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EP0226994B1 - Agent for desulphuration of molten iron and process for its production - Google Patents

Agent for desulphuration of molten iron and process for its production Download PDF

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Publication number
EP0226994B1
EP0226994B1 EP86117417A EP86117417A EP0226994B1 EP 0226994 B1 EP0226994 B1 EP 0226994B1 EP 86117417 A EP86117417 A EP 86117417A EP 86117417 A EP86117417 A EP 86117417A EP 0226994 B1 EP0226994 B1 EP 0226994B1
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EP
European Patent Office
Prior art keywords
coal
agent according
agent
gas
calcium carbide
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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.)
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EP86117417A
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German (de)
French (fr)
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EP0226994A1 (en
Inventor
Walter Meichsner
Werner Dr. Gmöhling
Manfred Tutte
Karl-Heinz Dr. Peters
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Thyssen Stahl AG
Evonik Operations GmbH
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SKW Trostberg AG
Thyssen Stahl AG
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Priority claimed from DE19853544562 external-priority patent/DE3544562C2/en
Priority claimed from DE3544563A external-priority patent/DE3544563C2/en
Application filed by SKW Trostberg AG, Thyssen Stahl AG filed Critical SKW Trostberg AG
Priority to AT86117417T priority Critical patent/ATE54673T1/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
    • 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 agents, processes for producing the agent and application of the agent for the desulfurization of molten iron outside the blast furnace.
  • iron smelting means pig iron and cast iron melting.
  • a preferred agent is a mixture consisting of 20 to 90% by weight technical calcium carbide and calcium carbonate, preferably in precipitated form and 2 to 20% by weight carbon distributed therein, the finely divided calcium carbonate / carbon mixture being known under the name diamide lime ( DE-PS 17 58 250).
  • US Pat. No. 3,998,625 describes a desulfurization agent consisting of a combination of lime and other constituents with magnesium
  • US Pat. No. 4,266,969 recommends the use of lime with carbon-containing material and a non-oxidizing conveying gas.
  • a disadvantage of the known agents is the large amounts of slag which, particularly in the torpedo pans but also in the open pans, lead to undesirable deposits and incrustations and also include considerable amounts of iron, which leads to considerable iron losses.
  • a fine-grained desulfurization agent for iron melts which consists of a combination of calcium carbide, at least one substance which releases hydrogen at the temperature of the iron melt and magnesium, the hydrogen-releasing substance according to the preferred embodiments of a solid or liquid hydrocarbon, such as Polyethylene or polypropylene.
  • This means can include additional coal, e.g. Brown or gas coal or anthracite included.
  • the task was therefore to develop a further desulphurization agent based on calcium carbide, which on the one hand does not introduce any further slag-forming constituents into the iron melt and on the other hand develops a gas quantity which is sufficient for the dispersion of the calcium carbide immediately after entering the iron melt and with favorable consumption values and short treatment times achieved low final sulfur levels.
  • This object was achieved by a fine-grained agent which is blown into the molten iron in fluidized form by means of a gas which consists of a mixture of technical calcium carbide and a dried coal which contains at least 15% by weight of volatile constituents and immediately after entering the iron melt releases a gas volume of at least 80 NL gas / kg coal.
  • Technical calcium carbide is understood to mean a commercially available product which contains 65 to 85% by weight of CaC 2 and the rest of which consists predominantly of lime.
  • the proportion of technical calcium carbide can vary within wide limits in the agent according to the invention. The contents of the remaining components fluctuate accordingly.
  • a desulfurization agent is preferably used which contains 50 to 98% by weight calcium carbide and 50 to 2% by weight coal.
  • the agent particularly preferably contains 80 to 96% by weight of calcium carbide and 20 to 4% by weight of coal.
  • the desulfurization agent according to the invention can additionally contain magnesium. Mixtures with contents of 47.5 to 95.5% by weight of technical calcium carbide, 50 to 2% by weight of dried coal and 2 to 40% by weight of magnesium are preferred.
  • a coal type is preferably selected as the carbon component, which as the dried product is pneumatically introduced into the molten iron, ie at a heating rate of 10 3 to 10 60 C / sec. releases about 90% by weight of the volatile constituents within less than 60 seconds, preferably less than 40 seconds.
  • the higher the level of volatiles in the coal the higher the effectiveness of the desulfurization agent.
  • Coals containing at least 25% by weight of volatile constituents are therefore particularly preferably used.
  • Coals are preferably used which develop a gas volume of at least 150 NL / kg in the dried form immediately after entering the iron melt. Coals these conditions are, in particular, lignite, flame coal, gas flame coal, gas coal and fat coal (see Table 1).
  • two or more types of coal with high volatile constituents can also be used in the mixture.
  • the moisture content of the dried coal is preferably less than 0.5% by weight in order to prevent acetylene formation by reaction with the calcium carbide.
  • Such degrees of dryness are achieved in commercially available drying devices such as swirl flow driers, entrained flow driers or grinding driers and when drying in a vacuum in simple units, in which the material to be dried is merely circulated.
  • the magnesium to be used should have a grain size of less than 1 mm.
  • a magnesium is preferably used which has already been comminuted ⁇ 500 ⁇ m, particularly preferred is a magnesium which has a grain size ⁇ 350 ⁇ m.
  • fluorspar it may prove expedient to add 1 to 10% by weight of fluorspar to the desulfurization mixture, e.g. to favorably influence the properties of the slag produced during the desulfurization treatment.
  • 1 to 10% by weight of fluorspar Preferably 2 to 6% by weight of fluorspar is added to the mixture.
  • fluorspar ball mill dust (waste from aluminum production) consisting of aluminum oxide with proportions of up to 30% by weight aluminum can be added to the agent.
  • the desulfurization agent according to the invention is produced in such a way that the dried coal is metered into the pre-broken or pre-ground calcium carbide and the mixture is ground in a mill to the desired degree of fineness. It can be useful to work under an inert gas blanket in order to remove any small amounts of acetylene from the mixing and grinding plant. You can also grind the carbide and coal separately and mix them together afterwards.
  • the constituents of the agent according to the invention are ground and mixed intensively, these being preferably comminuted to such an extent that at least 90% by weight of the mixture has a grain size ⁇ 200 ⁇ m, but particularly preferably 90% has a grain size ⁇ 100 ⁇ m and 40 to 65 wt .-% have a grain size ⁇ 50 microns. Certain deviations from this are irrelevant to the desulfurization effect.
  • the agent which consists of calcium carbide and dried coal, magnesium is metered in, so that the agent is pneumatically conveyed into the melt as a homogeneous mixture.
  • the technical calcium carbide content is preferably 47.5 to 95.5% by weight, particularly preferably 66 to 86% by weight, of the. on dried coal to 50 to 2% by weight, particularly preferably 20 to 4% by weight and that of fine-grained magnesium to 2.5 to 40% by weight, particularly preferably 10 to 30% by weight.
  • This method of separate fluidization and co-injection of the separately fluidized mixtures (coinjection) has the advantage that the magnesium can also be used in a larger form.
  • the desulfurization agent according to the invention is expediently blown into the molten iron as deeply as possible in fluidized form with a conveying gas amount of 3 to 30 NUkg.
  • the delivery rate of the agent should be 10 to 100 kg / min; preferably a rate of 30 to 80 kg / min of desulfurizing agent is used.
  • Non-oxidizing gases such as argon or nitrogen alone or as a mixture or dried air are preferably used as the conveying gas for the desulfurization agent.
  • the desulfurization agent according to the invention has considerable advantages over previously known agents in connection with the method according to the invention. Apart from the small amount of ash it contains, the coal brings practically no other slag-forming components into the iron melt. This means that considerably less slag is obtained when using the desulfurization agent according to the invention than when using calcium carbonate or calcium hydroxide as gas-releasing additives.
  • the coal Compared to the known hydrogen and carbon dioxide-releasing additives, the coal has the advantage that a sufficient amount of gas develops immediately after entering the molten iron and thus a practically complete dispersion of the finely divided calcium carbide and the magnesium in the molten iron is achieved. As a result, the desulfurization effect of the agent according to the invention is superior to the known desulfurization mixtures based on calcium carbide.
  • the agent according to the invention has the surprising advantage that the treatment times of the iron melts are reduced considerably, and more so than was expected after the reactivity of the magnesium and the calcium carbide.
  • the desulfurization agent according to the invention is just as suitable in connection with the blowing process described for hot metal desulfurization in the open pan as in the torpedo pan.
  • composition of the agent guarantees sufficient distribution so that a high degree of utilization of the desulfurizing agent is achieved.
  • the treatment times of the iron melts are short, so that the melt is only slightly cooled.
  • the amount of slag produced is small, which means that the iron losses when removing the slag are insignificant.
  • Number 10 relates to a known desulfurization agent consisting of 50% by weight of magnesium and 50% by weight of ball mill dust (A1 2 0 2 and Al).
  • Numbers 3, 7 to 9 and 12 and 13 show the results which were obtained in open pans with compositions composed according to the invention.
  • the means according to the invention are superior to the conventional means.
  • the amount of gas split off in 1 / kg is the amount of gas that escapes when the coal is heated to crude iron temperature very quickly.
  • the volatile constituents of the diamide lime are the amount of CO 2 released during carbonate decomposition.
  • the duration of gas evolution indicates the time (sec) in which approximately 90% of the total amount of gas is split off.

