US 3087715 A
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Description (OCR text may contain errors)
April 1963 w. H. DAILEY, JR 3,087,715
couausnon SYSTEM Filed March 28. 1961 I 2 zesl COOLER INVENTOR WILLIAM H. DAILEY JR.
BY w w- ATTORNEY United States Patent "ice 3,037,715 COMBUSTION SYSTEM William H. Dailey, Jr., Toledo, Ohio, assignor to Midland- Ross Corporation, Toledo, Ohio, a corporation of Ohio Filed Mar. 23, 1961, Ser- No. 98,793 3 Claims. Cl. 26333) This invention is directed to an improved combustion system and particularly to an improved combustion system for a rotary kiln that is adapted to heat particles of ore to an elevated temperature. More particularly, the invention is directed to the improvement in prior art rotary kiln combustion systems which comprises means for adding to said kiln a stream of heated air laden with ore particles of the kind being heated in said kiln and preferably in a manner to utilize at least a portion of such stream as combuston supporting air for the burner means utilized to fire such kiln.
In my co-pending application, Serial No. 98,560, filed on March 28, 1961, I have described a method of and apparatus for cooling a stream of heated agglomerates of ore which comprises passing the agglomerates downwardly through a hollow shaft-type structure in counterflow heat transfer relationship with a stream of cooling air. Such cooling apparatus may frequently be provided as part of an ore processing system which includes a rotary kiln adapted to heat fine particles of ore to an elevated temperature and agglomerating means such as a briquetting press for agglomerating the heated ore particles into larger bodies. The cooling step utilizing the cooling means described in the aforesaid co-pending application normally follows the agglomerating step in such ore processing systems.
The spent cooling air which emerges from such cooling devices as that described in the aforesaid copending application is generally quite highly heated and it is therefore economically desirable to provide means to reclaim the heat content of such stream. One obvious means for accomplishing this heat reclamation step comprises the step of using the spent cooling air as combustion-supporting air for the combustion system of the associated ore heating kiln. Such a step, which is shown, for instance, in De Vaney Patent 2,590,090, permits a significant reduction in the amount of fuel required to heat the kiln.
In some instances, however, the agglomerates which are delivered from the agglomerating means will be possessed of a considerable quantity of objectionably small unagglomerated ore particles. It is generally highly desirable to disengage these particles from the main stream of agglomerates because such particles are not well suited for consumption in the ultimate agglomerate consumer (normally a blast furnace). Suitable means for accomplishing the disengagement of small ore particles are also described in the aforesaid co-pending application. The means described therein comprises, generally, a restriction in the shaft cooler whereby to increase the velocity of the cooling air in the region of the restriction to a value which will fluidize and carry off the objectionably small ore particles. In a shaft-type agglomerate cooler employing such small particle disengagement means the stream of spent cooling air which passes therefrom will not only be quite highly heated but will also be rather heavily laden with small ore particles; in some cases the stream of spent cooling air from such a shaft cooler may carry up to as high as one pound of ore particles for every two and onehalf to four pounds of air. The prior art means for utilizing a stream of heated air as combustion supporting air in a kiln combustion system are not satisfactory because they would pass the small ore particles through the flame front of the burner which would tend to melt these particles. The ultimate deposition of melted particles on the internal 3,987,715 Patented Apr. 30, 1963 surface of a kiln leads to the formation on the lining of the kiln of rings which are highly objectionable because they restrict the proper flow of material through the kiln. Because of the danger of forming rings on the lining of the kiln there has been a definite reluctance on the part of prior artisans to utilize a stream of heated air heavily laden as ore particles as combustion-supporting air in a rotary kiln combustion system despite the fact that such a system permits not only the direct recovery of the heat content of the ore-laden heated air stream but also the direct recovery of the ore content of such stream.
It is, therefore, an object of my invention to provide means for recovering both the heat content and also the ore content of a stream of heated air that is laden with ore particles. It is a further object of my invention to integrate such means with the combustion system of a rotary kiln that is adapted to heat ore particles of like kind to the particles with which the heated air stream is laden. It is a further object of the invention to utilize at least a portion of the air stream as combustion-supporting air for the burner means utilized to fire such kiln.
