US3026728A

US3026728A - Bed depth gauge for rotary kiln

Info

Publication number: US3026728A
Application number: US1507A
Authority: US
Inventors: Moklebust Olav; John R Walker
Original assignee: RN Corp
Current assignee: RN Corp
Priority date: 1960-01-11
Filing date: 1960-01-11
Publication date: 1962-03-27
Anticipated expiration: 1979-03-27

Description

March 27, 1962 Filed Jan. 11, 1960 United States Patent 3,026,728 BED DEPTH GAUGE FOR ROTARY KILN Olav Moklebnst and John R. Walker, Birmingham, Ala.,

assignors to R-N Corporation, New York, N.Y., a corporation of Delaware Filed .Ian. 11, 1960, Ser. No. 1,507 9 Claims. (Cl. 73-298) The present invention relates to a gauge for determining the depth of a bed of fluent solid material in a rotary kiln during the rotational operation thereof and for a method of measuring such depth and also relates to a method of establishing and maintaining a predetermined desired depth of solid material in such a kiln with the aid of the gauge and the method of this invention.

In the operation of rotary kilns wherein elevated temperatures are used in treating solid materials to eflect chemical and/ or physical changes during the movement of the solid materials through the kiln, the operation is usually substantially continuous, with solid material being supplied to the kiln adjacent to one end, which is ordinarily slightly elevated with respect to the opposite end of the kiln. The kiln is rotated, usually slowly, with the material tumbling over upon itself and/or flowing as a fluent solid material and gradually working its way from the higher or material-inlet end of the kiln to the lower or outlet end thereof. Gases are passed through the kiln usually, but not necessarily, countercurrent to the flow of the solid material therethrough, these gases conventionally including combustible gases, products of combustion, and/or gases evolved from the operation taking place in the kiln.

In some operations which may be carried on in a rotary kiln of this type, it is very desirable that a relatively deep bed be established and maintained in the kiln, as the desired operations or reactions occur more readily or are carried on to a desired degree and/ or in a better manner when a relatively deep bed is maintained. In view of the nature of kilns as to construction, and as it is not practical to observe the bed in and intermediate the ends of the kiln visually, the art has been more or less at a loss to detect or accurately to measure the depth of a bed of fluent material in a kiln during the operation thereof, for example, at any point intermediate the ends thereof. The more or less exact determination of the depth of material in the bed thereof in a rotary kiln during operation is particularly important in conducting a reducing operation for iron ore in a kiln as taught, for example, in the patent to Moklebust No. 2,829,042. In this operation, which has been conducted on a relatively large pilot plant scale for some time, it has been found important to provide a bed of fluent solid material which is about 30% to about 50% of the inside volume of the kiln. In view of the fact that temperatures within the kiln are maintained in the order of magnitude of about 1900-2000 F., the problem of determining bed depth during operation is far from simple.

The present invention solves the several difficulties, in that it provides a device in the form of a gauge by which the bed depth can be quite accurately determined, whether the bed depth desired be a value within the limits aforesaid, or whether it be some wholly unknown depth which it is desired to determine in a particular instance. The present invention also is useful in guiding the operator of a device of this kind, so that a predetermined desired bed depth may be established and be maintained.

It has been found that the bed depth in a kiln may be influenced by two factors(a) the rate at which the solid material is supplied to the kiln adjacent to one end thereof and (b) the speed of rotation of the kiln. These factors practically determine bed depth for any given inclination of the kiln, which is a factor not ordinarily changed in "ice practice. It is understood, of course, that an increase in the inclination of the kiln, i.e. difference in height of one end over the other, will tend to increase the rate of solid material flow therethrough; and if the outlet is reasonably open, will tend to decrease the bed depth thereof. On the other hand, for a given arrangement, i.e. at a given inclination of the axis thereof, an increase in the rate of feed of solid material to the higher end and/ or a slowing of the rate of rotation of the kiln each independently tends to increase the depth of the bed of fluent solid material in the kiln, and vice-versa.

