US2506618A - Apparatus for sintering ores - Google Patents

Description

y 1950 N. A. SAINDERICHIN APPARATUS FOR SINTERING ORES Filed Jan. :51, 1945 IN V EN TOR. M004 A6 A SANDER/67W Patented May 9, 1950 can 3 Claims. 5;

This invention relates to methods and apps-- ratus for sintering metallic oxides, particularly ores of iron and other metals and oxides, preparatory to smelting.

Sintering is usually conductedin inclined rotary kilns of considerable length, in fact so long that the well-known whipping develops, and as a consequence deterioration of the refractory lining and abnormal pressure on bearings, etc. resum. The ores and fuel are generally mixed before being fed into the kiln, thus causing a considerable wastage of fuel, because of inadeouate control of the reducing action in the kiln. Heat is applied by burning fuel, such as powdered coal, oil or gas at the discharge end of the kiln without positive control over the direction of the flame nor over its temperature. Consequently the ores are treated in an oxidizing atmosphere at too high a temperature, thus forming fused slags which are the cause of ringing, i. e. the adherence of the semi-fused material to the refractory lining, which must be removed by one means or another. This ringing" occurs in the hottest part of the kiln and is principally due to the excess of temperature in the hottest zone of the flame where silicious iron oxide slags i'orm and fuse into a pasty mass. These pasty slags stick to the refractory lining of the kiln and must be removed continually by mechanical means which are difilcult to apply, since the ringing occurs at aj'distance of thirty to fifty feet from the discharge end of the kiln. It is almost impossible to continually and completely remove them, and if they are not removed the kiln may become completely obstructed. It is dimcult, if not impossible, in the rotary kilns now in use to control or correct the temperature and the composition of the mixture during the operation, since accurate fiame control is very difficult to attain and more or less segregation of the material takes place in the kiln due to the rolling motion of the charge. This rolling motion throughout the long kiln induces the segregation and prolongs it unnecessarily. Hence the material produced is lacking in homogeneity, size and composition.

After systematic research and experimental tests, I have discovered a method and apparatus by which the conditions governing sintering in rotary retorts for different oxides, and iron ores in particular, can be properly carried out and controlled. The method is conducted in two steps in two chambers, the first being the feeding and preheating zone, and the other the reaction zone, each zone being located in a separate cylinder having predetermined dimensions and independcut rotating speeds.

I use no burners whatever but maintain a reducing atmosphere in the reaction zone, where the chemical reaction takes place. By maintaining a reducing atmosphere in this zone and a relatively low temperature, pref erably around 1000 C. in the charge, no slagging of siliceous gangue matter with the iron oxide takes place as occurs in the fuel-fired oxidizing kilns, where the hottest zone reaches very high temperatures, on the order of 1300 to 1400" C., so that the slags fuse and the nodules become coated with a glassy iron silicate slag. This glazed coating renders the nodules less permeable to the reducing gases in the blast furnace and in. fact largely prevents reduction by CO gas in the upper zones of the blast furnace, thus requiring a longer time for the smelting process and more coke to produce a ton of pig iron.

In accordance with the present invention, a low and controlled temperature method of sintering finely-divided ores and other oxides, including flue dust, ,mill scale, and the like, is provided, whereby highly porous and therefore readily permeable nodules of any desired size are formed without glazing, because the temperature can be controlled and kept below tthat at which the silicates and other types of slag can form and fuse.

More particularly, the sintering method of this invention comprises first preheating the fineiy= divided material to be sintered or nodulized, hat ing provided sufficient free carbon, for instance eight to twelve per cent by volume, and supplying a measured and controlled amount of heated oxygen-containing gas, such as air, for oxidation of the carbon. The oxygen is supplied only in such volume in relation to the carbon and under such temperature conditions, that incomplete combustion of the carbon occurs, with the result that nascent carbon monoxide is generated at the interface between the contacting carbon and oxide. This nascent carbon monoxide attacks the oxide particles, and reduces th m at their sur faces, so that they soften and be ome sticky, with the result that as the sticky particles are brought into contact by the revolving action of the kiln. they agglomerate and form nodules. I have found that the most suitable air temperature is about '700-800 C. With air at 700 C. the COzCO: ratio is about :40. This mixture is a reducing gas and particularly so if the CO is in nascent state, as in this case. By proper and close control of the carbon and air volume at about 700 C. air temperature, I can raise the CQzCOz ratio to about :30 or above 2 to 1. Although the exothermlc nature of the CO formation raises the temperature of the charge to about 1000 C., the

formation and fusion of slag is prevented by controlling the supply of hot air so as to furnish only sufllcient oxygen for the generation of a reducing gas. The nodule size may be regulated by lengthening the time of balling until they attain the desired dimensions.

