US3232748A - Process for the production of steel - Google Patents

Description

Feb. 1, 1966 R. RINESCH PROCESS FOR THE PRODUCTION OF STEEL Filed July 20, 1964 INVENTOR RUDOLF RINESCH H IS ATTORNEYS United States Patent 3,232,748 PROCESS FOR THE PRODUCTION OF STEEL Rudolf Rinesch, Linz, Austria, assignor to 1801 Brassert Oxygen Technik AG., Zurich, Switzerland, 21 company of Switzerland Filed July 20, 1964, Ser. No. 386,475 Claims priority, application Austria, May 19, 1959, A 3,684/59 8 Claims. (Cl. 75-60) This is a continuation-impart of applications Serial No. 25,071 filed April 27, 1960, now abandoned, entitled Method of Controlling the Heat Content Of Solid and/or Liquid Charging Materials, and Serial No. 173,- 113 filed February 14, 1962, now abandoned, entitled Method of Supplying Heat to the Solid and/or Liquid Charge in Converting the Same to Steel.

This invention relates to the production of steel from charging materials, such as pig iron and scrap, by the top-blowing oxygen refining process.

Top blowing ipro'cesses comprise blowing an oxygen jet by means of a vertical lance onto the surface of a ferrous melt charged in an upright tilt-able crucible or converter in the presence of a basic slag, whereby the accompanying elements contained in the melt, such as carbon, silicon, phosphorus and manganese, are eliminated and partly incorporated in the slag. The combustion reactions of the accompanying elements are exothermic, and the liberated heat is sufiicient in most cases to heat the melt to the temperature required for teeming the steel made and to melt scrap in certain amounts, e.g., 10 to In such refining processes it is often desirable to be independent of the content of the so-called heat-carrying elements in the pig iron, which are those accompanying elements which liberate heat during their combustion, or to be able to add an amount of scrap larger than that which corresponds to the heat balance calculated in view of the given content of the heat-carrying ele ments.

The means previously suggested to solve these pro lems have not proved satisfactory. In order to increase the heat content it has been suggested to add further heat-carrying elements, such ferrosilicon, ferromanganese or the like, to the bath. These fuels, however, are highly expensive and enable an increase of the heat content only in moderate limits. On the other hand, it has been suggested to add finely divided carbonaceous substances to the refining agent itself, i.e., to the oxygen jet blown onto the surface. It has been found, however, that such an addition to the refining gas is practically useless for heating the bat-h when the refining process has already been started. There is a strong evolution of gas in the react-ion area during the refining process. The evolved gas consisting particularly .of carbon monoxide entrains these fuels into the upper part of the converter and they are not burnt until they are ejected at the top fro-m the mouth of the converter. Thus, they heat only the chimney and may cause a destruction of the covering means of the converter whereas they do not appreciably heat the bath. For this reason, this method has not given the desired results.

The heating methods belonging to the known prior art can generally be classified into three groups as follows:

Group A: heating solid charging materials in bottomblowing Bessemer converters and side-blowing converters;

Group B: heating in hearth furnaces;

Group C: heating in a separate vessel other than the refining vessel or in a furnace chamber separate from the actual refining furnace.

The processes ranging in Group A, as far as they use bottom tuyers, have the material disadvantage that directing a flame onto the surface of the charging materials is feasible only if blowing from the bottom is simultaneously carried on, or else the liquefied material would flow into the bottom tuyers. In side-blowing converters, the transversal blowing of a flame may cause a heavy wear of the refractory lining of the vessel. The same applies if a bottom-blowing converter is tilted so as to direct the flame onto the surface of the charging materials in the bottom-up converter position.

Heating in hearth furnaces (Group B) has hitherto been effected in such manner that the flames have been directed at an angle to the surface of the charge in the hearth furnace. In doing so, difficulties arisedue to the fact that the bulky scrap charged has a large surface area. The pieces of scrap begin to melt at the surface, the charge being gradually covered by a slag layer consisting mainly of oxidized iron. The conditions of heat transfer from the flame to the surface of the charge thus are continually changed, and also the thermal conductivity within the charging materials varies. This necessitates heating the furnace to a high temperature before and during the charging procedure, whereas the fuel supply must be decreased during the initial meltdown period, since the heat transfer conditions then are unfavorable, due to the insulating slag layer, and there is a considerable risk of damage to the refractory. 'Ihe melt-down of a charge in an open-hearth furnace usually starts at the surface of the charge and gradually proceeds downwardly, the heat transfer being effected mainly by radiation and only to a minor degree by convection and being heavily impeded altogether due to the aforementioned ditficulties. The main disadvantages of this heating in. open-hearth furnaces thus are an unsatisfactory ratio of effective heat to the total heat supplied and long melt-down periods.

