US 3357689 A
Description (OCR text may contain errors)
A. G. ARNESEN ETAL 3,357,689
APPARATUS FOR FEEDING SOLID MATERIALS INTO A ROTARY KILN Dec. 12, 1967 Filed March 16, 1965 4 Sheets-Sheet 1 INVENTORS ARNE GEORLG ARNESEN 8 TORALV BASEN fg mzdam their ATTORNEYS Dec. 12,1967 A. G. ARNESEN ETAL 3,357,689
APPARATUS FOR FEEDING SOLID MATERIALS INTO A ROTARY KILN Filed March 16, 1965 4 Sheets-Sheet :1
INVENTORS ARNE GEOIZG ARNESENG: TORALV BASEN q wpnfafuau their 47' T ORNE Y5 Dec. 12, 1967 ARNESEN ET AL 3,357,689
APPARATUS FOR FEEDING SOLID MATERIALS INTO A ROTARY KILN Filed March 16, 1965 4 Sheets-Sheet 3 INVENTORS ARNE GEOR G ARNESEN 8 TORALV BASEN Q maul their ATTORNEYS Dec. 12, 1967 A. G. ARNESEN E 3,357,689
APPARATUS FOR FEEDING SOLID MATERIALS INTO A ROTARY KILN Filed March 16, 1965 4 Sheets-Sheet 4 INVENTORS ARNE c5056 ARNESEN BY TORALV. BASEN their ATTORNEYS United States Patent Office 3,357,589 Patented Dec. 12, 1967 3,357,689 APPARATUS FSR FEEDHNG S'ULID MATERHALS ENTQ A RDTARY KILN Arne Georg Arnesen, Vagsbygd, near Kristiansand, and
Toralv liasen, Mo i Rana, Norway, assignors to Ricktrokemisk A/ S, ()slo, Norway, a corporation of Norway Filed Mar. 16, 1965, Ser. No. 440,203 Claims priority, application Norway, Mar. 17, 1964, 152,- .6 11 Claims. (Cl. 263-33) The invention relates to an apparatus and method for feeding solid materials into a rotary kiln.
It is known that in the prereduction of oxidic ores in rotary kilns, it is of advantage to supply solid, uncoked carbonaceous reducing agent directly to the high temperature zone of the kiln by means of feed conduits extending through the kiln wall. Each feed conduit constitutes a part of a so-called scoop feeder which during the rotation of the kiln scoops into and excavates a portion of a supply of the solid reducing agent held in a bin or similar container adjacent the kiln. Then, with further rotation of the kiln, this excavated material gradually slides down through the feed conduits and enters the kiln by gravity flow.
The scoop feeders which have heretofore been used in connection with rotary kilns have usually been quite open, whereby considerable amounts of air have been sucked into the kiln. The quantity of air which enters the kiln in this way cannot be controlled, and the result is that the combustion Within the kiln also cannot be controlled, so that the combustion may easily become excessive and the desired prereduction of the oxides not obtained. The atmosphere in the kiln may even become oxidizing, which again results in an increased consumption of reducing agent. Excessive combustion Will also heat the charge above its softening temperature so that it will sinter and stick to the kiln walls.
In order to avoid these drawbacks, attempts have been made to seal off the scoop feeders by means of enclosures surrounding them and the kiln in the area of the scoops. However, these enclosures of necessity had to be quite large and the surfaces requiring gas-tight seals against the rotating kiln correspondingly also had to be rather large. Practical experience has shown that it is difiicult to obtain good and reliable sealing between the surface of the kiln and the enclosures, and the arrangement is thus not of advantage.
Another considerable drawback of the known scoop feeders is that when they are used for introduction of for example raw, fine-grained baking coal, or other carbonaceous solids containing appreciable amounts of volatile material, there is a risk that the coal will not drop properly through the feed conduits. In particular, moist coals will only trickle slowly duits and partially stick to the conduit walls when the kiln has rotated so much that the inclination of the conduit is less than the angle of repose of the coals. The coals will thereby be retained in the conduits for a long period, and that portion of the coals which sticks to the hot feed conduits will easily become baked thereon and often even ignited so that the feed conduits will act as internal torches. The heat developed by these torches may easily cause local superheating of the charge in the kiln and of the kiln lining, which may result in sintering and clogging of the charge in the kiln and other operational disturbances. The feed conduits may even become completely clogged up so that the supply of raw material through them is stopped. The life of the conduits is also considerably reduced because of the strong heating and the contact with the burning carbon.
