EP0060706A1 - Procédé d'enlèvement par aspiration du laitier flottant sur la surface d'un métal en fusion - Google Patents

Procédé d'enlèvement par aspiration du laitier flottant sur la surface d'un métal en fusion Download PDF

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Publication number
EP0060706A1
EP0060706A1 EP82301304A EP82301304A EP0060706A1 EP 0060706 A1 EP0060706 A1 EP 0060706A1 EP 82301304 A EP82301304 A EP 82301304A EP 82301304 A EP82301304 A EP 82301304A EP 0060706 A1 EP0060706 A1 EP 0060706A1
Authority
EP
European Patent Office
Prior art keywords
slag
desiliconization
fluidity
molten metal
dephosphorization
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.)
Withdrawn
Application number
EP82301304A
Other languages
German (de)
English (en)
Inventor
Hisashi Matsunaga
Katuhiko Ishikura
Katuyosi Imamura
Fujio Kato
Seizo Mineyuki
Akiyoshi Minami
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Nippon Steel Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from JP3764581A external-priority patent/JPS5838484B2/ja
Priority claimed from JP3764281A external-priority patent/JPS5838483B2/ja
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Publication of EP0060706A1 publication Critical patent/EP0060706A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D3/15—Tapping equipment; Equipment for removing or retaining slag
    • F27D3/1545—Equipment for removing or retaining slag
    • F27D3/1554—Equipment for removing or retaining slag for removing the slag from the surface of the melt
    • F27D3/1572—Equipment for removing or retaining slag for removing the slag from the surface of the melt by suction
    • 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
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/02—Dephosphorising or desulfurising
    • 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
    • C21C7/0087—Treatment of slags covering the steel bath, e.g. for separating slag from the molten metal

