DE2042811B2 - Process for refining steel - Google Patents

Description

The invention relates to a method of the type specified in the preamble of claim 1, as known from GB-PS 9 44 479, for example. In this known method, which is directed to the refining of phosphorus-rich pig iron, a preferably 2000 to 3000 ⁰ C warm fresh gas is used, which contains no more than 40% oxygen and at least 40% CO2, while the rest in the we; borrowed from CO.

However, such high COr contents for fresh gas lead to disadvantages, since CO2 has a higher heat capacity than CO and therefore removes a relatively large amount of heat from the melt. From the point of view of reducing the supply of solid matter in the fresh gas, large CO2 contents are also inexpedient because CO2 does not react with oxygen, but only with carbon. Another disadvantage of the known method can be seen in the fact that all gases escaping from the fresh vessel reach the exhaust chimney in order to enter the atmosphere from there. Furthermore, it is noted that the known process, because of its high oxygen concentrations in the fresh gas, leads to high levels of metal slagging during refining.

From DE-OS 1508 159 is a method for Extraction and dedusting of high-calorie converter exhaust gas known, in which, if necessary, in Large pressure fluctuations occurring in a gas processing plant downstream of the converter can thereby be avoided that the gas processing system a regulated amount of processed converter exhaust gas is fed.

From DE-OS 14 S8 906 is a dedusting process known for converter exhaust gas, in which the required pre-cooling de :. Exhaust gas with the help of a endothermic chemical reaction, such as the decomposition of CO2 in the presence of carbon to form CO, is brought about.

Furthermore, from US-PS 30 03 865 a fresh process for chromium-containing alloyed steels is known to which air or mixtures of air and oxygen are added as fresh gas to prevent chromium burn-off to keep it low.

The invention is based on the object of developing a method of the type specified in the preamble of claim I in such a way that the oxygen concentration in the fresh gas is reduced.
This task is achieved by the in claim 1

2 ") listed features are solved.

The technical progress that can be made with the aid of the invention is to be seen primarily in the fact that through a recycling of the converter exhaust on the one hand the oxygen supply in the fresh gas to the necessary

jo values is decreased and the other at the same time the blown gas volume is kept constant in an economically advantageous manner, since not, as in State of the art occasionally encountered, chemically inert filling gases, but those occurring during normal operation

Ji steel mill gases can be used. With the help of the procedure According to the invention, the metal burn-off is thus kept low, the Badumrührurig on the required Height kept and at the same time the development of brown smoke on a dtn point of view

■ w Environmental pollution reduced to a tolerable level. The fact that the proportion of oxygen not required for metallurgical purposes is saved gives rise to an additional cost advantage.
In the subclaims are preferred embodiments

■ R> forms of the invention indicated.

The diluent gas, which according to the invention is added to the oxygen to be blown in, is involved it is preferably carbon monoxide, possibly also mixtures of carbon monoxide and carbon dioxide. That

in diluent gas is collected and processed of the exhaust gas emerging from the fresh vessel. As stated in claim 1, should be based on At least one part of diluent gas can be added to four parts of oxygen in order to achieve a noticeable reduction

ü to achieve the metal slagging. The relationship however, between diluent gas and oxygen can vary depending on various parameters such as the Melting temperature and the melt pool composition can be largely changed. Expediently

M) se becomes the most favorable ratio by determining the Decarburization rate and oxygen supply are stoichiometrically set.

When refining steel, various elements, such as silicon and aluminum, are often used

bi removed before the carbon content is targeted Values can be reduced. In such cases the rate of oxidation of silicon, Aluminum, etc. measured and in determining the

the amount of oxygen introduced into the freshness vessel in the unit of time to ensure that that sufficient amounts of oxygen are available for the fresh process and yet Oxygen surpluses can be avoided.

When refining simple carbon steels, pure oxygen will generally first be used as the fresh gas in order to add the diluting gas when the slag has an iron oxide content of at least 10%, but preferably 15 to 20%. A further increase in the iron oxide content in the slag would only increase the iron burn-up without significantly affecting old dephosphorization. In addition, iron oxide has a strong oxidizing effect, which would severely attack the lining of the fresh container.

Alloy steels are currently refined by blowing an oxygen into the vessel the oxygen reacts exothermically with the elements, for example chromium, in the melt, whereby the Temperature of the melt increased. When the invention Process are gases, namely carbon monoxide, blown in such a ratio that a to strong metal burn-off with the resulting increase in temperature of the melt is avoided. The known equilibrium conditions show that at atmospheric pressure at the end of the oxygen blowing a very high melt temperature must be achieved in order to achieve a low carbon content to decarburize and yet maintain a relatively high chromium content. With the invention Mixing ratios of the decarburization gases are generally not such high temperatures achievable. Therefore, it is necessary to lower the pressure of the carbon monoxide in the vessel. The lowering the pressure of the carbon monoxide changes the equilibrium conditions and shifts the lowest carbon content attainable at lower temperatures downwards without reducing the chromium content of the melt. the Reducing the pressure can be achieved by reducing the pressure in the vessel and / or introducing argon into it the vessel. The argon can be used together with oxygen, with oxygen and carbon monoxide, or also be blown with oxygen, carbon monoxide and carbon dioxide.

