GB2088904A - Melting sponge iron in the arc furnace - Google Patents
Melting sponge iron in the arc furnace Download PDFInfo
- Publication number
- GB2088904A GB2088904A GB8039323A GB8039323A GB2088904A GB 2088904 A GB2088904 A GB 2088904A GB 8039323 A GB8039323 A GB 8039323A GB 8039323 A GB8039323 A GB 8039323A GB 2088904 A GB2088904 A GB 2088904A
- Authority
- GB
- United Kingdom
- Prior art keywords
- reduced iron
- furnace
- iron
- charged
- molten steel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 89
- 229910052742 iron Inorganic materials 0.000 title claims abstract description 18
- 238000002844 melting Methods 0.000 title claims description 21
- 230000008018 melting Effects 0.000 title claims description 21
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 44
- 239000010959 steel Substances 0.000 claims abstract description 44
- 239000000463 material Substances 0.000 claims abstract description 32
- 239000002893 slag Substances 0.000 claims abstract description 14
- 238000010891 electric arc Methods 0.000 claims abstract description 8
- 238000000034 method Methods 0.000 claims description 36
- 238000009628 steelmaking Methods 0.000 claims description 7
- 238000002156 mixing Methods 0.000 claims description 5
- 239000002994 raw material Substances 0.000 abstract description 26
- 235000008733 Citrus aurantifolia Nutrition 0.000 abstract description 4
- 235000011941 Tilia x europaea Nutrition 0.000 abstract description 4
- 239000004571 lime Substances 0.000 abstract description 4
- 239000002801 charged material Substances 0.000 description 6
- 239000010410 layer Substances 0.000 description 5
- 230000009467 reduction Effects 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 230000000717 retained effect Effects 0.000 description 3
- 239000002344 surface layer Substances 0.000 description 3
- 230000002411 adverse Effects 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000008188 pellet Substances 0.000 description 2
- 239000011819 refractory material Substances 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000000994 depressogenic effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000001465 metallisation Methods 0.000 description 1
- 230000008439 repair process Effects 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
- F27B3/10—Details, accessories, or equipment peculiar to hearth-type furnaces
- F27B3/18—Arrangements of devices for charging
- F27B3/183—Charging of arc furnaces vertically through the roof, e.g. in three points
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21B—MANUFACTURE OF IRON OR STEEL
- C21B13/00—Making spongy iron or liquid steel, by direct processes
- C21B13/12—Making spongy iron or liquid steel, by direct processes in electric furnaces
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric furnaces
- C21C5/5211—Manufacture of steel in electric furnaces in an alternating current [AC] electric arc furnace
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric furnaces
- C21C5/527—Charging of the electric furnace
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
- Vertical, Hearth, Or Arc Furnaces (AREA)
Abstract
Reduced iron-base raw material having a reduced iron content of 95-100% with respect to total charge is charged into an electric arc furnace where an iron mass of a bulk density smaller than 0.3 g/cm<3> (e.g. scrap) is charged into the central portion of the furnace. The starting bulk is then melted by application of arc energy to form a molten steel pool at the central portion of the furnace, into which reduced iron is continuously charged together with a slag former such as lime at a rate corresponding to the capacity of the molten steel pool to melt the material.
Description
SPECIFICATION
Method for continuous steel making by an electric arc furnace using a high ratio of reduced iron
This invention relates to steel-making and more particularly to a method for making steel from reduced iron-base raw material by continuous operation.
The principal raw materials used in integrated steel making plants, such as a direct reduction plant, are reduced iron and scrap which are blended or mixed in a predetermined ratio.
The main production cost of steel is the cost of the main raw materials. Accordingly, in order to reduce the production cost as much as possible, it is preferred to reduce the cost of the raw material to a minimum. To this end, it is necessary to increase, to a maximum, the proportion of reduced iron since it is less expensive than scrap.
