US2189312A

US2189312A - Pulverization system

Info

Publication number: US2189312A
Application number: US601917A
Authority: US
Inventors: Frisch Martin
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1932-03-30
Filing date: 1932-03-30
Publication date: 1940-02-06
Anticipated expiration: 1957-02-06

Description

Feb. 6, 1940.. M. FRISCH PULVERIZA TION SYSTEM Originl Filed March so, 1932 2 Sheets-Sheet 1 INVENTOR" 4 H| x. Y

VIII/1142717?!) M M ATTORNEY Feb. 6, 1940. M. FRISCH 'PULVER'IZATION SYSTEM Original Filed March 30, 1932 2 Sheets-Sheet 2 INVENTOR Patented Feb. 6, 1940 PATENT OFFICE PULVERIZATION SYSTEM Martin Frisch, New York, N. Y., assignor 'toFoster Wheeler Corporation, New York, N. Y., acorporation of New York Application March 30, 1932, Serial No. 601,917 Renewed April 23, 1938 v 9 Claims.

My invention relates to apparatus for and method of pulverizing material and more particularly for pulverizing coal. My invention involves a novel combination of pulverizing apparatus and classifying apparatus.

The principal object of my invention is to provide an improved method of sweeping a pulverizingmill and particularly a ball type mill with air and returning partially pulverized material to the mill for further treatment.

Another object of. my invention is to increase the amount of partially pulverized material entering the classifier, thus increasing the local circulation of coal out of and back into the mill.

16 Increasing the amount of material to be circulated increases the pulveiizing capacity of the mill.

A still further object is to mix moist incoming material with recirculated oversize material 20 which hasalready been partially dried by its passage through the pulverizer. The oversize will absorb moisture from the fresh wet-material by contact and thus serve to distribute and dilute the moisture so that the average moisture content 25 of the material delivered to the. grinding elements is reduced. The capacity of a pulverizer is greater when fed with dry material than when fed with moist material. Hence the power consumption per unit of material pulverized will be lower.

80 In ball mills of the conical type, material being pulverized tends to take different positions along the axis of the mill depending upon its size. The coarser particles take a position toward the charging or inlet end of the mill while the finer 85 particles gather at the apex of the cone-shaped portion. As the material is pulverized it automatically travels from the inlet to the apex of the cone. Heretofore it has been the practice to sweep a ball mill with a current of air entering 40 the coal charging end leaving at the coal discharge end. In the present invention the current of air used to sweep the mill leaves the mill at the coal charging end. Since the direction of the current of air through the mill is counter-current 45 to the general direction of movement of material pulverized, more partially finished product will be drawn from the mill than was formerly the practice. Additionally, a greater drying of the material undergoing pulverization is effected because 50 the high temperature air first comes in contact with the high temperature material in the drum.

A classifier is located adjacent the material inlet end 01' the mill. Material to be pulverized. which may be raw coal containing a considerable amount of moisture, is fed through the classifier in such a manner that partially pulverized material, hereafter referred to as oversize, is mixed therewith before entering the mill. This has the effect of drying the raw coal pr other material and making it easier to pulverize, thereby reduc- 5 ing the power consumption per unit material pulverized. p

The greater the amount of oversize recirculated the greater will be the capacity of the mill. This result follows from the fact that ma- 10 terial undergoing pulverization in a ball mill consists of a large mass containing'fine particles of material which require no further treatment, and a considerable portion of oversize which is not commercially usable. Very fine and very coarse coal may be found throughout the ball mass. But the finer material eventually gathers at the small end of the conical shell remote from the feed trunnion. Even though the quality of the product desired from a pulverizer is usually described by stating the amount that will pass a screen of a given size, for example a screen of 200 meshes to the inch, it is possible for a pulverizer to deliver product of the required quality with a greater expenditure of work than necessary and hence at the expense of pulverizer capacity and with a greater power consumption. This follows from the factthat the material passing the 200 mesh screen is made up of a mixture of particles containing varying numbers per unit weight .which are all smaller than the aperture of a 200 mesh screen. Since the work done by a pulverizer per unit weight of material depends on the increase caused in the number of particles per unit weight of material pulverized, it follows that the greater the number of fine particles produced the smaller will be the output of a pulverizer, and the greater the power consumption. Consequently, the maximum capacity will be obtained from a pulverizer when the ratio of the number of new particles produced to the desired percentage through the required screen size is a minimum. It is obvious therefore that if particles are withdrawn from the pulverizer as soon as they are of the proper size to avoid over-pulveri zation, the pulverizer capacity will be at a maximum. This condition is best approached by withdrawing to a classifier material from the pulverizer at a rate greater than the desired capacity so that in the classifier the coarse ma- 5 terial may be separated from the finished product and returned to that portion of the grinding zone where most of the coarse material is to be found. To that end the air sweeping the mill is made to pick up a relatively great amount of oversize which is mostly carried into the classifier, some being dropped at once in the vicinity of the large grinding balls which are pulverizing relatively coarse material. Oversize is returned from the classifier to the region of coarse material in the rotating drum. This oversize is more quickly pulverized when mixed with coarser particles than when allowed to remain where it naturally segregates. Thus the fines are removed as soon as. possible and the oversize is subject to vigorous treatment at once. Another factor which also increases the capacity of the mill is that with a large portion of circulating oversize, that is, circulation between classifier and mill, the classifier is actingas a part of mill proper since in effect, it extends the volumetric capacity of the ,A great deal of heat is generated in the mill when material is pulverized. The oversize absorbs some of this heat and heat thus absorbed is used to dryraw material entering the classifier. It is of advantage then to place the classifier as close as possible tothe milland to increase the amount of oversize withdrawn, in order to obtain the most beneficial use of the heat carried out of the mill by the oversize.

- Other features and advantages of my invention will become apparent from the following detailed description of certain approved embodiments thereof, of which:

Fig. 1 is a vertical; longitudinal sectional view through the mill and classifier as arranged for a unit system; v

Fig. 2 is a transverse sectional view of the classifier taken on line 2-2 of Fig.- 1;

Fig. 3 is a view similar to Fig. 1 but showing a storage system; a

Fig. 4 is a transverse sectional view of a modifled form of classifier taken on line 4-4 of Fig. 3

Fig. 5 is a section taken on line 5-5 of Fig. 4 showing the arrangement of a pair of screw conveyors; and

Fig. 6 shows a vertical cross-sectional view of a modified form of classifier having a double spiral passage instead of a single spiral passage as in Fig. 2.

Referring now to Fig. 1, It represents a ball mill of the conical type. Hollow trunnions l1 and -'shell is mounted to rotate about a horizontal The classifier I8 is provided with a conduit connection l9 which extends into the hollow trunnion l2 of the ball mill. Between the end walls 20 and 2| of the classifier is a spirally curved member 22 which together with the partitioii 23 and the walls 24 and 24' provides a spirally shaped passage 25. The inlet to the passage 25 is' the conduit connection 19 while the outlet conduit is shown at26. The partition 23 and wall 21 provide a chute 28 for feeding material to be pulverized by the mill. A check damper 29 extends across and controls the flow area of the'chute '28. A chamber 30 is provided for receiving'oversize. A control damper 82 is hinged to the end of curved member 22. A control damper 83 is provided in the passageway 25. A by-passvalve or damper 84 is provided to permit passage of fluid through member 22 without passing through passage 25. These various dampers'may be suitably provided with shaft extensions passing through the classifier casing and nion opening II by supports 41.

- 32 of the screw conveyor A is the pulley 33, which through a belt and pulley 34 rotates the rotor of the air lock 38. I

The screw conveyor A extends into, and throughout the length of the conduit connection It of the classifier. A spider 35 fixed to the rotating steel shell rotates the horizontal shaft 32 of the conveyor. The central portion of the screw 36 is open to permit ready passage of air therethrough. 1

Access doors 3| are provided in the wall of the classifier in suitable positions.

A horizontal screw conveyor B extends into the opposite trunnion opening II. A shaft 31, to which screw 33 is attached, is rotated by a spider 33 connected to the steel shell. The screw 38 is formed so as to cause grinding balls or solid particles passing into trunnion I l to be carried back through the trunnion into the mill. The screw 38 is twisted in a direction opposite to screw 38, so that both conveyors will feed toward the center of the mill as the steel shell is rotated.

An exhaust fan 4|! having its inlet connected to conduit 26 beyond the classifier and driven by an electric motor 4| serves to draw a current of air, which mayor may not be preheated, through the mill from conduit 42. In conduit 42 a series of dampers 33 control flow of air into the hollow trunnion II. The damper 44 serves as an additional means for cutting oil. the air sup- -.ply.through conduit 42. Preheated or atmospheric air. as desired, may enter through conduit 42. A damper 45' serves totemper the preheated air with atmospheric air and also to vary the amount of air drawn into the mill. A manually adjustable damper 46 is shown in conduit 26.

Conduit 42 is suitably supported in the trun- The classifier is supoprted by supports 48.

