KR850001607B1 - Method for increasing vessel lining life for basic oxygen furnaces - Google Patents

Abstract

The lining life of a basic oxygen furnace, which employs slag forming ingredients containing up to 40 wt.% dolomitic lime, is increased by introducing additional dolomitic lime. The melt may be reblown with inert gas. The lining life can be incerased by more than 40 % while still meeting low sulpyur specifications for the steel.

Description

Life Extension Method of Refractory Lining in Basic Oxygen Refining Furnace

1A and 1B are cross-sectional views of a basic oxygen refining furnace for carrying out the method of the present invention.

The present invention relates to a steel refining process, and more particularly to a method for extending the life of the refractory lining in a basic oxygen refining furnace in which the refining process is carried out by oxygen blown upwards on the surface of the molten steel.

One problem that often occurs in basic oxygen steelmaking is that the life of the refractory lining is limited, which results in a reduction in production and the cost of relining, since the container has to be re-lined periodically.

In the past, dolomite lime was added to the slag to extend the life of the lining (Ref. Kristiansen et al, "The Effects of Operating Variables on Sulfur Performance in a BOF Shop," 1976 Open Hearth Proceeding, ISS-AIME, 28-). 41), however. Adding too much dolomite lime makes the slag more viscous and therefore unable to remove sulfur effectively.

Therefore, an object of the present invention is to extend the life of the refractory lining without any obstacle to the production of low sulfur content steel to extend the life of the basic oxygen refining furnace.

In order to extend the life of the refractory lining in a basic refractory lining vessel for producing steel by injecting oxygen into the molten iron on the surface of the melt, a slag former containing more than the amount of dolomite commonly used in the present invention is used. The slag and the melt can interact violently by supplying it to the vessel and blowing inert gas into the melt.

The term "inert gas" used in the present specification and claims is not an oxygen gas and refers to a gas having as many properties as possible such as low reactivity, low specific heat, absence of harmful pollutants, and high density. it means. Argon gas is preferable, but nitrogen gas or air may be used as long as it is not a problem of nitrogen pollution of the melt. In addition, other types of inert gases allowed in the present invention include helm, neon, krypton, xenon, carbon dioxide, steam, ammonia, and mixtures thereof, but argon gas having industrial purity or low purity is the best so far. Inert gas.

Inert gas is preferably supplied by mixing with oxygen through an oxygen lance.

Iron charged into a basic oxygen refining furnace generally contains carbon, silicon, sulfur and other impurities. The primary purpose of blowing oxygen is to remove carbon and silicon from the melt, which is oxidized to silicon dioxide and suspended on the surface of the melt, and carbon is oxidized to carbon monoxide and exits through the inlet of the vessel. Representatively, slag forming agents containing high calcium lime are added to the melt to form basic slag, and typically high calcium lime containing at least 90 w / o CaO removes sulfur from the melt by forming calcium sulfide. Dolomite lime, i.e., containing at least 30 w / o magnesium oxide, extends the life of the container lining but also increases the viscosity of the slag, thus impairing the interaction of the lime with the melt in the slag. As such, conventional methods for prolonging the life of container lining make it difficult to produce steel with low sulfur content, so the amount of dolomite lime charged into the container must be limited for conventional oxygen blowing.

In the past, dolomites corresponding to 0 to 40% of the total slag forming agent were used. Representative slag forming agents include high calcium lime, dolomite lime, limestone and fluorspar. More than the amount of dolomite lime conventionally used in accordance with the invention is added to the slag. That is, the dolomite lime in the amount specified according to the steel grade produced in each basic oxygen refining system is added to the container 1. In order to practice the present invention, the amount of dolomite lime added must exceed the usual amount. Of course, the slag forming compound should be supplied in sufficient amount so that the sulfur content of the melt 5 is reduced to a desired degree based on the stoichiometric and thermodynamic aspects of the desulfurization reaction.

