US2957519A

US2957519A - Spray drying apparatus and method

Info

Publication number: US2957519A
Application number: US695787A
Authority: US
Inventors: Walker Alexander Marriott
Original assignee: JOHN G HOAD
Current assignee: JOHN G HOAD
Priority date: 1957-11-12
Filing date: 1957-11-12
Publication date: 1960-10-25
Anticipated expiration: 1977-10-25

Description

A. M. WALKER SPRAY DRYING APPARATUS AND METHOD Oct. 25, 1960 j Filed Nov. 12. 1957 3 Sheets-Sheet 1 fi my/arr Wamm BY A TTOzP/VEY 415m NDEP Oct. 25, 1960 A. M. WALKER spam DRYING APPARATUS AND unmon Filed Nov. 12, 1957 3 Sheets-Sheet 2 'I-NVENTOR. I ,4; t'XA/VDA-P MA/Pz/orrmzms/e A. M. WALKER 2,957,519

SPRAY DRYING APPARATUS AND METHOD Oct; 25, 1960 Filed Nov. 12, 1.957 3 Sheets-Sheet 3 O "l',"fl A? I '1' /3 f m A 320 I ggagmm 32 /4Z0- f M 00 1 3/ 5 i Z p 30 M INVENTOR. A/DA-F/HA/P/PMWWILKER United tates Patent ice SPRAY DRYING APPARATUS AND METHOD Alexander Marriott Walker, 699 Shephardbush Road, Birmingham, Mich., assignor of one-half to John G. Hoad, Ann Arbor, Mich.

Filed Nov. 12, 1957, Ser. No. 695,787

7 Claims. (Cl. 159-4) This invention relates to improvements in spray dryers of the type employed to separate and to dry solids from aqueous solutions containing them to produce such items as milk powders, powdered eggs, powdered coffee, powdered malt, and certain powdered chemicals recoverable by dehydration.

In the prior art, considerable difiiculty has been en- 2,957,519 Patented Oct. 25, 196i) production of a uniform and satisfactory end product by the separation of solids from solutions containing them simultaneously with drying the end product.

Other objects of the invention will become apparent by reference to the following detailed description taken in connection with the accompanying drawings, in which:

Fig. l is a longitudinal sectional view of a spray dryer illustrating the invention.

Fig. 2 is a front elevational view taken on the line 2--2 of Fig. 1.

Fig. 3 is an enlarged cross sectional view of an improved spray head employed as an elementof the incountered in spray dryers due to impingement onto the prior to falling out of the air stream induced in the dryer.

Insome instances, the partly dried particles of solids are carried back into the zone of hot air at the hot air inlet causing the particles being dried to become overheated and scorched or burned which requires downgrading of the end product due to partial insolubility, 0a flavors, and the like. Such malfunctioning of a spray dryer not only adversely affects the end product therefrom but decreases its efliciencyand creates difiicult cleaning problems requiringthe dryer to be out of productive service at frequent intervals and for excessive periods of time.

With the foregoing in view, the primary object of the invention is to provide improved spray dryer construction wherein the particular form, location and arrangement of the spray head of the dryer in respect to the drying chamber and its outlet cooperate to' 'effect in the spray drying chamber increased efliciency through maintaining arelatively long period of suspension of particles of solids being dried in the drying chamber.

Another object of the invention is to provide an imthe venturi air stream spaced along said drying air nozzle,

the relationship of the fluid spray nozzles and hot drying air nozzle in respect to each other and the drying chamber and its outlet being such, with proper air nozzle and air outlet velocities, as to maintain a divergent counter- -rotating rolling turbulence of particle laden air in the drying chamber and assure an extremely long residence of particles in suspension therein whereby to induce a more thorough drying of the product particles being dried.

A' further object of the invention is to provide an improved spray dryer construction wherein'more thorough drying and increased .thermal efiiciency is obtained through the provision of an improved spray head adapted to cause hot drying air surrounding a spray of solutions containing products to be dried to enter the dryer in such a manner as to establish a divergent counter-rotatvention.

Fig. 4 is an enlarged elevational view of the improved spray head shown in Fig. 3.

