EP0061012B1 - Process for producing desulfurizing agents for pig iron and steel melts - Google Patents

Process for producing desulfurizing agents for pig iron and steel melts Download PDF

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Publication number
EP0061012B1
EP0061012B1 EP82101428A EP82101428A EP0061012B1 EP 0061012 B1 EP0061012 B1 EP 0061012B1 EP 82101428 A EP82101428 A EP 82101428A EP 82101428 A EP82101428 A EP 82101428A EP 0061012 B1 EP0061012 B1 EP 0061012B1
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EP
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Prior art keywords
weight
cao
calcium oxide
desulfurization
cac
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EP82101428A
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German (de)
French (fr)
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EP0061012A1 (en
Inventor
Albert Braun
Willi Dr. Portz
Georg Dr. Strauss
Hans-Martin Dipl.-Ing. Delhey
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Krupp Stahl AG
Hoechst AG
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Krupp Stahl AG
Hoechst AG
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Priority to AT82101428T priority Critical patent/ATE9232T1/en
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    • 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
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/064—Dephosphorising; Desulfurising
    • C21C7/0645—Agents used for 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
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/02—Dephosphorising or desulfurising
    • C21C1/025—Agents used for dephosphorising or desulfurising

Definitions

  • the invention relates to a process for the preparation of a desulfurization agent for pig iron and steel melts based on a calcium carbide containing calcium oxide, in which a finely divided calcium oxide is introduced into a calcium carbide melt produced in a conventional manner, which already has a calcium oxide content of up to 45% by weight an excess of 3 to 15 wt .-%, based on the amount desired in the CaC 2 -CaO crystal mixture, then cools the resulting mixture under solidification to temperatures of 350 to 450 ° C, at these temperatures breaks down to grain sizes smaller than 150 mm , and separates the inevitable grain fraction smaller than 4 mm from the remaining product.
  • a method is already known from EP-A1-19087.
  • DE-A1-2907069 describes an agent for the desulfurization of molten metals, in particular pig iron and steel, based on CaC z / CaO, which consists of a CaC 2 / CaO crystal mixture produced in the melt flow and then comminuted with a CaC 2 content of 35 to 65 wt .-%, based on the amount of CaC 2 / CaO exists.
  • DE-B2-2 252 795 also specifies that the addition of calcium carbonate to the desulfurization agents has a gas-releasing effect and, by means of rising gas bubbles, promotes a uniform distribution of the desulfurization agent in all parts of the melt and at the same time accelerates the separation of the desulfurization products.
  • the same advantages, or even greater advantages in the presence of carbonate provide water-releasing additives, e.g. B. Ca (OH) 2 , to the desulfurizing agents.
  • the known desulfurization agents especially for use by the immersion lance method, first had to be ground as finely as possible. According to this, these mixtures meet the requirements, but are expensive in terms of both manufacture and use. Despite the fine grinding, relatively large amounts of the desulfurizing agents had to be added to achieve the desired degree of desulfurization.
  • EP-A1-31 552 relates to a means for desulfurizing metal melts, in particular steel and pig iron melts, on the basis of CaC 2 -CaO crystal mixtures obtained in the melt flow, which is characterized in that in the crystal mixture Part of the CaO is hydrated to Ca (OH).
  • the process for the preparation of this agent is characterized, inter alia, in that for the preparation of the end product, the 20 to 55% by weight calcium carbide, more than 45 to 80% by weight calcium oxide and also chemically bound to calcium oxide Water contains, in a present and customarily produced calcium carbide melt, which already has a calcium oxide content of up to 45% by weight, introduces finely divided calcium oxide in an excess of 3 to 15% by weight, based on the amount desired in the end product, then the resulting mixture cools to temperatures of 350 to 450 ° C under solidification, breaks down to grain sizes smaller than 150 mm at these temperatures, separates the resulting grain fraction smaller than 4 mm from the remaining product and the latter in the presence of air or nitrogen with a moisture content from 5 to 20 g / m 3 (at 1.013 bar and 273.15 K) by breaking and grinding at temperatures below 100 ° C to grain sizes smaller than 10 mm crushed.
  • the object of the present invention was to provide an economical process for producing a desulfurization agent which offers an improved degree of utilization.
  • the present invention be produced desulfurizing free carbon and carbonate contained and 2 7CaO-crystal mixture is hydrated, part of the CaO to Ca (OH) 2 in the CaC.
  • CaC 2 -CaO crystal mixtures with a proportion of 40 to 80% by weight CaO (corresponding to 20 to 60% by weight CaC 2 ), in particular 45 to 80% by weight CaO (corresponding to 20 to 55 % By weight of CaC 2 ) or 40 to 65% by weight of CaO) corresponding to 35 to 60% by weight of CaC 2 ).
  • the desulfurization agent to be produced according to the invention is preferably characterized in that it contains 1 to 6% by weight, preferably 2.5 to 3.5% by weight. contains water chemically bound to calcium oxide.
  • the desulfurization agents to be produced according to the invention preferably contain 0.5 to 8% by weight of free carbon (e.g. coke breeze, anthracite, graphite, carbon black) and 0.5 to 20% by weight. % Carbonates of calcium, magnesium or sodium.
  • CaO and CaC 2 crystallize as a crystal mixture in which the CaC 2 and CaO crystals are intertwined, specifically at the specified CaC 2 / CaO quantity ratio, with one lying in the area of the eutectic or shifted to the lime side hypoeutectic composition.
  • H 2 0 is added, part of the CaO in the crystal mixture reacts according to the equation without the CaC 2 grown together with the CaO crystals being substantially attacked by the H 2 0.
  • the grinding grains which consist of CaO-CaC 2 crystal growths in which some of the CaO crystals are hydrated, disintegrate at the prevailing temperatures above 800 ° C according to the following reaction equation