It has now been discovered that the above-mentioned down along the walls of the feed con-' difiiculties can be avoided by use of a new form of scoop feeder which is provided with means for closing an opening leading from the scoop into the feed conduit and means for moving said closure means into and out of the closing position at predetermined times during revolution of the kiln. In this way, excavated solid material, for example moist coal, can be carried in the scoop beyond the angle of repose (where the coal otherwise would normally begin to trickle down through the feed conduit) to a selected angular position and then released all at once into the feed conduit by moving the closure means out of the closing position. The angular release position is selected with due regard for the kiln speed of rotation so that excavated solid material in the scoop will drop through the feed conduit very rapidly from the moment of release. In this way, the dwell time of the solid material in the feed conduit is so markedly reduced that there is little if any opportunity for the material to become overheated, or stuck or baked to the conduit wall or ignited Within the conduit.
Accordingly, in one embodiment of the invention, each feed conduit is provided with a flap which can pivot into and out of a closing position in relation to an opening leading from the scoop into the feed conduit. A pair of cams are arranged to intercept cam followers, connected to the pivot rod of the flap, at predetermined angular positions whereby the flap is first moved out of the closing position to permit excavated solid material in the scoop to move into the feed conduit and then the flap is moved back into the closing position whereby air or other gas is excluded from entering the feed conduit. Hence, the feed conduits can be maintained closed for the major part of each complete revolution of the kiln, the conduits being controllably opened and closed only for that brief interval of time required to permit excavated solid material to empty from the scoop and drop through the feed conduit into the kiln.
In another embodiment of the invention, a second opening leading into each feed conduit is provided adjacent the opening leading from the scoop into the conduit. A common, pivotable flap is so arranged as to pivot into alternate closing positions wherein first the scoop opening is closed and the second opening left open, and then the second opening is closed and the scoop opening left open. Preferably, a separate control such as a butterfly or slide valve is also provided to variably reduce the amount of gas flow through the second opening. In this Way, the scoop opening can be opened for a limited time to rapidly feed excavated solid material through the associated feed conduit into the kiln. During the balance of each revolution of the kiln, controlled amounts of air can be injected through the fully or partially open second opening while the scoop opening remains shut. This will provide a cooling elTect upon the flap and feed conduit to further prevent sticking or baking of solid material upon the interior of the conduit wall. Also, combustion and temperatures within the kiln can be more readily controlled with such injection of controlled amounts of air.
In still another embodiment of the invention, separate flaps are provided for the scoop opening and for the second opening leading into the feed conduit. In this way, both openings can be maintained closed over a limited interval during each revolution of the kiln. This makes for still more control over the amount of air or other gas that is permitted to enter the kiln through the feed conduits and provides the additional advantage that the injection of air or gas through the feed conduit, after delivery of excavated solid material therethrough, can be delayed for any desired time or even eliminated before the scoop again excavates a portion of solid material with start of the next revolution.
These and other features will be better understood by reference to the accompanying drawings which illustrate several embodiments of the invention and of which:
FIG. 1 is a side elevation of a rotary kiln provided with apparatus illustrated diagrammatically for feeding solid material thereto in accordance with the invention;
FIG. 2 is a section taken along line 2 -2 of FIG. 1;
FIG. 3 is a close-up view of a portion of FIG. 2, with parts broken away to illustrate additional details of structure;
FIG. 4 is a view similar to FIG. 3 showing a further stage of revolution for the kiln of FIG. 3;
FIG. 5 is a modification of the scoop-feed conduit structure of FIGS. l-4;
FIG. 6 is another modification of the same; and
FIG. 7 is still another modification of the same.
Referring to FIG. 1, a rotary kiln is there generally indicated by reference numeral 10. The kiln is supported and revolved upon conventional stands 12 in known manner. A hopper 14 and associated conduit 16 are provided for transporting charge into the feed end of the kiln which is also enclosed within plenum 18 in which oil gas can be collected and withdrawn through conduit 20. At the opposite end of the kiln, there is provided a discharge device 22 which is conventional (as is the structure described for the feed end) and delivers treated solid material to the outlet pipe 25.
