Rotary kiln
United States Patent 2484911

This invention relates to rotary kilns, and more particularly to the control of the place and of the character of combustion taking place in the kiln. Heretofore, a mixture of raw material and solid fuel, such as coke, has been supplied to the kiln at its feed end. Since, under such circumstances,...

Merritt, Seil Frances
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Frances, Merritt Seil
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75/474, 75/476, 75/477, 252/378R, 414/149, 432/110, 432/117
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This invention relates to rotary kilns, and more particularly to the control of the place and of the character of combustion taking place in the kiln.

Heretofore, a mixture of raw material and solid fuel, such as coke, has been supplied to the kiln at its feed end. Since, under such circumstances, there is no control of the combustion, it normally starts too early in the progress of the material through the kiln. This is not only inefficient, but it tends to cause rings to form on the kiln lining.

Moreover, it requires coke of particular characteristics, when so used.

Therefore, it is an object of this invention to control the place or zone of the combustion with respect to the length of the kiln. Another object is to be able touse cheaper grades of fuel, such as breeze, which is a by-product now difficult to use in rotary kilns. Another object of this invention is to devise directional air streams or jets so that not only can the place of addition of the fuel be controlled, but also the place of impingement of the delivered streams of air precisely into the combustion zone for efficient combustion therein. A further object is to devise means whereby coke can be delivered into the kiln at predetermined places so that it can not only be used as fuel, but can also be used for oxygencombining or reducing purposes, such as in the reducing of iron ore to yield metallic iron. A still further object is to arrange for the addition of reagents for chemical reaction purposes into predetermined places in the kiln. Still further objectives will appear as the specification proceeds. The invention resides in the use of scooping members carried by the kiln adapted to scoop up the coke or other additive for the kiln. Rotation of the kiln causes the scooped-up material to be carried up with the scoop rotating with the kiln until it reaches the zenith of rotation, whereupon it falls through an aperture or opening (hooded by the scoop) into the kiln. This arrangement may or may not be supplemented, in the concept of this invention, by the use of air-jets that are directionally controllable to deliver air into the zone of combustion that is determined by the place of such fuel-delivering scoop. The same scoop, or an additional scoop can, if desired, be used to deliver other additive material to the kiln, such as reagents for influencing the chemical reactions taking place in the kiln. And this invention may, if desired, include automatic devices for supplying such a scoop with predetermined amounts of fuel or of additives, or both. 65 The best embodiment of the invention now known to me is shown and described herein for illustrative purposes, but this is not to be taken as limiting, for obviously the invention is capable of other embodiments and especially structural modifications and rearrangements. The scope thereof is defined in the appended claims which should be read with the usual latitude for equivalents and reversal of parts.

The invention has been illustrated in the accompanying drawings, in which Figure 1 shows a vertical longitudinal view through a kiln in which this invention is embodied. Fig. 2 is a vertical transverse sectional view taken along the line II-II in Fig. 1. Fig. 3 is a vertical transverse view taken through the kiln showing a modification; while Fig. 4 is a partial vertical longitudinal view to show the modification of Fig. 3 from a different angle. Fig. 5 is a transverse vertical view through the kiln showing a modified form of feeding apparatus associated with the scoop means. Fig. 6 is a partial isometric view of the arrangement of Fig. 5.

In the drawings, I indicates generally a rotary kiln, having a cylindrical casing or shell 12, and a refractory lining 13; a stationary shield 14 at the discharge end, and a feed supply means I1 at the opposite end. The kiln is provided with the usual tires 16 running on rollers 17, and the kiln is rotated by suitable power means which are not shown. 20 represents an aperture passing through the lining .13 and the shell 12 of the kiln, which communicates with the interior of scoop means 21 providing a feed-conducting channel or curved conduit 22. The scoop is preferably, although not necessarily, rectangular in cross section, and it extends peripherally around the shell 12 through slightly more than 180 degrees. The scoop has a closed end 23 hooding the aperture 20, and an open entrance end 24. The scoop 21 is more or less horn-shaped as shown in Figs. 2 and 3 in that the cross-sectional area at its entrance end is greater than elsewhere, and the cross-sectional area diminishes as its closed end 23 is approached. Duplicate scoop means may be used at other places on the kiln, such as indicated generally at 25.

