US3441135A - Particle classification device and method - Google Patents

Particle classification device and method Download PDF

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Publication number
US3441135A
US3441135A US597066A US3441135DA US3441135A US 3441135 A US3441135 A US 3441135A US 597066 A US597066 A US 597066A US 3441135D A US3441135D A US 3441135DA US 3441135 A US3441135 A US 3441135A
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Prior art keywords
coarse
fine
stage
particles
gas
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Charles E Lapple
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Mikropul Corp
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Donaldson Co Inc
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
    • B04C—APPARATUS USING FREE VORTEX FLOW, e.g. CYCLONES
    • B04C5/00—Apparatus in which the axial direction of the vortex is reversed
    • B04C5/24—Multiple arrangement thereof

Definitions

  • FIG. 1 PARTICLE CLASSIFICATION DEVICE AND METHOD Sheet Z of 2 Filed Nov. 25, 1966 FIG. 1
  • This invention pertains to an improved particle classification device and more specifically to a classification device in which the classification occurs under a pressure less than atmospheric pressure.
  • Powders of various materials are utilized to an ever increasing extent in present day technology.
  • particle size is one of the most important properties of powders and governs such phenomena as flowability, packing density, and physical reactivity.
  • powders are ordinarily prepared to a given size specification by a process which is termed classification.
  • Classification in general is the separation of a powder into a coarse fraction containing coarse particles, having a size somewhat larger than a cut size, and a fine fraction containing fine particles having a size equal to or less than the cut size.
  • the cut size is equivalent to the separation point or the particular size of particles about which the powder is separated.
  • Particle size is usually expressed in terms of particle diameter. If particles are not spherical, an equivalent or apparent diameter may be used. One common method is to express size in terms of an equivalent spherical particle having the same settling velocity as the particle in question.
  • the best known type of classifying device is the screen or sieve which simply allows the fine particles to pass therethrough and maintains the coarse particles thereabove.
  • the usefulness of the screen or sieve is generally restricted to classifying particles coarser in size than 100 microns.
  • Air classifying devices are usually used for obtaining size classification in the range below 100 microns.
  • gravitational air classifying devices In general there are two types of air classifying devices: gravitational air classifying devices and centrifugal air classifying devices. Gravitational air classifying devices are limited primarily to particle classification above 50 microns because of the low separation velocities that are involved with finer sizes.
  • Centrifugal air separators which have much higher separation velocities, are used for most dry classification applications. Centrifugal air separators are generally grouped into two categories: one, the equipment is stationary and the air rotates therein, for example the cyclone separator; two, the equipment rotates and the air 3,441,135 Patented Apr. 29, 1969 passes therethrough, for example, the centrifuge. Although centrifugal air separators are capable of separating fine powders into fine and coarse fractions, the sharpness of separation is usually not good. That is, the dividing line between the fine and the coarse fractions is not well defined and both groups will have some particles of the same size therein.
  • FIGURE 1 is a diagrammatic view of an embodiment of the classifying device
  • FIGURE 2 is an enlarged axial sectional view of a single cyclone separator depicting the powder passing through a first stage of separation;
  • FIGURE 3 is a sectional view as seen from the line 3-3 in FIGURE 2;
  • FIGURE 4 is a view similar to FIGURE 2 depicting the powder passing through the last fine stage of separation.
  • the numeral 10 designates a first separator stage having an inlet 11, a fine fraction outlet 12, and a coarse fraction outlet 13.
  • the separator 10 may be any of the well known types including gravitational or centrifugal air separators, however, because the operation of the centrifugal air separators is far superior to that of the gravitational air separators, the use of centrifugal air separators in this device is preferred.
