US3647417A

US3647417A - Process for producing sponge iron

Info

Publication number: US3647417A
Application number: US855278A
Authority: US
Inventors: Rolf Emil Wetzel; Willi Janssen
Original assignee: Fried Krupp AG
Current assignee: Fried Krupp AG
Priority date: 1968-09-07
Filing date: 1969-09-04
Publication date: 1972-03-07
Anticipated expiration: 1989-03-07
Also published as: FR2017565A1; SE348761B; DE1758951A1; ES371092A1; DE1758951C3; DE1758951B2

Abstract

Fine sponge iron particles are mixed with iron ore and the mixture is then sintered before being charged to a kiln for reduction into sponge iron.

Description

United States Patent Wetzel et al. 1 Mar. 7, 1972 [54] PROCESS FOR PRODUCING SPONGE {56] References Cited IRON UNITED STATES PATENTS [72] Invemm m'f gfi mf hfi jfg mg 1,864,593 6/1932 Gustafsson ..75/34 W 2,826,487 3/1958 Davis, Jr. ...75/33 X [73] Assignee: Fried Krupp Gesellschaft mit beschrankter 3,428,445 2/1969 Rausch et al. ..75/3 Haftung, Essen, Germany 3,489,549 1/1970 Jomoto et a]. ..75/5 Filed: p 1969 3,497,348 2/1970 Rausch et al. ..75/33 [2]] App]. N 855,278 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-J. Davis AuomeySpencer & Kaye [30] Foreign Application Priority Data Sept. 7, 1968 Germany ..P 17 58 951.4 [571 ABSTRACT Fine sponge iron particles are mixed with iron ore and the U.S. mixture is then sintered before being charged to a for [51] Int. Cl. ..C2lb 13/14 reduction into Sponge iron [58] Field of Search ..75/3, 5, 33, 35

5 Claims, 2 Drawing Figures 50 I0 IRON CIRDNACEDLlS GASEOUS UNDERSIZE one FUEL FUEl AND smrsnso f "50 IPDN ORE MIXER i/HWR IGNITER gERSIZE RBONIZED FMHE L SINTER SINT'ER i H /C4KE $0 550? H/x (r 2 v QU yvfifi i in cf giw fi- U 1250, BRomv (041 CDNVEYI'R 3%? mm? PM g (Rt/SHE)? CRUSIIED SINTEP CAKE ,e' s aazfiwim 251??? grese BROWN COAL KILN IRON E SPGVGE IRON AND CARBONIZED BROWN C041.

mEmEom 7:912 3.647.417

' sum 2 0P2 (OK/N6 Exmusr GASES. Foam i AIR BROWN [04L r IGNITER? I CIR 0 mwx fn OVERSIZE (OK/N smrzneo exmu L mow ORE @4555 Law ren smrues (OK/N6 APPARATUS r MIXER FORCED Har 6/15 7 EXHAUST K/LN r CHARGE Hor elm/5.

KILN smuaE IRON AND MR NIZED .BROWN 0A1 v Inventors: Pol-[- EmLL Debi 2L \OLLLL D'anssrm Hk-kornass PROCESS FOR PRODUCING SPONGE IRON BACKGROUND OF THE INVENTION The present invention relates to a process for producing sponge iron using sintered ore as the material charged to the reducing apparatus.

The production of sponge iron includes the direct reduction of iron ores which have been mixed with reducing agent. In the case of ores containing fine particles, it is often required that the fine particles be brought together into lumps, before charging the reducing apparatus, in order to obtain sponge iron in lump form.

There are a number of processes for the production of sponge iron. In one of these processes green pellets are hardened on a traveling grate at low temperatures and then reduced to sponge iron in a rotary kiln.

Besides pelletizing, there is the sintering method for bringing the particles of a fine ore into lumps. Both of these processes are suited for use in the production of sponge iron.

Which process is actually used is primarily a question of economics.

In the case of pelletizing, the fine ore must be ground in ball or rod mills and then formed into pellets. The pellets must then be burned.

Sintering is effected by a burning of solid fuel previously mixed with the fine ore. The energy costs are essentially determined by the amount of solid fuel mixed.

SUMMARY OF THE INVENTION An object of the invention is to reduce the cost of the sintering method of lumping fine iron ores for the charging of reducing apparatus for forming sponge iron and to consequently make the sintering method a better alternative for the pelletizing method, especially where the cost of grinding and forming fine ore into pellets, followed by burning, is especially high.

