US2939693A - Rotary kiln - Google Patents

Description

9 June 7,'1960 A. F.0LD ETAL ROTARYKILN Filed Aug. 6, 1956 mvENToRs R. E GIBSON A F. OLD 61% H9102 BY AEY vip-.vr-

K 12,939,593 l ROTARY KILN Albert Floyd old, Brema B1ff, va.,ana Richard-Francis' Gibson, Albemarle, N.C.', assignors to Southern. Lightf f Thispinvention relates to heat treatment and more particularly to an improvedkiln structure and process espe- -cially adapted for the production offl lightweight .aggregate.'Y The apparatus and the general class of materials which are treated therein are in the same broad class as those 4described in our Patent No.Y 2,721,069" although I materials would--expandlwand-have useful properties in their.;expandedY form,' the presentA invention-y inclndes apparatus and process-by,means` of which thef'upper temperature limit may beclosielycontrolled in order to .achieve additional useful characteristics of thematerial ,such-as glassification of the outer skinl and walls, `this requiring very close control ofwthevtemperature, lwhich has' not been-commercially .possible heretofore. In thegkiln heat treatment processr it is necessary-that kthe material'be uniformly heated in yorder to obtainuclo'se control ofthe resulting product and to obtainrnairimum benefitV fromfthe powerinput tothe kiln.; l It has?V long been-known that chains or bars orother'njixingdevices on the inner wall of the. kiln -assistedin stirring the material so-that. the hot -gases `could more nearly funiforinly .heat .allportipns ofv it. However, the use of .such 'mixing .devices has tended to increase the erosion of "the kiln becauseof the continual lifting anddroppingof the material'v within the kiln. Furthermore,y the lifting .devices themselves because of being .exposed to thelhigliA kiln temperatures have had a relatively short life;

A further problem has beenthatbe sity of keeping an adequateow ofy material passing through the kiln at all times,.a temporaryinterruption yin the supply has oftentimes required thatth kiln'be shutdowninv order to prevent injury lto thefkillfand to maintain a--high4 quality product. A- shutdown ofl akiln of substantial size, in order to creplace'liningflifting devicesor because of a temporary cessation of supply, ysubstantially increases the cost of operation andreduces the outputk and is" therefore undesirable, it` being `the lcustom tolkeep kilns in continuous operation solfar; =as possible. Y-

` Y f V Accordingly, it is an object of' the present invention to provide an apparatus and process for the heat treatmentof raw materials to produceV an improved lightweight aggregate, the-process and apparatusgbeing particularly designed` to permit close controlofY such lheat treatment, and vparticularly vat the maximum temperature Yto which thel material is raised.'

A further object is to provide a kiln of nominal-'diam-?" causeof tlie. neces- 2,939,693 Patented June. 7 -1960 ice eter whichis substantially equivalent to a kiln of larger Ydiameter insofar astemp'erature control and eciencyof operation are'concerned.lA Y, ,A/,furthefobject is-toprovide akilnwhyicfhis highly ecintnopcration'Tandlin which erosion and exposure to "injurious'ly high 'temperature of l the wall@ and mixing devies, respectively, arel'reduced.' l

` A further object Aof the invention is to provi i Y v vinfwhich thebperator may be constantly'awarepf the 10 t'mperature of the'irnatleriallatlkey.looationswithin the that he maycontrol 'its operation accordingly. vOtherobject's' -ofthe invention will :become apparent j'fromft-he following descriptionv in conjunctionwith the accompanyingdrawings, in'whichz i rig. 1 is `aside-elevation of a kim @garnered ifi-ae` cordance'fwith the present invention; A Fig. 2, a-v'ertcal section to an enlarged scale of the intermediateA enlarged portion of the kiln of Fig. 1,;-.