A convenient and simple apparatus for conducting the described two-stage process comprises two inclined and. aligned rotary cylinders, the

upper cylinder containing the preheating zone and the lower cylinder the reaction zone. The

material to be sintered is preheated in the prewith it so as to discharge the carbon into the reaction zone in the stated percentage for admixture with the preheated oxide discharged simultaneously from the preheating cylinder. In case blast furnace flue dust is to be sintered, which always contains carbon, it is only necessary to addsuflicient carbon to the ore to bring the carbon content to the desired percentage. A preheated air blast of such volume and temperature to supply the necessary oxygen to induce the fortu're by one or more jet pipes introduced into the reaction zone. Volume and temperature of the air blast are so controlled as to prevent the term perature of the materials from rising to the point of slagging, yet sufliciently high to cause the oxide particles to partly reduce at the surface and thus soften, so when they roll over in contact with each other, they stick together and agglomerate into nodules, the size of which can be predetermined as described.

It will be seen that by the sintering method and apparatus of this invention, a highly desirable andinexpensive sinter is obtained which is not glazed and hence is readily permeable by the reducing gases in the subsequent blast furnace pieration, and which contains an excess of free carbon facilitating final reduction and melting and precluding reoxidation during handling prior tofland whilecharging into the blast furnace or the like. Fora more complete understanding of the intention, reference may be had to the accompanying drawings, in which: -"Figure 1 illustrates diagrammatically a preferred form of apparatus in which the sintering "process maybe conducted effectively and emciently; and

'Fig. 2 is a transverse section through the reacmation with the carbon of nascent carbon mon- 1 oxide is directed upon the oxide and carbon mixcommon shaft l3, but the gear reduction is such that the sintering cylinder is driven more slowly, so that the material remains therein at least as longas it does in the preheating cylinder, although the latter is longer. The free ends of both cylinders l0 and I! are sealed by stationary walls It and I5, respectively, and the annular space between the cylinders at their juncture is sealed by stationary partition It, so that the system is sealed for retention of heat and minimize.- tion of dust loss. Preheating cylinder i ii is provided with the usual longitudinal rabbling flanges or bars l1, so that the material is raised and tumbled through the gases, thus facilitating preheating. The spent gases flow out of preheater it through opening I4 and stack It.

In order to .provide a carbon content in the charge of between about 8 and about 12%, carbon in the form of finely-divided coke, coal, pitch, carbon black, or the like, is added thereto in the sintering cylinder H by means of a tube 20 which extends longitudinally through the entire length of the upper or preheating cylinder, the carbon being fed into the upper end of the tube 20 by means of hopper IS. The tube 20 revolves with the upper cylinder and by this motion the carbon is moved therethrough at a uniform rate and discharges at a measured rate into the lower or sintering cylinder l2. If the oxide to be sintered is flue dust having a carbon content of about 5%; about 3 to 9% carbon is added thereto by supplying the proper amount at l9. If the charge is fine or granular ore, mill scale, or other finely-divided oxide, virtually all the carbon charge, i. e., about 8 to about 12% is added at l9. This carbonis in excess 'of that theoretically required to effect the sintering at the given temperatures, but is so provided to assure substantially uniform carbonization of all the oxide particles. The excess carbon is dispersed evenly throughout the sinter and facilitates subsequent reduction and melting, as well as precluding reoxidation. Although addition of all of the carbon in the sintering cylinder I2 is preferred, the presence of carbon in the preheating cylinder, such as thatwhich is present in flue dust, is immaterial for the reason that insufl'lcient oxygen remains for the reaction and suflicient temperatures are not reached in pre-' heating cylinder ill. The carbon is preheated as it travels through tube 20 and discharges into sintering cylinder l2 at substantially the same point as does the oxide, as shown in Fig. 1. 'The agitation provided by rotation of the cylinder l2 insures intimate admixture of the oxide and carbon, so that each oxide particle is substantially coated with carbon.

The heat necessary to induce the formation of nascent carbon monoxide, which causessoftening and consequent agglomeration of the oxide 50 particles, is preferably supplied by the exothermic Itionand sintering cylinder as seen along the line -1-'-2 of Fig. 1.

