JPS58204119A - Desulfurizing agent for molten iron - Google Patents

Abstract

PURPOSE:To obtain iron of low S-content iron equivalent to a carbide base desulfurizing agent which can be blown stably even with a small amt. of a gaseous carrier in a desulfurization method of molten iron by blowing by using a desulfurizing agent consisting essentially of diamide lime having limited grain sizes. CONSTITUTION:A desulfurizing agent contg. diamide lime having mainly <=60mu grain size in an amt. of 80wt% or above is used for a desulfurization method of molten iron by blowing. The diamide lime exhibits outstanding gas conveyability and can yield extra-low S-content pig iron contg. about <=0.005% S. If the grain size thereof is too coarse, the gas conveyability decreases and it is difficult to obtain the superior low S-content pig iron contg. about <=0.010% S. If the ratio of the diamide lime is <=80wt%, the gas conveyability decreases as well.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a desulfurizing agent for molten iron for blow desulfurization, the main component of which is diamide lime containing calcium carbonate and carbon as main components. Here, molten iron refers to molten materials such as pig iron, cast iron, and steel.

As is well known, desulfurization of molten iron is an important technical issue in order to obtain steel products with excellent performance, and many proposals have been made regarding desulfurization agents and desulfurization methods.

Among these proposals, desulfurization agents containing calcium carbide (hereinafter sometimes abbreviated as "carbide") as a main component are widely used because calcium carbide (hereinafter sometimes abbreviated as "carbide") exhibits the best desulfurization performance.

However, its production consumes a large amount of electricity, and in recent years, where energy costs have skyrocketed, there has been a need to reconsider it from an economic perspective. However, due to its inferior desulfurization performance, it has not met the high requirements for desulfurization of molten iron, that is, the recent demand for the production of excellent extremely low sulfur content pig iron with a sulfur content of 0.010% or less. It has not yet been met.

On the other hand, well-known desulfurization methods include a method in which a desulfurizing agent is added to molten iron and mechanically stirred, and a method in which a powdered desulfurizing agent is blown into molten iron using a carrier gas.

Among these desulfurization methods, the blown wisteria sulfur method has become widely adopted because it exhibits excellent workability and excellent desulfurization efficiency. This blowing desulfurization method is a method in which a desulfurizing agent powder is entrained in a carrier gas θ) gas flow such as dry nitrogen, and desulfurization is carried out by blowing into the molten iron through a lance immersed in the molten iron. The blow desulfurization method is, for example,
While transporting the pig iron mixer truck that received pig iron from the blast furnace to the steel factory,
Instead of the mechanical stirring desulfurization method (so-called open iron KR method, etc.), the desulfurization station is temporarily stopped at a desulfurization station, and powdered desulfurization agent is blown into the hot metal in the mixer car. Intensive desulfurization has been widely put into practical use.

"Blowing desulfurization" as used herein is a technical term that is opposed to so-called "pour-in", etc., and specifically, desulfurization is carried out by injecting desulfurizing agent powder together with a carrier gas below the surface of the molten iron. It refers to the method of doing things.

As is well known, as the above-mentioned carbide desulfurization agent, carbide is used alone or in combination with other inorganic compounds such as quicklime, calcium fluoride, 11 um sodium carbonate, 11 um sodium chloride, etc. for the purpose of desulfurizing molten iron. However, it has been known in Japanese Patent Publication No. 47-26923 that diamide lime acts catalytically as a desulfurization aid and significantly enhances the desulfurization effect of carbide. .

The diamide lime desulfurization aid of Japanese Patent Publication No. 47-26923 has a swirling effect due to the release of carbon dioxide gas generated by thermal decomposition of calcium carbonate, and the carbon dioxide gas thus generated reacts with the fine carbon present in the diamide lime. It is believed that the generation of carbon monoxide, that is, the generation of a reducing atmosphere, strengthens the desulfurization reaction of carbides.

