US3168393A - Method of sintering blast-furnace feed - Google Patents

Description

Feb. 2, 1965 w. T. RILEY ETAL 3,168,393

METHOD oF SINTBRING BLAST-FURNACE FEED Filed sept. 7, 1961 f/arney United States Patent Office 3,108,393 Patented Feb. 2, 1965 lVIETHOD F SINTERING BLAST-FURACE FEED William T. Riley, Thornton Township, Cook County, and

Richard E. Stoll, Bloom Township, Cook County, Ill.,

assignors to United States Steel Corporation, a corporation of New Jersey Filed Sept. 7, 1961, Ser. No. 136,469 4 Claims. (Cl. 75-5) This invention relates to an improved sintering method and apparatus.

Although the invention is not thus limited, our method and apparatus are particularly useful in sintering iron oxide fines, such as ore or liuc dust. Conventional practice in sintering these materials involves feeding a mix of moistened iron oxide fines, sinter returns and carbonaceous fuel to a traveling grate, ignitingr the upper surface of the resulting bed shortly beyond the point of feeding, and drawing combustion air downwardly through the bed. Combustion takes place in a narrow zone which moves downwardly from the point of ignition to a burnthrough point near the discharge end of the grate. Typically the moisture content of the mix as fed to the grate is about 8 to 12 percent by weight. In the portion of the bed near the feed end, moisture condenses from the products of combustion as they pass downwardly through the relatively cool unsintered material beneath. Consequently moisture builds up in this portion of the bed and reaches a maximum content about 1 to 3 percent higher than its original content at an inversion point intermediate the length of the grate. We have observed this additional moisture lowers the permeability of the bed to flow of combustion air and thus hinders the whole operation.

An object of the present invention is to provide a method and means for avoiding loss of permeability in a sinter bed caused by moisture condensation and thereby increasing the capacity of a sintering machine.

A further object is to provide an improved sintering method and apparatus in which additional heat is supplied to a sinter bed at a critical location between the ignition point and the usual inversion point to minimize moisture condensation and thus prevent loss of permeability.

In the drawing:

FIGURE 1 is a somewhat diagrammatic side elevational view of a sintering machine which embodies additional heating means in accordance with our invention; and

FIGURE 2 is a graph which compares the relative permeability of a sinter bed `at different locations along its length.

FIGURE 1 shows a sintering machine, which is conventional apart from our additional heating means, and includes a supporting frame 10, an endless traveling grate 12 mounted on said frame and having a suitable drive, a feeder 13 above the grate near one end of the frame, an ignition hood 14 just beyond the feeder, and a series of windboxes 15 beneath the upper flight of the grate. The feeder deposits a sinter mix on the grate where it forms a bed B. In the example of an iron oxide sintering operation, the mix typically has a composition by weight on a a dry basis about as follows:

Percent Iron ore fines 60 to 75 Sinter returns 20 to 40 Carbonaceous fuel to 7 Sufficient moisture is added to raise the level to the range desired, usually 8 to 12% depending on the ore. The machine also is equipped with a plenum chamber and a suitable fan (not shown) for drawing a downdraft of combustion air through the bed and windboxes.

In accordance with our invention, we position a frame 16 across grate 12 at a location intermediate the length thereof, as hereinafter explained. Frame 16 carries a series of burners 17 to which are connected suitable sources of fuel (preferably gaseous) and air. These burners supply additional heat to bed B to drive oif moisture which has condensed from the products of combustion as they pass through the relatively cool unsintered material beneath the combustion zone. In this manner we prevent the moisture content from building up to a value at which it seriously interferes with permeability of the bed.

As an example to demonstrate the benefits which result from practice of our invention, we compared the bed permeability obtained on a conventional sintering machine with and without the additional heat. We used a Dwight- Lloyd sintering machine which has a rated capacity of 5000 tons per 24 hour day. The machine includes 2l windboxes on eight foot centers, and thus has an effective grate length of 168 feet. The plenum chamber is serviced by an induced draft fan designed to draw 395,000 cubic feet per minute through the plenum chamber. We fed a sinter mix of the following composition to the grate:

Percent Iron ore fines 47.0 Coke braize 5.5 limestone 8.0 Hot returns 20.0 Cold returns 10.0

Moisture 9.5

The grate speed was 12 feet per minute, and the bed depth 12.5 inches.

Referring to FIGURE 2, the two curves show rates of air ow through the sinter bed at dierent locations along the grate starting with the eighth windbox from the feed end. The solid line curve shows the rate of air flow Without additional heat, while the dotted line curve shows the rate with additional heat in accordance with our invention. In each instance We measured the ow rates at one minute intervals with an anemometer traveling with the grate. As the solid line curve shows, the flow rate increased steadily from the origin (eighth windbox) for a distance of about 24 feet, where it levelled, and it commenced to drop rapidly at a distance of about 40 feet from the origin. The ow rate reached a minimum or an inversion point at a distance about 58 feet from the origin, and thereafter increased rapidly. We positioned our burners over the bed just ahead of the location where the rate of air flow commences to drop, that is, about 20 feet in advance of the inversion point. We applied heat at the rate of about 150,000 B.t.u. per minute. In this manner we altogether eliminated the dip in the air ow rate, as the dotted line curve shows. We were able to increase the capacity of the sintering machine by about 11 percent.

In general we position our burners just ahead of the location at which the air flow rate tends to drop or about 15 to 20 feet in advance of where the inversion point tends to form. We supply heat at a rate of about 22,000 B.t.u. per 1% moisture to be driven olf per ton of sinter mix. We obtain the greatest permeability by driving off all the moisture in the unsintered material beneath the combustion zone, but we successfully eliminate the inversion point by driving off enough moisture to lower the moisture content to its original value.

While we have shown and described only a single embodiment of the invention, it is apparent that modifications may arise. Therefore, we do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

We claim:

1. In a sintering process which includes feeding a moistcned sinter mix to the grate of a downdraft traveling grate sintering machine to form a bed thereon, igniting the bed at its upper surface adjacent the point of feeding, and drawing Acombustion air downwardly through the bed, whereby combustion takes place in a narrow zone which moves downwardly from the point of ignition to a burn-through point near the discharge end of the grate, and whereby moisture in the products of combustion tends to condense as these products pass through relatively cool unsintered mix beneath said zone and the resulting additional moisture tends to create an inversion point intermediate the length of the bed, a method of preventing the formation of an inversion point comprising supplying additional heat to the bed to drive off condensed moisture from the unsintered material in advance of the location where the inversion point tends to form.

2. A method as defined in claim 1 in which the heat is supplied by -burning gaseous fuel over the bed l5 Vto 20 feet in advance'of the location where the inversion point tends to form. Y v t 3. A method as defined in claim 1 in which the heat is supplied by burning gaseous fuel over the bed l5 to 20 feet in advance of the location where the inversion point tends to form, and at a rate suicient to lower the moisture content at least to its original value as'a maximum.

4. In a sintering process in which a combustible sinter mix having a moisture content of 8 to 12 percent feeds to a single location on the grate of. a downdraft traveling grate sintering machine and forms a permeable bed thereon, the bed is ignited at a single location on its upper surface adjacent the location of feeding, and combustion air is drawn downwardly through the bed, whereby combustion takes place in a single narrow zone which moves downwardly from the location where the bed is ignited to a burn-through point near the discharge end of the grate, and wherein moisture in the products of combustion condenses as these products pass through relatively cool unsintered mix beneath said zone to an extent that the permeability of the bed commences to drop at a location spaced from the location where the bed is ignited and ultimately tends to reach an inversion point 15 to 20 feet beyond the location where permeability commences to drop, the combination therewith of a method of preventing the formation o f an inversion point comprising burning lgaseous fuel over the bed adjacent the location where its permeability commences to drop and thus supplying additional heat to the bed at a'rate sufficient to drive or condensed moisture from the unsintered Amix beneath said zone and lower the moisture content thereof at least'to its original value as a maximum.

References Cited in the file of this patent UNITED STATES PATENTS 1,292,059 Richards Jan. 2l, 1919 2,412,104 Stewart Dec. 3, 1946 2,498,766 Pettigrew Feb. 28, 1950 2,750,274 Leuep June 12, 1956

Claims (1)

1. IN A SINTERING PROCESS WHICH INCLUDES FEEDING A MOISTENED SINTER MIX TO THE GRATE OF A DOWNDRAFT TRAVELING GRATE SINTERING MACHINE TO FORM A BED THEREON, IGNITING THE BED AT ITS UPPER SURFACE ADJACENT THE POINT OF FEEDING, AND DRAWING COMBUSTION AIR DOWNWARDLY THROUGH THE BED, WHEREBY COMBUSTION TAKES PLACE IN A NARROW ZONE WHICH MOVES DOWNWARDLY FROM THE POINT OF IGNITION TO A "BURN-THROUGH POINT" NEAR THE DISCHARGE END OF THE GRATE, AND WHEREBY MOISTURE IN THE PRODUCTS OF COMBUSTION TENDS TO CONDENSE AS THESE PRODUCTS PASS THROUGH RELATIVELY COOL UNSINTERED MIX BENEATH SAID ZONE AND THE RESULTING ADDITIONAL MOISTURE TENDS TO CREATE AN "INVERSION POINT" INTERMEDIATE THE LENGTH OF THE BED, A METHOD OF PREVENTING THE FORMATION OF AN "INVERSION POINT" COMPRISING SUPPLYING ADDITIONAL HEAT TO THE BED TO DRIVE OFF CONDENSED MOISTURE FROM THE UNSINTERED MATERIAL IN ADVANCE OF THE LOCATION WHERE THE "INVERSION POINT" TENDS TO FORM.

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