US2436487A - Closed-loop material transport system, including an in-circuit pulverizer - Google Patents

Description

Feb..24,194's. up. SHERB'AN f2,436,4s1

CLOSEDLLOOI MATERIAL TRANSPORT SYSTEM, INCLUDING AN IN-CIRCUIT PULVERIZER Filed Dec. 11. 1943 2 sheets-sheet 1 I v (Je 724 @L Fi 1 26 20 I:Q2 m4. o /v 106 `68 38 INVENToR.

A ITORNH Y Feb. 24, 1948. D. v. sHEBAN 2,436,487

CLOSED-LOOP MATERIAL TRANSPORT SYSTEM, INCLUDING. AN IAN-CIRCUIT PULVERIZER med nec. 11, 194s 2 Sheets-Sheet Patented Feb. 24, 1948 TEM, INCLUDING AN VERIZER IN -CIRCUIT PUL- Daniel V. Sherban, Keyport, N. J., asslgnor to The Babcock & Wilcox Company, Rockleigh, N. J., a corporation of New Jersey Application December 11, 1943, Serial No. 513,842

The invention herein disclosed relates to a pulverizing apparatus especially adapted for use in a system wherein pulverized products are transported from the apparatusby means oi a current of air or other suitable gaseous carrier medium, and varying proportions of such products are returned to the apparatus for recycling. The apparatus and system will be found suitable for use with materials of various composition including, for example, such solids as coal, mineral ores, cement clinker, or other solids of similar physical characteristics.

'I'he invention may be usefully applied-in a pulverized fuel ring system wherein pulverized coal is discharged from the pulverizer or mill in a stream of carrier air, and the resulting fluent mixture delivered to a burner, or to a number of burners, with any surplus quantity of the mixture being returned to the mill to provide continuous circulation. In such a system, provision is made for feeding raw coal vto the pulverizer at rates sucent to replace the amounts taken by the burner or burners, and for supplying fresh or make-up air to the pulverizer at rates sumcient to maintain a current i air therethrough at all loads while providing an output mixture having the particular fuel-to-air ratio desired for any given load.

In certain types of pulverizers wherein grinding elements are relatively rotatable about a vertical axis, the coal and make-up air are conveniently supplied to the pulverizing zone from opposite sides, that is, the raw coal being fed from the upper side for discharge by gravity into the zone, and the fresh air being supplied from the under side foradmission to the zone in an annular stream. Since the fuel-air mixture is iluent in character, any surplus of the mixture to be returned to the mill may be mingled with the incoming supply oi make-up air, prior to admis- Y 1l Claims'. (Cl. 241-48) sion of the air to the grinding zone, thereby producing a carrier medium of modied density which may be admitted to the grinding zone through the passage or passages normally provided for the fresh air alone.

Under normal operating conditions, the coal and air are supplied to the pulverizer in such proportions that the resulting output mixture contains a smaller quantity of -air than is necessary for complete combustion; thus, the mixture with its normal content of primary air may be transported from the pulverizer without risk of pre- `mature combustion or explosion, and the required amount of secondary airvmay be added combustion of the entrained coal'particles.

at the burners to provide a suitably combustible mixture.

When a surplus of the mixture is returned to l the pulverizer, as in the circulating system herein disclosed, the fuel and air content'. of the returning mixture remains essentially the same as when originally discharged from the pulverizer,

tained throughout the return conduit system to prevent any appreciable quantity of pulverized coal from settling out of the returning stream. When the return mixture and the make-up or primary air are combined for flow through the grinding zone,l the proportion of air in the resulting mixture is appreciably higher than in the returning fuel air mixture, thereby tending to provide an atmosphere capable of supportinlg t is considered important therefore to avoid any condition which might lead to ignition of such a mixture to cause a possible explosion, either through the coking of pulverized coal accumulations in or adjacent the zone of mixing; or as a result of hot coke particles being carried into the mixing zone and allowed to accumulate therein, When a heated supply of primary air is employed, the hazard of the mixture becom-` ing ignited is somewhat increased, due to a cer-A tain amount of .heat being retainedin the returning coal-air mixture which would tend to promote coke formation.