Referring now to the drawings wherein like reference numerals refer to like and corresponding parts throughout the several views, the particular spray dryer 10 disclosed for the purpose of illustrating the invention consists of an insulated drying chamber 11 preferably somewhat longer-than its height having a spray head generally designated by the numeral 12 located at the front or inlet end thereof. The said spray head 12 is preferably of an elongated rectangular shape and is preferably lo.- cated above the horizontal center of the said inlet end 1100f the drying chamber 11. The spray head .12 includes a plurality of fluid spray nozzles 13 evenly spaced along and through a horizontally disposed elongated rectangnlar venturi type hot drying air nozzle 14 which extends substantially the full width of the said spray head 12. A solution containing products to be dried is sprayed in finely divided particles under pressure from said spray nozzles 13 into the drying chamber 11 in the presence of a relatively high velocity stream of heated drying air passing through the said elongated venturi type hot drying air nozzle 14. According to the size of the drying chamber 11 and the particular product being dried in the spray dryer 10, the venturi velocity of the hot drying air is preferably from 3000 to 5000 feet per 'rninute. Expressed in another manner, it has been found that the venturi velocity is preferably 8 to 12 times the drying chamber outlet velocity. It is important that the venturi velocity is sufficient at all times, not only to establish and maintain the required divergent counterrotating hot drying air circulating within the drying chamber, but also to entrain and recirculate previously admitted air with the venturi air stream.

The spray dryer 10 includes an insulated particle collection chamber 15 adjacent the rear or outlet end 111 of the said drying chamber 11 which has an air outlet 16 there-from across the full width thereof adjacent the floor 17 upon which the spray dryer 10 is constructed. The area of the air outlet 16 is preferably such as will provide a particle laden air with an outlet velocity from the drying chamber of from 200 to 500 feet per minute. The said particle collection chamber 15 is preferably provided with an exhaust fan 18 having a suitable damper 19 in the duct 20 therefrom by means of which the rate of withdrawal of air from the drying charnber 11 maybe regulated so as not to adversely affect the divergent counter-rotating rolling turbulence of particle ladened hot drying air within the said drying chamber 11 hereinafter described. Suitable outlets from the top of the particle collection chamberlS are connected by a manifold 151 to the intake ofthe said exhaust fan 18. The particle collection chamber 15 may be equipped with a dried particle collector such as a bag type particle collector 21 which usually is provided with a bag shaker 22 as indicated inFig. 1. Obviously, other types of dried particle collector means may be employed.

Although not shown, the dryer 10 may be provided with suitable dried product removal means such as trough conveyors or the like built on the floor 17 thereof, the particular product or products to be dried in the spray dryer generally determining the type of dried product removal means employed, and whether the dried product removal apparatus runs continuously or intermittently. Also, a plurality of dryers may be placed side-by-side in banks, if desired, as indicated by the dot and dash lines in Fig. 1.

Hot drying air is continuously supplied to the spray head 12 by means of a suitable blower 2-3 having its exhaust end discharging through a bank of heaters 24 connected by means of a suitable duct 25 to the plenum chamber 140 of the venturi type hot drying air nozzle 14 of the spray head 12. The intake end of the said blower 23 is preferably provided with a suitable intake air filter bank 26. The heaters 24 may be controlled by any suitable means, not shown, to maintain the hot drying delivered to the plenum chamber at or about the maximum temperature permissible to use without scorching or other deleterious effect upon the recovered end product.

The solution containing products to be dried is supplied from a source S under pressure to the nozzles 13 of the spray head 12 by a relatively high pressure pump 29 via distribution piping 30 and control valves 31. The spray nozzles 13 are preferably of a type that will spray a solution containing products to be dried in a fine particle form uniformly into the hot venturi air stream within the drying chamber 11 wherein the hot drying air absorbs the moisture and permits a fall-out of thoroughly dried product particles.