Furthermore, JP-A No. 51-90917 describes a desulfurization agent suitable for desulfurization in a torpedo pan consisting of a mixture of calcium carbide and diamide lime, characterized in that the amount of diamide lime is 40 to 70% by weight. A desulfurizing agent was proposed, and there are many methods in which the desulfurizing agent is prepared by mixing diamide lime or calcium carbonate powder and carbon powder with carbide powder, and injecting the desulfurizing agent into the molten iron through a lance together with a carrier gas. It has now been implemented.

However, as a result of recent high demands regarding desulfurization agents, in the molten iron blowing desulfurization method, there is an extremely close relationship between the gas transportability of the desulfurization agent powder and the desulfurization performance due to the carrier gas. Excellent desulfurization performance cannot be expected with a desulfurization agent powder that has poor properties. 2. Even with the molten iron desulfurization agent disclosed in JP-A No. 51-90917 mentioned above, there is still no energy-saving effect in addition to gas transportability. However, it has been found that the results are not necessarily satisfactory from the viewpoint of price, etc.

Surprisingly, the inventors of the present invention have found that in a pretreatment method for molten iron using the advanced blowing desulfurization method, which has recently been attracting particular attention, the present inventors have succeeded in reducing the desulfurization performance by 0.010%, which is equivalent to the desulfurization performance of conventional carbide-based desulfurization agents.
As a result of intensive research to provide a new desulfurization agent that provides the following extremely low sulfur content pig iron and is dramatically cheaper in terms of price, we have found that the particle size can be reduced in the molten iron blowing desulfurization method. Mainly 60
We have made the completely unexpected discovery that, contrary to conventional expectations, these problems can be solved when using a desulfurization agent whose main component is diamide lime of less than μ, and have completed the present invention. .

That is, the present invention provides a desulfurizing agent for molten iron used in the blow desulfurization method, which contains diamide lime having a particle size of mainly 60 μm or less in an amount exceeding 80% by weight.

Traditionally, limestone, which is a type of gas-generating substance that decomposes in molten iron and generates carbon dioxide gas, is far more inert than other desulfurizing agents, and the thermal decomposition of limestone is an endothermic reaction. It was thought that the cooling effect of molten iron was large, causing various problems in the blow desulfurization method, and that a large amount of diamide lime or When a large amount of gas-generating material consisting of calcium carbonate powder and carbon powder is mixed and blown into molten iron together with a carrier gas as a desulfurization agent, gas generation increases, splash occurs, and molten iron 2 and 2 are removed from the desulfurization container. Since the slag blows out and causes not only a decline in desulfurization performance but also operational difficulties and significant economic losses, such gas-generating substances are replaced by carbide as disclosed in JP-A No. 51-90917. Although it can be used as a desulfurization aid in a moderate amount, it was never expected that it could be used alone, so the present invention was completely unexpected.

Furthermore, in the blow desulfurization process, diamide lime exhibits incredible gas transport properties and can also provide extremely low sulfur content pigtails with a sulfur content of less than 0.005%.

In this specification, "particle size is mainly 60μ or less" means 60μ or less
Powder with a particle size of 0 μ or less has a weight coefficient of 80 or more, preferably 9
0% by weight or more, particularly preferably powder with a particle size of 46μ or less is 80% by weight or more, most preferably 90% by weight
That's all.

The desulfurizing agent for molten iron of the present invention is mainly composed of diamide lime with a particle size of 60 μm or less, but if the particle size is too coarse and exceeds 60 μm, the gas transportability decreases.
Unpleasant phenomena such as increased fluctuations in the concentration of the desulfurizing agent in the carrier gas during injection may occur, and the sulfur content may be reduced to 0. O]
This is not preferable because it becomes difficult to obtain an excellent extremely low sulfur content pig iron of 0% or less.