  • the cyclone type centrifugal air separators are utilized for purposes of simplicity. It should be understood, however, that the use of cyclone separators in the disclosed embodiment should not in any way limit the scope of this invention. Detailed views of a single cyclone separator are illustrated in FIGS. 2, 3, and 4.
  • FIGURES 2 and 3 illustrate the internal construction and operation of a typical cyclone separator wherein it is operating as the first separator stage 10 of the system in FIGURE 1.
  • the various portions of the cyclone separator in FIGURES 2 and 3 have been designated with the same numbers as those which were util'ued in conjunction with the first stage in the system illustrated in FIGURE 1 to indicate the manner in which the cyclone separator illustrated in FIGURES 2 and 3 will be connected into the system of FIGURE 1.
  • the main body of the separator 10 has a cylindrical portion and a frusto-conical portion 16 attached thereto.
  • the cylindrical portion 15 and the frusto-conical portion 16 are integrally attached and form a continuous cavity therein.
  • the inlet 11 is tangential to and in communication With the cylindrical portion 15 while the fine fraction outlet 12 is coaxial with and positioned in the upper surface of the cylindrical portion 15.
  • the coarse fraction outlet 13 is positioned at the extreme tip of the conical portion 10.
  • the particles entering the input 11 are conveyed by a gas, such as air or the like, and enter the cylindrical portion 15 of the body with a predetermined velocity. Because of this velocity and because the inlet 11 is tangential to the cylindrical portion 15, the gas and the mixture of coarse and fine particles travel in a downwardly spiraling path, indicated by the solid arrows, to form a vortex adjacent the inner surfaces of the cylindrical portion 15 and conical portion 16.
  • the downwardly spiraling gas and particles gradually change direction axially, and spiral upwardly in the center of the vortex indicated by the dotted arrows.
  • This upwardly spiraling gas and particle mixture forms a smaller vortex within the outer vortex formed by the downwardly spiraling gas.
  • the axial change of direction of the downwardly spiraling gas, or the mass transfer of gas from the outer vortex to the inner vortex, takes place gradually over the entire tapered length of the conical portion 16.
  • the heavy or coarse particles are forced outwardly in the vortices and eventually travel downwardly into the coarse fraction outlet 13. Simultaneously the fine particles remain in the gas and eventually spiral upwardly into the fine fraction outlet 12.
  • the cyclone separator 10, as well as the gas classifiers function by virtue of a greater gas drag per unit mass experienced by the smaller particles.
  • the greater gas drag can be seen by noting that the drag of a particle is proportional to the diameter of the particle while the mass of the particle is proportional to the diameter cubed and, therefore, the drag per unit mass of the particle is in versely proportional to the diameter squared.
  • the separator 10 causes a centrifugal force to be exerted on the particles in a direction to counteract the gas drag force. Those particles for which the centrifugal force is greater than the force due to the gas drag will be separated from the gas and forced toward the Walls of the separator 10 where they will pass out through the outlet 13 as the coarse fraction.
  • the inner and outer vortices of the separator 10 may continue past the lower end of the frusto-conical portion 16 into the outlet 13 where reentrainment of the coarse particles in the gas can occur.
  • a conduit 25 is in communication with the coarse fraction outlet 13 and carries a small portion of the gas and the coarse particles entrained therein to a destination which will be described presently.
  • the diameter of the conduit 25 is reduced somewhat at the junction of the coarse fraction outlet 13 to produce a slight aspirating eflfect which aids in drawing the coarse fraction from the outlet 13.
  • the coarse particles entering the conduit 25 from the outlet 13 are thoroughly mixed with the gas flowing in the conduit 25 and conveyed thereby.
  • one end of the conduit 25 is connected to the input 26 of a second coarse stage 27,
  • a fine fraction output 30 of the second coarse stage 27 is in communication with the input 11 of the first stage 10 through a conduit 31.
  • a coarse fraction output 32 of the second coarse stage 27 is in communication with an input 33 of the third coarse stage 29 through a conduit 34.
  • a coarse fraction output 35 of the third coarse stage 29 is connected to a coarse fraction reservoir 36, which accumulates the coarse fraction.
