DE19833036A1 - Process for the desulfurization of a pig iron melt - Google Patents

Abstract

Molten pig iron is desulfurized by injection of a high reducing additive content agent under conditions which take thermodynamic and reaction kinetics requirements into account. Preferred Features: The parameters are a relatively high ratio of the agent injection rate to the transport gas rate, a relatively high specific total gas quantity and a relatively high ratio of evolved gas quantity to transport gas quantity. The agent comprises (by wt.) 30-72 CaC2, 15-62% CaO and 8-20% gas-evolving additive, especially gas coal, flame coal, plastic or other hydrocarbon which evolves reducing gases at pig iron temperatures of 1150-1500 degrees C.

Description

The invention relates to a method for desulfurization a pig iron melt, one at least one fine granular desulfurizing agent and a gas release the melt treating agent containing the additive with the help of a transport gas in a pig iron smelter zebad is blown in.

Pig iron desulfurization processes are different Design types from practice and specialist literature (e.g. "Stahl und Eisen", No. 9/1997, pp. 53-58) be knows. This desulfurization is the pig iron smelter zebad in an appropriate container, which is in the generally through a torpedo pan or pipe pan is formed, each time the blast furnace tapping is filled.

For the desulfurization of pig iron, it is known to use calcium-containing desulfurizing agents, namely calcium carbide (CaC ₂ ) and / or lime (CaO) and to introduce these into the pig iron melt bath by means of a so-called mono-injection, the desulfurizing agent being removed from a conveying vessel is discharged and blown into the hot metal melt or the hot metal melt bath with a transport gas via a refractory blowing lance. This blowing in takes place during the entire treatment time with a constant blowing rate for desulfurizing agents and transport gas. Since both calcium carbide and lime are in the most solid state at pig iron temperatures of around 1,250 to 1,550 ° C, this desulfurization of liquid pig iron is a solid-liquid reaction.

This metallurgical process engineering of pig iron sulfurization with calcium carbide and calcareous ent sulphurizing agent is based on a theoretical re Actuator model, according to which the desulfurizing agent finally during the ascent from the Lanzenaus flow opening up to the bath surface with that in the pig iron dissolved sulfur can react. Starting from the his procedural model presentation are in generally practiced two process variants, näm Lich a time-optimized dense phase process and a cost-optimized process.

An essential feature of the time-optimized seal current process is setting a high Desulfurizing agent blowing rate transport gas rate ver ratio, d. H. the desulfurizing agent is with egg a relatively high loading density in the pig iron Blown melt bath. According to the theoretical Basics of the transitory reactor model are created a pseudo-homogeneous at this high loading density Mixture in the area of the lance tip according to Ab building the kinetic energy a large number smaller bubbles containing desulfurization is formed. This large number of small bubbles makes the sulfur containing pig iron melt a relatively large reaction space offered. This relatively large specific Bla The surface of the sensor therefore favors the contact of the Ent sulfurizing agent with the pig iron containing sulfur, whereby a relatively good degree of utilization of the felmittel is achieved.

In this dense phase process, the following features are used, for example: 60 to 90% technical CaC ₂ content and 10 to 40% diamide lime as desulfurizing agent; 80 to 150 kg / min desulfurization blowing rate; 22 to 54 mol / min transport gas rate; One-hole blowing lance, with a position of this blowing lance approximately perpendicular or at an angle of 10 to 30% ge inclined relative to the vertical of the torpedo pan.

The so-called cost-optimized method is based on an introduction device for pulverulent sulfurization reagents, roughly in accordance with EP-B-0 274 557, whereby an optimization of the pig iron desulfurization with respect to the previously described dense stream process could be achieved. This optimization is based on an expanded model of the above-mentioned transitory reactor theory, according to which the efficiency of the desulfurization agents mainly depends on the flow conditions in the pig iron or in the pig iron bath, the speed of the concentration compensation in the pig iron melt and the amount of desulfurization introduced per unit of time in the pig iron melt . In this process, the lowest possible sulfurization blowing rates, high transport gas rates and the use of two-hole blowing lances were used with such a lance position that the outlet nozzles are rotated by a fixed angle with respect to the longitudinal axis of the melting pan. A further optimization can be achieved here by using a eutectic calcium carbide mixture with a technical CaC ₂ content of about 67%, a CaO content of about 28% and flame coal with about 5%. In this case, the desulfurizing agent blowing rate is about 20 to 50 kg / min. at a trans port gas rate of about 98 to 280 mol / min. Compared to the dense stream process described above, the desulfurization costs in the last-mentioned process could be reduced by up to DM 1.50 per ton of pig iron, which is why essentially all torpedo and pipe ladle desulfurization is currently being operated using the last-mentioned, cost-optimized process . The main disadvantage of this last-mentioned method, however, is the fact that the desulphurizing agent blowing time or treatment time, which is sometimes considerably longer than that of the dense phase method, is seen.