It is a purpose of the invention therefore to maintain the iluid flow passages leading to the grinding zone clear of all coal or'coke accumulations, and to cause the make-up air and the returning coal and air to be vmixed in a zone where-there is the least tendency for coalor coke to collect.

An additional object is to maintain velocities of iluid flow into the mixing zone high enough tokeep the adjoining passages clear of any pulverized coal or coke that mightv tend to settle therein.

Another object is to cause the respective streams to enter the mixing zone in such directions and at such velocities as to promote thorough mingling of the streams throughout the zone.

A further Objectis to provide a mixing zone having an outlet direct to the grinding zone or adjoining region where the issuing stream will pickup additional coal particles, thereby increasing the proportion of coal to air in the mixture and providing a relatively non-explosive mixture for ilow through and from the pulverizer,

amaca? 3 the area of now from the mixing zone into the grinding zone to be small enough to maintain now velocities at least as high as the velocities' prevailing within the mixing zone, and higher than the rate of flame propagation for the fueland-air mixture in transit at that location- Among other objects, it is proposed to maintain the passages leading to and from the mixing zone clear of oversize particles or other foreign materials which might tend to obstruct the flow of air and pulverlzed coal.

More specific objects include the admission of coal-free air and coal-laden air to the pulverizer through concentrically arranged inlet areas; the mixing of both bodies of air in an'annular zone closely adjacent the grinding zone; and the admission of the coal-laden air through an opening v arranged out of the path of solids falling from the grinding zone.-

The foregoing objects and others not specincally mentioned are more fully set forth in the description to follow, together with various advantageous features of construction as illustrated in the accompanying drawings. in which:

Fig. 1 is a layout, in plan, of a pulverlzed coal circulating system embodying apparatus of my invention;

Fig. 2 is an elevational view, partly in section, of the pulverizer included in the system of Fig. 1;

Fig. 3 is a plan section of the pulverizer, taken along line 3-3 of Fig. 2;

Fig. 4 is an enlarged fragment of Fig. 2;

Fig. 5 is an enlarged fragmentary section, similar to Fig. 4, showing a modication.

The system according to Fig. 1 of the drawings, includes an air swept pulverizer I0 arranged to supply pulverized coal and primary air to burners I2 and I4 associated with a form of metallurgical furnace I6. here indicated as a billet heating furnace, although as will be understood. other types of furnaces may be employed and, if desired, the burners arranged for ring separate furnaces.

The pulverizer I0 is shown as being located adjacent the charging end I8 of the furnace I6 and its output ofv pulverlzed coal and primary air is discharged through pipe to the inlet of an exhauster fan 22 from which the mixture is delivered to a main distributor conduit 24 at its inlet end 26, the opposite end or return length 28 of the conduit being connected to the air inlet side of the pulverizer to form a closed circuit or loop as will be explained more in detail hereinafter. The pulverizer and fan are conveniently operated by a single motor 30.

or group of burners, that it may be desired to maintain in operation; the burners I2 along one side of the furnace being supplied through burner lines 32 leading from the conduit 24, the larger burners I4 at the discharging end of the furnace remote from the location of the pulverizer being supplied through burner lines 34, and the remaining side burners I2 through additional burner lines 32. Suitable valves, not shown, may be installed in each of the burner lines 32 and 34 to positively cut of the supply of fuel and primary air to any burner not in operation, and to regulate the supply of fuel to the various burners during operation. Any surplus quantity of the total pulverizer output above that diverted to the burner or burners in operation is returned to the inlet side of the pulverizer I0 for recycling in view of the looped arrangement of the conduit 24 which provides a closed circulatory system. A secondary supply of air may be admitted to the burners or to the furnace or furnaces for complete coinbustion of the fuel, but'the detailsof such secondary supply are not included in the present invention, and further disclosure is therefore considered unnecessary.

