US2634808A

US2634808A - Apparatus and method for spray drying and cooling

Info

Publication number: US2634808A
Application number: US496574A
Authority: US
Inventors: Gerald D Arnold
Original assignee: Individual
Current assignee: Individual
Priority date: 1943-07-29
Filing date: 1943-07-29
Publication date: 1953-04-14
Anticipated expiration: 1970-04-14

Description

INVENTORW Gee/41.0 D. Hen/040 1M, AMvAir/Ju ATTOQNEYS.

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APPARATUS AND METHOD FOR SPRAY DRYINGAND COOLING April 14, 1953 Patented Apr. 14, 1953 APPARATUS AND METHOD FOR SPRAY DRYING AND COOLING Gerald D. Arnold, Wauwatosa, Wis.

Application July 29, 1943, Serial No. 496,574

15 Claims.

This invention relates to improvements in apparatus and methods for spray-drying and cooling.

It is the primary object of the invention to provide'novel and improved means for spray drying and, particularly, to associate such means with means for immediately cooling the dried product. It is my purpose to dry the material in a pneumatic convection current of dry hot gas and to separate the dried product from the drying gases in the same chamber and the same vortex in which drying is effected.

It is a further object of the invention to provide a method of drying and cooling whereby the cooling may be eiiected in a continuously recirculated stream of fluid refrigerant which is recooled in such circuit, the dehydration of the product precluding the dust-like product from adhering to the cooling coils.

Other objects of the invention will be made apparent to those skilled in the art upon analysis of the following disclosure.

In the drawings:

Fig. 1 is a view partially in side elevation and partially in vertical section diagrammatically illustratin a drying and coolin um't embodying the invention.

Fig.2 is a view taken in section on line 22 of Fig. 1.

Fig. 3 is a view taken in section on the line 3-3 ofFig. 1.

Fig. 4 is an enlargement detail fragmentarily illustrating this position of the spray nozzle used in the dehydrating section of the apparatus.

Fig. 5 is an enlarged detail showing in section a portion of cooling coils used in the cooling section of the apparatus.

Fig. 6 is a fragmentary detail of a modified conveyor arrangement illustrated partly insection and partly in side elevation.

Like parts are designated by the same reference characters throughout the several views.

The drying and separating chamber 1 has a volute air inlet at 8 for the drying gas. Such gas is usually heated before its admission and the pipe 8 may therefore be understood to communicate with a heater or furnace (not shown).

As the arc of the inlet 8 approaches the cylindrical upper wall 9 of the drying chamber, it is also inclined helically downwardly, its downward pitch being approximately equal in one revolution to its thickness so that the air current delivered to the chamber 1 will tend to pass in one revolution beneath the current of gas newly admitted. This minimizes eddies in the chamber.

Below the cylindrical portion 9 of the separating and drying chamber, there is a frustov-conical section II) leading to a delivery section II which has a helically pitched undercut shoulder at l2 which acts like a screw upon the rotatin solids to advance them axially of the chamber toward its discharge port l4.

The chamber is provided at IS with a discharge sleeve for the gases. This communicates by means of boot [6 with the inlet to a blower casing 11. The tangential outlet l8 from the blower is preferably arranged to permit the runner of the blower to rotate in a direction opposite to that in which the gases and dried material rotate in the vortex formed in the separator I. Assuming the vortex in the drying and separating chamber to rotate counterclockwise as viewed, in Fig. 2 the disposition of the tangential outlet [8 will be such that the rotation of gases in the blower chamber l'l will be clockwise. This construction is preferred for reasons of sanitation, since thereby all baflles on which material might accumulate are omitted. However, it is not essential to the invention. When this feature is used, it will be understood that the vortex in the cyclone may be in etiher direction as long as the vortex in the fan is opposite.

