US2587573A - Desulfurizing process - Google Patents

Description

4 Sheets-Sheet 1 Filed *Juhe 9. 1949 INVENT R D. J. WYN NE 2,587,573

DESULFURIZING PROCESS Feb. 26, 1952 4 Sheets-Sheet 2 Filed June 9. 1949 INVENT R v yrwze Feb. 26, 1952 J, wYNNE 2,587,573

DESULFURIZING PROCESS Filed June 9. 1949 4 Sheets-Sheet 3 ATTORNEYS Feb. 26, 1952 J, WYNNE DESULFURIZING PROCESS Filed June 9, 1949 4 Sheets-Sheet 4 (9 70000 Lbs.

Q 30 000 Lbs.

w. nn 5 1% J .fi f l, t v t y .y

A furth rpurpqse'is to annoyanceac wa Patented Feb. 26, 1952 UNITED STATES OFFICE I 2537,57? nEsui FuRizmmPRocEss 1: Dominic lf'wynne, fieltimore Md designer or EssexReseasrch Ddrpcration, Wilmington; Del a, corporation-ofDelaware Application ilune 9,-194, SerialYNO.r91,959.

a 'tiiaimsl (01. 755

The present invention rela'testo the process of de'sulphurizin'g pig .zironb. j

A purposeof the invention is to chemically in} te'nsify -the desu'lljhuriz'tion-emd physically accelerate the agitation while desulphurizing molte'n pig; iron at pressures not'less than 'aitmo'spheric-pressure; .v

Ai urther purpose-is to maintafin 'ar bath of, mail? temmigiroinzin ca :desulzihurizingyessel con;-

tact iwithlia zdesulphurizingesmei. .toeenclos'e the molten @igmironxand slag ,:to exclude oxidizing gases;- including. "the atmosphere :and maintain stronggreduoing-conditions: around the moltempi'g V ironsgin'd -.:s1ag .-2a.nd: to" blow throughntheimolten pig iro'man; inert gas free afrbmrsubstantialcnam tities 'of compounds'iawlflch under :the conditions.

are'sqrore roxidizingxgthan, carbon .monoxideaqnd free from carbon monoxidein excess. of 33 ..per-. cent to chemically intensify r-the'desulphurizetion and tphysi cally accelerate the agitation,1 .-whi1e maintainingra .ipressure of. .at least atmospheric preseurefehove' ithe molten; pig iron .and-slag-al-f :Aefurthe'r .purpose is .to-eccomplishthe obi so? 'tiveswf. the apreced-ing paragraph andobtaingfle; sulphurizationzet.anteccepteble commercieltrate relatively independent. of the 1 depth of; the iron bathl and therefore at an increased rate ina deep beth.:byipassing.the inert gas throughxatleastyhalf thedepth-i'ofithe molteni irionat. narrate excess of. nneithirdicubiefoot oifgas per minute per" ton D mme molten iron to form -ca iuin"=sulnhide,-

WhI'c'hiiiay ormay not "be molten it the tempera- 2 sulphurizirfig agent',nref erably';along with fluo'r spar and westeblastfurnece slag.- v

ni'urtherpurposeis to utilize an" inert-gas p're dom-mam y-by 'volu-rne consistingof. riitr'o'ge'n-and permissibljy havingcarbommonoxideas itsgchiet rninor constituent -limited, however; to not over 33' percentcarbon-monoxide by volume.

A furtherpurpose to' employ an'inert gas predominantly "by volume co'nsistingof hydrogen and permissiblyhaving' carbon monoxide as the chief minor constituent, the-carbon monoxide content, hoWeven-bein'gnot-over 3-3 percent.

Aafurther purpose is-toemploy as aninert gas, a'g'a's predominantly by volume-consisting of-blast furnace gas, in which the contentof casrbon -dioxide-has been "reduced" to not-more than 3 percent-'and the content of carbon monoxide has been*reduced to not"more-than 33 percent by volume:

- As well-kn'own, it is customaryto-operate many immerses-under slight-1y diminishedpressure-be causehf the =sricti'o1'1'- of'e-stick; etc; opera tion employing sli'g h'tly less than atmospherie pressurein order to facilitate movement of gases would? therefore, be considered an operation at normal pressu-rees cornbar'ed withthel-ii'gh 'vacua set forth in Heiier-U. -'S;P'aten't-2,110,067.

