US3344998A - Pulverizer - Google Patents

Description

Oct. 3, 1967 N. w. EFT 3,344,998

PULVERIZER Filed July 27. 1964 5 Sheets-Sheet 1 FIG. I

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INVENTOR. NeI W. Eff BY ATTORNEY Oct. 3, 1967 N. w. EFT 3,344,998

PULVERIZER Filed July 27. 1964 Sheets-Sheet 2 N. W. EFT

PULVERIZER Oct. 3, 1967 Filed July 27. 1964 FIG.3

Fo css ROTATING Bowl.

FINE COAL A B COARSE COAL "G" ON COAL United States Patent Filed llilly 27, 1964, Ser. No. 385,216 4 Claims. (Cl. 241103) This invention relates to the pulverization of solid material, and more particularly to improvements to the c-onstruction and operation of pulverizers wherein materials are pulverized between relatively moving grinding surfaces.

The art of solid material pulverization is highly developed with incremental improvements occurring by increase-d grinding efciencies usually accompanied by improved classiiication of the pulverized materials within an air-swept pulverizer. In recent years improved grinding efficiency has been attained with increased unit capacities by increasing the effectiveness of grinding surfaces. This has been accomplished by increasing effective use of grinding surfaces by employing counter-rotating rings in ring and ball pulverizers, such as shown in U.S. Patent 3,093,327.

Even more effective grinding efficiency can be attained by maintaining a depth of material being pulverized within the grinding area such that the depth of material is less than 1/7 the diameter of the rolling grinding elements. When solid granular materials are delivered to a rotating horizontal plate having Ia perip-heral flange thereon the materials will form an upwardly inclined partially concave surface which will vary in its slope or angle of inclination depending upon the rate of plate rotation, the fineness Vand the moisture content of the granulated material, and the specific gravity of the solid material. Ordinarily, in the pulverization of material such as coal, rock and the like, the fineness of the materials passing through a grinding zone, the specific gravity of the material and the moisture content thereof in any dry grinding process will be suficiently alike that the surface of the material will assume an inclination of 25 to 45 below the horizontal on a flanged plate when the plate is rotated at a rate developing a centrifugal force of 6 to 12 Gs on the material.

While the free surface angle of the material formedv on a flanged rotating plate will be at least partially concave, the effective surface of material in any operating ring-roll or rolling ball type of pulverizer will be sufficiently remote from the center of plate rotation that the inclined material surface can be considered substantially at adjacent the outer circumference of the grinding ring.

This angle of inclination of the material, is coordinated with the desired depth of material, i.e. less than 1/7 the diameter of the rolling grinding element acting thereon, so as to cooperate in insuring highest grinding efficiency in the pulverization zone. In some cases the improved grinding effect is combined with an improved classification effect in an `air-swept pulverizer so as to attain progressive classification of fine `and coarse materials lbefore delivery of the airborne pulverized material to a mechanical classier.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For

3,344,998. Patented Oct. 3, 1967 a better understanding of the invention, its operating advantages and specific objects attained by its use, reference lshould be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawings:

FIG. l is a sectional elevation of a counter-rotating pulverizer constructed and arranged in accordance with the present invention;

FIG. 1A is an enlarged section of a portion of a pulverizer such as shown in FIG. 1;

FIG. 2 is an enlarged modified sectional elevation of a portion of a pulverizer of the general type shown in FIG. 1;

FIG. 3 is a sectional elevation of a further modification of the present invention as applied to a different type of pulverizer.

FIG, 4 is a section taken on line 4--4 of FIG. 3;

FIG. 5 illustrates the comparative effect of the angle of inclination of the material in a pulverizer of the type shown in FIG. 3; and

FIG. 6 is a graph illustrating the effect of the force due to rotation of the plate on the surface angle or angle of inclination of granulated solids.

While the present invention is illustrated in the drawings as applied to an air-swept pulverizer it will be understood that the same general type of grinding zone construction is equally as effective in a pulverizer of the gravity discharge type with classification of the ground product accomplished exteriorly of the pulverizer zone Iby mech-anical means.

One of the important aspects of the invention is illustrated in FIG. 6, which show the results of a series of tests during which granulated coal was fed to a rotating flanged plate. By rotating the plate -at different rates corresponding to the range of centrifugal forces acting on the granulated material in actual pulverizing installations, the optimized angle of surface inclination of the coal may be determined. Most pulverizers of the ball and race or ring and roll type operate at rates or rotation corresponding to G (force of gravity) values between 6 and 12 Gs, and within these values the angle of surface inclination is varied between 25 and 45 degrees below the horizontal as shown by the curves A and B. It was also further found that an approximate value of 40 below the horizontal was -a reasonably average value for substantially all coals, regardless of moisture content of the coal passing through an air-swept pulverizer, `and that while the upper and lower particle sizes passing through a pulverizing zone might change with different pulverizers, the predominant size ranges of the coal would fall in those ranges indicated by curves A and B in FIG. 6.

