US2249087A - Rotary kiln - Google Patents

Description

July l5, 1941.

l. J. MUELLER rRoTAmfl KILN Filed may 11', 1940 2 Sheets-Sheet l Gttornegs July 15,'1-941.

l1 J. MUELLER ROTARY KILN Filed May 11, 1940 2 Sheets-Sheet 2 Gttornegs as a whole.

Patented July 15, 1941 UNITED STATES. PATENT oFFlcE ROTARY KILN Louis J. Mueller, Martinsburg, W.' Va., assignor to The Standard Lime and Stone Company, Baltimore, Md., a corporation of Maryland Application May 11, 1940, Serial N0. 334,632

' 6 Claims. (Cl. 263-32) This invention relates to kilns of the types used for burning limestone, and for burning certain refractories, cements and fluxes. The invention is in the nature of an improvement upon that described and claimed in my copending application, Serial No. 232,662, filed September 30, 1938, now Patent 2,204,145, datedJune 11', 1940.

The material is burned in an inclined rotary tubular kiln, and the purpose of the inventions defined in the prior application and in the present application is to recover waste heat by impartingit to granular material about to be fed to the kiln. Generally stated, the granular material is fed to the kiln from a chamber which extends transversely across ,the entire area of the kiln near its feed and gas ofl'take end. The chamber is of limited thickness measured in the dlrection of the axis of the kiln and is kept full of the material to be fed. The chamber oommunicates with the kiln through a series. of parallel tubular members which are open from the material being treated. Hence a precise rule cannot be stated. However, it is truethat for end to end, are completely unobstructed and regulate the feed of the material to the kiln in relation to the inclination of the kiln and the rate at which it is rotated.

On the opposite s'ide, the chamber communi- 'A cates with the offtake'through a series of similar and conveniently shorter tubes which have no -fiow controlling function but which serve as a of the present invention is the enlargement of the diameter of the kiln by the use of conical sections adjacent the chamber so that the eiiective flow area through the materiall is-somewhat increased.

Another feature of the invention is the proportioning of the length of the tubular passages to their diameter and to the inclinationof the kiln By such proportioning a consistent or uniform feed definitely related to the rotary speed of the kiln may be had. Consequently,

stable operation can be assured simply by proper design. A

The rate of feed is a function of the angle of repose of ,the material to be burned, so that this enters as a factor in the design. Also, the vibration of the kiln incident toits operation introduces a disturbing factor, which varies with any given material and inclination of the kiln, the length of the tubes will ordinarily fall be-f tween 1% and 11A, times the transverse dimension of the tubes, and can be determined experimentally.

Another feature of the present invention is the use of an annular chamber which surrounds the transverse chamber first mentioned and is in restricted communication therewith, the parts being so arranged that the central chamber is kept filled at all times, and any empty space which may exist is local to the annular chamber. lThe effect of this arrangement is beneficial, because it limits. if it does not prevent, inleakage of air. It makes certain that the central chamber, in which the .effective heating occurs, is filled at all times.

Another feature of the invention is the construction of the tubular members as cells in a grid, which may be formed of heat resisting steel.

Because of the large size of most kilns, it is desirable to cast the grid in a number of sectorshaped sections, six being a desirable number, l

Another feature of the invention is the use of Y feed hoppers which communicate through trap gates with the annular feed chamber and which turn with this chamber as the kiln rotates. This arrangement, also, assists in resisting the inleakage of air.

. Various other features of novelty will become apparent as the description proceeds.

A commercial embodiment of the invention will now be described by reference to the accompanying drawings, in which:

Figure 1 is a view partly in elevation and partly in axial section'of the feed end of va rotary kiln equipped with the feeding mechanism according to the present invention.

Fig. 2 is a section @nine une 2 2 of Fig. 1.v

Fig. .3 is a fragmentary face viewof one ofthe honeycomb grids; and

Fig. 4 is a fragmentary section similar to the portion of Fig. 1 and showing on an enlarged scale how the grids are mounted.

upper or entrance end of the kiln.

and which ordinarily is driven by pinion 1 engaging a ring gear 8 encircling the kiln and fixed thereto. Various means for supporting the rotary kiln are known in the art and no attempt has been made to illustrate supporting means for the kiln.