" 'Fur'ther 'purposes appee'r in thespecificaticn and in 'theclainis: e The; present application "is "'2: continuation-"in pertbfmy application "Serial No." 601,654, filed June 26; 1945 forDesulphuri'zation'of Pig' Iron '28:" 19 4? for 'DesulphuriZation "ofPig Iron,- both ni'ovr"ehtiniiziined:

"The drewings illustrate brie-type of apparatus applicable totire inventionr Figured fis ad'ieigrobminetic toil planvi'ew *of'appera'tiis "by t which" inveritionfin'a'y "beapplied. 'Fifgure 238 an-end elevation of the structure or Fig-tire 1 thebasebeiii'g' shown-in sectionr 'iiigure Pisa. left 'end' elevation of "Figure '2: Figurm a diagrammatic central verticel'sec' ti'on' -01 the desu'lphurizing vessel.- {Figure 5- -15 a,--"gre2ph*re1ating'the percentage of original sulbnur *remainingf inthe pig iron-to l'o'ga m miccoordihates "as ordinates "and-the-num' her U cubic feetfof ihert 'gn's' per-tonetlatmo'se pheric tmp'erztureend pressure whichh'as "been 3 passed through the iron to linear coordinates as abscissae.

Where reference is made herein to pig iron it is intended to designate the alloy of iron with a high content of carbon3 to 4 percent or morewith varying contents of silicon, manganese, phosphorus and sulphur as conventionally obtained from the iron blast furnace, the cupola, the air furnace, or from any other source.

The treatment of molten pig iron with lime bearing desulphurizing slags was taught by Heuer in U. S. Patent 2,110,066. Heuer taught that carbon monoxide is a non-contaminating gas which can be blown through the molten mass to provide agitation. He stated that it was possible to absorb 10 percent of sulphur in the slag under favorable conditions and obtain a ratio of the percentage of sulphur in the slag to the percentage of sulphur in the iron of 250:1. In U. S. Patent 2,110,067 Heuer taught that the desulphurizing reaction should take place below the normal atmospheric pressure, as for example, at a pressure of '76 millimeters'of mercury. Mechanical agitation was suggested.

In U. S. Patent 2,193,593 Heuer taught the use .of: reducing agents other than carbon to reduce the oxygen activity in the desulphurizing process and thereby improve "the desulphurizing' action of the lime slags. As reducing agents Heuer disclosed metallic aluminum, magnesium or calcium. Mechanical agitation wassuggested.

In U. S. Patent 2,290,961 Heuer taught that therate of sulphur removal'using hispreviously described slags was too slow since it required approximately 12 minutes for each one inoh of depth of metal bath "in order to reduce sulphur from 0.07 percent to 0.005 per cent a reduction to less than 10 percent of the original sulphur Icontent. Thus for a depth of 60 inches of metal the time required would have been 720' minutes.

Heuer sought to secure thorough and rapid desulphurization by means of violent agitation.

A further purpose is to expedite'the desulphurizing reaction between a basic desulphurizing slag and molten pig iron by producing local agitation adjacent the slag-pig iron interface, and preferably by projecting streams of molten pig iron into the slag. Page 1, column 1, lines 22 to 27.

A further purpose is to agitate molten pig iron during desulphurization under theaction of a basic slag, by introducing beneath the surface of the slag and pig iron, a stream of noncontaminating gas, suitably nitrogen, carbon mom oxide, producer gas, or coke oven gas, at a pressure substantially above that at the surface of the 'pig iron and at a temperature substantially below that of the molten pig iron, and desirably also to maintain subatmospheric pressure above the surface of the molten pigiron so as to cause the gas to do a maximum of work-upon thepig iron. Page 1, column'l, lines-28 to 401-1 A further purpose is to introduce a stream of agitating gas beneath'the surface'of molten pig iron being desulphurized by abasic slag, the gas" being at a high enough pressure-onlow-enough temperature, either or both, to undergo rapid expansion while flowing through the metal and to concurrently evacuate the vessel, removing gas at a rate at least as great as that at which gas is supplied so as to maintain subatmospheric pressure in the vessel. The reduced pressure then performs a dual function; it chemically int fi the de u i i iee emit sever lly 4 accelerates the agitation." lines 5 to 17.

