US2750276A - Method and apparatus for smelting fine iron ore - Google Patents

Description

June 12, 1956 Filed Jan. 4, 1952 W. E. MARSHALL METHOD AND APPARATUS FOR SMELTING FINE IRON ORE 2 Sheets-Sheet l ATTORN 8Y3.

June 12, 1956 w, MARSHALL 2,750,276

METHOD AND APPARATUS FOR SMELTING FINE IRON ORE Filed Jan. 4, 1952 2 Sheets-Sheet 2 llllll INVENTOR.

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United States PatentC METHOD AND APPARATUS FOR SMELTING FINE IRON ORE William E. Marshall, Middletown, Ohio, assignor to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio Application January 4, 1952, Serial No. 264,859

15 Claims. (CI. 75-26) It has long been known that finely divided iron ore could be converted to a mixture of metallic iron and gangue by treating it at an elevated temperature with suitable reducing gases. The end product of such a procedure, however, has not been readily utilizable. If it is to be used directly, it involves a serious separation problem, and the finely divided iron must be melted down for most uses. It is possible to feed the finely divided mixture of iron and gangue into a blast furnace or the like where the usual iron smelting procedure is being carried on. Melting will effect a separation of the iron from the gangue; but any economies theoretically derivable from the pre-reduction of the iron are largely lost in such a procedure.

In a copending application Serial No. 226,231, filed May 14, 1951, and entitled Process and Apparatus for Reducing and Smelting Iron, I have described a procedure and apparatus in which a flame is produced in a bath-type furnace from a mobile fuel, the flame having a temperature of at least substantially 3000 F., and the products of combustion of the flame being reducing to iron oxide. The heat from the flame is employed to maintain a bath of iron'in molten condition in the bath-type furnace, and the products of combustion of the flame, which are reducing in character, are employed outside the bath-type furnace proper to reduce finely divided iron ore, the iron and the ganguebeing then melted inside the furnace by the heat of the flame. The conditions required for the practice of this process, and in particularthe production of a flame which has a sufiiciently high temperature and nevertheless is reducing toward iron, may be met' by the use of oxygen or oxygen-enriched air for purposes of combustion and by a preheating of the mobile fuel or the oxygen or oxygen-enriched air or both. In that application and in the present case, the'terrn mobile fuel isused to mean natural and artificial combustible gases, such as natural gas, methane, ethane, propane, butane, ethylene,.

acetylene, hydrogen and the like, which contain as their principal combustion components hydrogen or hydrocarbons, (but without more than 'a minor'concentration of gases containing combined oxygen, suchas carbon monoxide and water vapor), as wellas. to mean oil: or other liquid hydrocarbon fuels, and solid, pulverized, carbonaceous fuels, such as powdered coal, coke, or carbon black. The process is capable of effecting substantial economies especially where a plentiful supply of a mobilefuel is economically obtainable. Since the iron. ore is used in a finely divided condition, a cheaper iron ore may be employed; and the use of lump coke as a skeleton in a shaft furnace or asa fuel is avoided.

One of the principal objects'of this invention is the provision of improvements in the process and apparatus of the said copending application.

Another object is the provision of means and a methodwhich will facilitate the obtaining of a high: temperature flame from burningfuel while maintaining the reducing character of:the-products of combustion thereof.

Yet another object, of one aspect ofxthe invention, is.

the provision of means and amethodof accomplishing, the

Patented June 12, 1956 ICC smelting of iron by meansof mobilefuels in which the iron molten bath. of iron and slagis being maintained by the, flame.

Yet'another object of the invention is the provision of means and a method. for the' more economical and complete utilization of the: heat. generated in the process. Specifically, but without limitation, when it becomes necessary to cool the reducing products of combustion from the furnace in order toutilize them in reducing iron ore, I employ the heat-absorbed from: these gases in the production of the required temperatures at the'point of combustion.

Yet another object of the invention is the provision of a process and apparatus for accomplishing the general object of the said copending application, but ina simpler, less expensive, and-more positiveway.

