US2526659A - Continuous smelting process - Google Patents

Description

Oct. 24, 1950 E. s. HARMAN 2,526,659

7 CONTINUOUS SMELTING PROCESS Filed March 9, 1945 5 Sheets-Sheet 1 9 5 a a mm 6 m 2 S W W 9.. E 5 J W x e. um 1 mm U H b m m Oct. 24, 1950 Filed March 9 1945 Patented Oct. 24, 1950 UNITED STATES OFFICE i This invention relates to the reduction of ironore, and consists in improvements both in method.

and in apparatus.

My analysis of the problem of producing kiln iron indicates that, in order to secure high tonnages of molten iron with a predetermined vcarbon content, three conditions must be observed. First, the hearth must be maintained at a high temperature. Second, a reducing atmosphere must be maintained in the reducing zone without interferingwith the intensity of the flame heatingthe hearth andwithout limiting the length of the hearth zone. Third, the amount of carbon added to the reduced iron must be subject to independent control.

Another diflioulty. heretofore encountered in the production of iron in kilns is due to the fact that the iron before fusing or melting goes through an intermediate pasty state, at a temperature of from 1900 to 2000 F. At such temperature the pasty iron adheres to the kiln walls, accumulating to the point of choking off the kiln. The use of a boring bar has been suggested for the removal of the accumulated pasty iron.

20 ores of low iron content. .Other objects and features of invention will.

These. areonly a few of the difllculties heretofore encounteredin attempts to replace blast:

furnaces .with rotary kilns. .The difficulties have beeniso serious that at the present time no 5 significant amount of iron is produced in rotary.

,kilns, this in spite of the many advantages as to-costfand quality of metal obtainable in kiln operation.

.The objectcof my invention is to provide im-. provedapparatus and methods for the commer cial production of relatively pure iron particularly an iron that is superior to blast furnace or. duplex iron for the charging of open hearth and electric furnaces. In keeping with such object, I solve the problems and eliminate dif-' become'apparent in the ensuing specification. In general, my process consists in advancing iron ore and cement-forming materials, to-

However, if theiron is melted, as it normally is, get-her with a. limited amount of carbon, first in the kiln below the zone in which the accumuthrough a low temperature kiln zone wherein lation occurs, the socalled pasty zone will be 10- the orev is reduced, and then through a high cated quite a distance from the kiln end, whereby the boring bar must traverse the hearth zone inorder to reach the pasty iron. As there is a.

practical limit to the. length of the boring bar. that .may bev used, the size and length of the kiln must be restricted severely. No large capacity.

kiln can depend on a bar inserted through a discharge end of the kiln for removal ofpasty ironhave been made to operate kilns in sections that are superimposed one upon another, and in sections that are arranged in stepped tandem for-i mation, but such attempts have failed. because of difficulties in providing adequate foundations and in maintaining alignment of the sections. Also, trouble is encountered in obtaining the desired flow of material from one kiln to another.

In sectioned kilns, it is also extremely diflicult to, prevent leakage of hot gases through the housed joints between the kiln sections. These hot gases represent not only thermal and metallurgical losses, but tend to damage the kiln parts exposed thereto; 1 7

temperature. hearth zone. wherein the iron is. Additional carbon in regulated o uan 3Q tityiqis normally. introduced to the metallic iron inv coursesof. advance from. the kiln zone to the melted.

hearth zone. The flame in the hearth zone is preferably oxidizing in character.

,The reduction of the iron ore to iron is cffected largelyby the carbon charged in limited quantity with the ore, but partly by a reducing flame obtained by the conversion of the oxidizing; flame streaming from the hearth zone into the. reducing kiln zone.

40 The conversion of the flame from oxidizing to.-incandescence, is blown into the flaming gases leaving the hearth zone, in such manner as to bring. about intimate contact between the coke breeze and the flaming gases, without decreasing thetemperature of the flame in the hearth zone.

The amount of carbo'ninjected, to convert carbon dioxide into carbon monoxide, is sufficient to establish a COZCOz ratio adequate to produce an atmosphere. that is at least neutral and preferably I reducing. .While in electric furnace smelting the 5.5 ratio may be 50:50, in kiln practice I consider a f ratio of :35 to be safely reducing. As already Such carbon preferably come-i noted, the reaction between carbon and carbon dioxide is endothermic, with the consequence that the injection of carbon lowers the temperature of the gases at the point of injection.

The pre-conditioned or activated carbon for conversion of the flame may consist of the carbon component of carbon monoxide, or of a hydrocarbon cracked by preheating.

In further accordance with my invention the reducing and hearth zones are, to the extent hereinafter explained, structurally independent. The employment of a relatively short hearth kiln more one another, and connected at the adjacent ends readily permits the obtaining of the high temperatures, favoring rapid melting of the low carbon iron. The injection of carbon for the conversion of the oxidizing flame to'a reducing flame is advantageously effected in the course of flow of the products of combustion from the melting zone or hearth kiln to the reducing zone of the shaft kiln. Carbon' should also be addedto the reduced: iron at the delivery end of the shaft kiln, toprotect the reduced iron again'streoxidation, asJwil'l more fully appear belowi The point of separation of the hearth and shaft kilns should be located immediately after the'sintering zone in which the iron turns pasty, thus rendering this zone readily accessible to boring bars. The boring bars need not traverse the length of the hearth kiln to reach the pasty iron accumulations on the kiln walls.

