US 3193991 A
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Description (OCR text may contain errors)
y 1965 J. L. BROWNING ETAL 3,193,991
CONTINUOUS MIXING APPARATUS Filed Sept. 25, 1963 K m R A O P 2 GT M l U m m p m w w a "DO U m 5 C C H 2 W C O G a m T m 4 2 s T 2 2 A L C H I 6 J 4 2 E9 8 LR M2 2 A L GT P A FR h RA L S l TP A 2 NE 8 G R ES GE C 4 mm MA MW .6 O rm 2 m 4 S 8 DD D WE m u E WHT 7 INVENTORS. JOE L. BROWNING ALBERT J. co
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United States Patent "ice 3,193,991 CONTINUUUS MlXlNG APPARATUS Joe L. Browning and Albert J. Colli, Indian Head, Md, assignors to the United States of America as represented by the Secretary of the Navy Filed Sept. 25, 1963, Ser. No. 311,597 7 11 Claims. (Cl. 55185) (Granted under Title 35, U.S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
This invention relates to mixing apparatus, and more particularly to an apparatus for continuously mixing liquids with pneumatically conveyed solids.
In the past, the techniques utilized for continuously mixing the solid and liquid constituents of rocket propellants have possessed many inherent dangers and problems due to the nature of the apparatus which it was necessary to utilize. For example, continuous helical mixers have been used in which the solid and liquid constituents move slowly through the groove of a mixing screw and are blended by the resultant agitation. Mixers of this type are dangerous for the manufacture of propellants because of the possibility of having particles caught and fractured between moving parts with a resultant explosion. Also, helical mixers have a relatively large hold-up and small capacity for their size.
Continuous mixing of propellant constituents has also been accomplished in the past in blending machines wherein the solids are carried by an inert liquid diluent. There are many problems associated with the removing of the liquid diluent from the mix, however, and the uncertain eifect of small residual amounts of diluent in the product poses further problems. Also, it is very diflicult to accurately meter the slurry in order to obtain proper proportioning of the various constituents. Manifestly, it would be highly desirable if a continuous mixing apparatus could be provided, for mixing particulate solid and liquid constituents, which was free of the aforedescribed disadvantages.
It is therefore a primary object of the present invention to provide a new and improved continuous mixing apparatus.
It is another object of this invention to provide a new and improved mixing apparatus for continuously blending particulate solid materials with liquid constituents.
It is a further object of the present invention to provide a continuous mixing apparatus wherein the mixing chamber has no moving parts.
It is yet another object of the present invention to provide a continuous mixing apparatus having a relatively small hold-up in relation to its size.
With these and other objects in view, the present invention contemplates a continuous mixing apparatus including an elongated, porous-wall tube into which metered quantities of pneumatically conveyed solid particulate materials are inserted. The liquid or liquids to be blended with the solid materials are injected into the gas stream adjacent the entrance end of the porous tube. An addi tional supply of the carrier gas is introduced into a manifold surrounding the porous tube and flows rapidly through the pores of the tube wall. The gas flowing through the tube wall will move the solid particles and liquid droplets in a random manner as if fully developed turbulent flow were established in a conventional pipe. Also, the gas entering the tube through the walls thereof will also serve to reduce the drag between the materials in the porous tube and the tube wall. A centrifugal separator receives the output of the porous tube and separates the carrier gas from the solid and liquid mixture.
3,1933% Patented July 13, 1955 The carrier gas exiting from a centrifugal separator is filtered and recompressed for further use, while the solid and liquid mixture is withdrawn from the bottom of the separator through a slit plate and cast into the desired form.
Other objects, advantages and novel features of the invention will become readily apparent upon consideration of the following detailed description when read in conjunction with the accompanying drawings wherein:
FIG. 1 is a schematic representation of the system embodying the present invention;
FIG. 2 is an enlarged view, partially in section, of the mixing chamber of the present invention;
FIG. 3 is a sectional view taken along the line 33 of FIG. 2 further enlarged and illustrating the relative arrangernent of the porous mixing tube, surrounding manifoldand carrier gas supply pipes; and
FIG. 4 is a sectional view taken along the line 44 of FIG. 3 further enlarged and illustrating the arrangement of nozzles on the inner wall of the delivery tube which serve to inject the liquid constituent into the gas stream within the delivery tube.
Attention now is directed to the drawings, wherein like numerals of reference designate like parts throughout the several views, and more particularly to FIG. 1 for a description of the operation of the continuous mixing apparatus of the present invention. The system comprises a carrier gas tank 10 connected to a supply line 11 through a regulating device 12. The particular conveying gas used will be dictated by the nature of the solid and liquid ingredients to be mixed. Naturally, the gas will be one which will not react with any of the propellant constituents. The regulating device 12 is not shown in detail and may be any suitable type which will permit regulation of the rate of discharge of gas from the tank 10 and hence the velocity of the conveying gas through the system which in turn controls the mixing rate. A plurality of solid feeders 14 are connected to the supply line 11 and are provided for metering predetermined quantities of the solid particulate constituents of the propellant into the gas stream within the supply line 11. The specific nature of the feeders 14 will of course be dictated by the properties of the solid materials to be handled.
