US3039107A - Agglomeration of spray-dried materials - Google Patents

Description

June 12, 1962 P. BRADFORD AGGLOMERATION OF SPRAY-DRIED MATERIALS Filed March 10, 1961 L/PDYZBPADFOPD I N V EN TOR.

United States Patent 3,039,107 AGGLOMERATION 0F SPRAY-DRIED MATERIALS Purdy Bradford, Palos Park, 111., assignor to Swift & Company, Chicago, Ill., a corporation of Illinois Filed Mar. 10, 1961, Ser. No. 94,943 Claims. (Cl. 159-48) This invention relates generally to a method for preparing heat sensitive materials in a dry form, and more particularly, to a method whereby heat-sensitive materials in a dry particulate form, well adapted to reconstitution with a liquid, may be prepared.

This application is a continuation-in-part of my prior co-pending application Serial No. 696,281, now abandoned, filed November 13, 1957.

Spray-drying procedures,such as are disclosed in copending application Serial No. 572,575, filed March 19, 1956, by E. W. Comings et al., are particularly well adapted to the drying of heat-sensitive materials because the danger of heat damage to the product in spray drying is small. In accordance with such spray-drying processes,

the material to be dried is converted to an atomized form v and brought into contact with a drying gas in-a highly turbulent action. Atomization produces an extremely small particle size of the material being dried, thus insuring that a large area of the materialbeing dried is exposed to the drying gases. This small particle size, coupled with the high temperature and high velocity of the gas stream in the dryer, provides almost instantaneous drying of the particles. A particular advantage in this type of drying lies in the very short residence time of the medium in the area of high temperature necessary to produce a dried product. Also, recirculation of dried product and repeated exposure of the particles to high temperatures is avoided.

Although extremely small particle size is necessary in spray-drying procedures, this small particle size represents a disadvantage in the subsequent collection of the dried product, and also presents a solubility problem where the dried materials are intended for later reconstitution with water or some other liquid. Because of the small particle size, spray-dried materials are not readily soluble in liquids because of the entrapped air surrounding individual particles.

It is therefore an object of this invention to provide. a method for drying heat-sensitive materials in a form having physical characteristics well adapted to easy collection of the material.

A further object of the invention is the provision of a method whereby heat-sensitive materials may be dried and agglomerated to produce dried particles having an improved adaptability to reconstitution with liquids.

Additional objects, it not specifically set forth herein, will be readily apparent from the detailed description which follows. 7

In accordance with the method of this invention, a solution or suspension of the heat-sensitive material is atomized to produce a minimum particle size of the liquid and entrained solids. Atomization is achieved by discharging the solution or suspension into a co-current heated stream of drying gas in a zone of substantial turbulence, where dispersion and volatilization of the liquid medium take place. Additional co-current air at an elevated temperature and high velocity from a secondary air source en velops the atomized particles and serves to dilute the volatilized material, and aid in the removal of this volatilized material from the system. This secondary air source also prevents recycling of the dried product through the primary air stream, thus avoiding the deleterious effects which the higher temperature of the primary air stream would have on heat-sensitive materials if these materials are held at a high temperature for an extendec period of time. The substantially moisture-free particles are then conducted in the gaseous suspending stream intc a zone having a tapering conical section to a constrictec area where the stream of particles contacts c'o-currentl sprayed droplets of additional liquid. The additions liquid may be asubstance other than the first mentionec solution. For instance, such additional liquid may b: water. However, a quantity of the heat-sensitive materia? in the form of a solution or suspension may be advan tageously used for this purpose.

Because of the high velocity of the gaseous stream containing dried particles and the relatively low velocity 01 the droplets, the dry particles tend to impinge upon and collect on the surface of the droplets of additional liquid. forming large clusters or agglomerates of the product The agglomerated particles are conveyed in the gaseous stream into an area of expanding cross section, where ad ditional evaporation takes place. The dried agglomerated product is then conveyed to a liquid-gas separator for collection of the product.

It is fundamental to my invention that each of the various streams of 'gas and liquid are directed in substantially the same rectilinear direction. Thus, the term co-current used herein is intended to mean only rectilinear concurrency wherein there is no substantial additional component of motion in a different direction, such as would be experienced in vortical flow. However, it is intended that the term does embrace the movement of an expanding spray as it leaves a nozzle which is aimed concurrently with the other flow, and flow which is being compressed or expanded due to variations in the cross sectional area, of the ilow passageway, in a plane perpendicular to the direction of flow.

A further understanding of the invention can be had by reference to the detailed description taken in conjunction with the accompanying drawing.

The single FIGURE is a schematic drawing showing one embodiment of equipment well suited to the practice of this invention.

In the drawing a feed tank 10, equipped with a mechanical stirrer if desired, comprises a reservoir of the solution or suspension from which the dried material is to be produced. The liquid is conductedjto the drying area from the feed tank by means of a liquid pump 11 through a conduit 12 to an injector 13. A primary air blower l4 capable of delivering air at the rate of about 11,000 c.f.m. moves air through a heater such as a gas burner or electric heater generally 16 through conduit 17 to a nozzle inlet 18 in a nozzle 19 which surrounds the injector. The temperature of the gas leaving the primary air heater may be regulated in the range 4-()()800 F.

