US1533262A - Process of making iron and steel direct - Google Patents

Description

i No Drawing.

Patented Apr. 14, 19 25.

PATENT orrlcs.

SAMUEL PEACOCK, OF WHEELING, WEST VIRGINIA.

PROCESS OF MAKING IRON AND STEEL DIRECT,

To all whom it may concern:

Be it known that I, SAMUEL PnAooon, a citizen of the United States, residing at Wheelin in the county of Ohio and State of West irginia, have invented certain new and useful Improvements ,in Processes of Making Iron and Steel Direct; and I do hereby declare the following to be a full, clear, and exact description of the invention, suchas will enable others skilled in the art to which it appertains to make and use the same.

This is a process for making low carbon iron or steel directly from the ore in a blast furnace, and producing as a by-product a slag having the composition and properties ofcommercial glass.

In order that the exact process-may be the better understood it is said: The modern iron-making blast furnace is a counter-current heating apparatus, in which iron oxides are reduced by carbon monoxide gas and solid carbon, and the non-ferrous componcuts of the ore, fluxes and fuel ash are combined as fusible slags. It is essential that both .the metallic iron and the slags thus produced take and hold a free running molten form; that they may be separated from each other in the hearth, and be readily withdrawn from the furnace inclosurc as mobile liquids. lure iron melts at about 2800 F and for the necessary moltcn fluidity, it must be heated to about 3000" F.,a temperature not directly obtainable by burning carbon with air. The thermochemical balance involved in iron formation by reducing iron oxide with carbon monoxide is strongly exothermic, and when such reduction'takes place when the ore and carbon monoxide gas has been previously heated from 1000" to 1200 F., the heat liberated by the reaction is suflicient to melt the metal, notwithstanding that at the instant 'of its formation it exists as pure metallic iron. The molten iron thus formed, in dripping through the fuel to the hearth contacts more or less with fuel ash, white hot coke, and the hot combustion gases, and is partly reoxidized to iron oxide by carbon monoxide, and takes up carbon, silicon,

etc., and

Application filed December G, 1922. Serial No. 605,286.

roduces as an ultimate end-prod not a cru e iron-carbon compound havlng a melting point about 2400 F. and a high liquid mobility at about 2500 F. This product, known commercially as cast iron, has a number of uses, but its most important industrial application is in the manufacture of steel, for which purpose it is treated almost exclusively to remove wholly or in part the impurities unavoidably added to the iron in the blast furnace.

Unfortunately, the steel making methods largely Bessemer or open hearth treatments are high temperature reactions in which air is used to oxidize silicon, carbon, etc., and unavoidably nitrogen, carbon monoxide, metalloids oxycarbides, iron oxides and oxycarbides, hydrogen, nitrogen, dis-, sociation products, etc., are more or less introduced into the metal. As a result for steels of standard characteristics, the metal must be further treated, usually in an electric furnace, to remove the ill effects of the first refining steps. Open hearth steel making also employs iron oxides which are commonly not wholly reduced, and dissolve in the steel and contribute additional undesirable impurities.

If it were possible to disregard sulphur and phosphorus a blast furnace charge could be proportioned for a slag composition of low free running temperature, and the iron thus made would be low in silicon and carbon, but by using an excess-of fuel and slag, the iron would still be sufficiently impure to maintain a tapping mobility in the furnace crucible or hearth. The sulphur problem, however, precludes such operation. The sulphur goes into the furnace almost wholly as iron sulphide. The usual furnace practice for sulphur removal is to proportion the fluxes to make a highly basic or calcium slag, on the assumption that a molten basic silicate in contact with iron sulphide will effect a change and produce free iron and calcium sulphide. Such reaction, however, cannot range beyond the equilibrium balance, which is small; hence to remove any substantial quantity of sulphur, a large proportion of such basic slag must be used, entailing increased fuel costs and a lessened metal output per unit of plant investment. Also, the temperature must be forced to the highest obtainable in a blast furnace in order to maintain a working fluidity, as a basic orlimey slag to run freely must be heated to about 3000 F.