These and other objects of the invention, which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, I accomplish by that procedure and in that apparatus, of which I shall now describe certain exemplary embodiments. Reference is made to the accompanying drawings in which:

Figure 1 is a diagrammatic showing in the nature of a flow-sheet, of apparatus appropriate to the practice of my invention.

Figure 2 is a similar showing of a modified form of apparatus.

Referring to Figure 1, I have shown therein a bath-type furnace, indicated generally at 1, having a hearth 2 upon which a bath of iron 3 and a supernatant bath of slag 4 are maintained in molten condition by the heat of a flame 5 produced by a burner 6. The products of combustion of the flame enter a chamber 7 of the furnace which is arranged as a heat exchange apparatus. As shown, this chamber contains a conduit 8 in coiled or sinuous condition or otherwise arranged so as to effectuate an efiicient heat transfer. A suitable mobile fuel, such for example, as natural gas, is introduced into the conduit 8 from a suitable source by means of the conduit 9 shown outside the furnace. The mobile fuel, without being exposed to or commingled with the products of combustion of the. flame 5 is thus subjected to a high'temperature such that cracking occurs therein, the fuel separating principally into its components, carbon and hydrogen.

The cracked or partially cracked mobile fuel leaves the heat exchange means 8 through a conduit 10. Additional cracking or heating meansv may be employed, as in the stove 11, equipped with an interior sinuous conduit 12. The stove 11' may be heated by the combustion of a portion of the gases from the furnace 1 (which, being reducing in nature, contains combustible values), or by the combustion of fuel derived from any other source. To. this end .I have shown the stove 11 equipped with a burner 13 havingan inlet 14 for fuel and an inlet 1'5'for air.

The. cracked and heated gases from the stove 1-1 are conducted by a conduit 16. to the burner 6 of the furnace 1. In theburner they are mixed with. oxygen or oxygenenriched air (preheated if desired) entering the burner through a conduit 17 An intense flame within the furnace 1 is thus produced, while. the products of cornbustion of the flame remain reducing in character.

in my process-the cracking of the mobile fuel absorbs heat and requires about 20% to' 30% of the total heat used in the process; As a consequence, applying this heat to the mobile fuel, using for the purpose either the sensible heat from the gases. of furnace 1 or the heat of combustion of waste-gas=or othenextrinsicifuel, makes the process more efficient, and increases the:..rate. of production of molten iron. Further, since in some embodiments of my process the reducing gases from the products of combustion of the furnace 1 are employed outside the furnace to reduce iron ore and must be cooled for this purpose from the high temperature of the furnace to a tempera ture of around l300-l400 F. or slightly higher, it will be seen that the portion of my apparatus thus far de scribed offers a mode of transferring heat usefully and directly to gases entering the burner 6. The cracking temperature for most mobile fuels will be around 1600 F., so that it will be seen that this arrangement affords a means for withdrawing suflicient heat from the furnace gases to crack the mobile fuel and at the same time reducing the temperature of the furnace gases to a range at which efiicient reduction of iron ore will occur outside the furnace without causing such sintering of the reduced iron as would clog pipes, conduits and chambers in which the reduction is carried on, or in which the reduced or partially reduced iron ore is being carried.

A cracked mobile fuel, at temperatures around the cracking point, is, in itself, an eflicient reducer for iron ore, and may be employed directly for such reduction, the reduced or partially reduced iron and gangue being introduced into the furnace 1 through the burner 6 along with the fuel and oxygen or enriched air. To this end I have shown in Figure 1 a means for the introduction into the conduit 9 of finely divided iron ore and a finely divided flux such as lime. These means have diagrammatically been illustrated as comprising a hopper 18 for the iron ore and flux, and a screw feed means 19 driven by a motor 2% for producing a uniform rate of feed into the conduit 9. The velocity of the gases passing through the conduit and the associated heat exchanged devices and conduits will be sufficiently great to carry the iron ore and flux suspended therein. Indeed, I may also introduce into the incoming mobile fuel stream any reduced iron ore and flux derived from reduction apparatus, using the products of combustion of Figure 1, located outside the furnace l. I have shown such materials being also introduced into the conduit 9 through a conduit 21. The various finely divided materials introduced into the stream of mobile fuel and passing therewith through the cracking apparatus not only are subjected to reducing conditions, but serve also two primary functions. They catalyze the cracking of the mobile fuel, and they also act as scouring means to keep such apparatus free from an accumulation of carbon which might otherwise clog them, the carbon, of course, being derived from the cracking of the mobile fuel.

