US1338439A - Metallurgical method and apparatus - Google Patents

Description

a. F. GREENWOOD.

METALLURGICAL METHOD AND APPARATUS.

APPLICATION FILED lULYl9,1-918.

Patented Apr. 27, 1920.

2 SHEETS-SHEET I.

G. F. GREENWOOD.

METALLURGICAL METHOD AND APPARATUS.

APPLICATION FILED JULY 19, 1918.

' 1,338,439. Patented Apr. 27, 1920.

2 SHEEISSHEE1 2.

a vwewtoz W '3 $3M imme I UNITED STATES PATENT cur os.-

.GUYON I. GREENWOOD, OF GEORGEVILLE, QUEBEC, CANADA.

METALLURGICAL METHOD AND APPARATUS.

To all'wlwm it may concern:

.' Be it known that I, GUYoN' F. GnnEN improved method and system for roasting, v reducing and refining oxid, carbonate and other ores, the making of coke and similar' processes.

The object of my invention is to greatly" reduce the amount of coal or carbon required per ton of metal, to improve'the quality of the metal reduced, to reduce-thecost of the required plant, its maintenance and the labor cost of the product and to materially increase the by-product value.

It has been shown experimentally that "there are certain pressures and temperatures of the equilibria phenomenon occurring in the reduction of oxid ores ifsufiicient solid carbon is present, such that substantially any carbon dioxid produced or present will [disappear and take the form of carbon 7 monoxid where 'the reduction is carried on with exclusion of air, and I have therefore designed and constructed a furnace which will perform the required mechanical operations and maintain the pressure and temperatures indicated as necessary.

The first requirement for high efiiciency in this reduction system is the substantial elimination of carbon dioxid and the sub-' stitution of carbonmonoxid, as the gas resulting' from. the reaction, This is especially true Wit'lldI'OIl oxids, and holds with I the others also, while for any other similar purposes the value of my improved furnace will readily beseenfrom the following detailed description. Before describing in detail, the method and apparatus involved in this invention, I shall briefly refer to present practice in the iron and steel industry, so that a better conception of the improvements contemplate-d will be gained.

In general it may be statedthat the entire production of iron frornore in this country at the present time, starts'with the production of pig iron in the blast furnace, the

furnace being chargedwith a'mixture of ore, carbon in some form, and a flux, usually in the form of llme-orlimestone." The car- Speeification of Letters-Patent.

Patented Apr. 27 1920.

Application filed July 19, 1918. SeriaINo. 245,692.

bon serves as reducing agent and as fuel I for generating the required temperature and supplying the chemical heatunits involved twyers to maintain combustion of the fue1- for generating the heat as described. The

materials charged into the blast furnace must be in the form of lumps of suitable size and dimensions to permit the passage of gases upwardly through the furnace, and the depth or height of the charge must be sufiicient to provide the necessary space for progressive chemical actions between the gases and the charge as the gases pass upwardly through the same. Furthermore, the height of the furnace is prescribed or determined by considerationsof heat economy and pressure due to weight ,'of the column of charge so as to feed properly by gravity. The result has been the development of blast furnaces along the lines of relatively great dimensions involving, the

treatment of a large quantity of charge at blast furnace remains the approved and universallyr employed device for reducmgthe 90 a ore.

The gases comingfrom the blast furnaee contain carbon monoxid, carbon diojriid, n1- trogen, and other components. The more carbon dioxid present in the waste gases, the

greater is the fuel and heat efficiency presumed-t0 be. The combustion of carbon being an exothermic chemical action, not only in the stage of-carbon to carbon monoxid, but also from the carbon monoxid to carbon dioxid, it is obvious that the pres cenceof carbon dioxid represents two quantities of chemical heat units, whereas carbon monoxid represents but one. On the other hand, the carbon dioxid is reducible by lIOIl to carbon monoxid, so that the presence of the former under-certaintemperature conditions, where reduced iron is also present,

has the tendency toreoxidize the iron. The result is that the blast furnace practlce recognizes a zone condition where these gases, on their passage upward through the charge, are reacting with the charge perhaps several times one way or the other.

My invention provides an economical furnace and method for reducing oxid ores economy of fuel is gained, and a much better control of the purity of the product is assured, while at the same time the relatively complex and expensive blast furnace installation is entirely avoided. Furthermore, the furnace can be run with crushed or ground ore taken from the run of the mine and crushed or ground coke or charcoal, instead of requiring lumps of particular dimensions as in the blast furnace.

