US2291618A - Pulverizing apparatus - Google Patents

Description

Aug. 4, 1942. FRISCH PULWSRIZING APPARATUS Original Filed April 25. 19:52

2 Sheets-Shet l iNvN'roR ATTORNEY Aug. 4, 1942. M. mscn 2,291,618

PULVERI Z ING APPARATUS Original Filed April 25, 19252 2 $heets $heet 2' INVENTOR I /38 v40 [57 Z ATTQRNE? Patented Aug. 4, 1942 2,291,,orc runvanrmd arrana'rcs Martin Frisch, New York, i l.

ter Wheeler Summation,

K, assignor to Fo Ncw York, N. in, a

corporation of New Yorh Continuation of apnlioat ion. Serial No. 6%,232,

April 25,1932. This application February d, 1939, Serial No. 255,22n

33 (@l. SS -9) This invention relates to fuel pulverizers such as ball mill pulverizers, and more particularly relates to air-swept ball mills for pulverizing coal and to apparatus for, and methods of, indicating and controlling the charge therein, and controlling the output thereof.

This application isa continuation or applies tion Serial No. 607,282, filed April 25, i932.

In order to control the output and fineness of the product of ball mill pulverizers, it is necessary of the product and the grinding balls, not including the powdered material suspended in the air current, substantially constant irrespective of the rate of grinding of the product' If the volume of the charge is permitted to increase inaterially above normal, the charge may spill over into one or more'of. the trunnions, particularly the discharge trunnion, and may restrict the opening through which the air enters the pulverizer and the connection through which the product leaves the mill, thereby reducing the output or the pulverizer. I! the quantity of charge is permitted to fall materially below normal, there will be a deficiency of product and an excessive rate oi wear oi the grinding balls and the liners of the mill. It has heretofore been the practice to judge the correctness or the quantity oi charge, 'in ball mill pulverizers by the sound produced by the mill and to control the rate at which the in the may be increased until the mill plugs to maintain the quantity or volume of the charge in the mill, that is to say, the amount or mixture product was fed to the mill by hand in accordance with the sound. This has required the constant attention of experienced operators.

I In accordance with the present invention, provision is made tor positively indicating the quantity oi the charge in ball mill pulverizers and for automatically controlling the samelrrespective orpressure variations within the mill.

To control the output of pulverizers, it has been the practice heretofore to vary the feeding to the mill of the materialto be pulverized proportionally to the output desired without changing the air flow through the mill excepting to provide more or less air at the burners or at other points of use. When the capacity of the mill is varied by varying the feed, the quantity of material in the mill undergoing pulverization may change by several hundred percent if the rate of feed and the output are not synchronized exactly. If the output is substantially greater'than the rate of feed for any length of time, the quantity of material in the mill may be'completely depleted,

whereas if the output is less than the rate of up. Enact synchronization of the feed and the output has seldom been anything but accidental because the mill operator had other duties and could not spend all his time listening to the mill.

accordance "with the present invention, the capacity or output of pulverizing rnills is controlled Toy automatically maintaining a constant or substantially constant supply cit material in the mill and varying the flow of air through the mill to vary the output thereof. By maintaining a constant quantity or. material in the mill, a

constant state of agitation is maintained, in consequence or which a substantially constant conoentratlon oi pulverized material in suspension per unit quantity oi air is maintained. Hence Toy varying the air flow through the mill in ac cordance with the present invention, the quantity of pulverized material taken out entire mill may be readily varied without Magg /Actual meas urements have shown that, irrespective of the output of the mill, the quantity of pulverized ma terial talren out per pound of airis substantially the same over theoperating range in ball mill pulverlzers or the character disclosed, or otherexpressed, the quantity oi material re moved from the mill is substantially -propor= tional to the how oi air through the mill over the operating range. This result cannot he 0 tained with prior practice wherein the 'mill cut put is controlled by varying the reed and the air flow through the mill is maintained substan tially constant or is varied only to suit the requirements of the burner, because the amount oi pulverized material in suspension at any given time per unit quantity of air varies with the amount or material in the mill, and even though the air flow through the mill is maintained sun'- stantially the same, dififerent quantities of me terial will he taken out of the mill in a given time, depending upon the amount of material in the mill at that time. z

The nature and advantages of the invention will he apparent from the iollowing description taken in. conjunction with the accompanying drawings forming a part of this specification, and in which:

, Fig. l is a view in elevation, with parts in se- 'tion, of a hall mill pulverizer together with inw hodying the invention;

feed at any. given time, the amount of material M Fig. 2 is an end elevation of part of the structure shown in Fig. 1;

Fig. 3 is a. transverse sectional view taken on line 33 of Fig. i; L

the charge controlling apparatus applied to a ball mill having a cylindrical drum. and

Fig. 8 is a view showing the application of the feed controller to an air pressure control system.