Heuer intended to utilize the subatmospheric pressure to perform a dual function of chemically intensifying the desulphurization and physically accelerating the agitation. Heuer had previously taught that by reducing the pressure he could chemically intensify the desulphurization. He had also taught in U. S. Patent 2,110,066 that agitation could be accelerated by blowing carbon monoxide through the molten bath without the use of subatmospheric pressure. By blowing carbon monoxide through the molten pig iron to physically accelerate the agitation it is not, however, possible to' perform the other one of the dual functions of chemically intensifying the desulphurization without evacuating the vessel.

I have discovered that by substituting for the carbon monoxide gas an inert gas such as nitro- Page 1, column 2,

gen or hydrogen, the passage of the inert gas through the molten pig iron will remove carbon monoxide from the molten pig iron in addition to accelerating agitation, favoring the liberation of It will be evident on principles of mass action that removal of carbon' monoxide in reaction (2) favors the liberation of metallic calcium,

favors the combination of the metallic calcium with the sulphur and so favors desulphurization. Thus blowing an inert gas such as nitrogen or hydrogen through the molten bath in accordance with the present invention chemically position .of the gas and the proper methodwf application of the gas in order to chemically intensify the desulphurization if the desulphurizing vesselv is maintained at atmospheric pressure. although Heuersteaching of the selection ofgas composition and method of application of the. gas

is correct when applied to subatmospheric pressure. Heuertaught' in U; S. Patent 2,290,961 that the removal of sulphur from the molten pig iron proceeds at a rate which is dependent upon the depth of. the bath. .In contrast to the disclosure of Heuer U. S. Patent 2,290,961, however, I have discovered that if gas is blown'through a sum- 1 cient depth of molten pig iron at a rate beyond one-third cubic foot-of gas per-minute per ton 7 of. pig iron measured .at atmospheric temperature and pressurethe sulphur is removed from 4 the molten ,pig'iron at a rate which is independent of the depth of the pig iron bath andis much greater than that obtained by following the teaching of this Heuer patent. y Thus, unlike the experience reported in Heuer Q U. S. Patent 2,290,961, under my conditions of 'Thus proceeding according to the inventibh,

using 140 pounds of pig iron having an initial sulassists 2 -3 sulphur *t'o less than 1o percento? its angina-1 content inies's than-9b minutes, empio mg a lime aes phurizmg slag by blowing commercially pure n through the metal-slag system in amounts of about 30 cubic reetper-tomineasured at normali atmospheric temperature and presin value in less than' 90'n'1'i nhtesff6l about '45 cubic feet gas flow per to n.

-,'The o'haft in Figure shows a curve relating the percentage of "original *ShIphhr-lemaining the various melts 'd'esribed above-and the cubic feet-of nitrogen per ton passed through the metal. If I desire toiremove -90 percent of the original sul hur from the metal I find that a satisfactory rate is obtained'i-f about-=40 cubic feet per ton is assed through the metal in minutes or even "if this time is extendedto 120 minutes, measured at "atmospheric temperature and pressure." I therefore reeommend' a-ga's flow exceeding about one-third cubic foot of gas per minute per ton of iron-measured at the atmos pheric temperature and pressure, irrespective of the depth of metal or'ar'ea of the metal surface.

