US2953199A - Horizontal spray dryer - Google Patents

Description

Sept. 20, 1960 w. D. KOHLINS ETAL 2,953,199

HORIZONTAL SPRAY DRYER Filed Feb. 19, 1957 2 Sheets-Sheet 1 C l l I Sept. 20, 1960 w. D. KOHLINS ETAL HORIZONTAL SPRAY DRYER 2 Sheets-Sheet Filed Feb. 19, 1957 OOOODOOOOO OOOOOOOOOQ 0000000000 5 NVEINTORS. 5%.; M

A OFA/ff United States Patent Ofiice Patented Sept. 2%, 160

HORIZONTAL SPRAY DRYER William D. Kohlins, Eggertsville, James G. Moore, Buffalo, and Duncan B. Montgomery, West Seneca, N.Y., assignors to Blaw-Knox Gompany, Pittsburgh, Pa., a corporation of Delaware Filed Feb. 19, 1951, Ser. No. 641,187

8 Claims. 01. 1s9 -4 This invention relates to a horizontal spray dryer and is illustrated as embodied in such a dryer for the production of instant coffee in the form of hollow spheres, such form being desirable to provide the desired aroma and to reduce the hygroscopicity of the dried coffee. However, the dryer forming the subject of the present invention is not, of course, limited to any particular product and can be used to dry any liquids capable of being spray dried.

This application is a continuation in part of our copending application for horizontal spray dryer, Serial Number 590,046, filed January 7, 1956, now abandoned.

An important object of the present invention is to produce materials like dried instant coffee in the form of dense walled spheres so as to provide the desired aroma and to reduce hygroscopicity.

Another object is to provide a horizontal spray dryer in which undried material does not come into contact with the dryer walls but travels in suspension through the drying chamber until dry with the dried material settling to the bottom of the drying chamber where it is continuously removed.

Another object is to separately control the form of the spray of liquid to be dried, to rapidly shock or inflate the liquid particles into spheres, this being accomplished by introducing a primary stream of heated air at relatively high velocity directly around the spray nozzle.

Another object is to provide such a horizontal spray dryer in which, following the inflation of the droplets into spheres by said primary stream of air, the spheres are permitted to dry more slowly as they settle to the bottom of the dryer, this being accomplished by the introduction of a secondary stream of air below the primary stream of air and greater in cross sectional area.

Another object is to provide for the control of the relative volume of the streams of primary and secondary air to obtain a product of the desired quality with a minimum expenditure of heat and power.

Another object is to provide for the control of the relative temperatures of the streams of primary and secondary air to provide a product of the desired quality with a minimum expenditure of heat and power.

Another object is to provide a horizontal spray dryer of minimum length by positioning the spray nozzle near the top of the drying chamber so that the material falls through the greater part of the height of the drying chamber while drying.

Another object is to prevent the material being dried from contacting the inside of the dryer before being dried and particularly in the upper part thereof, this being effected by the introduction of a third stream of air to isolate the upper part of the dryer from the spray.

Another object is to provide such third stream of air in minimum volume so as to avoid the heating and handling an unnecessarily large overall volume of air.

Another object is to introduce such third stream of air in such manner as to destroy the aspirating effect of the spray and which aspirating effect tends to produce a large eddy or backfiow which in turn tends to carry undiied droplets against the inside of the dryer.

Another object of the invention is to provide for the adjustment of the volume of the third stream of air so isolating the upper part of the dryer from droplets in relation to the volume of the primary and secondary streams of air.

Another object is to provide for the regulation of temperature of said third stream of air in relation to said primary and secondary streams of air.

Another object is to provide such third stream of air and the primary stream of air in a form which is free from large eddies or swirls and which jointly progress as an internally stable body the full length of the spray dryer, this being accomplished by introducing these streams of air through multi-on'fice screens at the wet end of the dryer.

Another object is to efiectively isolate said three streams of air from one another prior to their simultaneous discharge into the drying chamber.

