US2805142A

US2805142A - Method for the production of pure iron, and iron carbon alloys including carbon and alloy steel

Info

Publication number: US2805142A
Application number: US409217A
Authority: US
Inventors: Arata Vincenzo Stefano
Original assignee: JAMES E BRASSERT
Current assignee: JAMES E BRASSERT
Priority date: 1954-02-09
Filing date: 1954-02-09
Publication date: 1957-09-03
Anticipated expiration: 1974-09-03

Description

Sept. 3, 1957 v. s. ARATA METHOD FOR THE PRODUCTION OF PURE IRON. AND IRON CARBON ALLOYS INCLUDING CARBON AND ALLOY STEEL 3 Sheets-Sheet 1 Filed Feb. 9. 1954 FIG.

ATTORNEYS Sept. 3, 1957 v. s. ARATA 2,805,142

METHOD FOR THE PRODUCTION OF PURE IRON, AND IRON CARBON ALLOYS INCLUDING CARBON AND ALLOY STEEL Filed Feb. 9, 1954 3 Sheets-Sheet 2 v INVENTOR. Vincenzo 8. Arch:

"MM uwgm mam S um a ATTORNfiXS V. SYARATA Sept. 3, 1957 2,805,142 METHOD FOR THE PRODUCTION OF PURE IRON, AND IRON CARBON ALLOYS INCLUDING CARBON AND ALLOY STEEL 3 Sheets-Sheet 3 Filed Feb. 9, 1954 "HI HI Vincenzo S. Arafu ATTORNE S Unite Stats METHOD FOR THE PRODUCTIQN F PURE IRGN,

AND IRON CGN ALLDYS iNCLUDlNG CAR- EON AND ALLSY STEEL Vincenzo Stefano Arata, New York, N. 1., assignor to James E. Brassert, New York, N. Y.

My present invention relates to the commercial production of pure iron and iron-carbon alloys, including carbon and alloy steel, directly from ore and carbonaceous material. In using the terms directly or direct process in the succeeding text, I mean that the process does not involve the production and handling of intermediate materials such as coke and pig iron, and that the iron or steel is produced directly in the molten state.

In the past, single charges of ore and carbonaceous reducing agent have been converted into steel in the electric furnace, but the methods that have been used up to now have had one of two principal disadvantages which have prevented their coming into general use. The first of these has been'the high estimated capital and operating costs of full-scale plants of this type. These high estimated costs have in turn been due to the operation of the plant purely on a batch process. The salient factor contributing to high estimated operating costs has been the high power consumption of 2500 kwh./metric ton or more and similarly the largest factor in capital cost has been the high cost of power-generating facilities for a given annual steel ingot capacity. These factors have tended to discourage the installation of plants employing the direct process in many localities.

My present invention embodies a method of treatment whereby power consumption can be decreased one-third to one-half resulting in a decrease almost as great in total cost, and a proportionate decrease in capital cost of generating facilities. Furthermore, according to my present invention, steels can be produced to the required analyses on a regular basis with a minimum number of olf heats.

According to one method for the production ofpure iron, of my invention as disclosed in United States Patent No. 2,747,985, the ore is finely crushed and intimately mixed with the required flux and with a determined quantity of finely divided carbonaceous reducing material. This quantity is determined so that after allowing for carbon lost in the flue dust escaping with the top gases, sufficient carbon is left in the charge to reduce between 60 and 90 percent of the iron content of the charge as calculated stoichiometrically. I normally use the following equations for this type of stoichiometric calculation:

In the production of steel in contrast to the production of pure iron, I determine the quantity of carbon charged analogously, except that I provide sufficient carbon to reduce approximately 85-100 percent of the iron content of the charge. According to my previous method of operation, all of the materials were charged, melted, and refined batchwise in the electric furnace, and the manner of accomplishing this together with a physical and chemi-. cal description of the process is described for the case of pure iron in the above-mentioned patent application. The production of steel is analogous except for the differ ences in carbon content of the charge noted above.

