CA2071668A1 - Adjustable flow rate device for rotating vane pulverizer - Google Patents

Abstract

Abstract of the Disclosure An air flow rate control device for a rotating or stationary vane throat in a bowl mill pulverizer. The air flow rate control device comprises an adjustable deflector mounted on the lower surfaces of the pitched vanes to provide varying air flow passage cross sections. In one embodiment the deflector comprises a flexible member whose shape can be varied using manual adjustment apparatus to alter the air flow passage cross-section.

Description

2 ~ 8 This invention relates to coal pulverizers and more particularly to an improved mechanism for controlling air flow rate through l:he air passages between pitched vanes in the pulverizer throat.

Pulverizers such as bowl mills are commonly used to prepare coal for introduction into the combustion chambers of steam generators; representative pulverizers are currently offered Eor sale by Babcock and Wilcox, Foster-Wheeler and Combustion Engineer:ing. Bowl mill pulverizers :~ ~ 10 typically perform a classification function through the use of a ver~ical air flow through a "throat" which is made up of a circular arrangement of pitched vanes surrounding the outer periphery of the pulverizing surface and forming air : ~
flow passages between a wind box and the classification area.: The~va~nes are made up of metal plates usually welded ; to and between inner and outer rings. The vane assembly or 2 ~ 8 "throat" may be s-ta-tionary or i-t may be mounted for rotation about a vertical axis.
Air flow ra-te through the passages formed by the pitched vanes is a function of the effective cross-sectional area of the passages and the pressure head produced by the fans, turbines or other air drive mechanisms. It is desirable to control air flow rate through cross~sectional area adjustment to optimize pulverizer performance.
One prior art mechanism for controlling cross-sectional area and flow rate comprises spacer blocks which are bolted to the inside ring of the vane assembly. The blocks can come in various sizes or may be bolted on top of one another to reduce the size of the air flow passage and the air flow velocity. In this approach the spacer blocks are in the path of particulate matter flow and, therefore, are subject to abrasion and wear. As a consequence, the spacer blocks must be made of a more ~expensive wear resistant material. Moreover, it is a time consuming and cumbersome job to install and remove the spacer blocks.
An alternative approach to air flow control is disclosed in my U.S. Patent No. 4,907,751, 'iRotating Throat ; for Coal Pulver~izer, issued March 13, 1990. In that patent I disclose the use of slide-on, wear resistant vane liners in the form of metal plates which overlie the upper : , : ~ :
~ ~ 25 principal surface of the pitched vanes. Each liner plate ~ : . .
~ has an integral angled~portion which rests on the top edge .

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2~7 ~ 668 oE the vane atld partially closes the air flow opening. The vane liners are held in place by means of arcuate over-plates or caps which are bolted to the top surface of the inner portion of the vane/throat assembly. The degree to which the arcuate plates extend over the openings also affects the area of the air flow passage and the air Elow rate. Like the spacer blocks, ad~ustment or change in air passage size can be achieved only by interchanging one set of liners or caps for others of a differen-t size.

According to the present invention an apparatus is provided modifying the size of the air flow openings between the pitched vanes of a pulverizer throat, which mechanism is out of the main stream of particulate flow and may be made of inexpensive materials.
In general, this is achieved by attaching a deflector device, such as a steel shape, to the undersides of the pitched vanes to reduce at least a portion of the cross-sectional area of each flow passage to a desired degree.
According to a second aspect of the invention, the deflector devices are readily ad~ustable to the desired degree; moreover~adjustment requires nelther removal nor interchange of parts.

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2~7~68 In a first e~bodiment oE the invention this is achieved through the disposition of hinged deElectors with adjustment mechanisms on the under surfaces of the pitched vanes. In the preferred form the deflectors are simple relatively light-gage steel shapes, the lower edges of which are hinged to the surfaces of the pitched vanes and the upper portions of which are connected to the vane under-surfaces by means oE a threaded fastener which permits infinite adjustment in the spacing between the deflector and the undersur~ace of the associated pitched vane. The passage between vanes may therefore be infinitely adjusted and caused to assume an essentially venturi shape wherein the cross-sectional area is gradually reduced toward the upper portion of the passage such that air flow rate gradually increases from a minimum at the entrance of the passage to a maximum at the exit of the passage.
In a second embodiment of the invention the deflectors are formed of an at least partially flexible sheet of material, for example light gauge spring steel, the upper edges of which are essentia~lly fixed to the surfaces of the pitched vanes and the lower edges of which are manually adjustable with respect to the vane undersurfaces.
sy adjustiny the position of the lower edge of the deflector, the spacing of the flexible portion of the deflector from~the vane can be varied so as to alter the cross-sectional~area of the air flow passages between vanes.

