US2559557A

US2559557A - Aerating feeding of pulverized materials

Info

Publication number: US2559557A
Application number: US544606A
Authority: US
Inventors: Ervin G Bailey; Ralph M Hardgrove
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1944-07-12
Filing date: 1944-07-12
Publication date: 1951-07-03
Anticipated expiration: 1968-07-03

Description

5 Sheets-Sheet l INVENTORJ /3 Erl/n Bai/ey i BY Pal/Jl? M Hardgrove ATTORNEY July 3., 1951 .Filed July l2, 1944 ig. l

July 3, 1951 E. G. BAILEY Erm.

AERATING FEEDING OF' PULVERIZED MATERIALS 5 Sheets-Sheet 2 INVENTORS Filed July 12, 1944 Ervin G Bai/e 5f lg 4 BY EaZ/ob M Hardgol/e ATTORNEY July 3, 1951 E. G. BAILEY ETAL AERATING FEEDING OF PULVERIZED MATERIALS Filed July 12, 1944 5 Sheets-Sheet 3 IN VEN TORS fm Hd a r. 5H@ QM .mh V P F./. EDM

A TTORNEY July 3, 1951 E. G. BAILEY l-n-Ax. 2,559,557

Filed July 12, 1944 AERATING FEEDING OF PULVERIZED MATERIALS 5 Sheets-Sheet 4 /4/ /40 f /39 /HS W212i/ l//7 /36 ne 5 INVENTORS Ef V177 6T Bai/eg 4 EQIP/7 MHdfc/yfoz/z-P ATTO R N EY July 3, 1951 E. G. BAILEY ETAL 2,559,557

AERATING FEEDING OF PULVERIZED MATERIALS I Filed July 12, 1944 5 Sheets-Sheet 5 ATTORNEY Patented July 3, 1951 AERATING FEEDING OF PULVERIZED MATERIALS Ervin G. Bailey, Easton, Pa., and Ralph M. Hardgrove, Westfield, N. J., assignors to The Babcock & Wilcox Company, Rockleigh, N. J., a corporation of New Jersey Application July 12, 1944, Serial No. 544,606

Claims. l

The present invention relates to feeders for regulating the discharge of finely divided material, such as pulverized coal or other materials in pulverulent form, from a storage space to a point of use.

Feeders for pulverulent material heretofore in use have not been satisfactory, particularly in installations in which the material is mixed with a gaseous carrier medium, such as air, in that a uniform rate of material discharge has usually been difficult to secure and tends to become more diioult with wear of the feeder parts. The capacity characteristics of such feeders are also subject to rather wide variation with the density of the material in the supply bin.

Pulverized coal stored in a bin for even a short time is subject to a settling action which often results in the formation of coherent masses of pulverized coal. The carrier air receiving the stored pulverized coal from a feeder often entrains these masses and their presence is evidenced by snow balling in the burning fuel and air mixture.

Variation in density of stored pulverized material causes a feeder to operate under a variable pressure and this results in a variation in the Weight of material discharged through a volume controlling device, such as a feeder wheel or orifice, and a resultant variation in the density of the final mixture of pulverized material and gaseous carrier medium. Ineifective control and a non-uniform pulverized coal and air mixture have been found particularly disadvantageous in connection with high capacity pulverized 'coal-fired furnaces requiring a continuous supply of finely pulverized coal uniformly distributed in the carrier or primary air and it is in thisfield that the present invention finds one of its most effective applications.

The primary object of the invention is the provision of an aerating feeder for delivering pulverized material from a storage space to a point of use in a uniform controllable mixture of pulverized material and gaseous carrier medium. A further object is the p-rovision of a pulverized material feeder capable of discharging a regulable stream-of pulverized material and carrier medium of substantially predetermined density over a Wide range of discharge capacity. Another object is the provision of feeder apparatus which will so process and handle pulverulent material from a storage container that any coherent masses therein will be disintegrated before discharge from the feeder. Another object is the Yverized coal burners for firing furnaces.

provision of feeder apparatus in which close clearances between relatively movable parts are avoided so that wear is kept at a minimum and changes in rated capacity due to wear thereby avoided. Another object is to provide a feeder which can be built in relatively low capacity sizes and yet retain its advantageous characteristics of good regulable control. Another object is the provision of an aerating feeder which provides for a recirculation of pulverized coal through the storage container thereby assisting in maintaining the pulverized coal therein in a non-compacted iiuid condition.