The principle of the invention involves the recognition that economy and certainty of operation are gained by limiting the supply of carbon to substantially that required as a reducing agent, and excluding air from the reduction step. 'Due to the exclusion of air, and the regulation of the temperature and pressure in the reducing chamber, the resulting gases are so regulated as to be constituted almost entirely of carbon monoxid undiluted with carbon dioxid or nitrogen, with the result that a highly advantageous form of fuel for generating electrical power is thus provided, and this power is employed in maintaining the necessary furnace temperature for conducting the reduction operation.

So far as I am awareit is broadly new to operate a reduction furnace under exclusion of air, and with control of the temperature and pressure, whereby the generation of a highly e'flicient fuel gas, free from nitrogen and carbon dioxid is secured in suflicient quantity of a quality that will provide the power to produce the necessary quantity of electrical energy for supplying the heat required in the reducing step.

To make the invention clearly understood, I shall describe a specific embodiment thereof, in connection with the accompanying drawing, in which,

Figure 1 represents diagrammatically a system involving the reduction drum, poiver plant and fusion and refining furnace;

Fig. 2 is a longitudinal sectional detail of a preferred construction of reduction drum, involving an electrical resister;

Fig. 3 is a detail, perspectively, of a portion of the resister to be incorporated in the lining of the reduction furnace.

Fig. 4 is a diagram of a system including a coking furnace.

WVe may consider a case in which the invention is applied, for example, to the reduction of hematite iron ore, previously crushed or ground, and preheated to a tGII1- perature of about 600 C. and suitable quantities of some form of carbon to serve as the reducing agent and a flux to act as a catalyzer and purifier. This mixture is introduced through the feed bell or hopper 10, and passes through the neck 11 into the rotary drum 12. Any approved type of union 13 is assumed to be provided for connecting the stationary neck 11 with the rotary drum proper 12, and, similarly, a union 1% permits the discharge of the reduced material through a discharge neck or chute 15, provided with bell valve 16. The drum 12 is set at a suitable inclination and is provided with flanges 17 which run on rollers 18, journaled in standards 19. A gear collar 20 meshes with a pinion 21 which is driven through suitable power connections so. as to slowly rotate the drum 12 upon its longitudinal axis. The drum is lined, as indicated at 22, with suitable refractory material, such as magnesite brick or burnt magnesite, in which is embedded a helical resister 23, which may advantageously have the cross sectional form of a trapezoid, the base of which is flush with the inner wall of the furnace lining, so that the resister, due to its shape, assists in holding the lining in place, but does not cause any obstruction to the free passage of the charge of ore, carbon and flux through the furnace. Mechanically considered, the drum represents a rotary device by which the charge is caused to slowly progress, from one end to the other, over the turns or convolutions of a heating resister element, the travel of the ore being caused'by the inclination of the drum and its rotary motion, which is continuously raising and tumbling the charge, thus thoroughly mixing and distributing the constitutent parts. Electrically considered, the rotary drum constitutes an electric furnace, of the resister type, in which the resister is in the form of a helical conductor through which a current is passed and by which a desired quantity of heat is produced, while, at the same time, it serves as a means for introducing current through the charge from one convolution to the next, the bridging particles of charge shunting a large portion of the current through the short circuit thus established, which greatly facilitates and renders verv uniform, the heating action. The electrical action is thus complex in its nature, part of it being represented in simple production of heat by the flow of current against the resistance of element 23, whereas an addi tional heating function takes place in the short circuit current passing through the charge, from one convolution to another. As the ore becomes more and more reduced its conductivity increases, so that the short circuit effect tends to develop progressively in the drum from the receiving end toward the discharge end. At the same time, however,- the temperature coelficient of thereduc'ed metal causes a decrease in conductiv- 5 ity with increased temperature, so that the short circuit effect is automatically controlled by. the chemical action as it progresses. The result of this complex action is that the operator is enabled, by suitable regulation of the current passing through the resister, to thus indirectly control the temperature and assure the desired'chemical action. For the purpose of supplying current to the resister-23', a terminal 24, 'is connected with the resister at one end, being inserted for example in an insulating bushing 2 1 mounted in the drum wall and lining. A similar terminal may be employed at the other end of this coil. Itis preferable, but not essential to have the entire coil connected in series relation throughout its entire length rather than to have it subdivided electrically into parallel portions. The terminals 24 are in the present example elec 25 trically connected with slip rings 25, mounted on the outer wall of the drum 12 and engaged bybrushes 26, which are electrically connected through conductors 27, 28, with the terminals 30, of a dynamo electric machine 31 of suitable power. The dynamo 31 is, for example, driven by shaft 32 of gas engine 33. This engine may be of any desired type. The engine is shown purely in diagrammatic form and is intended to re- 35 ceive its gas through intake pipe 35 and discharge its exhaust through pipe 36, which is .here shown as being delivered through the incoming charge of materials going to the reduction furnace, for preheating the same.

Mixed with air, in any approved manner, the gases drawn through the outlet 37 from drum 12 and freed from dust in the dust collector 38, constitute a valuable fuel mixture, as will be more apparent upon detailed consideration of the chemistry involved in the reduction operation taking place within .drum 12. V The drum 12 has approximately air tight .connection with the feeding in and discharging conduits, so that the suction action of the engine 23 has the effect of maintaining a reduced pressure within the drum and as fast as carbon monoxid is produced by the reduction of the ore with the solid carbon, this carbon monoxid is withdrawn and taken in by the engine as fuel for generating electrical power. The

production of carbon monoxid depends solely upon the chemical combination; of the solid carbon and the oxygen of the ore, when these elements are brought together at a temperature and under a pressure within the limits of variation that eliminate carbon dioxid and facilitate the production of carbon monoxid. By maintaining the tempera- O ture at about 750 C. and the pressure somewhat below-atmospheric,"conditions favorable to the production of monoxid are assured and the production of carbon dioxid substantially ceases. The constant with- 7 drawal of gas as fast as it is produced, gives the required reduction of pressure, removes the carbon monoxid rapidly away from exposure to any iron oxid, and thus further tends to avoid forming the dioxid, or reoxidizing the metal. It is evident that any suitable form of rheostat R in'the circuit with the resister 23 will give adequate control of the temperature within the reduction drum. The pressure within the re- I duction chamber may, for example, be controlled by the speed of the engine 33.

With regard to the chemical heat units, the heat generated in the production of carbon monoxid is less than that consumed in reducing the iron oxid. These heat units may be seen from the following formula and tables; in which a temperature of 15 C. is assumed, for simplicity.

The reaction represents a deficit of 108,120 heat units. In order to make up this deficit and to balance extraneous heat losses such 5 as radiation, etc., electrical energy is consumed in the resister furnace. The tendency of the chemical action to result in .a reduction of temperature enables the operator to control the temperature at the desired point 0 by supplying heat through electrical power. Theoretically, the heat required for the chemical action to continue without change of temperature is shown by the above equation to be 108,120 calories. The combustion of carbon monoxid to carbon dioxid in the gas engine theoretically renders available nearly twice the quantity of heat electrically required to maintain the reduction action in the resister furnace, as indicated by the following:

' 3OO+3OI3CO or 3 (00,0) =2o4,120

' and the total heat produced is 291,600, thus leaving an excess of 96,000 heat units.

The gas engine, or for example, the Diesel type injects the carbon monoxid gas into the compressed air within the cylinder, developing mechanical power from the available heat energy of the reaction. The electrical generator being on the same shaft with the gas engine translates its mechanical energy into electrical energy and supplies it to the electrical heating element, namely, the helical coil 23 within the rotary drum 12.

In addition to the reaction between iron oxid and carbon, taking place within drum 12 there are further reactions which must be provided for in figurin the quantity of carbon in the mixture. The ore contains, for example, in many instances, compounds of manganese and of magnesium and can be readily figured by the skilled metallurgist and taken care of in making up the proportions of the ingredients which go into the charge. The present invention is not directed particularly to these additional details and it is thou ht the above description of the reduction of iron oxid will suffice to make the invention clear. I

With regard to the flux introduced with the charge, it is, of course, obvious that either limestone or burnt lime may be used; but in one case heat units represented in driving off carbon dioxid from the carbonate and reducing the carbon dioxid with carbon, would have to be figured in the re,- duction furnacevoperation, whereas in the other they are already supplied prior to the reduction. The charge is not fused in the reduction furnace, but is delivered through the discharge passage 15 into some suitable form of fusing and refining furnace, (represented diagrammatically in the form of an electric furnace 39.)

