US2397737A - Process of desulphurizing - Google Patents

Description

April 2, 1946. P. HEUER PROCESS OF DESULPHURIZING 4 Sheets-Sheet 1 Filed July 14, 1942 April 2, 1946. R. 'P. HEUER PROCESS OF DESULPHURIZING Filed July 14, 1942 4 Sheets-Sheet 2 April 2, 1946. R. P. HEUER 2,397,737

PROCESS OF DESULPHURIZ ING Filed July 14, 1942 4 Sheets-Sheet s April 2, 1946. s r R. P. HEUER 2,397,737

I PROCESS OF DESULPHURIZING Filed July 14, 1942 4 Sheets-Sheet 4 3 'Jm Jor quent use Patented Apr. 2, 1946 7 UNITED? STATES PATENT OFFICE rnocsss or nnsurrnumzmo -Russell Pearce Heucr, Villa Nova, Pa., assignor to Essex Research Gomoration, Wilmington, DeL, a corporation of Delaware Application July 14, 1942, Serial No. 450,892

- basic desulphurizlng slag in contact with the 5 Claims.

My invention relates to a process for the treatment of pig iron and the production of steel and principally to the desulphurization of pig iron. This application is a continuation in part of my copending applications, Serial No. 304,484, filed November 15, 1939, and Serial No. 374,989, filed January 18, 1941, for Desulphurizing apparatus and process.

A. purpose of the invention is to operate a coke blast furnace to produce pig iron higher in sulphur than that ultimately desired, and preferably at a lower cost than normal, by operating the blast furnace at a lower temperature andior with less basic slag and/or with low grade raw materials causing higher sulphur in the charge, and to provide improved apparatus in which to treat the molten pig iron thus produced with a basic slag external to the blast furnace hearth, to remove the excess sulphur from the molten pig iron. The pig iron thus produced may be used in the form of cast iron or as raw material for making steel.

A further purpose is to remove molten pig iron at periodic intervals from the blast furnace, to

transfer it in molten state by a runner or other suitable mechanism to a fore-hearth or ladle adto desulphurizing action and transferring the desulphurized iron to a transfer ladle for subsein the manufacture of steel, or other purposes.

A further purpose is to desulphuriz e pig iron in a suitable forehearth or ladle adjacent to the blast furnace, to separate the molten pig iron from the desulphurizing slag and to deliver the desulphurized pig iron free from desulphurizlng slags to a transfer ladle for conveying the molten iron to steel making furnaces.

A further purpose is to 'desulphurize molten pig iron by means of a slag in a forehearth or ladle adjacent to a blast furnace or other furnace capable of providing molten iron, the forehearth or ladle having its axis of symmetry in a,

substantially vertical position and provided with means for producing a rotary motion of the contents of the forehearth or ladle about the axis of symmetry,

A further purpose is to place molten iron in the refractory lining of a desulphurizing ladle whose axis of symmetry is vertical, with a basic desulphurizing slag floating on the molten iron, and impart rotary motion to the metal, desirably in a horizontal plane, while desirably also producing relative movement between the slag and the iron.

A further urpose is to rotate molten iron or iron by an impeller or preferably a plurality of impellers turning on a vertical axis and prei'erably in a ladle whose axis of symmetry is vertical. The impellers will preferably turn in the same direction. 1

A further purpose is to employ. a plurality of impellers operating in contact with molten iron, and a basic desulphurizing slag on the molten iron, at different levels, one effective below the slag-metal interface and another effective at or above the interface. I

A further purpose is to rotate molten iron in the presence of a supernatant slag in a ladle having its axis of symmetry substantially vertical and to produce a, relative movement between the slag and metal, to facilitate the transfer of impurities from the metal to the-slag, by means of a dam or obstruction which impedes the flow of the slag whilst permitting greater flow of the metal.

A further purpose is to obtain relative movement between molten iron and desulphurizlng slag floating on the molten iron by means of a dam in contact with the slag and adjustable with respect to the level of the slag-metalinterface. The dam may be rigidly positioned or floating and if floating, it will desirably be flexibly re-' A further purpose is to agitate molten pig iron in the presence-of a slag by means of a rotating impeller capable of raising the molten pig iron above the normal level of the slag-pig iron interface.

A further purpose is to lift molten iron into contact with a basic desulphurizing slag by a pumping impeller having an upwardly and outwardly inclined passage whose inlet is below the.

slag-metal interface and whose outlet is above the interface.

A further purpose is to employ a refractory impeller having one or preferably a plurality of flat preferably vertical surfaces and rotating about a substantially vertical axis.

A further purpose is to employ a refractory impeller for stirring molten metal having a preferably helical groove in an outer surface of generally cylindrical character.

A further purpose is to render a stirring or pumping impeller of refractory material adiustable" as to level byconnecting the impeller to the impeller shaft through an impeller extension which can be replaced by an extension of different length.

a further purpose is to promote reaction between molten metal and a desulphurizing slag floating on the molten metal by imparting horizontal rotatory motion to the charge in a desulphurlzing vessel whose axis of symmetry is vertical and whose horizontal cross section is oval.

