US3704011A

US3704011A - Discharge mechanism for shaft kiln

Info

Publication number: US3704011A
Application number: US171175A
Authority: US
Inventors: John W Hand; Don L Lockwood; Robert K Harris
Original assignee: Mintech Corp
Current assignee: Mintech Corp
Priority date: 1971-08-12
Filing date: 1971-08-12
Publication date: 1972-11-28
Anticipated expiration: 1989-11-28
Also published as: CA963654A

Abstract

A positive displacement volumetric discharge mechanism of the screw auger conveyor type. A series of radially disposed conical screw type augers and underlying retarder plates substantially close the lower end of an annular chamber of a vertical shaft kiln. The augers are rotated to convey solid materials from a bed of such materials in the kiln chamber radially outwardly to an annular discharge throat. The conical augers are formed so that the volume of material conveyed increases with the radial distance from the center of the kiln in order to maintain a constant and uniform downward flow of solid materials throughout out the cross section of the kiln.

Description

United States Patent Hand et al.

both of Denver; Robert K. Harris, Littleton, all of C010.

[73] Assignee: Mintech Corporation, Denver, C010. [22] Filed: Aug. 12, 1971 [21] Appl. No.: 171,175

[52] US. Cl ..263/29, 214/18 V, 266/25 [51] Int. Cl ..F27b l/20 [58] Field of Search ..263/29; 266/25; 214/18 V [56] References Cited UNITED STATES PATENTS 2,021,991 11/1935 Depew ..214/1sv 3,373,982 3/1968 Jones,Jr ..263/29 NOV. 28, 1972 Primary ExaminerJohn J. Camby Attorney-Ralph F. Crandell [5.7] ABSTRACT A positive displacement volumetric discharge mechanism of the screw auger conveyor type. A series of radially disposed conical screw type angers and underlying retarder plates substantially close the lower end of an annular chamber of a vertical shaft kiln. The augers are rotated to convey solid materials from a bed of such materials in the kiln chamber radially outwardly to an annular discharge throat. The conical augers are formed so that the volume of material conveyed increases with the radial distance from the center of the kiln in order to maintain a constant and uniform downward flow'of solid materials throughout out the cross section of the kiln.

10 Claims, 7 Drawing Figures 7 PATENIEDHUVZB I972 3.704;O1 l

SHEET 1 OF 4 PATENTEDnnvzelsrz 3 7 04 011 sums or 4 DISCHARGE MECHANISM FOR SHAFT KILN BACKGROUND OF THE INVENTION The field of the invention is that of discharge mechanisms for vertical circular shaft kilns. More particularly, the invention relates to a discharge mechanism finding particular, but not necessarily exclusive, use in connection with large diameter vertical shaft kilns of the type adapted for conducting reactions in which the solid reactants have bridging or clinkering tendencies.

Kilns and furnaces adapted to accommodate a continuous gravity-induced flow of discreet or particulate solid. materials in exposure to fluids, either gas or liquid, for purposes of carrying out a reaction between the solids and the fluid, have long been known and utilized for the processing and treatment of many substances. Appropriately styled shaft kilns, such units are extensively employed in many industrial applications. In some applications thermal reactions are promoted by means of hot gases which flow upwardly in reaction contact with solid materials contained y within the kiln. In such processes the efficacy of the reaction is, in large measure, determined by the uniformity of solids movement through all zones of the kiln, and the uniformity of the gas flow permeating the bed of solids. The shaft kiln or furnace includes as a significant factor a mechanism for controlling uniformly the discharge of solids from the kiln in order to effect a uniform flow rate for all solids moving through the unit.

While some solid materials are relatively free flowing, both before and after reaction, others, particularly under reaction conditions, tend to compact or agglomerate into clinker-like bodies, and a bed of such materials can be made to move downwardly through the kiln only with difficulty. The agglomerating effects become particularly severe adjacent the discharge mechanism. At this point, the agglomerated materials frequently form clinkers or bridges across the discharge mechanism openings thereby effectively closing these openings and preventing further flow of material through the kiln. The operation must then be stopped, the clinkers or bridges removed, and the operation allowed to proceed.

One form of discharge grate is shown in U.S. Pat. No. 3,027,147, issued Mar. 27, 1962 to Lewis H. Brake] and John B. Jones, .lr., for Circular Shaft Kiln Discharge Grate. This patent discloses a circular shaft kiln discharge grate embodying circular or annular pusher members adapted for orbital movement between concentric deflector members and subjacent retarder plates. The retarder plates define annular throats underlying the deflector members, while the concentric deflector members define annular throats overlying each of the retarder plates. The pusher members are positioned between the deflector members and the retarder plates to push material, through the grate mechanism.