However, reduced iron has a lower electrical and heat conductivity than scrap and is more dense, so that when it is initially charged into an electric arc furnace at a high blending ratio of, for example, above 95%, there are various operational troubles as described below. Figs. 1-(l) and (11) shown in diagrammatic form a furnace 1 and materials charged therein showing respectively a main raw material charge 2 having a high content of reduced iron and molten steel pool 5 of the charged material. This material 2 charged into the furnace 1 is melted by application of heat of arcs 4 which are generated from the ends of electrodes 3 to from the molten steel pool 5.However, because of the above-mentioned lower conductivity of the reduced iron, the melting of the charged material proceeds primarily in the surface portion thereof and the melting of the central and deep portions only proceeds slowly. Since the bulk density of the reduced iron which has been blended in large amounts is high, the molten steel produced does not easily penetrate into the deep portion of the material and thus it remains on the surface layer as particularly shown in Fig. 1 (it). As a result, the arc 4 generated from the end of each electrode is invariably directed to the surface layer of the charged material or to the surface of the molten steel situated on the surface layer, so that the surrounding refractory material constituting the furnace body is directly exposed to the radiant heat of the arc affecting the furnace body to a considerable extent. Further, since the heat of the arc is not wholly absorbed in the charged material, the heat efficiency is not high, resulting in a high electric power consumption and a lower productivity than is desirable. Such a phenomenon likewise takes place even when the manner of charging of the material is changed.
Fig. 2--(1) shows another example of charging of a raw material, where the material is charged near the wall of the furnace which is different from that shown in Fig. 1-(l). However, the molten steel is formed as shown in Fig. 2-(ll), which is similar to that shown in Fig. 1--(II).
In order to overcome the disadvantages involved in the high ratio of reduced iron in the charging material, many operation methods have already been attempted. Typical methods include (1) a method in which 1 5-20% of the total weight of the main raw material (reduced iron and scrap) is charged by the use of a charging bucket and then melted, and the balance of the raw material corresponding to the remaining amount (7585%) of the total weight to be charged is continuously charged on to the molten steel pool, and (2) A "residual molten steel method" in which some molten steel from a previous process is retained in a steel-makiny furnace in an amount corresponding to about 1 5-25% of the total weight to be charged and the remainder is continuously charged into the retained metal pool.
However, a disadvantage of the method (1) is that when the material is molten at an initial stage of the batchwise charge, the resulting pool is similar to that of Fig. 1-(ll) or 2-(ll) and thus the furnace wall may be damaged by the radiant heat of the arc and the heat efficiency is lowered. In order to overcome these disadvantages an attempt has been made to distribute the material in such a way that it is locaily charged around the furnace wall by the use of a charging bucket of the "Bell type" sponge bucket, bui the charged material is melted from its upper layer, so that this method is still not satisfactory as a countermeasure.On the other hand, the residual molten steel method (2) is also disadvantageous in that since a substantial amount of the molten steel is allowed to remain from a previous charge a so-called "light charge" takes place (i.e. the volume which the furnace can take of each charge is reduced by the mount of molten metal retained from the previous charge) and thus productivity is lowered. It is difficult to check for damage such as that occurring on the furnace bed between charges, and also it is impossible to make a hot repair of the furnace bed and is thus very difficult to conduct in a practical manner the continuous operation of an electric arc furnace for steel making especially when reduced iron is used at a high ratio of about 95-1 00%.
It is generaily accepted that an optimum mixing or blending ratio of reduced iron is in the range of about 7080% from the viewpoint of protection of refractory furnace walls, electric power consumption and productivity. Continuous operation methods using a higher blending ratio of reduced iron have not been practically used.
US patent 3,443,930 disclosed a process in which an initial load of scrap is placed centrally on the furnace bottom and the reduced sponge iron is charged peripherally at the furnace sidewalls.
However, the same patent shows up to about 90 percent of the charge being sponge iron pellets and in the examples. it shows 80% or 75% of the metallic charge consisting of sponge iron pellets.