' I have found that if the two kilns are set at an angle to each other, adequate foundations can be provided for both kilns, even though the kilns are disposed at different levels. The material moving from the lower end of the upper kiln cascades into the upper end of the lower kiln. In order to permit operation of the kilns under slight internal pressure,-whereby better control of the combustion gases'and maximum temperature may be secured with economy, air seals are provided at the kiln joints. At these seals, cool air is urged into the kilns, rather than permitting hot gases to leak out of the kilns. 7

My apparatus may, as already noted, further include independently firedhot air stoves, or recuperators, for preheatingthe air for combustion. Waste stack gases may be burned for such purpose. A vertical kiln ishaft'may also be ineluded as a p'art of th'eikil'n train,- rawimaterials: being charged into the kiln 'shaftand there heatedby waste kiln gases blown through the shaft.

In the accompanying drawings, I diagrammatically illustrate apparatus in which and inthe operation of which the invention is realized:

Figure 1 is a fragmentary plan view of apparatus: embodying the invention;

- Figure 2 is a fragmentary view of the apparatus, partly in side elevation and partly in section, on the plane IIII of Figure l;

Figure 3 is a fragmentary end elevation of thev apparatus, as seen on the plane III.III of Figure 1;

Figure 4 is a view of the apparatus, partly in elevation and partly in section, on the plane IV-IV of Figure 1;

Figure 5 is an enlarged cross-sectional View, taken on the plane VV of Figure 4;

Figure 6 is a view in end elevation as seen on the plane VI-VI of Figure 5;

Figure '7 shows to larger scale a transverse sectional view on the plane VII-VII of Figure 1, but with certain parts shownin elevation;

Figure 8 shows to larger scale a transverse sectional view, taken on the plane VIII-VIII of Figure, 1; I

by means of a housing I2. The apparatus includes a shaft I3 for preheating raw material, a hopper I4 for charging the preheated raw material into the shaft kiln ID, a burner I5 for injecting, a high-temperature oxidizing flame into the hearth kiln II, and an injector I6 for introducing carbon to the flame and gases streaming from the hearth kiln I! (through the flue formed by'the interior of the housing I2) into the shaft kiln I0, to convert such flame and gases from oxidizing to reducing characteristics. Cleaners II are provided, to prepare the waste kiln gas for service as fuel in blast stoves I8 that heat the combustion air for the hearth kiln. The air is forced through the stoves by blowers I9.

The devices for preheating and charging the material are shown in Figures 1, 2 and 4 to 6. Ore, limestone, and coal or'coke are fed into the preheater shaft I3 by a'skip-hoist or conveyor 20. The material in the shaft I3-is heated by hot waste kiln gas forced by a blower 2| through a branched conduit 22 that opens into the lower end of the shaft I3. The shaft I3'includes in its lower end a centrally open cone 23 (Figure 5),

below which the several terminal branches of duct 22 open. The chamber or space below the cone 23 is effective to promote more uniform gas flow and better material distribution within the shaft.

Since the shaft I3 is under internal gas pressure, a bell-valve 24 is provided at the inlet of the shaft, while the duct 25 leading from the outlet of the shaft terminatesin a bell-valve hopper 26. The heated material discharged through the bellvalve hopper 28 moves through a duct 2! into agrinder 28, and thence over a conveyor 2'9 (Figure 4) to the kiln hopper I41 In order to preventthe loss of any of the fine material, the conveyor 29 and the kiln hopper I4 are enclosed within air tight. housings 30 and 3I', respectively.

, Scales (not shown) are provided for weighingmaterialcharged into the preheater shaft I3.

The shaft and hearth kilns Ill and II are sup ported upon foundations 32. Thetwo kilns are inclined-to the horizontal and set at different levels, and, as viewed in plan, they extend at right angles to one another. The kilns are adapted to be rotated by means of powerfullyrotated pinions (not shown) meshing with gears 33.

The shaft kiln I0 includes a zone Illa for the further heating of the preheated and ground material delivered by the hopper I4, and a reduction zone Illb, enlargedat Illc to form a reservoir or holding zone just ahead of sintering zone Id.

The sintering. zone is reduced in diameter, to-

increase the efficacy of the heat within the kiln in rendering: the reduced iron pasty.

The hearth kiln II is set below the lower end of the shaft kiln III, to facilitate the flow of material from the latter kiln into the former.

As sintering (the transition of the reduced iron to pasty condition) may not be entirely complete by the time the advancing material enters thehearth kiln, the upper end of the latter kiln is with refractory linings IlIe-and II 6.

onstricteias at Ila, providing a zonein which thesintering action is further accelerated,' and completed. The melting or fusion of thereduced iron is effected in hearth zone III), while a wide hearth zone I I serves to receive molten iron: for discharge,. either continuously or'intermittently, through a tap hole 34 into a'ladle 35 mountedfor travel on tracks 36. The cem'entclinker, advance ing through the zone He, continues through a zone I Id whence it is discharged through a hopper 31 to a conveyor 38. The conveyor carries the cement clinker to a cooler (not shown), and-from the cooler the clinker is conveyed to storage bins or cars, to await pulverization, to form cement. The hopper 3? is provided at its discharge opening with an automatic bell-valve that is in this case water cooled.

While the drawing shows the separation of the hearth kiln and shaft kiln to be at the sintering zone, it is to be understood that this division may be providedimmediately beyond the end of-the sintering zone, the important feature being that the-zone where pastiness occurs shall be accessible jacks may be equipped with rollers arranged to engage the kiln shell when the jacks are elevated. With such an arrangement the hearth kiln may be moved out of the kiln-train, and through the use of the jacks the kiln may be raised from its normal bearings and portable bearings mounted on track buggies may be inserted under the kiln. The kiln may then be moved out of the line of production for relining, and a spare kiln previously heated may be moved into the line. This makes possible the relining of'a worn hearth kiln, without undue interruption of production.-