Another object is to provide such a horizontal spray dryer in which walls of the drying chamber are cooled to reduce the tendency of solids to stick to the walls of the drying chamber.

Another object is to employ at least a part of the air used in cooling the shell of the drying chamber as preheated air supplied to the main air heater from which heated air is supplied to the drying chamber.

Another object is to provide inlet and outlet blowers which can be balanced to provide any required negative operating pressure within the drying chamber to suit the particular material being dried.

Other objects and advantages of the invention will be.) apparent from the following description and drawings in which:

Fig. 1 is a longitudinal vertical sectional view through a spray dryer embodying the present invention, parts being shown in elevation.

Fig. 2 is an enlarged fragmentary view similar to Fig. 1 and showing, in section, the rotary air sweep for the end wall at the dry end of the spray dryer.

Fig. 3 is an enlarged vertical transverse section taken on line 3-3, Fig. 1.

Fig. 4 is a fragmentary horizontal sectional view taken on line 44, Fig. 3.

Fig. 5 is a fragmentary enlarged sectional view similar to Fig. 1 and taken on line 5-5, Fig. 3, to illustrate the form of a bafile used in conjunction with the delivery of the air streams.

The horizontal spray dryer of the present invention has a horizontal drying chamber 9 formed by a pair of sheet metal end heads 10 and 11 connected to each other by an outer shell 12 and a conforming inner shell 13. The end head 11 is at the dry end of the dryer and is preferably of outwardly converging conical form while the end head 10 is provided with a large circular opening closed by a vertical screen 14.

The inner and outer shells are secured in spaced re lation to each other by a plurality of ribs 15 which, as best shown in Fig. 4, are interposed between the inner and outer shells 12 and 13 and can be secured to each of these shells in any suitable manner as by welding. As best shown in Fig. 4, these vertical ribs 15 are horizontally spaced, preferably at uniform intervals, to provide a series v of vertical air passages 16.

These air passages are for the circulation of ambient air to cool the inner shell 13 and for this purpose, at one side of the dryer, the shell 12 is provided with an air inlet opening 17 for each of the passages 16 and on the opposite side of the dryer, this outer shell 12 is provided with an outlet opening 18 for the opposite end of each of the passages 16. Each inlet opening 17 connects 26 which converge downwardly to form a hopper dis- 7 charging into a trough 28. which extends the full'length of the dryer. The trough 28 has a semicylindrical bottom and houses a conveyor screw 29., one end of which can be suitably journalled in the end head and the .other end of which is journalled in an end head 30 for the trough 28, this end of the trough 28 being its discharge end and having a downwardly directed discharge spout The air discharge line 24, as best shown in Fig. 1, connects with the scroll 35 of a main fan or blower 36, the shell of this fan having an air inlet 38 leading to the center of a'bladed fan wheel 39 which discharges ambient air drawn in from the inlet 38 through the outlet 40 of the fan housing. This fan is preferably arranged above the shells 12, 13 and discharges into the shell 41 of a heater 42.

While any suitable form of heater can be employed, it is shown as being in the form of a direct fired combustion heater having, within the shell'41, branch pipes 43 from. a gas supply line 44 and these branches carrying a plural ity of burners 45 which burn flames 46 in the air stream passing through the heater casing 41 so as to heat this air. If, of course, the product being dried is not compatible with products of combustion, a different type of heater would be used.

The screened or dry end of the dryer is shown as enclosed by a conical end head 50 the large rim of which is joined to the end head 10 at its opening for the screen 14 so as to form a continuation of this end head and to provide a plenum chamber for the hot air discharged from the heater 42. A horizontal air inlet pipe 51 for 'the primary stream of drying air extends through the upper part of the conical end head 59 and also through the upper part of the screen 14. This horizontal air pipe is supplied with heated air from the outlet end 52 of the heater shell 41. The space around this primary air pipe 51 within the conical end head 50 is divided into two chambers 53 and 54 by apair of horizontal partitions 55 which extend horizontally from the primary air supply pipe 51 and are bounded by this pipe, the shell and a quantity of ambient air from an inlet duct 59 to the duct 56. The amount of ambient air so admitted as the secondary air can be under control of a damper '60 which can be regulated by hand.

