US2745732A - Method of reducing ores by a particular fuel combustion mixture - Google Patents

Description

May 15, 1956 OSTER 2,745,732

METHOD OF REDUCING ORES BY A PARTICULAR FUEL COMBUSTION MIXTURE Filed 001?. 28, 1952 THOMAS H, OSTER INVENTOR.

50.777 61 BY Z Mm A T TORNE VS United States Patent METHOD OF REDUCING ORES BY A PARTICULAR FUEL COMBUSTION MIXTURE Thomas H Oster, Dear-born, Mi'ch., assignor to Ford Motor Company, Dearborn, Mich a corporation of Delaware Application October 28, 1952, Serial No. 317,282

11 Claims. ((11. 7526) This application is av continuation in part of application Serial No. 253,890, filed October 30, 1951, in the name of Thomas H. Oster.

This invention is concerned with the art of utilizing fuels and more particularly with a process for the economical combustion of solid fuels which may well be high in very fusible ash and to simultaneously recover any metal values which may exist in the ash of the fuel or which may incidentally be added to the fuel. This invention also contemplates the substitution of gaseous or liquid fuel for all or a portion of the solid fuels where emphasis is to be placed upon the recovery of m tal values from added ore rather than from the ash of the fuel.

As the supply of high grade fossil fuels in general and good coking coals in particular are becoming somewhat depleted it has become imperative from an economical standpoint to find suitable substitutes. Many of the more readily available fossil fuels are characterized by a high ash content and by the fact that this ash content exhibits a low fusion point. This combination of circumstances renders the combustion of these fuels diflicult and inefficient in the ordinary type of coal burner due to the erosion of the brick work by molten slag and by the inevitable partial insulation of the heat absorbing surfaces of the boiler by the ash. In an effort to overcome these difficulties the art has recently developed a fossil fuel burning device termed the horizontal cyclone burner.

Briefly, this device comprises a water cooled steel cylinder with its axis slightly inclined from the horizontal and provided at one end with means for the reception of a stream of crushed fuel and primary air and at the other endwith an exit for the products of combustion. This type of burner and its operating characteristics are amply and ably described in an article entitled The horizontal cyclone burner, by A. E. Grunert, L. Skog and L. S. Wilcoxson, appearing at page 613 et seq., of the American Society of Mechanical Engineers, Transactions, volume 69, 1947.

It is an object of this invention to improve the operation of this type of burner and to enable it to be used to recover metal values inherent in the ash of the fossil fuel, or deliberately added to the fuel stream. This invention is probably best understood by reference to the drawing which depicts a vertical section through a typical horizontal cyclone burner. In this drawing the horizontal steel shell is indicated generally at 10. This shell is protected over its entire inner surface with pipe coils ll through which water is circulated to protect refractory lining 12 and recover useful heat from the reactions occurring in the cyclone burner. One end of shell terminates in an inlet 13 for the reception of crushed fossil fuel or fluid fuel and primary air. The opposite end of shell 13 terminates in re-entrant opening 14 designed to permit the escape of the products of combustion while at the same time inhibiting the loss of ash or slag. Immediately adjacent inlet 13 is a tangential opening 15 for the additionv of secondary air under substantial pressure for a purpose which will become apparent as the description proceeds. Molten material is released through. slag discharge 16.

In the conventional operation of a burner of this type a stream of coal, crushed to pass a 4 inch screen. is permitted to flow into inlet 13 with a small stream of primary air. of the fuel is injected through tangential opening 15 under a pressure of approximately 20' to 30 inches of water. entrance of the secondary air stream is sufiicient to cause the gases within the burner to rotate rapidly and to cause any given gas particle to describe a helical path in its travel from the inlet to the outlet of the burner. The interior of the burner is operated at a temperature sufficiently high to melt the ash produced. The particles of molten ash are hurled by centrifugal force against the peripheral wall of the chamber and by virtue of their sticky or viscous nature these molten particles coalesce to form a continuous coating thereover. Similarly particles of incompletely burned solid fuel are hurled against the walls of the chamber and trapped in this viscous slag layer and held there while they are completely coked and then consumed. During this burning time the slag layer and entrapped fuel particles continuously and slowly cir-' culate around the periphery of the burner in a helical path and gradually advance toward the exit. In conventional powerhouse practice the solid particles of fuel are completely consumed before the ash is discharged from:

