GB2067094A - Edge-runner mill - Google Patents

Abstract

The invention relates to coal pulverizing edge-runner mills having a rotating table. The table (30) has an annular recess a plurality of rollers (54) bearing on the table (30) at the recess (42). Each roller is individually biased towards the table (30) so that movement of the axis (66) of one of the rollers (54) does not affect the others. <IMAGE>

Description

SPECIFICATION Roller pulverizing mill There are several common uses for mills which are used to pulverize solids. One example is the pulverization of coal to prepare it for firing in a furnace.

One type of mill, commonly known as a ball mill, as its name implies, uses large metal balls to pulverizethe material. Ball mills are generally reliable but have several disadvantages. For any given quantity of coal or other material to be pulverized they are comparatively large and therefore require a rather large capital expenditure. Further, they consume much energy in their operation.

When a less expensive mill is required, roller mills are often employed. Roller mills which are presently used to pulverize coal generally employ several rollers which bear down on a rotating table onto which the coal is fed to pulverize the coal. In some designs, the rollers have flat tread portions which tend to wear unevenly over a period of time. This results in a pulverized coal in which the particulate size is not uniform. Other designs have structure which urge the rollers down against the rotating table in such a way that when the coal between the table and roller exerts an upward force on a roller, the other rollers are jostled. The result is the creation of vibration during operation and a consequent excessive degree of wear and a loss of efficiency.

In other designs, the rollers begin to yaw after a period of operation because of wear in the parts which are designed to guide the rollers. This creates excessive rolling friction so that the rollers often skid over the table rather that roll over it. When this happens, the skidding roller is not pulverizing the coal properly, and consequently the efficiency of the mill quickly deteriorates.

It is an object of the present invention to overcome drawback found in the prior art such as those discussed above. Accordingly, a roller mill is provided with a rotating table and a plurality of rollers which bear down on the table at a circular trough therein. Each of the rollers are individually spring biased down against the table so that movement of the axis of rotation of one of the rollers will not affect any of the other rollers.

Fig 1 is a side view partly in section showing a pulverizing mill made in accordance with the present invention; and Fig 2 is a view partly in section and in larger scale than is Fig 1 showing a detail of the preferred embodiment.

Fig 3 is a plan view partly in section taken substan tiafly along the line 3-3 of Fig 1; and Fig 4 is a view showing certain parts of the present invention positioned for servicing.

Fig 1 shows a coal pulverizing mill indicated generally as 10 having an outer shell 12 which has an upper portion 14, which is joined to a middle portion 16 at a flange seam 17 and a lower portion 18. The shell 12 is mounted on a platform which in turn is supported on legs 22 and 24 which extend upwardly from footing 26 and 28 respectively. Located within the shell 12 is a circular table 30 which is mounted as by bolts 32 on a wheel 34 which is rotated by a motor 36 directly below the wheel 34. The table 30 which has a hollow center portion 38 includes an annular track 40 ofwear resistance material which may be hard steel. The track 40 is recessed at 42. A cover 44 bridges the hollow center portion 38 to prevent particulate matter from entering the hollow portion 38.

The cover 44 is secured to the table 30 by bolts 46 and the annular track 40 is secured to the table by bolts 48 so that the cover 44 and track 40 rotate with the table 30 when it is turned by the motor 36.

Unpulverized coal is introduced into the mill through a coal pipe 50 which extends down through the top 52 of the mill 10 to a location above the center of the table 30. The coal falls on the table to be moved radially outward by centrifugal force to the annulartrack40. The coal then passes between the track 40 and rollers 54, which bear down on the track 40, within the recess 42. Although the preferred embodiment employs several rollers 54, only one is shown in Fig 1 for the sake of simplicity.

The roller 54 has a tread portion 56 which is curved in cross section so that it has the shape of the outer portion ofatorus. The tread 56 is the peripheral surface of a tire portion 58 which is made of hardened metal and which is secured to a wheel portion 60 positioned within the tire portion 56. The roller 54 includes an outer race 62 which rotates about bearings 64 which in turn rotate about an axle 66. The axle 66 includes a journal portion 68 which in effect forms the inner race for the bearings 64 and an increased diameter portion 70 positioned between the journal portion 68 and a tapered portion 72. The tapered portion 72 is integrally connected to the end of a shaft portion 74. The axle 66 is mounted rigidly with a support 76.The rigid connection between the axle 66 and the support 76 is accomplished by a press fit between the support 76 and the tapered portion 72.

The shaft portion 74 is of a diameter small enough to define between it and the support 76 an annular chamber 78 which is supplied with seal air of sufficient pressure so that air will flow from the chamber 78 through a port 80 to an annular space behind a cover 82 so that air will constantly flow out from between the cover 82 and the wheel portion 60 of the roller 54. This will prevent coal dust from getting into the bearings 64. Seal air is provided only at the outer side at the roller 54 because the inner side can be protected by a cover 84 which is fixed to the wheel portion 60 to prevent coal dust from entering the bearings from the inner end of the wheel 54.