A further purpose is to agitate molten pig iron in the presence of a u ernatant slag in a ladle by means of electromagnetic action.

A further purposeis to whirl a pig iron bath by horizontal rotary electromagnetic stirring and to maintain a substantial bodyof molten desul phurizing slag on the bath, the slag permissibly invention. The forms shown have been chosen from the standpoints of satisfactory operation and convenient illustration of the principlesinvolved. All of the figures are dia ramm invention.

Figure 2a shows a diilerent length of impeller extension from that shown in Figure 2.

Figure 3 is a side elevation of a variant form of stirring impeller in accordance with the inrotating with the iron but preferably being dammed against rotation or more desirably being oppositely rotated.

.A further purpose is to impart an electromagnetic stirring motion, preferably in a horizontal rotary direction, to molten pig iron-on which a substantial body of desulphurizing slag is floatmg. and to induce an upward stirring component in the iron preferably by an inclined vane.

Afurther purpose is to produce agitation in desulphurizing slag by electromagnetic flux from a multiphase winding surrounding the iron and provided with a ring-like magnetic core, the winding and/or core being inclined to the horimolten pig. iron in contact with a supernatant zontal so as to produce helical stirring components. A further purpose is to avoid contamination of silica and siliceous materials with molten iron drawn from a blast furnace or similar source of molten iron to an adjacent desulphurizing vessel,

by passing the molten iron through a skimming the vessel on a tilting axis adjacent the metal tap opening.

Further purposes appear in the specification and in the claims.

The invention relates both to the apparatus for treating the molten metal and to the processes therefor.

The present application incorporates by refer- V ence my United States patents and patent application, Patent No. 2,110,066, granted March 1, 1938, for Iron andsteel desulphurization; Patent No. 2,110,067, granted March 1, 1938, for Iron desulphurization; Patent No. 2,177,716, granted October 31, 1939, for Desulphurizing apparatus; Patent No. 2,193,593, granted March 12, 1940, for iron'desulphurization; and Serial No. 304,484, flied November 15, 1939, for Desulphurizing apparatus and process. It is the purpose and intent that subjects matter may be transferred from this application to the present application as required. Reference should be had to these patents and this application for further disclosure of the process.

In the drawings no attempt has been made to illustrate all of the possible embodiments of the vention.

Figure 4 is a side elevation of a further variant form of stirring impeller.

Figure 5 is a section of Figure 4 on the line Figure 6 is a diagrammatic central vertical section of a modified form of desulphurizing vessel. 1 Figure 7 is a section of Figure 6 on the line Figure 8 is a centralvertical section of a further modification in'the desulphurizing vessel.

Figure 9 is a section'of Figure 8 along the line 9-9. Figure 10 form of dam applied to the structure of Figure 8. Fi ure 1 is a fragmentary t p plan view of Figure 10. g

Figure 12 is a fragmentary central vertical section showing a further modification in the dam of Figure 8. 1 7 V Figure 13 is a central vertical section of a further' modification in the desulphurizing vessel.

I Figure 14 is asection of Figure 13 on the line "-44.

Figure 15 is a side elevation of a modified form of desulphurizingvessel with an electrical diagram of a polyphase inductor coil applied there- 'to, the magnetic core being sectioned away for convenience in illustrating the coil. i Fi ure 16 is a section ofFigure 15 on the lin B-IS.

Figure 17 is a diagrammatic top plan view of variant form of electromagnetic stirringladle.

Figure 18 is a fragmentary side elevation of Figure 17,

Figure 19 is a. diagrammatic horizontal section of a modified desulphurizing vessel.

Figure 20 is a curve showing the rate of sulphur removal from pig iron under special controlled conditions. 7

In the drawings like numerals refer to like parts, and in the specification like symbols refer to like-subjects matter.

Throughout the specification, wherever reference is made to pigiron, it is intended to designate the product of the blast furnace which characteristically has a high carbon content,- usually of 3% to 4%, or more, and always in excess of 2%, with varying contents of metalloids. The product of the blast furnace is referred to as pigiron whether it is intended to be used in the form of cast iron or whether it is to be used in making steel. v

In the production of pig iron from low-sulphur 'burdens (such as wood charcoal and low sulphur ores) it is unnecessary to operate the blast furnace in such a manner as to obtain strong desulphurizing conditionsiri the hearth and bosh isa fragmenthowing a modified of the blast furnace. As a result the operation of the charcoal blast furnace is quite economical except for the excessive costs of wood charcoal and of low sulphur ores. In most instances, how'- ever, because of the high cost of wood charcoal,

it is necessary to substitute coke for wood charcoal as a blast furnace fuel. when this is done, a strong desulphurizing action must be obtained in the hearth and bosh of the blast furnace in order to obtain a product having low enough sulphur to beconunerciallyusable. For a strong desulphurizing action, it is necessary to have a higher temperature and a slag containing more lime than fora weaker desulphuriz'ation. More fuel must be used in order to provide the higher temperature. a

A typical slag from a charcoal blast furnace approximates:

' Percent 510: 47.0 A120: 18.0 CaO 27.0 MgO 3.0 8 0.10

In the above slag the silica exceeds the lime plus magnesia. The sulphur in the pig iron approximates 0.02%.

