US2520384A

US2520384A - Furnace

Info

Publication number: US2520384A
Application number: US750137A
Authority: US
Inventors: Edward W Davis
Original assignee: University of Minnesota
Current assignee: University of Minnesota
Priority date: 1947-05-23
Filing date: 1947-05-23
Publication date: 1950-08-29
Anticipated expiration: 1967-08-29

Description

Filed May 25, 1947 /NVENTOR EDWARD W DAvIs ATTORNE v.5

Patented Aug. 29, 1950 FURNACE Edward W. Davis, Minneapolis, Minn., assignor to Regents of the University of Minnesota,

Minneapolis, Minn., a corporation of Minnesota Application May 23, 1947, Serial No. 750.137

4 Claims. (Cl. 263-29) The present invention relates to a furnace which may be used for any of a number of operations and which is particularly adapted for the agglomeration of ores.

In many industrial operations furnaces are employed in which the material flows downwardly by gravity and is discharged from the bottom. For the treatment of solid materials these furnaces frequently result in difficulties in nonuniform passage of the solids through the furnace. Frequently. it will be found that the material in the center of the furnace descends at a much greater rate than does the material near the walls. Various attempts have been made to correct this situation and to secure relatively uniform descent of material through the furnace. Such prior attempts have not met with entire success and their operation leaves much to be desired.

The rate of descent of solid material in a column apparently depends upon the density of the material in the column. Thus, when the material is more loosely packed it descends at a greater rate than it does when it is rather densely packed. This difference in the rate of descent is noted in packed columns when a stopped column again starts to flow. The particles discharged from the bottom of the column provide space for particles above to descend, thus making the particles in the particular vicinity less densely packed and accordingly giving them a greater rate of descent. This greater rate of descent again reduces the density in the particular vicinity and results in further increase in the rate of descent. As a result when the material starts to flow in one particular channel it will be found that material tends to flow into that channel and accordingly the rate at that particular point is very rapid, whereas at other points the rate may be zero.

In furnaces containing a combustion zone it has been found very difficult therefore to maintain a horizontal combustion zone. This combustion zone frequently takes a position of some angle to the horizontal, and this angle may change from time to time as the rate of descent in any particular portion of the cross section varies. Accordingly, it is extremely difllcult to maintain uniform treatment conditions in the furnace.

It has now been found that it is possible by simple means to control the rate of descent so as to effect substantially uniform descent across a cross section of a furnace. At the same time 2 it has been found possible to stop channeling effects once they have been started.

It is, therefore, an object of the present invention to provide a novel furnace construction making possible substantially uniform flow of material by gravity through the furnace. It is another object of the present invention to provide a novel furnace construction which makes possible the stopping of channeling effects in a furnace. It is a further object of the invention to provide a novel furnace construction which provides means for breaking up clumps which may be formed in the furnace operation.

These and other objects of the invention will be more fully apparent from the following description with particular reference to the drawing which is a vertical section through the side of a furnace embodying the present invention.

The furnace is composed of a generally cylindrical side wall portion Ill which may be composed of suitable refractory material which is contained within a shell I I which may be of steel or other metallic construction. The furnace is suitably supported above a base by means of columns l2 which are positioned below the refractory wall and from which the lower portion of the furnace depends. The lower portion of the furnace is composed of a metallic shell 13 which may be a continuation of the side walls of the furnace terminating in a generally conical bottom section II. The bottom of the furnace discharges through automatic valve l5 into a trap l6 and thence automatic valve Ill to atmosphere.

The means for controlling the rate .of descent is disposed within the bottom part of the furnace. This is composed of a generally conical feeder member l8 having a horizontal portion l9. This feeder member is supported on rollers 20 which are carried on shafts 2i which are journaled in a bracket 22. The under side of the feeder member bears on the rollers 20 and may be rotated or oscillated thereon. The means for rotating the feeder members may include a ring gear 23 driven by gear 24 supported on shaft 25 which is journaled in bracket 26. The shaft 25 extends through the side of a furnace and may be suitably driven by means of pulley 21 or may be given an oscillatory motion through a pulley or by means of a lever or other suitable mechanism. The lower portion of the furnace has converging metallic sides 30 which, together with the generally conical feeder l8, form an annular hopper and direct the material toward the discharge-space 3|. One or more scrapers 32 may be provided to scrape the material of! the edge of the horizontal portionpf the feeder plate to permit it to drop down into the discharge hopper as the bottom I! is oscillated or rotated.

The feeder member I8 is constructed so that as it is rotated or oscillated the discharge space 3| between walls 30, and parts IQ of the bottom will be alternately enlarged and restricted. This may be accomplished in a number of ways. Thus, wall 30 and the bottom [8-49 may have a few corrugations therearound. Then when the bottom [8 is rotated or oscillated, the space 3i will enlarge and contract as the corrugation crests move closer or farther away from each other. Or, the tipportion 33 may be cast slightly off center with reference to the axis of rotation of bottom [8 and, hence, as the bottom member I8 is oscillated or revolves, a slight gyratory motion of the conical portion and tip 33 of the feeder member will be provided. The feeder member may be rotated at a very low rate of speed or merely oscillated back and forth through any desired arc, for example 10 degrees. This slight movement is suificient to effect the necessary discharge of material, regulate the rate of descent and break up channeling.

An air inlet 34 is provided in the bottom hopper portion of the furnace below the feeder member. This inlet may be used to supply air or other treating gas to the furnace. The air flows up around the outside of the feeder-plate through the discharge space 3l and then distributes itself upwardly. The tip portion 33 of the feeder member is generally conical in shape and is suitably constructed such that the air underneath the feeder plate may be discharged through openings 35 on the under side of the tip and thus serve to effect a more uniform distribution of the air or gas through the material in the furnace.