  • the grinding grain Because of the gas development at the reactive crystal interfaces, the grinding grain literally bursts with the release of lime, which is highly reactive in statu nascendi, and with enlargement of the CaO-CaC 2 crystal surfaces grown together in the grain. With an almost eutectic crystal structure, there is an ideally large reaction area.
  • the released reducing gases offer ideal conditions for the implementation of the CaO with the sulfur dissolved in the molten metal.
  • Such a desulfurization agent is particularly suitable for desulfurization processes in which the time for the desulfurization agent to react with the sulfur is very short.
  • This process includes the immersion lance process, in which the desulfurization agent should be converted as completely as possible by blowing desulfurization agents into a molten metal below its surface in the short time between the desulfurization agent exiting the melt and rising to the bath surface.
  • the desulfurization agent to be produced according to the invention is superior to the best known carbide-based mixtures in the desulfurization effect. Because of the intergranular gas reaction in the grinding grain, the conversion of CaC 2 to CaO and the resulting enlargement of the crystal surfaces are more effective, the gas development is much more uniform and less violent than with known desulfurization agents, e.g. B. according to DE-AS 2 252 795, which gas-releasing additives such as Ca (OH) z are mechanically mixed in from the beginning. Desulphurization therefore takes place more quietly and with less metal ejection, particularly in the open pan and the torpedo pan.
  • the material can be used in a coarser manner, so that expensive fine grinding can be dispensed with.
  • the use of the desulfurization agent to be produced according to the invention enables greater accuracy with regard to the respectively required final content due to its homogeneous composition.
  • the production costs for the agent to be produced according to the invention are considerably lower than for known agents based on carbide.
  • the process of the invention is characterized in particular in that free carbon and carbonate are added to the product, which has been broken down to grain sizes of less than 150 mm and freed from the grain fraction of less than 4 mm, and the mixture in the presence of air or nitrogen with a moisture content of 5 to 20 g / m 3 (at 1.013 bar and 273.15 K) by crushing and grinding at temperatures below 100 ° C, preferably from 10-50 ° C, crushed to grain sizes smaller than 10 mm, preferably 0.1 mm.
  • the calcium oxide which is introduced into the melt, is preheated to temperatures up to 2000 ° C., preferably up to 1100 ° C., and is introduced into the melt hot at these temperatures, it is possible to determine the CaO content in the Increase carbide to 80 wt .-%, the preheating is chosen higher, the higher the desired proportion of additionally dissolved calcium oxide should be between 40 and 80 wt .-%. This enables use in low-carbon pig iron and steel melts and also increases the desulfurization yield, based on calcium carbide.
  • the portions smaller than 4 mm which have been screened off after the preliminary crushing essentially consist of CaO and can be returned to the process as finely divided calcium oxide, where they serve as the starting product together with fresh CaO. It was not foreseeable for the person skilled in the art that, by screening off the portions falling less than 4 mm after the preliminary breaking, those portions which have no or only a slight desulfurization effect are removed from the product, and the effectiveness of the end product is considerably increased.
  • the product produced according to the invention can be ground much better than products obtained by known processes. This is particularly important because in some cases the product has to be used with a grain size of less than 0.1 mm.
  • Calcium carbide e.g. B. produced electrothermally, the lime-coke mixture in the Möller is set to a weight ratio of 100:40, which corresponds to a carbide with a CaO content of about 40 wt .-%.
  • CaO with a grain size of 3 to 8 mm and a Ca (OH) 2 - and CaC0 3 content of in each case less than 1% by weight is injected into the jet of the molten carbide tapped from the furnace into a crucible at such a speed and entered in such amounts that, until the crucible is filled, there is a total CaC 2 : CaO weight ratio of 43:57, which is an excess of 14% by weight CaO, based on the CaO desired in the CaC 2 -Ca0 crystal mixture - Contains 50% by weight.
  • the mixture is then cooled until the average temperature of the solidified carbide block is approximately 400 ° C., and the block is pre-crushed to sizes smaller than 150 mm.
  • the fractions smaller than 4 mm obtained during the preliminary crushing essentially contain the CaO used in excess, while the remaining product with grain sizes larger than 4 mm represents a crystal mixture of 50% by weight CaC 2 and 50% by weight CaO.
  • 850 kg of this CaC 2 -CaO crystal mixture are mixed with 100 kg limestone (grain size less than 1 mm) and 50 kg of coke breeze (grain size less than 3 mm) and while passing 1,500 m 3 / h of air with a moisture content of 10 g / m 3 (at 15 ° C) in a rotary mill with a throughput of 500 kg / h at 50 ° C to grain sizes smaller than 0.1 mm.
  • the screened grain fraction smaller than 4 mm is used together with fresh lime (CaO) as the starting product.
  • the product obtained contains 2% by weight of chemically bound water.
  • Example 2 The procedure is as in Example 1, with the changes that the CaO is preheated to a temperature of about 1100 ° C. and the amount of CaO is increased so that a total CaO content of 62.5 wt .-%, which corresponds to an excess of 4 wt .-%, based on the desired content in the finished end product of 60 wt .-% CaO.
  • 1800 kg of the product worked up and ground according to the invention are used to desulfurize a 300 t steel melt with a sulfur content of 0.02% by weight at 1,650 ° C.
  • the sulfur content of the melt is reduced to less than 0.005% by weight.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)

Abstract

The disclosure provides mixtures for the desulfurization of metal melts, especially steel and crude iron melts, based on CaC2-CaO-crystal blends produced in the fused mass. More specifically, the mixtures contain free carbon and carbonate and have a portion of the CaO in the CaC2-CaO-crystal blend hydrated to Ca(OH)2. The disclosure also relates to a process for making the mixtures.