The various features of novelty which characterize our invention are pointed out With particularity in the claims annexed to and forming a part of this specication. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described preferred embodiments of our invention.

Of the drawings:

Fig. 1 is a sectional elevation of a storage receptacle and aerating feeder constructed in accordance With the invention and taken on the line l-l of Fig. 3;

Fig. 2 is a plan View of the apparatus shown in Fig 1;

Fig. 3 is a horizontal section taken on the line 3-3 of Fig. 1;

Fig. 4 is an elevation partly in section of another embodiment of the invention;

Fig. 5 is a horizontal section taken on the line 5-5 of Fig. 4;

Fig. 6 is a side view partly in section of the apparatus shown in Fig. 4;

Fig. '7 is an enlarged View of the lower portion of the feeder apparatus shown in Fig. 6;

Fig. 8 is an elevation partly in section of another embodiment of the invention;

Fig. 9 is a plan view of the appartus shown in Fig- 8;

Fig. 10 is a partial side elevation of the Fig. 8 embodiment, showing the driving connections for the aerating feeder shaft |33, and

Fig. 11 is a detail view showing the bevel gears for driving the aerating feeder shaft.

One field of use of the aerating feeder of this invention is in feeding pulverized coal to pul- Because of its advantageous feeding characteristics it is well adapted for use in pulverized coal firing installations wherein the feeder is used in conjunction with an air swept pulveriaer. In installations of this type the feeder' receives and stores pulverized coal from the operation of the pulverizer, and when the pulverizer is idle at low furnace ratings or at some particular predetermined furnace rating, the feeder will be operative on a feed of stored pulverized coal to deliver pulverized coal to the furnace. As an alternative operating procedure, the feeder can be operated simultaneously with the pulverizer to ilre the furnace.

An example of this type of application is shown in the embodiment of the invention illustrated in Figs. l to 3, wherein the aerating feeder is positioned in the upper portion of a cylindrical receptacle I0, the lower portion of which serves as a storage space for pulverized coal. Airborne pulverized coal from an air swept pulverizer (not shown) is introduced into the upper part of the receptacle through a plurality or tangentially arranged pipes Il, arrangedin pairs at circumferentially spaced positions. The tangential introduction and angular ilow of the high velocity streams effects a centrifugal separation of pulverized coal particles and carrier air with the separated coal dropping to the lower part of the receptacle I6 which acts as a coal storage reservoir, while the separated air is vented from the upper portion of the receptacle for disposal as hereinafter described. The diameter of the receptacle Iii is selected for the desired degree of centrifugal separation and the vertical dimension of the receptacle is selected to provide an adequate separating space above the maximum operating level of separated coal in the lower portion.

An axially arranged shaft I2 mounted in bearings I3 and I4 in the base and top plates I5 and I6 respectively oi the receptacle has its upper end connected into a gear reducer unit I1 on the top plate. A pair of agitator blades I8 are attached to the shaft I2 and on rotation assist the movement of pulverized coal within the receptacle Ill toward the lower end of an elevating screw conveyor I9 also mounted on the shaft. The elevating conveyor I9 operates within a tubular casing 2l) open at its lower end to'receive pulverized coal from the reservoir space and at its upper end to discharge pulverized coal into a chamber 2l defined by a cylindrical casing 22.