- Theoperation of the arrangement shown by Fig. 1 is as follows:

Let it be assumed that the pulverizing unit is to be used for supplying pulverized coal directly to a burner. Coal which has been crushed to a suitable "size enters the mill through passage 28 arranged on the side of the classifier iii. A damper 29 operates to control the passage of coal to the screw conveyor A rotated by the spider 35 fixed to the steel shell of the mill. Coal is carried into the mill by the screw conveyor A and is pulverized by the grinding balls and by attrition between the coal particles which are cascaded over each other by the rotation of the steel shell. The shell or drum l5 may be rotated through ring gear I! by means of a suitably mounted pinion gear driven in any desired manner' as from an electric motor. New grinding balls may be fed to the mill through the slide door 45. The screw conveyor driven through spider 39 is adapted to carry the new balls into the mill. The screw conveyorJB acts to prevent coal and grinding balls from obstructing the trunnion opening Ii.

The fan 40 driven by motor ll operates to sweep the mill with a current of air. Air entering the mill through conduit 42 is directed downwardly and varied in amount by dampers 43. The damper 44 may be used to cut off the air supply in 'a single movement when desired. The air entering conduit 42 may be atmospheric or preheated. An opening controlled by damper 45' serves to temper'preheated air by mixing atmospheric air therewith, and also serves as a means for admitting additional air.

The

dampers

43, 44, 45', and 46 which are manually adjustable, determine the amount and character of air to be used in sweeping the mill. The quantity and velocity of the current of air passing through the mill determines the fineness or grade of material carried out of the mill. The greater the quantity and the higher the rate of flow, the greater the proportion of large particles of coal removed from the mill. Opening damper 46 at the inlet to the fan and partially closing damper 44 with damper 45' completely closed effects a slowing up of the rate of fiow and a lessening of the quantity of material withdrawn. This operation causes only very fine coal dust to be removed with a minimum of coarse particles or oversize. An operation which permits fines to remain in the mill after having ben reduced to a usable state requires a great deal of additional power per unit material pulverized. The fan is preferably driven at constant speed to maintain a constant uninterrupted fiow through the discharge conduit to the burner.

In practice,-the present invention permits the use of large quantities of air at a high rate of flow with the view to reducing, the power consumption per unit of coal pulverized to a minimum. This is brought about by the location and use of classifier l8. As indicated on thedrawings, the classifier is of large size and is preferably of a volume at least as great as'one quarter the volume of the rotatable drum. Air carrying a heavy cloud of coal dust leaves the mill through the central open portion of conveyor A and enters the spiral passage 25, and thence passes through fan 46 to use. The oversize separated out of the moving cloud of dust, due to the change of direction in the classifier and preferably expansion of the area of fiow, is collected in chamber 36 and passes through the rotating valve 3| to conveyor A. Oversize and raw coal are mixed by the conveyor before entry to 'the mill. This mixing causes heat from the oversize to dry the raw coal somewhat. As is well known, 'coal having a high moisture content requires as much as 20% more power for pulverization. It is desirable to reduce the moisture content as much as possible in order to reduce the power consumption.

The operation of the classifier can be readily controlled by

members

62, 83 and 84.

A modified form of classifier is shown in the arrangement according to Fig. 3. The function and operation of the classifier in this figure is the same as in Fig. 1. The arrangement of mill and classifier is very well adapted for use in what has become known as a "storage system as distinguished from the system shown in Fig. 1 in which the pulverized material leaving the exhaust fan goes directly to use.

Elements in Fig 3 which correspond to like ele-'- In the trough-like bottom 5| of the classifierv are two

screw conveyors

52 and 53. 54 is a motor and reduction gearing. v The conveyors are driven by motor 54 through belt 55 and gears 56 and 51. Since the screw conveyors rotate in opposite directions the screw on one conveyor is opposite to the other. This causes material to be thrown to the center of the trough and forced through the inlet trunnion opening.

Conduit 26 leads to a dust separator 58 of the cyclone type which is well known in the art to which this application pertains. At the bottom of the separator is a rotatable valve or air lock 59 through which collected material passes to storage bin 60. This air lock may likewise comprise a continuously rotating member including axial vanes.

Between the cyclone separator and fan 46 is a therein similar to valve 59. A manually controlled damper 69 is located in the vent 63. The

. air return conduit is connected to the conduit 42 through which air reenters the mill.

The operation of the mill and classifierin Fig. 3 is similar to Fig. 1. The fan 46 is located beyond the cyclone separator 58 and draws the coal dust laden air from the classifier thereto. Pulverized coal thus separated out drops to the bottom of the separator 58 and passes through valve 59 to storage bin 66 from which place it is used as desired. The opening in conduit 6| regulated by adjusting slide 62 varies the velocity and quantity of air pulled through the mill in much the same manner as damper 46. Damper 44 and the opening varied by slide 45 have the same function as the elements having like reference 'characters in Fig. 1.

