US2285429A - Pulverization - Google Patents

Description

June 9, 1942. M. FRISCH 2,2855429 PULVERIZATION Filed ma 26, 1938 2 Sheets-Sheet 1 INVENTOR hWXL-FM Patented June 9, 1942 PULVERJZATION Mai-cm Frisch, New York, N. Y., assignor to Foster Wheeler Corporation,

New York, N. Y., a

- corporation of New York Application May 26, 1938, Serial No. 210,091

Claims.

This invention relates to the comminution of materials and more particularlypertains to the pulverization of fuels such as coal and the like.

This application is a continuation-in-part of application Serial No. 53,362, filed December 7,

Large scale pulverization of fuels, such as coal, for firing the furnaces of steam generators and other uses, is generally accomplished in pulverizing mills into which is separately fed the material to be pulverized and a stream of air. verized material is entrained in the air stream The pul-' flowing through the mill and the mixture is withdrawn from the mill at one point thereof and is conducted either to storage or to burners. In some instances the material to be pulverized is fed into the mill atone point thereof and the air is supplied at an adjacent point, while in other cases the air is supplied at an entirely different or at a substantially oppositely disposed point of the mill with respect to the point at which the material is fed. In these latter instances, particularly with pulverizing mills of the ball type, it has been found that with a given ball charge and power input, the fuel is pulverized much finer than i required for satisfactorily utilizing the fuel in burners or the like. With ball mills of the rotating drum type the trunnion diameters are definitely limited for any given size, mill so that it is diflicult to take advantage of the increased grinding capacity, due to the fact that when the air flowing through the mill is materially increased over normal practice, the pressure drop through the mill becomes uneconomically high in addition to which there is a tendency for the mill operation to become unstable;

Moreover, with present practice, preheated air is supplied to the mill under pressure which is usually throttled by dampers prior to the introduction of the air to the mill since it is desirable to have the mill operating under suction rather than under pressure. The throttling of this available air pressure ordinarily results in an economic loss.

The present invention overcomes the foregoing disadvantages and provides pulverizing apparatus, and a method of pulverizing materials, which reduces the fuel or other material to a degree of fineness which can be satisfactorily utilized with a large output of the pulverized material. Additionally, with the present invention the available air pressure instead of being throttled with damper is converted into a relatively high velocity prior to its introduction into the mill thus the required quantity of air may be admitted to the pulverizer through smaller areas than are now required and without putting the mill under. superatmospheric pressur Other purposes and advantages will become apparent from the following description considered in connection with the accompanying drawings forming a part thereof in which:

Fig. 1 is a view in elevation of a preferred form of pulverizing apparatus embodying the present invention;

Fig, 2 is a vertical sectional view on an'enlarged scale, taken on line 2-2 of Fig.' 1;

Fig. 3 is a vertical longitudinal sectional view, on an enlarged scale, of the pulverizer shown in Fig. 1; and

Fig. 4' is a combined sectional and elevational view of another form of ball mill embodying the invention.

Like characters of reference refer to the same or similar parts throughout the several views.

The invention is disclosed a embodied in and carried out by a pulverizing mill of the rotating drum, ball type but it will be understood that this form, although preferred, is merely illustrative of one application of the principles of the invention and that the invention may be applied toother types of mills, such as stationary drum'types, having grinding means other than a ballcharge.

Referring to Figs. 1 to 3 of the drawings, reference character l0 designates the drum of a pulverizing mill, the drum in this instance being generally frusto-conical in form and being provided at its ends with trunnions II and I2, which are mounted in and rotatably supported by bearings l3 and I4 respectively, resting on supporting members l5 and I6 respectively. Mounted exteriorly at one end of the drum I0 is the gear IT by means of which the drum is rotated on its trunnions by any suitable driving means, not

advantageously utilizing the air pressure so that shown. The drum i lined with a suitable form of liner l8 and is provided with a charge of grinding balls l9.