Positioned adjacent the exterior of the kiln is a bin or container 24, supported upon stand 26. A hopper 28 and associated conduit 30 are arranged to supply the bin 24 with particulate solid material, for example solid carbonaceous reducing agent, which is desired to be fed into the kiln. At least one feed conduit 32, two being specifically illustrated, extends through the kiln wall. As will be noted in FIG. 1, the inner ends of the feed conduits 32 are staggered out of radial alignment and extended slightly past each other whereby solid material dropping out of any one conduit cannot enter any other conduit and instead is controlled to fall to the bottom of the kiln.
The end of each feed conduit 32 outside the kiln 10 is joined to an intermediate member 34 which in turn is joined to the scoop 36. The scoop 36 is provided with an opening 38 which leads into the feed conduit 32 and through which excavated solid material in the scoop may be permitted to enter the feed conduit (FIG. 3). The intermediate member 34 is provided with a second opening 40 which is located adjacent and approximately at right angles to the scoop opening 38, and faces the direction of revolution of the kiln which, as indicated by the arrow, is counter clockwise (FIG. 4). A short conduit 41 projects out from the second opening 40 in alignment therewith.
A flap 42 is supported on a pivot rod 44 and arranged to pivot into and out of two alternate closing positions, one of which closes the scoop opening 38 and leaves the second opening 40 open (FIG. 4) and the other of which closes the second opening and leaves the scoop opening open (FIG. 3).
At one end of the pivot rod 44, the ends of three rigid arms 46, 48 and 50 are fixedly attached so that the rigid arms may pivot with the pivot rod. The opposite ends of the arms 46, 48 and 50 are spaced apart from each other and, preferably, the spaced ends of the outer two arms 46 and 50 form with the pivot rod a generally triangular configuration. The centrally located rigid arm 48 supports, at its spaced end, one end of a spring 52 the opposite end of which is attached to a fixed support 55 on the exterior of the kiln 10.
The spaced ends of the outer two rigid arms 46 and 50 are provided with cam followers 46A and 50A. A pair of earns 54 and 56 are supported by conventional means (not shown) in a manner such that the inclined surfaces of the cams will intercept the paths of travel of the cam followers 46A and 50A and thereby engage said followers during kiln revolution. In this connection, the cam followers 46A and 50A of the feed conduit 32 spaced axially further away from the cams 54 and 56 (FIG. 1) are supported upon a pivot rod 44 which is suitably lengthened so that the followers will be engaged by the same cam surfaces in the same way as will be the followers 46A and 50A of the axially closer feed conduit 32.
Operation of the kiln in connection with the above-.
described feed apparatus may be readily understood by reference to FIGS. 2, 3 and 4. For the major portion of each complete revolution of the kiln 10, each of the flaps 42 will be in the position illustrated in FIG. 4 wherein the scoop opening 38 is closed and the adjacent opening 40 is open. During all or part of this time, controlled amounts of air or other gas can be injected into the kiln 10 through the second opening 40 and the associated feed conduit 32.
With revolution of the kiln, each scoop 36 passes through the supply of solid particulate material held in the bin 24. The scoop 36 excavates a portion of the solid material which remains therein even though the scoop travels to a position beyond the angle of repose of the material, because the flap 42 is in the closing position with respect to the scoop opening 38. As is known, the angle of repose of a solid particulate material is the maximum angle with the horizontal at which the material will retain its position without tending to slide, and it is a distinct feature and advantage of this invention that excavated solid material in the scoops 36 may be carried as much beyond the angle of repose as may be desired before being fed into the kiln 10 from a preselected angular position.
The time when excavated solid material in the scoop 36 is permitted to enter feed conduit 32 is determined by the position of the cam first engaged after excavation of solid material, which is cam 54. Considering the direction of kiln revoltuion, the working surface of cam 54 is inclined toward the kiln 10. As a result, the cam follower 46 is pushed toward the kiln as it moves along the working surface of cam 54 and this applies a torque to the pivot rod 44 which in turn begins to pivot the flap 42 out of closing position with respect to the scoop opening 38. Excavated solid material therefore begins to drop from the scoop 36 into the feed conduit 32. In this connection, as the pivot rod 44 begins to pivot, the distance between the spaced end of the central arm 48 and the fixed support 54 increases whereby the central rigid arm 48 elongates the spring 52. Just beyond the point of maximum elongation (when the spring overlies the axis of pivot rod 44), the tension of the spring 52 acts to reduce the distance between the spaced end of arm 48 and support 54 whereby the flap 42 is pivoted with positive, direct action into closing position with respect to opening 40. All of this happens within the space of time cam follower 46A travels along cam 54 so that the scoop opening 38 is opened and the second opening 40 closed very rapidly by the action of the spring 52 (FIG. 3).