Referring to Figs. 1, 2 and 3, reference character It designates the steel shell of the drum of a conical type ball mill for pulverizing coal or other material, but as will appear hereinafter, the novel charge controlling apparatus may be used with various types of ball or tube mills. The drum or shell is provided with trunnions II and I 2 which are rotatably mounted in bearing supports l3 and l4. A ring gear I5 is suitably fastened to the conical portion of the drum and is driven by motor it through a shaft l1 and a pinion l8. Shaft. I1 is journalled in bearing brackets l9 and I9. The interior of the steel shell is lined with a plurality of liners 2| made of steel or other suitable wear resisting material. The drum contains grinding balls 2| and coal 2!. Coal to be pulverized is fed to the mill through trunnion II from a chute 23. Air for sweeping the mill is introduced through .an opening 24 located in the side of the chute. The size of the opening is varied by adjusting the slide 25. A discharge conduit 2 extends into the trunnion l2 and is supported on the foundation 2'! by a support 28. An exhauster fan F is connected to the discharge conduitand maintains a suction within the mill, the degree of suction depending upon the position of damper 25 and the size of opening 24, and the speed of fan F. Fan F is driven by a variable speed electric motor I 5., the operating speed of which may be varied by a rheostat l5l in the motor circuit.

A disc-type coal feeder has been shown, but it will be understood that any suitable feeder, such as one of the screw or plunger types, may be used if desired. The hopper 30 is supplied with coal from a bunker in the usual manner. This coal falls onto a rotating feed table or disc II and is swept therefrom by a shear plate 32 into the conduit 33. The feed table is driven by an electric motor 34 through suitable'reduction gearing 35. From conduit 83 the coal enters c a ging-trunnion II by means of the chute.

- Two relatively small metal indicator tubes 36 and 31 are situated adjacent the discharge conduit and enter the mill through the discharge trunnion. These tubes are rigidly fastened in place and have their inner ends bent downwardly. Theextremeinnerendsoftheindicator tubes are each given adifferent position with re-. specttothequantityofchargein the mill. The

outer ends of the indicator tuba are suitably connectedtoutubea4land4l. Positionedin indicator tube 36 is a fitting 42 and a pet-cock 43. Similarly in indicator tube 31 is a fitting 42' and a pet-cock 48'. As shownin Fig. 5, the fittingisprovidedwithathreadedphmflwhi h hasapasageflthroughwhichairfromtheatmospherelsdrawn. The

terminatesin -achamber44 fromwhichtheairisadmittedto theindicatortubesthroughport41,the rate of 7s flow through the port 41 being determined by the position of the threaded plug.

Another small metal tube II, which may be termed a reference tube, is arranged parallel to the indicator tubes and has an open inner end within the mill permanently out of contact with the charge in the mill. The reference tube is provided with a fitting 5| similar in all respects to fitting 42. The U tubes are connected in parallel to the reference tube by a suitable tube connection 52. I

The operation of the means for indicating the quantity of charge in the mill is as follows: As shown in Fig. 3, variations in quantity of charge in the mill have been indicated by the surface lines H, N and L. The arrow indicates the direction of rotation of the drum. Assume that the quantity of charge in the mill is that represented by line N, which may be considered as a normal charge. Under this condition the inner ends of tubes 36 and 50 are uncovered while the charge has covered the inner end of tube'll. Due to the suction or low pressure in the mill resulting from operation of the fan F, air is drawn into the mill through the conduits 36, 31 and II. The closing of conduit 31. by the charge makes the drawing of air through the same difficult and the pull of air through this conduit may be even substantially prevented. With substantially the same opening in fittings 42 and ii or by suitable .adjustment thereof. the suction applied to the pipes 36 and 50 will be substantially the same.

wherefore there will be no substantial difference of level of liquid in the U tube 40. On the other hand, there is an appreciable suction on the right-hand leg of U tube 4| compared with the left-hand leg which is in communication with pipe 31. Consequently, the liquid will rise in the right-hand leg of U tube 4| to a substantial height with reference to liquid in the left-hand leg. Thus. a comparison of the difference of height in the U tubes 40 and 4| will indicate the quantity of charge in the milk Referring now to the charge apparatus, a control tube 53 is provid'ui adjacent tubesflandflandisopeninsidethemillat surface N and has positioned therein a fitting l4 like fitting 42 and a filter 55. Likewise, a fitting SI and a filter 51 are located in the reference tube St. .The control and reference tubes are connected to a feed controller I.

