EP0530552B1 - Process for desulfuration treatment of molten pig iron - Google Patents

Abstract

The invention relates to a process for treating molten pig iron for desulphurisation thereof in a vessel. The characteristic of the invention is that the treatment is carried out in three phases: In the initial phase, those solids are blown in which deoxidise the initial slag and increase its basicity, and effect a circulating motion of the melt or form a basic deoxidised covering slag. In the middle phase, a desulphurising agent is blown in for the main desulphurisation and, in the final phase, those solids are blown in which purify the melt and effect a final desulphurisation and affect the resulting desulphurisation slag in such a way that its content of iron granules is low. <IMAGE>

Description

The invention relates to a method for treating pig iron melts for their desulphurization in a container, in particular in a transfer pan, which have an acidic, oxidized initial slag, by blowing fine-grained solids into the melt with a conveying gas via an injection lance, the treatment in three phases is carried out, as well as a variant in which the initial slag is removed from the pig iron melt before the treatment and a new covering slag is formed.

In the desulphurization of pig iron, it is known to use two treatment materials, for example an alkaline earth carbonate, such as calcium carbonate, and a metallic reducing agent, such as fine-grained magnesium (DE-OS 27 08 424, DE-OS 27 08 424, DE-OS 26 50 113, US) PS 3 998 625) or a mixture of two treatment substances and a further treatment substance, for example calcium carbide and a gas-releasing coal as a mixture and fine-grained magnesium (EP-OS 0 226 994), or three treatment substances, for example calcium carbide, a gas-releasing coal and finely divided magnesium (US Pat. No. 4,832,739) to fluidize separately and to combine the fluidates immediately before they enter the melt.

• 1. Roheisen, das im Hochofen erzeugt wurde, weist eine saure, oxidierte Anfangsschlacke auf. Wird, wie bei den vorbeschriebenen, zum Stand der Technik gehörenden Verfahren, in der Anfangsphase mit feinkörnigem Magnesium entschwefelt, können die sich bildenden Magnesiumsulfide (MgS) von der Schlacke nicht aufgenommen werden.
• 2. Eine ausreichende Dispergierung der Entschwefelungsmittel und eine auf den Reaktionsverlauf abgestimmte Badumlaufbewegung lassen sich nicht optimal einstellen.
• 3. Eine auf den momentanen Schwefelgehalt der Roheisenschmelze abgestimmte Zufuhr von feinteiligem Magnesium läßt sich nicht optimal durchführen.
• 4. Eine Konditionierung/Modifikation der Endschlacke, d. h. eine Verrringerung der Eisen-Aufnahme, laßt sich nicht optimal erreichen. Ferner läßt sich das Ausspülen von schwebenden Magnesiumsulfiden in der Schmelze und die Umsetzung von gelöstem Magnesium mit dem Schwefel der Schmelze nicht optimal durchführen.

This injection technique, known as co-injection, has improved the desulphurization of pig iron melts. In a further development of the co-injection of calcium carbide and magnesium at a ratio of 3.5: 1, pretreatment and post-treatment with approx. 90 kg and approx. 136 kg calcium carbide have also been carried out (73 rd Steel-making Conference Proceedings, Vol. 73, Detroit Meeting, March 25-28, 1990, pp. 351-355). Another similar method is known from DE-OS 39 42 405. However, there are still disadvantages:

• 1. Pig iron produced in the blast furnace has an acidic, oxidized initial slag. If, as in the previously described processes belonging to the prior art, desulfurization is carried out with fine-grained magnesium, the slag cannot absorb the magnesium sulfides (MgS) that form.
• 2. Adequate dispersion of the desulfurizing agent and a bath circulation movement that is matched to the course of the reaction cannot be optimally adjusted.
• 3. A supply of finely divided magnesium which is matched to the instantaneous sulfur content of the pig iron melt cannot be carried out optimally.
• 4. A conditioning / modification of the final slag, ie a reduction in the iron absorption, cannot be optimally achieved. Furthermore, the flushing out of floating magnesium sulfides in the melt and the reaction of dissolved magnesium with the sulfur of the melt cannot be carried out optimally.

