US2833345A - Spray drying apparatus - Google Patents

Description

May 6, 1958 E. VAN DER PYL A 2,833,345

SPRAY DRYING APPARATUS 2 Sheets-Sheet 1 Filed May 6, 1953 INVENTOR. [DWAKD VAN 05E FYL May 6, 1958 E. VAN DER PYL SPRAY DRYING APPARATUS 2 Sheets-Sheet 2 Filed May 6, 1953 T& Q a

INVENTOR. EDNA/e0 VAN DEE PYL ATv-oz vfY SPRAY DRYING APPARATUS Edward Van der Pyl, Holden, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Application May 6, 1953, Serial No. 353,420

Claims. c1. 1s9-4 The invention relates to spray drying apparatus.

One object of the inventon is to provide a simple and thoroughly practical spray drying apparatus. Another object is to provide a spray drying apparatus for drying a slip or slurry to form particles or pellets of a predetermined size. A further object is to provide apparatus whereby the size of the particles or pellets may be varied in size. Another object is to provide a'water-cooled spray head to prevent drying'of the slip or slurry. Another object is to provide means for recirculating any desired portion of the slurry to avoid segregation. Another object is to automatically control the flow of slurry to compensate for any inconsistency, that is, percent of solids. Another object is to provide means to circulate fluid through the spray head for cleaning purposes to clean-out before running a different material through the dryer. Another object is to provide a spray head which may be used in either an upper-draft or a down-draft spray dryer. Another object is to provide a nozzle that will spray a highly abrasive material without detrimental wear in the slurry orifice. Another object is to provide a nozzle through which a slurry may pass at a low velocity and impinged by air at high velocity after it leaves the nozzle so as to minimize wear in the nozzle parts.

Other objects will be in part obvious or in part pointed out hereinafter.

The accompanying drawings illustrate efficient apparatus for making the particles but our process is not limited to the use of this particular apparatus. In the drawings,

Fig. 1 is a front elevation of spraying and drying mechanism, certain portions being shown in section;

Fig. 2 is an axial sectional view, on an enlarged scale, of the spraying head and connections;

Fig. 3 is a cross sectional View, on an enlarged scale, taken approximately on the line 3-3 of Fig. 2;

' Fig. 4 is a partial sectional view of the nozzle of Fig. 2 but showing an arrangement for producing larger particles;

Fig. 5 is a vertical sectional view, on an enlarged scale, taken approximately on the line 5-5 of Fig. 2; and

Fig. 6 isa diagrammatic view, showing an automatically actuated valve and the controls therefor for automatically regulating the by-pass of slurry.

Referring to Fig. 1, a mixing bowl 10 has therein a multiple vane paddle 11 on the lower end of a vertical shaft 12 mounted in bearings 13 and connected by coupling units 14 to the output shaft 15 of a reduction gear unit 16 driven by an electric motor 17. The mixing bowl 10 is charged with metal oxide powder'and water and the rotation of the paddle 11 produces and maintains a slip with the fine particles well and evenly distributed therein. As one example of practising the invention, I took 95 parts by weight alumina powder, 5 parts by'weight plastic ball clay powder, 4 parts by weight powdered dextrin, and /2 part by weight powdered carboxy methyl cellulose. Thesewere mixed together in a tumbling barrel for about one-half to one hour, or until a uniform I silicon,

i passage through the nozzle.

ice

mixture was obtained. Water, 100 pounds, was then put in the kettle followed by 200 pounds of the above dry material. After mixing about an hour, the mixture was considered to be too viscous to flow properly, and therefore 12 pounds additional water was added. After further mixing the mixture was considered satisfactory. Oxides or hydroxides or other compounds readily decomposable by heat to form'oxides can be used as metal oxide source materials. The metal compound can be'that of aluminum, barium, beryllium, calcium, chromium, cobalt, columbium, magnesium, manganese, molybdenum, nickel, strontium, tantalum, thorium, tin, titanium, uranium, vanadium, zinc, zirconium. I can also use spinel, mullite or various mixturesin'cluding many min erals. 1 p

