Title:
METHOD OF PRODUCING CARBON AND IRON-CONTAINING BRIQUETTES
United States Patent 3725034
Abstract:
A novel composite briquette useful in producing iron is made by briquetting a reactive coal calcinate made as described in Work et al. U.S. Pat. Nos. 3,140,241 and 3,140,242, and iron oxide, with a bituminous binder, using proportions to insure at least 50 percent carbon plus hydrogen by weight, then curing the briquettes in the presence of a gas containing at least 5 percent of oxygen at briquette temperature of 450° to 575°F, and then further heating the cured briquettes at 1600° to 1800°F, whereby at least 90 percent of the iron is reduced. The briquette is distinguished by consisting of iron particles embedded and evenly distributed through a uniform solid carbonaceous structure.


Inventors:
Joseph, Robert T. (Richboro, PA)
Work, Josiah (Harlingen, TX)
Application Number:
05/194559
Publication Date:
04/03/1973
Filing Date:
11/01/1971
Assignee:
FMC Corporation (New York, NY)
Primary Class:
Other Classes:
75/764
International Classes:
C22B1/16; C10B53/08; C10L5/02; C10L5/04; C21B13/00; C22B1/244; (IPC1-7): C21B1/28; C22B1/24
Field of Search:
75/3,4 201
View Patent Images:
US Patent References:
3140242Processes for producing carbonaceous materials from high oxygen coals1964-07-07Work et al.
3140241Processes for producing carbonaceous materials1964-07-07Work et al.
2512076Method of carbonizing coal with iron oxide1950-06-20Singh
1711153Ore-dust treatment1929-04-30McIntire
1290143N/A1919-01-07Eppelsheimer
1193680N/A1916-08-08Fulton
Foreign References:
AU210474A
AU215227A
CA563392A
Primary Examiner:
Curtis, Allen B.
Claims:
1. The method of producing carbonaceous iron-bearing briquettes which comprises (A) preparing a reactive calcinate by the steps of catalyzing coal particles in the presence of oxygen at a temperature of from 250°F to just below temperatures at which substantial amounts of tar-forming vapors are evolved, shock-heating to higher temperatures in one or more fluid beds to remove substantially all of the tar-forming vapors, heating the char thus freed of tar formers to a higher temperature below 1800°F to reduce volatiles to below 5 percent while retaining at least 1 percent of hydrogen in the material, and cooling the thus produced highly reactive calcinate, (B) mixing and briquetting the reactive calcinate with a bituminous binder and an iron-bearing particulate material to produce a mixture containing at least 50 percent by weight of binder plus calcinate, in which the binder is 12 to 25 percent of the total binder plus calcinate, (C) curing the so produced briquettes by heating for 80 to 180 minutes in gas containing at least 5 percent of oxygen to produce a temperature of between 450° and 570°F in the interior of the briquettes, (D) further heating the briquettes in the absence of oxygen to a temperature of between 1600° and 1800°F for 10 to 180 minutes to simultaneously coke the briquettes and reduce the iron-bearing particulate material to at least 90 percent metallic iron and (E) cooling the resultant briquettes.

2. The method of claim 1, in which the green briquette contains at least 60 percent by weight of binder plus calcinate.

3. The method of claim 1, in which the curing is done in an atmosphere containing 15 to 21 percent of oxygen.

4. The method of claim 3, in which the interior of the briquette attains a temperature at about 550°F in the curing stage.

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the production of briquettes containing carbon and iron.

2. The Prior Art

Many workers in the field of iron technology have studied the problem of eliminating the blast furnace as a source of metallic iron, or alternatively of increasing blast furnace throughput to reduce costs. One such method involves pelletizing of iron oxide together with a carbonaceous material, and then heating to cause reduction of the iron oxide to iron by the carbonaceous material. In general, very high temperatures are employed in order to get reduction -- for example, see Beggs et al. U.S. Pat. No. 3,443,931 issued May 13, 1969, where temperatures of 2300° to 2600° F are employed. While the process produces a high-iron-content pellet, there is little or no cost saving over ordinary blast-furnace methods.

It has also been proposed to briquette iron oxide carbonaceous material to produce briquettes for feeding into a blast furnace. Simpson, in U.S. Pat. No. 1,661,636 issued Mar. 6, 1928, suggests such an operation for the recovery of iron values in blast-furnace flue dust. While such operations give a more intimate contact between the iron oxide and the carbon, and thus facilitate blast-furnace operation, the cost of the briquetting offsets the savings in the blast furnace so that such processes have not been commercially practiced to any notable extent.

The problem of reducing blast-furnace costs is still present.

OBJECT OF THIS INVENTION

This invention has for its object an improvement in the manufacture of iron from iron oxide, which will reduce costs over prior-art methods.

