US2989395A - Method and apparatus for suction draft sintering - Google Patents

Description

June 20, 1961 K. MEYER METHOD AND APPARATUS FOR SUCTION DRAFT SINTERING Filed May 2, 1956 INVENTOR.

BY My ATTORNEYS.

at each side of the charge. and more air flows through the gap, starving the flow i United States Patent METHOD AND APPARATUS FOR SUCTION DRAFT SINTERING Kurt Meyer, Frankfurt am Main, Germany, assignor to Dravo Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed May 2, 1956, Ser. No. 582,256 7 Claims. (Cl. 75-5) This invention relates to the sintering of mineral substances on a continuously moving band, and is for an improvided method and apparatus for sintering such material.

In various industrial and metallurgical operations finely divided raw materials have to be agglomerated. For example finely divided iron ores are agglomerated by sintering with or without preliminary pelletizing and other ores are likewise sintered or roasted. In such a process the raw material is mixed with a combustible material, as for example coke, and the mixture is charged onto a continuously traveling sintering band or conveyor, the bottom of which constitutes a grate for supporting the charge, but which permits air or gases to pass therethrough. The sintering band then passes over a suction box and under an enclosure where flames are drawn down through it to ignite the combustible material. This part of the apparatus is referred to as the ignition chamber. Beyond the ignition chamber the conveyor continues to pass over a succession of suction boxes which are connected with suction fans or other means for creating a draft downwardly through the material on the belts.

material is burned, and the material remaining on the 'belt is sintered or cindered.

' The charge to be sintered is usually deposited upon the belt to a uniform depth and as evenly as possible. Notwithstanding the initial even distribution' of the material, the charge contracts'both in depth and from the edges inwardly as sintering takes place. Contraction from the sides of the charge toward the center develops a' gap As this gap increases, more of air through the charge on the center of the conveyor. The sintering operation at the sides of the charge is accelerated by the passage of a large volume'of air through it, but this is at the expense of the "material at the center where sintering gradually slows down. The sintering process therefore does not extend evenly over the whole surface of the grate, and consequently when the. charge is discharged from the conveyor, the material at the center of the'mass will still be glowing and incompletely s'intered.

Attempts have heretofore been made to correct this condition by making the charge higher at the sides, or

by placing compacting rollers at the sides between the charging station and the ignition furnace to compact the verse section through a conventional sintering apparatus;

FIG. 2 is a similar section through an apparatus provided with my invention and operating according to my process;

FIG. 3 shows in more or less schematic fashion a side elevation of another form of apparatus for practicing my invention; i

FIG. 4 is a schematic plan view of the apparatus shown in FIG. 3, but with the feed hopper omitted;

and r FIG. 5 is a view similar to FIG. 4, showing a further modified construction.

Referring first to FIG. 1 the conventional apparatus comprises a suction box 1 over which travels a continuous succession of grate-like pallets 2, these being con,- nected to form a continuous band or conveyor. At each side of the pallets are retaining guides 3, and 4 designates the charge which is carried along on the'pallets. Leading from the suction box 1 is a conduit 5 which is connected to a suction fan or other draft-creating means (not shown); As the charge iscarried along over the wind box 1, air is drawn down through the charge 4 and combustible 'componentsin the charge are burned while the mass of material remaining on the pallets or conveyors is sintered. As schematically shown in FIG. 1 the mass shrinks away from the sides 3, leaving wedgeshaped or V-shaped openings or gaps 6, and as the OP.- eration continues the formation of these gaps increases and the flow of air is increasingly concentrated toward the sides, the air taking the path of least resistance. This results in the uneven combustion or sintering of the mass across the width of the conveyor as indicated :by the area 4a in which the charge is being starved'and combustion is substantially slowed down.

According to the present invention the apparatus is similarly constructed to that shown in FIG. '1,- 'but at the top of the sintering band or conveyor at the level of the top of the charge there are horizontally-extending overhanging strips or plates, 7. These strips are located at a point extending from a short distance beyond'the ignition furnace to a point where the sintering operation is completed and near the discharge end of the'conveyor. The strips are of a width such that they overhang the charge to a point beyond the area Where the V-shaped or wedge-shaped gaps develop, and they are at an elevation where they will just clear or ride against the top of the charge on the conveyor. Thus they tend to deflect the direct How of air downwardly from 'the edge portions of the mass, and most of the air will enter the charge in the space between the two overhanging plates and then will have to travel laterally toward the sides of the charge. ,Hence by impeding the flow of air through the side portions of the charge and increasing the resistance to air flow through the charge at the side edges, sintering will occur moreuniformly across the entire width of the charge and the difliculty which has heretofore been encountered is substantially eliminated through this unexpectedly simple expedient. The strips may be of a rigid or flexible character. i