A typical slag from a coke blast furnace has the following approximate composition:

In the above slag the silica is less than the lime plus magnesia. The sulphur in the pig iron approximates 0.03

The temperatures of the slag and pig iron tapped from a charcoal blast furnace are about 1450 C. and 1410* C. respectively. In the coke blast furnace, the respective temperatures of the slag and pig iron as tapped are approximately 1525 C. and 1475 C. Thus it is unnecessary for the charcoal blast furnace to expend as much heat to produce slag and pig iron as does the coke blast furnace.

From the above data it will be obvious that the cost of removing sulphur from the pig iron simultaneously with smelting of the ore in a blast furnace is. considerable. It is one purpose of the present invention to cheapen the cost of manufacturing pig iron, whether for use as cast viron containing 0.10% sulphur or 0.05% sulphur or less depending upon individual conditions.

' erically as ReQ oxides, where R is an alkaline iron or for making steel, by omitting the strong desulphurizing action now considered necessary in the coke blast furnace because of the sulphurbearing burdens. The smelting is conducted in the coke blast furnace under conditions of temperature and basicity of slag suitable to produce pig iron at lower cost but with a higher sulphur content in the iron than that ultimately desired.

After produc- The pig iron, containing a higher sulphur con-.

is there subjected to a strongly basic slag under reducing conditions.

The desulphurizing slag contains basic oxides I I of the alkaline earth or alkali metals such as calcium oxide, barium oxide, strontium oxide, sodium oxide, etc. These are referred to genearth or alkali metal and .1: is the numeral 2 or 1, depending upon the valence of the metal. The oxides of the slag tend to react with sulphur of the pig iron thus:

From reactions 1 and 2 it will be evident that there will be a low activity of sulphur and sulphur can be removed from the pig iron to enter the slag most efllciently if there is a low oxygen activity. In other .words, the sulphur activity may be lowered directly by lowering the oxygen activity. The desulphurizing slag is, therefore, caused to act upon the pig iron in the presence of a deoxidizing agent, as for-example an excess of carbon preferably under diminished pressure, or in the presence of carbon compounds such as calcium carbide or metallic reducing agents such as manganese, silicon, aluminum, calcium, magnesium or the like. There will, of course, very desirably be substantially complete exclusion of oxygen and oxidizing substances from-the desul- 'in the coke blast furnace when operated under conditions of moderate temperature and moderate basicity of the slag suitable to produce pig iron of lower cost but with a higher sulphur content than that ultimately desired. Ore of low iron content and coke or ore of high sulphur content may be used. The sulphur-content of the pig iron produced in the coke blast furnace under such economical conditions may be 0.25%, 0.3%

or even higher. or course, the invention may also be applied to pig iron of normal sulphur content, containing, say 0.04% S.

'I'hepigiron to be desulphurized is brought into I I contact with a, desulphurizing slag under the v proper conditions. For example, the desulphurizing slag can first be charged into a ladle or other vessel and themolten iron can then be added.

ay-s The preferable slag will have CaO as its active desulphurizing oxide. As previously explained. other alkaline earths or alkaline oxides can be used. The inventor has found, however, that CaO is very desirable and economical as a desulphurizing agent and it will be used ,in many of the illustrations, although quite evidently other oxides described could be used in similar manner after making due allowance for known differences in physical and chemical properties of the other oxides.

CaO in the pure state has a high melting point (2570" 0.). It is conventional to reduce the melting point of CaO to form readily fusible slags by adding S102 and perhaps A: and other oxides.

Thus, for example, it is possible to form a slag which is tree-flowing at 1400' 0. having the approximate composition:

, Percent CaO 44 M30 4. A120: 15 S10: 3'7

In such a slag the activity of the lime is reduced by the presence or 37% silica and 15% alumina. Slags of this approximate composition are used as desulphurizing agents in the blast furnace and are capable of-building up a 60:1 ratio of the, percentage of sulphur in the slag to the percentage of sulphur in the pig iron.- It has been found that such a slag can be used in the present invention, especially if the slag and pig iron to be desulphurized are subjected to a diminished pres sure, desirably 150 millimeters of mercury or less,

and in the substantial absence of oxygen and oxidizing substances, thereby causing the sulphur ratio to rise to 100:1 or 200:1 or more, depending upon specific conditions. a

If ordinary blast furnace slag is used, it may desirably be mixed with say -5%'to or even 20% or more by weight of fluorspar and, if desired, up to 20% or more by weight of burned lime or' substances high in 0210 such as burned 2.66%. A similar slag under an absolute pressure of 35 millimeters of mercury reduced the sul- Blast furnace slag mixed with" lime and/or fluorspar as just explained, may be employed in any of the forms of the invention disclosed herein whether the deoxidizing agent be carbon at atmospheric pressure or at reduced pressure, or other deoxidizing agent as explained above.