the exit end as a molten slag. Practically all of the necessary combustion air per cent) is supplied tothe burner as a conib'mation of the primary and secondary air. The gaseous products of combustion are discharged from this burner into a boiler setting and there admixed with the remaining 15 per cent of tertiary air to insure complete combustion. Similarly in powerhouse practice it is conventional to preheat the air employed for combustion by means of economizers heated by the stack gases leaving the boiler setting. Accordingly, these boilers are normally operated with air preheated to a temperature of between 360 and 590 degrees F.

The usual operation of this type of burner may be subjected to a substantial modification whereby the metal values inherent in the ash or" the fuel may be recovered or metal ore may be added to the stream of solid, liquid, or gaseous fuel and the metal values recovered therefrom. While by no means so limited, this invention will be described primarily as adapted to the recovery of the iron content of coal ash and from iron ore or other ferruginous material added to the incoming solid fuel. In order to effect a substantial lowering in the level of oxidation of the ferric compounds either present in the coal ash or added as iron ore, it is essential that the burner be operated under substantial reducing conditions and the large volumes of combustible gases so produced be burned with appropriate amounts of tertiary air after leaving the burner and entering the boiler setting. This can be accomplished either by increasing the amount of solid, liquid or gaseous fuel fed to the system or by reducing the total of the primary and secondary air streams. If the conditions within the burner are maintained suliiciently reducing it is possible to discharge along with the molten slag, iron either as molten iron or as a molten iron oxide or if desired, as the low melting eutectic of ferrous and ferric oxides. To obtain these results it is essential that the amount of carbon dioxide and water vapor in the burner be limited since concentration of these gases obtained in ordinary combustion are oxidizing to iron at high temperature and may even oxidize the lower oxides of iron.

Since the reduction of ferric compounds to the ferrous or elemental stage is a decidedly endothermic reaction and since the oxidation of carbon to carbon monoxide as The bulk of the air needed for'oombustion.

This pressure combined with the tangential opposed to the usual carbon dioxide is comparatively a much weaker exothermic reaction it is essential that other means be employed to maintain the temperature of the interior of the cyclone burner at a value which will insure rapid and complete reaction and maintain the ash molten Without the addition of excessive amounts of flux.

Recent technical advances have opened new methods of adding this essential heat to the burner chamber. The incoming air may be preheated well beyond powerhouse practice and sufficiently so that the heat so added plus the heat of combustion of the volatiles in any coal which may be employed and the oxidation of the resultant coke to carbon monoxide will add suflicient heat to the process of combustion to insure the requisite temperature and to provide the energy demanded for the reduction of ferric compounds to iron or to the ferrous state. As an alternative to supplying all of the heat deficiency by heating the incoming air, the air stream may be enriched by the addition of oxygen. The advent of the so-called tonnage oxygen process which is currently producing oxygen for an over-all cost of about five dollars per ton, has made such additions economically feasible. it is to be understood that the preheating of the incoming primary and secondary air or the enrichment of the incoming air with oxygen are not necessarily strictly alternative procedures, but may be employed simultaneously. In any event, conditions must be established which will dependably maintain the temperature of the interior of the burner well above the melting point of the particular slag being produced. It is further to be understood that the addition of more or less iron ore to the incoming fuel stream is a very potent tool for controlling the temperature of the reactor due to the highly endothermic nature of the iron reactions taking place within the burner. increasing amounts of secondary air will of course increase the temperature, but will hinder the iron reduction if employed in excess.