Numerous attempts have been made in the past to make the direct process fully continuous, in order to reduce capital and operating costs. I have found in many years of practice that fully continuous production is inconsistent with regular analysis and reliable quality of steel produced. Therefore the present process can be considered to be a batch process with respect to the refining period and to the cycle of a single electric furnace, but it can be considered to be continuous with respect to the charging of raw materials and the production of steel in the plant as a whole, as well as with respect to the utilization of gas from each individual furnace. The elements of the plant are connected in such a way that the operation of the preheating chambers is continuous, and the effect of the preheating (and partial reduction) step is to decrease power consumption from 2500 kwh./ metric ton to 2000 kwh./metric ton or less. My process therefore involves a number of electric furnaces and a number of preheating chambers. With respect to the flow of solid materials, each electric furnace is connected in parallel with at least one other electric furnace and in series with at least one preheating chamber. With respect to the flow of gas, the same is true, except that in the majority of cases all of the electric furnaces will be in parallel with each other and in series with all of the preheating chambers, which in turn will be parallel with each other.

Before describing the operation of my process by a concrete example, it may be advisable to point out several ways in which the carrying out of my process will deviate from and represent an improvement upon 'past methods of conducting the direct process.

First, in the making of steel from ore and carbonaceous material by the direct process, the most critical period is the refining period during which the heat is adjusted with respect to its final carbon content, and the sulphur and phosphorous contents are brought down to the correct levels. Most coals contain appreciable sulphur and this element is alway the most diflicult to eliminate in the direct process. This is due to the fact that the direct process employs a slag high in FeO and the elimination of sulphur requires a strongly basic slag low in FeO. Therefore, frequently it is necessary to remove the first slag and replace it by a strongly basic slag rather low in FeO. This procedure cannot be efficiently or reliably carried out while excess carbonaceous material (usually coal or coke) remains on top of the slag, as has been attempted in the past, since the removal of the first slag would bring the carbon of the coal in contact with the metal and carburizc it so that the steel would not show the correct tapping analysis in carbon. Therefore it is not feasible to charge excess carbon to the furnace and still maintain a regular and controlled analysis of the steel produced. Accordingly, in my process, after allowing for carbon lost in the flue dust and for carbon going into the steel, 1 only charge sufficient carbon to reduce -100 percent of the iron content of the raw materials, and I conduct the refining process batchwise so as to provide the opportunity to charge a second slag for removal of impurities, including sulphur and phosphorous.

Second, if it is attempted to produce steel continuously in the electric furnace by continuously charging fresh materials, it will be impossible to refine the molten metal into steel in the same furnace; this is due to the difficulty of separating the metal being refined from the incoming material. The incoming, impure materials tend to increase the oxygen and sulphur contents of the metal bath, to introduce dirt and other contaminants, and to vary the analysis of the product. Such continuous operation has been tried in the past, and has re sulted in irregular analysis of the steel produced. There fore, in the present invention the charging cycle of 3 each furnace is discontinuous and represents only a portion of the total heat time, and the refining is carried out batchwise.

Third, those furnaces, which'have operated continuously to produce steel by the direct processhave been required to hold high temperature slags and iron continuously and this has resulted in high refractory losses and frequent breakouts, which have seriously inter rupted operations and in many actual cases rendered the process impractical. According to my cycle of operation, a portion of every cycle of each furnace after each heat is allocated for repairingthe walls and the bottom of the furnace, as is normally done in a batch process; this gives the operator time to anticipate and prevent costly breakouts and to maintain a satisfactory furnace lining. Furthermore, in ,my cycleof operations, which lasts normally five hours, the reduction operation requires approximately four hours, and during this period only the locations adjacent to the arcs are at high'temperature. Accordingly, reduction proceeds throughout the greater part of the charge'at temperatures less than 1200510., and the walls and roof remain .Only during the refining period, which requires about half an hour of the total cycle, is the temperature 'of the materials adjacent to the walls raised above the-melting temperature of steel. Thisfactor has such an important bearing on the life of the lining as to spell Ethedifierence betweenfeasibility and non-practicability of the direct steel process, and it is a basic feature of my-present invention.