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' , ' . '.' " ' ' '' ' " ' :' ' ' ', ' , ' ' 2~7~68 A manual adjustment mechanism i5 mounted on the vane undersurface and the lower edge of the flexible deflector is Eastened thereto. In one preferred embodiment the manual adjustment mechanism comprises an axial guide and 5traveler to which the lower edge of the deflector can be connected. The manual adjustment is operable to increase or decrease-the distance between the ends of the deflector. In a particular embodiment, the axial guide comprises a threaded bolt rotatably mounted in a mounting bloc~. A
10traveler nut on the threaded bolt travels axially therealony as the bolt is rotated. The lower edge of the flexible deflector is fastened to the traveler nut such that rotation of the threaded bolt results in the increase or decrease of the distance between the ends of the deflector.
15The force exerted on the flexible portion of the deElector as its ends are brought together or pulled apart ; alters the shape of the defl~ctor and of the associated airflow passage. The air flow passages between vanes may therefore be infinitely adjusted between low and hlgh 20velocity venturi conEigurations wherein the cross-sectional area is gradually reduced toward the upper portion of the :
passage such that air flow rate gradually increases from a minimum at the entrance of the passage to a maximum at the exit of the passage.
25These and other advantages will be more readily achieved from a reading o~ th~ following specification which :: : : :~ `:

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2~7 ~ ~8 descrihes one or more illustrative embodiments of the invention in de-tail.

In the Drawin~s FIGURE 1 is a perspective view partly in section of a bowl mill pulverizer utilizing a rotating vane arrangement employing an embodiment o-f the present invention;
FIGURE 2 is an exp:Loded perspective view of components oE the air Elow rate con-trol device in the pulveri.zer of Figure 1;
FIGURE 3 i5 a.side view of the assembled air flow rate control device;
FIGURE 4 is a front view of the device of Figure 3:
FIGURE 5 is a plan view of a portion of the rotating vane assembly of Figure 1;
FIGURE 6 is a perspective view of a portion of the rotating vane assembly of Figure 1 utilizing an alternate embodiment of the air flow rate control device of the present invention;
FIGURE 7 is a perspective view of the manual adjustment mechanism of the alternate embodiment of the inventicn as shcwn in Figure 6;:and;
FIGURE 8 is an end view of the manual adjustment 25~ mechani~sm of Figure 7.