Fig. 3, la section on the line 3-3 of Fig. V2; andk l f Y Fig. 4, a section on line 4---4 oi"1,f"ig.` A2.

f Although the kiln of the present invention may be used for the processing of various 4n'ia'iteri-als it Vhas been rfound'to. be` particularly useful in the treatment of nonargillaceous" slate which is` described in our Patent 2,721,069. It hasbeen found that gan improved lightweightaggregate .A may be. producedlfrom such argillaceous slate ifthe material vis raised" toA a. .temperature in theppp'er portion of thecriticaltemperature. range. Bysubjecting thefmaterialto' the' upper-,portion of the critical .temperaturerange it has. ,been pc'ssible lto,pro .duce materialhaving faglassy eirternalskin and'one'4 in '.Whchs[substantially all of the' int'ernalfcellifwlls, are "glassy'f" Y" u 'fa/ l ...--T heg1aSSy.phase prddu reas'ns., -For` exa'mple,` -asfanlfaggrgate ,in concreteit `hasfben -ffound thatthe ,mixture requires less Water .because-the1agg'regate lhasg'lessrabsorbency. It fis: well known that' reduction of .fthe quantityof vwater--used-in .producing concretedncrea'ses its strength.. ,A2 further 40 ,advantageis that'fbleeding of the` concret isfdecrsed j'iffa lsmal lemnmmt df waters used.

It has been. diicult or substantially. :tp

"ture within close enoughl limits, and attempstof'lieat vmaterial tothe upper 'portion ofthe critioal "'rang'e have Lresulted.,in.'ooalescence of tlieamaterial, the ,breaking down of ir lcells` and'Y other deiiciencies, resulting 'in Joss. .The present'inventionnot only plfvidesjforl,anPa-Iatus vand process lfor producing glassy phase )aggregate under vclosely controlled temperature conditions butfalso for .increasedleiciency of operation and reduction in:wear Aon the lining and lifting devices of the kiln. V A, Briefly stated, one embodiment ofthe present invenftionisV a kiln having a short enlarged section with lift- ;ingidevic' therein at its feeding end, a section of uniform A diametefoffapproximately half the total length-connected .to thefjfeeding end, a substantially enlargedsection of substantial length with lifting devics'therein,.another sectionl of; reduced diameter, anda .sectionof slightly 6o enlarged-diameterat, the dischargeend. Temperature responsive and indicatingdevicesare ,mountedV at speciiied locations on Vthe kiln wall and connected-to gauges at a central-*control pointbymeans of Iwhich the operator `.may atany :moment ascertain-.the condition of material -at spacedlocationslwithin the kiln., .f "f

In passing 'imo and thmughv the VVfeed end .the raw material is thoroughly, exposedutoV discharging gasesgby being liftedl Yandgdropped whichresu-lts fin substantially V lowering the ternlgierature Yof the discharginfggg"A e'sjgfas ".0 nellasgremOY-ing' misturaand extremely .fine Irrfils from' the raw material as it enters rtheV kiln. Themate- 3 rial then passes through approximately 50% of the kilns length during which it is slowly raised in temperature, lifting devices not being necessary in this portion, thereby eliminating most of the wear on the lining which would otherwise occur to substantial degree. The material then enters the substantially enlarged section which is approximately 25% of the total length of the kiln and .is provided with lifting devices. Within the enlarged'section the material is exposed thoroughly to the hot gases, its

axial movement being controlled by the structure and varrangement of the lifting devices and the speed of rotation of the kiln.

After leaving the enlarged section in which the material is heated to just below thercriticalrange, it passes into the zone vof .extreme heat in which it is rapidly raised to the necessary temperature and then discharged.

Referring to the drawings, a kiln is illustrated having an enlarged feed end section 11, a nominal size intermediate portion 12, a substantially enlarged section or mixing chamber 13, a relatively short section of nominal size 14, and a slightly enlarged section within which the maximum temperature occurs and from which the material discharges.

A t the feed end the kiln extends into a housing 17 from which a stack 18 extends, the raw material supply chutes 19 and 20 .preferably extending into the stack and `housing into the enlarged feed end section 11 of the kiln.