A boring bar izjmount ed on a carriage 43 movable on tracks 34 and 45, is'pr'ovided for removing accumulated pasty 'iron from the walls of the kiln zones Ifld and Ila. Another boring bar 42, mounted on a carriage 4'! movable on a track 48, is provided for removing any slag or iron carry-over'that may accumulate on the wall of the kiln zone IId. The housing I2 and the devices associated therewith are best shown in Figures '7' to 9. The kiln ends Ifld and Ila extend into apertures 50 and in the walls of the housing. The apertures are provided witlrcircumferenti'al grooves 50a and 5 I a, into which air under pressure is admitted through ducts 58b and Eli), for preventing leakage of hot gases between the kiln ends and-'the housing. An apron or chute 53 serves to guide material discharged from the kiln I'IJ- into the kiln II, and this chute may be water-cooled. Carbon or other material may, through a funnel-shaped hopper 54, be added to the pasty iron" passing from the shaft kiln II! to the'hearth kiln I I. a As shown. the kilns Ill and II are interiorlycoated Coal or other fuel is conveyed to coal preparation equipment 56 by a conveyor 51'. The coal preparation equipment 56 will include coal pul verizers, and coal preheaters.- In the-event that coke breeze is used; it will'be heated to-a'tem'pera ture approximating 1800 F., by burning the distilled gases with sufficient combustion air in con-- The treated fuel is tact, with the coke particles. conveyed through a, duct 58 to the powdered incandescent cokeburner I5. Preheatedcombustion air is fed through a line 59 extending from" to the gas purifiers H, which may consist of dustprecipitators and gas Washers, and then through a conduit (H to the hot blast stoves I8 for combustion therein. Kiln gases in excess of the requirements of stoves I8 are led away through a conduit 62, and conserved for combustion elsewhere.

The air blowers I9 are connected to thehot blast stoves by a conduit 65 that'has three valved branches 65a entering the hot blast stoves I8, and the'waste gas conduit 5| has three valved branches 6Ia entering the stoves. -A conduit 66, having three valved branches 66a, connects the stoves to a stack for carrying off the stack gases. All of these conduits and connections make possible the operation of any one of the hot blast stoves, or the joint operation of any two or more of the stoves. I Figures 10 and 11 show an apparatus generally similar to that shown in Figures 1 to 9, with respect to kiln and burner arrangements, but provided with simpler and less expensive devices charging the raw materials and preheating the combustion air. Parts similar to the parts of the apparatus'of Figures 1 to 9 are indicated with like numerals in Figures 10 and 11. The dissimilar parts include a conduit III for leading waste kiln gas directly to a recuperator I I, wh'ere.-. in waste gas is burned for preheating the air supplied by a cold blast line 12. The kiln zone Illa is provided with slack chains I3 suspended from the inside of the kiln at spaced-apart points and serving to settle the dust that otherwise would be carried over to the recuperator. I

The coke,'or coal, and limestone are charged into thekiln end zone Illa through a hopper 1-5 discharging upon an apron 16 in a housing 11 for the kiln end. Iron ore in slurry form is charged through a conduit I8 to the apron l6, whence it flows into the kiln end zone Illa.

Inthe" operation of the apparatus of Figures 1 to 9 ore, limestone and coal are charged into the shaft I3 and are there heated to about 400 F. by the waste kiln gases whose temperature'is between 650 F; and 700 F. The temperature of the gases leaving the preheater shaft will be about 350 F. With low velocity of the gases flowing through the material, and with a relatively shallowdepthof material, the required blower'pressure willbe about-1 to 1 /2 pounds per square inch. The use of the preheater shaft avoids the undesirably high stack temperatures of prior kilnsi Additionally, the'cost of drying and crushing the v ore and limestone preparatory to charging is elim-' inated.

furnaces of' low capacity may be rehabilitated,

as an parts or the plant except the hearth and bosh section of the furnace may be utilized. The blowing equipment may be low pressure blowers, as the blast pressure need only be high enough to overcome the resistance through the stoves. But whatever the structure, the ore is roasted prior to smelting, thus making it possible to use high sulphur ores or pyrites of low cost.

In cases where fuel is cheap and the drying of ore and limestone prior to grinding is not desired, the preheater l3 and the blower 2| may be eliminated, and the material may be discharged into the rotary kiln, in which case stack gas losses will be somewhat higher. Where a small and-less expensive installation is desired, the apparatus of Figures 10 and 11 may be employed. Such installations may be used to produce liquid metal having desired carbon and siliconcontents to replace or's'upplement either steel scrap or pig iron. A suitable starting material is the fine ore or flue dust always obtained in and detrimental to the operation of blast furnaces. Such fine ore is charged in the form of slurry into the kiln. Lump ore under /2 in. may be charged, if desired. Raw limestone, preferably though not necessarily ground, but at least crushed, is charged in quantities as required into the kiln. The slag may be fused and tapped with the item, if it isnot so viscous as to adhere to the kiln walls to an objectionable extent. A better method is to maintain a kiln temperature below the melting point of the slag, or to maintain a calcium content in the slag suihcient to raise the slag melting point above the kiln temperature, it being noted that the reaction between the lime and the impurities in the liquid iron is just as effective when the slag is solid as when the slag is fused.

The charging of the ore in the form of a sludge or slurry and the provision of the dust-catcher chains in the high end of the shaft kiln reduces the flue dust content in the waste kiln gases to a minimum, so that the use of the most elaborate elements I l of the apparatus of Figures 1 to 9 may be avoided. The 're'cupera'tors used in place of stoves will operate with burning gases that contain more 'dust than gas treated in gas washers and dust catchers, and they are less expensive than blast s'toves.

In the event that liquid slag is discharged continuously, a, slag tap hole is provided in the clinkering zone lid, and the lower "end of the kiln H is dammed slightly to act as a, retaining wall, preventing slag discharge through the kiln end.