Where carbon is the deoxidizing agent, it may in some cases be supplied by the carbon dissolved in the pig iron, which normally contains more than 2% of carbon, and in other cases this dissolved carbon may be supplementedby a carbon lining in the reaction vessel and/or by loose carbon added to the reaction vessel.

The $102 content of the .desuiphurizing slag can also be further decreased, and slag have been synthesized containing as little as SiOz or less, as for example using a mixture of 40 parts blast furnace slag, 30 parts fiuorspar, 30 parts lime, -which slag would contain about 12% $102. It has been found that such slags are very adsilica to the desired percentage by'the addition or silica sand, after allowing for the silica present as impurity in the lime and fluorspar. Magnesia-present as a normal-impurity in a good grade of lime is not objectionable. Alumina present as a small amount of impurity is also not ob-.

been subjected to the-action of the lime-fluorsparstrong reducing conditions and the desulphun phur content of the iron to 0.001% and the slag contained 2.83% sulphur.

silica slag above referred to, at 1400" C. for one tainer composed of carbon inthe form of graphite. The slag and molten pig iron were under izing vessel was arranged so as to prevent direct contact with the atmosphere or with combustion gases'high in oxygen, carbon dioxide or water vapor. Under these conditions the slag picked up as much as 10.79% sulphur, and the pig iron had its sulphur content reduced to 0.03% sulphur,

so that there was more than one hundred times as high a percentage of sulphur in the slag asin the pig iron.

In other cases in which the pig iron'initially contained only about 0.03% sulphur, the sulphur content of the pig iron was reduced to 0.002%

than one-tenth of that in the iron before treatment according to the invention.

A study has been made of the use of sodium oxide, NazO, in the form of slags containing this oxide or its compounds as a substitute for lime in desulphurizing' slags. Th'e desulphurizing action of these compounds of sodium oxide, for example sodium carbonate, on pig iron is well known vantageous especially where the slag and pig iron K under treatment cannot be subjected to low pressures.

A desulphurizing slag having the composition;

' Percent C870 45 CaFa 40 S102 15 and this alternative can be used. It is found, however, that NazO is readily attacked by carbon and silicon in the pig iron at temperatures of 1450 C. or below. The reaction produces carbon monoxide, silica and sodium vapor. The latter is very efiective in converting FeS into NazS and thus desulphurizing the pig iron. The sodium vapor causes dimculty in the handling of soda slags, and the reaction must be managed in such away as to limit the formation'of volatile soda derivatives in order to avoid excessive loss as fume. It is possible to use slags containing Na'zO combined with SiOz and/ or A: and other oxides to overcome vvolatilization loss incident to sodium carbonate. The revivification of soda slags to remove sulphur and permit reuse presents special difflculties not present in the case of lime slags.

Detailed reference to the steps necessary when I soda slags are used is, therefore, omitted, and the discussion is generally confined to slags contain-- also soda or other alkali metal oxides in combination. 1

The quantity of oxides of the t p B in the initial slag should exceed 30% for best results.

Due to the cheapness and freedom from volatilization, it is preferable to use a lime slag, although such preference is subject to change under varying economic and-metallurgical conditions.

In choosing the slag, it is desirable to have onewhich will be of low viscosity and workable at temperatures of 1400" 0., and for this purpose. the slag should preferably be freely fluid at as low as 1200 C. or in some cases at 1300 C.

It is very advantageous to use a slag which shows a high ratio of sulphur concentration in the slag, after use, to sulphur concentration in the desulphurized or partially desulphurized pig iron.

Much latitude is offered in the choice of slag composition. In general the slag composition and pressure should be chosen so that a ratio of sulphur in the slag to sulphur in the iron should exceed 100:1 and preferably exceed 200:1.

As explained in detail below, it is often advantageous to employ a desulphurizing slag which can be revivifled or treated to remove its sulphur so that it can be used over and over again. The lime slags referred to'fulfill this requirement.

The desulphurizing slag, after it has picked up, for example, 12%,sulphur, is revivified by removing sulphur from the slag until, for example, less than 1% sulphur remains. This revivified slag is then used repeatedly to desulphurize further quantities of molten pig iron.

Des'ulphurz'zing apparatus In order to obtain the best desulphurizing action with many slags I have found that it is necessary to keep the temperature of the pig iron' as high as possible. For example, laboratory experiments with a slag comprising 80 parts blast furnace slag, parts lime, 10 parts fluorspar,

treating a pig iron initially containing 0.16%

To take advantage of this accentuated desu1-' phurlzing action at higher temperature, I place the desulphurizing vessel in a position adjoining the blast furnace. In this manner I avoid any temperature loss such as would occur if the molten iron from the blast furnace is first placed in a transfer ladle and then transported to a desulphurizing vessel located, for example, at the mixer in the steel making plant.