Surrounding the discharge sleeve 15 for the gases is a wall l9 providing an annular well at 20 for a set of spray apertures 23 opposite the respective nozzles 2|. The pipes 22 leading to the several nozzles may be connected by a header 24 supplied with the material to be dried through pipe 25 from a high pressure pump such as gear pump 26. Such material is usually preheated and concentrated and strained, but the 1 inventor is not concerned with this preliminary treatment. The annular well at 20 in which the several nozzles are disposed is open at its top to permit the nozzles and their associated header to be lifted as a unit for cleaning or inspection of the nozzles. It preferably, however, is provided with a cover 200 tightly fitted about pipes 22 to I prevent atmospheric air from reaching thechamber 1 through the well 20- and apertures 23. The nozzles and the respective apertures 23 through which their spray is directed are preferably arranged upon a helical path corresponding in pitch to the helical path followed by the current of gases admitted through the conduit,

The.

8 to the drying and separating chamber. stream of drying gas is held centrifugally to the cylindrical wall portion 9 of the chamber 1 in the path or the spray discharged from the several nozzles 2! so that none of the atomized mapelled from the separator while the gas, turning.

at this point to escape through outlet sleeve !5, will be substantially free of the dried material.

To minimize the velocity of the air at the point where it leaves the separating chamber, thereby minimizing the amount of dried product "which Will be carried out of the chamber with the air, I employ the principle of rotating the gases in the fan casing in a direction which is reverseto their direction of rotation in the separating chamber, as-above explained. I have found that the clockwisevortex in the fan'chamber will'be com municated downwardly from the fancasing inlet 'until-it interactswith the counterclockwise vortex in the separating chamber. At this point of interaction, which willusually occur immediately below the flared inlet 2 to: the discharge sleeve. l5, the rotative= velocityof the gases will be: substantially eliminated and. the gases will have'.only avertical or axial velocity which will not-normally be enough to' liftdust' from the separator.

However, .inasmuch as spray-dried material is frequently of considerable value, I preferto em ploya. second stage; of; separation .forremoving from. the drying gases the last: vestige of' dust;

The separator 30 in which the second stage separation occurs receives tangentially the discharge from blowerv I'l. It .has av discharge. sleeve. at 31 which'may open at 32 toouterair. Around the sleeve:3l is..a .sleeve33 whichmayrecirculate. some of the .gases. and. dust in themanner disclosedin my: Patent Ser. No. 466,576, filed November. 23, 1942,,now abandoned .entitled Gene triiugal Separators.

Thesolidsare: delivered through discharge end 34 of the secondary separatorin: the manner already described and, through pip 35, they reach'a conveyor. tube 36. intowhich theiirst separator also discharges.

A screw conveyor comprising threesectionsjil,

38 and 39 operates inttube 36. Thesectionsare,

continuous, each with the other, save where interrupted by transverse bafiles 40 and 41 which close approximately the upper half of the conveyor tube 36'between the respective conveyor sections. When the material dehydrated is being supplied from the separators in sufiicient quantity to substantially fill the tube 36, such material will be passed virtually without interruption from one conveyor section to another. However, when the material is inadequate to fill the tube, then the gap between conveyor sections will tend to allow a.-certain.residuum of material to remain between .sections where it willcooperate with the bafile. to form aseal precluding any transferof air or. othergas from one section to the other.

The purpose of this arrangement is to insure.

thesealingofthe conveyor tube to. preclude the mixing. of .the .hot, humid air used for dehydration vwiththe chilled, gas later. used for cooling thematerial- Al1.of the material, whether derived from the dehydrator-separator. 'l or. the secondary separator- 30, passesthrough theconveyor tube 36 into pipe 43 which is in a closed refrigeration circuit which includes cooler separator 45, fan casing 46, and refrigerator casing 41. The cooler separator 45 is preferably substantially identical with the separator shown at 3B. The cooling gas set in motion in the fan casing 46 circulates through the closed system with sufficient velocity to entrain the material delivered into pipe 43 and to project such material tangentially into cooler separator 45 with sufficient velocity for the centrifugal separation of the solids from the gas. The solids are discharged through the rotary valve at into a barrel or other container 49. while the gases pass upwardly through the gas return pipe 50 to the eye of th fan casing 46. Since the gases rotate counterclockwise in cooler separator; the fan casing 46 is preferably arranged for clockwise circulation so that the vortexcommunicated downwardly from the fan into the separator will oppose and tend to neutralize at some. point within: the'sseparator the vortex established therein,- thus minimizingthe amount of material which will be carrie'd'upewardly from'cooler separator "45* with the gases.