"The kiln is rotatively supported by means of rings 22 at spaced locations on its exterior which are mountedon rollers 23 carried by blocks 24. The kiln may be driven from a ring gear 25 by suitable power means, not shown.

` At the discharge end the kiln has a firing hood 26 With further reference to the feed portionll ofthe` kiln it will be observed .that it has a straight reduced neck 31 extending into the housing 17 and a tapered connecting portion 32 attached to the section 12 of the kiln. The straight neck facilitates receiving the kiln within the housing and provides a recess at its junction with the section 11 for receiving material from the chute. A plurality of lifting devicesv 34 are placed within the portion 11 for initially mixing and stirring the entering raw material, thus removing moisture and extremely ne particles ',andincidentally lowering the temperature of thestack gases.

AJust beyond the rtapered connecting portion 32 a temperature responsive device 36such as a thermocouple or ythe like, is engaged with a collector ring 37 on the outer wall of the kiln. The device is connected by a kline 38 toV a gauge 39 which may be conveniently mounted -at a central location such as adjacent to'or within the hood 26 so that .the operator may be able to see it from within the hood.

As thermaterial slowly moves through the kiln from the .entrance to the discharge end its temperature is Egradually' raised. The speed of movement lengthwise vof the kiln depends on the vangle of inclination of its axis to the horizontalV and the speed at which the kiln is rotating.

VThe ymixing chamber Y13 through which the material next ows has tapered connecting portions 41` and 42 atits entering and leaving ends respectively, and a central advantageous in connection with processing of the raw material Vdescribed to have them arrangedas shown.

',lfhe vliftingdevices 44 arelinclinediat an angleto face ,intentie section 12 ,and'tend to hold hacker"retardthe flow of material into the section 43 whereas the lifting devices 46 are inclined the other way within the portion 42 to speed up the flow so that heated material may be more rapidly moved into the zone of maximum temperature and also to cause hot gases entering the enlarged section to become turbulent at this point.

lt will be observed that the depth of the raw material within the section 43 is higher than the lifting devices at the bottom of the kiln and is of substantial depth.

As a result, the material being lifted and dropped instead of falling on the lining of the kilnand the lifting devices falls on to the bed of materialfat the kilns bottom. Thus, wear and erosion onthe .kiln lining and lifting devicesis substantially minimized. i

Because :of the large y,volume of,A materialfwithin the mixing chamber 13 and the thorough lifting, dropping and stirring therein, the velocity of the hot gases passing therethrough is reduced substantially, say on the order of 60%, and excellent heat transfer isV afforded. `The temperature of the -gases leaving the enlarged section are substantially lowered resulting in lower heat `losses through radiation and the like from the remainder of the kiln namely, sections 11 and 12.

In addition to the decrease in wear already mentioned, the enlarged section mixing chamber assures equalheating of all sizes of material so that closer temperature control in the succeeding sections is possible. Furthermore, 1in the event that the supply of raw material to the jfeed end is temporarily interrupted it is not necessary to shut down operation of the kiln because of the substantially larger quantity of material that iso-being processed therewithin which is capable of absorbing a correspondingly larger amount of heat than a smaller quantity without overheating either the material or the kiln."

From the enlarged section 13 the material flows into the smaller section 14 -and then into the firingvsection 15 which may be slightly larger than the section 14 if desired. f Within the tiring section the material is quickly raised to the upper limit of the critical range of temperature -atwhich it enters the glassy phase and is then discharged from the kiln.

`Other temperature control devices such as that indicated Y,at 50 just prior to the materialsl entering the enlargedV section 1?:Y and 51 just prior to the materials entering the section of maximum heat may be provided. By observing the temperature at various critical locations in the kiln as indicated lthe operator may be informed constantly of the condition of the material. i

The dimensions of the various sections of the kiln may be varied to `suitrthe material being processed and 'operating requirements. As an example, however, of one embodiment, the kiln has a total length of feet, a nominal diameter of 8 feet, and a mixing section of approximately 91/2 feet diameter, the tapered portions of theenlarged section being approximately 5 feet in length and the entire enlarged portion being approximately 25% of the ykilns length as mentioned above.V Variations from about 15,-35% should produce good results, depending on the `other conditions. Further, the pitch or angle of inclination of the axis to the. horizontal is about 3%; of an inch per foot, it being understood that the size of the enlarged section is related to the pitch of the kiln.