In a procedure in which all of the iron ore which is to be reduced in the process is introduced as such into the stream of fuel, the combustion gases from furnace 1 may be burned elsewhere for the useful generation of heat, or may in part be purified and used to dilute the incoming fuel. But it is more economical to use the reducing values of the gases from furnace 1 for pre-reducing iron ore, the reduced product being then introduced into the furnace along with the cracked fuel as hereinabove described, or in any of the direct modes of introduction described in my copending application Serial No. 226,231. The furnace gases from furnace 1, which have now been cooled in the heat exchange apparatus 7, 8 as hereinabove described, may be carried by a conduit 22 to a preheater and partial reductionchamber 23. A finely divided mixture of iron ore and flux, such as lime, may be introduced into the conduit 22 so as to be carried along by the gas stream therein. Introduction apparatus is diagrammatically shown as comprising a hopper 24, a screw feed means 25 and an electric motor 26. It will be understood that other feeding means may be substituted. It will also be understood that any mixture of iron ore and flux which is introduced into my apparatus will be in sufi'iciently dry condition to prevent plugging the system or the generation of such a concentration of water vapor as would interfere with the reduction of the iron values in the ore.

The reduction chamber 23 is preferably of that type in which the finely divided materials, i. e. the iron ore and flux are maintained fluidized or in a condition of con tinuous agitation by reason of the flow of incoming gases through the conduit 22. The finely divided materials accumulate in the chamber 23' until they spill over the partition 27 therein, entering a downtake 28 and accumulating above a valve 29 connected with a conduit 3d. The material collecting above valves 2) and 32 will be in at least partially reduced condition. The action of reduc- -tion, which in part involves the combination of hydrogen in the gases with the oxygen of the iron ore, serves to produce a concentration of water vapor in the gases which impairs their reducing efficiency in spite of the fact that they still otherwise contain substantial reducing values. As a consequence, I carry these gases through a dust separator 31 of the centrifugal or other type and through conduit 33 to a gas dehydrator 34 where the moisture-vapor content. is largely removed. Solids from the dust separator 31 collect above a valve 32, and are delivered to the conduit 3%.

A pump 35 is used to move the gases. The reducing capacity of the gases is now to a large extent restored; but the gases have been so lowered in temperature that it becomes necessary to reheat them to the range at which efficient reduction of iron ore will occur. This may be accomplished by means of the stove 36, the gases passing through a sinuous conduit or heat exchange means 37 within the stove. The stove may be fired by waste gases derived from the system or by fuel from some other source; and I. have shown a burner 33 equipped with an inlet 39 for fuel and an inlet 40 for air.

The hot, dry gases, which are now again reducing toward iron, are carried by a conduit 41 to the entrance end of conduit 30 into which are introduced, as above described, the solids from the first reduction step. These solids are entrained in the reducing gases in the conduit and are carried thereby to a second reducing chamber 42 which, again, preferably is of the fluidizing type. The reduced material accumulates in the downtake 43 of this chamber while the gases are carried to a dust separator 44. Solids separated by this device are carried by a branch connection to the downtake 43 where they accumulate above a valve 45. This valve connects the downtake to the conduit 21 by means of which the reduced solids are carried to the intake conduit 9 for the mobile fuel, as hereinabove described.