The chamber 2I is centrally located in the upper portion of the receptacle Ill, the casing 22 being supported from the top plate I3. The top of the chamber is connected by outlet pipes 23 to corresponding pulverized coal burners (not shown). A horizontally arranged bottom port plate 24 encircles the upper end of the conveyor casing and is provided with two circular concentrically arranged annular ports 25 having upwardly extending boundary flanges 23. Each of the ports VV25 and its pair of ilanges 28 is covered in spaced relationship by an annular cap member 21 having a pair of depending annular flanges 28 radially spaced romthe 'sides of the flanges 26 and cooperating therewith to form reversed passages therebetween. The cap members 2l are attached by radial arms 29 to a vertically adjustable hub-B on the shaft I2 and as pulverized coal is delivered to thechamber 2I by the conveyor I3, the rotation of the arms 23 and the members 21 tends to keep the air passages free of coal. Circumferentially spaced overflow ports 3I are-provided in the casingr22 at a predetermined level above plate 2d yfor thedischarge of pulverized coal from chamber 2I when the bed of coal therein rises above that level.

A second cylindrical casing 32 is alxed to the top plate Iii and arranged coaxially of and eX- terlorly spaced from the casing 22. Two radial division plates 33 are extended-downwardly from plate I6 and between the

casings

22 and 32 t0 divide the annular space therebetween into two

passageways

34 and 35. The plates 33 are attached to a plate 36 which is spaced below the plate 24 and transversely encircles the conveyor casing 20. The segmental section of the casing 32 bounding the passageway 35 is extended downwardly to connect with the plate 36. The segmental section of the casing 22 bounding the passageway 34 is also extended downwardly to connect with the plate 3S. Thus the

plates

24 and 36 with the complementary sections of the

casings

22 and 32 deilne an air distributing chamber 3l communicating with the passageway 35. An air flow path is thereby provided from an external source, such as fan 38, through a discharge duct 39 and openings'd in the plate I6, downwardly through passageway 35 into chamber 31.

Air passing from the distribution chamber 31 to the chamber 2| will ilow upwardly through the annular ports 25 inthe plate 24 and between the pairs of flanges 26 to the underside of the rotating cap members 21. Each cap 21 divides a stream of air into two portions flowing over-the upper ends of the flanges 26 and then downwardly between the

flanges

26 and 28, with the air entering the chamber 2l in four annular streams through annular orices 4I formed beween the lower ends of flanges 28 and the plate The reversed air passageways between chambers 31 and 2l impose a resistance to the flow of 'air therethrough with the dimensions of 4the

flanges

26 and 28 so selected and the bottom of flanges 28 so spaced from plate 24 that the greatest restriction to air flow is through the annular orifices 4I. The air velocity through the oriilces 4I will be correspondingly rhigher than through other sections of its flow path and the pulverized coal within the chamber 2l will be swept from the orifices, so that a minimum abrasive rwear of the coacting and relatively moving parts will occur. The flow resistance due to the orifices-4I may be modified by vertical adjustment of hub 30 on shaft I2, and such adjustments may -be made to compensate for any wear that may occur.

The operation of motor 42 driving the fan 38 will create a flow of air through duct '39 and passageway 35 into the air distributing chamber 31, with the rate of flow being controlled by a regulating valve 43 in duct 39. Simultaneously the motor 42 will drive shaft I2 through gear reducer I1, causing pulverized coal to be -discharged into chamber 2I Iby the conveyor I9. Preferably, the rate of pulverized coal discharge into chamber 2| will be substantially constant and in excess of the maximum discharge capacity of the aerating feeder to points of use. The streams of air entering the aerating chamber 2I will pass through the mass of pulverized coal therein, thoroughly aerating the coal and entraining ra quantity of coal in proportion to the velocity of kthe air flow. Since the coal is delivered to the chamber at a greater rate than it will be entrained and discharged with the air to the points of use, thesurplus coal will overilow through ports 3 I, keeping the level of aerated coal in chamber 2| substantially constant.