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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)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Cereal-Derived Products (AREA)

Description

Die Erfindung betrifft Mittel, Verfahren zur Herstellung des Mittels und Anwendung des Mittels zur Entschwefelung von Eisenschmelzen außerhalb des Hochofens. Unter Eisenschmelzen werden hier Roheisen- und Gußeisenschmelzen verstanden.The invention relates to agents, processes for producing the agent and application of the agent for the desulfurization of molten iron outside the blast furnace. Here, iron smelting means pig iron and cast iron melting.

Die Entschwefelung des Roheisens außerhalb des Hochofens in der Transport- oder Umfüllpfanne gehört inzwischen zum Stand der Technik. Als bevorzugtes Entschwefelungsmittel haben sich Gemische auf Basis von Calciumcarbid durchgesetzt, da diese bei hoher Wirtschaftlichkeit eine schnelle Entschwefelung des Roheisens bewirken und zu niedrigen Endschwefelgehalten führen. Ein bevorzugtes Mittel stellt ein Gemisch bestehend aus 20 bis 90 Gew.% technischem Calciumcarbid und Calciumcarbonat, vorzugsweise in gefällter Form und 2 bis 20 Gew.% darin verteiltem Kohlenstoff dar, wobei das feinteilige Calciumcarbonat/Kohlenstoff-Gemisch unter dem Namen Diamidkalk bekannt ist (DE-PS 17 58 250).The desulfurization of the pig iron outside the blast furnace in the transport or transfer ladle has become part of the state of the art. Mixtures based on calcium carbide have established themselves as the preferred desulfurizing agent, since these, with high economy, bring about rapid desulfurization of the pig iron and lead to low final sulfur contents. A preferred agent is a mixture consisting of 20 to 90% by weight technical calcium carbide and calcium carbonate, preferably in precipitated form and 2 to 20% by weight carbon distributed therein, the finely divided calcium carbonate / carbon mixture being known under the name diamide lime ( DE-PS 17 58 250).

Aus der DE-AS 25 31 047 ist ein Verfahren zum Entschwefeln von Roheisen bekannt, das als Entschwefelungsmittel eine Mischung aus Calciumcarbid, Kalkstickstoff oder Kalk mit einem Anteil von 0,5 bis 3,5 Gew.% Aluminium- oder Magnesiumpulver, bezogen auf die Calciumverbindungen, verwendet.From DE-AS 25 31 047 a method for desulfurizing pig iron is known which uses a mixture of calcium carbide, calcium cyanamide or lime with a proportion of 0.5 to 3.5% by weight of aluminum or magnesium powder, based on the, as the desulfurization agent Calcium compounds used.

In der US-Patentschrift 3 998 625 wird ein Entschwefelungsmittel, bestehend aus einer Kombination von Kalk und weiteren Bestandteilen mit Magnesium beschrieben, sowie in der US-Patentschrift 4 266 969 der Einsatz von Kalk mit kohlenstoffhaltigem Material und einem nichtoxidierenden Fördergas empfohlen.US Pat. No. 3,998,625 describes a desulfurization agent consisting of a combination of lime and other constituents with magnesium, and US Pat. No. 4,266,969 recommends the use of lime with carbon-containing material and a non-oxidizing conveying gas.

Nachteilig bei den bekannten Mitteln sind die größen anfallenden Schlackenmengen, die besonders in den Torpedopfannen aber auch in den offenen Pfannen zu unerwünschten Ablagerungen und Verkrustungen führen und darüber hinaus beträchtliche Mengen Eisen einschließen, was zu erheblichen Eisenverlusten führt.A disadvantage of the known agents is the large amounts of slag which, particularly in the torpedo pans but also in the open pans, lead to undesirable deposits and incrustations and also include considerable amounts of iron, which leads to considerable iron losses.

Es ist auch bereits vorgeschlagen worden, statt Calciumcarbonat dem Calciumcarbid einen Zusatz zuzumischen, der bei der Temperatur der Eisenschmelze Wasserstoff abspaltet (DE-PS 22 52 796). Ein derartiges Entschwefelungsmittel hat sich jedoch in der Praxis nicht bewährt, da offenbar die Abspaltung des Wasserstoffes nicht in der Weise erfolgte, daß eine ausreichende Dispergierung des Calciumcarbids in der Eisenschmelze bewirkt werden konnte.Instead of calcium carbonate, it has also already been proposed to add an addition to the calcium carbide which releases hydrogen at the temperature of the molten iron (DE-PS 22 52 796). However, such a desulfurization agent has not proven itself in practice, since apparently the hydrogen was not split off in such a way that sufficient dispersion of the calcium carbide in the iron melt could be brought about.

Es wurde auch schon vorgeschlagen, Entschwefelungsmittel bei der Behandlung von Gußeisenschmelzen zusammen mit Kohlenstoff, z.B. in Form von Pechkoks, Blutkohle, Lederkohle einzusetzen, aber die hierzu vorgeschlagenen Kohlensorten enthalten praktisch keine flüchtigen Bestandteile (s. angegebenen Stand der Technik in der DE-PS 17 58 250).It has also been proposed to use desulfurizing agents in the treatment of molten cast iron together with carbon, e.g. use in the form of pitch coke, charcoal, leather coal, but the coal types proposed for this purpose contain practically no volatile constituents (see the prior art specified in DE-PS 17 58 250).

Aus AU-A-4 254 285 ist ein feinkörniges Entschwefelungsmittel für Eisenschmelzen bekannt, das aus einer Kombination von Calciumcarbid, wenigstens einer bei der Temperatur der Eisenschmelze Wasserstoff abspaltenden Substanz und Magnesium besteht, wobei die Wasserstoff-abspaltende Substanz nach den bevorzugten Ausführungsformen aus einem festen oder flüssigen Kohlenwasserstoff, wie z.B. Polyethylen oder Polypropylen, besteht. Dieses Mittel kann zusätzliche Kohle, wie z.B. Braun -oder Gaskohle oder Anthrazit enthalten.From AU-A-4 254 285 a fine-grained desulfurization agent for iron melts is known, which consists of a combination of calcium carbide, at least one substance which releases hydrogen at the temperature of the iron melt and magnesium, the hydrogen-releasing substance according to the preferred embodiments of a solid or liquid hydrocarbon, such as Polyethylene or polypropylene. This means can include additional coal, e.g. Brown or gas coal or anthracite included.

