US1863622A - Process of producing iron or steel directly from the ore and controlling the sulphur content thereof - Google Patents

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June 21, 1932. w, DAwS 1,863,622

PROCESS OF PRODUCING IRON OR STEEL DIRECTLY FROM THE ORE AND CONTROLLING THE SULPHUR CONTENT THEREOF Filed July 28, 1928 5 Sheets-Sheet 1 Per 6290/ //-0/2 //7 7/7 5/0 June 21, 1 932. 7 w V 5 1,863,622

PROCESS OF'PRODUCING IRON OR STEEL DIRECTLY FROM THE ORE AND CONTROLLING THE SULPHUR CONTENT THEREOF Filed July 28, 1928 5 Sheets-Sheet 2 g Q Q s,&

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S-nvemtoz EdwaroWDov/s 1,863,622 PROCESS OF PRODUCING IRON OR STEEL DIRECTLY FROM THE ORE AND E. W. DAVIS June 21, 1932.

CONTROLLING THE SULPHUR CONTENT THEREOF Filed July 28, 1928 5 Sheets-Sheet 5 5 Wu e44 oz Edward W. 30w 5 333111 abtowm a June 21, 1932. w, DAV|$ 1,863,622

PROCESS OF PRODUCING IRON OR STEEL DIRECTLY FROM THE ORE AND CONTROLLING THE SULPHUR CONTENT THEREOF Filed July 28, 1928 5 Sheets-Sheet 4 a w M f w avwemtoz Edward 14. Dav/s $391340 Gwynne/3A Jun 21, 1932.

E. w. DAVIS 1,863,622 PROCESS OF PRODUCING IRON OR STEEL DIRECTLY FROM THE ORE AND CONTROLLING THE SULPHUR CONTENT THEREOF Filed July 28, 1928 5 Sheets-Sheet 5 5 nvanto 1 Edward W flay/'5 33 flifozme-ur Patented June 21, 1932 i :mwaan wants, or mrumroms, mom, assreuon 'ro navrs STEEL OFFICE :enoorzss conroaarromn conronarrou or nnnnwaaa PROCESS PRODUCING IRON 0B STEEL DIRECTLY FROM THE ORE AN D CONTROLLING THE SULPHUR CONTENT THEREOF Y Application filed my as,

of iron or steel take place in a furnace of the reverberatory type, and in particular to a process for controlling the sulphur content of the metalfproduct.

In my co-pending application Serial No.

' 293,491, filed July 17,1 92s,1 have described a rocess for the production of pig iron or steel y the direct reduction of ores in furnaces of the reverberatory type wherein an economic recovery of the iron content'of the ore or other iron-bearing material treated is made possible by properly utilizing the ability of carbon to unite very rapidly with reduced I iron when suitable temperatures are employed. The present invention contemplates,

according to a'preferred embodiment, the use of the ruledisclosed in the above-mentioned application in conjunction with certain new rules or principles of operation whereby not only is it made possible to effect an optimum recovery of the metal content of the ore that is 5 being smelted, but also to control the sulphur content f the metal product. This p cess rises from the discovery of "certain relationships existing between the percentage of sulphur retained by the metal and certain operating factors of the smelting operation, and represents a considerable modification of and departure from the principles hitherto considered as governing the production of low sulphur metal in smelting operations. According to the smelting process heretoforegenerally employed for producing fluid metal directly from the ore, that is, by means of the blast furnace, and as well,'--ac,cording to the proposals hereto-.- fore made for-reducing ores and producing fluid metal therefrom in furnaces of the reverberatory type, it has been considered essential, in the production of low sulphur metal, so to proportion the fluxing constituents of the charge as to produce a strongly basic slag. I- have discovered, however, that low sulphur metal may be produced in reverberato smelting processes using acid and neutra sla s with the same facility as basic slags, provided the'iron oxide coniezg Serial No. 296,019.

tent of the slag is kept below a certain limiting percentage. I have also ascertained that this limiting percentage of iron oxide in the slag is variable with respect to the nature of the slag and the percentage of sulphur desired in the finished product. My invention makes it unnecessary therefore to limit the slag to a particulartype as heretofore was believed to be the case. 1 Y

My investigations show that with a given furnace, working on a given ore and with a given method of feeding, the sulphur content of the metal produced can be decreased by (1) increasing the temperature of the furnace; (2) increasing the carbon content of the charge; and increasing the basicity of the slag-forming ingredients of the charge.