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Referring firs-t to Figure 1, a howl mill type pulverizer 10 comprises grinding wheels 12, 14 and 16 operating to pulverize coal in a bowl 18. Surrounding the bowl 18 and rotatable therewith is a rotating vane assembly 20 which includes an essentially circular arrangement of uniformly spaced pitched steel vanes 22 through which air is caused to flow upwardly around the periphery of the grinding bowl 18 for the purpose of carrying Eines upwardly to a classification area. Vanes 22 are welded to a steel inner : ring 24 which is mounted for rotation around bowl 18.
Larger particles of ground coal pass downwardly through the vanes 22 into the lower section of the bowl mill 10. The overall construction and operation of a bowl mill type ~5 pulverizes is well-known and will be apparent to those skilled in the art.
In the embodiment of Figures 1, the pitched vanes 22 have major upper and lower plane surfaces 22a and 22b.
Surface 22a, if unprotected, i5 subject to rapid wear due to ~ ~ 20 the abrasive actian of coal particles falling downwardly : ~ through the vane arrangement 20 as afo~esaid. The lower plane surfaces 22b, although exposPd to upwardly traveling fines, do not experience significant abrasion and, : therefore, need not be~protected. To protect the upper surfaaes 22a,~various devices may: be used; for example, a layer of high;~ hardness, wear resistant material may be r7 ~ ~ ',. ' - ' ' ;' ' ' ' - -;, '~ " ' ' ' ~ , ' . ' ' ' ' ; ' 2 ~ 8 welded to a soft steel plate to form a composite. The liner arrangement disclosed in my prior U.S. Patent No. 4,907,751, the specification ~nd disclosure of which is incorporatedherein by reference, may also be employed. Alternatively, the vane plates may be hardened by heat treating or constructed entirely of high-hardness material.
In accordance with the present invention, air flow control devices 26 are adjustably mounted on the lower surfaces 22b oE the vanes 22 for the purpose of controlliny air flow velocity through the air passages defined by the vanes 22 as hereinaEter described.
Referring now to Figures 2 through 5, the vanes 22 are shown to comprise rectangular composite steel plates which are welded between inner and outer rings 20 and 28.
As represented by the structure of Figure 1, outer ring 28 is not essential, but is the preferred construction.
Smaller top plates 30 are welded to the vanes 22 at an angle to lie in a horizontal plane in the embodiment of Figure 1.
Each of the air flow control devices 26 comprises a deflector in the form of a (relatively light gage) spring steel shape 32 having a lower portion 32a, an intermediate planar portion 32b and a reversely bent top portion 32c which, when the shape 32 is properly installed on the lower surface of the vane 22 as hereinafter described, underlies the small top~plate 30 of the vane 22.
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207 1 ~68 As shown in Figures 2 and 3 a hinye plate or cup 34 is welded to the lower face of the vane 22 near the bottom to receive and hold the lowermost extremity 32a of the shape 32, the degree of overlap being on the order of one-to-two inches to permit a hinge action and a sliding relative motion for purposes hereinafter explained.
A tubular nut 36 having a threaded inner bore is welded to the shape 32 in the intermediate planar portion 32b so as to protrude throuyh the sh~pe 32 and lie with its longitudinal axis extending essentially horizontally in the installed condition. An Allen-head bolt 38 is threaded into the tubular nut 36 for purposes hereinafter described.
An unthreaded tube 40 having an internal diameter which is slightly larger than the outside diameter of the tube 36 is bevel cut and weldPd to the lower surface of the vane 22 adjacent the top thereby to receive in relative sliding engagement the tube nut 36 carrying the Allen-head bolt 38. A pocket 39 is cut into the lower face 22b of the vane 22 to receive and provide a stop for the base of the nut 38.
In the assembled condition shown in Figure 3, the bottom extremity 32a of the shape 32 fits into the hinge plate 34, the bolt 38 is threaded into the nut 36 and the nut 36 is disposed into the tube 40 such that the top ~portion 32~c;of~the shape 32 immediately underlies and bears lightly agalnst the lower~surface of the minor vane plate : : : ~ : ~, .. . . . . ..

2~7~8 30. The spring action of the steel shape 32 while engaged within the hinge plate 34 serves as a bias to urge the shape 32 toward the lower face of the vane 22 and adjus-tment of the rela-tive spacing between the shape 32 and the lower surfaces of vane 22 is determined by rotating the threaded bolt 38 in the nut 36. As will be apparent from an examination of the assembly of Figure 3 urging the bolt 3~
farther into the trapped tubula:r nut 36 displaces the shape 32 away from the lower surface of the vane 22. In the assembled environment of Figure 1, displacing the shape 32 away from the lower surface of the vane 22 reduces the area in the cross sec-tion. between vanes 22 and causes a corresponding increase in air flow velocity, assuming a constant air flow pressure head. Moreover, the shape 32 slides slightly upwardly in the hinge plate 34 to accommodate the essentially rectilinear motion which is produced by the particular orientation of the adjustor mechanism including tubes 36 and 40 and nut 38.
It Wl11 also be seen in Figure 3 that the shape o~
; 20 the air flow passage between vanes is essentially that of a : ~ venturi; 1.e.,~lt is only marginally reduced near the entry of the passage but then becomes gradually smaller as a : result of~the location of the shape 32 in the passage and the greater degree of spacing between the shape and the vane 22 which occurs~toward the top of the passage. Accordingly, air is permltted to~ accelerate gradually and relatively `

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uniformly toward the top of the air flow passags. As will be apparent to those skilled in the mechanical fabrication arts, the hinye 34 may be constructecl in a varie-ty of alternative ways and the adjustment mechanism provided in this case by the tubes 36 and 40 and the Allen-head bolt 38 may also be constructed and implemented in a variety of ways. For example, rotary hinges may be employed where the adjustmen-t mechanism is mounted essentially orthogonally to the vane, this arrangement calling for a variation in the shape of the top oE the shape 32 and a filler device beneath the plate 30 at the top of the vane. The shapes 26 may be made from a variety of materials Erom relatively light gage spring steel to harder, thicker steels and may also be plated, coated or heat treated for increased durability as desired. Many such alternatives, as well as accommodations to diEfering vane and vane wheel designs, will occur to those skilled in the mechanical arts.
Referring now to Figure 6, an alternate embodiment ; is shown in which air flow control devices 26 comprise flexible deflectors 44 adjustably mounted on the lower :~
surfaces~ of the vanes~22 for the purpose of controlling air flow~velocity through the air passages defined between the vanes. Deflectors 44 in the illustrated embodiment comprise rectangular sheets of flexible, light-gauge spring steel, ;2~5 although materials having suitable durability may be used.
Each of~ the deflectors 44 has a lower end 46 essentially :; : ~:: :