STATEMENT OF THE INVENTION

In accordance with this invention, a calcinate produced as described in U.S. Pat. Nos. 3,140,241 and 3,140,242, is mixed and briquetted with a bituminous binder in sufficient quantity to produce a green briquette containing 12 to 25 percent by weight of binder based on calcinate and binder, together with a finely divided source of iron, the proportions of the ingredients being such that the total green briquette contains at least 50 percent by weight of calcinate plus binder and preferably at least 60 percent; the green briquettes are then heated to a briquette temperature of between about 450° to 575°F for about 80 to 180 minutes in the presence of a gas containing at least 5% of oxygen and preferably 15 to 21 percent to cure the briquettes, and the cured briquettes are then heated in the absence of oxygen to between about 1600° and 1800°F for about 10 to 180 minutes and preferably 10 to 30 minutes to coke the briquettes while simultaneously reducing the iron to at least 90 percent metallic iron. The resultant briquettes are useful in producing iron either in a cupola or a blast furnace; they have a sufficient excess of carbon to produce at least a part of the heat necessary to attain iron-melting temperatures in a cupola, and are useful in blast-furnace operation to markedly increase production rates.

The product of this invention differs from iron-containing carbonaceous briquettes made by prior-art techniques in that it consists of finely divided particulate metallic iron embedded and evenly distributed through uniform solid carbonaceous structure which is uniform in appearance and oxygen reactivity, in which it is impossible to differentiate the carbonaceous solid derived from the calcinate from the carbonaceous solid derived from the binder -- the two carbonaceous components have reacted so that they are indistinguishable under a light microscope, and react uniformly with oxygen.

DETAILED DESCRIPTION OF THE INVENTION

This invention depends for its efficiency on the unique high reactivity of coal calcinate made in accordance with U. S. Pat. Nos. 3,140,241 and 3,140,242. The calcinate is so reactive that it will reduce iron oxide powder to iron oxide at temperatures in the 1600° to 1800°F range, below the sintering point of the iron produced, so that the reduction of the oxide produces iron which has the same relationship to the briquette structure that the original iron oxide powder had. As a result, the briquettes formed are strong and can be mechanically handled. Moreover, the chemical bond between binder and calcinate, which contributes to the unique character of the briquettes made in accordance with U. S. Pat. Nos. 3,140,241 and 3,140,242, is not seriously disturbed, so that the composite briquettes will, like those made without iron, burn without spalling, making them amenable not only to cupola production of iron but also to use in the blast furnace, where they contribute substantially to throughput.

The calcinate used in making composite briquettes is made by grinding coal, preferably below the rank of anthracite, to a size consist amenable to fluidization. The coal may be predried, or dried in the first (catalyzation) step, where it is heated while suspended in a gas, either in fluid bed or gas transport, in the presence of oxygen which may come from the coal (U. S. Pat. No. 3,140,242) or from the gas (U.S. Pat. No. 3,140,241) to a temperature of at least 250°F and below that at which any substantial amount of tar-producing vapors is evolved, for a period of time which ranges from a few seconds in transport to from about 10 to 30 minutes in fluid bed, to render the particles nonfusing in the next stage. In the carbonization stage, the catalyzed coal particles are shock-heated in one or more fluidized beds to tar-producing temperatures (about 500° to 900°F, depending on the coal) for a sufficient time to remove substantially all of the tar-forming vapors. The resultant low-temperature char, now free of condensible volatiles but still containing noncondensible volatiles, is then calcined to higher temperatures to reduce the volatile content to a sufficiently low level so that the calcinate can be briquetted without producing so much gas as to disrupt the briquettes -- below 5 percent of volatiles and preferably below 3 percent. However, the time and temperature are selected to get a char which will still react with the binder used for making the briquettes; to get this reactivity, the finished calcinate should contain at least about 1 percent of hydrogen. This result can be obtained by calcining at a temperature below 1800°F, preferably at 1400° to 1600°F, for a period of about 10 to 30 minutes. The highly reactive calcinate so produced is then cooled with nonreactive gases before exposure to air.

In making form coke, this reactive calcinate is mixed with a bituminous binder, which is most preferably a pitch formed by air-blowing the tar distilled from the coal in the carbonization stage, using enough binder to thoroughly coat the particles, all as described in U. S. Pat. No. 3,140,241. The mixture is formed into briquettes, which are cured by heating in the presence of an oxygen-containing gas, preferably containing at least 5 percent and preferably 15 percent or more, of oxygen; generally, the gas is supplied at 400°F to induce an exothermic reaction in the briquettes, which apparently causes the binder to react with the calcinate and raise the briquette temperature to about 550°F. On calcination to about 1400° to 1600° to drive off volatiles, briquettes are formed in which the material derived from binder is indistinguishable from material derived from calcinate particles.