The apparatus of the present invention may be summarized as comprising a tube which extends through a wall of the kiln and rotates with it, the tube extending from the outside to a point short of the axis of the kiln. It is contemplated that such a tube may be fixed in position with the inner end thereof at such a position that some solid material will flow or pass out through the tube on each revolution of the kiln. Under these circumstances, the angle at which the solid material first passes out through the tube on any one revolution of the kiln may be ascertained; and from this, the depth of material in the kiln may be accurately determined, particularly when the angle is one between the tube position and the vertical and when the tube is approaching, rather than moving away from, its substantially vertical position at the lower portion of its orbital path. When the tube is in this quadrant of its rotation when the solid material first passes out therethrough on any revolution of the kiln, the angle of the tube with respect to the vertical, coupled with the position of the inner end of the tube, is accurately indicative of the amount of solid material in the kiln. This is based upon the assumption that the angle of repose of the material in the kiln remains constant, which will normally be the case as long as a particular type of solid material charge to the kiln in about the same grouping of particle size ranges is being handled. In any event, by taking two similar readings of the angle of the tube, when adjusted to two diilerent and known radial positions and at which solid materials pass outwardly therethrough respectively, the angle of repose of the fluent solid material in the kiln can be calculated geometrically. In the next quadrant of the tube rotation the corresponding angle is not nearly as sensitive, but is only generally indicative of the amount of material in the kiln. Alternatively, if it is desired that the gauge be eitective to determine various quite diiferent depths of material in the kiln, the tube may conveniently be arranged to be radially adjustable in a direction which is both axial of the tube and radial of the kiln, so as to position the inner end of the tube a predetermined adjustable distance short of the axis of the kiln. In this way the tube may be adjusted to a position such that some material will move out through it during each revolution of the kiln and particularly during the movement of the tube in each such revolution from a substantially horizontal position to a substantially vertical lower position, and the angle at which such material first passes out of the tube may then be determined, the adjustment of the tube plus the angle as thus determined being jointly indicative of the depth of material in the kiln. It will be understood that in many instances at least it will be desirable, if not essential, that the tube be closable so as to remain closed during periods in which it is not in use for determining the depth of the material as aforesaid. For this reason the tube may be provided with a suitable closure as a conventional gate valve, accessible from the outside thereof.

It is sometimes found in practice that opening the tube for the ascertainment of the bed level, even during the measurement or test itself, is suflicient to disrupt the operations within the kiln and also that the inflow of atmospheric air through the tube under these circumstances is enough to blow away carbonaceous material which tends to collect on top of the bed due to its relatively lower specific gravity, so that an accurate measurement. of bed depth cannot be obtained with the tube open. Under these circumstances, it is possible to operate with the end of the tube closed and by either visual or audible detection of the first solid material falling into the tube and tending to move outwardly therethrough. Such audible detection by listening without additional hearing devices has been practiced successfully. On the other hand, if a part or all of an end portionof the tube outside the kiln is made of a transparent material, then the first solid material passing to this point can be visually ascertained, even though the outer end of the tube is closed. 7 7

Further details of the present invention and the several methods by which the gauge thereof may be used will be explained in greater detail hereinafter in discussing a preferred embodiment thereof, which is shown in the accompanying drawings, in which: V I

FIG. 1 is a diagrammatic view, principally in elevation, of a kiln embodying the present invention; 7

FIG. 2 is a view in transverse section taken substantially on the line 2 -2 of FIG. 1 and on an enlarged scale, showing a tube in position to detect the depth of material in a kiln during the operation thereof, and also showing in dotted lines a tube in the same position with respect to the kiln for sensing a higher level of solid material and showing at another rotated position a tube in the samerelative position with respect to the kiln substantially at the level of the material in the kiln as shown in full lines; and I p I H FIG. 3 is a fragmentary view, generally similar to that of FIG. 2, showing some of the solid material flowing out through the tube at a further rotated position of the kiln beyond that point shown in full lines in FIG. 2.

Referring first to the general view of a kiln shown in FIG. 1, with which the apparatus andmethod of the present invention may be associated as hereinafter set forth, there is shown a rotary kiln comprising a rotating hollow cylindrical member, which may be suitably mounted in a manner only diagrammatically shown for rotation about the axis of the kiln 10 andis arranged to be driven or rotated in a manner generally hereinafter described. Generally housing the left hand end of the kiln 10 is a combustion chamber 11, through which a suitable fuelmay be projected along with some combustion-supporting air so as to provide a current of gases, in part combustible and in part burnt, which will pass through the kiln 10 from left to right, as seen in FIG. 1, the gases passing to and through a housing 12 surrounding the right hand end of the kiln 10 as seen in FIG. 1 and the gases passing thence out through a suitable stack 13. Solid materials may be supplied to the kiln 10 in any suitable manner diagrammatically illustrated by an arrow 1411, but which may, for example, take the form of a screw conveyor as shown in greater detail in the Moklebustpatent above referred to. V

Solid materials may be removed from the kiln 10 in any conventional manner, not shown in the accompanying drawings, but which arediagrammatically shown as an exit passage associated with the combustion chamber 11 in the Moklebust patent aforesaid. It will be understood that the rate of supply of the solid materials to the kiln may be varied by any suitable means, not shown, but of which many examples are known to those skilled in the art. This will be discussed further hereinafter.