I have also found that the desulphurizing power of slags comprising large. amounts of blast furnace slag is very sensitive to the ratio of lime to silica present in the slag. -At equilibrium the desulphurizing power of these slags as measured by the ratio of sulphur in the slag to sulphur in the iron varies not as the ratio of lime to silica in the slag, but approximately as the logarithm In deto the base ten of thelime-silica ratio. sulphurizing iron after its removal from the blast furnace, it is very important that the iron, as

it is transferred from furnace to dcsulphurizing vessel, be not contaminated by admixture of im purities containing silica. Many natural sources I of contaminating silica are present at the blast furnace, such as the fire'clay used in closing the blast furnace tap-hole, loam used in fettling the iron runners, and coke breeze used for coveringthe exposed surface of the molten iron in runners, etc. For best results these contaminations can be avoided by causing the molten iron to pass through a small tea-pot ladle or similar device just before it enters the desulphurizing vessel. in this way the siliceous impurities are separated and the desulphurizing slag is kept uniform with ient speed. The present inventor has performed experiments without agitating the molten slag and molten pig iron. Figure 20 shows the rate of sulphur removal under certain fixed conditions, using a slag consisting of 40% blast furnace slag, 30% fluorspar and 30% burnt lime, without. agitation. In this figure the molten pig iron contained 0.07% sulphur at the beginning of the experiment. This iron was treated with-desul phurizing slag of the composition Just noted under deoxidizing conditions and freedom from air contamination, and samples of iron, were withdrawn for chemical analysis at specified times. In Figure 20 the experimental data has been plotted in a curve showing, as the ordinate, the percentage of sulphur present in the iron, and, as the abscissa, the elapsed time for the reaction expressed in minutes per inch of depth of the metal bath.

The rate of sulphur removal is proportional to the depth of molten metal. From the curve it will be seen that, in order to lower the sulphur content from 0.07% to 0.005%, approximately 12 minutes are required for each one inch of depth of metal bath.- In a customary pig iron ladle a depth of metal of 60 inches or more is to be expected. Thus for a depth of 60 inches, anelapse'd time of 720 minutes or 12 hours would be required to desulphurize to the above extent. This time is too long for most operating conditions.

The rate of reaction can be speeded up appreciably by agitating the molten metal and/or the slag in order to produce relative motion between the slag and the metal at their point of contact, the so-called slagmetal interface. It is believed that the slow speed of desulphurization which is obtained in a quiet bath is due to the resistance which the sulphur encounters in the regions closely adjoining the slag-metal interface whilst passing from the metal to the slag. When contact is first established between the pig iron and the slag, the slag rapidly absorbs sulphur but the reaction soon slows down because, without agitation, the system approaches equilibrium only in the'limited region which is not too far removed from the slag-metal interface. By providing a relative motion between the mass of the slag and the iron, thereby bringing fresh slag and iron into the zone adjacent to the slag-metal interface, it is possible to speed the removal of the sulphur. By continuing this process of relative motion the difliculties of slow speed operation as described above in quiet baths can be overcome. The present invention is concerned with agitation to produce relative motion between the slag and the metal in order to speed up the reaction and obtain a higher content of sulphur in the slag and/ora lower content of sulphur in the v iron than would otherwise be obtained.

Figure 1 illustrates a desulphurizing vessel 20 equipped with a mechanical agitating device for of molten pig iron.-. The slag layer might approximate 1% to or more of the depth of the molten iron. The shape of the vessel is approxi- .mately circular or oval in cross section and the axis of symmetry, that is, the axis running per- 'pendicular to the plane of circular or oval cross section, is vertical.

The axis of symmetry as referred to herein will be what is commonly called the major axis in the ordinary case. Where the ladle cross section is circular, it will be the axis of generation of the ladle.

The vessel is provided with a suitable steel shell 2| substantially gas tight and-capable of protecting the contents from access of the atmosphere or other oxidizing gases. Therefractory lining 22 consists preferably of carbon or magnesite bricks which have suitable resistance to the corrosive action of the ladle contents. In'order to conserve heat, these refractory bricks may be backed up with refractories 23 having lower thermal conductivity, as for example flreclay brick having an appreciably larger percent of pore space .than normal for such products. In

some cases fireclay brick may also be used in direct contact with the contents of the ladle, as

for example in the lower part where the slag does.

not come into contact with the fireclay refractories for long periods of time.

may vary with diiferent installations. The impeller and its operating mechanism make a gastight seal with the cover 24 and may be removed as a unit from the desulphurizing vessel and a cover substituted as shown inFigure la.