Under the aforesaid Conditions it is possible to increase the size from'a labbr'atorysample of 140 pounds to 70,000 pounds with relatively no increase in the time iequi'red fe'r the desulphuri-Z'ation. This feature was not obtained in the Heuer patents. I

Heue r in s. Patent 2,290,961 maimed invention in reducing the time or desulphuriza'tion from 12 hours to 4 hours, a decrease of 66% percent. By the present invention I can Still further decrease the time required to desulphu'r-i'ze a -60 i'nch'depth of molten pig iron from four hours to one and one-half hours, a reduction or 152 /2 percent; This-same reduction can be obtained in depths of molten-pig iron exceeding the 60-inch depths to which'l-Ieue'r refers, up to depths of the order of feet, anauown to depths Of the order-of three fet-ol ove'r oneroot. I i By the present invention all the difficultiesinherent in met'allurg-ieal apparatus'operating um der vacuum areavoided. Inbarryingout the invention -1 bring the molten pig-iron and suitable 'des'ulphurizing slag or'other agent into contact in a substantially closed vessel which protects the'contents from theoxidizing action of the atmosphere.

Asuitable inert gas is then-blown into the molten pig iron by means of a tuyre or tuyeres. The'gas rises through the molten pig iron and escapes through a vent in the upper part of the desulphurizing vessel. inert gas is used, andwhen the gas is made to rise through a substantial depth of metal exceed ingtwo feet, the gas escaping through-the'vent in the desulphurizing vessel at the beginning of the cycle contains carbon monoxide picked up from the molten pig ironsystem and it ignites spontaneously in the atmosphere. As the blow ing continues and carbon "monoxide" is gradually removed from; the system, the amount of carbon monoxidein the exit gas decreases until the exit gas contain too little carbon monoxide to burn,

When an incombustihle.

6 and the e will go out. I continue to new beyond the'poi-ht at which tnename goes oilt.

This removal of carben monoxide which *bf fected at atmospheric'pressufe by the proper-passage of the inert gas, reduces the partiarpressure of carbon monoxide 'w ithin the de'sulphuriaing vessel and reduces the partial 'pre'ssureof-oxy the desulph-uri'z'ing vessel, so that the 'desul phurizing action-or the slag is cheln'ially i-nteiis ifled.

The flow of a suitable gas as described abeye through the molten pig iron then performs a dual function, it chemicallyintehsifie -the desu'lphuriz'a'ti'o'n and it "physically accelerates the agitation. 5

The gas used should, of course, not contamin'a'te the pig iron are therefore a gas carrying a substantial sulphur content such as hydrogen sulphide or sulphur dioxide should be avoided.

As inert "or non reactive gases f'nitrogen, helium, hydrogen, ammonia, and the other rare inert gases such as argon are desirable, either alone or in mixtures with-one another in any'pr'opor' tions, theba-lance impurities. Gases of this type are either chemical elements or chemical compounds which, upon contact with molten iron, are decomposed into their elements, and thus for the purposes described herein, may be considered as chemical elements I have treated molten pig iron containing 0:035 percent sulphur with a lime bearing d'esulphurizing slag and 'chen iically pure nitrogen accordance with the present invention and obtained in 70 minutes a desulphurized iron containing 0.001 percent sulphur. The final 'desulphuri'zi-ng slag contained more than 10 percent of sulphur, and the ratio of the percent of sulphur the slag to the percent of sulphur in the iron ex ceeded 10,000zl.

I am familiar with the fact that the passing of the gas into molten iron in the presenceof slag has been used to speed up the rate of desulphurization. The desirable desulphurizing re sult above reported was not merely the result of rapid clesulphurization which would be caused by any kind of gas.

For example, a similar trial was made with the same analysis of molten pig iron and sl 'a'g', 'under otherwise identical conditions, but carbon-inc inoxide was substituted for nitrogen in similar amount The desulphurized iron after 'lO minutes still contained 0.015 percent of sulphur, and the ratio of sulphur in the slag to sulphur in the molten pig iron was only approximately 600:1. Thus the use of nitrogen gas accomplishes a desulphurizing effect which is unusual because it performs a dual function of chemically intensifying the desulphu-rization and physically accelcrating-the agitation.