The present invention provides a method for making steel from reduced iron which comprises initially charging reduced iron material comprising about 95100% of reduced iron into an electric arc steel making furnace where an initial iron mass of a bulk density smaller than 0.3g/cm3 is provided in the central portion of said furnace, melting said iron mass and said reduced iron material to form a molten steel pool in the central portion of the furnace, and thereafter continuously charging reduced iron and slag forming material in amounts corresponding to the capacity of the molten steel pool to melt said material.
The-balance of said reduced material is preferably scrap and preferably the weight of said initial iron mass comprises 0.25% of the total weight to be charged at an initial stage of the charging, and the bulk density of said initial iron mass is less than 0.1 g/cm3.
The total weight of the reduced iron material and the initial iron mass initially charged is preferably in the range of 1 5-20% of the total weight to be charged. Preferably the slag forming material is provided in sufficient amount to ensure that the arc generated from the electrodes of said furnace is covered with a slag layer.
The invention also provides steel manufactured in accordance with the method of the invention.
in the drawings:
Figs. 1-(I) and (II) already referred to, are schematic views showing, for a known method, the state of a principal raw material charge and its state after melting, respectively;
Figs. 2-(l) and (II) also already referred to are schematic views, similar to Figs. 1--(I) and (II), showing another known method;
Figs. 3-(l) and (II) are schematic views similar to Figs. 1 and 2 but showing a raw material charge and its state after melting, according to a method of the invention; and,
Fig. 4--(1) is a graph of the temperature of molten steel against the electric power and Fig.
4-(II) is a graph of the amount of a raw material charge against the electric power.
As shown in Fig. 3-(l), when the raw material is charged in such a way that an initial iron mass or portion 6 of a bulk density smaller than that of reduced iron by itself is provided at approximately the central portion of the furnace as the initial bulk in the furnace and then melted, it is possible to prevent the radiant heat of the arc affecting the refractory furnace walls, ensuring a high heat efficiency and smooth continuous operation of the furnace for steel making even when the raw
material is blended with a ratio of about 95100% of reduced iron with respect to the total weight to be charged, with a balance of
scrap.
Thus, at the initial stage of melting, a molten steel pool is formed at the central portion of the furnace as shown in Fig. 3-(lI) while leaving
unmelted material around the periphery of the pool. As a result, the radiant heat of the arc is intercepted by the unmelted material, preventing its adverse influence on the furnace walls. The reason why the manner of melting of the material is different from those shown in Figs. 1 and 2 is as follows:
The bulk density at the central portion of the charged raw material is smaller and the thickness of the initial reduced iron layer is small, so that immediately after commencement of the melting, the central portion is depressed and the ends of the electrodes are lowered with the depression formed by the molten steel produced around the central portion.This permits the further melting of the reduced iron to proceed from the central portion of the charged bulk where the molten steel is present. Thus, the unmelted material surrounding the molten pool at the initial stage of the melting remains, with the result tha' the efficiency of absorption of the radiant heat of the arc in the raw material is enhanced. This ensures not only the protection of the refractory material of the furnace walls, but also an improved heat efficiency. The term "mass or portion of smaller bulk density" means an initial mass which is of relatively low bulk density and which can be more quickly melted than the surrounding initial charge of reduced iron at an initial stage of the process.
Accordingly said initial mass should have a bulk density of less than 0.3 g/cm3 and preferably less than 0.1 g/cm3.
In order to provide the initial smaller bulk density mass approximately at the centre of the furnace, the following methods are advantageous:
Prior to the charging of the reduced iron raw material, a steel drum, pressed used car body scrap, return screp or purchased scrap of small bulk density is manually charged or charged by mechanical means such as a crane in the centre of the furnace and then the initial reduced iron material is charged over the low bulk density mass; or alternatively the drum or other low bulk density scrap and the initial reduced iron material are packed together in a charging bucket in a suitable order and the mixture is charged into the furnace in such a manner that the low bulk density mass is provided approximately at the centre of the furnace.The weight of the low bulk density mass of a bulk density of less than 0.3 g/cm3 is 0.25% of the total weight to be charged at an initial stage of charging to facilitate the melting of the initial bulk. Further, the weight of the initially charged raw material is preferably 1 5-20% of the total weight to be charged.