The supply line 11 is connected by means of a delivery tube 15 to a mixing chamber, designated generally by the reference numeral 16. A liquid feeder 18 is connected to the delivery tube 15 by means of a liquid feed line 19. The liquid feeder 18 may be of any suitable type which is capable of providing an adjustable flow rate. An interconnection between the supply line 11 and the mixing chamber 16 is provided by a bypass line 26 and connecting branch lines 21.
A centrifugal separator 22 is connected to the exit end of the mixing chamber 16. The separator 22 is coupled to a filter 24 and a compressor 25 through a discharge line 26. The compressor 25 serves to Withdraw the conveying gas from the separator 22 through the filter 24, and then to return the recompressed gas to the gas tank It The bottom of the separator 22 is connected to a casting chamber 28 through a slit plate 29. The solid and liquid mixture is withdrawn through the slit plate 29 into the casting chamber 28 and is then cast into the desired shape. A vacuum pump 30 is provided for degassing the solidliquid mixture by maintaining a vacuum over the material being drawn through the slits. The output of the vacuum pump 30 is returned to the system through the discharge line 26 at a point adjacent the intake of the compressor 25. V
V The mixing chamber'16 will now be described in further detail with particular reference to FIGS. 2, 3 and 4. The mixing chamber comprises a cylindrical porous walled tube 31 which is disposed within and coaxial with a cylindrical manifold 32. The manifold 32 has a plurality of apertures formed therein which accommodate the ends of the branch lines 21. A hollow-walled section 34 is formed on the end of the delivery tube and projects a short distance into the entrance end of the porous mixing tube 31. A plurality of nozzles 35 are formed by holes drilled through the inner wall of the hollowwalled section 34, and as can be best seen in FIG. 4, the nozzles 35 are uniformly spaced about the periphery of the inner wall of the section 34. It will be noted that the nozzles 35 are in fluid communication with the interior 36 of the section 34 which is in turn in fluid communication with the liquid supply line 19.
Operation In order that a better understanding of the invention might be had, its mode of operation will now be described. Gas fiow is initiated in the supply line 11 and brought up to the desired velocity by means of the regulator 12. The vacuum pump 30 is then started. The solid feeders 14 are next started and begin metering quantities of solid particulate material at a predetermined rate into the gas stream in the line 11 to become entrained therein. The liquid feeder 18 is then started and set to deliver at the desired rate. The liquid constituent will flow through the feed line 19, into the interior space 36, and then out through the nozzles 35 to impinge upon the stream of gas and entrained solids at right angles thereto. This begins the mixing operation.
Additional conveying gas will fiow through the bypass line 20 and into the interior of the manifold 32 through the branch lines 21. The bypassed gas will then flow through the pores of the mixing tube 31 and into the interior thereof. The additional gas flowing through the pores of the mixing tube 31 will establish a velocity gradient along the mixing tube 31 with the exit velocity of the gas stream being significantly higher than the entrance velocity. The solid-liquid mixture entrained in the gas stream will, of course, be accelerated along with the gas although at a lesser rate. The lesser acceleration of the solid-liquid mixture and the introduction of additional gas through the pores of mixing tube 31 will result in a continuous reduction in the concentration of material in the gas stream. Under these circumstances, the conditions of turbulent fiow in a conventional pipe have been duplicated and thorough mixing is achieved.
By disposing the nozzles 35 perpendicular to the high velocity gas stream in which the solid particles are entrained, the kinetic energy of the liquid stream is used to penetrate the gas stream so that the liquid is suddenly subjected to a high velocity gas. The liquid is introduced near enough to the mouth of the delivery tube 15 so that the droplets of liquid do not impinge upon the tube Wall. This is accomplished by sizing the cross-sectional area of the nozzles 35 so that the resultant velocity vector will allow the liquid to converge outside of the tube. A sheet of extremely small liquid droplets evenly distributed over the cross-section is formed outside the mouth of the tube 15. By making this liquid sheet sufiiciently dense, a very high percentage of the pneumatically conveyed solids will be immediately exposed to the liquid. The turbulent fiow conditions and acceleration effects in the remainder of the mixing tube 31 will then serve to complete the mixing process and produce a solid-liquid mixture which is substantially homogeneous.
Upon leaving the mixing chamber 16, the conveying gas stream and the entrained solid-liquid mixture enter the centrifugal separator 22 for separation of the gas from the solid-liquid mixture. The gas leaving the top of the separator will be filtered, recompressed and then returned to the gas tank 10 for recycling. The solidliquid mixture is continuously withdrawn from the bottom of the separator through a slit plate and cast into the desired shape. The vacuum pump 30 will, as previously mentioned, serve to degasthe mixture by maintaining a vacuum over the material being drawn through the slits.