Referring now to Fig. 4 where the pulverizer feed controller is shown in detail, I designates the casing of the controller in which is located a bell float 62, the lower edge of which is submerged in a liquid such as-water or mercury. The edge of the bell float may be provided inside with a band ll of cork or other material for floating the endtothebellfioatandslidesthmgh-guidell arrangedinthebossltlocatedcentrallyofthe cover-plate. The rod is threaded and carries two adjustingnutstlandll. Theaenutsareprovided with spherical faces. The upper end of the rodispresseddownwardlybytheweightedlever 44 which is pivotally fastened by pin 4! to a may be moved along the lever to any position for adjustment purposes. The upward movement of the bell float is limited by the adjustable stop 81. The slotted portion of lever]! fits between the nuts having sphericaliaces. In the coverplate is a threaded bore 88 for connecting the reference tube with chamber 98. Similarly, in the depressed bottomportion 9| of casing 6! is another threaded bore 88 for connecting the control tube 53 to chamber 92.

Liquid is supplied for sealing chamber 90 frgm chamber 92 by means of an opening 93 covered by a cap-screw 94. The liquid may be drained from the casing by removing cap-screw 95.

" Switch points 69 and 18 of the mercury switch 86 are adapted to be electrically connected by a movable mass of mercury therein in a known manner. Switch point 69 is connected. by a wire 8% to one terminal of the electric motor 34 and switch point it is connected by wire ill to a source oi electric current such as a generator G. A wire E38 connects the generator G with the other terminal of motor 33. Switch points ti and at are connected to wires Hill and mi, respectively. When the movable mass of mercury in switch lit electrically connects points El and 58, current flows through a signal lamp tilt.

The operation of the mill and pulverizer iced controller is as follows:

The electric motor 33, when in operation, drives the feeding mechanism at such a rate that more coal is supplied to the mill than needed. The supply will usually be in excess of load reouirements and will at least correspond to the maximum capacity of the mill. As the quantity of charge increases, the inner end or" control tube becomes more and more obstructed. The reference tube E! is permanently beyond contact with the charge. The control tube is thus rendered less efiective to conduct air from the atmosphere through the port ti to the mill. A pressure approaching atmospheric pressure is thereby built up in the control tube and transmitted to the chamber 92 of the controller. Since the chamber 99, by means of the reference tube, is put under a pressure directly related to the suction pressure in the mill, a differential pressure will result which causes the bell float to use I The glass tube H of the mercury switch is tilted by movement transmitted thereto through lever 12 and rod 14 from the bell float. The mass of mercury is thereby caused to move away from switch points 69 and thus breaking the motor circuit and stopping the feeding mechanism. When this occurs, the signal lamp circuit is closed by the mass of mercury which now connects switch points 61 and 68. Current then flows through the signal lamp and lights the same indicating that the motor circuit is broken and the feeding rnechanism is out of operation.

When the quantity of charge inthe mill is re-' till duced and the inner end of the control tube 53 is uncovered, the procedure just described is reversed and the feeding mechanism put into operation again. I With the charge of material in the mill maintaincd substantially constant as heretofore described, the capacity or output of the mill is varied by varying the flow of air througlr the mill. This is accomplished as previously menlized, the flow of air through the mill is varied by varying the speed of the fan F,- and a constant suction is maintained in the mill irrespective of the air flow by varying the position of damper 25 to vary the size of opening 24.

In Fig. 6, air under pressure from any suitable source, such as a compressed air line or forced draft duct, is carried through conduit I04.

