US3406027A

US3406027A - Method for regulating the thermal balance of a bath of molten material during a continuous refining process of the material

Info

Publication number: US3406027A
Authority: US
Inventors: Juan Manuel Kindelan Y Bonill; Vayssiere Pierre
Original assignee: Institut de Recherches de la Siderurgie Francaise IRSID
Current assignee: Institut de Recherches de la Siderurgie Francaise IRSID
Priority date: 1964-11-18
Filing date: 1965-11-17
Publication date: 1968-10-15
Anticipated expiration: 1985-10-15
Also published as: CS150167B2; DE1458878C3; ES319495A1; AT283405B; OA01861A; GB1074220A; DE1458878B2; BE672264A; FR1423035A; DE1458878A1; NL6514239A; SE304297B

Description

Oct. 15, 1968 3,406,027

J. M. KINDELAN Y GOMEZ DE BONILLA ETA- METHOD FOR REGULATING THE THERMAL BALANCE OF A BATH OF MOLTEN MATERIAL DURING A CONTINUOUS REFINING PROCESS OF THE MATERIAL Filed Nov. 17, 1965 & 19m

Va gdho 7 km hm Qn m \z/ k-T \w R a United States Patent O M 9 Claims. (or. 75-51 ABSTRACT OF THE DISCLOSURE A method of regulating the thermal balance of a bath of molten material during a continuous refining process of the material, which includes the steps of maintaining a molten bath of the material to be refined, continuously adding material to be refined to this bath, refining the materials in a bath while continuously adding additional materials to the bath at a predetermined temperature in order to maintain a proper heat balance in the bath during the refining process, and continuously discharging refined material from the bath.

The resent invention relates to a method for regulating the thermal balance of a bath of molten material during a continuous refining process of the material, and more specifically for regulating the thermal balance of a bath of molten metal during continuous refining of this metal.

It is well known that during refining of pig iron, that is during oxidation of carbon, silicon and third elements contained therein, considerable heat is produced so as to raise the temperature of the bath of molten metal and this additional heat produced during the refining process permits to maintain the bath of molten metal in liquid state even though the solidification temperature of the bath is raised when the iron is transformed into steel. When the refining process is carried out as an intermittent process, that is if only a batch of metal is refined, the rise of the temperature in the bath of molten metal during the refining process is so great that additional materials in cold condition may be added to the bath of molten metal without the danger of producing a solidification of the bath. Such additional materials are fed into the bath of molten metal to produce a metal of the quality desired at a temperature suitable for maximum production. Thus, for instance limestone is added to the bath to facilitate dephosphorization thereof. Minerals in reduced or nonreduced condition may also be added to increase the charge, and at the end of the refining process the metal is deoxidized by adding a reduction material thereto for instance ferromanganese. The quantity of the additional materials fed into the bath may vary according to the desired quality of the metal to be produced and according to the desired output.

In an installation for a continuous refining process, the problem is more difficult. Essentially, in such a continuous process one tries to obtain an end product of desired quality and at a convenient temperature, but in certain cases one requires in addition that the output of the liquid metal obtained is as constant as possible to assure proper progress of operations taking part upstream and downstream of the refining installation and to avoid thermal losses. It will be understood that if the delivery of refined metal is a very small one, the thermal loss per ton of metal produced will rise considerably.

It is an object of the present invention to provide for a continuous refining process of material, especially for a Patented Oct. 15, 1968 continuous refining process of metal, in which optimum thermal conditions are maintained in the metal bath regardless of the thermic conditions created by the reactions taking place during actual refining process.

With these objects in view, the method of the present invention of regulating the thermal balance of a bath of molten material during a continuous refining process of the material mainly comprises the steps of maintaining a molten bath of the material to be refined, continuously adding material to be refined to the bath, refining the material in the bath while continuously adding additional materials to said bath at predetermined temperature in order to maintain a proper heat balance in the bath during the refining, and continuously discharging refined material from the bath.

More specifically at least one of the materials added to the bath may be added simultaneously in two streams of material in which the material in one stream is in cold condition and the material in the other stream is in hot condition while the total mass of material fed by the two streams into the bath of the molten metal is maintained constant. The material in the cold stream of material may be in the form of a pulverulent material and the material in the hot stream of material may be also in pulverulent or in liquid form.