The charge may be melted without resorting to any specific technique. That is, it can be melted by application of electric power thereto in the usual manner, showing a good state of melting as shown in Fig. 3--(11).
According to the method of the invention, after the initial raw material which has been charged in a batchwise manner has been at least partially melted and a molten steel pool of suitable size has been formed at the central portion of the furnace (and preferably after the melting has proceeded to the stage shown in Fig. 3-(Il)), a mixture of the reduced iron and a slag forming material such as lime can be continuously charged on the basis of a charging curve corresponding to the heat capacity of the molten steel pool and the arcs.
In Fig. 4-(l) there is shown a graph of the temperature of molten steel against electric power and in Fig. 4-(Il) there is shown a graph of the charging rate of approximately 100% reduced iron (curve (i)) and the charging rate of lime (curve (ii)) corresponding to the temperature curve for molten steel. The reduced iron is continuously fed at a rate according to the charging curve shown.
When there is sufficient slag to cover the arc with a slag layer, the melting operation can be effectively continued while preventing the radiant heat reaching the furnace wall. The feed is so controlled that the initial charge is not left unmelted finaliy. When the initial charge in the furnace has completely melted and the molten steel reaches a predetermined temperature, the melting operation is completed. When the continuous feed operation (after the first batchwise charge) is conducted in accordance with the charging curve of Fig. 4, the feed and feeding intervals should be properly controlled in respect of the capacity of the furnace, the electric power level and the grade of the reduced iron.
The present invention will be particularly illustrated by way of the following example.
In a 70 ton electric arc furnace a compressed used car body or steel drum was placed in the central portion of the furnace, over which about 16 tons of initial charge comprising 95100% of reduced iron (grade: metallization rate 9094%, total Fe 9093%) with a balance of scrap is initially charged into the furnace, followed by arc melting under ordinary conditions to form a molten steel pool of an appropriate size substantially in the central portion of the furnace.
Thereafter, reduced iron of the above type and lime were continuously fed into the furnace at a charging rate specified by the electric power input while maintaining sufficient slag to cover the arc with a slag layer. The final feed was so controlled so that it melted; that is, the reduced iron and slag were charged in amounts corresponding to the capacity of the molten steel pool to melt the raw material. When all the charged material was molten and had reached a predetermined temperature, the melting operation was completed and about 75 tons of a molten steel of the class prescribed in JIS G31 12 was obtained.
For comparison, the melting operation was conducted using a known method with a raw material comprising 8085% of reduced iron.
The results of the test according to the method of the present invention are as follows (the results being indicated by indices when those of the prior art are taken as 100). Steel yield (%):99.6, productivity (ton/hr) :101.0 (between taps):
Electric power consumption (KWH/ton) :101.0, and Refractory consumption (kg/ton) :94.0 (compared by the amount of hot repairing material used).
As will be apparent from the above results, although in accordance with the method of the present invention reduced iron is used which has a very high ratio of 95100% with respect to the total weight to be charged, there are no substantial adverse effects on the steel yield, productivity and electric power consumption and the refractory consumption is reduced by about 6%. In addition, the proportion of reduced iron in the raw material increases by 1 0-20% as compared with prior art methods, so that the cost of raw material is reduced to a great extent.
As will be understood from the foregoing, the method of the present invention in which reduced iron is used in very high proportion does not produce any troubles in practical operation and can reduce the damage to the furnace walls caused by being exposed to radiant heat of the arc, as is frequently experienced in the prior art methods, ensuring a stable, continuous operation.