It has been found, in accordance with this invention, that a substantial amount of iron-bearing powder can be introduced into the briquetting mixture without losing this intimate chemical bond between calcinate and binder, and that, when the cured briquettes are coked in the range of 1600° to 1800°F, the hydrocarbonaceous portion of the briquette will reduce the iron-bearing powder to metallic iron. The iron, since it is well below its fusion point, does not melt or even sinter, so that there is no disruption of the briquettes. As a result, the product remains nonspalling. It can be used to produce iron by feeding into a cupola, where combustion of the hydrocarbonaceous material will produce some of the heat necessary to melt the iron; or it can be fed into a blast furnace to add its iron to the product, and give up its hydrocarbonaceous portion as a source of heat and reductant for iron ore fed into the furnace.

The green briquettes, as made up, will contain at least 50 percent, and preferably at least 60 percent, of total briquette weight of hydrocarbonaceous material comprising from 12 to 25 percent of binder and 88 to 75 percent of calcinate, the balance being the iron-containing material. The iron-containing material may be iron ore i.e., hematite, magnetite, or other oxide or iron bearing material. It may be blast-furnace dust, which is a mixture of iron oxide, carbonaceous material and ash; it may be mill scale, which is largely iron oxide; it may be finely shreaded steel scrap, which inevitably is so heavily oxidized that it cannot be conveniently remelted in a cupola; or it may be any other finely divided source of iron such as basic oxygen-furnace dust.

The source of iron oxide is very much heavier than the calcinate-binder matrix, so that the volume ratio of calcinate-binder to iron source is always much higher than the weight ratio. However, at the highest levels of iron-containing material (40 to 50 percent by weight) it is desirable to operate near the upper limit of binder-to-calcinate ratio in the green-briquette mix. The amount of binder in the mixture will also depend on the desired strength.

The green briquettes are cured as described in U. S. Pat. No. 3,140,241, by exposing them to gas containing from 5 to 21 percent of oxygen, preferably at least 15 percent. The gas flowing about the briquettes is heated to about 400°F (375° to 450°F); this induces an exotherm in the briquettes which brings their interior temperature to between about 450° and 575°F, and preferably about 550°F. About 80 to 180 minutes in the curing oven complete the merger of calcinate and binder into a uniform mass which encloses the iron-bearing material.

The cured shapes are then calcined for about 10 to 180 minutes, and preferably 10 to 30 minutes, to a range of 1600° to 1800°F -- about 100° to 200°F higher than that generally used in making form coke. The atmosphere used should be free of carbon dioxide, which will react rapidly with the green briquettes, and contain as little water vapor as possible; a neutral flame from propane is desirable.

In order to maintain the temperature range of 1600° to 1800°F, this coking gas may be tempered with a portion or all of the off-gas from the coking vessel which has been cooled and cleaned of tar and solids generated in the coking vessel. The hot coked shapes are cooled by passage of some of this same cooled cleaned off-gas over and through the bed of hot briquettes.

On examination under the light microscope, the briquettes consist of a uniform matrix of carbonaceous material, having dispersed therein unmelted particles of iron, in essentially the form in which the original iron-bearing material was charged to the original green briquettes. It is impossible to see any lines of demarcation between the original calcinate and original binder. The iron particles are embedded in this matrix. On oxidating the carbonaceous material burns uniformly, like a single substance would.

The iron content of the iron-bearing substance is analyzed by the standard method of the Metal Powder Producers Association, coded as MPIF 7-61, which enables the determination of the total iron content, the sum of the iron that is free or metalized or of zero valence and the iron that is combined bearing a valence of plus 2 or plus 3. This same method also enables the determination of free or metallic iron in the same substance. Before mixing, curing and coking in conjunction with the production of "reactive form coke" this total iron content of the iron-bearing substance may be as high as 85 percent, as is sometimes the case with shredded auto bodies, or it may be zero as is the case with virgin ores. In the reduced iron product, the amount of free or metallic iron in relation to the total iron content is the degree or percent of reduction. That ratio is always greater than 90 percent in briquettes made in accordance with the instant invention.

The quality of the final coked briquettes is measured, for all practical purposes, by two specific characteristics. The first measure is the resistance to crushing or "crushing strength" which is determined by the force necessary to crush or destroy a form coke specimen when the force is applied between the parallel plates of any suitable hydraulic or mechanical device designed to apply force. In the case of pillow briquettes, this figure is expressed as total force and is specific to the size and shape of the briquette being tested. In the case of regular cylinders, 1 inch square in cross section between the parallel bases, the force necessary to crush is expressed in units of force per square inch.