Further, in iron making, it is economically important to reduce the iron oxides in the upper part of the furnace, by means of the carbon monoxide gases made at the tuyer zone. Carbon monoxide reduces iron oxide freely at 1000 F. I But if a basic or limey slag must be used in order to eliminate sulphur, the temperature at the top of the bosh should exceed 2600 F., and at this temperature the free iron made above the bosh attacks the carbon monoxide present, thus producing iron oxide and free carbon in accordance with the following equation:

Fe+CO:FeO+C.

That is, elemental iron is converted back to iron oxide, and such iron oxide on the furnace hearth reacts with white hot coketo form iron carbide. It is at this phase that the iron silicides are formed.

-It is true that these conditions are desirable in making certain grades of cast iron, but for steel making it is obvious that energy is beingexpended to no useful end.

Again, phosphorus is present in iron ores, fluxes, etc., in the form of.iron, calcium, and aluminum phosphates. These phosphates have a comparatively low melting point and when fused prior to contact with red hot carbon, are reduced to phosphides. lron phosphide dissolves in molten iron, but aluminum and calcium phosphides do not. These latter phosphides react with the iron oxides present to form iron phosphides, but do not react in contact with molten iron only. At the high temperatures used in modern blast furnaces, iron oxides are always present, from the top of the bosh to the tuyer zone, due to the high temperature reaction reversions; hence nearly all of the phosphorus in the furnace burden ultimatcs on the hearth as iron phosphide, and dissolves in the molten iron. The silicon and carbon forced into the iron is a somewhat simpler reaction, due to the conditions imposed by sulphur elimination, by a very hlighhearth temperature, and by a very hot s ag.

It will thus be seen from the foregoing that the problem of making iron or steel directly from iron oxides is beset with a great number of difliculties. To obviate these difficulties it has been heretofore proposed to proceed as follows:

A blast furnace charge containing an alkali chloride has been proposed to produce a free running basic slag at a temperature of, say, 2000 F. It was thought that the but not appreciably below 2400 F. The

reactions may be approximated as follows: g1 FeS+2NaCl:FeOl -}-Na S.

COS+Na O+2FeQ The elimination of phosphorus as phos-' phorus chloride by interaction of a metal chloride and phosphate at about 240.? F. 1s, of course, a well known reaction, and

has been the subject of repeated patent ap plications.

But unfortunately in practice the in tensely'redueing atmosphere of an iron making blast furnace quickly converts the phosphates present in the phosphides. Therefore, in the presence of sodium chloride, sodium phosphides will largely predominate by double decomposition, thus I Further, in the presence of carbon monoxide and ferric oxide, the formation of gaseous phosphorus carbonyl takes place. The specific reaction is notknown to me atthis time, but at the temperature of the charge, approximately 2400 F., the following equation illustrates the decomposition:

The identity of the phosphorus carbonyl has not been established. But it is a gas at ordinary temperatures, and in contact with air at very low temperatures, it ignites and burns with a non luminous flame, with the formation of dense clouds of phosphorus pentoxide.

I am further aware that it has been heretofore proposed to decompose iron, sulphur, and phosphorus compounds in the charge by means of a dissociated metal chloride, see for, example, U. SJPatent #1061950, Simpson, et al., May 13, 1913. However, this furnace charge to patented process specifically denies the use of carbon or carbon compounds in any of the reactions involved, except for the carburizing of previously made pure iron, the specific proportions being designated. The patented process also requires a temperature of 3000 F. and upward, a degree of heat not practically obtainable in a blast furnace. The patent specifically states that ordinary air blast furnaces of all descriptions are unsuitable for this process.

Thus it appears, in so far-as my knowledge goes, none of the prior pro- .cedures adapted for making steel direct from the ore, have been able to get rid of I from the foregoing procedures and solves the difliculties involved by the following steps: That is, in carrying out my invention, the reduction of iron oxides to metallic iron in a blast furnace is effected by the usual charges with additions containing sodium chloride, or other suitable chlorides of the metals or alkali earth metals, and only suflicient lime to make a very fluid slag, at say 2400 F. and in the usual manner of operating such furnaces.