Hot air is supplied from the outlet end 52 of the heater casing 41 to the chamber 5-4 through a duct 61 under control of a damper 62 which can be manually operated. The temperature of this stream of air can be regulated by bleeding in a regulated amount of cool ambient air from a duct 63. The amount of ambient air so admitted can be under control of a damper 64 which can be adjusted manually. The liquid to, be dried is supplied under pressure to a horizontal pipe v65 which extends coaxially through the horizontal duct 51 for the primary air. This pipe terminatesin a spray nozzle 66 which discharges a spray 6810f droplets into the spray-chamber 9 from immediately adjacent-theoutletof the primary air pipe 51. The spray .4 68 is generated at the discharge end of the duct 51 for the primary air so that the droplets are shocked or rapidly inflated into spheres with a-consequent rapid reduction in the water content of the droplets, the spheres being then subjected to produce dense walls, to the slower drying action while descending, under the influence of gravity, through the secondary stream of drying air emerging through the multi-orifice screen 14 from the chamber 53.

The air escapes from the drying chamber 9 through an outlet opening 70 in the upper part of its conical end wall 11 at the dry end ofjthe-dryer. This outlet opening communicates with a horizontal duct 71 which discharges this air into the upper part of the shell 72 of a first separator 73. This separator 73 is shown as having an internal vertical partition 74 which is arranged transversely of the air flow and connects with the top and side walls of the separator shell 72 but terminates a substantial dis tance above the bottom wall thereof. Accordingly, the air entering the separator 73 from the horizontal duct 71 is first deflected downwardly and then horizontally and then upwardly and then is again deflected horizontally in passing out through the upper discharge duct 75 of the separator 73. With these abrupt changes in direction, the greater part of any solids in the air entering the sepa-. rator 73 are deflected against the partition 74 and the walls of the shell 72 and settle downwardly into the trough 28 which is common to this separator 73 as well as to-the shell 13 of the dryer. The partition 74 preferably can be adjustable as to position and can be agitated, the specific features of the separator 73 forming no part of the present invention. a

The duct 75 discharges into a second separator 78 which can be of any suitable form to remove any remaining solids from the air stream. It is shown as being of the centrifugal type having a conical bottom 79 leading to a discharge 80 for the solids and having its air outlet 81 connected with the inlet of a centrifugal fan or blower 82 which discharges the air through a duct 83. It will be seen that the effects ofthe exhaust blower 82, the blower 36 and preheated air blower 21 are cumulative in moving air through the apparatus and that these can be adjusted or balanced to provide any desired negative pressure within the drying chamber 9. .It will further be seen that this negative pressure serves to draw cool ambient air in through the ducts 59 and 63, under control of the dampers 60 and 64, to reducethe temperature of the corresponding streams of air.

An air sweep, indicated generally at 88, is used to prevent the accumulation of solids on the conical end wall 11 at the dry end of the drying chamber. This air sweep is shown as having a hollow body in the form of two angularly disposed arms '89 radiating from a tubular hub 90. The arms 89 are coaxial with the conical end head 11 and their angularity is such as to conform to the conical end head. The free ends of these arms can be braced by a cross brace or arms 91 which can connect with a cap 92 at the inner end of the tubularhub 90. This hub is journalled concentrically in the end head 11 of the drying chamber 9 and the arms 89 of the sweep are provided with a plurality of perforations 93 through which streams of air are discharged against the inner face of the conical end head 11 for the purpose of cooling the same to prevent the accumulation of solid material thereon. The tubular' hub of the rotary sweep 88 is journalled in a bearing bushing 94 suitably supported in the apex of the end head 11 of the drying chamber. A pulley 96 having a drive belt 98' is fast to the outer end of the tubular hubj90 and it will be noted from Fig, 1 that this pulley is arranged in a space 100 between the end head 11 of the drying chamber 9 and the primary separator 73. Also located in this space 100 is a conduit 101 through which air is forced into-the tubular hub 90 fordistributon by the rotary sweep 88 against the end head 11 of the drying chamber.