The amount of pulverized coal entrained by a stream of air passing through a quantity of pulverized coal will be proportional to the velocity of the air flow and the mass of the pulverized coal. -While the depth of aerated pulverized coal within the chamber 2| will be maintained constant by the overflow ports 3|, the mass of pulverized coal present therein will vary with variations in the rate of air flow. As the velocity of the air through the aerating chamber increases, the density of the aerated pulverized coal will decrease in proportion to the rate of air ow and the ratio by weight of air to coal in the stream of air-borne coal discharging from the apparatus through ports 3| will also be proportionately reduced. There is a denite relationship between the rate of air flow entering the feeder, the density of aerated coal therein and the density of the air and coal mixture discharged from the feeder apparatus. Moreover these relationships are consistent and reproducible throughout the operating range of the feeder. Therefore, the feed rate of air-borne pulverized coal delivered by the aerating feeder can be determined by measurement of the air flow entering the feeder, and a calibrated air flow meter in duct 39 or in the inlet to fan 38 will also indicate the rate of ilow of coal from the feeder to points of use. Likewise, since the coal flow is proportional to air flow, the coal laden air delivered by the feeder and secondary air added at the burners for combustion can be coordinated for automatic combustion control. Moreover, it has been further found that within the limits usually encountered in operation of air swept pulverizers, the feeder delivery of air and pulverized coal will be consistent with normal changes in the neness of the pulverized coal handled.

' While the agitation of the pulverized coal in the aerating chamber by reason of the passage of air therethrough will tend to break up and disperse any compacted particles of coal delivered by the elevating conveyor I9, any coherent particles of coal that reach the surface of the aerated coal mass will be too heavy to be airborne and will remain near the surface of the coal mass until either dispersed by further action of the air or passed through the overflow ports and returned to the storage space.

In tests of this feeder apparatus it has been found advantageous to keep the height of the overflow ports 3| above the plate 24 at a minimum consistent with maintaining a uniform bed of aerated coal within the feeder chamber and also advantageous to select a position for the overflow ports so that the differential static pressure measured between a position in air chamber 31 and a position in or adjacent the outlet ports 23 will be generally uniform within the normal capacity range of the apparatus. This is accomplished with a proper depth of pulverized coal since the increased. pressure drop with increased air flow thru the restricted air passages between chambers 31 and 2| will be compensated by reduced pressure drop through the aerated coal within the chamber 2| because of the decrease in the density of the aerated coal.

The pulverized coal and carrier air delivered to the receptacle I9 through the inlet pipes is separated as described with the coal being deposited within the receptacle. The separated air is vented through a segmental passage 34 formed by

casings

22, and 32, and plates 33, and having an open bottom 44 and one or more discharge connections 45. The opening 44 is at a level below the inlet pipes The Vent connections 45 are extended by conduits (not shown) to direct substantially dust-free air vented from the upper portion of the reservoir IU to external points of use or disposal. The vented air may be directed to burners in the furnace served by the feeder apparatus wherein the vented air is combined with pulverized coal to be burned or, alternately, the vented air may be directed to dust separators, or the like, for further cleaning and subsequent discharge of the dust-free vented air to the atmosphere.

Figs. 4-7 illustrate an installation of the aerating feeder in a storage system of pulverized coal firing. In installations of this type the pulverized coal is delivered to a storage tank or reservoir and subsequently fed by a feeder to burners of a pulverized coal consuming furnace in accordance with the heat requirements of that furnace.

As shown a stream of air-borne pulverized coal is tangentially delivered to a centrifugal type separator 46 in whichthe mixture is separated by centrifugal force with the coal being deposited within a reservoir or storage bin 41 While the separated carrier air is vented through an outlet 48 to points of disposal. A screw conveyor 49 is transversely positioned across the bottom of the reservoir 41 and is extended within a tubular housing through the bottom part of a cylindrical casing 5l] to engage a conventional driving mechanism including a constant speed motor and gear reducer. The speed of rotation of the conveyor 49 is selected to eiect a substantially constant movement of coal therethrough at a predetermined rate in excess of the designed capacity of the associated aerating feeder. The tubular housing of conveyor 49" is open to the lower portion of an open-topped cylinder 5|. The cylinder 5| is centrally located Within the casing 59 and its lower end is secured to the inner wall of an inverted truncated cone 52 which is pierced by the housing of conveyor 49 and cooperates with the cylinder 5| to provide a passageway for the upward movement of pulverized coal transferred from reservoir 41 by the conveyor 49. The cylinder 5| extends upwardly to a location approximately 1A; of the total inside height of the casing 5|) and the pulverized coal therein discharges over its upper end into an aerating feeder chamber 53.