Assuming by way of example that the oxide material to be si'ntered is blast furnace flue dust, containing about 5% free carbon, as is common, the'dust is charged into the preheating tube III by hopper II and is preheated-by the hot gaseous \"products flowing through preheating cylinder i0 -:frnm"sintering cylinder l2 into which the former projectsand with which it communicates, as shown. Sintering'cylinder I2 is preferably of larger diameter but shorter in length than the preheating cyIinder l0. As shown in Fig. l, the two cylinders..'lui and 42 are gear driven from a nature of the incomplete combustion of the carbonin a measured and closely controlled amount of oxygen supplied by preheated air at IOU-800 C. The preheated air is supplied by jet pipes 2i projecting through end walls l5 and is into sintering cylinder l2, with their jet apertures directed downwardly onto the mixture of oxide and carbon. Upon being heated by the air to 700-800 C. the desired exothermic incomplete combustion of the carbon is induced in the mixture .so that its internal temperature is raised to about the oxide particles and the. carbon in contaut therewith are heated by the incomplete combustion of carbon, and nascent carbon monoxide is formed at the interface between the contacting carbon and oxide particles. Inasmuch as na cent carbon monoxide is extremely reactive, it reduces and renders the surfaces of the particles adhesive to each other, so that the contacting particles agglomerate and frit together. As they are rolled over in the cylinder i2, these small agglomerates of softened and sticky particles adhere to others, thus balling and forming nodules of any size desired for the subsequent treatment, preferably from about A, to inch in size, depending upon the time they are kept in contact during sintering. When the nodules attain the desired size they are discharged by spout gate 22.

Because they are composed of surface-softened particles, which stick together by virtually point contact without fusion of the whole particle, the nodules are porous but not so readily friable that they crush or disintegrate during normal handling and charging into the blast furnace, for example. As stated, the carbon is supplied in greater quantity than is .theoretically necessary to effect the sinter, not only to assure adequate carbon for each particle by maintaining the carbon monoxide-carbon dioxide ratio above equi-- librium, but also to include some excess of carbon in the finished nodules, which are thereby rendered more readily reducible in the blast furnace as well as being precluded from oxidation prior to charging.

Although the invention is particularly applicable to sintering iron ores for blast furnace use,

it may be applied with equal facility to sintering the oxides of other metals at temperatures below those at which their slags fuse, the temperature being only that which is necessary to induce the formation of carbon monoxide in the nascent state, when it is most active as a surface-softening agent for the oxide to be sintered. Also, although the apparatus disclosed herein is simple and effective, the process may be conducted in other forms of apparatus that will secure the desired result, and it is to be understood that neither the process nor the apparatus are limited to those described or illustrated herein, except within the scope of the appended claims.

I claim:

1. In sintering apparatus, the combination of a rotary sintering cylinder, a rotary preheating cylinder discharging into said sintering cylinder and in gaseous communication therewith, means for rotating said cylinders at different speeds, a feeding spout for supplying the material to be sintered to said preheating cylinder, a spout rotatable with and extending through said preheating cylinder and into said sintering cylinder for supplying carbon to the point of discharge of said sinter material into said sintering cylinder, and a Jet pipe introduced into said sintering cylinder and directed upon the charge therein for providing a blast of preheated air, whereby the sintering action takes place in the sintering cylinder and the hot gaseous products flow therefrom through said preheating cylinder.

2. In sintering apparatus, the combination of a rotary sintering cylinder, a rotary preheating cylinder discharging into said sintering cylinder and in gaseous communication therewith, means for rotating said cylinders at different speeds a feeding spout for supplying the material to be sintered to said preheating cylinder, a tube extending axially throughsaid preheating cylinder and rotating therewith and projecting into said sintering cylinder for supplying carbon to the point of discharge of said sinter material into said sintering cylinder, and a jet pipe introduced into said sintering cylinder and directed upon the charge therein for providing a blast of preheated air, whereby the sintering action takes place in the sintering cylinder and the hot gaseous products flow therefrom through said preheating cylinder.

3. In sintering apparatus, the combination of a rotary sintering cylinder, a rotary preheating cylinder discharging into said sintering cylinder and in gaseous communication therewith, means for rotating said cylinders at different speeds a feeding spout for supplying the material to be sintered to said preheating cylinder, a tube mounted concentrically in said preheating cylinder for rotating therewith and discharging into said sintering cylinder, 9. spout for supplying car bon to said tube for progressive feed therealong as said tube rotated to discharge into said sintering cylinder, means sealing said cylinders against ingress of air, and air jet means in said sintering cylinder for directing preheated air upon the charge therein, whereby the sintering action takes place in the sintering cylinder and the hot gaseous products flow therefrom through said preheating cylinder.

NICOLAS A. SAINDERICHIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 847,664 Hill Mar. 19, 1907 1,446,857 Peiter Feb. 2'7, 1923 1,866,203 Folliet et al. July 5, 1932 1,917,942 Kalling et al. July 11, 1933 2,296,498 Brassert Sept. 22, 1943 2,350,910 Lower June 6, 1944 2,356,024 Andersen et a1. Aug. 15,1944

FOREIGN PATENTS Number Country Date 9,901 Great Britain of 1911

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