US2091514A - Classifying material - Google Patents

Description

Aug. 31, 1937. A. F. MESTON CLASSIFYING MATERIAL Filed June 3, 1933 2 Sheets-Sheet 1 Aug. 31,v 1937. A. F. MESTON CLASSIFYING MATERIAL 2 Sheds-Sheet 2 Filed June 3, 1933 Patented Aug. 31, 1937 UNITED S -res CLASSI-FYING MATERIAL Archibald F. Meston, Middlesex, N. J., assignor to Research Corporation, New York, N. Y., a corporation of New York Application June 3, 1933, Serial No. 674,228

Claims. (01. 209-139) the buoyant and sustaining forces of the fluidstream. A particular branch of this art is known as classification by air flotation and the invention will be illustrated by describing it in terms of this branch of the art.

It is well known that when a small particle of the order of 100 microns in diameter, orless, is allowed to fall freelyin a quiet body of fluid, it

falls perpendicularly with increasing velocity. to-

wards the earth because of the action of the force of gravity, but the increase in velocity or acceleration continues only over a short period of time; the velocity soon becomes constant. This is because the frictional resistance of the fluid to the movement of, the particle increases with increase in the velocity of the particle and, at the constant velocity attained, the forcenecessary to overcome this resistance just equals the force of gravity. The velocity V attained by a particle of radius r. and specific gravity S,falling 'in a fluid of viscosity 1; and specific gravity S when the resistance offered by the fluid just balances the force of gravity, here de'noted by the gravitational constant g, has been given by Stokes (Applied Colloid Chemistry-Bancroft, page 136), as follows:

In air flotation, the air in which the particles aresuspended is moved upwardly at a velocity V which will prevent all particles Smaller in radius than a desired value of r from moving downwards. This value of V which will cause the particles'of desired fineness to be carried along with the'air stream may be determined by the aid of the above formula, or it may be determined by experiment. Apparatus to carry out air flotation usually consists of a fan to move the air and suspended par- ,55 which the classification of the particles takes place. -An othe r' object is to provide means that will permit changes in the gas velocity Vof the air passing through the chamber and resultant changes in the radius r of the particles without altering. the volume of air passing through the 5 chamber per unit of time. Still another object is to make possible various separations inthe same chamber by effecting simple changes in the chamber while the classification system is in operation. Further objects include the provision of apparatus 10 in which the area of the separating chamber may be altered, but wherein the cross-section of the chamber will be uniform throughout its length; the provision of apparatus in which the character of the inlet and outlet and the uniform velocity 15 in the separating provide non-turbulent flow of fluids; and the provision in such apparatus of area-changing inserts of telescopic construction whereby the height requirements of the apparatus are limited. 'Other objects such as the removal 20 from the apparatus, separately and in improved manner, of the air and fine particles and the coarse particles will be pointed out in the following description with the aid of the accompanying drawings. I e

Referring to the drawings: Fig. 1 is a side view, partly in section, of one embodiment of the,invent ion;

Fig. 2 is a plan view of the operating mechanismshown in Fig. 1;. Y 6

Fig. 3 is a sectional elevation of another embodiment of the invention;

Fig. 4 shows a detail in sectional elevation useful in the invention as illustrated in Figs. land and Fig. 5 is a fragmentary view, in sectional elevation, of a detail useful in employing the invention.

Fig. 1 shows a classifying or separating apparatus comprising a construction for keeping the cross-section of a separating passage substan- 40 tially constant for most of its length and yet provide means for altering the area of this crosssection. Separating chamber is cylindrical in shape and is used in vertical position'as shown;

At the bottom of the chamber is a conically shaped 45 section 5| and below 5| is aninletpipe 52. The outlet from chamber 50 is through openings in spider 53, which supports guide 56, into collecting chamber 54 and therethrough outlet flue 55. The cross-sectional area of chamber 50 is' altered by inserting into the chamber one or more members as those marked 51 and 58. These members are movable relative to the chamber 50 and to each other and are preferably cylindrical in shape which makes it easy to provide and control such 55 movements through simple stuffing boxes as indicated at 59 and 60. The mechanism for moving the members 51 and 58 consists of racks GI and 62 incorporated in or attached to the sides of the 5 members and which'mesh with pinions 63 and 64, respectively. The relationship of the various pinions and racks is more clearly shown in Fig. 2. Because it is necessary that the two pinions 63 turn in opposite directions, an auxiliary gear 65 is provided. A chain and sprocket drive for turn ing pinions 63 simultaneously is indicated by 66. Pinion 64 is turned directly by crank 68 through shaft 61. g 7 Referring to Stokes law, it is to be noted that the radius of the particle r which will be sustained in a fluid stream moving vertically at velocity V changes according to the relationship V=r This makes it apparent that if members 51 and 58 are raised and no members restrict the cross section of passage bounded by chamber 50, the velocity of the air passing (assuming constant volume per unit of time) will be a minimum and the-particles that will be held in suspension and carried through the chamber will be of the small- 'est sizes only. It is not to be expected that the results to be obtained by reducing the cross section determined and is not always the same in asingle classification problem. I

With the invention as shown in Figshl and 2, three different air velocities can be had in chamher 5!} as desired with a constant volume of air passing. A greater number of air velocities of smaller diflerential canbe secured by increasing the number of movable inserts, of which mem bers 51 and 58 are merely illustrative examples. All the inserts: in use should be'brought down to near the bottom oi.chamber 5D if'uniform air velocity is desired, butthey can be left in stag gered eifect, -as shown in the figure, if progressive changes. in velocity are wanted. The bottom surfaces of the inserts should be rounded oif or so shaped that the velocity changes are not too abrupt; Otherwise serious eddies will ,result in the separating passage and the classification will not be uniform in all the air reaching space 54.