Secondary air is provided by means of a secondary air blower 21, and the air is passed through conduit 22 into a secondary air heater 23. The secondary air heater may be heated by means of steam from a source, not shown, passing through steam inlet 24 and outlet 25. From the secondary air heater the air is conducted through conduit 26 to a secondary air inlet 27 on a tubular dryer generally 30. The output end of the tubular dryer housing is connected to a tapering conical section 43, forming an injection zone the cross section of which is at a minimum at 32. Connected to said tapering conical section is an additional conical section 33, the walls of which gradually diverge to form a cross-sectional area of increasing size. Conical section 33 is connected to the input end of a gassolid separator such as a cyclone collector 34, equipped with appropriate vents as at 35 and a take-off valve 36. The dried particulate material is collected in a container 37.

A second source of the solution or suspension is conveyed through conduit 40 to a secondary liquid pump 3 which conveys the liquid through a conduct 42 to throat 32 of the Venturi structure. A nozzle 31 is 'ided for distribution of the liquid particles. The ndary liquidstream may be introduced into the drier flow rate in the range of 10-100 gallons per hour. or installations not utilizing the solution of heat sensimaterial as the additional liquid for agglomerating roses, it will be obvious that the conduit 40 will not onnected to the feed tank 10. Instead the secondary Id pump 41 is connected by an appropriate conduit source (not shown) of such additional liquid as be required; for example the pump 41 may be coned to a tank of water. Under the latter circum- :e the feed rate of the secondary liquid does not difier tantially from that set forth for a second quantity 1e spray-dried solution. operation, the liquid solution or suspension is pumped l the feed tank to the injector under a pressure rangfrom about to 60 p.s.i. Atomizing air from the my air source envelops the liquid particles as they nate from the injector. The primary air has a vey of 600 to 1300 feet per second and a temperature bout 750 F. at the nozzle exit. As the primary air the liquid meet, the latter is dispersed very finely to 1 droplets of below about 40 microns mean diameter ng dissolved or entrained solids. The heated, high vey air suspension of the droplets is conducted into the I of the tubular dryer. The secondary air stream, 1h moves at a lower velocity than the primary air rm and is at a lower temperature, surrounds the priair jet, preventing recycling of the dried product picking up the vapor evaporated from the feed. The ndary air stream is forced into the dryer at the rate bout 60,000 c.f.m. and is maintained at a temperaof about 70-160" F. The turbulence and high temture of the primary air stream rapidly dries the small .eles while the secondary air stream serves to dilute moisture evaporated from the feed and to carry the arsed particles. The high initial temperature of the iary air stream is rapidly reduced by evaporation of r from the feed. The rate of evaporation and then ate of temperature decrease is a function of the priair velocity at the nozzle. to pressure of the commingled primary and secondary treams provides the impetus for the discharge of this m into the gradually decreasing cross-sectional area 1c discharge end of the dryer and into the throat of Venturi structure. At this point, the dried particles, ng a mean diameter in the range of about 5 microns, dc with and impinge upon droplets of the fluid medium hating from a nozzle or spray located in the throat. velocity of the stream of dried particles passing into Venturi throat ranges from about 200-800 feet per nd, and preferably 300-600 feet per second, while temperature is about 120-180 F. Because of the differential velocity between the liquid droplets and 'apidly moving gaseous stream of dried particles, the d is broken down into droplets having a mean diamef from -100 microns. The dried particles ime the fluid droplets, and an agglomeration or building if the particle size of the droplets to from about 1000 microns average mean diameter is effected. irther evaporation of liquid is realized as the aglerated particles are conveyed by means of the gas vm through the gradually expanding portion of the .uri structure. The temperature of the air stream 1g this final drying is reduced to about 100-160 F., exact temperature depending, of course, on the size re dryer, the velocity of the drying air, and the resie time of the agglomerated particles in the dryer. adjustment of these conditions is within the ability ne skilled in the art. The dried agglomerated partiare collected in a cyclone collector, a bag house or r suitable gas-solids separator. In the embodiment rated in the drawing, a cyclone collector is shown.

4 Air containing moisture is discharged through vents, and the dried particles are removed at the base of the collector.

The following example, which is included herewith for purposes of illustration, demonstrates the drying and agglomeration of milk particles in a system such as is disclosed herein, and also shows the effect of the air velocity at the throat of the Venturi agglomerator on the size of the drops produced by the agglomeration spray.