Following delivery of the excavated solid material through feed conduit 32 to the kiln, the scoop opening at a second selected angular position is closed by flap 42 and the second opening 40 is simultaneously opened so that air or other gas may be injected therethrough into the kiln. This is done by contact of the cam follower 50A with the working surface of cam 56 which, in the direction of kiln revolution, is inclined away from the kiln.-As a result, the cam 56 pushes follower 50A away from the kiln which causes the flap 42 to move back to the position illustrated in FIG. 4 under the same spring action described above for the opposite movement of the flap in connection with FIG. 3. By the foregoing arrangement, the spring 52 alternately applies its energy to the flap 42 as torques of opposite direction. The torque direction reverses each time the flap 42 pivots between its two described positions whereby the spring 52 assists the pivoting motion and also maintains the flap locked under tension in each of its two positions.
As will be evident, the time interval over which the scoop opening 38 remains open during each revolution of the kiln is determined by the angular distance between earns 54 and 56. This distance is correlated with the speed of revolution to insure that all or the excavated solid material in each scoop 36 will be emptied out of the scoop. Generally speaking, an angular distance corresponding to an arc of from about to about 30 measured from the kiln axis of revolution will be satisfactory, although other distances can also be used. For example, as the cam 54 is positioned closer to a vertical plane passing through the kiln axis of revolution, the action of gravity will be increased upon the excavated solid material in the scoop so that less time will be required for completely emptying the scoop of the solid material. On the other hand, as the cam 54 is positioned further away from the vertical plane passing through the axis of revolution, and thereby closer to the angle of repose, the action of gravity upon excavated solid material in each scoop will be less so that the scoop openingwill have to remain open longer for a given speed of revolution. For each type of solid material which is to be fed into the kiln, a few simple tests will readily determine the optimum spacing between the cams 54 and 56. Of course, the earns 54 and 56 are independently adjustable in position so that the angular distance between them can be varied as desired.
FIG. 5 illustrates a modification of the apparatus shown in FIGS. 14 wherein the short conduit 41 leading to the second opening 40 is equipped with means for reducing the amount of gas flow through the opening 40 independently of the flap 42. The specific means illustrated in the drawing is a butterfly type valve 58, although obviously other known means can be employed.
FIG. 6 illustrates a further modification wherein the second opening 40 of FIGS. 1-4 is eliminated so that the scoop 36 and opening 38 constitute the only access to the feed conduit 32. In this modification, the kiln 19 will be completely sealed except for the time that the scoop opening 38 is opened to allow excavated solid material in the scoop to enter the feed conduit 32. In certain applications, this will be found of advantage and it is of course possible to feed air or other gas into the kiln with the modification of FIG. 6 by means of separate pipes or other supply means.
FIG. 7 illustrates a further modification in which the scoop opening 38 and the second opening 40 are provided with separate pivotable flaps 42A which are moved into and out of their respective closing positions under the same spring action described above in connection with FIGS. 14. This particular modification may be found of advantage in certain applications because air or other gas can be fed to the kiln for any desired interval of kiln revolution while the scoop opening is closed and, dur'ng the remainder of each revolution of the kiln, the kiln may be completely sealed.
It will be understood that it is intended to cover all changes and modifications of the preferred embodiments of the invention herein selected for purposes of illustration which do not depart from the spirit and scope of the invention.
What is claimed is:
1. Apparatus for feeding solid material into a rotary kiln which comprises means for holding a supply of the solid material adjacent the exterior of the kiln, at least one conduit extending through the kiln wall and having a scoop at its end outside the kiln, said scoop having an opening through wh ch solid material may pass into said conduit and being arranged to excavate a portion of said supply of solid material during each revolution of the kiln, a flap mounted adjacent said scoop opening and being pivotable into a first position which closes said scoop opening and into a second position which opens scoop opening, means for pivoting said flap alternately between said first and second positions, said pivoting means including a tensioned spring the energy of which is alternately applied to said flap as torques having opposite directions, there being a reversal of said torque direction each time said flap pivots from one to the other of said first and second positions so that said spring assists the pivoting motions of said flap and also maintains said flap locked under tension in either one of said first and second positions, whereby excavated solid material in said scoop may be carried to a selected angular position and then admitted into said conduit for delivery into the kiln.