There are several advantages in employing a ladle whose axis of symmetry is vertical for desymmetry is vertical than in one whose axis of' symmetry is horizontal. In a normal ladle whose axis of symmetry is vertical, a larger proportion of the pig iron will be at relatively great depth in the ladle than in a ladle whose axis of symmetry is horizontal. Therefore in a ladle whose axis of symmetry is vertical, there is greater importance in securing eiilcient stirring and stirring which is effective from the standpoint of desulphuriza tion.

Different types of impellers may be used to impart stirring primarily in a horizontal plane, but with an upward stirring component. Figure 2 shows a pumping type of impeller of circular 1 cross section made suitably of carbon refractories.

The body of the impeller 4| has pumping passages 42 extending diagonally upward and outward as shown. The number of pumping passages 42 is not critical. The effect of the pumping impeller is to lift molten metal from the bath into contact A roof or cover 24 is provided for the ladle.

Fireclay or other suitable refractories 25 such as carbon or magne'site can be used in lining this roof. For best results a flat roof should be used and in such construction the refractory brick are best held in position by suspending them by hangers or other suitable means (not shown) from the extemalsteel shell 28.

An opening 21 is provided for charging the molten iron and slag. Usually the slag .will be charged before the molten iron although this is not always critical. The iron will be tapped from the blast furnace or other source of supply through a runner 28. In order to prevent'silica and other undesirable impurities from entering a hollow interior 48 into which cooling air or the desulphurizing ladle,'a skimming ladle 29 is provided. The iron leaves the runner '28 and mer about the trunnion 34. Thereupon the skimming ladle and cover are removed and a suitable permanent cover 35 is placed on the ladle to cover the opening 21 as shown in Figure 10.

An opening 36 is provided in the cover 24 of. the ladle for an impeller 37. This impeller is'preferably a self-contained unit having an electric motor 38 and speed reducer 39. The motor will preferably be of variable speed direct current motor producing an impeller speed of to 200 revolutions per minute or more. The speed chosen with the desulphurizing' slag. The inlet 43 of the pumping impeller will preferably be located below the slag-metal interface 44 and the outlet 45 above the slag-metal interface, as shown, to cause distribution of molten metal directly into the slag. The level of the impeller 4| is made adjustable as required, by using any one of several different lengths of extensions 46. Extension 46 may be also made of carbon refractory or maybe made of so-called sillimanite refractory or other high aluminous material. Figure 2a shows a different length of extension 46'. The impeller assembly is carried on therotating shaft 41 which may be made of suitable heat resistant metal with other fluid is blown by a suitable pipe 49. The impeller, extension and shaft are desirably threaded to one another at 50 and 5|.

Another form of impeller capable of lifting pig iron is shown in Figure 3. In this case the impeller head 4| is desirably made of carbon refractory. It is attached to the rotating mechanism by means of a sillimanite, cyanite or other extension 46 The carbonrefractory is machined to provide a spiral fiuting 52. The impeller is mounted so that the spiral fluting preferably extends-into the pig iron and below the slag-metal interface 44. The rotation of the stirrer produces a corresponding rotary movement in the slag and metal with which it is in contact.

By virtue of the fluting, a vertical motion is also produced which preferably lifts the iron andthe slag above the level which it would normally take if the fiuting were absent." The efiect of the pumping impeller is to lift the molten metal from the bath and bring it into better contact with the desulphurizing slag thereby exposing fresh slag-metal interfaces to speed up the sulphur removal. 7

An alternative apparatus for producing the required agitation is shown in Figures 4 and 5.

,fiexibly' restrain it, as by a refractory chain on an- This consists of a rotating stirrer of carbon or other suitable refractory which is supported by a sillimanite extension 46 as shown in Figures 2 and 3. The stirrer H can be made from a round carbon electrode of suitable diameter, for example 10 inches to 15 inches or more if necessary. The round electrode can be machinedto form a rectangular or other section 53 having one or more plane surface 54. For example, a rectangle 5 inches wide and inches-to inches or more in length might be used. The stirrer is immersed in the slag and metal. By its rotation a corresponding rotary motion of .the contents of the ladle is produced.

For better results two or more stirrers 4| and 4I 'may be used as shown in Figures 6 and 7. If

two stirrers are used, they should be spaced so that the clearance between the rotating carbons should not be too great, as for example, a clearance of approximately 6 inches to 18 inches. These stirrers may rotate in the same direction or in opposite directions. If they are rotated in the same direction, the entire mass of liquid contents of the ladle will be given a corresponding rotating motion as shown by the arrows in Figure 7.

Where a plurality of stirrers are to be used as in Figures 6 and '7, improved results are obtained by having the stirrers effective at different levels in the bath. Thus in Figure 6 the stirrer 4| extends deeper into the bath than the stirrer M the latter stirrer operating chiefly in the slag and not extending any great depth below the slagmetal interface. These two stirrers produce a relative movement between the slag and the metal and also between respective portions of the metal.