Example I Whole milk was atomized by breaking the liquid up into a fine spray or fog into a primary air stream having an initial velocity of 1000 feet per second. and a total volume, when mixed with the secondary air stream, of 12,000 cubic feet per gallon of milk atomized at the entrance of the dryer. An agglomerating spray of whole milk was introduced at varying velocities at the throat of the Venturi structure, and the resulting drop size of the agglomerating spray was noted. The percent agglomerating spray based on the weight of the whole milk introduced into the dryer was determined. The following table is a correlation between velocity of the agglomerating spray and the amount of agglomerating spray ncccs sary to produce a given drop size:

Agglomcratlng Drop Size of Pei-cont Venturi 'lhrout Agglomerating glomeration Velocity, it. Spray (Alter Spray [toper second impingement), quired microns Further work indicates that as much as 5% agglomerating spray could be employed to produce dried particles of a satisfactory size and constitution. As the stream carrying dried particles enters the throat of the Venturi structure, the velocity of the stream increases, and at this time the stream intersects and impinges upon the liquid curtain emanating from the secondary liquid source.

It can be readily appreciated that a method is provided herein whereby highly heat-sensitive materials may be treated in a complete drying and agglomeration procedure with no deterioration of the material. Typical materials which may be dried and agglomerated in accordance with the method of this invention are such products as milk, egg whites, egg yolks,,whole eggs, orange juice, coffee, enzyme extracts and heat-sensitive biological materials. 1

Obviously, many variations and modifications of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A method for producing a dried product in particulate form of a size and density adapted to improved rcconstitution with a liquid which comprises: dispersing a product contained in a liquid carrier co-currently into a heated high velocity primary air stream, said primary air stream being of sutlicicnt mass and velocity to formdroplets of said product and carrier having a mean diameter of below about 40 microns, said primary air stream also containing sufiicient heat to .form dry particles from all of said droplets; co-currently delivering a secondary air stream of relatively cooler air surrounding said primary air stream to absorb moisture evaporated from the droplets and to dilute said primary air after said particles are formed, said sccondary air stream being of suflicient mass and velocity to prevent said particles from being recycled to the hot primary air stream; converging the total flow of said primary and secondary air streams and said partotal flow a spray of an additional liquid directed substantially co-currently with said flow whereby said dry particles will agglomerate with droplets of said liquid spray to form larger relatively dry particles.

2. The method of claim 1 wherein the larger, agglomerated particles are subjected to further drying by expanding said total flow so as to promote further drying of said larger particles.

3. The method of claim 1 wherein the injected spray comprises up to about 5 percent of the quantity of said product in said liquid carrier dispersed in said primary air stream.

4. The method of claim 1 wherein the spray of an additional liquid consists of water.

5. The method of claim 4 wherein the product dried is a food material. f

6. A. method for producing a dried food product in particulate form of a size and density adapted to improved reconstitution with a liquid which comprises: dispersing a food product contained in a liquid carrier cocurrently into a heated high velocity primary air stream, said primary air stream being of sufiicient mass and velocity to form droplets of said food product and carrier having a mean diameter of below about 40 microns, said primary air stream also containing sufiicient heat to form dry particles from all of said'droplets; co-currently delivering a secondary air stream of relatively cooler air surrounding said primary air stream to absorb moisture evaporated from the droplets and to dilute said primary air after said particles are formed, said secondary air stream being of suflicient mass and velocity to prevent said particles from being recycled to the hot primary air stream; converging the total flow of said primary and secondary air streams and said particles carried thereby; and injecting into said converging total flow a spray of an additional quantity of said food product in said liquid carrier directed substantially co-currently with said flow whereby said dry particles will agglomerate with droplets of said liquid spray to form larger relatively dry particles. t

7. The method of claim 6, wherein the larger agglomerated particles are subjected to further drying by expanding said total flow so as to promote further drying of said larger particles.

8. The method of claim 6, wherein the injected spray comprises up to about 5 percent of the quantity of said food product in said liquid carrier dispersed in said primary air stream.

9. A method for producing a dried mill; product in particulate form of a size and density adapted to improved reconstitution with water which comprises: dispersing liquid milk cocurrently into a heated high velocity primary air stream, said primary air stream being of sufficient mass and velocity to form droplets of said milk having a mean diameter of about below 40 microns. said primary air stream also containing sufiicient heat to form dry milk particles from all of said droplets; co-currently delivering a secondary air stream to absorb moisture evaporated from the droplets and to dilute said primary air after said particles are formed, said secondary air stream being of sutficient mass and velocity to prevent said particles from being recycled to the hot primary air stream; converging the total flow of said primary and secondary air streams and said dried'milk particles carried thereby; and injecting into said converging total flow a substantially co-current spray of relatively coarse droplets of said liquid milk, said injected spray constituting up to about 5 percent by weight of the total liquid milk processed, whereby said dried particles will agglomerate with said relatively coarse droplets to form larger rela tively dry milk particles.

10. The method of claim ,9, wherein the larger agglomerated particles are subjected to further drying by expanding the total flow of said air streams beyond the point at which said coarse spray is injected.

References Cited in the file of this patent UNITED STATES PATENTS Barzelay May 20, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent. No. 3,039,107 June 12 1962 Purdy Bradiord It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Paterit should read as corrected below.

Column 6, line 13, for "about below! read below about,

Signed and sealed this 9th day of October 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

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