The suspension or slip in the mixing bowl 10 is pumped by a diaphragm pump 20 to a two-fluid spray nozzle unit 21 (Fig. 2). Referring to Fig. '1, the connections including shut-off gate 23 which, when open, allows the slipto flow from the bowl into a hose 24 which is connected The two-fluid spray nozzle is preferably a water-cooled nozzle to prevent drying of the slurry or suspension during As illustrated in Fig. 2, the

' pipe 27 is welded into an aperture 28 formed in a laterally projecting boss 29 of a housing 30. Similarly a pipe 31 is welded within an aperture 32 formed in a laterally projecting boss 33 of the housing 30. The housing is provided with a central passage 34 which connects the pipe 27 with the pipe 31. The slurry or suspension being forced through the pipe 27 by the pump 20 [is forced upwardly through a passage 35 formed in a slurry nozzle 36. The pipes 27 and 30 are water-cooled in the follow ing manner:

A tube 37 is arranged concentric with the pipe 27 and is welded onto the outer peripheral surface of the boss 29. A collar or end cap 38 fits on the pipe 27 and within the tube 37 and is welded to both the pipe-27 and the tube 37 so as to form a water cooling chamber 39 surrounding the pipe 27.

7 Similarly a tube 40 is arranged concentric relative to the pipe 31 and is welded onto the external cylindrical surface of the boss 33. A collar or end cap 41 fits on the pipe 31 and within the end of the tube 40 and is welded to both the pipe 31 and the tube 40 to enclose the right hand end of a water-cooling chamber 42. In order to facilitate circulation of cooling fluids, such as water, the housing 30 is provided with a plurality of holes 43 (Figs. 2 and 5) which connect the chamber 39 with the chamber 42. Coolant may be passed through a pipe 44, into the chamber 39, through the holes 43, through the chamber 42 and out through the pipe45 so as to cool a slurry or suspension of material passing Within the pipe 27 and they pipe 31.

The diaphragm pump 20 may be operated in any suitable manner; as shown an electric motor 46"operates a reduction gear unit 47 which drives a belt 48 which drives a pulley 49 secured to which is an eccentric 50 operating a connecting rod 51 which operates the'diaphragnr 52 A long cylinder 55 functions as a dome or accumulator to keep the flow as steady as possible. On this may be mounted an air pressure gauge 56. i

A pipe 57 is connected to a water main and to a valve, 58 which is connected to a pipe 59 which is connected to a T-union 60. The T-union 69 is connected bya' hose 61 to a valve 62 which is connected to the T-union 26 on the left hand end of the pipe 27 (Fig. l). The valve 62 is normally closed and may be opened manually to facilitate flushing out the pipes 27 and 31, and also the nozzle unit 21.

, Referring again to Fig. 1, the pipe 31 is connected to a valve 69. The pipe 45 is connected to a hose 70 which is connected to drain. I

The T-union 60 is connected by a hose 71 to the pipe 44 .and1so therefore, when the valve 58 is open, water passingthrough the nozzle as, during operation of the process, the: atmosphere within the funnel 74 is hot. Some water can be added to the slip, if desired, by opening the valve 62, more or less.