Accordingly, it will be understood that the invention includes .a novel kiln having at least one enlarged vsection Vwith mixingdevices in whichthe transfer of 4heat tothe duced havingv desirable characteristics not 'previouslyobtainable.

i It will be obvious to those skilled in the art that various` becomes plastic and expands at a critical temperature range to produce a lightweight aggregate, comprising introducing the raw material into the upper end of a rotatably mounted elongated inclined kiln,`initially removing moisture and extremely fine particles by lifting and dropping the material in the gases discharging from the kiln, rotating the kiln to cause the material to progress downwardly therethrough, subjecting it to a slow' moving substantially restricted ilow of heatedproducts of combustion at a temperature below that required to produce the aggregate for approximately one half of the kilns length, accumulating a relatively large mass of material just prior to its reaching the firing end of the kiln at which the maximum temperature is attained, continuously lifting and dropping the accumulated mass of material as the heated gases pass therethrough to raise substantially all of said material to just under the critical temperature range and reduce the temperature of said gases substantially, .and passing said material into the tiring end of the kiln and heating it to the upper range of the critical temperature suicient to produce expansion and glassitication, and then immediately discharging it from the kiln.

2. The method of heat treating raw material to pro-` duce a glassied aggregate at a critical temperature, comprising spreading it at a relatively shallow depth along a portion of substantial length in a rotary inclined kiln while subjecting it to the flow of heated gases at a temperature below the critical temperature to produce the aggregate, accumulating a relatively deep mass of the material in a'relatively shorter length of the kiln, continuously lifting and dropping the relatively deep mass, passing hot gases through the material as it is lifted and dropped to substantially raise its temperature close to but below a critical upper limit, passing Vthe material into a zone of maximum temperature slightly above that attained in the preceding zone, and sufficient to produce expansion and glassicationof its outer skin and of its cell walls, and immediately discharging the material.

3. A rotary kiln for producing a glassied aggregate, comprising an elongated substantially cylindrical housing having spaced portions of different diameter and inclined from its feed end to its discharge end, said kiln having a major portion of nominal diameter adjacent to its feed end and subject to a low initial temperature, an intermediate mixing chamber constituting approximately 15-35 percent of the length of the kiln and subject to an intermediate temperature lower than that necessary to produce glassiiication of an aggregate, and a portion connected to the mixing chamber to receive the material therefrom and subject to the maximum temperature in said kiln for attaining glassiiication of an aggregate and for immediately discharging the material therefrom, said mixing chamber being substantially larger in diameter than the portions to which it is connected and having tapering sections for connection thereto, and liftingv devices mounted in said mixing chamber von the inner wall thereof, saidlifting devices which are mounted on the inner Wall of the tapering section leading into said charnber beinginclined upwardly with reference'to the axis of the kilnY on the rising side of the kiln Wall in order to impede the axial movement of the material into said mixing chamber, and the lifting devices which aremounted on the inner wall of the tapering section leading from said chamber'being inclined downwardly with reference to the axis of the kiln on the rising side of the kiln wall in order to assist in the axial movement of the material from out of the chamber.

4. The invention defined in claim 3, and temperaturev responsive means on the kiln adjacent to the mixing chamber and to the feed end of the kiln.

References Cited in the file of this patent UNITED STATES PATENTS 977,244 Wiebe Nov. 29, 1910 1,649,839 Marston Nov. 22, 1927 1,793,408 Kronstad Feb. 17, 1931 1,834,963 Newhouse Dec. 8, 193-1 2,104,040 Hurt Jan. 4, 1938 2,111,783 Hults Mar. 22, 1938 2,430,601 Cleary Nov. 11, 1947 2,715,283 Halldorsson Aug. 16, 1955 l

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