In FIGS. 3 and 4 the organization of the apparatus is more completely shown. The sintering co'nveyordes'ignated generally as 10 passes over drums 11 and 12;" 11 being the charging end, and 12 being at the discharge end. The charging hopper is schematically indicated at 13,; and 14 is the ignition furnace located over a'suction box-1 5,

Beyond the ignition furnace there are a succession of suction boxes 16, it being preferable to use a succession of shorter boxes rather than one continuous long box because of the better control of draft conditions which can be secured.

In FIGS. 3 and 4, instead of showing overhanging fixed plates such as the plates 7, there are shown flexible endless belts 17 passing over rollers 18 and 19 on shafts 20. These belts may be formed of woven asbestos or other material which will withstand the heat, and as a matter of fact discarded industrial conveyor belts may be adapted to this purpose. These belts are so positioned that they extend over the edges of the charge on the conveyor in the same manner that the plates 7 extend over them, leaving'the central area of the charge unobstructed to the passage of air. The belts are sufficiently flexible that the suction in the suction boxes 16 tends to draw the lower reaches of them down into contact with the surface of the charge on the conveyor and thereby make a more effective barrier to the flow of air downwardly through the charge with the plates 7 of FIG. 2. Because of the suction of the belts against the charge on the conveyor, the bottom reaches of the belts 3 will be dragged along with the charge on the conveyor, the top reaches of the belts of course traveling in a direction opposite to the direction in which the charge is moving. The pulleys for the belts will simply idle on their supporting shafts.

It will be seen that the belts 17 are spaced from the ignition chamber 14 so that initially there is a zone in which air can travel downwardly across the whole width of the charge without any obstruction, and this assures that the charge will have been ignited and combustion be well under way before the charge at the edges of the conveyor reaches a point where the direct down flow of air is obstructed by the belts 17.

Where rigid plates are used, as in FIG. 2, they will extend along the conveyor substantially the same distance as the belts 17, and they will be similarly spaced from the ignition furnace 14. The belts 17 or the plates 7 terminate in advance of the point where the conveyor passes over the drum .12, and hence do not interfere with the passage of the conveyor around the drum 12, or the discharge of the contents from the conveyor.

Referring to FIG. 5, it may be desirable in some cases to so form the air baffles that they will gradually increase their coverage of the side areas of the charge toward the discharge end of the sintering conveyor. As illustIated in 'FIG. 5, this may be accomplished by setting the baifling means at an angle to the longitudinal axis of the conveyor, or otherwise arranging them so that they eflectively taper in width from the end which is toward the ignition chamber toward the discharge end, increasing in their effective width toward the discharge end. In FIG. I have shown the plates 7 set at an angle to accomplish this purpose, and it will be understood that the air baflding belts 17 shown in FIG. 4 might likewise be set at such an angle, or instead of having the plates of uniform width and set at an angle, they could be tapered in width to effectively accomplish the same purpose. In FIG. 5, 21 designates the conveyor, and 22 are the air baffling means which, as indicated, may be eithter the plates 7 of FIG. 2 or the flexible belts 17 of FIGS. 3 and 4. Also instead of the plates 7 being metal plates, they can be flexible strips formed of asbestos fabric or other substantially airimpervious material that will withstand the heat to which they would be subjected. Since the air draws the gases downwardly through the charge, the deflecting strips, of whatever material, are not in the direct path of the flames or products of combustion, and the downward flow of air tends to keep them cool.

While the invention has been described in connection with the sintering of material on a continuously traveling conveyor, the same procedure can be followed in the sintering of material in pans which are closed on four sides by providing overhanging strips such as 7 on the four sides of the pan instead of on two sides.

Not only does the invention result in more uniform sintering, but it has been determined that the speed of operation can be accelerated. For example a machine which normally operated at a linear speed of approximately five feet per minute could, with the practice of my invention, operate at a speed of five feet six inches, to five feet ten inches per minute, and the sintering output could be increased from 550 tons to 610 to 620 tons, or approximately 10%.