In the present specification, "diamide lime" refers to a mixture mainly composed of fine precipitated calcium carbonate and carbon, which is precipitated from an aqueous solution or an aqueous suspension by a chemical reaction.

Diamide lime includes, for example, a mixture of calcium carbonate and carbon that is produced as a by-product when producing dicyandiamide from lime nitrogen, or when producing thiourea etc. from lime nitrogen. A mixture of calcium carbonate and carbon, obtained in the production of carbon, is optimally used. Dicyandiamide is produced by reacting a lime nitrogen suspension with carbon dioxide gas, and the by-product diamide lime, which is a filtration residue at this time, generally has a calcium carbonate content of 70 to 90% and a carbon content of 5 to 15% by weight. Does it contain other impurities such as iron oxide, aluminum oxide, and silicon oxide? It is a mixture whose main components are extremely fine calcium carbonate and carbon.

Normally, diamide lime is dried into a fine powder using various equipment and methods, and if necessary, subjected to classification and other treatments before being used as a desulfurizing agent for molten iron in blow desulfurization. In addition, when diamide lime is dried with hot air etc. in a dryer, the extremely fine diamide lime that is carried out of the dryer system and collected by the hot air etc. usually exceeds a weight factor of 15% and is about 5%
The so-called treated diamide lime, which contains a large amount of carbon, may be used alone or in combination with the above-mentioned diamide lime, which generally contains 5 to 15 parts by weight of carbon, and can be used in the present invention. It can also be used as a desulfurizing agent for molten iron.

In the molten iron desulfurization agent of the present invention, the weight ratio of diamide lime is 8.
The amount exceeding 0 weight it% is 80% diamide lime.
If the content is less than 0.0% by weight, gas transportability tends to decrease, and it is difficult to obtain extremely low sulfur content of less than 0.0% or less with a small unit of desulfurization agent for the molten iron (and it is economically wasteful). Because it increases,
Preferably, the weight ratio of diamide lime is used in an amount exceeding 85 parts by weight, more preferably in an amount exceeding 90 parts by weight, particularly preferably in an amount of 95 parts by weight or more.

The carrier gas used in the present invention is mainly an inert gas such as nitrogen, argon, or air, but the method for injecting the desulfurizing agent for molten iron of the present invention into molten iron using a carrier gas is continuous. Contain powder desulfurization agent periodically or intermittently 1. A device in which a small amount of powdered desulfurizing agent is passed from a rotary pulp tank into a blowing pipe, and it is conveyed and blown in with a carrier gas, or a device in which the powdered desulfurizing agent stored in a pressure vessel is fluidized and then blown in with a carrier gas. , etc. can be used.

However, among these blowing devices, the ``device for taking out flowable solids from a pressure vessel'' disclosed in Japanese Patent Application Laid-open No. 49-31516, which can blow with a small amount of carrier gas, and devices similar to this, is preferable because it can highly exhibit the effect of the desulfurizing agent for molten iron of the present invention.

The small amount of carrier gas per powdered desulfurizing agent means that the amount of carrier gas required for blowing is small, and the powdered desulfurizing agent effectively contacts the molten iron and exhibits the desulfurization effect. There are many advantages such as the degree of deterioration is small and the equipment can be small-scale.
In other words, the ratio of carrier gas/powder desulfurization agent is I Q Nt/
kq or less, preferably 2 to 10 NL/kq or less, more preferably 2 to 8 NtAy or less, particularly preferably 2 to
A condition of 9 or less is preferably adopted for 6N17', but surprisingly, the molten iron desulfurization agent of the present invention has excellent gas transportability that allows stable injection even with such a small amount of carrier gas. and provides an extremely low sulfur content pig that is equivalent to conventional carbide desulfurization agents.

Thus, the present invention provides a blow desulfurization method, particularly a desulfurization method in which a desulfurizing agent of molten iron is fluidized in a pressure vessel and is blown into the molten iron in an amount of carrier gas of less than 10 Nt carrier + 17 gas/kf powder desulfurizing agent. The present invention provides a desulfurizing agent for molten iron suitable for.