• in der Anfangsphase solche Feststoffe eingeblasen werden, die die Anfangsschlacke desoxidieren und ihre Basizität erhöhen sowie eine Umlaufbewegung der Schmelze bewirken und
• in der mittleren Phase ein oder mehrere Entschwefelungsmittel zur Hauptentschwefelung eingeblasen werden und
• in der Schlußphase solche Feststoffe eingeblasen werden, die die Schmelze reinigen und eine Schlußentschwefelung bewirken, sowie die sich gebildete Entschwefelungsschlacke so beeinflussen, daß ihr Gehalt an Eisengranalien gering ist.

The present invention has set itself the task of influencing the initial slag so that it is receptive to the magnesium sulfides and ensures optimal dispersion of the desulfurizing agent in the melt with a bath circulation movement optimally matched to the course of the reaction. Finally, interferences that are based on uncontrolled re-sulfurization are to be eliminated, so that the addition of fine-grained magnesium is better matched to the sulfur content of the melt and the modification of the slag to limit the absorption of iron in the slag, as well as the rinsing out of the magnesium sulfides from the melt can be improved.
The object is achieved in a method of the type described at the outset according to claim 1 in that

• in the initial phase, such solids are blown in that deoxidize the initial slag and increase its basicity and cause a circulating movement of the melt and
• in the middle phase one or more desulfurization agents are blown in for the main desulfurization and
• in the final phase, such solids are blown in, which clean the melt and bring about a final desulfurization, and influence the desulfurization slag formed in such a way that its content of iron granules is low.

Claim 2 identifies a process variant in which the acidic, oxidized initial slag is removed from the pig iron melt before the treatment. In this variant, in the initial phase, solids are blown in that form a basic, deoxizing, slag covering the pig iron melt and cause the melt to circulate. The features of the two further phases correspond to those of claim 1.

In deviation from previous desulfurization processes, in which desulfurizing agents are blown into the pig iron melt from the start of the treatment, the actual desulfurization phase is preceded by a treatment as an initial phase and a further treatment as a final phase after the treatment. In this way, the disadvantages described can be avoided in an advantageous manner and an improved desulfurization of the pig iron melts can be achieved.

• in der Anfangsphase (I) desoxierende und/oder kalkhaltige und/oder gasabspaltende Feststoffe,
• in der mittleren Phase (II) der Behandlung als Entschwefelungsstoffe magnesiumhaltige Feststoffe und/oder Calciumverbindungen gegebenfalls mit gasabspaltenden Feststoffen und Flußmitteln

eingeblasen. Die kalkhaltigen Feststoffe können ausgewählt werden aus der Gruppe Kalk, Kalkstein und Dolomit. Die gasabspaltenden Feststoffe für die Anfangsphase sind ausgewählt aus der Gruppe Flammkohle, Gasflammkohle, Braunkohle, Kalkstein und Dolomit, während die gasabspaltenden Feststoffe für die II. und III. Phase ausgewählt sind aus der Gruppe Flammkohle, Gasflammkohle, Braunkohle und Diamidkalk.To be favoured

• in the initial phase (I) deoxizing and / or calcareous and / or gas-releasing solids,
• in the middle phase (II) of the treatment as desulfurizing substances, magnesium-containing solids and / or calcium compounds, optionally with gas-releasing solids and fluxes

blown in. The calcareous solids can be selected from the group of lime, limestone and dolomite. The gas-releasing solids for the initial phase are selected from the group of flame coal, gas flame coal, lignite, limestone and dolomite, while the gas-releasing solids for the II. and III. Phase are selected from the group of flame coal, gas flame coal, lignite and diamide lime.

The deoxidizing solids that are blown into the pig iron melt during phase I are selected from the group aluminum and polyethylene. Polyethylene works directly in the slag area and reduces oxygen activity; overall, the absorption capacity of the initial slag for sulfides is increased.

The calcium compounds which are blown into the pig iron melt as a desulfurizing agent during the middle phase and the final phase are selected from the group of flowable, reactive lime and technical calcium carbide. The magnesium-containing solids that are blown into the pig iron melt during the middle phase of the treatment are selected from the group consisting of metallic magnesium, with or without coatings, alone or in a mixture with lime, CaC₂, calcium aluminates, alumina and magnesium oxide.

The fluxes which are blown into the melt in the final phase of the treatment are selected from the group of fluorspar and soda (sodium carbonate).

According to a further embodiment, the calcareous solids can be mixed with an aluminum-containing substance. The same applies to technical calcium carbide. The aluminum-containing solids are selected from the group aluminum, metallurgical aluminum.