The chamber 53 is defined by the cylindrical casing 54 which is coaXially spaced within casing 50. The casing has a top plate 55 with multiple discharge opening 5B therein, and an annular bottom port plate 51 extending between the casing and the cylinder 5|. The plate 51 is provided with an annular port opening 58 concentric with and generally eduidistant between thev the adjacent walls. Upwardly extending circular flanges 59 on each side of the port 58 and the passageway therebetween is covered in spaced relationship by a cap member 69 having a pair of depending annular flanges 6| outwardly spaced from the flanges 59 and cooperating therewith to form reversed passages.

As hereinbefore described in connection with Figs. 1, 2 and 3, the cap member 69 is supported by arms 62 which are attached to a vertically adjustable hub 63 on a rotatable shaft 64. The shaft 54 extends upwardly through the chamber 53 to engage an external motor and gear reducer drive 65. The shaft 64 is maintained in .1 axial alignment by vertically spaced bearings 6E above plate 51.

4`in a :bearing housing-seas to insure a uniform

radial clearance'between flanges

59 and 5|.

Overflow ports El are located in the casing V54 As the level of coal in chamber 53 rises vto the ports 61 the excess coal will overflow therethrough into an annular' chamber 55 between the casings 5|] and 54. The excess coal deposited in chamber 5S is returned to the reservoir ll-I by means of screw conveyors 59 posi- .tioned at opposite sides of the cone 52 and'ex- .tending in parallel spaced .relationship to conveyor 49 in the bottom of reservoir 4l. Gonveyors 49 and 69 are preferably operated from -the same drive mechanism and the combined capacity of the two return conveyors 69 is equal -to or greater than the capacityof conveyor 45.

The portion of casing `54 around cylinder 5| and below the port plate 51, defines an air-dis .tributing chamber 'I3 which is connected by a duct 1| extending through the wall 50-to the outlet of a constant speed fan l2. A control valve 'I3 in the fan inlet duct 'I4 regulates .the flow of 'air drawn to the fan and delivered to the cham ber 1|). Preferably, as shown in Fig. 6 an air `seal pipe 15 is connected between the fan outlet and-the bearing housing to prevent flow of coal laden air into the bearings 56.

'In operation conveyor 49 transfers pulverized coal from the reservoir 4'! to the aerating chamn -ber 53. while the conveyors 69 return any excess coal overflowing through ports 61 into the conveyors, back to the reservoir 4l. The coal within chamber 53 is thoroughly aerated by the `streams of air delivered thereto and a portion of the coal so aerated is swept up by the passing air to be discharged from the feeder to points of use` The operation of the motor andgear drive |55 will cause the slow speed rotation of the arm 62 and the cap member Bil which will assist in distributing the pulverized coal in the aerating chamber as well as assist in keeping the annular orice 16 clear of coal.

The modied construction illustrated in Figs. 8 and 9 is especially designed for mounting in a locomotive tender. For this purpose a storage receptacle |55 is elongated longitudinally of the tender and provided with rounded end portions lto effectively utilize the available tender space,

`and the aerating feeder section of the unit is 'mounted on the top of the receptacle. Air-borne -pulverized coal is delivered to a pair of centrifugal type separators |06 on the top of the receptacle bythe tangentially arranged pipes |01. The coal and air of the mixture are separated within the separators |05 with the coal being deposited within receptacle IE5 and the air being vented vthrough a centrally located, open ended pipe |38 divided into branches |09 leading to points of disposal (not shown).

A conveyor-elevator |||l of a well known bulk flow type is used to transport pulver-ized coal from the bottom ofthe receptacle |35 to an aerating feeder chamber I I mounted on the top of :the receptacle |55. The conveyor lill operates lwithin a housing ||2 of rectangular cross section and is driven by a sprocket ||3 `within a dusttight casing |15 mounted at one end and on top of the receptacle |05. The sprocket ||3 is driven at a constant speed by a conventional drive mechanism including a gear motor 5.

