US3174846A

US3174846A - Method of briquetting iron oxide fines

Info

Publication number: US3174846A
Application number: US271938A
Authority: US
Inventors: Andre H Brisse; Donald E Rohaus
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1963-04-10
Filing date: 1963-04-10
Publication date: 1965-03-23
Anticipated expiration: 1982-03-23
Also published as: BE646000A

Description

March 23, 1965 ssr; E 3,174,845

METHOD OF BRIQUETTING IRON OXIDE FINES Filed April 10, 1965 Limesfone v'. on to D II a 64 0B O I. I

/ran Oxide Healing Apparatus L aw -remperature Coal Mixer 7 600FI to INVENTORS.

ANDRE H. BR/SSE and DONALD E. ROHAUS y Afforney rates This invention relates to an improved method of briquetting iron oxide fines with a bituminous coal binder.

Before iron oxide fines can be charged to a blast furnace or similar reducing reactor, they must be formed into agglomerates large enough not to be blown from the furnace. The agglomerates must have sufiicient mechanical strength to avoid excessive degradation in handling at ordinary temperatures, and also to withstand temperatures and conditions encountered in blast furnace operation. Optionally limestone or dolomite can be included in the agglomerates in quantities to make them selfdluxing. Briquetting is one of several processes currently used for agglomeratin'g iron oxide fines. Usually a briquetting process involves pressing the fines into pillow-shaped bodies under high pressures in a roll-type press. The fines can be briquetted at high temperatures without a binder, or at lower temperatures with a binder, such as bituminous coal, pitch, molassess, sulfite liquor and others. A bituminous coal binder serves an additional purpose of furnishing carbon which can be used in the reducing reactions in a furnace. However, it is difiicult to produce coalbonded briquettes which have sufficient mechanical strength. Unless coal is heated to a temperature at which it is plastic, it does not provide a good bonding action, but at such temperatures it oxidizes readily and loses its bonding properties.

An object of our invention is to provide an improved method of briquetting iron oxide fines using a bituminous coal binder with or without fiux and obtaining agglomerates which have satisfactory mechanical strength both cold and under conditions found in a blast furnace.

A further object is to provide a briqu'etting method which attains the foregoing advantage by heating the materials to a critical apparent temperature range before briquetting, yet preventing the expected oxidation of the coal at this temperature.

A more specific object is to provide a briquetting method in which iron oxide fines and flux, if used, are heated to a temperature higher than the optimum briquetting temperature and mixed with low-temperature coal fines and the mixture promptly briquetted without destroying the bonding properties of the coal.

In the drawing:

The single figure is a schematic liowsheet of our briquetting method.

As the fiowsheet shows, we continuously introduce iron oxide fines and optionally fines of a fluxing material (limestone or dolomite) from feeders it) and 12 to a heating apparatus 13. Conveniently this apparatus is a rotary kiln which has a burner 14 and blower 15. Both the iron oxide and flux fines are minus A inch or smaller, and preferably at least 60 percent minus 16 mesh. We burn a gaseous or liquid fuel in the heating apparatus, preferably with excess air and under oxidizing conditions to obtain efficient combustion and fuel utilization. In this manner We heat the fines to a temperature substantially above that at which we subsequently form the briquettes, as hereinafter explained, but not to a temperature at which the particles sinter or calcine.

Next we continuously transfer fines from the heating apparatus to a mixer 16 and also continuously introduce low-temperature bituminous coal fines from a feeder 17 to the mixer. The coal fines can be at ambient temperature, as when they come from storage, or they can be preare t ice heated to a temperature below that at which they oxidize appreciably, as when they come from a dryer. Therefore We intend the term low-temperature as applied to the coal fines to refer to any temperature below about 200 F. The coal fines preferably are minus 8 mesh. Conveniently the mixer is a conventional pugmill which is insulated to retain heat. We continue mixing until we obtain a uniformly dispersed mixture of the various types of particles. We find we must retain all particles in the mixture for at least 30 seconds to achieve the proper uniformity. The mixture contains about 5 to 15 percent by weight coal and the remainder iron oxide and flux. At least 5 percent coal is needed to bond the other particles; if briquettes contain more than 15 percent coal, their strength at high temperatures diminishes. We preferably include flux in whatever quantity is needed to react with impurities in the iron oxide and coal when the agglomerates later are introduced to a blast furnace.