In the process according to the invention, lime-containing and gas-releasing solids are preferably blown into the melt in the initial phase of the treatment in order to deoxidize the initial slag and to make a circulating movement of the melt. By adding calcareous solids, such as lime as a base carrier, the basicity of the slag is increased and neutralization is achieved in this way. The melt is stirred by the gas-releasing solids together with the injected conveying gas. The silicon and the iron oxide (FeO) of the melt are converted into silica (SiO₂) and iron (Fe) by the generated orbital movement in the sense of deoxidation.

In the middle phase of the treatment, magnesium and calcium carbide are preferably blown in as the desulfurizing agent, the slag pretreated in the manner described being able to absorb the magnesium sulfides formed. Blowing in gas-releasing solids in this phase is also an advantage.

In the final phase of the treatment, calcium carbide and gas-releasing solids are preferably blown into the melt. The gases split off, together with the conveying gas, help to flush out the magnesium sulfides suspended in the melt and to react the magnesium dissolved in the melt with sulfur. Flux may be blown in to condition the slag. The desulfurization slag formed is influenced by these substances in such a way that their iron granules content is low.

In the process according to the invention, in deviation from the previously known desulfurization processes, a large number of solids - base carriers, deoxidizing agents, desulfurizing agents, gas releasing agents, slag conditioners - are blown into the pig iron melt independently of one another in an optimally timed dosage.

According to a further preferred embodiment of the method according to the invention, the fine-grained solids are removed as a mixture and individual solids from separate pressure delivery vessels and blown into the melt via a common delivery line followed by a blowing lance. In this way an optimal dosage of the individual solids can be achieved.

However, two or three fine-grained solids can also be taken as a mixture as well as individual solids from separate pressure delivery vessels and blown into the melt via a common delivery line followed by a blowing lance. While in the process variant according to claim 4 there must be a separate pressure delivery vessel for each fine-grained solid, the effort for pressure delivery vessels can be restricted in the method variant according to claim 5.

mit:

Vg

= Summe der eingeblasenen Fördergasmenge, der durch Gasabspaltung in der Schmelze freiwerdenden Gasmenge und der Gasmenge durch Verdampfung von metallischem Magnesium aus Magnesiumhaltigen Feststoffen

T_l

= Temperatur der Schmelze, °K

g

= Erdbeschleunigung, m/s²

_l

= Dichte der Schmelze, kg/m³

H_b

= Höhe der Schmelze, die von Gasblasen durchströmt wird, m

P_o

= Druck der Schmelze, bar

Gschm

= Gewicht der behandelten Schmelze, t

Die dissipierte Energiedichte wird bevorzugt auf Werte zwischen 200 bis 1.000 W/t Roheisen eingestellt. In weiterer Ausgestaltung des Verfahrens wird die dissipierte Energiedichte in der Anfangsphase der Behandlung auf Werte zwischen 600 bis 1.000 W/t Roheisen und in der mittleren und Schlußphase auf Werte zwischen 200 bis 700 W/t Roheisen eingestellt.
Ferner wird bevorzugt die Menge der eingeblasenen Magnesiumhaltigen Feststoffe mit absinkendem Schwefelgehalt verringert und die Menge der eingeblasenen Calciumverbindungen sowie der gasabspaltenden Feststoffe und/oder die Menge des eingeblasenen Fördergases erhöht.According to a further feature of the invention, the amount of the conveyed gas injected is controlled as a function of the amount of solids injected and the total amount of stirring gas Vg so that a dissipated stirring energy ED _diss in the melt of at least 100 watts / t of pig iron results according to the relationship:

With:

Vg

= Sum of the quantity of gas blown in, the quantity of gas released by the elimination of gas in the melt and the quantity of gas due to the evaporation of metallic magnesium from solids containing magnesium

T _l

= Temperature of the melt, ° K

G

= Gravitational acceleration, m / s²

_l

= Density of the melt, kg / m³

H _b

= Height of the melt through which gas bubbles flow, m

P _o

= Pressure of the melt, bar

Gschm

= Weight of the treated melt, t

The dissipated energy density is preferably set to values between 200 to 1,000 W / t pig iron. In a further embodiment of the method, the dissipated energy density is set to values between 600 to 1,000 W / t pig iron in the initial phase of the treatment and to values between 200 to 700 W / t pig iron in the middle and final phase.
Furthermore, the amount of the solids containing magnesium blown in with a decreasing sulfur content is preferably reduced and the amount of the calcium compounds blown in and the gas-releasing solids and / or the amount of the conveyed gas injected is increased.

