US2602594A - Method and apparatus for controlling material and fluid to rotatable drum pulverizers - Google Patents

Description

July 8, 1952 5555 2,602,594

METHOD AND APPARATUS FOR CONTROLLING MATERIAL AND FLUID TO ROTATABLE DRUM PULVERIZERS Filed Dec. 12, 1946 .9 M W5 1W 5 H F 7 t 0 2 D I A M n W Wm H 6 4 apparatus ij be apparent to Patented July 8, 1952 METHOD AND APPARATUS FOR CONTROL- LING MATERIAL AND FLUID TO ROTAT ABLE DRUM PULVERIZERS Adolf Hesse, Worcester, Mass, assignor to Riley Stoker Corporation, Worcester, Mass, a corporation of Massachusetts Application December 12, 1946, Serial No. 715,679

' 7 Claims. (01. 241-19) This invention relates to a method and apparatus for pulverizing material, and more particularly to pulverizing systems having provision for controlling automatically the feed of the material to the pulverizing zone.

In pulverizing various materials it is a common practice to employ an airy-swept ball mill, such a mill comprising'a rotatable drum or shell having loose grinding balls therein and means for producing a current of air through the drum to entrain and remove the finely pulverized particles of material in suspension. It is also a common practice to. control the feed of the coarse material to the drum in such a manner as to maintain a substantially constant levelof the material within the drum. I have discovered however that when grinding certain materials,

such as coal, having varying moisture contents,

there are disadvantages in maintaining-a-constant level within the drum. Inparticular, I have found that such a practice imposes serious limitations upon the capacity of the mill, for as the 'moisture content increases, the material tends to pack and adhere to the surface of the drum ina solidmass, thereby preventing the balls from cascading in the manner required for eflicient pulverization. Attempts to overcome this difficulty by heatingthe air supply havebeen only partially successful.

1 It is accordingly one object of the invention to provide a method and apparatus whereby materials with varying moisture contents may be pulverizedsatisfactorily.

. It is a further object of the invention to provide a method and apparatus for pulverizing material, such that the efiect of variations in the moisture content of the material will be minimized so far as limitinglthe pulveriz ing capacity is concerned.' I Y i W It is a further object of-the invention to pro: videa ball 'mill and. associated apparatus capable of handling moisture bearing material and sorconstructed and arranged" that the'capacity of the mill will not be seriously aii'ectedby var- V iations in the moisturecontent of the material.

. It'is a.v further objectgof the invention to provide a new and highly advantageous methodand for controlling the feed of moisturebearing material to a ball mill, such as to.v avoid serious limitations on the mill capacity with increasing'moisturecontent.

With these and; other objects in view, as will ventionresidesin the combination-pf parts and the steps of the processsetjforth in the speck skilled lin the art, the. in-.- 1

fication and covered by the claims appended hereto. 7

Referring to the drawings illustrating one embodiment of theinvention, and in which like reference numerals indicatelike, parts, a Fig. 1 is a longitudinal sectional view of a pulverizer and associated control apparatus;

Fig, 2 is an enlarged view showing a portion of Fig. 1 in detailj and a Fig. 3 is a fragmentary sectional detail of a portion of the control apparatus. 1

The embodiment illustratedoomprises a horizontal rotatable drum or shell I!) forming a pulverizing. zone and containing loose grinding bodies such as steel balls ll. Hollow trunnions l2 and M are provided on opposite ends of the drum, and these trunnions are rotatably sup ported in'suitable bearings l5 and IE respectively. Helical ribs I! are provided on the interior surfaces of the trunnions to assist in retaining the balls within the drum. I

An annular gear I8 is secured to the drum, and it will be understood that this gear is driven in known manner by a suitable pinion (not shown). Thus the drum will be rotated, and material within the drum will be pulverized by the impactof the cascading balls [1' upon the material. The. fine material will be entrained and carried out. of'the drum by ,a currentof a suitable gas, such as air, which travels through the drum. Theair, which is preferably heated in known manner, is delivered to the trunnion l4 through a stationary conduit 20,- and it es capes through the trunnion l2 into a stationary conduit 2| leading toa fan 22. The conduit-20 is" provided with an opening 24 through which relatively cold air from the surrounding atmosphere maybe admitted under the control of a damperv 25. Moisture-bearing material, such as coal," is'delivered to the drum l0 through a chute '21 leading to the trunnion I4 from a suitable feeder 28. This feeder is of a well-known type comprising'a horizontal rotatable table 30 and a stationary blade 3| to deflectpmaterial from the table into the chute 21, the material being delivered'to the table through a downspout 32. Thejtable 30 is driven by an elec-l tric motor 34 which is connected to a suitable source 350i electrical energy, the motorspeed being under the control of a rheostat 36;."