The drawing shows an embodiment of a recovery system for carrying out the invention Procedure. The system contains a vessel 1 containing molten steel 2, a closed one Hood 3, one through the hood 3 into the vessel! protruding lance 4, shut-off devices 5, a gas cleaning and Cooling chamber 6, a suction fan 7, sensing and measuring devices 8, an outlet pipe 9, a compressor 10, an outlet pipe 11, a storage chamber 12, a reduction system 13 for carbon dioxide, a Storage container 14, a feed device 15 for argon, an argon separator 19, a compressor 16, an oxygen supply 17 and a silo 18. The lance 4

ίο can have any shape. The cooling and Cleaning chamber 6 can have a heat exchanger and a bag filter or other suitable cooling and Cleaning facilities included. The suction fan 7 sucks the gas emerging from the vessel 1 into the Recovery plant. In addition, the system, and thus the inventive Process usable for a vacuum degassing process using nitrogen and hydrogen and lead and other volatile additions are removed from the melt contained in the vessel 1. the Sensing and measuring devices 8 serve: the determination of the composition, the pressure and the temperature of the gases. The compressor 10 conveys the gases into the chamber 12. In the chamber 12 is a measuring device built-in for composition, pressure and temperature of the gases. Through the outlet pipe 11 is a strong heated gas can be used for other heating purposes in the steelworks. The reduction apparatus 13 includes Coke or graphite to reduce carbon dioxide too

jo carbon monoxide. The compressor 16 conveys the dilution gas into the lance 4. The silo 18 is used Addition of slag formers, for example lime. The argon separator 19 separates argon from the others Gases so that argon is stored and fed into it as required

J5 system can be introduced.

The following example serves to explain various special features of the invention Procedure.

Two chromium-containing melts were decarburized.

4 (i The first melt, in the following as batch A be calibrated, was only decarburized with oxygen. the second melt, hereinafter referred to as batch B, was made by supplying oxygen and carbon monoxide decarburized. Table I shows the initial analyzes of batches A and B, analyzes of batches Λ and B in different stages of decarburization. Gas analyzes and gas flow rates for Batches A and B too different stages of the decarburization process and the temperatures of the melts in different

»Ο stages of decarburization.

Tabel

Batch blowing time 17th Tempe
rature of
melt Melt analyzes % Mn % Si % Cr % FE 26.7 gas
by
sentence Cabbage: ngase iin
Fresh pour Vol% (min) 26th (C) η ' Ζ "
in V_. 0.15 0.10 14.35 rest 26.7 [mVh ■ l | CO
Vol% 100 A O 35 1620 0.53 0.14 0.10 13.80 - 26.7 45.4 100 (As of ₆ - 0.31 0.11 0.10 13.33 - 26./ 45.4 - 100 the
Technology) 1710 0.18 0.10 0.10 12.75 - 26.7 45.4 - 100 - 0.14 0.10 0.10 11.40 - 26.7 45.4 - 100 1740 0.12 0.085 0.10 10.15 _ 45.4 - 100 1750 0.10 45.4

continuation

Batch Blowing Time Tempe- Schmcl / analyscn
rature of
melt

(min)

(C)

% Mn

% Si

Cias
by
sentence Coal gases in
Fresh gas ImVh · ti CC) O,
VoI- "» Vol-% 26.7 45.4 - 26.7 45.4 85 15 26.7 45.4 85 15 26.7 45.4 85- ')> 5-15 26.7 45.4 90-95 5 IO 26.7 45.4

(eHindu ngsgcmiiß)

0 1710 0.65 0.13 0.12 14.70 4.5 1590 0.45 0.15 0.11 14.90 9 - 0.29 0.16 0.11 14.80 12th 1670 0.26 0.16 0.10 14.93 22nd 1730 0.23 0.16 0.10 14.70 31 I 730 0.20 0.16 0.10 14.76

rest

The table shows that the only with Oxygen to a content of 0.43% C, batch A decarburized suffered a chromium loss of about 30%, while Batch B, which has been decarburized with oxygen and carbon monoxide to a content of 0.45% C, does not suffered noticeable loss of chromium. Weilerhin the table shows that carbon monoxide is a very high percentage of the gas in the blast stream during the entire decarburization process for batch B. The carbon content of the melt was initially only 0.65% with a relatively high chromium content.

_ '(i Were the carbon content of the melt initially been higher, for example 3%. d; inn the content of carbon monoxide in the blast stream would have been lower can, for example 20%. With a high carbon content in the melt, a higher oxygen content is required.

> ■> stop and a lower carbon monoxide content permitted. The maximum permissible oxygen content in the blow stream with insignificant oxidation of the metals decreases if the carbon content of the melt decreases.

1 sheet of drawings

Claims (5)

Patent claims: 1. Process for refining steel, in which an oxygen and carbon oxides and optionally Fresh gas containing argon is blown into the fresh vessel, characterized in that that the exhaust gas is collected and to be injected after processing as a diluent gas Oxygen in a proportion of ι ο at least 1 part of diluent gas to 4 parts Oxygen is added, with at least the carbon monoxide content of the exhaust gas collected is reused. Z method according to claim 1, characterized in that that the carbon dioxide content of the fresh gas captured is reduced to carbon monoxide before the treated exhaust gas is added to the oxygen. 3. The method according to claim 1 or 2, characterized in that the processing of the collected Exhaust gas includes cleaning and cooling. 4. The method according to claim 1 to 3, characterized in that the diluent gas only then is added to the blown oxygen when the slag formed in the fresh vessel is at least Contains 10% iron oxide. 5. The method according to claim 4, characterized in that the diluent gas only then the Oxygen is added when 15 to 20% iron oxide is contained in the slag.