It is considered an advantage of the invention that the problems associated with the known desulfurization processes described at the outset can be overcome and that an improved desulfurization effect can be achieved due to the three-phase treatment according to the invention. Advantageously, with the method according to the invention, the metallurgical process control can be adapted using process engineering means using desulfurization components that are matched to the process stages. Further advantages can be seen in the fact that a considerable reduction in the consumption of expensive desulfurizing agents is achieved with corresponding economic benefits. In addition, the utilization of these agents is optimized not only by avoiding oxidation and re-sulfurization, but also by setting the most favorable conditions in each case by controlling the kinetically important parameters, namely turbulence and the availability of the desulfurizing agent per unit of time. The significantly lower consumption of desulfurizing agents has a positive and cost-effective impact, both overall and indirectly, in conjunction with low iron losses, lower amounts of slag, short treatment times and lower heat losses.

Bild 1:

den Ablauf der Entschwefelung einer Roheisenschmelze mit fünf getrennt zugeführten Stoffen

Bild 2:

den Ablauf der Entschwefelung einer Roheisenschmelze mit zwei Gemischen und zwei Einzelstoffen, d. h. insgesamt mit vier Komponenten und

Bild 3:

den Ablauf der Entschwefelung einer Roheisenschmelze mit zwei Gemischen und einem Einzelstoff, d. h. insgesamt mit drei Komponenten.

The invention is explained below with reference to Figures 1, 2 and 3.
Show

Image 1:

the process of desulfurization of a pig iron melt with five separately fed substances

Picture 2:

the process of desulfurization of a pig iron melt with two mixtures and two individual substances, ie with a total of four components and

Picture 3:

the process of desulfurization of a pig iron melt with two mixtures and a single substance, ie with a total of three components.

As shown schematically in Figure 1, in the initial phase of the treatment, the pig iron melt, which is located in a transfer pan, for example, is stirred vigorously with the gas split off from the gas coal; the slag deoxidizes through the decomposition products of the gas coal and through reaction of the silicon content of the pig iron to silica and Fe. Lime (CaO) is added in a short time to increase the basicity. In the middle phase of the treatment, when the lime is withdrawn, fine-grained magnesium and relatively little calcium carbide are blown into the melt; the addition of gas coal is throttled to limit turbulence in the melt. The addition of magnesium is reduced in accordance with the course of the sulfur content in the melt. For this, the blowing in of calcium carbide and coal is increased to intensify the bath movement.
At the beginning of the final phase of treatment, after switching off the magnesium additive, calcium carbide is either blown in further as required or the additive is reduced; for this purpose, the melt is stirred vigorously, on the one hand by the conveying gas and on the other hand by the gas split off from the gas coal. In this way, the magnesium sulfides are advantageously flushed out of the melt. To condition the slag, a flux is blown into the melt in the final phase of the treatment.
In this embodiment, the five solids used - lime, gas coal, calcium carbide, magnesium and flux - are individually in separate pressure vessels, from which they are removed and blown into the melt via a common feed line with subsequent blowing lance. The pressure delivery vessels have known controllable metering valves with which the solids can be blown into the melt simultaneously or successively and the quantities per unit of time can be varied, as shown in Figure 1.

In the exemplary embodiment according to Figure 2, the solids lime and gas coal, which are blown into the pig iron melt in the initial phase of the treatment, and the solids calcium carbide and gas coal, which are blown into the pig iron melt during the middle phase and the final phase, are each mixed as a mixture Pressure delivery vessel included. As a result, the expenditure on apparatus for pressure-carrying vessels can be reduced by one vessel, but the targeted influencing of the pig iron melt can be carried out somewhat less optimally than with the exemplary embodiment according to Figure 1 by using two mixtures.

A further variant of the treatment method according to the invention is shown in the exemplary embodiment according to FIG. 3, in which the components lime, gas coal and flux are present as a mixture, furthermore the components calcium carbide and gas coal as a mixture and magnesium as a single solid in separate pressure vessels. In this way, the outlay on equipment for the pressure delivery vessels can be further reduced.

It also applies to this exemplary embodiment that the targeted influencing of the pig iron melt and the initial slag can be carried out somewhat less optimally than the exemplary embodiment according to Figure 1.