A related structure is disclosed in U.S. Pat. No. 3,554,509, issued Jan. 12, 1971 to Craig C. Waddle and Robert K. Harris for Discharge Grate For Circular Shaft Kiln." This patent discloses a discharge grate for a circular shaft kiln, which grate includes a concentric plurality of coplanar annular retarder plates defining concentric annular throats. A plurality of radially extending pusher rods each mounts a series of annular sector-shaped pusher plates which, when positioned over the annular throats, retard the flow of solids through the grate, and which, upon reciprocation of the rods, move to open the throats and push material off the edges of the retarder plates. At the same time, the

pusher rods and plates serve to break up any clinkers or agglomerated materials which would tend to bridge across the annular openings and impede material flow through the kiln.

A conventional cylinder type grate mechanism is shown in U.S. Pat. No. 3,101,935, issued Aug. 27,-1963 to Erich Zeltner for Method and Kiln For Burning Cement, Lime, Dolomite and the Like. The grate mechanism comprises rotating cylinders formed with a plurality of radially extending fingers on a grate shaft. The cylinders are rotated to cause the fingers to break up agglomerates of material formed in the kiln. Free flowing materials, however, would fall through the grate without control. 7

Among the problems present in prior art constructions are, as mentioned above, the discharging from a vertical shaft kiln of materials which tend to agglomerate or clinker during reaction and tend to bridge across grate discharge mechanism openings. Many of the discharge grate mechanisms known in the prior art are complex structures with attendant maintenance problems. Many require sliding seals which make the mechanisms impractical for-use with high temperature and high pressure reaction systems. It is also desirable that the discharge mechanism provide for a uniform downward flow of material through the kiln without causing channeling or cavitation resulting from uneven flow of materials at certain sections or areas of the kiln.

OBJECTS OF THE PRESENT INVENTION The principal object of the present invention is to provide an improved positive displacement volumetric discharge mechanism for a vertical shaft kiln. More particularly, it is an object to provide an improved mechanism which effectively operates with both particulate free flowing materials and materials which, during the kiln reaction, agglomerate to form clinkers or flow-restricting agglomerates.

Another object of the invention is to provide a grate mechanism of the foregoing character which will afford uniform discharge of solids from the kiln without causing channeling or cavitation, and thereby maintain a uniform reaction bed height within the kiln.

- A further object of the present invention is to provide a discharge mechanism of the foregoing character which will operate over a wide range of temperature and pressure conditions.

A more specific object of the invention is to provide a discharge mechanism for vertical shaft kilns which produces a positive volumetric displacement without regard to bridging or agglomeration of kiln bed materials, and which further provides a relatively constant uniform controllable flow rate through the shaft kiln.

Still a further object of the present invention is to provide a discharge grate mechanism which requires a minimum of maintenance, is rugged and long wearing under adverse conditions, is simple to design and operate and is highly effective without regard to the character, particle size or physical characteristic of the material contained within the kiln. v

Other objects and advantages of the present invention will become apparent from the following description of the invention.

SUMMARY OF THE INVENTION generally annular kiln chamber defined by the outer refractory lined walls of the kiln and an inner refractory lined column. Particulate solid materials are introduced at the top of the kiln and the discharge mechanism is provided for controllably discharging materials from the bottom of the kiln. The discharge mechanism structure embodies essentially a plurality of conical screw augers disposed radially in a generally horizontal plane and substantially closing the bottom of the annular kiln chamber. The augers are positioned with their apex or inboard ends rotatably journaled on the center column and their base or outboard ends journaled on the kiln wall. The kiln refractory liner is undercut and overlies the outboard ends of the conical augers. A retarder plate structure is positioned beneath the conical augers to close the annular kiln chamber, but defines with the outer kiln shell an annular throat through which solid materials may be discharged by the conical augers. The augers each are provided with a spiral rib, and the pitch and spacing of the ribs are such I as to accommodate the total quantity of material to be discharged from a point adjacent the inner column. In this manner a uniform volumetric flow of material is obtained and the general level of solid material in the kiln is maintained at a uniform level. The augers may be constructed with helical ribs the pitch of which increases from the inboard to the outboard end, or alternatively, the height of which increases from the inboard to the outboard end of the auger while the pitch remains constant, or a combination of both. Power means are provided for continuously, controllably and uniformly rotating the augers in order to discharge material from the shaft kiln at a selected controlled rate.

DESCRIPTION OF THE DRAWINGS I FIG. 1 is a half-transverse section through a transversely circular shaft kiln showing in top plan one illustrative mechanism embodying the present invention.

FIG. 2 is a section axially through the arrangement shown in FIG. 1 with certain non-essential parts omitted for purposes of clarity.

FIG. 3 is a fragmentary detail section, on a relatively enlarged scale, taken substantially in the plane of line 33 on FIG. 1.

FIG. 4 is a fragmentary view, partially reduced in scale, taken in the plane of line 44 on FIG. 3.

FIG. 5 is a section view taken substantially in the plane of line 5-5 on FIG. 3.

FIG. 6 is a section view, partially reduced in scale, taken substantially in the plane of line 6-6 on FIG. 3.

FIG. 7 is a diagrammatic representation of a screw auger of the type shown in FIG. 3 for purposes of illustrating the proportional configuration thereof.