This as well as other objects which will become apparent in the discussion that follows are achieved, according to the present invention, by at least partially replacing the prior art solid fuel in the sinter mixture by sponge iron. In an especially economic form of the invention, the undesired fines from a sponge iron producing, reducing apparatus are fed back and mixed with the fine ore before sintering. Such sponge iron fines have provided difiiculty for the further treatment of sponge iron coming from a reducing apparatus and it has been necessary to agglomerate them in order to be able to feed them on with the larger sponge iron particles. The strength properties of the sintered material obtained using sponge iron of minus 3 millimeter particle size is not appreciably altered from that obtained using mixes containing only the solid carbonaceous fuel of the prior art.

It has been found in practice that the greatest economy is achieved if the particle size of the sponge iron fines used for the sinter mixture is held below 3 millimeters, since sponge iron above that size is more valuable as an iron product than as an additive for a sinter mix.

From a knowledge of the amount of sponge iron fines available for recirculating into the sinter mixture and a knowledge of the amount of solid carbonaceous fuel which previously had to be put in the sinter mixture, it is possible to determine how much of the solid carbonaceous fuel can be replaced by the sponge iron fines. The amount x of solid fuel that can be replaced is given by the following formula:

FY rs/ e (l where y equals the weight of sponge iron fines in kilograms, H equals the amount of heat liberated per kilogram of sponge iron fines, and H equals the amount of heat liberated per kilogram of solid carbonaceous fuel. In determining the H- values, it is assumed that the carbon is burned to CO and the sponge iron to Fe,O

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow diagram of the invention. FIG. 2 is a modification of a part of the flow diagram of FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A sinter mix is prepared from iron ore, sponge iron, and some water to provide some green strength to the mix and to maintain porosity in the sinter bed. To this mix may be added auxiliary components, sinter fines separated from the mate rial charged to a reducing apparatus, and a solid fuel such as coke fines or coal dust, should the amount of sponge iron be insufficient to provide the total heat required for the sintering.

Besides its primary meaning of raw ores extracted from the earth, "iron ore is meant to include materials such as the iron oxides resulting from the oxygen torch cutting of steels, etc.

It has been found that relationships dependent on particle size in the sinter mix are substantially the same for the mix of the present invention containing sponge iron as for the mix of the prior art containing only solid carbonaceous fuels.

A preferred amount of sponge iron for the sinter mix has been determined to be from 5 to 25 weight percent. The lower limit results in a complete utilization of the minimum amount of minus 3 millimeter sponge iron that can be found to occur in a process such as that of Example I below. The upper limit is the maximum amount of minus 3 millimeter sponge iron that can be required in a process such as that of Example II, where no solid carbonaceous fuel is used.

The sinter mix is loaded onto a moving conveyor and sintered in the same manner practiced in the prior art for sinter mixes containing only solid carbonaceous fuel.

The resulting sinter cake is crushed in a roll crusher and this crushed product is fed while still hot to a size-separating device such as a grizzly, whereupon the undersize is fed back to the mixer for the sinter mix. The oversize is mixed with solid fuel and desulfurizing material and then put in a rotary kiln for reduction. Examples of such desulfurizing material are raw dolomite and limestone.

The sponge iron issuing from the rotary kiln is subjected to a size separation operation by screening to remove the fraction under 3 millimeters. This minus fraction is fed back to the sinter mixer. The oversize sponge iron is treated further as desired, for example in an arc furnace.

As the solid fuel for mixing with the charge to the rotary kiln in the final reducing operation to change the sintered material into sponge iron, it is preferred to use brown coal or similar solid fuels having excessive amounts of volatile components. In the claims and drawings, brown coal is meant to include equivalents of brown coal with regard to volatile component content. Any carbonized brown coal remaining following the reduction can be fed right along with the minus 3 millimeter sponge iron back to the sinter mixer, if the rate of minus 3 millimeter sponge iron production should be insufficient to provide the required amount of heat for the sintering operation. On the other hand, the undersize mixture of sponge iron and carbonized brown coal can be separated by a magnetic separator operation. In a preferred modification, the undersized fraction is not separated in a magnetic separating operation, while the oversize is separated in such manner, the oversize carbonized brown coal being mixed into the kiln charge and the oversize sponge iron being fed on for further processing.

A preferred flow diagram of the process of the invention is shown in FIG. 1. In addition to the process operations discussed above, FIG. 1 shows a tube drier operated by the hot gas exhaust of the kiln. The brown coal is dried and preheated in this tube drier before being fed to the mixer to be mixed with the oversize sintered iron ore to form the kiln charge. Use of the tube drier improves the heat economy of the entire process.