In order to illustrate the principles of my invention I am indicating graphically in the appended drawings the relationships which I have found to exist ,between the sulphur content of the metal and the iron oxide content of the slag, and between the basicity or acidity of the slag, the iron oxide of the slag and the sulphur content of the metal, as well as the relationship between the'sulphur of the metal and the carbon-iron ratio of the charge.

In the drawings, resenting the results of many tests-showing the relation between the sulphurcontent of the metal and the iron contentof the slag;

Fig. 2 shows a series of curves indicating the relation that it is necessary to maintain be tween acidity and iron content of the slag in order to produce metal analyzing 03%, 05% and .O8% sulphur;

Fig. 3 represents a series of curves showin the efiect of change of the coal-iron ratio 0 the charge when operating under' acid condi- Fig. 1 is agraph repthe effect of change of the coal-iron ratio 0 Z i the charge when operating under basic conditions and with a slag containing approximately four parts lime (GaO) to 3 parts silica (SiO 1 ig. 5 represents a'series of curves showing the effect of change of the coal-iron ratio of the charge when operating under acid conmi ditions with a 65%acid slag and with a difand sulphur content of the metal, obtained in smelting operations carried out with a mag-- netite ore containing about 60% iron, about 13.5% silica and small amounts of lime, magnesia and alumina, and with'the amounts and character of fluxing additions varied all the way from strongly acid conditions on the one hand to strongly basic conditions on the other. The graphical representation of these results clearly shows that an acid slag must be lower in iron for a given sulphur analysis than a basic slag. The more basic the slag is, the more iron it can contain for a given sulphur content of the metal. This is indicated on the graph by the two limit curves, the lower one being for strongly basic slags, i. 'e., 65% base, and the upper one for strongly acid slags, i. e.,-70% acid. From these results it is apparent that as the iron is reduced in the slag the sulphur is eliminated from the metal.

, A change of 1% in the iron content of the makes a considerable difference in the once is much greater with the acid 'slags than with the basic slags.

The data from which the curves shown in Figs. 2, 3, 4 and 5 were plotted was obtained from the results of smelting operations carried on with the magnetite ore above mentioned. All of the smelting operations, the.

results of which were used in'making up the curves shown in Figs. 1, 2, 3 and 4, were conducted as batch operations at temperatures of around 1500 C., during the earlier portion of the reducin stage and before any substantial melting takes place, and at approximately 1600 C. during the later stage when the re: duction is completed and carburizing and melting of the reduced metal takes place. By a batch operation,'I mean a smelting operation'in which the ore, carbonaceous reducing agent, and all or a part of the fluxing additions suflicient to form a complete charge are introduced at one time and such charge is melted down and tapped without making continuous or periodic additions of ore or carbon during the operation.

All of these temperatures were recorded by use of an optical pyrometer sighted on the surface of the molten bath and are intended merely to serve as an indication but not as a measurement of the actual temperature of the carburization reaction itself or other reactions taking place in the smelting zone. With different ores and with different carbon content of the charge, and /or different amount and character of slag-forming materials present, the temperature at which the furnace should be maintained will depend upon the changed conditions within the furnace and will vary with such changes.

In the smelting operations, the results of which were used in making up the curves shown in Fig. 5, the charge was fed substantially continuously through openings in the roof of an acid-lined reverberatory furnace.

Sufiicient of the mixture was introduced to build up and maintain a body of charge with a relatively large sloping surface exposed to the heating action of the flame passing through the furnace, thus permitting the reduced metal as it carburized and melted to run into the bath which formed at the .bottom.

The czfi'bonafceous material used in all of these smelting operations was Pocahontas coal crushed to 6 mesh size.