"In the particular machine referred to, the conveyor had approximately 73 square yards of surface exposed to suetion of the suction boxes, it being about 2.2 yards wide and 33 yards long in this area. A fabric strip ofapproximately 8 inches in width and 13 yards in length was fixed along each side of the belt, so that the charge on the belt moved under the strip with the results above noted.

In another instance a large iron ore sintering assembly having approximately 75 square meters of suction surface was used having a width of 2.5 meters and a length of approximately 30 meters. Flexible strips approximately 40 cm. Wide and 14 meters long were secured along each side of the conveyor. An unexpected increase in output of 6 to 7% was obtained. In both instances it was noted that the product at the center of the strip did not glow at the point of discharge, indicating that the sintering had been uniform, and that the cooling induced by the suction toward the end of the travel had been uniform.

While I have described certain specific embodiments of my invention, it will be understood that various changes and modifications may be made within the contemplation of my invention and under the scope of the following claims.

I claim:

1. Apparatus for the down draft sintering of mineral substances comprising a grate-like support for the charge to be sintered, a suction box under the support for drawing air downwardly therethrough and having an outlet for the removal of air and gases therefrom, and baflle means extending in the direction of the length of the support along the sides of the support in the area above the suction box in overhanging relation to a charge placed on the support leaving the central area of the charge continuously uncovered throughout its length for deflecting the direct down draft of air away from the sides of the charge and principally to the area of the charge exposed between the said baffles.

2. Sintering apparatus as defined in claim 1 wherein the baffles are of flexible material which are drawn down against the charge by suction.

3. Apparatus for the down draft sintering of mineral substances comprising an air pervious grate-like conveyor for supporting the material to be sintered and moving it during the sintering operation, means at the side of the conveyor for retaining a charge of loose material thereon, charging apparatus adjacent one end of the conveyor, an ignition furnace following the charging apparatus, means under the conveyor between said ignition furnace and the opposite end of the grate-like conveyor for drawing air downwardly through the conveyor, and bafiles extending along the top of the conveyor at each side thereof along at least part of the distance between the ignition furnace and said other end of the conveyor, said baffles overhanging the charge at the sides only of the conveyor and leaving the center area along the length of the conveyor continuously uncovered so as to restrict the down flow of air at the sides and offer no impedance to the air flow in the area between the baflles.

4. Sintering apparatus as defined in claim 3 wherein said baflles are of increasingly effective width toward said other end of the conveyor.

5. Sintering apparatus as defined in claim 3 wherein said baffles are comprised of flexible strips.

6. Sintering apparatus as defined in claim 3 wherein said baflies are in the form of endless belts disposed along each side of the conveyor, the belts having a bottom reach positioned to contact the surface of the charge on the conveyor.

7. 'In the method of sintering mineral substances in which combustion air is drawn down through the charge to be sintered where the charge tends to shrink from the sides toward the center, the step which comprises baffling the air flow from the marginal edges only of the charge toward the center and thereby retard combustion at the edges of the charge and diminish shrinkage at the edges in advance of the sintering at the center.

References Cited in the tile of this patent UNITED STATES PATENTS Dwight Mar. .23, 1909 Swart Nov. 20, 1923 Bunce et a1 Sept. 12, 1933 Ahlmann Jan. 17, 1939 Burrow et a1. Mar. 16, 1954

Claims (1)

1. APPARATUS FOR THE DOWN DRAFT SINTERING OF MINERAL SUBSTANCES COMPRISING A GRATE-LIKE SUPPORT FOR THE CHARGE TO BE SINTERED, A SUCTION BOX UNDER THE SUPPORT FOR DRAWING AIR DOWNWARDLY THERETHROUGH AND HAVING AN OUTLET FOR THE REMOVAL OF AIR AND GASES THEREFROM, AND BAFFLE MEANS EXTENDING IN THE DIRECTION OF THE LENGTH OF THE SUPPORT ALONG THE SIDES OF THE SUPPORT IN THE AREA ABOVE THE SUCTION BOX IN OVERHANGING RELATION TO A CHARGE PLACED ON THE SUPPORT LEAVING THE CENTRAL AREA OF THE CHARGE CONTINUOUSLY UNCOVERED THROUGHOUT ITS LENGTH FOR DEFLECTING THE DIRECT DOWN DRAFT OF AIR AWAY FROM THE SIDES OF THE CHARGE AND PRINCIPALLY TO THE AREA OF THE CHARGE EXPOSED BETWEEN THE SAID BAFFLES.

Images