The conveyor housing I I2 is ext-ended from one side of the drive casing ||5 into and through the receptacle |65 in a closed circuit returning to anotherside of thecasing I5. The top of the conveyor housing ||2 is open along the Vbottom of the receptacle |05 to receive stored pulverized coal and has an opening in the bottom of its upper horizontal section to provide a discharge port I communicating with the aeratingfeeder through a spout |||l conveying the `discharged material to the lower intermediate part of 'the aerator chamber` The conveyor is operated 'to discharge into the feeder chamber III at apredetermined rate in excess of the designed capacity `of the aerating feeder. The vertical upward run of the conveyor I I6 is supported by an idler ,drum I|9 positioned on the top of the receptacle '|05` A casing |20 encloses the drum |.I3 and is connected with the receptacle |05 through a port |2| so that any spillage of coal in passing over the drum III!! will be returned to the storage space.

The aerating feeder chamber III is defined by a cylindrical wall |23, a top plate |24 vwith .two outlet ports |25 therein, and a horizontally arranged bottom port plate |25. The plate |26 is provided with two circular concentric ports |21 having upwardly extended boundary flanges |28 and the passageways therebetween are covered in spaced relationship by the cap member |29 having pairs `of depending circular flanges |30 radially spaced from flanges |28 and cooperating therewith to form reversed passages therebetween. As hcreinbefore described in connection with Figs. l, 2, and 3 the cap |29 is supported by arms ISI attached to a vertically adjustable hub |32 on shaft |33. The shaft is centrally located within chamber I I I and is maintained in axial alignment by the bearings |35. The shaft |33 engages a bevel gear drive |36 mounted on the top plate |24 and is variably oscillated by the horizontal shaft |31 which is driven by a crank |38, a connecting rod |39 and an eccentric Y|140 on the shaft |4| of the motor IIB. The oscillatory movement of the shaft |33 may be for a part of one revolution or for several revolutions. Circumferentially `spaced overflow pipes |42 are located within chamber .with their upper or inlet ends at a predetermined level above plate |26 for the discharge of pulverized coal from the chamber when the bed of coal therein rises above that level. vThe pipes |42 project through the top of the receptacle and coal passing therethrough .is returned to the storage space of the receptacle |95. The walls of spout IIS are extended below the surface of the bed of ypulverized coal within chamber I to provide a seal against the flow of air or aerated coal into the conveyor-elevator I0.

In operation the conveyor-elevator transfers pulverized coal from the storage space to the aerating feeder chamber II'I, while the overow pipes |42 will return any excess coal therein, back .to the storage space. Air owing through the chamber will aerate the coalV and entrain a portion of -the aeratedcoal for discharge from the feeder to points of use. The reversing rotational movement of the cap member |29 will keep the reversed passages of the air inlet ports clear of coal.

It is recognized that the weight of vpulverlzed material in a storage reservoir .will subject the material in the bottom of that reservoir to a variation in pressure which will influence its density and degree of aeration, and be dependent upon the height of the material stored. Since a feeder is usually arranged to receive pulverized material withdrawn from the bottom of a storage reservoir, the feeder will usually handle a material having a variable density. Furthermore, if the reservoir is subjected to vibration, as would be true when the reservoir is associated withfa railroad locomotive, the pulverized coal would be compacted due to that vibration and the density thereof would be greatly increased. However, it will be noted in the feeder of the present invention, that a change in the rate of pulverized material delivery to the aerating chamber as caused by variations in the density of the material withdrawn from the reservoir, will not affect the feeding characteristics of the aerating feeder.

This is accomplished by air flotation of the pulverized material from a bed of aerated material having a substantially uniform depth within the feeder chamber and by compensating for any variation in the delivery rate thereto by an increase or decrease in the overflow rate of surplus material rejected therefrom.

It will also be noted that the aerating feeder is superior to other types of pulverized coal feeders in its ability to deliver a stream of air-borne pulverized coal wherein the weight of the pulverized coal entrained will be proportional to the rate of air flow delivered to the feeder and since the air flow can be metered, the air flow measurement will also be an indication of the rate at which pulverized coal is being delivered by the feeder.