Referring now particularly to Figs. 1, 3 and 4, the spray head 12 consists of an elongated insulated sheet metal structure formed to provide a plenum chamber 140 across the rear thereof to which the duct 25 from the hot drying air blower 23 is connected so that filtered and heated drying air from the hot drying air blower 23 may enter and pass through the said spray head 12 uniformly. The spray head 12 is formed to provide an elongated horizontally disposed venturi type air nozzle 14 having a narrow elongated throat 141 and air outlet 142 through which hot drying air is jetted at a relatively high velocity into the drying chamber 11, the said hot drying air outlet 142 of the venturi type air nozzle 14 being disposed within the front wall 110 of the drying chamber 11. The said outlet 142 of the venturi type air nozzle 14 preferably has a lower horizontal longitudinal diffuser wall 1420 and an upwardly sloping upper longitudinal diffuser wall 1421. The said venturi type air nozzle 14 of the spray head 12 is disposed at such an elevation in the front wall 110 of the drying chamber 11 that drying air jetted therefrom into the said drying chamber 11 will establish a rolling counter-rotating drying air circulation therein as indicated by the arrows in Fig. 1. As viewed in Fig. 1, the rolling counter-rotating drying air circulation consists of an upper counterclockwise path A and a lower clockwise path B, which circulation may be termed a divergent counter-rotating rolling turbulence within the drying chamber 11. The said divergent counter-rotating rolling turbulence within the drying chamber 11 also may be described as a transverse horizontally axised counter-rotating double-toric air stream. Although the venturi type air nozzle 14 has its lower longitudinal diffuser wall 1420 substantially horizontal and its upper longitudinal diffuser wall 1421 sloping upwardly as best shown in Fig. 3, the entire elongated venturi type lair nozzle 14 may be constructed symmetrical in cross section, in which event, the said venturi type air nozzle 14 preferably would be positioned on an upwardly sloping axis to establish the divergent counter-rotating rolling turbulence of drying air within the dryingchamber 11 including an upper counterclockwise path A and a lower clockwise path B as viewed in Fig. 1.

The spray nozzles 13 of the spray head 12 employed to introduce a spray of fluid containing particles to be dried into the hot drying air stream entering the drying chamber 11 preferably extend through the narrow elongated throat 141 of the elongated venturi type air nozzle 14 and into the drying chamber 11 as best shown in Figs. 1 and 3. The said spray nozzles 13 are suitably laterally spaced along the air nozzle 14 so that a substantially uniform spray of fluid containing particles to be dried is sprayed into the path of drying air entering the drying chamber through the said air nozzle 14 opposite the juncture of the upper counterclockwise path A and lower clockwise path B of the counter-rotating drying air circulation in the drying chamber 11, see Fig. 1. The spray head 12, the length of the elongated venturi type air nozzle 14 and the location of the spray nozzles 13 are arranged to avoid the spraying of solution containing particles to be dried directly onto the side walls 112 of the drying chamber 11. The said spray nozzles 13 are each preferably mounted in a flanged mounting sleeve 32 extending through the front wall 1400 of the plenum chamber 140 below a hinged clean-out and inspection door 1401 therein. Suitable apertured discs 320 support the shank of each spray nozzle 13 within its flanged mounting sleeve 32.

According to the invention, hot drying air is continuously forced through the elongated horizontally disposed rectangular venturi type hot drying air nozzle 14 of the spray head 12 into the drying chamber 11 creating therein a divergent counter-rotating rolling turbulence or circulation of drying air while the spray nozzles 13 of the said spray head 12 uniformly sprays a fine spray of solution containing a product or products recoverable by dehydration into the said drying chamber at the juncture of the divergent counter-rotating air paths therein. This creates within the drying chamber 11 a condition wherein particles of solution carrying products being dried therein are suspended for a longer time than in conventional spray dryers whereby to assure substantially complete absorption of all moisture by the hot drying air and a fallout of more thoroughly dried and uniformly satisfactory end product than obtainable with conventional spray dryers.