Further, the reduction in cost of the raw material leads to a pronounced reduction of production cost. The method of the invention has further advantages that the raw material may be varied in composition as required even though the supply and demand relationship of raw materials vary, so that an increase in proportion of reduced iron results in a reduction in amount of impurities and an improvement of steel grade, and the reduction in amount of scrap used results in an appreciable saving of allied apparatus and management service.
Claims (8)
1. A method for making steel from reduced iron which comprises initially charging reduced iron material comprising about 95100% of reduced iron into an electric arc steel making furnace where an initial iron mass of a bulk density smaller than 0.3 g/cm3 is provided in the central portion of said furnace, melting said iron mass and said reduced iron material to form a molten steel pool in the central portion of the furnace, and thereafter continuously charging reduced iron and slag forming material in amounts corresponding to the capacity of the molten steel pool to melt said material.
2. A method as claimed in claim 1 , wherein the balance of said reduced iron material is scrap.
3. A method as claimed in claim 1 or 2, wherein the weight of said initial iron mass comprises 0.25% of the total weight to be charged at an initial stage of the charging, and the bulk density of said initial iron mass is less than 0.1 g/cm3.
4. A method as claimed in any of claims 1 to 3, wherein the total weight of the reduced iron material and the initial iron mass initially charged is in the range of 1520% of the total weight to be charged.
5. A method as claimed in any of claims 1 to 4, wherein the slag forming material is provided in sufficient amount to ensure that the arc generated from the electrodes of said furnace is covered with a slag layer.
6. A method for making steel as claimed in claim 1 substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.
7. Steel manufactured by the method of any of claims 1 to 6.
8. A method for continuous making steel from reduced iron which comprised charging reduced iron blending about 95100% of reduced iron into an electric arc furnace for making steel where an iron mass of a bulk density smaller than 0.3 g/cm3 is set around the central portion of said furnace, melting said iron mass and said reduced iron to form a molten steel pool around the central portion of the furnace, and continuously charging a reduced iron and a slag former in amounts corresponding to the heat capacity of the molten steel pool to melt said material.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8039323A GB2088904B (en) | 1980-12-08 | 1980-12-08 | Melting sponge iron in the arc furnace |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8039323A GB2088904B (en) | 1980-12-08 | 1980-12-08 | Melting sponge iron in the arc furnace |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2088904A true GB2088904A (en) | 1982-06-16 |
| GB2088904B GB2088904B (en) | 1984-10-17 |
Family
ID=10517839
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8039323A Expired GB2088904B (en) | 1980-12-08 | 1980-12-08 | Melting sponge iron in the arc furnace |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2088904B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2146355A (en) * | 1982-06-02 | 1985-04-17 | New Zealand Steel Ltd | Melting sponge iron in an eletric furnace |
| EP0663450A1 (en) * | 1994-01-14 | 1995-07-19 | Voest-Alpine Industrieanlagenbau Gmbh | Method of producing iron melt |
| EP1985952A1 (en) * | 2007-04-26 | 2008-10-29 | DANIELI AUTOMATION SpA | Method to control the feed of the metal charge for electric arc furnaces |
-
1980
- 1980-12-08 GB GB8039323A patent/GB2088904B/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2146355A (en) * | 1982-06-02 | 1985-04-17 | New Zealand Steel Ltd | Melting sponge iron in an eletric furnace |
| EP0663450A1 (en) * | 1994-01-14 | 1995-07-19 | Voest-Alpine Industrieanlagenbau Gmbh | Method of producing iron melt |
| EP1985952A1 (en) * | 2007-04-26 | 2008-10-29 | DANIELI AUTOMATION SpA | Method to control the feed of the metal charge for electric arc furnaces |
| US8902949B2 (en) | 2007-04-26 | 2014-12-02 | Danieli Automation Spa | Method to control the feed of the metal charge for electric arc furnaces |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2088904B (en) | 1984-10-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |