US2174630A - Classification system for pulverized materials - Google Patents

Description

H. HARDINGE CLASSIFICATION SYSTEM FOR PULVERIZED MATERIALS Filed Nov. 12 1936 2 Sheets-Sheet 1 Oct. 3, 1939. H. HARDINGE.

CLASSIFICATION SYSTEM FOR PULVERIZED MATERIALS I Filed Nov. '12, 1936 r mm HARLOWE HARDING-E M MW. W

- Patented Oct. 3, 1939'- UNITED STATES almost cmssmcsnon srsnm ron.

. PULVERIZED m'ramns Barlowe Hardinge, York, Pa. asslgnor to Hardin Oompa Incorporated, York, Pa., a corporation of ew York Application November 12, 1930, Serial No. 110,429 3 Claims. (01. 83-3) This invention relates to grinding mills and pulverizers, and more particularly to a system for classifying the material pulverized in the mills or pulverizers.

, object of. the invention is to provide'an improved pulverizing apparatus in which the feed, oversize, and air all enter and leave at the same end of the apparatus. i

Another object of the invention is to provide an improved pulverizing apparatus in which the material is fed to a grinding mill in such 'a manner that it mingles with the dry oversize material discharged from a classifier prior to coming in contact with dry air being conducted to the mill,

'16 so that the wet feed is partially ,dried, thereby enabling the fresh dry air which subsequently contacts the feed to quickly remove orabsorb moisture in the feed before the feed enters the mill.

- With the foregoing and other-objects and advantages in view, the invention consists in the preferred construction and arrangement of the several parts which willbe hereinafter fully described and claimed.

25 In the accompanying, drawings:

Figure 1 is a general view, partly in vertical section, and partly in elevation, showing one form of the invention in connection with a cylindrical ball mill; and

30 Fig. 2 is a view, similar to Fig. 1, of another form of the invention in connection with a conical mill.

Referring'to the drawings and especially to Fig. 1, the material pulverizing. and collecting system may be characterized as a closed-circuit system in which fluid currents, such as air, are circulated throughout the system. It includes a pulverizing mill H, which may be of any 'wellknown construction having hollow trunnions I 2,

40 II, at each end, the trunnion I 2 in the instant case being closed by a plate or cover ll, so that only the trunnion l3 at the other end of the mill is open.

' The air or other elastic fluid whicli conveys 4 the fine product is caused to circulate continuously through the system by a blower II, which discharges directly'into the open end I: of the mill ll through fixed conduit 16 and rotating conduit I'I. I v

5o Conduit I1 is mounted in the discharge hollow trunnion II, being spaced a suitable distance from the interior of said trunnion, so as to prm .vide an annular space II for the dust andfiuid leaving the mill ll.

The inner end of conduit l1 pr jects into the mill II a suitable distance, and a grate l9 extends from the inner portion of said conduit outwardly to a conical ball rejector 20 extending inwardly from the end wall of the mill ll.

Extending from the wall of the ball rejector 5 20 to the conduit l1 and located on the outer side of the grate I 9, are lifters 2|, the purpose of which will be hereinafter described.

It is usual to'feed material into .pulverizing millsautomatically. The material descends from 1 a bin into a hopper 22 and is permitted to pass into chute 22 by means of a rotary pocket feeder 24.

Feeders of this type are known as an air-lock type of feeder and such feeders are adapted toprevent positive pressure from being carried upwardly into the hopper 22. However, it will be understood that any type of. feeder which would choke off the air from entering the hopper will be satisfactory. 'Ihe feed from chute 23 passes in-and around 7 the bottom of a classifier "and enters conduit 28.- In passing through the classifier 25, the

feed joins with the oversize dropped from the classifier. This helps to dry the wet feed, as the 25 oversize is very dry. and mingling with the feed, picks. up any free moisture and-has the advantage of absorbing this moisture over a large surface area so that the air also entering the mill II will evaporate this 'moisture more rapidly than if the feed were placed in contact with the air without first mingling with the' oversize.

Below theconduit 28 is a movable gate 21, which is provided to prevent back pressure of air from entering the lower portion of the classifier 25 before it should. The gate 21 is so balanced that pressure of the oversize and the feed on top of it, overcomes the back pressure of air below, and the oversize and feed trickle down past the gate into conduit 28, and from thence enter the 40 conduit l-l near the inner end of said conduit 16.

The blower l5 draws air in the suction conduit 29 from an outside source, and if appreciable moisture is present, it is preferable to provide means for supplying hot air through conduit 29, as this hot air will dry the moisture in the feed more rapidly than cold air, as is well known in the art. The hot air then travels through conduit l6 and mixes with the feed and oversize entering conduit it from the feedconduit .28 and conveys the feed and oversize by forced draft through the rotating conduit ll into the mill ll. e

As shown by the arrows,;1"lg. 1, the air after entering. the mill H reverses and-flows outwardly through the grate "and into the annular space I8 between conduit l1 and trunnion l3. The ball rejector 20, heretofore referred to, forms a pocket. and the lifters 2| pick up any tramp oversize, small balls and refuse which may" lodge between the grate l3 and the ball rejector 20. The oversize then slides down the lifters 2| as they rotate with the mill II and enters the conduit H where the air forces the oversize back into the mill l I.

The air circulating through the mill ll picks up the-fine product in the form of dust, and carries this dust outwardly through the grate I 3, and annular space I8, and conduit 30, to classifler 25. I The classifier 25 has an inner casing 3| along the outside of which flows the current of materlal-laden air entering through conduit 30. The vortex created within the classifier causes the heavier particles to be cast outof the stream of flowing air. These heavy or'large' particles leave the inner casing 3i at its lower end 32,

which directs such particles towardsthe fresh feed inconduit 25, and as stated before, helps'to dry the incoming feed. Oversize also drops out around the casing of the classifier 25 and in sliding down the sides, also mingles with the incom- The fines then pass through conduit 33 into a burner 34,- if the operation is one using the conventional form of what is known as a unit pulverizer fordirect firing of powered fuel.

7 It will be noted that the blower l places the while system under'pressure; with a mill under pressure, loss of air would be likely to occur at the joint 35 between the inner end of the nonrotating' conduit 30, andthe outer end of the rotating trunnion II of the mill ll, if no provision-were made to prevent such occurrence. Therefore, I enclose the. joint "with a box- 31, which forms a Joint with the flangeorouter end 38 of the trunnion l3. This Joint is made to' "fit as closely as is practicable by methods ordinarily used.

Connected to the'chamber under sufficient pressure into the joint'to prevent the escape of. dirty air and oversize from the apparatus at this joint.

In order to control the operation of the device, there is a damper 40 which regulates the amount of incoming air from the Blower l5;

entering the mill II. V

There is also a damper 4| which regulates the same air, but in this case bypasses the air around the mill H directly to the classifier 25, through conduit 42 which connects conduit IS with conduit 30.

When during operation the capacity is reduced below the rated output of the apparatus by partially closing damper 40-, the yelocity in the system, particularly in the classifier 25 and conduit 33, may be below the velocity which is suflicient to carry all of the material in suspension.

' current of air is reversed and in passing through her GI, from whence it passes from'the classifier .through conduit 62.

. within box :1 by pipe 39, is a small blower 35, which forces-air I the feeder 38 is located above conduit 69, at its the one hand and a pull effect on the other.

-the There method .ofoperation, not only because the comis a distinct advantage in this bination of thefeed mixing with the oversize and the air, dries the feed, thereby increasing the grinding capacity of the mill, but the whole unit is simple inoonstruction, and there is considerable saving in floor space over the conven tional form of pulverizing unit, where there are apparatus at both ends of the mill.

Referringnow to the form of the invention shown in Fig. .2, the air or other elastic fluid which conveys the fine'product'is caused to circulate continuously through the system by blower 5|, which discharges directly into the hollow trunnion end 52 of a pulverizing conical type -of mill 53, through conduits 54 and 55.

The hollow trunnion end of the mill 53, opposite to the trunnion 52 is closed by a cover plate 56, so that within the mill the direction of the the mill the current of air picks up fine particles which are desired to be collected.

The air,laden with material, passes through grate 51 and leaves the mill through annular space 58 between conduit 55 and trunnion 52.

Lifters 59 pick up anytramp oversize, small balls and refuse, and such material slides down the lifters asthey rotate with the mill 53 and enters the conduit 55 where the air forces the oversize back into the mill 53.

Y The air, laden with material, which leaves the knill through the space 58, passes through conduit 50 and enters the outer chamber of classi- Conduit 62 is vci'mnectedwith a cyclone dust collector 63 in which the material is relieved fromthe air by- ;the action taking place within the collector. 1

The air is drawn from the collector 63 through conduit 64- by means of blower 5|, whose suction side isconnected with conduit 64.