Burner assemblies or arrangements 30 are associated with the shield 14. They preferably are of the type shown and claimed in my Patent No. 2,137,185, patented November 15, 1938. The gist of this arrangement is that it is constructed and arranged to direct a flame onto the furnace burden or bed of material being heat-treated therein, in a manner whereby the impingement of the flame on the burden can be accurately and precisely controlled. For illustrative purposes, I have shown only one such burner in Fig. 1, although a number may be used, and I have shown a nozzle 31 passing through a ball arrangement 32 capable of angular adjustment, and the ball arrangement is adjustably held in an opening 33 in the stationary shield 14. 34 represents a conduit for conducting gas, or air, or air and fuel, to the burner, whichever is to be used therein. Dotted lines 35 indicate the predetermined zone in which the flame from the burner 31 can be controlled, especially to include a plane transverse of the kiln which corresponds to the scoop means 21. Heattreated material is discharged through channel 26 in shield 14.

Adjacent the aperture 20 through the kiln, the refractory casing 13 can be arranged as shown in Figs. 3 and 4, wherein the aperture 20 is surrounded on the interior of the kiln by dam means exemplified by an annular boss-like protuberance 37, and the refractory bricks 38 and 39 (for instance) adjacent thereto are stepped down from the level of the protuberance 37 down to be flush with the lining 13. This arrangement is not shown in Figs. 2 and 3, but of course could be used therein.

Material to be fed to the kiln through the scoop means 21 can be held in a pile 40 as shown in Fig. 2, or it can be held in a hopper 41, as shown in Fig. 5, having a chute 42 whose outlet is controlled to be opened and closed by a closure or gate 43, preferably pivoted at 44, whose pivot pin has an arm 45 terminating as an enlargement such as a ball 46 adapted to slide up, along, and then drop off a curved inclined plane-shaped block 47 carried exteriorly of the kiln shell 12.

The block 47 has a curved inclined from face 48 and a rear face 49 that is radially disposed to the shell 12.

In operation, the charge of material to be heat treated in the rotary kiln, is supplied thereto through the feeding arrangement 15. Rotation of kiln that is inclined downwardly toward the discharge end, causes the material to progress along the interior of the kiln as a bed extending from the feed end to the discharge end of the kiln. Meanwhile the material is heated by means of the burners shown generally at 30. In the preferred form, only air is supplied by this burner arrangement, while solid fuel is supplied to the kiln at a predetermined place or zone by means of the scoop 21, but it is within the concept of this invention to use the combination of fuels-either solid or liquid or both.

As the kiln rotates, its scoop 21 rotates with it and when the open end 24 of the scoop reaches the nadir of its travel (as shown in Fig. 2), the scoop picks up a quantity of fuel from the pile 40.

Continued rotation of the kiln causes the fuel so picked up to slide or be carried along in the scoop until it reaches the closed end 23. Further rotation carries the fuel in the closed end 23 upwardly until the aperture 20 approaches its zenith, whereupon gravity causes the fuel to fall through the aperture 20 into the kiln. The annular boss-like arrangement 37 of Figs. 3 and 4, if used, protects the flow of furnace charge back out through the aperture 20 because the boss acts more or less like a dam around the aperture.

This method of supplying fuel to the kiln permits the use of residuals, such as coke breeze, anthracite refuse, river coal, peat sawdust, or mixtures of these. And they may be so fed without drying or grinding. Proper combustion is assured by directing the impingement of the air stream or streams from the burner 30 directly onto the bed in the kiln in the zone thereof which receives the solid fuel so fed by means of the 6 scoop 21.