Carbon monoxide, on the other hand, merely performs the single function of accelerating the agitation without intensifying the desulphurization reaction. ,v

Mixtures of nitrogen gas with carbon monoxide may be used satisfactorily if the carbon monoxide does not exceed 33 percent. by volume. The car bon dioxide should not exceed 3 percent byvolume. A suitable'gas containing a mixture of inert gas-and asmall amount of carbon monoxide can be prepared if natural gas, methane or similar hydrocarbon'is mixed with air and reacted'as follows:

The resulting gas will comprise "about 20 per= was Hz 1.2 CO 23.8

This gas should be treated to remove carbon dioxide, in any suitable manner as by compressing to about 250 pounds per square inch and washing it with water in a packed tower. A product containing less than 1 percent C02 and a ratio of nitrogen to carbon monoxide in excess of 2 to 1 by volume is obtained. The ratio of nitrogen .to carbon monoxide can be further increased, for example, to 5 or more to 1 by volume if the blast furnace gas is burned preferably with a deficiency of air to convert some of the carbon monoxide to carbon dioxide and is then compressed and washed to remove carbon dioxide.

I have used hydrogen gas instead of nitrogen gas and have obtained satisfactory results. Asa source of hydrogen gas I may use hydrogen gas prepared by electrolysis. I may also use hydro-v gen gas prepared from steam in the conventional manner by reacting with a reducing agent such the treatment of iron in the desulphurization' vessel; In using a mixture of hydrogen gas and carbon monoxide it is important that the carbon monoxide should not exceed 33 percent by volume.

Hydrocarbon gases such as coke oven gas,

methane or propane deposit carbon in the tuyres' and are likely to stopthe fiow of gas. While these gases are otherwise suitable, they are not to be,

recommended because of this deposition of.

carbon.

From the foregoing it is evident that many different gases or combinations may be used, depending upon their availability and the results desired. In general the cheapest and best gas for use in many cases will be comprised princi-z pally of hydrogen and/or nitrogen with the amount of any accompanying gases containing oxygen reduced to a practical minimum, and, in the case of carbon monoxide not exceeding 33 percent by volume and in the case of carbon dioxide not exceeding 3 percent by volume.

In order to desulphurize large masses of iron at a rate which is the same for different depths and which, therefore, is unusually rapid for large commercial quantities'of molten pig iron, it is necessary not only that highly active agitating conditions exist, but also that very dynamic desulphurizing reaction conditions occur due to the chemical intensification of the desulphurization.

Unless these two effects are simultaneously achieved the results will be unsatisfactory. For example, W. C. Newell, A. J. Langner and J. W. Parsons experimented with ideas communicated to them by Heuer and reported the desulphuriz-f ing results obtained in Foundry Trade Journal, vol. 85, (1948) No. 1668, pages 165-172. These experimenters used desulphurizing slags containing fiuorspar and tricalcium silicate. They brought the slag into contact with molten iron and passed nitrogen through the iron-slag system. They concluded that the role of nitrogen when bubbled into the slag seemed to be solely that of a mixer of slag and metal, and no desulphurizing action proportional to the volume bubbled was observed. The highest ratio of sulphur in the slag to sulphur in the iron which these ,workers were able to obtain with such slags was 56:1. Thus, the results were unsatisfactory and not the desirable results which Iihave obtained as shown in Figure 5. It is possible that their failtue was due to the fact that they passed the nitrogen into theslag-metal system at a point only slightly below the slag-metal interface and thus obtained mixing action solely without chemical intensification, I have found that it is necessary to have the nitrogen gas pass through a substantial depth of metal before coming to the slag-metal interface.- It is for this reason I recommend that tuyeres be located at a depth of approximately one-half the metal depth or preferably even lower than that. In any event the record indicates that the mere passing of nitrogen gas through a pig iron-slag system does not necessarily achieve the fine results which I have accomplished; and indicates that these prior workers, following the teachings of Heuer, were unable to get results in any respect approaching those which I have obtained.