The gases from the dust separator 44 have relatively low reducing efliciency, but contain substantial combustible values. Hence, they are carried by a conduit 46 to a gas holder or accumulator 47 where they may be stored for use. It will be understood that the gases so held may be the combustible gases used for heat in the stoves 11 and 36 and that excess quantities of them may be employed for other purposes, such as the drying of the ore and flux for introduction into separators 18 and 24, the production of oxygen for use in the burner 6, or for the enrichment of the air used in that burner, for the generation of power, or for any other uses of a combustible gas.

Referring now to Figure 2, like parts have been given like index numerals and will not be again described. The mobile fuel for the burner 6 is shown as being cracked in the stove 11, entering the heat exchange apparatus within that stove through a conduit 48. In this particular embodiment of my apparatus, the upper part of the furnace 1 is used for a different purpose hereinafter described. It is not beyond the scope of my invention, however, to use some portion of the sensible heat of the products of combustion of furnace 1 to preheat the mobile fuel and crack it at least in part. The cracking may be accomplished with or without the introduction of iron oreand flux and/ or partially or completely reduced iron and gangue into the mobile fuel, as will readily be under- 5. stood from the description of; Figure? 1-, although in Figure 2 I have not shown means for this purpose.-

The furnace 1* has an upper chamber 49 connected with the main part of: the furnace by a relatively constricted: throat 50. In this embodiment of my invention,'I- carry on a reduction of the iron ore. in the chamber -49-directly by means of the reducing gaseswhi'ch are the products of combustion of the flame 5.

Finely divided iron ore' and flux are. introduced into the chamber 49, as from a hopper-51, by means of a screw feed 52 equipped witha motor 53. The purpose of the constriction 50- is to increase the velocity of the products of combustion-passingfrom the furnace properinto the chamber 49 so as to maintain the finely divided solids in a state of suspension in the chamber-49; The: velocity of the gases may be still. further increased by the introduction through the conduit 54' of additional quantities of reducing gas preferably derived-from the stack gases as hereinafter described, or' of fresh' reducing gas: such as natural gas or the like.

It will be-underst'ood that" the reduction in the chamber 49 will be taking place at a very high temperature; It has been described above that the temperature of the flame in the bath-type furnace 1 might be: of the order of about 3000 F. or higher in order-to maintainthe iron and slag in suitably molten condition- The temperatures, therefore, in the chamber 49 will be lower than about 3000 F. only by the amount of cooling which has occurred during the passage of the gases tothe chamber 49 and the amount of cooling by dilution which has occurred through the introduction of reducing gases through the conduit 54. The temperatures in therchamber -49', therefore, will be high enough to produce sintering 'or' coalescence of the reduced materials. Nodulization will occur, but only after the reduction: is substantially complete. When heavy enough nodules are formed'so-"that the gases'at their specific velocity can no-longer keep-them in'suspension, they will fall through therthroat 50=intothe main part of the furnace and be melted into the sla'grand iron baths 4 and 3.

While as indicated above, unreduced iron ore and flux may be fed into the chamber 49 and there reduced as described, the process is more efiicient if a pre-reduction of the iron ore is practiced. This reduction need not necessarily be a complete reduction and in most instances will not be so. But the furnace 1 will deliver large quantities of products of combustion which are high in reducing values, and these reducing values will by no means be entirely absorbed or converted in the chamber 49. Consequently, I prefer to deliver the gases from this chamber through a conduit 55, a dust separator 56 and a conduit 57 to the dehydrator 34. The same type of pump 35 may be employed to move the gases; and if the gases are cooled, as when the dehydration is accomplished by cooling with cold water, it will be necessary to reheat the gases in the stove 36 hereinabove described.