It will be understood that, as viewed in Fig. l, the shell 6 of the kiln extends tothe left fora considerable distance, such kilns commonly being between 150 and 400 feet in length. The inclination of the axis of the kiln to the horizontal is subject to variation, depending on the material being treated. In ordinary commercial practice the range is between per ft. and 3/4 per ft.-

In the commercial use of the present invention inclinations of the order of y" per ft. are customarily used, but this is subject to variation depending upon the character of the material being burned and the treatment desired.

It will be understood that the slow rotation of the kiln causes the granular material to move from the higher entrance end toward the lower exit end and in its passage the material is burned by flames directed through the exit end of the kiln, in a manner familiar to those skilled in the art. The treated material discharges from the low end of the kiln while the products of combustion flow upward and discharge from the Thus there is a counterflow relation by means of which material approaching the burning zone receives some heat from the waste gases flowing to the upper end of the kiln. The prime purpose of the present invention is to increase this heat interchange and recover the maximum practicable quantity of heat from the products of combustion.

Near the entrance end of the kiln the shell is flared outwardly, as indicated at l, thus forming a tapered or conical entrance portion clearly shown in Fig. 1. A portion of the refractory -lining of the kiln is indicated at I8 and it is understood that the kiln may be similarly lined.

Theflared portion 8 of the kiln terminates adjacent an inwardly directed channel ange II and from there on is cylindrical to the line I2, after which it is formed with a reduced conical section I3 connected with the on-take Il. Associated with the off-take Il there is a packed I,

joint I8 designed to permit the kiln to rotate relatively to Athe intake connection i8 of the fan I1.

A second channel flange I8; is formed within the shell and is spaced in the direction of the shell between the flanges rather than cutting it away entirely is simply to retain a portion of the shell and thus secure better strength than can be had if the shell is completely cut away. As far as the operation of the kiln is concerned, the used of the slots has no significance, the important thing being to permit feeding from the chamber 28 freely to the chamber 21.

Sustained by the flange IVI is a grid structure 2I (see Figs. 2 and 3) which is formed of heat resisting alloy steel, conveniently fby casting. Because of the' large size of most kilns it is not ordinarily practicable to form the grid 2l in one piece, and accordingly it is formed in duplicate segmental sections, these sections being indiexcept that the tubular passages in this grid are preferably made shorter. The grid 2i has a flow controlling function and in this flow controlling function the length of the tubular passages through the grid enters as an important factor. The grid 28 has no flow controlling function. On

' the contrary it is simply a, sustaining means for the screen or reticulated partition 30, also of heat resisting alloy steel, which is mounted against that, side of the grid 26 which is remote from the olf-take I4. Except for saving of weight and material, the grid 26 could be identical with the grid 2|. The use of heat resisting steel for the grids is important, but it is even more important in connection with the screen 88, because the small particles of stone tend to stick to a screen of ordinary steel and soon clog it seriously.

The chamber between the grids 2| and 26 is hereinafter called the feed chamber, but in addition is a heat exchange chamber as hereinafter explained. As the kiln rotates, granular material which fills the chamber flows from this chamber through the tubular passages in the grid 2|. thence passes to the lower portion of the` conical entrance end of` the kiln, passing in a shallow stream from that entrance end into the cylindrical main portion 6 of the kiln where the main burningtreatment takes place.

The' length of the tubular passages in the grid 2I4 is proportioned to give the desired rate of feed and is a function of the angle of repose of the material being treated and the inclination of the kiln structure. Ordinarily the length of the passage lies between 1% and 11/4' times the transverse dimension of the same passage.

'I'he passages are completely unobstructed.

Surrounding the feed chamber 21 and turning with the kiln is a supply chamber 28 which is annular in form and conveniently rectangular in cross section. It may be constructed in any desired manner, its bounding shell being indicated generally by the numeral 29.