Description

Die Erfindung betrifft ein Verfahren zu Herstellung eines Entschwefelungsmittels für Roheisen- und Stahlschmelzen auf der Basis eines Calciumoxid enthaltenden Calciumcarbides, wobei man in eine in üblicher Weise erzeugte Calciumcarbidschmelze, welche bereits einen Calciumoxidgehalt bis zu 45 Gew.-% aufweist, feinteiliges Calciumoxid einträgt, in einem Überschuß von 3 bis 15 Gew.-%, bezogen auf die im CaC2-CaO-Kristallgemenge gewünschte Menge, dann die erhaltene Mischung unter Erstarren auf Temperaturen von 350 bis 450 °C abkühlt, bei diesen Temperaturen auf Korngrößen kleiner als 150 mm vorbricht, und den dabei zwangsläufig anfallenden Kornanteil kleiner als 4 mm vom verbleibenden Produkt abtrennt. Ein derartiges Verfahren ist bereits aus EP-A1-19087 bekannt.The invention relates to a process for the preparation of a desulfurization agent for pig iron and steel melts based on a calcium carbide containing calcium oxide, in which a finely divided calcium oxide is introduced into a calcium carbide melt produced in a conventional manner, which already has a calcium oxide content of up to 45% by weight an excess of 3 to 15 wt .-%, based on the amount desired in the CaC 2 -CaO crystal mixture, then cools the resulting mixture under solidification to temperatures of 350 to 450 ° C, at these temperatures breaks down to grain sizes smaller than 150 mm , and separates the inevitable grain fraction smaller than 4 mm from the remaining product. Such a method is already known from EP-A1-19087.

Die DE-A1-2907069 beschreibt ein Mittel zur Entschwefelung von Metallschmelzen, insbesondere von Roheisen und Stahl, auf der Basis CaCz/CaO, welches aus einem im Schmelzfluß hergestellten und anschließend zerkleinerten CaC2/CaO-Kristallgemenge mit einem CaC2-Anteil von 35 bis 65 Gew.-%, bezogen auf die CaC2/CaO-Menge, besteht.DE-A1-2907069 describes an agent for the desulfurization of molten metals, in particular pig iron and steel, based on CaC z / CaO, which consists of a CaC 2 / CaO crystal mixture produced in the melt flow and then comminuted with a CaC 2 content of 35 to 65 wt .-%, based on the amount of CaC 2 / CaO exists.

Weiterhin ist aus DE-B2-22 52 795 bekannt, Metallschmelzen mit technischem Carbid (ca. 80 Gew.-% CaC2, Rest CaO) oder auch mit Mischungen von technischem Carbid mit Zusätzen an Kohlenstoff und gabaspaltenden Stoffen, z. B. Ca(OH)z, zu entschwefeln. Der DE-B2-2 252 795 zufolge verursacht der in Form von «Schwarzstoffen», wie Steinkohle, Anthrazit, Braunkohle, Koks oder Petrolkoks zugesetzte Kohlenstoff in der Schmelze eine reduzierende Atmosphäre, die die entschwefelnde Wirkung der eingeblasenen Entschwefelungsmittel erheblich begünstigt. Die DE-B2-2 252 795 gibt auch an, daß die Zugabe von Calciumcarbonat zu den Entschwefelungsmitteln gasabspaltend wirkt und durch aufsteigende Gasblasen eine Gleichmäßige Verteilung des Entschwefelungsmittels in allen Teilen der Schmelze fördert und zugleich die Abscheidung der Entschwefelungsprodukte beschleunigt. Die gleichen Vorteile, bzw. in Anwesenheit von Carbonat noch größere Vorteile, erbringen wasserabspaltende Zusätze, z. B. Ca(OH)2, zu den Entschwefelungsmitteln. Um einen guten Ausnutzungsgrad zu bekommen, hat man die bekannten Entschwefelungsmittel, insbesondere für den Einsatz nach dem Tauchlanzenverfahren, zunächst möglichst feinkörnig mahlen müssen. Danach entsprechen diese Gemische zwar den gestellten Anforderungen, sind jedoch sowohl bezüglich Herstellung als auch Einsatz teuer. Trotz der Feinmahlung mußten zur Erzielung des gewünschten Entschwefelungsgrades verhältnismäßig große Mengen der Entschwefelungsmittel zugesetzt werden.Furthermore, it is known from DE-B2-22 52 795 to melt metal with technical carbide (approx. 80% by weight CaC 2 , remainder CaO) or also with mixtures of technical carbide with additions of carbon and gabas-splitting substances, e.g. B. Ca (OH) z to desulfurize. According to DE-B2-2 252 795, the carbon added in the form of "black matter" such as hard coal, anthracite, lignite, coke or petroleum coke causes a reducing atmosphere in the melt, which significantly enhances the desulfurizing effect of the blown desulfurizing agents. DE-B2-2 252 795 also specifies that the addition of calcium carbonate to the desulfurization agents has a gas-releasing effect and, by means of rising gas bubbles, promotes a uniform distribution of the desulfurization agent in all parts of the melt and at the same time accelerates the separation of the desulfurization products. The same advantages, or even greater advantages in the presence of carbonate, provide water-releasing additives, e.g. B. Ca (OH) 2 , to the desulfurizing agents. In order to get a good degree of utilization, the known desulfurization agents, especially for use by the immersion lance method, first had to be ground as finely as possible. According to this, these mixtures meet the requirements, but are expensive in terms of both manufacture and use. Despite the fine grinding, relatively large amounts of the desulfurizing agents had to be added to achieve the desired degree of desulfurization.