Es bestand daher die Aufgabe, ein weiteres Entschwefelungsmittel auf Basis von Calciumcarbid zu entwickeln, das einerseits keine weiteren schlackebildenden Bestandteile in die Eisenschmelze einbringt und andererseits eine für die Dispergierung des Calciumcarbids ausreichend große Gasmenge unmittelbar nach dem Eintritt in die Eisenschmelze entwickelt und bei günstigen Verbrauchswerten und kurzen Behandlungszeiten niedrige Endschwefelgehalte erzielt.The task was therefore to develop a further desulphurization agent based on calcium carbide, which on the one hand does not introduce any further slag-forming constituents into the iron melt and on the other hand develops a gas quantity which is sufficient for the dispersion of the calcium carbide immediately after entering the iron melt and with favorable consumption values and short treatment times achieved low final sulfur levels.

Gelöst wurde diese Aufgabe durch ein feinkörniges Mittel, das in fluidisierter Form mittels eines Gases in die Eisenschmelze eingeblasen wird, das aus einem Gemisch von technischem Calciumcarbid und einer getrockneten Kohle besteht, welche mindestens 15 Gew.% flüchtige Bestandteile enthält und unmittelbar nach dem Eintritt in die Eisenschmelze ein Gasvolumen von mindestens 80 NL Gas/kg Kohle freisetzt.This object was achieved by a fine-grained agent which is blown into the molten iron in fluidized form by means of a gas which consists of a mixture of technical calcium carbide and a dried coal which contains at least 15% by weight of volatile constituents and immediately after entering the iron melt releases a gas volume of at least 80 NL gas / kg coal.

Unter technischem Calciumcarbid wird ein handelsübliches Produkt verstanden, das 65 bis 85 Gew.% CaC2 enthält und dessen Rest überwiegend aus Kalk besteht. Der Anteil an technischem Calciumcarbid kann in dem erfindungsgemäßen Mittel in weiten Grenzen schwanken. Dementsprechend schwanken die Gehalte der übrigen Bestandteile.Technical calcium carbide is understood to mean a commercially available product which contains 65 to 85% by weight of CaC 2 and the rest of which consists predominantly of lime. The proportion of technical calcium carbide can vary within wide limits in the agent according to the invention. The contents of the remaining components fluctuate accordingly.

Bevorzugt wird ein Entschwefelungsmittel verwendet, das 50 bis 98 Gew.% Calciumcarbid und 50 bis 2 Gew.% Kohle enthält. Besonders bevorzugt enthält das Mittel 80 bis 96 Gew.% Calciumcarbid und 20 bis 4 Gew.% Kohle.A desulfurization agent is preferably used which contains 50 to 98% by weight calcium carbide and 50 to 2% by weight coal. The agent particularly preferably contains 80 to 96% by weight of calcium carbide and 20 to 4% by weight of coal.

Das erfindungsgemäße Entschwefelungsmittel kann zusätzlich Magnesium enthalten. Bevorzugt sind Mischungen mit Gehalten von 47,5 bis 95,5 Gew.% technischem Calciumcarbid, 50 bis 2 Gew.% getrockneter Kohle und 2 bis 40 Gew.% Magnesium.The desulfurization agent according to the invention can additionally contain magnesium. Mixtures with contents of 47.5 to 95.5% by weight of technical calcium carbide, 50 to 2% by weight of dried coal and 2 to 40% by weight of magnesium are preferred.

Bevorzugt wird als Kohlekomponente eine Kohlesorte gewählt, die als getrocknetes Produkt beim pneumatischen Einbringen in die Eisenschmelze, d.h. bei einer Erhitzungsgeschwindigkeit von 103 bis 1060C/sec. etwa 90 Gew.-% der flüchtigen Bestandteile innerhalb von weniger als 60 sec., bevorzugt weniger als 40 sec., freisetzt. Je höher der Anteil an flüchtigen Bestandteilen in der Kohle ist, umso höher ist im allgemeinen die Wirksamkeit des Entschwefelungsmittels. Besonders bevorzugt werden daher Kohlen verwendet, die wenigstens 25 Gew.-% flüchtige Bestandteile enthalten.A coal type is preferably selected as the carbon component, which as the dried product is pneumatically introduced into the molten iron, ie at a heating rate of 10 3 to 10 60 C / sec. releases about 90% by weight of the volatile constituents within less than 60 seconds, preferably less than 40 seconds. Generally, the higher the level of volatiles in the coal, the higher the effectiveness of the desulfurization agent. Coals containing at least 25% by weight of volatile constituents are therefore particularly preferably used.

Bevorzugt werden Kohlen verwendet, die in getrockneter Form unmittelbar nach dem Eintritt in die Eisenschmelze ein Gasvolumen von mindestens 150 NL/kg entwickeln. Kohlen, die diese Bedingungen erfüllen, sind insbesondere Braunkohlen, Flammkohle, Gasflammkohle, Gaskohle und Fettkohle (vgl. Tabelle 1).Coals are preferably used which develop a gas volume of at least 150 NL / kg in the dried form immediately after entering the iron melt. Coals these conditions are, in particular, lignite, flame coal, gas flame coal, gas coal and fat coal (see Table 1).