Because of the steadily increasing in recent years Requires deeply desulphurized pig iron (with final welding field von 0.005 W) and the resulting the additional extension of the treatment time the capacity of the existing desulfurization plant were often no longer available, and the pig iron duck Sulfurization becomes a bottleneck within a Raffinati chain of crude steel production.

The invention is therefore based on the object Desulfurization process in the preamble of claim ches 1 presupposed way to further develop that compared to the known known last (Cost-optimized) procedure a shortening of the one blowing times with relatively low investment costs and with a reduction in desulfurizing agent costs is achieved.

This object is achieved by the in the Kenn Character of claim 1 specified process features  achieved, advantageous embodiments of this Er are specified in the subclaims.

The invention makes use of the thermodynamic and reaction kinetic influencing factors on the raw iron melt. The most important factors influencing the effectiveness of hot metal desulfurization with calcium carbide and lime are therefore shown below:

• - High ratio of desulfurization blowing rate to transport gas rate to about the formation of a large number of small bubbles / bubbles the effect improve the level of desulfurization;
• - High gas quantities for an accelerated concentrate equalization in pig iron melting (pig iron Melt bath);
• - low desulfurization blowing rates around the Efficiency of desulfurization via a ring tion of those offered in pig iron per unit of time Increase the amount of desulfurizing agent;
• - reducing conditions (i.e. reduction or loading oxygen), since calcium carbide and Cal ciumsulfid have a higher affinity for oxygen than to sulfur;
• - Desulphurising agent with low demixing for ensuring reproducibility desulfurization;  
• - Lance design and position of the blowing lance in the vessel holding the pig iron melt (Torpedo pan or the like.) When optimizing the Flow conditions in the vessel.

Essential features of the invention are therefore therein seen that the melt treatment agent with a relatively high proportion of reducing additive used material and the blowing of this melt means of action when combining several, thermo dynamic and reaction kinetic requirements visible process parameters is carried out. Compared to the prior art described above the inventive method at relatively low Transport gas rates with a corresponding share Desulfurizing agent and a relatively high proportion reducing, gas-releasing additive be driven. Especially due to the relatively high level part of reducing additive becomes a Enlargement of the reactive surface of the desulfurization agent with simultaneous intensive mixing pig iron melting enabled. Through the simultaneous consideration of thermodynamic and reaction kinetic influencing factors or process pa rameter becomes both a time-optimized and a cost-optimized mode of operation achieved, d. H. a ver reduction in injection times with simultaneous reduction desulphurization costs.

In this method according to the invention, at least the following parameters - with the resulting effects - are included in the combination of the method parameters:

• - A relatively high ratio of melt treatment solvent blowing rate to transport gas rate. Here this results in a relatively high loading density, those in the pig iron melt pool are a lot smaller Gas bubbles or gas bubbles causes in which the desulfurizer particles are located. Because small nere gas bubbles have a relatively large specific upper possess area (bubble surface), with a high loading density a reduction in Ent sulfur consumption reached.
• - A relatively high specific total gas volume. By high specific total gas volumes will result from a particularly intensive mixing of the pig iron (Stirring effect) an improved distribution of the Ent Sulfur in pig iron and an accelerating ter concentration balance achieved, which in turn overall contributes to a particularly high efficiency the desulfurization of the pig iron.
• - A relatively high ratio of through the addition The amount of gas split off to the amount of transport gas. This is because the addition released or split gases Ent Sulfur particles from existing gas bubbles detach and in direct contact with the swiss bring molten pig iron melt, which just if the desulfurization efficiency improves or is increased.

In addition to these process parameters, relatively high proportion or the relatively large amount of re reducing effect and split by the additive called gases, causing deoxidation of the raw  iron accelerates and a sulfurization of the reak tion product calcium sulfide to a minimum is set.

In this desulphurization process according to the invention, it has a particularly favorable effect if a mixture of calcium-containing desulphurization agents, containing calcium carbide (CaC ₂ ) and / or lime (CaO), and a gas-releasing additive, a reducing gas-releasing agent, is used as the melt treatment agent Melt treatment agent contains the following proportions - in% by weight:

30 to 72%, preferably 40 to 65%, CaC ₂
15 to 62%, preferably 20 to 50%, CaO
8 to 20%, preferably 10 to 15%, gas releasers

Various means can be used as gas releasers be used, namely gas coal, flame coal, Plastics or other hydrocarbons, each at hot metal temperatures of around 1,150 to 1,500 ° C Eliminate reducing gases (release).

The melt treatment agent is advantageously with a Rate of about 0.67 to 3.36 g per mole of transport gas, preferably about 1.34 to 2.24 kg per mole of transport gas, blown into the pig iron melt bath. The spe specific melt treatment agent blowing rate can expediently in the range from about 0.13 to 0.40 kg / (min t of pig iron), preferably about 0.15 to 0.25 kg / (min t pig iron), can be selected while the from the specific amount of transport gas and the specific split off gas amount formed specific total gas amount in the range of about 0.36 to 0.89 mol / (min.t  Pig iron), preferably about 0.44 to 0.67 mol / (min.t Pig iron) is selected.