InFig. 3 a construction is shown which alters the cross-section of the separationchamber by 60 inserting a space occupyingmember along the periphery of the chamber. -The eifect of'this is very substantial as the area is proportional to thesquare of the diameter and any decrease in diameter causes a decrease in the chamber area in accordance with this relationship. In Fig. 3 the separating chamber '10 has insertedvwithin it space reducing members H and 12. They are preferably made as double walled tubes of smooth surface and are moved up and down by any suit- 70 able means such as those already described. They are held in the desired position by clamping screws l3.- While other exits for thejair may be provided, the inner insert '12 may be made to function as the air outlet and this is connected at 75 the upper end to any flexible tube 14 which will adjust itself to the movements of member 12 and which will confine the air until it reaches the final collecting device that removes the suspended fine particles from the air leaving the classifying apparatus. Here again if separation is to take place in air at constant velocity the inserts in use should be lowered to near the bottom of the chamber 10. a

Close separations or classification of particles sometimes require chambers of considerable height. In such chambers inserts which telescope such as that shown in Fig. 4 are useful. This modification makes it unnecessary to provide head room for the withdrawal of full length inserts. Telescope construction can also be used in making up. the individual inserts shown in Fig. 3.

While the invention is primarily concerned'wlth reduction in area of separation chambers in the fluid flotation practice of particle separation, it is important that any apparatus intended for this practice should be provided with means for removing the heavy particlesor tailings, without making frequent -shut downs necessary. Fig. 5 shows the inlet Bll of a classifier entering the separation chamber 8| in spaced relation to. the

walls of the chamber thus leaving an annular.

space 82' into which the tailings may'slide. Space "is provided with a bottom' 83 and an outlet door 84. Such a device is extremely useful where it is intended to withdraw the tailings with a small amount of air and pass them through an attrition or frictional device, such as a fan, for dislodging fine particles that may be clinging to larger particles and returning them to the separating chamber again, for further classification. For'such purpose an outlet pipe, not shown, is inserted through door 84 for continuously or periodically conducting the tailings tothe friction device and. conducting means are "provided to return the worked-over tailings to the classifier.

The above descriptions'makeclear many of the' operations to give better control of the classiflcation methods is objectionable. With the apparatus provided by the invention and the method of using it which has been described, it is possible'to maintaincontrol of the classification of the particles against changes in the volume of the air (or other fluid) carrying the particles, changes in specific gravity of the fluid or of the particles or in the viscosity of the fluid. If all these conditions are kept constant but changes in size in the floated product are desired these can be secured by altering the velocities at which the separations are made, and these alterations are.

' easily made without interrupting plant-operations by manipulating the area changing inserts in the separating chambers.

The invention has been described in terms of.

air flotation, but it is useful wherever advantage can be taken of the principle defined in Stokes law. Separation. under some conditions is obtained satisfactorilyv in liquids as well as in gaseous fluids.

1. Apparatus for the differential separation of plurality of cylindrical members of differing cross-sectional areas concentrically positioned within said casing so as to close ofl a portion of the axial space in said chamber against the passage of fluid and to define an annular passage between said members and said casing and vertically adjustable so as to occupy varying portions of the axial space in said chamber said embers being shaped and related to provide a substantially continuous confining surface for the fluid at all relative positions of said members. 2. Apparatus for the differential separation of solids from suspension in a fluid medium comprising a vertical cylindrical casing defining a chamber, means for conveying fluid to the lower portion-of said chamber, means for withdrawing fluid from the upper portion of said chamber, a plurality of cylindrical members of differing cross-sectional areas concentrically positioned within said casing so as to close ofi a portion of the peripheral space in said chamber against the passage oi fluid and vertically adjustable so as to occupy varying portions of the peripheral space in said chamber said members being shaped and related to provide a substantially continuous confining surface for the fluid at all relative positions of said members.

3. Apparatus for the differential separation of solids from suspension in a fluid medium comprising a' vertical cylindrical casing defining a chamber, means for conveyingfluid to the lower portion of said chamber, means for withdrawing fluid from the upper portion of said chamber, a plurality of telescoping cylindrical members of differing cross-sectional areas concentrically positioned within said casing so as to close off a portion of the axial space in said chamber against the passage of fluid and to define an annular a plurality of telescoping cylindrical members of;

differing cross-sectional areas concentrically positioned within said casing so as to close oil a portion of the peripheral space in said chamber against the passage of fluid and vertically adjustable so as to occupy varying portions of the peripheral space in said chamber said members being shaped and related to provide a substantially continuous confining surface for the fluid at all relative positions of said members.

5. Apparatus for the difierential separation of solids from suspension in a fluid medium comprising a vertical cylindrical casing defining a chamber, means for conveying fluid to the lower portion of said chamber, means for withdrawing fluid from the upper portion of said chamber, a plurality of cylindrical members of differing cross-sectional areas concentrically positioned within said casing and vertically adjustable: therein,'and means for closing the space between" said members at all relative positions thereof so as to provide a fluid passage of va-' riable cross-section having substantially continuous confining surfaces.

ARCHIBALD F. MESTON,

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