The references to coal as the material being pulverized, and to air as the carrier medium, are not to be taken literally. but are to be interpreted as embracing other solids, combustible or otherwise, and other gaseous media, capable of adaptation to the system described. In a broad sense, also, the burners I2 and I4 become selected points of delivery or use, for example, bins or other containers, irrespective of whether the material transported is a fuel or is a material of noncombustible character.

Referring to Fig. 2, the pulverizer I0, is by way of example, of a known ball-mill type having its grinding zone located in the lower portion of an enclosing casing or housing 36 generally circular in cross-section about a vertical axis. The grinding elements include a circular series of grinding balls 38 which cooperate with upper and lower grinding rings 40 and 42 'respectively to reduce the coal to the desired degree of neness; the raw coal being delivered to the pulverizing chamber 44 above the level of the grinding rings by means of a known type of motor driven feeder 46 mounted on the pulverizer casing 36.

In this form of pulverizer, the lower grinding ring 42 is maintained stationary, being mounted on an annular support 48 integral with the base plate 50 which forms the bottom wall of the casing or housing 36. The upper grinding ring 40, concentric with the lower grinding ring 42, is rotated about its central vertical axis to cause the balls 3B to roll relative to both grinding rings; the upper grinding ring 40 being drivenby motor 30 operating through pinion shaft 52 and suitable gearing within housing 54 to rotate the drive member 56 and drive ring 58. Grinding pressure between the balls and rings may be resiliently and adjustably maintained by means Well known in the art.

A conical wall 60 surrounding the lower grinding ring 42 and flaring upwardly toward the casing 36 serves to guide the incoming raw coal into the zone of action of the balls 38; the wall 60 extending upwardly from the annular support 48 to define an annular compartment 62 in which fresh make-up' air is admitted through conduit 64 and from which such air is discharged inwardly through a series of circumferentially spaced ports 66 in the annular support 48. The air admitted through conduit 64 may be heated or un- `heated, as desired, and the conduit fitted with the usual regulating damper or dampers, as desired.

A downwardly flaring cup-like member 58, rotatable with the drive member 56 and constituting in effect an integral extension thereof, terminates in a cylindrical outer surface portion 16 adjacent its lower edge at a level corresponding to the reduced inner edge portion 12 of the lower grinding ring 42, thereby forming a relatively narrow annular passage or throat 14 through which carrier air is admitted to the grinding zone above. The coal is fed to the region exteriorly of thecircle of balls 38 and as the coal becomes pulverlzed, the particles are swept upwardly by the stream of carrier fluid admitted to the grind s in the region lnteriorly oi' the circle and discharged laterally through -a' circumferential series of ports 'i6 in the drive ring 68. The finer particles continue upwardly through the cham,- ber M and are discharged from the pulverizer through the outlet 20, while the coarser particles dropout ofthe current and are returned to the pulverizing zone for further reduction.

The extension member 68, as shown. comprises an assembly of plate members including, for example, a downwardly flaring conical side ywall plate 78, a cylindrical upper side wall plate 00, and a circular top or closure plate 82, A conical plate 80 arrangedinwardly of the conical plate I8 and diverging downwardly therefrom provides an effective thickness for the lower side wall portion of. member 68 of gradually increasing cross section toward the bottom a pipe 06 formed as a ring being positioned between the downwardly diverging plates 'i8 and 04 and being welded to their lower edges to afford rigidity to the assembly and to provide a rounded bottom edge or rim 88. .A downwardly flaring conical plate 90 having an upturned circumferential lip portion 92 is positioned below the rim 80, being secured to the inner plate 84, for example, by means of circumferentially spaced ribs 90.

kThemember 68 is provided exte'riorly with a series of circumferentially spacedv vanes 05 adjacent its lower edge, such varies extending downwardly to provide portions within the throat 'i0 and serving to maintain the throat area clear of coarse, heavy particles of material that might interfere with free fluid flow therethrough; the

