US2647739A

US2647739A - Method for calcination

Info

Publication number: US2647739A
Application number: US189749A
Authority: US
Inventors: Frank R Kemmer
Original assignee: Individual
Current assignee: Individual
Priority date: 1950-10-12
Filing date: 1950-10-12
Publication date: 1953-08-04
Anticipated expiration: 1970-08-04

Description

Aug. 4, 1953 P4B. KEMMER METHOD FOR CALCINATION Filed Oct. 12. 1950 NIH. ,a NN n :lull/lll Patented Aug. 4, 1953 UNITED TATES 'PAT ENT `O FF ICE METHOD FOR CALCINATION Frank R. Kommer, Larchmont, N Y.

Application ctoher 12, 1950, Serial Nol 189,749

1 Claim. l This invention relates to amethod land .apparatus for heat treating materials in rotary kilns.

The'invention is particularly useful' in vthe carl.- cining of Portland' cement @linker rand, for that reason', will vbe lirs't `illustrated by description in connection with such use.

IThe method and apparatus fof the invention make possible an increase of a filfth or somewhat more in the capacity of the same kiln fired in a conventional manner and with a usual burner,

produce an abnormally high and desirable temperature in the -olinker at the discharge end of 'the ki-ln`shorten the combustion zone, and thus decrease the length of kiln required.

The invent-ion provides also a method and apparatus in which powdered anthracite coal may he used as the fuel, in those regio-ns in which anthracite is mined locally and is the least eX- pensive fuel. The complete substitution of anthracite for such usual fuels as oil, gas, or pfowdered bituminous coal has not been successful heretofore in cement manufacture; the low content of volatile matter and the high `percentagvze of fixed carbon in anthracite coal retard the comi.

'bustion' of this coal when it is tried as the powdered uel in a cement kiln. As a result, the flame is not of the usual plume shape but is consider- 'ahly longer. The long flame gives more Wide distribution of the heat and less concentration of it Where desired in the firing end of the kiln. The limit -tothe amount of anthracite that may be substituted has been around 50% of the total weight of coal used in the firing process.

Briefly stated, the invention comprises .a burner for anaerform suspension of a fluid fuel or'powdered coal, the burner having a slit orifice servlng' to shape the llame of the burning fuelv into a nat band, and means for approximately parallel- ,izing the band flame, both angularly and longitudinally, with the surface of the charge in the kiln. In the preferred embodiment, the invention includes also means for directing a stream 'of secondary air, for the combustion or the fuel, between the lbandV llame and the cement or other material being heated?. This apparatus in operation gives a band llame in close proximity to the einncsed surface of the charge and approximately parallel thereto.

The invention comprises, also., the `method of heat treating material' with the spaced band or ribbon flame as described herein..

The inventionk will be; further illustrated by description in connection with. the. attached drawings 'to which inference` is made.

Fig. l shows a side sectional view of the 'firing (Cl. 26S-52) 2 `end .of .a .rotary kiln constructed in accordance with the invention.

Fig. 2 is 4a ysectional View online A2.--2 of Fig. l.

Fig. 3 is a sectional view on line 3--3 of Fig. l.

Fig. 4 is a sectional view on line 4--4 of Fig. l.

Thesectional views are in the direction of the arrows on the respective section lines. The figures are .in part diagrammatic. The parts not illustrated are conventional.

There are shown :an inclined rotary kiln with outer lshell l0 driven lby conventional ring `gear l2 and gear wheel l'd, the ycharge |-6` undergoing heat treatment, and' va layer I8 of the material of the charge cakedupon the refractory lining 2,0 inside the shell of the kil-n. l

The burner 22 hasv a discharge end v24 in the lshapel of a slit. The slit is vangular-ly inclined, asshown in Fig.l 2, so that the flame 26 is approximately parallel to the exposed surface of the material I6 'being 4heat treated. While the flame v26 spreads andbecomes irregular, it retains the general form of a ribbon or band.

Secondary .air is admitted through the duct 28 and drawn upward` yby the natural draft of the system. A deecting baille 3S extends across. the wall 32 of the duct and dellects the stream of secondary air, to the Iright in Fig. l, that iis, under and into the band flame 2B. This direction of the secondary air prevents the band llame from striking down for any substantial period of time upon the material being heated. This direction of the secondary air also promotes prompt combustion of the fuel.