As shown in FIG. 1 a pulverizer housing 10 is provided with a grinding zone 11 in the lower portion thereof while the upper portion of the pulverizer housing is provided with a mechanical air classifier 12. The grinding elements include a lower grinding ring 13, having an upper annular grinding surface 14 and mounted for rotation about a vertical axis. A plurality of grinding balls -15 are disposed upon and in intimate contact with the annular grinding surface 14 of the lower grinding ring. In addition the lower annular grinding surface 16 of an upper grinding ring 17 rests on the row of balls 15'. The arrangement of the pulverizer shown is such that the upper grinding ring 17 rotates opposite in direction to that of the lower grinding ring 13. As shown in FIG. l both the upper and lower grinding rings are driven from worm gear drive mechanisms 20 and 21 positioned beneath the pulverizer housing 10. The lower ring 13 is driven by a stub shaft 22 connected through a yoke 23 to the lower ring while the upper ring is driven by a shaft 24 which extends upwardly through the hollow central portion of the stub shaft 22 and transmits the rotational force and a series of single turn springs 26 to the upper grinding ring 17. As disclosed in the patent already referred to the grinding pressure exerted on the rings and balls is regulated by means of adjusting bolts 27 which interconnect the drive yoke 25 and the upper ring 17 through the springs 26.

In the illustrated form the invention, raw material is delivered to the upper part of the housing through a feeder 30. Carrier or classifying air is delivered to the lower portion of the grinding zone through an air housing 31 which directs air circumferentially of the ring to an annular space 32 beneath a throat 33 formed between the outer circumference 34 of the lower grinding ring and annular throat member 35 attached to the housing 10. The carrier air passing upwardly through the annular throat 33 entrains pulverized material discharged by centrifugal force from the grinding zone.

In accordance with the present invention the outer circumference of the lower ring is provided with an upstanding rim or ledge 36 spaced outwardly of the row of grinding balls. The height of the ledge is such as to provide an angle of approximately 40 below the horizontal, the angle being that formed by the intersection of a horizontal line and a line described by joining the point in the surface of the lower ring which is in vertical alignment with the centerline of the row of balls and a point on the inner circumference of the ledge 36. With this arrangement, material is maintained beneath the row of balls less than 1/7 of the diameter of the balls.

With the throat construction described and illustrated in FIGS. 1 and 1A, air passing upwardly through the throat 33 will recirculate inwardly adjacent the upper ring 17 and the row of balls 15 (see FIG. 1A) and will tend to entrain material which will be further pulverized between the upper grinding ring 17 and the balls 15. The air, with entrained pulverized material, will thereafter pass upwardly past the yoke 25 of the pulverizer where the increased cross-sectional flow area will reduce the air velocity and tend to separate large particles of pulverized material therefrom for reintroduction into the grinding zone 11. The remaining air borne pulverized material will pass upwardly through the pulverizer into the classifier 12 where the centrifugal force applied thereto will further classify the pulverized material so that the material leaving the pulverizer through the outlet 37 with the carrier air will be of the desired fineness. The separated coarser solid material in the classifier will be discharged downwardly through an annular discharge port 40 for reintroduction into the pulverizing zone 11 and further pulverization.

A modified construction of a pulverizer grinding zone is schematically shown in FIG. 2 where a rotating lower annular grinding ring 41 having an upper grinding surface 42 supports a ball 43 which is one of a circularly arranged series of grinding balls. The upper annular grinding ring 44 has a lower grinding surface 45 bearing on the upper surface of the ball 43. The ring 44 may be rotated as in the FIG. 1 construction, or may be stationary, as shown in U.S. Patent 2,670,138. The upper edge 46 of the ledge 47 is extended outwardly of the row of pulverizing balls to a point substantially at the elevation of the uppermost point of contact between the upper ring 44 and the row of grinding balls 43. As hereinbefore pointed out, the uppermost edge of the ledge 47 is so located as to provide a material surface profile 4S which is at an angle of 40 below the horizontal and thus is sufficient to optimally provide material on the lower 4i grinding ring 41 less than 1/7 the diameter of the grinding ball 43. Carrier air is delivered to the pulverizer in a manner similar to that shown in FIG. 1 for upward flow through an annular throat 50 formed between a stationary throat ring 51 and the exterior surface 52 of the lower ring assembly including the ledge 47.

It will be appreciated the particular construction and arrangement shown is intended to encourage recirculation of carrier air and entrained pulverized material inwardly of the pulverizer and above the upper grinding ring 44 in a pattern as shown `by the arrows 53. It has been found that forming the throat as in FIG. 2 causes a mass of pulverized material to collect Well above the upper grinding ring and serve as a buffer so that a major portion of the moving coal and air mixture will pass inwardly of the grinding zone above the upper grinding ring 44. This type of construction is particularly effective in a pulverizer where the upper grinding ring 44 is stationary and the lower grinding ring 41 is rotatable.