A' pipe 105 is connected to conduit I84. Valves I06 and Hill are located in pipe l05.- The feed controller is connected to reference tube 50 by a tube 50' and to control tube 53 by a tube 53'. Orifice plates Hi8 and I09 in tubes 50 and 53 respectively, are used for the same purpose as fitting 42 shown in Fig. 5. By closing valve I06 and opening valve 'llll, air under atmospheric pressure is admitted through the orifice plates and the operation of the mill and charge controlling equipment associated therewith is the same as that set outfor the apparatus shown in Fig. 1. When. valve Gill is closed and valve Mill open, air under a pressure higher than atmospheric is admitted through the orifice plates. A positive flow of air is thus introduced through the tubes till and 53. This prevents the tubes from being clogged with coal dust while at the same time permitting the quantity of charge within the mill to determine the operation of the feed controller 35d even if the suction in the mill should decrease to such a low value as to be insufficient to actuate the feed controller slid. In such an eventuality the motive force for operating the controller would be the excess in pressure in tube over that existing in tube 5910. Consequently, if the air pressure in pipe tilt is in excess of the pressure within the mill, the feed controller will operate as described, even if a positive pressure is maintained within the mill.

in Fig. 7, an air swept mill of the cylindrical type is shown. The trunnion 5 ill is supported by hearing member iii. The cylindrical drum por-- tion M2 is iastened to the trunnion and is filled with a charge of grinding balls 2!] and coal 22. A cone M3 is arranged axially of the trunnion and is fastened thereto by any suitable means and projects inwardlyof the drum intermediate the discharge conduit 26 and the cylindrical wall of the drum. During operation,'the material in the drum comes in contact with cone M3 which prevents the material from entering the discharge conduit 26. Goal particles'obstruct the inner end of tube 63 when the quantity of charge is too great in the same manner as shown in connection with Fig. l. The operation of the feed controller and cylindrical type ball mill is as described for the form shown in Fig. 1. It will be thishunt field circuit. A source of electricity generally indicated by generator G supplies current to the motor circuit ill-4 l8. A solenoid H9 is connected in asolenoid circuit which is ar- I tioned, by varying the size of opening 24 by ad justment of slide 25 or by changing the speed of Ian F, or both. .If both control means are utiranged in parallel with the motor circuit and is indicated by wires and 91. As shown in Fig. 4, wires 96 and Si are connected to switch points 68 and 10, respectively. A resistance I2!) is located in the solenoid circuit. When switch points 68 and 10 are connected by the mass of mercury in glass tube H of the mercury switch, current from generator G flows through lead Hi to wires 86 and H1. After flowing through the solenoid II! and the motor 34, the current from wires 31' and Illenters the lead I22 and thus the circuits are completed. J

The core I23 of the solenoid II! is connected by link I24 to a lever I25 for turning valve I26. A spring I21 is hooked in lever I25 and fastened at I23. When the solenoid is energized, as shown in Fig. 8, valve I26 is in a position for distributing air under pressure from tank I29 through conduit connections I30 and I3I to chamber I32 of servo-motor I33. Motor compressor I34 compresses air into tank I29 through a conduit I35. Air is exhausted from the servomotor through a conduit connection I31 to valve I26. Stops I38 and I33 prevent over travel of piston I40. The piston rod I4I is connected to rheostat arm I42 by a link I43. The rheostat arm swings about a pivot I44. The motor 34 is operating at full speed with the parts in the position shown. If the quantity of charge in the mill becomes too great, the bell float rises, as described in connection with Fig. 1, and the connection between switch points 69 and is broken. The solenoid is thus de-energized and spring I21 shifts the valve I26 counter-clockwise 90 degrees. In this position of the valve, air under pressure is admitted through conduit connections I30 and I31 to chamber I45 and exhausted from chamber I32 through conduit connection I3I. The piston then travels to the left as viewed in the drawings. This causes the rheostat arm to be moved to contact point I46 with the result that the speed of the motor 34 is reduced to approximately haif. With the motor 34 driving the feeding mechanism at reduced speed, a considerable reduction is realized in the quantity of coal fed to the mill.

It will be seen that with all of the arrangements disclosed, the charge level or the quantity of the charge in the mill is controlled and indicated in response to the differential of the pressure existing in a so-called control tube or fluid conducting member through which air, in the forms disclosed, flows into the mill and which has an opening disposed in the mill so that it will be covered and uncovered by the material being pulverized, and the pressure existing in a so-called reference tube or fluid conducting memher through which air flows into the mill and which has an opening disposed in the mill above the maximum desired level of the charge so that it will not be covered by the material being pulverized. Variations in the charge level cause variations in the extent to which the material closes and opens the mill end of the control tube and hence causes changes in pressure in the control tube. Since the mill end of the reference tube is always fully open and the pressure responsive devices which control the feeding means and the indicating means respond to the difference in pressures in the control and reference tubes, the control and indication of the charge level in the mill is effected regardless of any pressure variations in the mill itself. The material being pulverized in effect operats as a valve whichopensandclosesthemillendsoftheoontrol tubes and thereby causes the operation of the pmure responsive devices which control the feeding means and indicate the quantity of charge in the mill.