For a further consideration of what I consider to be novel and inventive attention is directed to the following portion of the specification, the drawing, and the appended claims:
In the drawing:
FIGURE 1 is an elevatio-nal view, shown partially in section, of a kiln embodying the present invention;
FIGURE 2 is a sectional view taken on line 2-2 of FIGURE 1;
FIGURE 3 is a sectional view taken on line 33 of FIGURE 1;
FIGURE 4 is a fragmentary view of an alternative embodiment of the invention; and
FIGURE 5 is a fragmentary view of an alternative embodiment of the invention.
In accordance with the present invention a rotary kiln 11 of cylindrical configuration, as defined by wall means 12, is provided to heat particles of an ore to an elevated temperature. Kiln 11 is rotated by driving means includ ing a ring gear 13 attached to the kiln and a driving pinion 14 attached to a drive shaft 15 which is driven by any suitable motive means (not shown). Kiln 11 has an inlet end 16 and an outlet end 17 and is disposed with the outlet end being lower in elevation than the inlet end. Ore particles are added to kiln 11 at inlet end 16 from an external source (not shown) by means of inlet chute 18 which passes through stationary inlet hood 19. The particles which are added to kiln 11 cover a portion of the internal surface 21 thereof forming on the covered portion 21a a bed of particles 22. Bed 22 has an upper surface 22a which is generally inclined somewhat upwardly from the horizontal by virtue of the rotation of kiln 11. The bed of particles 22 is also caused to flow in a direction generally toward outlet end 17 by virtue of the rotation of kiln 11 which allows the force of gravity to act more freely on the particles.
The ore particles are heated as they pass through kiln 11 by means of counter flow heat exchange thereto from the products of a combustible reaction of streams of fuel and combustion-supporting air and this combustible reaction is initiated by means of a burner 23 mounted adjacent outlet end 18 in a stationary outlet hood 31. Burner 23 which receives a stream of fuel from conduit 24-, and a stream of combustion-supporting air from conduit 29, as described in greater detail below, is preferably of the long flame type rather than the short flame type to provide for more uniform heat transfer through the length of kiln 11. The ore particles heated in this fashion ultimately pass from outlet end 17 of rotary kiln 11 for further processing by other equipment (not shown).
In some instances the heated ore particles are compacted into large bodies or agglomerates by various means such as a briquetting press. The compacted bodies or agglomerates, which are at elevated temperature and which may be accompanied by a considerable quantity of unagglomerated particles, must generally be cooled to a safe handling temperature and must also be disengaged from the small particles associated therewith. Both of these steps may be accomplished by means of a shafttype cooling unit equipped with small particle disengaging means of the type described more fully in my copending application Serial No. 98,560, filed on March 28, 1961. In a cooling unit of this type the agglomerates are cooled and small particles disengaged therefrom by means of a stream of cooling air blown upwardly through a shaft filled with such agglomerates. The spent cooling air passing from such a cooling unit will generally be highly heated and also relatively heavily laden with small ore particles. A cooling unit of this construction is indi cated diagrammatically as S in the drawing to indicate a source of heated air laden with ore particles.
Because of economics it is highly desirable to reclaim both the heat content and the ore content of the stream of air from source S. The ore content of such stream may be reclaimed by delivering the entire stream of air to an inlet pipe adapted to discharge the air stream into the kiln in such a manner that the ore particles carried by the stream will precipitate therefrom onto the bed of ore particles in the kiln. Such an expediency is not generally effective to reclaim the heat content of such stream, however, unless the kiln burner is operated on such a deficiency of combustion-supporting air that the products issuing therefrom are capable of further combustion when they ultimately diffuse with the heated air stream.
I have, therefore, devised a better system for reclaiming both the heat and ore content of the heated ore-laden stream. In the system which I have devised the conduit means for conveying the stream of heated ore-laden air from source S to kiln 11 includes separating means for separating the stream of heated ore-laden air into two portions with one portion being less heavily ore-laden than the other. The less heavily laden portion then passes the kiln where its heat content is reclaimed by utilizing this air stream in the most effective manner, i.e., as combustion-supporting air for the kiln combustion system.