The dehydrated and hot reducing gases are delivered by a conduit 58 to a conduit 59 into which a mixture of dry, finely divided ore and flux such as lime, is delivered, as by means of the hopper 24, screw 25, and motor 26. These solids are entrained in the hot reducing gases and carried to a reducing chamber 60 such as the chambers 23 and 42 previously described. The reduced solids enter the downtake 61 of this reducing chamber, while the gases from the reducing chamber go to a dust separator 62. The solids from this separator are carried by a branch connection 63 to the same downtake, as are also the solids from the dust separator 56, by a downtake 64. These solids accumulate above a valve 65 by means of which they are delivered to the hopper 51. It will be clear that the downtake 61 is connected to the hopper by a gas-tight connection, in this embodiment of my process, so that the reduced materials are not re-exposed to the atmosphere.

The gases from the dust separator 62, which are now relatively low in. reducing valuesalthough they: containv example, cokefor increasing: the-carbon content-.of thev iron. or alloying ingredients-for the direct production of alloy steels-.-v

Modifications maybe made in my invention without departing from thespirit. of. it. In particular, the various. 1' individual features of. any apparatus described herein may be combined in various ways. Having; thus described my invention. in' certain exemplary embodiments,

what I claim as new-and desire to secure by Letters- Patent isa.

1. Ina: process of? reducing and. smelting iron ore including the steps of "producing-in a furnacewitha mobile'fuel-a flame-having a temperature of at least substantially 3000 F., the products of combustion-of which are reducing to iron oX-ide, employing said reducingproducts-"of combustion in-heated condition to reducefinelydivided: iron ore to iron,iand melting said. reduced iron. by means of the heatv of said fiame,-thefurther steps. of -cracking; said mobilev fuel-priorto ignition thereof to produce said flame by the application of heat to said mobile-fuel; and. having present in said fuel at the time of craekingtafinely divided material which 'is introducedr-into .saidfurnace. through said flame.

2. The process claimedvin claim 1 wherein the said finely divided. material comprises. iron-bearing material entrained in saidmobile fuel.

3. A process of reducing and smelting iron ore which comprises producing in a furnace with a mobile fuel a flame having a temperature of at least substantially 3000' F., the products" of combustion of which are reduc'ingft'o iron oxide, employing a portion of the sensible heat of said 'products' of combustion to crack said mobile fuel at 'l'east-in part prior to the ignition thereof to produce said flame, employing said reducing products of combustion in heated condition to reduce divided iron ore to iron and melting said reduced iron in said furnace, including the step of entraining finely divided material in said fuel prior to the cracking thereof.

4. The process claimed in claim 3, wherein finely divided iron-bearing material is entrained in said mobile fuel prior to the cracking thereof, and wherein said finely divided iron-bearing material is introduced into said furnace along with said fuel.

5. A process of reducing and smelting iron which comprises producing in a furnace with a mobile fuel a fiame having a temperature of at least substantially 3000 F., the products of combustion of which are reducing to iron oxide, said furnace having upper and lower chambers, passing said products of combustion into said upper chamber at a velocity sufiicient to maintain finely divided iron-bearing material in suspension therein, and feeding finely divided iron-bearing material into said upper chamber, the temperature of said products of combustion being sufficient to bring about agglomeration of particles of said iron-bearing material when at least partially reduced, whereby agglomerates of said particles attain a weight too great to be supported by said products of combustion, whereupon said agglomerates pass by gravity from said upper chamber and are melted in said lower chamber.

6. The process claimed in claim 5, wherein the velocity of said products of combustion is increased by the introduction into said furnace of reducing gas at a point remote from the origin of said flame.

7. The process claimed in claim 6, wherein the products of combustion after passing through said upper chamber are dried and employed to reduce iron ore at least in part, the reduced material being then introduced in particulate form into said upper chamber.

8. The process claimed in claim 7, in which said mobile fuel is cracked prior to the ignition thereof to form said flame, and has entrained therein finely divided ironbearing material during said cracking.

9. In apparatus for the purpose described, a sealed furnace having a hearth chamber and an upper chamber, said upper chamber being divided from said hearth chamber by a constricted throat, burner means for forming in said hearth chamber a flame with a mobile fuel having a temperature of at least about 3000 F., the products of combustion of which are reducing, said constricted throat serving to increase the velocity of said products of combustion as they pass into said upper chamber, and means for feeding into said upper chamber a finely divided iron-bearing material.