When the material-laden air enters the outer chamber of the classifier 6i, its velocity is lessened and its carrying capacity is reduced, with the result thematerial of undesired coarseness drops to the lower portion of the inner cone 61 of the classifier. k

In the form of the invention shown in Fig. 2,

lower end with the. inner end portion of conduit 54.

The lower portion of the classifier 5| is connected to conduit 69 by a conduit 10, and the lower portion of the inner cone 51 of the classifier has a depending chute 1|, which directs the oversize towards conduit Below the point in conduit 59 at which the con- I duit Ill is connected, there is a gate 12, similar in function to the gate 21 heretofore described.

In this form of the invention, there will be no back pressure at the point wltifre the oversize enters the mill, as there may e very nearly a neutral pressure, or perhaps a suction, if the mill is operating in balance. This balanced operation is obtained by the blower 5| forcing the air through conduit 54 into the mill 53, and also sucking in air through conduit 64 fromlcollector 53 and classifier 6|, thereby creating a push on Vent 65 and damper 66 comprise means by which variations in pressure within the system' may be controlled.

In order to prevent leakage of air at the joints, and more particularly to obtain a clean system,

the vent Ii discharges excess air and moisture, as well as places the system as a whole under partial vacuum; The amount of air passage through vent '65 is controlled by regulating the damper 66.

Moreover, it the feed is very wet, hot air must be introduced. In such event, the damper 66 is opened wider to cause av pronounced suction throughout the system, and hot air is then drawn in through conduit from an outside source, the fiow ofthe hot air through conduit 15 being controlled by damper ll.

Even though conduit 15 is on the pressure side of the blower 5|, since the whole system is now under a partial vacuum, air will be actually drawn in, since the conduit 54 will be at a negative pressure with respect to theatmosphere.

Thus,there is inthis form of the invention, as in the form of the invention shown in Fig. 1, means whereby the feed, oversize, and the hot air all mingle together before theyenter the mill 58.

The mill 53 shown in this form of the invention, is of the well-known type of conical mill.

Even though the coarse feed is introduced through the discharge end of such form of mill, the coarse feed will migrate to the barrel or center oi the mill, where the material will be ground by the heavy balls. There is a distinct advantage 0! an arrangement of this type over the use of a plain cylindrical mill 0! the'iorm shown in Fig. 1, since the latter type of mill has no definite way of forcing the coarse material towards the far end of the mill. Accordingly, time must be relied upon to distribute the feed throughout the mill II in order to obtain the necessary grinding results.

Having thus described my invention. what I claim is:

1. A rotary drum mill having a combined feed and discharge opening only at one end of the drum and closed at the other end, a blower, an inlet conduit leading from said blower to said drum for conducting air into the drum, a feed conduit for material connected to said inlet conduit exteriorly oi the drum, a classifier, a conduit connecting the classifier with said drum whereby dust-laden air circulated through the drum is carried to said classifier, a grate mounted in the drum and spaced from the discharge end of the mill and surrounding but not extending across the inlet conduit whereby the matter discharged from the mill to said classifier-drum conduit passes through said grate and the incoming feed enters the mill unrestrictedly through said inlet conduit, and means between the grate and the discharge end of the drum for removing oversize material caught between said grate and the discharge end of the drum, said last named means having an end portion entering the feed conduit to discharge oversize into said teed conduit.

2. A rotary drum mill having a combined feed and discharge opening only at one end of the drum, a screen mounted within the drum and spaced from the discharge end thereof, said screen having a central opening therein for the incoming feed, means between the screen and the discharge end of the drum for removing oversize material caught between said screen and the discharge end of the drum, said last named means having an end portion enteringthe central opening to discharge oversize into said central opening.

3. An apparatus or the class described comprising a drum mill containing a plurality of grinding bodies iree to move in all directions therein, said mill being closed at one end and having an opening at the opposite endya horizontal conduit positioned in said opening for de-' livering heated air under pressure to the mill, another conduit extending from said opening to an air classifier and adapted to convey the ground products suspended in exhaust air to said classifier, a screen mounted within the mill and spaced from the discharge end thereof, said screen having a central opening therein registering with the first mentioned conduit, means between the screen and the discharge end 01' the mill for removing oversize material caught between said screen and the discharge end, said means having an end portion entering the first mentioned conduit to deliver the oversize to said conduit, means to pass the feed in a relatively turbulent condition through the classifier and in such pronmity to the exhaust air from the mill that fines and dust in the feed are removed therefrom, and means to convey the dust-free air and classifier oversize to the heated air conduit where they are dried and delivered to the mill.

EAR-LOWE HARDINGE. 50

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