However, this is relatively immaterialain the cooling section of thedevice for: the reason .that': the closed circuit for. refrigerating gases: pres-- cludesany 'lossof material provided the material 1 has been dehydrated sufficiently andxprovided. further that; theico'oling-coils55 inztheechame" ber' 41 have sufiicienttareaiand operate .atlsuchl temperatures as not. to; coolth'e refrigerating.

gasesibelow the .dew point;

Under such: conditions thedust like. material.

carriedv with the circulating gases :fromtheicooleri separator'45 and passing through-the fan-case:

ing 46 will not adhere to the 700113155 butwill. pass through such coils withgthelgaseous current. and be returned to the separator and commingled.

with the material newly arriving; through conveyor tube 36.-

The coils themselveswill preferably be designed 1 in such a way as to minimize any, tendency?- for adherence of dust thereto; The refrigerant supplied from compressor 56 through radiator; 51 preferably passes'through pipes58 (Fig.5) which are arranged in banks or tiers, the several .runs

of pipe. in each tier being, enclosed in ;a common envelope 60 which has smooth wall surfaces joined above'and below-the tier of ,pipesto'form smooth walled passages at 6| through which the-- gaseous coolant and any entrained. dust will pass virtually unimpeded. Thesheaths- 60 .not only 1 serve to protect the.pipesthemselves-from. dust.

accumulation, but they also provide 1 extended heat absorption surfaces for-the coils.

If desired, banks of fin coils may besubstituted as disclosed inmy companion application entitled Closed Hammer Mill Circuits, executed of even date herewith and now Patent No. 2,400,382.

If, notwithstanding, thetendency of the circus-- latinggas to scour the surfaces 60, shouldany dust accumulate thereon, these surfaces may readily be cleaned bymerely opening the,door 62- withwhich the coolingchamber 4'! is provided; Dehydration of the material acted upon inthe apparatus should preferably becarried to such an extent as to reduce themoisture content of.

thematerial below 10%, and preferably as lowas 6%, to avoid raising the humidity of .the cool-s ing gas circulating inthe cooling section of the: The gas circulated for cooling.

apparatus. purposes should not. becooled below- 32 to. 38

degrees.F., and should .becirculated in suflicient 5.. quantity so that the return gas reaching the cooling chamber 41 from the fan should preferably be about 60 degrees. Cooling below 60 degrees F. is not only expensive but tends to cause condensation on the material, undesirably dampening it. Under these conditions the dehydration of the material to the specified moisture content will keep both the material and the dehydrating gas dry even while passing over the refrigerating coils.

Although it is necessary to discharge to the atmosphere the hot humid air used for dehydration, the auxiliary separator of the type disclosed will preclude any substantial loss of the dehydrated material at this point and the operation of the system in accordance with the method above described will prevent the loss of any material whatever in the cooling section. The organization disclosed has the further advantage that it is not only eflicient and economical of material, but it is compact and relatively inexpensive and delivers a high quality of material which would be impossible to achieve but for the immediate cooling following dehydration.

Particularly where the material is a food product it is desirable for the purpose of promoting sanitation, as well as preventing possible fire loss, to incorporate in each of the several separators an obliquely disposed partition or wall such as that shown at 65 in the dehydrator-separator i in Fig. 1. This oblique wall 65 spans the angle between the wall I9 and the top 9 of the dehydrator separator to exclude the material from what would otherwise constitute dead space in which dust collects and cakes in the ordinary separator. The wall 85 should extend far enough to be secured by the current of newly admitted gases to prevent any accumulations thereon.

For many installations it may be desirable for the dryer cyclone l and the auxiliary cyclone 38 to discharge directly into the return conveyor circuit which handles the refrigerating gases. Fig. 6 suggests a possible arrangement of this sort.