It is essential to extend the life of the refractory lining 2 using a larger amount of dolomite lime than is commonly used. Preferably, if high calcium lime is used to remove the sulfur component, the amount of dolomite lime will be at least equal to the amount of lime supplied as shown in the following examples. Even if the amount of dolomite lime is two or three times the amount of lime supplied, the sulfur content of the steel can be reduced as required.

It is necessary to stir or mix the vessel because the viscosity of the slag is increased by a large amount of dolomite lime. Therefore, by supplying an inert gas to the vessel, the stirring takes place to intensify the interaction between the slag and the melt.

The present invention can be carried out in conjunction with the method of US Pat. No. 4,149,878 to use argon in a basic oxygen refining furnace, and also can produce low nitrogen and low oxygen steels as disclosed in the patent.

Inert gases should be intervened to intensify the interaction between the slag and the melt. Preferably, as shown in FIG. 1a, an appropriate amount of inert gas is supplied to the oxygen line to intervene in the melt through the oxygen lance. As an alternative, as shown in FIG. 1B, the inert gas may be supplied through a separate lance so that the oxygen-inert inert gas impinges on the surface of the melt 5. However, there is no need to waste money by adding another lance to the basic oxygen smelter.

After the oxygen injection in the basic oxygen process, the sulfur content of the melt is one of the difficult parameters to control, so in some cases, the sulfur content after oxygen injection in the present invention will be higher than desired. However, according to the present invention, by adding at least one sulfur removing compound such as high calcium lime to the slag of the container and blowing the melt again with only an inert gas, the sulfur content can be lowered to the desired level by causing the intense interaction between the slag and the melt. have.

If a sufficient amount of sulfur removal compound is contained in the slag, simply blowing an inert gas into the melt can lower the sulfur content to the desired level as described above.

EXAMPLE

A series of dissolution operations were carried out in a basic oxygen refining furnace with the following characteristics.

Typically, the amount of dolomite lime charged to the vessel is 16,000 pounds, using a slag forming agent consisting of 16,000 pounds of dolomite lime, 24,000 pounds of high calcium lime and 2,000 pounds of fluorite.

The charge of dolomite lime was increased to 35,000 pounds, high calcium lime was reduced to 10,000 pounds, and argon gas was injected into the vessel according to the method disclosed in the above-mentioned US Pat. No. 4,149,878. Argon gas was injected at a constant flow rate of 3,500 ft ³ per minute in the latter part of the oxygen injection. As a result, the lifespan of the refractory lining was extended to 1,100 times in the previous 780 refining operations and increased to about 41%. Even though a very large amount of dolomite lime was added, there was no difficulty in producing low-sulfur steel. In addition, in the present embodiment, fluorite, which is known to promote sulfur removal, was not used, but steels in compliance with low sulfur regulations could be manufactured. Therefore, it is possible to reduce the fluorspar charged in the container according to the present invention, the maximum sulfur content allowed by the regulation for the steel produced according to the present invention was 0.025%.

Therefore, it can be seen that the results of the present invention can be obtained significantly, and the lifespan of the refractory lining is improved by about 40% or more, compared with the conventional one, and the life of the lining of the basic oxygen refining furnace without showing the inevitable desulfurization capacity as in the prior art. It can be seen that the increase is shown well and the specific examples bringing the specific desulfurization effect is as follows.

Example of desulfurization effect

＊ The amount corresponding to each column is about 225 tons

Claims (1)

In the steelmaking process using basic oxygen refining furnace, oxygen is injected into the melt from the upper surface of the melt through oxygen lance and slag containing up to the range (0-40%) that dolomite lime does not lower the desulfurization ability of slag. In the method of adding the forming agent to the melt to extend the life of the refractory lining of the refining furnace, the slag viscosity is increased to reduce the desulfurization ability of the slag, that is, slag containing dolomite lime of 40% to 77% By adding a forming agent to the molten metal and injecting an inert gas with oxygen on the surface of the melt, the slag and the melt are sufficiently stirred so that the desulfurization reaction between the melt and the slag does not interfere with the increased slag viscosity. Life extension method.

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