At a desired point along the length of the kiln 10, there is arranged a suitable tube which extends from the outside of the kiln into it in a substantially radial direction and terminates short of the axis of the kiln. Thus, as shown in FIGS. 2 and 3, the kiln 10 is shown as formed of an outer metal shell 14 having a suitable refractory lining 15 which may be constructed of firebrick or the like. As the kiln is illustrated in FIGS. 2 and 3, as rotating in a clockwise direction, the fluent solid material therein shown at 16 will be caused by the rotation of the kiln to assume a position substantially as shown in full lines in the drawings.

In a preferred form of the invention, a sleeve 17, preferably of suitable metallic material, is built into the kiln wall and may, if desired, be welded or otherwise secured to the shell 14 thereof. This sleeve extends most, if not all the way, through the refractory lining 15. Preferably slidably arranged within this sleeve 17 is a tube 18, which is shown separated from the tube 17 by intermediate packing material shown at 19. The arrangement is such that the tube 18 is held frictionally within the sleeve 17 by the packing material 19, so that it is held against inadvertent movement, while being movable notwithstanding the friction of the packing material by the application of a sufficient force. The tube 18 may thus be said to be in frictional sliding relation within the sleeve 17. The tube 18 extends from outside the kiln as shown to a point indicated at 20, which is short of the axis of the kiln, the position of which is shown at 21. The adjusted position of the tube 18 in a direction which is both axial of the tube 13 and radial of the kiln 10 may be determined by a suitable scale indicated at 22, which may be marked or engraved upon the outside of the tube itself and may be read, for example, by determining what mark is visible at the outside of the shell 14 or the tube sleeve 17. Alternatively, a'suitable index device (not shown) could be provided for enabling an accurate reading of the scale 22 or a scale could be provided on the outside of the kilnwith an index carried by the tube cooperating therewith.

There is further provided a stationary scale 23 shown supported by means as the legs 24, extending from a stationary base support, so as to position the scale 23 adjacent to the orbital path of movement of the tube 18 during a lower portion of its path. By the use of the scale 23, an operator is enabled to determine quite accurately the angle with respect to the vertical at which solid material first passes out through the tube 18 on any revolution of the kiln.

If now we consider that the level of the solid material in the kiln as shown in full lines in FIG. 2 is at a level a; while a somewhat higher level is shown at b; and a still higher level is shown at c, both levels b and 0 being indicated in dotted lines in FIG. 2, then the material at level a will not pass out through the tube while it is at its lower substantially vertical position as shown in FIG. 2; but some material will probably pass out when the tube has moved to the position shown in FIG. 3, i.e. about 3045 beyond the vertical. This position of the tube and the material at level a will give some indication, but a rather rough and inexact indication, of the it is in the lower right quadrant of its movement (as seen material in the kiln were up to the level c, it is noted that with the tube 18 extending inwardly to the same position shown in full lines in FIG. 2, and in fact substantially at the position shown at 18a, the lower right portion of this figure in dotted lines, then some material will flow out through the tube while it is at this lower right inclined position. Here, however, because the tube is at such a position with respect to the level of the material in the kiln that the material will pass out through the tube while tube is in the lower right quadrant of its rotation (as seen in FIG. 2) between a horizontal position and a substantially vertical lower position, the indication is quite exact. Thus, with the material at the level 0, this material will start to flow out through the tube 18 while it is at a position (as 18a) substantially 38 before the vertical.

Furthermore, with the tube extended inwardly to the same position, and when it is located at the position shown in full lines in FIG. 2, i.e. a substantially vertical lower position, and when the material in the kiln is at the level b, the material will start to flow out through the tube 18 substantially at the position shown in FIG. 2. Thus, the differences in material level between the levels 0 and b will correspond to tube positions between about 38 before the vertical and a vertical position, which in practice gives a quite accurate indication of the level of the material in the kiln. It will be noted that the indication afforded by the material flowing out through the tube during the next quadrant of its rotation in the rotation of the kiln (lower left quadrant) is only approximate, although this does give some useful indication of the general level of material in the kiln. It is, therefore, a preferred mode of operation in accordance with the present invention that the tube 18 will be so disposed, i.e. as to the position of its inner end, that some material will pass out through the tube during the movement of the tube in the lower right hand quadrant of its rotation as seen in FIG. 2.