refcrringto Fig. 1, a pipe 75 is-connected to an air pressuremain and to avalve76 which is connected by -a pipe 77 to a water trap 78 which is connected by a pipe79 to a reduction valve 8 which is connected by a pipe 81 to a T-union82 which is connected by piping 83 tothe housing 30. j t 1 Referring to Fig. .2, fluid under pressure from the pipe 83 passes to the housing 30 into an annular air chamber 85 which is incommunication with a plurality of perforations or. holes 86-. formed in a diffusion plate 87. The perforations or holes 86 in the diffusion plate 87 serve to diffuse the air under. pressure passing from the chamber 85 into the noule apertureflThe thickness of the diffusion plate ;87 serves to determine the relative positions of the'no zzle aperture 90. and the slurry nozzle orifices 91, thereby providing means for adjusting the combinedactions of the nozzles. The diffusion plate 87 has a central: aperture which fits around the outer periphery ofsthe slurry nozzle 36 and is held in position on the housingl30 by a cap 88 which is preferably screw-threaded onto, the housing-30 to facilitate changing the diffusion plate 87 when desired. Air passing through the perforations or holes 86entersa chamber 89 and is forced upwardly through a frusto-conical nozzle aperture 90 so as to form an upwardly converging jet of air surrounding the orifice 91 of the slurry noule 36. This slurry or slip issuing from" the orifice 9 1 of the slurry nozzle 36 is immediately atomized by the air issuing from the chamber 89. Consequently thegslip becomes a spray of particles which are directed upwardly through a hollow ring 92 (Fig. 1) open on the upper side and from it hot gas is being'distributed upwardly. We will now describe the means for producing and directing the flow of hot gas.

kcferringgto Fig. l, a; pipe 95 is connected to a gas main and to a valve 96. i The. valve 96 is connected by a pipe 97, elbow 98 and pipe 99 to a carburetor 100 which has adjustable air inlets, the shape of the carburetor and the locationof the airinlets being such as to cause air to beentrained into and mixed with the combustible gas entering thecarburetor 100; the carburetor 100 is connected by an. elbow 101 and, short pipe 102 to a second carburetor 103having fixed air inlets 104 .for the admission of additional air. The carburetor 103 is connected by an elbow pipe 105 to the hollow ring 92 and supports it. Consequently when the mixture of air. and gas is ignited, an :upwardly directed ring of flame is produced abovet hehollow ring 92; the spray enters this hollow ring of flarne and moves upwardly therewith and eventually, because of the rapid uprushof gas and hot air prevents the material from falling back through the ring 92, the spray spreadsout in expanding funnel'shape and falls downwardly into the funnel74. ,The locus of the upformed by the spray drying apparatus, it is desirable to control the stream of air under pressure passing from the conical aperture 90. The upperend of the slurry nozzle 36 is provided with an external frusto-conical surface 36a, the vertex angle of which is approximately 60. The vertex angle of the conical aperture 90 has been illustrated as approximately 35. Depending upon the material being treated and the resulting product desired, the

' latter angle may be varied from 35 to 9 by providing a series of caps 88 with the desired angle for the conical aperture 90. By varying the relationship of the frusto conical surface 36a and the conical aperture 90, the path of air under pressure passing from the spray nozzle may be variedso as to produce variations in the size of the particles or pellets produced.

The position of the conical aperture 90 may be varied relative to the frusto-conical surface 36a by providing diffusion plates 87 of different thicknesses so as to raise or lower the position of the aperture 90 relative to the surface 36a. As illustrated in Fig. 2, the diffusion plate 87 positions the conical aperture 90 so'that theupper face of the cap88 lies in the same plane with the upper end of the slurry nozzle 36 so that air passing from the nozzle converges upon the stream of slurry directly above the nozzle so as to break down the slurry into relatively fine particle or pelletsizes. If it is desired to increase the size of the particles or pellets produced, a thinner diffusion plate may be employed, as shown in Fig. 4, so that the slurry nozzle 36 projects above the upper surface of the cap 88. In the latter positions of the conical surface 36a and 90, air passingfrom the nozzle impinges upon the stream of slurry at a greater'distance from the nozzle so that; the air velocity on the stream of slurry is somewhat reducedthereby breakingthe slurry down into larger particle or pellet size. The size of the particles or pellets, produced may also be varied by using a cap 88 having a conical aperture with adifferent vertex angle. With a smaller vertex angle the air passing through the nozzle will impinge upon the stream of slurry at a greater distance from the nozzle thereby eifecting' a reduced velocity of air which serves to break down the slurry into particles or pellets of larger size.