The wheel support 76 is mounted on a shaft 84 which at each of its ends is rigidly fixed to and concentric with a sleeve 86 as shown best perhaps in Fig 2. The sleeve 86 is force fitted onto the shaft 84 and is itself encircled by a flexible bushing 88 which is force fitted on the sleeve 86. An outer sleeve 90 is force fitted around the flexible bushing 88 and is itself fitted in a journal 91 and secured therein against rotation as by welding. The journal 91 is mounted in an opening in the outer shell 12 and secured thereto by bolts 92, as shown in Fig 2 and 3.

The seal air is supplied through a channel 93 in the shaft 84, and escapes through openings therein within the support 76 so that seal air will flow into the chamber 78.

It has been explained that the support 76 is biased downwardly against the table 30. To this end the support includes an upwardly extending lug 94 which is acted upon by plungers 96 each of which is slideable mounted within one of bearing directly on the table 30 is controlled by means of a shaft 108 which is secured to the plunger 96 and which is threaded through a sleeve 110 which in turn is threaded through a bushing 112 which is secured to the access door 102. The busing 112 is fixed to the spring base 104 so that axial movement of the bushing 112will move the spring base 104 axially within the spring housing 98.

The busing 112 can be turned by means ofaturn- ing nut 114 which is secured to it The shaft 108 can be turned by means of a turning nut 1 T6 which is fixed to the shaft 108.

When it is desired to adjust the spring force, which is applied against the lug 94 when the roller54 is bearing directly against the table 30, the nut 116 is rotated. Rotation of the nut 116 turns the shaft 108 and since the shaft is threaded with the sleeve 110 the shaft 108 is moved axially. This movesthe plunger 96 axially. Itis possible to adjustthe plunger 96 so that it just touches the lug 94 when the roller 54 is bearing directly on the table 30, that is, when there is no coal on the table 30 underthe roller 54. It is also possible to adjustthe plunger 96 so thatthere is a gap between it and the lug 94.

After the plunger 96 has been adjusted as desired, a locking nut 118, which is threaded to the shaft 108, is tightened against a bushing 120 which isv positioned between locking nut 118 and the turning nut 114.

At times it is desirable to adjustthe position of the spring base 104. For example, it may be found that for particular coals the force exerted on the roller 54 by the spring 106 at any given position ofthe roller 54 should be increased or decreased. This is made possible by turning the turning nut 114 to move the sleeve 110 axially in the desired direction to position the spring base 104. The sleeve 110 and the spring base 104 are fixed in position by means of a locking nut 122 which is threaded on the sleeve 170 and is turned against washer 124 which bears against the bushing 112. Afterthe spring base 104is positioned, the plunger 96 can be adjusted in the manner previously described.

Coal drops down the coal pipe 50 to impinge on the cover 44 and move radially outward because of the centrifugal force exerted by the rotating table 30.

The coal passes into the recess 42 to be pulverised by the rollers 54 which are rotating overthe coal within the recess 42. The shape of the tread portion 56 of each roller 54 and the shape of the recess 42 tend to confine for a time the coal which is between the roller 54 and the recess 42 so that particles which are not contacted by the roller 54 and table 30 are exposed to pressure. The pressure is high enough to break down coal particles and thus pulverize them even when they are not contacted directly by the roller 54 and table 30.

The pulverized coal is blown upward by air which is introduced through a conduit 126. The airflows through an annular air chamber 128 and then up through air ports 130 into the space within the outer shell 12 above the table 30. The airthen moves the pulverized coal upward in the direction of arrows "A" to pass through a series of vanes 132 which4 impart rotation to the mixture of air and coal around the longitudinal axisof the coal pulverizing mill 10.

This acts as a centrifugal separator in that the heavier particles are thrown outward and eventually drops down in a housing 134 in the direction of the arrows "b". These coarse particles drop through doors 136 which are hinged and free to move inward as shown in phantom line under the weight of the coarse particles. The doors help prevent pulverized coal moving upward in the direction of the arrows "A" from passing into the housing 134.

The fine particles move inward and are entrained rn air moving in the direction of the arrows "C" to pass up through a coal collector 138 defined by a vertical annular plate 140 which is concentric with and joined to the bottom of an outwardly flared plate 142 The mixture consisting of air and coal fines passes upward through the top 52 to a conduit which is not part of the present invention and which conveys the mixture of pulverized coal fines and airto the point of use which may be a coal fired steam generator.

In practice some particles are large and heavy enought after passing overthetable30thatthey cannot be raised by the air rushing upward from the air ports 130. Such particles are actually dropped down through the air ports 130 into the chamber 128. They then drop down through chutes 144 and 146 to be recycled into the coal pulverizing mill 10.