The processes of Group C require undue expenditures in complicated equipment.

It is an object of the invention to avoid the difficulties and disadvantages described and to provide for a considerable latitude in the selection of the solid and liquid charging materials for refining processes of the kind mentioned above. The process of the invention comprises charging the solid charging materials into an upright crucible provided with a vertical blowing lance adapted to be lifted and lowered and having connections to an oxygen supply and to a fuel supply so that it is capable of operating selemively as a burner lance and as an oxygen blowing lance; directing a flame of fuel and oxygen from said lance operating as a burner lance against said solid charging materials so as to heat them and to form a crater of liquefied charging materials in the center of the charge; continuing liquefying and heating said charging materials to provide refining conditions; shutting off the fuel supply; and refining said charge in the same crucible with said lance operating as an oxygen blowing lance to remove the impurities contained in the melt. This method enables the supply of any desired amount of heat to the charge either to enable the conversion of pig iron having only a small content of heat-carrying elements or to enable the incorporation of large (amounts of scrap in pig iron having a normal content of heat-carrying elements or to realize both possibilities.

' With the process of the invention the proportions of solid and liquid materials may be selected at random. It

is possible to compose the charge only from solid piglets.

It is also possible to compose the charge from piglets, liquid pig iron and scrap, and it is further possible to compose the charge from piglets and scrap. The process of the invention thus is independent of the availability and kind of a source of liquid crude iron (blast furnace or cupola). The process, therefore, is of particular interest for integrated ironworks in which the steel plant is erected in a first stage, whereas blast furnaces are built in a further stage of extension. The process of the invention is moreover important for steel mills which are far away from ore deposits and sources of coke supply, because in this case the transportation of solid pig iron is to be preferred.

In an embodiment of the invention the flame directed against the charge is formed by burning a mixture of a hydrocarbon oil and oxygen.

In a further embodiment of the invention the flame is formed by burning a mixture of a combustible gas, preferably natural gas, and oxygen. This embodiment has the advantage that any risk of contamination of the melt with sulphur is eliminated.

A further embodiment of the invention comprises heating and liquefying the solid charging materials in an upright crucible by means of the vertical lance operating as a burner, combining the liquefied charging materials with liquid pig iron, further heating the combined charge to provide refining conditions and thereafter completing refining by means of the lance operating as an oxygen lance, the proportions of oil and oxygen being so controlled ,during the heating step that the burner flame will selectively have an oxidizing, a neutral or a reducing efiect. This enables keeping the charge at the desired temperature or heating it between individual refining phases, i.e., .upon an interruption of the refining, or at the end of the refining process, if this is desired for fining or alloying purposes.

In carrying out the invention, I prefer to use a blowing device comprising a blowing tube having a jacketed cooling shell, in which a circulation of a coolant is maintained, and a fuel supply conduit extending axially in the blowing tube and having a tip which terminates before the mouth of the blowing tube. Owing to this construction of the device, the fuel is atomized before the convergent-divergent subcooling zone of the outfiowing gas. The combustion of the fuel will then take place on the surface of the charge and there will be no loss of unburnt fuel.

The device is diagrammatically illustrated in the accompanying drawing showing a vertical sectional view.

The blowing tube 1 is surrounded by a jacketed, concentric shell consisting of the guide tube 2 and the outer tube 3. The lower part of the guide tube is designed to form a streamlined guide body 4. The blowing tube 1 and the outer tube 3 are connected at the mouth of the blowing tube to form a conical nozzle 5 of massive material having a convergent-divergent passage therein. A slidable fuel supply tube 6 extends axially in the blowing tube 1 and can be pulled upwardly out of the blowing device. The tip of the tube 6 terminates a certain distance before the nozzle tip so that the fuel is atomized before the subcooling zone of the outflowing gas. The mouth of the tube 6 may comprise baflie plates 7, e.g. of helical shape, to ensure an improved atomization and distribution.

The following Example 1 compares the heat balances of two melts A and B based on pig irons having the same composition and aiming at the same yield of 30 metric tons. In the first case (Melt A) 10% scrap and in the second case (Melt B) 30% scrap are to be added.