Schließlich betrifft die ältere, nicht vorveröffentlichte EP-A1-31 552 ein Mittel zum Entschwefeln von Metallschmelzen, insbesondere von Stahl- und Roheisenschmelzen, auf der Basis von im Schmelzfluß gewonnenen CaC2-CaO-Kristallgemengen, welches dadurch gekennzeichnet ist, daß im Kristallgemenge ein Teil des CaO zu Ca(OH) hydratisiert ist. Das Verfahren zur Herstellung dieses Mittels ist gemäß EP-A1-31 552 u. a. dadurch gekennzeichnet, daß man zur Herstellung des Endproduktes, das 20 bis 55 Gew.-% Calciumcarbid, mehr als 45 bis 80 Gew.-% Calciumoxid sowie an Calciumoxid chemisch gebundenes Wasser enthält, in eine vorliegende und in üblicher Weise erzeugte Calciumcarbidschmelze, welche bereits einen Calciumoxidgehalt bis 45 Gew.-% aufweist, feinteiliges Calciumoxid einträgt, in einem Überschuß von 3 bis 15 Gew.-%, bezogen auf die im Endprodukt gewünschte Menge, dann die erhaltene Mischung unter Erstarren auf Temperaturen von 350 bis 450 °C abkühlt, bei diesen Temperaturen auf Korngrößen kleiner als 150 mm vorbricht, den dabei zwangsläufig anfallenden Kornanteil kleiner als 4 mm vom verbleibenden Produkt abtrennt und letzteres in Gegenwart von Luft oder Stickstoff mit einem Feuchtigkeitsgehalt von 5 bis 20 g/m3 (bei 1,013 bar und 273,15 K) durch Brechen und Mahlen bei Temperaturen unterhalb 100 °C auf Korngrößen kleiner als 10 mm zerkleinert.Finally, the older, unpublished EP-A1-31 552 relates to a means for desulfurizing metal melts, in particular steel and pig iron melts, on the basis of CaC 2 -CaO crystal mixtures obtained in the melt flow, which is characterized in that in the crystal mixture Part of the CaO is hydrated to Ca (OH). According to EP-A1-31 552, the process for the preparation of this agent is characterized, inter alia, in that for the preparation of the end product, the 20 to 55% by weight calcium carbide, more than 45 to 80% by weight calcium oxide and also chemically bound to calcium oxide Water contains, in a present and customarily produced calcium carbide melt, which already has a calcium oxide content of up to 45% by weight, introduces finely divided calcium oxide in an excess of 3 to 15% by weight, based on the amount desired in the end product, then the resulting mixture cools to temperatures of 350 to 450 ° C under solidification, breaks down to grain sizes smaller than 150 mm at these temperatures, separates the resulting grain fraction smaller than 4 mm from the remaining product and the latter in the presence of air or nitrogen with a moisture content from 5 to 20 g / m 3 (at 1.013 bar and 273.15 K) by breaking and grinding at temperatures below 100 ° C to grain sizes smaller than 10 mm crushed.

Aufgabe der vorliegenden Erfindung war es, ein wirtschaftliches Verfahren zur Herstellung eines Entschwefelungsmittels bereitzustellen, das einen verbesserten Ausnutzungsgrad bietet.The object of the present invention was to provide an economical process for producing a desulfurization agent which offers an improved degree of utilization.

Es wird daher vorgeschlagen, daß die erfindungsgemäß herzustellenden Entschwefelungsmittel freien Kohlenstoff und Carbonat enthalten und im CaC27CaO-Kristallgemenge ein Teil des CaO zu Ca(OH)2 hydratisiert ist. Hierbei geht man vorzugsweise von CaC2-CaO-Kristallgemengen mit einem Anteil von 40 bis 80 Gew.-% CaO (entsprechend 20 bis 60 Gew.-% CaC2), insbesondere 45 bis 80 Gew.-% CaO (entsprechend 20 bis 55 Gew.-% CaC2) oder 40 bis 65 Gew.-% CaO) entsprechend 35 bis 60 Gew.-% CaC2) aus. Das erfindungsgemäß herzustellende Entschwefelungsmittel ist bevorzugt dadurch gekennzeichnet, daß es 1 bis 6 Gew.-%, vorzugsweise 2,5 bis 3,5 Gew.-%, vo.'. an Calciumoxid chemisch gebundenem Wasser enthält. Die erfindungsgemäß herzustellenden Entschwefelungsmittel enthalten neben dem im Schmelzfluß gewonnenen CaC2-CaO-Kristallgemenge bevorzgut 0,5 bis 8 Gew.-% freien Kohlenstoff (z. B. Koksgrus, Anthrazit, Graphit, Ruß) und 0,5 bis 20 Gew.-% Carbonate des Calciums, Magnesiums oder Natriums.It is therefore proposed that the present invention be produced desulfurizing free carbon and carbonate contained and 2 7CaO-crystal mixture is hydrated, part of the CaO to Ca (OH) 2 in the CaC. CaC 2 -CaO crystal mixtures with a proportion of 40 to 80% by weight CaO (corresponding to 20 to 60% by weight CaC 2 ), in particular 45 to 80% by weight CaO (corresponding to 20 to 55 % By weight of CaC 2 ) or 40 to 65% by weight of CaO) corresponding to 35 to 60% by weight of CaC 2 ). The desulfurization agent to be produced according to the invention is preferably characterized in that it contains 1 to 6% by weight, preferably 2.5 to 3.5% by weight. contains water chemically bound to calcium oxide. In addition to the CaC 2 -CaO crystal mixture obtained in the melt flow, the desulfurization agents to be produced according to the invention preferably contain 0.5 to 8% by weight of free carbon (e.g. coke breeze, anthracite, graphite, carbon black) and 0.5 to 20% by weight. % Carbonates of calcium, magnesium or sodium.

Beim Erstarren aus dem Schmelzfluß kristallisieren CaO und CaC2 als Kristallgemenge, in dem die CaC2- und CaO-Kristalle ineinander verwachsen vorliegen, und zwar bei dem angegebenen CaC2/CaO-Mengeverhältnis mit einer im Bereich des Eutektikums liegenden bzw. zur Kalkseite verschobenen untereutektischen Zusammensetzung. Beim Zusatz von H20 reagiert ein Teil des CaO im Kristallgemenge nach der Gleichung

Figure imgb0001
ohne daß das mit den CaO-Kristallen verwachsene CaC2 wesentlich vom H20 angegriffen wird.When solidifying from the melt flow, CaO and CaC 2 crystallize as a crystal mixture in which the CaC 2 and CaO crystals are intertwined, specifically at the specified CaC 2 / CaO quantity ratio, with one lying in the area of the eutectic or shifted to the lime side hypoeutectic composition. When H 2 0 is added, part of the CaO in the crystal mixture reacts according to the equation
Figure imgb0001
 without the CaC 2 grown together with the CaO crystals being substantially attacked by the H 2 0.