In some instances it may be desired to prevent inflow or outflow of gases to or from the inside of the kiln in order not to interfere with the desired operations therein. In such a case, with the situation with respect to the process described in the Moklebust patent, it is usually necessary to provide for closing the tube 18 to the atmosphere except during the periods when the tube is being used for determining the depth of material in the kiln. Any suitable closure means may be provided for this purpose. There is shown, however, in FIGS. 2 and 3, a gate valve 25 which may be provided on the outer portion of the tube 18 to effect this result.

As shown in FIGS. 2 and 3, the tube 18 has a portion 30 outside the kiln, but inwardly from the valve 25 therein, which is formed of a transparent material such as a heat-resistant glass which can accommodate itself to abrasion and to the relatively sudden temperature changes incident to hot material coming into contact therewith. By the use of this transparent portion, it is possible, with the valve 25 closed, to ascertain by visual observation when the first solid material tends to move outwardly through the tube 13, as such material will move into the transparent section thereof shown at 30. In this way, it is possible to prevent inflow of atmospheric air into the interior of the kiln during the operation thereof, which would ensue if the valve 25 were opened. Such inflow of air to the kiln, in view of the slightly sub-atmospheric pressure existing within the kiln, is sometimes sufiicient to blow away from the vicinity of the tube some of the lighter portions of the solid body within the tube, i.e. the carbonaceous materials, so that a true reading of the bed level is not obtainable. It is also possible, Whether or not the transparent section 3% be provided, to ascertain the first movement of solid materials to the outer end of the tube by listening carefully, as the kiln rotation is sufficiently slow to permit this operation.

It will be understood that the accuracy of the bed depth determination depends to some extent upon there being a substantially uniform angle of repose of the solid materials in the kiln. This is normally the case under any condition of stabilized operation and is of course a function of the proportions of ore to carbonaceous materials and/or other materials present, such as limes-tone, and is further a function of the particle size or range of particle sizes of the solid materials present. In any event, if it is desired to ascertain the angle of repose accurately, this may be done by taking two readings as hereinabove set out with the tube 18 set at different radial positions for each reading (preferably substantially different) and by suitable geometric calculations. These calculations are of such relatively simple character that they are believed obvious to any one skilled in the art, once the mode of taking the exact readings is explained as has now been done.

Assuming that the kiln is operating on a substantially normal basis and it is desired merely to check the depth of material in the kiln at levels fairly close to a predetermined desired level, a tube such, for example, as

shown at 18, but without the necessity for providing for radial adjustment thereof, may be used, it being understood that at the desired depth or level of material in the kiln, some material will pass out through the tube on each revolution of the kiln. Under these circumstances, radial adjustability of the tube is unnecessary and in fact the tube could be built into the kiln as a permanent and fixed part thereof. The determination of the amount of material in the kiln with such a device is then merely one of determining the angle at which the solid material first starts to flow out through the tube with respect to the vertical, i.e. the angle at which the tube is disposed with respect to the scale 23 preferably in the quadrant as aforesaid in which the tube is approaching its lower substantially Vertical postion. This angle, coupled with the known dimensions and position of the tube, is directly indicative of the amount or depth of material in the kiln.

In the event, however, that some relatively wide variations may be expected or are to be determined in the depth of material in the kiln, then the radial adjustability of the tube 13 with respect to the sleeve member 17 becomes important. Under these circumstances, it may be necessary to start with the tube 18 at a radial inner position at which no material will flow out through the tube on each revolution of the kiln; then move the tube 18 outwardly by predetermined increments, checking after each radial adjustment whether or not solid material flows or passes out through the tube. After an adjustment has been reached at which some material will flow through the tube 18, the angle at which this material first passes out during each revolution is determined. The adjusted position of the tube 18, coupled with the angle at which the tube is disposed when solid material first flows or passes out therethrough, is then jointly accurately indicative of the amount of material in the kiln.

Another desirable mode of operation of the entire apparatus is to utilize the depth detection means and methods aforesaid in conjunction with the means for controlling the kiln operations, so as to establish and maintain a desired depth of material in the kiln. It is found, as aforesaid, that for any given postion of the kiln axis, i.e. angle of inclination thereof with respect to the horizontal, the amount of solid material or depth of material in the kiln may be varied by varying either or both of two factors: (1) the rate at which solid materials are supplied to the kiln and (2) the rate of rotation of the kiln. Inasmuch as it is quite usual to supply solid materials to the kiln at a fixed rate determined by other factors, it is usually more practical adjustably to control the rate of rotation of the kiln in order to control bed depth. For this reason, as shown in FIG. 1, the kiln lid is provided with a rotating ring or band 26 engaged in any conventional manner by rotating means as rollers or possibly pinions indicated diagrammatically at 2.7, one of which is driven through a suitable speed-changing device 28 from a prime mover here indicated as a motor 29. All these means, i.e. the motor (which usually also includes speed-reducing means). The speed-changing device '28 and the particular drive 26-27 may be per so old and in any event form no part of the present invention other than that some suitable means should be provided by which the speed of rotation of the kiln may be varied under the control of an operator.

If, for instance, the operation is such that the bed is approximately at the right depth, but it is desired to maintain exact conditions, it may be suflicient to determine the exact depth by the use of a tube adjusted or fixed at the proper point in a radial direction and then determining the angle at which solid material will first flow out, the adjustment of the tube preferably being such that material will flow out through the tube 18 while it is moving in the quadrant of its orbital path approaching its lower substantially vertical position as aforesaid. This gives an indication of the existing depth of the bed.

The speed of rotation of the kiln may then be adjusted by the means provided, so as to bring the depth to the proper value; so that upon further test, the angle at which material first flows out through the tube will be adjusted to a desired value. In this respect, it will be understood that the slowing down of the speed of rotation of the kiln will result in increasing the bed depth and vice-versa.

Any combination or variation of the method steps generally suggested above which will occur to those skilled in the art as a result of the foregoing disclosure and any variation or alternative of the structural embodiments of the means herein particularly disclosed which will similarly be suggested by the foregoing disclosure and which, in the case of either apparatus or method, come Within the scope of the appended claims are to be considered as parts of this invention.

What is claimed is:

1. A gauge for determining the depth of a bed of fluent solid material in a continuously rotating kiln of known inside diameter during the operation thereof, comprising a tube having one end open to the outside of the kiln, said tube extending substantially radially inwardly of the kiln and rotating therewith, so that the inner end of said tube is located at a point which is fixed with respect to said kiln and which is between the outer Wall and the axis of the kiln and is a predetermined distancefrom said axis, said inner end of said tube being so located that some of said fluent solid'material from the bed thereof in said kiln will pass outwardly through said tube by gravity during each revolution of said kiln, and a stationary circumferential scale fixedly mounted outside said kiln and disposed substantially in a' plane perpendicular to the axis of said kiln and adjacent to the path of said tube for assisting an observer in determining the angle at which said tube is disposed with respect to the vertical at the instant that some of said solid material of said bed starts to pass out through said tube on any one revolution of said kiln, said angle and the posi tion of the inner end of said tube being jointly indicative of the depth of said solid material in the kiln.

2. A gauge for determining the depth of a bed of fluent solid material in a rotary kiln in accordance With claim 1, in which the inner end of said tube is at such a position in respect to the level of the material to be determined that some solid material will pass outwardly through said tube during that portion of the orbital path of said tube in the rotation of said kiln in which said tube is approaching but has not reached a substantially vertical position at the lower portion of said orbital path.

3. A gauge for determining the depth of a bed of fluent solid material in a rotary kiln in accordance with claim 1, further comprising valve means for said tube for closing it against flow of any materials therethrough except during times in which said tube is in use in the determination of the depth of solid material in a kiln as aforesaid.

4. A gauge for determining the depth of a bed of fluent solid material in a rotary kiln in accordance with claim 1, further comprising means mounting said tube for adjustive movement in and with respect to said rotating kiln solely in a direction which is both substantially axial of said tube and radial of said rotary kiln, so as to make the gauge constructed as aforesaid sensitive to substantially different depths of solid material in said kiln.

5. A gauge for determining the depth of a bed of fluent solid material in a rotary kiln in accordance with claim 1, further comprising a tubular sleeve mounted in the wall of said kiln and extending substantially radially through said wall, means including packing means mounting said tube in frictional sliding relation in said tubular sleeve, so that said tube may be adjusted to different positions only in a direction which is both substantially axial of said tube and radial of said rotary kiln, and scale means for indicatingthe adjusted position of said tube in said direction, all so as to make the gauge constructed as aforesaid sensitive to substantially different depths of solid material in said kiln.