Any iron compound, usually an oxidic ore added to the fuel stream meets the same fate as that of the coal particles when solid fuel is employed. The ore particles will be entrapped in the viscous helically flowing slag stream and while so entrapped, subject to the reducing action of the ambient gases. The precise degree to which the reduction of the iron compounds is to be carried out in a cyclone burner will be dictated by the economic conditions obtaining at the particular installation under consideration. If coal is a primary fuel and such fuel is high in ash content, or if its iron content is low, it will probably be found to be more economical to maintain highly reducing conditions in the cyclone burner and reduce the bulk of the ore compounds to metallic iron since the high ash content of the coal would result in a slag more dilute in iron compounds than is desired for blast furnace operation. By completely reducing the iron compounds, the resultant molten iron may be separated from the supernatent slag by a simple gravity separation. This complete reduction necessitates an effluent gas containing substantial percentages of carbon monoxide and/or hydrogen and hence possessed of a high latent heating value. This gas should be burned immediately in a boiler or furnace setting adjacent the cyclone burner.

Under other circumstances as when coke is expensive, coal is cheap and blast furnace facilities are available, it may be more economical to permit the oxidation in the cyclone burner to be more complete and to discharge as a molten product either ferrous oxide or a mixture of ferrous and ferric oxides. If economical, burner conditions can readily be established and the thruput of the burner increased by discharging from the burner a molten oxide of iron carrying in suspension sufficient unconsumed but thoroughly coked fuel to give a product which may be charged into a conventional blast furnace without the addition in that machine of further coke for its reduction to pig iron.

It is desirable, if conditions anywhere within the cyclone burner are favorable to the production of elemental iron to limit the velocity of the helical flow of the gases to a value which will be insuflicient to elevate such elemental iron from the bottom of the' burner once it has formed there or descended there from other parts of the burner. A longitudinal trough running along the lowermost elements of the cylinder will assist materially in this separation. In this manner, the molten elemental iron will be protected from possible reoxidation by the supernatant layers of molten slag and unburned fuel and will promptly flow to slag discharge 16 and there be recovered. If necessary a separate tap hole 17' may be provided intermediate the ends of the cyclone burner for the recovery of either molten iron or lower oxides of iron if it is desired to protect such products from reoxidation prior to discharge from slag discharge 16.

By suitably proportioning the dimensions of the cyclone burner and regulating the velocity of gas therein it is possible to operate it with a region adjacent the inlet completely reducing even after the addition of some secondary air and then to add further along the burner tertiary air through inlet 18. When so operated, the heat released by the addition of the tertiary air will be transferred towards the inlet end of the burner very rapidly by radiation and will be available to supply the heat necessary for the reduction of iron compounds. By this procedure the amount of iron capable of being reduced by a given amount of fuel is increased. This is an economic advantage where there is a limited outlet for the latent heat of curnbustion of the gaseous products of the burner.

The cyclone burner may well be substituted for the conventional sintering process to condition finely divided ores for charging into a blast furnace or open hearth. Finely divided iron oxides are being produced in increasing quantities by the iron and steel industry. One fruitful source of such material is the flue dust produced in the normal operation of the blast furnace. As the quality of the iron ores available deteriorates, the amount of flue dust produced per ton of pig iron increases. Most of the beneficiating processes proposed to date for the utilization of ores too lean in metal values or siliceous to rich in silica for use in the blast furnace involve the crushing or pulverizing of the ores. Such pulverized products must be sintered or otherwise agglomerated before they can be used. When these pulverulent materials are treated in the cyclone burner, the operation may be conducted at any point on the oxidation-reduction spectrum that may be dictated by local economic conditions. If conducted in an oxidizing atmosphere, the pulverulent material is simply fused without reduction. However, with progressively stronger reducing atmospheres, the ferric compounds may be reduced to magnetite, or to a mixture of magnetite and ferrous oxide or even to elemental iron. As stated above, it is possible to also produce a mixture of reduced oxides and coke which may be directly charged into the blast furnace.

Throughout this specification the cyclone burner has been described as a cylindrical structure slightly inclined to the horizontal. However, it is to be understood that the invention contemplates other positions including hori zontal and vertical cylinders.