The lower end it of cyclone 1 and the pipe 35 from the bottom of cyclone 30, are both shown in Fig. 6 provided with rotary valves 68, 69, operated at a rate to pass all solids but no substantial amount of dehydrating gases. These valves discharge directly into conduit 430 which leads from the cooling chamber 41 to the cooler separator cyclone 45. Thus the screw conveyor is dispensed with and pneumatic convection is substituted, while the humid gases from separators I and 30 are still excluded from the refrigerating gas of the closed circuit which includes cooler separator 45.

While my apparatus and method have been described in detail it may be appropriate to note by way of summary that the drying of the material to the predetermined point mentioned permits the cooling thereof in a closed circuit so that in the entire apparatus there is only one point at which powdered material can possibly escape, that being in the course of the necessary discharge of the saturated drying gases. Both the drying section and the cooling section accomplish a plurality of functions in the respective vortices. In a single vortex in the chamber 1 the material to be dehydrated is dried by the gaseous current in which it is pneumatically conveyed and is concurrently separated centrifugally from such current. In the vortex of the cooling section the material is not only cooled by. the. gaseous current by which itis 6. conveyed, but is simultaneously oentrifugally separated from the. gas of such current- In the drying section dehydration is facilitated by the fact that the blower fan used to establish the vortex maintains the chamber 1 under subatmospheric pressure which reaches a mini-v mum in the central portion of the vortex into which the material to be dehydrated is released by the atomizing nozzles 2|. Under such subatmospheric conditions as exist in the central,- portion of the vortex and in a chamber maintained under subatmospheric pressure by the exhaust fan, dehydration of the atomized material is normally instantaneous.

If, in dealing with certain material, it is de-- sirable to provide a stream of air about the atomizing nozzle to partially relieve the vacuum or to entrain the atomized product, it is only necessary to omit or remove or open the cover 200 for well '20, whereupon air will be admitted through the well to enter the chamber 1 through the apertures 23, along with the atomized spray.

I claim:

l. A dehydrator-separator comprising the combination with a chamber wall of circular cross section provided with a tangential inlet for dehydrating gas, of a gas discharge sleeve centrally located in said chamber and about which a current of dehydrating gas flows in a vortex, means for establishing a pressure differential to induce the creation of a vortex of dehydrating gas, an atomizing nozzle for material to be dehydrated. said nozzle being positioned outwardly radially of said sleeve and directed outwardly toward said chamber wall for delivering atomized material into the vortex of dehydrating gas, said tangential inlet being of substantial radial extent to deliver a moving column of dehydrating gas across the nozzle in a direction transverse to the axis of the vortex, means disposed outside said sleeve for supplying such material to said nozzle under pressure to be atomized by the nozzle, and mechanical means for effecting and controlling the discharge of dehydrated material from the bottom of the chamber, the vortex current of dehydrating gas in said chamber being adapted to effect both the dehydration of the atomized material and the separation of the dehydrated product centrifugally from the current.

2. A drying and separating chamber including a casing of generally circular form having a and provided with an outlet for solids, said casing being provided with a tangential inlet and a centrally disposed outlet sleeve for gases, a wall spaced outside of said sleeve and connected thereto within the casing and forming an annular well between the sleeve and wall, an atomizing nozzle disposed in said well and provided with supply connections for material to be der hydrated, said nozzle being directed outwardly toward said casing into the path of gas admitted thereto from said inlet, and the wall having an aperture for passing the atomized material from the nozzle to the interior of the casing.

3. A device of the character described comprising a drying and separating chamber including a casing with a tangential inlet and a centrally disposed gas outlet sleeve, a wall about said sleeve in spaced relation thereto, the annular space between the wall and sleeve constituting a well, means providing a connection between the wall and sleeve within the casing at the bottom of the well, the wall being provided with. u

aesagsoa:

spaced. apertures; affording-1* communication bestween the well iandithe casing, a set :of atomizing nozzles within:.the.;well registering with the respective I apertures for discharging: a spray of atomized material through the: apertures into thezcasing; a header: provided with connections to theseveral' nozzles for; supplying material thereto; said header and nozzles (being unitarilyt movable axially- With respect tmthecasing for withdrawing the nozzles-from the well.

