the conduit 59 may extend through the wall of the dryer at any convenient location. As shown in the drawing, one suitable location for conduit 59 is through cold air duct 35. The desired helical flow pattern may be provided by locating the opening of conduit 59 in a tangential relation to the walls of spray chamber 13 or by suitable bafiiing means.

Compressed air from an external blower or other source (not illustrated) may be supplied to the conduit 59 so that the dry component from the feed hopper is entrained in the air stream in the conduit 59. Alternatively, since dryer 11 is under a slight negative pressure, the dry component may be drawn by such vacuum directly into chamber 13, if hopper 55 is located in close proximity to cold air duct 35.

The product discharge means 21 comprises a chute 61 which communicates with the frusto-conical portion 29 of the chamber 13. Discharge means 21 further comprise a pair of gates 63 which are slidably received in the chute 61, and a screw conveyor 65, through which the dried product is discharged for further processing, such as packaging (not illustrated). Gates 63 comprise a two door dump port and are alternately opened and closed by a cam (not illustrated), to maintain a seal between conveyor 65 and the chamber 13. A similar arrangement 49 is provided for removal of dried particles from the cyclone separator 47. Such an arrangement is well known in the art.

In accordance with the method of the present invention, a flow of hot, low-humidity air is established into the chamber 13 through the hot air supply duct 16, by means of blower 31. A controlled flow of a dry component of the desired final dry product is established from the hopper 55 through the conduit 59. A controlled flow of the liquid dispersion containing the balance of the components of the desired final dry product is established through the spray nozzle 43, to provide a spray of atomized droplets expanding outwardly toward the walls of the chamber 13. In accordance with known spray drying technology, there is thereby obtained rapid evaporation of liquid from the droplets.

In accordance with the present invention, the dry component introduced through conduit 59 in a manner so as to be swept in a helical pattern around the inside periphery of the chamber 13 is subsequently mixed with partially dried particles from the atomized liquid dispersion.

The resulting mixture of components are further dried as they are swirled downwardly in the chamber 13 and into the chute 61 of the product discharge means 21. They are thereafter removed by the screw conveyor 65 for subsequent processing.

The air, containing vapor transferred to it from the liquid dispersion and some entrained dry product particles, 1

passes through the moist air duct 45 and into the cyclone separator 47. The dry product particles recovered from the air are discharged from the bottom of the cyclone separator 47 through the discharge port 49, and the moist air is discharged through the exhaust port 53. The recovered dry product from the cyclone separator may then be combined with the bulk of the dry product obtained from the product discharge means 21.

A particular advantage of the present invention over a conventional spray-drying technique is that the dry component, which is introduced tangentially at or near the inner wall of the drying chamber 13 through the conduit 59, is swirled in a helical pattern around the inner wall. This provides a sheet or curtain of dry particles adjacent the inner wall which prevents partially dried (and therefore sticky) atomized droplets of liquid dispersion from reaching and adhering to the walls of the chamber. This fact makes it possible to operate the spray dryer continuously for periods of time far in excess of conventional spray dryers without requiring cessation of operations for cleanup.

A further advantage of the spra -drying technique of the present invention is that the dry component added through conduit 59 is subtracted from the total solids level of the liquid dispersion. This, in effect, permits the spraydrying technique to be used to provide final dried products containing levels of components which would be extremely diflicult to form into liquid dispersions with overall levels of solids suitable for spray drying. The addition of part of the desired final level of components as a dry component in the spray dry process also operates, in effect, to increase the efficiency and lower the operating costs by reducing the total amount of moisture which must be evaporated.

The practice of the present invention is particularly adapted for producing dry topping mixes which have high levels of fat and sugar and which have properties similar to sweetened whipped cream after they are mixed with milk or water. A typical composition for a dry topping mix in powder form has from 32 to 38 percent fat, 30 to 50 percent sweetening agents, to percent caseinates and 5 to 10 percent of emulsifiers. All percentages are by weight of dry mix. These compositions may generally be prepared by forming a liquid dispersion or emulsion of the components and subsequently spray drying the emulsion to provide a powdered topping mix.

The total amount of sweetening agent in a dry topping mix varies according to taste but is generally from about percent to about percent by weight of the dry topping mix. When spray drying topping mixes with relatively high levels of sweetening agents, e.g., from above about 35 percent by weight of the dry topping mix of sweetening agent, problems of sticking or clinging to the walls of the drying chamber are encountered. In accordance with the present invention, these and other problems may be overcome by providing a liquid dispersion comprising a portion of the total amount of desired sweetening agent. The liquid dispersion is then sprayed into a suitable chamber to provide moist droplets which are subsequently dried in their passage through the chamber. The remaining portion of the total amount of desired sweetening agent is then added to the chamber as a substantially dry component and mixed with partially dried droplets of the liquid dry dispersion.

It is preferred to add at least about 5 percent by weight of the total desired level of sweetening agent as a substantially dry component during spray drying of a liquid dispersion containing the balance of the sweetening agent. A sugar, preferably sucrose, is generally the sweetening agent used in topping mixes. However, other carbohydrate sweetening agents, such as corn syrup solids (dextrose) and lactose may also be used.