..It is, desirable that thetemperature .of the air enterin the drum II! should vary withth'e purpose a temperature responsive bulb 43 ismounted within the duct 2| and connected to the relay by a tube 44 or other means for the. transmission of control impulses to the relay.

As an example of one suitable arrangement, the bulb 43 may contain a volatile liquid which produces an increasing fluid pressure upon an inthe duct wall, a portion SI of this socket being removable to facilitate assembly of the parts. The outwardly extending portion of the pipe 46 is connected to the relay arm 39 by a flexible cable 53 which passes over an idler sheave 54, a weight 55 being provided'togkee'p{the cable taut.

Within the inner end of the pipe "46 there is provided an electric switch. (Fig. 3) comprising apair of stationary contacts 51 mounted on a disk 58 of insulating material. Beneath the disk 58 there is provided a diaphragm 59 of a suitable flexible material, such as rubber, having on crease in temperature, the relay being con-- structed to respond to such changes in fluid pressure. With this arrangement, if the moisture content of the material entering the drum increases, an increased amount of heat will be absorbed from the air stream and utilized. in evaporating the extra moisture, thereby lowering the temperature of the air in the outlet duct 2|. The bulb. .43 andlthe relay 38 will respond to this changein temperature and, move. the damper 25 toward its. closedlposition, reducing the inflow of cold air through the opening 2 4, and increasing the temperature of the airstream entering the drum until the desired temperature adjacent th bulb 43 has been substantially restored; Similarly, a decrease inthe. moisture content of the entering material will result in a reverse move-' ment. of the damper 25. Consequently the, tern-- perature of the air stream inthe duct 2|"will be maintained substantially constant. To avoid excessive hunting, the relay 38 is preferably constructed with a time delay mechanism, in known manner.; 1

I have discovered that superior operating re suits will be obtained if.- the levelof the material within the. drum I6, is varied in accordance with the.- moisture content. of the entering ma terial. By lowerin this. level upon an increase. in; the -rooisture content, it is feasible. to operate the mill at, a higher grinding rate than would otherwise be possible. Apparently, by decrease ing the. quantity of the. material within the drum, relation, to. the quantity of bal1s, ..'tli.'e tendency oi the material to pack into. a solid mass is reduced. In order tobring about. this variation in level, I. preferably employ a con troldevice which is responsive to the level oi the; material within the drum, and I connect therelayarm 39: to. this device sothat it will, be raised or lowered as the damper 2-5 is closed or opened, the position of thisv damper being an indication, oi the moisture-content of' theme terial supplied by the reader." The control device-is. arranged to. transmit a control impulse to a" relay,,whicl1' in turn actuates the rheostat 3.6 and thereby regulates-the rate at which the material-is fed'to the drum.

In, the particular embodiment. illustrated, there i s ..pro ided av generally. horizontal pipe 46 which extendsthrough the trunnion l2, and into ..the adjacent portion of the, drumlfl, theinnerjend of. thepipe being bent downwardly. This pipe is pivotally supported orfulcrum'ed, inter-medi ate its length on the outer wall of the duct 2|, through, which the pipe extends. As best shown in- Ei'g. 2,, the. pipe .6 passes iam t i ally thr u h. a, horizontal cylindrical; member 41 and. is held p ace." ther in. by a set-scr w 8.1- This mem: ber "15" mounted in'a cylindrical socket 50 in its upper surface a contact member 60 adapt- .ed to bridge the contacts 51 upon upward movement of the diaphragm. The disk 58 and the diaphragm 59 are separated by a spacer ring 62,

and the various parts are held in place by a threaded ring 63 directly beneath the diaphragm. Two insulated wires 64- extend upwardly from the respective contacts 51, through the pipe 46, and thence through a flexible tube 66 (Fig. 1) which connects the outer end of the pipe to a relay 61. This relay is of a well-known type havin a crank arm68 connected by a link 69 to the rheostat 36 to actuate the same, the relay being supplied with electrical energy from a suitable sourceflll. It will be understood that closure of the switch 51-60; will complete a low-voltage circuitt ough the wires, 64, thereby transmitting a controbimpulse'to the relay 61, which will respond by moving the crank' arm as and adjusting the rheostat as. The ma 61 is preferably constructed in known manner with a time-delay mechanism to avoid excessive huntmg.

If desired, the wires 64; the contacts 51 and 60, the disk- 58, the diaphragm 6B,.and the rings 62 and as may all be omitted, leaving the m norend of 'the-pipe 46 entirely'open. In that case, the relay-6l will be constructed to respond. in: known manner to; variations in air pressure. transmitted thereto throughth'e pipe 4.6Iand the flexible'tube 66.