The initial classification of material discharged from the grinding zone will occur during initial contact of the air passing through the throat 50` with the material passing over the ledge 47. In this type of construction further classification of the pulverized material will occur as the carrier air and entrained material pass above the grinding ring where the increase in flow area reduces the velocity of the carrier air .permitting the coarse material to return to the inner side of t-he grinding zone (see arrows 5.4). Meanwhile the carrier air with entrained material will pass upwardly to a separator or classifier such as that indicated at 12 in FIG. 1. It will be appreciated that the upper edge 46 of the ledge 47 could be lowered along the slope of the material surface 48 maintained in the pulverizing zone. The carrier air fiow through the grinding zone would then be similar to that shown in the FIGS. 1 and 1A arrangement.

The pulverizer s-hown schematically in FIGS. 3 and 4 is of the general type wherein a bowl or grinding ring 60 is rotated at a desirable speed while the shaft 61 supporting the rolls 62 may also be rotated in the opposite direction at a selected speed. In the embodiment shown, the rolls 62 are relatively narrow in their grinding surface dimension so that alternate rolls may be spaced vertically to provide an increased number of grinding rolls in contact with the rotating ring 60 within the pulverizer housing 63. T-he rolls may be pivotally supported from a yoke 64 positioned on the sha-ft 61 so that during rotation centrifugal force will cause the rolls 62 to move outwardly against the grinding ring 60. Alternately it is of course understood the rolls 62 may be controlled in their outward movement :by hydraulic or spring loading arrangement so as to regulate the force applied by the rolls 62 against the `grinding ring 60. In either case, the angle of the inner surface 65 of grinding ring 60 and the face of the roll 62 should be approximately 40 below t-he horizontal, and the depth of material on the ring should be less than approximately yf the -diameter of the roll 62.

The relationship between a rotating grinding ring and a roll is schematically illustrated in four different forms in FIG. 5. The arrangement shown in FIG. 5A illustrates a ring and roll arrangement such as disclosed in U.S. Patent 2,815,903 wherein the upper edge 70 of the grinding ring 71 determines the an-gle of inclination of the material maintained in the grinding zone. In pulverizers of this type the grinding surfaces of the ring 71 and the roll 72 are substantially parallel. With a material angle of approximately 40 -below the horizontal, roll 72 (shown in FIG. 5A) will have only t-he lower portion of the roll in contact with the material being `ground and will be effective as a grinding surface at its lower end only. Moreover, the dept-h of material maintained in the grinding Zone will be insufficient for eflicient grinding purposes and the pulverizer would have a tendency to choke. The wear on the roll 72 will be excessive and unequal along the grinding surface.

The most desirable arrangement of grinding ring and grinding roll is shown in FIG. 5B wherein the surface of the grinding ring 74 is at an angle of approximately 40 below the horizontal and the upper edge 73 of a grinding ring 74 is spaced above t-he surface of the grinding roll 75 so as to maintain a depth of material on the grinding ring less t-han approximately 4/7 the diameter of the roll 75. The grinding roll 75 surface will be substantially parallel to the surface of the ring 74 when in operative relation thereto and high grinding efficiency wit-h essentially uniform ring and roll wear will result.

In the diagram shown in FIG. 5C the angle below the horizontal relative to the surface of t-he ring 76 is considerably less than the preferred substantially 40 slope which the material will assume during rotation of the grinding ring. The outermost corner 77 of the grinding roll 78 will perform a major portion of the grinding due to the depth of material maintained between the ring surface 76 and the roll 78. In a pulverizer constructed in this manner the roll and ring will not be eiiicient in grinding, will exhibit unequal wear and will be unsatisfactory both as to capacity and the ability to produce ne material.

The arrangement shown in FIG. 5D presents a horizontally disposed grinding ring surface 80, which arrangement will permit only a small portion of the outer section of roll 81 to function. Thus the roll will be subject to concentrated wear, and the pulverizing capacity will be reduced accordingly.

In each of the arrangements of FIG. 5 the roll may be supported for rotation from the exterior of the grinding ring as shown for example in U.S. Patent 2,815,903 or from the center of the pulverizer, as shown in FIGS. 3 and 4.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form and mode of operation of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claim, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. In a pulverizer having a housing and a grinding zone within the housing, said grinding zone including a ring having an annular -grinding surface on the upper side thereof, means for rotating said ring about a vertical axis, a plurality of rolling grinding elements positioned in grinding relation to the annular grinding surface of said ring, means for introducing materials to be pulverized to the grinding zone, means for discharging pulverized material from said -grinding zone and said housing, said annular grinding surface forming an inverted frustum of a cone having a base angle of approximately 25 to 45, and means including an upper circumferential edge on said ring for maintaining a bed of material on the annular surface of said ring having an upper surface inclination of approximately 40 below the horizontal and to form a bed of material between said ring and elements having a depth of less than approximately the average diameter of a rolling grinding element.