The discharge mechanism shown in the drawings exemplifies the present invention and finds particular but not necessarily exclusive use in association with transversely circular shaft kilns or furnaces of moderate to large diameter for handling materials which tend to compact, agglomerate or bridge during the kiln reaction. The kiln structure comprises generally an axially vertical tubular shell 20 of appropriate rigid material and of any expedient construction. The kiln construction depends primarily upon the reaction to be carried out and the prevailing kiln conditions-The kiln shell 20 is generally provided with an appropriate refractory inner liner 21 which may be formed in one or more layers of any suitable refractory material. In the kiln construction embodying the present invention, the kiln is provided with an inner central column 22 which may be provided with an outer refractory layer 23. The reaction chamber 24 defined by the respective

refractory layers

21, 23 is generally annular in cross section and of a height appropriate to the particular kiln design. Solid particulate reaction materials are fed into the kiln at the top by an appropriate feeding mechanism (not shown) to form a reaction bed, and are discharged from the bottom of the kiln assembly through an appropriate hopper and bulk discharge assembly (not shown). The kiln is supported by a superstructure (not shown) and suitable conveyor, power and related adjunct equipment is provided as is conventional in the art.

For purposes of providing a positive volumetric control for regulating the flow of solid reaction materials through the kilnthe present invention contemplates a novel and unobvious discharge mechanism indicated generally by the numeral 30. This mechanism'is constructed not only to provide for a controlled downward flow of solid reaction materials through the kiln, but

also to facilitate the upward flow of fluid reaction materials through the moving bed of solids maintained in the kiln by the discharge mechanism 30. Referring to FIG. 2, the interior refractory liner 21 on the kiln shell 20 terminates, at its lower end at a point closely adjacent but spaced above the discharge mechanism 30, and defines an interior overhang or shoulder 25. The shoulder is closely juxtaposed above the discharge end of the discharge mechanism 30 thereby to prevent the free flow of solid materials through the discharge mechanism. The amount of overhang required depends primarily upon the angle of repose of the material being treated in the kiln. The angle of repose of a given material is the angle from the horizontal of the slope or side of an imaginary pile on which the material will not rest but will slide off of the pile. It will be appreciated that some materials will have a very low angle of repose and will flow readily, while other materials will have a high angle of repose approaching or exceeding Where the materials have a high angle of repose, there may be a tendency of such materials to bridge, that is, such materials may not be free flowing but will require positive conveying in order to be discharged through the kiln grate mechanism.

In the mechanism of the present invention, the grate I mechanism 30 includes a plurality of conically shaped screw conveyors or augers 31 radially disposed in coplaner relationship over the kiln cross sectional area. Underlying the conical augers 31 is a retarder plate structure 32 which positively. prevents the gravity flow of solid materials through the kiln. Appropriate power drive means and controls 33 are provided for driving the conical conveyors to positively and volumetrically discharge material over the outer peripheral edge of the retarder plate structure 32. Various structural supports including bearings, retarder plate supports, driving mechanism supports and the like are provided in connection with and as a part of the discharge mechanism.

The screw conveyors or augers 31 form an essential part of the discharge mechanism and are horizontally disposed with the axis of rotation extending radially between the center column 22 and the outer shell 20 in such a manner,-as shown in FIG. 1, as to substantially enclose the bottom end of the kiln and prevent the free or gravity flow of solid materials therethrough. An illustrative conical conveyor or auger 31 is shown in detail in FIG. 3. Referring more particularly to FIGS. 3, 4, 5, and 6, each conical auger 31 is formed by a generally conical shell 35 mounted on a shaft 36. The shaft 36 is journaled at the end thereof adjacent the apex or inboard end of the conical shell 35, in a bearing structure 38 mounted on the interior surface of the central column 22 of the kiln structure. For this purpose the end of the shaft 36 is reduced in diameter as at 39 and extends through the wall of the kiln column 22 into the bearing structure 38. The bearing structure comprises a bearing member or housing 40 mounted by a suitable bracket 41 on the kiln column 22. The refractory liner 23 on the column is provided with an appropriate aperture 42 through which the shaft extends.

At its opposite end, that is the end adjacent the large or outboard end or base of the shell 35, the shaft 36 is journaled in a bearing member 44 mounted by a suitable mounting support 45 on the exterior wall of the kiln shell 20. Where the kiln reaction may include high temperature or high pressure reactions, a rotary seal 46 is provided between the shaft 36 and the kiln shell 20. The shaft is rotated by an appropriate driving mechanism indicated generally at 48 (FIG. 4) which will be described in more detail below,

The conical augers 31 are positioned in the kiln with their narrow or apex ends adjacent the interior column 22 and their outer large or base ends underlying the lower end or shoulder 25 formed by the refractory liner 21. If desired, the refractory liner 21 may be shaped with semi-circular recesses 49 defining the shoulder 25 and closely surrounding the large or base end of the conical auger 31 as shown in FIG. 6. Alternatively, the interior refractory lining 21 may terminate just above the large ends of the conical auger structure as shown in FIG. 2. As can be seen from FIG. 1, the conical augers 31 are arranged to substantially close the lower end of the kiln.