The plant of Figures 1 to 9 is capable of producing three hundred fifty tons, or more, per day. In the event that an output in excess of that obtainable with a single kiln unit is desired, two or more kiln units may be installed. They may be arranged parallel to each other, and a single set'of auxiliaries, such as recuperators, blowers and material or slag handling equipment, or the stoves and preheater shaft of the more elaborate plant of Figures 1 to 9, will serve for the several kiln units.

. The plant of Figures 1 to 9 may beadapted for the selective charging of lime and ore of different analyses. A vertical partition wallmay be used to divide the preheater shaftl3, and two mixes of charging materials may be S9160, tively withdrawn from the shaft througha divided hopper.

In the practice of the present invention, the minimum carbon addition required is 114 pounds per ton of iron '(which yields carbon free iron) if .s:co:co2 ratio of :30 is to be maintained in the shaft kiln atmosphere. This minimal carbon consumption is dependent upon a, partial reduction of the ore by the carbon monoxide content of the kiln gases. About 450 pounds of carbon per. ton of iron (or about 25% to 30% of the. total fuel consumed) is required for complete' reduction of the iron ore by solid carbon. The amount of carbon charged with the ore can belimited to that required for reduction (about one-quarter of'that charged in a blast furnace), when carbon is added, as advantageously it is, at the entrance to the melting zone. The carbon content of the iron may be varied anywhere between zero and saturation (a little over 4%) by adding appropriate amounts of carbon to the reduced iron. Thus, to produce an iron having a; 1.5% carbon content, at least 30 lbs. of carbon per ton'of iron must be added as the iron reaches the'hearth kiln. When the waste gas temperature is 350 F., 876 lbs. of carbon per ton of iron are required for combustion purposes. Hence, to produce iron containing 1.5% carbon, the minimum total carbon requirement will be l14+876+30 or 1020 lbs. per ton of iron. This quantity corresponds to 1457 lbs. of coal having a 70% carbon content. The solid carbon used may be charcoal, or oil coke, if coal or coke is not available.

The source of the sulphur in iron made from Lake Superior ore is the coke charged with the ore. Since my process consumes only one-fourth the quantity of coke consumed in blast furnace operation, the sulphur content of my kiln iron will be only one-fourth that of blast furnace iron. Qres-fromcertain other sources have a high sulphur content, and thus increase the sulphur content of the charge. In these cases, as well as in cases where it is desired to produce cement clinker from the slag, a high lime content in the charge is required. Ihe slag should be clinkered rather than molten, since a clinkered slag will not attack the kiln lining (which can be made with a cement, clinker base), and since melting will adversely affect the cement-forming properties of the slag. When low carbon iron is made and cement clinker is not produced, a low lime charge may be made, in which case the slag will be liquid. The most serious objection to liquid slag is its tendency to attack the kiln lining. The most satisfactory practice is to maintain the slag in clinker form, even though this practice requires crushing the slag-forming materials. Ordinarily cement-forming material is charged in amounts to make about 9.8 tons of cement clinker per tonof iron, and in such case about twice as much limestone is charged as in blast furnace'prac tice.

A flame containing preferably at least 70% carbon monoxide and having a temperature of 2300 F. enters the lower end of the shaft kiln l0.

Carbon, or coke, or coal is fed through the hopper 54 into the material delivered from the reduction kiln, in amounts varied as required to protect the iron from reoxidation in the hearth kiln, and to remove any 'FeO present in the burden of the hearth kiln, as .well as to supply whatever carbon content may be desired in the finished kiln iron. Thirty pounds of carbon per ton of iron is normally a suitable amount.

Nodulized iron at approximately 2000 F. is deposited into the hearth kiln along with carbon and cement clinker. The reoxidation loss is minimized, because of the carbon applied tothe nodules, and since the-time required to melt the ,iron-at this temperature is materially less than that required to melt a relatively cold sponge iron in an open hearth. The molten iron runs along the sloping kiln bottom to the tap hole; and is discharged assoon as the iron is'i'nelted." Alternatively, ifthe iron is "tapped periodically from in sufiicientguantities partiallyto burn the gas distilled 'from'f'thefueL The -gases so distilled may be recirculated v through the fuel, and the surplusv gas may be bled off into a gas mainto be used as fuel for other purposes. Fuel-air ratio proportionersare preferably installed in the E burner I5, so that a properpercentage of carbon dioxide is maintained in the melting zone of the hearth kiln. Thelflameshouldnot be supplied with excess airj'as this would necessitate additional fuel for converting the oxidizing flame toa reducing-flame; as explained below. A- small .carbon monoxide content ispreferable from 'the standpoint of fuel economy, W oxidation loss, andgeneration of hightemperatures. .If desired, the burner l5 mayinolude upper and lower flame injectors, and the lower injectors may be ad- =justed to give; arreducing flame, thus forming over the bath arelatively thin'layer' of reducing atmosphere, through which radiates heat from .the oxidizing flame. of the larger injectors.

Where low initial construction cost is desired; blast-stoves.- may b.e,-=-provided only for the air for the reducing'flame injectors, the air for the oxidizing flame injectors being preheated in..re-

cuperators,

The oxidizinggases leaving the hearth kiln are converted toreducing'g'ases before entering the heating and Jr 'educing.-:rl' iln [0; "This conversion can be effected simply by-addingcarboni monoxide to the. oxidizing flame through the injector I6. Carbon or other fuel may" similarly be injected {into "the oxidizing ,flam'e; In' atmospheres in which the C0: C02 ratio is 50,'re'action between iironpxide andsolid carbon oc'curs; according to theequation: n; r Y r occur in atmospheres of considerably smaller carbon monoxide content. These reactions profceed at velocities dependent on the partial pressures of the carbon monoxide and carbon dioxide gases and follow the phaserule. For the purpose of the presentinventi'on it is sufficient if the i Q: CO2 ratioat- :the jentrance, to the shaft kiln be maintained at :35.