In this procedure according to the invention, fer ner a gas quantity ratio between split gas and transport gas at about 2 to 8, preferably at about 3 to 5.

Nitrogen is preferably used as the transport gas, although other suitable transport gas types in the Be may trap can be used, especially ge dried compressed air, natural gas and / or argon.

This is generally the case with this method according to the invention proceeded that the melt treatment agent in fer mixed state of desulfurizing agent and Additive (gas splitter) pneumatically into the pig iron Melt bath is blown.

Below is an embodiment of the invention according to the method compared to the above known "cost-optimized methods" described described. In these processes, pig iron was used melt in a torpedo pan with melt treatment desulphurizing agents or mixtures, some Proportion of technical calcium carbide (most effective ent sulfurization component) of 67%.

In the process according to the invention, the proportion of Gas releasing agent (flame coal) in the melt treatment agent mixture limited to 13% in order to impair the Marksmanship due to possible segregation tendencies to minimize. About hot metal desulfurization anyway with an optimal specific total gas quantity of  carry out at least 0.5 mol per ton of pig iron the melt treatment agent blowing rate - compared to the known method - from 30 kg / min increased to 40 kg / min.

A comparison of the process data between the inventions method according to the invention and the known "Cost optimized process" is in the below Table 1 listed.

Table 1

In a second table, the recorded operating data on the one hand for the method and on the other hand for the well-known cost-optimized process ren specified.

Table 2

The above comparison shows that the method according to the invention makes it possible to achieve further reductions which have a cost-saving and time-saving effect, in particular in comparison with the known method

• - when the desulfurization or melt beet is consumed means of action with - 21.3%,
• - with the blowing times with - 41.1%,
• - in the number of blowing lances (due to the reduced blowing time) with - 41.1% and
• - for pig iron losses with - 9.2%.

To the advantages stated above by the various In addition to the reductions, the expense for transporting and processing the ent sulfur slag can be reduced.

Claims (9)

1. A process for desulfurizing a pig iron melt, wherein a melt treatment agent containing at least one fine-grained desulfurization agent and a gas-releasing additive is blown into a pig iron melt bath with the aid of a transport gas, characterized in that the melt treatment agent has a high proportion of reducing action Additive is used and the blowing in of this melt treatment agent is carried out when combining several process parameters which take thermodynamic and reaction kinetic requirements into account. 2. The method according to claim 1, characterized in that at least the following parameters are included in the process parameters:

• 1. a relatively high ratio of melt treatment agent blowing rate to transport gas rate,
• 2. a relatively high specific total gas quantity,
• 3. a relatively high ratio of the amount of gas split off to the amount of gas transported.

3. The method according to claim 1 or 2, characterized in that a Ge mixture of calcium-containing desulfurizing agents containing calcium carbide (CaC ₂ ) and / or lime (CaO), and as a gas-releasing additive, a reducing gas releasing agent is used as the melt treatment agent, this Melt treatment agent contains the following proportions - in% by weight:
30 to 72%, preferably 40 to 65%, CaC ₂
15 to 62%, preferably 20 to 50%, CaO
8 to 20%, preferably 10 to 15%, gas releasers. 4. The method according to claim 3, characterized in that as gas releasing gas coal, flame coal, art substances or other hydrocarbons used in raw iron temperatures of about 1,150 to 1,500 ° C redu split off decorative gases, are used. 5. The method according to claim 2, characterized in that the melt treating agent at a rate of about 0.67 to 3.36 kg per mole of transport gas, preferably about 1.34 to 2.29 kg per mole of transport gas, in the hot metal melt bath is blown in. 6. The method according to claim 2, characterized in that the specific melt treatment agent-A Blow rate in the range of about 0.13 to 0.40 kg / (min t Pig iron), preferably about 0.15 to 0.25 kg / (min t Pig iron), and those from the spec. Amount of transport gas and the spec. split off gas amount formed spec. Total amount of gas in the range of about 0.36 to 0.89 mol / (min.t pig iron), preferably about 0.44 to 0.67 mol / (min.t pig iron), is selected. 7. The method according to claim 2, characterized in that a gas quantity ratio between split off  Gas and transport gas at about 2 to 8, preferably at about 3 to 5 is selected. 8. The method according to at least one of claims 2 to 7, characterized in that as a transport gas Nitrogen, dried compressed air, natural gas and / or Argon, but preferably nitrogen is used. 9. The method according to at least one of claims 1 to 3, characterized in that the melt bath loading agent in a completely mixed state Desulphurising agent and additive pneumatically in the hot metal melt bath is blown in.