The materials to be added during the refining process to the base material to be refined may include for instance cooling materials such as reduced or nonreduced minerals, scorificating materials such as for instance limestone, deoxidation material such as for instance term-manganese, remolten scrap iron, etc.

An essential feature of the present invent-ion is to regulate the thermal conditions in an installation for continuously refining a material especially a metal regardless of the conditions created by the actual refining process. Basically the process according to the present invention permits to regulate the additions to the metal bath in such a manner that the refined metal will have the composition and temperature desired regardless of the output of the refined metal.

In many cases it is desirable to maintain the output of the refined liquid metal substantially constant in order to obtain an optimum production and to assure proper and continuous optimum operations upstream and especially downstream of the refining installation, for instance in an apparatus for continuous casting downstream of the refining installation. Therefore in such a continuous process one cannot simply add materials to the refining installation while considering only the final temperature of the metal discharged as is often the case in a discontinued or batchwise refining operation. In a continuous refining process it is therefore advisable to regulate the feeding of the additional materials into the bath or molten metal in such a manner that the output of refined metal remains constant.

This will lead to certain difficulties as will be understood from the following remarks.

It may happen that the pig iron to be refined in the refining container contains only a relatively small percentage of carbon so that the amount of heat produced during the refiningprocess is correspondingly small, in which case one has to considerably reduce the addition of cold material to the bath of molten metal, which may result in a reduction of output of refined metal. This reduction in output of refined metal will not only affect the installations downstreaam of the refining installation and result in a slowdown thereof, but also in additional cooling of the metal in the refining container, which in turn will lead to increased thermal losses.

These disadvantages are completely avoided with the method of the present invention according to which the cold materials to be fed into the bath of molten metal are completely or partially replaced by preheated or molten materials which will cool in a lesser degree or not cool at all the hot metal bath as they are fed thereinto, but the total amount of materials fed into the refining container can remain constant to assure thereby a constant output of refined metal. The additional materials may be fed into the bath of molten metal at different temperatures, for instance at a temperature equal to the ambient temperature of the surrounding air, or at temperatures 'between 800 and 1000" C. if the additional materials are fed in solid condition into the bath, or at a temperature of about 1500 C. when the additions are in liquid form. According to the present invention one may feed the same kind of material simultaneously in a hot and in a cold stream into the bath of molten metal or one may feed different materials alternatively in hot or cold condition into the bath according to the thermal conditions thereof. Basically, the method of the present invention consists therefore to furnish into the metal bath to be refined the enthalpy of the added materials in order to maintain desired thermic conditions in the bath of molten material in a continuous refining process which produces a substantially constant output of refined metal.

According to a preferred method the additional materials fed into the bath are in pulverulent form which permits a ready absorption of the added material in the molten metal bath and a substantial uniform distribution of the pulverulent particles through the mass of molten metal in the bath, or the added materials are introduced in liquid form, which is especially interesting for additions of deoxidizing materials such as for instance ferro-manganese which is introduced at the end of the refining process usually in a separate container where the addition of preheated material is often desirable. Molten scrap iron may also be introduced in liquid form since introduction in solid state is sometimes difiicult in 13. continuous refining installation. These materials may be molten in a furnace heated by gas obtained during the actual refining process.

The amounts of the materials to be added are regulated in dependence on the temperature of the liquid metal which is to be refined and this temperature may be sensed by means of a thermocouple placed in a protective sheath into the molten metal baths or by an optical pyrometer.

It is to he understood that the added materials may serve also to a certain extent to regulate the output of the refined material; if the output of material upstream of the refining installation diminishes, the present invention permits to increase feeding of material in cold or hot condition into the refining installation in such a manner that the output of refined metal will remain substantially constant.

The apparatus according to the present invention mainly comprises a first substantially closed container of heat resistant material adapted to contain a bath of molten metal to be refined, first feeding means communicating with the first container for feeding molten metal to be refined into the container, second feeding means communicating with the container for feeding metal to be refined in comminuted form and in cold condition into the container, means for blowing compressed oxygen into the molten bath of metal into the container for refining the metal and producing thereby a hot gas, a hopper having an outlet end and adapted to contain refining material in pulverulent form to be fed into the bath of molten material, a substantially closed second container, heater means in the second container, first conduit means connecting the outlet end of the hopper with the interior of the first container for feeding material from the hopper into the bath of molten metal, second conduit means connecting the outlet end of the hopper with the interior of the second container for feeding material in the hopper into the second container, third conduit means for feeding the hot gas produced in the first container into the heater means of the second container to heat the material in the latter, fourth conduit means for feeding the heated material from the second container into the bath of molten material in the first container, and outlet means for continuously discharging refined metal from the first container.