In the form of the invention shown, the material to be pulverized is fed to the drum simultaneously at both ends thereof and air, preferably heated, is also supplied to the drum simultaneously at both ends thereof. Moreover, the pulverized material and air mixture is withdrawn from the drum simultaneously at both ends thereof and classifiers are supplied at both ends of the drum so that the oversize material carried from the drum by the air stream will be separated from the material which has been'sufli-' ciently pulverized and the oversize is returned to the drum at both ends thereof simultaneously.

The material to be pulverized is fed from .a source of supply to a feeder 20 driven by an electric motor 2| or other suitable means and the feeder delivers the material at the desired rate to vertically inclined feed pipes 22 and 23 which are connected together at their upper ends and at their lower ends are connected to combined feeders and classifiers 24 and 25 respectively. Th material is delivered by the feed pipes 22 and 23 to the outer ends of the feed passages 26 and 21 through a passage in each classifier such as designated 28 in classifier 24 (Fig. 2) which is controlled by a damper or valve 29. The material is.

' screws. The tubes are supported at their outer ends in bearings in the classifiers.

Air under pressure, preferably preheated, is supplied from a suitable source through air con duits 35 and 36 disposed at the sides of the combined feeders and classifiers 24 and 25 to the tubes 32 and 33 through a plurality of longitudinal slots 31 in the outer ends of the tubes. Dampers 35' and 36 control the air conduits 35 and 36 respectively. In this manner preheated air is supplied simultaneously at both ends to the drum after the pressure of the air has been converted into a relatively high velocity with the result that the drum operates under a suction and not under pressure. The air supplied. at both ends to the drum flows over the ball and material charge therein to approximately the center of the mill and in doing so picks up ma- The air terial which has been pulverized. streams'impinge upon each other at the center of the drum'where their directions of flow are reversed, and the material and air mixture flows out of the drum simultaneously at both ends thereof through thepassages 26 and 21 over the feed screws 3|] and 3|. The outer end portions of the passages 26 and. 21 are connected to the lower ends of the classifiers 24 and 25 respectively. The material and air mixture flows from each of these passages into a vertically inclined passage in each classifier such as passage 38 in classifier 24, which connects with a curved pas- I sage ineach classifier such as passage 39, generally of inverted U form. by means of which passages the mixture is delivered to the delivery pipes 40 and 4! respectively. These pipes are vertically inclined and are connected at their upper ends to a union 42 through which the pulverized material and air mixture is delivered to a conduit 43 which conducts the mixture to an ex-- hauster fan 44 by which it is impelled through a conduit 45 to burners or to storage. The exhauster fan in this instance is driven by an electric motor 46. The conduit 43 is provided with an opening to the atmosphere which is controlled so that air maybe drawn into the conduit 43 from the atmosphere in the desired volume to thereby control the capacity output of the mill. This means may take the form of a damper pivoted at one end which may be manually adjusted by an arm 41. Automatic means may be provided to release the damper so that it will move to a position in which the opening to the atmosphere in the conduit is fully open. and the conduit 43 is completely closed upon the occurrence of any accident to the mill or its associated equipment which might cause a cessation or retardation of the flow from the mill of the pulverized material and air mixture thereby avoiding flame propagation from a furnace to the mill and consequentexplosion or other damage.

It will be understood that the classifiers may be of any desired form and that the type of classifier shown is to be considered as a preferred form only. The degree of separation of material from the pulverized material and air mixture or the fineness of the mixture leaving the classifier may be controlled bydampers suitably positioned in the classifier, such as the dampers 48, 49 and 50. It will be understood that as the pulverized material and air mixture flows downwardly through the outlet end of the curved passage 39 into the conduits 46 and 4|, the oversize material will be deposited in the hopper 5| and will be returned to the feed passages 26 and 21 by means of a valve 52 in each classifier, which in this instance is operatively connected to the feed screws 36 and 3| by suitable driving mechanism 53 which serves to rotate the valves about their axes. In this manner, the oversize material is returned to both ends of the mill simultaneously along with the original feed.

With this arrangement it will be perceived that the outlet flow area from the mill for the relatively dense pulverized material and air mixture is greatly increased over prior arrangements and in some instances is approximately doubled. Although the flow area available through the tubes supporting the feed screws is somewhat smaller than in prior arrangements generally, the available pressure of the air is converted into a relatively high velocity in these small tubes thereby utilizing the pressure rather'than wasting it by throttling as has heretofore been done, with the result that the air pressure is fully utilized without putting the mill under superatmose pheric pressure. By simultaneously feeding the material to be pulverized at both. ends of the drum, the effectiveness of the ball charge is increased for the reason that the time required for the feed to be absorbed within the ball charge is materially reduced as compared with prior practice. This is due to the fact that the material will travel from both ends or from oppositely disposed points toward the middle of the drum where the tendency of the material to ball ratio up at the outlet end thereof. As the velocity of a the air is increased, the resistance, increases and as the level of the material increases the resistance further increases so that there results a self-accelerating condition which at times leads to the plugging of the mill. By feeding the material to be pulverized at both ends, or at difl'erent or oppositely disposed portions thereof, and with classifiers disposed at both outlets of the mill as in the formof the invention illustrated, the resistance to the outflow of the pulverized material and air mixture will be very materially reduced and the level of the material and oversize within the classifiers willalso be materially reduced. Moreover, with air blowing through each classifier into the min there will be a tendency with prior arrangements due to the greater ef-.

fectiveness of the ball charge and also due to the fact that it is possible to greatly reduce the fineness of the material and'hence the work done thereon.

Instead of the particular form of mill shown in Figs. 1 to 3, other forms may be utilized. For example, the mill, may be formed as indicated in Fig. 4, with the walls 60 thereof converging from the central portion toward each end, or

the mill or drum may be made cylindrical in form and liners may be used to provide the same effect, that is, with a larger grinding area at the middle of the drum than at both ends. These forms of mill tend to pull the charge away from the outlets at both ends and also tend to move .the coarse material toward the center of the mill thereby increasing the time of contact'of the material with the grinding elements which will result in increased efiiciency of pulverizetion.

If desired, the material to be pulverized may be fed into themill at one end only, rather than at both ends simultaneously as previously described. This may be accomplished by closing one of the feed pipes 22 or 23, or by directing the material discharged from the feeder 20 in such manner that it enters only one of the feed pipes 22 or 23, or by closing the passage 28 in one of the classifiers by the damper or valve arate, axially disposed passages connectingwith substantially oppositely disposed portions of the' drum, means for feeding material to-be pulverized to the drum through one passage of each group, means fdr supplying air through another passage of each group, means for withdrawing pulverized material from the drum through one of the passages of each group, means for sep- I one of the passages of each group.

29, or by any other suitable means. Otherwise the operation will be substantially the same as hereinbefore described, that is, air, preferably preheated, will be supplied to the drum simul-' taneously at both ends thereof, the pulverized material and air mixture will be withdrawn from the drum simultaneously at both ends thereof,

and oversize material which is separated from,

the fuel and air mixture in the classifiers will be returned to the drum at both ends thereof simultaneously Since the arrangements herein disclosed may be varied in their several parts or in their entirety, and the methods may be altered in one or. more of'their constituent steps without departing from the principles of the invention, it

will be understood that the invention is not tobe limited except by the scope of the appended claims..

What is claimed is: v

1. Pulverizing apparatus comprising a rotatable drum, pulverizing means inthedrum, means for separately feeding material to be pulverized and air to the drum at substantially oppositely disposed po nts thereof through separate passages, and means for withdrawing pulverized material entrained in air from the drum atsaid,

substantially oppositely disposed points thereof through'the passages through whichmaterial is fed to the drum.