'below the throat 1I where it is mingled with fluid entering from the passage |20 formed betweenA the rim 88 and plate 90,01 `the rotating member 68, the mixture of the two bodies of fluid then passing upwardly through the4 throat 'I4 and grinding zone above. f

The stream of coal and air returned to the pulverizer by means of conduit sections 86 and |00 is caused to ow upwardly to enter thev space |02 centrally of the rotating member 66, whereupon the direction of its flow is reversed and the stream converted to one of annular form directed downwardly through the passage |22 between the conical side wall portions of the rotating member 68 and the stationary member |06. The downward flow of the returned fuel and air is continued through the annular passage I 20 where the stream is deflected upwardly b'y the lip 92 into -impingement with the upwardly flowing stream of make-up air within the mixing zone H8. 'i

lIn this arrangement of pulverizer. the central inlet |04 for the returning fuel-and-air mixture is above the level of the throat 14 and therefore out of the path of any material such as pyrites or other coarse, heavy particles that might fall through the throat and interfere with normal uid flow conditions in the fluid circulation system. Such an arrangement is particularly desirable in circulation systems wherein a measure high velocity of flow throughout, the velocity of posed conduit section |00 extends from the base plate opening 98 into the upper portion of the space |02 interiorly of the member 68, the section |00 terminating in an open upper end |04 of circular cross section constituting the area of ad-I Vslightly less than the inner edge of the plate 90 to provide an annular clearance space ofsuitable width for relative rotation.

In the operation-of the system described, .the supply of make-up air admitted to the pulverizerthrough conduit 6l is distributed throughout the annular compartment 62 from which it is directed through the circumferentially spaced ports 66 to the annular space III disposed between the ring support 48 and the conical baille memberv |06,

the upper wall of each port 66 being inclined downwardly at its inner end, as at ||6, to afford entrance to thev space ||4 at a, level below the outer edge of plate 90. The air then passes up- Wardly to the annular zone ||8 immediately vdischarge 'through the outlet passage |20 being sufficient to effect thorough mingling of the coalladen air with the 'coal-free air within the annular zone H8. The two bodies of air of different densities thus delivered to the zone ||8 are combined to form a fluid mixture of modified density in which the solid particles are substantially uniformly distributed throughout and in which under certain conditions the air content may be sulcient to provide an explosive mixture. The hazard'of a fire or an explosion of the mixture is substantially eliminated however by effecting the mixture of the two bodies in a zone of high 'fluid flow velocities where there is the least tendency for coke to collect, and where velocities are preferably higher than the rate of ilame propagation forl the -fuel and air mixture in transit; in the embodiment disclosed, the mixing being eiected in an annular zone of restricted dimensions closely adjacent the pulverizer throat 14 where velocities are maximum, in practicea suitable mixing level being at a distance below the throat 'I4 of approximately two times the width of the throat or corresponding passage where maximum velocities are initiated, such velocities being maintained into the grinding zone or adjacent region where additional fuel particles are immediately picked up to restore the normal fuel content and thereby render the mixture relatively non-explosive for discharge from the pulverizer. The downward. flow of fluid at high velocity through the passages |22 and |20 also `serves to overcome any tendency for coal to work up toward and into the inlet opening |04.

In Fig. 5, showing a modicatiomparts correspending to those included in Fig, 4 are identified by the same reference characters. In this em bodiment of the invention, the inner conical wallv the cone |24 and attached thereto, may be em ployed to further improve distribution, and to assist in overcoming a part of the entrance pressure drop. Blades |28, circumferentially spaced and secured to the inner side wall portion 84 of member 68, tend to further induce air flow and prevent coal from working up toward the inlet |04, particularly when the amount of coal in the mill is above normal; the blades |23 being pitched forwardly and having their free edges |30 closely adjacent and substantially parallel to the outer surface of the stationary cone |06 whose slope, in this form, is continuous from the rim of the inlet opening |04 to the base plate 50'. A manifold |32, in the form of a ring and provided with openings |34 about its circumference, may be suitably connected to a source of high pressure air orother fluid for the purpose of clearing the space ||4 of pyrites or other debris that might have accumulated, the openings |34 registering with corresponding openings in the cone |06 to provide jets directed toward the ports 66 so that the obstructing material may he dislodged and forced into the chamber 62 from which it may be readily removed. l