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, 2~7~ 8 coplanar with surface 22a, an intermediate portion 47 angled outwardly from the plane of lower end 46, and an upper end 48 essentially parallel to but spaced from lower end 46. Upper end 48 exhibits a folded portion 49 turned at approximately right angles to the planar surface of end 48. Top plate 30 o~
the vane 22 in the embodiment shown in Figure 6 includes a complementary flange 42 having an L-shaped cross-section to matingly receive the Polded portion 49.
Referring now to Figures 6 to 8, a manual adjustment mechanism for the lower end 46 of the deflectors comprises a box 50 fixed such as by welding to the lower surface of vane 22. Box 50 has a longitudinal guide slot 52 formed in the upper surface thereof to receive a short threaded shaft 66 welded to and projecting outwardly from the face of a nut 64 mounted on a threaded stud bolt 54 trapped at both ends 56,58 in rotatable fashion within the box 52. Lower end 58 o~ stud 54 projects beyond the interior of the mounting block 50 and has formed thereon an Allen--head~60 which accep-ts an Allen wrench 61 in a known manner to effect rotation of the stud.
~ The~ nut 64 threaded on stud 54is held against rotation by the dimensions of the slot 52. Accordingly, nut 64 is caused~ to travel axially therealong in response to rotation of the stud. Traveler nut 64 is shown in the illustrated embodiment as a~standard hexagonal nut with a threaded bore, but may take other forms. For example, the nut ::: : ~ :: ,~

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may be elonga-ted, or have a cross-section other -than hexagonal.
Lower end 46 of deflector 44 has formed therein a hole (no-t shown) aligned with and of a suitable size to admit stud 66. The lower end 46 of de~lec-tor 4~ is fastened to stud 66 and mounting block 40 by way o~ a washer 68 and lock nut 70 as best shown in Figure 8. Tigh-tening loclc nut 70 sandwiches lower end 46 between washer 68 and the surEace of mounting block 50 in a tight friction-f:it.
10In Figure 6, three deflectors 44a, 44b, and 44c mounted on respective vanes 22 are shown adjusted to difEerent positions corresponding to low, intermediate and high air flow velocity between the vanes as indicated by the arrows.
Altering the shape of the deflector 44 from the relaxed or unadjusted position indicated at 44a, in which the deflector is essentially Elat, to the flexed or curved configurations ~; shown at 44b and 44c is accomplished by forcing the lower end 46 toward the upper end 48 held in place by ~-shaped flange 42. The resulting forces exerted on deflector 44 serve to : ~ 20 flex the intermediate portion 47 outwardly into the air flow passage defined between the deflector and the top surface 22a :
of an adjacent~vane 22. It can be seen that this results in ; the shaping of the air flow passage into~a progressively more : well-defined venturi. As is well-known, the velocity of fluid : ~ :
flow exiting the narrow throat of the venturi increases in an inversely:proportional:~manner to its cross-sectional areaO

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2~)rl:~66~3 The closer the ends of deElector ~4 are brouyht toge-ther, the smaller the cross-sectional area of the air flow passage, resulting in increasing air flow velocity through the passaye as the deflec-tor progresses from the relaxed, low-velocity venturi conEiguration shown at 44a to the high-velocity venturi configuration shown in 44c.
To increase or decrease the distance be-tween ends 46 and 48 of deflector 44 k,etween the positions shown in 44a, 44b and 44c, lock nut 70 is first loosened enough to permit the lower end 46 oE the deflector to slide with stud 66 along the surface of mounting block 50. Allen wrench 61 is then inserted in Allen-head socket 60 of the threaded guide bolt 54 to rotate the bolt, causing traveler nut member 64 and stud 66 to be axially translated therealong within the guide slot 52.
Lower end 46 of deflector 44 fastened to stud 66 is thereby moved up or down in relation to the top plate 30 of vane 22 in order to increase or decrease the distance between ends 46 and : 48. When the desired configuration of deflector 44 has been reached, lock:nut 70 is tightened down to lock lower end 46 in place on mounting block 50 to prevent inadvertent movement : ; ~ during the operation of the vane assembly.
: It can be seen ln Figure 6 that as the lower end 46 of deflector 44 is translated toward upper end 48, causing the intermediate portion 47 of the deflector to flex outwardly :: :
25~ into the air flow passage, folded portion 49 on upper end 48 is moved slightly out o~ engagement with L-shaped ~lange 42 on : : :