Thusit will be evident that in desulphurizing pig iron at a rate relatively independent. of depth of bath, a molten pig iron bath should be maintained having a depth of from one to fifteen feet, a desulphurizing slag or other agent should be brought into contact with the moltenpigiiron, the molten pig iron and slag or other agent should be enclosed to exclude oxidizing gases including the atmosphere and to maintain strong reducing conditions around the moltenpig iron and slag, an inert gas free from substantial quantities of compounds which under the conditions are more oxidizing than carbon monoxide and free from carbon monoxide in excess of 33 percent-by volume should be blown through a sufficient depth of the molten pig iron at a. rate in excess of one-third cubic foot of gas per minute per ton of iron measured at room temperature and atmospheric pressure, and pressure not less than atmospheric pressure-should be maintained in the vessel. If these conditions are followed the, partial pressure of carbon monoxide in the iron is reduced and at least percent of the original sulphur content of the iron is removed to the slag in 90 to minutes irrespective of the depth of the molten pig iron bath- H Under the desulphurizing conditions above described, it is possible to obtain practically completeremovalof sulphur from pig iron using .aoeama simple and'inexpensive-slags, such :as-for, .ex-

;,ample, a slag containin ;45 percent burned. lime,

40 percent ;fiuorspar and 15 percent silica. This slag; ,Whenadded to molten pig iron and treated with an inert gas such as nitrogen produces a desulphurized iron containing as low. as 0.001 percent sulphur or lower.

Other slags containing, for example, ,30 per,- cent of conventional waste iron blast furnace slag, 40 percent burned lime and. 30--percent fiuorspar when used in cooperation with treatment with an inertgas such as nitrogen. will produce desirable results. The-latter slag "will pick up from the iron percent ormore of its weight in sulphur. An equivalent weight of lime originally present in the slag willbeconverted into calcium sulphide which remains in the slag. For each 32 partsby weight of sulphur entering the slag as calcium sulphide, 56 parts oflime are used up, and '72 parts 'cf-.-calcium sulphide are formed in the slag. --Thus the-initial slag containing BQ-parts blast furnace slag, 40 parts burned lime and 30 parts-.fluorspanafter picking up 10 parts of sulphur, then-contains the original 30 parts of blast furnace slag and 30 parts of fluorspar, but only 22.5 parts of burned lime and 22.5; parts of newly'formed calcium sulphide. This-slag still has. a good desulphurizing power and is capable of producing iron containing 0.001 percent sulphur or less.

' Another suitable slag contains 70 percent conventional waste iron blast furnace slag, 20 percent burned lime and 10 percent fluorspar. Intermediate ranges of lime, silica, fiuorspar and the like may be-used. A typical analysis for iron blast furnace, slag (before-use) isz Percent CaO 44 MgO The desulphurizingpower of lime slags is generally better with higher ratios of lime to silica and with higher percentages of fiuors-par. Lower ratios of lime to silica and lower percentages of fluorspa-r than illustrated above may still be utilized. Ordinary waste blast furnace slag alone may be used with considerable effect. Inaddition to lime in the slag, other oxides of the type R O, where a is either integer one or two, as for example NazQ andR is a metal of the alkali or alkaline earth'group may be advantageously used as desulphurizing agents. The "desulphurizing agent need not be a fluid, but mayzbei'a plastic mass or a solid. For example, powdered burnedlime may be used, or powdered burned lime along with too little silica or fluorspar'to make" the' mass molten may be'employed.

As explainedabove, the reaction is attributable to the calcium, or similar metal, and calcium-may be contributed byother materials instead of or along with calcium oxide, such as calcium carbide or calcium silicate'or any compound capable .offorming calcium sulphide.

Molten pig iron having sufficient s'uperhe'at to go through the desulphurizing treatment without application of external heat is conveniently brought from the blast furnace or other source of molten pig iron in a ladle car operating on rails 2| and carrying tilting supports 22 which in the desired position of tilting engage fixed trunnions 23 positioned in spaced relation beside 10 the track. Therladle car .isndesirably tilted-by the, lifting of a crane which engage the ladle at 24. Figure 2 shows in dot-and-dash view the tilting position. The ladle car pours through one .of its spou .25 into a small charging opening 26 in the removable cover 2'! of a desulphurizing vessel 28 supported in suitable. position-beside the track. The desulphurizing vessel generally will not be I provided with heating means.

located adjacent the bottom,and in any'ease far enough down so that the gas will pass through more than half. the height of the moltenpig iron. The ladle can pour from either pouring opening 33. For pouring purposes the ladle has trunnions 34 and tilting supports 35 which are engaged by a crane for tilting the ladle.