The retarder plate structure 32 underlies the conical augers as well as the lower end of the refractory liner 21 but terminates short of the kiln shell 20 to form an annular discharge throat 52 adjacent the large ends of the conicalaugers 31 and the kiln shell 20, through which throat 52 solid material may be discharged by the conveying action of the conical augers 31. The

discharged material is collected in an appropriate hopper or chute mechanism (not shown) and conveyed out of the kiln system.

The retarder plate structure 32 is formed by a plu-' rality of retarder plate segments 54 which are either integrally or mechanically united and corresponding in number respectively to the number of auger units 31. Eachretarder plate segment 54 is conically dished or shaped to provide a concave conical channel which fits around or conforms generally to the adjacent conical auger and is mounted in close juxtaposition therewith as shown in FIG. 5. Each retarder plate segment 54 is braced by a plurality of supporting

ribs

55, 56, 57

which strengthen the channel plate segment 54 and prevents warping or distortion during high temperature reactions. The respective segments 54 are joined to adjacent like segments at their upper edges to provide joints 58 as illustrated in FIG. 6. In this manner, the retarder plate segments or sections 54 form a unitary, generally annular, dished or scalloped retarder plate structure 32. I

I The retarder plate segments 54 are mounted in the kiln by suitable mounting structures. To this end, the segments are provided with mounting flanges 59 at their inner end (FIG. 3), which flanges are secured to mounting brackets 60 secured to the interior kiln column 22. At their outer edges, the retarder plate segments 54 are provided with depending flange portions 61 which are secured to brackets 62 mounted on the kiln shell wall 20. Any suitable provision may be made on the retarder plate segments 54 to provide for the discharge throat 52.

For purposes of providing a uniform reaction within the kiln, preventing channeling and insuring an even, uniform downward flow of material throughout the kiln cross section, it is desirable that the discharge or grate mechanism discharge the solids material uniformly, positively and volumetrically with respect to the overall cross section of the kiln. In order to prevent cavitation, the solids material adjacent the central column 22 must be discharged at the same rate as the solids material adjacent the interior surface of the outer refractory liner 21. Expressed another way, the draw-down in the kiln must occur uniformly over the entire annular cross section. Each particle of material in the bed should travel downwardly at the same rate of speed as any other particle anywhere in the kiln at the same elevation. For this purpose, the screw augers 31 transport the material being-discharged from the innermost perimeter of the annular cross section of the kiln to the outermost perimeter and thence through the discharge throat 52. Thus, it is required that the conveying capacity of each screw auger 31 increase at a greater rate from the inboard end to the outboard end than would be the case if the pitch and depth of the screw flighting on the conical axis remained constant.

For conveying purposes, the screw augers 31 are provided with a spiral screw flight indicated at 65 over the extent of its length. In the embodiment shown, the screw flights are hollow to provide for the conducting of coolant therethrough, as will be described hereinafter. The surface of the conveyor is insulated by a refractory layer 66 adjacent and intermediate the screw flights 65.

' sured progressively from the inboard end, that is the small diameter end, to the outboard, that is the large diameter end or base. Both p and d may of course be increased simultaneously to accomplish the desired result. On FIG. 7., subscripts are utilized to indicate and distinguish increasing quantities progressively further from the inboard or small end of the auger (i.e.-, the right-hand end as shown in FIG. 7). I

The relationship wherein the pitch (p) is progressively increased may be expressed mathematically as follows:

Equation 1: D =D 2L tan Equation 2:

v L +D) 21r RDd(Dd) Where: g

D diameter of the screw at its origin or inboard end;

D'= diameter of the screw at any point L distance from the origin (shown in FIG. 7 as D,, D D etc.

a distance L,, L L etc. respectively from the origin) 6 angle subtended by one side of the screw and the center line of rotation;

4) angle subtended by the screw flighting and a plane normal to the axis of rotation (tan qb multiplied by thecircumference, being the pitch (p) of the flighting for one revolution);

v velocity of the bed of material traveling vertically downward in the vessel above the screw, in distance per unit of time;

R rotational speed of the screw in revolutions per unit of time;

d depth of the screw flighting;

L distance from origin along centerline of screw;

Q transport capacity of the screw in quantity per unitof time (volume of material capable of being rotation, the relationship between the inboard and outboard diameters is expressed as set forth in Equation 1 above. This relationship can be readily observed from FIG. 7.