Definitions

  • This invention relates to a method for removing slag from the surface of molten metal by suction. More particularly, the invention relates to a method that achieves easy discharge of slag through suction by increasing its fluidity.
  • Molten iron from a blast furnace is freed of slag before it is poured into a vessel, but the separation of molten iron from slag is often incomplete and the blast furnace slag floats on the surface of the molten iron in the vessel.
  • slag is formed by reaction of the molten iron with a flux added in each refining stage, and floats on the surface of the melt.
  • molten slag is poured from a tilting vessel. This method is simple but is unable to achieve complete separation of the two materials.
  • slag is skimmed manually or by mechanical force, but this method is not preferred for the following reasons: 1) the temperature of the molten iron is decreased since its surface is exposed to the atmosphere; 2) the operator is exposed to very high temperatures; and 3) it takes much time to skim all the slag from the molten iron.
  • a more effective method is to use a slag cleaner that is positioned above the slag and draws it off by suction.
  • a typical slag cleaner is illustrated in Fig. 1, wherein a slag cleaner 4 with a suction head 5 is positioned slightly above the surface of the slag 3 floating on molten iron 2 in a vessel 1. The suction head 5 is connected to a vacuum pump or other vacuum source, and slag 3 is drawn through the head and discharged overhead.
  • a conventional slag cleaner is described in U.S. Patent No. 4,160,662.
  • One great problem with the slag is that its composition and physical properties such as temperature vary across the section of the molten metal and it contains some portions having low fluidity. It is difficult to draw off low-fluidity slag by the slag cleaner and it can only be removed by mechanical force.
  • the molten iron In desiliconization of molten iron, solid oxide such as iron oxide is injected into the melt, and the resulting slag has a low total Fe content and hence a low fluidity.
  • the molten iron After desiliconization and discharging the slag, the molten iron is dephosphorized or, instead, it is desulfurized and dephosphorized simultaneously, followed by discharging of the resulting slag.
  • dephosphorization or simultaneous desulfurization and dephosphorization is achieved by using a flux mainly composed of CaO and supplying solid oxide (e.g. iron oxide) or gaseous oxygen or both. In either case, the resulting slag has a high melting point and hence low fluidity.
  • the slag to be treated desirably has a basicity ( weight ratio of CaO/SiO 2 ) of at least 3.0 and a total Fe content of 15 wt % or less.
  • the slag obtained by treating slag having a fairly high basicity and low total Fe content has a low fluidity and cannot be completely removed by a slag cleaner unless much time is spent, or the cleaner is replaced by less efficient.mechanical skimming.
  • one object of the present invention is to provide a method that increases the fluidity of slag on molten metal so that it can be easily removed by a suction-type slag cleaner.
  • Another object of the present invention is to provide a method for forming slag of increased fluidity without causing any adverse'effect on dephosphorization or simultaneous dephosphorization and desulfurization.
  • the present invention achieves easy removal of slag by suction by means of lowering the melting point of the slag and increasing its fluidity.
  • the s.lags to be treated by the method of the present invention include blast furnace slag floating on the surface of molten metal and those slags which are formed by purifying molten iron with a flux and which contain various impurities in a removable form.
  • One of the purification operations that produce the slag to be treated by the present invention is desiliconization.
  • the other purifications are dephosphorization and simultaneous desulfurization and dephosphorization that follow desiliconization.
  • the slag to be treated desirably has a high basicity and total Fe content for achieving efficient dephosphorization, but the resulting slag then has a low fluidity. Therefore, the principal object of the present invention is to increase the fluidity of such slag.
  • the fluidity modifier used in the present invention is preferably one or more materials selected from the group consisting of CaF 2 , sintered ore, iron ore (fine ore is preferred), slag from desiliconization, water-quenched slag from desiliconization and gaseous oxygen.
  • Sintered ore is preferred since it contains not only iron oxide but also a suitable amount of Si0 2 .
  • the slag from desiliconization is the slag formed by desiliconization which is the first step of several purifications to be performed on the molten metal from a blast furnace. This slag has a very high Si0 2 content since it contains melt-derived Si in the form of SiO 2 .
  • the present invention adds the high SiO 2 slag to the blast furnace slag, the slag from dephosphorization, or the slag from simultaneous desulfurization and dephosphorization, to thereby form a slag having a low basicity (say, less than 3.0), and hence a high fluidity.
  • the slag formed by desiliconization can be used as a fluidity modifier for the slag produced in the subsequent step of dephosphorization or simultaneous desulfurization and dephosphorization.
  • the slag used as a fluidity modifier preferably has a uniform and small size of, say, 2 mm.
  • the slag from desiliconization may be water-quenched after being drawn off by a slag cleaner.
  • Such slag is called “water-quenched slag from desiliconization” and can also be used as a fluidity modifier in the present invention.
  • FIG. 2 shows the relation between drawing time and slag removal efficiency observed in this experiment.
  • FIG. 3 shows the relation between drawing time and slag removal efficiency observed when gaseous oxygen was blown for 2 to 5 minutes onto 800 kg of blast furnace slag floating on 70 tonnes of molten iron at 1365°C after 40 kg of CaF 2 was added to it. Almost all the slag could be removed by the method of the present invention, whereas only 60% of untreated blast furnace slag could be removed by suction alone.
  • the fluidity modifiers of the present invention can be added to blast furnace slag at any time, but this is not so with the slag formed as a result of various refining operations, and the timing of addition is very important.