In this furnace the charge is melted, the impurities slagged off and the reduced molten metal obtained. This final treatment of the reduced ore does not, in itself, constitute a feature of the present invention and need not be described in'detail, especially as it will vary considerably according to the particular requirements of each case.

The heat units roughly indicated to be available in the above comparisons are of course, not all recoverable. in practice. The efficiency of the engine, for instance, will determine what percentage can be actually secured. I do not, therefore, want to be limited to complete dependence upon'the heat units available from combustion of the gas from the reduction drum. I may desire to use outside power to make up any difference which may appear due to inefficiency of the engine. referably, however, where it is desired to make the system entirely independent of outside electric power, I'may carry out the invention as shown diagrammatically in .Fig. 4.

In 4, the numeral 40 designates a coal supply bin or hopper, from which coal is fed to a rotary drum furnace 41, similar to the reducing furnace 12, where it' is electrically heated, with exclusion of air, to drive off a combustible gas" and produce coke. The gas is withdrawn through pipe 42, and scrubber or tar remover 43 and enters the engine 44 where it is mixed with air and burned to generate electrical power as by means of the dynamo 45 mounted on through a branch circuit 48-49 containing rheostat 50, to the heating member of furnace 41.

Coke from furnace 41 is delivered, with ore and flux from hopper or bin 51, into the electrical heat drum 52 similar to that already described. This furnace is supplied with heating current from line wires 46--47, by branch circuit 5354, containing a rheostat 55. Air is excluded from drumi 52, and reduction of the oxid ore with carbon is conducted at a temperature and pressure at which carbon monoxid gas is obtained, practically free from carbon dioxid. This substantially pure carbon monoxid is withdrawn and taken into an engine 56 which is shown by way of example in the diagram as operating upon the same crank shaft with engine 44, thus also generating electric power bymeans of the dynamo 45. Exhaust gases from engines 44 and 56 may be used for preheating the coal and the mixture of ore and flux, the exhaust pipes 5758 being indicated as leading to the respective hoppers or bins.

The reduced metal and flux, according to the embodiment shown, is delivered from 2. A method of reducing oxid ores which i comprises reducing the oxid by means of carbon and heat w1th exclusion of,a1r, at a temperature and pressure less than atmospheric favoring the production of carbon 7 monoxid,-removing the carbon monoxid and burning it to carbon dioxid, and utilizing the available energy of the reaction to develop and supply an electric current for furnishing heat to the reduction operation.

' 3. A method of oxid ore reduction comprising the reduction of the oxid by means of carbon and heat with exclusion of air at a temperature and pressure less than atmospheric that will substantially avoid formation of carbon dioxid and the consequent partial reoxidation of the ore or parts thereof, but will facilitate the production and removal of carbon monoxid, removing and burning it to carbon dioxid and utilizing the available energy of the reaction to deduction operation.

5. A method of reducing oxid ores which comprises advancing a mixture containing oxid ore and carbon in heat conductive relation with an electrical heating element while excluding air, and continuously withdrawing the resultant carbon monoxid from the locus of reaction.

6. A method of reducing oxid ores which comprises advancing a mixture containing oxid ore and carbon in heat conductive relation with an electrical heating element while excluding air, withdrawing the resultant carbon monoxid gas from the locus of reaction and burning it with air in a gas engine, translating the available heat energy thereof into electrical energy, and utilizing the electrical energy for supplying said'heating element.

7. A method of reducing oxid ores which comprises advancing a mixture containing oxid ore and carbonin heat receptive rela-v tion with an electrical heating element while excluding air, withdrawing the re-i sulting carbon monoxid gas and burning it with air in a gas engine, utilizing the resulting mechanical energy to produce electrical energy for supplying'said heating element, and using the sensible heat of the exhaust from said engine to preheat the said oxid ore. r

8. In a system of reducing oxid ores the combination of a reducing element constructed to reduce the oxid ore by means of ,carbon and heat with exclusion of air at a temperature and pressure less than atmospheric that Will facilitate the production and removalof carbon monoxid gas, a gas engine actuated by said gas, and an electric generator driven by said enginefor generating heat 'ijor said reduction operation.

-9. In a sy'stcm ofreducing oxid ores the' combination of a reducing element which vreducesthe oxid ore by means of carbon and 'heat with exclusion. of air and at less than atmospheric pressure'in such manner that substantially pure-carbon monoxid .gas is given off by the reaction, a gas engine actuated by'burning sa1d gas with a1r, and means for preheating said oxid ores from the exhaust of said gas engine.