As the particles mix, the iron oxide and flux particles transfer heat to the coal particles. To obtain the information we need to control the process, We insert a thermocouple 13 in the stream of particles discharging from the mixer 16. The apparent temperature measured by this thermocouple should be in the range of about 600 to 800 F., although we recognize that the ore and flux particles remain at higher temperatures than the coal particles. We adjust the heat input to bring the apparent temperature of the mixture to the foregoing range. For example, if the coal particles are at an ambient temperature of about 70 R, we heat the ore and flux particles to a temperature of about 850 to 1050 F. in the heating apparatus 13. Under ordinary oxidizing conditions bituminous coal particles ignite below 600 F., yet surprisingly in our process the coal particles do not oxidize appreciably even though we take no special measures to prevent their oxidation. It is possible the coal particles may give off volatile matter which replaces air in the relatively confined mixer 16 and thus produces a non-oxidizing atmosphere, and also that the rate of heat transfer is sufficiently slow during mixing that the coal particles do not reach their ignition temperature.

Finally we continuously introduce the mixture of heated particles to a conventional briquetting press 19, illustrated as of the roll type. Heat continues to be transferred from the hotter particles to the cooler as the particles pass through the press. The press compacts the particles under a load of about 30,000 to 65,000 pounds per linear inch of effective roll width and thus forms them into pillow-shaped briquettes. Typically the finished briquettes are of a size about 1 /2 by by inch, and they have satisfactory mechanical strength, both at ordinary temperatures and under conditions prevalent in a blast furnace. They also show a high degree of microporosity which is desirable in materials used in a blast furnace. If the briquettes are formed properly, the coal flows around the other particles. Discrete coal particles in the briquettes are evidence of insufficient mixing or failure of the mixture to reach the proper apparent temperature range. We regard this range as critical, since briquettes formed from mixtures at temperatures outside this range are of noticeably poorer quality.

The following specific examples further demonstrate the advantages of our invention:

Example 1 We fed a mixture of minus inch Venezuelan iron ore fines and minus /8 inch limestone fines directly into a 15 foot by 2 foot gas-fired rotary kiln, where we heated the particles to a temperature of approximately 950 to 1925 F. We transferred the heated particles to a 5 foot by 1 foot single shaft pug mill, and also fed minus inch Pittsburgh Seam bituminous coal fines at ambient temperature directly into the pug mill alongside the hot orelimestone particles. We mixed the particles to form a uniform mixture which had an apparent temperature of about 725 to 800 F. The mixture contained the different particles in the following proportion by weight:

Percent Ore 85 Limestone Coal We discharged the mixture by gravity from the pug mill into a screw feeder, which fed it into a 10% inch Komerak-Greaves roll-type briquetting press. We provided a briquetting load of about 54,000 pounds per linear inch. The briquettes measured 1 /2 by by inch. To test their strength we tumbled them 200 revolutions in an ASTM tumbler, and screened the tumbled product at 3 mesh. We observed the screen retained about 83 percent of the product. We regard briquettes as satisfactory if this test shows at least 60 percent thus retained.

Example 2 We produced briquettes by the same procedure described in Example 1, and tested them the same way, except that the kiln discharge temperature Was about 850 to 925 F. and the apparent temperature of the mixture about 600 to 650 F. We found about 70 percent of the product was retained on 3-mesh after tumbling.

Example 3 To demonstrate the advantages of heating the particles by the procedure we have described, we mixed similar ore, limestone and coal particles in the same proportions at ambient temperatures. We briquetted the mixture in the same press under similar loading (a) at ambient temperature, (b) heated to about 350 F. in a gas-fired kiln, and (c) heated to about 450 F. We were unable to heat the mixture to any higher temperatures in the kiln without burning the coal particles. We found about 23 percent, 38 percent and 48 percent respectively of the product Was retained on 3-mesh after tumbling in the three tests.

From the fore-going description and examples, it is seen our invention affords a simple procedure for =briquetting iron oxide with a bituminous coal binder. By heating the materials in the way we describe, we are able to use higher briquetting temperatures than are possible otherwise, thus producing stronger briquettes better suited for blast furnace use.