10. The apparatus claimed in claim 9,-including means for feeding into said hearth chamber a reducing gas at a point remote from the origin of said flame whereby to increase the velocity of the gases passing into said upper chamber.

11. Apparatus as claimed in claim 9, in combination with means for receiving the products of combustion from said upper chamber and drying and reheating them, reducing apparatus in which said dried and reheated products of combustion are associated with finely divided iron ore and flux to effect at least a partial reduction of said iron ore and means for feeding the solid material so treated into said upper chamber of said furnace.

12. In apparatus for the purpose described, a furnace for melting iron, said furnace having a sealed hearth chamber, burner means in said hearth chamber for producing a flame in said furnace, said flame having reducing products of combustion, means ahead of said burner for cracking said mobile fuel in the presence of finely divided iron-bearing material entrained therein prior to the ignition thereof to form said flame, means for associating said products of combustion with finely divided iron ore whereby to reduce said iron ore, and means for delivering the reduced'material into said hearth chamber so that said reduced material is melted.

'13. The structure claimed in claim 12, wherein said furnace has an upper chamber through which said products of combustion pass and means in said upper chamber for causing said products of combustion to act on finely divided iron-bearing material suspended therein.

14. The structure claimed in claim 13, including means for associating the products of combustion after passing through said upper chamber with finely divided iron ore in a reducing apparatus and means for delivering the reduced product to and entraining it in the said mobile fuel ahead of said cracking means.

15. In apparatus for the purpose described, a furnace having a sealed hearth chamber for melting iron, an upper chamber through which said products of combustion pass, burner means for producing in said hearth chamber from a mobile fuel a reducing flame having a temperature of at least about 3000 F., a heat exchanger in said upper chamber exposed to the heat of said products of combustion, means for passing said mobile fuel through said heat exchanger ahead of said burner means, and means for entraining in said mobile fuel ahead of said heat exchanger a finely divided, iron-bearing material.

References Cited in the file of this patent UNITED STATES PATENTS 190,926 St. John May 15, 1877 1,490,012 Kapteyn Apr. 8, 1924 1,704,029 Baily Mar. 5, 1929 1,775,713 Baily Sept. 16, 1930 1,948,697 Brassert Feb. 27, 1934 2,330,487 Grace Sept. 28, 1943 2,420,398 Kinney May 13, 1947 2,503,555 Lykken Apr. 11, 1950 2,538,201 Kalbach Jan. 16, 1951 2,544,697 Lewis Mar. 13, 1951 2,547,685 Brassert et al Apr. 3, 1951 FOREIGN PATENTS 370,636 Great Britain Apr. 14, 1932

Claims (1)

1. IN A PROCESS OF REDUCING AND SMELTING IRON ORE INCLUDING THE STEPS OF PRODUCING IN A FURNACE WITH A MOBILE FUEL A FLAME HAVING A TEMPERATURE OF AT LEAST SUBSTANTIALLY 3000* F. THE PRODUCTS OF COMBUSTION OF WHICH ARE REDUCING TO IRON OXIDE, EMPLOYING SAID REDUCING PRODUCTS OF COMBUSTION IN HEATED CONDITION TO REDUCE FINELY DIVIDED IRON ORE TO IRON, AND MELTING SAID REDUCED IRON BY MEANS OF THE HEAT OF SAID FLAME, THE FURTHER STEPS OF CRACKING SAID MOBILE FUEL PRIOR TO IGNITION THEREOF TO PRODUCE SAID FLAME BY THE APPLICATION OF HEAT TO SAID MOBILE FUEL, AND HAVING PRESENT IN SAID FUEL AT THE TIME OF CRACKING A FINELY DIVIDED MATERIAL WHICH IS INTRODUCED INTO SAID FURNACE THROUGH SAID FLAME.

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