As the floatation effect of the air passing through the aerating feeder chamber is a function of the size of the particle, oversize masses of pulverized coal will not be entrained, and the aerating feeder thus insures the delivery of an air-borne stream of pulverized coal particles of the desired uniform size characteristics which is so desirable in burning pulverized coal eiliciently at high rates of heat liberation per unit of furnace volume as require/d in locomotive ring.

In the claims, the word air is intended to generically cover any gaseous carrier medium suitable for removing pulverized material in the manner described.

We claim:

l. Apparatus for feeding pulverized material comprising walls defining an aerating chamber having multiple air-borne material outlet ports in the top wall thereof, conveyor means for delivering pulverized material into the lower portion of said chamber, means for limiting the height of pulverized material within said chamber, walls forming an air distributing chamber beneath said aerating chamber and receiving air from an outside source, a plate member between said aerating chamber and said distributing chamber having an opening therethrough for passage of air, flanges attached to said plate extending upwardly on each circumferential side of said opening, and a rotatable cap member having depending flanges superimposed in spaced relationship to said opening and upwardly extending flanges.

2. Apparatus for feeding pulverized material comprising walls defining an aerating chamber having an air-borne material outlet port in the upper part thereof, a conveyor arranged to deliver pulverized material into said chamber, walls defining an air distributing chamber beneath said aerating chamber, a plate member between saidaerating chamber and said distributing chamber having an opening therethrough for passage of air, flanges attached to said plate extending upwardly on each side of said opening, a cap member having depending flanges superimposed in spaced relationship to said opening and upwardly extending flanges, and means for imparting a reversing rotational movement to said cap member.

3. In apparatus for feeding pulverized material, walls defining an aerating chamber having an airborne material outlet in the upper part thereof, conveyor means continuously delivering pulverized material into said chamber, means limiting the height of pulverized material within said chamber, walls forming an air distributing chamber beneath said aerating chamber and receiving air from an outside sorrce, a plate member between said aerating clzamber and said distributing chamber having an opening therethrough for passage of airflanges attached to said plate extending upwardly on all sides of said opening, a cap member having depending flanges su'perimposed in spaced relationship to said opening and said upwardly extending flanges tor define therewith an air flow path therebetween of pre.

determined dimensions, and means for moving said cap member relative to said opening while maintaining substantially the predetermined dimensions of said air flow path.

4. In apparatus for feeding pulverized mate-` rial, walls defining an aerating chamber having an air-borne material outlet in the upper part thereof, conveyor means operable from above the chamber and continuously delivering pulverized material into said chamber and upwardly through the bottom thereof, means limiting the height of pulverized material within said chamber, walls forming an air distribuitng chamber beneath said aerating chamber and receiving air from an outside source, a plate member between said aerating chamber and said distributing chamber hav-r ing an opening therethrough for passage of air,

flanges attached to said plate extending upwardly on all sides of said opening, a cap member having depending flanges superimposed in spaced relationship to said opening and said upwardly extending flanges to deilne therewith an air flow path therebetween of predetermined dimensions,`

and means for turning said cap member relative to said opening while maintaining substantially the predetermined dimensions of said air flow path.

5. In apparatus for feeding pulverized material, walls defining an inner casing presenting an aerating chamber having an air-borne material outlet in the upper part thereof, conveyor means continuously delivering pulverized material into said chamber and upwardly through the bottom thereof, means including an outer casing limiting the height of pulverized material within said chamber, walls forming an air distributing chamber beneath said aerating chamber and receiving air from an outside source, a plate member between said aerating chamber and said distributing chamber having an opening therethrough for passage of air, flanges attached to said plate extending upwardly on all sides of said opening, a cap member having depending flanges superimposed in spaced relationship to said opening and said upwardly extending flanges to define therewith an air flow path therebetween of predetermined dimensions, and means for turning said cap member relative to said opening while maintaining substantially the predetermined dimensions of said air now path.

