EP0582970B1 - Additive for desulfurization of liquid pig and cast iron and process for desulfurizing - Google Patents

Abstract

An additive for desulphurisation of liquid pig and cast iron on the basis of fine-grained magnesium and at least 3% by weight of a metallurgically active silicate mineral in a chain-type, sheet-type or three-dimensional structure and/or one of the minerals syenite and/or rhyolite alone or as a mixture. The additive for desulphurisation can contain as further components calcium carbide and/or calcium oxide. The magnesium can be enveloped by these components in the manner of a shell. Preferably, the additive is conveyed as such or by the co-injection method pneumatically via a lance into the molten iron.

Description

The invention relates to means and methods for the Desulphurization of molten iron, especially pig iron and cast iron melting.

The desulfurization of molten iron with the help of magnesium as a highly effective desulfurizing component in the Steel industry generally found entrance. Because of the violent Reaction of the magnesium in the molten iron can but magnesium cannot be used alone, but requires mixtures that increase the reactivity of the magnesium dampen. For this one uses lime, fluorspar Slag residues from aluminum smelting electrolysis (so-called Al dross), calcium carbide etc. Such fine-grained Mixtures are mainly made using a diving lance blown in.

A problem with the pneumatic production of such magnesium containing desulfurization mixtures uneven or jerky conveyance of the mixtures dar; this leads to increased expenditure on the desulfurization mixture. To remedy this, it has already been proposed to wrap the magnesium grain around on this Way a flowable or pneumatically well conveyable Get mixture. Such wrappings usually bring only unwanted, additional slag portions in the iron melt.

After a very complex process, the fine-grained, Magnesium containing desulfurization mixture in one Metal sheath packed and in the form of a so-called sheath wire promoted in the molten iron, creating a very ensures even introduction of the agent into the melt becomes. This procedure is only used in special Cases and applied for small batches of a few tons.

Finally, another problem is the tendency to separate of magnesium from diluents in finished mixtures during transport or handling. This creates and low-magnesium Zones in the mix. This leads to the technical Application of the mixtures to uneven, not predictable Final sulfur values of the treated melts. The wrapping offered a way out of this difficulty of magnesium and accompanying substances with one and the same envelope. Show mixtures treated in this way high segregation stability and good conveyability on (DE-OS 38 31 831). Of course, the technical effort the preparation of such mixtures in which the Particles all have the same surface, large.

The problem of the separation of desulfurization mixtures was also attempted to be avoided by fluidizing the magnesium component separately from the "diluent" and blowing it into the melt in a specific, precisely adjustable weight ratio (co-injection). This co-injection requires complex technical equipment to operate the process in a reliable manner.
A disadvantage of this process is that, at the desired very low final sulfur contents or at relatively low starting sulfur contents and at high temperatures of the iron melt, because of the high solubility of the magnesium in iron, a multiple of magnesium was required than would have been necessary per se in accordance with the reactions achieved . In order to overcome these disadvantages, the so-called sequential injection was proposed, in which carbide and magnesium were alternately injected, or carbide and magnesium were injected simultaneously at the end of the desulfurization treatment. Calcium carbide is blown in to flush the dissolved magnesium out of the melt. This method also requires a lot of equipment.

The magnesium has a so-called post-desulfurization property. After the desulfurization treatment has ended with conventional mixtures can still magnesium-sulfur particles are excreted, the final sulfur value the melt change further.

The state of equilibrium of the treated melt becomes reached late or imperfectly; this is also undesirable.

All of the processes mentioned lead to inevitable iron losses. Up to 3% by weight of the total amount of iron are absorbed by the doughy or dry slag and pulled off with it and get to the heap. Adding fluorspar can help are created, however, contain fluorspar Slag is not without concern for environmental reasons and are generally rejected.

There has therefore long been a need for a desulfurizing agent for pig iron and cast iron melting, which completely or at least the disadvantages mentioned partially avoided and available at low cost. There was also a desire for a magnesium-containing one Desulfurization to find a "diluent" which is not only ballast, but also active in the Desulfurization reaction intervenes.

The invention has for its object an improved Desulfurizing agent for desulfurizing pig iron and To create cast iron melts, which the disadvantages of Does not have the prior art.

This object is defined by what is defined in claim 1 Desulfurizing agent dissolved.

Preferred embodiments are defined in claims 2-4. Procedure for Desulphurization with the agent are defined in claims 5 and 6.