A very simple separating means for accomplishing this air separation step is shown in FIGURE 3. In this embodiment the stream of heated ore-laden air is delivered from source S to kiln 11 by conduit means indicated generally at 26. Conduit means 26 includes separating means formed by straight-run portion of conduit 26a and branch conduit 29 which communicates with straight-run portion 26a and forms an angle therewith. Separation of the air stream from source S into two streams, one less heavily ore-laden than the other, is accomplished by such separating means by virtue of the fact that the mass (and therefore the momentum) of the ore particles carried by the air stream from source S is many many times greater than the mass of the air particles. Hence, the ore particles tend to resist the change in direction made by the air particles which separate from the main stream by turning into branch conduit 29. Thus the separated portion of the air stream passing through branch conduit will be substantially less heavily ore-laden than the separated portion which continues through straight-run portion 26a downstream of branch conduit 29. Thus the less heavily ore-laden portion may be passed directly to burner 23 for consumption as combustion-supporting air. The more heavily ore-laden portion, on the other hand, is then passed to air inlet tube 27, either directly from straightrun portion as is shown in FIG. 3 or through intermediate conduit means such as elbow section 28 as is shown in FIG. 4.
Alternative separating means are illustrated in FIG. 5 which shows conduit means 126 for delivering a stream of heated ore-laden air from source S to kiln 11. Conduit means 126 includes a centrifugal or cyclone separator 32 of conventional construction for separating the heated air stream into a less heavily ore-laden portion and a more heavily ore-laden portion. The less heavily ore-laden portion is passed from the top of separator 32 to burner 23 by means of conduit 33 and the more heavily ore-laden portion is passed therefrom to inlet tube 27 by means of conduit 34.
The ore particles which are contained in the portion of the air stream passed into kiln 11 through air inlet tube 27 will ultimately precipitate therefrom in a trajectory that is determined largely by the direction of tube 27. By virtue of the fact that at least some of these particles may be heated to fusion temperature by heat transfer thereto from the flame issuing from burner 23, it is important that tube 27 be directed toward that portion 21a of internal surface 21 of kiln 1 1 which is covered by the bed of particles 22 being processed if the formation of rings on the kiln lining is to be avoided. Furthermore, since the particles which are recharged into kiln 11 from inlet tube .27 will ultimately pass from kiln 1.1 for further processing along with the fresh particles charged into kiln 11 through tube 18 it is important that the portion 21a of surface 21 toward which inlet tube 27 is directed be located sufiiciently remote from outlet end 17 to allow them to be reheated to the desired processing temperature, the degree of remoteness of portion 21a from outlet end 17 being determined primarily by the difference between the temperature of the recharged particles and the final desired particle processing temperature.
The best modes known to me to carry out this invention has been described above in terms sufficiently full, clear, concise, and exact as to enable any person skilled in the art to make and use the same. It is to be understood, however, that certain modifications of the above described modes of practicing this invention can be made by a skilled artisan without departing from the scope of the invention which is defined only by the appended claims.
1. In apparatus for heating particles of ore to an elevated temperature, said apparatus including wall means defining a cylindrical kiln having an internal surface, an inlet end, and an outlet end, said kiln, being disposed with said outlet end lower in elevation than said inlet end; charging means adjacent the inlet end of said kiln for charging a stream of ore particles thereinto to form a bed of particles therein covering a portion of the internal surface of said kiln; means for rotating said kiln to cause said bed of particles to pass from said inlet end to said outlet end; burner means for promoting the combustible reaction of a stream of fuel and combustion-supporting air, said burner means being located adjacent the outlet end of said kiln and being adapted to deliver the products of said combustible reaction to said kiln to flow therethrough in counter-flow heat transfer relationship with said bed of particles; and further including the improvement in means for adding a stream of heated air laden with ore particles of the kind being heated in said kiln in a manner to utilize at least a port-ion of the heated air stream as combustion-supporting air for said burner, said improvement comprising, in combination: an air inlet tube adjacent the outlet end of said kiln and being directed toward a region of that portion of the internal surface of the kiln which is covered by said bed of particles; conduit means from a source of heated air laden with ore particles of the kind being heated in said kiln; said conduit means leading to said kiln and including separating means for separating the stream of heated air into two portions, the first of said two portions being less heavily laden with ore particles than the second of said portions and being delivered by said conduit means to said burner to serve as combustion-supporting air, the second of said portions being delivered by said conduit means to said air inlet tube of said kiln to pass thereinto,
whereby the particles contained in said second portion will precipitate therefrom onto said bed.
2. Apparatus according to claim- 1 wherein said separating means comprises a centrifugal separator.
3. Apparatus according to claim -1 wherein said separating means comprises a straight-run portion of conduit and a branch conduit communicating with said straightrun portion of conduit and defining an angle therewith and further serving to withdraw the first portion of said 6 stream from said stream leaving said second portion of said stream flowing through said straight-run portion downstream of said branch conduit.
References Cited in the file of this patent