Sollte est sich als zweckmäßig erweisen, können auch zwei oder mehrere Kohlesorten mit hohen Gehalten an flüchtigen Bestandteilen im Gemisch verwendet werden.If it proves to be expedient, two or more types of coal with high volatile constituents can also be used in the mixture.

Der Feuchtigkeitsgehalt der getrockneten Kohle beträgt bevorzugt weniger als 0,5 Gew.-%, um eine Acetylenbildung durch Reaktion mit dem Calciumcarbid auszuschliessen. Erreicht werden solche Trocknungsgrade in handelsüblichen Trockenvorrichtungen wie Drallstrom-, Flugstrom- oder Mahltrockner sowie beim Trocknen im Vakuum in einfachen Aggregaten, worin das zu trocknende Gut lediglich umgewälzt wird.The moisture content of the dried coal is preferably less than 0.5% by weight in order to prevent acetylene formation by reaction with the calcium carbide. Such degrees of dryness are achieved in commercially available drying devices such as swirl flow driers, entrained flow driers or grinding driers and when drying in a vacuum in simple units, in which the material to be dried is merely circulated.

Das zu verwendende Magnesium sollte eine Körnung kleiner 1 mm besitzen. Bevorzugt wird ein Magnesium verwendet, das bereits < 500 pm zerkleinert ist, besonders bevorzugt wird ein Magnesium, das eine Korngröße < 350 um, besitzt.The magnesium to be used should have a grain size of less than 1 mm. A magnesium is preferably used which has already been comminuted <500 μm, particularly preferred is a magnesium which has a grain size <350 μm.

Es kann sich als zweckmäßig erweisen, dem Entschwefelungsgemisch einen Anteil von 1 bis 10 Gew.% Flußspat beizumischen z.B. um die Eigenschaften der bei der Entschwefelungsbehandlung entstehende Schlacke günstig zu beeinflussen. Bevorzugt werden dem Gemisch 2 bis 6 Gew.% Flußspat zugemischt. Anstelle von Flußspat kann dem Mittel Kugelmühlenstaub (Abfälle aus der Aluminiumherstellung), bestehend aus Aluminiumoxid mit Anteilen von bis zu 30 Gew.% Aluminium zugesetzt werden.It may prove expedient to add 1 to 10% by weight of fluorspar to the desulfurization mixture, e.g. to favorably influence the properties of the slag produced during the desulfurization treatment. Preferably 2 to 6% by weight of fluorspar is added to the mixture. Instead of fluorspar, ball mill dust (waste from aluminum production) consisting of aluminum oxide with proportions of up to 30% by weight aluminum can be added to the agent.

Die Herstellung des erfindungsgemäßen Entschwefelungsmittels erfolgt in der Weise, daß die getrocknete Kohle dem vorgebrochenen oder vorgemahlenen Calciumcarbid zudosiert und das Gemisch in einer Mühle auf den gewünschten Feinheitsgrad zerkleinert wird. Hierbei kann es sich als zweckmäßig erweisen, unter Inertgasdeckung zu arbeiten, um evtl. entstehende geringe Acetylenmengen aus der Misch- und Mahlanlage sofort zu entfernen. Mann kann aber auch das Carbid und die Kohle getrennt vermahlen und nachträglich zusammenmischen.The desulfurization agent according to the invention is produced in such a way that the dried coal is metered into the pre-broken or pre-ground calcium carbide and the mixture is ground in a mill to the desired degree of fineness. It can be useful to work under an inert gas blanket in order to remove any small amounts of acetylene from the mixing and grinding plant. You can also grind the carbide and coal separately and mix them together afterwards.

Die Bestandteile des erfindungsgemäßen Mittels mit Ausnahme von Magnesium, werden intensiv vermahlen und gemischt, wobei diese bevorzugt so weit zerkleinert werden, daß mindestens 90 Gew.-% des Gemisches eine Korngröße < 200 um, besonders bevorzugt aber 90% eine Korngröße < 100 pm und 40 bis 65 Gew.-% eine Korngröße < 50 um, aufweisen. Gewisse Abweichungen hiervon sind ohne Belang auf den Entschwefelungseffekt.The constituents of the agent according to the invention, with the exception of magnesium, are ground and mixed intensively, these being preferably comminuted to such an extent that at least 90% by weight of the mixture has a grain size <200 μm, but particularly preferably 90% has a grain size <100 μm and 40 to 65 wt .-% have a grain size <50 microns. Certain deviations from this are irrelevant to the desulfurization effect.

In einer bevorzugten Ausführungsform wird dem Mittel, das aus Calciumcarbid und getrockneter Kohle besteht, Magnesium zudosiert, so daß das Mittel als homogenes gemisch pneumatisch in die Schmelze gefördert wird. Bevorzugt wird der Gehalt an technischem Calciumcarbid auf 47,5 bis 95,5 Gew.% besonders bevorzugt 66 bis 86 Gew.%, der. an getrockneter Kohle auf 50 bis 2 Gew.% besonders bevorzugt 20 bis 4 Gew.% und der an feinkörnigem Magnesium auf 2,5 bis 40 Gew.% besonders bevorzugt 10 bis 30 Gew.% eingestellt. Andererseits hat es sich häufig als zweckmäßig erwiesen, das Carbid/Kohle-Gemisch nach seiner Herstellung getrennt vom Magnesium zu lagern, zu fluidisieren und beide Bestandteile erst in der Förderleitung oder in der Lanze zu vereinigen und auf diese Weise gemeinsam in die Schmelze einzubringen. Dieses Verfahren der getrennten Fluidisierung und des gemeinsamen Einblasens der getrennt fluidisierten Gemische (Coinjection) hat den Vorteil, daß das Magnesium auch in größerer Form verwendet werden kann.In a preferred embodiment, the agent, which consists of calcium carbide and dried coal, magnesium is metered in, so that the agent is pneumatically conveyed into the melt as a homogeneous mixture. The technical calcium carbide content is preferably 47.5 to 95.5% by weight, particularly preferably 66 to 86% by weight, of the. on dried coal to 50 to 2% by weight, particularly preferably 20 to 4% by weight and that of fine-grained magnesium to 2.5 to 40% by weight, particularly preferably 10 to 30% by weight. On the other hand, it has often proven expedient to store the carbide / coal mixture separately from the magnesium after its production, to fluidize it and to combine both components only in the delivery line or in the lance and in this way to introduce them into the melt together. This method of separate fluidization and co-injection of the separately fluidized mixtures (coinjection) has the advantage that the magnesium can also be used in a larger form.

Das erfindungsgemäße Entschwefelungsmittel wird zweckmäßigerweise in fluidisierter Form mit einer Fördergasmenge von 3 bis 30 NUkg Mittel so tief wie möglich in die Eisenschmelze eingeblasen. Hierbei soll die Förderrate des Mittels 10 bis 100 kg/min beträgen; bevorzugt wird mit einer Förderrate von 30 bis 80 kg/min Entschwefelungsmittel gearbeitet.The desulfurization agent according to the invention is expediently blown into the molten iron as deeply as possible in fluidized form with a conveying gas amount of 3 to 30 NUkg. The delivery rate of the agent should be 10 to 100 kg / min; preferably a rate of 30 to 80 kg / min of desulfurizing agent is used.

Als Fördergas für das Entschwefelungsmittel verwendet man vorzugsweise nichtoxidierende Gase wie Argon oder Stickstoff allein oder als Gemisch oder getrocknete Luft.Non-oxidizing gases such as argon or nitrogen alone or as a mixture or dried air are preferably used as the conveying gas for the desulfurization agent.

Das erfindungsgemäße Entschwefelungsmittel weist in Verbindung mit dem erfindungsgemäßen Verfahren erhebliche Vorteile gegenüber bisher bekannten Mitteln auf. So bringt die Kohle, abgesehen von der in ihr enthaltenen geringen Aschemenge praktisch keine weiteren schlackebildenden Bestandteile in die Eisenschmelze ein. Damit fällt bei Einsatz des erfindungsgemäßen Entschwefelungsmittels erheblich weniger Schlacke an als bei der Verwendung von Calciumcarbonat oder Calciumhydroxid als gasabspaltende Zusätze.The desulfurization agent according to the invention has considerable advantages over previously known agents in connection with the method according to the invention. Apart from the small amount of ash it contains, the coal brings practically no other slag-forming components into the iron melt. This means that considerably less slag is obtained when using the desulfurization agent according to the invention than when using calcium carbonate or calcium hydroxide as gas-releasing additives.

Im Vergleich zu den bekannten Wasserstoff und Kohlendioxid abspaltenden Zusätzen hat die Kohle den Vorteil, daß ein ausreichende Gasmenge unmittelbar nach dem Eintritt in die Eisenschmelze entwickelt und damit eine praktisch vollständige Dispergierung des feinteiligen Calciumcarbids und des Magnesiums in der Eisenschmelze erreicht wird. Hierdurch ist die Entschwefelungswirkung des erfindungsgemäßen Mittels den bekannten Entschwefelungsgemischen auf Basis Calciumcarbid gegenüber überlegen.Compared to the known hydrogen and carbon dioxide-releasing additives, the coal has the advantage that a sufficient amount of gas develops immediately after entering the molten iron and thus a practically complete dispersion of the finely divided calcium carbide and the magnesium in the molten iron is achieved. As a result, the desulfurization effect of the agent according to the invention is superior to the known desulfurization mixtures based on calcium carbide.

Gegenüber bekannten Entschwefelungsgemischen mit Gehalten von 50 Gew.% und mehr Magnesium, beinhaltet das erfindungsgemäße Mittel den überraschenden Vorteil, daß die Behandlungszeiten der Eisenschmelzen erheblich reduziert werden und zwar stärker als es nach der Reaktionsfähigkeit des Magnesiums und des Calciumcarbids zu erwarten war.Compared to known desulfurization mixtures with a content of 50% by weight or more of magnesium, the agent according to the invention has the surprising advantage that the treatment times of the iron melts are reduced considerably, and more so than was expected after the reactivity of the magnesium and the calcium carbide.

Das erfindungsgemäße Entschwefelungsmittel eignet sich im Zusammenhang mit dem beschriebenen Einblasverfahren ebenso gut zur Roheisenentschwefelung in der offenen Pfanne wie in der Torpedopfanne.The desulfurization agent according to the invention is just as suitable in connection with the blowing process described for hot metal desulfurization in the open pan as in the torpedo pan.

Darüberhinaus ist der besonders geringe Bedarf an Einblasgas vorteilhaft. Die Zusammensetzung des Mittels garantiert eine ausreichende Verteilung, so daß ein hoher Ausnutzungsgrad des Entschwefelungsmittels erreicht wird.In addition, the particularly low requirement for injection gas is advantageous. The composition of the agent guarantees sufficient distribution so that a high degree of utilization of the desulfurizing agent is achieved.

Bei Anwendung des erfindungsgemäßen Mittels bzw. Verfahrens wird eine deutliche Steigerung des Entschwefelungsgrades erreicht bzw. es wird eine merklich verringerte Menge an Entschwefelungsmittel zur Erzielung der gleichen Entschwefelungswirkung benötigt.When the agent or method according to the invention is used, a significant increase in the degree of desulfurization is achieved or a markedly reduced amount of desulfurizing agent is required to achieve the same desulfurization effect.

Bei Anwendung des erfindungsgemäßen Entschwefelungsmittels sind die Behandlungszeiten der Eisenschmelzen kurz, so daß auch nur eine geringe Abkühlung der Schmelze erfolgt. Die entstehenden Schlackemengen sind gering, wodurch die Eisenverluste beim Abziehen der Schlacke unbedeutend sind.When using the desulfurization agent according to the invention, the treatment times of the iron melts are short, so that the melt is only slightly cooled. The amount of slag produced is small, which means that the iron losses when removing the slag are insignificant.

Die nachfolgenden Beispiele sollen die Erfindung näher erläutern.The following examples are intended to explain the invention in more detail.

BeispieleExamples

In Tabelle 2 sind unter den laufenden Nummern 1 und 2 die Ergebnisse dargestellt, die mit herkömmlichen Entschwefelungsmitteln auf Basis von Calciumcarbid und Diamidkalk in der offenen Pfanne erhalten wurden. Die Nummer 10 betrifft ein bekanntes Entschwefelungsmittel bestehend aus 50 Gew.% Magnesium und 50 Gew.% Kugelmühlenstaub (A1202 u. AI).In Table 2, the numbers 1 and 2 show the results obtained with conventional desulfurization agents based on calcium carbide and diamide lime in the open pan. Number 10 relates to a known desulfurization agent consisting of 50% by weight of magnesium and 50% by weight of ball mill dust (A1 2 0 2 and Al).

Unter den Nummern 3, 7 bis 9 sowie 12 und 13 sind die Ergebnisse wiedergegeben, die mit erfindungsgemäß zusammengesetzten Mitteln in offenen Pfannen erhalten wurden.Numbers 3, 7 to 9 and 12 and 13 show the results which were obtained in open pans with compositions composed according to the invention.

Die in Tabelle 3 wiedergegebenen Ergebnisse sind diejenigen von in Torpedopfannen erhaltenen Entschwefelungsbehandlungen mit den unter 1 bis 6 angegebenen Gemischen.The results shown in Table 3 are those of desulfurization treatments obtained in torpedo pans with the mixtures given under 1 to 6.

Sowohl beim Arbeiten in der offenen Pfanne als auch beim Arbeiten in der Torpedopfanne zeigen sich die erfindungsgemäßen Mittel den herkömmlichen Mitteln überlegen.Both when working in the open pan and when working in the torpedo pan, the means according to the invention are superior to the conventional means.

Die in Tabelle 2 verwendeten Abkürzungen bedeuten:

  • SA Ausgangs-Schwefel-Gehalt der Roheisenschmelze
  • S, Endschwefelgehalt der RE-Schmelze nach der Behandlung
  • kg E-Mittel die aufgewendete Menge Entschwefelungsmittel pro t Roheisen t RE
  • a-Wert Kennziffer für die Wirksamkeit der Entschwefelung (Quotient aus aufgewandter Menge Entschwefelungsmittel und Differenz zwischen Ausgangs- und Endschwefelgehalt der Roheisenschmelze) x 100
  • CaD 8515 85 Gew.% techn. Carbid + 15 Gew.% Diamidkalk
  • Carbid technisches Calciumcarbid
  • % Gew.%
    Figure imgb0001
The abbreviations used in table 2 mean:
  • S A Initial sulfur content of the pig iron melt
  • S, final sulfur content of the RE melt after the treatment
  • kg E-means the amount of desulphurising agent used per t pig iron t RE
  • a-value Indicator for the effectiveness of the desulfurization (quotient of the amount of desulfurization agent used and the difference between the initial and final sulfur content of the pig iron melt) x 100
  • CaD 8515 85 wt.% Techn. Carbide + 15% by weight diamide lime
  • Technical calcium carbide
  • % Wt%
    Figure imgb0001

Die in vorstehender Tabelle zu den verschiedenen Kohlesorten angegebenen flüchtigen Bestandteile wurden Römpps Chemie-Lexikon, 8. Auflage, 1983, Bd. 3, S. 2142 entnommen.The volatile constituents given in the table above for the different types of coal were taken from Römpps Chemie-Lexikon, 8th edition, 1983, vol. 3, p. 2142.

Die abgespaltene Gasmenge in 1/kg ist diejenige Gasmenge, die bei sehr schnellem Erhitzen der Kohle auf Roheisentemperatur entweicht.The amount of gas split off in 1 / kg is the amount of gas that escapes when the coal is heated to crude iron temperature very quickly.

Unter den flüchtigen Bestandteilen des Diamidkalks versteht man die bei der Carbonatzersetzung freiwerdende CO2-Menge.The volatile constituents of the diamide lime are the amount of CO 2 released during carbonate decomposition.

Die Zeitdauer der Gasentwicklung gibt an, in welcher Zeit (Sec) etwa 90% der gesamten Gasmenge abgespalten werden.

Figure imgb0002
Figure imgb0003
 The duration of gas evolution indicates the time (sec) in which approximately 90% of the total amount of gas is split off.
Figure imgb0002
Figure imgb0003

Claims (22)

1. Fine-grained agent for the desulphurisation of molten iron based on calcium carbide which is blown in fluidised form by means of a gas into the iron melt, characterised in that it consists of industrial calcium and a dried coal which contains at least 15 wt.% of volatile components and, at the temperature of the iron melt, evolves a gas volume of at least 80 standard litres of gas/kg.
2. Agent according to claim 1, characterised in that it contains 50 to 98 wt.% of industrial calcium carbide and 50 to 2 wt.% of coal.
3. Agent according to claim 1 or 2, characterised by a content of 80 to 96 wt.% of industrial calcium chloride and 20 to 4 wt.% of coal.
4. Agent according to one of the preceding claims, characterised in that in the case of a rate of heating of the coal of 103 to 106°C./sec. to the temperature of the iron melt, about 90 wt.% of the volatile components are liberated in less than 60 sec., preferably less than 40 sec.
5. Agent according to one of the preceding claims, characterised in that the volatile components of the coal are split off at the temperature of the iron melt within less than 10 sec.
6. Agent according to one of the preceding claims, characterised in that a part of the calcium carbide component is replaced by an additional content of magnesium in such a way that it contains 47.5 to 95.5 wt.% of industrial calcium carbide, 50 to 2 wt.% of coal and 2.5 to 40 wt.% of magnesium.
7. Agent according to claim 6, characterised in that the content of industrial calcium carbide amounts to 66-86 wt.%, of dried coal to 20 to 4 wt.% and of fine-grained magnesium to 10 to 30 wt.%.
8. Agent according to one or more of the preceding claims, characterised by a coal which, after entry into the iron melt, liberates a gas volume of at least 150 standard litres of gas/kg. of coal.
9. Agent according to one or more of the preceding claims, characterised in that the moisture content of the dried coal amounts to less than 0.5 wt.%.
10. Agent according to one or more of the preceding claims, characterised in that the dried coal contains at least 25 wt.% of volatile components.
11. Agent accordiong to one of the preceding claims, characterised in that the coal is a lignite.
12. Agent according to one of claims 1 to 10, characterised in that one selects the coal from the group consisting of flame coal, gas glame coal and gas coal.
13. Agent according to one of the preceding claims, characterised in that at least 90 wt.% of the mixture has a grain size of < 200um.
14. Agent according to one of the preceding claims, characterised in that at least 90 wt.% of the mixture has a grain size of < 100 urn. and 40 to 65 wt.% a grain size of < 50 pm.
15. Agent according to one or more of the preceding claims, characterised in that a part of the calcium carbide component and possibly of the magnesium component is replaced by an additional content of fluorspar, whereby the proportion of fluorspar of the agent amounts to 1 to 10 wt.%.
16. Agent according to claim 15, characterised in that it contains 2 to 6 wt.% of fluorspar.
17. Process for the production of the agent according to one of claims 1 to 16, characterised in that one dries the coal, doses to the previously broken industrial calcium carbide and comminutes the mixture in a mill to the desired degree of fineness.
18. Process for the desulphurisation of molten iron, characterised in that the desulphurisation agent according to one or more claims 1 to 16 is blown in fluidised form into the iron melt with an amount of conveyor gas of 3 to 30 standard litres/kg. of agent.
19. Process according to claim 18, characterised in that one blows in the agent into the iron melt with a conveyor rate of 10 to 100 kg./min.
20. Process according to claim 18 or 19, characterised in that, as conveyor gas, one uses at least one non-oxidising gas of the group nitrogen, argon, natural gas and propane.
21. Process according to claims 18 to 20, characterised in that one stores the finely-divided magnesium and the calcium carbide-coal mixture separately, fluidises and thereafter combines in the conveyor pipe or lance.
22. Process according to claim 21, characterised in that one chronologically varies the proportion of magnesium in the mixture during the blowing in.
EP86117417A 1985-12-17 1986-12-15 Agent for desulphuration of molten iron and process for its production Expired - Lifetime EP0226994B1 (en)

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