The operation of the invention will now be apparent from the above disclosure. The drum;

, l0 will be rotated, causing theballs H to pul verizethe material therein by; their cascading action in known manner. Coarse material will be delivered to the drum by the feeder 28 under the control; of therheostat 3,6;- The fan. will draw hot air throughthe duct, 20, thejdrum .16; and the duct 21', this air entraining finelypu l verized particles of materialginthe; drum. Cold air will be drawnt-hrough the openingfl, under the control of the damper'2.5,;:thus reducing the temperaturepf the air entering" the drum-x ii the moisture {content "of, the. material suppliedto the drum increases; more heat will b atseiteii from the air in evaporating this ettle-am the temperaturewithin' the; o t-retai er? 21 will decreaseslightly. The bulb '4 3f'wi'll immediately sense this decrease; causingthe relayf 38 "to fre i spond; and swing the crank arm 39.1.10. the

partially sine he. d mp r. n red c ithj quantity OfCOld "air 'j admitted through the Qpen ing .4 to;prevent-'any- -appreciable' drop in the temperature within the duct- 2411* A the arm 39 oves t t e r ht t ab e. hiwi we th outer en ron pipe 46; and lower t mnei end thereofinto the mass or at iial with'in the drum ill. As thediaphragnrfi 'p i I the feederspeed until 5 Supplied by the feeder 28 to the drum; l until: the level therein has droppedsufficiently to open the switch 51-50 and reverse'the' relay: :Similarly', if th'e moisture content of the material entering the drum decreases, less heat will be absorbed from the air, the bulb'43 will sense a slightrise in temperature, and the relay arm 39 will swing to the left. This Will' open the damper- 25 to admit more cold'air, and at'the same time it willlower the outer end of-the pipe 46 and raise the'inn'e'r' end thereof. The diaphragm'fiflwill be lifted out of contact with the mass of material within the drum, the' s'witch 51-150 will-open, and the-relay 61' willadjust the rheostat 36 to increase the fe'eding rate of' the feeder 28 until the level of material within the drum has been raised to bring the material into contact with the diaphragm 59 and close the switch 5160, thereby reversing the relay. v I 4 v If the diaphragm 59 and the associated parts 51," 58, 6B, 62, B3,'and64 are Omitted, and the relay is constructed to respond to pneumatic pressure impulses rather than to electrical impulses-the general operation of the entire apparatus Will 1101, be affected. Lowering the inner endof the pipe 26 into the material will increase the air pressure within the pipe and therelay will. respond by reducing the feeder speed until the material level has been correspondinglylowered. Raising the inner end of the pipe out. of the material will decrease the air pressure within the pipe and the relay will respond by increasing the material level has been correspondingly raised. I

' It will thus be seen that the level of thematerial within the drum will lie-automatically lowered when the moisture content of the enterin material increases, and automatically raised when the moisture content decreases. This method of level control greatly decreases the tendency of the material to pack into a solid mass when the mill is operating at high capacity, and it makes it possible to increase the output of the mill very appreciably without danger of such packing. It also renders it unnecessary for the operator to be so careful as heretofore in avoiding the feeding of unduly wet material.

The inner portion of the pipe 46, whether or not the switch 51-60 is included, may be described as a level-sensing device, since it is arranged to provide control impulses, either pneumatic or electrical, for the relay 61 in response to variations in the spatial relationship between itself and the level of the material within the drum. It will be noted that the effect on the relay will be the same whether the sensing device is lowered or the material level is raised. In either case the relay will reduce the feeding rate. Similarly, either a raising of the sensing device or a lowering of the material level will cause the relay to increase the feeding rate. As a result the material level will remain close to the sensing device at all times, regardless of the position to which the latter may be moved in response to variationsin the moisture content of the material.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Pulverizing apparatus comprising a rotatable druni, loose grinding bodies within the drum, regulatable feeding means to supply moisturebearing material to the drum to be pulverized therein, means producing a current of hot gas through the drum to entrain and remove fine particles of material in suspension, a controller 6. for the feeding means, a level-sensingadeviceare ranged toprovide control impulses for the controller in rlesponse to variations in the'spatial relationship between the said device and the level of thematerial'within'the drum, and means to raise or lowerrthe level-sensing device as the tem-; perature of the gas leaving the drum-increases or decreases respectively; I 2; Pulverizing apparatus comprising-a rotatable-drum; loose grinding bodies within the drum, regulatablefeeding means to-supply moisturebearing'material to the drum to. bepulverized therein, means producing-a current ofhot; gas

through the drum to entrain and remove fine para ticles of material in suspension,- a. level-sensing device located within the drum, connections be-'-- tween the level-sensing device'and the feeding means to increase or decrease the feedingrate as the distance between thesaid device and the level of'the material within thev drum increases or decreases respectively, and means to raise or lower thelevel-sensing device as the temperature of the gas leaving. the drum increases or decreases respectively. l I