The desulfurizing agent for molten iron of the present invention exhibits remarkable gas transportability even when used only with diamide lime, as will be specifically shown in the examples below. Not only does it not cause blockage of pipes, but it also virtually eliminates pulsation and vibrations of the pig iron mixer, so it can be operated extremely safely and in a short time with excellent desulfurization efficiency. Desulfurization performance can be improved by using various desulfurization agents, desulfurization aids, etc., alone or in combination, and in combination with diamide lime in an appropriate amount depending on the purpose [5].

These include CaC2, MgC2, At4C3
Metal carbides such as; calcium cyanamide; fluorite, cryolite, sodium silicofluoride, I, ip, NaF, MgF2
Inorganic fluorides such as Na, K, Mg, Ca,
Hydroxide such as f3a: Na, Mg, Ba
Carbonates and carbonate double salts such as , Sr; Na, K, Mg,
Oxides or chlorides of Ca, B, AA, Si, etc.:
As a hydrogen generating substance in molten iron; hydrides such as Na, Ca, etc.; organic compounds such as polyethylene, polypropylene, polyamide, polystyrene, polyacrylonitrile, urea; as a water generating substance in molten iron; ash Borates containing crystal water such as borite S and pandelma borax; perlite, kaolin, clay, monmo 11 lonite, asbestos, slaked stone, alum,
Mica and similar substances; carbohydrates such as sugar and starch; organic compounds such as stearic acid, phthalic acid, and glycolic acid; polyvinyl alcohol, polyvinyl acetate, etc.; , coal, coke, petroleum coke, charcoal, etc.; and others; however, the particle size is preferably 60 μm or less as described above.

Among the conventionally known desulfurization agents and desulfurization aids mentioned above, inorganic fluoride or /? The melting point desulfurization material containing diamide lime as a main component is preferable because it works synergistically with diamide lime to improve desulfurization performance, facilitate slag removal after desulfurization, and improve gas transportability. The amount of super heavy inorganic fluoride or/and carbon material is 20% by weight of the agent.
Amounts of less than 5 parts by weight are preferred, preferably less than 15 parts by weight, more preferably less than 10 parts by weight, particularly preferably 5 parts by weight or less.

In addition, in the inorganic fluoride and carbon material, since carbon as a carbon material is usually contained in diamide lime in a proportion of 5 to 15% by weight as mentioned above, the molten iron of the present invention containing diamide lime as a main component As an auxiliary agent added to the desulfurization agent, it is preferable to use an inorganic fluoride, but from the viewpoint of ease of handling, for example, the inorganic fluoride contains CaF2 of 80 to 98% by weight and other impurities at a maximum of about Particularly preferred are fluorite containing SiO□ of 16% by weight, Ft203, MgO, and the like. Further, as the carbon material, coke and coal are preferable from the viewpoint of ease of handling, cost, etc.

Desulfurizing agents for molten iron containing inorganic fluoride or /F and carbon substances in an amount exceeding 100 weight percent of the molten iron desulfurizing agent containing diamide lime as a main component are particularly effective against the fire resistance of mixed pig iron cars. This is because the work environment becomes unfavorable due to an increase in damage to objects or an increase in carbon monoxide, etc. in the exhaust gas discharged from the pig iron mixing vehicle.

When using the molten iron desulfurization agent of the present invention, safe blowing operations can be performed and a significantly superior desulfurization performance equivalent to that of conventional carbide desulfurization agents can be obtained. Although it is not clear, in addition to these advantages not obtained with conventional powder desulfurization agents, the desulfurization agent for molten iron of the present invention does not require the use of substantially carbide, so there is no moisture in the flag produced. There are no carbides that can react with and explode, and therefore, there are also advantages such as the fact that slap can be removed and disposed of extremely safely.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Examples 1 to 7 and Comparative Example 1 Hot metal with a sulfur content of 0.039 to 0.043% 270 to
A desulfurizing agent shown in Table 1 was blown into a 350 T capacity torpedo ladle filled with 300 T using a blowing device described in JP-A No. 49-31518 using dry nitrogen gas as a carrier gas at a speed of 80 to 150 kv/min. Desulfurization was carried out by blowing into hot metal using a lance under the following conditions.