Another deflector 3l is mounted on the side wall of the hood or tiring head. It may be a part of the ceramic or cement construction of the head as shown, for instance, in Fig. 2. The location of this second deflector is adjacent to the end of the kiln and on the up-side thereof as the kiln is rotated. The position is. below the level of the upper edge of the band llame. This deector ex'- tends in a sloping manner generally toward this upper edge of the flame. This delector 3| serves the purpose of tilting the stream of secondary air, so as to cause its upper surface to parallel more closelyv the angle of the band name.

In case of cement manufacture, secondary air ordinarily is that which issues from the elink'- er cooler.4 disposed below the rotary kiln. In a representative run with the apparatus described, vthe temperaturey of the secondary air delivered from the cooler to the kiln. was 819 F., as com.- pared.- to only 692 for the same setup with standard.. round.' burner andy plu-me flame.

Materials of construction for the various parte of: the kiln firing end: described are those which 'clination downward towards the down tothe zone IB.

ffmerely 'lelizing This parallelizing of the burner and the are usual in apparatus of this kind. Thus, the shell I in the kiln may be steel, the lining 20 a high grade refractory block, the duct 28 l'lre brick, the burner 22 with the slit opening 24 steel, and the deflector 30 fire clay in fired condition.

Some of the principal advantages of the invention are stated above. There are others.

What is desired in the calcination of cement or the like is intense heat transfer by radiation. The equipment shown in Figs. 1 and 2, for instance, keeps the flame out of contact with the said material and inthe quadrant or quarter of the kiln containing material I6. The flame is in extremely close juxtaposition to the material, however, so that the radiation to the material is much greater for unit area of exposed surface thereof than to the more remote parts of the circumference of the kiln. There is obtained not only increased transfer of heat to the materialto be calcined, with proportionate attendant in-I cr'easein the rate at whichLthe material may be fed through the kiln, but alsoa decreasedper- -centage o'f'thetotal heat .lost .through the kiln As a result of lesser heating. of the kiln lining, there is a decrease inthe thickness of the caked layer I8 inside the kiln, as from the usual Sor 9 inches to about to 6 inches. This increases the effective free space within the kiln.

Using this system in Portland cement manufacture, there is possible an increase of vproduc- 'tion per kiln in excess of 18% of the normal pro- -duction' capacity.' To obtain this increase of capacity, without decrease ofthe `final temperae ture of calcination below theu'sualVthe speed of rotation of the kiln'is increased. l

With the apparatus and method described, the firingzone in the cement kiln may be shortened from the usual 25-30 feet to 15-20 feet.

The operation of the equipment and the method will be evident from the discussion that has been given above. In general, thekilnis mounted at a slight indischarge end andy 'rotated ina usual manner. The fuel if oil is atomized' or if coal is suspended in finely powdered form in the barrel of the burner-22. The atomizing or suspending medium isair. The atomized oil or the aeriform lsuspension of the coal is then delivered through the slit 24 constituting the firing or discharge end of the burner. Natural gas may be used as the fuel, with all the air for its combustion introduced outside the stream of the gas issuing from the slit inthe burner. 4 n

The burner is mounted by usual means, as by bolts securing it to a supporting framework (not shown) at such an angle radially that" the length ofthe slit 24 is approximately parallel'to'the exposed surface of the material being calcined.

`This gives a flame that at the start is also approximately parallel -to the s aidfsurface, all as shown in Figs. 2 and 4. In the case of cement clinker this angle of repose in the rotating kiln is about as shown in Fig. 2. The :angle varies somewhat and reaches about the angle shown by the steeper line Il. before-sliding or tumbling In addition to the angular mounting of the burner radially inthe manner stated, the `mounting meansA also establish the longitudinal axis of the burnerapproximately in the sameslope as the slope of the rotarykiln itself. The means are usual, the. setting being yadjusted to give thelongitudinal paral- .or powdered coal burner.

band shaped name issuing from the burner prevent the flame, as it extends into the kiln, from striking down on the material being calcined and the stream of secondary air under the flame furnishes additional protection against overheating; the invention includes not only the parallelizing of the burner and the band flame with the kiln, as stated, but also the discovery that striking of the flame at a sharp angle upon the material being calcined is objectionable and in fact is not permissible, particularly when there is used a fuel of such great caloric power as powdered anthracite coal.

