US2975984A - Pulverizing apparatus - Google Patents

Description

March 1961 KARL-HEINZ KAYATZ 2,975,984

PULVERIZING APPARATUS Filed March 3, 1958 FIG.2

2 I a W K MZ En V mmn H a K ATTORNEY PULVERIZING APPARATUS Karl-Heinz Kayatz, Hamburg-Grossflotthelr, Germany,

assignor to Babcock 8c Wilcox Limited, London, England, a company of Great Britain Filed Mar. 3, 1958, Ser. No. 718,877

Claims priority, application Germany Mar. 6, 1957 7 Claims. (Cl. 241-52) This invention relates to pulverizing apparatus, and more particularly to a pulverizer having a circular row of rolling grinding elements disposed in a horizontal plane between a rotating upper and a stationary lower grinding race or ring. The raw material to be pulverized is delivered to the central portion of the grinding elements for radial movement outwardly through the pulverizer. r

Heretofore, pulverizers of the type described having a centrally located raw material inlet position were usually provided with a rotating lower grinding ring onto which the material drops. Under these conditions, the material likewise receives a rotary motion so that a centrifugal force corresponding to the peripheral speed of the rotating grinding ring acts on the raw material to convey the material through the pulverizing or grinding zone. The effect of the centrifugal force has been found to be undesirable since the forces acting on the material cause the material to be Withdrawn prematurely from the elements of the grinding zone. It is possible, under these conditions, that the material, or a major part thereof, can travel through the grinding zone without being subjected to the action of the grinding elements. When this happens, the material must be recirculated through the grinding zone a number of times to attain sufficient size reduction. 7 i

In addition to a pulverizing unit of the type described, it is also known to construct the mill with a stationary lower grinding ring. However, these known pulverizers do not have a centrally located raw material inlet because the necessary space for the inlet is unavailable. due to the presence of the driving mechanism for the upper ring of the grinding zone. In this type of pulverizer, the material inlet is arranged radially outward of the grinding zone in pulverizing housing. With this construction, the material must enter the grinding zone in a reversed direction with respect to the centrifugal action of the grinding element rotation, thereby limiting the capacity of the unit. customarily, such a material inlet position is usually located at a single point or over a limited circumferential segment of the grinding zone. Under these circumstances, the incoming raw material tends to accumulate at the inlet opening and it is difiicult, if not impossible, to attain an even ditsribution of the material around the circumference of the grinding ring, since distribution is inherently slow and uneven as a result of the dragging effect of the grinding elements. Furthermore, in such an arrangement, the distribution of carrier air flow to the grinding zone is impeded because the carrier medium has to be introduced to the inner peripheral edge of the stationary lower grinding ring. The air-borne pulverized material mixture must then flow through the 2,975,984 Patented Mar. 21, 1961 ice mechanism of the upper grinding ring. The moving parts of the driving mechanism are therefore subjected to increased wear by erosion by the moving stream of airborne material. Such movement of air-borne material also leads to high pressure losses due to the restricted movement of the carrier medium through the passageways in the driving mechanism of the upper ring.

In the present invention, the pulverizer is constructed and arranged to overcome the above described drawbacks in the known pulverizing units. This is accomplished by utilizing a stationary lower grinding ring and providing a central raw material inlet for the delivery of the material to the pulverizing zone from above. Such an arrangement results in a substantially uniform distribution of the raw material throughout the inner periphery of the stationary lower grinding ring. Under these conditions, the grinding elements advantageously receive a well-distributed circumferential flow of the raw material for pulverization. The raw material entering the grinding zone moves outwardly over the lower stationary grinding ring in a radial direction so that the raw material is repeatedly subjected to the grinding action of the rolling grinding elements moving through the grinding zone. action of the rolling grinding elements aids in a gradual outward movement of the material being pulverized.

In the pulverizers of the present invention, the discharge of the pulverized material from the grinding zone can be effected by gravity discharge or by entrainment in a carrier air stream. In the gravity discharge type of construction, the pulverized material discharging over the outer edge of the stationary lower grinding ring falls by gravity into a collecting spout from which it is removed by known conveying means and delivered to an external classifier. As is also known, the external classifier removes the selected finely pulverized material for discharge to point of use, while the 'oversized, relatively coarse materials are returned to the pulverizer for further pulverization.