'4.- A drying and separating chamber comprisin combination; a chambercasing provided with a tangential inlet and a centrally disposed outlet sleeve, a fan and fancasing having an inlet communicatingwith'said sleeve for withdrawing air from-saidcasing and drawing air intothetangential"lnletof said casing to establisha vortex current therein, a; wall about the sleeveand connectedthereto within the casing; saidwall being spaced from the sleeve to constitute-therewith an annular" well about the sleeve; and an atomizing 'nozzle disposeclin said well and adapted to be withdrawn upwardly therefrom, said-nozzle being directed outwardly ofsaid wall into the-path of the'vortex current of dehydrating gasin-thecasing, and the wall hav-- ingan aperture registering with the nozzle for admitting the spray of' the nozzleto the said current; a

Thedevice of c-laim- 4 in which the inlet of the fan--casing 'is= axially aligned-with the sleeve andthe-blowerfancasing "has a tangential outlet providing for vortex rotationin said fan casing in' adirecti'on'opposite to the direction of vortex rotation-in *th'e separator casing.

1 65' The-deviceof -claim 4 in which the chamber casing is provided about' said sleeve and Wall with an' obliquelydisposed' false wall extending to the top' of'thecasing and constituting means for-excluding-dust from the 'top inner portion of thecasing-closest to the gas-outlet sleeve;

72 A-drying'and separating chamber compri's-- ing'the combination with a chamber casing havinga tangential inlet and a central'outlet casing within-the'chamberand an end wallclosing' said and outlets; of means for passing dehydrating gas and entrained 'material from the-outlet of one=ofsaid'separators to'the inlet of the other,

each-of 'said'separators having a discharge outletfor solids; and a conveyor system includinga conduit communicating with the aforesaid outlets for solids-of the respective separators'for receiving-'material from both separators, said conveyorcomprising'aplurality of separate screw sections-in said conduit; and said conduit having-5 partition means extending transversely of its upper portion between conveyor sections whereby to establish a seal in'said conduit, saidpartitionmeans terminating in spacedrelation to thelower portion of theconduit whereby to leave a-passage for: solids.

95 Drying" and' cooling apparatus comprising acentrifugal dehydrator-separator provided with a=-tangential-gas inlet, a central gas outlet and gas-circulating means-for establishing gas flow mtothe :inlet.:and' LOllt" or the outlet forrinducingza vortexaoff dehydrating: gas within the" dehydrator-vseparator between the inlet and outlet, a nozzle arranged to discharge material for de hydration into the .vortex within the dehydratorseparator, said dehydrator separator having a,

discharge port *for material dehydrated and separated'lin the vortex, a refrigerating separator having'a closed. recirculating gaseous circuit exclusive of said dehydrator-separatoraandinclud+ ing a circulating blower, means for delivering the" separated dehydrated material from said discharge port into said closed recirculating gaseous circuit while substantially precluding communication of the recirculating gas in the closed circuit with the dehydrating gas, andmeans for chilling the dehydrated material. in'-- eluding a" refrigerator exposed in said closed circult to gas circulated therein by said blower; aconnection from thedehydrator-separator material-discharge part into said recirculating gaseous circuitfordelivering-into the closed cir cuit of the refrigerating separator solids received from the discharge port of Y the dehydrator-separator for the cooling of said solids in gas circulating in the closed circuit of the'refrigerating separator and the centrifugal discharge of the cool solids from such last mentioned gas in the refrigerating separator, and means controlling thedischarge of solids from" the refrigerating separator;

'10. In a dehydrator the-combination with apair of'cyclone separators'having gas inlets and outlets and means for'passing dehydrating gas and" entrained material from the outlet of one of said separators to the inlet of the other, each of said separators having a discharge outlet for solids, ancl a closed conveyor system exclusive of'said separators and including a tube communicating with the aforesaidsolids outlets of the respective separators for receiving material from both separators, said system comprising a closed pneumatic conveyor meansincorporating said conveyor tube and the respective separator" solids outlets but'isolatedfrom the means for conveying& gas and entrained material betweenseparators, and rotary'means for passing solids to said tube, while excluding gases from passing from-the separatorsto the conveyor means.-

11. A method of' dehydration which includes theestablishment of a vortex of dehydrating gas and the spraying of atomized material from within the vortex" outwardly into the vortexto be conveyed and dehydrated by the gas of thevor= tex andiseparated centrifugally from the vortex": by the energy thereof, the segregation of thedehydrating gas from the solids separated there-- from while changing the direction of rotation of the segregatedgas and the substantiallycontinuous discharge of'both the: gas and the separated solids from the vortex.