FIG. 2 shows a modification of the flow diagram of FIG. I. Only a sufficient amount of the unchanged part of FIG. 1 has been redrawn to indicate the setting of the modification. In this modification, a low-temperature coking apparatus is used to first produce carbonized brown coal from the raw brown coal. The coking apparatus is driven by the hot exhaust gases of the kiln. The gases given off by the raw brown coal are used to heat the kiln and to operate the sinter bed igniter. The carbonized brown coal is fed while still hot to the kiln charge mixer. This modification allows better utilization of the available energy in the brown coal.

Representative of the practice of the present invention are the following examples EXAMPLE I A sinter mix was prepared with 20 percent sinter fines, 8 percent water, 3 percent coke dust, 10 percent sponge iron fines, remainder Kiruna ore. This mix was charged on a conveyor as shown in FIG. 1 and ignited to produce sintering. The sinter cake was subjected to the Micum drum test, which gave the minus 10 millimeter particle size as 23.5 percent. Thus, a sufficient sinter strength is obtained. Reduction of this sintered material in a rotary kiln gave a sponge iron having a total iron content of 75.5 percent and a zero-valent iron content of 69.3 percent. Dividing 69.3 by 75.5, it is seen that a metallizing efficiency of 92 percent is achieved. The sponge iron minus 3 millimeter fraction amounted to 7.8 percent, while the amount below millimeters was 14.8 percent.

Kiruna ore is a magnetic ore, whose essential mineralogical component is magnetite, Fe O The chemical analysis of Kiruna ore is given in Table 1. its ignition loss is 1.0 percent. The sieve analyses for the coke dust, sponge iron fines, and Kiruna ore are given in Table 2. The sinter fines were minus 3 millimeter material. The coke dust had 87 percent fixed carbon.

TABLE 1 Kiruna Ore Component Fe 59.2 Fat) 23.8 Fe,0 58.3 Mn 942 P 1.9

S 0.03 SiO, 2.9 Al,0, 0.8 CaO 6.8 MgO L35 TABLE 2 Sieve Analyses of the Raw Materials Raw Material in A Micum drum according to DIN 5 l,7 l 2 (DlN=German industrial Standard) was used for the Micum drum test. It had an internal diameter of one meter and an effective length of onehalf meter. The drum was driven at 25 r.p.m. On the inner wall of the cylinder are mounted four baffles at the positions 0, 90, 180, and 270. These bames run parallel to the drum axis and protrude 100 millimeters inwardly toward the axis. Twenty-five kilograms of sinter coke of particle size between and 40 millimeters were loaded into the drum. The drum was then rotated for 1 minute. The drum contents were then sieved in a stack of sieves to determine the percentage having a particle size below 10 millimeters. According to A. Send and B. Weilandt in the magazine Stahl und Eisen, V. 81 (1961), pages 303 to 310, the amount of minus 10 millimeter product can be viewed as a measure of the strength of the sintering. The more minus 10 millimeter material produced, the lower the sinter strength.

The kiln for the reduction measured 14 meters in length and had an internal diameter of 1.2 meters. The sieve analysis of the crushed sinter cake charged to this kiln is given in Table 3.

TABLE 3 Sieve Analysis of Sinter Product Particle Size in mm. 17

plus 30 [4.8 20-30 28.3

l5-20 18.4 l0-l5 20.4

Total: 100.0

This sinter product was fed to the kiln at the rate of 400 kilograms per hour. The requisite brown coal, lower heating value H =4600 kilocalories per kilogram sieve analysis in Table 2, was charged with the sinter product into the kiln at the rate of 200 kilograms per hour. More brown coal was blown burning into the kiln by means of an injector at the rate of kilograms per hour, at the sponge iron output side of the kiln. No other fuel was needed, the total brown coal serving both as reducing agent and as fuel. The temperature at the sponge iron output side of the kiln was l,l00 C., while the exhaust gases left the kiln at the sinter product charging side at 870 C.

EXAMPLE ll A sinter mix was prepared with 20 percent sinter fines, 8 water, 20 percent sponge iron fines, remainder Kirma ore. This example represents a complete replacement of carbonaceous fuel by sponge iron. This mix was charged on a conveyor as shown in FIG. 1 and ignited to produce sintering. The minus 10 millimeter fraction in the Micum drum test was 27 percent. Reduction gave a sponge iron with a total iron content of 77.2 percent and a zero-valent iron content of 7 l .9 percent corresponding to a metallizing efficiency of 93.1 percent. The sponge iron fraction below 3 millimeters amounted to 8.3 percent and that below 5 millimeters was l6.l percent. The process variables were otherwise those in Example I.