The projected area (A) of the screw auger, looking downwardly from the top of the column, may be computed according to the following equation, (which is derived from the equation for determining the area of a trapezoid):

The volume of solidmaterial capable of being transported (Q) at any point P, which is a distance L from the origin or apex of the auger, the distance L being essentially-the distance from the inner column 22 to the outer or outboard edge of theauger 31, may be computed according to the following'equation, which expresses the total volume of material capable of being transported during a given number of revolutions (R) per unit of time of each auger:

The volume of material (Q) to be transported by an auger must equal the volume of solid material (V) moving down through the portion of the column directly above the given screw auger in a unit of time. This volume of transported material (V) is computed as follows:

The total transport capacity (Q) must equal the total transported material (V) at any given point P. There- Rearranging this equation in terms of the variable tan Lv(D+D 2R1rm'd 1J'-d This is thus the derivation'of Equation 2 expressed above. By computing the tangent of the angle 4) from the above'equation, the pitch of the auger flight at any point P along the auger can be readily determined by multiplying the tangent of the angle (b by the circumference D of the auger at any given point. In this manner, the auger configuration can be readily determined. A similar, although somewhat more mathematically complex, formula may be derived fro increasing the height (d), and thus the conveying capacity, of the spiral auger flight from the inboard orsmall end of the convey the sameto the discharge throat 52. The weight of the column on the material adjacent to the augers 31 will force any agglomerated material into the auger mechanism and the latter will effectively break up any clumps or agglomerates which may have formed during I the kiln reaction.

The augers are rotatably driven by a suitable driving mechanism 48. In theillustrative mechanism shown in the drawings, there is provided a ratchet wheel secured to the shaft 36 and defining a plurality of equally spaced teeth 71. Hydraulically driven dogs or cams 72 engage the ratchet teeth 71 and rotate the ratchet wheel, and thereby the shaft 36, at the desired rate. The use of two such hydraulically driven dogs, the hydraulic motors 74 for which are secured to the kiln structure by appropriate brackets 75, provide a relatively continuous rotary operation. The use of one such driving dog mechanism will produce a somewhat more intermittent rotation. With the use of two driving mechanisms, however, one can be driving the ratchet wheel 70 while the other is retracting into position for a subsequent driving operation. Alternatively, electrically driven or hydraulically driven motors and suitable reducing transmissions may be utilized. It should be appreciated, of course, that relatively high torques will be involved, particularly when the material in the kiln tends to agglomerate and compact. Thus it is desirable to provide relatively simple yet powerful motors for rotating the respective augers.

In the present construction each individual auger 31 is rotated individually by 'its own associated driving ratchet mechanism 48. This enables the kiln operator to make adjustments to the rate of rotation of each auger 31 depending upon the flow of material through the kiln. Once the mechanism has been set, little attention is required except where one screw auger becomes jammed or inoperative, in which case its particular driving motor may be shut down. It has been observed that one or more such augers may be shut down without adversely affecting the flow of materials through the kiln.

The spiral screw flights 65 may either be solid, or as mentioned above, may be hollow to provide for the circulation of coolant therethrough. The latter construction is utilized for kiln configurations in which high temperature reactions are to be conducted. For such purposes, provision is made for circulating a coolant through the entire auger structure. To this end, the auger shaft 36 is hollow providing an internal passage 80 and there is positioned axially within said passagea coolant inlet conduit 81. The conduit 81 communicates with an external coolant supply conduit 82 while the internal passage 80 of the shaft serves as the outlet passage and communicates through a rotary seal structure 83 with an outlet conduit 84. The inlet conduit 81 extends axially through the shaft 36 into close proximity with the bearing supporting end 39 thereof so that coolant which flows through the conduit 81 is directed into the bearing end of the shaft to cool the same. The inlet conduit 81 is supported within the shaft 36 by a bulkhead 85 which also serves as a barrier preventing the direct flow of coolant from the inlet conduit 81 into the outlet passage 80. The barrier 85 thus defines an interior end chamber 86 within the hollow shaft 36.

Coolant flows from the end chamber 86 outwardly from the shaft through appropriate apertures 88 in the wall thereof into a chamber 89 defined at the inboard or apex end of the auger shell 35. From this chamber 89 the coolant flows through an aperture 90 into the hollow spiral screw auger flights 65. The flights 65 define a chamber 91 through which the coolant flows, and as can be seen from FIG. 3, the coolant flows from the inboard or apex to the outboard or base end of the shell 35. At some point in the last flight there is provided an outlet aperture 92 which permits the coolant to flow out of the spiral flights 65 into the interior chamber 94 defined by the screw shell 35. From the interior chamber 94 the coolant flows through passages 95 in the hollow shaft 36 into the exhaust chamber and thence through the seal 83 to the outlet conduit 84.

With the foregoing construction, coolant can be circulated from the inlet conduit 82 through the shaft 36, the spiral flights 65, into the interior of the auger shell 35, and thence out through the hollow shaft to the outlet conduit 84, thereby providing a thorough and extensive coolant circulation system. Both the inboard and outboard bearings 38 and 44, respectively, are cooled by the flow of the coolant.

Suitable provision may be made for the introduction of reaction fluids to the kiln. For this purpose the retarder plates'54 underlying each screw auger 31 may be perforated, slotted or otherwise vented to provide channels for the introduction of reaction fluids. When the kiln is constructed for use with hot materials, the retarder plates are also appropriately refractory lined or supplied with coolant. v

The dischargemechanism described herein provides a positive volumetric discharge of the solid material moving downwardly through the kiln. Any tendency of the reaction materials to clinker or bridge is prevented by the continual grinding action of the screw auger conveyors. The unit thus described is capable of providing continuous downward flow of solid materials 1 at a rate dependent upon the rate of rotation of each auger. As pointed out above, even if one or more augers are completely stopped, the remaining augers have been observed to provide sufficient conveying capacity to prevent channeling, cavitation and otherwise irregular flow through the kiln.