Byvaryingtheairflowthroughthe millwhile substantially constant, a substantially constant state of agitation is maintained and a substantially constant concentration of pulverizer material in suspension per unit quantity of air is maintained. Operation of the mill in this manner provides a ready control without a lag of the output or capacity over theh operating range while maintaining a substantially constant ratio of pulverized fuel to air leaving the mill at all times and irrespective of the output of the mill.

While the invention has been shown and described in connection with the regulation of the motor driving the feeding mechanism, it will be understood that it is not necessarily limited thereto. In certain instances, it may be desirable to keep the motor running at constant speed and to adjust the position of the shear plate on the disc type feeder shown. This may be done easily by connecting the servo-motor I33 shown in Fig. 8 to the shear plate.

Since many variations may be made in the forms of the invention herein disclosed, it will be understood that the invention is not to be limited excepting by the scope of the appended claims.

What is claimed is:

l. Pulverizing apparatus comprising a rotatable drum, feeding means for supplying material to be pulverized to the drum, a motor for driving the feeding means, means for controlling operation of the motor comprising a movable member, means providing separate chambers on opposite sides of said movable member, a tube connecting one of said chambers with the interior of the drum at a point at times within the body of material in the drum, a second tube-connecting the other of said chambers with the interior of the drum at a point permanently outside the body of material in the drum, a switch actuated by said movable member, a solenoid actuated by said switch. and a pressure fluid servo-motor actuated by said solenoid.

2. A pulverizer comprising a closed revoluble drum, means for feeding material to the drum at a greater rate than it can be pulverized, a motor for driving said feeding means, a first tube and a second tube having openings in said drum. said tubes being adapted to conduct a limited amount of air from the atmosphere to the drum, means determined by the quantity of charge in said drum for rendering said second tube less eifective to conduct air to the drum, a switch for starting and stopping said motor, said switch being adapted in its off-position to close a circuit for lighting a signal lamp, and a differential pressure responsive member connected to said tubes, said pressure responsive member being adapted to open said switch when the quantity of charge is greater than a predetermined maximum and to close said switch when the quantity of charge falls below a predetermined minimum.

3. In combination with pulverizing apparatus including an air-swept revoluble drum adapted to contain a body of material, indicating means including a plurality of pressure differential members, a first tube connected to all of said members and subject to variations in pressure of air sweeping the drum, :1. second tube connected to one of said members and having an opening adaptedtobecoveredbythemateriaiinthe thequantityofmaterialinthemill 15 drum,andathirdtubeconnectedtoanotherd said members and having an opening adapted to beoovered by the materialinthedrum,saidseeondandthirdtubesbeingarrangedtohavetheir openings closed by diilerent quantities in the a 4. In combination with pulverizing apparatus including an air-swept revolvable drum supported on trunnions and adapted to contain a body of material, a short inwardly projecting conical extension on one oi said trunnions adapted to receive overflow material from the drum, indicating means comprising a pressure diflerential member, a iirst conduit connected to said diflerentiallmember and with an'opening sometimes within the bodyot the overflow material from the drum within the conical trunnion extension, and a secondconduit connecting said diflerential member with a point in said trunnion extension permanently outside the body of overflow material therein.-

5. Pulverizing apparatus comprising a drum, means to supply material to the drum, means in the drum for pulverizing the material therein, means causing air to flow through the drum, means for controlling the supply means to control the level of the material in the drum comprising a pressure responsive member connected to the supply means, a tube connecting said mem ber with the drum below the maximum desired level of the material in the drum, and another tube connecting said member with the drum at a point above the maximum level of the material in the drum.-

6. Pulverizing apparatus comprising a drum, means to supplymaterial to the drum, means in the drum for pulverizing the material therein, means causing air to flow through the drum, means for controlling the supply means to control the level'oi the material in the drum comprising a pressure responsive member connected to the supply means, a tube connecting said member with the drum at substantially the normal level of the material in the drum, and another tubeconnecting said member with the drum at a point above the maximum level of the material in the drum, said tubes having com-l munication with the atmosphere so as to conduct air from the atmosphere into the drum.

'I. Pulverizing apparatus'comprising a drum, means to supply material to the drum, means in the drum for pulverizing'the material therein, means causing air to flow through the drum, means for controlling the supply means to control the level of the material in the drum commeans to regulate the level of the material in the drum.