Wenn ein solches Entschwefelungsmittel in eine Metallschmelze eingeblasen wird, so zerfallen die Mahlkörner, die aus CaO-CaC2-Kristallverwachsungen bestehen, in denen ein Teil der CaO-Kristalle hydratisiert ist, bei den herrschenden Temperaturen oberhalb 800 °C nach folgender ReaktionsgleichungIf such a desulfurization agent is blown into a molten metal, the grinding grains, which consist of CaO-CaC 2 crystal growths in which some of the CaO crystals are hydrated, disintegrate at the prevailing temperatures above 800 ° C according to the following reaction equation

Figure imgb0002
Figure imgb0002

Wegen der Gasentwicklung an den reaktiven Kristallgrenzflächen zerplatzt das Mahlkorn regelrecht unter Freisetzung von in statu nascendi hochreaktivem Kalk und unter Vergrößerung der im Korn verwachsenen CaO-CaC2-Kristalloberflächen. Bei nahezu eutektischem Kristallaufbau ergibt sich eine ideal große Reaktionsfläche. Die freiwerdenden reduzierend wirkenden Gase bieten dabei ideale Voraussetzungen für eine Umsetzung des CaO mit dem in der Metallschmelze gelösten Schwefel.Because of the gas development at the reactive crystal interfaces, the grinding grain literally bursts with the release of lime, which is highly reactive in statu nascendi, and with enlargement of the CaO-CaC 2 crystal surfaces grown together in the grain. With an almost eutectic crystal structure, there is an ideally large reaction area. The released reducing gases offer ideal conditions for the implementation of the CaO with the sulfur dissolved in the molten metal.

Ein solches Entschwefelungsmittel eignet sich insbesondere hervorragend bei Entschwefelungsprozessen, bei denen die Zeit für den Umsatz des Entschwefelungsmittels mit dem Schwefel sehr kurz ist. Zu diesem Verfahren gehört das Tauchlanzenverfahren, bei dem durch Einblasen von Entschwefelungsmitteln in eine Metallschmelze unterhalb deren Oberfläche in der kurzen Zeit vom Austritt des Entschwefelungsmittels in die Schmelze bis zum Aufsteigen an die Badoberfläche die Umsetzung des Entschwefelungsmittels möglichst vollständig erfolgen sollte.Such a desulfurization agent is particularly suitable for desulfurization processes in which the time for the desulfurization agent to react with the sulfur is very short. This process includes the immersion lance process, in which the desulfurization agent should be converted as completely as possible by blowing desulfurization agents into a molten metal below its surface in the short time between the desulfurization agent exiting the melt and rising to the bath surface.

Das erfindungsgemäß herzustellende Entschwefelungsmittel zeigt sich den besten bekannten Gemischen auf Carbidbasis in der Entschwefelungswirkung überlegen. Wegen der interkristallinen Gasreaktion im Mahlkorn ist die Umsetzung von CaC2 zu CaO und die dadurch bedingte Vergrößerung der Kristalloberflächen wirkungsvoller, die Gasentwicklung viel gleichmäßiger und weniger heftig als bei bekannten Entschwefelungsmitteln, z. B. gemäß DE-AS 2 252 795, denen gasabspaltende Zusätze wie Ca(OH)z von vorne herein mechanisch untergemengt sind. Die Entschwefelung erfolgt deshalb insbesondere in der offenen Pfanne und der Torpedopfanne ruhiger und mit geringeren Metallauswürfen. Wegen der höheren Reaktivität des erfindungsgemäß herzustellenden Entschwefelungsmittels als Folge der Vergrößerung der Kristalloberflächen beim Zerplatzen des Mahlkorns in der Schmelze kann das Material grobkörniger eingesetzt werden, so daß teures Feinmahlen entfallen kann.The desulfurization agent to be produced according to the invention is superior to the best known carbide-based mixtures in the desulfurization effect. Because of the intergranular gas reaction in the grinding grain, the conversion of CaC 2 to CaO and the resulting enlargement of the crystal surfaces are more effective, the gas development is much more uniform and less violent than with known desulfurization agents, e.g. B. according to DE-AS 2 252 795, which gas-releasing additives such as Ca (OH) z are mechanically mixed in from the beginning. Desulphurization therefore takes place more quietly and with less metal ejection, particularly in the open pan and the torpedo pan. Because of the higher reactivity of the desulfurization agent to be produced according to the invention as a result of the enlargement of the crystal surfaces when the grinding grain bursts in the melt, the material can be used in a coarser manner, so that expensive fine grinding can be dispensed with.

Die Verwendung des erfindungsemäß herzustellenden Entschwefelungsmittels ermöglicht wegen seiner homogenen Zusammensetzung eine größere Treffsicherheit auf den jeweils geforderten Endgehalt. Die Herstellungskosten für das erfindungsgemäß herzustellende Mittel liegen erheblich niedriger als für bekannte Mittel auf Carbidbasis.The use of the desulfurization agent to be produced according to the invention enables greater accuracy with regard to the respectively required final content due to its homogeneous composition. The production costs for the agent to be produced according to the invention are considerably lower than for known agents based on carbide.

Das Verfahren der Erfindung ist im einzelnen dadurch gekennzeichnet, daß man dem auf Korngrößen kleiner als 150 mm vorgebrochenen und vom Kornanteil kleiner als 4 mm befreiten Produkt freien Kohlenstoff und Carbonat zumischt und das Gemisch in Gegenwart von Luft oder Stickstoff mit einem Feuchtigkeitsgehalt von 5 bis 20 g/m3 (bei 1,013 bar und 273,15 K) durch Brechen und Mahlen bei Temperaturen unterhalb 100 °C, vorzugsweise von 10-50 °C, auf Korngrößen kleiner als 10 mm, vorzugsweise als 0,1 mm, zerkleinert.The process of the invention is characterized in particular in that free carbon and carbonate are added to the product, which has been broken down to grain sizes of less than 150 mm and freed from the grain fraction of less than 4 mm, and the mixture in the presence of air or nitrogen with a moisture content of 5 to 20 g / m 3 (at 1.013 bar and 273.15 K) by crushing and grinding at temperatures below 100 ° C, preferably from 10-50 ° C, crushed to grain sizes smaller than 10 mm, preferably 0.1 mm.