The invention is further explained below by means of comparative and exemplary embodiments which relate to the desulfurization agent consumption and the desulfurization effect, namely Table 1 shows Comparative Examples 1 to 14, while Tables 2 to 5 show Examples 15 to 25 according to the invention.

Comparative examples

In the treatments of comparative examples 1 to 5, dried compressed air was used as the conveying gas. In the case of treatments of comparative examples 6 to 14, argon was the production gas. Despite the different pan contents, all treatments are comparable due to approximately the same lance depth. The stated solid and conveying gas delivery rates were constant over the duration of the treatment. The hot metal temperatures for all treatments were in the range of 1,300 to 1,380 ° C. To compare the desulfurization agent consumption, the proportions of calcium carbide were converted to magnesium based on experience with regard to the desulfurization efficiency. This so-called magnesium equivalent is specified as specific consumption in the last column.

Examples according to the invention

In all of the treatments of Examples 15 to 25, argon or nitrogen was used as the production gas.

Phase I:

Einblasen von 1,5 kg/t = 348 kg eines Gemisches aus 90 % Feinkalk und 10 % Flammkohle (Körnung: < 0,1 mm) in 4,2 Minuten mit 450 Nl/min N₂.

Phase II:

Einblasen von 328 kg CaM 20 (76 % techn. Calciumcarbid,, 20 % Magnesium, 4 % Flammkohle) entspr. 1,41 kg/t, in 9,1 Minuten entspr. 36 kg/min (konstant). Fördergas: Argon, 800 Nl/min (konstant).

Phase III:

Einblasen von 80 kg eines feinkörnigen Gemisches aus 80 % Flußspat und 20 % Flammkohle in 2,6 Minuten mit 500 Nl/min. Die sehr leichte Schlacke mit offenbar geringem Eisengehalt war feinkrümelig und ließ sich gut abziehen. Der S-Gehalt nach der Behandlung betrug 0,0048 % bei einem Mg-Äquivalent von 0,44 kg/t.

Quantity of pig iron 232 t, approx. 1.2 t pan slag before treatment, S content before treatment: 0.042%

Phase I:

Blowing in 1.5 kg / t = 348 kg of a mixture of 90% fine lime and 10% flame coal (grain size: <0.1 mm) in 4.2 minutes with 450 Nl / min N₂.

Phase II:

Injection of 328 kg CaM 20 (76% technical calcium carbide, 20% magnesium, 4% flame carbon) corresponds to 1.41 kg / t, in 9.1 minutes corresponds to 36 kg / min (constant). Conveying gas: argon, 800 Nl / min (constant).

Phase III:

Blowing in 80 kg of a fine-grained mixture of 80% fluorspar and 20% flame coal in 2.6 minutes at 500 Nl / min. The very light slag with apparently low iron content was finely crumbly and was easy to remove. The S content after treatment was 0.0048% with a Mg equivalent of 0.44 kg / t.

Phase I:

Einblasen von 200 kg eines feinkörnigen Gemisches aus 75 % Kugelmühlenstaub und 25 % Kalksteinmehl in 3,2 Minuten mit 520 Nl/min.

Phase II:

Einblasen aus 2 verschiedenen Förderbehältern (Koinjektion) 258 kg CaC5 (95 % techn. Calciumcarbid, 5 % Flammkohle), mit 38 kg/min (konstant) sowie 128 kg Mg 50 KMS (50 % Mg, 50 % Kugelmühlenstaub) mit 19 Kg/min und 780 Nl Argon/min.

Phase III:

Der CaC5-Strom wurde beibehalten und sofort nach Abschalten des Mg-50-Stromes wurde aus einem 4. Förderbehälter, der ebenfalls in Reihe geschaltet war, Calciumaluminatstaub (< 0,3 mm, ca. 50 % CaO, 44 % Al₂O₃, Rest MgO + SiO₂) zugeschaltet. Insgesamt wurden 120 kg CaC5 und 80 kg Ca-Aluminat in dieser Phase eingeblasen. Der Argondurchfluß wurde zur Erhöhung der Rührleistung auf (konstant) 1.200 Nl/min erhöht. Die Roheisenprobe nach der Behandlung ergab 0,0034 % S; Mg-Äquivalent = 0,52 kg/t.

Pig iron quantity 227 t, S _A = 0.036%

Phase I:

Blowing in 200 kg of a fine-grained mixture of 75% ball mill dust and 25% limestone powder in 3.2 minutes at 520 Nl / min.