It is possible to produce an iron of the desired carbon content by regulating the amount of carbon present in the helically flowing slag and by adjusting the time of residence of the reduced iron in the cyclone burner. However, the carbon content in the final product is most economically regulated by completely reducing the iron and saturating it with dissolved carbon, and then through a separate opening introducing a stream of crushed iron oxide. This addition serves the double purpose of reducing the carbon content of the melt and reducing the iron oxide to metallic iron and hence enhancing the yield. Similarly, it is possible to produce an alloy of iron and any of the metals no more difficult to reduce than iron by the simple expedient of adding the appropriate metal or its compounds to the incoming stream of iron ore. Under some circumstances, substantial amounts of metals more dif icult to reduce than iron may be produced and alloyed with the product. As an example, if conditions within the burner are established highly reducing and the temperature is maintained well above that necessary to keep the iron in a molten state, silicon will readily reduce from the ores richer in silica.

The above discussion has been predicated primarily upon the use of a solid fuel which will furnish a slag or ash having a melting point which may be adjusted if necessary by the judicious addition of slag forming metals to give a slag of the proper melting point. However, it is equally possible to substitute for a portion or all of the solid fuel, either gaseous or liquid fuel or both, having the same thermal content. In the event a lean gaseous fuel is employed, provision must be made to preheat such gaseous fuel to a temperature sufliciently high so that the temperature in the cyclone burner does not fall below a point at which the liquid products will freeze. Depending upon the particular economic conditions obtaining at any given installation and at any particular time such a burner may be operated entirely upon solid fuel, entirely upon gaseous fuel, entirely upon liquid fuel or upon any mixture of these fuels which economic expediency may dictate. It is to be understood that since liquid and gaseous fuels are substantially ash free, suflicient slag forming ingredients should be added with the fuel-ore mixture to give slag having the desired melting temperature. Since the gangue in ore and the ash in coal is predominantly siliceous in nature, a most satisfactory flux would probably be limestone or burnt lime modified if necessary by fluorspar to reduce the melting point to the desired level. Again to avoid oxi dation of any iron which may be produced, it is necessary to limit the total of the oxidizing gases present in the process of combustion to the extent dictated by the equilibrium obtaining between such oxidizing gases and liquid iron. These oxidizing gases are commonly carbon dioxide and water vapor. It is not possible to set a definite numerical limitation upon the exact quantities of carbon dioxide and water vapor which may be permitted due to variations in the product desired from the furnace and variations in the ratio of carbon dioxide to water vapor. The desired oxidation level in the gas, at least in the reducing portion of the burner can readily be determined by experimentation with each individual burner.

I claim:

1. The process of burning fluid fuel comprising injecting tangentially at high velocity a stream of preheated oxidizing gas into a refractory lined cylindrical container, causing fluid fuel and subdivided metal bearing material to become entrained in the stream of oxidizing gas, producing a slag by the fusion of at least a portion of the metal bearing material, maintaining the temperature of the interior of the container sufficiently high to maintain all of the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxidizing gas so that at least a portion of the slag will describe a helical path along the periphery of the container, maintaining conditions within the container sufficiently reducing to lower the state of oxidation of the metallic compounds to the desired degree, tapping off the slag and reduced metallic compounds from the periphery of the container, ejecting the highly heated gaseous products of the reaction into a combustion chamber and then burning these gaseous products of combustion with a further addition of oxidizing gas before said gaseous products of combustion have substantially cooled.

2. The process of burning fluid fuel comprising injecting tangentially at high velocity a stream of preheated air into a refractory lined cylindrical container, causing fluid fuel and subdivided metal bearing material to be come entrained in the stream of air, producing a slag by the fusion of at least a portion of the metal bearing material, maintaining the temperature in the container sufficiently high to maintain all of the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of air so that at least at portion of the slag will describe a helical path along the periphery of the container, maintaining conditions within the container sufliciently reducing to lower the state of oxidation of the metallic compounds to the desired degree, tapping off the slag and reduced metallic compounds from the periphery of the container, ejecting the highly heated gaseous products of the reaction into a combustion chamber and then burning these gaseous products of combustion with a further addition of oxidizing gas before said gaseous products of combustion have substantially cooled.