When the pulverizer is constructed as an air swept unit, the pulverized material discharging over the outer periphery of the stationary lower grinding ring is entrained by an annular upwardly directed stream of carrier medium or air. The entrained particles of pulverized material are subjected to gravity separation in the pulverizer housing immediately above the grinding zone and the remaining entrained pulverized material is subjected to centrifugal classification in the upper 'part of the pulverizer housing.

In the pulverizer construction of the present invention, the introduction of the carrier air stream to the unit may be from below the pulverizing zone, thus producing an upward movement adjacent the outer periphery of the lower grinding ring, as described above. Thus, the carrier air stream may be directed horizontally from the outside of the pulverizing zone, movinginwardly against the grinding elements whereby very intensive whirling within the grinding zone is attained. Alternately, the carrier air may be introduced trom the central portion of the pulverizer grinding zone for movement of the carrier air stream-outwardly through the grinding elements of the pulverizing. zone. The stationary centrally disposed dis- The tributor cone which directs the material to the lower stationary grinding ring can be provided with air inlet slots which direct the flow of air through the grinding zone. When the carrier air is delivered to the central portion of the grinding zone, such carrier air is ordinarily preheated so that the carrier air is effective in predrying the raw material reaching the grinding zone of the pulverizer. Some of the air may be introduced centrally of the pulverizing zone together with the incoming raw material.

If the carrier air stream entering the pulverizing zone moves in the same direction as that in which the material moves, the pulverized material is quickly entrained and removed from the grinding zone. Furthermore, the preheated carrier air is effective in heating the distributing cone of the pulverizing zone so that wet material delivered to the unit is not apt to cake thereon and is more readily introduced into the grinding elements.

When unusually high moisture raw material is introduced to the pulverizer, it is advantageous to introduce at least some of the preheated carrier air with the material through the central material inlet duct. The preheated air fiows in a direction parallel to the introduction of the entering raw material and is particularly effective in predrying the material before it enters the grinding zone. Such an arrangement for the introduction of carrier air also assists in the movement of the raw material through the grinding zone.

Provision is also made for separating foreign matter such as stones, iron and the like, which might be present in the raw material delivered ot the pulveri'zer. For this purpose, a conical coarse mesh screen is provided to cover the upper rotating grinding ring. The incoming raw material passes through the coarse screen whereas oversized material is discharged outwardly as a result of centrifugal force since the screen rotates with the upper grinding ring. In addition to the rotating movement of the screen, the upper grinding ring and the screenare also subjected to vibrations caused by vertical movements of the rotating grinding ring during its grinding operation.

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 a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should 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 an elevation, partly in section, of an airswept pulverizer constructed according to the present invention;

Fig. 1A is a modified form of the invention shown in Fig. 1; and V Fig. 2 is a section taken on the line 2--2 of Fig. 1.

In the illustrated embodiment of the invention, an airswept pulverizer is shown. It will be understood that substantially the same grinding zone construction can be used for a gravity discharge type of unit. 'In the latter instance, air flow through the unit for carrier purposes would be unnecessary.

'As shown, a tubular inlet duct 2 projects downwardly through the top of the pulverizer housing 1 to "a position upwardly adjacent the grinding zone of the pulverizer. The duct 2 is centrally located and as shown is preferably co-axial with the pulverizer housing. The grinding elements formingthe pulverizing zone of the unit include a lower stationary grinding ring 3, a circumferential row of rolling grinding balls 4 and an upper rotating grinding ring 5. The rotating grinding ring is driven by a motorized gear reducer 6 having an upwardly extending shaft '7 which is Cardan-suspended on the upper grinding ring'S. The main shaft 7 is shown as being sealed by a labyrinth gland which consists of a container 8, a sealing medium 9, and ahollow cylinder 10 projecting into the container and which is supported on a distributor cone 11. The container 8 has an annular inside wall 12 which is spaced from the outer wall of the container to form an annular spacing for the sealing medium. The hollow cylinder 10 projects into the annularspace. The sealing medium consists of a fluid with a boiling point above the operational temperature of the pulverizer and a higher specific gravity than the ground material produced in the pulverizer. The diiference in the specific gravity of the materials results in a lack of penetration into the sealing medium so that the pulverized material merely rests on the surface of the sealing medium. The fluid can be so constituted that it solidifies at room temperatures but is liquid at a higher temperature. A preferred sealing medium is a metal alloy which is liquid at temperatures of 60 to C. and has a boiling point beyond the operational temperature of the mill. The metal alloy may be such as to require preheating before the pulverizer has started up Where the heating may be accomplished by electric, gas or steam heating means.