I claim:

l. In a pulverizer having grinding elements in the lower portion of an enclosing housing, said housing having an outlet leading fromits upper portion, said elements comprising a member formed with a grinding surface arranged annularly about'a vertical axis and a circle of grinding members arranged coaxially with said surface and adapted to cooperate therewith for pulverizing material fed into said housing at a location above said grinding elements, means forming an annular throat concentric with fand adjacent a circumference of said annular grinding surface, means for causing a stream of carrier air to flow upwardly through said throat for transporting pulverized material particles t'o and through said outlet, means for admitting a portion of said carl rier air to a zone ,within said housing displaced inwardly and upwardly from the entrance .to said annular throat, means for directing said portion to a surrounding annular zone below and adjacent said throat, means for separately admitting another portion-of said carrier air to said annular zone, means' for causing said portions to become mingled within said annular zone, and means for directing 'said mingled portions upwardly through said throat to provide said stream of carrier air.

2. I an air swept pulverizer adapted for inclusion in a circulation system such as described, means forming a grinding zone in the lower portion of the pulverizer housing, said means including a ring member having an annular grinding surface formed about a vertical axis and spaced above the inside bottom wall of said housing, ymeans including a downwardly expanding conical baille for defining an` annular throat adjacent the inner circumference of said grinding member, said baille terminating in a. lower.

rim portion forming the inner circumferential boundary of said throat, means for admitting material-laden air to said pulverlzer comprising a conduit arranged centrally of said conical bale and extending upwardly therein beyond the level of said lower rim portion and throat, a conical baille coaxial with said conduit and sloping downwardly therefrom to the base of said housing to define an annular space below and adjacent said throat, said baiiles being spaced throughout to form an annular passage for conducting material-laden air from said conduit to said annular space, a support for said ring member formed with a series of circumferentially spaced ports for directing material-free air to said annular space, means for causing said streams of air to be mixed within said annular space at a location closely adjacent said throat, and means for causing the resulting mixture to ow upwardly through said throat into said grinding zone.

3. In an air swept pulverizer adapted for in- .clusion in a circulation system such as described,

upper and lower grinding rings together with an intermediate circle of rollable grinding elements cooperating therewith to form an annular grinding zone within the lower portion of the pulverizer housing, means including a downwardly expanding conical baffle for defining an annular throat adjacent the inner circumference of said lower grinding ring, said baiile terminating in a lower rim portion forming the inner circumferential boundary of said throat, means for admitting material-laden air to said pulverizer comprising a conduit arranged centrally of said conical baffle and extending upwardly therein beyond ythe level of said lower rim portion and throat, a conical baille coaxial with said conduit and sloping downwardly from the upper end thereof to the base of said housing to define an annular space below and adjacent said throat, said conical bailes being spaced throughout to form an annular passage for conducting material-laden air from said conduit to said annular space, said first named battle having a conical inner surface portion diverging downwardly from a conical outer'surface portion to provide an effective wall thickness progressively greater towards its lower edge thereby progressively decreasing the distance between said baille's at increasing diameters to provide a relatively high velocity of discharge of materialladen air into said annular space, means for separately directing material-free air into said annular space and causing said air Ato become mingled with said material-laden air within said space, and means for inducing upward flow of the resulting material and air mixture through said throat.