9. Pulverizing apparatus comprising a drum, means to supply material to the drum, means in the drum for pulverizing the material therein. means causing air to flow through the drum, control means for the supply means, and means comprising a plurality of tubes connecting the control means with the interior of the drum for controlling said control means in accordance with the level of the material in the drum, one of said tubes having its drum end disposed intermediate the maximum and levels of the material in the drum and another of said tubes having its drum end disposed above the maximum level of the material in the drum.

10. Pulverizing apparatus comprising a drum, means to supplymaterial to the drum, means in the drum for pulverizing the material therein, means causing air to flow through the drum, control means for the supply means, and means comprising a plurality of tubes connecting the control means with the interior of the drum for controlling said control means in accordance with the level of the material in the drum, one of said tubes having its drum end disposed intermediate the maximum and minimum levels of the material in the drum and-another of said tubes having its drum end disposed above the maximumlevel of the material in the drum, said tubes having communication with the atmosphere to permit the flow of air through the tubes into the drum.

11.Pulverizing apparatus comprising a drum, means to supply material to the drum, means in .the drum for pulverizing the material therein, means causing air to flow through the drum, and means for indicating the quantity of the material in the drum including a plurality of tubes connecting the indicating means with the interior of the drum-and responsive to the level of the material-therein, one of said tubes having its drum end disposed intermediate the maximum and minimum levels of the material in the drum and another tube having its drum end disposed above the maximum level of the material in the 12. Pulverizing apparatus comprising a drum,

means to supply material to the drum, means in prising a pressure responsive member connected to the" supply means, a tube connecting said member with the drum at substantially e nor- 7 mal level of the material in the drum, and another tube connecting said member with the drum at a point above the maximum level or the material in the drum, said tubes having communication with a source 0! air underpressure to conduct air therefrom into the drum.

8. A pulverizer comprising a rotatable drum, puiverizing means in the drum, means for feeding material'to be pulverized into the drum, suction meansconnected to said drum, a'hollow member having a relatively small opening disposed in the drum intermediate the desired maximum and minimum levels of the material and adapted to be obstructed by material in the drum, a second hollow member having an opening disposedin the drum above the maximum f desiredlevel oi the material, pressure responsive means connected to both hollow members and operable by the pressure diflerence between said members, and means actuated by said pressure responsive means {or controlling the ieeding the drum for pulverizing the material therein,

means, causing air to flow through the drum,

pressure responsive means for indicating the quantity of the material in the drum, and means comprising a plurality oi tubes connecting'the indicating means with the interior of the drum and responsive to the level of the material therein, one of said tubes having its drum end'disposed intermediate the maximum and minimum levels of the material in the drum and another tube having its drum end disposedabove the maximum level of the material in the drum.

- l3. Pulverizing apparatus comprising a drum, means to supply material to the drum, means in the drum for pulverizing the material there-7 in, means causing air to flow through the drum, means for indicating the quantity of the material :in the drum comprising a first and second pressure responsive device, a first pipe connected with each device and with the interior of the drum at a point above the maximum level of the material in the drum, a second pipe connected with each device and with the interior of the the drum at a point below the maximum level of the material therein, and a third pipe cbnnecteidtothe second device and with the inte- 'materialin rior of the drum at a point above the minimum level lot th material in the drum.

i4. Pulverizing apparatus comprising a drum, means to supply material to the drum, means in the drum for pulverizing the material therein, means causing air to flow through the drum,

means for indicating the quantity of the mate-' rial in the drum comprising a first and second U-tube an indicating material in each U-tube,

a firstpipe connected with one leg of each U- tube and with the interior of the drum at a' means causing air to flow through the drum, control means for the supply means, means comprising a plurality of tubes connecting the control means with the interior of the drum for controlling said control means in accordance with the level of the material in the drum, one oi said tubes having its drum end disposed intermediate the maximum and minimum levels of the material in the drum and another of said tubes having its drum end disposed abov the maximum level 01' the material in the drum, and means for suppiving air under pressure to said tubes at their ends'opposite their drum ends.