The noved features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

The single figure is a schematic sectional view of a refining apparatus according to the present invention for carrying out the method of the present invention.

Referring now to the drawing, it will be seen that the apparatus according to the present invention mainly comprises a container 1 having walls from refractory material and provided in the bottom wall 2 thereof with an outlet nozzle 3. The container 1 is adapted to contain pig iron in molten condition fed through the open upper end of the container 1 into the latter and which flows through the outlet nozzzle 3 into a channel 4 of refractory material, which communicates at the lower end thereof with a substantially closed refining container 5. The discharge of molten metal from the container 1 through the outlet nozzle 3 thereof is regulated by displacement of an elongated valve member 6 having a lower substantially conical end aligned with the nozzle 3 and connected at the upper end thereof to a lever mechanism 6a serving to move the member 6 toward and away from the outlet nozzle 3 to open the latter to a variable degree. A lance 7 supplied with oxygen under pressure through a conduit 8 extends through the top wall of the container 5 and has an inner end adjacent the level of the bath of molten metal in the container 5 for blowing compressed oxygen into the metal bath to refine the metal of the bath. A hopper 9 adapted to contain a mineral to be fed into the bath of molten metal in the container 5 is arranged above the container 5 and a feed screw 10 is arranged adjacent the outlet end of the hopper for discharging the material therefrom into another lance 11 extending through the top wall of the container 5 and having an inner end adjacent the level of the bath of molten material therein. The discharge from the hopper into the lance 11 may proceed in a direct or in an indirect way. In the first case the mineral contained in the hopper 9 is fed exclusively through the conduit 12 into the upper end of lance 11 and in this case the valve 13 in the conduit 12 is completely open. In the second case, the mineral contained in the hopper 9 is fed through a conduit 15 provided with a valve 16 into a fiuidizing container 14 and in this case the valve 16 is open whereas the valve 13 is closed. The mineral thus fed into the container 14 is heated and fluidized therein by a fluidizing burner 17 of known construction having an internal combustion chamber. During the operation of the refining apparatus the burner 17 is provided with gas produced during the refining process in the container 5 and fed from the latter through a conduit 18 and a branch conduit 18a communicating with the burner 17 and provided with a valve 19. A conduit 20 open at one end thereof communicates at the other end thereof with the conduit 18a for feeding combustion air into the latter. The combustion of the gas takes place in the interior of the burner 17 and the gas escaping from the burner 17 through the openings 21 thereof heats and fluidizes the pulverulent material in the container 14. The thus fluidized hot pulverulent material is fed through a conduit 22 provided with a valve 23 into the conduit 12 downstream of the valve 13 thereof to pass through the lance 11 into the interior of the container 5. The temperature of the heated material as it leaves the container 14 may be higher than 800 C. but it is to be understood that by properly adjusting the

valves

13, 16 and 23 and by regulating the combustion in the burner 17 by means of the valve 19, it is possible to feed through the lance 11 pulverulent material of a temperature which varies from ambient temperature to a temperature of over 800 C.

A conveyor belt 24 supported on roller 25 permits to feed scrap iron in comminuted form into the container 5.

An additional container 26 is preferably arranged above the container 5 and the container 26 may be supplied with scrap iron through the opening 27 in the cover thereof. The scrap iron in the container 26 is molten by means of a gas burner 28 which is operated by gas produced during the refining process in the container 5 and guided into the burner 28 through a conduit 18b branching off from the conduit 18 communicating with the interior of the container 5. A valve 30 is arranged in the conduit 18b to open and close the latter as necessary, and a conduit 29 communicating at the outer end with the atmosphere and with the inner end thereof with the conduit 18b serves to provide combustion air to the gas burner 28. While the arrangement illustrated in the drawing in which the scrap iron in the container 26 is molten by means of a gas burner supplied with gas from the container 5 is a preferred arrangement, it is to be understotod that the container 26 and the burner means therein may also be replaced by an electric furnance in which scrap iron to be fed into the container 5 may be molten.