  • the fine fraction is conducted back to the input 11 of the first stage 10 through the conduit 31 and is recirculated through the first stage 10. Also, the coarse fraction leaving the second coarse stage 27 through the coarse fraction outlet 32 is conveyed to the input 33 of the third coarse stage 29 through the conduit 34, where it is again separated, with the fine fraction leaving the fine fraction outlet 28 and being conveyed to the input 26 of the second coarse stage 27 through the conduit 25.
  • each of the additional stages 27 and 29 will increase the sharpness of separation, For example, assuming that the first stage 10 separates the powder entering input 11 so that percent of the fraction leaving the outlet 13 is coarse particles, the second coarse stage 27 will separate an additional percentage of the fine particles from the recirculated coarse particles, and the third coarse stage 29 will separate a further percentage of the remaining fine particles from the coarse particles.
  • the outlet 35 of the third coarse stage 29 has substantially pure coarse particles passing therethrough, however, to obtain absolutely pure coarse particles it would require, theoretically, an infinite number of stages.
  • the fine fraction outlet 12. of stage 10 is connected to an input 45 of a second fine stage 46 through a conduit 47.
  • a coarse fraction outlet 48 of the second fine stage 46 is connected to the input 11 of the first stage 10 through the conduit 31.
  • a fine fraction outlet 49 of the second fine stage 46 is connected to an input 50 of a third fine stage 51 through a conduit 52.
  • a coarse fraction outlet 53 of the third fine stage 51 is in communication with the conduit 47, and thus the input 45 of the second fine stage 46.
  • a fine fraction outlet 54 of the third fine stage 51 is in communication with a fine fraction filtering device 55 through a conduit 56.
  • FIGURE 4 An axial sectional view of the third fine stage 51 is illustrated in FIGURE 4.
  • the construction and operation are substantially similar to the construction and operation previously described in conjunction with the first separator stage 10 illustrated in FIGURE 2.
  • the solid arrows portray the outer vortex spiralling downwardly and the dotted arrows portray the inner vortex spiralling upwardly within the separator.
  • the majority of particles in the fine stage 51 are fine particles, which leave the outlet 54 as the fine fraction, and that there are only a few coarse particles, which leave the outlet 53 and return to the input 45 of the second fine stage 46.
  • the filtering device 55 is designed to separate fine particles from the gas conveying them.
  • the gas separated from the fine fraction in the filtering device 55 is conducted to an input 38 of a pressure means 39 through a conduit 57.
  • the pressure means 39 is illustrated diagrammatically as a fan and may be any device capable of impelling gas molecules through the system.
  • the conduit 57 has a valve means 58 therein to regulate the flow of gas through the conduit 57.
  • the pressure means 39 has an outlet 60 which is connected to the input 11 of the first stage 10 through a conduit 61.
  • the conduit 61 has a valve 62 therein to regulate the amount of flow entering the input 11.
  • the powder which is to be separated is introduced into the conduit 61 by means of a mixing device 65.
  • the mixing device 65 is diagrammatically illustrated as a simple hopper in communication with the conduit 61 at a position where the diameter is reduced slightly to create an aspirating effect which aids in drawing the particles from the mixing device 65. It should be understood that the mixing device 65 could be placed in communication with the conduit 31 adjacent the input 11 of the separator 10 and the entire conduit 61 could then be eliminated. However, the device 65 has been illustrated in the position illustrated for ease of explanation.
  • the reduced diameter in the conduit 61 at the junction of the mixing device 65 is not essential but it enhances the operation thereof. It should be further understood that a much more sophisticated device might be utilized which could form a portion of the pressure means 39 but since it does not constitute a portion of this invention, it will not be elaborated upon further.
  • a valve means 66 is placed in the outlet of the mixing device 65 to regulate the flow of particles therethrough.
  • the pressure means 39 forces the conveying gas through the conduit 61 to the input 11 of the first stage 10
  • the powder will be drawn from the mixing device 65 and conducted with the gas.
  • the powder will be classified by the stages 10, 27, 29, 46, and 51, after which the fine fraction will be removed from the gas by the filtering device and the coarse fraction will accumulate in the reservoir 36.
  • the conduit connected therewith is reduced slightly in diameter to produce an aspirating efiect in the outlet.