In order to speed up the rate of reaction it is desirable to have a relative movement between the slag layer and the metal. The natural tendency would be for the slag layer and the metal layer to rotate together and the relative motion between the two would not be as great as desirable. Increased relative-motion can be obtained by using the apparatus shown in Figures 8 and 9. A dam 55 is immersed in the slag layer and if desired, below the slag-metal interface 44. Any desired number of dams may be used. The effect of the dam is to impede the rotation of the slag whilst permitting a relatively unhampered rotation of the pig iron, thereby causing relative motion between the pig iron and the slag. The dam may if desired occupy the opening 21 when metal is not being charged, with suitable packings to exclude air.

Where there is considerable variation in the level of the pig iron, it is desirable to make the height-of the dam adjustable so that the dam will always extend down to the slag-metal interface and also preferably slightly below the interface as shown. In Figures 10 and 11 I show a refractory dam 55' suitably of carbon refractory supported on a bracket 56 andadjustable as to height by an adjusting screw 51 threaded through the-bracket and making thrust bearing connection with the dam 55'. To prevent the dam from rotating, a guide 58 extends from the dam through an opening in the bracket 56.

In some instances it is preferable to use a floating dam 55 as shown in Figure 12. This dam, preferably of carbon refractory, automatically adjusts itself with respect to the level of the slagmetal interface and its volume-weight may be adjusted by adding weights 59 to make it float with any desireddegree of submergence. While the dam 55 may float freely, it is preferable to chored to the vessel 20 at iii. The structures of Figures 10 to 12 will be provided with a suitable gas-tight'cover as shown in Figure 1.

To further promote better transfer of the impurities from the molten iron to the slag, the apparatus shown in Figures 13 and 14 can be applied either alone. or in conjunction with the dam 55 and/or the two stirrers 4| and 4| as shown. In this type of apparatus the refractory lining is constructed to form an inclined vane 62 extending around the ladle circumference from point 53 near the bottom to point. 64 near the top arid providing a vane shelf 65 which is a maximum at 63 and a minimum at 64. The vane 62 is capable of converting some of the rotary motion of the liquid iron in the ladle into vertical motion, thereby bringing the metal from the bottom of the ladle upward to establish contact with the supernatant slag. The rotatory action of the metal may be imparted by the stirrers 4i and 41 or in other suitable ways. I 7

Instead of using the mechanical agitators for producing a rotary motion in the molten pig' iron in the ladle, it is also possible to produce a rotary motion by means of electromagnetic action. using polyphase alternating current to produce rotating magnetic fields in an iron core suitably placed around the periphery of the ladle, preferably at or below the slag-metal interface, the current induced by the alternating electromagnetic field in the molten metal contained in the ladle causes a rotary motion of the metal in the way that rotary motion is produced in a polyphase induction motor.

Figures 15 and 16 showsuch a polyphase stirring ladle having a winding 66 intended for threephase alternating current, with phase field coils 6'1, 68 and 69 connected to a source at I0, II and I2 and connected together at 13 (Figure 15). Star connection is shown, but it will be evident that any suitable system of connections may be used. The winding is surrounded by amannular magnetic core 14 suitably slotted to receive the winding as at 15 and desirably laminated. Low frequency alternating current at, for example, 25 to cycles will preferably be used.

The device of Figures 15 ,and 16 will cause simultaneous rotation of both the slag and the metal. To secure differential movement between the slag and the metal, a slag dam 55 of any desired type will desirably be used as shown in Figure 16; or an inclined vane 62 as also shown in this figure; or mechanical stirrers will be employed as shown at 4 I and 4| in'Figure 16, preferably causing the slag to rotate oppositely from the metal.

Figures 1'7 and 18 illustrate a variant electromagnetic stirring device. The desulphurizing vessel 20 is surrounded by a polyphase winding 16 of Gramme ring type, wound on an annular magnetic core 11, suitably laminated, and provided with magnetic poles 18. In the specific construction, a three-phase winding consists of phase coils 19, 80, and BI connected in delta formation to three- phase lines 82, 83, and 84 from an alternating current source at commercial frequency. The magnetic core TI and the poles 18 will desirably be assembled from separate units, fastened together in any suitable manner.

The winding 16 and core 11 are very desirably inclined or canted with respect to the horizontal as shown in Figure 18, so that in addition to a horizontal rotary or-whirling motion in the iron,

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' substantial portion of the iron bath and not merely through the wall of the ladle. It is preferable, therefore, to use a small number of poles, for example from two to six poles.

The ladle of Figures 17 and 18 is desirably provided with a slag dam 55 and with impellers II and ll. While the iron whirls in upward helical paths, the whirling of the slag is retarded by the dam 55., The impellers M and 4|, which operate in the slag, will desirably rotate the slag oppositely from the rotation of the iron. For example, if the iron rotates in the direction of the arrow 85, the slag will preferably be rotated by them-- peiiers in the opposite direction.

It will, of course, be understood that in Figures to 18 the ladies will be provided withair tight closures.