Thesimplest and preferred method of .converting the-oxidizing flamew to.a reducingrflame is to blow incandescent pulverized coke breeze into the chambenspaee; so asto bring about -intimate -eontactbetween theparticles of coke and the gases l avin the nsa th.=;k n-; .Tn rte coke breeze-injected must, of course, be adequate to convert a sufficient amountof carbon dioxide into carbon monoxide to render the heating kiln atmosphere neutral or reducing, Suflicient fuel maybe burned in theinjector' l Bto heat the particles of coke to ineandes'c'ence-or'the coke may be heated before entering the'injector by burning gases distilled from th'e coal in direct contact with the coke. :The used oil or gas fuel to convert the oxidizing flame toia reducing flame is also held in contemplation, even though the high hydrocarbon conte'ntof 'sucli fuel produces a high water vapor contentin the combustion gases. As already mentioned; water'vapor is oxidizing, and, in fact, water vapor seems to increase the oxidiz-v ing properties of combus tionga'ses. Howevenas in-the cas'e'of the carbon 'dioxidein the combustion products. 'the oxidizing tendencies of. the water vapor can be counteracted by the provision of a corresponding excess of hydrogen or carbon monoxide. 5

. [If i 7 Of the heat workperformedin smelting iron ore, approximately 25% is done in the hearth kiln and the remainin'g75% is' done in the heating and reducing kiln, '-Ihe relation between the heat consumed and sup'p1ied,fand the relation between the fuel consumption and the temperatures ob- 't'ained' at'va'riou's points; are made evident in the following calculations, in which the flame conversion effected by'additionof carbon monoxide is considered first: 1

It. is assumed that the stack gas will have a COzCOzratio of :30 and that thefuel used is coke breeze'oranthracite culm' burned in mun tiple burners injecting a lower reducing flame and an upper oxidizing flame in such ratio that the average analysis ='6f theicombustion gases in the hearth zone shows a COZCOz ratio of 10:90. The combustion air is preheated to 1500 F. The tem' peratures and products of combustion may be calculated as follows:

PRODUCTS OF COMBUSTION OF 1 LB. OF

, CARBON 'C'OAND CO2 Air reqrii redifor b- 5 0.57s lb. Carbonhflltlbi I 7 Products df'eofiibtaibt 't'oo'o," 0.67s 1b.; Ai isuird acci; =o.578 lb. Carbon, 0.9115; I Products of combustion "t6 00., 11.3 lb.

Total products. of GQmbustion=,0.678 11.3 11 .987 lb. per lb. carbon .v

002:0.9 X 14,750; 13,280 B. t. u.

. Qarbohftdbc added for conversionfisre te a. red c t phe e having a 00500? 'ra'tio'of70:30, a co flame is dq sat: thscsa emwetowthe s kiln, e

amount of carbon required as CO can be calculated as follows:

Carbon present in gas as CO2, 0.91b.

which must equal 30%, hence Carbon 100%=0.0:0.3:3.0 1b.

and Carbon as CO=3.0-0.9:2.1 lb.

The initial content of the flame is 0.1 carbon. Hence carbon to be added:2.10.I=2-.0 lb.

Temperature of added CO flame Carbon added, 2.0 lb.

Total products of combustion, 13.55 lb.

Heat supplied by air at l500 F.=l1.55 1440 0.2-47:4100 B. t. u.

Heat supplied by combustion to C0':2 43 5:

8750 B. t. u.

Total heat supplied, 12850 B. t. u.

Total net heat supplied per lb. of carbon fired in hearth By combustion of one lb. of carbon to CO2 in hearth, 17377 B.t.u.

By combustion of two 1b. of carbon to CO at hearth exit, 12850 B.t.u.

Total heat supplied, 30227 B.t.u.

Air required 11 .55 lb Flame temperature: :3690 F.

10076 B. t. u.

Stack loss per 1b. carbon at 350 F. and COICOz ratio of 70:30, 588 B.t.u.

Net heat available per lb. carbon:10076588= 9488 B.t.u.

Heat required per lb. of iron For heating in reduction kiln, 1330 B.t.u.

For reaction in reduction kiln, 1580 B.t.u.

For radiation in reduction kiln, 300 B.t.u.

Total heat required in reduction kiln, 3210 B.t.u. Total heat required in hearth kiln, 972 B.t.u. Total heat required (above stack gas), 4564 B.t.u. Less heat recovered from CO2 and CO released,

394 B.t.u. Net heat required (above stack gas), 4170 B.t.u.

Carbon required per lb. iron Heat supplied per lb. of total carbon 4170 Carbon required 0.438 1b.

Weight of gases per lb. or iron leaving hearth:

0.l46 11.978=1.75 lb.

Temperature gases leaving hearth:

Average temperature at sintering zone Temperature of gases leaving hearth, 3580 F.

34a0 =1160 3690 A;=2460. Average temperature-43620 F. :3620 F.

The theoretical temperature at the bosh of a blast furnace is 3090 F. Hence, the theoretical temperature of 3620 F. at the kiln sintering zone is ample for raw material heating and reduction purposes.

Turning now to the case in which incandescent pulverized carbon is added at the entrance to the shaft kiln for the purpose of converting the CO:CO2 ratio from 10:90 to 70:30, the reaction and consequent heat relationships will be as follows, it being assumed that the carbon thus added is in the form of a low volatile coal heated to 200 F. by partial combustion to CO:

Amount of coal to be burned to CO to heat the coal to 2000 F,

Heat required per lb.- of carbon 0.42 (2000-60) 1=815 B.t.u.

Heat of combustion of 1 lb. of carbon to CO, 4375 B.t.u.

Amount carbon to be burned =0.l86 lb. carbon per lb. carbon Hence, for every pound of carbon added, approximately 0.8 lb. will be solid and about 0.2 lb. will be in th form of CO.