The cover has a metallic casing 36 and refractory lining 31.

-The refractory for lining the desulphurizing vessel and the cover will preferably be carbon refractory bricks or. carbon refractory rammed lining. HoWever,-the desulphurizing agent need not be aslag but may be a solid or plastic mass, such as powdered burned lime or powdered burned lime mixed with too little silica or flourspar or both to make-the mass a fluid at the-temperature of the molten iron and the refractory lining 'may desirably be of'some other character, such as burned magnesite, or other basic material.

- The desulphurizing vessel whenoperating con tains a charge-of molten-pig iron 38 and a slag or other desulphurizing agent 40 floating thereon. During desulphurization, the desulphurizing vessel conveniently restson a base 4|.

From the desulphurizing vessel, the desulphurized pig iron is removed by a transfer ladle 42 of conventional character, which receives the pig iron poured from one of the spouts 33.

The desulphurizing slag is removed by a similar transfer ladle, not shown.

In operation, assuming all of the vessels are initially empty, a desulphurizing slag or-desulphurizing agent, sufiicient in quantity to form from 1 to 30 percent of the weight of the pig iron to be treated, preferably one percent, is charged into the covered desulphurizing vessel. Acha-rge of molten pig iron in the ladle car-is then brought-from the blast furnace or other suitablesource. A flow of inert gas such as" nttrogen as before explained: is then started through-the tuyeres and iron is pouredinto the vessel" through the charging opening 26. Gasris emitted through the charging opening 26101 through the pouring spouts, but during the. operation" of blowing these openings should. be partially closed as by luting to'keep out air 'infiltration. Even though the gas employed may be substantially pure nitrogen, the pig iron, initially having a normal sulphur content in excess of 0.02 percent and commonly of the order of 0.034 percent, will introduce 'so much carbon monoxide in the gas due to the desulphurizing'reaction that the gas emitted at the beginningof the desulphurization will contain sufficient carbon monoxide to burn with a chaacteristic flame when it comes in contact with the atmosphere.

In order to take advantage of both the agitation and the accentuation of the desulphurizing reaction, the gas flow is continued using gas M from any suitable source supplied at.super-at-. -mospheric pressure and room temperature, at a rate in excess of one-third cubic foot of gas p minute per ton of molten pig iron measured at room temperature and atmospheric pressure The charge of molten pig iron will preferablybe about 150 tons, and the depth of molten pig iron will be desirably about seven to ten feet. The maximum diameter of the molten pig iron under treatment will preferably be not over twice the depth.

The flow of gas will be continued for a suitable time until the desired percentage of original sulphur is removed. Usually about 90 to 120-minutes will remove 90 percent of the original 'sulphur content of the pig iron. The metal can then be removed from the vessel. The slag-can be removed before the metal is removed or may be retained in the vessel and removed after the metal, for example using one of the pouring spouts for the slag and another for themetal. It is desirable to obtain a sharp separation between the slag and the molten pig ironwhile the molten pig iron remains under strong reducing conditions, as otherwise resulphurization may occur. If necessary, a second slag can be introduced for wash purposes after the first slag has been removed, to assure more complete separation, the second slag being if desired, jused as the desulphurizing slag for the next cycle.

When reference is made herein to percentages or proportions in gases they are by volume, whereas in solids or liquids they are by weight. Tons are tons of 2,000 pounds.