3. The process of burning fluid fuel comprising injecting tangentially at high velocity a stream of oxygen enriched preheated air into a refractory lined cylindrical container, causing fluid fuel and subdivided metal bearing material to become entrained in the stream of oxygen enriched air, producing a slag by the fusion of at least a portion of the metal bearing material, maintaining the temperature of the interior of the container sufficiently high to maintain all of the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxygen enriched air so that at least a portion of the slag will describe a helical path along the periphery of the container, maintaining conditions within the container sufliciently reducing to lower the state of oxidation of the metallic compounds to the desired degree, tapping off the slag and reduced metallic compounds from the periphery of the container, ejecting the highly heated gaseous products of the reaction into a combustion chamber and then burning these gaseous products of combustion with a further addition of oxidizing gas before said gaseous products of combustion have substantially cooled.

4. The process of burning fuel comprising injecting tangentially at high velocity a stream of oxidizing preheated gas into a refractory lined cylindrical container, causing fuel and subdivided metal bearing material to become entrained in the stream of oxidizing gas, producing a slag by the fusion of at least a portion of the metal bearing material, maintaining the temperature of the interior of the container sufficiently high to maintain all of the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxidizing gas so that at least a portion of the slag will describe a helical path along the periphery of the container, maintaining conditions within the container sulflciently reducing to lower the state of oxidation of the metal bearing material to the desired degree, tapping off the slag and reduced metal bearing material from the periphery of the container, ejecting the highly heated gaseous products of reaction into a combustion chamber and then burning these gaseous products of combustion before they have substantially cooled.

5. The process of burning fuel comprising injecting tangentially at high velocity a stream of oxidizing preheated gas into a refractory lined cylindrical container, causing fuel and non-fuel subdivided metal bearing material to become entrained in the stream of oxidizing gas, producing a slag within the container, maintaining the temperature of the interior of the container sufliciently high to maintain all of the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxidizing gas so that at least a portion of the slag will describe a helical path along the periphery of the container, maintaining a level of oxidation Within the container corresponding to the oxidation level desired in the products of the container, tapping off slag and the molten metal bearing material from the periphery of the container, and ejecting the gaseous products of reaction from the container.

6. The process of burning fuel comprising injecting tangentially at high velocity a stream of oxidizing preheated gas into a refractory lined cylindrical container, causing fluid and solid fuels and non fuel subdivided metal bearing material to become entrained in the stream of oxidizing gas, producing a slag within the container, maintaining the temperature of the interior of the container sufliciently high to maintain all of the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxidizing gas so that at least a portion of the slag will describe a helical path along the periphery of the container, maintaining a level of oxidation within the container corresponding to the oxidation level desired in the products of the container, tapping off slag and the molten metal bearing material from the periphery of the container and ejecting the gaseous products of the reaction from the container.

7. The process of burning fuel comprising injecting tangentially at high velocity a stream of oxidizing preheated gas into a refractory lined cylindrical container, causing fluid and solid fuel and a non fuel subdivided metal bearing material to become entrained in the stream of oxidizing gas, producing a slag within the container, maintaining the temperature of the interior of the container sufliciently high to maintain all of the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxidizing gas so that at least a portion of the slag will describe a helical path along the periphery of the container, maintaining the interior of the container sufficiently reducing to lower the state of oxidation of the metal to the desired degree, tapping off slag and reduced metal from the periphery of the container and ejecting the gaseous products of the reaction from the container.