Mounted on the periphery of the shell 28 which encloses the chamber 28 are a. plurality of feed hoppers 3l. Two are shown and are ordinarily sufficient. The number of such hoppers is not vital. The hoppers 3| flare, as shown, and each hopper communicates with the chamber 28 through an opening co-extensive with the inner small end of the hopper.

This opening is controlled by an inward opening gate 32 which is fixed on a rock shaft 33.

Fixed to the shaft 33 at one end is an arm 3| with adjustable counterweight 35, the arm extending in such a direction that when the hopper 8i is moving through the upper part of its orbit 36 and a gate closing lever 31. The lever 36 is tripped to open the gate 32 at` the proper time by means of 'an inclined cam member 38. The cam member 38 is hinged to a fixed support 39 at 4| and is held upward in its active position by the coil compression spring 42. The purpose of yieldingly mounting the cam 38, as shown, is to permit it'to retreat, so.that if the chamber 28 is full to a degree that opening movement' of the gate 32 is prevented,v the parts will not be overstressed and damaged. ,The gate closing lever 31 operates only in the event that the gate should stick and fail to close. A xed striker 40 is mounted in such position that it will engage the lever 31 and force the gate closed should the counter weight fail to close it.

Referring to Fig. 2, the kiln turns inthe direction indicated by the arrow A. Consequently the material in the chamber 28 is carried up in this chamber and cascades along the dotted line BB. The space above and'to the right of the line B-B is ordinarily empty. Consequently In the operation of the kiln'the supply chamber 28 is kept full at all times, except for a limited space above and to the right ofthe line B-B.

Under these conditions the feed chamber 21 willl be keptiillecl at all times. Rotation of the-kiln causes the. granular material to feed through the 'tubular passages in the grid 2| and thence `fiow in a thin stream down the tubular kiln and through the burning zone. x

The waste heat carried by the products of combustion will be effectively transferred to the y charge of material in the feed chamber 21 bethe cam 38 is located in'the position indicated in Fig. 2 so that the hopper 3| willalwa'ys discharge into the empty portion of the chamber 28. To ill the hopper 3| use is made of a chute 44 to which granular material is fed at a suitable rate. ,Chute 44 is positioned to ldeliver to the hoppers 3| at a point about 60 in advance of the trip cam 38 so that the hopper 3| will be charged before the gate 32 commences to open. Pivoted to the lower end of the hopper 44 is cylindrical gate 45 with sector shaped shrouds 46. The shrouds are pivoted at 41 on the hopper 44. In Fig. 2 the gate is shown in full lines in its open position, the closed position being y indicated in dotted lines..

Pivoted to the gate 45 is an arm 48 which is offset so as to be out of the path of the hoppers 3| but in the path of the striker rod 49 carried by the leading side of each hopper. A-stop 5|! limits the swing of arm 48 in a counterclockwise direction. As the kiln rotates in the direction indicated in Fig. 2 the rod 49 strikes the arm'l48 and the stop 50 limits motion of the arm so that the arm starts to open the gate 45 as the leading portion of a hopper 3| comes under the chute 44. The hinged mounting of the arm 4,8 and the stop is used simply to prevent damage tothe parts in the event that the kiln turns backward, as it sometimes does when being brought to rest. The parts are so dimensioned that gate 45 will be held open only while the hopper 3| is in position to receive a charge `from the hopper and closed at all other times. Further the parts are so dimensioned that the hoppers 33 will not be over filled during the period that the gate 45 is held open.

As a practical matter, control is exercised over the rate of supply of material to the chute 44, but the control mechanism is not a feature of the present invention and hence need not be discussed. It should be observed, however, that if any hopper fails to discharge into the supply chamber 28, because the chamber is full, the hopper simply dumps its load as the kiln rotates, thus disposing of any excess feed.