In the light of the foregoing, it will be seen that my investigations have made it possible togreatly increase the flexibility of the smelting process. By proper correlation of the various factors of temperature,basicity or acidity of the slag and carbon-iron ratio of the charge, I have made it possible to control the sulphur content of the metal product within a wide range and to obtain low sulphur metal by carrying out the ore reduction under basic,

acid or neutral conditions, as desired.

For example, let us assume that it is-desired to obtain a metal product with a sulphur content of .'03% and that the smelting operation is to be carried out in an acid-lined furnace, as a batch operation. The charge will then be made up with proportions of coal, ore and fluxing additions so chosen that when the ore has become reduced and the reduced metal has carburized and melted down into a fluid state, a product of the desired sul hur content will be produced. To be speci c, if it is proposed to use a slag consisting of 60% acid materials such as silica, and 40% basic materials such as lime, reference to Fig. 2, will show that in order to produce metal having .03% sulphur the iron content 'of the slag should be. about 1.15% with a 60% acid slag. The coal-iron ratio of the charge will then be so chosen as to proerations. Any of the ordinary forms of iron ore may be used as well as flue dust, gas

washer sludge, 'pyrites" cinder, mill scale.

turnings, bormgs and other mill and machine shop waste. The invention is particularly applicable to the treatment of the fine oxide ores and other iron oxide materials which it has heretofore been impossible in handle economically in a blast furnace whhout resorting to beneficiating operations.

It will be understood that the method of feeding is a factor to be considered and that difi'erent results as regards sulphur content of the metal. and iron content of the slag Will be obtained in a batch operation than in a smelting operation in which the charge is fed continuously or substantially continuously. This is illustrated by comparing the results shown in Fig. 3 with the results indicated' in Fig. 5. These different results ma be explained in part 'at least as due to di erences in the ratio of surface of the charge exposed to the heating gases, and to differences in the timefactorj The relation which these respective constituents of the metal product and the slag bear to one another is, however, substantially the same irrespective of the method of. feeding so that ods of feeding.

As a specific example of the batch method of smelting, the following is set forth: a charge was made up of 2926 lbs. of magnetite in finely divided form and analyzing about 60% iron, 13.5% silica and small amounts of lime, magnesia and alumina, etc.; 975 lbs. Pocahontas coal crushed to -6 meshwsize and 900 lbs. of limestone crushed to -4 mesh size. The coal was mixed with 2576 lbs. of magnetite, sufiicient water being added to prevent dust losses. The mixture was evenly distributed over the hearth of an open hearth furnace and covered with the remainder'of the ore mixed with a like amount by weight of limestone. The rest of the limestone was added at intervals during the smelting operation. The temperature was brou ht up to about '1500 0., and held there or about three hours. The reduction of the ore to a considerable depth in the charge was substantiall completed at the end of this period, wh eupon the temperature was then raised to about 1600 C. and held there for about ten hours. or until the reduced metal had become carburized and melted, when the metal was tapped. The slag at the end of the operation analyzed 1.63% iron and the metal analyzed 3.01% carbon, 0.016% sulphur, 0.057% phosphorus and 0.41%. silicon. ile a cover was used in carrying out the above operation, it is not essential'if the heating is carried out under the proper control as to temperature so that advantage is taken of the ability of carbon to unite'very rapidly with reduced iron as described in my co-pending application hereinbefore mentioned. That is to say, by operating at a temperature above that at which the rate of carburization changes very abruptly and 3 becomes relatively great.

I I'find that in carrying out the process as a batch operation it is desirable to so control the time and rate of heating during the early portions of the reducing stage that the evolu- 65 tion of gases which attends the reducing opthe rules as to correlation apply to all-methcontain about .05% sulphur.

eration will not becomeso rapid as to cause spouting or local eruptions in the charge. This spouting is disadvantageous not only because of the increased difliculty of control of the iron content of the slag, but also because of the fact that molten or partially fused material is carried over into the checkers with consequent stoppage of the passa es.