EXAMPLE [I] In Example I, the product at the sponge iron output side of the kiln had 45 percent carbonized brown coal in the minus 3 millimeter fraction. The analysis of the brown coal as charged into the kiln was as given in Table 4. The minus 3 millimeter mixture of iron and carbonized brown coal was used to replace the sponge iron fines of the sinter mix of Example I.

The heat evolution was kept the same using formula (1) above.

EXAMPLE rv The 3 percent coke dust of Example I was replaced by a 5 percent amount of carbonized brown coal with 52 percent fixed carbon. The sponge iron product from the kiln was first screened as in Example III to remove material of below 3 millimeter particle size. The product of over 3 millimeter particle size was then magnetically separated and the carbonized brown coal of over 3 millimeter particle size was used for mixing with the sinter product in replacement of part of the brown coal used for mixing with the sinter product in Example I when charging the kiln. The carbonized brown coal in the plus 3 mm. fraction amounted to 8 percent.

EXAMPLE V EXAMPLE VI In the Example I, a low temperature coking apparatus in the form of a circulating gas retort made by the firm Lurgi is used for the drying and coking of brown coal in two stages. The hot exhaust gases of the kiln are fed into the coking stage at a temperature of about 800 C. The resulting coking exhaust gases, which have a heating value of 1,500 kilocalories per standard cubic meter, are partially used for the drying stage of the retort. Another part is used as fuel in replacement of the injected coal for the kiln at the rate of 400 standard cubic meters per hour to maintain a working temperature of l,l50 C. Another part is used for igniting the sinter mix on the conveyor system. Operation at the kiln differs additionally in that the 200 kilograms per hour reduction coal is replaced by 250 kilograms per hour carbonized brown coal from the retort. This carbonized brown coal has a sieve analysis as given in Table 5. The temperature and pressure for the above mentioned standard cubic meter of gas are Celsius and 760 mm.

TABLE Sieve Analysis of Carbonized Brown Coal Particle Size in ntrnv X: greater than 8 B Total:

iron, sinterin the sinter mix bglutilizing for at least part of the heat require for srntermg the eat lrberated by burning of the sponge iron in said mix, changing the product of the step of sintering into sponge iron, separating the minus 3 millimeter size fraction from the sponge iron product of the step of changing, and using said size fraction in the step of preparing.

2. A process as claimed in claim 1, the step of changing including the step of mixing brown coal with the product of the step of sintering, the steps of separating and using incorporating the resulting carbonized brown coal minus 3 millimeter size fraction.

3. A process as claimed in claim 2, further comprising the steps of magnetically dividing the resulting carbonized brown coal and the sponge iron in the size fraction above 3 millimeters and using the carbonized brown coal in the step of changing.

4. A process as claimed in claim 1, the step of changing including the step of mixing brown coal with the product of the step of sintering, the step of changing including a reduction step in a rotary kiln, the process further comprising the step of preheating and drying the brown coal, before mixing it with the product of the step of sintering, using the hot gas exhaust of the rotary kiln.

5. A process as claimed in claim 1, the step of changing including a reduction step in a rotary kiln, the process further comprising the steps of subjecting brown coal to a low temperature coking using the hot gas exhaust of the rotary kiln, mixing the carbonized brown coal in the step of changing with the product of the step of sintering, using part of the coking exhaust gases from the brown coal for igniting the sinter mix in the step of sintering, burning part of the coking exhaust gases from the brown coal, and introducing the hot gaseous products of the step of burning into said kiln.

Claims

2. A process as claimed in claim 1, the step of changing including the step of mixing brown coal with the product of the step of sintering, the steps of separating and using incorporating the resulting carbonized brown coal minus 3 millimeter size fraction.
3. A process as claimed in claim 2, further comprising the steps of magnetically dividing the resulting carbonized brown coal and the sponge iron in the size fraction above 3 millimeters and using the carbonized brown coal in the step of changing.
4. A process as claimed in claim 1, the step of changing including the step of mixing brown coal with the product of the step of sintering, the step of changing including a reduction step in a rotary kiln, the process further comprising the step of preheating and drying the brown coal, before mixing it with the product of the step of sintering, using the hot gas exhaust of the rotary kiln.
5. A process as claimed in claim 1, the step of changing including a reduction step in a rotary kiln, the process further comprising the steps of subjecting brown coal to a low temperature coking using the hot gas exhaust of the rotary kiln, mixing the carbonized brown coal in the step of changing with the product of the step of sintering, using part of the coking exhaust gases from the brown coal for igniting the sinter mix in the step of sintering, burning part of the coking exhaust gases from the brown coal, and introducing the hot gaseous products of the step of burning into said kiln.