4. In an air swept pulverizer adapted for inclusion in a circulating system such as described, upper and lower grinding rings together with an intermediate circle of rollable grinding elements cooperating therewith to form an annular grinding zone within the lower portion of the pulverizer housing, means for admitting materialladen airto said pulverizer comprising a conduit arranged centrally of said grinding zone and terminating in an open upper end at approximately the level of said circle of grinding elements, means for directing said material-laden air from the upper end of said conduit to an annular mixing zone below and adjacent said grinding zone, said last named means comprising a downwardly flaring conical baille disposed over the upper open end of said conduit and terminating in a lower rim portion defining an annular throat adjacent the inner circumference of said lower grinding ring, said baille forming the outer wall oi' an y resulting modified mixture to flow upwardly` through said throat.

5. In an air swept pulverizer adapted for inclusion in a circulation system such as described, upper and lower grinding rings together with an intermediate circle ofvrollable grinding elements cooperating therewith to form an annular grinding zone within the lower portion of the pulverizer housing, means for admitting material-laden air to'said pulverizer comprising a conduit arranged centrally of said grinding zone and terminating in an open upper end at approximately the level of said circle of grinding elements, means for directing said material-laden air from the upper end of said conduit to an annular mixing zone below and adjacent said grinding zone, said last named means comprising. a downwardly iiaring conical baille disposed over the upper open end of said conduit and terminating in a lower rirn portion defining an` annular throat adjacent the inner circumference of said lower grinding ring, saidy baille including a top portion formed as a cone having' its apex pointed downwardly toward the open end `of said conduit, means for` mixing an additional supply of air with said material-laden air in said mixing zone, and means for causing the resulting modified mixture to fiow upwardly through said throat.

6. In a closed circulating system of the type described, an air. swept pulverizer having a normal output of pulverized combustible material and air in a ratio providing a substantially nonexplosive mixture, said pulverizer having a grinding zone Within an enclosing housing having an outlet at one side of said zone through which said mixture is discharged, means defining said grinding zone comprising a member providing an annular grinding surface having an inlet and an outlet marginal circumference, means at the side toward said outlet feeding combustible material to said grinding zone adjacent said inlet circumference, means for returning to said pulverizer a portion of said output mixture composed of pulverized combustible material and air in substantially the aforesaid ratio, said last named means being arranged to direct said portion `to an annular mixing space disposed adjacent the side ofy said grinding' zone remote from said outlet, said mixing space terminating in an4 annular outlet passage of restricted flow area adjacent said outlet circumference, means for supplying material-free carrier air to said pulverizer arranged to direct said air into said mixing space thereby combining said material-free air with the combustible-material-laden air returned from said outlet and producing a modified mixture of potential explosive character, means for causing saidmodi-l fied mixture to flow through said outlet passage for transporting pulverized combustible material from said grinding zone to provide said normal output mixture, and means for maintaining the velocity of flow of said modified mixture within and from said mixing space higher than the rate of flame propagation of said mixture as produced in said space.

'1. In a closed circulating system of the type described, an air swept pulverizer having a nor.

mal output of pulverizedcombustlble material and air in a ratio providing a substantially noning zone adjacent said outer circumference,

means for returning to said pulverizer a portion of said output mixture composed of pulverized combustible material and air in substantially the aforesaid ratio, said last named means being arranged Ito direct said portion to an annular mixing space disposed adjacent the lower side of said grinding zone, said mixing space terminating in an annular outlet passage of restricted flow area adjacent said inner circumference, means for supplying material-free carrier lair to said pulverizer arranged to direct said air into said mixing space thereby combining said material-free air with the combustible-materialladen air returned from said outlet and producing a modified mixture of potential explosive character, means for causing said modified mixture to flow through said outlet passage for transporting pulverized combustible material from said grinding zone to provide said normal output mixture, and means for maintaining the velocity of ow of said modified mixture within and from said mixing space higher than the rate of flame propagation of said mixture as produced in said space.