2. A pulverizer comprising a housing enclosing a grinding zone including a lower grinding ring having an upper wearing surface thereon, means for rotating said grinding ring about a substantially vertical axis, a circumferential series of rollin-g grinding balls resting on the wearing surface of said grinding ring for the pulverization of solid materials therebetween, an upper grinding ring having a lower grinding surface bearing on said rolling lgrinding balls, means for rotating said upper grinding ring about a vertical axis and in ya direction opposite to that of said lower grinding ring, means for delivering material to be pulverized to the central portion of said grinding zone for outward movement across the grinding surface of said lower ring, and means for maintaining an outwardly moving mass of material between said grinding surface and said grinding balls including means forming an upper circumferential edge to said lower grinding ring with the angle formed in a plane intersecting said axis of rotation between a horizontal iine at said edge and a line drawn between said edge and the intersection of the vertical centerline of each of said balls with the surface of said ring being approximately 40, said mass having a depth less than 15% of the diameter of said grinding balls.

3. A pulverizer comprising a housing enclosing a pulverizing zone including grinding ring, means for rotating said grinding ring about a vertical axis, said grinding ring having a wearing surface thereon formed as an inverted truncated cone having a base angle of approximately 40, a plurality of rolling grinding elements having a circumferential wearing surface substantially parallel to said ring wearing surface when substantially in contact therewith for the pulverization of solid materials between said ring and grinding element, means for applying a grinding pressure to said rolling grinding elements, means for delivering material to be pulverized to the central portion of said rotating ring, an upright circumferential lip on the outer periphery of said ring, the upper edge of said lip being positioned outwardly and above the wearing surfaces of said ring to maintain a moving bed of material between the rolling grinding elements and said ring surface having a depth less than substantially 1/7 the diameter of said rolling grinding element.

4. A pulverizer comprising a housing enclosing a grinding zone including a lower grinding ring having an upper wearing surface thereon, means for rotating said grinding ring about a substantially Vertical axis, a circumferential series of rolling grinding balls resting on the wearing surface of said grinding ring for the pulverization of solid materials therebetween, an upper grinding ring having a lower grinding surface bearing on said rolling grinding balls, means for delivering material to be pulverized to the central portion of said grinding zone for outward movement across the grinding surface of said lower ring, and means for maintaining an outwardly moving mass of material between said grinding surface and said grinding balls including means forming an upper circumferential edge to said lower grinding ring with the angle formed in a plane intersecting said axis of rotation between a horizontal line at said edge and a line drawn between said edge and the intersection of the vertical centerline of each of said balls with the surface of said ring being approximately 40, said mass having a depth less than 15% of the diameter of said grinding balls.

References Cited UNITED STATES PATENTS 2,670,138 2/ 1954 King et al 241-103 X 2,909,330 10/1959 Hardinge 241--118 X ANDREW R. JUHASZ, Primary Examiner

Claims (1)

1. IN A PULVERIZER HAVING A HOUSING AND A GRINDING ZONE WITHIN THE HOUSING, SAID GRINDING ZONE INCLUDING A RING HAVING AN ANNULAR GRINDING SURFACE ON THE UPPER SIDE THEREOF, MEANS FOR ROTATING SAID RING ABOUT A VERTICAL AXIS, A PLURALITY OF ROLLING GRINDING ELEMENTS POSITIONED IN GRINDING RELATION TO THE ANNULAR GRINDING SURFACE OF SAID RING, MEANS FOR INTRODUCING MATERIALS TO BE PULVERIZED TO THE GRINDING ZONE, MEANS FOR DISCHARGING PULVERIZED MATERIAL FROM SAID GRINDING ZONE AND SAID HOUSING, SAID ANNULAR GRINDING SURFACE FORMING AN INVERTED FRUSTUM OF A CONE HAVING A BASE ANGLE OF APPROXIMATELY 25 TO 45*, AND MEANS INCLUDING AN UPPER CIRCUMFERENTIALLY EDGE ON SAID RING FOR MAINTAINING A BED OF MATERIAL ON THE ANNULAR SURFACE OF SAID RING HAVING AN UPPER SURFACE INCLINATION OF APPROXIMATELY 40* BELOW THE HORIZONTAL AND TO FORM A BED OF MATERIAL BETWEEN SID RING AND ELEMENTS HAVING A DEPTH OF LESS THAN APPROXIMATELY 15% THE AVERAGE DIAMETER OF A ROLLING GRINDING ELEMENT.

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