Operation It will be assumed that the liquid to be dried is instant coffee having in the order of 28% to 50% solids to be dried in the form of dense walled spheres having a moisture content not exceeding about 3% It will also be assumed that the dry bulb temperature of the ambient air is in the order of 80 Fahrenheit and the wet bulb temperature of the ambient air is in the order of 66 Fahrenheit so that the relative humidity is 49%.

The bulk of the ambient air used in the drying chamber 9 is admitted through the inlet 38 of the blower 36 which discharges into the casing 41 of the heater. A second stream of ambient air which is, however, preheated, is also adrnitted to the scroll 35 of the fan 36, this being supplied from the inlet of a blower 21, Fig. 3. This last blower draws in ambient air and discharges it into the manifold 20 from which it flows out through the branches 19. Each branch 19 connects, Figs. 3 and 4, with one end of a passage 16 formed between the inner and outer shells 13, 12 of the drying chamber 9 by the ribs 15. In passing through these passages 16 the ambient air cools the inner shell 13 so as to reduce the tendency for incompletely dried or thermoplastic materials to adhere to the inside of this inner shell 13. From the discharge end of the passages 16 the air, now preheated by contact with the inner shell 13, escapes through the branches 22 of a manifold 23. From this manifold 23 the preheated air passes through a duct 24 to the scroll 35 of the blower 36.

In passing through the heater casing 41 the air contacts the flames 46 of the gas burner 42 and is heated to the required temperature, in the order of from about 500 to 550 Fahrenheit, passing thence to the outlet end 52 of the heater shell 41. This hot air is then divided into three streams before being admitted to the drying chamber 9.

Of these the primary high velocity stream of air passes from the outlet end 52 of the heater shell 41 through the horizontal duct 51 and discharges directly into the upper part of the drying chmber 9 immediately adjacent the screen 14 which does not, however, extend over the outlet of this horizontal duct 51 to impede this primary stream. This primary stream is from about 25% to 30% of the total volume of air admitted to the drying chamber 9. Into this stream of hot primary air issuing from the horizontal duct 51 is discharged a spray 68 of fine droplets of the coffee solution or other product being dried. The liquid can advantageously be supplied to the nozzle 66 at a pressure of from about 325 to 400 p.s.i. and at a temperature of from about 105 to 130 Fahrenheit. The contact between these droplets and this primary stream of air shocks or rapidly inflates each droplet into a hollow sphere, the larger proportion of water in the droplet being abstracted during this process by direct evaporation from the droplet into the hot stream of primary air. With a cofiee solution having a concentration of about 30% solids discharged from the nozzle 66, the coffee droplets in the spray 68 are rapidly formed into hollow spheres with a reduction of the moisture content to about 13%.

A secondary stream of heated air passes from the outlet end 52 of the heater shell 41 through the horizontal duct 56 into the chamber 53 within the lower part of the conical end head 50 at the wet end of the dryer. The volume of secondary air so admitted to the chamber 53, particularly with reference to the volume of the primary air admitted through the horizontal duct 51 is under control of a manual damper 58. This volume of secondary air can be from about 60 to 70% of the total air used. Also the temperature of the stream of secondary air admitted to the chamber 53 is under control of a manual damper 60 which can be adjusted to bleed in the required amount of cool ambient air to obtain the desired temperature dififerential between the primary air emerging from 51 and the secondary air entering the chamber 53. The temperature of this secondary streani of air approximates the temperature of the primary air stream, namely, in the order of from about 500 to 550 Fahrenheit.