The reaction is expressed by the equation The gases approaching the outlet of the hearth kiln comprise 9CO2+1CO. The carbon added at the entrance to shaft kiln-is in the form of 8C+2CO, and the desired atmosphere is 7CO+3CO2. For every pound of carbon burned in the hearth, 0.545 lb. of carbon is added at the entrance to shaft'and the mixture there will be:

The heat supplied by burning 1.09 lb. of carbon to CO, together with the heat of reaction of 4.36 lb. of carbon burned to CO, will be The oxygen required to fire20% of the carbon added to CO for heating the carbon to incandes cence is 1.33 0.109=0.145 1b., and the air brought in is 0. 4 =0.631 lb. per 1b. of carbon fired :2940 B. t. u. per 1b. of carbon fired :1438 B. t. u. per lb. of carbon fired With an air temperature of m the heat brought in by the air will be 0.63l (1500-60) 0.24'7:224 B.t.u. per lb. of carbon fired. Hence,

'end of the hearth, the amount of carbon fired in the hearth is 1 2940:1178 B. t. u.

The stack loss per lb. of carbon in this case will be the same as in the previous case, in which the COzCOz ratio in the exit or waste gas is 70:30. The stack gas temperature being 350 F., the stack loss will be 588 B.t.u. per lb. of total carbon.

The total carbon used will be 1.545 lb. per lb. of carbon fired in the hearth kiln, and the total net heat supplied per lb. of total carbon fired will be the same as in the previous case, the CO:CO2 ratio being the same. Hence, the total carbon fired per lb. of iron will be the same, i. e'.. 0.438 lb. However, the amount of hightemperature heat supplied to the hearth kiln-will be con-' siderably greater, since approximately two-thirds of the total carbon fired is burned to CO2 in the V hearth, as compared with approximately. only one-third, when CO gas instead of incandescent carbon is added at the entrance to the shaft kiln. The theoretical flame temperature of combustion in the hearth kiln will be the same in both cases, but in the latter case, in which two-thirds of the total carbon is burned to CO2, the temperature of the gases at the outgo end of the hearth kiln will be materially higher, since the heat given up in the hearth (being the same in both cases) com prises a smaller percentage of the heat available to the hearth. However, the heat required in said latter case for the endothermic reaction between the CO2 and the incandescent carbon at the en-. trance to the shaft kiln takes up heat from the gases, so that the gases entering the shaft'kiln are at the same temperature in both cases.

From the foregoing calculations it will be understood that, in the case in which CO is added to the flaming gases leaving the hearth kiln, the total heat supplied to the hearth is 0.146 17,377=2535 B. t. u. per lb. of iron. The hearth absorbs 972 B. t. u. per 1b. of iron from the gases, leaving 1563 B t. u. per lb. of iron in the gases. In the case in which incandescent carbon is added to the flaming gases at the outgo of the total fuel or 0/6475 0.438=0.284 lb. carbon per lb, of iron, wherefore the heat supplied to the hearth is 0.284 17,377=4925 B. t. u. per .lb. of iron. Upon giving up 972 B. t. u. in the hearth, the gases still contain 3953 B. t. u. per lb. of iron. In other words, with one and the same over-all fuel consumption in both cases, there is a:variation of approximately 100% inthe amount of high temperature heat which is supplied to the hearth kiln, and manifestly the operator can enjoy wide control over the amount of high temperature heat supplied to the hearth without substantial variation in fuel consumption.

From the foregoing specification, it will be understood that either liquid or gaseous fuel may be used in the hearth kiln; that under proper conditions liquid or gaseous fuel may be used for converting the oxidizing gases of the hearth to reducing gases for the shaft kiln; and that the methane (and like neutral gases included in such fuel), as it breaks down into hydrogen and car-' bon, provides reducing agents that are effective 14 "If oil-or gas is burned in the hearth, the exit gases will contain water and carbon dioxide, and if incandescent carbon is added at the entrance of the hearth, there'actions will be somewhat as follows:

2HzO+2COz+2C=H2O+Hz+CO+,2CO-+C0z= H2O+H2+3CO+CO2 The character of the resulting gas will be slightly reducing, for while the Hail-I20 ratio is 50:50, or neutral, the COZCOz ratio is 75:25, which is highly reducing.

If oil or gas is also injected at the shaft kiln, the; methane or other hydrocarbon will break down into carbon and hydrogen in the presence of the hot gases flowing from the hearth kiln. Alternatively, the methane or other hydrocarbon 'may be cracked in the injector. The reactions occurring will be somewhat as follows:

The resulting atmosphere is highly reducing,

as the (302002 ratio is 75:25, and the, H2IH2O' ratio is 84:16. The economy of such practice is dependent upon the analysis and cost of the fuel,

quired is that fed with the ore for reduction, to'

' indicate the amountof oxygen required to be added:

' Heat supplied Pounds (W) of oxygen enriched air per lb. carbon Products of combustion per lb. carbon (1+W) 1b. Flame temperature desired with O2- enriched "flame 5650 F.

In other words, 2.67 lbs. of oxygen enriched air per lb. of carbon must be supplied to raise the temperature of the carbon monoxide flame to 5650 F.

The amount of oxygen required for burning carbon to carbon monoxide is (16:12) or 1.33 lb. per lb. .of carbon. Therefore, the oxygen percentage in the oxygen enriched air is (1.33X:2.6'7) or 49.8% T

and the nitrogen content of the air is 50.2%. The original nitrogen content of the air is 0.77 lb. per lb. of air. Since 0.77 lb. of nitrogen comprises 50.2% ofeachpound of oxygen enriched air, it

follows that each pound of original air will correspond to 0.77:0.502 or 1.535 lb. of enriched air which contains 0.498 1.535 or 0.764 lb. of oxygen. The original oxygen content of the air being 0.23 lb. per pound of air, 0.534 1b. of oxygen must be added, which represents 0.534= 100: 1.535 or 34.8% of the enriched air.