6. A gauge for determining the depth of a bed of fluent solid material in a kiln which is rotated continuously during the operation thereof, comprising a tubular sleeve built into a wall of the kiln and having its axi substantially radial of said kiln and rotating therewith, a tube extending through said sleeve and extending-in a direction radial of the kiln from outside said kiln to a point inside and approaching but short of the axis of said kiln, means including packing means mounting said tube in frictional sliding adjustive relation inside said sleeve, scale means for indicating the adjusted radial position of the inside end of said tube at any adjusted position thereof, a gate valve for closing the outside of said tube, said tube being adapted for radial adjustment such that when said valve is open, some of said fluent solid material in said kiln may pass out through said tube by gravity on each revolution of said kiln, and a stationary circumferential scale disposed substantially in a plane perpendicular to the axis of said kiln and adjacent to the path of said tube for determining the angle at which said tube is disposed with respect to the vertical at the instant that some of the solid material starts to pass out through said tube during any revolution of said kiln, said angle and the adjusted position of the inner end of said tube being jointly indicative of the depth of said solid material in the kiln.

7. The method of'establishing and maintaining a predetermined depth of fluent solid material in a rotary kiln during the operation thereof, wherein solid material is substantially continuously supplied to the kiln adjacent to one end thereof, wherein a decrease in the speed of rotation of the kiln and an increase in the rate of supply of solid material to the kiln each independently serve to increase the depth of fluent solid material therein, and wherein a tube is provided which extends radially inwardly through a part of the wall of the kiln, which tube is adjustable in a direction which is both axial of the tube and radial of the kiln, so as to position the inner end of the tube at an adjustably variable distance short of the axis of the kiln; said method comprising the steps of adjustably positioning the tube, so that its inner end will be in such a position that when the solid material is at the predetermined depth in the kiln which it is desired to establish and maintain, some solid material will pass out through the tube on each revolution of the kiln, during that quadrant of the rotation of said tube in which it moves from a substantially horizontal position to a substantially vertical lower position; effecting a rough adjustment of the speed of the kiln and the rate of feed thereto until some of the material in the kiln passes out through the tube on each revolution of the kiln; determining the angle at which said tube is disposed with respect to the vertical and prior to said tube reaching its substantially vertical lower position at the instant at which the solid material starts to pass out through said tube, said angle in conjunction with the position of the inner end of said tube being accurately indicative of the amount of solid material in the kiln; and further adjustably varying the speed of rotation of the kiln as a fine adjustment until said angle is changed by the adjustment made to a predetermined value.

8. The method of establishing and maintaining a predetermined depth of fluent solid material in a rotary kiln during the continuous rotation thereof, wherein solid material is substantially continuously supplied to the kiln adjacent to one end thereof, wherein a decrease in the speed of rotation of the kiln results in increasing the depth fluent solid material therein, and wherein a tube is provided rotating with the kiln and extending radially of the kiln from the outside thereof to a point within the kiln which is a predetermined distance short of the axis thereof, such that some solid material will pass outwardly through the tube by gravity during each revolution of the kiln when the solid material in the kiln is at the desired redetermined depth; said method comprising rotating said kiln at a predetermined rate of speed in a desired selected range approximating a desired speed, and after the kiln operation has been stabilized, determining the depth of solid material in the kiln by measuring the angle at which solid material first passes outwardly through said tube during each revolution of said kiln, readjusting the rate of kiln rotation in accordance with variations of the level of solid materials in the kiln from a predetermined desired value to a value such that solid material starts to pass out through said tube during each revolution of the kiln when the tube is at a predetermined angle with respect to the vertical, so as to adjust the depth of solid materials in said kiln to said desired value.

9. The method in accordance with claim 8, in which the position of said tube which is measured and at which the solid material starts to pass out therethrough during each revolution of said kiln is one in which said tube is moving through the quadrant of its orbital path extending from a substantially horizontal position to a substantially vertical lower position.

. References Cited in the file of this patent UNITED STATES PATENTS 368,441 Baker Aug. 16, 1887 746,861 Masterson et a1. Dec. 15, 1903 2,092,657 Smith Sept. 7, 1937 2,419,257 Evans Apr. 22, 1947 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,026,728 March 27, 1962 Olav Moklebust et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 55, for "it. is in the lower right quadrant of its mqnement (as seen" read level a of material in the kiln. 0n the other hand if the line 64, for "tube" read it same line 64, for

"rotation" read movement Signed and sealed this 21st day of August 1962.

(SEAL) Attest:

ESTON G. JOHNSON DAVID L. LADD Attesting Officer Commissioner of Patents