The air temperature in the drying chamber 9 is from about 305 to 330 Fahrenheit.

An important feature resides in the provision of the screen 14 between the secondary air chamber 53 and the spray chamber 9. The screen is preferably in the form of a perforated plate with many small closely spaced holes so as to create a uniform orifice pressure drop across the entire area of the screen 14 which encloses the chamber 53. Such a screen prevents any major turbulence in the stream of secondary air entering and flowing through the drying chamber 9 and insures the progress of the stream of secondary air as an internally stable body the full length of the drying chamber 9.

Following the formation of the hollow spheres in the primary stream of hot air issuing from the horizontal duct 51 these spheres settle by gravity into the stream of hot secondary air flowing through the lower part of the spray chamber 9 and which occupies a much greater cross sectional area of the spray chamber than the primary stream of air.. These spheres give up additional moisture to this stream of secondary hot air as they settle toward the bottom of the chamber but at a much slower rate since the hollow spheres rapidly solidify and the moisture is required to escape through the solid skins of these spheres. The length and height of the spray chamber is selected to insure that the spheres are dry, namely, to less than about 3% moisture content by the time they reach the bottom of the spray chamber. In this regard it will be noted that the horizontal duct 51 for the primary stream of hot air and also the nozzle 66 are located well above the horizontal center of the drying chamber 9 and close to the top thereof so as to provide the maximum distance of fall of the hollow spheres to the bottom of this drying chamber.

On reaching the bottom of the drying chamber the spheres are picked up by the screw conveyor 29 and discharged unbroken through the discharge spout 31.

The spray 68 has an ejector action upon the air in the drying chamber 9 particularly in tending to produce a backflow of air above the spray. If permitted, such a backfiow of air would carry with it some of the droplets or moist spheres and which would deposit both on the inner shell 13 above the spray 68 and also on the area of the screen 1 4 surrounding this spray. To prevent this result, a third stream of hot air from the outlet end 52 of the heater shell 41 passes through the vertical duct 61 into the chamber 54 formed in the extreme upper part of the conical end head 50 by the pair of horizontal partitions 55 which abut the horizontal primary air duct 51 as best shown in Fig. 3. This third stream of air can be from about 5 to 10% of the total volume of air. This third stream of hot air emerges from the extreme upper end or segment of the perforated screen 14 to proceed, as with the secondary air, without eddies or swirls as an internally stable body above the spray 68 and? along the top of the shell 13. This third stream of hot air effectively prevents any backfiow created by the spray 68 and also provides a layer of air which isolates both the upper part of the screen 14 and alsothe roof of the chamber 9 from contact with the droplets discharged in the spray 68 or the spheres formed from these droplets.

The volume of this third stream of air is preferably held to a minimum since it has no great drying effect and if provided in excess would merely waste heat and result in the handling of an excessive amount of air. Also, the temperature of this air of the third stream is not particularly critical and a substantial amount of cool ambient air can be admitted through the duct 63 under control of the manual damper 64.

Any materials reaching the end head 11 at the dry end of the dryer are prevented from accumulating thereon by the rotary sweep 88 which discharges a plurality, of streams of cool air" from the orifices 93 in its rotating hollow, Sidirectly against the conical end head 11'. These streams serve both t'o'cool this end head and also todislodge any, materials tending to collect onthis end head. These materials, of course, falldownwardly to the screw-conveyor. 29. V

7 By far thepreponderance of the dry product from the drying chamber 9 falls directly into thetrough 20 and is immediately conducted awayby the conveyor screw 29. A, small amount, however, of dry'material will be carried. out of the dryingcharnber 9 with the escaping moist air, this moist air passing in tofthe first separator 73. The separator can be; in the form of, a simple fallout separator having a bafiie 74,which, requires the leaviug air to first pass downwardlygand; then abruptly upwardly s'o thatithesolid partiolestend tov settle out; Such particles v are discharged by, the screw 29- through the outlet 31.