16. A. pulverizer comprising a-closed revoluble drum, means for feeding material to the drum at a greater rate than it can be pulverized, a

motor tor driving said ieeding means, a first tube and a second tube having open nss in said drum,

said tubes being adapted to conduct a limited amoimt of air from the atmosphere to the drum, the openings in said ilrst tube being disposed above the maximum desired level of the material in the drum, means determined by the'quantity oi charge in said drum for rendering said second tube less eilective to conduct air to the drum, a switch for starting and stopping said motor, and a diilerential pressure responsive member connected to said tubes; said pressure responsive member being adapted to open said switch when the quantity of charge is greater than a predetermined maximum and to close said switch when the quantity or charge falls below a predetermined minimum. 4

17. A pulverizer comprising a rotatable shell, pulverising means in the shell, means ior feeding material'to be pulverize thereinto, the shell having an air inlet and an outlet above the maximum desired level or the material therein, means causingairtoflowintothe h lithroughtheinlet and over the surface or the material therein and through the outlet carrying pulverized suspension, and means for indicating the quantity of material in the drum operated by the difle'renoe in prasu'rs between members conducting separate, relatively small quantities of air between points outside oi and \rithin the drum includingmovablemeans common to each otsaidmem' andcontinuouslysubjccttothe pressures disposed in the drum below thcimaximum de- 'siredieveloithematerialtherein.

,oneol'said'latterpointsheing' separate, relatively small quantities oi air between points outside of and within the drum including movable means common to each of said members and continuously subject to the pressures therein, one of said latter points being disposed in the drum below the maximum desired level of the material therein.

19. A pulverized comprising a drum, means for supplying material to the drum, means causing air to flow into the drum and out thereof carrying pulverized material in suspension, and means for controlling the supply means operated by the difference in pressure between members conducting separate, relatively small quantities oi air between points outside oi and within the drum including movable means common to each of said members and continuously subject to the pressures therein, one 0! said latter points being disposed in the drum below the maximum desired level oi the material therein.

L 20. A pulverizer comprising a drum, means for supplying material to the drum, means causing air to flow into the drum and out thereof carrying pulverized material in suspension, and means for controlling the supply means operated by the diflference in pressure between members conducting separate, relatively small quantities of air between points outside of and within the drum, one oi said latter points being disposed in the drum below the maximum desired level or the material in the drum and another or said points beingdisposedinthedrumabovesaidmaximum fdesired level.

common to each oi said members and continupcnsiontoflowouto fthemiil,

small quantities of air to flow in separate confined streams between points within and without the mill respectively, a portion of one of said streams being below the maximum desired level of material in the mill, varying'the flow of air through the latter stream by obstructive action -oi the material'in the mill as the level of the .material therein varies while maintaining at all times gee flow of air through another confined stream, and controlling the supply of material to the mill by the differences in pressure of the streams resulting from the variations in the flow of said one streamdue to the obstructive action of .the material in, the mill with respect to the free flow in said other stream.

24. The method of pulverizing material in a mill which comprises supplying material to the mill to be pulverized, supplying air to the mill, causing air carrying pulverized material in suspension to flow out of the mill, causing relatively small quantities of air to flow in separate confined streams between points within and without the mill respectively, a portion of one of said streams being below the maximum desired level of material in the mill, varying the flow of air through the latter stream by obstructive action of the material in the mill as the level of the material therein varies while maintaining at all times free flow of air through another confined stream, and operating means to indicate the level of the material in the mill by the differences in pressure of the streams resulting from the varia-v tions in the flow of said one stream due to the obstructive action of the material in the mill with respect to the free flow in said Other stream.

25. Apparatus for holding material comprising a container, means for supplyingmaterial to the container, means for removing material from the container, and means for controlling the supply means so as to maintain a substantially constant level of material in the container operated by the difierence in pressure between members conducting separate, relatively small quantities of air between points outside of and within the container including movable means common to each of said members and continuously subject to the pressures therein, one of said latter points being disposed in the container below the desired level of material therein.

26. Apparatus for holding material comprising a container, means for supplying material to the container, means for removing material from the container, and means for controlling the supply thereby to maintain in the drum a substantially constant concentration of pulverized material in suspension per unit quantityoi air, and means operable independently of the supply 9f material. to the drum for varying the flow of air through the drum to vary the quantity of pulverizedmaterial withdrawn from the drum whereby the output oi pulverized material from the drum may be varied substantially without a lag:

28. Pulverizing apparatus comprising a drum, pulverizing means in the drum, means for supplying material to be pulverized to the drum, means includinga fan arranged to operate at different speeds for causing air to flow into the drum and out thereof carrying pulverized material in suspension, means controlled by the level of the material in the drum for controlling the 'means for supplying material to the drugn to maintain a substantially constant quantity of substantially without a lag.