But the process is carried out at a somewhat lower temperature than is habitually employed in a hot blast coke furnace. More particularly stated, my process consists in the discovery that in a reducing atmosphere, the sulphur and phosphorus compounds of iron that are in contact with carbon monoxide and a metal chloride such as NaCl effeet such reactions that the sulphur and phosphorus present take on gaseous forms at temperatures of from 2300 F. to 24:00 F., and escape with the combustion gases, thus rendering it unnecessary to employ a high calcium slag at say 3000 F. to rob the iron sulphide present of its sulphur, as has been the custom heretofore. And further, thatbecause of such gaseous elimination of sulphur and phosphorus without employing extremes of temperature, (such as 3000 F.) a low carbon and silicon iron or practically a steel, is made directly from the ore, in a blast furnace, employing carbon and carbon monoxide as the reducing reagents.

The charge is so proportioned that the slag formed by my process not being excessively basic, is therefore Very fluid and will contain little or no iron silicates; hence, this slag constitutes a by-product which is suitable for direct use in making glass. The quantity of alkali metal chloride or other suitable alkali metal compound employed will depend upon the quantity of the alkali metal silicate it is desired to produce and will be readily calculated by the furnace operator in each instance. Said chloride sufi'ers more or less colatilizati on in the process, but as its boilingpoint is well above 1800 F., the alkali vapor condenses on the 'cold burden above the bosh and is returned to the process, ultimating as a silicate and forming part of the slag. As this slag contains neither sulphur, phosphorus, nor iron, 11} 1s directly available for making commerclal glass, thus reimbursing all flux costs.

The ferrous metal W111 contain from .0151,

to 01% carbon, with traces only of silicon,

sulphur, or phosphorus. On account of the low operating temperature and low slag burden, the blast pressures are low, and both the slag and the iron may be discharged from the furnace in constant streams, substantially as practiced in copper smelting, the furnace hearth constituting a forehearth effect.

Industrially the process should reduce the slag and fuel burden by as much as, say, go

35% to 40%, and produce a by-product in the glass making slag, which should have a commercial value, at least in excess of all flux costs. Also, as steel is produced directly by'this process, the usual Bessemerizingdor open hearth treatment may be eliminate It is obvious that any metal chloride or alkali earth metal chloride whose boiling point is too high to permit the chloride to escape with the combustion gases, or which is higher than say 500 C. may be employed in this process; but I prefer the use of sodium chloride or potassium chloride on account of their glass making properties.

By the terms metal chloride used in the claims I mean to include all chlorides of metals whose boiling points are higher than 500 C. and by the term alkali metal chlorides I mean to include the chlorides of alkali earth metals.

What is claimed is 1. The process of making steel direct from the ore, which consists in charging a blast furnace with the usual steel making materials containing a sufiicient quantity of lime and an alkali metal chloride to make a free running slag at 2400 F.; smelting the charge thus produced in the usual manner at temperatures below 2700 F. to pass off furnace with iron ore carbon and fluxing materials containing a quantity of lime only suflicient to make a fluid slag at 2400 F. and a quantity of sodium chloride sufficient to render said slag suitable for glass making purposes; igniting said charge; maintaining the temperature below 2700 F and recovering the steel and slag thus produced.

3. The process of making steel direct from the ore, which consists in providing a blast furnace charge containing a quantity of lime insufficient to extract the sulphur from the iron sulphide present and a quantity of sodium chloride sufiicient to render the slag suitable for glass making purposes; igniting said charge; maintaining the temperature sufficiently high to make the desired alkali metal chloride sufficient to render the steel and glass making slag; and recovering slag su1table for glass making purposes; 10 the latter. ign ting said charge; maintaining thetem- 4. The process of making steel direct from perature sufliciently highto make the desired the ore, which consists in providing a blast steel and glass making slag; and recovering furnace charge containing a uantity of lime the latter.

' insufiicient to extract the su phur from the In testimony whereof I affix my signature.

iron sulphide present and a quantity of SAMUEL PEACOCK.