Any remaining, solids can, be removed from the moist air'in any suitable manner depending upon the character ofv the material and "the se raration-I economies involved, A cyclone separator 78 is shown for this purpose, although it will be understood that electronic precipitators or other forms: of. separators can be employed where required, 7 I

Specific examples of the practice of the invention in producing'spheresof instant coffee are as follows Example 1- :Example 2 Example 3 Air temperature from heater 42 F 520 545 500. Percent solids in feed 65 29 31 31 Temperature of feed 65 F.-. 108 120 126 Pressure of feed 65 p.s.i 260 400 400 Temperature drying-chamber 9 v F 325 325 325 Pressure drying chamber 9 p.s.i 2 25 3 Temperature exhaust 7l F- 290 295 290 Final moisture-product 1 percent" 1.5 2.4 2.0 Bulk densityproduct t V lbJcu. it I 13. 5 12.5 12. 5

Average producti0n2.375lb./hr. Powder/sq. it.cross sectional area As significant featureslofthe invention it will be noted that: the liquid spray-68 is projectedsconcurrently into the primary stream of; hot air and the particlestherefrom, settle into the secondary stream ofairflowing below the primary stream of air; the primary; air stream is admitted to the upper part of the drying chamber 9 and, is of smaller cross: sectional size and has a greater velocity than the secondary air stream which occupies the greater part of the cross sectional area of the spraychamber 9; the secondary air stream emerges from the multi-orifice screen 14 as an internally stable body; the relative volume, temperatures and; rate of flow of the air supplied to the primary and secondary streams can be regulated; a third stream of air is projected into the drying chamber 9 above the primary air stream to travel along the top of the drying chamber; thisthird air stream emerges from the multi-ori-fice screen 14 as an internally stable moving body; the volume, rate of flow and temperature of the third stream of air, with reference to the primary air stream, can be regulated; and the three air streams are provided bythe very simple structure comprising the primary air duct 51, conical end; head 50, multi-orifice screen'14 and partitions 55. It will be noted thatthe depth of the second. stream of 'air from the duct 53 is substantially equal in height and cross section to the height and cross section of the drying chamber 9-and that the nozzle 66 is recessed in the duct 51 thereby to avoid turbulence in thisrsecondstream and provide aninternally stable'or; rectilinearly-streamlined' flow of this second stream.

7 From the foregoing it will be seen that the .present inventionprovides a horizontal spra y'dryer achieving the many objectives set forth and is. particularly adaptedfr'or the production of the dryproduct in unbroken hollow spheres which are shocked or rapidly inflated from droplets and then dried at aslower rate.

We'claim:

1. A horizontal spray dryer, comprishiga-horizontally.

elongated tubular shell, an end head enclosing each end of said tubular shell, a multi-orifi'ce screen spacedirom one end head to provide horizontally a relatively long drying chamber at one side thereof and horizontally. a relatively short space at the opposite side'thereof, a first horizontal duct extending through said one end head, space andscreen and arranged to project, a primary stream ofgas into said drying chamber anddirectly. and in a substantially straight path toward the otherend head, means within-said first duct arranged to project: a spray ofliquid particles into said primary gas stream issuing. from said first duct, horizontal partition meansbounded by said one'end head, screen and firstductand dividing. said space into an upper and alower chamber, means arranged toforce gas to said lower chamber to pass through said-screen and form a: secondary streamof'hot gas flowing 'below and substantially parallel with. said primarystream-of gas and through which said particles settle, meansarrangedtoheatthe gas supplied to said ducts, means arranged to forcegas to said upper chamber. to pass through said screen-and form a third, stream of gas flowing above and substantially parallel with said primary stream and isolating the top of said dryingchame her and said screen from said particles, and means arwherein said first duct is arranged above the'longitudinalcenter of said shell and said lower chamber is of substantially greater; size than said upper'chamber.