6. Apparatus for feeding pulverized materialr comprising wall means defining an aerating chamber having in its upper part an air-borne material outlet port through which there isa normally continuous flow of air-borne material, pulverized material delivery means normally continuously delivering pulverized material into said chamber at a rate in excess of the rate of flow of pulverized material through said port, said aerating chamber having an opening at its lower part beneath the mass of pulverized material in the chamber, the wall of said chamber being provided with an overflow port through which the excess of pulverized material flows from said chamber to limit the head of pulverized material above said opening, and means causing the fiow of aerating and carrier air through said opening and upwardly through the mass of pulverized material at a predetermined rate to maintain predetermined ratio of pulverized material and carrier air for flow through said first mentioned port.

7. Method of feeding gas-borne pulverized material which comprises, normally continuously delivering pulverized material to a confined zone at a rate in excess of the rate of gas-borne dis'- charge of materials from that zone, iluidizing said material within said zone and effecting the gasborne discharge of the material from the upper part of said zone by causing the flow of aerating and carrier gas upwardly through the mass of pulverized material within said zone, and causing an overflow discharge of the gas fluidized pulverized material from said zone and thereby limiting the head of pulverized material and predetermining the ratio of gas to pulverized material in the gas-borne delivery from said Zone.

8. Apparatus for feeding pulverized material comprising walls defining an aerating chamber having an air-borne material outlet port in the upper part thereof, a conveyor for delivering pulverized material into the lower intermediate por tion of said chamber to maintain a mass of the material in the chamber, a bottom for said aerating chamber having an opening therethrough for the passage of air into said chamber, means causing air to now upwardly through said opening and then upwardly through the mass of pulverized material in the chamber, means for maintaining a substantially uniform depth of pulverized material on said bottom plate member, and a cap member superposed relative to the air opening in said bottom and the mass of pulverized material.

9. Apparatus for feeding pulverized material comprising Walls defining an aerating chamber having an air-borne material outlet port in the upper part thereof, a conveyor for delivering pulverized material into the central part of the lower portion of said chamber to maintain a mass of the material in the chamber, walls defining an air distributing chamber beneath said aerating chamber receiving air from an outside source, a bottom for the aeratingV chamber disposed between said aerating chamber and said distributing chamber having an opening therethrough for the passage of air into said aerating chamber,

means causing air to now upwardly through-,said opening andy then upwardly through the mass ofi` pulverized. material in the chamber, and means including an over-now port communicating with. the aerating chamber for limiting the volumeY off aerated pulverized material within saidV aeratingv chamber.

10. The combinationwith a cylindricallyshaped receptacle for stored pulverized coal having. a

substantially tangential inlet for receiving: air-- borne pulverized material and an outlet'for venting substantially dust-free air therefrom, said inlet with-the receptacle constituting an air and coal separator, of an aerating feeder' chamber defined by wallsl having an air-borne materialV outlet port inthe Lipper part thereof, means for deliveringfpulverized material from said receptacle to said aerating'chamber, a bottom plate member for said aerating chamber having an REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Greiner Mar. 15, 1881 Duckham Oct. 30, 1894 Heavey Oct. 24, 1899 Hay Nov. 16, 1915 Caven Nov. 30, 1915 Lassiter Dec. 28, 1915 Short Feb. 22, 1916 Heyl Aug. 1, 1916 Pian Sept. 25, 1917 Cooper Apr. 30, 1918 Pruden May 11, 1920 Barnhurst July 5, 1921 Trent Nov. 3, 1925 Pontoppidan Feb. 8, 1927 Barker Jan. 1, 1929 Conrath May 12, 1931 Lissman July 11, 1933 Leiman Dec. 12, 1933 Goebels Aug. 28, 1934 Nielsen Jan. 14, 1936 Graemiger Mar. 22, 1938 Marr July 12, 1938 Vogel-Jorgensen Nov. 12, 1940 Kenedy Mar. 3, 1942 Burch Aug. 24, 1943 FOREIGN PATENTS Country Date Great Britain Feb. 21, 1930 Number Number