While a certain illustrative discharge mechanism structure has been shown in the drawings, and described above in considerable detail, it should be understood that there is no intention to limit the invention to the specific form and structure disclosed. On the contrary, the intention is to cover all modifications, alternative constructions, equivalents and uses falling within the spirit and scope of the invention as expressed in the appended claims.

We claim as our invention:

1. A positive displacement volumetric discharge mechanism for the controlled discharge of solid materials from a vertical circular shaft kiln defining a kiln chamber which is generally annular in cross section, said mechanism comprising a plurality of cone-shaped augers radially disposed within said kiln and substantially closing the lower end of said annular chamber, a retarder plate underlying said augers and having an outer peripheral edge defining an annular discharge throat adjacent the outboard ends of said augers,

means for rotating said augers, a spiral rib on each of said augers defining an auger channel the volume of which increases, from the inboard end of said auger radially outwardly to the outward end of said auger adjacent said discharge throat, in direct proportion to the cumulative sum of solid material conveyed thereby from the center of the kiln to the discharge throat so that a uniform material level of solid material is maintained within said kiln as solid material is discharged therefrom through said throat.

2. A positive displacement volumetric discharge mechanism as defined in claim 1 wherein said spiral rib defining the auger channel is of uniform height and of progressively increasing pitch from the inboard end of said auger to the outboard end thereof, thereby defining an auger channel of volumetrically increasing capacity.

3. A positive displacement volumetric discharge mechanism as defined in claim 1 wherein said spiral rib is of constant pitch and the height of said rib progressively increases from the inboard end of said auger to the outboard end thereof thereby defining a solid material conveying auger channel of progressively increasing volume.

4. A positive displacement volumetric discharge mechanism as defined in claim 1 wherein said spiral rib defining the auger channel is of progressively increassaid augers independently of each other, a spiral rib on each of said augers for moving material contained ing height and progressively'increasing pitch from the inboard end of said auger to the outboard end thereof thereby defining an auger channel of volumetrically increasing capacity.

5. A positive displacement volumetric discharge mechanism for the controlled discharge of solid materials from a vertical circular shaft kiln, said kiln having a shell defining an inner material confining wall spacedly surrounding a central bearing column having an outer material confining wall, said inner and outer walls defining a kiln chamber which is generally annular in cross section, a plurality of cone-shaped augers radially disposed within said kiln and substantially closing the lower end of the annular chamber thereof, a retarder plate underlying said augers and defining with the outer kiln wall an annular discharge throat, said outer kiln wall overhanging said annular throat and the outboard end of said cone-shaped augers, means for rotating said augers, a spiral rib on each of said augers defining with said retarder plate a solid material conveying channel from the inboard end of said auger radially outwardly to the outboard end of said auger adjacent said discharge throat, with said solid material conveying auger channel having a volume which increases progressively from the inboard end of said auger to the outboard end thereof in direct proportion to the cumulative sum of solid material conveyed thereby from the center of the kiln to the discharge throat so that a uniform material level of solid material is maintained within said kiln as solid material is discharged therefrom through said throat.

6. A positive displacement volumetric discharge mechanism for controllably discharging material from a vertical circular shaft kiln having an outer shell with an undercut inner refractory liner thereon and a central support post axially vertical within said kiln thereby defining a generally annular kiln chamber, a plurality of conical augers radially disposed in the lower end of the kiln and each of said augers having an inboard end supported on the central post and an outboard end supported in the kiln shell, said augers substantially closing the lower end of said annular chamber, each of said augers having its outboard end extending radially outwardly below the undercut refractory liner, an annular retarder plate spacedly underlying said augers and having an outer peripheral edge adjacent said kiln shell and defining therewith an annular throat underlying said undercut refractory wall, means for rotating each of auger channel from the inboard end of said auger radially outwardly to the outboard end of said auger adjacent said'discharge throat, with said solid material conveying auger channel having a volume which increases progressively from the inboard end of said auger to the outboard end thereof in direct proportion to the cumulative sum of solid material conveyed by the auger from the center of the kiln to the discharge throat so that a uniform material level of solid material is maintained within said kiln as solid material is discharged therefrom through said throat.