From the foregoing, it, Will be readily apparent that the present invention provides a new and improved continuous mixing apparatus possessing numerous advan tages not attainable with prior art devices. For example, the consistency of the material to be mixed will not be a sensitive parameter to the degree of dispersion. What would be a thick, relatively immobile mass in a conventional mixer, in the present invention will be a particulate mixture entrained in a carrier gas. Also, since the present invention involves no moving parts within the mixing chamber, a hazard of considerable significance in the mixing of propellants and explosives is eliminated. And further, the entire system including the feeders, mixer, centrifugal separator, casting chamber and compressor could be closed for the mixing toxic materials.
Certain modifications of the disclosed embodiment will immediately suggest themselves to those skilled in the art. For example, a series of grooves could be cut out of the exterior surface of the mixing tube 31. The velocity of the carrier gas through the grooved channel would then be greater than through the thicker porous section. The stream of higher velocity gas through the channel would form a continuous helicoid extending the length of the tube. An approach of this kind might enable a still higher degree of dispersion to be attained. Also, although the illustrated embodiment shows only a single liquid feeder, it is manifest that additional liquid feeders could be provided with mixing of the liquid constituents taking place in the interior space 36 or in the mixing tube 31 through the provision of separate sets of nozzles for each liquid.
It is to be understood that the disclosed embodiment simply represents a preferred form of the present invention. Numerous other arrangements may be readily devised by those skilled in the art to achieve a similar apparatus still embodying the principles of the present invention and falling within the spirit and scope thereof.
What is claimed is:
1. An apparatus for continuously mixing liquids with pneumatically-conveyed, particulate solids comprising a porous tube,
means for injecting in one end of said tube a stream of gas having particulate solids entrained therein, means disposed in said one end of said tube for introducing liquid into said gas stream,
and means including a manifold surrounding said tube for applying pressurized gas to the exterior of said tube whereby turbulent flow within said tube is produced by gas flowing into said tube through the pores thereof.
2. The mixing apparatus of claim 1 wherein the liquid is introduced in a direction substantially perpendicular to the flow direction of said gas stream.
3. The mixing apparatus of claim 1 wherein the other end of said tube empties into a centrifugal separator,
said separator serving to separate the conveying gas from the solid-liquid mixture.
4. The mixing apparatus of claim 3 wherein means are provided for compressing the gas output from said centrifugal separator and recirculating said gas to entrain further particulate solid matter.
5. An apparatus for continuously mixing liquids with pneumatically-conveyed, particulate solids comprising a porous mixing tube,
a delivery tube coaxial with said mixing tube and projecting into one end thereof,
means for supplying to said delivery tube a high velocity stream of gas having particulate solids entrained therein,
means disposed on the inner end of said delivery tube for injecting liquid into said gas stream in a direction substantially perpendicular thereto,
and means including a manifold surrounding said bulent flow within said mixing tube is produced by gas flowing into said tube through the pores thereof.
6. The mixing apparatus of claim 5 wherein said delivery tube is a hollow walled tube,
and said liquid injecting means includes a plurality of nozzles formed on the inner wall of said delivery tube adjacent the end thereof.
7. The mixing apparatus of claim 5 wherein a centifugal separator is coupled to the other end of said porous mixing tube for separating the conveying gas from the solid-liquid mixture.
8. The mixing apparatus of claim 7 wherein means are provided for compressing the gas output from said centrifugal separator and recirculating said gas to entrain further particulates sol-id matter.
9. An apparatus for continuously mixing liquids with pneumatically conveyed particulate solids comprising a delivery tube,
means for creating a ligh velocity gas stream within said delivery tube,
means for metering solid particulate materials into said delivery tube upstream of the exit end thereof,
a porous-walled mixing tube coaxial with said delivery tube,
a hollow-walled section formed on the exit end of said delivery tube and projecting into the entrance end of said mixing tube,
a plurality of nozzles formed on the inner wall of said hollow-Walled section,
means for feeding liquid into said hollow walled section for injection into said gas stream through said nozzles,
and means including a manifold surrounding said porous mixing tube for applying high pressure gas to the exterior of said mixing tube whereby turbulent flow within said mixing tube is produced by gas flowing into said mixing tube through the pores thereof.
10. The mixing apparatus of claim 9 wherein a centrifugal separator is coupled to the exit end of said mixing tube for separating the conveying gas from said solidliquid mixture.
11. The mixing apparatus of claim 10 wherein means are provided for filtering and recompressing the gas output from said separator and for returning said gas to said gas stream creating means.
References Cited by the Examiner UNITED STATES PATENTS 1,934,840 11/33 Claude].
2,294,973 9/42 Ford 261122 2,884,375 4/59 Seelig et al. 2594 XR 2,951,061 8/60 Gomory 2594 XR 3,153,578 10/64 Taylor 2594 XR WILLIAM J. STEPHENSON, Primary Examiner.