I provide means for removing the gases of combustion after they have to. a certain extent given up their heat and at a place to promote the circulation above indicated. To that end, and still referring to Fig. l, I have provided a double elbow pipe which enters the funnel 74 through a hole just large enough to receiveit and extends by way of a portion 116 which becomes wider in the vertical dimension without increasing in width in the horizontal dimension, to a cyclone separator 1 17 which, as cyclone separators are well known, need not be described in detail. The cyclone separator eliminates from the moving gases most of the entrained solids therein which fall downwardly into a metal receptacle 120. The gases move upwardly through an elbow pipe 121 connected to the cyclone separator 117; the other end of the elbow pipe 121 is connected to the inlet end of a centrifugal blower 125 the outlet of which is connected to a pipe 126 leading to a chimney or the like. A damper 127 operated by an arm 128 the end of which is bent over and can be placed in any one of a number of holes 129 in a plate 130 for adjusting the position of the damper 127 is preferably provided to control the amount of air being drawn from the funnel 74 by the blower 125.

By closing the valve 69 I can force all of the slip pumped bythe pump 20 to be ejected from the orifice 91. On the other hand, by opening the valve 69 more or less,

. I can allow more or less of the slip to by-pass the passage 35 of the spray nozzle unit 21 to be returned to the mixing:bowl10 by way of a long hose which, as clearly shown in Fig. 1, extends from the valve 69 to a position just above the bowl 10. a

As shown in Fig. 1 a manually operable valve 69 is provided for controlling the by-pass of slurry through the lay-pass pipe 135 so. as to regulate. the. amount of: slurry passing, through the slurry orifice 91. ofv the slurry nozzle 36. I

If desired, an automatic controlm'ay. b'e'provided such as for example, an automatic. diaphragm-actuated valve 106 (Fig. 6). in the by-pass pipe 135.. This diaphragmactuate'd valve 106'may. be: any-of. the well .known'commercial type valves. .A controlling mechanism.is provided for controlling. the. actuation of the valve 106. This mechanism may comprise athermocouple 1-07v located in the pipe 116 through which. exhaust gases and pallets pass. The thermocouple 107 is connected to a. pneumatic temperature recorder-controller. 108,. such as, for example that manufactured by thev Wheelco Instrument Co. of Chicago, Illinois. The power lines 109 supply current to the recordercontroller 108. A. pipe. 112. connected to any suitable source of air under pressure is supplied to the recorder-controller.108'. This mechanism as shown diagrammatically in Fig. 6 is. arranged. so that if the temperature of the gases exhausting. through. the pipe 116 from the funnel74 increases, the thermocouple 107 through the recorder-controller 108' will actuate the diaphragm valve 106-tocut down the by-passing slurry through the pipe 135 so as' to force a greater quantity of the slurry upwardly through the slurry nozzle 36 and the orifice 91 thus introducing more moisture into the dryer to be dried. and vice versa. I' provide means for discharging, the pellets formed from the funnel 74 without materially disturbing the atmosphere in the funnel. 74-andt cylinder 1.10 To that end I provide a hollow rectangular downward extension 138 of the funnel 74 (which has a small opening on the bottom) and in this extension 138'isarevolvinggate 139 which may. have the shape of, a paddle: wheel and which is mounted on a rotatable shaft 140: A pulley 141: secured on the shaft 140 isd-riven by" a-belt 142froma pulley 143 on. the outputend of reduction gearing [44 driven by an-electric motor 145. It will' readily be seen that the accumulation of particlesin the. bottom of the funnel 74 is intermittently but regularly discharged into any suitable collecting container suehzasthe refractory sagger 150. In this connection it should be noted that the valve 96'and the damper 127 can: bes'o adjusted that the pressure of the hot gases witl'iin'thev funneli 7.4. and the cylinder 110 is substantially at atmospheric pressure or, preferably, just barely below it so as to avoid discharging gases of combustion into the room where the apparatus is located.

Preferably I provide various devices for measuring the parameters of the process, for example an air gauge 151 connected to the T-union 82, a door 152 having a glass pane 153 for viewing the interior of the cylinder 110, and the door 152 is shown as mounted on a hinge pin 154 suitably secured to the cylinder 110 and held in closed position by a wing nut 155. thermometer 160 on the elbow pipe 121 to measure temperature therein and a thermometer 1 62 located in the funnel 74 but readily removable therefrom for reading.