  • the fluidity modifiers could be added in either the early or middle stage of each refining operation, but in fact, various troubles occur. For instance, if CaF 2 is added in the early or middle stage of desiliconization of molten iron, the resulting slag forms so much that continued desiliconization becomes difficult. If CaF 2 is added in the early or middle stage of simultaneous dephosphorization and desulfurization following desiliconization of molten iron and slag discharge, the resulting slag also foams considerably and continued dephosphorization and desulfurization become difficult.
  • dephosphorization is inhibited if simultaneous dephosphorization and desulfurization is performed by supplying solid oxide overhead. If sintered ore is added in the early or middle stage of simultaneous dephosphorization and desulfurization, the total Fe content of the resulting slag becomes greater than the value (7 to 8%) suitable for desulfurization, and not only is the desulfurization efficiency decreased but also re-sulfurization occurs. If water-quenched slag from desiliconization is added in the early or middle stage of dephosphorization or simultaneous dephosphorization and desulfurization, the basicity of the slag being treated is decreased to reduce the dephosphorization efficiency.
  • the desired slag can be formed by adding the fluidity.modifiers in the last stage of each refining operation, after completion of each refining operation, or by starting the addition in the last stage of each refining operation and ending it after completion of each refining.
  • the term "the last stage of each refining operation" means, but it is not limited to, less than 6 minutes, say, 3 to 5 minutes, before completion of each refining operation.
  • CaF 2 is capable of increasing the fluidity of slag in a short time, so excessive slag foaming can be avoided by stopping the process of slag formation as soon as the desired slag fluidity is obtained. If sintered ore is added in one of the three stages mentioned above, little or no. reduction occurs in the refining efficiency due to increased total Fe content of the slag being refined. At the same time, sintered ore contains Si0 2 which decreases the basicity of the slag being treated, but there is no possibilty of re-sulfurization since the timing of its addition enables rapid slag formation.
  • the slag from desiliconization or water-quenched slag from desiliconization is used in the subsequent refining operation, it is added in one of the following stages: i) after completion of dephosphorization or simultaneous desulfurization and dephosphorization, ii) in the last stage of dephosphorization or simultaneous desulfurization and dephosphorization, or iii) the addition starts in the last stage of the respective refining operations and ends after completion of those refining operations.
  • Example 2-1 when CaF 2 was added in the early stage of desiliconization (comparative run), considerable slag foaming occurred and the refining operation had to be suspended after 10 minutes. The final Si content was as high as 0.43%. When CaF 2 was added 3 minutes before the end of the desiliconization (run of the present invention), no slag foaming occurred and the desired .desiliconization could be achieved. All the slag formed could be removed by eleven minutes of sucking ' .
  • Example 2-2 when CaF 2 was added in the early'stage of simultaneous dephosphorization and desulfurization (comparative run), considerable slag foaming took place and the refining operation had to be suspended after 8 minutes. The final P and S contents were as high as 0.073% and 0.021%, respectively.
  • CaF 2 was added 3 minutes before the end of the refining operation (run of the present invention), no slag foaming occurred and the desired dephosphorization and desulfurization could be achieved. Ninety percent of the slag formed could be removed by ten minutes of sucking.
  • Iron ore was added to 100 tonnes of molten iron (0.55% Si, 0.018% S, 0.115% P) at 1340°C in a vessel and desiliconized for 15 minutes under agitation with gas while oxygen was blown from above.
  • the treated iron had 0.15% Si, 0.018% S and 0.115% P.
  • the resulting slag was water-quenched as it was drawn from above by a slag cleaner of Kubota, Ltd.
  • a CaO flux was added to the molten iron in the same vessel, and the iron was dephosphorized for 15 minutes under agitation with an impeller while iron oxide was added and oxygen was blown from above. After completion of the dephosphorization, 300 kg of the water-quenched slag from desiliconization was added. The resulting slag had a basicity of 2.2 and was drawn off by a slag cleaner .
  • the dephosphorized iron had 0.01% Si, 0.017% S and 0.015% P.
  • FIG. 4 compares the efficiency of removing the slag from dephosphorized iron in Example 3-1 according to the present invention and that of removing slag without addition of the water-quenched slag from desiliconization.
  • the slag could be removed in a short time by the method of the present invention.
  • the slag became increasingly hard (less fluid) as the surface temperature of the molten iron was decreased, and only about half of the slag could be removed.
  • Molten iron was desiliconized as in Example 3-1, and after discharging the resulting slag, a CaO/CaCl 2 flux was added to the molten iron in the same vessel, and the iron was desulfurized and dephosphorized simultaneously for 20 minutes under agitation with an impeller while iron oxide was added and oxygen was blown from above.
  • Three minutes before completion of the refining operation 500 kg of water-quenched slag from desiliconization prepared as in Example 3-1 were added.
  • the resulting slag had a basicity of 2.5 at the time of completion of the refining operation, and it was drawn off by a slag cleaner.
  • the refined iron had 0.01% Si, 0.009% S and 0.012% P, and these values were exactly the same as intended.
  • FIG. 5 shows the efficiency of removing the slag from simultaneously desulfurized and dephosphorized slag in Example 3-2 according to the present invention and that of removing slag without addition of the water-quenched slag from desiliconization.
  • the slag could be removed in a short time by the method of the present invention, whereas in the conventional method which did not use water-quenched slag from desiliconization as a fluidity modifier, only about 30% of the slag could be removed.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Analytical Chemistry (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
EP82301304A 1981-03-16 1982-03-15 Procédé d'enlèvement par aspiration du laitier flottant sur la surface d'un métal en fusion Withdrawn EP0060706A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP37642/81 1981-03-16
JP3764581A JPS5838484B2 (ja) 1981-03-16 1981-03-16 溶融金属処理スラグの吸引方法
JP3764281A JPS5838483B2 (ja) 1981-03-16 1981-03-16 溶銑処理スラグの吸引除去方法
JP37645/81 1981-03-16