With the condition described, it is now possible to substitute powdered anthracite to the extent of 100% for bituminous coal or oil.

It isl possible under my conditions also to form quickly the coating I8 in the firing end of the kiln. VThis quick formation of the coating is contrary to experience with the conventional piume flame of a cylindrical burner. v. With the conventional ,burner and llame, thereis considerable Vlapseof time after akiln has been rebrickedand placed under Afire before the coating yI8 forms.

..cined. In general, the size ofthe slit is one which has approximately the same area as the conventional round outlet of the usual type of oil We have found particularly satisfactory results when thelength of the burner slit is4 about tento ninety times the width of the slit. With coal, dimensions that .are suitable for the outlet slitin the burner are lengths ofl 3 to 6 feet and lwidths of to 2 inches or so. The length of the burner slit will be larger, the larger the kiln diameter. Three feet lis about the right length of slit for a 9 foot kiln and vefeet for a 12 foot kiln. l

In general, the length of theslit in the burner is about 30% to 40% of the overall diameter of the kiln;-that is of the shell l0, or about v20% to 30% less than the width ofthe exposed surface ofthe charge being calcined and represented by I5 in the drawings. p

The spacing of the burner is about 4 to 10 inches above the level of the. upper surface of material I6. Y

The invention will` be further illustrated by the specific example of the practice of it.

Example I have applied my method and apparatus to a rotating kiln having a steel shell 9 feet in diameter by 1,25 feet long, with a lining of refractory 6 inches thick, with aconventionalburner of a diameter of 8 inches, Vand-with powdered bituminous coal asthe fuel. The ordinary plumelike flame made possible an output of clinker averaging 39 barrels per hour. With my slit burner, of length of slit approximately 3 feet and width'l, inch, I increasedtheoutput to an average of 46.2 barrels of cement clinker pei` hour,

va gain of 18% in rate of production.

method, Thus the flame temperature was raised by approximately 43 F. to 2746 F., with the possibility of maintaining a flame temperature of 3000 F. if desired. IThe temperature of clinker discharge from the kiln was 2l70 F. as compared to 2040" F. in the conventional operation. The temperature to which the secondary air was preheated in the clinker cooler was 760 F. as compared to 600 F. with the usual round burner. In a series of separate kilns in which my method and apparatus were used, it was found in each instance that the speed of the kiln could be increased. In fact, the speed was increased. Also the speed of the clinker cooler was increased, to take away the clinker and prevent accumulation of the increased production to an undesirable depth in the bed in the cooler. The proportion of total heat supplied which goes into the nished product was increased, with resulting fuel economy per barrel of cement made.

The procedure of the example and the general method described is useful also in calcining limestone to lime, aluminum hydrate to alumina, magnesite to magnesa for basic refractories, sintering red mud from bauxite rening by the Bayer process, nodulizing ores of iron or manganese, and volatilizing zinc oxide from zinc plant residues.

So used, my method and apparatus give increased capacity per` kiln and fuel economy per ton of output. Also there may be used anthracite to the extent of '75% or so, the remainder being oil or bituminous coal. For some uses, anthracite may be employed exclusively.

When the material is changed from the Portland cement of the example, the temperature established in the material is made that which is accepted practice for the particular material used. The rate of feed and consequently the rate of production per kiln is increased, however,

to make full use of the greater rate of heat trans'- fer from the closely spaced wide band of llame to the material being processed.

It will be understood that it is intended to cover all changes and modications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departure from the spirit and scope of the invention.

What is claimed is:

The method of heat treating material in an inclined rotary kiln which comprises advancing the material with inclined exposed surface through the kiln by rotation thereof, introducing into the lower quadrant of the firing end of the kiln, which quadrant contains the material to be treated, a ame that extends generally parallel to the length of the kiln, that is of the general shape of a band, that is disposed in close proximty to the inclined surface of the said material, and that is tilted so that the flame is approximately parallel to the angle of repose of the said material, and introducing and deflecting a protective stream of air between the said band and material, so that the stream is guided into a path that is approximately parallel to the flame and surface of the said material, the introduction of the air serving to prevent contact of the name with the material.

FRANK R. KEMMER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,034,180 Glenn Mar. 17, 1936 2,487,369 Plotner Nov. 8, 1949 2,555,289 Nagel May 29, 1951 2,584,808 Newhouse Feb. 5, 1952