. I will now give a description 'of a typical plant in which the electric furnaces are operated in parallel and according to a definite cycle, in order to give a clear picture of its operation.

Such a plant will consist of a number of units, as hereinafter more specifically defined, each unit including as elements electric furnaces connected in series with one or more preheating chambers. The purpose of the preheating chambers is to preheat and in most cases also to partially reduce the ore. In all cases, the electric furnaces of eaclr unit Willbe connected in parallel with each other with respect to the flow of gas and of solid materials, and the preheating chambers of each unit will be similarly connected in parallel with each other. The preheating (partial reduction) chambers in each unit may be of var-ions types (for example, rotary kiln or shaft furnace) and may function differently with respectto their physical and chemical treatment of the raw materials. For example, each unit may'include'two parallel sets of kilns ofwhich .each'set is made'up of two kilns in series so that preheating and roasting of the ore and a degree of coking of the carbonaceous material (by which a large portion of the volatile materials is rapidly eliminated) take placein the'first kilos of the series, while partial reduction and additional Ipreheating take place in the second kilns of the series. However, partial reduction and preheating in the second kilns should never go so far as to result in sintering of the iron-containing materials, i. e., in practice the temperature of the material leaving the second kilns should be600-1000" C. In other plants operating with different types of carbonaceous reducing agent, the individual units may consist simply of one or two parallel kilns into which are charged properly prepared iron'ore and carbonaceous material and which discharge in parallel into a battery consisting of at least two electric furnaces.

The preheating chambers should preferablybc so designed as to permit regulation of the-residence time of the charge materials passing through them so that the discharge cycle. of materials from the preheating chambers into the electric furnace is not rigidly determined by the charge cycle of the same materials into the chambers. This feature enables the charging and discharging of the several preheating chambers tobe relatively inde pendent of one another and more flexibly adaptable to the electric furnace cycle.

For example, in case the preheating chambers consist of rotary kilns, such regulation can be accomplished by providing control of either the degree of tilt of the kilns or of their rate of rotation, or both.

The number of units in a large plant is of course adapted to the production requirements of the entire plant without'departing from the principles followed in a small plant or in an individual unit. It should also be stated that although, with respect to the flow of materials, only the furnaces and preheat chambers in .a single unit may be in parallel with each other, with respect to the flow of gas, all of the furnaces in the entire plant are preferably connected in parallel, and the same holds true for all of the preheat units with respect to the flow of gas.

Each individual unit may consist of at'least two and possibly more electric arc furnaces'with carbon or graphite electrodes preferably of the Soderberg type. The furnaces may be either of the conventional cylindrical type or rectangular or of any convenient shape; they may be either tilting or stationary. They need not be-arc furnaces since I may also perform my present invention with other types of electric furnace.

I shall now explain my invention in detail with respect to one specific embodiment thereof selected by way of example and with reference to the accompanying drawings in which:

Fig. '1 is a schematic plan view, partly in section, of a unit for carrying out my process;

Fig. 2 is a schematic end view, partly in section, of the unit .shown in Fig. 1;

Fig. 3 is a schematic side view, partly in sectiomof the unit ,shown'in Fig. 1;and

Fig. 4'is a graphical representation of timing relationships between different phases of the operation of the unit-shownin Fig. 1.

Figs. .13, inc., show a single pair of rotary kilns, 2 and 2 operating in parallel with each other and in series with a single pair of electric furnaces, 10 and 10'. This combination represents one of the simplest methods of carrying out my process. In Fig. 1, horizontal screw conve'yors 1 and 1 charge the material continuously into chutes and from these chutes through passageways into kilns 2 and 2'. Such passageways should always be kept full of charge material so as to maintain a seal preventing the escape of the gases which pass through the kilns. After partial reduction and preheating in the

kilns

2 and 2 arecomplete, the materials pass into a common hopper 4 which, as shown in Fig. 2 has two exits, 5 and 6, each with it own valve. The chute passing out'of exit5 in turn diverges, as shown in Fig. 3 into two chutes, 7 and 8, also provided with individual valves, and through these chutes the materials fall into furnace 10. The passage of materials through exit 6 into furnace 10 is entirely analogous, through chutes .7 and 8'.