Publications (1)

Publication Number Publication Date
EP0060706A1 true EP0060706A1 (fr) 1982-09-22

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EP82301304A Withdrawn EP0060706A1 (fr) 1981-03-16 1982-03-15 Procédé d'enlèvement par aspiration du laitier flottant sur la surface d'un métal en fusion

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EP (1) EP0060706A1 (fr)
AU (1) AU527082B2 (fr)
BR (1) BR8201399A (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1985004191A1 (fr) * 1984-03-21 1985-09-26 British Steel Corporation Appareil et procede pour extraire un materiau

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE699180A (fr) * 1967-05-29 1967-11-29
FR2051700A1 (fr) * 1969-07-11 1971-04-09 Republic Steel Corp
FR2258459A1 (fr) * 1974-01-17 1975-08-18 Kubota Ltd
FR2259908A1 (en) * 1974-01-31 1975-08-29 Carad Slag conditioner - for facilitating dissolution of lime content in basic steel refining slag
FR2327320A1 (fr) * 1975-10-06 1977-05-06 Mercier Corp Agent de fluidisation de scories et procede d'utilisation de cet agent pour la production de fer et d'acier

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE699180A (fr) * 1967-05-29 1967-11-29
FR2051700A1 (fr) * 1969-07-11 1971-04-09 Republic Steel Corp
FR2258459A1 (fr) * 1974-01-17 1975-08-18 Kubota Ltd
FR2259908A1 (en) * 1974-01-31 1975-08-29 Carad Slag conditioner - for facilitating dissolution of lime content in basic steel refining slag
FR2327320A1 (fr) * 1975-10-06 1977-05-06 Mercier Corp Agent de fluidisation de scories et procede d'utilisation de cet agent pour la production de fer et d'acier

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1985004191A1 (fr) * 1984-03-21 1985-09-26 British Steel Corporation Appareil et procede pour extraire un materiau

Also Published As

Publication number Publication date
AU8151282A (en) 1982-11-04
BR8201399A (pt) 1983-02-01
AU527082B2 (en) 1983-02-17

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Inventor name: ISHIKURA, KATUHIKO

Inventor name: MINEYUKI, SEIZO

Inventor name: KATO, FUJIO

Inventor name: MINAMI, AKIYOSHI

Inventor name: MATSUNAGA, HISASHI

Inventor name: IMAMURA, KATUYOSI