In the drawing, two alternate arrangements for introducing carrier medium to the grinding elements is shown. As shown on the left hand side of the drawing, the pre-heated carrier medium can be introduced through an inlet duct 13 for inward flow toward the elements 4 of the grinding zone. The carrier medium leaving the pulverizing zone moves upwardly along the wall of the housing in an annular stream toward the upper portion of the pulverizer. In the alternate arrangement shown on the right hand side of the pulverizer drawing, the distributor cone 11 is provided with a plurality of slots 14 which are constructed to direct a flow of carrier medium in a generally horizontal direction outwardly through the pulverizing zone for upward movement between the exterior of the upper grinding ring and the pulverizer housing. It will be noted that the slots 14 may also be shaped to direct the carrier medium downwardly and outwardly toward the grinding surface of the lower grinding ring 3.

As shown in the drawing, carrier medium can also be introduced through the material inlet duct 2 so as to move downwardly through the central portion of the grinding zone to pass outwardly through the grinding zone.

The upper rotating grinding ring 5 is provided with a conically shaped coarse screen 15 which intercepts the incoming raw material so. that oversized foreign materials in the incoming raw material are deflected outwardly over the upper screen surface to be discharged against the rising annular stream of carrier medium. As known in the art, provisions may be made for the discharge of foreign materials from the annular space between the outer surface of the lower grinding ring and the inner surface of the housing. Such means are effective in removing foreign materials from the lower portion of the pulverizer without such foreign materials passing the rolling grinding elements 4.

The upper portion of the pulverizer housing 1 is provided with a classifying zone which in the present instance is large enough to accommodate a plurality of centrifugal classifiers 17, each of which is provided with an upper circumferential series of vanes 18 which are adjustable for determining the size range of the material discharging through the outlet ducts 19. In the embodiment of the invention disclosed, each of the ducts 19 is connected with a pulverized coal burner (not shown). With such an arrangement, the air-home pulverized coal stream is effectively and uniformly divided in the classifying zone 16 of the pulverizer so that each burner will receive a, controlled quantity of air-borne pulverized coal. Such controlled quantity of fuel to each burner is independent of the supply to any other burner.

While in accordance with the provisions of the statutes the invention has been illustrated and described in the best form and mode of operation of the invention now known, 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 the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. Apparatus for pulverizing solid materials comprising a housing having a pulverizing zone in the lower portion thereof, said pulverizing zone including a stationary horizontally disposed lower annular grinding ring and a rotatable upper annular grinding ring, a circumferential row of rolling grinding elements positioned between said lower and upper grinding rings, means for introducing fluid carrier medium into said pulverizing zone, means for rotating said upper grinding ring including an upright drive shaft flexibly connected to said ring and means for eXerting a downward force on said upper ring through said shaft, means for introducing raw solid materials into the central portion of said pulverizing zone including an upright duct coaxial with said grinding elements and projecting downwardly into said housing to a lower end position spaced above said lower grinding ring, and means for removing pulverized solid materials discharged by centrifugal force from the outer circumference of said pulverizing zone to a position exterior of said housing by said fluid carrier medium.

2. Apparatus for pulverizing solid materials comprising a housing having a pulverized material outlet duct in the upper portion thereof and a pulverizing zone in the lower portion thereof, said pulverized zone including a stationary horizontal disposed lower annular grinding ring and a rotatable upper annular grinding ring, a circumferential row of rolling grinding elements positioned between said lower and upper grinding rings, means for rotating said upper grinding ring including an upright drive shaft flexibly connected to said ring and means for exerting a downward force on said upper ring through said shaft, feeder means for introducing raw solid materials into the central portion of said pulverizing zone, means for discharging pulverized solid materials from the outer circumference of said grinding zone, and means for passing an annular stream of carrier medium through said pulverizing zone in an outward substantially horizontal direction and thereafter in an upward direction between the outer periphery of said rotating upper grinding ring and said housing toward said outlet duct.

3. Apparatus for pulverizing solid materials comprising a housing having a pulverized material outlet duct in the upper portion thereof and a pulverizing zone in the lower portion thereof, said pulverizing zone including a stationary horizontally disposed lower annular grinding ring and a rotatable upper annular grinding ring, a circumferential row of rolling grinding elements positioned between said lower and upper grinding rings, means for rotating said upper grinding ring including an upright drive shaft flexibly connected to said ring and means for exerting a downward force on said upper ring through said shaft, means for introducing raw solid materials and preheated carrier medium into the central portion of said pulverizing zone, means for discharging the pulverized solid materials from the outer circumference of said grinding zone, and means for passing a separate annular stream of carrier medium upwardly adjacent the outer circumference of said pulverizing zone and toward said outlet duct.