By this process I make various particles sizes depending upon the adjustment of the spray nozzle and other factors, and these may include particles as large or even larger than No. 20 grit size down to as small or even smaller than No. 320 grit size. With suitable equipment designed to produce an extremely fine spray or fog, it is believed that a large part of the product can be made finer than No. 320 mesh when desired. Of course for the smaller sizes the particle size of the metal oxide should be small as the ultimate particles are aggregates of very many individual oxide particles. In general increase of the air pressure by adjusting the air valve 76 and the reduction valve 80 decreases the particle size of the product 170 in the sagger 150. Increase of the volume of gas being burned as by setting the valve 96 accelerates the drying which may be required for maxi- I may also provide a amount of slip being. sprayed. can, as already indicatedi, becontrolled by the alve 6911p to the maximum-amount beingdelivered by the pump 20. There are thusmany, variables and the apparatus can be adjusted to. produce.

particles of. the desired sizeand. when that. has been.done.

tially spherical particles or pellets within the size limits indicated.

The pump 20is preferably a low volume lowvelocity pump for passing a highly abrasive slurry at arelatively low velocity through the aperture 36 and the orifice. 91 of the slurry nozzle 36 thereby reducing wear, in. the orifice to a minimum. slurryand air under pressure mix at a point-outside the nozzle thusaiding in minimizing abrading action of the slurry on the nozzle parts.

The spray nozzle unit 21 has been illustrated in Fig. l in an up-draftspray drying apparatus. This spray nozzle unitv 21' is equally applicable to a spray dryingapparatus in which a down-draft is employed.

The apparatus disclosed in this application is. somewhat similar to that disclosed but not claimed in the cm pending application, Serial No. 325,862 filed December 13, 1952,.and now abandoned. 1

It will thus be seen that there has been provided by this invention a process for the manufacture of. spherical particles according to which. the various objects hereinabove set forth. together with many thoroughly practicaladvantages arev successfully achieved. As'many possible embodiments may be made of the above invention and as many changes might be made in the embodiments above set forth, it. is to be understood that all matter hereinbefore set. forth or shown in the accompanying drawings isxto be interpreted as illustrative and not inva limiting sense.

I claim:

1. Inv a spray drying apparatus, a vertically-arranged dryingcha-mber, a slurry feed tube passing through said chamber, a two-fluid spray nozzle therefor comprising a slurry nozzle operatively connected with a central portion of the slurry feed tube, an air nozzle surrounding thedischarge end of said slurry nozzle, the axes of said nozzles being arranged in axial alignment with the vertical axes of said chamber, a slurry tank, means including a pump to feed slurry from said tank to one end of said feed tube and nozzle, means to feed a controlled stream of air under pressure to said air nozzle, a by-pass pipe connected between the other end of said slurry feed tube :and said tank, a valve between the other end of said feed tube and said by-pass pipe to regulate back pressure within the slurry tube so asto vary the quantity of slurry passing through the slurry nozzle, and a ringshaped burner surrounding said nozzle to produce a circular flame to aid the nozzles in producing a relatively high funnel shaped spray of slurry to facilitate the drying operation.

2. In a spray drying apparatus, a vertically-arranged cylindrically-shapeddrying chamber, a slurry feed tube passing through one end of said chamber, a two-fluid spray nozzle therefor comprising a slurry nozzle operatively connected with a central portionof the slurry feed tube, an air nozzle surrounding the discharge end of said slurry nozzle, the axes of said nozzles being arranged in axial alignment with the axis of said drying chamber,

means to cool said slurry tube as it passes through said chamber to prevent drying and caking of slurry passing through said tube, a slurry tank means including a pump to feed slurry from said tank to one end of said feed tube and nozzle, means to feed a controlled stream of air under pressure to said air nozzle, a bypass pipe connected between the other end of said slurry feed tube mum production and for the larger particle sizes. The and said tank, an automatically actuated valve in said by- In applicants apparatus. the.

pass pipe automatically to vary back pressure within the slurry feed tube by varying the amount of by-passed slurry so as to regulate the quantity of slurrypassing through the slurry nozzle, means including a thermostat actuated by exhaust gases from the dryer and operative connections between said thermostat and said valve automatically to control said valve.