3; Apparatus for drying liquids into hard, dense walled hollow spheres, comprising a horizontally elongated shell forming a drying chamber, a first horizontal duct having an outlet of much smaller cross sectional size than the cross sectional size of saiddrying chamber and said outlet being arranged in the upper part ofsaid drying chamber and with said duct arranged to project a first' stream of gas horizontally into one end of said shell and in a substantially straight path toward the opposite end thereof, means in said duct arranged to project a spray of'said liquid in the form, of particles into the center of said first stream of gas concurrently therewith, means heating said first stream of gas before contact with said particles to a temperature to cause said particles to rapidly inflate into incompletely dried hollow spheres, a second duct having an outlet of a size substantially equal in height and cross section to the height and cross'section of said drying chamber and with said second duct. arranged to project a second stream of hot gas having a depth substantially equal inheight and cross section to the height and cross section of said drying. chamber horizontally into said one end of said shell below, concurrently and in contact with said first stream of gas, a multi-orifice screen arranged across said outlet for said second duct to provide a rectilinearly stream-linediflow in said second stream of hot gas, said incompletely. dried hollow spheres settling through said second stream of hot gas and slowly drying therein to render the walls of said spheres hardand dense, and means at the bottom, of

said drying chamber to collect and remove the dried streams and wherein means are provided for applying a cooling medium to the gas passing through said second,

duct to reduce the temperature of said second stream of gasbelow the temperature of'said first stream of gas.

5. A horizontal spray ly elongated enclosed shell forming a drying chamber,

forth in claim 3 wherein said; heating means are common to said first and second;

dryer, comprising a horizontal;

means arranged to project a primary stream of gas horizontally into one end of said shell and directly in a subst-antially straight path toward the opposite end thereof, means at said one end of said shell arranged to project a spray of liquid particles to be dried into said primary gas stream concurrently therewith, means arranged to project an internally stable secondary stream of gas horizontally into said one end of said shell below and substantially parallel with said primary stream of gas and through which secondary stream said particles settle, said upper primary stream being of materially smaller cross sectional size than said lower secondary stream, means arranged to supply said gas under pressure to said projecting means for both said primary and secondary streams, means arranged to heat the gas so supplied, means arranged to project a third stream of gas horizont-ally along a substantially straight path into said one end of said shell above and substantailly parallel with said primary stream of gas to travel along the top of said drying chamber, and means arranged to exhaust the moist gas from said opposite end of said shell.

6. A horizontal spray dryer as set forth in claim wherein a multi-orifice screen is "arranged across the outlet of said means to project a third stream of gas, to effect an orifice pressure drop in the third stream of gas passing therethrough and to render said third stream of gas internally stable.

7. A horizontal spray dryer as set forth in claim 5 wherein damper means are provided for regulating the volume of gas supplied to said third stream with reference to the volume of gas supplied to said primary stream.

8. A horizontal spray dryer as set forth in claim 5 wherein means are provided for regulating the temperature of the gas supplied to said third stream in relation to the temperature of the gas supplied to said primary stream.

References Cited in the file of this patent UNITED STATES PATENTS 1,138,380 Harris et a1. May 4, 1915 1,157,947 Merrell Oct. 26, 1915 1,497,201 Wheat June 10, 1924 1,734,260 La Mont Nov. 5, 1929 1,782,054 Uhl Nov. 18, 1930 1,794,978 Pease Mar. 3, 1931 1,866,769 Harris July 12, 1932 2,188,506 Hall Jan. 30, 1940 2,278,473 Musher Apr. 7, 1942 2,758,927 Chase Aug. 14, 1956 2,818,917 Vincent Jan. 7, 1958 FOREIGN PATENTS 377,747 Germany June 26, 1923 889,439 France Oct. 1, 1944

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