In the desulfurization agent according to the invention, in addition to fine-grained Magnesium at least one naturally occurring silicate mineral with ribbon, leaf or spatial network structure contain.

• im Temperaturbereich des zu behandelnden Eisens flüssig sind bzw. aufgrund ihrer chemischen Zusammensetzung schnell verflüssigt werden,
• aufgrund ihrer Gehalte an Kalium, Natrium oder Calcium sich aktiv an der Entschwefelungsreaktion beteiligen,
• aufgrund ihrer physikalischen Eigenschaften sowie ihrer Struktur, auf entsprechende Korngröße gebracht, das Magnesium umhüllen, so daß dieses praktisch die gleichen Fließeigenschaften aufweist wie diese Mineralien selbst,
• aufgrund ihrer chemischen Zusammensetzung bei der Temperatur der Eisenschmelze selbst entschwefelnd wirken und/oder Gase abspalten.

The proportion of these silicate minerals is 10 to 60% by weight. These silicate minerals are characterized by the fact that they

• are liquid in the temperature range of the iron to be treated or are quickly liquefied due to their chemical composition,
• actively participate in the desulfurization reaction due to their potassium, sodium or calcium content,
• due to their physical properties and their structure, brought to the appropriate grain size, envelop the magnesium so that it has practically the same flow properties as these minerals themselves,
• due to their chemical composition at the temperature of the molten iron itself have a desulfurizing effect and / or release gases.

As naturally occurring silicate minerals Montmorillonite, e.g. Pearlite (band structure), kaolinite (Leaf structure) or those from the feldspar group (spatial network structure), like albite (sodium feldspar), potash feldspar or anorthite (lime feldspar) or syenite (with contents on alkali feldspar) or rhyolite with sprinklers from Plagio glass and biotite as well as nepheline (a sodium aluminum silicate) used.

In the simplest case, there is the desulfurization agent from a mixture of magnesium, silicate mineral and optionally calcium carbide and / or calcium oxide.

In a further embodiment of the invention, the magnesium with the silicate minerals and the other components envelops. This is done by a normal circulation process in a suitable mixer, provided the silicate Minerals brought to approximately the same grain size have been like the magnesium. Under this condition the silicate minerals envelop the fine-grained magnesium bowl-shaped.

The other components such as Calcium carbide and / or calcium oxide installed at the same time will. However, these components can also be used in one additional shell applied to the silicate cover will.

5 bis 92 Gew.-% Magnesium

10 bis 60 Gew.-% Feldspat, Nephelin-Syenit oder Rhyolit oder Montmorillonit

5 bis 92 Gew.-% Calciumcarbid und/oder Calciumoxid.

Of course, it is also possible to first apply the calcium carbide / calcium oxide layer and then the layer of the silicate minerals. Such a desulfurization agent therefore consists of:

5 to 92 wt% magnesium

10 to 60% by weight feldspar, nepheline syenite or rhyolite or montmorillonite

5 to 92% by weight calcium carbide and / or calcium oxide.

Through this wrapping, which if necessary with the help of a usual anhydrous binder applied to the magnesium the magnesium grain is about the same Flowability imparted like the mineral components of the desulfurizing agent. So that becomes a pneumatic receive well-funded funds that span the entire Blowing duration evenly in the pre-calculated Allow quantity to be introduced into the molten iron.

The magnesium also loses through this coating its metallic surface, with which its segregation tendency not only reduced during transport and handling, but is practically avoided. You can with such Desulphurization mixtures according to the invention which are technological avoid complex blowing technique of co-injection.

The silicates with their alkali content, such as in particular the nepheline, but also the potash and soda feldspars in turn contribute to desulfurization by by splitting off their alkali portion alkali sulfides form, which are deposited in the slag. At the same time effect these feldspars together with the Alkali sulfur compounds and other additives of the desulfurizing agent liquefaction of the slag and thereby reducing their absorption capacity for iron granules.

Because of the chemical and physical properties certain silicate minerals, e.g. of the rhyolite, which expands at the temperature of the molten iron and foams and due to its good wettability the iron slowly rises in the molten iron while doing so absorbs the unwanted sulfur-containing components, Surprisingly, the effect of back desulfurization is eliminated; the final sulfur content once reached changes no further.

Those according to the invention have a particularly advantageous effect Silicates used with regard to the slag properties out. It turned out to be completely surprising that when using the silicates the iron content in the slag is significantly lower than with slag, those using previously known desulfurization mixtures arise. There is a lower iron content in the slag of course synonymous with a higher iron yield and favors the economics of the process. At the same time, the slag can be easily and completely Remove from the iron bath using normal measures.