EXAMPLE 1 Melt A (10% scrap) Hot metal analysis: Percent C 4 Si 0.4 Mn 1.0

P 0.33 Charge: Hot metal kg 30,600 Scrap kg 1 3,400

Total kg 34,000

Assumed converter loss p'ercent" 11.8 Yield k 30,000 Lime kg 2,000 Limestone kg 900 Amount of slag kg 5,000 Fe in slag kg 2 900 C Si 1 Mn p P 30,600 kg. hot metal- 1, 522 1 22 flfi K9108 3,400 kg. scrap 5 5 14 2 34,000 kg. charge 1, 227 127 320 30,000 kg. liquid steel 15 60 9 Loss of heat-carrying elements 1, 212 127 260 101 O2 requirement, 1,700 cubic metres (S.T.P.).

Melt B (30% scrap) Hot metal analysis: Percent C 4 Si 0.4

P 0.33 Charge:

Hot metal k 23,500 Scrap kg 1 10,000

Total kg 33,500

Assumed converter loss percent 10.4 Yield kg 30,000 Lime kg 1,550 Limestone kg 700 Amount of slag kg 3,900 Fe in slag kg 2 700 C Si Mn 1? 23,500 kg. 540 94 .535 Kg 78 10,000 kg. 15 15 42 6 33,500 kg. 955 109 277 54 30,000 kg. st e1 15 60 9 Loss of heat-carrying elements 940 109 217 75 O requirement, 1,330 cubic metres (S.T.P.).

3 Melt A scrap) HEAT INPUT (A) Heat of combustion: Kcal.

Carbon 3,500,000 Silicon 1,078,000 Manganese 1 467,000 Phosphorus 1 725,000 Iron 1,030,000

Total 6,800,000

1 Slagging heat considered.

HEAT OUTPUT (A) To crude iron temperature (1200 C.): Kcal.

Oxygen 750,000 Lime and Limestone 1,150,000 Scrap 700,000

(B) To final temperature:

Waste gases 50,000 Slag 550,000 Crude steel and scrap 2,500,000

(C) Heat of fusion of slag and losses:

Heat of fusion of slag 600,000 Vessel losses 500,000

Total 6,800,000

Mel! B (30% scrap) HEAT INPUT (A) Heat of combustion: Kcal.

Carbon 2,720,000 Silicon 1 923,000 Manganese 1 391,000 Phosphorus 1 537,000 Iron 802,000

Total 5,373,000

1 Slagging heat considered.

HEAT OUTPUT (A) To crude iron temperature (1200 C.): Kcal.

Oxygen 600,000 Lime and Limestone 1,000,000 Scrap 2,000,000

(B) To final temperature:

Waste gases 50,000 Slag 500,000 Crude steel scrap 2,500,000

(C) Heat of fusion of slag and losses:

Heat of fusion of slag 600,000 Vessel losses 500,000

Total 7,750,000

Difference between heat input and output From the foregoing calculations it is evident that in the case of Melt B an amount of heat of 2,377,000 kcal. is lacking. This deficit is compensated according to the invention by supplying a fuel oil which is burnt with oxygen. With a calorific value of the oil of 9,900 keel/kg, an amount of 2,377,000:9,900=240 kg. of oil will theoretically be required. As the thermal efficiency may be assumed to be about 30%, an amount of 800 kg. of oil and an amount of 1920 cubic metres (S.T.P.) of oxygen will have to be supplied in practice, thus providing an excess of oxygen of 10%.

Example 2 illustrates the production of steel from a charge consisting only of solid charging materials, namely about 80% piglets and about 20% scrap, in a conventional 30 ton top-blowing crucible having a closed bottom and a shell of substantially cylindrical shape.

Charging 7,250 kg. scrap. 3. 00

Blowing oil plus Oz 5.00

Adding 500 kg. lime,

kg. bauxite: Blowing oil plus 0;

Adding 600 kg. lime stopping oil supply:

Blowing O2 8. 60 700 6, 700 Sampling 5. O0 Tapping 3. 00

1 H3 is 1.85 m. above the bottom of the crucible.

Example 2 shows that the total duration of the heating was 35 minutes. The original height of the material charged was 2350 mm. After melting, the bath height was only 1000 mm. It was thus necessary to continuously approach the lance operating as a burner to the bath, as is evident from Example 2. Whereas the nozzle distance above H initially was 3000 mm., it was gradually reduced to 1250 mm. above H and upon termination of the heating procedure the subsequent refining step, totalling 8.60 minutes, was carried out at a nozzle distance of 700 mm. above H It can moreover be gathered from the respective nozzle distances how the crater formation proceeds. During the initial five minutes of heating the flame begins to erode the center of the charged material. After this initial phase, the crater gradually becomes narrow and deep.