The amount of carbon burned at the hearth kiln, when CO is added at the hearth kiln exit, is 0.43813 or 0.146 lb. per pound of iron. For each 10% of this carbon burned to CO the amount of oxygen required is 0.0146 l.35 or 0.0194 lb. of oxygen-. The amount of enriched air required is 0.019%:0A98 or 0.039 1b., of which 0348x0039 or 0.01358 lb. is added oxygen. is resorted to Where incandescent solid carbon is If such working added at the hearth kiln exit, the cost of oxygen would be twice as great, because instead of of the total fuel is burned at the hearth. Carbon monoxide generated at 5650 F. with oxygen enriched air ma be injected either from the lower burners of the hearth or fromall of the burners, to provide a protective blanket over the hearth metal.

' The useof oxygen for obtaining high hearth temperatures with a carbon monoxide flame is particularly suitable to the reduction of ferromang'anese or.ferro-silicon, both of which are more susceptible than iron'to oxidation.

The use of an oxygen-fed carbon monoxide flame to produce high temperature heat for the hearth section is but one of several permissible methods of obtaining the essential high temperature heat required to utilize fully the capacity of the hearth-zone. And as already described, another method of obtaining a flame sufficiently hot to suppl the heat required by the hearth zone is to preheat both the fuel and the combustionair. It is to be understood, therefore, that my invention is not limited to particular method of providing the essential highfia-me temperature, not to the specific procedural or structural features disclosed.

The shaft kiln may be adapted to be axially oscillated rather than rotated, or it ma be both oscillated and rotated. The melting chamber or hearth zone may consist in the rotary kilri shown,

or in a stationary furnace, or a ti-lting furnace,-

the primary purpose in separating the hearth zone or melting chamber from the reducing z'on'e being to remove the heating and metallurgical reactions from the melting process, whereby the best conditions for each may be established independently of the other, or substantially so. The reduction of the ore proceeds continuously, and in the course of advance of the ore towards the discharge end of the shaft kiln the ore requires progressively a more intensive reducing atmosphere, as it is exposed to progressively higher temperatures. Perfect accommodation to this circumstance of operation is gained b the separation of the shaft kiln from the hearth.

The coal used in the practice of invention is pulverized, and may be coked by heating it with hot gases in cyclone apparatus, thus driving off the volatiles as icy-product gas. produced may be heated to incandescence by passing it through a rec'uperator. The apparatus disclosed in Letters Patentl To's-.- 1,954,350, 1,954,- 351 and 1,954,352 granted in the year 1934 to F; L. Dornbrook et .al. may be used for this purpose.

,The' gas generated in this coke' producing operation will consist largely of hydrogen and as The coke so 16 such, is" not the most desirable for firing th'e kilns.

If there is an auxiliary field of use for byproductv gas and end products such as tar, the means used for carbonizing the coal for injection into the carbon dioxide flame may profitably be employed for carboniiain'g the coal to be burned in the melting kiln. A larger quantity of byproducts is then obtained, and may be credited against the cost of reducing the iron ore. With the useful employment of byproducts, all of the benefits now available to' the iron and steel in dustry throughthe employment of coke ovens in connection with blast furnaces will be realized in the practice of my kiln process, and at a much lower cost. There is an additional advantage insuch practice; that is, carbonized coal need not be quenched and then reheated to incandesc'ence', as it is in a' blast furnace. The gas yield is higher in my process, because I do'not employ fegener'zitdrs in my coking apparatus. In the byproduct coke industry about 40% of the total gas generated is used in heating regenerator checkers.

The iron produced by my process is relatively pure. The carbon content is low, since the iron contacts only'relativeiy small amounts of coal or coke. The iron contains but a trace of sulphur due to the high lime content of the kiln charge. The silicon content is low, since the kiln charge does not contain the excess carbon found in the blast furnace charge, and the silica in the ore is not reduced to silicon.

Because of its comparatively high degree of purity, kiln iron made according to my process ma directly be refined into steel in open hearths or in electric furnaces. There is no need to dilute a relativel pure iron with scrap iron, or other iron that is relatively free from carbon, sulphur, Silicon and phosphorus, as must be done with blast furnace iron. Steel production at a reasonable price is thus rendered independent of scrap iron supply. The production of any given open hearth or electric furnace is much greater when operated with my kiln iron, particularly when the iron is charged in molten condition, with no cold scrap or the like added. The fuel or power consumption of open hearth or electric furnace is lowered accordingly, as is also the" consumption of slag-forming materials, smaller amou'nts'of impurities being present in the furnace charge and requiring removal. Since the slag of furnaces using my charging metal contains smaller amounts of impurities, the ability of the slag to remove impurities is encumbered to less degree.

The use of my hot kiln iron in an open hearth charge serves to preserve the usual manganese content of their'on ore (which is retained by the kiln iron), for in thehrelatively short time required to refine the kiln iron in an open hearth smaller quantities of the manganese are lost by oxidation than when blast furnace iron is refirie'd.

Fr'o'rii the standpoint of increasing steel capacity, it should be noted that the installation of my combustion iron and cement clinker plant aflords increased steel capacity without requirihg" additions to existing coke plant or open 17 ess makes iron production possible in localities lacking resources of coking coals. Since fuel oil or"natural gas may be used in the process, iron may now be produced in localities remotefrom the coal fields, but economically accessible to oil and'gas fields. i

It may be remarked that my process may utilize cheap coal or culm in place of expensive coke. This saving will amount" to about ofthe cost of the charging material, depending, of course, upon the cost differential between the coke and the coal, gas, or oil used in the kiln. If the value of the cement clinker is credited to the cost of production, the cost of my kiln iron will be only about 65% of that of blast furnace iron. The finished kiln iron, if molten, is equivalent to liquid scrap having the desired carbon content, and low sulphur and silicon contents, and is therefore worth at least $2.00 per ton more than blast furnace iron.