Because of the fact that some air leaks into a system such as shown in Fig. 3, or preheated air may be purposely introduced and mixed with the return air in order to accelerate the drying of the coal during the pulverizing process, a vent 63 must be provided for the discharge of the excess air. A portion of the air which is returnedby the fan to the inlet end of the mill escapes around the damper 69 to conduit 63 and into chamber 65. From chamber 65 the air flows through the fiat screens or bags 66 to the atmosphere through outlet 61. The coal dust thus collected passes through the valve conduit to storage bin 66.

In the modified form of classifier shown in Fig. 6,. the stream of air and pulverized material in passage .10 is divided at a central point intermediate the axes c and d of the classifier, This gives what may be termed a double spiral fiow for passage of air carrying pulverized material and'is adapted to materially increase the capacity of the classifier. The guide walls H and 12 together with the casing 13 provide two'spiral passages 14 and I5. Oversize which drops out at the termination of these passages is caused to pass through air looks or

valves

16 and 11 which may be rotated from the shaft .18 of the screw conveyor 19 in the same manner as indicated in Fig. 1. The oversizeis mixed with raw coal entering the conveyor 19 .and is conveyed to the mill. Control and by-pass valve or'damper members may be provided as in the embodiment. of

, Fig. 1.

While mylnvention' has been described in connection with a ball mill of the conical type, it will be understood that its application is not specifically limited thereto, but may be employed with other types of mills, and it is to be further understood that I do not limit myself to any particular embodiment except as defined in the appended claims.

Having thus described my invention, what I claim is:

1. In an apparatus for pulverizing material, a rotatable shell having hollow trunnions, pulverizing means in the shell, a classifier having an inlet connection extending into one of the trunnions, a conveyorarranged in said inlet connection for moving material into the shell, a conveyor extending into the other trunnion for preventing passage of material therethrough, said conveyors being connected to be driven from the rotatable shell, and suction means connected to causea current of air to fiow in through said other trunnion and out through the first mentioned trunnion for carrying pulverized material from the shell to the classifier.

2. In an apparatus for pulverizing material, a rotatable shell having hollow trunnions, pulverizing means in the shell, a classifier having an inlet connection extending into one of the trunnions, a conveyor arranged in said inlet connection for moving material into the shell, a conveyor extending into the other trunnion for preventing passage of material therethrough, said conveyors being connected to be driven from the rotatable shell, suction means connected to cause a current of air to fiow in through said other trunnion and out through the first mentioned trunnion for carrying pulverized material from the mill to the classifier, and means for controlling the flow of air.

3. A feeder and classifier for pulverization apparatus comprising inner and outer members forming a spiral passage and a supply passage,

a conveyor in the lower part thereof in communication with the supply passage, a pocket above the conveyor and in communication with the spiral passage, and means to conduct material from said pocket to said conveyor.

4. A feeder and classifier for pulverization apparatus comprising inner and outer members forming a spiral passage and a supply passage, a conveyor in the lower part thereof in communication with the supply passage, a pocket above the conveyor and in communication with the spiral passage, and an air lock between said pocket and said conveyor.

5. A feeder and classifier for pulverization apparatus comprising a curved passage and a sup ply passage separate from each other, a conveyor in communication with the supply passage, a pocket in communication with the curved passage, means to conduct material from the pocket to the conveyor, and a passage connecting the initial and terminal portions of the curved passages.

6. A'feeder and classifier for pulverization apparatus comprising a curved passage and a supair to fiow through the shell for carrying pulverized material from the shell, and a conduit between the shell and the suction means, a unitary feeder and classifier comprising a spiral passage and a supply passage separate from each other, the spiral passage having one end connected with one of said trunnions and the other end connected with said conduit so that air is drawn through said one trunnion and the spiral passage, a movable conveyor at the discharge end of the supply passage, a pocket in communication with the spiral passage, and means to conduct material from the pocket to the conveyor.

8. In pulverization apparatus including a shell having hollow trunnions, pulverizing means in the shell, suction means for causing a current of air to flow through the shell for carrying pulverized material from the shell, and a conduit between the shell and the suction means, a unitary feeder and classifier comprising a spiral passage and a supply passage separate from each other, the spiral passage having one end connected with one of said trimnions and the other end connected with said conduit so that air is drawn through said one trunnion and the spiral passage, a movable conveyor at the discharge end of the supply passage, a pocket in communication with the spiral passage, and an air lock between the pocket and the conveyor.

9. In pulverization apparatus including a shell having hollow trunnions, pulverizing means in the shell, suction means for causing a current of air to flow through the shell for carrying pulverized material from the shell, and a conduit between the shell and the suction means, a classifier-comprising a plurality of separate spiral passages, each spiral passage'having one end connected with one of said trunnions and the other end connected with said conduit so that air is drawn through said one trunnion and each of the spiral passages, a movable-conveyor at the lower portion of the classifier, a pocket in communication with each of the spiral passages, and means for conducting material from the pockets to the movable conveyor.

' MARTIN FRISCH.