.' 10. A method'of reducing oxid ores which comprises" reducing the oxid by means of carbon and heat with exclusion of air, regulating the temperature and pressure within the limits required to produce carbon monoxid and substantially avoid the forma tion of carbon dioxid, removing said carbon monoxid, burning it to carbon dioxid, and

utilizing the energy of the reaction to de-.

velop and supply heat to the reduction operation.

11. In a system of reducing oxid ores the combination of a reducing element constructed to reduce the oxid by means of carbon and heat with exclusion of air, at a temperature and pressure less than atmospheric that will facilitate the production and removal'of carbon monoxid gas, a gas engine operated by said gas, an electrlc generator' actuated by sa1d englne, means for preheating said ore by the exhaust from said gas engine and an electric refinin furnace operatively connected to said re ucing element and said electric generator.

12. A system of reducing oxid ores electro-thermally with exclusion of air, in which carbon or ore or both act as a conductor for the heating electric current and are heated largely by the passage of said current through them, in combination with automatic means 'for maintaining the delivery of carbon monoxid gas-therefrom.

13. In an electro-thermal system of re ducing oxid ores'by means of carbon and heat, the combination of a source of electrical energy, a reducing element constructed to receive the ore and carbon and provided with electrical heating means for heating the ore and carbon largely by passing an electric current through them, said ore and carbon acting as an electrical conductor therein, and means in said reducing element adapted to independently maintain the flow .of electric current and consequent heating in case of an open circuit or partial open circuit in any part. of the body of said ore and carbon.

14:. A method of reducing oxid ores comprising rotating a 1. etort having an electrical heating element therein, passing a suitable -mixture of .ore and carbon therethrough and heating said mixture by said electrical heating element so as to produce the metal of the ore, "carbon monoxid gas and the residuum.

15. A method of.reducing-oxid ores comprising rotating a retort having an electrical heating element therein, passing a suitable mixture of ore and carbon therethrough and heating said mixture by said electrical heating element with exclusion of air so as to produce the metal of the ore, carbonmonoxid gas and the residuum.

16. Apparatus for reducing oxid ores with carbon and heat, comprising a rotatable receptacle for said ores, an electric heating element associated with said receptacle, and means for deriving from the carbonaceous gas, resulting from such reaction, an electric current for energizing said heating element.

17. The method of reducing ores, which comprises advancing a mixture containing the ore and carbon across and in contact with successive portions of an electrical heating element, While excluding air, and continuously withdrawing the resulting carbonaceous gas.

18. The method of reducing oxid ores which comprises advancing a mixture containing ore and carbon across and in contact with successive portions of an electrical heating element, while excluding air, continuously withdrawingthe resultant carbon monoxid gas from the locus of reaction, burning it with air in a gas engine, translating the available heat energy thereof into electrical energy, and utilizing the electrical energy for supplying said electrical heating element.

. bon monoxid gas from the locus of reaction,

burning it wlth air in a gas engine, trans-' lating the available heat energy thereof into electrical energy, and utilizing the electrical energy for supplying said electrical heating element.

20. The method of reducing ores which comprises continuously feeding and tumbling a mixture containing finely divided ore and carbon in the form of a relatively shallow body through and in contact with a rotating helical electric heating element, while excluding air, continuously withdraw-- ing the resultant carbon monoxid gas from the locus of reaction, urning it with air in a gas engine, translating the available heat energy thereof into electrical energy, and utilizing the electrical energy for supplying said electrical heating element.

21. The herein described metallurgical process which comprises electrically heating coal with exclusion of air to produce combustible gas and coke, burning the gas to produce electric power, and utilizing the coke for reducing ore.

22. The herein described metallurgical process which comprises electrically heating coal with exclusion of air to produce combustible gas and coke, mixing the coke and ore, electrically heating the mixture with exclusion of air to reduce the ore while again generating combustible gas, and burning the gas from both sources to produce electric power for the system.

23. The herein described metallurgical process which comprises electrically heating coal with exclusion of air to produce combustible gas and coke,'mixing the coke and ore, electrically heating the mixture with exclusion of air to reduce the ore while again generating combustible gas, electrically refining the metal, and burning the gas from both sources to produce electric power for the system.

GUYON F. GREENWVOOD.

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