The cost of scrap in normal markets is usually greater than the cost of blast furnace hot metal, and hence the cost of steel ingots produced from a 100% charge of molten kiln iron will be materially less than the cost of steel produced by conventional methods. The reduction in the cost of melting, and the higher tonnages secured in the open hearth charged with kiln iron, further reduce the cost of steel ingots. The net effect is that the cost of open hearth ingots is reduced by herein described which includes firing the melting zonewith high temperature oxidizing flames to melt the metal in such zone, leading the products of combustion from the melting zone through the reducing zone, and reducing a substantial part of the carbon dioxide in said products of combustion flowing into said reducing zone by injecting into such products carbon particles preheated to incandescence for immediate reaction with the carbon dioxide.

,3. In the method which comprises reducing iron ore in a reducing zone and delivering'the 30 to taking into consideration the credit reduced metal into a melting zone, the invention herein described which includes sintering the reduced metal before delivery into said melting zone and impregnating and coating the sinter with carbon, firing the melting zone with hightemperature oxidizing flames to melt the sintered 'metal while protected by the carbon against reoxidation, leading the products of combustion from the melting zone into the reducing zone, and reducing a substantial part of the carbon dioxide in said products of combustion flowing into said reducing zone by injecting into such products carbon particles preheated to incandescence for immediate reaction with the carbon dioxide.

4. In the method which comprises reducing iron ore in a reducing zone and delivering the reduced metal into a melting zone, the invention herein described which includes sinterin the reduced metal and spraying carbon thereon to form carbon impregnated and coated nodules before delivery into said melting zone, firing the melting furnace size. In duplex plants the corresponding figure ranges from 20 to tons per hour. However, duplex steel is not acceptable for'many purposes, such as deep drawing sheet steel, due to the presence in duplex steel of undesirably high amounts of objectionable iron-nitrogen compounds originating from the Bessemer steel used in the production of duplex steel. My kiln iron, on the other hand, when charged hotinto an open hearth increases the operating capacity of the hearth by 100 to 300%, thus reaching a capacity comparable to duplex plants, while'yielding steel comparable if not superior, to open hearth steel, made from blast furnace iron and scrap.

Within the terms and intent of the appended claims many refinements and variations in the procedure and structure described may be made without departing from the principles of the invention. This application is a continuation-inpart of patent application Serial No. 436,849, filed March 30, 1942, now abandoned.

I claim as my invention:

1. In the method which comprises reducing iron ore in a reducing zone and delivering the reduced metal into a melting zone, the invention herein described which includes firing the melting zone with high temperature oxidizing flames to melt the metal in such zone, leading the products of combustion from the melting zone through the reducing zone, and reducing a substantial part of the carbon dioxide in said products of combustion flowing into said reducing zone by injecting into such products carbon preheated to a temperature for immediate reaction with the carbon dioxide.

2. In the method which comprises reducing iron ore in a reducing zone and delivering the reduced metal into a melting zone, the invention zone with high-temperature flames to melt the A reducing zone by injecting into suchlproducts carbon particles preheated to incandescence for immediate reaction with the carbon dioxide.

5. In the method which comprises reducing iron ore in a reducing zone and delivering the reduced'metal into a melting zone, the invention herein described which includes sintering the re-- duced metal and spraying carbon thereon to.

form carbon impregnated and coated nodules before'delivery into said melting zone, firing the melting zone with high-temperature flames to melt the-metal under the protection of said carbon against re-oxidation, leading products of combustion from the melting zone into the reducing zone, and reducing a substantial part of the carbon dioxide in said products of combustion flowing into said reducing zone by injecting into such products a hydrocarbon preheated and cracked for the immediate reaction of the hydrogen and carbon contents thereof with the carbon dioxide. I

6. The method which comprises reducing iron ore in a reducing zone and delivering the reduced metal into a melting zone, firing the melting zone with high temperature oxidizing flames to melt the metal in such zone, leading the products of combustion from said melting zone through said reducing zone, and reducing a substantial part of the carbon dioxide in said products of combustionfiowing into said reducing zone by injecting into such products a hydrocarbon preheated and cracked for the immediate reaction of the hydrogen and carbon contents thereof with said carbon dioxide.

EUGENE S. HARMAN.

(References on following page) Berglund. Dec. 5, 1916 REFERENCES CITED Number j '1 Name 7 Date The following references are of record in the 1,717,160 Kmhlme 1929 me of this patent: 1,815,899 Brassert July 28, 1931 1,864,593 Gustarfsson June 28, 1934 UNITED STATES PATENTS 2,035,550 Karwat n Mar. 31, 1936 Numqer Name Date 2,045,639 Eulenstein June 30, 1936 809,291 Fleischer Jan. 9, 1906 FOREIGN TE 839,126 Ellis Dec. 25, 1906 927,046 Hegel July 6, 1909 Number Country Date 1,102,939 Junquera July 7, 1914 10 22,236-

Great Britain Oct. 9, 1911

Claims (1)

1. 2. IN THE METHOD WHICH COMPRISES REDUCING IRON ORE IN A REDUCING ZONE AND DELIVERING THE REDUCED METAL INTO A MELTING ZONE, THE INVENTION HEREIN DESCRIBED WHICH INCLUDES FIRING THE MELTING ZONE WITH HIGH TEMPERATURE OXIDIZING FLAMES TO MELT THE METAL IN SUCH ZONE, LEADIN THE PRODUCTS OF COMBUSTION FROM THE METLING ZONE THROUGH THE REDUCING ZONE, AND REDUCING A SUBSTANTIAL PART

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