Phase II:

Injection from 2 different conveying containers (co-injection) 258 kg CaC5 (95% technical calcium carbide, 5% flame carbon), with 38 kg / min (constant) and 128 kg Mg 50 KMS (50% Mg, 50% ball mill dust) with 19 Kg / min and 780 Nl argon / min.

Phase III:

The CaC5 stream was maintained and immediately after switching off the Mg-50 stream was calcium aluminate dust (<0.3 mm, approx. 50% CaO, 44% Al₂O₃, balance MgO) from a 4th delivery container, which was also connected in series + SiO₂) switched on. A total of 120 kg CaC5 and 80 kg Ca aluminate were blown in during this phase. The argon flow was increased to (constant) 1200 Nl / min to increase the stirring power. The pig iron sample after treatment gave 0.0034% S; Mg equivalent = 0.52 kg / t.

Pig iron quantity: 226 t, S _A : 0.038%
This attempt was done in the same way as Beh. No. 16 carried out, with only minor deviations in quantities and times. In contrast to the Beh.-Nr. During phase II, the delivery rates were systematically changed linearly over time: CaC5 initially 24 kg / min, in the end 48 kg / min; Mg 50 KMS initially 27 kg / min, in the end 12 kg / min. The amount of feed gas was varied accordingly between 680 and 800 Nl / min.
With the same Mg equivalent of 0.52 kg / t, the final sulfur content was 0.0022%.

The data of the further trial treatments (as well as that of the ones already described) are contained in the tables. Therefore only special features of the individual tests are described below.

Large initial amount of slag. Divided / deoxidized with dolomite and metallic aluminum granulate. Linearly varied delivery rates in phase II, analogous to Beh.-Nr. 17th

The oxidized slag was largely removed before the start of the treatment and a basic, deoxidized slag was formed by blowing in a lime-fluorspar mixture. Flame coal was used as a stirring and deoxidizing agent.

5 production containers were used in series, with 3 components being variably blown in in phase II, with a decreasing Mg output a higher proportion of carbide and flame coal with the same quantity of production gas. The flow of the latter two was not interrupted for the transition to phase III.

The slag was largely removed before treatment. In the final phase, cleaning was carried out with pre-melted calcium aluminate, and the stirring energy was introduced by means of a large amount of conveying gas.

In all 3 phases, fine lime was blown in by co-injection with flame coal (1st phase), magnesium and flame coal (2nd phase) and fluorspar and flame coal (3rd phase). The funding rates were kept constant.

CaC5 was injected continuously in all 3 phases.

The acidic, oxidic slag was largely removed beforehand and 200 kg of fine lime, packed in sacks, were added. The lance was then retracted and stirred with 1800 Nl / min argon for 2.5 minutes. During phases II and III, fine lime was blown in, first salt-coated magnesium was added, then fluorspar, with the amount of gas being increased again in this phase to intensify the stirring effects. The Mg output was reduced linearly, the lime rate kept constant.

In this treatment, ball mill dust was continuously blown in for all 3 phases for deoxidation, as a by-product and for slag conditioning. Limestone (phase I) and salt-coated magnesium (phase II) were switched on. In phase III, increased gas throughput was used.

Instead of magnesium, CaD 7525 (75% technical calcium carbide and 25% diamide lime) was used for the desulfurization. This desulfurizing agent is not as advantageous as e.g. B. CaC5 with magnesium (in co-injection), because it requires long treatment times and there is a high iron loss in the final slag, due to the larger amount of slag and its high proportion of iron granules. The main goal was to reduce iron losses.
The beneficial effect of fluorspar in this sense is known, but when added to the CaD, the desulfurization effect deteriorates. In this case, this did not occur, as the result shows. The slag was light and crumbly and contained little iron.