The molten scrap iron in the container 26 is discharged therefrom through the outlet opening 32 controlled by a valve member 31 and is operated through a lever mechanism 31a.

When the valve member 31 is opened, the molten metal in the container 26 may flow through the inclined channel 33 into the container 5.

The slag which forms in the container 5 floats on top of the metal bath therein and is discharged through an opening 34 in the side wall of the container 5. A partition 35 in the container 5 having a bottom face spaced from the bottom wall of the container and a top portion extending above the level of the metal bath therein prevents the slag floating on the top of the metal bath to flow toward the outlet opening 37 of the container 5, whereas the molten metal in the container may pass through the passage 36 beneath the bottom edge of the partition 35 to the outlet opening 37 to flow from there into a further container 38 arranged at the right side, as viewed in the figure, of the container 5.

The amounts of hot and cold minerals fed into the container 5 and the amounts of scrap iron in either solid or molten condition are fed into the container 5 according to the thermal conditions of the bath therein and such that the total mineral fed and the total metal fed will remain constant. The temperature in the bath is measured by optical pyrometer or by means of a thermocouple located in a protective sheath in the bath adjacent the outlet 37 and the additions to the bath of either hot or cold material are regulated according to the temperatures sensed.

The refined metal is discharged from the container 5 through an overflow 37 into an adjacent container 38 for supplementary treatment therein. The supplementary treatment may consist of deoxiding the refined metal by means of an addition of ferro-manganese. 'l he ferro-manganese may be supplied to the metal in the container 38 either in hot or in cold condition depending on the thermal conditions of the refined metal in the container 38. Perm-manganese in pulverulent form and substantially cold condition may be supplied to the metal bath in the container 38 from a hopper 39 provided with a feed screw 40 at the outlet end thereof which feeds when operated the pulverulent ferro-rnanganese in the hopper 39 through a conduit 41 into the container 38. An additional container 42 arranged above the container 38 may be fed through an inlet opening 43 in the cover thereof with ferro manganese and the ferro-manganese in the container 42 may be molten by means of a gas burner 44 supplied with the necessary gas through a conduit 18c branching off from the conduit 18. A valve 46 in the conduit permits to regulate the flow of gas to the gas burner 44, while a branch conduit 45 communicating at the outer end thereof with the atmosphere and with the inner end thereof with the conduit 18c downstream of the valve 46 supplies the necessary combustion air to the gas burner 44. The molten form-manganese from the container 42 may be discharged therefrom through an outlet opening 48 arranged in the bottom wall thereof above the container 38 and 'which is controlled by a valve member 47 operated by a lever mechanism 47a. The relationship of cold ferro-manganese and ferro-manganese in hot and molten condition discharged from the hopper 39 and container 42, respectively, in the container 38 is controlled in dependence on the thermic conditions in the metal bath maintained in the container 38, the temperature of which may be sensed by an additional pyrometer, not shown in the drawing. The total amount of ferro-manganese fed into the bath in the container 38 is preferably maintained constant and the thus further treated metal is discharged from the container 38 through an overflow passage 49.

The various containers and other elements above described are supported on a metal frame 50 schematically illustrated in the figure.

Two examples of the method of operation are given below:

Example ].The hematite pig iron to be refined by a continuous refining process contains 4% carbon, 0.60% silicon and 0.18% phosphorus. The temperature of the liquid pig iron is 1230 C. in the container or ladle 1. This pig iron is fed to the refining container 5 at a rate of 200 kilogrammes per minute. The volume of container 5 is 0.3 cubic meter containing permanently one ton of metal refined by oxygen, the rate of flow thereof being 12 normal cubic metres per minute. During the refining operation the temperature of the bath is raised to 1585 C.

Mineral or ore is then added at a temperature of 25 C. and at a rate of 9 kilogrammes per minute, and also mineral at 600 C. at a rate of 10 kilogrammes per minute. The ore contains 60% iron and is substantially constituted of hematite Fe O the weight of gangue is negligible.

After two hours of operation in the above conditions, it is noted that the temperature of the bath is raised to 1610 C. The thermic conditions of the additions are then modified, while the total weight of ore fed is kept constant.

In that way 17.8 kilogrammes per minute of ore at 25 C. and 1.2 kilogrammes per minute of ore at 600 C. are added. The temperature is gradually lowered and after three hours of operation it is maintained at 1585 C.