4. Apparatus for pulverizing solid materials comprising a housing having a pulverized material outlet duct in the upper portion thereof and a pulverizing zone in the lower portion thereof, said pulverized zone including a stationary horizontal disposed lower annular grinding ring and a rotatable upper annular grinding ring, a circumferential row of rolling grinding elements p0- sitioned between said lower and upper grinding rings,

means for rotating said upper grinding ring including an upright drive shaft flexibly connected to said ring and means for exerting a downward force on said upper ring through said shaft, feeder means for introducing raw solid materials and carrier medium into the central portion of said pulverizingzone, means for discharging pulverized solid materials from the outer circumference of said pulverizing zone, and means for passing a separate annular stream of carrier medium through said pulverizing zone in an outward substantially horizontal direction and thereafter in an upward direction between the outer periphery of said rotating upper grinding ring and said housing toward said outlet duct.

5. Apparatus for pulverizing solid materials comprising a housing having a pulverizing zone in the lower portion thereof, said pulverizing zone including a stationary horizontally disposed lower annular grinding ring and a rotatable upper annular grinding ring, a circumferential row of rolling grinding elements positioned between said lower and upper grinding rings, means for rotating said upper grinding ring including an upright drive shaft flexibly connected to said ring and means for exerting a downward force on said upper ring through said shaft, means for introducing raw solid materials and a controlled flow of carrier medium into the central portion of said pulverizing zone including an upright duct coaxial with said grinding elements and projecting downwardly into said housing to a lower position space above said upper grinding ring, a conical screen positioned between said upper grinding ring and the lower end of said upright duct to divert oversized material to the outside of said pulverizing zone, and means for removing pulverized solid materials discharged from the outer circumference of said pulverizing zone to a position exterior of said housing.

6. Apparatus for pulverizing solid materials comprisinga housing having a pulverized material outlet duct in the upper portion thereof and a pulverizing zone in the lower portion thereof, said pulverizing zone including a stationary horizontally disposed lower annular grinding ring and a rotatable upper annular grinding ring, a circumferential row of rolling grinding elements positioned between said lower and upper grinding rings, means for rotating said upper grinding ring including an upright drive shaft :operatively connected to said upper ring and a drive motor connected to the lower portion of said drive shaft and supported therefrom, whereby the weight of said motor and drive shaft are superposed on said upper ring, means for gravitationally introducing raw solid materials from above through a duct into the central portion of said pulverizing zone, means for discharging the pulverized solid materials from the outer circumference of said grinding zone, and means for introducing carrier medium horizontally against said grinding elements and passing an annular stream of said carrier medium upwardly to entrain pulverized material discharging from the outer circumference of said pulverizing zone and toward said outlet duct.

7. Apparatus for pulverizing solid materials comprising a housing having a pulverized material outlet duct in the lower portion thereof and a pulverizing zone in the lower portion thereof, said pulverizing zone including a stationary horizontally disposed lower annular grinding ring and a rotatable upper annular grinding ring, a circumferential row of rolling grinding elements positioned between said lower and upper grinding rings, means for rotating said upper grinding ring including an upright drive shaft operatively connected to said upper ring and a drive motor connected to the lower portion of said drive shaft and supported therefrom, whereby the weight of said motor and drive shaft are superposed on said upper ring, means for gravitationally introducing raw solid materials from above through a duct into the central portion of said pulverizing zone, a conical screen beneath said duct and having its outer edge attached to said upper ring, means for discharging the pulverized solid materials from the outer circumference of said 'grindingzone, 'and means forintroducing carrier medium References Cited in the file of this patent UNITED STATES PATENTS Schiefller July 2, 1907 Grey Mar. 28, 1922 '8 Green et a1. Mar. 15, 1932 Baileyret al. Aug. 27, 1935 Hobbs Sept. 17, 1 940 Lynch May 4, 1943 Dickey Apr. 13, 1948 MacPherson Aug. 26, 1958 FOREIGN PATENTS Great Britain Jan. 3, 1924 Italy Nov. 11, 1939 Germany Nov. 25, 1926 Germany Feb. 10, 1939 Germany Jan. 17, 1952 Germany Sept. 17, 1953

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