The improved spray head 12 consisting of elongated horizontally disposed rectangular venturi type hot drying air nozzle 14 with a plurality of laterally spaced spray nozzles 13 extending therethrough located above the horizontal center of the front or inlet end of the drying chamber 11 creates divergent counter-rotating rolling air streams A and B. These counter-rotating hot drying air streams A and B join or unite at the outlet 142 of the venturi 14 and the spray nozzles 13 to receive at their juncture a continuous spray of fine particles of a solution containing a product to be dried whereby to provide a spray dryer operation with an extremely long period of suspension of particles being dehydrated therein which is not only thermally efficient in its drying function but reduces the final moisture content of the dried product to as low as 1% to 2% before fall-out in the drying chamber 11 or movement from the drying chamber 11 to the particle collection chamber 15.

The uniform divergent counter-rotating flow of hot drying air in the drying chamber with uniformly dispersed particles to be dried carried in suspension therein in a rolling counter-rotating turbulence or air flow prevents a premature fall-out of particles being dried, and thereby avoids the sticking of improperly dried particles to the walls of the drying chamber 11, and, at the same time, the improved spray dryer produces a thoroughly dried end product at relatively low drying temperatures whereby to eliminate scorching or burning of the end product and its resultant downgrading.

In the particular embodiment of the invention disclosed, filtered hot drying air is forced by a suitable blower 23 through the improved spray head 12 into the drying chamber 11 in the presence of a spray of a solution containing a product or products recoverable by ssure dehydration, and, an exhaust fan 18 is employed to exhaust air from the particle collection chamber 15 through the bagtype particle collector 21 therein without adversely afiectingthe particular improved rolling turbulence of drying air in the drying chamber 11. While the foregoing combined pressure and exhaust means for providing air flow through the spray dryer may be preferable in some installations, it is obvious that other means for providing circulation of drying air through the dryer may be employed such as using only a pressure source at the spray head or using only a negative pressure source created by an exhaust fan communicating with the particle collection chamber, it being important that air jetting through the venturi type hot air nozzle into the drying chamber be of such direction, velocity and location as to create and maintain therein a divergent counterrotating rolling drying air turbulence within the drying chamber 11 to assure a long residence in suspension in the drying chamber of particles of solids being dried.

Although but a single embodiment of the invention has been disclosed and described in detail, it is obvious that many changes may be made in the size, shape, arrangement and detail of the various elements of the invention as defined by the appended claims.

I claim:

1. In a spray dryer, an insulated rectangular drying chamber, an elongated spray head in one cross Wall thereof located above and parallel to the horizontal transverse axis of said wall, and an air outlet passage across the opposite wall thereof located substantially at the bottom of said opposite wall, the said spray head consisting of a transversely disposed elongated venturi type hot drying air inlet nozzle including a plurality of evenly spaced fluid spray nozzles extending through said elongated venturi nozzle of a type adapted to spray solutions containing products recoverable by dehydration into the venturi air stream, the said hot drying air inlet nozzle being directed at an upwardly sloping angle with respect to horizontal to create a divergent counter-rotating rolling air turbulence Within said drying chamber, the said air outlet passage from said drying chamber being sufficiently large to avoid disturbance of said rolling air turbulence Within said drying chamber as particle laden air passes therefrom, means continuously supplying hot drying air through said venturi inlet nozzle creating said divergent rolling air turbulence within said drying chamber.

2. In a spray dryer, an insulated rectangular drying chamber, an elongated spray head in one cross wall thereof located above and parallel to the horizontal transverse axis of said wall, and an air outlet passage across the opposite wall thereof located substantially at the bottom of said opposite wall, the said spray head consisting of a transversely disposed elongated venturi type hot-drying-air inlet nozzle and a plurality of evenly spaced fluid spray nozzles extending through said elongated venturi nozzle, the said fluid spray nozzles being of a type adapted to spray solutions containing products to be dried into the venturi air stream, the said venturi type hot-drying-air inlet nozzle being formed with lower horizontal and upper upwardly sloping diffuser walls directed to creat a divergent counter-rotating rolling air turbulence Within said drying chamber, the said air outlet passage from said drying chamber being sufliciently large to avoid disturbance of said rolling turbulence within said drying chamber as particle laden air passes therefrom, means continuously supplying hot drying air through said transversely disposed elongated venturi inlet nozzle, means supplying solutions, containing products to be dried, under pressure through said fluid spray nozzles into said venturi air stream within said drying chamber, and means withdrawing particle ladened air from said drying chamher.