The silicates used according to the invention influence the components contained in the mixture as diluents in that they liquefy them (or at least convert to a viscous state), with which favors the uptake of sulfidic products and their Separation behavior is improved.

According to a preferred embodiment, the desulfurization agent has a proportion of 3 to 95% by weight of feldspar or nepheline syenite in addition to magnesium as a further desulfurizing component.
Furthermore, a proportion of a mixture consisting of 5 to 50% by weight rhyolite / montmorillonite can be added to the magnesium as a further desulfurizing component.

The addition of flow aids require the invention proposed desulfurization agent in general Not. Should such an addition e.g. due to the technical design of the blowing system as required prove, these affect the effectiveness of the Desulfurizing agent not.

The invention is illustrated below by means of examples explained in more detail:

example 1

There was a mixture consisting of 50 wt .-% magnesium with a grain size of 0.2-0.9 mm and 50% by weight of sodium feldspar, with comparable grain size in a 170 t pig iron smelter after fluidizing, blown in with a submersible lance.

The mean of eleven melts showed an initial sulfur content of 0.046% and a final sulfur content less than 0.006%. The desulfurizing agent requirement per ton of pig iron smelting amounted to 1.08 kg, which 0.54 kg of magnesium consumption per ton of pig iron. The slag was easy to remove. Most of all was the salary low in iron granules with 16% by weight.

Example 2

There was a mixture consisting of 25 wt .-% fine particles Magnesium, 45% by weight calcium carbide and 30% by weight pearlite used.

The mean of nine treatments with one average melt weight of 115 t an initial sulfur content of 0.038 wt .-% and after Treatment a final sulfur content of 0.004 wt .-%. The The blowing rate was 1.46 kg desulfurizing agent per ton, which results in a magnesium consumption of 0.36 kg per ton calculated. The blowing time was about 7 minutes.

All slags treated with the agent according to the invention Melting, had low iron levels in the form of granules in the range of 10 to 20% by weight, the Slag without running along / pulling the iron melt could be removed very well.

Example 3

A granulated mixture consisting of 25% by weight Magnesium, 45% by weight calcium oxide and 30% by weight feldspar used with nine melts of approx. 115 t.

The initial sulfur content was approx. 0.040% by weight the final sulfur content after treatment is less than 0.005 % By weight. The injection quantity: 1.55 kg mixture / t iron. Out of it a magnesium consumption of 0.39 kg Mg / t is calculated.

The blowing time was about 7 minutes. The slag contained Granules in the range of 10-20% by weight. She was without one Running along / pulling the iron melt away very well.

Example 4

In another series of experiments, the effect of the new Desulfurizing agent using the so-called co-injection process checked. For this was in a torpedo pan with a capacity of approx. 200 t of molten iron worked.

The fine-grained magnesium component (0.2-0.9 mm) was mixed with 20% by weight rhyolite; the calcium carbide component was mixed with 40 wt .-% feldspar. The relationship of the two co-injection components was approximately 3.5: 1. By from 0.040% initial sulfur to 0.005% final sulfur a magnesium requirement of 0.35 kg / t was determined, against a magnesium requirement of 0.47 kg / t a working method according to the state of the art. As special The low content of Iron granules of less than 15 wt .-% determined. The Slag continued to run after long periods of treatment still perfectly off the torpedo pan.

Claims (6)

1. A reagent, capable of being transported pneumatically, for desulfurization, based on magnesium, of pig iron and foundry iron,

   in which the magnesium, if necessary, is coated with silicate materials containing alkalies, and is coated with calcium carbide and/or calcium oxide,

   and the reagent consists of

   5 - 92 weight % magnesium,

   10 - 60 weight % feldspar, nepheline syenite or rhyolite or montmorillonite,

   5 - 92 weight % calcium carbide and/or calcium oxide.
2. A reagent according to claim 1, which contains 25 - 92 weight % magnesium.
3. A reagent according to claims 1 to 2, which contains 50 - 92 weight % magnesium.
4. A reagent according to claims 1 to 3, in which the magnesium is coated with silicate minerals.
5. A method for the desulfurization of liquid iron using the reagents according to claims 1 to 4, in which the reagents are transported pneumatically through a lance into the liquid iron.
6. A method according to claim 5, in which the magnesium is fluidized separately from the remaining ingredients, and in which the magnesium is combined in the lance with these remaining ingredients as a component of co-injection.