  • conduit with a reduced diameter is illustrated to simplify the disclosure but it should be understood that other devices, for example the rotary valve means 66, might be utilized at the junctions speci fied and the particle classifying device would operate all such embodiments or alterations which come within the scope of this invention and are deemed to be obvious from this disclosure.
  • FIGURE 1 shows a diagrammatical illustration of a pump 59 having the inlet thereof interposed in the conduit 57 and the outlet thereof vented to atmosphere. It will be understood that any pump capable of reducing the pressure within the system to the required amount may be utilized and that shown is for illustrative purposes only.
  • FIGURE 1 The entire system illustrated in FIGURE 1 is closed or isolated from the atmosphere and the pressure therein is reduced somewhat below atmospheric pressure by the pump 59.
  • the amount that the internal pressure by the reduced below atmospheric pressure to provide the desired cut size depends upon a variety of factors including the size of particles, which it is desired to classify, the type and size of classifier or separator utilized and the velocity of the gas at the outlet 60 of the pressure means 39.
  • a cut size of 0.5 micron may be realized with a particle having a specific gravity of 2.70. If the same cyclone is operated as a classifier at atmospheric pressure with an inlet gas velocity of 50 feet per second a cut size of only 1.7 microns may be realized with similar particles.
  • To realize a cut size of 0.5 micron at atmospheric pressure would require an inlet gas velocity of 500 feet per second. An inlet gas velocity of such a magnitude would require an exorbitant power to attain.
  • a cut size of less than 0.3 microns can be achieved by a further reduction in pressure. However, such smaller cut sizes cannot be obtained by an increase in velocity since it would require that the inlet gas velocity exceed the velocity of sound.
  • a twelve-inch diameter rotary classifier operating with a rotor speed of 3600 r.p.m., and an air rate of 40 cubic feet per minute would only give a cut size of 2 microns at atmospheric pressure with all other variables equal.
  • To achieve the comparable cut size at atmospheric pressure would require at rotor speed of 20,000 r.p.m., at which the rotor tip speed is approximately sonic.
  • lower cut sizes would theoretically be achieved by increasing rotor speed, lower cut sizes are precluded by structural limitations, except at radically reduced capacity. These limitations do not apply when reduced cut sizes are achieved by reducing gas pressure in the classifier.
  • the single stage 10 could be operated at a reduced pressure and would separate subrnicron particles. However, passing the separated particles through additional stages and recirculating them in a fashion similar to that described in conjunction with the system illustrated in FIGURE I greatly improves the sharpness of separation.
  • the present invention provides means for classifying submicron particles without requiring excessively high rotor speed or gas inlet velocities.
  • the present invention greatly improves the sharpness of classification, or separation at a predetermined particle size.
  • An improved particle classification system comprising:
  • separating means in said system having at least a classifying chamber with a powder inlet and fine and coarse fraction outlets for separating powders into fine and coarse fractions, said system being substantially sealed for precluding communication with the atmosphere;
  • pressure reduction means operatively connected to said system for reducing the pressure of the gas therein below atmospheric pressure an amount dependent upon the cut size about which the coarse and fine fractions are separated to reduce the density of the gas and the drag on individual powder particles.
  • An improved particle classification system as set fourth in claim 1 wherein the means for separating the fractions includes a plurality of separators connected by their respective inlets and outlets and making up a plurality of stages so the fractions leaving the fine and coarse outlets of the first stage pass through second stages which in turn separate the fractions again and recirculate some through said first stage.
  • An improved particle classification device comprising:
  • pressure means operatively connected to said first, second, and third separating stages for reducing the pressure therein sufiiciently below atmospheric pressure to separate the fine and coarse fractions at a cut size below approximately ten microns.
  • An improved method of particle classification including the steps of:

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  • Cyclones (AREA)
  • Combined Means For Separation Of Solids (AREA)
US597066A 1966-11-25 1966-11-25 Particle classification device and method Expired - Lifetime US3441135A (en)

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JP (1) JPS5336191B1 (de)
AT (1) AT288286B (de)
CH (1) CH481685A (de)
GB (1) GB1188566A (de)
NL (1) NL6716019A (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3599791A (en) * 1967-12-28 1971-08-17 Grenobloise Etude Appl Hydraulic sorting apparatus
JPS62237977A (ja) * 1986-04-08 1987-10-17 日清製粉株式会社 粉体分級システム
US20060037910A1 (en) * 2004-08-19 2006-02-23 Aksys Ltd. Citrate-based dialysate chemical formulations
US20150076037A1 (en) * 2012-03-19 2015-03-19 New Steel Soluções Sustentaveis S.A. Process and system for dry recovery of fine and superfine grained particles of oxidized iron ore and a magnetic separation unit
US11511287B1 (en) * 2019-12-26 2022-11-29 The University Of Tulsa Annular axial mixing system for gas-liquid flow

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6315183B2 (ja) * 2014-03-18 2018-04-25 株式会社Ihi ガスサイクロン

Citations (8)

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Publication number Priority date Publication date Assignee Title
US1629593A (en) * 1925-06-09 1927-05-24 Albert H Stebbins Dust-extracting unit
US2377524A (en) * 1939-11-21 1945-06-05 Hammermill Paper Co Method of and means for separating solid particles in pulp suspensions and the like
US2790550A (en) * 1954-10-25 1957-04-30 Sturtevant Mill Co Apparatus for centrifugal separation
US2910178A (en) * 1957-09-07 1959-10-27 Dept Of Mines Material classification
US2939579A (en) * 1956-07-13 1960-06-07 Hardinge Harlowe Air classifier
US3001727A (en) * 1957-11-20 1961-09-26 Dca Food Ind Flour milling process
US3095369A (en) * 1961-06-14 1963-06-25 Westfalia Dinnendahl Air-circulation classifier
US3266226A (en) * 1962-10-18 1966-08-16 Klockner Humboldt Dentz Ag Supervisory apparatus for dust separators operating at other than atmospheric pressures

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1629593A (en) * 1925-06-09 1927-05-24 Albert H Stebbins Dust-extracting unit
US2377524A (en) * 1939-11-21 1945-06-05 Hammermill Paper Co Method of and means for separating solid particles in pulp suspensions and the like
US2790550A (en) * 1954-10-25 1957-04-30 Sturtevant Mill Co Apparatus for centrifugal separation
US2939579A (en) * 1956-07-13 1960-06-07 Hardinge Harlowe Air classifier
US2910178A (en) * 1957-09-07 1959-10-27 Dept Of Mines Material classification
US3001727A (en) * 1957-11-20 1961-09-26 Dca Food Ind Flour milling process
US3095369A (en) * 1961-06-14 1963-06-25 Westfalia Dinnendahl Air-circulation classifier
US3266226A (en) * 1962-10-18 1966-08-16 Klockner Humboldt Dentz Ag Supervisory apparatus for dust separators operating at other than atmospheric pressures

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3599791A (en) * 1967-12-28 1971-08-17 Grenobloise Etude Appl Hydraulic sorting apparatus
JPS62237977A (ja) * 1986-04-08 1987-10-17 日清製粉株式会社 粉体分級システム
US20110171271A1 (en) * 2004-08-19 2011-07-14 Hhd Llc Citrate-Based Dialysate Chemical Formulations
US7544301B2 (en) 2004-08-19 2009-06-09 Hhd Llc Citrate-based dialysate chemical formulations
US20090274774A1 (en) * 2004-08-19 2009-11-05 Hhd Llc Citrate-Based Dialysate Chemical Formulations
US7883725B2 (en) 2004-08-19 2011-02-08 Hhd Llc Citrate-based dialysate chemical formulations
US20060037910A1 (en) * 2004-08-19 2006-02-23 Aksys Ltd. Citrate-based dialysate chemical formulations
US8202547B2 (en) 2004-08-19 2012-06-19 Baxter International Inc. Citrate-based dialysate chemical formulations
US8414768B2 (en) 2004-08-19 2013-04-09 Baxter International Inc. Citrate-based dialysate chemical formulations
US8828232B2 (en) 2004-08-19 2014-09-09 Baxter International Inc. Citrate-based dialysate chemical formulations
US9254356B2 (en) 2004-08-19 2016-02-09 Baxter International Inc. Dialysis system for preparing a citrate dialysate from a base concentrate and an acid concentrate
US20150076037A1 (en) * 2012-03-19 2015-03-19 New Steel Soluções Sustentaveis S.A. Process and system for dry recovery of fine and superfine grained particles of oxidized iron ore and a magnetic separation unit
US9327292B2 (en) * 2012-03-19 2016-05-03 New Steel Soluções Sustentaveis S.A. Process and system for dry recovery of fine and superfine grained particles of oxidized iron ore and a magnetic separation unit
US11511287B1 (en) * 2019-12-26 2022-11-29 The University Of Tulsa Annular axial mixing system for gas-liquid flow

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Publication number Publication date
GB1188566A (en) 1970-04-22
JPS5336191B1 (de) 1978-09-30
NL6716019A (de) 1968-05-27
CH481685A (fr) 1969-11-30
DE1607478A1 (de) 1970-07-09
AT288286B (de) 1971-01-15

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