The results are shown in Table 1.

The following diamide lime, carbon, quicklime, and calcium carbonate were used in the desulfurizing agent composition column of Table 1.

1) Diamide lime A dried by-product during the production of dicyanodiamide from lime nitrogen is used, and its chemical composition is CaCO385 weight ratio, 08% by weight, SiO, 2.1% by weight, At, 0.
31.4 Weight factor, F2O3 1.2% by weight, MgO0,
8% by weight, and 1.5% by weight of others.

2) Finely pulverized commercially available grains are used, and their chemical composition is Ca.
F291% by weight, 5i026.1% by weight, Ft203
0.9% by weight, and 2% by weight.

3) Finely pulverized commercially available carbon coke is used, and its chemical composition is 90% by weight as C.

4) For quicklime carbide Finely pulverized quicklime is used, and its chemical composition is 95% by weight as CaO.

5) Use crushed calcium carbonate limestone, its chemical composition is CaCO
398.6% by weight, MgCO30.9% by weight, other 0
．． It belongs to the 5th weight section.

Among the above raw materials, excluding calcium carbonate, diamide lime, barbarian 2 and/or carbon, or quicklime were mixed uniformly in an inert atmosphere and used as a desulfurizing agent.

The particle size distribution of the raw materials mentioned below is shown in Table 2.

Table 2 The meanings of the terms used in Table 1 are as follows.

Weight of hot metal (T) (b) Carrier gas/desulfurization agent powder: Blow speed of desulfurization agent (kq/m1n) (c) Blow pressure: Desulfurization agent powder is entrained in carrier gas,
The pressure (ky/cnt) of the carrier gas connected to the discharge port when blowing into hot metal is relatively low compared to the pressure (ky/cnt) of the carrier gas connected to the discharge hole 4 in FIG. 2 of JP-A-49-31518. This corresponds to pressure P3.

B) Desulfurization performance: 81 - Sulfur content in hot metal before desulfurization (sub) S2 - Sulfur content in hot metal after desulfurization (sub)) As can be seen from Table 1, the The desulfurization agent exhibits excellent gas transportability and desulfurization performance, and the extremely low sulfur content pig that was conventionally obtained with carbide desulfurization agents can be obtained with diamide lime alone or with a desulfurization agent mainly composed of diamide lime. Moreover, desulfurization could be carried out smoothly at a blowing rate of 130 to 150 kg/min.

On the other hand, in Comparative Example 1 in which calcium carbonate was used as the desulfurization agent, the blowing pressure fluctuated significantly even when the amount of carrier gas was 4 ONL/kq, and even though the blowing speed was lowered to 80 kgZ, the blowing pressure In addition, the desulfurization performance was significantly inferior to that of the desulfurization agent for molten iron of the present invention.

Claims (1)

[Scope of Claims] (1) Diamide lime with a particle size of mainly 60μ or less
A desulfurizing agent for molten iron used in the blow desulfurization method containing an amount exceeding the weight limit. (2. The molten iron desulfurization agent 100 described in claim 1)
The desulfurizing agent for molten iron used in the blow desulfurization method according to claim 1, wherein the amount of inorganic fluoride and/or carbon material is less than 20% by weight. (3) The blowing desulfurization method fluidizes the desulfurization agent in molten iron and
The desulfurizing agent for molten iron according to claim 1 or 2, which is a method in which a carrier gas amount of Nt carrier gas/ly desulfurizing agent or less is blown into the molten iron.