The heat transfer from the liquefied material in the crater takes place by radiation and by convection. This results in a favorable thermal eificiency. A total amount of 1691 litres of oil was consumed. With a calorific value of the oil of 9700 kcal./kg., this corresponds to an efiiciency of 53%.

What I claim is:

1. A process for the production of steel from charging materials comprising pig iron and scrap, said pig iron containing impurities, at least part of said charging materials being solid, comprising charging said solid charg ing materials into an upright crucible provided with a vertical blowing lance adapted to be lifted and lowered and having connections to an oxygen supply and to a fuel supply so that it is capable of operating selectively as a burner lance and as an oxygen blowing lance; directing a flame of fuel and oxygen from said lance operating as a burner lance against said solid charging materials so as to heat them and to form a crater of liquefied charging materials in the center of the charge; continuing liquefying and heating said charging materials to provide refining conditions; shutting off the fuel supply; and refining said charge in said crucible with said lance operating as an oxygen blowing lance to remove said impurities contained in said pig iron.

2. A process as set forth in claim 1, wherein said solid charging materials consist of piglets.

3. A process as set forth in claim 1, wherein said flame is formed by burning a mixture of a hydrocarbon oil and oxygen,

4. A process as set forth in claim 1, wherein said flame is formed by burning a mixture of a combustible gas and oxygen.

5. A process for the production of steel from charging materials comprising pig iron containing impurities and scrap, at least part of said charging materials being solid, comprising charging said solid charging materials into an upright tiltable crucible provided with a vertical blowing lance capable of altitude adjustment and having connections to an oxygen supply and to a fuel supply so that it is capable of operating temporarily as a burner lance and as an oxygen blowing lance; directing a flame from said lance operating as a burner lance against said solid charging materials so as to beat them and to form a crater of liquefied charging materials in the center of said charge; continuing heating until the main portion of said solid charging materials is melted; adding liquid vpig iron and further continuing heating until refining conditions are provided; and thereafter refining the charge after having shut off the fuel supply with said lance operating as an oxygen blowing lance to remove the impurities contained in said pig iron.

6. The process set forth in claim 5 comprising adjusting the proportions of fuel and oxygen supplied to said lance to render said flame oxidizing.

S 7. The process set forth in claim 5 comprising adjusting the proportions of fuel and oxygen supplied to said lanceto render said flame neutral.

8. The process set forth in claim 5 comprising adjusting the proportions of fuel andoxygen supplied to said lance to render said flame reducing.

leferences Cited by the Examiner UNITED STATES PATENTS 1,140,550 5/1915 Weissengerger 75-60 2,818,247 12/1957 Francis 75-60 2,820,706 1/1958 Larsen 7560 DAVID L. RECK, Primary Examiner.

BENJAMIN HENKIN; Examiner.

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF STEEL FROM CHARGING MATERIALS COMPRISING PIG IRON AND SCRAP, SAID PIG IRON CONTAINING IMPURITIES, AT LEAST PART OF SAID CHARGING MATERIALS BEING SOLID, COMPRISING CHARGING SAID SOLID CHARGING MATERIALS INTO AN UPRIGHT CRUCIBLE PROVIDED WITH A VERTICAL BLOWING LANCE ADAPTED TO BE LIFTED AND LOWERED AND HAVING CONNECTIONS TO AN OXYGEN SUPPLY AND TO A FUEL SUPPLY SO THAT IT IS CAPABLE OF OPERATING SELECTIVELY AS A BURNER LANCE AND AS AN OXYGEN BLOWING LANCE; DIRECTING A FLAME OF FUEL AND OXYGEN FROM SAID LANCE OPERATING AS A BURNER LANCE AGAINST SAID SOLID CHARGING MATERIALS SO AS TO HEAT THEM AND TO FORM A CRATER OF LIQUEFIED CHARGING MATERIALS IN THE CENTER OF THE CHARGE; CONTINUING LIQUEFYING AND HEATING SAID CHARGING MATERIALS TO PROVIDE REFINING CONDITIONS; SHUTTING OFF THE FUEL SUPPLY; AND REFINING SAID CHARGE IN SAID CRUCIBLE WITH SAID LANCE OPERATING AS AN OXYGEN BLOWING LANCE TO REMOVE SAID IMPURITIES CONTAINED IN SAID PIG IRON.

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