8. The process of burning fuel comprising injecting tangentially at high velocity a stream of oxidizing preheated gas into a refractory lined cylindrical container, causing fluid and solid fuels and a non fuel subdivided metal bearing material to become entrained in the stream of oxidizing gas, producing a slag within the container, maintaining the temperature of the interior of the container sufficiently high to maintain all of the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxidizing gas so that at least a portion of the slag Will describe a helical path along the periphery of the container, maintaining the interior of the container sufliciently reducing to lower the state of oxidation of the metal to the desired degree, tapping off slag and reduced metal from the periphery of the container, ejecting the gaseous products of reaction from the container and recovering the latent and sensible heat carried by these gaseous products of reaction. a

9. The process of burning fuel and agglomerating subdivided metal bearing material comprising injecting tangentially at high velocity a stream of oxidizing preheated gas into a refractory lined cylindrical container, causing fuel and non fuel subdivided metal bearing material to become entrained in the stream of oxidizing gas, maintaining the temperature of the interior of the container sufliciently high to maintain all of the products of the reaction except carbon in a fluid state, Water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxidizing gas so that at least a portion of the fused products of reaction will describe a helical path along the periphery of the container, tapping off the fused products of reaction from the periphery of the container and ejecting gaseous products of reaction from the container.

10. The process of burning fuel and agglomerating subdivided ferruginous material comprising injecting tangentially at high velocity a stream of oxidizing preheated gas into a refractory lined cylindrical container, causing fuel and ferruginous subdivided material to become entrained in the stream of oxidizing gas, maintaining the temperature of the interior of the container sufliciently high to maintain all of the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxidizing gas so that at least a portion of the fused products of reaction will describe a helical path along the periphery of the container, tapping off the fused ferruginous products of the reaction from the periphery of the container and ejecting gaseous products of reaction from the container.

11. The process of burning fuel and agglomerating subdivided ferruginous material comprising injecting tangentially at high velocity a stream of oxidizing preheated gas into a refractory lined cylindrical container, causing fuel and ferruginous subdivided material to become entrained in the stream of oxidizing gas, said fuel and oxidizing gas being introduced in approximately stoichiometric proportions, maintaining the temperature of the interior of the container sufficiently high to maintain all or" the products of the reaction except carbon in a fluid state, water cooling the refractory to protect it from attack by molten oxides, adjusting the velocity of the tangential stream of oxidizing gas so that at least a portion of the fused products of reaction will describe a helical path along the periphery of the container, tapping off the fused ferruginous products of the reaction from the periphery of the container and ejecting the gaseous products of reaction from the container.

References Cited in the file of this patent UNITED STATES PATENTS 861,593 De Laval July 30, 1907 885,766 De Laval Apr. 28, 1908 1,315,551 Hampton Sept. 9, 1919 1,490,012 Kapetyn Apr. 8, 1925 2,184,300 Hodson Dec. 26, 1939 2,357,301 Bailey Sept. 5, 1944 2,530,078 Ramsing Nov. 14, 1950

Claims (1)

1. THE PROCESS OF BURNING FLUID FUEL COMPRISING INJECTING TANGENTIALLY AT HIGH VELOCITY A STREAM OF PREHEATED OXIDIZING GAS INTO A REFRACTORY LINED CYLINDRICAL CONTAINER, CAUSING FLUID FUEL AND SUBDIVIDED METAL BEARING MATERIAL TO BECOME ENTRAINED IN THE STREAM OF OXIDIZING GAS, PRODUCING A SLAG BY THE FUSION OF AT LEAST A PORTION OF THE METAL BEARING MATERIAL, MAINTAINING THE TEMPERATURE OF THE INTERIOR OF THE CONTAINER SUFFICIENTLY HIGH TO MAINTAIN ALL OF THE PRODUCTS OF THE REACTION EXCEPT CARBON IN A FLUID STATE, WATER COOLING THE REFRACTORY TO PROTECT IT FROM ATTACK BY MOLTEN OXIDES, ADJUSTING THER VELOCITY OF THE TANGENTIAL STREAM OF OXIDIZING GAS SO THAT AT LEAST A PROTION OF THE SLAG WILL DESCRIBE A HELICAL PATH ALONG THE PERIPHERY OF THE CONTAINER, MAIN-

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