Wahlweise und bevorzugt ist dieses Herstellungsverfahren dadurch gekennzeichnet, daß

  • a) die Zugabe des Calciumoxids, die sogenannte Magerung des Carbids, unter Ausnutzung des Wärmeinhaltes des Carbids in einem Tiegel durchgeführt wird,
  • b) man das Calciumoxid, welches in die Calciumcarbidschmelze eingetragen wird, auf Temperaturen bis zu 2 000 °C vorerhitzt und heiß in die Schmelze einbringt, wobei die Vorerhitzung um so höher gewählt wird, je höher der gewünschte Anteil an zusätzlich gelöstem Calciumoxid zwischen 40 und 80 Gew.-% liegen soll,
  • c) von einer Calciumcarbidschmelze ausgegangen wird, welche zwischen 20 und 45 Gew.-% Calciumoxid enthält,
  • d) man die nach dem Vorbrechen abgesiebten Anteile kleiner als 4 mm in den Prozeß zurückführt.
This manufacturing process is optionally and preferably characterized in that
  • a) the addition of the calcium oxide, the so-called thinning of the carbide, is carried out using the heat content of the carbide in a crucible,
  • b) the calcium oxide, which is introduced into the calcium carbide melt, is preheated to temperatures of up to 2,000 ° C. and introduced hot into the melt, the preheating being chosen to be higher, the higher the desired proportion of additionally dissolved calcium oxide between 40 and Should be 80% by weight,
  • c) a calcium carbide melt is assumed which contains between 20 and 45% by weight calcium oxide,
  • d) the portions smaller than 4 mm which have been screened off after preliminary crushing are returned to the process.

Wenn das Calciumoxid, welches in die Schmelze eingetragen wird, vorher auf Temperaturen bis zu 2000°C, vorzugsweise bis zu 1 100 °C, vorerhitzt und mit diesen Temperaturen heiß in die Schmelze eingebracht wird, so ist es möglich, den CaO-Gehalt im Carbid bis auf 80 Gew.-% zu erhöhen, wobei die Vorerhitzung um so höher gewählt wird, je höher der gewünschte Anteil an zusätzlich gelöstem Calciumoxid zwischen 40 und 80 Gew.-% liegen soll. Dadurch wird die Anwendung in kohlenstoffarmen Roheisen- und Stahlschmelzen ermöglicht und außerdem die Entschwefelungsausbeute, bezogen auf Calciumcarbid, erhöht.If the calcium oxide, which is introduced into the melt, is preheated to temperatures up to 2000 ° C., preferably up to 1100 ° C., and is introduced into the melt hot at these temperatures, it is possible to determine the CaO content in the Increase carbide to 80 wt .-%, the preheating is chosen higher, the higher the desired proportion of additionally dissolved calcium oxide should be between 40 and 80 wt .-%. This enables use in low-carbon pig iron and steel melts and also increases the desulfurization yield, based on calcium carbide.

Die nach dem Vorbrechen abgesiebten Anteile kleiner als 4 mm bestehen im wesentlichen aus CaO und können als feinteiliges Calciumoxid wieder in den Prozeß zurückgeführt werden, wo sie zusammen mit frischem CaO als Ausgangsprodukt dienen. Nicht vorhersehbar war für den Fachmann, daß durch das Absieben der nach dem Vorbrechen abfallenden Anteile kleiner als 4 mm aus dem Produkt die Anteile entfernt werden, welche keine oder nur eine geringe Entschwefelungswirkung besitzen, und so die Wirksamkeit des Endproduktes erheblich gesteigert wird.The portions smaller than 4 mm which have been screened off after the preliminary crushing essentially consist of CaO and can be returned to the process as finely divided calcium oxide, where they serve as the starting product together with fresh CaO. It was not foreseeable for the person skilled in the art that, by screening off the portions falling less than 4 mm after the preliminary breaking, those portions which have no or only a slight desulfurization effect are removed from the product, and the effectiveness of the end product is considerably increased.

Das erfindungsgemäß hergestellte Produkt läßt sich wesentlich besser mahlen als nach bekannten Verfahren erhaltene Produkte. Dies ist deshalb von besonderer Wichtigkeit, weil das Produkt in manchen Fällen mit einer Körnung kleiner als 0,1 mm eingesetzt werden muß.The product produced according to the invention can be ground much better than products obtained by known processes. This is particularly important because in some cases the product has to be used with a grain size of less than 0.1 mm.

Anhand der folgenden Beispiele wird die Erfindung näher erläutert :The invention is explained in more detail using the following examples:

Beispiel 1example 1

In bekannter Weise wird aus Kalk und Koks Calciumcarbid, z. B. elektrothermisch, hergestellt, wobei die Kalk-Koks-Mischung im Möller auf ein Gewichtsverhältnis von 100 : 40 eingestellt wird, was einem Carbid mit einem CaO-Gehalt von ca. 40 Gew.-% entspricht. In den Strahl des aus dem Ofen in einen Tiegel abgestochenen schmelzflüssigen Carbides wird CaO mit einer Körnung von 3 bis 8 mm und einem Ca(OH)2- und CaC03-Gehalt von jeweils weniger als 1 Gew.-% mit einer solchen Geschwindigkeit und in solchen Mengen eingetragen, daß, bis der Tiegel gefüllt ist, insgesamt ein CaC2 : CaO-Gewichtsverhältnis von 43 : 57 vorliegt, was einem Überschuß von 14 Gew.-% CaO, bezogen auf den im CaC2-Ca0-Kristallgemenge gewünschten CaO-Gehaft von 50 Gew.-%, entspricht. Dann wird abgekühlt, bis die Durchschnittstemperatur des dabei erstarrten Carbidblokkes etwa 400 °C beträgt, und der Block auf Größen kleiner als 150 mm vorgebrochen.Calcium carbide, e.g. B. produced electrothermally, the lime-coke mixture in the Möller is set to a weight ratio of 100:40, which corresponds to a carbide with a CaO content of about 40 wt .-%. CaO with a grain size of 3 to 8 mm and a Ca (OH) 2 - and CaC0 3 content of in each case less than 1% by weight is injected into the jet of the molten carbide tapped from the furnace into a crucible at such a speed and entered in such amounts that, until the crucible is filled, there is a total CaC 2 : CaO weight ratio of 43:57, which is an excess of 14% by weight CaO, based on the CaO desired in the CaC 2 -Ca0 crystal mixture - Contains 50% by weight. The mixture is then cooled until the average temperature of the solidified carbide block is approximately 400 ° C., and the block is pre-crushed to sizes smaller than 150 mm.