With respect to the flow ofgas, uptakes 11, provided with appropriate valves convey the gas evolving from reduction taking place within furnace 10 into collector main 9. Uptakes 11' similarly connect furnace 10 to collector main 9 which is common to both of the furnaces. (In case there are more than two furnaces in the unit or in' the plant as a whole, collector main 9 should be common to "all of the furnaces. In a'ny'c'ase the furnaces 'are operated in cycle so as to maintainas nearly "as possible a steady flow or gas for use elsewhere "in the plant.) According to my process it'must be possible to'shut on the chambers 2 and 2' by means of valves in the passagewaysl3 and 3' between collector main 9 and thelcharnbers. Thiss e stt 1 1 Rmat s-t a n th sn fiq ias of my process, which permits operating a number of preheating (and partial reduction) chambers in parallel with each other and in series with a number of electric furnaces also operating in parallel with each other. Any chamber or furnace unit should be separable at will from all of the other units comprising the whole, with respect to the flow of both solids and gases. All of the units of the plant should operate under a slight superpressure which is maintained by valves in passages 11, 11', 3, 3', or by equivalent valves located, for example, in collector main 9.

In certain cases it might be desirable to maintain combustion in the kilns by adding air. Such air injection is carried out by means of

injectors

15 and 15 which conduct air to act as a combustion medium for the gases in

passages

3, 3; the flame can of course be regulated to be more or less oxidizing. The gases are exhausted from the rotary kilns 2, 2' through a common passageway 16, and part of the gases may be recycled into collector main '9. Because of the high temperature of the gases leaving the

electric furnaces

10 and 10, passageways 11 and 11, '9, 3 and 3' must be provided with suitable refractory linings.

Fig. 4 is a diagram illustrating a particular method of operating a plant according to my process. The diagram refers to a plant unit having two electric arc furnaces in parallel with each other which are fed by two kilns, also in parallel with each other, and it illustrates the normal cycle of operation of each of the two kilns and each of the two furnaces. Each furnace operates according to It is understood that the following description is applicable also to a plant having more chambers and furnaces than illustrated and in which the total period and the relation of the various cycles may vary in accordance with the characteristics of the charge and the number of chambers and furnaces comprising the plant. At the beginning of a campaign furnaces are brought up to temperature by melting in them several successive scrap charges. Afterwards they are ready to receive the first ore-containing charge. The charge proceeds as follows: several shovelfuls of coal are first introduced, for example, into furnace 10, through open door 14 (the valves in

passages

11, 7 and 8 being closed). The introduction of coal serves the purpose of absorbing and eliminating the oxygen of the air which is present in the interior of the furnace prior to opening

chutes

7 and 8, and thereby avoiding the slight explosion which might otherwise occur when the considerable amounts of carbon contained in the entering charge are suddenly brought into contact with the air within the furnace. The appearance of flames at the door 14 of the furnace indicates that gas is present within and, upon this observation, the charge controlling valves in

passages

7 and 8 are opened (valve 5 being open and valve 6 closed).

Passages

7 and 8 are kept open until charge has been deposited beneath the electrodes to a thickness of at least one foot, after which they are again closed. Since the charge coming from above is deposited somewhat unevenly, the surface of the charge is then raked to form a smooth bed beneath the electrodes. On top of this bed a layer of iron scrap several inches thick is charged through the door. Subsequently the electrodes are lowered and as soon as all three of the electrodes touch the surface of the scrap, power at maximum voltage and minimum amperage is supplied to start the arc. It is necessary to employ maximum voltage to increase the power absorption during the initial period when the conductivity of the charge and therefore flow of current are low. The reason it'is necessary 6 to maintain ahighinitial power consumption is that normally the electrodes are regulated so that they are raised and lowered by increases and decreases of both amperage and total power and it is necessary to avoid that the electrodes should sink into the charge due to the small amount of current passing them and the low power consumed. It should be emphasized that it is impossible to start the arc unless use is made of the high conductivity of the scrap layer; this layer permits the current to flow and a small bath of molten material is rapidly formed. However, it should be noted that in some cases the partial reduction operation may have produced suflicient metallic iron or may have sufliciently raised the temperature of the charge so that, due to the high conductivity of the charge entering the electric furnace the are will start spontaneously; in this case the charging of the scrap layer can bedispensed with. Normally no difficulties present themselves in this phase, but in case one of the electrodes should tend to sink into the charge, a small amount of scrap or reduced iron should be added through door 14 in such a way as to make a good contact. After the proper steps have been taken to insure that the current and power are balanced between the three electrodes the ore begins to be reduced in quantity and the gases appear at door 14.; At'this point'door 14 is closed and