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the undersurface oE-top plate 30 toward the lower surface 22b of vane 22. Friction and the compressive force on deflector 44 serve to hold upper end 48 in place as shown at 44b and 44c; L-shaped flange ~2 engages folded portion 49 when the deflector is relaxed as shown at 44a to prevent its dislocation from the undersurface of top pla-te 30. It will of course be understood by those skilled in the art that various methods of fastening upper end 48 of deflector 44 to vane 22 are possible.
10It will also be understood by those s]cilled in the art that the manual adjustment mechanism shown in Figures 6-8 comprising mounting block 50, threaded guide bolt 54, traveler nut 64 and stud 66 is an illustrative embodiment only, and that other embodiments which will be apparent to those skilled in the art may lie within the scope of the claimed invention.
Additionally, the shape oE deflectors 44 is not limited to : that shown in the illustrated embodiment, but may vary with the shape of the vanes 22 or the preferences of the manufacturer or operator, so long as they function essentially as described above.

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Claims (26)

1. In a pulverizer of the type which includes an essentially circular arrangement of pitched vanes forming air flow passages therebetween and having upper and lower plane surfaces:
air flow rate control means comprising deflector means mounted on the lower plane surfaces of at least some of said vanes.

2. Apparatus as defined in claim 1, wherein means are provided for varying the spacing of at least a portion of the deflector means from the lower surface of the vane.

3. Apparatus as defined in claim 2, wherein a portion of said deflector means is flexible and can be flexed outwardly into said air flow passage.

4. For use with a pulverizer of the type which includes a circular arrangement of pitched vanes forming air passages and having upper and lower exposed surfaces, apparatus for adjusting the air flow rate through said passages comprising:
deflector means mounted on the lower surfaces of respective vanes; and adjustment means associated with each of said deflector means for selectively varying the spacing of at least a portion thereof from the lower surface of the vane to adjust the cross-sectional area of the associated passage.

5. Apparatus as defined in claim 4, wherein a first end of the deflector means is connected to said lower surface, and the adjustment means comprises manual adjustment means for connecting a second end of the deflector means to the lower surface of the vane, said manual adjustment means being selectively operable to vary the spacing between said first end and said second ends of the deflector means.

6. Apparatus as defined in claim 4, wherein said first end of the deflector means is essentially fixed with respect to the vane, and said second end is adjustable toward and away from said first end.

7. Apparatus as defined in claim 4, wherein the deflector means is an at least partially flexible sheet approximating the width and height of the associated vane.

8. Apparatus as defined in claim 6, wherein the deflector means has an intermediate flexible portion between said first and second ends.

9. Apparatus as defined in claim 8, wherein said adjustment means is manually operable to extend said intermediate flexible portion into the air flow passage to define a venturi therebetween.

10. Apparatus as defined in claim 9, wherein said deflector means in a first, unadjusted position is essentially flat and in a second, adjusted position the intermediate portion curvingly extends into said air flow passage.

11. In combination: a pulverizer vane assembly including a rigid inner support ring and a plurality of pitched rigid vanes secured to and extending radially from said ring at circumferentially uniformly spaced intervals, each of said pitched vanes having parallel planar upper and lower surfaces and forming air passages therebetween; and position-adjustable means disposed on the lower surfaces of the pitched vanes for selectively varying the effective area of said air passages.

12. Apparatus as defined in claim 11, wherein said position-adjustable means comprises a plurality of deflector plates and means for adjustably mounting individual deflector plates on respective lower vane surfaces, said adjustment means being operable to vary the shape of the deflector.

13. Apparatus as defined in claim 12, wherein said adjustment means comprises guide means mounted on said lower :': :

surface, traveler means for axial travel along said guide means, and connector means for connecting one end of the deflector means to said traveler means.