Claims (19)

1. A process for the metallurgical treatment of pig iron melts in a container, more particularly a refill ladle, which contain an acid, oxidized initial slag, by the injection of fine-grained solids into the melt with a feed gas via an injection lance, the treatment being performed in three phases, characterized in that

   a) in the initial phase such solids are injected as deoxidize the initial slag and increase its basicity and also produce a circulatory movement of the melt,

   b) in the middle phase one or more desulphurization agents are injected for the main desulphurization, and

   c) in the final phase such solids are injected as purify the melt and produce a final desulphurization and also so influence the desulphurization slag formed that its iron granule content is low.
2. A process for the metallurgical treatment of pig iron melts in a container, more particularly a refill ladle, by the injection of fine-grained solids into the melt with a feed gas via an injection lance after the removal of an acid, oxidized initial slag, the treatment being performed in three phases, characterized in that

   a) in the initial phase such solids are injected as form a basic, deoxidized slag covering the pig iron melt and produce a circulatory movement of the melt,

   b) in the middle phase one or more desulphurization agents are injected for the main desulphurization, and

   c) in the final phase such solids are injected as purify the melt and produce a final desulphurization and also so influence the desulphurization slag formed that its iron granule content is low.
3. A process according to claims 1 or 2, characterized in that

   a) in the initial phase deoxidizing and/or lime-containing and/or gas-separating solids are injected,

   b) in the middle phase of the treatment magnesium-containing solids and/or calcium compounds, possibly with gas-separating solids are injected as desulphurization substances,

   c) in the final phase calcium components, possibly with gas-separating solids and fluxing agents are injected.
4. A process according to claims 1 to 3, characterized in that the fine-grained solids are taken as a mixture and individual solids from separate pressurized feed vessels and injected down to the melt via a common feed line followed by an injection lance.
5. A process according to claims 1 to 3, characterized in that each time two or three fine-grained solids are taken as a mixture and individual solids from separate pressurized feed vessels and injected down to the melt via a common feed line followed by an injection lance.
6. A process according to claims 1 to 5, characterized in that the quantity of the injected feed gas in dependence on the quantity of the injected solids and the total quantity of stirring gas Vg are so controlled that a dissipated stirring energy ED_diss of at least 100 W/t of pig iron is obtained in the melt in accordance with the relation:

   

   where:

   Vg   = sum of the quantity of injected feed gas, of the quantity of gas released by gas separation in the melt and of the quantity of gas due to the evaporation of metallic magnesium from magnesium-containing solids

   T₁   = temperature of the melt in °K

   g   = terrestrial acceleration in m/sec²

   ₁   = density of the melt in kg/m³

   H_b   = height of the melt through which gas bubbles flow, in m

   P_o   = pressure of the melt in bar

   Gschm   = weight of the treated melt in t.
7. A process according to claim 6, characterized in that the dissipated energy density ED_diss is adjusted to values between 200 and 1000 W/t pig iron.
8. A process according to claims 1 to 7, characterized in that the dissipated energy density ED_diss is adjusted in the initial phase of the treatment to values between 600 and 1000 W/t pig iron and in the middle and final phases to values between 200 and 700 W/t pig iron.
9. A process according to claims 3 to 9, characterized in that the quantity of the injected magnesium-containing solids is reduced as the sulphur content falls and the quantity of the injected calcium compounds and of the gas-separating solids and/or the quantity of the injected conveying gas is increased.
10. A process according to claims 3 to 9, characterized in that the lime-containing solids are selected from the group:
    lime (CaO), limestone (CaCO₃), dolomite.
11. A process according to claims 3 to 10, characterized in that the gas-separating solids for the initial phase are selected from the group:
    bright-burning coal, gas-flame coal, lignite, limestone, dolomite.
12. A process according to claims 3 to 10, characterized in that the gas-separating solids for the second and third phases are selected from the group:
    bright-burning coal, gas-flame coal, lignite, dyamide lime.
13. A process according to claims 1 to 12, characterized in that the deoxidizing solids are selected from the group:
    aluminium, polyethylene.
14. A process according to claims 3 to 13, characterized in that the calcium compounds are selected from the group:
    free-flowing reactive lime, technical calcium carbide.
15. A process according to claims 3 to 14, characterized in that the magnesium-containing solids are selected from the group:
    metallic magnesium, with or without coatings, on its own or mixed with lime, CaC₂, calcium aluminates, alumina, magnesium oxide.
16. A process according to claims 3 to 15, characterized in that the fluxing agents are selected from the group:
    fluospar, soda (sodium carbonate).
17. A process according to claims 3 to 16, characterized in that the lime-containing solids are mixed with an aluminium-containing solid.
18. A process according to claim 14, characterized in that the technical calcium carbide is mixed with an aluminium-containing solid.
19. A process according to claims 17 or 18, characterized in that the aluminium-containing solids are selected from the group:
    aluminium, primary aluminium pig.

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