29. Pulverizing apparatus comprising a drum,

pulverizing means in the drum, means for sup-' 1 plying material to be pulverized to the drum, an exhauster fan having its suction connected with the drum, an air inlet opening through which air is supplied to the drum, means operable independently of the supply of material to the drum for controlling the flow area of the air inlet opening, and means controlled by the level of the material in the, drum for controlling the means for supplying material to the drum to maintain a substantially constant quantity of material in the drum to maintain a substantially constant state of agitation therein irrespective of M the withdrawal of pulverized material therefrom thereby to maintain in the drum a substantially constant concentration of pulverized material in suspension per unit quantity of air, the arrangement being such that by varying the flow area of means so asto maintain a substantially constant level of material in the container operated by the difierence in pressure between members conducting separate, relatively small quantities of air betwen points outside of and within the container, one of said latter points being disposed in the container below the maximum desired level of material therein and another of said points being disposed in the container above said maximum desired level.

2'7. Pulverizing apparatus comprising a drum,

' pulverizing means in the drum, means for supplying 'material to be pulverized to the drum, means causing air to flow into the drum andout thereof carrying pulverized material in suspension, means controlled by the level of the material in the drum for controlling the means for supplying material to the drum to maintain a substantially constant quantity of material in the drum to maintain a substantially constant state of agitation therein irrespective of the withdrawal of pulverized material therefrom said air inlet opening the flow of air through the drum. may be varied to vary the quantity of pulverized material withdrawnirom the drum whereby the output of pulverized material from the drum may be varied substantially without a lag.

30. Pulverizing apparatus comprising a drum, pulverizing means in the drum, means for supplying-material to be pulverized to the drum, an exhauster fan having its suction connected with the drum, means for driving the fan, means for a varying the speed of the fan, an air inlet opening through which air is supplied to the drum, means operable independently of the supply of material to the drum for controlling the flow area of the air inlet opening, and means controlled by the level of the material in the drum for controlling the means for supplying material to the drum to maintain a substantially constant quantity of material in the drum to maintain a substantially constant state of agitation therein irrespective of the withdrawal of pulverized material therefrom" thereby to maintain in the drum a substantially constant concentration of pulverized material in suspension per unit quantity of air, the arrangernent being such that by varyin the flow area 01' said air inlet opening and by varying the speed of the fan the flow of air through the drum may be varied to vary the quantity of pulverized material withdrawn from the drum whereby the output of pulverized material from the drum may be varied substantially without a lag.

31. Pulverizing apparatus comprising a rotatable drum, means for rotating the drum, pulverizing means in the drum, means for supplying material to be pulverized to the drum, means causing air to flow into the drum and out thereof carrying pulverized material in suspension, means controlled by the level of the material in the drum (or controllin the means for supplying material to the drum to maintain a substantially constant quantity of material in the drum to maintain a substantially constant state of agitation therein irrespective of the withdrawal of pulverized material therefrom thereby to maintain in the drum a substantially constant concentration of pulverized material in suspension per unit quantity of air, and means operable independently of the supply of material to the drum for varying the flow of air through the drum to vary the quantity of pulverized material withdrawn from the drum whereby the output of pulverized material from the drum may be varied substantially without a lag.

32. The method of pulverizing material which comprises supplying material to'be pulverized to a pulverizing zone, causing air to flow into and out of said zone carrying pulverized material in suspension, controlling the supply of material to said zone automatically in response to variations in the level of the material in said zone to maintain a substantially constant quantity of material in said zone to maintain a substantially constant state oi agitation therein irrespective or the withdrawal oi. pulverized material therefrom thereby to maintain in said zone a substantially constant concentration or pulverized material in suspension per unit quantity of air, and varying the flow of air through the drum independently of the supply of material to the drum to vary the quantity of pulverized material withdrawn from the drum whereby the output of pulverized material from the drum may be varied substantially without a lag.

33. The method of pulverizing material which comprises supplying material to be pulverized to a pulverlzing zone, causing air to be drawn into said zone through an inlet opening and to be withdrawn iromthe mill carrying pulverized material in suspension, controlling the supply of material to said zone in response to variations in level of the material in said zone to maintain a substantially constant quantity of material in said zone to maintain a substantially constant state 01' agitation therein irrespective of the withdrawal of pulverized material therefromthereby to maintain in said zone a substantially constant concentration of pulverized material in suspension per unit quantity of air, varying the flow of air through the drum independently of the supply or material to the drum to vary the quantity of pulverized material withdrawn from the drum whereby the output oi pulverized material from the drum may be varied substantially without a lag, and varying the flow area of said inlet opening to maintain a substantially constant suction in the mill irrespective of the flow of air therethrough.

MARTIN FRISCH.

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