Die beim Vorbrechen anfallenden Anteile kleiner als 4 mm enthalten im wesentlichen das im Überschuß eingesetzte CaO, während das zurückbleibende Produkt mit Korngrößen größer als 4 mm ein Kristallgemenge von 50 Gew.-% CaC2 und 50 Gew.-% CaO darstellt. 850 kg dieses CaC2-CaO-Kristallge- menges werden mit 100 kg Kalkstein (Körnung kleiner 1 mm) und 50 kg Koksgrus (Körnung kleiner 3 mm) vermischt und unter Durchleiten von 1 500 m3/h Luft mit einem Feuchtigkeitsgehalt von 10 g/m3 (bei 15 °C) in einer Rotationsmühle mit einem Durchsatz von 500 kg/h bei 50 °C auf Korngrößen kleiner als 0,1 mm gemahlen. Die abgesiebte Kornfraktion kleiner als 4 mm wird zusammen mit frischem Kalk (CaO) wieder als Ausgangsprodukt eingesetzt. Das erhaltene Produkt enthält 2 Gew.-% chemisch gebundenes Wasser.The fractions smaller than 4 mm obtained during the preliminary crushing essentially contain the CaO used in excess, while the remaining product with grain sizes larger than 4 mm represents a crystal mixture of 50% by weight CaC 2 and 50% by weight CaO. 850 kg of this CaC 2 -CaO crystal mixture are mixed with 100 kg limestone (grain size less than 1 mm) and 50 kg of coke breeze (grain size less than 3 mm) and while passing 1,500 m 3 / h of air with a moisture content of 10 g / m 3 (at 15 ° C) in a rotary mill with a throughput of 500 kg / h at 50 ° C to grain sizes smaller than 0.1 mm. The screened grain fraction smaller than 4 mm is used together with fresh lime (CaO) as the starting product. The product obtained contains 2% by weight of chemically bound water.

Durch Einblasen von 1 500 kg dieses Produktes in eine 300 t-Roheisenschmelze mit einem Schwefelgehalt von 0,03 Gew.-% bei Temperaturen von 1 400 °C wird der Schwefelgehalt der Eisenschmelze auf weniger als 0,005 Gew.-% gesenkt.By blowing 1,500 kg of this product into a 300 t pig iron melt with a sulfur content of 0.03% by weight at temperatures of 1400 ° C., the sulfur content of the iron melt is reduced to less than 0.005% by weight.

Beispiel 2Example 2

Es wird wie im Beispiel 1 verfahren, mit den Änderungen, daß das CaO vor dem Eintragen auf eine Temperatur von etwa 1100 °C vorerhitzt und die Menge an CaO so erhöht wird, daß sich insgesamt im Tiegel ein CaO-Gehalt von 62,5 Gew.-% ergibt, was einem Überschuß von 4 Gew.-% entspricht, bezogen auf den im fertigen Endprodukt gewünschten Gehalt von 60 Gew.-% CaO.The procedure is as in Example 1, with the changes that the CaO is preheated to a temperature of about 1100 ° C. and the amount of CaO is increased so that a total CaO content of 62.5 wt .-%, which corresponds to an excess of 4 wt .-%, based on the desired content in the finished end product of 60 wt .-% CaO.

1800 kg des erfindungsgemäß aufgearbeiteten und gemahlenen Produktes werden zur Entschwefelung einer 300 t-Stahlschmelze mit einem Schwefelgehalt von 0,02 Gew.-% bei 1 650 °C eingesetzt. Dabei wird der Schwefelgehalt der Schmelze auf weniger als 0,005 Gew.-% gesenkt.1800 kg of the product worked up and ground according to the invention are used to desulfurize a 300 t steel melt with a sulfur content of 0.02% by weight at 1,650 ° C. The sulfur content of the melt is reduced to less than 0.005% by weight.

Beispiel 3Example 3 a) Eine 300 t-Roheisenschmelze mit folgender Analyse (Gew.-%) :a) A 300 t pig iron melt with the following analysis (% by weight):

4,5 % Kohlenstoff, 0,8 % Silizium, 0,7 % Mangan, 0,08 % Phosphor, 0,064 % Schwefel, Rest Eisen wurde nach dem Tauchlanzenverfahren mit dem erfindungsgemäßen Entschwefelungsgemisch aus Beispiel 1 in einer offenen Pfanne entschwefelt. Die Tauchtiefe der Lanze betrug 1,8 m. Die Einblasgeschwindigkeit betrug 100 kg/min. Der Gesamtverbrauch des Entschwefelungsgemisches betrug 4,5 kg/t, mit dem der Schwefelgehalt auf 0,009 Gew.-% gesenkt wurde. Das entspricht einem Entschwefelungsgrad von 86 %.4.5% carbon, 0.8% silicon, 0.7% manganese, 0.08% phosphorus, 0.064% sulfur, the remainder iron was desulphurized in an open pan by the immersion lance method with the desulfurization mixture according to the invention from Example 1. The depth of the lance was 1.8 m. The blowing speed was 100 kg / min. The total consumption of the desulfurization mixture was 4.5 kg / t, with which the sulfur content was reduced to 0.009% by weight. This corresponds to a degree of desulfurization of 86%.

b) Bei einem Vergleichsversuch mit einem zum Stand der Technik gehörenden Gemisch, bestehend aus 85 Gew.-% technischem Carbid (78 Gew.-% CaC2-Gehalt) und 15 Gew.-% CaC03 benötigte man mit der gleichen Tauchtiefe und Einblasgeschwindigkeit wie unter 3 a) 6,0 kg/t, um bei gleichem Schwefelausgangsgehalt denselben Entschwefelungsgrad zu erreichen.b) A comparison test with a mixture belonging to the prior art, consisting of 85% by weight of technical carbide (78% by weight CaC 2 content) and 15% by weight CaC0 3, required the same immersion depth and blowing speed as under 3 a) 6.0 kg / t in order to achieve the same desulfurization level with the same initial sulfur content.

Bei dem erfindungsgemäßen Entschwefelungsgemisch ergibt sich gegenüber dem bei diesem Vergleichsversuch benutzten bekannten Entschwefelungsgemisch eine Ersparnis von 25 %, bezogen auf die absolute Menge an Entschwefelungsgemisch, und eine Ersparnis von 45 %, bezogen auf den CaC2-Anteil. Im selben Maß verkürzt sich auch die Behandlungszeit.In the desulfurization mixture according to the invention, compared to the known desulfurization mixture used in this comparative test, there is a saving of 25%, based on the absolute amount of desulfurization mixture, and a saving of 45%, based on the CaC 2 content. The treatment time is shortened to the same extent.

Claims (3)

1. Process for making an agent for the desulfurization of crude iron and steel melts on the basis of calcium carbide containing calcium oxide, wherein finely divided calcium oxide in an excess of 3 to 15 weight%, based on the quantity desired in the CaC2/CaO-crystalline blend, is introduced into a calcium carbide melt prepared in customary manner which already has up to 45 weight% calcium oxide contained in it ; the mixture so obtained is cooled to temperatures of 350 to 450 °C to effect solidification and pre- crushed at these temperatures to particles with a size of less than 150 mm and particles with a size smaller than 4 mm which are invariably obtained are separated from the remaining product, which comprises admixing the latter with free carbon and carbonate, and comminuting the mixture in the presence of air or nitrogen with a moisture content of 5 to 20 g/m3 (at 1.013 bar and 273.15 K) by crushing and grinding at temperatures lower than 100°C, preferably 10-50 °C, to particles with a size of less than 10 mm, preferably smaller than 0.1 mm.
2. Process as claimed in claim 1, wherein the desulfurizing agent contains 1 to 6 weight%, preferably 2.5 to 3.5 weight%, water chemically combined with calcium oxide.
3. Process as claimed in claim 1 or 2, wherein the desulfurizing agent contains 0.5 to 8 weight% free carbon and 0.5 to weight% calcium, magnesium or sodium carbonate.
EP82101428A 1981-03-24 1982-02-25 Process for producing desulfurizing agents for pig iron and steel melts Expired EP0061012B1 (en)

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AT82101428T ATE9232T1 (en) 1981-03-24 1982-02-25 PROCESS FOR THE MANUFACTURE OF A DESULPHURIZING AGENT FOR MELTED PIG IRON AND STEEL.

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DE3111510 1981-03-24
DE19813111510 DE3111510A1 (en) 1981-03-24 1981-03-24 DESULFURATION MIXTURE AND METHOD FOR THE PRODUCTION THEREOF

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CA1240842A (en) * 1984-05-16 1988-08-23 Heinrich Rellermeyer Method, process and composition for desulfurizing pig-iron melts
US4572737A (en) * 1984-06-27 1986-02-25 The Boc Group, Inc. Agents for the removal of impurities from a molten metal and a process for producing same
BR8606249A (en) * 1985-12-17 1987-09-29 Sueddeutsche Kalkstickstoff FINALLY GRANULATED COMPOSITION FOR THE DESULFURATION OF CAST IRON AND PROCESS FOR ITS PREPARATION
DE3908071A1 (en) * 1989-03-13 1990-09-20 Hoechst Ag MEANS AND METHOD FOR DISCHARGING METAL MELTS
US5358550A (en) * 1992-10-26 1994-10-25 Rossborough Manufacturing Company Desulfurization agent
US5407459A (en) * 1993-09-23 1995-04-18 Alcan International Limited Process for the preparation of calcium aluminates from aluminum dross residues
AT406690B (en) * 1994-12-09 2000-07-25 Donau Chemie Ag AGENT FOR TREATING RAW IRON AND CAST IRON MELT FOR THE PURPOSE OF DESULFURATION
US6238633B1 (en) 1997-06-30 2001-05-29 Aluminum Waste Technology, Inc. Process for preparing calcium aluminate from aluminum dross
US6372014B1 (en) 2000-04-10 2002-04-16 Rossborough Manufacturing Co. L.P. Magnesium injection agent for ferrous metal
US6352570B1 (en) 2000-04-10 2002-03-05 Rossborough Manufacturing Co., Lp Magnesium desulfurization agent
US6770115B2 (en) * 2002-10-18 2004-08-03 Remacor, Inc. Process for magnesium granules
US6989040B2 (en) * 2002-10-30 2006-01-24 Gerald Zebrowski Reclaimed magnesium desulfurization agent
US7731778B2 (en) * 2006-03-27 2010-06-08 Magnesium Technologies Corporation Scrap bale for steel making process
US20080196548A1 (en) * 2007-02-16 2008-08-21 Magnesium Technologies Corporation Desulfurization puck

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DE2252795C3 (en) * 1972-10-27 1982-09-09 Skw Trostberg Ag, 8223 Trostberg Desulphurizing agent for pig iron and ferro-alloy melts
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JPH0152446B2 (en) 1989-11-08
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BR8201621A (en) 1983-02-16
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DD202182A5 (en) 1983-08-31
DE3111510A1 (en) 1982-10-07

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