2. Pulverizing apparatus comprising a drum,

pulverizing means in the drum, groups of sep- 7c arating oversizematerial from the pulverized material,-and means for returning the oversize'ma terial to the drum through one of the passages of each group. I

3. Pulverizing apparatus comprising a-drum, pulverizing means-in the drum, groups of separate, axially disposed passages connecting with substantially oppositely disposed portions of the drum, means for feeding material to be pulverfized' to the drum through an outer passage .of

each group, means for supplying air through an inner passage of each group, and means for withdrawing pulverized material from the drum I through an outer passage of each group.

4. Pulverizing apparatus comprising a drum. pulverizing means in the drum, groups of two separate, axially disposed passages connecting with substantially oppositely disposed portions of the drum, means for feeding materlalto be pulverized to the drum through the outer passage of each group, meansv for supplying air through the inner passage of each group, and means for withdrawing pulverized material from the drum through the outer passage of each group. 4 g

,5. Pulverizing apparatus comprising a drum. pulverizing means in the drum, groups of separate, axially disposed passages connecting with substantially oppositely disposed portions of the drum, means for feeding material to be pulverized to the drumthrough one passage of one group, means for supplying air through another passage of each-group, and means for withdrawing pulverized material from the drum through 6. Pulverizing apparatus comprising a drum, pulverizing means in the drum, groups'of separate, axially disposed passages connecting with substantially oppositely disposed portions of the drum, means for feeding material to be pulverized to the drum through onepassage of one a group, means for supplying air through anotherv passage of each group, means for withdrawing pulverized material from the drum through one of the passages of each group, means for sep-'.

arating oversize material from the pulverized material, and means for returning the oversize materialto the drum through one sages of each group; 7. Pulverizing apparatus comprising a drum, pulverizing means in the drum, means providing substantially co-axially arranged passages connecting with the drum, means for supplying air to the inner passage for d livery therethrough to the drum, means for supplying .material to be pulverized to an-outer passage, and rotatable helical means in said outer passage for moving the material supplied thereto into the drum, said v helical means being disposed in the outer peripheral portion oi said outer passage to providea flowpath' in the inner peripheralportion thereofthrough which pulverized material entrained 7 in air may be withdrawn from the drum.

8.-Pulverizing apparatus comprising a drum, pulverizing means in the drum; means forming a passage connecting with the interior of the drum, a tubular member in said passage spaced of, the pasv from the irmer wall thereof, means for supplying air to the tubular member for flow therethrough to the drum, means for supplying material to be pulverized to said passage, ,a helix in said passage for moving the material supplied thereto into the tating the helix,the helix being disposed in the outer peripheral portion of said passage to provide a flow path in the inner peripheral portion thereof through whichpulverlzed material entrained in air may be withdrawn from the drum.

9. Pulverizing, apparatus comprising a drum rotatable about a substantially horizontal axis, pulverizing means in the drum, a substantially horizontally disposed passage connecting with the interior of the drum, a tubular member. in said passage spaced from the inner wall thereof, means for supplying air to the tubular member for flow therethrough to the drum, means for supplying material to be pulverized to said passage, a helix in said passage for moving the material supplied thereto into the drum,

drum, and means for romeans forming rotated and to move sage into the drum, the

means for connecting the tubular member to" the drum to cause said member to be rotated with the drum, and means for connecting the helix to the tubular member to cause the helix to be the material in said pashelix being disposed in the outer peripheral portion of said passage to provide a flow path in the inner peripheral portion thereof through which pulverized material entrained in air may be withdrawn from the drum.

10. The method of pulverizing material which comprises feeding material to a pulverizing zone simultaneously at different portions thereof, supplying air to said zone simultaneously at said different portionsthereof, withdrawing pulverized material from said zone simultaneously at said different portions, separating oversize material from the withdrawn pulverized material and re- 20 turning the oversize material to said zone.

L MARTIN FRISCH.

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