passages

7 and 8 and 11 are opened. From time to time the amperage is increased in the normal manner and the voltage decreased to the minimum point consistent with good operation since it is advisable to transfer to the charge as much heat as possible (this transfer being representedaccording to Joules equation W=I R).

From time to time either of

passages

7 or 8 can be closed for a while to equalize the level of the charge in both ends of the furnace and to permit observing the operation of the furnace through peepholes.

After completion of two hours of the charge cycle'of furnace 10, charging of furnace 10 is commenced by opening valve 6 and in this manner kilns 2 and 2' will be supplying the entire charge requirements of both furnaces 10 and 10' for a period of one hour.' Three hours after the beginning of the charge cycle of furnace 10, valve 5 is closed so thatthe charge proceeds through valve 6 only into furnace 10 so as to complete the charge cycle of furnace 10. After stopping the charging of furnace 10, reduction continues in this furnace for approximately one hour. Then gas uptake passagell is closed and door 14 may be opened slightly permitting the gases to blow out. The bath is then agitated with a stirrer. When no further gas appears the reduction cycle is complete. Door 14 can now be fully opened, if necessary, in order to determine whether pieces of the charge are adhering to the walls, in which case they can be put back into the bath. At this time a test sample is taken to determine the carbon content of the melt. The taking of this test sample is very important at the beginning of the campaign when it is desired in succeeding heats to obtain a steel of a definite carbon content without adjusting the bath by adding a second slag. By charging the furnace in accordance with my patent application U. S. Serial No. 286,213, or in accordance with those modifications of this patent application which are described above as applying to steel manufacture, it is possible to produce a bath containing a regularly constant content of carbon. When operating with high-grade ores of low P and S content, and with ores containing MnO and of low P and S content, it is recommended that several shovelfuls of or ferro-silicon be added on top of the slag in order to reduce part of the FeO or MnO content of the slag into the metal without increasing the carbon content. This step is naturally taken only in case the carbon content of the first test is at the correct level or lower; if the melt carbon is higher than the required final carbon content it is not possible to add ferro-silicon,

' 7 since it is first necessary to reoxidize with a second slag to remove the carbon and-the effect ofa prior addition of ''a reducing material such-as ferro-silicon would be lost.

After the proper additions have "beenmade, slag notch 12 -i s--opened {or if the furnace is a tilting "type, it is tilted) 'and'the slag -is tapped. The height of the slag notch-is maintained "at'sue'h'a level 'in a stationary furnace that the final levelof *t-hesteel reaches the bottom ofthe slag notch andthat allot the slag is properly tapped. This is -an-easy matter to provide in a plant of this type. After the first slag has been tapped, a second slag can be charged in the normal manner. Additions of ferromanganese, term-silicon, or other materials are then made,--and-the temperature of thesteel is brought to the required-level. Subsequently tapping hole 13 is opened and the metal tapped into ladles. -Fina-lly the walls and if necessary the bottom are repaired with magnesite or doloniitei-n the regular "manner. *Several shovelfuls 'of limestone are fed over the bottom and the'furnace is now ready'to-recommenc'e its cycle. The combined refining, tappingra-nd repairing cycle will take approximately one hour. However, the flexibility of the plant permitsuthe oharging-of furnaee 1 --to he dclayed'or accelerated, or it also-permits thecycledoffurnacelo to be prolonged.

'I he oyc'leaof furnace is entirely analogous to that of furnace 10 except for a phase lag of approximately two hours.

.Sinceit is advisable that, withrespect tothe how of gas, all of the preheating chambers of each unit and normallysofthe entire plant be connected in --parallel with each other, a certain superpre'ssure-is necessary'to maintainthe flowof gas-through the-entire system. This pressure gis estimated at several millimeters of water-column for alunit, and greater for several parallel units. Such superpressure must he also maintained in the furnaces duringgtherreduction tpartof the cycle, although not in the refiningiperiod when the furnaces-is disconnected from the remainder .of ithesystem. Therefore it is charactenistic ;of our process that the individual furnaces duringpthe reducing cycle, and the connec-ted gas system as a whole, .he maintained under a slight superpressure. If adequate :s'uperpressure cannot :be maintained under normal conditions, it is necessary to create such superpressure by, for instance,.compressing a portion of the waste gases :and recycling it into the furnaces during the reduction cycle.

In conclusion, thesadvantages to be obtained by practicingihe presently -claimed improvements in all types of ironand steel production :arise .from the combination of cont nuous charging and preheating .and batch refining. Whereas previously it has not been feasible, practically and .econQmically, to produce steel .on a large scale by the direct process, my claimed improvements will overcome this disability. The :two sets of desirable conditions obtainedsby the combinations .of my claims are listed as follows:

A. Advantages .of continuous operation obtained by thisprocess:

.(i'l) Continuous charging into .and .out of the preheating chambers of each unit; :and into the plant .as a whole. o

12) Regular production of metal from the plant as a whole due %to. staggering the tapping :of the individual furnaces-in accordance with the typicalcycle.

(at) Power consumption .per .ton .of metal .decreased by preheating :and/ or partial reductiomcharges resulting in thezcase of steel production in a considerable decrease in :power con ump on p ton as ompa e with .2500 kwhJn etric-ton in a batch :Process.

(4) 'E-ulland efiicient use -,of -the;g as'from the electric furnace .plant ,as a whole to preheat :and partially reduce the-char 7 t5) Constant volumecf ga delivered brothe u in the plant.

' 'B. Advantages-of batch refining cycles obtained -hythis process: 7

1*) Regular productionfromore ineachplantunitlof all gradeslof high, medium, low carbon and alloy steel products of-unifor-m analysis :and to-specification.

(2) A long refractory life dne to t-he fact that temperature of furnace walls is maintained low for aflmajor portion-of each cycle. The temperatures only exceed 7 the melting temperatures of the materials during the short refining period; Roof temperatures are likewise keptlow.

(3) A period is allowed during .each cycle forrepairs to the bottom, walls and roof, thereby permitting an enormous increase'in lining life. as compared with .a con.- tinuousrefining operation.

--C. Advantage uniqueto :this process:

A further advantagethat is notcharacterist-ic of either a purely continuous or a purely rbatchloperation is that within each unit, if .sufiicient elements are provided, in

the event of aibreakdown of a single preheat chamber or of a single lfurnace, another sequence .of chamber or furnace operation can be substituted. Frequently such substitution would not disturb in any degree the ,continuous features of'the operation. As an example, in an individual .unitaconsisting of two preheat chambers and three electric iurnaces, the preheat chambers may he so designed that .one can handle the full rated charge of the unit, and that the .cycles :of :two furnaces can be staggeredsoas to handle this charge in the event the third furnace is temporarily shutdown. *Such substitutions provide a degree of flexibility that cannot be obtained in either a batch or a continuous plant, and the greater average availability reduces .dowh timepostand over.- head charges, .thus improving theefiicienqy of operation.

In the following claims, the term innit refers :to a number .of .electticfurnaces and preheating chambers, ineluding that number .of electric furnaces (never less than two a du ual y no m r whi h i o n t i r spectto the flow..of solid raw materials, in series with ,a single preheat chamber or i i-series with several preheat chambers connected in parallel with each other, and including the n mber of preheat chambers thus connected in parallel.v T he term battery refers to all of the electric furnaces in the unit or to ,all of the preheating chambers in the unit.