7. A positive displacement volumetric discharge mechanism for controllably discharging'material from a vertical circular shaft kiln having an outer shell with an undercut inner refractory liner thereon and a central support post axially vertical within said kiln thereby defining a generally annular kiln chamber, a plurality of conical augers radially disposed in the lower end of the kiln and substantially closing the lower end of saidchamber, each of said augers having the large outboard end thereof extending radially outwardly below the undercut refractory liner, an annular retarder plate spacedly underlying said augers and having an outer peripheral edge adjacent the kiln shell and defining therewith an annular throat underlying said undercut refractory wall, an axial trunnion shaft on each end of each conical auger, bearing means on said central support post for supporting the trunnion shaft at the inboard end of each said auger, bearing means on said kiln shell wall supporting the trunnion shaft at the outboard end of each said auger, the shaft at the outboard end of each said auger extending outwardly through the kiln shell wall, driving means external of the kiln and operatively engaged with each said extending shaft end for rotating each said auger, said spiral rib defining with said retarder plate a solid material conveying auger channel from the inboard end of said auger radially outwardly to the outboard end of said auger adjacent said discharge throat, with said solid material conveying auger channel having a volume which increases progressively from the inboard end of said auger to the outboard end thereof in direct proportion to the cumulative sum of solid material conveyed by the auger from the center of the kiln to the discharge throat so that a uniform material level of solid material is maintained within said kiln as solid material is discharged therefrom through said throat.

8. A positive displacement volumetric discharge mechanism as defined in claim 7 wherein said auger is defined by a hollow conical shell closed at each end by an inboard base member and an outboard base member respectively, said rib is formed by a channel cooperating with the auger shell to define an interior spiral rib conduit, and said auger is supported by a hollow shaft which extends through said inboard and outboard base plates to define said trunnion shaft portions, the inboard end of said shaft being closed, a conduit extend ing axially through said hollow shaft and terminating in an open end closely adjacent the inboardv end of said shaft, an interior bulkhead within said auger shell adjacent the inboard end thereof and defining an interior chamber therewith, an interior bulkhead within auger shaft adjacent the inboard end thereof and defining an interior chamber therewith, means defining apassage through said inboard end of said auger shaft communicating between said interior chambers, means defining a passage between said interior auger chamber and said rib chamber adjacent the inboard end of said auger rib, and means defining a passage through said shaft communicating between the outboard end of said auger chamber and said hollow shaft, means exterior of said kiln for supplying a coolant to said shaft conduit, and means for exhausting coolant from said hollow shaft whereby coolant can be circulated through said shaft conduit into said inboard chambers and thence through said hollow ribs to said auger chamber and exhausted from said auger chamber through said hollow shaft so that the said auger and rib structure can be cooled during high temperature operations of said kiln.

9. A positive displacement volumetric discharge mechanism as defined in claim 7 wherein said annular retarder plate comprises a plurality of segments, each segment being conically concave and adapted to partially surround an adjacent superposed conical auger, and means on said segments for attaching said segments together to define an annular retarder plate structure and for mounting said structure in said annular kiln chamber.

10. A positive displacement volumetric discharge mechanism for the controlled discharge of solid materials from a vertical circular shaft kiln defining a kiln chamber which is generally annular in cross section, said mechanism comprising a plurality of cone-shaped augers radially disposed within said kiln and substantially closing the lower end of said annular chamber, a

being of uniform height and of progressively increasing pitch from the inboard end of said auger to the outboard end thereof, the pitch angle of the auger rib being determined by the equation the pitch angle L the distance from the inboard end of the auger along the auger centerline v the velocity of the bed of solid material traveling vertically downwardly in the kiln above the auger D the diameter of the auger at its inboard end D= the diameter of the auger at distance L from its inboard end d= the height of the auger rib R= the rotation speed of the auger said auger thereby defining a solid material conveying auger channel the volume of which increases progressively in direct proportion to the cumulative sum of solid material conveyed thereby from the center of the kiln to the discharge throat so that a uniform material level of solid material is maintained within said kiln as solid material is discharged therefrom through said throat.

Claims

1. A positive displacement volumetric discharge mechanism for the controlled discharge of solid materials from a vertical circular shaft kiln defining a kiln chamber which is generally annular in cross section, said mechanism comprising a plurality of cone-shaped augers radially disposed within said kiln and substantially closing the lower end of said annular chamber, a retarder plate underlying said augers and having an outer peripheral edge defining an annular discharge throat adjacent the outboard ends of said augers, means for rotating said augers, a spiral rib on each of said augers defining an auger channel the volume of which increases, from the inboard end of said auger radially outwardly to the outward end of said auger adjacent said discharge throat, in direct proportion to the cumulative sum of solid material conveyed thereby from the center of the kiln to the discharge throat so that a uniform material level of solid material is maintained within said kiln as solid material is discharged therefrom through said throat.

4. A positive displacement volumetric discharge mechanism as defined in claim 1 wherein said spiral rib defining the auger channel is of progressively increasing height and progressively increasing pitch from the inboard end of said auger to the outboard end thereof thereby defining an auger channel of volumetrically increasing capacity.