Any suitable method may be used for providing the liquid dispersion. One suitable method is to dissolve the water-soluble components of the topping mix in the desired level of Water. Water is generally used at levels of from about percent to about 120 percent by weight of the topping mix components, preferably about percent. The oil-soluble components of the topping mix, such as the emulsifiers and the fat, are melted and blended and the blend is slowly added to the aqueous solution with vigorous agitation. A stable liquid dispersion is subsequently formed by passing the mixture through a one or two stage homogenizer.

The emulsifiers used in the dry topping mix may be any which are known in the dry topping mix art, such as partial glycerol esters, lactylated glycerol esters, partial glycol esters or combinations of these.

The following examples further illustrate various features of the present invention but are intended to in no way limit the scope of the invention which is defined in the appended claims.

EXAMPLE I A liquid dispersion of components for producing a dry topping mix was prepared containing the following ingredients.

Ingredient: Weight percent Hydrogenated cocoan-ut oil 27.4 Sugar 20.0 Corn syrup solids 8.4 Sodium caseinate 4.2

Emulsifier 7.5 Coloring 0.0002 Flavoring 0.18 Water 30.0

This liquid dispersion was placed in the liquid dispersion reservoir 37 of the spray drying system heretofore described. The liquid dispersion was transferred by pump 39 to the spray nozzle 43 where it is atomized in the chamber 13. Hot, dry air was drawn through the duct 16 into chamber 13 by the blower 31 to dry the atomized droplets of the liquid dispersion.

Concurrently with the atomization and drying of the liquid dispersion, dry granular sugar was metered from the hopper 55 at a rate so as to provide 16.5 percent by weight of the total sweetening agent in the dry topping mix. The dry granular sugar was transferred to the drying chamber 13 through conduit 59 by compressed air at 45 p.s.i.g.

The dryer was operated continuously for six hours to produce 2,570 pounds of a dry topping composition containing 48.7 percent sugar. There was no indication of product buildup or sticking to any of the interior surfaces of the chamber 13 after 5% hours of operation.

EXAMPLE II A dry topping mix was prepared in accordance with Example I except that dry granular sugar was metered at a rate so as to provide 80 percent by weight of the total sweetening agent in the dry topping mix. The dry topping mix contained 43.8 percent by weight of total sweetening agent. There was no indication of product buildup or sticking to any of the interior surfaces of the chamber 13 after five hours of operation.

EXAMPLE III A dry topping mix was prepared in accordance with Example I except that dry granular sugar was metered at a rate so as to provide six percent by weight of the total sugar in the dry topping mix. The dry topping mix contained 42.4 percent by weight of total sugar. There was no indication of product buildup or sticking to any of the interior surfaces of the chamber 13 after three hours of operation.

EXAMPLE IV A dry topping mix was prepared in accordance with Example I except that all the sugar was included in the liquid dispersion. During spray drying, product sticking was severe and operation of the dryer had to be halted afte /4. hour of operation.

Various modifications of the subject matter of the pres ent invention will become apparent to those skilled in th art from the detailed description given herein. It 81101114 be understood that this invention is to be limited onl in accordance with the appended claims.

I claim:

1. A process for preparing a dry topping mix whicl comprises in combination the steps of mixing the desiret ingredients including a portion of the total amount 0 the sweetening agent to form a liquid dispersion, spray ing said liquid dispersion into a drying chamber, intro ducing the remaining portion of the sweetening agent ii a substantially dry state into said drying chamber result ing in admixture of said sprayed liquid dispersion ant said remaining portion of said sweetening agent and dry ing said admixture to provide a dry homogeneous topping composition.

2. The process of claim 1 wherein a major amount 0 said sweetening agent is sucrose.

3. The process of claim 1 'wherein the portion of th sweetening agent that is added in a substantially dry statt to the drying chamber is at least about five percent by weight of the total amount of sweetening agent in tht dry topping mix.

4. A process for preparing a dry composition by spray drying which comprises the steps of providing a dispersior of a first mix in a fluid, spraying said dispersion into a drying chamber to provide substantially dry particles 0: said first mix, introducing a substantially dry second mi) into said drying chamber, said substantially dry secont mix being introduced in a manner so that it is swirlec around the periphery of said drying chamber, said addi tion of said substantially dry second mix resulting in ad mixture with said substantially dry first mix and furthe1 drying said admixture within said drying chamber to pro vide a dry homogeneous composition, said addition 0: said substantially dry second mix further providing a cor tain of particles around the periphery of said drying chamber so as to prevent particle build-up on the walls 0: said chamber.

'5. A process in accordance with claim 4 wherein a dry topping mix is prepared.

References Cited UNITED STATES PATENTS 2,077,819 4/1937 Zizinia 34-5.

2,088,606 8/1937 Peebles et a1 34-5'.

2,297,726 10/1942 Stephanofli 341( JOHN J. CAMBY, Acting Primary Examiner.

US. Cl. X.R.