3. Pulverizing apparatus able drum, loose grinding bodies withinthedrum, regulatablefeeding means to supply moisture bearing material to the drum to be pulverized therein, means producing a current of hot gas through the. drum to entrain and remove fine particles'of material in suspension, the heat in-the gas serving to evaporate moisture from the ma: terial and the temperature of the gas being thereby reduced, a regulator arranged to vary the temperature. of the gas entering ,the'drum in accord: ance with the temperature ofthejgas leaving the drum, a level-sensing device located within the drum, connections between the level-sensing device and thefeeding means to increase or decrease the feeding rate as the distance between the said device and the level of the material within the drum increases or decreases respectively, and means connecting the'said regulator to the levelsensing device to raise or lower the said device as the temperature of the gas entering the drum is decreased or increased respectively.

4. Pulverizing apparatus comprising a rotatable drum, pulverizing means within the drum, regulatable feeding means to supply moisturebearing material to the drum to be pulverized therein, a fan arranged to draw a current of hot air through the drum to entrain and remove fine particles of material in suspension, the Heat in the air serving to evaporate moisture from the material and the temperature of the air being thereby reduced, means including a damper to admit relatively cool air for mixture with the hot air entering the drum, a regulator arranged to control the damper in accordance with the temperature of the air leaving the drum, a levelsensing device located Within the drum, connections between the level-sensing device and the feeding means to increase or decrease the feeding rate as the distance between the said device and the level of the material within the drum increases or decreases respectively, and means connecting the said regulator to the level-sensing device to raise or lower the said device as the damper is opened or closed respectively.

5. Pulverizing apparatus comprising a rotatable drum, pulverizing means within the drum, regulatable feeding means to supply moisturebearing material to the drum to be pulverized therein, an inlet duct to supply hot air to the drum, an air outlet duct connected to the drum,

comprising a. rotatx aian connectednto the outlet duct to. draw air through the drum to entrainand remove finepartic'le'sqof material in suspension, the heat in the air serving to evaporate: moisture fro'm'the material and the temperature of the air being thereby reduced, means including a damper to admit relatively cool air tothe inlet duct for mixture with the hot air entering the drum, a regulator arranged to control the damper-in accordanceiivith the temperature of the airin the outlet duct, 'a level-sensing devicelocated within the drum, connections between the level-sensing device andthe feeding means to increase or decrease the feeding rate; as the distance between the said device and the level of the material within the drum increases or decreases respectively, and means connecting the said regulator to the level-sensing. devicev to raise or lower the said device as the damper is opened or closed respectively.

6. The method of operating a pulverizer of the type having a rotatable drum containing loose grinding bodies comprising the steps of supplyi-ng moisture-bearing material to the drum for pulverization by the grinding bodies, causing a current of hot gas to flow through the drum to entrain fine particles of the material and carry them in suspension outof the drum, the heat in the gas serving to evaporate moisture from the material and the temperature of the gas being thereby-reduced as the gas travels through the drum, and controlling the rate of supply of the material in accordance with both the level of the material within the drum and the temperature of the gas leaving the drum as required to lower the said level upon a decrease in the temperature of the gas leaving the drum and viceversa.

-'7. The method-of operating a pulverizer of the type having a rotatable drum containing loose grinding bodies comprising the steps of supplying moisture-bearing material to the drum for pulveriization' by the grinding bodies, causing a current of. hot gas'to flow ,throughithe drum to entrain fine particles of the material and carry them in suspension out of the drum, the heat in the gas serving to, evaporatemoisturefrom the material and the temperature of the gas being thereby reduced as the gas travels through the drum, controlling the temperature of the gas entering the drum in accordance with -thetemperature 'ofthe gas leaving: the drum, andcontrolling the rate of supply of the-material in accordance with both the level: ofthe materialwithin the drum and'the temperature ofwthe-igasg leaving the drum as required to lower the said level upon a decrease in the, temperature of the gas lea-vingthe drum and viceversa. j v

ADOLF HESSEi UNITED sTATEs PATENTS Number Name Date Re. 20,156 Hardgrove Nov. '3, 1936' 1,157,979 Fasting Oct. 26, 1-915 1,783,358 Crites et al. Dec. 2-, 193-0 1,814,560 Kreising'er July 14, 1931 1,898,086 Frisch Feb. 21, 1933 1,988,677 Arnold Jan. 22, 1-935 1,990,173 Frisch Feb. 5, 1935- 2109,5149 Harmon r Mar. 1 1938 2,152,367 Smith Mar. 28, 1939 2,266,292 Arnold Dec. '16, 1941 2,316,875 Laboulais Aug. 2'0, 1943 2,318,576 Arnold l May 1 1, 1943 2,334,949 ONeil 'et' at Nov 23-, 1-943 2,349,519 Re ic'henstein e May 23, 1944 '2,452,500 smith Oct, 26,1948

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