The operation of the furnace will be described with particular reference to the preparation of ore agglomerates from finely divided ore. Small compacts of ore may be prepared as disclosed in Patent No. 2,411,873. A quantity of these green damp compacts may be suitably heated to a temperature of incandescence externally and then fed into the furnace. green compacts may then be placed over the top of the incandescent layer and a low concentration of gaseous fuel and air may be introduced through the air inlet 34. This mixture of air and gas rises, as previously described, and eventually contacts the incandescent compacts and is there burned to provide the heat necessary to maintain an incandescent zone. The products of combustion leave the incandescent zone, pass upwardly and serve to dry and preheat the green compacts. The pulley 21 may be driven at any suitable speed or oscillated back and forth to effect the desired discharge of material and thus control the rate of flow of the material through the furnace. As the material descends in the furnace there is a tendency for channeling as a result of localized discharge. However, as the feeder member l8 rotates .or is oscillated, it serves as a result of its configuration or eccentricity to alternately increase and decrease the distance between the wall 30 and the surface of bottom l8. If channeling is occurring in any particular part of the furnace, it is quickly interrupted as the feeder is rotated or oscillated. V

The presently described device also serves an additional purpose. In such ore agglomerating A layer of damp.

processes it is the purpose of the process to effect an agglomeration without actually effecting any fusion of the ore particles. This necessitates accurate temperature control. In some instances it may be found that temperatures temporarily get out of control and produce some fusion of the material in the furnace. Under ordinary circumstances this would tend completely to clog the furnace inasmuch as any clumps of fused material would not discharge through the small space ordinarily afforded for discharge. By means of the slight eccentricity of motion .or corrugation of the feeder member l8 and walls 30. it is possible to obtain a slight crushing action as this member rotates, and it is thus possible to break up clumps which may be fused only slightly but which nevertheless have been fused sufficiently that they would not discharge in the absence of such slight crushing action.

The following data will give an idea of a particular structure which has been found very satisfactory for the agglomeration of iron ores:

A furnace having a three foot internal diameter and in which the feeder member 18 moved through an arc of only ten degrees was found to function very satisfactorily. An oscillatory rate of approximately 3 strokes per minute was found desirable. It will be apparent, therefore, that the amount of movement of the feeder member need not be great to effect the desired control of the rate of descent and to effect the desired rate of discharge and the breaking up of any clumps which may be formed.

The particular discharge from the bottom of the furnace is, of course, not critical. The automatic discharge valves illustrated make possible a sealed furnace without any great amount of loss of air or gas through the bottom of the furnace. In this way it is possible to build a furnace without too large an overall height. Where this factor is not important it will be apparent, of course, that the automatic discharge valves may be eliminated and a long seal pipe employed which will effect suihcient resistance to the flow of gas that practically no gas will be lost through the discharge part of the furnace. At the same time the resistance to upward flow of gas is sufficiently low to permit practically all the air and gas to flow in that direction. Numerous variations in the bottom portion of the furnace may be employed without effecting the operation of the essential portion of the invention.

It will be apparent that numerous variations may be made in the particular structure employed without departing from the spirit of the invention. It is to be understood, therefore, that the invention is not limited to the specific embodiments described but may be varied within the scope of the following claims.

What I claim is:

l. A furnace comprising an upstanding wall section terminating at the lowermost end thereof in an inwardly tapering frusto-conical wall section, said frusto-conical wall section being open at the lowermost end thereof and having the internal face thereof provided with a plurality of corrugations extending upwardly from said lowermost end along the slant height of said frusto-conical wall section, a generally conical feeder member nested within said frusto-conical wall section, said feeder member tapering upwardly and inwardly toward the vertical axis of said frusto-conical wall section, the lower end of said conical feeder member opposite the lowermost end of said frusto-conical wall section being spaced from said wall section to provide a discharge opening between said feeder member and the lowermost end of said frusto conical wall section, the outer face of said conical feeder member being provided with a plurality of corrugations extending upwardly from said dismounted on the top of said generally conical feeder member, said eccentric conical member being positioned within the corrugated inner wall of said frusto-conical wall section.

3. A furnace as set forth in claim 2 0haracterized in that said eccentric conical member and said generally conical feeder member having a passage formed at the point of connection between said members to permitthe-flow of gas from inside the conical feeder member to the outside thereof.

4. A furnace as set forth in claim 1 characterized in that said frusto-conical wall section is provided with a horizontally disposed portion extending outwardly from the lowermost end thereof, and said generally conical feeder memher is provided with a horizontally disposed portion extending outwardly from the lower end thereof and positioned generally parallel to the horizontal portion provided on said frustoconical wall section, the opposed faces of each of said horizontally disposed outwardly extending portions being provided with corrugations, and a scraper member mounted on said furnace and extending between the opposed corrugated faces of said horizontally disposed outwardly extending portions.

EDWARD W. DAVIS.

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

UNITED STATES PATENTS Number Name Date 1,152,050 Roitzheim Aug. 31, 1915 1, 66,904 Harding Jan. 4, 1916 1,429,925 Candlot Sept. 26, 1922 1,669,012 Nordstrom May 8, 1928 1,779,571 Ullgren Oct. 28, 1930 2,057,610 Diehl Oct. 13, 1936 2,409,527 Azbe Oct. 15, 1946 FOREIGN PATENTS Number Country Date 264,127 Germany Sept. 16, 1913 384,336 Germany Nov. l, 1923 520,573 France Feb. 16, 1921 543,085 Germany Feb. 3, 1932