6. A positive displacement volumetric discharge mechanism for controllably discharging material from a vertical circular shaft kiln having an outer shell with an undercut inner refractory liner thereon and a central support post axIally vertical within said kiln thereby defining a generally annular kiln chamber, a plurality of conical augers radially disposed in the lower end of the kiln and each of said augers having an inboard end supported on the central post and an outboard end supported in the kiln shell, said augers substantially closing the lower end of said annular chamber, each of said augers having its outboard end extending radially outwardly below the undercut refractory liner, an annular retarder plate spacedly underlying said augers and having an outer peripheral edge adjacent said kiln shell and defining therewith an annular throat underlying said undercut refractory wall, means for rotating each of said augers independently of each other, a spiral rib on each of said augers for moving material contained within said kiln radially outwardly and discharge the same through said annular throat, said spiral rib defining with said retarder plate a solid material conveying auger channel from the inboard end of said auger radially outwardly to the outboard end of said auger adjacent said discharge throat, with said solid material conveying auger channel having a volume which increases progressively from the inboard end of said auger to the outboard end thereof in direct proportion to the cumulative sum of solid material conveyed by the auger from the center of the kiln to the discharge throat so that a uniform material level of solid material is maintained within said kiln as solid material is discharged therefrom through said throat.

7. A positive displacement volumetric discharge mechanism for controllably discharging material from a vertical circular shaft kiln having an outer shell with an undercut inner refractory liner thereon and a central support post axially vertical within said kiln thereby defining a generally annular kiln chamber, a plurality of conical augers radially disposed in the lower end of the kiln and substantially closing the lower end of said chamber, each of said augers having the large outboard end thereof extending radially outwardly below the undercut refractory liner, an annular retarder plate spacedly underlying said augers and having an outer peripheral edge adjacent the kiln shell and defining therewith an annular throat underlying said undercut refractory wall, an axial trunnion shaft on each end of each conical auger, bearing means on said central support post for supporting the trunnion shaft at the inboard end of each said auger, bearing means on said kiln shell wall supporting the trunnion shaft at the outboard end of each said auger, the shaft at the outboard end of each said auger extending outwardly through the kiln shell wall, driving means external of the kiln and operatively engaged with each said extending shaft end for rotating each said auger, said spiral rib defining with said retarder plate a solid material conveying auger channel from the inboard end of said auger radially outwardly to the outboard end of said auger adjacent said discharge throat, with said solid material conveying auger channel having a volume which increases progressively from the inboard end of said auger to the outboard end thereof in direct proportion to the cumulative sum of solid material conveyed by the auger from the center of the kiln to the discharge throat so that a uniform material level of solid material is maintained within said kiln as solid material is discharged therefrom through said throat.

8. A positive displacement volumetric discharge mechanism as defined in claim 7 wherein said auger is defined by a hollow conical shell closed at each end by an inboard base member and an outboard base member respectively, said rib is formed by a channel cooperating with the auger shell to define an interior spiral rib conduit, and said auger is supported by a hollow shaft which extends through said inboard and outboard base plates to define said trunnion shaft portions, the inboard end of said shaft being closed, a conduit extending axially through said hollow shaft and termInating in an open end closely adjacent the inboard end of said shaft, an interior bulkhead within said auger shell adjacent the inboard end thereof and defining an interior chamber therewith, an interior bulkhead within auger shaft adjacent the inboard end thereof and defining an interior chamber therewith, means defining a passage through said inboard end of said auger shaft communicating between said interior chambers, means defining a passage between said interior auger chamber and said rib chamber adjacent the inboard end of said auger rib, and means defining a passage through said shaft communicating between the outboard end of said auger chamber and said hollow shaft, means exterior of said kiln for supplying a coolant to said shaft conduit, and means for exhausting coolant from said hollow shaft whereby coolant can be circulated through said shaft conduit into said inboard chambers and thence through said hollow ribs to said auger chamber and exhausted from said auger chamber through said hollow shaft so that the said auger and rib structure can be cooled during high temperature operations of said kiln.

10. A positive displacement volumetric discharge mechanism for the controlled discharge of solid materials from a vertical circular shaft kiln defining a kiln chamber which is generally annular in cross section, said mechanism comprising a plurality of cone-shaped augers radially disposed within said kiln and substantially closing the lower end of said annular chamber, a retarder plate underlying said augers and having an outer peripheral edge defining an annular discharge throat adjacent the outboard ends of said augers, means for rotating said augers, each auger having a spiral rib thereon defining an auger channel of volumetrically increasing capacity from the inboard end of said augers radially outwardly to the outboard end of said augers adjacent said discharge throat, said ribs being of uniform height and of progressively increasing pitch from the inboard end of said auger to the outboard end thereof, the pitch angle of the auger rib being determined by the equation where phi the pitch angle L the distance from the inboard end of the auger along the auger centerline v the velocity of the bed of solid material traveling vertically downwardly in the kiln above the auger D the diameter of the auger at its inboard end D'' the diameter of the auger at distance L from its inboard end d the height of the auger rib R the rotation speed of the auger said auger thereby defining a solid material conveying auger channel the volume of which increases progressively in direct proportion to the cumulative sum of solid material conveyed thereby from the center of the kiln to the discharge throat so that a uniform material level of solid material is maintained within said kiln as solid material is discharged therefrom through said throat.