12'. The method of dehydration recited in claim 10 in combination with the further method steps, of delivering such solids substantially free of dehydrating gas into a closed circuit of circulating cooling gas, establishing a recirculating flow of cooling gas in the closed circuit, establishing a vortex of cooling gas in the closed circuit, and

entraining the dehydrated solids in the cooling; gas of said vortex to be'simultaneously cooled thereby and centrifugally expelled from said yor tex, and finally withdrawing the'expelled cooled anddehydrated solids'from the last-mentioned vortex.

13; The-"method of cooling which involves; the:

establishment of a current of cooling gas in a closed circuit, establishing a vortex of cooling gas in said closed circuit, delivering finely divided dehydrated material into said cooling gas to be entrained thereby for movement with said gas through said vortex and the discharge of such material independently of the gas from the vortex, substantially all of the cooling of the material, as well as its separation from the gas, being efiected in said vortex.

14. In a combination dehydrator-separator and cooler, in which the material to be dehydrated is introduced into a vortex of dehydrating gas wherein it is simultaneously dehydrated and separated from such gas, the combination with closed circuit connections and a cooling gas therein of means for introducing the resulting dehydrated solid directly into the path of said cooling gas to be entrained thereby, a circulating blower for establishing a high velocity current of said cooling gas through such connections, a refrigerator in the path of the circulating cooling gas for abstracting heat therefrom in the course of its circulation, and a centrifugal separating chamber included in said connections and having a tangential inlet and an axial outlet for said cooling gas and a separate axial outlet for removing the dehydrated cooled solid, said blower maintaining a sufiicient velocity of said cooling gas to efiect separation of the cooled solid from said cooling gas centrifugally in the said chamber while such solid is being cooled by exposure to the refrigerated gas, said separating chamber having means controlling the discharge of solids therefrom independently of said cooling gas in said closed circuit.

15. In a method of dehydrating and cooling, in which dehydration is effected in a gaseous vortex at suflicient velocity to separate the dehydrated material from the dehydrating gas, the steps which comprise establishing cooling gas fiow in a closed circuit in a current with sufiicient velocity to entrain the dehydrated solids, in-

10 troducing said dehydrated solids into said circuit independently of said dehydrating gas to be entrained in the cooling gas current in such circuit, establishing in said circuit a vortex of said cooling gas and entrained solids in which the solids are simultaneously cooled and centrifugally discharged from said current, separating the cooling gas from the solids, refrigerating the cooling gas, whereby to extract from the cooling gas heat derived from the solids previously cooled, and expelling the cooled and dehydrated solids substantially free of the recirculating gas, the recirculating gas being confined in said closed circuit out of contact with said dehydrating gas whereby to avoid condensation of moisture in the latter.

GERALD D. ARNOLD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 999,707 Ellis Aug. 1, 1911 999,972 Ekenberg Aug. 8, 1911 1,215,889 Stutzke Feb. 13, 1917 1,829,477 Douthitt Oct. 27, 1931 1,989,406 Doolittle Jan. 29, 1935 2,076,873 Arnold Apr. 13, 1937 2,118,252 Kraft May 24, 1938 2,132,972 Schmidt Oct. 11, 1938 2,220,186 Walker Nov. 5, 1940 2,230,196 Clayton Jan. 28, 1941 2,314,159 Peebles Mar. 16, 1943 2,326,142 Hall Aug. 10, 1943 2,363,281 Arnold Nov. 21, 1944 2,367,770 Hall Jan. 23, 1945 2,368,699 Arnold Feb. 6, 1945 2,387,458 Majonnier Oct. 23, 1945 FOREIGN PATENTS Number Country Date 15,231/28 Australia Aug. 22, 1928 524,905 France May 23, 1921