'8. In a pulverizer adapted for inclusion in a circulating system such as described, said pulverizer having a grinding zone of annular formation about a vertical axis, said housing having an outlet' therefrom at the upper side of' said grinding zone, means defining said grinding zone comprising a ring member concentric with respect to said axis and providing an annular grinding surface between an inlet and an out- -let marginal circumference each disposed at a different radial distance from said axis. means feeding coal to the upper side of said grinding zone adjacent said inlet circumference, means forming an annular throat concentric with and adjacent said outlet circumference, means for causing a stream of carrier air to flow upwardly through said throat for transporting pulverized coal to and through said outlet, means for admitting a portion of said carrier air to a zone within said housing displaced radially and upwardly from the entrance to said annular throat,

means for directing said portion to an annular mixing zone below and adjacent said throat, means for combining an additional carrier air portion with said first named portion within said mixing zone, said carrier air portions consisting of coal-free and coal-laden air respectively, and means for effecting iiow of said respective carrier air portions into said mixing zone and of said combined portions within and from said zone at velocities high enough to maintain the associated ow passages clear of coke accumulations.

9. In van air swept pulverizer adapted for inclusion in a closed circulating system of the type disclosed, said pulverizer having grinding elements in the lower Aportion ofan enclosing housing, said housing having an outlet leading from its upper portion, said elements comprising a member formed with a grinding surface arranged annularly about a vertical axis between an inner and an outer marginal circumference each at a different radial distance from said axis', means defining an annular throat adjacent said inner circumference, means deiining an annular space below and adjoining said throat, means for directing separate bodies of air into said space in streams distributed substantially throughout its circumference,` one of said bodies of air comprising a` material-laden portion of the total pulverizer output and one substantially clean air from a separate source, means for causing one of said bodies of air to flow outwardly from said axis to enter said space, means for causing the other of said bodies to flow inwardly toward said axis to enter said space to eiIect a mixture with said oppositely entering body of air, and fan means causing upward flow of said mixture into and through said throat.

10. In a pulverizer having grinding elements in the lower portion of an enclosing housing, said housing having an outlet leading from its upper portion, said elements including a member formed with a grinding surfacearranged annularly about a vertical axis between'a material inlet circumference and a material outlet circumference disposed at dinerent radial spacings from said axis, means forming an annular throat adjacent said outlet circumference means for causing air to flow through said throat for transporting particles of pulverized material to and through said outlet, means for admltting said air to said pulverzeiin separate streams of which one stream is composed of relatively clean air and another is composed of air in which pulverized material particles are suspended, said streams being admitted to the interior of said housing in concentric relation relative to said vertical axis, means deiinlng an annular space in the region below and adjacent said throat, means for causing said streams to become mingled in said annular space, and means for directing the resulting mixture upwardly through said throat.

11. In an air swept pulverlzer adapted for inrounded lower rim portion forming the inner circumferential boundary of said throat, means for supplying fluid streams of different densities to said pulverlzer for subsequent mingling ,and flow through said throat, means for admitting one of said streams to the interior of said pulverizer'comprising a pipe arranged centrally of said bell-shaped member and extending upwardly therein beyondthe level of said lower rim portion and throat, means for admitting the other of said streams to the interior 'of said pulverizer annularly of said upwardly extending pipe, means for reversing the now of said first named stream to form an annular stream tiowing downwardly adjacent the interior wall of said bellshaped member toward an annular zone belowand adjacent said throat, a deiiector ring surrounding said pipe having an upper surface portion formed to deflect said downwardly flowing stream into mixing relation with the other of said streams in said zone, and means for causing the resulting mixture to now upwardly through said throat.

DANIEL V. SHERBAN.

REFERENCES CITED The following references are of record in the 'file of this patent:

UNITED STATES PATENTS Number Name Date 1,778,755 De Wolf Oct. 21, 1930 684,152 Wheildon Oct. 8, 1901 2,403,976 Harvey- July 16, 194s 2,071,38() Bailey et al. Feb. 23, 1937 FOREIGN PATENTS Number Country Date 547,500 France Sept. 23, 1922 362,491 Great Britain Dec. 2, 1931 154,112 Germany Aug. 6, 1904

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