When reference is made to impurities in the gaseous content, it will be understood that carbon dioxide is included as such an impurity.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless beconr'e evident to others skilled in the art, to obtain all or part of the benefits or my invention without copying the process shownj'and I, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my claims. Z

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

1. The process of desulphurizing pig iron, which comprises maintaining a bath of molten pig iron in a desulphurizing vessel in contact with a calcium desulphurizing agent capable-of reacting with sulphur in the molten pig to form calcium sulphide, enclosing the molten pig iron and desulphurizing ,"fagent to exclude'oxidizing gases including theatmosphere and*'maintain strong reducing conditions around "the molten pig iron and the desulphurizing agent,'blowing through at least a two foot depth of-molten pig iron an inert gas which is free from'ea'rbon monoxide in excess of 33'percent by volume-, not combustible in the air and is free frorn'substantial quantities of compounds which, under the conditions, are more oxidizing than carbon monoxide while maintaining a pressure of at-least atmospheric in the vessel, leading the inert gas after it has passed through the vessel out of the enclosed space and continuing the blowing with the inert gas beyond the point at which the efiluent gas is combustible in the atmosphere.-

- 2. The process of desulphurizing pig iron,

' in contact with a lime desulphurizing agent'in a desulphurizing vessel, enclosing the molten pig iron and agent to exclude oxidizing gases, in-

eluding the' atmosphere, and maintaining strong reducing conditions around the molten pig iron and agent, blowing through at least one-half of -'the depth of the molten pig iron an inert gas which is free from carbon monoxide in excess of 33perc'ent by volume, noncombustible in the air,

' free from substantial quantitie of compounds ii i) which-under the conditions, are more oxidizing than carbon monoxide at a rate in excess of onewhile maintaining a pressure in the vessel at least as great as atmospheric pressure, leading the inert gas after it has passed through the vessel 'out into the atmosphere and there initially buming the same and continuing the blowing with the inert gas beyond the point at which the gas is combustible when it comes out into the atmosphere.

3. The process of desulphurizing pig" iron, which comprises maintaining a bath of molten pig iron having 'a depth ofat least two feet in contact with a calcium desulphurizing agent in a desulphurizing vessel, enclosing the molten pig iron and agent to exclude oxidizing gases, including the atmosphere, and maintaining strong reducing conditions around the molten pig iron and agent, blowing through at least a, two foot depth of molten pig iron an inert gas which is free from carbon monoxide in excess of 33 percent by volume, noncombustible in the air and 'free from substantial quantities of compounds REFERENCES CITED The following references are of record in the file of this patent:

UNITEl STATES PATENTS Number .Name Date 97,897 Ennis Dec. 14, 1869 2,110,066 Heuer Mar. 1, 1938 2,290,961 Heuer July 28, 1942 FOREIGN PATENTS Number Country Date 460,138 Great Britain Jan. 18, 1937 609,850.

Great Britain Oct. 7, 1948

Claims (1)

1. THE PROCESS OF DESULPHURIZING PIG IRON, WHICH COMPRISES MAINTAINING A BATH OF MOLTEN PIG IRON IN A DESULPHURIZING VESSEL IN CONTACT WITH A CALCIUM DESULPHURIZING AGENT CAPABLE OF REACTING WITH SULPHUR IN THE MOLTEN PIG TO FORM CALCIUM SULPHIDE, ENCLOSING THE MOLTEN PIG IRON AND DESULPHURIZING AGENT TO EXCLUDE OXIDIZING GASES INCLUDING THE ATMOSPHERE AND MAINTAIN STRONG REDUCING CONDITIONS AROUNG THE MOLTEN PIG IRON AND THE DISULPHURIZING AGENT, BLOWING THROUGH AT LEAST A TWO FOOT DEPTH OF MOLTEN PIG IRON AN INERT GAS WHICH IS FREE FROM CARBON MONOXIDE AN EXCESS OF 33 PERCENT BY VOLUME, NOT COMBUSTIBLE IN THE AIR AND IS FREE FROM SUBSTANTIAL QUANTITIES OF COMPOUND WHICH, UNDER THE CONDITIONS, ARE MORE OXIDIZING THAN CARBON MONOXIDE WHILE MAINTAINING A PRESSURE OF AT LEAST ATMOSPHERIC IN THE VESSEL, LEADING THE INERT GAS AFTER IT HAS PASSED THROUGH THE VESSEL OUT OF THE ENCLOSED SPACE AND CONTINUING THE BLOWING WITH THE INERT GAS BEYOND THE POINT AT WHICH THE EFFLUENT GAS IS COMBUSTIBLE IN THE ATMOSPHERE.

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