The liquid metal is discharged from the container 5 at a rate of kilogrammes per minute and fed to the container 38, the volume of which is 0.2 cubic metre containing one ton of metal. The temperature at the inlet is 15 80 C., 0.9 kilogramme per minute of non-refined ferromanganese at 25 C. is added. The tempenature at the outlet is 1560 C.

Example 2.-The hematite pig iron to be refined by a continuous refining process contains 4.1% carbon, 0.60% silicon and 0.19% phosphorus. The temperature of liquid pig iron is 1225 C. in ladle 1. This pig iron is fed to the refining container 5 at a rate of 200 kilogrammes per minute. The container 5 contains permanently one ton of metal refined by 12 normal cubic metres per minute of technically pure oxygen. During the operation the ternperature of the bath is raised to 15 80 C.

Scraps are then added in the following manner: 72 kilogrammes per minute of scraps at 25 C. and 20 kilogrammes per minute of melted scraps the temperature of which is 1580 C.

After one hour and a half of operation it is noted that the temperature of the bath is lowered to 1560 C. The respective weights of cold and hot scraps are then modified: 68 kilogrammes per minute of melted scraps at 1580 C. and 24 kilogrammes per minute of scraps at 25 C. After two hours and a half the temperature of 1580" C. is again obtained.

The refined metal flows into container 38 at a rate of 250 kilogrammes per minute at a temperature of 1575 C. In order to cause the thermal losses in container 38 to be lowered, 0.3 kilogramme per minute of melted ferromanganese at 1400 C. and 0.6 kilogramme per minute of non-refined ferrornanganese at 25 C. are added. The temperature of the metal at the outlet of container 38 is 1560 C.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of methods and apparatus for regulating the thermal balance of a bath of molten material during a continuous refining process differing from the types described above.

While the invention has been illustrated and described as embodied in a method and apparatus for regulating the thermal balance of a bath of molten iron during a continuous refining process, it is not intended to be limited to the details shown, since various modifications and struc tural changes may be made without departing in any Way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of the invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of regulating the thermal balance of a bath of molten metal during a continuous refining process of said metal, comprising the steps of maintaining a molten bath of the metal to be refined; continuously adding metal to be refined to said bath; refining said metal in said bath while continuously adding additional materials to said bath, at least one of said materials being fed simultaneously in two streams of material, in which the material in one stream is in hot condition and the material in the other stream is in cold condition; regulating the ratio of the rates of flow between the material in hot condition and the material in cold condition, at a value depending on the enthalpy of said bath; maintaining the combined flow of each of said additional materials at a constant value depending on the chemical requirements of said molten metal, and continuously discharging the refined metal from said bath.

2. A method as set forth in claim 1, and including the steps of sensing the temperature in said bath of molten metal and regulating the rat of flow of the hot stream of said one material to the rate of flow of the cold stream thereof in dependence on the sensed temperature of said bath.

3. A method as set forth in claim 1, wherein the temperature of the stream of hot material is varied in accordance with the thermic condition of said bath.

4. A method as set forth in claim 3, and including the step of sensing the temperature in said bath and preheating part of said one material to a temperature in dependence on the sensed temperature of said bath prior to feeding said material in a hot stream of material into said bath.

5. A method as set forth in claim 1, wherein the material in the stream of cold material is a pulverulent material.

6. A method as set forth in claim 1, wherein the material in the stream of hot material is a pulverulent material.

7. A method as set forth in claim 1, wherein the material in the stream of hot material is in liquid form.

8. A method as set forth in claim 1, wherein said refining process is an exothermic process producing a hot gas and including a step of preheating at least one of said additional materials with said hot gas produced during the refining process.

9. A method as set forth in claim 1, wherein said molten bath is formed from steel producing metal and wherein the step of refining said metal in said molten bath includes the step of blowing oxygen into said molten bath thereby producing a hot gas, and including the steps of feeding said hot gas into contact with at least one of said additional materials for preheating the same prior to the feeding thereof into said bath of molten metal.

References Cited UNITED STATES PATENTS 2,962,277 11/ 1960 Morrill -60 2,975,047 3/1961 Leroy et a1. 75-60 FOREIGN PATENTS 257,168 1/ 1965 Australia. 594.996 3/1960 Canada. 514,352 1939 Great Britain. 744,935 2/ 1956 Great Britain.

L. DEWAYNE RUTLEDGE, Primary Examiner.