2. Apparatus as in claim 1 wherein said flap is supported on a pivot rod and three rigid arms are atfixed to one end of said pivot rod, one end of each of said arms being afiixed to said pivot rod and the other ends of said arms being spaced apart from each other, a cam follower provided at each of the spaced ends of'the outer two of said arms, and wherein said pivoting means includes a first cam positioned to engage one of said cam followers and thereby pivot said flap from said first to said second position, and. a second cam positioned to engage the second of said cam followers and thereby pivot said flap from said second back to said first position.
3. Apparatus as in claim 2 wherein said cams are spaced apart an angular distance corresponding to an arc of from about 5 to about 30 measured from the kiln axis of revolution.
4. Apparatus for feeding solid material into a rotary kiln which comprises means for holding a supply of the solid material adjacent the exterior of the kiln, at least one conduit extending through the kiln wall and having a scoop at its end outside the kiln, said scoop having an opening through which solid material may pass into said conduit and being arranged to excavate a portion of said supply of said material during each revolution of the kiln, a second opening adjacent said scoop opening and also leading into said condu t, means for alternately closing said scoop opening while leaving said second opening open and for closing said second opening while leaving said scoop opening open, and means for moving said closure means into and out of the alternate closing positions, whereby excavated solid material may be carried to a selected angular position and then ad mitted into said conduit for delivery into the kiln.
5. Apparatus as in claim 4 which includes a plurality of said conduits extending from the kiln wall to the kiln axis of revolution, each said conduit being positioned out of radial alignment with any other of said conduits, whereby solid material conveyed through any one conduit cannot enter any other conduit.
6. Apparatus as in claim 4 wherein said closure means comprises a flap supported on a pivot rod located between said scoop and second openings, said flap being pivotable about said pivot rod from one alternate closing position to the other alternate closing position.
7. Apparatus as in claim 4 which includes separate means independent of said closure means for varying the amount of gas flow through said second opening.
8. Apparatus as in claim 6 wherein one end of said pivot rod is fixedly attache-d to one end each of three rigid arms, the opposite ends of said arms being spaced apart from each other and the spaced ends of the outer two of said arms forming with the pivot rod a generally triangular configuration, a coil spring attached at one end to a fixed support on the kiln and at the other end to the spaced end of the rigid arm located between said two outer arms, a cam follower provided at the spaced end of each of said two outer arms, and wherein said closure moving means comprises a first cam positioned to engage one of said cam followers and thereby pivot said flap into one alternate closing position, and a second cam positioned to engage the second of said cam followers and thereby pivot said flap into the second alternate closing position.
9. Apparatus as in claim 8 wherein said cams are independently adjustable in position and are so arranged as to intercept the paths of travel of said cam followers during each kiln revolution, the cam first engaged after excavation of solid material causing said flap to close said second opening and leave said scoop opening open whereby excavated solid material may be admitted into said conduit, and the cam second engaged causing said flap to close said scoop Opening and leave said second opening open, whereby controlled amounts of gas may be admitted into said conduit before the next excavation.
10. Apparatus as in claim 8 wherein said cams are spaced apart an angular distance corresponding to an arc of fromabout 5 to about'30" measured from the kiln axis of revolution.
11. Apparatus for feeding solid material into a rotary kiln which comprises means for holding a supply of the solid material adjacent the exterior of the kiln, at least one conduit extending through the kiln wall and having a scoop at its end outside the kiln, said scoop having an opening through which solid material may pass into said conduit and being arranged to excavate a portion of said angular position and then admitted into said conduit for.
delivery into the kiln.
References Cited UNITED STATES PATENTS 644,057 2/ 1900 Carman 263-32 1,415,990 5/1922 Carstens 26332 1,830,002 11/1931 Schitterle 263-33 FREDERICK L. MATTESON, JR., Primary Examiner.
JOHN J. CAMBY, Examiner.