When it is desired to service the roller 54 or any of the parts associated with the support 76, bolts 148 and 150 are removed so that access door 102 can be swung outward. The access door 102 has fastened to its lower end a hinge element 152 which is rotatably connected to a hinge element 154 secured to the middle portion 16 of the outer shell 10. Rotation of the access door 120 outward and downward will move the spring housing 98 as well as the plunger 96 and other elements within the spring housing 98 outward away from the interior of the coal pulverizing mill 10. Any roller 54 can be swung out if its associated journals 91 are removed. As shown in Fig 3,journals 91 are each positioned between an opening which extends into a side of the access door 102 and the main body ofthe middle portion 16 of the outer shell 12. In other words, the journal fits within a semicircular opening in the access door 102 and a corresponding semicircular opening the middle portion 16 of the outer shell 12.

Fig 4 shows a roller 54 and its associated supports 76 moved out for servicing. The support 76 has been provided with a bracket 160 which may be secured to it by bolting or welding or any other method. Simi larly, the associated spring housing 98 has been provided with bracket 162. The brackets 160 and 162 are fastened together by a bolt 164 which is secured to the bracket 160 by nuts 166 and 168. Similarly, the bolt 164 is secured to the bracket 162 by nuts 170 and 172. When the support 76 is so secured to the roller 54, outward movement of the access door 102 will cause the spring housing 98 and the associated support 76 and roller 54to move outward.

Fig 4 shows a suitable apparatus 170 for moving the access door 102 out. It will not be described in detail because it is in a part of the present pulverizing mill 10.

Further, a crane 172 can be used to provide additional support as the access door moves out and additional support is needed as the center of gravity of the access door, support 76 and roller 54, move out beyond the hinge about which the access door is pivoted.

Fig 4 shows at 174 the semicircular opening in the middle portion 16 of the coal pulverizing mill 10 in which the shaft 84 is supported at one of the ends thereof. The shaft 84 and its associated journal 91 must be moved out of the semi-circular opening 174 and the corresponding semicircular opening 174 in the associated journal 91 (not shown) to allow the support 76 to move to the position shown in Fig. 4.

Once in this position, the roller 54 can be serviced.

For instance, if excessively worn, the roller 54 can be replaced. The bearing 64 can be cleaned and lubricated as desired.

The foregoing describes part one preferred embodiment of the present invention other embodiments being possible without exceeding the scope of the present invention as desired in the following

Claims (9)

claims. CLAIMS

1. A pulverizing mill comprising: an outer shell; a table rotatably mounted within said outer shell, said table having an annulartrack including an annular recess; means for rotating said table; means for placing material to be pulverized on said table; a plurality of rollers, each having a tread portion defining generally the outer portion ofatorus bearing on said table within said recess; a plurality of supports, each having one of said rollers rotatably mounted thereon, each said support being pivotally secured to said outer shell; and a plurality of spring means, each independently biasing one of said supports to urge said associated roller toward said table.

2. The pulverizing mill defined in claim 1, wherein said outer shell includes an access door, qne of said spring means being connected with said access door and further comprising hinge means pivotally mounting said access door to the remaining portion of said outer shell so that said access door can be opened to move said one spring means out of said outer shell.

3. The coal pulverizing mill defined in claim 2 further comprising means to connect said access door with one of said supports so that opening said access door will cause said one support and associated roller to move out of said outer shell to be accessible for servicing and repairing.

4. The coal pulverizing mill defined in claim 3, wherein said means to connect said support with said access door comprising means to connect said one support to said one spring means.

5. The pulverizing mill defined in claim 3, wherein said support is mounted on a horizontal shaft, said shaft being rotatably connected at each of its ends with said shell.

6. Acoal pulverizing mill comprising: an outer shell; a horizontal table rotatably mounted within said shell, having an annular recess in the upper surface thereof; means to rotate said table; means to place coal on said table; a plurality of rollers having a tread portion defining generally the outer portion ofatorus bearing on said table within said recess; a plurality of supports, each of said rollers being rotatably mounted on one of said supports, each of said supports being pivotally mounted with respect to said outer shell; a plurality of spring means, each of said spring means being connected with said shell to exert a spring force only on one of said supports to urge the one of said rollers associated with said one support down against said table; ; whereby, when one of said rollers moves vertically, said movement will have no effects on the others of said plurality of rollers.

7. The coal pulverizing mill defined in claim 6 further including means for introducing air into said shell to move pulverized coal upward and out of said mill.

8. The coal pulverizing mill defined in claim 7 further including means to separate coarse particles of pulverized coal from fine particles of pulverized coal being moved by said air, means to allow said fine particles to leave said pulverizing mill, and means to recycle said coarse particles onto said rotating table.

9. A pulverizing mill substantially as described herein with reference to and as illustrated by the accompanying drawings.