A modified method of feeding solid fuel to the kiln through the scoop 21 is shown in Figs. 5, 6 and 7, wherein, when the block. 47 carried exteriorly of the kiln shell 12 approaches its zenith, it engages the ball 46 on the arm 45 and the inclined face of the block causes the pivot pin 44 to rotate, whose rotation causes the closure or gate 43 to open to deliver a charge of solid fuel into the up-moving open end 24 of the scoop 21. Continued rotation of the kiln causes the ball 46 to drop off the radially disposed rear face 49 of the block 47 which causes the gate or closure 43 to close the chute 42 again. Continued rotation of the kiln then causes the fuel load in the scoop 21 to be delivered into the kiln through the aperture 20. If a further scoop such as 25 is used, it can operate in the same way either to feed fuel to the kiln, to feed a quantity of material to be heat-treated in the kiln, or some reagent or additive, as hereinafter described.

A further possible modification is that scoop means such as 21 or 25 may be associated with the kiln but in reverse direction, so that by its use, material can be discharged from the kiln prior to its otherwise normal exit through the discharge channel 26. That is, the scoop is so directed around the kiln with respect to rotation of the kiln, that rotation of the kiln causes material to pass from the kiln into the scoop and then out from the scoop. In other words, passage of material in the discharge scoop is just the opposite to what it is in the feed scoops 21 and 25. When a scoop is so used as a discharge means, the dam means 37 is omitted so as not to interfere with outflow of material from the kiln through the aperture into the scoop. By such an arrangement, portions of the charge of the kiln can be tapped off so that a determination can be made of what has taken place or the extent of heat-treatment in the kiln.

Up to the present time, it has been economically impossible to feed the fuel for combustion with a raw charge because the combustion started too early in the kiln and caused ridges or rings to build in the kiln. By using this method of feeding, it is possible to feed the fuel, whether it be coarse or fine, wet or dry, liquid or solid, into the kiln at a predetermined place. By regulating the impingement of the air on the bed, it is possible to take care of the recovered heat by preheating the air, and it is also possible to control the zone of combustion so that the heat is libl led at a predetermined place.

In Fig. 1 the distance A may be 25 feet if it is desired to have the combustion take place in a zone 13 feet to 6 feet from the end of the kiln.

If, on the other hand, it is desired to have the combustion take place earlier, the distance B, which may be 25 feet plus any desired number, may be used. If a reagent is desired, such as lime, in the nodulizing of iron ore, it may be added at point C which may be any desired distance from the ends of the kiln.

In feeding a rotary kiln it is quite often difficult to feed as large a charge as is desired because of the "spill-over" at the back end of the kiln.

Any charging device which has been used up to the present time interferes with the flow of the products of combustion out of the kiln and, therefore, requires a relatively high stack or a large fan to remove the products of combustion. By using this same idea in feeding the kiln, it is possible to feed 10 feet or 15 feet, or any desired distance from the entrance end of the kiln in such a way that the back flow of the feed will never leave the kiln.

Another advantage in this method is that by using larger percentages of fuel than that necessary for combustion, it is possible to reduce the iron ore to metallic iron which may be discharged from the kiln as a liquid.

I claim: 1. Rotary kiln apparatus having a cylindrical kiln provided with a casing and a refractory lining, means for feeding material to be heattreated therein at one end thereof, means for discharging material at the other end thereof, means for rotating the kiln; and means for delivering solids material into the kiln through its casing during rotation of the kiln comprising an aper- .o ture through the kiln, channel means connected with the aperture disposed exteriorly of the kiln and having one open end through which solid fuel may be supplied to the kiln at a predetermined place between the ends thereof; and a .2 second aperture through the kiln as well as another channel means disposed exteriorly of the kiln and having one open end through which g solid chemical reagent may be supplied to the kiln at a predetermined place between the place of the feed of solid fuel and one end of the kiln.

2. Apparatus according to claim 1, with the addition of means for controllably directing air jets into the kiln, and means for controllably directing flames onto the burden of the kiln, with the location of said apertures being at any strategic point along the casing of the kiln.

GILBERT EDWARD SEl. REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENTS Number 1,707,191 2,002,972 2,345,092 Number 5,976 15,612 22,236 Name Date Minogue ----------- Mar. 26, 1929 Avnsoe ---------- May 28, 1935 Breslau ----------- Mar. 28, 1944 FOREIGN PATENTS Country Date Great Britain ------ May 16, 1907 Great Britain ------_ July 7, 1913 Great Britain .----. Oct. 10, 1911