The second measure is the tendency to produce personnel dust. In the test called the "Jar Shaker Test", four briquettes are shaken together in a closed 16-ounce or 32-ounce jar of low form with a screw cap. The shaking machine, such as a standard wrist shaker, is used. The "Burell" machine listed in the A. H. Thomas Catalogue for 1968 as number 8900 has been employed. This device was set at maximum amplitude. In this test, dust is considered as the dry fine powder that passes the 325 mesh USS sieve. After the shaking period is ended, the jar is removed from the test rig and opened. The cloud that arises is classified as "dusty", "slightly dusty" or "non-irritating to the nose and throat". This dusting characteristic is also measured by the ASTM "Tumbler Test", D-294, modified to turn 700 revolutions in 28 minutes instead of 1,400 revolutions in 56 minutes.

Quality of these reactive form coke specimens which were produced from reactive calcinate, bituminous binder and iron-bearing substances, as measured by these tests, has been found to be as much as 300 pounds stronger in crushing resistance and only one-third as dusty as their control counterpart made without the addition of iron-bearing substances.

SPECIFIC EXAMPLES OF THIS INVENTION

Example I

One hundred sixty grams of iron oxide (Fe2 O3), a chemical reagent, were mixed with 160 grams of calcinate produced from a Wyoming high-oxygen sub-bituminous B coal (Elkol) in accordance with U. S. Pat. No. 3,140,242, and 40 grams of binder made by air-blowing the tar produced in making the calcinate to a softening point of 150°F, and portions were compressed in a mold 11/8 inch in diameter, in a Carver laboratory press at 20,000 psi on the gauge to produce compacted cylinders 11/8 inch in diameter and 3/4 inch high. These samples were cured in a circulating-air oven at 450°F for 120 minutes. These cured cylinders were coked in a muffle furnace in a non-oxidizing atmosphere of coal-volatile matter and nitrogen at 1750°F for 30 minutes. After cooling, these cylinders were clean to touch, and were substantially free of dust when shaken. Analysis of this material showed a 92 percent conversion of oxide to free iron.

Example II

A mix of 20 grams of auto body scrap from a body-shredding works was made with a green-briquette mix consisting of 87 grams of calcinate from an Illinois No. 6 coal (bituminous A) by the process of U. S. Pat. No. 3,140,241 and 13 grams of binder from this same source (air-blown to 150°F softening point). The auto body scrap was highly oxidized, and was in fine shreds about one-half inch in average length. This mix was formed into cylinders 11/8 inch in diameter and 3/4 inch high. On briquetting, the shredded iron was readily crushed to a powder and wetted. A sample of the cylinders was dissolved in toluene and washed free of calcinate and binder. The residue was easily separated with a strong magnet and analyzed for free and combined or total iron by methods previously described. The remainder of the cylinders were cured in air at 450°F for 120 minutes. These cured specimens were coked at 1750°F for 30 minutes in N2 and coal-volatile matter. Eight such coked cylinders were crushed as heretofore described. The average crushing strength was 4,300 psig. The analyses for iron before and after devolatilization at 1,700°F were as follows:

Green Cylinders Coked Before Coking Cylinders Free iron 30% 95 % Total iron 75% 99 % Conversion ratio - free iron to total iron 40% 95.9%

The oxidized automobile scrap used in this example is very difficult to dispose of by known techniques; our method is an economic way to utilize this otherwise largely waste material.

Example III

A mix of 34 pounds of calcinate produced from Illinois No. 6 coal, 6 pounds of oxidized binder pitch produced concurrently with this calcinate and 10 pounds of mill scale, ground to pass a 1/8 inch square hole, was made in the integral pug mill mixer attached to a Komarek-Greaves 10 inch diameter roll briquette press. Green briquettes were produced at a compression force of 10,000 pounds per inch of linear roll width or 40,000 pounds of total force. These briquettes were cured in air in a 1 foot wide moving basket oven at 450°F gas temperature for 120 minutes. They were coked in a vertical shaft kiln 9 inches in inside diameter and 9 feet high at 1650°F, using combustion gas tempered with nitrogen and containing no oxygen. The cured briquettes were held at 1650°F for 30 minutes in passage through the kiln. Analyses of these coke specimens were as follows:

Mill Scale Added Control Crushing strength 1,041 lbs. total force 600 lb. total force Dust index Jar Shaker Test -325 mesh 3.0% by wt. 7.9% by wt. Modified tumbler index 22.4% by wt. 35.4% by wt. Density by mercury displacement 1.24 gm./cc 0.98 gm./cc Binder content 13.1% by wt. of mix 13.1% by wt. of mix Mill scale added 20.0% by wt. of mix 0.0% by wt. of mix *Free iron (metallic iron, elemented iron, etc.) 92% by wt. Total iron (combined iron) 99% by wt. Conversion ratio -free iron to total iron 93% Briquette size 11/4" × 1" × 7/8" 11/4" × 1" × 7/8" *The briquette crushings were pulverized and the iron separated with a strong magnet. The magnetic material was analyzed by the methods, previously described, for "free iron" and "total iron."

Obviously, examples can be multiplied without departing from the scope of the invention as defined in the claims.