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. A method of briquetting iron oxide fines comprising heating the fines to an elevated temperature, introducing the heated fines and low-temperature bituminous coal fines to a mixer in proportions to provide about 5 to percent by Weight of coal, mixing the fines for at least 30 seconds to attain a mixture in which the iron oxide and coal particles are uniformly dispersed, the temperature to which the iron oxide fines are heated being adjusted to produce an apparent temperature in the mixture in the range of about 600 to 800 F, and compacting the mixture into briquettes directly following the mixing step and while its apparent temperature remains in said range, the coal itself serving as a binder in the briquettes.

2. A method as defined in claim 1 in which the heating step is conducted by burning fuel with an excess of air and in an oxidizing atmosphere.

3. A method as defined in claim 1 in which the lowtemperature coal fines are at ambient temperature and the iron oxide lines are heated to a temperature in the range of about 850 to 1050 F.

4. A method as defined in claim 1 in which the iron oxide fines are minus A inch and at least 60 percent minus 16 mesh, and the coal particles are minus 8 mesh.

5. A method as defined in claim 1 in which the compacting step is performed in a roll type press under a load of about 30,000 to 65,000 pounds per linear inch of effective roll width.

6. A method of briquetting iron oxide fines and flux fines, the flux being selected from the group consisting of limestone and dolomite and combinations thereof, said method comprising heating iron oxide fines and flux fines to an elevated temperature, introducing the heated fines and low-temperature bituminous coal fines to a mixer in proportions to provide about 5 to 15 percent by Weight of coal and the remainder iron oxide and suificient flux to react with impurities in the iron oxide and coal, mixing the fines for at least 30 seconds to attain a mixture in which the various types of particles are uniformly dispersed, the temperature to which the iron oxide and flux particles are heated being adjusted to produce an apparent temperature in the mixture in the range of about 600 to 800 F. and compacting the mixture into briquettes directly following the mixing step and while its apparent temperature remains in said range, the coal itself serving as a binder in the briquettes.

7. A method as defined in claim 6 in which the heating step is conducted by burning fuel with an excess of air and in an oxidizing atmosphere;

8. A method as defined in claim 6 in which the lowtemperature coal fines are at ambient temperature and the iron oxide and flux fines are heated to a temperature in the range of about 850 to 1050 F.

9. A method as defined in claim 6 in which the iron oxide and flux fines are minus /1 inch and at least 60 percent minus 16 mesh, and the coal particles are minus 8 mesh.

10. A method as defined in claim 6 in which the com pacting step is performed in a roll type press under a load of about 30,000 to 65,000 pounds per linear inch of effective roll width.

References Cited in the file of this patent UNITED STATES PATENTS 1,661,636 Simpson Mar. 6, 1928 1,711,153 McIntire Apr. 30, 1929 1,923,803 Trent Aug. 22, 1933 2,794,728 Lesher June 4, 1957 2,823,109 Sudo Feb. 11, 1958 2,918,364 Lesher Dec. 22, 1959

Claims

1. A METHOD OF BRIQUETTING IRON OXIDE FINES COMPRISNG HEATING THE FINES TO AN ELEVATED TEMPERATRUE, INTRODUCING THE HEATED FINES AND LOW-TEMPERATURE BITUMINOUS COAL FINES TO A MIXER IN PROPORTIONS TO PROVIDE ABOUT 5 TO 1K PERCENT BY WEIGHT OF COA, MIXING THE FINES FOR AT LEAST 30 SECONDS TO ATTAIN A MIXTURE IN WHICH THE IRON OXIDE AND COAL PARTICLES ARE UNIFORMLY DISPERSE, THE TEMPERATURE TO WHICH THE IRON OXIDE FINES ARE HEATED BEING ADJUSTED TO PRODUCE AN APPARENT TEMPERAURE IN THE MIXTURE IN THE RANGE OF ABOUT 600* TO 800*F., AND COMPACTING THE MIXTURE INTO BRIQUETTES DIRECTLY FOLLOWING THE MIXING STEP AND WHILE ITS APPARENT TEMPERATURE REMAINS IN SAID RANGE, THE COAL ITSELF SERVING AS A BINDER IN THE BRIQUETTES.