14. Apparatus as defined in claim 13, wherein said guide means comprises a threaded member manually rotatable within a mounting block to cause said traveler means to travel axially therealong.

15. In a rotating vane assembly for a pulverizer, the vane assembly comprising a circular arrangement of pitched vanes fixed to the vane assembly to define air passages therebetween, the vanes having upper and lower surfaces, apparatus for adjusting the air flow rate through said passages comprising:
at least partially flexible deflector means mounted on the lower surfaces of at least some of said vanes;
adjustment means associated with each of said deflector means for selectively varying the spacing of at least a portion of said deflector means from said lower surface to adjust the cross-sectional area of at least a portion of the associated passage.

16. Apparatus as defined in claim 15, wherein the deflector means in a first, unadjusted position defines the associated passage as a low veloclty venturi and in a second, adjusted position defines the associated passage as a higher velocity venturi.

17. Apparatus as defined in claim 16, wherein the deflector means comprises a sheet of at least partially flexible material of approximately the dimensions of the lower surface of the vane, the deflector essentially flat in said first, unadjusted position, the deflector having a curved portion extending into said air flow passage in said second position.

18. Apparatus as defined in claim 17, wherein said deflector means comprise a sheet of spring steel.

19. Apparatus as defined in claim 17, wherein said adjustment means is mounted on said lower surface of the vane.

20. Apparatus as defined in claim 19, wherein one end of said deflector means is essentially fixed to said lower surface, and an opposite end of said deflector means is attached to said adjustment means so as to be movable by said adjustment means toward and away from said fixed end.

21. In a vane assembly for a pulverizer, the vane assembly comprising a circular arrangement of pitched vanes fixed to the vane assembly to define air passages .20 therebetween, the vanes having upper and lower surfaces, apparatus for adjusting the air flow rate through said passages comprising:
at least partially flexible deflector means mounted on the lower surfaces of respective vanes;
manual adjustment means associated with each of said deflector means on said vanes for selectively adjusting the shape of said deflector means between a first essentially flat configuration and a second curved configuration.

22. Apparatus as defined in claim 21, wherein the deflector means in said curved configuration extends into and reduces the cross-sectional area of the associated air passage to increase air flow velocity.

23. In a vane assembly for a pulverizer, the vane assembly comprising a circular arrangement of pitched vanes fixed to the vane assembly to define air flow passages therebetween, the vanes having upper and lower surfaces, apparatus for adjusting the air flow rate through said air passages comprising:
deflector means mounted on the lower surfaces of at least some of the vanes, said deflector means comprising at least partially flexible sheets having a height and width approximately equal to that of the lower surface of said vanes, said deflector means fastened at a first end to an upper end of the lower surface of said vanes, a second end of said deflector means connected to manual adjustment means fastened to a lower end of said lower surface of the vane;
said adjustment means manually operable to move said second end of said deflector means toward and away from said fixed end to flex at least a portion of said deflector means between a first, essentially flat configuration corresponding to a maximum distance between said ends of the deflector means, and a second curved configuration corresponding to a lesser distance between said ends, so as to extend a portion of the deflector means into the air passage associated therewith to decrease the cross-sectional area along a portion thereof in the manner of a venturi.

24. Apparatus as defined in claim 23, wherein said manual adjustment means comprises guide means mounted on the lower surface of the vane, traveler means on said guide means for axial travel therealong, and connector means for connecting said traveler means to said deflector means.

25. Apparatus as defined in claim 23, wherein said deflector means in said first, essentially that configuration defines said air passage as a low velocity venturi, and in said second curved configuration defines said air passage as a higher velocity venturi.

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26. In a pulverizer of the type which includes an essentially circular arrangement of pitched vanes forming air flow passages therebetween and having upper and lower plane surfaces:
air flow rate control means comprising deflector means mounted on the lower plane surfaces of at least some of said vanes, said deflector means comprising upper and lower planar end portions fastened to the lower plane, surfaces of the vanes, said planar end portions connected by a flexible intermediate portion:
adjustment means on said lower plane surface of each vane, connected to said lower planar end portion of the deflector means to selectively move said lower planar end portion toward and away from said upper planar end portion, said intermediate portion of the deflector means having an essentially planar configuration in a first, unadjusted position corresponding to a maximum distance between said upper and lower planar ends, and a curved configuration extending into the associated air flow passage in a second, adjusted position corresponding to a lesser distance between said upper and lower planar ends.

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