I claim:

1. Themethod ,ofoperating aplant for the production of molten pure iron and iron carbon alloys from ores, said plant being of the typeincluding one or more plant units, each unit comprising two or more electric furnaces connected with each other in parallel with respect to the in-flow ,of ,solidcharge materials and the out-flow of evolved gas and one or more preheating chambers connected in ,sprieswith said furnaces with respect to said flows, in which the cycle of each individual furnace includes a reduction period during which the flow of evolved gases from said furnace is connected so .as to preheat solid charge materials continuously entering said furnace from one or more of the preheating chambers by countercurrent flow in such chamber, a batch refining period during which said furnace is disconnected from the rest of the unit'with respect to the flows of solid charge materials and evolved gas, and a repair period during which said furnace is conditioned for the'sncceeding cycle.

2. The method of claim 1 inwhich the solid charge material includes, iron ore and carbonaceous material in aproportion to said ore such that the available carbon, after allowances for fiue dnstand alloying, does not exceed the amount theoretically suflicient to reduce of the iron content of said ore.

3. The method of claim 1 in which the temperature of the furnace walls and roof is maintained below about 1300 C. duringat least two-thirds of the cycle.

4. The method of claim 1 in which a gas pressure of'at'least several millimeters of water column gauge, is

maintained in each furnace and in the gas system of the unit connected thereto during its reduction period.

5. The method of claim 1 in which the preheating of the solid charge materials in the chambers is conducted at such a temperature or for such a period of time as to produce, as the solid charge material fed into a furnace at the beginning of a cycle, a material of a conductivity suflicient to start an electric furnace are.

6. The method of claim 1 in which the preheating of solid charge materials in the chambers is conducted at 600 C.-1000 C.

7. The method of operating a plant for the production of molten pure iron and iron carbon alloys from ores, said plant being of the type including one or more plant units, each unit comprising two or more electric furnaces connected with each other in parallel with respect to the in-flow of solid charge materials and with respect to the out-flow of evolved gas and one or more preheating chambers connected in series with said furnaces with respect to the flow of said charge materials and evolved gas, comprising the steps of partially reducing said charge materials in said chambers by preheating with said evolved gas to a temperature of 600 C.1000 C., further reducing said charge materials in a single furnace while at the same time charging said single furnace with said charge materials, disconnecting said single furnace from the unit with respect to the flow of said charge materials and evolved gas, completing the reduction and melting of the charge materials in said single furnace.

References Cited in the file of this patent FOREIGN PATENTS

Claims

1. THE METHOD OF OPERATING A PLANT FOR THE PRODUCTION OF MOLTEN PURE IRON AND IRON CARBON ALLOYS FROM ORES, SAID PLANT BEING OF THE TYPE INCLUDING ONE OR MORE PLANT UNITS, EACH UNIT COMPRISING TWO OR MORE ELECTRIC FURNACES CONNECTED WITH EACH OTHER IN PARRALLEL WITH RESPECT TO THE IN-FLOW OF SOLID CHARGE MATERIAL AND THE OUT-FLOW OF EVOLVED GAS AND ONE OR MORE PREHEATING CHAMBERS CONNECTED IN SERIES WITH SAID FURNACES WITH RESPECT TO SAID FLOWS, IN WHICH THE CYCLE OF EACH INDIVIDUAL FURNACE INCLUDES A REDUCTION PERIOD DURING WHICH THE FLOW OF EVOLCED GASES FROM SAID FURNACE IS CONNECTED SO AS TO PREHEAT SOLID CHARGE MATERIALS CONTINOUSLY ENTERING SAID FURNACE FROM ONE OR MORE OF THE PREHEATING CHAMBERS BY CONTERCURRENT FLOW IN SUCH CHAMBER, A BATCH REFINING PERIOD DURING WHICH SAID FURNACE IS DISCONNECTED FROM THE REST OF THE UNIT WITH RESPECT TO THE FLOWS OF SOLID CHARGE MATERIALS AND EVOLVED GAS, AND A REPAIR PERIOD DURING WHICH SAID FURNACE IS CONDITIONED FOR THE SUCCEEDING CYCLE.