3. In a spray dryer, an insulated rectangular drying chamber, an elongated laterally extending spray head in one cross wall of said drying chamber located at least at the height of thelongitudinal center of said, wall,.an d an air outlet passage in the opposite cross wall 'subst'an tially coextensive thereof and located adjacent the bottom of the said drying chamber, the said spray head consist-' ing of a transversely extending elongated venturi type hot drying air inlet nozzle having a narrow venturi throat substantially coextensive thereof and including an upwardly' sloping upper diffuser. wall and. a substantially hoirzontal lower diffuser wall, and a pluralityofisubstantially evenly spaced fluid spray nozzles extending through the throat of the venturi nozzle of a type adapted to spray solutions containing products recoverable by dehydration into the venturi air stream.

4. In a spray dryer, an insulated rectangular drying chamber, an elongated horizontally and laterally extending venturi type hot drying air inlet nozzle having a narrow throat substantially coextensive thereof and located at least at the height of the longitudinal center of one cross wall of the said drying chamber including a hot drying air plenum chamber therebehind, the said venturi nozzle including upper and lower diffuser walls arranged to discharge hot drying air into said drying chamber at an upwardly sloping angle sufficient to establish a divergent counter-rotating rolling turbulence of drying air within the drying chamber, a plurality of substantially evenly spaced fluid spray nozzles extending through the venturi nozzle throat adapted to spray solutions containing products recoverable by dehydration into the venturi air stream as it enters the drying chamber, and an air outlet passage in the opposite cross wall of said drying chamber substantially coextensive of the Width thereof.

5. The method of recovering products by dehydration from solutions containing them comprising introducing into a drying chamber a high velocity single horizontally and laterally extending continuous hot drying air stream entering said drying chamber above the horizontal center thereof and forming therein relatively slow upper and lower divergent counter-rotating rolling turbulence longitudinally of said drying chamber, uniformly spraying a solution containing products recoverable by dehydration longitudinally and concurrently into the said single air stream at intervals thereacross, and permitting hot drying air to leave said drying chamber at a sufficiently low velocity via a single horizontally disposed exit air stream of substantially greater width than the width of the entering air stream located below the said horizontal center of said drying chamber to insure maintenance of said divergent counter-rotating rolling turbulence therein.

6. The method of recovering products by dehydration from solutions containing them comprising introducing into an elongated drying chamber at one end thereof a single horizontally and laterally extending wide laterally continuous hot drying air stream located above the center of said drying chamber and of a sufficiently high velocity to divide itself into and maintain a divergent counterrotating rolling turbulence in said drying chamber, uniformly spraying a solution containing products recoverable by dehydration longitudinally and concurrently into the said single air stream at intervals thereacross, and causing hot drying air to leave said drying chamber at the opposite end thereof at a relatively low velocity adjacent the bottom thereof.

7. The method of recovering products by dehydration from solutions containing them comprising introducing into a drying chamber at one end thereof a single hori zontally disposed and laterally extending vertically narrow, laterally elongated continuous hot drying air stream above the center of said drying chamber of a sufliciently high velocity to divide itself into and maintain a divergent counter-rotating rolling turbulence in said drying chamber, spraying a solution containing products recoverable by dehydration longitudinally and concurrently into the said single air stream at uniform intervals thereacross, and causing hot drying air to leave said drying chamber at the opposite end and 'adjacent the bottom thereof at 1,088,436 -Merrell Feb. 24, 1914 a velocity of approximately one-eighth to one-twelfth the 1,193,173 Merrell et a1. Aug. 1, 1916 initial velocity of the said hot drying air stream. 1,226,011 Rogers May 15, 1917 1,537,060 Beardslee May 12, 1925 References Cited in the file of this patent 5 2,559,989 Nyrop July 10, 1951 UNITED STATES PATENTS 2,33 97 Barzelay -4--- May 20, 1958 478,980 Blackman July 19, 1892 FOREIGN PATENTS 999,972 Ekenberg Aug. 8, 1911 627,050 Great Britain July 27, 1949