3. In a spray drying apparatus, a vertically-arranged cylindrical drying chamber, a slurry feed tube passing through said chamber, a two-fluid spray nozzle therefor comprising a slurry nozzle operatively connected therewith at a central portion thereof, an air nozzle surrounding the discharge end of said feed nozzle, a slurry tank, means including a pump to feed slurry from said tank to one end of said feed tube, means to feed a controlled stream of air under pressure to said nozzle, the axes of said nozzles being positioned in alignment with the axis of said drying chamber, a by-pass pipe conneetedbetween the other end of said feed tube and said tank, an automatically actuated diaphragm throttle valve'in said by-pass pipe to vary the pressure within the slurry tube by controlling the amount ofby-pass slurry thereby to 4. In a spray drying apparatus comprising a vertically-' arranged cylindrical drying chamber, a slurry feed tube passing therethrough, a two-fluid nozzle therefor including a housing located'mid-way of said tube, a vertical aperture in said housing, a slurry nozzle supported in said aperture having a central aperture for discharging a slurry, an air nozzle surrounding the discharge end of said slurry nozzle, the axes of said nozzles being positioned in alignment with the axis of said drying chamber,

a slurry tank, means including a pumpto feed slurry from said tank to one end of said tube and nozzle, means to feed a controlled stream of air under pressure to said air nozzle, a tube surrounding said slurry feed tube. as it passes through the drying chamber to form a cooling chamber, means to circulate a cooling fluid therethrough,

a by-pass pipe connected between the other end of said feed tube and said tank, said cooling chamber serving to prevent drying and caking of slurry passing through said tube to said nozzle and said by-pass pipe, an automatically actuated valve in said by-pass pipe to facilitate regulation of back pressure of .slurry within the slurry tube by controlling the amount of by-pass slurry thereby to regulate the quantity of slurry passing through the slurry nozzle, and means including a thermostat actuated by exhaust gages from the drying chamber to control said valve.

5. A nozzle for spray drying apparatus comprising a slurry feed tube, a two-fluid nozzle therefor including a housing operatively connected to said tube, a vertical aperture in said housing, a slurry nozzle supported in said aperture having a central aperture for conveying a slurry, said hollow nozzle having a downwardly flaring external frusto-conical surface on its outer periphery at the upper end thereon, an annular air chamber in said housing surrounding said vertical aperture, a perforated diffusion plate enclosing the upper end of said chamber and a cap to hold said plate on said housing, said cap having an internal frusto-conical aperture forming an air nozzle, said nozzles being arranged so that slurry passing through the slurry nozzle is picked up by air under pressure from the air nozzle after it leaves the slurry nozzle so as to minimize wear on the nozzles, the thickness of said plate determining the relative positioning of said frusto-conical surfaces to facilitate varying the action of said nozzle on a slurry passing therethrough so as to facilitate varying the size of particles or pellets produced.

References Cited in the file of this patent UNITED STATES PATENTS 726,442 Macdonald Apr. 28, 1903 772,496 Brening Oct. 18, 1904 954,451 Merrell Apr. 12, 1910 1,471,765 Wilson Oct. 23, 1923 1,597,033 Gibbons Aug. '24, 1926 1,757,573 Heinrich May 6, 1930 1,779,516 Stevenson Oct. 28, 1930 1,779,551 Forney Apr. 7, 1931 2,561,394 Marshall July 24, 1951 2,564,060 Gettins Aug. 14, 1951 2,566,229 Mackay Aug. 28, 1951 2,595,114 Wieseitier Apr. 29, 1952

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