As the kiln is rotated, a hopper 3|, arriving in the full line position of Fig. 2, receives a charge from the chute 44. Continued rotation of the kiln brings the hopper 3| to the dotted line position of Fig. 2 where the gate 32 is opened by the action of thecam 38 which overpowers the closing tendency of the counter weight 35. Thus the charge cause the products of combustion must pass through this chamber in heat exchanging relation with the granular material which fills it. The products of combustion', thus deprived of the major portion of their heat, pass through the screen 30 and grid 26 to the offtake |4. The olftake fan |1 is provided to insure the necessary draft and should be adequate ,to overcome the resistance offered to flow of productsA of combustion through chamber 21. y Since the chamber `21 is kept filled at all times, the tendency of atmospheric air to enter the kiln through a .hopper 3| when its gate 32 is open is minimized. The `tapered configuration of the kiln shown at 9 increases the area of the chamber 21l and to a considerable extent reduces the resistanceto off-'flow of the products of combustion.

Substantial economies are effected by the in vention becausefthe waste heat is not only reycovered but it is applied to heat the chargefap- For example, =while I prefer' the .hexagonalor' honeycomb grid illustrated, this is subject to modification. It has the advantage of strength combined with lightness and freedom from harm'- ful shrinkage strains.V For these reasons the hexagonal arrangement` appears to be the best that can be devised, but from the standpoint of the operation of the kiln other forms-are technically possible and are within the broad scope of the invention.

Iclaim:

1. The combination of a kiln rotatable on a slightly inclined axis; a feed chamber for granular material to be treated in the kiln, said chamber being concentric with the kiln and extending transversely thereof, communicating with the feed end of the kiln and rotating therewith; a

grid controlling supply from said chamber tov forming passages substantially parallel with theI axis of rotation and large enough to pass the A granular material, and of a lengthbetweenflS/a and 11A times the transverse dimension of the passage; supply means serving to keep said chamber filled with granular material; and means for withdrawing hot gases from the kiln through .said grid and chamber.

2. The combination of aninclined rotary kiln; a connection at one end for withdrawing gaseous products of combustion therefrom; a feed chamber extending transyerselyacross the kiln and located adjacent'the gas off-take end, said feed chamber being bounded by oppositely disposed spaced walls each comprising a gridmade up of slender webs forming tubular passages lextending in the direction of the axis of the kiln; screen- 'enlargement adjacent said olf-take;

ing means sustained by that grid which is near the oil-take for preventingv discharge of granular material Vthrough said grid', and means for supplying granular material i'nto said chamber to maintain said chamber lled.

Y 3. The combination defined in claim 2 in which the grids are of honeycomb formation.

'withdrawing gaseous products of. combustiontherefrom, the kiln being formed with a tapered a feed chamber extending transversely of the kiln adjacent the large end of said tapered portion, said chamber being defined by oppositely disposed spaced walls extending across the kiln, each wall comprising a grid formed of slender webs which intersect to form elongated tubular passages extending in the direction of the axis of the kiln. a screen sustained by that gridwhich is adjacent the o-take end, arranged to prevent the escape of granular material to the off-take; means forming an annular supply chamber surrounding said feed chamber andturning with the kiln, there being openings between said chambers to permit the passage of granular material from said annular chamber to said feed chamber; and means for supplying granular. material to said annular chamber while the kiln is rotating, the annular chamber serving as a surplus supply and thus assuring continuous complete filling of the feed chamber.

5. The combination of a kiln rotatable on a slightly'inclined axis, said kiln having la aring entrance end rotating therewith; means forming a feed chamber for granular material to be treated in the kiln, said chamber being located in said flaring entrance end and extending transv verselyacross the same; a grid controlling supply from said .chamber to the kiln and rotating with the kiln and chamber. said grid comprising connecting slender webs forming passages substantially parallel with the axis of rotation and 6. The combination of a kiln rotatable on a.

slightly inclined axis, said kiln having a aring entrance end rotating therewith; means forming, a feed chamber for granular material .to be treated in the kiln, said chamber being located in said flaring entrance end and extending transversely across the same; a grid controlling supply from said chamber to the kiln and rotating with the kiln and chamber, saidgrid comprising zigzag slender webs which form polygonal passages substantially parallel with the axis of rotation and large enough to pass the granular material, the zigzagconnguratlon of the webs serving to permit flexure of the webs as an incident to thermal expansion whereby destructive stresses are avoided; supply means serving to keep saidchamber filled with granular material throughout the entire area of said feed chamber transversely of the kiln; and means for withdrawing chamber.

hours J. Momma.

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