hen operating with continuous or substantially continuous feeding of the charge as hereinbefore mentioned, the temperature may be maintained at any point desired throughout the smelting operation since the conditions which tend to. produce spouting, namely a relatively large body of" unreduced material upon'which is superimposed a body of molten metal and slag which tends to penetrate into the underlying charge and cause unduly rapid reductlon of the charge 85 and evolution of. gas-to take place, are absent. As illustrative of the effect of varying the rat'o of-carbon to iron in the charge on the sulphur content of the metal when carrying out the smelting operation with substantially continuous feeding of the charge as above mentioned, the following examples are given:

Let us assume that an operating temperature of 1600 C. is being maintained and that a magnetite ore assaying iron and 12% 95 silica, with small amounts of lime, magnesia, etc., is used. With a charge of the following proportions: 100 lbs. of ore, 33 lbs-of ocahontas coal and 7 lbs. of limestone,-the

metal will contain ordinarily about 25% mol- I sulphur. If the weight of the coal used in the charge is increasedto 43 lbs. per lbs. of ore, the sulphur in the metal will be reduced to about 15% sulphur. -If a charge of 100 lbs. of ore, 43 lbs. of Pocahontas coal and 25 lbs. of limestone is used, the metal will Instead of varying the carbon content of the charge while maintaining the other factors constant, it may be desirable to vary the temperature, the nature and chemical com-. position of the slag, or themethod offe'eding, while maintaining the other factors constant, or to vary more than one or all ,of the factors. This will be determined by the economic and practical consfderations which confront the articular operator,- such as availability an cost of fluxing materials and fuels chemical composition and structure of the ore, the type of furnace available and the limit determined upon for the sulphur content of the product.

It may also be desired to vary the conditions during the course of the smelting-operat'on and, if so, the rules 'hereinbefore set forth make it. possible to effect any desired regulation and control of the sulphur. For example, if the furnace is being operated at 1600- C. and with a neutral slag, a satisfacto'ry method for decreasing the sulphur cona I aseaeaa tent of the metal is to increasethe carbon content of the charge, since an increase in temperature or basicity of the charge will in this case only slightly decrease the sulphur content of the metal and may be injurious to the furnace. However, if the furnace is being operated at 1500 (3., and with a neutral slag, I the best method is usually to increase the temperature, as this not only decreases the sulphur content of the metal but also increases the melting capacity of the furnace. If the furnace is being operated with a strongly acid slag, a decrease in the sulphur content ,of the metal can be produced by increasing the 35 basiclty of the slag-formin ingredients of the charge. If a variety 0% fuel are available, the sulphur content of the metal can ordinarily be reduced by using a more graphitic form of carbon or fuels that are low in sulphur.

What I claim is I 1. In a process of producing fluid iron or steel directly from the ore by smelting a mixture of ore, carbon and fluxing materials with 2 an oxidizing flame in a furnace of the reverberatory type, and in which the slag-forming constituents of the charge are so adjusted as to kind and amount as to form a slag containing insuflicient basic constituents to combine with all of the sulphur that is to be removed, v the step which comprises regulatin the sulphur content of the metal produce by controlling the iron oxide content of the slag.

2. In a process of producing fluid iron or steel directly from the ore by smelting a mixture of ore, carbon and fiuxing materials with an oxidizing flame ina furnace of the roverberatory type, and in which the slag-forming constituents of the charge are so adjusted as to kind and amount as to form an acid slag containing insuflicient basic constituents to combine with all of the sulphur that is to be removed the step which comprises regulating the sulphur content of the metal produce 46 by controlling the iron oxide content of the s ag Y 3. In a process of producing fluid iron or steel directly from the ore by smelting a mixture of ore, carbon and fluxing materialswith an oxidizing flame in a furnace of the reverberatory type, and in which the slag-forming constituents of the charge are so adjusted as to kind and amount as to form a basic slag containing insufiicient basic constituents to combine with all of the sulphur that is to be removed the step which comprises regulatin the sulphur content of the metal produce by controlling the iron oxide content of the slag. 60 i n testimony whereof, I have signed my name to this specification this 12th day of July, 1928. 1

EDWARD W. DAVIS.

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