Instead of a moving wave form of electromagnetic stirrer as shown in Figures 15 to 18, a poolsurrounding coreless induction form of any well known type may be used. In Figure 1 an inductor coil 66 surrounds the upper portion of the metal bath adjacent the slag-metal interface' The neighboring structural parts of the ladle will desirably be made of non-magnetic metals or alloys or non-metallic materials. A suitable alternating current of low frequency, for example to 100 cycles, will be connected to the coil 86'. The coil will desirably carry a high wattless current due to resonance obtained through suitably connected condensers as well known in the art. In some respects the inductor coil stirring is undesirable as it is accompanied by considerable heat obtained at relatively high cost.

The ladies for containing the molten metal and slag to be rotated as described above should have a vertical axis of symmetry about which the rotation takes place. For example, the interior could be shaped in the form of a cylinder or inverted truncated cone. The major axis of the cylinder or cone stands approximately vertical and rotation occurs about this axis. It is not necessary that the cross section of the ladle on a plane at right angle to this axis of symmetry be circular.

Indeed, it may be advantageous to use some other shape as for example an elliptical or oval section, thereby facilitating the formation of new areas of slag-metal interface as the metal rotates about I its natural axis. 'For example, the oval cross section shown in Figure 19 when rotated by any of the means described turns about an axis located at the point 86. An element 81 of slag-metal interface is rotated by this motion to the position 81'. By so doing the area of the interface is increased. Further rotation causes the element to move to ill with attendant decrease in areaof the slag-metal interface. At postion 81 the area 'is again increased. Thus a repeated formation of new areas of interface occurs by rotating the slag and metal in an oval shaped vessel.

An illustrative cycle of operations with reference particularly to Figure 1 is as follows: The desulphurizing ladle is charged through the opening 21 with the required amount of desulphurizing slag from the not 88. This desulphurizing slag may, for example, comprise '10 per cent of molten blast furnace slag previously'withdrawn from the blast furnace, 20 per cent ofiburned lime and 10 per cent fluorspar. The blast furnace is tapped and about 150. tons of iron is transferred into the ladle 29. As described above, all siliceous contaminations should be removed from the flowing stream of iron by dams or skimming devices. The desulphurizing ladle and its charge is then closed against free accessof air or oxygen'to the interior. Desulphurizing is continued using agitation until the proper sulphur content of the iron has been obtained. For best results vacuum may be applied to the ladle, as through a vacuum connection 80. s

After the desulphurizin reaction is completed, the slag is removed by tilting the ladle 20 about the axis and allowing the slag to run out the opening 9i (suitably closed against air contamination when not in use) into the slag pot ll. Thereupon the ladle is tilted in the reverse direction about'the axis 92 and the iron is poured through the tea-pot spout 83 (suitably sealed when not in use) into the transfer ladles 84. A symmetrical axis is also provided at 92 for pouring the entire ladle K content, slag and iron, in emergency. Two or more transfer ladles 04 may be used if necessary and the stream of metal from the desuiphurizing ladle can be interrupted by tilting the ladle 20 whilst a new transfer ladle is brought into position. Itis important that any desulphurizing slag remaining in the desulphurizing ladle be kept from entering the transfer ladles 94. Th inclined tea-pot spout 83 i effective to prevent this. Iffurther precautions are necessary the small tea-pot skimmer ladle 95 can be placed just ahead of the transfer ladles 94.

With good agitation and eflicient siags, a pig iron containing 0.015% sulphur or 0.010% sulphuror less may be obtained from a blast furnace product containing initially as much as 0.10% to 0.30% sulphur or more. The sulphur content of the slags may rise to 5% or 10% sulphur or more and a ratio of sulphur in slag to sulphur in the iron oi 500:1 or 1000:1 and even 5000z1 or more, all depending upon the chosen conditions. Of course, the processes and apparatus described herein may be used for the removal of sulphur from molten pig iron supplied by furnaces other than a blast furnace, as for example a cupola. The use for such purposes is expressly .included herein.-

In view of the invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the structure showmand I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is: 4

1. The process of desulphurizing molten pig iron, which comprises treating molten pig iron under deoxidizing conditions in a closed space with a basic desulphurizing slag floating on the pig iron and projecting streams of molten pig iron upwardly into the slag at the'slagpig iron inter! face.

2. The process of desulphurizing molten pig phurizing slag on the iron while rotating the slag I in a direction opposite to the direction of rotation of the iron.

4. The process of desulphurizing molten pig.

iron, which comprises electromagnetlcally whirl- 9 Zing the iron in a generally horizontal rotating 'path, imparting an upward stirring component to the iron and maintaining a substantial body of molten desulphurizing slag on the iron. Y

5. The process of desulphurizingmolten pig iron, which comprises electromagnetically stirring molten pig iron in a helical path, tending to bring submerged metal to the surface, and maintaining a substantial body of molten desulphurizing slag 10 on the iron.

RUSSELL PEARCE HEUER.

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